SYNTHESIS OF ZnSe final

05/01/2023 [email protected]

PROJECT PRESENTATION ON“Synthesis Of ZnSe

Nanocrystals”By:

Jitesh Kumar BE/15007/12Atish Sinha BE/15009/12

Gaurav Raj Anand BE/15067/12


ContentsIntroduction

Objective

Methodology

Work Done(Step 1)

Characterization Process

Expected Results

Work done (Step 2)

Further Work

References


IntroductionNanocrystals• A nanocrystal is a crystalline particle with at least one dimension measuring less than 1000

nanometers (nm), where 1 nm is defined as 1 thousand-millionth of a meter (10-9 m).• The size of nanocrystals distinguishes them from larger crystals. For example, silicon

nanocrystals can provide efficient light emission while bulk silicon does not and may be used for memory components.

• When embedded in solids nanocrystals may exhibit much more complex melting behaviour than conventional solids and may form the basis of a special class of solids. They can behave as single-domain systems (a volume within the system having the same atomic or molecular arrangement throughout) that can help explain the behaviour of macroscopic samples of a similar material without the complicating presence of grain boundaries and other defects.

• Semiconductor nanocrystals having dimensions smaller than 10nm are also described as quantum dots.


Applications of Nanocrystals

Illumination Flat panel display

Optical and Infrared Lasers

Removal of pollutants and

toxinsSolar Panels

Refining of Crude Oils

Drug Manufacture

Protein Analysis

Biotags for Gene

Identification


Zinc Selenide• Zinc selenide (ZnSe) is a light-yellow, solid compound

comprising zinc (Zn) and selenium(Se).• It is an intrinsic semiconductor with a band gap of about

2.70 eV at 25 °C (77 °F). • ZnSe rarely occurs in nature, and is found in the mineral

that was named after Hans Stille called "stilleite“.• Fig. 1 ZnSe Unit Cell 3D Fig. 2 Zinc Selenide


• Properties of ZnSe

ZnSe can be made in both hexagonal

(wurtzite) and cubic (zincblende) crystal

structure.

It is a wide-bandgap semiconductor of

the II-IV semiconductor group (since zinc and

selenium belong to the 12th and 16th groups of the periodic table,

respectively).

The material can be doped n-

type doping with, for instance, halogen elements. P-type

doping is more difficult, but can be achieved by

introducing gallium .


• Material of Properties of Zinc SelenideOptical Properties

Bulk Absorption Coefficient @ 10.6µm <= 0.0005 cm-1

Temperature Change of Refractive Index @ 10.6µm 61 x 10-6/°C

Refractive Index Inhomogeneity @ 632.8 nm < 3 x 10-6

Thermal Properties

Thermal Conductivity @ 20° C 0.18 W/cm/°C

Specific Heat 0.356 J/g/°C

Linear Expansion Coefficient @ 20° C 7.57 x 10-6/°C


Mechanical PropertiesYoung’s Modulus 67.2 GPa (9.75 x 106 psi)Rupture Modulus 55.1 MPa (8,000 psi)Knoop Hardness 105-120 kg/mm2Density 5.27 g/cm3Poisson’s Ratio 0.28

Fig 3 ZnSe Transmission Charts Thermo-Optic Coefficient @ Various Wavelengths dn/dT (10-5°C-1)


• Applications of ZnSe

ZnSe is used to form II-VI light-emitting

diodes and diode lasers. It emits blue light.

ZnSe doped with chromium (ZnSe:Cr) has been used as

an infrared laser gain medium emitting at about

2.4 µm.

In daily life, it can be found as the entrance optic in the

new range of "in-ear" clinical thermometers, seen as a small yellow

window

ZnSe activated with tellurium is a scintillator with

emission peak at 640 nm, suitable for matching

with photodiodes. It is used in x-ray and gamma

ray detectors.


Objective

Synthesis of Zinc Selenide Nanocrystals

Study of its optical and electrical properties

Application in Photovoltaic Cells


Methodology• The methodology used in preparation of ZnSe nanocrystals by us is called

solvo thermal synthesis method.• In this case, we use water as a solvent, because of which it is called

hydrothermal synthesis.• Solvothermal synthesis is a method for preparing a variety of materials

such as metals, semiconductors, ceramics, and polymers.• The process can be used to prepare many geometries including thin films,

bulk powders, single crystals, and nanocrystals. • In addition, the morphology (sphere (3D), rod (2D), or wire (1D)) of the

crystals formed is controlled by manipulating the solvent supersaturation, chemical of interest concentration, and kinetic control.

• The method can be used to prepare thermodynamically stable and metastable states including novel materials that cannot be easily formed from other synthetic routes.


• Over the last decade, a majority (~80%) of the literature concerning solvothermal synthesis has focused on nanocrystals.

• A magnetic stirrer was used for this process, which was set at different RPMs for a good number of hours for mixing and drying.

• A microwave was used for further drying.


Work Done (Step 1)In the typical synthesis of CdSe, highly pure CdCl2 powder (99.9%) and

elementalSelenium (99.999%) was used without further purification. Ethylene

glycol and Hydrazine hydrate were also used.

In this synthesis process, CdCl2 (4.0 g) and elemental selenium (2.0 g) was taken

with deionized water, ethylene glycol and

hydrazine hydrate in the volume ratio of 7:3:1

respectively in a 200ml capacity conical flask.

Then, the solution was refluxed under vigorous

stirring at 60°Cfor 6 hrs. The black

precipitates was collected and washed with

anhydrous ethanol andhot distilled water several

times, then dried in vacuum at 50°C for 5 h.

The sample was carefully filtered out and put in a

microwave at 300 degree Celsius for 5 minutes.

Finally, ZnSe Nanocrystals were obtained.


Expected ResultsX-Ray diffraction spectra of ZnSe.


TEM of ZnSe nanocrystals and corresponding particle size distribution.


PL Spectra of ZnSe Nanocrystals


Characterization Process

XRD UV Spectroscopy SEM FTIR

Spectroscopy


Work Done (Step 2)Another sample of ZnSe nanocrystals was prepared using the same method. The ZnSe nonocrystals were again dried.

The process now to be carried out was doping the sample with Magnesium(0.5g)

Magnesium was then made into a solution by mixing few millilitres of distilled water to it and then to ZnSe.

Drying was carried on in a similar manner with the help of microwave.


Future Work• The sample ZnSE/ Mg doped is to be sent to Cochin University

through courier for characterization.• The characterization would involve following processes:a)XRD b)UV characterizationc)SEM d)FTIR Spectroscopy• The results will be expected in around a week.• The results of the ZnSe nano crystals and ZnSe/Mg doped

nanocrystals will be put for a comparision.• A detailed report would follow.


References• L. Pavesi (2000). "Optical gain in silicon nanocrystals". Nature 408: 440.

doi:10.1038/35044012.• Jump up ^ S. Tiwari (1996). "A silicon nanocrystal based memory". Appl. Phys.

Lett. 68: 1377. doi:10.1063/1.116085.• Jump up ^ J. Pakarinen (2009). "Partial melting mechanisms of embedded

nanocrystals". Phys. Rev. B 79: 085426. doi:10.1103/physrevb.79.085426.• Jump up ^ D. V. Talapin (2012). "Nanocrystal solids: A modular approach to

materials design". MRS Bulletin 37: 63. doi:10.1557/mrs.2011.337.• Cr2+ excitation levels in ZnSe and ZnS, G. Grebe, G. Roussos and H.-J. Schulz, J.

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Thank You!!• Questions, if any are invited.

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SYNTHESIS OF ZnSe final