ViewPageProof PCS 7700

8/19/2019 ViewPageProof PCS 7700

1/14

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/289529299

Preparation and characterization of semiconductor GNR-CNT nanocomposite and

its application in FET

ARTICLE in JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS · JANUARY 2016

Impact Factor: 1.85 · DOI: 10.1016/j.jpcs.2016.01.001

READS

11

3 AUTHORS, INCLUDING:

Sedighe Salimian

Kharazmi University

6 PUBLICATIONS 20 CITATIONS

SEE PROFILE

All in-text references underlined in blue are linked to publications on ResearchGate,

letting you access and read them immediately.

Available from: Sedighe Salimian

Retrieved on: 24 February 2016

https://www.researchgate.net/profile/Sedighe_Salimian?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_4https://www.researchgate.net/profile/Sedighe_Salimian?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_4https://www.researchgate.net/?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_1https://www.researchgate.net/profile/Sedighe_Salimian?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_7https://www.researchgate.net/institution/Kharazmi_University?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_6https://www.researchgate.net/profile/Sedighe_Salimian?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_5https://www.researchgate.net/profile/Sedighe_Salimian?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_4https://www.researchgate.net/?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_1https://www.researchgate.net/publication/289529299_Preparation_and_characterization_of_semiconductor_GNR-CNT_nanocomposite_and_its_application_in_FET?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_3https://www.researchgate.net/publication/289529299_Preparation_and_characterization_of_semiconductor_GNR-CNT_nanocomposite_and_its_application_in_FET?enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA%3D%3D&el=1_x_2


2/14

Dear Author,

Please, note that changes made to the HTML content will be

added to the article before publication, but are not reflected

in this PDF.

Note also that this file should not be used for submitting

corrections.


3/14

Preparation and characterization of semiconductor GNR-CNTnanocomposite and its application in FETQ2

Sedighe Salimian a,n, Mohammad Esmaeil Azim Araghi a, Ahmad Nozad Golikand bQ1a Faculty of Physics, Kharazmi University, 49 Mofateh Avenue, Tehran 15719-14911, Iranb Material Research Center, Metalogy Group, Tehran, Iran

a r t i c l e i n f o

Article history:

Received 5 November 2015Received in revised form

21 December 2015

Accepted 2 January 2016

Keywords:

Graphene nanoribbon

Nanocomposite

Rectifying effect

p–n junction

Quantum capacitance

a b s t r a c t

So far, little is known about the experimental potential of graphene nanoribbon-carbon nanotube (GNR-

CNT) heterostructure as a semiconductor nanocomposite. The present work examined the structuralfeatures, topography and electronic properties of GNR-CNT nanocomposite by using Raman spectroscopy,

transmission electron microscopy, scanning tunneling microscopy and spectroscopy (STS). The homo-

genous semiconductor GNR-CNT nanocomposites were produced under optimized synthesis conditions.

The narrow band gap was exhibited by optimization of the reduction step. The STS of the micro-scale

surface of the nanocomposite shows local density of state in selected areas that represent the 0.08 eV

band gap of a homogenous nanocomposite. The potential of the semiconductor nanocomposite was

considered for application in stacked graphene nanoribbon-eld effect transistors (SGNR-FETs). A simple

method of device fabrication is proposed based on a semiconductor stacked GNR nanocomposite. The

high hole mobility and rectifying effect of the p–n junction of the SGNR nanocomposite on TiO2 are

demonstrated. The optimal thickness for the back gate TiO2 dielectric for the tested devices was 40 nm.

This thickness decreased leakage current at the p–n junction of the SGNR/TiO2 interface, which is pro-

mising heterojunction for optoelectronics. The thickness of gate dielectric and quantum capacitance of

the gate was investigated at the low 40 nm thickness by calculating the mobility. In the proposed SGNR-

FET, holes dominate electrical transport with a high mobility of about 1030 cm2/V s.

&

2016 Published by Elsevier Ltd.

1. Introduction

After publication of the study by Geim and Novoselov et al. in

2004 [1], graphene has been regarded as a new material for fun-

damental and practical study because of its unique mechanical,

thermal, optical and electrical properties that include high mobi-

lity at room temperature [2–4]. Graphene is a zero band gap semi-

metal with nite minimum conductivity [5], which is a major

problem for electrical applications. The electronic band structure

of graphene is intrinsically different from that of a semiconductor

with a band gap and metal with a high density of state (DOS) at

the Fermi level. Graphene has a conical shape for conduction and a

valence band having zero band gap and zero DOS at the Fermi

level. This gives rise to linear energy dispersion and massless Dirac

fermions that produce exceptional properties such as high con-

ductivity and mobility [6]. These unique behaviors make graphene

a good candidate for the next generation of electronic devices;

however, graphene cannot be used effectively for eld effect

transistors because it has a poor On/Off ratio. Thus, a major chal-

lenge with graphene is to open a well-dened band gap to solve

the problem of low On/Off current proportion. In nanosized gra-

phene structures, connement geometry and increased edge to

area ratio inuence their electronic properties and promise inter-

esting physical properties for electrical and optical device appli-

cations. Quantum connement can be increased by preparing a 1D

strip of graphene nanoribbon to increase the graphene band gap

[7–10], downscaling the width of the GNR and decreasing the

mobility to less than that for a graphene sheet [11,12].GNRs have been prepared using methods such as unzipping,

top-down lithography, and bottom-up processes like the synthesis

of GNR from a molecular precursor [12–15]. Magda et al. [15]

observed the highest band gap of 2.3 eV using STS in which they

deposited monomer precursors on the metal surface. Furthermore,

lithographic and plasma unzipping methods [16] usually produce

rough GNR edges that decrease carrier mobility because GNR

mobility is limited by line edge roughness scattering [17]. The

difference in mobility results from the difference in the methods

used to create the GNR. A better method would be one using

chemical approaches to produce smoother edges. The highest

1

2

3

4

5

6

7

8

90

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

89

0

1

2

3

4

5

6

7

8

9

0

1

23

4

5

6

7

8

9

0

1

2

3

4

5

6

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/jpcs

Journal of Physics and Chemistry of Solids

http://dx.doi.org/10.1016/j.jpcs.2016.01.001

0022-3697/& 2016 Published by Elsevier Ltd.

