synthesis of znse nanocrystals

1. PROJECT SYNOPSIS ON
“Synthesis Of ZnSe
Nanocrystals”
By:
Jitesh Kumar BE/15007/12
Atish Sinha BE/15009/12
Gaurav Raj Anand BE/15067/12

2. Contents
Introduction
Objective
Methodology
Proposed Work
Future Work
References

3. 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.

4. 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

5. 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

6.  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
.

7.  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

8. Mechanical Properties
Young’s Modulus 67.2 GPa (9.75 x 106 psi)
Rupture Modulus 55.1 MPa (8,000 psi)
Knoop Hardness 105-120 kg/mm2
Density 5.27 g/cm3
Poisson’s Ratio 0.28
Fig 3 ZnSe Transmission Charts Thermo-Optic Coefficient @ Various
Wavelengths dn/dT (10-5°C-1)

9.  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.

10. Objective
Synthesis of Zinc Selenide
Nanocrystals
Study of its optical and
electrical properties
Application in Photovoltaic
Cells

11. Methodology
 A novel developed hydrothermal microemulsion technique is used
to synthesize nanoparticles, nanorods and nanowires, and it
has been considered as an effective synthetic method.
 It is well known that microemulsion is one of the effective media to synthesize
nanoparticles.
 In water-in-oil microemulsions, nano-sized water
droplets are surrounded by a layer of surfactant and cosurfactant
molecules to form reverse micelles, and steadily dispersed in oil
phase.
 They provide an ideal environment for the preparation
of nanoparticles.
 When microemulsion is combined with hydrothermal treatment, the crystallinity
of nanocrystals would be improved greatly.
 Here, we first report synthesis of ZnSe nanocrystals
by combining the reverse microemulsions of water/Triton X-100/2-
propanol/cyclohexane with hydrothermal treatment. The crystalline
structure and optical properties of as-prepared ZnSe nanocrystals
have also been investigated.

12. Proposed Work
Nano-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 types
of 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 oil
phase and the aforementioned
reactant solution (Zn(AC)2 or
NaHSe)
as aqueous phase. Here the
volume ratio of cyclohexane,
Triton X-100
to 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.

13. Future Work
X-Ray diffraction spectra of ZnSe.
TEM of ZnSe nanocrystals and corresponding particle size distribution.
PL Spectra of ZnSe Nanocrystals

14. 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

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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

16. Thank You!!
 Questions, if any are invited.