of HgTe and PDDA. White light electroluminescence is seen in multilayers of
CdSeaCdSapoly(phenylenevinylene), CdTeaPDDA. White light emission has also
been obtained from drop cast films consisting of CdSeaZnS, CdSaZnS and polylaurlymethacrylate (see Figure 4.27). The characteristics of all the above devices can
be changed by altering the nanocrystal size.
4.4.2
Collective Properties
The fact that the physical properties of nanocrystal organizations can be different from those of the isolated particles is being realized. Pellets of monodisperse
nanocrystals, obtained by the use of a bifunctional ligand that binds to more than
one nanocrystal or by applying pressure to dried nanocrystalline matter, have been
used for electrical transport measurements [189–192]. Pellets made of small Au
and Pd nanocrystals exhibit non-metallic behavior with specific conductivities in
the range 10
6 W
À1 cm
À1 [189–191]. The conductivity however increases dramatically with an increase in the diameter of the nanocrystals. An insulator–metal
transition has indeed been reported for pellets made of @12.5 nm Au and Ag
nanocrystals [192]. Electrical transport measurements on layer-by-layer assemblies
of nanocrystals on conducting substrates have been carried out by adopting a
sandwich configuration [193–195]. Nanocrystalline films with bulk metallic conductivity have been realized with Au nanocrystals of 5 and 11 nm diameter spaced
with ionic and covalent spacers [194, 195]. The conductivity of a monolayered twodimensional arrays of metal nanocrystals has been studied with patterned electrodes [196–201]. Structural disorder and interparticle separation distance are
identified as key factors that determine the conductivity of such layers [196–199].
Fig. 4.27. Emission spectra of semiconductor
nanocrystal polymer composites that were
used to make a white light emitting film.
(From left) CdSaZnS core–shell nanocrystals
(diameter 3 nm), CdSeaZnS of diameters 1.3,
2.3, 2.8 nm respectively. The excitation was
from a single source (mercury lamp with
emission wavelength of 365 nm) (adapted
from [187]).
4 Mesoscopic Assembly and Other Properties of Metal and Semiconductor Nanocrystals
82
CdSeaCdSapoly(phenylenevinylene), CdTeaPDDA. White light emission has also
been obtained from drop cast films consisting of CdSeaZnS, CdSaZnS and polylaurlymethacrylate (see Figure 4.27). The characteristics of all the above devices can
be changed by altering the nanocrystal size.
4.4.2
Collective Properties
The fact that the physical properties of nanocrystal organizations can be different from those of the isolated particles is being realized. Pellets of monodisperse
nanocrystals, obtained by the use of a bifunctional ligand that binds to more than
one nanocrystal or by applying pressure to dried nanocrystalline matter, have been
used for electrical transport measurements [189–192]. Pellets made of small Au
and Pd nanocrystals exhibit non-metallic behavior with specific conductivities in
the range 10
6 W
À1 cm
À1 [189–191]. The conductivity however increases dramatically with an increase in the diameter of the nanocrystals. An insulator–metal
transition has indeed been reported for pellets made of @12.5 nm Au and Ag
nanocrystals [192]. Electrical transport measurements on layer-by-layer assemblies
of nanocrystals on conducting substrates have been carried out by adopting a
sandwich configuration [193–195]. Nanocrystalline films with bulk metallic conductivity have been realized with Au nanocrystals of 5 and 11 nm diameter spaced
with ionic and covalent spacers [194, 195]. The conductivity of a monolayered twodimensional arrays of metal nanocrystals has been studied with patterned electrodes [196–201]. Structural disorder and interparticle separation distance are
identified as key factors that determine the conductivity of such layers [196–199].
Fig. 4.27. Emission spectra of semiconductor
nanocrystal polymer composites that were
used to make a white light emitting film.
(From left) CdSaZnS core–shell nanocrystals
(diameter 3 nm), CdSeaZnS of diameters 1.3,
2.3, 2.8 nm respectively. The excitation was
from a single source (mercury lamp with
emission wavelength of 365 nm) (adapted
from [187]).
4 Mesoscopic Assembly and Other Properties of Metal and Semiconductor Nanocrystals
82