n CorrespondingQ3 author.E-mail address: [email protected] (S. Salimian).

Please cite this article as: S. Salimian, et al., J. Phys. Chem. Solids (2016), http://dx.doi.org/10.1016/j.jpcs.2016.01.001i

Journal of Physics and Chemistry of Solids ∎ (∎∎∎∎) ∎∎∎–∎∎∎

http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://www.sciencedirect.com/science/journal/00223697http://www.elsevier.com/locate/jpcshttp://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-mailto:[email protected]://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001mailto:[email protected]://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://www.elsevier.com/locate/jpcshttp://www.sciencedirect.com/science/journal/00223697http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


4/14

mobility reported thus far for monolayer GNR on a SiO2 substrate

was produced by chemical vapor deposition and measured

200–500 cm2/V s [18]. Although chemical synthesis could be use-

ful for large volume production, nding an isolated single layer of

GNR in a large amount of nanocomposite would mean costly de-

vice fabrication.

Research on the preparation of GNR and consideration of its

potential continues. No reports thus far have investigated the ap-

plication of GNR to large volume production. Our research un-derlines the importance of obtaining a carbon based nano-

composite with the characteristics of a semiconductor in order to

develop new electronic devices. The present study used the

longitudinal unzipping approach for GNR preparation [9,13,19,20].

This method is inexpensive with cost-effective chemical process,

high yield and stable aqueous solution. The synthesis yield is a

carbon nanocomposite with a GNR-CNT heterostructure. Utilizing

an isolated single layer GNR for this production requires expensive

device fabrication. The present study investigated a new potential

of GNR-CNT nanocomposite and optimized chemical synthesis to

achieve carbon nanocomposite semiconductor with narrow band

gap of about 0.08 eV. Then the produced GNR nanocomposite was

used in a simple fabrication method and its potential was in-

vestigated for semiconductor carbon nanostructure FETs. The

carrier mobility achieved by the SGNR was higher than those

previously reported for GNR. The TiO2 was used for the back gate

dielectric. The synthesized GNR nanocomposite was highly

p-doped and a strong rectifying effect was shown for SGNR-FET on

n-type TiO2. This indicates that the FET is appropriate for optoe-

lectronic applications like p–n junction diodes. In addition, ac-

cording to our previous research, SGNR nanocomposite is a com-

pelling semiconductor for sensor application and exible electro-

nics [21]. Although the band gap was three times greater than the

thermal energy at room temperature and the On-state increased,

the On/Off ratio remained low for transistor applications. This

could be as a result of the high concentration of GNR edges in the

nanocomposite, which creates Off leakage current. The proposed

GNR-CNT nanocomposite is a promising material with a simple

fabrication approach [21] in technology.

2. Exprimental

2.1. GNR-CNT nanocomposite preparation

In this study, GNRs were synthesized by chemical unzipping of

multiwall carbon nanotubes (MWCNTs) [13] based on Hummers

method [22]. The preparation procedure was followed as ex-

plained by Kosynkin et al. [13]. The main difference between the

synthesis used in current study and Kosynkin et al.'s synthesis is in

the size of used MWCNTs. We also investigated the potential of

GNR-CNT nanocomposite as a semiconductor carbon nanos-

tructure, in large volume production, instead of single layer GNR as the considered material. Patterning the graphene sheet into a

ribbon with a width of o10 nm opens an effective band gap from

the quantum connement effect [15,23,24]. The width of the GNR

formed by chemical unzipping depends on the diameter of the

nanotubes from which the GNRs originated. Therefore, raw

MWCTs o8 nm was used in diameter for unzipping. All chemicals

except the MWCNT were purchased from Merck (Germany).

MWCNTs were acquired from Neutrino (Iran).

Preparation of graphene nanoribbons based on unzipping CNTs

involves two steps: rstly, preparation of oxidized graphene na-

noribbon (GONR) and secondly reduction of GONR. Two-step

synthesis of GNR, with the ratio and exact amount of each

chemical used in the samples A through F, are presented in

Tables 1 and 2. The nanoribbons obtained by this technique have

much ‘smoother’ edges than those which are made by conven-

tional lithographic means.

In a typical procedure for GONR preparation (Table 1), 15 mg of

95% MWCNTs with diameters of o8 nm were suspended in 15 ml

of 98% concentrated sulfuric acid treated with 500 wt% potassium

permanganate (KMnO4) (Fig. 1(a)). The solution was heated in an

oil bath up to 70 °C to consume the KMnO4. Heating process was

as follows:

1. At rst, the reaction was heated at 55 °C for 30 min. The pro-

gress of the reaction was checked by preparing two test tubes.

