Research ArticleCharacterization of Cobalt Sulfide Thin Films Synthesized fromAcidic Chemical Baths

Tizazu Abza 1 Dereje Gelanu Dadi1 Fekadu GashawHone1 Tesfaye ChebelewMeharu1

Gebremeskel Tekle1 Eyobe Belew Abebe2 and Kalid Seid Ahmed2

1Hawassa University Department of Physics Hawassa Ethiopia2Adama Science and Technology University Department of Materials Science and Engineering Adama Ethiopia

Correspondence should be addressed to Tizazu Abza zabishwork2gmailcom

Received 13 December 2019 Accepted 26 March 2020 Published 30 April 2020

Academic Editor Isabel J Ferrer

Copyright copy 2020 Tizazu Abza et al is is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Cobalt sulfide thin films were synthesized from acidic chemical baths by varying the deposition timee powder X-ray diffractionstudies indicated that there are hexagonal CoS face-centered cubic Co3S4 and cubic Co9S8 phases of cobalt sulfide e crystallitesize of the hexagonal CoS phase decreased from 528 nm to 225 nm and that of the cubic Co9S8 phase increased from 11 nm to60 nm as the deposition time increased from 2 hrs to 35 hrse scanning electronmicroscopic images revealed crack and pinholefree thin films with uniform and smooth background and few large polygonal grains on the surface e band gap of the cobaltsulfide thin films decreased from 175 eV to 13 eV as the deposition time increased from 2 hrs to 35 hrs e photoluminescence(PL) spectra of the films confirmed the emission of ultraviolet violet and blue lights e intense PL emission of violet light at384 nm had red shifted with increasing deposition time that could be resulted from the increase in the average crystallite size eFTIR spectra of the films indicated the presence of OH C-O-H C-O double sulfide and Co-S groups As the deposition timeincreased the electrical resistivity of the cobalt sulfide thin films decreased due to the increase in both the crystallite size and thefilmsrsquo thickness

1 Introduction

Metal chalcogenide thin films are getting increasing atten-tion in a variety of electrical optical and optoelectronicdevices due to their physical and optoelectronic properties[1 2] Cobalt sulfide is one of the magnetic transition metalchalcogenides that exists in a number of phases such asCo4S3 Co1-xS Co2S3 CoS CoS2 Co3S4 and Co9S8 esemultiphase structures are resulted from the existence ofcobalt in the oxidation state of +2 +3 or +4 [3 4]ereforecobalt sulfide has a complicated chemical compositionese different phases of cobalt sulfide are of particularinterest due to their unique applications as supercapacitors[5ndash7] water splitter to produce hydrogen [8 9] catalysts[10ndash12] diluted magnetic materials [13 14] counter-electrodes for dye synthesized solar cells [15 16] anodematerials for advanced sodium and lithium ion batteries

[17ndash19] optical waveguides thermal sensors solar selectivecoatings and optical filters [20]

Currently various deposition technologies includingchemical bath deposition are used to deposit metal chal-cogenide thin films [1] Chemical bath deposition (CBD) hasbeen employed as a thin film deposition technique for metalsulfides selenides oxides and others for a period of nearly acentury and half [21] Despite an edged technique CBD stillhas a big unexploited potential to deposit different chal-cogenides with intended properties by controlling the de-position parameters [22] e first formal deposition ofcobalt sulfide thin films by the CBD method is credited toBasu and Pramanik almost 120 years after the CBD tech-nique had been used as a thin film deposition technique [23]Review of literatures indicates that there are very few reportson chemical bath-deposited cobalt sulfide thin films[3 20 24ndash26] Lokhande reported chemical bath-deposited

HindawiAdvances in Materials Science and EngineeringVolume 2020 Article ID 2628706 9 pageshttpsdoiorg10115520202628706

cobalt sulfide thin films using sodium thiosulfate as a sulfursource cobalt sulfate as cobalt source and disodium EDTAas complexing agents in an acidic solution [27] As far as theauthors are aware there is no report on cobalt sulfide thinfilms deposited under acidic baths except Lokhandersquos reporterefore characterization of cobalt sulfide thin filmssynthesized by changing various deposition conditionsunder acidic medium could have paramount importance fortechnologies that use cobalt sulfide thin films In this workwe report the synthesis and characterization of cobalt sulfidethin films from acidic baths using thioacetamide cobaltacetate and EDTA as starting materials

2 Experiment Procedure

Before the actual deposition of the cobalt sulfide thin filmsthe preparation conditions were optimized Aqueous solu-tions of analytical grade cobalt acetate (Loba Chemie)thioacetamide (Titan) and disodium EDTA (Fine Chem-icals) were used as starting reagents In a typical experiment9ml (1M) of cobalt acetate was mixed with 3ml (02M) ofdisodium EDTA in a 150ml beaker under continuousstirring en 63ml of deionized water was added to makeup the volume to 75ml e pH of the solution was adjustedto 46 before the addition of thioacetamide After the ad-dition of 15ml (1M) thioacetamide the pH was readjustedto 46 by a drop wise addition of HCl e solution color atthis instant was pink e stock solution was transferred tothe water bath of temperature adjusted to 85degC e pre-cleaned soda lime glass substrates were suspended verticallyin the stock solution Four samples were prepared by takingout a deposit in 30 minutes interval starting from 2 hrs afterthe deposition began e color of the films changed frombrown to black as the deposition time increased e filmswere partially reflecting like a mirror e reflectivity of thefilms increased with increasing the deposition time andfilms deposited at 3 hrs and 35 hrs reflect as a plane mirrore gravimetry film thickness measurement method wasused to estimate the thickness of the cobalt sulfide thin filmse obtained film thickness for cobalt sulfide thin filmsdeposited at 2 hrs 25 hrs 3 hrs and 35 hrs was 356 nm361 nm 385 nm and 434 nm respectively As the depositiontime increases ions get sufficient time for deposition on thesubstrate surface thus increasing the layer thickness [20]

Crystallographic study of the thin films was carried outby a Shimadzu X-ray diffractometer with Cu K-α mono-chromatic radiation (λ 015406 nm) operating at 40 kV and30mA e optical absorption of the samples was investi-gated by a Shimadzu UV-3600 Plus UV-VIS-NIR spectro-photometer and the FTIR spectrum was recorded using aPerkin Elmer Frontier MIRFIR infrared spectrometer esurface morphology and elemental composition of the thinfilms were investigated using a field emission scanningelectron microscope (FESEM Zeiss Sigma) integrated withan energy dispersive X-ray analyzer (EDX)e fluorescencemeasurement was carried out by using a Horiba Jobin YvonFluoroMax-4 spectrofluorometer using a xenon lamp for theelectron excitation e electrical resistance of the films wasmeasured by the two-probe method

3 Results and Discussion

31 StructuralAnalysis Figure 1 shows the XRD patterns ofcobalt sulfide thin films deposited at different depositiontime e XRD patterns of the films deposited at 2 hrs and25 hrs exhibited two clearly visible peaks at 2θ values of148deg and 212deg with preferred orientation along 212deg due to(102) plane of the hexagonal CoS structure (Pdf 011-279)Five additional faint peaks were also observed for the filmdeposited at 2 hrs as shown in Figure 1 and Table 1 epeak at 164deg is the reflection from the (111) plane of theface-centered cubic Co3S4 and the peak at 244deg is thereflection from the (220) plane of the cubic Co9S8 e peakat 4564deg could not be assigned for a particular phase as boththe cubic Co9S8(Pdf19-0364) and the face-centered cubicCo3S4(Pdf02-1338) structures have a common (400) planeabout this 2θ value e peak at 504deg is also common forCo3S4 Co9S8 and Co4S3 as can be observed from the listedPdf card numbers on the same table e peaks at 4564degand 504deg disappeared and six new peaks appeared at 1726deg1836deg 2232deg 2352deg 2954deg and 3076deg for the cobalt sulfidethin film deposited at 25 hrs e new observed peaks arerelated to the hexagonal CoS and cubic Co9S8 with no newpeaks related Co3S4 and Co4S3 phases A new peak relatedto the hexagonal CoS structure was observed at 2θ value of204deg when the deposition period increased to 3 hrs As thedeposition period increased to 3 and 35 hrs the intensity ofthe prominent peaks decreased and the faint peaks van-ished gradually However the intensity of the peaks at1836deg and 2232deg which started to appear from 25 hrsdeposition time increased gradually For the depositionperiod of 2 hrs 25 hrs and 3 hrs the preferred orientationwas along the (102) plane of the hexagonal CoS structuree preferred orientation changed to the (200) plane of thecubic Co9S8 structure for 35 hrs deposition period Inaddition the preferred orientation of the hexagonal CoSstructure changed from about 2126deg to 2034deg at 35 hrsdeposition time e peak at 124deg observed in the cobaltsulfide thin films deposited at 2 hrs 25 hrs and 3 hrs doesnot match to any of the observed cobalt sulfide phases estructural analysis showed that as the deposition periodincreased the presence of the face-centered Co3S4 [28] andthe hexagonal CoS structures decreased and the Co9S8phase increased [12]

e average crystallite size of the films was calculatedusing Schererrsquos equation as follows [29]

D kλ

β cos θ (1)

where D is the average crystallite size k 09 is the particleshape factor λ= 015406 nm is the wavelength of the X-rayused β is the full-width half maximum of the diffractionpeaks and θ is the Bragg diffraction angle e obtainedcrystallites sizes along the (102) plane of CoS were 528 nm517 nm 471 nm and 225 nm for films deposited at 2 hrs25 hrs 3 hrs and 35 hrs respectively For the Co9S8 phasethe obtained crystallite sizes for the cobalt sulfide thin filmsdeposited at similar deposition periods were 1095 nm

2 Advances in Materials Science and Engineering

2426 nm 5632 nm and 6002 nm respectively ese re-sults show that the dominant hexagonal CoS phase observedat 2 hrs deposition time was gradually decreased and at

35 hrs of deposition time it was dominated by the cubicCo9S8 phase [29] e Co3S4 phase did not show consistentcrystallite size variation with deposition time

Table 1 Some structural parameters of cobalt sulfide thin films and their reference Pdf file numbers

Deposition time (hrs) Measured 2θ (deg) Phase Index Standard

2

124 mdash mdash148 CoS Pdf 01-1279 mdash164 Co3S4 Pdf 75-1561 (111)2118 CoS Pdf 01-1279 (102)2464 Co9S8 Pdf 75-2023 (220)4564 Co9S8Co4S3 Pdf 190364Pdf021338 (400)(400)505 Co3S4Co9S8 Co4S3 Pdf 75-1561Pdf 190364Pdf021338 (511)(331)(331)

25

1224 mdash mdash mdash148 CoS Pdf 01-1279 mdash164 Co3S4 Pdf 75-1561 (111)1836 Co9S8 Pdf 75-2023 (200)2114 CoS Pdf 01-1279 (102)2232 CoSCo9S8 Pdf 01-1279Pdf 190364 mdash(200)2352 CoS Pdf 01-1279 mdash2464 Co9S8 Pdf 75-2023 (220)2954 Co9S8 Pdf 75-2023 (331)3076 CoS Pdf750605Pdf 01-1279 (100)---

3

1226 mdash mdash mdash1482 CoS Pdf 01-1279 mdash1632 Co3S4 Pdf 75-1561 (111)1824 Co9S8 Pdf752023 (200)2024 CoS Pdf 01-1279 mdash2146 CoS Pdf 01-1279 (102)2202 CoSCo9S8 Pdf 01-1279Pdf 190364 mdash(200)2352 CoS Pdf 01-1279 mdash2458 Co9S8 Pdf 75-2023 (220)498s4 Co9S8 Pdf 190364 (331)

35

1492 CoS Pdf 01-1279 mdash1528 CoSCo9S8 Pdf 01-1279Pdf 75-2023 mdash(111)1844 Co9S8 Pdf 75-2023 (200)2034 CoS Pdf 01-1279 mdash2136 CoS Pdf 01-1279 (102)2212 CoSCo9S8 Pdf 01-1279Pdf 190364 mdash(200)5048 Co3S4Co9S8 Co4S3 Pdf 75-1561Pdf 190364Pdf021338 (511)(331)(331)

t = 35 hrs

t = 3 hrs

t = 25 hrs

t = 2 hrs

4000

3500

3000

2500

2000

1500

1000

500

0

Inte

nsity

(au

)

0 10 20 30 40 50 60 70 80 902θ (deg)

Figure 1 XRD pattern of cobalt sulfide thin films deposited at different deposition time

Advances in Materials Science and Engineering 3

32 Morphology and Composition Analysis Figures 2(a) and2(b) show typical SEM images of cobalt sulfide thin filmsdeposited at 2 hrs and 3 hrs respectively e films coveredthe substrate uniformly with cottony spherical grains at thebackground No pinholes and cracks were observed for bothfilms e SEM images also show isolated spherical-shapedand polygonal-shaped grains on the surface of the filmsdeposited at 2 and 3 hrs respectively e size of the po-lygonal-shaped grains varied from 09 μm to 228 μm Manyauthors reported complex multifaceted SEM images ofcobalt sulfide thin films formed by a network of elongatedgrains [3 20 30 31] However few authors reported SEMimages similar to the current result [24 25 32] particularlywhen they used Na2S as an anion source Na2S is expected togenerate free S2minus easily to assist ion-by-ion depositionmechanism for the film growth e observed morphologyin the current work could be resulted from the ion-by-ionfilm growth mechanism which is common in most of theacidic bath-deposited chalcogenide thin films [22 33]However the larger top grains indicate the adsorption ofcluster of grains on the surface of the substrate at the finalgrowth stage of the films which were initially grown in thesolution

Typical EDX spectra of the cobalt sulfide thin films arepresented in Figures 3(a) and 3(b) e EDX analysis of thethin films deposited at 2 hrs and 3 hrs revealed the presenceof cobalt (Co) and sulfur (S) with no Co to S ratio variationwith deposition time e ratio of Co S in the cobalt sulfidethin films deposited at 2 hrs and 3 hrs is 23 77 e sig-nificant dominance of sulfur could be resulted from theexistence of free sulfur in the interstitial site as well as thecobalt vacancy in the crystal structure However manyreports show Co-dominated cobalt sulfide thin films[20 30] e presence of carbon oxygen sodium alumi-num and other elements could be related to the glasssubstrate and the carbon coating of the films before SEMEDX measurements [34]

33 Optical Properties

331 UV-Vis Spectroscopic Study e UV-Vis opticalproperties of the cobalt sulfide thin films deposited at dif-ferent deposition periods were investigated bymeasuring theabsorbance of the films in the wavelength range of500ndash1500 nm All the films have broad absorption edge andhigh absorption in the visible region Energy band gaps andtransition type of the thin films were obtained using Sternrelationship (Equation (2)) at the near-fundamental ab-sorption edge [35]

A k hv minus Eg1113872 11138731113960 1113961

n2

hv (2)

where A is the absorbance k is the constant v is the fre-quency of the radiation h is Planckrsquos constant and n is 1 forthe direct transition and 4 for the indirect transition In thecase of direct transition (Ah])2 the photon energy (h])(Equation (2)) has linear relation in the region next to theonset of fundamental absorption [36] Such a linear relation

is observed in all the current samples as shown in Figure 4implying a direct transition thus n 1e band gap energy(Eg) was obtained by extrapolating the linear portion of the(Ahv)2 vs (hv) curve towards the hv axis e band gaps ofthe thin films deposited at 2 hrs 25 hrs 3 hrs and 35 hrswere 175 eV 165 eV 155 eV and 13 eV respectively(Figure 4) e decrease in the band gap could be due to theincrease in the thickness and the crystallite size with de-position time as the terminal thickness and crystallite sizehave a significant influence on the band gap of the films [20]e relatively higher band gap values of the films comparedto the commonly reported value could be related to theexistence of excess sulfur in the thin films e high ab-sorbance in the visible light region and the band gaps of thefilms within the range from 13 eV to 175 eV make the filmsan appropriate material as an absorber layer in thin film solarcells [37 38] as well as efficient visible light photocatalyst[39]

