Search results for "Impurity"

Microscopic defects and impurity analyses of multicrystalline silicon solar cells from different manufacturing routes

2013

It is important to fully understand the physical behavior of solar cells made by materials from alternative process routes. Solar cells from Elkem Solar Grade Silicon and standard polysilicon have been investigated with light beam induced current and electroluminescence imaging. The low efficiency regions have been further analyzed by Scanning Electron Microscopy under different imaging modes. It was found that cell regions of low performance had undergone plastic deformations resulting in the creation of crystalline defects appearing as subgrain patterns. Similar patterns were observed in both ESS™ and standard polysilicon. Energy-dispersive X-ray spectroscopy (EDS) and electron backscatte…

Atoms embedded in an electron gas: Phase shifts and cross sections

1983

The Fermi-level scattering phase shifts and the transport cross sections are reported for atoms embedded in a homogeneous electron gas. The applications of the results are discussed, using the electronic stopping power for slow ions and impurity resistivity as examples. Peer reviewed

Dielectric study of orientational disorder in (CO2)1−x(N2O)xmixed crystals

1990

The dipolar relaxation dynamics of solid solutions of carbon dioxide and nitrous oxide has been investigated using dielectric spectroscopy. The temperature dependence of the relaxation rate reveals an ideal Arrhenius behavior for all concentrations, with energy barriers which scale linearly between the two pure compounds. The attempt frequencies are anomalously high. The distribution of relaxation times due to the static random fields as introduced by the substitutional impurity molecules is almost negligible. The melting temperature is determined by a critical relaxation rate of 40 kHz.

Rapid characterization of alkylpolyphosphonates by CZE with indirect photometric and mass spectrometric detection.

2006

Methods for the rapid characterization of industrial alkylpolyphosphonates (APPs) by infusion MS and CZE with indirect photometric (IPD) and MS detection are described. Technical-grade APPs, including alkylaminepolyphosphonates with 3-5 phosphonate groups and different hydrocarbon skeletons, hydroxyethyl-amino-bis(methylenephosphonic acid), hydroxyethylidene-diphosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid, were examined. A 10 mM solution of adenosine triphosphate disodium salt at pH 2.2 was used as BGE. The nominal compounds of the industrial APPs and their impurities were well resolved in less than 15 min. The peaks were identified by using extracted ion electropherograms…

From orientational glasses to structural glasses: What computer simulations have contributed to understand experiments

2002

Abstract Orientational glasses, produced by random dilution of molecular crystals, exhibit a freezing transition of the quadrupole moments. Monte Carlo simulations of lattice models (generalization of the Edwards–Anderson spin glass model) have been used to elucidate this behavior. While short range models exhibit a static glass transition at zero temperature only, the infinite range Potts glass exhibits a transition where a glass order parameter appears discontinuously. At higher temperature, a dynamical transition occurs, described by mode-coupling theory (MCT). MCT has also been tested by Monte Carlo and molecular dynamics simulations of coarse-grained models of glass-forming polymers. W…

Local Environment of Co2+ Ions in β″-Alumina Crystals

1992

Influence of Mn site doping on electrical resistivity of polycrystalline La1-yAyMn1-xBxO3 (A=Ba, Sr; B=Cu, Cr, Co) Manganites

2008

We have the measured electrical resistivity of La1-yBayMn1-xCuxO3 (0.17?y?0.30; 0.04?x?0.10), La1-ySryMn1-xCrxO3 and La1-ySryMn1-xCoxO3 (0.270?y?0.294; 0.02?x?0.10) polycrystalline samples in the 25-325 K temperature range. The increase of Mn site doping concentration leads to an increase of the electrical resistivity of the samples and the appearance of a ?double-peak? structure in the electrical resistivity versus temperature graphs. The first peak represents the insulator-metal transition in vicinity of the paramagnetic-ferromagnetic transition (TC). We have found that the intensity of the second peak increases with an increase of concentration of Mn substituents, due to the hole scatter…

Alkylsilyl compounds as enablers of atomic layer deposition: analysis of (Et3Si)3As through the GaAs process

2016

A new chemistry has been developed to deposit GaAs, the quintessential compound semiconductor. The ALD process is based on a dechlorosilylation reaction between GaCl3 and (Et3Si)3As. Characteristic ALD growth was demonstrated, indicating good applicability of the alkylsilyl arsenide precursor. ALD of GaAs produced uniform, amorphous and stoichiometric films with low impurity content. This was done with saturating growth rates and an easily controlled film thickness. Crystallization was achieved by annealing. Even though the growth rate strongly decreased with increasing deposition temperature, good quality film growth was demonstrated at 175 to 200 °C, indicating the presence of an ALD wind…

Ab initio calculations of Nb doped SrTiO3

2010

We present and discuss the results of the large scale Hartree–Fock calculations of Nb impurities substituting for Ti ions in SrTiO3 using ab initio computer code CRYSTAL and several supercells containing up to 135 atoms. The local structure optimisation, the electronic charge redistribution, chemical bond covalence and the band-structure changes induced by the defect are analysed. According to the results of our calculations, Nb is a shallow donor; six nearest O ions are slightly displaced outwards from the Nb ion. The calculated bond population between nearest Ti and O ions (64 me) is much larger than that between Nb and O ions (8 me), since Nb impurity is more ionic than the host Ti.

Theoretical study of Fe doping and oxidation–reduction influence on the photorefractive effect in BaTiO_3

1993

We numerically solve charge-transport and Poisson equations for photorefractive BaTiO3 single crystals with a band model, using four impurity levels, Fe2+–Fe3+, Fe3+–Fe4+, VO••–VO•, and VO•-VOx. Densities and photoinduced spatial distributions of each population are computed as a function of annealing O partial pressure. Space-charge field and beam-coupling gain are also computed as a function of annealing O partial pressure, temperature, Fe concentration, grating wave vector, and light intensity. We discuss the intervening mechanism of impurity centers and the correlations between experimental conditions of crystal growth, oxidation–reduction treatments, and measurement parameters.