One tube containing 1 ml of deionized (DI) water and 2 –3 drops

of hydrogen peroxide (30%) was used to monitor the reactionprogress in which several drops (4 or 5) of the reaction mixture

were added to the test tube; if the color of the solution was

yellow/brown, the reaction was complete.

2. The second test tube containing 1 ml of DI water only was used

to check the level of permanganate consumption; a red hue

solution indicates permanganate consumption and a complete

reaction.

3. It is also remarkable to notice that there is important informa-

tion in the color of the reaction mixture itself; when the color

went from black to dark brown with disappearing of the green

color of permanganate in acid, the reaction was completed.

4. Since the reaction was not complete after 30 min at 55 °C (the

permanganate was not entirely consumed), continued heating

was required. The temperature was increased to 65 °C and wasthen stabilized. Subsequently, the reaction progress was

checked again using the test-tube procedure. Finally, when the

reaction appeared nearly complete, the temperature was in-

creased and maintained consistently to 70 °C and the solution

was stabilized.

5. Then the mixture was cooled by pouring it into an ice bath and

adding hydrogen peroxide (H2O2) (30%) to prevent precipitation

of insoluble MnO2.

6. After 3 h of centrifuging at 4000 rpm, the solution was washed

several times with DI water followed by ethanol/hydrochloric

acid. Finally, the cleaned GONR-CNT nanocomposite was col-

lected by centrifuging.

For GNR preparation, reduction of GONR in aqueous of

6

6

6

7

7

7

7

7

77

7

7

7

8

8

8

8

8

8

8

8

8

8

9

9

9

9

9

9

9

9

9

9

10

10

10

10

1010

10

10

10

10

11

11

11

11

11

11

11

11

1111

12

12

12

12

12

12

12

12

12

12

13

13

13

Table 1

Synthesis conditions for the preparation of GONR samples A through F.

Sample MWCNT/KMnO4 H2O2 (ml)

A (15 mg/75 mg); 1/5 0.5

B 1/5 0.5

C 1/5 0.5

D 1/5 0.5

E (15 mg/135 mg); 1/9 1

F 1/9 1

Table 2

Synthesis conditions for the preparation of GNR samples A through F.

Sample GONR composite

(mg)

DI (ml) NH4OH (ml) N2H4 H2O (ml)

A 12.5 75 75 75

B 30 75 30 30

C 15 75 45 45

D 15 1% SDS (in 75 cc

DI)

45 45

E 15 1% SDS (in 75 cc

DI)

120 120

F 60 75 135 135

S. Salimian et al. / Journal of Physics and Chemistry of Solids ∎ (∎∎∎∎) ∎∎∎–∎∎∎2


http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


5/14

ammonium hydroxide (NH4OH) (27%) and hydrazine monohydrate

(N2H4 H2O) (98%) can be done with or without surfactant (Table 2,

Fig. 1(a)). Here we used Sodium Dodecyl Sulfate (SDS) surfactant

for samples D and E in which 1% SDS was prepared in 75 ml DI.

The reduction steps were as follows:

1. The collected GONR nanocomposite, from step 5 (Table 1), was

added to a ask of 75 ml DI water (with or without SDS).

2. NH4OH and N2H4 H2O were added to the mixture, which was

then immersed in an oil bath at 90 °C.

After 1 h of reduction without stirring, the dark GNR-CNT na-nocomposite sediment was washed (Fig. 1(b)), centrifuged and

dried by using the same method which was used for GONR. The

reaction process and produced nanocomposite are shown sche-

matically in Fig. 1.

2.2. Device fabrication

After cleaning the silicon substrate using the RCA method, the

TiO2 was evaporated using an electron beam gun on (100) silicon

at about 30, 40, 60 nm. To reduce agglomeration, the nano-

composite suspension was sonicated at room temperature for

5 min. After centrifuging and washing the GNR in DI water, one

spot of viscous GNR was spin-coated at 3000 rpm for 1 min onto

the TiO2/silicon substrate. In order to achieve a continuous de-

position of nanocomposite layer on a hard substrate, it is necessary

to deposit a thick layer. The channel thickness was about 100 mm.

A shadow mask covered the channel and 50 nm of source-drain

aluminum electrodes were evaporated on the top. A schematic of

the devices is shown in Fig. 2(a). Fig. 2(b) shows the absence of

metal contact between the source and the drain using an optical

microscope.

3. Results and discussions

Since reduction affects the basic structure of the material

(MWCNT), characteristic changes were revealed by STS, STM and

Raman identications and measurements to determine which

samples were semiconductors under different synthesis condi-

tions (Table 2).

3.1. GNR-CNT nanocomposite characterization

Raman spectra was recorded at ambient temperature using a

standard backscattering geometry with 785 nm excitation wave-

length produced by a high-power laser diode source capable of

supplying 50 mW of power. We used transmission electron mi-

croscopy (TEM, model Philips EM208S) operated at 100 kV to

1

2

3

4

5

6

7

8

90

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

89

0

1

2

3

4

5

6

7

8

9

0

1

23

4

5

6

7

8

9

0

1

2

3

4

5

6

Fig. 1. (a) The schematic of the reaction process (b) The synthesis yield is a carbon nanocomposite with GNR-CNT heterostructures (left side) and different types of unzipped

CNTs (right side).

Fig. 2. (a) Schematic of devices (cross section); (b) channel under optical microscopy (top view).

S. Salimian et al. / Journal of Physics and Chemistry of Solids ∎ (∎∎∎∎) ∎∎∎–∎∎∎ 3


http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


6/14

image the nanoribbons structure. Scanning tunneling spectro-

scopy (STM, model DME Doalscope) measurements were per-

formed for the topographic and spectroscopic measurements.