332 FTIR Analysis FTIR spectroscopy can provide fun-damental information on the molecular structure of organicand inorganic components Figure 5 shows the FTIR spectraof cobalt sulfide thin films deposited at 2 hrs and 35 hrsBoth spectra consist of five absorption peaks e film de-posited at 2 hrs has absorption peaks at 3209 cmminus11638 cmminus1 1428 cmminus1 1067 cmminus1 and 607 cmminus1 and cobaltsulfide thin film deposited at 35 hrs has absorption peaks at3202 cmminus1 1560 cmminus1 1400 cmminus1 1068 cmminus1 and 609 cmminus1e peak at 3200 cmminus1 and 1638 cmminus1 are characteristicpeaks to the stretching vibration and bending vibration ofOH groups due to H2Omolecules indicating the absorptionof water by the samples [40] e absorption peaks at1428 cmminus1 and 1067 cmminus1 were assigned to C-O-H and C-Ostretching vibrations respectively e carbon containingcompounds could be either from the starting reagents as allof them are carbon containing reagents or from atmosphericCO2 In addition the intense peaks at 1067 cmminus1 and1068 cmminus1 correspond to the bending vibration of sulfonatedgroups in the CoS Co3S4 and Co9S8 phases e peakobserved at 607 cmminus1 is a characteristic peak of Co-Sstretching vibration modes and the polysufide bond group[41 42] e presence of the 608 cmminus1 frequency polysufideband is consistent with excess of sulfur in the thin films asconfirmed by the EDX analysis e observed bands of theOH bending vibration and C-OH deformation vibrationsignificantly shifted to lower frequency position with in-creasing deposition time signifying the weakening of dif-ferent modes of vibrations of different functional groupsparticularly the OH and C-OH groups However no sig-nificant shift on the position of the bands for the sulfonatedgroup bending vibration and the double sulfide group isobserved with deposition time e increase in the ab-sorption intensity of the polysulfide group could be relatedto the increase in the particle size and thickness of the filmswith deposition time e band broadening observed in thesulfur containing group indicates the nonuniform distri-bution of particle size and shape with deposition time etwo most intense absorption bands due to the sulfur

4 Advances in Materials Science and Engineering

containing compound at the frequency of 607 cmminus1 and1068 cmminus1 implies the existence of minimum impurities dueto other nonsulfide groups [5]

34 Photoluminescence Analysis e photoluminescence(PL) property of the cobalt sulfide thin films was studied byusing xenon lamp for electron excitation at room

temperature e emission spectra were observed in therange of 340ndash500 nm Broad intense peaks corresponding toviolet light were observed at 381 nm 384 nm 386 nm and391 nm for cobalt sulfide thin films deposited at 2 hrs 25 hrs3 hrs and 35 hrs respectively (Figure 6)e violet emissionpeaks could appear at 366 nm as the size of CoS nano-particles reduces [43] e peak broadening could beresulted from the nonuniform distribution of grains due to

260000240000220000200000180000160000140000120000100000

800006000040000

020000

240000(b)

220000

200000

180000

160000

140000

120000

100000

80000

60000

40000

20000

0

CKa

CKa

CaKa

CaKb

CaKb

OKa

OKa

FeLa

FeL1

CoL

aC

oL1

CoL

aC

oL1

Nak

aM

gKa

Nak

aM

gKa

AlK

aSi

ka

Sika

MoL

1M

oLa

MoL

bSk

aSk

b

MoL

1M

oLa

MoL

bSk

aSk

b

FeKe

sc

CoK

esc

CaKa

CaKb

CoK

esc

CoK

a

FeKa

FeKb

Cok

b

Cok

a

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

(a)

Figure 3 EDX spectra of cobalt sulfide thin films deposited at (a) 2 hours and (b) 3 hours

2microm

(a)

2microm

(b)

Figure 2 SEM images of cobalt sulfide thin films deposited at (a) 2 hrs and (b) 3 hrs

Advances in Materials Science and Engineering 5

the presence of different phases of cobalt sulfide e redshift in the violet light PL emission could be due to theconduction and valence bands broadening as a result ofincrease in crystallite size with deposition time e fluo-rescence spectra of all the thin films have shown blueemission peaks at the same wavelength of 467 nm Blue PLemission peak of wavelength 460 nm was reported by Emadiet al [44] for cobalt sulfide nanoparticles Films depositedfor a period of 3 hrs and 35 hrs have shown additionalultraviolet emission peaks of 349 nm As the PL properties ofsemiconductors are extremely sensitive to the local envi-ronment and to the presence of structural defects the violetand blue emissions are expected to be originated from Covacancy and S interstitial-related defects [24 45]

35 Electrical Resistivity Measurement e electrical resis-tivity of the films was measured by the two-probe method atroom temperature e measured values for films depositedat 2 hrs 25 hrs 3 hrs and 35 hrs were 17 times 106 5 times 1045 times 103 and 13 times 104Ωmiddotcm respectively e room tem-perature resistivity of the films is in the range of semi-conductorsrsquo resistivity except the film deposited at 2 hrs eresistivity values agreed with other researchersrsquo report[46 47] e decrease in resistivity could be attributed to theincrease in film thickness and crystallite size as the depo-sition period increases [48 49] is results in the valenceand conduction band broadening which inturn results inband gap narrowing e narrow band gap films becomemore conductive as electrons can easily be raised from the

0

4

8

12

(Ahv

)2 (eV

)2

13 18 2308hv (eV)

t = 2 hrst = 25 hrs

t = 3 hrs35 hrs

Figure 4 e band gaps of cobalt sulfide thin films obtained from the (Ahv)2 vs hv plots

Wave number (cmndash1)

10095909580757065605550454035

0 1000 2000 3000 4000

Deformation C-O-H

C-O streching or sulfonatedgroup bending

Polysulfidegroup

607 10681067

609

14001560 3202

32091638

1428

Perc

enta

ge tr

ansm

ittan

ce

Bending OH Streching OH

2 hrs35 hrs

Figure 5 FTIR spectra of cobalt sulfide thin films deposited at 2 and 35 hrs

6 Advances in Materials Science and Engineering

valence band to conduction band by room temperaturethermal energy

4 Conclusion

Cobalt sulfide thin films were synthesized from acidicchemical baths containing cobalt acetate thioacetamideand disodium EDTA by varying the deposition time eeffects of deposition time on the structural morphologicaloptical photoluminescence and electrical properties of thefilms were investigatede films consisted of mixed phasesof hexagonal CoS face-centered cubic Co3S4 and cubicCo9S8 phases e films deposited at 2 hrs and 25 hrs aredominated by the hexagonal CoS phase and that depositedat 35 hrs are dominated by the cubic Co9S8 phase efilmsrsquo surface morphologies were dominantly formed fromcompacted cottony spherical grains without pinholes andcracks e EDX and the FTIR spectra confirmed thepresence of Co and S in the films PL investigation con-firmed emission of ultraviolet violet and blue lights uponexcitation by xenon lampe violet light gets red shifted asthe deposition period increased from 2 hrs to 35 hrs eoptical analysis result revealed high visible light absorptionof the films and a red shift in the band gap with increasingdeposition time e two-probe electrical measurementshowed decrease in the resistivity of the films with increasein the crystallite size

Data Availability

e XRD UV-VIS FTIR and photoluminescence data usedto support the findings of this study are available from thecorresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors acknowledge the Hawassa University forfunding this research work

References

[1] L Deshmukh and S Mane ldquoLiquid phase chemical depositionof cobalt sulphide thin films growth and propertiesrdquo DigestJournal of Nanomaterials and Biostructures vol 6 no 3pp 931ndash936 2011

[2] L P Mgabi B S Dladla M A Malik S S Garje J Akhtarand N Revaprasadu ldquoDeposition of cobalt and nickel sulfidethin films from thio- and alkylthio-urea complexes as pre-cursors via the aerosol assisted chemical vapour depositiontechniquerdquo 6in Solid Films vol 564 pp 51ndash57 2014

[3] S S Kamble A Sikora S T Pawar N N Maldar andL P Deshmukh ldquoCobalt sulfide thin films chemical growthreaction kinetics and microstructural analysisrdquo Journal ofAlloys and Compounds vol 623 pp 466ndash472 2015

[4] X Chen Z Zhang Z Qiu C Shi and X Li ldquoHydrothermalfabrication and characterization of polycrystalline linneite(Co3S4) nanotubes based on the Kirkendall effectrdquo Journal ofColloid and Interface Science vol 308 no 1 pp 271ndash2752007

[5] A Mohammadi N Arsalani A G Tabrizi S E MoosavifardZ Naqshbandi and L S Ghadimi ldquoEngineering rGO-CNTwrapped Co3S4 nanocomposites for high-performanceasymmetric supercapacitorsrdquo Chemical Engineering Journalvol 334 pp 66ndash80 2018

20 hrs25 hrs

30 hrs35 hrs

12 times 107

90 times 106

60 times 106

30 times 106

00

PL in

tens

ity (a

u)

400 450 500350Wavelength of emission peaks (nm)

(a)

340 380 440360 400 420Film thickness (nm)

316

318

32

322

324

326

E em

issio

n (eV

)(b)

Figure 6 (a) e photoluminescence spectra and (b) the emission energy of intense PL peak (Eemission) vs film thickness of cobalt sulfidethin films deposited at various deposition time

Advances in Materials Science and Engineering 7

[6] F Tao Y-Q Zhao G-Q Zhang and H-L Li ldquoElectro-chemical characterization on cobalt sulfide for electro-chemical supercapacitorsrdquo Electrochemistry Communicationsvol 9 no 6 pp 1282ndash1287 2007

[7] S B Kale A C Lokhande R B Pujari and C D LokhandeldquoCobalt sulfide thin films for electrocatalytic oxygen evolutionreaction and supercapacitor applicationsrdquo Journal of Colloidand Interface Science vol 532 pp 491ndash499 2018

[8] L-L Feng G-D Li Y Liu et al ldquoCarbon-armored Co9S8nanoparticles as all-pH efficient and durable H2-evolvingelectrocatalystsrdquo ACS Applied Materials amp Interfaces vol 7no 1 pp 980ndash988 2015

[9] L-L Feng M Fan Y Wu et al ldquoMetallic Co9S8 nanosheetsgrown on carbon cloth as efficient binder-free electrocatalystsfor the hydrogen evolution reaction in neutral mediardquo Journalof Materials Chemistry A vol 4 no 18 pp 6860ndash6867 2016

[10] L Zhu D Susac M Teo et al ldquoInvestigation of CoS2-basedthin films as model catalysts for the oxygen reduction reac-tionrdquo Journal of Catalysis vol 258 no 1 pp 235ndash242 2008

[11] A W Peters Z Li O K Farha and J T Hupp ldquoAtomicallyprecise growth of catalytically active cobalt sulfide on flatsurfaces and within a metal-organic framework via atomiclayer depositionrdquo ACS Nano vol 9 no 8 pp 8484ndash84902015

[12] S Dou L Tao J Huo SWang and L Dai ldquoEtched and dopedCo9S8graphene hybrid for oxygen electrocatalysisrdquo Energy ampEnvironmental Science vol 9 no 4 pp 1320ndash1326 2016

[13] N Rumale S Arbuj G Umarji et al ldquoTuning magneticbehavior of nanoscale cobalt sulfide and its nanocompositewith an engineering thermoplasticrdquo Journal of ElectronicMaterials vol 44 no 7 pp 2308ndash2311 2015

[14] S-J Bao Y Li C M Li Q Bao Q Lu and J Guo ldquoShapeevolution and magnetic properties of cobalt sulfiderdquo CrystalGrowth amp Design vol 8 no 10 pp 3745ndash3749 2008

[15] M Congiu M Bonomo M L D Marco et al ldquoCobalt sulfideas counter electrode in p-type dye-sensitized solar cellsrdquoChemistry Select vol 1 no 11 pp 2808ndash2815 2016

[16] J Huo J Wu M Zheng Y Tu and Z Lan ldquoEffect of am-monia on electrodeposition of cobalt sulfide and nickel sulfidecounter electrodes for dye-sensitized solar cellsrdquo Electro-chimica Acta vol 180 pp 574ndash580 2015

[17] D J Yu Y F Yuan D Zhang et al ldquoNickel cobalt sulfidenanotube array on nickel foam as anodematerial for advancedlithium-ion batteriesrdquo Electrochimica Acta vol 198pp 280ndash286 2016

[18] F Han C Zhang B Sun W Tang J Yang and X Li ldquoDual-carbon phase-protective cobalt sulfide nanoparticles withcable-type and mesoporous nanostructure for enhanced cy-cling stability in sodium and lithium ion batteriesrdquo Carbonvol 118 pp 731ndash742 2017

[19] X Zhang H Wang and G Wang ldquoCobalt sulfide nano-particles anchored in three-dimensional carbon nanosheetnetworks for lithium and sodium ion batteries with enhancedelectrochemical performancerdquo Journal of Colloid and Inter-face Science vol 492 pp 41ndash50 2017

[20] S S Kamble A Sikora S T Pawar R C KambaleN N Maldar and L P Deshmukh ldquoMorphology reliance ofcobalt sulfide thin films a chemo-thermo-mechanical per-ceptionrdquo Journal of Alloys and Compounds vol 631pp 303ndash314 2015

[21] G Hodes Chemical Solution Deposition of SemiconductorFilms CRC Press Boca Raton FL USA 2002

[22] T Abza F K Ampong F G Hone I Nkrumah R K Nkumand F Boakye ldquoA new route for the synthesis of CdS thin

films from acidic chemical bathsrdquo International Journal of6in Films Science and Technology vol 6 no 2 pp 67ndash712017

[23] P K Basu and P Pramanik ldquoSolution growth technique forthe deposition of cobalt sulphide thin filmrdquo Journal of Ma-terials Science Letters vol 5 no 12 pp 1216ndash1218 1986

[24] S Ariponnammal and T Srinivasan ldquoGrowth and charac-terization of cobalt sulphide nanorodsrdquo Research Journal ofRecent Sciences vol 2 pp 102ndash105 2013

[25] Z Yu J Du S Guo J Zhang and Y Matsumoto ldquoCoS thinfilms prepared with modified chemical bath depositionrdquo6inSolid Films vol 415 no 1-2 pp 173ndash176 2002

[26] F C Eze and C E Okeke ldquoChemical-bath-deposited cobaltsulphide films preparation effectsrdquo Materials Chemistry andPhysics vol 47 no 1 pp 31ndash36 1997

[27] C Lokhande ldquoChemical deposition of CoS films from acidicbathrdquo Indian Journal of Pure amp Applied Physics vol 30 no 5pp 245ndash247 1992

[28] J Pu Z Shen J Zheng et al ldquoMultifunctional Co 3 S 4sulfur nanotubes for enhanced lithium-sulfur battery per-formancerdquo Nano Energy vol 37 pp 7ndash14 2017

[29] J H Joshi D K Kanchan M J Joshi H O Jethva andK D Parikh ldquoDielectric relaxation complex impedance andmodulus spectroscopic studies of mix phase rod like cobaltsulfide nanoparticlesrdquo Materials Research Bulletin vol 93pp 63ndash73 2017

[30] S Mane S Kamble and L Deshmukh ldquoCobalt sulphide thinfilms chemical bath deposition growth and propertiesrdquoMaterials Letters vol 65 no 17-18 pp 2639ndash2641 2011

[31] S Y Chae Y J Hwang J-H Choi and O-S Joo ldquoCobaltsulfide thin films for counter electrodes of dye-sensitized solarcells with cobalt complex based electrolytesrdquo ElectrochimicaActa vol 114 pp 745ndash749 2013

[32] M Sonawane S Gosavi and R Patil ldquoNanocrystalline CoSthin films prepared by modified chemical bath depositionmethodrdquo Journal of Chemical Biological and Physical Sciences(JCBPS) vol 4 no 3 p 2416 2014

[33] K Yamaguchi T Yoshida T Sugiura and H Minoura ldquoAnovel approach for CdS thin-film deposition electrochemi-cally induced atom-by-atom growth of CdS thin films fromacidic chemical bathrdquo 6e Journal of Physical Chemistry Bvol 102 no 48 pp 9677ndash9686 1998

[34] D P Dutta G Sharma and I K Gopalakrishnan ldquoSinglemolecular precursor route to nanocrystalline Jaipurite syn-thesis characterization and magnetic propertyrdquo MaterialsLetters vol 62 no 8-9 pp 275ndash1278 2008

[35] T Abza F K Ampong F G Hone R K Nkum andF Boakye ldquoPreparation of cadmium zinc sulfide(Cd1minusxZnxS) thin films from acidic chemical bathsrdquo 6inSolid Films vol 666 pp 28ndash33 2018

