tion of particles. The stabilizing agents employed include surfactants such as long
chain thiols or amines or polymeric ligands such as polyvinylpyrrolidone (PVP).
Reduction of metal salts dissolved in appropriate solvents produces small metal
particles of varying size distributions [35–38]. A variety of reducing agents have
been employed for the reduction. These include electrides, alcohols, glycols, metal
borohydrides and certain specialized reagents such as tetrakis(hydroxymethyl)
phosphonium chloride. Si and Ge nanocrystals can be obtained by reduction of
GeCl 4 or silanes with strong reducing agents such as lithium or sodium naphthalide [39–41].
Kinetic control of precipitation (arrested precipitation) is generally used to obtain
semiconductor nanocrystals such as CdS [42], CdSe [43], ZnS, HgTe, PbS, CuS,
Cu 2 S, AgI, ZnO, AgI and TiO 2 [44–46]. The nanoparticles so obtained possess a
broad distribution in diameter. Thermolysis methods involving the decomposition
of organometallic precursors in high boiling organic solvents are used to prepare
CdSe [47], CdS [47], PbSe [16], InP [17], ZnSe, GaAs, InSb, GaP nanocrystals [45–
50]. Reverse micellar methods exploit the ‘‘water pools’’ in water-in-oil mixtures to
synthesize nanocrystals and have been successfully utilized in the preparation of
Ag, Au, Co, Pt, Co, CdS, CdTe, AgS nanocrystals [51, 52]. The synthesis of nanocrystals at the air–water interface, as in Langmuir–Blodgett films, or at a liquid–
liquid interface, is currently attracting wide attention [30, 53, 54]. CdS, PbS and
MgS nanocrystals have been prepared by exposing Langmuir–Blodgett films of
fatty acids to H 2 S [55]. It has been shown recently that films of metal and semiconductor nanocrystals can be prepared using a water–toluene interface [56]. A
typical film of Au nanocrystals is shown in Figure 4.2. Traditionally, clusters of
controlled sizes have been generated by abalation of a metal target in vacuum followed by mass selection of the plume to yield cluster beams [57, 58]. Such cluster
beams could be subjected to in situ studies or be directed on to solid substrates.
In order to obtain nanocrystals in solution, Harfenist et al. [59] steered a massselected Ag cluster beam through a toluene solution of thiol and capped the vacuum prepared particles.
Colloids of alloys have been made by the chemical reduction of the appropriate
salt mixture in the solution phase. In the case of semiconductor nanocrystals, a
mixture of salts is subjected to controlled precipitation. Thus, AgaPd and CuaPd
colloids of varying composition have been prepared by alcohol reduction of mixtures of silver nitrate or copper oxide with palladium oxide [60]. FeaPt alloy nanocrystals have been made by thermal decomposition of the Fe and Pt acetylacetonates in high boiling organic solvents [61]. AuaAg alloy nanocrystals have been
made by co-reduction of silver nitrate and chloroauric acid with sodium borohydride [62, 63]. Semiconductor nanocrystals of the form Cd x Mn 1Àx S, CdS x Se 1Àx
have been obtained by the inverted micelle methods as well as in glasses by sol–gel
methods [23, 64]. Alloys of controlled composition are also made by thermal decomposition of carefully chosen precursors, to achieve homogeneity. For example,
Mn 2 (m
˙
SeMe) 2 (CO) 8 was used as selenium source to obtain Cd 1Àx MnSe nanocrystals [65]. AuaAg alloying and segregation has been brought about by the use of
lasers on AuaAg layered particles [66, 67].
4 Mesoscopic Assembly and Other Properties of Metal and Semiconductor Nanocrystals
54
chain thiols or amines or polymeric ligands such as polyvinylpyrrolidone (PVP).
Reduction of metal salts dissolved in appropriate solvents produces small metal
particles of varying size distributions [35–38]. A variety of reducing agents have
been employed for the reduction. These include electrides, alcohols, glycols, metal
borohydrides and certain specialized reagents such as tetrakis(hydroxymethyl)
phosphonium chloride. Si and Ge nanocrystals can be obtained by reduction of
GeCl 4 or silanes with strong reducing agents such as lithium or sodium naphthalide [39–41].
Kinetic control of precipitation (arrested precipitation) is generally used to obtain
semiconductor nanocrystals such as CdS [42], CdSe [43], ZnS, HgTe, PbS, CuS,
Cu 2 S, AgI, ZnO, AgI and TiO 2 [44–46]. The nanoparticles so obtained possess a
broad distribution in diameter. Thermolysis methods involving the decomposition
of organometallic precursors in high boiling organic solvents are used to prepare
CdSe [47], CdS [47], PbSe [16], InP [17], ZnSe, GaAs, InSb, GaP nanocrystals [45–
50]. Reverse micellar methods exploit the ‘‘water pools’’ in water-in-oil mixtures to
synthesize nanocrystals and have been successfully utilized in the preparation of
Ag, Au, Co, Pt, Co, CdS, CdTe, AgS nanocrystals [51, 52]. The synthesis of nanocrystals at the air–water interface, as in Langmuir–Blodgett films, or at a liquid–
liquid interface, is currently attracting wide attention [30, 53, 54]. CdS, PbS and
MgS nanocrystals have been prepared by exposing Langmuir–Blodgett films of
fatty acids to H 2 S [55]. It has been shown recently that films of metal and semiconductor nanocrystals can be prepared using a water–toluene interface [56]. A
typical film of Au nanocrystals is shown in Figure 4.2. Traditionally, clusters of
controlled sizes have been generated by abalation of a metal target in vacuum followed by mass selection of the plume to yield cluster beams [57, 58]. Such cluster
beams could be subjected to in situ studies or be directed on to solid substrates.
In order to obtain nanocrystals in solution, Harfenist et al. [59] steered a massselected Ag cluster beam through a toluene solution of thiol and capped the vacuum prepared particles.
Colloids of alloys have been made by the chemical reduction of the appropriate
salt mixture in the solution phase. In the case of semiconductor nanocrystals, a
mixture of salts is subjected to controlled precipitation. Thus, AgaPd and CuaPd
colloids of varying composition have been prepared by alcohol reduction of mixtures of silver nitrate or copper oxide with palladium oxide [60]. FeaPt alloy nanocrystals have been made by thermal decomposition of the Fe and Pt acetylacetonates in high boiling organic solvents [61]. AuaAg alloy nanocrystals have been
made by co-reduction of silver nitrate and chloroauric acid with sodium borohydride [62, 63]. Semiconductor nanocrystals of the form Cd x Mn 1Àx S, CdS x Se 1Àx
have been obtained by the inverted micelle methods as well as in glasses by sol–gel
methods [23, 64]. Alloys of controlled composition are also made by thermal decomposition of carefully chosen precursors, to achieve homogeneity. For example,
Mn 2 (m
˙
SeMe) 2 (CO) 8 was used as selenium source to obtain Cd 1Àx MnSe nanocrystals [65]. AuaAg alloying and segregation has been brought about by the use of
lasers on AuaAg layered particles [66, 67].
4 Mesoscopic Assembly and Other Properties of Metal and Semiconductor Nanocrystals
54