The Raman spectrum of GNR-CNT nanocomposites is shown in

Fig. 3 by presence of three main peaks; G (1580 nm), D (1350 nm),

and 2D (2700 nm) [25–

28]. D band and 2D band, both are second

order double resonances including one and two phonon scattering

respectively [37]. D band presents the disorder and defect in a

sample or at the edge of a graphene sample. In unzipping process,

broad D band in GONR also can be originated from oxygen-con-

taining functional groups which reduce, in width and intensity,

after adding reduction agents. Lower D-band intensity in GNR in

6

6

6

7

7

7

7

7

77

7

7

7

8

8

8

8

8

8

8

8

8

8

9

9

9

9

9

9

9

9

9

9

10

10

10

10

1010

10

10

10

10

11

11

11

11

11

11

11

11

1111

12

12

12

12

12

12

12

12

12

12

13

13

13

Fig. 3. Raman spectra of samples A through F excited with 785 nm laser radiation; raw MWCNT and GONR nanocomposites before and after reduction (GNR).



http://-/?-http://-/?-http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-http://-/?-http://-/?-


7/14

comparison to that of GONR shows that the reduction has oc-

curred as a result of the reducing agents. Therefore, when GNRs'

D-band intensity is higher than that of MWCNTs, it would mainly

originate from GNRs' open edges (Fig. 3, Sample A). Hydrazine

reduction produced an agglomeration of unzipped GNR-CNT na-

nocomposites caused by hydrophobicity (Fig. 4) [32,33]. The GNRs

attached to each other at the edges producing an extended gra-

phene layer with GNR building blocks [35,36]. It can cause the

creation of narrow band gap in GNR-CNT nanocomposite. Thus,

2D-band intensity decreases with increasing reduction agents

(Fig. 3, Samples E and F).

The ratio of D band and G band represents the mount of dis-

order in carbon nanostructure samples. Thus, D band evaluate the

quality of carbon-based materials by comparing I G/I D ratio [15].

Table 3 shows the intensity values for I D/I G and I D/I 2D which are

commonly used to evaluate the quality of carbon material [15]. It

shows that the lowest defect intensity, the highest 2D peak ratio

(I D/I 2D¼3) and the highest reduction (lower D-band intensity in

GNR in comparison to GONR) were found in sample A which in-

dicate successive opening reaction and reduction in synthesis

process.

In general, the Radial Breathing Modes (RBM) are carbon na-

notube identication peaks located below 400 nm [29–31]. This is

unique quantum behavior and appears in single wall carbon na-

notubes [38]. However, the breathing vibration in few-walled CNTscannot be neglected [39]; the radial vibrations of multiple tubes

make the weak RBM mode, which can be detected using Raman

spectroscopy. The diameter of the CNT is therefore of great

signicance and a higher diameter pushes the radial vibration

beyond the detection limit, whereas a lower diameter means it

appears clearly when using Raman spectroscopy. RBM modes in

MWCNT (o8 nm) are therefore observable due to their low dia-

meter size and few-walled inner vibration; especially when the

inner shell is less than 2 nm [38]. In this experiment, the RBM

modes of sample A decreased after unzipping MWCNT (Fig. 5),

which shows that the unzipping of MWCTs was carried out

successfully.

Fig. 6 shows TEM images of the transformation of MWCNTs into

nanoribbons after unzipping. The reduced graphene nanoribbons

show single layer and multi-layer GNRs. Dark sections appear due

to the agglomeration of GNRs and CNTs in the carbon grid and

folded-in areas of the sheet. In Fig. 6(f), the remaining MWCNTs

are shown together with the GNRs. This shows that the nalproduct of the unzipping process is a mixture of extended GNRs

and MWCNTs. As it was mentioned previously, reduction produces

an agglomeration which is caused by hydrophobicity and GNRs

attached at the edges producing an extended graphene layer

[35,36]. Then the extended GNR (Fig. 6(g)) included small GNR

building blocks.

Scanning tunneling spectroscopy (STS) and Microscopy (STM)

were used to study large-scale areas (micro-to-micro), on three

different samples: A, B and D. Samples A and B were selected from

Table 3, because they showed respectively the least number of

defect, the narrowest D peak after reduction and they both have

the highest intensity for 2D peak (Fig. 3). In addition, sample D

was selected to investigate surfactant effect in nanocomposite.

Figs. 7, 8 and 9 show the STS and STM of stacked fragments of GNR-CNT nanocomposites (A, B and D) drop casted onto alumi-

num foil.

The tunneling current of the samples versus bias voltage was

measured using STS; it is an average of current measured in spe-

cic area. The measurements show nonlinear I–V curves in dif-

ferent places on sample A (Fig. 7(b) and (c)). The numerical deri-

vation dI/dV denes the local density of state (DOS) (Fig. 7(d)).

From this result, it can be understood that the interference of

electron waves produced DOSs at measured positions. Fig. 7

(d) shows the decrease the dI/dV signal that can be attributed to

the decrease in DOS at the edges of the area [10]; the dI/dV curve

is related to the scanned area (1 mm2) (Fig. 7(a)). A gap-like feature

was observed at about 0.08 eV between two arrows in the gra-

phene tunneling spectrum of sample A (Fig. 7(d)). This gap was

1

2

3

4

5

6

7

8

90

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

89

0

1

2

3

4

5

6

7

8

9

0

1

23

4

5

6

7

8

9

0

1

2

3

4

5

6

Fig. 4. Agglomeration caused by hydrophobicity after GONR reduction.