[36] T B Nasr N Kamoun M Kanzari and R Bennaceur ldquoEffectof pH on the properties of ZnS thin films grown by chemicalbath depositionrdquo 6in Solid Films vol 500 no 1-2 pp 4ndash82006

[37] H Ferhati and F Djeffal ldquoGraded band-gap engineering forincreased efficiency in CZTS solar cellsrdquo Optical Materialsvol 76 pp 393ndash399 2018

[38] M Neuwirth E Seydel J Seeger A Welle H Kalt andM Hetterich ldquoBand-gap tuning of Cu2ZnSn(SSe)4 solar cellabsorbers via defined incorporation of sulphur based on apost-sulphurization processrdquo Solar Energy Materials andSolar Cells vol 182 pp 158ndash165 2018

[39] M Xu H Niu J Huang et al ldquoFacile synthesis of graphene-like Co3S4 nanosheetAg2S nanocomposite with enhanced

8 Advances in Materials Science and Engineering

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9

2426 nm 5632 nm and 6002 nm respectively ese re-sults show that the dominant hexagonal CoS phase observedat 2 hrs deposition time was gradually decreased and at

35 hrs of deposition time it was dominated by the cubicCo9S8 phase [29] e Co3S4 phase did not show consistentcrystallite size variation with deposition time

Table 1 Some structural parameters of cobalt sulfide thin films and their reference Pdf file numbers

Deposition time (hrs) Measured 2θ (deg) Phase Index Standard

2

124 mdash mdash148 CoS Pdf 01-1279 mdash164 Co3S4 Pdf 75-1561 (111)2118 CoS Pdf 01-1279 (102)2464 Co9S8 Pdf 75-2023 (220)4564 Co9S8Co4S3 Pdf 190364Pdf021338 (400)(400)505 Co3S4Co9S8 Co4S3 Pdf 75-1561Pdf 190364Pdf021338 (511)(331)(331)

25

1224 mdash mdash mdash148 CoS Pdf 01-1279 mdash164 Co3S4 Pdf 75-1561 (111)1836 Co9S8 Pdf 75-2023 (200)2114 CoS Pdf 01-1279 (102)2232 CoSCo9S8 Pdf 01-1279Pdf 190364 mdash(200)2352 CoS Pdf 01-1279 mdash2464 Co9S8 Pdf 75-2023 (220)2954 Co9S8 Pdf 75-2023 (331)3076 CoS Pdf750605Pdf 01-1279 (100)---

3

1226 mdash mdash mdash1482 CoS Pdf 01-1279 mdash1632 Co3S4 Pdf 75-1561 (111)1824 Co9S8 Pdf752023 (200)2024 CoS Pdf 01-1279 mdash2146 CoS Pdf 01-1279 (102)2202 CoSCo9S8 Pdf 01-1279Pdf 190364 mdash(200)2352 CoS Pdf 01-1279 mdash2458 Co9S8 Pdf 75-2023 (220)498s4 Co9S8 Pdf 190364 (331)

35

1492 CoS Pdf 01-1279 mdash1528 CoSCo9S8 Pdf 01-1279Pdf 75-2023 mdash(111)1844 Co9S8 Pdf 75-2023 (200)2034 CoS Pdf 01-1279 mdash2136 CoS Pdf 01-1279 (102)2212 CoSCo9S8 Pdf 01-1279Pdf 190364 mdash(200)5048 Co3S4Co9S8 Co4S3 Pdf 75-1561Pdf 190364Pdf021338 (511)(331)(331)

t = 35 hrs

t = 3 hrs

t = 25 hrs

t = 2 hrs

4000

3500

3000

2500

2000

1500

1000

500

0

Inte

nsity

(au

)

0 10 20 30 40 50 60 70 80 902θ (deg)

Figure 1 XRD pattern of cobalt sulfide thin films deposited at different deposition time

Advances in Materials Science and Engineering 3

32 Morphology and Composition Analysis Figures 2(a) and2(b) show typical SEM images of cobalt sulfide thin filmsdeposited at 2 hrs and 3 hrs respectively e films coveredthe substrate uniformly with cottony spherical grains at thebackground No pinholes and cracks were observed for bothfilms e SEM images also show isolated spherical-shapedand polygonal-shaped grains on the surface of the filmsdeposited at 2 and 3 hrs respectively e size of the po-lygonal-shaped grains varied from 09 μm to 228 μm Manyauthors reported complex multifaceted SEM images ofcobalt sulfide thin films formed by a network of elongatedgrains [3 20 30 31] However few authors reported SEMimages similar to the current result [24 25 32] particularlywhen they used Na2S as an anion source Na2S is expected togenerate free S2minus easily to assist ion-by-ion depositionmechanism for the film growth e observed morphologyin the current work could be resulted from the ion-by-ionfilm growth mechanism which is common in most of theacidic bath-deposited chalcogenide thin films [22 33]However the larger top grains indicate the adsorption ofcluster of grains on the surface of the substrate at the finalgrowth stage of the films which were initially grown in thesolution

Typical EDX spectra of the cobalt sulfide thin films arepresented in Figures 3(a) and 3(b) e EDX analysis of thethin films deposited at 2 hrs and 3 hrs revealed the presenceof cobalt (Co) and sulfur (S) with no Co to S ratio variationwith deposition time e ratio of Co S in the cobalt sulfidethin films deposited at 2 hrs and 3 hrs is 23 77 e sig-nificant dominance of sulfur could be resulted from theexistence of free sulfur in the interstitial site as well as thecobalt vacancy in the crystal structure However manyreports show Co-dominated cobalt sulfide thin films[20 30] e presence of carbon oxygen sodium alumi-num and other elements could be related to the glasssubstrate and the carbon coating of the films before SEMEDX measurements [34]

33 Optical Properties

331 UV-Vis Spectroscopic Study e UV-Vis opticalproperties of the cobalt sulfide thin films deposited at dif-ferent deposition periods were investigated bymeasuring theabsorbance of the films in the wavelength range of500ndash1500 nm All the films have broad absorption edge andhigh absorption in the visible region Energy band gaps andtransition type of the thin films were obtained using Sternrelationship (Equation (2)) at the near-fundamental ab-sorption edge [35]

A k hv minus Eg1113872 11138731113960 1113961

n2

hv (2)

where A is the absorbance k is the constant v is the fre-quency of the radiation h is Planckrsquos constant and n is 1 forthe direct transition and 4 for the indirect transition In thecase of direct transition (Ah])2 the photon energy (h])(Equation (2)) has linear relation in the region next to theonset of fundamental absorption [36] Such a linear relation

is observed in all the current samples as shown in Figure 4implying a direct transition thus n 1e band gap energy(Eg) was obtained by extrapolating the linear portion of the(Ahv)2 vs (hv) curve towards the hv axis e band gaps ofthe thin films deposited at 2 hrs 25 hrs 3 hrs and 35 hrswere 175 eV 165 eV 155 eV and 13 eV respectively(Figure 4) e decrease in the band gap could be due to theincrease in the thickness and the crystallite size with de-position time as the terminal thickness and crystallite sizehave a significant influence on the band gap of the films [20]e relatively higher band gap values of the films comparedto the commonly reported value could be related to theexistence of excess sulfur in the thin films e high ab-sorbance in the visible light region and the band gaps of thefilms within the range from 13 eV to 175 eV make the filmsan appropriate material as an absorber layer in thin film solarcells [37 38] as well as efficient visible light photocatalyst[39]

332 FTIR Analysis FTIR spectroscopy can provide fun-damental information on the molecular structure of organicand inorganic components Figure 5 shows the FTIR spectraof cobalt sulfide thin films deposited at 2 hrs and 35 hrsBoth spectra consist of five absorption peaks e film de-posited at 2 hrs has absorption peaks at 3209 cmminus11638 cmminus1 1428 cmminus1 1067 cmminus1 and 607 cmminus1 and cobaltsulfide thin film deposited at 35 hrs has absorption peaks at3202 cmminus1 1560 cmminus1 1400 cmminus1 1068 cmminus1 and 609 cmminus1e peak at 3200 cmminus1 and 1638 cmminus1 are characteristicpeaks to the stretching vibration and bending vibration ofOH groups due to H2Omolecules indicating the absorptionof water by the samples [40] e absorption peaks at1428 cmminus1 and 1067 cmminus1 were assigned to C-O-H and C-Ostretching vibrations respectively e carbon containingcompounds could be either from the starting reagents as allof them are carbon containing reagents or from atmosphericCO2 In addition the intense peaks at 1067 cmminus1 and1068 cmminus1 correspond to the bending vibration of sulfonatedgroups in the CoS Co3S4 and Co9S8 phases e peakobserved at 607 cmminus1 is a characteristic peak of Co-Sstretching vibration modes and the polysufide bond group[41 42] e presence of the 608 cmminus1 frequency polysufideband is consistent with excess of sulfur in the thin films asconfirmed by the EDX analysis e observed bands of theOH bending vibration and C-OH deformation vibrationsignificantly shifted to lower frequency position with in-creasing deposition time signifying the weakening of dif-ferent modes of vibrations of different functional groupsparticularly the OH and C-OH groups However no sig-nificant shift on the position of the bands for the sulfonatedgroup bending vibration and the double sulfide group isobserved with deposition time e increase in the ab-sorption intensity of the polysulfide group could be relatedto the increase in the particle size and thickness of the filmswith deposition time e band broadening observed in thesulfur containing group indicates the nonuniform distri-bution of particle size and shape with deposition time etwo most intense absorption bands due to the sulfur

4 Advances in Materials Science and Engineering

containing compound at the frequency of 607 cmminus1 and1068 cmminus1 implies the existence of minimum impurities dueto other nonsulfide groups [5]

34 Photoluminescence Analysis e photoluminescence(PL) property of the cobalt sulfide thin films was studied byusing xenon lamp for electron excitation at room

temperature e emission spectra were observed in therange of 340ndash500 nm Broad intense peaks corresponding toviolet light were observed at 381 nm 384 nm 386 nm and391 nm for cobalt sulfide thin films deposited at 2 hrs 25 hrs3 hrs and 35 hrs respectively (Figure 6)e violet emissionpeaks could appear at 366 nm as the size of CoS nano-particles reduces [43] e peak broadening could beresulted from the nonuniform distribution of grains due to

260000240000220000200000180000160000140000120000100000

800006000040000

020000

240000(b)

220000

200000

180000

160000

140000

120000

100000

80000

60000

40000

20000

0

CKa

CKa

CaKa

CaKb

CaKb

OKa

OKa

FeLa

FeL1

CoL

aC

oL1

CoL

aC

oL1

Nak

aM

gKa

Nak

aM

gKa

AlK

aSi

ka

Sika

MoL

1M

oLa

MoL

bSk

aSk

b

MoL

1M

oLa

MoL

bSk

aSk

b

FeKe

sc

CoK

esc

CaKa

CaKb

CoK

esc

CoK

a

FeKa

FeKb

Cok

b

Cok

a

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

(a)

Figure 3 EDX spectra of cobalt sulfide thin films deposited at (a) 2 hours and (b) 3 hours

2microm

(a)

2microm

(b)

Figure 2 SEM images of cobalt sulfide thin films deposited at (a) 2 hrs and (b) 3 hrs

Advances in Materials Science and Engineering 5

the presence of different phases of cobalt sulfide e redshift in the violet light PL emission could be due to theconduction and valence bands broadening as a result ofincrease in crystallite size with deposition time e fluo-rescence spectra of all the thin films have shown blueemission peaks at the same wavelength of 467 nm Blue PLemission peak of wavelength 460 nm was reported by Emadiet al [44] for cobalt sulfide nanoparticles Films depositedfor a period of 3 hrs and 35 hrs have shown additionalultraviolet emission peaks of 349 nm As the PL properties ofsemiconductors are extremely sensitive to the local envi-ronment and to the presence of structural defects the violetand blue emissions are expected to be originated from Covacancy and S interstitial-related defects [24 45]

35 Electrical Resistivity Measurement e electrical resis-tivity of the films was measured by the two-probe method atroom temperature e measured values for films depositedat 2 hrs 25 hrs 3 hrs and 35 hrs were 17 times 106 5 times 1045 times 103 and 13 times 104Ωmiddotcm respectively e room tem-perature resistivity of the films is in the range of semi-conductorsrsquo resistivity except the film deposited at 2 hrs eresistivity values agreed with other researchersrsquo report[46 47] e decrease in resistivity could be attributed to theincrease in film thickness and crystallite size as the depo-sition period increases [48 49] is results in the valenceand conduction band broadening which inturn results inband gap narrowing e narrow band gap films becomemore conductive as electrons can easily be raised from the

0

4

8

12

(Ahv

)2 (eV

)2

13 18 2308hv (eV)

t = 2 hrst = 25 hrs

t = 3 hrs35 hrs

Figure 4 e band gaps of cobalt sulfide thin films obtained from the (Ahv)2 vs hv plots

Wave number (cmndash1)

10095909580757065605550454035

0 1000 2000 3000 4000

Deformation C-O-H

C-O streching or sulfonatedgroup bending

Polysulfidegroup

607 10681067

609

14001560 3202

32091638

1428

Perc

enta

ge tr

ansm

ittan

ce

Bending OH Streching OH

2 hrs35 hrs

Figure 5 FTIR spectra of cobalt sulfide thin films deposited at 2 and 35 hrs

6 Advances in Materials Science and Engineering

valence band to conduction band by room temperaturethermal energy

4 Conclusion

Cobalt sulfide thin films were synthesized from acidicchemical baths containing cobalt acetate thioacetamideand disodium EDTA by varying the deposition time eeffects of deposition time on the structural morphologicaloptical photoluminescence and electrical properties of thefilms were investigatede films consisted of mixed phasesof hexagonal CoS face-centered cubic Co3S4 and cubicCo9S8 phases e films deposited at 2 hrs and 25 hrs aredominated by the hexagonal CoS phase and that depositedat 35 hrs are dominated by the cubic Co9S8 phase efilmsrsquo surface morphologies were dominantly formed fromcompacted cottony spherical grains without pinholes andcracks e EDX and the FTIR spectra confirmed thepresence of Co and S in the films PL investigation con-firmed emission of ultraviolet violet and blue lights uponexcitation by xenon lampe violet light gets red shifted asthe deposition period increased from 2 hrs to 35 hrs eoptical analysis result revealed high visible light absorptionof the films and a red shift in the band gap with increasingdeposition time e two-probe electrical measurementshowed decrease in the resistivity of the films with increasein the crystallite size

Data Availability

e XRD UV-VIS FTIR and photoluminescence data usedto support the findings of this study are available from thecorresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors acknowledge the Hawassa University forfunding this research work

References

[1] L Deshmukh and S Mane ldquoLiquid phase chemical depositionof cobalt sulphide thin films growth and propertiesrdquo DigestJournal of Nanomaterials and Biostructures vol 6 no 3pp 931ndash936 2011

[2] L P Mgabi B S Dladla M A Malik S S Garje J Akhtarand N Revaprasadu ldquoDeposition of cobalt and nickel sulfidethin films from thio- and alkylthio-urea complexes as pre-cursors via the aerosol assisted chemical vapour depositiontechniquerdquo 6in Solid Films vol 564 pp 51ndash57 2014

[3] S S Kamble A Sikora S T Pawar N N Maldar andL P Deshmukh ldquoCobalt sulfide thin films chemical growthreaction kinetics and microstructural analysisrdquo Journal ofAlloys and Compounds vol 623 pp 466ndash472 2015

[4] X Chen Z Zhang Z Qiu C Shi and X Li ldquoHydrothermalfabrication and characterization of polycrystalline linneite(Co3S4) nanotubes based on the Kirkendall effectrdquo Journal ofColloid and Interface Science vol 308 no 1 pp 271ndash2752007

[5] A Mohammadi N Arsalani A G Tabrizi S E MoosavifardZ Naqshbandi and L S Ghadimi ldquoEngineering rGO-CNTwrapped Co3S4 nanocomposites for high-performanceasymmetric supercapacitorsrdquo Chemical Engineering Journalvol 334 pp 66ndash80 2018

20 hrs25 hrs

30 hrs35 hrs

12 times 107

90 times 106

60 times 106

30 times 106

00

PL in

tens

ity (a

u)

400 450 500350Wavelength of emission peaks (nm)

(a)

340 380 440360 400 420Film thickness (nm)

