[47]. These nanocrystals could be size-selected to yield monodisperse CdSe nanocrystals [125]. Upon drying on a flat substrate, these CdSe nanocrystals assemble into superlattices that containing several layers of two-dimensionally ordered
nanocrystals. TEM images showing the different facets of the two-dimensional
layers in these superlattices are shown in Figure 4.15. Hexanethiol capped PbS
nanocrystals, prepared by phase transferring Pb ions into an organic medium
using hexanethiol, followed by reaction with Na 2 S were also organized into twodimensional lattices (see Figure 4.16) [126, 127]. Motte et al. obtained a hexagonally ordered two-dimensional array of Ag 2 S nanocrystals synthesized by the
reverse micelle method [64]. Ordered arrays of InP nanocrystals prepared by
the thermolysis method have also been obtained [17].
4.3.2.3 Arrays of Oxide Nanocrystals
The very first report of two-dimensional arrays was of Fe 3 O 4 nanocrystals [128].
Bentzon et al. observed that the ferrofluid obtained by thermolysis of iron pentacarbonyl upon drying (over a period of several weeks) yielded well ordered twodimensional arrays of Fe 3 O 4 nanocrystals. Since then, easier methods have been
devised to obtain arrays of Fe 3 O 4 nanocrystals [129]. Two-dimensional arrays of
amine-capped metal oxide nanocrystals such as Co 3 O 4 have been obtained by startFig. 4.12. TEM images of Au 55 monolayers showing a
hexagonal (a) and a cubic (b) structure. The monolayers were
prepared on a polyethyleneimine functionalized carbon grid.
The magnified inset in (a) shows single clusters in the
hexagonal form (reproduced with permission from [134]).
4 Mesoscopic Assembly and Other Properties of Metal and Semiconductor Nanocrystals
66
nanocrystals. TEM images showing the different facets of the two-dimensional
layers in these superlattices are shown in Figure 4.15. Hexanethiol capped PbS
nanocrystals, prepared by phase transferring Pb ions into an organic medium
using hexanethiol, followed by reaction with Na 2 S were also organized into twodimensional lattices (see Figure 4.16) [126, 127]. Motte et al. obtained a hexagonally ordered two-dimensional array of Ag 2 S nanocrystals synthesized by the
reverse micelle method [64]. Ordered arrays of InP nanocrystals prepared by
the thermolysis method have also been obtained [17].
4.3.2.3 Arrays of Oxide Nanocrystals
The very first report of two-dimensional arrays was of Fe 3 O 4 nanocrystals [128].
Bentzon et al. observed that the ferrofluid obtained by thermolysis of iron pentacarbonyl upon drying (over a period of several weeks) yielded well ordered twodimensional arrays of Fe 3 O 4 nanocrystals. Since then, easier methods have been
devised to obtain arrays of Fe 3 O 4 nanocrystals [129]. Two-dimensional arrays of
amine-capped metal oxide nanocrystals such as Co 3 O 4 have been obtained by startFig. 4.12. TEM images of Au 55 monolayers showing a
hexagonal (a) and a cubic (b) structure. The monolayers were
prepared on a polyethyleneimine functionalized carbon grid.
The magnified inset in (a) shows single clusters in the
hexagonal form (reproduced with permission from [134]).
4 Mesoscopic Assembly and Other Properties of Metal and Semiconductor Nanocrystals
66