Table 3

Intensity ratios of main peaks in the Raman spectra of samples A through F.

Sample I D/ I G I D / I 2D

A 0.3 3

B 0.57 10

C 1 –

D 1 –

E 0.58 23

F 1.2 –

Fig. 5. RBM modes, excited with 785 nm laser radiation, of raw MWCNT and GONR

nanocomposites of sample A before and after reduction (GNR).



http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


8/14

found to arise from suppression of electronic tunneling to gra-

phene states near the Fermi level [34].

This is promising band gap for carbon nanotechnology and

indicates that homogenous GNR-CNT heterostructure nano-

composites with optimized narrow band gap can be used to de-

velop easy strategies for device fabrication.

The reduction step plays an important role in decreasing oxi-

dization and the amount is critical for preventing agglomeration

and producing homogenous nanocomposite. A lower reduction

amount (30 ml) was tested for sample B for comparison with

sample A (75 ml) (Table 2). Fig. 8 shows that the tunneling I–V

curve has a linear aspect (Fig. 8(b)) and there are energy states at

the Fermi level of DOS (dI/dV curve) which are CNT mid-gap states

(Fig. 8(c)); the dI/dV curve is related to the red square scanned

area (0.05 mm2

) (Fig. 8(a)). This behavior indicates that reduction

was not complete. As long as there is a high concentration of

oxidized CNT in the nanocomposite, the GNR-CNT nanocompositeband structure does not have band gap.

According to Table 2, sample D contained more reductant in a

surfactant solution (45 ml of reduction in 1% SDS surfactant solution)

than sample B (30 ml of reduction in 75 ml DI water) to prevent ag-

glomeration. The STS of sample D shows nonlinearity of an insulator

(Fig. 9) which could be an effect of the surfactant used. Vibration in the

tunneling I–V curve is instrumental noise related to the nanometer

range of the selected scale area (400 nm2, green line). A large area

(0.036 mm2, red line) has a lower vibrational effect.

3.2. Electrical measurement of SGNR-FET

As sample A showed semiconductor characteristics, it was

chosen for device fabrication. The electrical characterization of

6

6

6

7

7

7

7

7

77

7

7

7

8

8

8

8

8

8

8

8

8

8

9

9

9

9

9

9

9

9

9

9

10

10

10

10

1010

10

10

10

10

11

11

11

11

11

11

11

11

1111

12

12

12

12

12

12

12

12

12

12

13

13

13

Fig. 6. TEM images of the stepwise opening of MWCNTs to form GNRs. The dark parts are carbon grid: (a) and (b) raw MWCNTs; (c) and (d) oxidized graphene nanoribbons;

(e) reduced graphene nanoribbons; (f) reduced graphene nanoribbons (left side) showing GNR sheet and (right side) agglomerated raw MWCNT; (g) highly transparent GNR

partially folded onto itself.



http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


9/14

1

2

3

4

5

6

7

8

90

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

89

0

1

2

3

4

5

6

7

8

9

0

1

23

4

5

6

7

8

9

0

1

2

3

4

5

6

Fig. 7. (a) STM image of GNR nanocomposite of sample A drop casted on Al foil at 1 mm2 area scale. Two triangle bars show the material thickness on top of Al substrate is

about 50 nm. (b) and (c) nonlinear I –V curve of selected areas. (d) Derived I–V (dI/dV); DOS shows sample A is a semiconductor nanocomposite; the insect shows a gap-like

feature of sample A with narrow energy gap at about 0.08 eV.



http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001


10/14

devices was performed using HP instrument. The channel re-

sistance of sample A showed nonlinear behavior at about 106 Ω.

This amount of resistance was expected because of the small

diameter of the raw CNTs used. Dayen et al. [40] also reported

channel resistance for GNR in the range of 40–700 kΩ at 300 K.

The charge carrier density was controlled using a gate eld

rather than a source drain eld. The thickness of the gate dielectric

must decrease [41–43]; however, for graphene on a SiO2 substrate,scattering electrons using the optical phonons of the substrate had

a greater effect at room temperature than scattering the graphene

phonons. TiO2 is a high-k material with a low band gap. High-k

materials can decrease charged impurity scattering from the in-

creased screening effect and improve gate charge control on the

channel because of higher gate capacitance [42, 48,50].

Sample B was next spin-coated onto the three substrates de-

vices 1, 2 and 3 with 30 nm, 40 nm and 60 nm evaporated TiO2,

respectively (Fig. 10). The electrical performance of the SGNR-FETs

varied according to the thickness of the TiO2. Fig. 10(b) shows a

smooth cross-section of device 2 with 40 nm TiO2. The bright lines

at the top are evaporated TiO2. At low roughness, the 40 nm

sample had a low scattering center at the SGNR/TiO2 interface. The

evaporated TiO2 thickness was conrmed using an interferometer.

The contribution of current from the holes in Fig. 11 indicates that

the holes dominated transport.

The band gap at 0.08 eV is about three times larger than the

thermal energy at room temperature. It appears that the super-

position of electrical properties of the GNRs in the SGNR had a

constructive effect in the On-state (mA current range) and a de-

structive effect in the Off-state (Fig. 11). Utilizing the narrow band

gap graphene stack for FET increased the mobility of the SGNR-FET, but is not a guarantee of improvement of Off-state perfor-

mance. Off leakage could be the result of the variability in the band

gap and edge effects [8,44] from the combined GNRs in the

nanocomposite.