316

318

32

322

324

326

E em

issio

n (eV

)(b)

Figure 6 (a) e photoluminescence spectra and (b) the emission energy of intense PL peak (Eemission) vs film thickness of cobalt sulfidethin films deposited at various deposition time

Advances in Materials Science and Engineering 7

[6] F Tao Y-Q Zhao G-Q Zhang and H-L Li ldquoElectro-chemical characterization on cobalt sulfide for electro-chemical supercapacitorsrdquo Electrochemistry Communicationsvol 9 no 6 pp 1282ndash1287 2007

[7] S B Kale A C Lokhande R B Pujari and C D LokhandeldquoCobalt sulfide thin films for electrocatalytic oxygen evolutionreaction and supercapacitor applicationsrdquo Journal of Colloidand Interface Science vol 532 pp 491ndash499 2018

[8] L-L Feng G-D Li Y Liu et al ldquoCarbon-armored Co9S8nanoparticles as all-pH efficient and durable H2-evolvingelectrocatalystsrdquo ACS Applied Materials amp Interfaces vol 7no 1 pp 980ndash988 2015

[9] L-L Feng M Fan Y Wu et al ldquoMetallic Co9S8 nanosheetsgrown on carbon cloth as efficient binder-free electrocatalystsfor the hydrogen evolution reaction in neutral mediardquo Journalof Materials Chemistry A vol 4 no 18 pp 6860ndash6867 2016

[10] L Zhu D Susac M Teo et al ldquoInvestigation of CoS2-basedthin films as model catalysts for the oxygen reduction reac-tionrdquo Journal of Catalysis vol 258 no 1 pp 235ndash242 2008

[11] A W Peters Z Li O K Farha and J T Hupp ldquoAtomicallyprecise growth of catalytically active cobalt sulfide on flatsurfaces and within a metal-organic framework via atomiclayer depositionrdquo ACS Nano vol 9 no 8 pp 8484ndash84902015

[12] S Dou L Tao J Huo SWang and L Dai ldquoEtched and dopedCo9S8graphene hybrid for oxygen electrocatalysisrdquo Energy ampEnvironmental Science vol 9 no 4 pp 1320ndash1326 2016

[13] N Rumale S Arbuj G Umarji et al ldquoTuning magneticbehavior of nanoscale cobalt sulfide and its nanocompositewith an engineering thermoplasticrdquo Journal of ElectronicMaterials vol 44 no 7 pp 2308ndash2311 2015

[14] S-J Bao Y Li C M Li Q Bao Q Lu and J Guo ldquoShapeevolution and magnetic properties of cobalt sulfiderdquo CrystalGrowth amp Design vol 8 no 10 pp 3745ndash3749 2008

[15] M Congiu M Bonomo M L D Marco et al ldquoCobalt sulfideas counter electrode in p-type dye-sensitized solar cellsrdquoChemistry Select vol 1 no 11 pp 2808ndash2815 2016

[16] J Huo J Wu M Zheng Y Tu and Z Lan ldquoEffect of am-monia on electrodeposition of cobalt sulfide and nickel sulfidecounter electrodes for dye-sensitized solar cellsrdquo Electro-chimica Acta vol 180 pp 574ndash580 2015

[17] D J Yu Y F Yuan D Zhang et al ldquoNickel cobalt sulfidenanotube array on nickel foam as anodematerial for advancedlithium-ion batteriesrdquo Electrochimica Acta vol 198pp 280ndash286 2016

[18] F Han C Zhang B Sun W Tang J Yang and X Li ldquoDual-carbon phase-protective cobalt sulfide nanoparticles withcable-type and mesoporous nanostructure for enhanced cy-cling stability in sodium and lithium ion batteriesrdquo Carbonvol 118 pp 731ndash742 2017

[19] X Zhang H Wang and G Wang ldquoCobalt sulfide nano-particles anchored in three-dimensional carbon nanosheetnetworks for lithium and sodium ion batteries with enhancedelectrochemical performancerdquo Journal of Colloid and Inter-face Science vol 492 pp 41ndash50 2017

[20] S S Kamble A Sikora S T Pawar R C KambaleN N Maldar and L P Deshmukh ldquoMorphology reliance ofcobalt sulfide thin films a chemo-thermo-mechanical per-ceptionrdquo Journal of Alloys and Compounds vol 631pp 303ndash314 2015

[21] G Hodes Chemical Solution Deposition of SemiconductorFilms CRC Press Boca Raton FL USA 2002

[22] T Abza F K Ampong F G Hone I Nkrumah R K Nkumand F Boakye ldquoA new route for the synthesis of CdS thin

films from acidic chemical bathsrdquo International Journal of6in Films Science and Technology vol 6 no 2 pp 67ndash712017

[23] P K Basu and P Pramanik ldquoSolution growth technique forthe deposition of cobalt sulphide thin filmrdquo Journal of Ma-terials Science Letters vol 5 no 12 pp 1216ndash1218 1986

[24] S Ariponnammal and T Srinivasan ldquoGrowth and charac-terization of cobalt sulphide nanorodsrdquo Research Journal ofRecent Sciences vol 2 pp 102ndash105 2013

[25] Z Yu J Du S Guo J Zhang and Y Matsumoto ldquoCoS thinfilms prepared with modified chemical bath depositionrdquo6inSolid Films vol 415 no 1-2 pp 173ndash176 2002

[26] F C Eze and C E Okeke ldquoChemical-bath-deposited cobaltsulphide films preparation effectsrdquo Materials Chemistry andPhysics vol 47 no 1 pp 31ndash36 1997

[27] C Lokhande ldquoChemical deposition of CoS films from acidicbathrdquo Indian Journal of Pure amp Applied Physics vol 30 no 5pp 245ndash247 1992

[28] J Pu Z Shen J Zheng et al ldquoMultifunctional Co 3 S 4sulfur nanotubes for enhanced lithium-sulfur battery per-formancerdquo Nano Energy vol 37 pp 7ndash14 2017

[29] J H Joshi D K Kanchan M J Joshi H O Jethva andK D Parikh ldquoDielectric relaxation complex impedance andmodulus spectroscopic studies of mix phase rod like cobaltsulfide nanoparticlesrdquo Materials Research Bulletin vol 93pp 63ndash73 2017

[30] S Mane S Kamble and L Deshmukh ldquoCobalt sulphide thinfilms chemical bath deposition growth and propertiesrdquoMaterials Letters vol 65 no 17-18 pp 2639ndash2641 2011

[31] S Y Chae Y J Hwang J-H Choi and O-S Joo ldquoCobaltsulfide thin films for counter electrodes of dye-sensitized solarcells with cobalt complex based electrolytesrdquo ElectrochimicaActa vol 114 pp 745ndash749 2013

[32] M Sonawane S Gosavi and R Patil ldquoNanocrystalline CoSthin films prepared by modified chemical bath depositionmethodrdquo Journal of Chemical Biological and Physical Sciences(JCBPS) vol 4 no 3 p 2416 2014

[33] K Yamaguchi T Yoshida T Sugiura and H Minoura ldquoAnovel approach for CdS thin-film deposition electrochemi-cally induced atom-by-atom growth of CdS thin films fromacidic chemical bathrdquo 6e Journal of Physical Chemistry Bvol 102 no 48 pp 9677ndash9686 1998

[34] D P Dutta G Sharma and I K Gopalakrishnan ldquoSinglemolecular precursor route to nanocrystalline Jaipurite syn-thesis characterization and magnetic propertyrdquo MaterialsLetters vol 62 no 8-9 pp 275ndash1278 2008

[35] T Abza F K Ampong F G Hone R K Nkum andF Boakye ldquoPreparation of cadmium zinc sulfide(Cd1minusxZnxS) thin films from acidic chemical bathsrdquo 6inSolid Films vol 666 pp 28ndash33 2018

[36] T B Nasr N Kamoun M Kanzari and R Bennaceur ldquoEffectof pH on the properties of ZnS thin films grown by chemicalbath depositionrdquo 6in Solid Films vol 500 no 1-2 pp 4ndash82006

[37] H Ferhati and F Djeffal ldquoGraded band-gap engineering forincreased efficiency in CZTS solar cellsrdquo Optical Materialsvol 76 pp 393ndash399 2018

[38] M Neuwirth E Seydel J Seeger A Welle H Kalt andM Hetterich ldquoBand-gap tuning of Cu2ZnSn(SSe)4 solar cellabsorbers via defined incorporation of sulphur based on apost-sulphurization processrdquo Solar Energy Materials andSolar Cells vol 182 pp 158ndash165 2018

[39] M Xu H Niu J Huang et al ldquoFacile synthesis of graphene-like Co3S4 nanosheetAg2S nanocomposite with enhanced

8 Advances in Materials Science and Engineering

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9

32 Morphology and Composition Analysis Figures 2(a) and2(b) show typical SEM images of cobalt sulfide thin filmsdeposited at 2 hrs and 3 hrs respectively e films coveredthe substrate uniformly with cottony spherical grains at thebackground No pinholes and cracks were observed for bothfilms e SEM images also show isolated spherical-shapedand polygonal-shaped grains on the surface of the filmsdeposited at 2 and 3 hrs respectively e size of the po-lygonal-shaped grains varied from 09 μm to 228 μm Manyauthors reported complex multifaceted SEM images ofcobalt sulfide thin films formed by a network of elongatedgrains [3 20 30 31] However few authors reported SEMimages similar to the current result [24 25 32] particularlywhen they used Na2S as an anion source Na2S is expected togenerate free S2minus easily to assist ion-by-ion depositionmechanism for the film growth e observed morphologyin the current work could be resulted from the ion-by-ionfilm growth mechanism which is common in most of theacidic bath-deposited chalcogenide thin films [22 33]However the larger top grains indicate the adsorption ofcluster of grains on the surface of the substrate at the finalgrowth stage of the films which were initially grown in thesolution

Typical EDX spectra of the cobalt sulfide thin films arepresented in Figures 3(a) and 3(b) e EDX analysis of thethin films deposited at 2 hrs and 3 hrs revealed the presenceof cobalt (Co) and sulfur (S) with no Co to S ratio variationwith deposition time e ratio of Co S in the cobalt sulfidethin films deposited at 2 hrs and 3 hrs is 23 77 e sig-nificant dominance of sulfur could be resulted from theexistence of free sulfur in the interstitial site as well as thecobalt vacancy in the crystal structure However manyreports show Co-dominated cobalt sulfide thin films[20 30] e presence of carbon oxygen sodium alumi-num and other elements could be related to the glasssubstrate and the carbon coating of the films before SEMEDX measurements [34]

33 Optical Properties

331 UV-Vis Spectroscopic Study e UV-Vis opticalproperties of the cobalt sulfide thin films deposited at dif-ferent deposition periods were investigated bymeasuring theabsorbance of the films in the wavelength range of500ndash1500 nm All the films have broad absorption edge andhigh absorption in the visible region Energy band gaps andtransition type of the thin films were obtained using Sternrelationship (Equation (2)) at the near-fundamental ab-sorption edge [35]

A k hv minus Eg1113872 11138731113960 1113961

n2

hv (2)

where A is the absorbance k is the constant v is the fre-quency of the radiation h is Planckrsquos constant and n is 1 forthe direct transition and 4 for the indirect transition In thecase of direct transition (Ah])2 the photon energy (h])(Equation (2)) has linear relation in the region next to theonset of fundamental absorption [36] Such a linear relation

is observed in all the current samples as shown in Figure 4implying a direct transition thus n 1e band gap energy(Eg) was obtained by extrapolating the linear portion of the(Ahv)2 vs (hv) curve towards the hv axis e band gaps ofthe thin films deposited at 2 hrs 25 hrs 3 hrs and 35 hrswere 175 eV 165 eV 155 eV and 13 eV respectively(Figure 4) e decrease in the band gap could be due to theincrease in the thickness and the crystallite size with de-position time as the terminal thickness and crystallite sizehave a significant influence on the band gap of the films [20]e relatively higher band gap values of the films comparedto the commonly reported value could be related to theexistence of excess sulfur in the thin films e high ab-sorbance in the visible light region and the band gaps of thefilms within the range from 13 eV to 175 eV make the filmsan appropriate material as an absorber layer in thin film solarcells [37 38] as well as efficient visible light photocatalyst[39]

332 FTIR Analysis FTIR spectroscopy can provide fun-damental information on the molecular structure of organicand inorganic components Figure 5 shows the FTIR spectraof cobalt sulfide thin films deposited at 2 hrs and 35 hrsBoth spectra consist of five absorption peaks e film de-posited at 2 hrs has absorption peaks at 3209 cmminus11638 cmminus1 1428 cmminus1 1067 cmminus1 and 607 cmminus1 and cobaltsulfide thin film deposited at 35 hrs has absorption peaks at3202 cmminus1 1560 cmminus1 1400 cmminus1 1068 cmminus1 and 609 cmminus1e peak at 3200 cmminus1 and 1638 cmminus1 are characteristicpeaks to the stretching vibration and bending vibration ofOH groups due to H2Omolecules indicating the absorptionof water by the samples [40] e absorption peaks at1428 cmminus1 and 1067 cmminus1 were assigned to C-O-H and C-Ostretching vibrations respectively e carbon containingcompounds could be either from the starting reagents as allof them are carbon containing reagents or from atmosphericCO2 In addition the intense peaks at 1067 cmminus1 and1068 cmminus1 correspond to the bending vibration of sulfonatedgroups in the CoS Co3S4 and Co9S8 phases e peakobserved at 607 cmminus1 is a characteristic peak of Co-Sstretching vibration modes and the polysufide bond group[41 42] e presence of the 608 cmminus1 frequency polysufideband is consistent with excess of sulfur in the thin films asconfirmed by the EDX analysis e observed bands of theOH bending vibration and C-OH deformation vibrationsignificantly shifted to lower frequency position with in-creasing deposition time signifying the weakening of dif-ferent modes of vibrations of different functional groupsparticularly the OH and C-OH groups However no sig-nificant shift on the position of the bands for the sulfonatedgroup bending vibration and the double sulfide group isobserved with deposition time e increase in the ab-sorption intensity of the polysulfide group could be relatedto the increase in the particle size and thickness of the filmswith deposition time e band broadening observed in thesulfur containing group indicates the nonuniform distri-bution of particle size and shape with deposition time etwo most intense absorption bands due to the sulfur

4 Advances in Materials Science and Engineering

containing compound at the frequency of 607 cmminus1 and1068 cmminus1 implies the existence of minimum impurities dueto other nonsulfide groups [5]

34 Photoluminescence Analysis e photoluminescence(PL) property of the cobalt sulfide thin films was studied byusing xenon lamp for electron excitation at room

temperature e emission spectra were observed in therange of 340ndash500 nm Broad intense peaks corresponding toviolet light were observed at 381 nm 384 nm 386 nm and391 nm for cobalt sulfide thin films deposited at 2 hrs 25 hrs3 hrs and 35 hrs respectively (Figure 6)e violet emissionpeaks could appear at 366 nm as the size of CoS nano-particles reduces [43] e peak broadening could beresulted from the nonuniform distribution of grains due to

260000240000220000200000180000160000140000120000100000

800006000040000

020000

240000(b)

220000

200000

180000

160000

140000

120000

100000

80000

60000

40000

20000

0

CKa

CKa

CaKa

CaKb

CaKb

OKa

OKa

FeLa

FeL1

CoL

aC

oL1

CoL

aC

oL1

Nak

aM

gKa

Nak

aM

gKa

AlK

aSi

ka

Sika

MoL

1M

oLa

MoL

bSk

aSk

b

MoL

1M

oLa

MoL

bSk

aSk

b

FeKe

sc

CoK

esc

CaKa

CaKb

CoK

esc

CoK

a

FeKa

FeKb

Cok

b

Cok

a

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

(a)

Figure 3 EDX spectra of cobalt sulfide thin films deposited at (a) 2 hours and (b) 3 hours

2microm

(a)

2microm

(b)

Figure 2 SEM images of cobalt sulfide thin films deposited at (a) 2 hrs and (b) 3 hrs

