in the process. Monodisperse quantum dots (the particle size distributions have a
width that is about 5% of the mean) with good luminescence properties are produced, the only report to date of a solvothermal route to surfactant-capped semiconductor chalcogenide nanoparticles.
Cu 2x Se particles were obtained by Qian and coworkers [69] starting from CuI,
Se, and ethylenediamine, with T ¼ 90
C, t ¼ 4 h. The particles are spherical and
quite monodisperse. Qian and coworkers have also reported [70] a solvothermal
preparation of CuInSe 2 , obtaining 15 nm particles from CuCl 2 , InCl 3 and Se in
either ethylenediamine or diethylamine, at 180
C for 15 h in ethylenediamine,
and 36 h for diethylamine. CuInSe 2x S x [71] also has been prepared by Qian and
coworkers using InCl 3 , CuCl 2 , S and Se with ethylenediamine as the solvent.
Recently microwave-solvothermal reactions and flow-solvothermal reactions have
been reported. These methods may be of particular interest in devising scalable
synthesis of nanoparticlates. Komarneni et al. [72] have prepared a number of oxide nanoparticles, including 5–20 nm MnFe 2 O 4 , CoFe 2 O 4 , NiFe 2 O 4 and ZnFe 2 O 4
ferrite particles, usually by the reaction of metal nitrates in suitable ammoniacal
solution. These solutions are microwaved, typically for around 4 min. In flowhydrothermal techniques, a preheated solvent is mixed with the reactants just
prior to introduction into a heated chamber with a back-pressure regulator. The
reactants are pumped using a standard HPLC pump through the system. In this
way Poliakoff et al. [73] have prepared CeO 2 aZrO 2 . A residence time of 9 s at a
(regulated) pressure of 25 MPa was sufficient to yield the product, which comprised nanoparticles with sizes as small as 4 nm. These two methods may well
have great promise, not only for scale-up, but also for good monodispersity.
2.4.4
Gas-Phase Synthesis of Semiconductor Nanoparticles
Most gas-phase methods of semiconductor nanoparticle synthesis involve atmospheric or low pressure evaporation of either powders or the pre-formed semiconductor, or the co-evaporation of the two elemental components, for example zinc
metal and sulfur [74]. However, the use of these techniques usually results in deposits of particles with larger size distributions, in some cases ranging from 10 to
200 nm. Sercel et al. have reported the synthesis of GaAs nanoparticles by using
the organometallic precursor trimethylgallium, GaMe 3 , which on mixing in a furnace flow reactor with arsine gas, AsH 3 , gives crystalline GaAs particles [75]. These
approaches suffer from the problem of particle aggregation due to the absence of a
surface passivating (capping) agent. The only report of gas-phase semiconductor
nanoparticle synthesis using a capping agent was by Salata et al. who produced
PbS and CdS nanoparticles covered with a polymer layer by reacting a polyvinyl
alcohol precursor containing Pb(NO 3 ) 2 or Cd(NO 3 ) 2 in the gas phase with H 2 S gas
[76].
An investigation of the prereactions which occur between H 2 S/H 2 Se and
Me 2 Cd/Me 2 Zn when growing II–VI semiconductor films by CVD techniques,
showed that the gas-phase reactions result in the formation of chalcogenide de2.4 The General Methods Available for the Synthesis of Nanodimensional Materials 23
width that is about 5% of the mean) with good luminescence properties are produced, the only report to date of a solvothermal route to surfactant-capped semiconductor chalcogenide nanoparticles.
Cu 2x Se particles were obtained by Qian and coworkers [69] starting from CuI,
Se, and ethylenediamine, with T ¼ 90
C, t ¼ 4 h. The particles are spherical and
quite monodisperse. Qian and coworkers have also reported [70] a solvothermal
preparation of CuInSe 2 , obtaining 15 nm particles from CuCl 2 , InCl 3 and Se in
either ethylenediamine or diethylamine, at 180
C for 15 h in ethylenediamine,
and 36 h for diethylamine. CuInSe 2x S x [71] also has been prepared by Qian and
coworkers using InCl 3 , CuCl 2 , S and Se with ethylenediamine as the solvent.
Recently microwave-solvothermal reactions and flow-solvothermal reactions have
been reported. These methods may be of particular interest in devising scalable
synthesis of nanoparticlates. Komarneni et al. [72] have prepared a number of oxide nanoparticles, including 5–20 nm MnFe 2 O 4 , CoFe 2 O 4 , NiFe 2 O 4 and ZnFe 2 O 4
ferrite particles, usually by the reaction of metal nitrates in suitable ammoniacal
solution. These solutions are microwaved, typically for around 4 min. In flowhydrothermal techniques, a preheated solvent is mixed with the reactants just
prior to introduction into a heated chamber with a back-pressure regulator. The
reactants are pumped using a standard HPLC pump through the system. In this
way Poliakoff et al. [73] have prepared CeO 2 aZrO 2 . A residence time of 9 s at a
(regulated) pressure of 25 MPa was sufficient to yield the product, which comprised nanoparticles with sizes as small as 4 nm. These two methods may well
have great promise, not only for scale-up, but also for good monodispersity.
2.4.4
Gas-Phase Synthesis of Semiconductor Nanoparticles
Most gas-phase methods of semiconductor nanoparticle synthesis involve atmospheric or low pressure evaporation of either powders or the pre-formed semiconductor, or the co-evaporation of the two elemental components, for example zinc
metal and sulfur [74]. However, the use of these techniques usually results in deposits of particles with larger size distributions, in some cases ranging from 10 to
200 nm. Sercel et al. have reported the synthesis of GaAs nanoparticles by using
the organometallic precursor trimethylgallium, GaMe 3 , which on mixing in a furnace flow reactor with arsine gas, AsH 3 , gives crystalline GaAs particles [75]. These
approaches suffer from the problem of particle aggregation due to the absence of a
surface passivating (capping) agent. The only report of gas-phase semiconductor
nanoparticle synthesis using a capping agent was by Salata et al. who produced
PbS and CdS nanoparticles covered with a polymer layer by reacting a polyvinyl
alcohol precursor containing Pb(NO 3 ) 2 or Cd(NO 3 ) 2 in the gas phase with H 2 S gas
[76].
An investigation of the prereactions which occur between H 2 S/H 2 Se and
Me 2 Cd/Me 2 Zn when growing II–VI semiconductor films by CVD techniques,
showed that the gas-phase reactions result in the formation of chalcogenide de2.4 The General Methods Available for the Synthesis of Nanodimensional Materials 23