Geoscience Reference
In-Depth Information
Zhou et al.
[195]
have reported the synthesis of ZnS nanoplates in the tempera-
ture range 160
200
C in 24 h. They have used sulfur powder and ZnCl
2
in the
presence of ethylenediamine. The use of zinc acetate and sodium diethyldithiocar-
bamite with an experimental temperature of 150
200
C for 12
72 h produces
ZnS nanocrystallites with a different morphology.
The growth of
70 nm monodispersed PbS nanocubes to dendrites has been
achieved using Pb(NO
3
)
2
and dithizone as reagents and ethylene diamine as solvent
at about 140
C for 5 h
[196]
. PbS and PbSe nanocrystals have been prepared under
near supercritical conditions
[197]
. According to the authors
[198]
, the reaction of
S and Se with a Pb salt in a ethylenediamine solvent is reported to give the respec-
tive phase with particle sizes in the range of 20
B
100 nm.
-MnS nanocrystallites with rock salt structure has been
reported in Ref.
[199]
. The crystals are well faceted, pyramid-like single crystals of
α
The synthesis of
α
-MnS. The experimental temperature was varied from 100
C to 250
C to get the
optimum condition for the formation of
-MnS crystals with a defined morphology.
Manganese acetate and thiourea were used as precursors with benzene as the sol-
vent. CdS
x
Se
1
2
x
(0
α
,
x
,
1) nanorods with a diameter of 10
20 nm and length up
150 nm were synthesized at 140
C in about 10 h
[200]
(
Figure 10.44
).
In recent years, it has been proved that a shell of one composition (e.g., ZnS)
can be synthesized over a core of another nanocrystal (e.g., CdS). The core can
also be used as a seed to grow larger particles by adjusting the concentration after
the initial growth. Such core-shell QD fabrication from these sulfide-based semi-
conductor materials is becoming very popular. Several such nanoparticles core-
shell structures like CdSe/CdS, CdS/PbS, CdS/HgS, Cd/HgS/CdS, CdSe/CdS/ZnS,
CdTe/CdSe, CdSe/ZnTe, and CdSe/ZnS have been fabricated for applications
in optoelectronic devices and as efficient fluorescent labels or photoelectro-
chemical tests for various biomedical applications. The development of this avenue
of research is due to not only the quantum size effects but also the fact that
the average sizes of nanoparticles used are comparable with the size of
biomacromolecules.
Wang et al.
[201]
have synthesized zinc tellurides with zinc blende structure,
under mild hydrothermal conditions within the temperature range 100
to 100
160
C
using NaOH as the solvent. Ji et al.
[202]
have synthesized Bi
2
Te
3
, CoSb
3
, PbTe,
Bi
2
S
3
, etc. using solvothermal and hydrothermal methods. PbSe and Bi
2
S
3
show
unique morphological features. The thermoelectric properties of these compounds
have been studied in detail.
The processing of nanostructures of these sulfides, tellurides, and selenides is
very popular in recent years owing to their unique physical characteristics. Tai
et al.
[203]
have synthesized thermoelectric indium telluride nanostring-cluster
hierarchical structures under solvothermal conditions using mixed solvents of ethy-
lenediamine and ethylene glycol at 200
C in 24 h. The indium telluride hierarchal
structures have been explained through a diffusion-limited reaction mechanism.
Denac et al.
[204]
have reported the solvothermal synthesis of nanocrystalline
CdSe and CdTe. Williams
[205]
has carried out a systematic investigation of the
hydrothermal synthesis and characterization of CdSe nanocrystals.