Advances in Materials Science and Engineering 5

the presence of different phases of cobalt sulfide e redshift in the violet light PL emission could be due to theconduction and valence bands broadening as a result ofincrease in crystallite size with deposition time e fluo-rescence spectra of all the thin films have shown blueemission peaks at the same wavelength of 467 nm Blue PLemission peak of wavelength 460 nm was reported by Emadiet al [44] for cobalt sulfide nanoparticles Films depositedfor a period of 3 hrs and 35 hrs have shown additionalultraviolet emission peaks of 349 nm As the PL properties ofsemiconductors are extremely sensitive to the local envi-ronment and to the presence of structural defects the violetand blue emissions are expected to be originated from Covacancy and S interstitial-related defects [24 45]

35 Electrical Resistivity Measurement e electrical resis-tivity of the films was measured by the two-probe method atroom temperature e measured values for films depositedat 2 hrs 25 hrs 3 hrs and 35 hrs were 17 times 106 5 times 1045 times 103 and 13 times 104Ωmiddotcm respectively e room tem-perature resistivity of the films is in the range of semi-conductorsrsquo resistivity except the film deposited at 2 hrs eresistivity values agreed with other researchersrsquo report[46 47] e decrease in resistivity could be attributed to theincrease in film thickness and crystallite size as the depo-sition period increases [48 49] is results in the valenceand conduction band broadening which inturn results inband gap narrowing e narrow band gap films becomemore conductive as electrons can easily be raised from the

0

4

8

12

(Ahv

)2 (eV

)2

13 18 2308hv (eV)

t = 2 hrst = 25 hrs

t = 3 hrs35 hrs

Figure 4 e band gaps of cobalt sulfide thin films obtained from the (Ahv)2 vs hv plots

Wave number (cmndash1)

10095909580757065605550454035

0 1000 2000 3000 4000

Deformation C-O-H

C-O streching or sulfonatedgroup bending

Polysulfidegroup

607 10681067

609

14001560 3202

32091638

1428

Perc

enta

ge tr

ansm

ittan

ce

Bending OH Streching OH

2 hrs35 hrs

Figure 5 FTIR spectra of cobalt sulfide thin films deposited at 2 and 35 hrs

6 Advances in Materials Science and Engineering

valence band to conduction band by room temperaturethermal energy

4 Conclusion

Cobalt sulfide thin films were synthesized from acidicchemical baths containing cobalt acetate thioacetamideand disodium EDTA by varying the deposition time eeffects of deposition time on the structural morphologicaloptical photoluminescence and electrical properties of thefilms were investigatede films consisted of mixed phasesof hexagonal CoS face-centered cubic Co3S4 and cubicCo9S8 phases e films deposited at 2 hrs and 25 hrs aredominated by the hexagonal CoS phase and that depositedat 35 hrs are dominated by the cubic Co9S8 phase efilmsrsquo surface morphologies were dominantly formed fromcompacted cottony spherical grains without pinholes andcracks e EDX and the FTIR spectra confirmed thepresence of Co and S in the films PL investigation con-firmed emission of ultraviolet violet and blue lights uponexcitation by xenon lampe violet light gets red shifted asthe deposition period increased from 2 hrs to 35 hrs eoptical analysis result revealed high visible light absorptionof the films and a red shift in the band gap with increasingdeposition time e two-probe electrical measurementshowed decrease in the resistivity of the films with increasein the crystallite size

Data Availability

e XRD UV-VIS FTIR and photoluminescence data usedto support the findings of this study are available from thecorresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors acknowledge the Hawassa University forfunding this research work

References

[1] L Deshmukh and S Mane ldquoLiquid phase chemical depositionof cobalt sulphide thin films growth and propertiesrdquo DigestJournal of Nanomaterials and Biostructures vol 6 no 3pp 931ndash936 2011

[2] L P Mgabi B S Dladla M A Malik S S Garje J Akhtarand N Revaprasadu ldquoDeposition of cobalt and nickel sulfidethin films from thio- and alkylthio-urea complexes as pre-cursors via the aerosol assisted chemical vapour depositiontechniquerdquo 6in Solid Films vol 564 pp 51ndash57 2014

[3] S S Kamble A Sikora S T Pawar N N Maldar andL P Deshmukh ldquoCobalt sulfide thin films chemical growthreaction kinetics and microstructural analysisrdquo Journal ofAlloys and Compounds vol 623 pp 466ndash472 2015

[4] X Chen Z Zhang Z Qiu C Shi and X Li ldquoHydrothermalfabrication and characterization of polycrystalline linneite(Co3S4) nanotubes based on the Kirkendall effectrdquo Journal ofColloid and Interface Science vol 308 no 1 pp 271ndash2752007

[5] A Mohammadi N Arsalani A G Tabrizi S E MoosavifardZ Naqshbandi and L S Ghadimi ldquoEngineering rGO-CNTwrapped Co3S4 nanocomposites for high-performanceasymmetric supercapacitorsrdquo Chemical Engineering Journalvol 334 pp 66ndash80 2018

20 hrs25 hrs

30 hrs35 hrs

12 times 107

90 times 106

60 times 106

30 times 106

00

PL in

tens

ity (a

u)

400 450 500350Wavelength of emission peaks (nm)

(a)

340 380 440360 400 420Film thickness (nm)

316

318

32

322

324

326

E em

issio

n (eV

)(b)

Figure 6 (a) e photoluminescence spectra and (b) the emission energy of intense PL peak (Eemission) vs film thickness of cobalt sulfidethin films deposited at various deposition time

Advances in Materials Science and Engineering 7

[6] F Tao Y-Q Zhao G-Q Zhang and H-L Li ldquoElectro-chemical characterization on cobalt sulfide for electro-chemical supercapacitorsrdquo Electrochemistry Communicationsvol 9 no 6 pp 1282ndash1287 2007

[7] S B Kale A C Lokhande R B Pujari and C D LokhandeldquoCobalt sulfide thin films for electrocatalytic oxygen evolutionreaction and supercapacitor applicationsrdquo Journal of Colloidand Interface Science vol 532 pp 491ndash499 2018

[8] L-L Feng G-D Li Y Liu et al ldquoCarbon-armored Co9S8nanoparticles as all-pH efficient and durable H2-evolvingelectrocatalystsrdquo ACS Applied Materials amp Interfaces vol 7no 1 pp 980ndash988 2015

[9] L-L Feng M Fan Y Wu et al ldquoMetallic Co9S8 nanosheetsgrown on carbon cloth as efficient binder-free electrocatalystsfor the hydrogen evolution reaction in neutral mediardquo Journalof Materials Chemistry A vol 4 no 18 pp 6860ndash6867 2016

[10] L Zhu D Susac M Teo et al ldquoInvestigation of CoS2-basedthin films as model catalysts for the oxygen reduction reac-tionrdquo Journal of Catalysis vol 258 no 1 pp 235ndash242 2008

[11] A W Peters Z Li O K Farha and J T Hupp ldquoAtomicallyprecise growth of catalytically active cobalt sulfide on flatsurfaces and within a metal-organic framework via atomiclayer depositionrdquo ACS Nano vol 9 no 8 pp 8484ndash84902015

[12] S Dou L Tao J Huo SWang and L Dai ldquoEtched and dopedCo9S8graphene hybrid for oxygen electrocatalysisrdquo Energy ampEnvironmental Science vol 9 no 4 pp 1320ndash1326 2016

[13] N Rumale S Arbuj G Umarji et al ldquoTuning magneticbehavior of nanoscale cobalt sulfide and its nanocompositewith an engineering thermoplasticrdquo Journal of ElectronicMaterials vol 44 no 7 pp 2308ndash2311 2015

[14] S-J Bao Y Li C M Li Q Bao Q Lu and J Guo ldquoShapeevolution and magnetic properties of cobalt sulfiderdquo CrystalGrowth amp Design vol 8 no 10 pp 3745ndash3749 2008

[15] M Congiu M Bonomo M L D Marco et al ldquoCobalt sulfideas counter electrode in p-type dye-sensitized solar cellsrdquoChemistry Select vol 1 no 11 pp 2808ndash2815 2016

[16] J Huo J Wu M Zheng Y Tu and Z Lan ldquoEffect of am-monia on electrodeposition of cobalt sulfide and nickel sulfidecounter electrodes for dye-sensitized solar cellsrdquo Electro-chimica Acta vol 180 pp 574ndash580 2015

[17] D J Yu Y F Yuan D Zhang et al ldquoNickel cobalt sulfidenanotube array on nickel foam as anodematerial for advancedlithium-ion batteriesrdquo Electrochimica Acta vol 198pp 280ndash286 2016

[18] F Han C Zhang B Sun W Tang J Yang and X Li ldquoDual-carbon phase-protective cobalt sulfide nanoparticles withcable-type and mesoporous nanostructure for enhanced cy-cling stability in sodium and lithium ion batteriesrdquo Carbonvol 118 pp 731ndash742 2017

[19] X Zhang H Wang and G Wang ldquoCobalt sulfide nano-particles anchored in three-dimensional carbon nanosheetnetworks for lithium and sodium ion batteries with enhancedelectrochemical performancerdquo Journal of Colloid and Inter-face Science vol 492 pp 41ndash50 2017

[20] S S Kamble A Sikora S T Pawar R C KambaleN N Maldar and L P Deshmukh ldquoMorphology reliance ofcobalt sulfide thin films a chemo-thermo-mechanical per-ceptionrdquo Journal of Alloys and Compounds vol 631pp 303ndash314 2015

[21] G Hodes Chemical Solution Deposition of SemiconductorFilms CRC Press Boca Raton FL USA 2002

[22] T Abza F K Ampong F G Hone I Nkrumah R K Nkumand F Boakye ldquoA new route for the synthesis of CdS thin

films from acidic chemical bathsrdquo International Journal of6in Films Science and Technology vol 6 no 2 pp 67ndash712017

[23] P K Basu and P Pramanik ldquoSolution growth technique forthe deposition of cobalt sulphide thin filmrdquo Journal of Ma-terials Science Letters vol 5 no 12 pp 1216ndash1218 1986

[24] S Ariponnammal and T Srinivasan ldquoGrowth and charac-terization of cobalt sulphide nanorodsrdquo Research Journal ofRecent Sciences vol 2 pp 102ndash105 2013

[25] Z Yu J Du S Guo J Zhang and Y Matsumoto ldquoCoS thinfilms prepared with modified chemical bath depositionrdquo6inSolid Films vol 415 no 1-2 pp 173ndash176 2002

[26] F C Eze and C E Okeke ldquoChemical-bath-deposited cobaltsulphide films preparation effectsrdquo Materials Chemistry andPhysics vol 47 no 1 pp 31ndash36 1997

[27] C Lokhande ldquoChemical deposition of CoS films from acidicbathrdquo Indian Journal of Pure amp Applied Physics vol 30 no 5pp 245ndash247 1992

[28] J Pu Z Shen J Zheng et al ldquoMultifunctional Co 3 S 4sulfur nanotubes for enhanced lithium-sulfur battery per-formancerdquo Nano Energy vol 37 pp 7ndash14 2017

[29] J H Joshi D K Kanchan M J Joshi H O Jethva andK D Parikh ldquoDielectric relaxation complex impedance andmodulus spectroscopic studies of mix phase rod like cobaltsulfide nanoparticlesrdquo Materials Research Bulletin vol 93pp 63ndash73 2017

[30] S Mane S Kamble and L Deshmukh ldquoCobalt sulphide thinfilms chemical bath deposition growth and propertiesrdquoMaterials Letters vol 65 no 17-18 pp 2639ndash2641 2011

[31] S Y Chae Y J Hwang J-H Choi and O-S Joo ldquoCobaltsulfide thin films for counter electrodes of dye-sensitized solarcells with cobalt complex based electrolytesrdquo ElectrochimicaActa vol 114 pp 745ndash749 2013

[32] M Sonawane S Gosavi and R Patil ldquoNanocrystalline CoSthin films prepared by modified chemical bath depositionmethodrdquo Journal of Chemical Biological and Physical Sciences(JCBPS) vol 4 no 3 p 2416 2014

[33] K Yamaguchi T Yoshida T Sugiura and H Minoura ldquoAnovel approach for CdS thin-film deposition electrochemi-cally induced atom-by-atom growth of CdS thin films fromacidic chemical bathrdquo 6e Journal of Physical Chemistry Bvol 102 no 48 pp 9677ndash9686 1998

[34] D P Dutta G Sharma and I K Gopalakrishnan ldquoSinglemolecular precursor route to nanocrystalline Jaipurite syn-thesis characterization and magnetic propertyrdquo MaterialsLetters vol 62 no 8-9 pp 275ndash1278 2008

[35] T Abza F K Ampong F G Hone R K Nkum andF Boakye ldquoPreparation of cadmium zinc sulfide(Cd1minusxZnxS) thin films from acidic chemical bathsrdquo 6inSolid Films vol 666 pp 28ndash33 2018

[36] T B Nasr N Kamoun M Kanzari and R Bennaceur ldquoEffectof pH on the properties of ZnS thin films grown by chemicalbath depositionrdquo 6in Solid Films vol 500 no 1-2 pp 4ndash82006

[37] H Ferhati and F Djeffal ldquoGraded band-gap engineering forincreased efficiency in CZTS solar cellsrdquo Optical Materialsvol 76 pp 393ndash399 2018

[38] M Neuwirth E Seydel J Seeger A Welle H Kalt andM Hetterich ldquoBand-gap tuning of Cu2ZnSn(SSe)4 solar cellabsorbers via defined incorporation of sulphur based on apost-sulphurization processrdquo Solar Energy Materials andSolar Cells vol 182 pp 158ndash165 2018

[39] M Xu H Niu J Huang et al ldquoFacile synthesis of graphene-like Co3S4 nanosheetAg2S nanocomposite with enhanced

8 Advances in Materials Science and Engineering

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9

containing compound at the frequency of 607 cmminus1 and1068 cmminus1 implies the existence of minimum impurities dueto other nonsulfide groups [5]

34 Photoluminescence Analysis e photoluminescence(PL) property of the cobalt sulfide thin films was studied byusing xenon lamp for electron excitation at room

temperature e emission spectra were observed in therange of 340ndash500 nm Broad intense peaks corresponding toviolet light were observed at 381 nm 384 nm 386 nm and391 nm for cobalt sulfide thin films deposited at 2 hrs 25 hrs3 hrs and 35 hrs respectively (Figure 6)e violet emissionpeaks could appear at 366 nm as the size of CoS nano-particles reduces [43] e peak broadening could beresulted from the nonuniform distribution of grains due to

260000240000220000200000180000160000140000120000100000

800006000040000

020000

240000(b)

220000

200000

180000

160000

140000

120000

100000

80000

60000

40000

20000

0

CKa

CKa

CaKa

CaKb

CaKb

OKa

OKa

FeLa

FeL1

CoL

aC

oL1

CoL

aC

oL1

Nak

aM

gKa

Nak

aM

gKa

AlK

aSi

ka

Sika

MoL

1M

oLa

MoL

bSk

aSk

b

MoL

1M

oLa

MoL

bSk

aSk

b

FeKe

sc

CoK

esc

CaKa

CaKb

CoK

esc

CoK

a

FeKa

FeKb

Cok

b

Cok

a

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

000 100 200 300 400 500 600 700 800 900 1000

Cou

nts

kev

(a)

Figure 3 EDX spectra of cobalt sulfide thin films deposited at (a) 2 hours and (b) 3 hours

2microm

(a)

2microm

(b)

Figure 2 SEM images of cobalt sulfide thin films deposited at (a) 2 hrs and (b) 3 hrs

Advances in Materials Science and Engineering 5

the presence of different phases of cobalt sulfide e redshift in the violet light PL emission could be due to theconduction and valence bands broadening as a result ofincrease in crystallite size with deposition time e fluo-rescence spectra of all the thin films have shown blueemission peaks at the same wavelength of 467 nm Blue PLemission peak of wavelength 460 nm was reported by Emadiet al [44] for cobalt sulfide nanoparticles Films depositedfor a period of 3 hrs and 35 hrs have shown additionalultraviolet emission peaks of 349 nm As the PL properties ofsemiconductors are extremely sensitive to the local envi-ronment and to the presence of structural defects the violetand blue emissions are expected to be originated from Covacancy and S interstitial-related defects [24 45]

35 Electrical Resistivity Measurement e electrical resis-tivity of the films was measured by the two-probe method atroom temperature e measured values for films depositedat 2 hrs 25 hrs 3 hrs and 35 hrs were 17 times 106 5 times 1045 times 103 and 13 times 104Ωmiddotcm respectively e room tem-perature resistivity of the films is in the range of semi-conductorsrsquo resistivity except the film deposited at 2 hrs eresistivity values agreed with other researchersrsquo report[46 47] e decrease in resistivity could be attributed to theincrease in film thickness and crystallite size as the depo-sition period increases [48 49] is results in the valenceand conduction band broadening which inturn results inband gap narrowing e narrow band gap films becomemore conductive as electrons can easily be raised from the