One of the most ef cient ways to determine the semiconductor

behavior of materials is assessing p–n junction characteristics [52].

In Fig. 12, a p–n junction diode was inserted at the interface to

allow for different densities for the carriers at the SGNR/TiO2 junction having an asymmetric I–V curve. The semiconductor be-

havior of SGNR upon formation of p–n junction on TiO2 thin lm

(Fig. 12) conrms the band gap characteristic (Fig. 7(d)) of sample

A. Fig. 12 shows the rectifying behavior at the SGNR/TiO2 interface

after application of source-drain voltage and constant applied back

gate voltages (V BG¼10 V, 0 V, 10 V). The p–

n junction diode with

6

6

6

7

7

7

7

7

77

7

7

7

8

8

8

8

8

8

8

8

8

8

9

9

9

9

9

9

9

9

9

9

10

10

10

10

1010

10

10

10

10

11

11

11

11

11

11

11

11

1111

12

12

12

12

12

12

12

12

12

12

13

13

13

Fig. 8. (a) STM images of GNR nanocomposite of sample B drop casted on Al foil at 0.05 mm2 area scale. Red square shows selected area for measurement. (c) Linear I–V curve

and (d) Derived I–V (dI/dV); DOS of sample B included CNT mid-gap states around fermi level with no energy gap.



http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


11/14

the lowest leakage current is shown in Fig. 12(b). The current shift

(prole does not pass zero current at zero V source-drain) for

positive and negative back gate voltage is from the effect of charge

carriers induced by the back gate eld effect. Fig. 13 shows thiseffect on charge carrier concentration. By applying zero and ne-

gative back gate voltages, the (p-doped) higher p-doped GNR stack

and the (n-doped) higher n-doped TiO2 dielectric were produced

1

2

3

4

5

6

7

8

90

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

89

0

1

2

3

4

5

6

7

8

9

0

1

23

4

5

6

7

8

9

0

1

2

3

4

5

6

Fig. 9. Red (0.036 mm2) and green (400 nm2) squares are two different sizes of

selected areas of sample D; nonlinear I–V curve of measured squares originates

from surfactant effect and vibrations are instrumental noise related to the nan-

ometer range of the measured scale size.

Fig. 10. Cross-section images of Si substrate with TiO2 deposits of about: (a) 30 nm (b) 40 nm (c) 60 nm.

Fig. 11. Electrical transport curves of SGNR-FETs; V BG v.s. I SD for V SD¼0.5 V.



http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-


12/14

at the junction. In a positive (negative) biased channel, the junc-

tion is in forward (reverse) bias.

The schematic energy band diagram of the SGNR/TiO2 hetero-

junction shown in Fig. 14 corresponds to that shown in Fig. 12(b).

The main difference between the narrow band gap SGNR and the

wide band gap TiO2 is caused by the hole barrier [51]. In reverse

bias, the minority charge carriers ow through the junction from

both directions; in forward bias, just one direction of the majority

charge carrier ows across the junction. Holes require more en-

ergy to pass this potential barrier.

Table 4 shows the increased number of electrons and the hole

mobility of device 2 compared to the other two devices. All three

devices operated at the quantum capacitance limit (QCL) when QC

was less than their classical capacitance (CC) [49]. The equivalent

circuit is shown in Fig. 15. QC was calculated using Eq. (1)

[45,46,47] which shows that QC is in the QCL regime, C insulator was

calculated using Eq. (2) and mobility was calculated using Eq. (3):

( )π =

ℏ ( )

C e

v

2eV

1Q

2 ch

f 2

=+ ( )

C C C

C C 2insulator

OX Q

OX Q

μ =·

· · ( )

L g

W C V 3m

i D

4. Conclusion

In this research we synthesized a GNR-CNT nanocomposite by

chemical unzipping of CNT for potential use as a carbon nanos-

tructure semiconductor. The CNTs were converted into the GNRs

through longitudinal unzipping. Measurement of the structural

and elemental properties was done by Raman spectroscopy, TEM,

STM and STS. Controllable reduction is a specic requirement for

preparation of semiconductor carbon nanocomposites. Although

complete unzipping and complete reduction are dif cult to per-

form on CNTs, partial synthesize is suf cient to achieve a homo-

genous semiconductor by optimizing synthesis; in this case, op-

timizing the mount of reductant. The energy gap of optimized

6

6

6

7

7

7

7

7

77

7

7

7

8

8

8

8

8

8

8

8

8

8

9

9

9

9

9

9

9

9

9

9

10

10

10

10

1010

10

10

10

10

11

11

11

11

11

11

11

11

1111

12

12

12

12

12

12

12

12

12

12

13

13

13

Fig. 12. Rectifying I–V curves, V SD v.s. I SD at V BG¼10, 0, 10 V and TiO2 of (a) 30 nm (b) 40 nm (c) 60 nm.



http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


13/14

nanocomposite using STS in micro scale size was observed at

0.08 eV above the Fermi level. This narrow band gap in spite of unzipping small-size MWCNTs is likely to be because of the pro-

ducing an extended graphene ribbon with GNR building blocks.

