Normally the size dependence of the chemical potential is used to explain the growth dynamics of semiconductor nanoparticles. Instead we show that very small CdTe nanoparticles continue to grow at high dilution, the growth rate is virtually independent of monomer concentration, nucleation continues after the growth of larger particles has saturated, and the growth rate has a much greater nonlinear dependence on particle size than predicted by theory. We suggest that nanoparticle growth is fast in the liquid phase and then saturates as the particles change phase from liquid to crystal at a threshold size which depends on the growth temperature and not the monomer concentration. The photoluminescence quantum efficiency becomes high when tellurium is depleted in the reaction solution giving a cadmium enriched surface.
We report a systematic study of charge transport in a range of low-molar-mass and extended (having
at least six aromatic rings) nematic liquid crystals, some of which are reactive mesogens, with a high
degree of shape anisotropy, i.e., the length-to-width (aspect) ratio is exceptionally high. We demonstrate
that the hole mobility is independent of the macroscopic, but not microscopic, ordering of the nematic
and isotropic phases of these nematic liquid crystals with a long, rigid, and extended aromatic molecular
core, because no discontinuity is observed at the transition between these phases. A room-temperature
mobility of up to 1.0 × 10-3 cm2 V-1 s-1 is obtained in the nematic phase, which is attributed to the
short intermolecular distances between the highly polarizable but rigid long aromatic cores. We show
that the intermolecular separation can be easily fine-tuned by changing the lateral and terminal aliphatic
groups of these nematic liquid crystals. Hence, the charge mobility can be varied by up to 2 orders of
magnitude without altering the core structure of the molecules, and this chemical fine control could be
used to limit hole transport and so provide better charge balance in organic light-emitting diodes. X-ray
diffraction is used to obtain the intermolecular separation and shows local lamellar order in the nematic
phase.
Molecular dynamics simulations of binary colloidal monolayers, i.e., monolayers consisting of mixtures of two different particle sizes, are presented. In the simulations, the colloid particles are located at an oil-water interface and interact via an effective dipole-dipole potential. In particular, the influence of the particle ratio on the configurations of the binary monolayers is investigated for two different relative interaction strengths between the particles, and the pair correlation functions corresponding to the binary monolayers are calculated. The simulations show that the binary monolayers can only form two-dimensional crystals for certain particle ratios, for example, 2:1, 6:1, etc., while, for example, for a particle ratio of 7:1 the monolayers are found to be in a disordered, glassy state. The calculations also reveal that in analogy to the Wigner lattice the configurations are very sensitive to the relative interaction strength between the particles but not to the absolute magnitude of the interaction strength, even when particle size effects are taken into account. Consequently, it is argued that a comparison between the calculated configurations and actual binary particle monolayer systems could provide useful information on the relative interaction strength between large and small particles. Possible mechanisms giving rise to disparities in the interaction strength between large and small particles are described briefly.
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