0

4

8

12

(Ahv

)2 (eV

)2

13 18 2308hv (eV)

t = 2 hrst = 25 hrs

t = 3 hrs35 hrs

Figure 4 e band gaps of cobalt sulfide thin films obtained from the (Ahv)2 vs hv plots

Wave number (cmndash1)

10095909580757065605550454035

0 1000 2000 3000 4000

Deformation C-O-H

C-O streching or sulfonatedgroup bending

Polysulfidegroup

607 10681067

609

14001560 3202

32091638

1428

Perc

enta

ge tr

ansm

ittan

ce

Bending OH Streching OH

2 hrs35 hrs

Figure 5 FTIR spectra of cobalt sulfide thin films deposited at 2 and 35 hrs

6 Advances in Materials Science and Engineering

valence band to conduction band by room temperaturethermal energy

4 Conclusion

Cobalt sulfide thin films were synthesized from acidicchemical baths containing cobalt acetate thioacetamideand disodium EDTA by varying the deposition time eeffects of deposition time on the structural morphologicaloptical photoluminescence and electrical properties of thefilms were investigatede films consisted of mixed phasesof hexagonal CoS face-centered cubic Co3S4 and cubicCo9S8 phases e films deposited at 2 hrs and 25 hrs aredominated by the hexagonal CoS phase and that depositedat 35 hrs are dominated by the cubic Co9S8 phase efilmsrsquo surface morphologies were dominantly formed fromcompacted cottony spherical grains without pinholes andcracks e EDX and the FTIR spectra confirmed thepresence of Co and S in the films PL investigation con-firmed emission of ultraviolet violet and blue lights uponexcitation by xenon lampe violet light gets red shifted asthe deposition period increased from 2 hrs to 35 hrs eoptical analysis result revealed high visible light absorptionof the films and a red shift in the band gap with increasingdeposition time e two-probe electrical measurementshowed decrease in the resistivity of the films with increasein the crystallite size

Data Availability

e XRD UV-VIS FTIR and photoluminescence data usedto support the findings of this study are available from thecorresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors acknowledge the Hawassa University forfunding this research work

References

[1] L Deshmukh and S Mane ldquoLiquid phase chemical depositionof cobalt sulphide thin films growth and propertiesrdquo DigestJournal of Nanomaterials and Biostructures vol 6 no 3pp 931ndash936 2011

[2] L P Mgabi B S Dladla M A Malik S S Garje J Akhtarand N Revaprasadu ldquoDeposition of cobalt and nickel sulfidethin films from thio- and alkylthio-urea complexes as pre-cursors via the aerosol assisted chemical vapour depositiontechniquerdquo 6in Solid Films vol 564 pp 51ndash57 2014

[3] S S Kamble A Sikora S T Pawar N N Maldar andL P Deshmukh ldquoCobalt sulfide thin films chemical growthreaction kinetics and microstructural analysisrdquo Journal ofAlloys and Compounds vol 623 pp 466ndash472 2015

[4] X Chen Z Zhang Z Qiu C Shi and X Li ldquoHydrothermalfabrication and characterization of polycrystalline linneite(Co3S4) nanotubes based on the Kirkendall effectrdquo Journal ofColloid and Interface Science vol 308 no 1 pp 271ndash2752007

[5] A Mohammadi N Arsalani A G Tabrizi S E MoosavifardZ Naqshbandi and L S Ghadimi ldquoEngineering rGO-CNTwrapped Co3S4 nanocomposites for high-performanceasymmetric supercapacitorsrdquo Chemical Engineering Journalvol 334 pp 66ndash80 2018

20 hrs25 hrs

30 hrs35 hrs

12 times 107

90 times 106

60 times 106

30 times 106

00

PL in

tens

ity (a

u)

400 450 500350Wavelength of emission peaks (nm)

(a)

340 380 440360 400 420Film thickness (nm)

316

318

32

322

324

326

E em

issio

n (eV

)(b)

Figure 6 (a) e photoluminescence spectra and (b) the emission energy of intense PL peak (Eemission) vs film thickness of cobalt sulfidethin films deposited at various deposition time

Advances in Materials Science and Engineering 7

[6] F Tao Y-Q Zhao G-Q Zhang and H-L Li ldquoElectro-chemical characterization on cobalt sulfide for electro-chemical supercapacitorsrdquo Electrochemistry Communicationsvol 9 no 6 pp 1282ndash1287 2007

[7] S B Kale A C Lokhande R B Pujari and C D LokhandeldquoCobalt sulfide thin films for electrocatalytic oxygen evolutionreaction and supercapacitor applicationsrdquo Journal of Colloidand Interface Science vol 532 pp 491ndash499 2018

[8] L-L Feng G-D Li Y Liu et al ldquoCarbon-armored Co9S8nanoparticles as all-pH efficient and durable H2-evolvingelectrocatalystsrdquo ACS Applied Materials amp Interfaces vol 7no 1 pp 980ndash988 2015

[9] L-L Feng M Fan Y Wu et al ldquoMetallic Co9S8 nanosheetsgrown on carbon cloth as efficient binder-free electrocatalystsfor the hydrogen evolution reaction in neutral mediardquo Journalof Materials Chemistry A vol 4 no 18 pp 6860ndash6867 2016

[10] L Zhu D Susac M Teo et al ldquoInvestigation of CoS2-basedthin films as model catalysts for the oxygen reduction reac-tionrdquo Journal of Catalysis vol 258 no 1 pp 235ndash242 2008

[11] A W Peters Z Li O K Farha and J T Hupp ldquoAtomicallyprecise growth of catalytically active cobalt sulfide on flatsurfaces and within a metal-organic framework via atomiclayer depositionrdquo ACS Nano vol 9 no 8 pp 8484ndash84902015

[12] S Dou L Tao J Huo SWang and L Dai ldquoEtched and dopedCo9S8graphene hybrid for oxygen electrocatalysisrdquo Energy ampEnvironmental Science vol 9 no 4 pp 1320ndash1326 2016

[13] N Rumale S Arbuj G Umarji et al ldquoTuning magneticbehavior of nanoscale cobalt sulfide and its nanocompositewith an engineering thermoplasticrdquo Journal of ElectronicMaterials vol 44 no 7 pp 2308ndash2311 2015

[14] S-J Bao Y Li C M Li Q Bao Q Lu and J Guo ldquoShapeevolution and magnetic properties of cobalt sulfiderdquo CrystalGrowth amp Design vol 8 no 10 pp 3745ndash3749 2008

[15] M Congiu M Bonomo M L D Marco et al ldquoCobalt sulfideas counter electrode in p-type dye-sensitized solar cellsrdquoChemistry Select vol 1 no 11 pp 2808ndash2815 2016

[16] J Huo J Wu M Zheng Y Tu and Z Lan ldquoEffect of am-monia on electrodeposition of cobalt sulfide and nickel sulfidecounter electrodes for dye-sensitized solar cellsrdquo Electro-chimica Acta vol 180 pp 574ndash580 2015

[17] D J Yu Y F Yuan D Zhang et al ldquoNickel cobalt sulfidenanotube array on nickel foam as anodematerial for advancedlithium-ion batteriesrdquo Electrochimica Acta vol 198pp 280ndash286 2016

[18] F Han C Zhang B Sun W Tang J Yang and X Li ldquoDual-carbon phase-protective cobalt sulfide nanoparticles withcable-type and mesoporous nanostructure for enhanced cy-cling stability in sodium and lithium ion batteriesrdquo Carbonvol 118 pp 731ndash742 2017

[19] X Zhang H Wang and G Wang ldquoCobalt sulfide nano-particles anchored in three-dimensional carbon nanosheetnetworks for lithium and sodium ion batteries with enhancedelectrochemical performancerdquo Journal of Colloid and Inter-face Science vol 492 pp 41ndash50 2017

[20] S S Kamble A Sikora S T Pawar R C KambaleN N Maldar and L P Deshmukh ldquoMorphology reliance ofcobalt sulfide thin films a chemo-thermo-mechanical per-ceptionrdquo Journal of Alloys and Compounds vol 631pp 303ndash314 2015

[21] G Hodes Chemical Solution Deposition of SemiconductorFilms CRC Press Boca Raton FL USA 2002

[22] T Abza F K Ampong F G Hone I Nkrumah R K Nkumand F Boakye ldquoA new route for the synthesis of CdS thin

films from acidic chemical bathsrdquo International Journal of6in Films Science and Technology vol 6 no 2 pp 67ndash712017

[23] P K Basu and P Pramanik ldquoSolution growth technique forthe deposition of cobalt sulphide thin filmrdquo Journal of Ma-terials Science Letters vol 5 no 12 pp 1216ndash1218 1986

[24] S Ariponnammal and T Srinivasan ldquoGrowth and charac-terization of cobalt sulphide nanorodsrdquo Research Journal ofRecent Sciences vol 2 pp 102ndash105 2013

[25] Z Yu J Du S Guo J Zhang and Y Matsumoto ldquoCoS thinfilms prepared with modified chemical bath depositionrdquo6inSolid Films vol 415 no 1-2 pp 173ndash176 2002

[26] F C Eze and C E Okeke ldquoChemical-bath-deposited cobaltsulphide films preparation effectsrdquo Materials Chemistry andPhysics vol 47 no 1 pp 31ndash36 1997

[27] C Lokhande ldquoChemical deposition of CoS films from acidicbathrdquo Indian Journal of Pure amp Applied Physics vol 30 no 5pp 245ndash247 1992

[28] J Pu Z Shen J Zheng et al ldquoMultifunctional Co 3 S 4sulfur nanotubes for enhanced lithium-sulfur battery per-formancerdquo Nano Energy vol 37 pp 7ndash14 2017

[29] J H Joshi D K Kanchan M J Joshi H O Jethva andK D Parikh ldquoDielectric relaxation complex impedance andmodulus spectroscopic studies of mix phase rod like cobaltsulfide nanoparticlesrdquo Materials Research Bulletin vol 93pp 63ndash73 2017

[30] S Mane S Kamble and L Deshmukh ldquoCobalt sulphide thinfilms chemical bath deposition growth and propertiesrdquoMaterials Letters vol 65 no 17-18 pp 2639ndash2641 2011

[31] S Y Chae Y J Hwang J-H Choi and O-S Joo ldquoCobaltsulfide thin films for counter electrodes of dye-sensitized solarcells with cobalt complex based electrolytesrdquo ElectrochimicaActa vol 114 pp 745ndash749 2013

[32] M Sonawane S Gosavi and R Patil ldquoNanocrystalline CoSthin films prepared by modified chemical bath depositionmethodrdquo Journal of Chemical Biological and Physical Sciences(JCBPS) vol 4 no 3 p 2416 2014

[33] K Yamaguchi T Yoshida T Sugiura and H Minoura ldquoAnovel approach for CdS thin-film deposition electrochemi-cally induced atom-by-atom growth of CdS thin films fromacidic chemical bathrdquo 6e Journal of Physical Chemistry Bvol 102 no 48 pp 9677ndash9686 1998

[34] D P Dutta G Sharma and I K Gopalakrishnan ldquoSinglemolecular precursor route to nanocrystalline Jaipurite syn-thesis characterization and magnetic propertyrdquo MaterialsLetters vol 62 no 8-9 pp 275ndash1278 2008

[35] T Abza F K Ampong F G Hone R K Nkum andF Boakye ldquoPreparation of cadmium zinc sulfide(Cd1minusxZnxS) thin films from acidic chemical bathsrdquo 6inSolid Films vol 666 pp 28ndash33 2018

[36] T B Nasr N Kamoun M Kanzari and R Bennaceur ldquoEffectof pH on the properties of ZnS thin films grown by chemicalbath depositionrdquo 6in Solid Films vol 500 no 1-2 pp 4ndash82006

[37] H Ferhati and F Djeffal ldquoGraded band-gap engineering forincreased efficiency in CZTS solar cellsrdquo Optical Materialsvol 76 pp 393ndash399 2018

[38] M Neuwirth E Seydel J Seeger A Welle H Kalt andM Hetterich ldquoBand-gap tuning of Cu2ZnSn(SSe)4 solar cellabsorbers via defined incorporation of sulphur based on apost-sulphurization processrdquo Solar Energy Materials andSolar Cells vol 182 pp 158ndash165 2018

[39] M Xu H Niu J Huang et al ldquoFacile synthesis of graphene-like Co3S4 nanosheetAg2S nanocomposite with enhanced

8 Advances in Materials Science and Engineering

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9

the presence of different phases of cobalt sulfide e redshift in the violet light PL emission could be due to theconduction and valence bands broadening as a result ofincrease in crystallite size with deposition time e fluo-rescence spectra of all the thin films have shown blueemission peaks at the same wavelength of 467 nm Blue PLemission peak of wavelength 460 nm was reported by Emadiet al [44] for cobalt sulfide nanoparticles Films depositedfor a period of 3 hrs and 35 hrs have shown additionalultraviolet emission peaks of 349 nm As the PL properties ofsemiconductors are extremely sensitive to the local envi-ronment and to the presence of structural defects the violetand blue emissions are expected to be originated from Covacancy and S interstitial-related defects [24 45]

35 Electrical Resistivity Measurement e electrical resis-tivity of the films was measured by the two-probe method atroom temperature e measured values for films depositedat 2 hrs 25 hrs 3 hrs and 35 hrs were 17 times 106 5 times 1045 times 103 and 13 times 104Ωmiddotcm respectively e room tem-perature resistivity of the films is in the range of semi-conductorsrsquo resistivity except the film deposited at 2 hrs eresistivity values agreed with other researchersrsquo report[46 47] e decrease in resistivity could be attributed to theincrease in film thickness and crystallite size as the depo-sition period increases [48 49] is results in the valenceand conduction band broadening which inturn results inband gap narrowing e narrow band gap films becomemore conductive as electrons can easily be raised from the

0

4

8

12

(Ahv

)2 (eV

)2

13 18 2308hv (eV)

t = 2 hrst = 25 hrs

t = 3 hrs35 hrs

Figure 4 e band gaps of cobalt sulfide thin films obtained from the (Ahv)2 vs hv plots

Wave number (cmndash1)

10095909580757065605550454035

0 1000 2000 3000 4000

Deformation C-O-H

C-O streching or sulfonatedgroup bending

Polysulfidegroup

607 10681067

609

14001560 3202

32091638

1428

Perc

enta

ge tr

ansm

ittan

ce

Bending OH Streching OH

2 hrs35 hrs

Figure 5 FTIR spectra of cobalt sulfide thin films deposited at 2 and 35 hrs

6 Advances in Materials Science and Engineering

valence band to conduction band by room temperaturethermal energy

4 Conclusion

Cobalt sulfide thin films were synthesized from acidicchemical baths containing cobalt acetate thioacetamideand disodium EDTA by varying the deposition time eeffects of deposition time on the structural morphologicaloptical photoluminescence and electrical properties of thefilms were investigatede films consisted of mixed phasesof hexagonal CoS face-centered cubic Co3S4 and cubicCo9S8 phases e films deposited at 2 hrs and 25 hrs aredominated by the hexagonal CoS phase and that depositedat 35 hrs are dominated by the cubic Co9S8 phase efilmsrsquo surface morphologies were dominantly formed fromcompacted cottony spherical grains without pinholes andcracks e EDX and the FTIR spectra confirmed thepresence of Co and S in the films PL investigation con-firmed emission of ultraviolet violet and blue lights uponexcitation by xenon lampe violet light gets red shifted asthe deposition period increased from 2 hrs to 35 hrs eoptical analysis result revealed high visible light absorptionof the films and a red shift in the band gap with increasingdeposition time e two-probe electrical measurementshowed decrease in the resistivity of the films with increasein the crystallite size

Data Availability

e XRD UV-VIS FTIR and photoluminescence data usedto support the findings of this study are available from thecorresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors acknowledge the Hawassa University forfunding this research work

References

[1] L Deshmukh and S Mane ldquoLiquid phase chemical depositionof cobalt sulphide thin films growth and propertiesrdquo DigestJournal of Nanomaterials and Biostructures vol 6 no 3pp 931ndash936 2011