The semiconductor GNR was utilized as a channel for the eld

effect transistor with a TiO2 dielectric. Asymmetry in ambipolar

graphs of the SGNR-FET shows that holes dominated electrical

transportation with higher mobility (1030 cm2/V s) as calculated

using equivalent circuit and quantum capacitance. The negative

voltage of the back gate induced high density in the charge car-

riers at the SGNR/TiO2 interface and formed a p–n junction diode

with low leakage current. The suggested band diagrams describe

the process of charge transferring well. It is a promising low cost

proposed structure for optoelectronic applications requiring

stacked GNRs with high charge carrier mobility. This characteristic

should help pave the way toward development of GNR nano-composite-based semiconductor nanotechnology. Research on

GNR-CNT nanocomposites is a step toward developing this mate-

rial for practical applications and is attractive for mass-scale pro-

duction of GNRs in combination with CNTs which can be applic-

able for ease of device fabrication.

Acknowledgments

The rst author is grateful to the University of Kharazmi an Qd

Material Research Center for nancial support for this research

work.

References

[1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Science 306 (2006) 666–669.

[2] W.J. Yu, X. Duan, Sci. Rep. 3 (2013) 1248.[3] C.N.R. Rao, K.S. Subrahmanyam, H.S.S. Ramakrishna Matte, A. Govindaraj, Mod.

Phys. Lett. B 25 (2011) 427–451.[4] F. Perreault, A. Fonseca de Faria, M. Elimelech, Chem. Soc. Rev. 44 (2015)

5861–5896.[5] M.W. Lin, C. Ling, Y. Zhang, H.J. Yoon, M.M.C. Cheng, L.A. Agapito, N. Kioussis,

N. Widjaja, Z. Zhou, Nanotechnology 22 (2011) 265201.[6] F. Akbar, M. Kolahdouz, S. Larimian, B. Radfar, H.H. Radamson, J. Mater. Sci.:

Mater. Electron. 26 (2015) 4347–4379.[7] H. Owlia, P. Keshavarzi, Mat. Sci. Semicon. Proc. 39 (2015) 636–640.[8] M. Poljak, K.L. Wang, T. Suligoj, Solid State Electron. 108 (2015) 67–74.[9] L. Jiao, L. Zhang, X. Wang, G. Diankov, H. Dai, Nature 458 (2009) 877–880.

[10] S.H. Phark, J. Borme, A.L. Vanegas, M. Corbetta, D. Sander, J. Kirschner,

1

2

3

4

5

6

7

8

90

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

8

9

0

1

2

3

4

5

6

7

89

0

1

2

3

4

5

6

7

8

9

0

1

23

4

5

6

7

8

9

0

1

2

3

4

5

6

Fig. 13. Effect of back gate on charge carrier concentration at SGNR/TiO2 junction.

Fig. 14. Energy band diagram of a SGNR/TiO2 heterojunction of device 2 at:

(a) equilibrium; (b) reverse bias; (c) forward bias.

Table 4

Electrical parameters of devices.

Device le (cm2 /V s) lh (cm

2 /V s)

1; TiO2 (30 nm) 102 354

2; TiO2 (40 nm) 223 1030

3; TiO2 (60 nm) 74 1030

Fig. 15. Equivalent circuit for dielectric and graphene interface.



http://-/?-http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://-/?-


14/14

Nanoscale Res. Lett. 7 (2012) 255.[11] X. Wang, Y. Ouyang, X. Li, H. Wang, J. Guo, H. Dai, Phys. Rev. Lett. 100 (2008)

206803.[12] Y. Yang, R. Murali, IEEE Electron Dev. Lett. 31 (2010) 237–239.[13] D.V. Kosynkin, A.L. Higginbotham, A. Sinitskii, J.R. Lomeda, A. Dimiev,

B. Katherine Price, J.M. Tour, Nature 458 (2009) 872–876.[14] H. Söde, L. Talirz, O. Groning, C.A. Pignedoli, R. Berger, X. F eng, K. Müllen,

R. Fasel, P. Ruf eux, Phys. Rev. B 91 (2015) 045429.[15] G.Z. Magda, X. Jin, I. Hagymási, P. Vancsó, Z. Osváth, P. Nemes-Incze, C. Hwang,

L.P. Biró, L. Tapasztó, Nature 514 (2014) 608–611.[16] I.M. Fernandez, D. Wang, Y. Zhang, Nano Lett. 12 (2012) 6175–6179.

[17] J.H. Chen, W.G. Cullen, C. Jang, M.S. Fuhrer, E.D. Williams, Phys. Rev. Lett. 102(2009) 236805.

[18] A. Behnam, A.S. Lyons, M. Bae, E.K. Chow, S. Islam, C.M. Neumann, E. Pop, NanoLett. 12 (2012) 4424–4430.

[19] A. Sinitskii, A. Dimiev, D.V. Kosynkin, J.M. Tour, ACS Nano 4 (2010) 5405–5413.[20] L. Jiao, L. Zhang, L. Ding, J. Liu, H. Dai, Nano Res. 3 (2010) 387–394.[21] M. Asad, S. Salimian, M.H. Sheikhi, M. Pourfath, Sens. Actuators A-Phys. 232

(2015) 285–291.[22] W.S. Hummers Jr, R.E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339.[23] R. Sako, H. Hosokawa, H. Tsuchiya, IEEE Electron Dev. Lett. 32 (2011) 11704692.[24] L.F. Huang, G.R. Zhang, X.H. Zheng, P.L. Gong, T.F. Cao, Z. Zeng, J. Phys.: Con-

dens. Matter 25 (2013) 055304.[25] Y. You, Zh Ni, T. Yu, Z. Shen, Appl. Phys. Lett. 93 (2008) 163112.[26] M.S. Dresselhaus, A. Jorio, A.G. Souza Filho, R. Saito, Phil. Trans. R. Soc. A 368

(2010) 5355–5377.[27] A.C. Ferrari, D.M. Basko, Nat. Nanotechnol. 8 (2013) 235.[28] A.C. Ferrari, J.C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri,

S. Piscanec, D. Jiang, K.S. Novoselov, S. Roth, A.K. Geim, Phys. Rev. Lett. 97

(2006) 187401.[29] S. Costa, E. Borowiak-Palen, M. Kruszynska, A. Bachmatiuk, R.J. Kalenczuk,Mater. Sci.-Poland 26 (2008) 433–441.

