Comparison between calculated and experimental values of the lowest excited electronic state of small CdSe crystallites
TL;DR: On considere deux types de forme cristalline et une constante dielectrique variant dans l'espace d'analyses en bon accord avec les experiences recentes.
Abstract: The lowest excited electronic state of small CdSe crystallites is calculated within a tight-binding approximation. Two types of crystal shape and a spatially varying dielectric constant are considered. The results are found to compare favorably to recent experiments.
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TL;DR: The BOLS correlation mechanism has been initiated and intensively verified as discussed by the authors, which has enabled the tunability of a variety of properties of a nanosolid to be universally reconciled to the effect of bond order deficiency of atoms at sites surrounding defects or near the surface edges of the nano-material.
775 citations
TL;DR: This work investigates the size-dependent valence and conduction band-edge energies of CdSe, CdTe, PbS, and PbSe semiconductor quantum dots (QDs) through the use of photoelectron spectroscopy in air (PESA).
Abstract: Through the use of photoelectron spectroscopy in air (PESA), we investigate the size-dependent valence and conduction band-edge energies of CdSe, CdTe, PbS, and PbSe semiconductor quantum dots (QDs). The results are compared to those of previous studies, based on differing experimental methods, and to theoretical calculations based on k·p theory and state-of-the-art atomistic semiempirical pseudopotential modeling. To accurately map out the energy level landscapes of QDs as a function of size, the QDs must be passivated by comparable surface chemistries. This is highlighted by studying the effect of surface chemistry on the valence band-edge energy in an ensemble of 4.7 nm CdSe QDs. An energy level shift as large as 0.35 eV is observed for this system through modification of surface chemistry alone. This shift is significantly larger than the size-dependent valence band-edge shift that is observed when comparable surface chemistries are used.
615 citations
TL;DR: In this article, the binding energy of amine and carboxylic acid ligands to a range of CdSe nanoparticle facets has been investigated and the dominant binding interaction is between oxygen atoms in the ligands and cadmium atoms on the nanoparticle surfaces.
Abstract: First principles electronic structure simulations are used to study the atomistic detail of the interaction between organic surfactant molecules and the surfaces of CdSe semiconductor nanoparticles. These calculations provide insights into the relaxed atomic geometry of organics bound to semiconductor surfaces at the nanoscale as well as the electronic charge transfer between surface atoms and the organics. We calculate the binding energy of phosphine oxide, phosphonic and carboxylic acids, and amine ligands to a range of CdSe nanoparticle facets. The dominant binding interaction is between oxygen atoms in the ligands and cadmium atoms on the nanoparticle surfaces. The most strongly bound ligands are phosphonic acid molecules, which bind preferentially to the facets forming the sides of CdSe nanorods. The calculated relative binding strengths of ligands to different facets support the hypothesis that these binding energies control the relative growth rates of different facets, and therefore the resulting ...
335 citations
TL;DR: In this paper, the band gaps, band structure, and excited state (exciton) energies of CdS, GaAs, and GaP semiconductor clusters are calculated using pseudopotentials.
Abstract: The band gaps, band structure, and excited‐state (exciton) energies of CdS, GaAs, and GaP semiconductor clusters are calculated using pseudopotentials. In addition, the sensitivity of the exciton energies to the size, shape, crystal structure, and lattice constant of the unit cell are investigated. The calculated exciton energies of CdS clusters are in excellent agreement with experiment over a wide range of cluster sizes. Also, the exciton states of small CdS clusters are sensitive to whether their crystal structure is zinc blende or hexagonal. Such a sensitivity is absent in large CdS clusters. Furthermore, small GaAs clusters are shown to exhibit anomalous redshift of their absorption spectra, in sharp contrast to CdS and large GaAs clusters whose spectra always shift to blue with decreasing cluster size. Finally, the lowest‐energy non‐Franck–Condon transition in GaP clusters always shifts to blue with decreasing cluster size, whereas the higher‐energy Franck–Condon transition in small clusters exhibits the anomalous redshift. These novel findings reveal that (1) the optical spectroscopy of semiconductor clusters is strongly material and crystal structure dependent; (2) the spectroscopy of small clusters is dramatically different from those of large clusters and bulk; and (3) these effects cannot be explained, even qualitatively, using the effective‐mass approximation.
296 citations
TL;DR: In this paper, the electronic properties of CdSe nanocrystals in the absence and presence of a dielectric medium were studied in detail for an isolated nanocrystal.
Abstract: We present a detailed study of the electronic properties of CdSe nanocrystals in the absence and presence of a dielectric medium. The electronic structure of the nanocrystal is modeled within the framework of the empirical pseudopotential method. We use a real-space grid representation of the wave function, and obtain the eigenvalues and eigenstates of the one-electron Hamiltonian using a slightly modified version of the filter-diagonalization method. The band gap, density of states, charge density, multipole moments, and electronic polarizabilities are studied in detail for an isolated nanocrystal. We discuss the implications of the results for the long range electrostatic and dispersion interactions between two CdSe nanocrystals. To study the effects of the surroundings we develop a self-consistent reaction field method consistent with the empirical pseudopotential method. We use the eigenstates of the isolated nanocrystal and iterate the self-consistent equations until converged results are obtained. The results show that the electronic properties of polar CdSe nanocrystals are quite sensitive to the environment. © 1999 American Institute of Physics. @S0021-9606~99!70910-4#
237 citations