[2] L P Mgabi B S Dladla M A Malik S S Garje J Akhtarand N Revaprasadu ldquoDeposition of cobalt and nickel sulfidethin films from thio- and alkylthio-urea complexes as pre-cursors via the aerosol assisted chemical vapour depositiontechniquerdquo 6in Solid Films vol 564 pp 51ndash57 2014

[3] S S Kamble A Sikora S T Pawar N N Maldar andL P Deshmukh ldquoCobalt sulfide thin films chemical growthreaction kinetics and microstructural analysisrdquo Journal ofAlloys and Compounds vol 623 pp 466ndash472 2015

[4] X Chen Z Zhang Z Qiu C Shi and X Li ldquoHydrothermalfabrication and characterization of polycrystalline linneite(Co3S4) nanotubes based on the Kirkendall effectrdquo Journal ofColloid and Interface Science vol 308 no 1 pp 271ndash2752007

[5] A Mohammadi N Arsalani A G Tabrizi S E MoosavifardZ Naqshbandi and L S Ghadimi ldquoEngineering rGO-CNTwrapped Co3S4 nanocomposites for high-performanceasymmetric supercapacitorsrdquo Chemical Engineering Journalvol 334 pp 66ndash80 2018

20 hrs25 hrs

30 hrs35 hrs

12 times 107

90 times 106

60 times 106

30 times 106

00

PL in

tens

ity (a

u)

400 450 500350Wavelength of emission peaks (nm)

(a)

340 380 440360 400 420Film thickness (nm)

316

318

32

322

324

326

E em

issio

n (eV

)(b)

Figure 6 (a) e photoluminescence spectra and (b) the emission energy of intense PL peak (Eemission) vs film thickness of cobalt sulfidethin films deposited at various deposition time

Advances in Materials Science and Engineering 7

[6] F Tao Y-Q Zhao G-Q Zhang and H-L Li ldquoElectro-chemical characterization on cobalt sulfide for electro-chemical supercapacitorsrdquo Electrochemistry Communicationsvol 9 no 6 pp 1282ndash1287 2007

[7] S B Kale A C Lokhande R B Pujari and C D LokhandeldquoCobalt sulfide thin films for electrocatalytic oxygen evolutionreaction and supercapacitor applicationsrdquo Journal of Colloidand Interface Science vol 532 pp 491ndash499 2018

[8] L-L Feng G-D Li Y Liu et al ldquoCarbon-armored Co9S8nanoparticles as all-pH efficient and durable H2-evolvingelectrocatalystsrdquo ACS Applied Materials amp Interfaces vol 7no 1 pp 980ndash988 2015

[9] L-L Feng M Fan Y Wu et al ldquoMetallic Co9S8 nanosheetsgrown on carbon cloth as efficient binder-free electrocatalystsfor the hydrogen evolution reaction in neutral mediardquo Journalof Materials Chemistry A vol 4 no 18 pp 6860ndash6867 2016

[10] L Zhu D Susac M Teo et al ldquoInvestigation of CoS2-basedthin films as model catalysts for the oxygen reduction reac-tionrdquo Journal of Catalysis vol 258 no 1 pp 235ndash242 2008

[11] A W Peters Z Li O K Farha and J T Hupp ldquoAtomicallyprecise growth of catalytically active cobalt sulfide on flatsurfaces and within a metal-organic framework via atomiclayer depositionrdquo ACS Nano vol 9 no 8 pp 8484ndash84902015

[12] S Dou L Tao J Huo SWang and L Dai ldquoEtched and dopedCo9S8graphene hybrid for oxygen electrocatalysisrdquo Energy ampEnvironmental Science vol 9 no 4 pp 1320ndash1326 2016

[13] N Rumale S Arbuj G Umarji et al ldquoTuning magneticbehavior of nanoscale cobalt sulfide and its nanocompositewith an engineering thermoplasticrdquo Journal of ElectronicMaterials vol 44 no 7 pp 2308ndash2311 2015

[14] S-J Bao Y Li C M Li Q Bao Q Lu and J Guo ldquoShapeevolution and magnetic properties of cobalt sulfiderdquo CrystalGrowth amp Design vol 8 no 10 pp 3745ndash3749 2008

[15] M Congiu M Bonomo M L D Marco et al ldquoCobalt sulfideas counter electrode in p-type dye-sensitized solar cellsrdquoChemistry Select vol 1 no 11 pp 2808ndash2815 2016

[16] J Huo J Wu M Zheng Y Tu and Z Lan ldquoEffect of am-monia on electrodeposition of cobalt sulfide and nickel sulfidecounter electrodes for dye-sensitized solar cellsrdquo Electro-chimica Acta vol 180 pp 574ndash580 2015

[17] D J Yu Y F Yuan D Zhang et al ldquoNickel cobalt sulfidenanotube array on nickel foam as anodematerial for advancedlithium-ion batteriesrdquo Electrochimica Acta vol 198pp 280ndash286 2016

[18] F Han C Zhang B Sun W Tang J Yang and X Li ldquoDual-carbon phase-protective cobalt sulfide nanoparticles withcable-type and mesoporous nanostructure for enhanced cy-cling stability in sodium and lithium ion batteriesrdquo Carbonvol 118 pp 731ndash742 2017

[19] X Zhang H Wang and G Wang ldquoCobalt sulfide nano-particles anchored in three-dimensional carbon nanosheetnetworks for lithium and sodium ion batteries with enhancedelectrochemical performancerdquo Journal of Colloid and Inter-face Science vol 492 pp 41ndash50 2017

[20] S S Kamble A Sikora S T Pawar R C KambaleN N Maldar and L P Deshmukh ldquoMorphology reliance ofcobalt sulfide thin films a chemo-thermo-mechanical per-ceptionrdquo Journal of Alloys and Compounds vol 631pp 303ndash314 2015

[21] G Hodes Chemical Solution Deposition of SemiconductorFilms CRC Press Boca Raton FL USA 2002

[22] T Abza F K Ampong F G Hone I Nkrumah R K Nkumand F Boakye ldquoA new route for the synthesis of CdS thin

films from acidic chemical bathsrdquo International Journal of6in Films Science and Technology vol 6 no 2 pp 67ndash712017

[23] P K Basu and P Pramanik ldquoSolution growth technique forthe deposition of cobalt sulphide thin filmrdquo Journal of Ma-terials Science Letters vol 5 no 12 pp 1216ndash1218 1986

[24] S Ariponnammal and T Srinivasan ldquoGrowth and charac-terization of cobalt sulphide nanorodsrdquo Research Journal ofRecent Sciences vol 2 pp 102ndash105 2013

[25] Z Yu J Du S Guo J Zhang and Y Matsumoto ldquoCoS thinfilms prepared with modified chemical bath depositionrdquo6inSolid Films vol 415 no 1-2 pp 173ndash176 2002

[26] F C Eze and C E Okeke ldquoChemical-bath-deposited cobaltsulphide films preparation effectsrdquo Materials Chemistry andPhysics vol 47 no 1 pp 31ndash36 1997

[27] C Lokhande ldquoChemical deposition of CoS films from acidicbathrdquo Indian Journal of Pure amp Applied Physics vol 30 no 5pp 245ndash247 1992

[28] J Pu Z Shen J Zheng et al ldquoMultifunctional Co 3 S 4sulfur nanotubes for enhanced lithium-sulfur battery per-formancerdquo Nano Energy vol 37 pp 7ndash14 2017

[29] J H Joshi D K Kanchan M J Joshi H O Jethva andK D Parikh ldquoDielectric relaxation complex impedance andmodulus spectroscopic studies of mix phase rod like cobaltsulfide nanoparticlesrdquo Materials Research Bulletin vol 93pp 63ndash73 2017

[30] S Mane S Kamble and L Deshmukh ldquoCobalt sulphide thinfilms chemical bath deposition growth and propertiesrdquoMaterials Letters vol 65 no 17-18 pp 2639ndash2641 2011

[31] S Y Chae Y J Hwang J-H Choi and O-S Joo ldquoCobaltsulfide thin films for counter electrodes of dye-sensitized solarcells with cobalt complex based electrolytesrdquo ElectrochimicaActa vol 114 pp 745ndash749 2013

[32] M Sonawane S Gosavi and R Patil ldquoNanocrystalline CoSthin films prepared by modified chemical bath depositionmethodrdquo Journal of Chemical Biological and Physical Sciences(JCBPS) vol 4 no 3 p 2416 2014

[33] K Yamaguchi T Yoshida T Sugiura and H Minoura ldquoAnovel approach for CdS thin-film deposition electrochemi-cally induced atom-by-atom growth of CdS thin films fromacidic chemical bathrdquo 6e Journal of Physical Chemistry Bvol 102 no 48 pp 9677ndash9686 1998

[34] D P Dutta G Sharma and I K Gopalakrishnan ldquoSinglemolecular precursor route to nanocrystalline Jaipurite syn-thesis characterization and magnetic propertyrdquo MaterialsLetters vol 62 no 8-9 pp 275ndash1278 2008

[35] T Abza F K Ampong F G Hone R K Nkum andF Boakye ldquoPreparation of cadmium zinc sulfide(Cd1minusxZnxS) thin films from acidic chemical bathsrdquo 6inSolid Films vol 666 pp 28ndash33 2018

[36] T B Nasr N Kamoun M Kanzari and R Bennaceur ldquoEffectof pH on the properties of ZnS thin films grown by chemicalbath depositionrdquo 6in Solid Films vol 500 no 1-2 pp 4ndash82006

[37] H Ferhati and F Djeffal ldquoGraded band-gap engineering forincreased efficiency in CZTS solar cellsrdquo Optical Materialsvol 76 pp 393ndash399 2018

[38] M Neuwirth E Seydel J Seeger A Welle H Kalt andM Hetterich ldquoBand-gap tuning of Cu2ZnSn(SSe)4 solar cellabsorbers via defined incorporation of sulphur based on apost-sulphurization processrdquo Solar Energy Materials andSolar Cells vol 182 pp 158ndash165 2018

[39] M Xu H Niu J Huang et al ldquoFacile synthesis of graphene-like Co3S4 nanosheetAg2S nanocomposite with enhanced

8 Advances in Materials Science and Engineering

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9

valence band to conduction band by room temperaturethermal energy

4 Conclusion

Cobalt sulfide thin films were synthesized from acidicchemical baths containing cobalt acetate thioacetamideand disodium EDTA by varying the deposition time eeffects of deposition time on the structural morphologicaloptical photoluminescence and electrical properties of thefilms were investigatede films consisted of mixed phasesof hexagonal CoS face-centered cubic Co3S4 and cubicCo9S8 phases e films deposited at 2 hrs and 25 hrs aredominated by the hexagonal CoS phase and that depositedat 35 hrs are dominated by the cubic Co9S8 phase efilmsrsquo surface morphologies were dominantly formed fromcompacted cottony spherical grains without pinholes andcracks e EDX and the FTIR spectra confirmed thepresence of Co and S in the films PL investigation con-firmed emission of ultraviolet violet and blue lights uponexcitation by xenon lampe violet light gets red shifted asthe deposition period increased from 2 hrs to 35 hrs eoptical analysis result revealed high visible light absorptionof the films and a red shift in the band gap with increasingdeposition time e two-probe electrical measurementshowed decrease in the resistivity of the films with increasein the crystallite size

Data Availability

e XRD UV-VIS FTIR and photoluminescence data usedto support the findings of this study are available from thecorresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors acknowledge the Hawassa University forfunding this research work

References

[1] L Deshmukh and S Mane ldquoLiquid phase chemical depositionof cobalt sulphide thin films growth and propertiesrdquo DigestJournal of Nanomaterials and Biostructures vol 6 no 3pp 931ndash936 2011

[2] L P Mgabi B S Dladla M A Malik S S Garje J Akhtarand N Revaprasadu ldquoDeposition of cobalt and nickel sulfidethin films from thio- and alkylthio-urea complexes as pre-cursors via the aerosol assisted chemical vapour depositiontechniquerdquo 6in Solid Films vol 564 pp 51ndash57 2014

[3] S S Kamble A Sikora S T Pawar N N Maldar andL P Deshmukh ldquoCobalt sulfide thin films chemical growthreaction kinetics and microstructural analysisrdquo Journal ofAlloys and Compounds vol 623 pp 466ndash472 2015

[4] X Chen Z Zhang Z Qiu C Shi and X Li ldquoHydrothermalfabrication and characterization of polycrystalline linneite(Co3S4) nanotubes based on the Kirkendall effectrdquo Journal ofColloid and Interface Science vol 308 no 1 pp 271ndash2752007

[5] A Mohammadi N Arsalani A G Tabrizi S E MoosavifardZ Naqshbandi and L S Ghadimi ldquoEngineering rGO-CNTwrapped Co3S4 nanocomposites for high-performanceasymmetric supercapacitorsrdquo Chemical Engineering Journalvol 334 pp 66ndash80 2018

20 hrs25 hrs

30 hrs35 hrs

12 times 107

90 times 106

60 times 106

30 times 106

00

PL in

tens

ity (a

u)

400 450 500350Wavelength of emission peaks (nm)

(a)

340 380 440360 400 420Film thickness (nm)

316

318

32

322

324

326

E em

issio

n (eV

)(b)

Figure 6 (a) e photoluminescence spectra and (b) the emission energy of intense PL peak (Eemission) vs film thickness of cobalt sulfidethin films deposited at various deposition time

Advances in Materials Science and Engineering 7

[6] F Tao Y-Q Zhao G-Q Zhang and H-L Li ldquoElectro-chemical characterization on cobalt sulfide for electro-chemical supercapacitorsrdquo Electrochemistry Communicationsvol 9 no 6 pp 1282ndash1287 2007

[7] S B Kale A C Lokhande R B Pujari and C D LokhandeldquoCobalt sulfide thin films for electrocatalytic oxygen evolutionreaction and supercapacitor applicationsrdquo Journal of Colloidand Interface Science vol 532 pp 491ndash499 2018

[8] L-L Feng G-D Li Y Liu et al ldquoCarbon-armored Co9S8nanoparticles as all-pH efficient and durable H2-evolvingelectrocatalystsrdquo ACS Applied Materials amp Interfaces vol 7no 1 pp 980ndash988 2015

[9] L-L Feng M Fan Y Wu et al ldquoMetallic Co9S8 nanosheetsgrown on carbon cloth as efficient binder-free electrocatalystsfor the hydrogen evolution reaction in neutral mediardquo Journalof Materials Chemistry A vol 4 no 18 pp 6860ndash6867 2016

[10] L Zhu D Susac M Teo et al ldquoInvestigation of CoS2-basedthin films as model catalysts for the oxygen reduction reac-tionrdquo Journal of Catalysis vol 258 no 1 pp 235ndash242 2008

[11] A W Peters Z Li O K Farha and J T Hupp ldquoAtomicallyprecise growth of catalytically active cobalt sulfide on flatsurfaces and within a metal-organic framework via atomiclayer depositionrdquo ACS Nano vol 9 no 8 pp 8484ndash84902015

[12] S Dou L Tao J Huo SWang and L Dai ldquoEtched and dopedCo9S8graphene hybrid for oxygen electrocatalysisrdquo Energy ampEnvironmental Science vol 9 no 4 pp 1320ndash1326 2016

[13] N Rumale S Arbuj G Umarji et al ldquoTuning magneticbehavior of nanoscale cobalt sulfide and its nanocompositewith an engineering thermoplasticrdquo Journal of ElectronicMaterials vol 44 no 7 pp 2308ndash2311 2015

[14] S-J Bao Y Li C M Li Q Bao Q Lu and J Guo ldquoShapeevolution and magnetic properties of cobalt sulfiderdquo CrystalGrowth amp Design vol 8 no 10 pp 3745ndash3749 2008

[15] M Congiu M Bonomo M L D Marco et al ldquoCobalt sulfideas counter electrode in p-type dye-sensitized solar cellsrdquoChemistry Select vol 1 no 11 pp 2808ndash2815 2016

[16] J Huo J Wu M Zheng Y Tu and Z Lan ldquoEffect of am-monia on electrodeposition of cobalt sulfide and nickel sulfidecounter electrodes for dye-sensitized solar cellsrdquo Electro-chimica Acta vol 180 pp 574ndash580 2015

