the temperature range 120–300
C. This reaction produced TOPO-capped nanocrystallites of CdSe. The size of the particles is controlled mainly by the temperature of reaction, with larger particles being obtained at higher temperatures. This
TOPO method has advantages over previous synthetic methods, including, producing monodispersity (s G 5%) and the ability to produce hundreds of milligrams
of materials in a single experiment. Alivisatos subsequently used higher temperatures for injection and growth to improve the quality of the material prepared
[35]. In a series of recent papers interesting rod and tetrapodal structures have
been grown especially in the CdSe system [36]. The method was readily adapted to
the production of core–shell structures [37, 38] with materials having high quantum efficiencies being prepared.
In an early paper the use of a single-source precursor, oligomeric Cd(Se(C 2 H 5 )) 2
[39] was used for the preparation of CdSe in 4-ethylpyridine. Such a compound
obviates the need for the use of hazardous compounds such as toxic dimethylcadmium, (CH 3 ) 2 Cd, which are especially toxic at high temperatures. The use of
single-molecule precursors, i.e. a single compound containing all elements required within the nanocrystal, such as alkyldiseleno- or alkyldithio-carbamato
complexes has been reported [40, 41]. An early example was the synthesis of cubic
PbS [42] (see Figure 2.4) and PbSe [43], this work has been emulated and developed recently for the production of various morphologies [44]. Clusters of the
general formula [M 10 Se 4 (SPh) 16 ]
4À (M ¼ Zn or Cd and SPh ¼ phenyl thiolate)
have been used to great effect in the synthesis of nanoparticulates of both the
simple and core–shell type [45]; dialkyl-diseleo and dithio-carbamates have also
been used to prepare core shell nanoparticles [46].
In devising safer syntheses for nanoparticulates based on the original TOPO type
of methodologies it has occurred to more than one group that the use of metal
alkyls may not be required [47–49]. In an early experiment cadmium chloride and
TOPS were used to prepared CdS. More recently Peng has produced a series of
papers in which cadmium salts, especially the acetate, have been used to prepare
good quality CdSe [48, 49]. In the most recent report a blend of octadecene and
oleic acid was used to produce CdS under conditions in which sulfur was the limiting reagent. Particle size control could be achieved by varying the amount of oleic
acid in the reaction mixture. In related work lead-containing materials have been
prepared. A recent review of the general area of the synthesis of nanodispersed
semiconductors is available [50].
A TOPO-based method has been used [51] by Alivisatos et al. in the synthesis of
InP nanocrystals (2–5 nm in diameter). The reaction used InCl 3 in TOPO followed
by addition of P(Si(CH 3 ) 3 ) 3 , with annealing of the resulting InP nanocrystals. The
band gap for bulk InP is 1.35 eV whereas the InP nanocrystallites produced exhibit
values ranging from 1.7 eV to 2.4 eV [51]. InAs has been prepared by a similar
method by the dehalosilylation reaction between As[Si(CH 3 ) 3 ] 3 and InCl 3 , surface
oxidation did not change the properties of the resulting particles [52]. III/V semiconductors are less ionic in character than their II/VI analogs and thus do not
crystallise as readily. Kaner et al. [53] used solid state metathesis involving the reaction of sodium pnictides with group III halides, at high temperatures, in a closed
2.4 The General Methods Available for the Synthesis of Nanodimensional Materials 21
C. This reaction produced TOPO-capped nanocrystallites of CdSe. The size of the particles is controlled mainly by the temperature of reaction, with larger particles being obtained at higher temperatures. This
TOPO method has advantages over previous synthetic methods, including, producing monodispersity (s G 5%) and the ability to produce hundreds of milligrams
of materials in a single experiment. Alivisatos subsequently used higher temperatures for injection and growth to improve the quality of the material prepared
[35]. In a series of recent papers interesting rod and tetrapodal structures have
been grown especially in the CdSe system [36]. The method was readily adapted to
the production of core–shell structures [37, 38] with materials having high quantum efficiencies being prepared.
In an early paper the use of a single-source precursor, oligomeric Cd(Se(C 2 H 5 )) 2
[39] was used for the preparation of CdSe in 4-ethylpyridine. Such a compound
obviates the need for the use of hazardous compounds such as toxic dimethylcadmium, (CH 3 ) 2 Cd, which are especially toxic at high temperatures. The use of
single-molecule precursors, i.e. a single compound containing all elements required within the nanocrystal, such as alkyldiseleno- or alkyldithio-carbamato
complexes has been reported [40, 41]. An early example was the synthesis of cubic
PbS [42] (see Figure 2.4) and PbSe [43], this work has been emulated and developed recently for the production of various morphologies [44]. Clusters of the
general formula [M 10 Se 4 (SPh) 16 ]
4À (M ¼ Zn or Cd and SPh ¼ phenyl thiolate)
have been used to great effect in the synthesis of nanoparticulates of both the
simple and core–shell type [45]; dialkyl-diseleo and dithio-carbamates have also
been used to prepare core shell nanoparticles [46].
In devising safer syntheses for nanoparticulates based on the original TOPO type
of methodologies it has occurred to more than one group that the use of metal
alkyls may not be required [47–49]. In an early experiment cadmium chloride and
TOPS were used to prepared CdS. More recently Peng has produced a series of
papers in which cadmium salts, especially the acetate, have been used to prepare
good quality CdSe [48, 49]. In the most recent report a blend of octadecene and
oleic acid was used to produce CdS under conditions in which sulfur was the limiting reagent. Particle size control could be achieved by varying the amount of oleic
acid in the reaction mixture. In related work lead-containing materials have been
prepared. A recent review of the general area of the synthesis of nanodispersed
semiconductors is available [50].
A TOPO-based method has been used [51] by Alivisatos et al. in the synthesis of
InP nanocrystals (2–5 nm in diameter). The reaction used InCl 3 in TOPO followed
by addition of P(Si(CH 3 ) 3 ) 3 , with annealing of the resulting InP nanocrystals. The
band gap for bulk InP is 1.35 eV whereas the InP nanocrystallites produced exhibit
values ranging from 1.7 eV to 2.4 eV [51]. InAs has been prepared by a similar
method by the dehalosilylation reaction between As[Si(CH 3 ) 3 ] 3 and InCl 3 , surface
oxidation did not change the properties of the resulting particles [52]. III/V semiconductors are less ionic in character than their II/VI analogs and thus do not
crystallise as readily. Kaner et al. [53] used solid state metathesis involving the reaction of sodium pnictides with group III halides, at high temperatures, in a closed
2.4 The General Methods Available for the Synthesis of Nanodimensional Materials 21