PROJECT SYNOPSIS ON

“Synthesis Of ZnSe Nanocrystals”

By:Jitesh Kumar BE/15007/12

Atish Sinha BE/15009/12Gaurav Raj Anand BE/15067/12

Contents

Introduction

Objective

Methodology

Proposed Work

Future Work

References

Introduction

Nanocrystals 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 toxins

Solar 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 Selenide

Optical 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 A novel developed hydrothermal microemulsion technique is used

to synthesize nanoparticles, nanorods and nanowires, and ithas been considered as an effective synthetic method.

It is well known that microemulsion is one of the effective media to synthesizenanoparticles.

In water-in-oil microemulsions, nano-sized waterdroplets are surrounded by a layer of surfactant and cosurfactantmolecules to form reverse micelles, and steadily dispersed in oilphase.

They provide an ideal environment for the preparationof nanoparticles.

When microemulsion is combined with hydrothermal treatment, the crystallinity of nanocrystals would be improved greatly.

Here, we first report synthesis of ZnSe nanocrystalsby combining the reverse microemulsions of water/Triton X-100/2-propanol/cyclohexane with hydrothermal treatment. The crystallinestructure and optical properties of as-prepared ZnSe nanocrystalshave also been investigated.

Proposed WorkNano-sized ZnSe particles were synthesized using a microemulsion-mediated hydrothermal route. All

the reagents were of analytical grade and used without further purification.

Firstly, we prepared sodium hydrogen selenide (NaHSe)

aqueous solution (0.2 M, 10 ml) by mixing sodium borohydride (NaBH4) and

selenium powder in deionized water under nitrogen atmosphere at room temperature, while

10 ml of 0.2 M zinc acetate aqueous solution was prepared by dissolving

Zn(AC)2∙ 2H2O in deionized water.

Then two typesof reverse microemulsion were prepared and named MZn and MSe, respectively.

Each microemulsion was composed of Triton X-100 as

surfactant, 2-propanol as cosurfactant, cyclohexane

as a continuous oilphase and the

aforementioned reactant solution (Zn(AC)2 or NaHSe)as aqueous phase. Here the

volume ratio of cyclohexane, Triton X-100to 2-propanol was 20:3:6.

After cooling to room temperature naturally, the yellow precipitates were

separated from the reaction media by centrifugation, washed with deionized water and anhydrous

ethanol for several times, and then dried at 50 °C

under vacuum.

Finally, ZnSe Nanocrystals were obtained.

Future Work

X-Ray diffraction spectra of ZnSe.

TEM of ZnSe nanocrystals and corresponding particle size distribution.

PL Spectra of ZnSe Nanocrystals

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. Phys. C: Solid State Phys. vol. 9 pp. 4511-4516 (1976) doi:10.1088/0022-3719/9/24/020

Zhang BP, Wang WX, Yasuda T, Segawa Y, Edamatsu K, Itoh T. Appl Phys Lett1997;71:3370–2.

Shavel A, Gaponik N, Eychmüller A. J Phys Chem B 2004;108:5905–8. Zeng RS, Rutherford M, Xie RG, Zou BS, Peng XG. Chem Mater

2010;22:2107–13. Wang C, Zhang WX, Qian XF, Zhang XM, Xie Y, Qian YT. Mater Chem

Phys1999;60:99–102.

Xiong S, Huang SH, Tang AW, Teng F. Mater Lett 2007;61:5091–4. Aparna C. Deshpandea, Shashi B. Singha, Majid Kazemian Abyaneha, 

Renu Pasrichab, S.K. Kulkarni - Low temperature synthesis of ZnSe nanoparticles – 2008

Lin Yang, Lingyun Liu, Dingquan Xiao, Jianguo Zhu - Preparation and characterization of ZnSe nanocrystals by a microemulsion-mediated method – 2011

Thank You!!

Questions, if any are invited.