vessel, to produce III/V nanoparticles. A relatively low temperature method involving similar reactions in organic solvents has been reported for the preparation
of GaP and GaAs nanoparticles, using gallium (III) halides and (Na/K) 3 E (E ¼ P,
As) [54]. This method avoids the use of hazardous phosphines or arsines. Nanocrystallites of InAs and InP were also synthesised [55] from the reaction of InX 3
(X ¼ Cl, Br, I) with As(SiMe 3 ) 3 or P(SiMe 3 ) 3 , respectively. Other analogous chemical routes to indium pnictides have also appeared in the literature [55].
GaAs nanocrystallites have been prepared by reacting GaCl 3 with As(SiMe 3 ) 3 in
boiling quinoline, however, as yet unidentified species were found to mask the
optical properties of the resulting particles and hence quantum size effects could
not be properly determined [56, 57]. The alcoholysis or thermolysis of silylated
single molecule precursors is one of several processes used for nanoparticle synthesis of III/V and II/V semiconductor materials. Another preparative method for
the syntheses of GaAs [58] and InP [59] is by the methanolysis of organometallic
compounds such as [Cp*(Cl)In(m-P(SiMe 3 ) 2 ] 2 . The chemical route led [60, 61] to
bulk, amorphous, Cd 3 P 2 after rapid flocculation of Cd 3 P 2 nanoparticles. In order
to control the kinetics a single molecule precursor with bulkier substituents
was used, Cd[P(SiPh 3 ) 2 ] 2 [61, 62]. The methanolysis gave soluble nanoparticles of
Cd 3 P 2 with diameters ranging from 30–40 A ˚ , however, the particles were not crystalline.
Other chemical routes to metal phosphides include phosphinolysis reactions and
reactions between metallo-organics and P(SiMe 3 ) 3 ; all involve elimination and
condensation processes. Buhro [61] reported the synthesis of several binary phosphide semiconductors along with ternary phases (e.g. ZnGeP 2 ), using solutionphase metallo-organic routes. A recent review of the preparation of II/V materials
has appeared [63].
2.4.3
Hydrothermal and Solvothermal Methods
An alternative approach to the use of high-temperature solvents, which can be both
toxic and expensive, is to use more usual solvents conventionally limited by their
rather low boiling points. However, solvents can be used well-above their boiling
point at atmospheric pressure if heated in a sealed vessel (an autoclave or ‘bomb’)
the autogenous pressure then far exceeds the ambient pressure raising the boiling
point of the solvent. Such solvothermal reaction conditions are extensively used in
the preparation of inorganic solids, especially zeolites [64]. For a comprehensive
review of this method for nanoparticles see [65].
A few illustrative examples of this methodology follow. Qian and coworkers [66]
have reported wurtzite ZnSe nanoparticles with sizes in the 18 nm range starting
from the elements in ethylenediamine (T ¼ 120
C, t ¼ 6 h.) This reaction yields a
complex with the formula ZnSe(en) where en is ethylenediamine. Seshadri has
used toluene as the solvent in a neat preparation of CdSe from cadmium stearate
and Se powder [67, 68], tetralin (tetrahydronaphthalene) was added as a reducing
agent. Tetralin is aromatized to naphthalene in the presence of Se, producing H 2 Se
2 Strategies for the Scalable Synthesis of Quantum Dots and Related Nanodimensional Materials
22
of GaP and GaAs nanoparticles, using gallium (III) halides and (Na/K) 3 E (E ¼ P,
As) [54]. This method avoids the use of hazardous phosphines or arsines. Nanocrystallites of InAs and InP were also synthesised [55] from the reaction of InX 3
(X ¼ Cl, Br, I) with As(SiMe 3 ) 3 or P(SiMe 3 ) 3 , respectively. Other analogous chemical routes to indium pnictides have also appeared in the literature [55].
GaAs nanocrystallites have been prepared by reacting GaCl 3 with As(SiMe 3 ) 3 in
boiling quinoline, however, as yet unidentified species were found to mask the
optical properties of the resulting particles and hence quantum size effects could
not be properly determined [56, 57]. The alcoholysis or thermolysis of silylated
single molecule precursors is one of several processes used for nanoparticle synthesis of III/V and II/V semiconductor materials. Another preparative method for
the syntheses of GaAs [58] and InP [59] is by the methanolysis of organometallic
compounds such as [Cp*(Cl)In(m-P(SiMe 3 ) 2 ] 2 . The chemical route led [60, 61] to
bulk, amorphous, Cd 3 P 2 after rapid flocculation of Cd 3 P 2 nanoparticles. In order
to control the kinetics a single molecule precursor with bulkier substituents
was used, Cd[P(SiPh 3 ) 2 ] 2 [61, 62]. The methanolysis gave soluble nanoparticles of
Cd 3 P 2 with diameters ranging from 30–40 A ˚ , however, the particles were not crystalline.
Other chemical routes to metal phosphides include phosphinolysis reactions and
reactions between metallo-organics and P(SiMe 3 ) 3 ; all involve elimination and
condensation processes. Buhro [61] reported the synthesis of several binary phosphide semiconductors along with ternary phases (e.g. ZnGeP 2 ), using solutionphase metallo-organic routes. A recent review of the preparation of II/V materials
has appeared [63].
2.4.3
Hydrothermal and Solvothermal Methods
An alternative approach to the use of high-temperature solvents, which can be both
toxic and expensive, is to use more usual solvents conventionally limited by their
rather low boiling points. However, solvents can be used well-above their boiling
point at atmospheric pressure if heated in a sealed vessel (an autoclave or ‘bomb’)
the autogenous pressure then far exceeds the ambient pressure raising the boiling
point of the solvent. Such solvothermal reaction conditions are extensively used in
the preparation of inorganic solids, especially zeolites [64]. For a comprehensive
review of this method for nanoparticles see [65].
A few illustrative examples of this methodology follow. Qian and coworkers [66]
have reported wurtzite ZnSe nanoparticles with sizes in the 18 nm range starting
from the elements in ethylenediamine (T ¼ 120
C, t ¼ 6 h.) This reaction yields a
complex with the formula ZnSe(en) where en is ethylenediamine. Seshadri has
used toluene as the solvent in a neat preparation of CdSe from cadmium stearate
and Se powder [67, 68], tetralin (tetrahydronaphthalene) was added as a reducing
agent. Tetralin is aromatized to naphthalene in the presence of Se, producing H 2 Se
2 Strategies for the Scalable Synthesis of Quantum Dots and Related Nanodimensional Materials
22