[30] M.S. Dresselhaus, A. Jorio, M.A. Pimenta, An. Ac. Bras. Cie n̂c. 78 (2006)423–439.

[31] H. Telg, M. Fouquet, J. Maultzsch, Y. Wu, B. Chandra, J. Hone, T.F. Heinz,

C. Thomsen, Phys. Status Solidi B 245 (2008) 2189–2192.[32] S. Pei, H.M. Cheng, Carbon 50 (2012) 3210–3228.[33] S. Park, J. An, J.R. Potts, A. Velamakanni, Sh Murali, R.S. Ruoff, Carbon 49 (2011)

3019–3023.[34] Y. Zhang, V.W. Brar, F. Wang, C. Girit, Y. Yayon, M. Panlasigui, A. Zettl, M.

F. Crommie, Nat. Phys. 4 (2008) 627–630.[35] F. Cataldo, G. Compagnini, G. Patané, O. Ursini, G. Angelini, P.R. Ribic,

G. Margaritondo, A. Cricenti, G. Palleschi, F. Valentini, Carbon 48 (2010)

2596–2602.[36] C.Y. Moon, Y.S. Kim, E.C. Lee, Y.G. Jin, K.J. Chang, Phys. Rev. B 65 (2001) 155401.[37] J.S. Chen, V. Stolojan, S.R.P. Silva, Carbon 84 (2015) 409–418.[38] R. Kamalakannan, K. Ganesan, S. Ilango, N. Thirumurugan, V.N. Singh,

M. Kamruddin, B.R. Mehta, A.K. Tyagi, Appl. Phys. Lett. 98 (2011) 192105.[39] K.N. Cheng, Y.H. Lin, G.R. Lin, Laser Phys. 23 (2013) 045105.[40] J.F. Dayen, A. Mahmood, D.S. Golubev, I.R. Jeune, P. Salles, E. Dujardin, Small 4

(2008) 716–720.[41] L. Liao, X. Duan, Mater. Sci. Eng.: R: Rep. 70 (2010) 354–370.[42] J.H. Chen, C. Jang, M. Ishigami, S. Xiao, W.G. Cullen, E.D. Williams, M.S. Fuhrer,

Solid State Commun. 149 (2009) 1080–1086.[43] M. Akbari Eshkalak, R. Faez, S. Haji-Nasiri, Phys. E: Low Dimens. Syst. Na-

nostruct. 66 (2015) 133–139.[44] M. Poljak, M. Wang, E.B. Song, T. Suligoj, K.L. Wang, Solid State Electron. 84

(2013) 103–111.[45] J. Xia, F. Chen, J. Li, N. Tao, Nat. Nanotechnol. 4 (2009) 505–509.[46] S. Dröscher, P. Roulleau, F. Molitor, P. Studerus, C. Stampfer, K. Ensslin, T. Ihn,

Phys. Scr. T 146 (2010) 014009.[47] S. Luryi, Appl. Phys. Lett. 52 (1988) 501–503.[48] S.K. Jang, J. Jeon, S.M. Jeon, Y.J. Song, S. Lee, Solid State Electron. 109 (2015)

8–11.

[49] M.A. Khayer, R.K. Lake, IEEE Trans. Elect. Dev. 56 (2009) 2215–2223.[50] F. Schwierz, Nat. Nanotechnol. 5 (2010) 487–496.[51] L. Hans, Solid Surface, Interfaces and Thin Films, Fifth ed., Springer, New York,

2010.[52] D.T. Phan, G.S. Chung, J. Phys. Chem. Solids 74 (2013) 1509–1514.

6

6

6

7

7

7

7

7

77

7

7

7

8

8

8

8

8

8

8

8

8

8

9

9

9

9

9

9

9

9

9

9

10

10

10

10

1010

10

10

10

10

11

11

11

11

11

11

11

11

1111

12

12

12

12

12

12

12

12

12

12

13

13

13


l i hi i l S S li i l h Ch S lid (2016) h //d d i /10 1016/j j 2016 01 001i
https://www.researchgate.net/publication/253214436_Solid_Surfaces_Interfaces_and_Thin_Films?el=1_x_8&enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA==https://www.researchgate.net/publication/253214436_Solid_Surfaces_Interfaces_and_Thin_Films?el=1_x_8&enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA==http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001https://www.researchgate.net/publication/253214436_Solid_Surfaces_Interfaces_and_Thin_Films?el=1_x_8&enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA==https://www.researchgate.net/publication/253214436_Solid_Surfaces_Interfaces_and_Thin_Films?el=1_x_8&enrichId=rgreq-e1a67b7b-49c1-48ca-8661-698d579259b3&enrichSource=Y292ZXJQYWdlOzI4OTUyOTI5OTtBUzozMTg2MTg1ODYyODgxMjhAMTQ1Mjk3NTk5ODEyOA==http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001http://dx.doi.org/10.1016/j.jpcs.2016.01.001

Documents

ViewPageProof PCS 7700