[17] D J Yu Y F Yuan D Zhang et al ldquoNickel cobalt sulfidenanotube array on nickel foam as anodematerial for advancedlithium-ion batteriesrdquo Electrochimica Acta vol 198pp 280ndash286 2016

[18] F Han C Zhang B Sun W Tang J Yang and X Li ldquoDual-carbon phase-protective cobalt sulfide nanoparticles withcable-type and mesoporous nanostructure for enhanced cy-cling stability in sodium and lithium ion batteriesrdquo Carbonvol 118 pp 731ndash742 2017

[19] X Zhang H Wang and G Wang ldquoCobalt sulfide nano-particles anchored in three-dimensional carbon nanosheetnetworks for lithium and sodium ion batteries with enhancedelectrochemical performancerdquo Journal of Colloid and Inter-face Science vol 492 pp 41ndash50 2017

[20] S S Kamble A Sikora S T Pawar R C KambaleN N Maldar and L P Deshmukh ldquoMorphology reliance ofcobalt sulfide thin films a chemo-thermo-mechanical per-ceptionrdquo Journal of Alloys and Compounds vol 631pp 303ndash314 2015

[21] G Hodes Chemical Solution Deposition of SemiconductorFilms CRC Press Boca Raton FL USA 2002

[22] T Abza F K Ampong F G Hone I Nkrumah R K Nkumand F Boakye ldquoA new route for the synthesis of CdS thin

films from acidic chemical bathsrdquo International Journal of6in Films Science and Technology vol 6 no 2 pp 67ndash712017

[23] P K Basu and P Pramanik ldquoSolution growth technique forthe deposition of cobalt sulphide thin filmrdquo Journal of Ma-terials Science Letters vol 5 no 12 pp 1216ndash1218 1986

[24] S Ariponnammal and T Srinivasan ldquoGrowth and charac-terization of cobalt sulphide nanorodsrdquo Research Journal ofRecent Sciences vol 2 pp 102ndash105 2013

[25] Z Yu J Du S Guo J Zhang and Y Matsumoto ldquoCoS thinfilms prepared with modified chemical bath depositionrdquo6inSolid Films vol 415 no 1-2 pp 173ndash176 2002

[26] F C Eze and C E Okeke ldquoChemical-bath-deposited cobaltsulphide films preparation effectsrdquo Materials Chemistry andPhysics vol 47 no 1 pp 31ndash36 1997

[27] C Lokhande ldquoChemical deposition of CoS films from acidicbathrdquo Indian Journal of Pure amp Applied Physics vol 30 no 5pp 245ndash247 1992

[28] J Pu Z Shen J Zheng et al ldquoMultifunctional Co 3 S 4sulfur nanotubes for enhanced lithium-sulfur battery per-formancerdquo Nano Energy vol 37 pp 7ndash14 2017

[29] J H Joshi D K Kanchan M J Joshi H O Jethva andK D Parikh ldquoDielectric relaxation complex impedance andmodulus spectroscopic studies of mix phase rod like cobaltsulfide nanoparticlesrdquo Materials Research Bulletin vol 93pp 63ndash73 2017

[30] S Mane S Kamble and L Deshmukh ldquoCobalt sulphide thinfilms chemical bath deposition growth and propertiesrdquoMaterials Letters vol 65 no 17-18 pp 2639ndash2641 2011

[31] S Y Chae Y J Hwang J-H Choi and O-S Joo ldquoCobaltsulfide thin films for counter electrodes of dye-sensitized solarcells with cobalt complex based electrolytesrdquo ElectrochimicaActa vol 114 pp 745ndash749 2013

[32] M Sonawane S Gosavi and R Patil ldquoNanocrystalline CoSthin films prepared by modified chemical bath depositionmethodrdquo Journal of Chemical Biological and Physical Sciences(JCBPS) vol 4 no 3 p 2416 2014

[33] K Yamaguchi T Yoshida T Sugiura and H Minoura ldquoAnovel approach for CdS thin-film deposition electrochemi-cally induced atom-by-atom growth of CdS thin films fromacidic chemical bathrdquo 6e Journal of Physical Chemistry Bvol 102 no 48 pp 9677ndash9686 1998

[34] D P Dutta G Sharma and I K Gopalakrishnan ldquoSinglemolecular precursor route to nanocrystalline Jaipurite syn-thesis characterization and magnetic propertyrdquo MaterialsLetters vol 62 no 8-9 pp 275ndash1278 2008

[35] T Abza F K Ampong F G Hone R K Nkum andF Boakye ldquoPreparation of cadmium zinc sulfide(Cd1minusxZnxS) thin films from acidic chemical bathsrdquo 6inSolid Films vol 666 pp 28ndash33 2018

[36] T B Nasr N Kamoun M Kanzari and R Bennaceur ldquoEffectof pH on the properties of ZnS thin films grown by chemicalbath depositionrdquo 6in Solid Films vol 500 no 1-2 pp 4ndash82006

[37] H Ferhati and F Djeffal ldquoGraded band-gap engineering forincreased efficiency in CZTS solar cellsrdquo Optical Materialsvol 76 pp 393ndash399 2018

[38] M Neuwirth E Seydel J Seeger A Welle H Kalt andM Hetterich ldquoBand-gap tuning of Cu2ZnSn(SSe)4 solar cellabsorbers via defined incorporation of sulphur based on apost-sulphurization processrdquo Solar Energy Materials andSolar Cells vol 182 pp 158ndash165 2018

[39] M Xu H Niu J Huang et al ldquoFacile synthesis of graphene-like Co3S4 nanosheetAg2S nanocomposite with enhanced

8 Advances in Materials Science and Engineering

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9

[6] F Tao Y-Q Zhao G-Q Zhang and H-L Li ldquoElectro-chemical characterization on cobalt sulfide for electro-chemical supercapacitorsrdquo Electrochemistry Communicationsvol 9 no 6 pp 1282ndash1287 2007

[7] S B Kale A C Lokhande R B Pujari and C D LokhandeldquoCobalt sulfide thin films for electrocatalytic oxygen evolutionreaction and supercapacitor applicationsrdquo Journal of Colloidand Interface Science vol 532 pp 491ndash499 2018

[8] L-L Feng G-D Li Y Liu et al ldquoCarbon-armored Co9S8nanoparticles as all-pH efficient and durable H2-evolvingelectrocatalystsrdquo ACS Applied Materials amp Interfaces vol 7no 1 pp 980ndash988 2015

[9] L-L Feng M Fan Y Wu et al ldquoMetallic Co9S8 nanosheetsgrown on carbon cloth as efficient binder-free electrocatalystsfor the hydrogen evolution reaction in neutral mediardquo Journalof Materials Chemistry A vol 4 no 18 pp 6860ndash6867 2016

[10] L Zhu D Susac M Teo et al ldquoInvestigation of CoS2-basedthin films as model catalysts for the oxygen reduction reac-tionrdquo Journal of Catalysis vol 258 no 1 pp 235ndash242 2008

[11] A W Peters Z Li O K Farha and J T Hupp ldquoAtomicallyprecise growth of catalytically active cobalt sulfide on flatsurfaces and within a metal-organic framework via atomiclayer depositionrdquo ACS Nano vol 9 no 8 pp 8484ndash84902015

[12] S Dou L Tao J Huo SWang and L Dai ldquoEtched and dopedCo9S8graphene hybrid for oxygen electrocatalysisrdquo Energy ampEnvironmental Science vol 9 no 4 pp 1320ndash1326 2016

[13] N Rumale S Arbuj G Umarji et al ldquoTuning magneticbehavior of nanoscale cobalt sulfide and its nanocompositewith an engineering thermoplasticrdquo Journal of ElectronicMaterials vol 44 no 7 pp 2308ndash2311 2015

[14] S-J Bao Y Li C M Li Q Bao Q Lu and J Guo ldquoShapeevolution and magnetic properties of cobalt sulfiderdquo CrystalGrowth amp Design vol 8 no 10 pp 3745ndash3749 2008

[15] M Congiu M Bonomo M L D Marco et al ldquoCobalt sulfideas counter electrode in p-type dye-sensitized solar cellsrdquoChemistry Select vol 1 no 11 pp 2808ndash2815 2016

[16] J Huo J Wu M Zheng Y Tu and Z Lan ldquoEffect of am-monia on electrodeposition of cobalt sulfide and nickel sulfidecounter electrodes for dye-sensitized solar cellsrdquo Electro-chimica Acta vol 180 pp 574ndash580 2015

[17] D J Yu Y F Yuan D Zhang et al ldquoNickel cobalt sulfidenanotube array on nickel foam as anodematerial for advancedlithium-ion batteriesrdquo Electrochimica Acta vol 198pp 280ndash286 2016

[18] F Han C Zhang B Sun W Tang J Yang and X Li ldquoDual-carbon phase-protective cobalt sulfide nanoparticles withcable-type and mesoporous nanostructure for enhanced cy-cling stability in sodium and lithium ion batteriesrdquo Carbonvol 118 pp 731ndash742 2017

[19] X Zhang H Wang and G Wang ldquoCobalt sulfide nano-particles anchored in three-dimensional carbon nanosheetnetworks for lithium and sodium ion batteries with enhancedelectrochemical performancerdquo Journal of Colloid and Inter-face Science vol 492 pp 41ndash50 2017

[20] S S Kamble A Sikora S T Pawar R C KambaleN N Maldar and L P Deshmukh ldquoMorphology reliance ofcobalt sulfide thin films a chemo-thermo-mechanical per-ceptionrdquo Journal of Alloys and Compounds vol 631pp 303ndash314 2015

[21] G Hodes Chemical Solution Deposition of SemiconductorFilms CRC Press Boca Raton FL USA 2002

[22] T Abza F K Ampong F G Hone I Nkrumah R K Nkumand F Boakye ldquoA new route for the synthesis of CdS thin

films from acidic chemical bathsrdquo International Journal of6in Films Science and Technology vol 6 no 2 pp 67ndash712017

[23] P K Basu and P Pramanik ldquoSolution growth technique forthe deposition of cobalt sulphide thin filmrdquo Journal of Ma-terials Science Letters vol 5 no 12 pp 1216ndash1218 1986

[24] S Ariponnammal and T Srinivasan ldquoGrowth and charac-terization of cobalt sulphide nanorodsrdquo Research Journal ofRecent Sciences vol 2 pp 102ndash105 2013

[25] Z Yu J Du S Guo J Zhang and Y Matsumoto ldquoCoS thinfilms prepared with modified chemical bath depositionrdquo6inSolid Films vol 415 no 1-2 pp 173ndash176 2002

[26] F C Eze and C E Okeke ldquoChemical-bath-deposited cobaltsulphide films preparation effectsrdquo Materials Chemistry andPhysics vol 47 no 1 pp 31ndash36 1997

[27] C Lokhande ldquoChemical deposition of CoS films from acidicbathrdquo Indian Journal of Pure amp Applied Physics vol 30 no 5pp 245ndash247 1992

[28] J Pu Z Shen J Zheng et al ldquoMultifunctional Co 3 S 4sulfur nanotubes for enhanced lithium-sulfur battery per-formancerdquo Nano Energy vol 37 pp 7ndash14 2017

[29] J H Joshi D K Kanchan M J Joshi H O Jethva andK D Parikh ldquoDielectric relaxation complex impedance andmodulus spectroscopic studies of mix phase rod like cobaltsulfide nanoparticlesrdquo Materials Research Bulletin vol 93pp 63ndash73 2017

[30] S Mane S Kamble and L Deshmukh ldquoCobalt sulphide thinfilms chemical bath deposition growth and propertiesrdquoMaterials Letters vol 65 no 17-18 pp 2639ndash2641 2011

[31] S Y Chae Y J Hwang J-H Choi and O-S Joo ldquoCobaltsulfide thin films for counter electrodes of dye-sensitized solarcells with cobalt complex based electrolytesrdquo ElectrochimicaActa vol 114 pp 745ndash749 2013

[32] M Sonawane S Gosavi and R Patil ldquoNanocrystalline CoSthin films prepared by modified chemical bath depositionmethodrdquo Journal of Chemical Biological and Physical Sciences(JCBPS) vol 4 no 3 p 2416 2014

[33] K Yamaguchi T Yoshida T Sugiura and H Minoura ldquoAnovel approach for CdS thin-film deposition electrochemi-cally induced atom-by-atom growth of CdS thin films fromacidic chemical bathrdquo 6e Journal of Physical Chemistry Bvol 102 no 48 pp 9677ndash9686 1998

[34] D P Dutta G Sharma and I K Gopalakrishnan ldquoSinglemolecular precursor route to nanocrystalline Jaipurite syn-thesis characterization and magnetic propertyrdquo MaterialsLetters vol 62 no 8-9 pp 275ndash1278 2008

[35] T Abza F K Ampong F G Hone R K Nkum andF Boakye ldquoPreparation of cadmium zinc sulfide(Cd1minusxZnxS) thin films from acidic chemical bathsrdquo 6inSolid Films vol 666 pp 28ndash33 2018

[36] T B Nasr N Kamoun M Kanzari and R Bennaceur ldquoEffectof pH on the properties of ZnS thin films grown by chemicalbath depositionrdquo 6in Solid Films vol 500 no 1-2 pp 4ndash82006

[37] H Ferhati and F Djeffal ldquoGraded band-gap engineering forincreased efficiency in CZTS solar cellsrdquo Optical Materialsvol 76 pp 393ndash399 2018

[38] M Neuwirth E Seydel J Seeger A Welle H Kalt andM Hetterich ldquoBand-gap tuning of Cu2ZnSn(SSe)4 solar cellabsorbers via defined incorporation of sulphur based on apost-sulphurization processrdquo Solar Energy Materials andSolar Cells vol 182 pp 158ndash165 2018

[39] M Xu H Niu J Huang et al ldquoFacile synthesis of graphene-like Co3S4 nanosheetAg2S nanocomposite with enhanced

8 Advances in Materials Science and Engineering

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9

performance in visible-light photocatalysisrdquo Applied SurfaceScience vol 351 pp 374ndash381 2015

[40] M B Muradov O O Balayeva A A Azizov et al ldquoSynthesisand characterization of cobalt sulfide nanoparticles bysonochemical methodrdquo Infrared Physics amp Technology vol 89pp 255ndash262 2018

[41] HWan X Ji J Jiang et al ldquoHydrothermal synthesis of cobaltsulfide nanotubes the size control and its application insupercapacitorsrdquo Journal of Power Sources vol 243pp 396ndash402 2013

[42] Y Pengfei S Lili H Xiangyu X Chuanhui W Haiying andW Feng ldquoControlled synthesis of cobalt sulfide nano-crystalline by ultrasonic spray pyrolysis processrdquo Rare MetalMaterials and Engineering vol 45 no 7 pp 1700ndash1704 2016

[43] N Khaorapapong A Ontam and M Ogawa ldquoVery slowformation of copper sulfide and cobalt sulfide nanoparticles inmontmorilloniterdquo Applied Clay Science vol 51 no 1-2pp 182ndash186 2011

[44] H Emadi M Salavati-Niasari and F Davar ldquoSynthesis andcharacterization of cobalt sulfide nanocrystals in the presenceof thioglycolic acid via a simple hydrothermal methodrdquoPolyhedron vol 31 no 1 pp 438ndash442 2012

[45] Y-s Zhou Y-c Zhu J-j Chen G-h Du and B-s Xu ldquoInsitu synthesis of cobalt sulfide nanostructure-filled carbonnanotubes and their luminescence propertyrdquo Materials Let-ters vol 86 pp 139ndash141 2012

[46] S Sartale and C Lokhande ldquoDeposition of cobalt sulphidethin films by successive ionic layer adsorption and reaction(SILAR)method and their characterizationrdquo Indian Journal ofPure amp Applied Physics vol 38 pp 48ndash52 2000

[47] R Mane M Uplane and C Lokhande ldquoPreparation andcharacterization of spray deposited CoS thin filmsrdquo IndianJournal of Physics vol 75A no 2 pp 169ndash174 1999

[48] M Bouderbala S Hamzaoui B Amrani et al ldquoicknessdependence of structural electrical and optical behaviour ofundoped ZnO thin filmsrdquo Physica B Condensed Mattervol 403 no 18 pp 3326ndash3330 2008

[49] M Oztas and M Bedir ldquoickness dependence of structuralelectrical and optical properties of sprayed ZnOCu filmsrdquo6in Solid Films vol 516 no 8 pp 1703ndash1709 2008

Advances in Materials Science and Engineering 9