Search results for "Free electron model"
showing 10 items of 36 documents
Optical properties of InN nanocolumns: Electron accumulation at InN non‐polar surfaces and dependence on the growth conditions
2009
InN nanocolumns grown by plasma-assisted molecular beam epitaxy have been studied by photoluminescence (PL) and photoluminescence excitation (PLE). The PL peak energy was red-shifted with respect to the PLE onset and both energies were higher than the low temperature band-gap reported for InN. PL and PLE experiments for different excitation and detection energies indicated that the PL peaks were homogeneously broadened. This overall phenomenology has been attributed to the effects of an electron accumulation layer present atthe non-polar surfaces of the InN nanocolumns. Variations in the growth conditions modify the edge of the PLE spectra and the PL peak energies evidencing that the densit…
Electron transport process in simple amorphous metals at moderately low temperatures
2001
Abstract The dependence of electroresistivity ϱ( T ) and electron contribution to thermoconductivity ϰ( T ) of simple amorphous metals is investigated. Calculation of kinetic coefficients is carried out in the nearly free electron approximation (Ziman theory). The form-factor was calculated in the quasiphonon model. In this approximation on the short wavelength part of “dispersion curve” a minimum exists (“roton-like minimum”). It is shown that at moderately low temperatures 10 K ≤ T ≤ 100 K the ratio ϱ(T) − ϱ(0) T 2 has a maximum and the T 2 [ ϰ ( T ) − ϰ (0)] is minimal in this temperature region. Such “anomaly” in the temperature dependence of the kinetic coefficient is due to additional…
Electrical resistivity of simple metal amorphous alloys at moderately low temperatures
2003
Abstract An approach is developed that allows to explain the unusual dependence of the electrical resistivity ρ(T) of amorphous alloys on temperature T. Interactions between the free electrons and the longitudinal acoustic excitations in the small-wavelength region (“the roton region”) are shown to cause such a behaviour of ρ(T) at moderately low temperatures. The features of the electron–phonon interactions in an amorphous alloy as compared to the crystal state case are discussed. The theory is illustrated by numerical calculations of the electrical resistivity ρ(T) for Mg–Zn and Cu–Sn amorphous alloys at the different alloy concentrations in the 0 K temperature range. Qualitative agreemen…
Quantum chemical modelling of electron polarons and green luminescence in PbTiO3perovskite crystals
2002
In an extension of our previous study on the electron polarons and excitons in KNbO3, KTaO3 and BaTiO3 (Kotomin E A, Eglitis R I and Borstel G 2000 J. Phys. Condens. Matter 12 L557; Eglitis R I, Kotomin E A and Borstel G 2002 J. Phys. Condens. Matter 14 3735) by the semiempirical Hartree–Fock method we present here results for free electron polarons in the PbTiO3 perovskite crystal. We discuss the origin of the intrinsic visible band emission of PbTiO3 perovskite oxides (so-called 'green luminescence') which has remained a topic of high interest during the last quarter of a century. We present a theoretical calculation modelling this emission in the framework of a concept of charge transfer…
DC electrical resistivity of Nb-Doped BaTiO3 and EPR measurements
1992
DC electrical resistivity measurements along the c-axis of Nb-doped BaTiO3 single crystals are presented in a wide range of temperature, covering the four phases, with special attention to the rhomboedral one. The temperature dependence of the conductivity leads to convincing arguments in favour of a polaronic mechanism. Below the orthorhombic-rhomboedral transition point, a strong increase of the resistivity is observed. The correlation of this behavior with EPR analysis in the same temperature range, is consistent with a sharp trapping of the ''free'' electrons, when the temperature decreases.
Core hole screening and decay rates of double core ionized first row hydrides.
2013
Because of the high intensity, X-ray free electron lasers allow one to create and probe double core ionized states in molecules. The decay of these multiple core ionized states crucially determines the evolution of radiation damage in single molecule diffractive imaging experiments. Here we have studied the Auger decay in hydrides of first row elements after single and double core ionization by quantum mechanical ab initio calculations. In our approach the continuum wave function of the emitted Auger electron is expanded into spherical harmonics on a radial grid. The obtained decay rates of double K-shell vacancies were found to be systematically larger than those for the respective single …
Three-dimensional electrons and two-dimensional electric subbands in the transport properties of tin-dopedn-type indium selenide: Polar and homopolar…
1991
Electron-scattering mechanisms in n-type indium selenide doped with different amounts of tin are studied by means of the Hall effect (30--300 K) and photo-Hall effect (300 K). The electron mobility at room temperature is found to increase with the free-electron concentration in samples with low tin content. The same behavior is observed when the electron concentration increases due to thermal annealing or photogeneration. That is explained through the presence of two kinds of free electrons contributing to the charge transport along the layers: high-mobility three-dimensional (3D) electrons in the conduction band, and low-mobility two-dimensional electrons in the electric subbands. These 2D…
Analysis of the Electronic Structure of Non-Spherical Ligand-Protected Metal Nanoclusters: The Case of a Box-Like Ag67
2016
In this work we introduce a new strategy to investigate the electronic shell structure of ligand-protected metal nanoclusters of polyhedral core shape. The central idea is to identify the symmetry of the Kohn–Sham molecular orbitals of an atomistic structure based on their projection onto the electronic states of a jellium system with a similar shape of the background charge density. Herein, we study the connection between a reduced atomistic model of the recently reported box-like [Ag67(SR)32(PR3)8]3+ nanocluster and a jellium box consisting of 32 free electrons. With this approach, we determine the symmetry of electronic states of the metal core and identify those that are involved in the…
Inhomogeneous free-electron distribution in InN nanowires: Photoluminescence excitation experiments
2010
Photoluminescence excitation (PLE) spectra have been measured for a set of self-assembled InN nanowires (NWs) and a high-crystalline quality InN layer grown by molecular-beam epitaxy. The PLE experimental lineshapes have been reproduced by a self-consistent calculation of the absorption in a cylindrical InN NW. The differences in the PLE spectra can be accounted for the inhomogeneous electron distribution within the NWs caused by a bulk donor concentration $({N}_{D}^{+})$ and a two-dimensional density of ionized surface states $({N}_{ss}^{+})$. For NW radii larger than 30 nm, ${N}_{D}^{+}$ and ${N}_{ss}^{+}$ modify the absorption edge and the lineshape, respectively, and can be determined f…
Internal photoemission in solar blind AlGaN Schottky barrier photodiodes
2005
We have analyzed the photoresponse of solar blind AlGaN Schottky barrier photodiodes below the alloy band gap energy, in the 3.5-4.5 eV range, and we show that it is dominated by internal photoemission. The n-type Schottky barrier height is shown to increase linearly with the band gap energy of the AlGaN alloy. The amplitude of the internal photoemission signal is about 20 times smaller than the value given by the Fowler theory based on a free electron model. We explain this result by taking into account the interband transitions and the ballistic transport of photoexcited electrons in the metal. This low value of internal photoemission allows us to achieve a spectral rejection ratio betwee…