Valence Bands and Core Levels of the Isoelectronic Series LiF, BeO, BN, and Graphite Studied by ESCA
TL;DR: In this article, the core lines and valence bands of LiF, BeO, BN and graphite have been studied by the ESCA technique and the energy differences between inner levels and the valence band are compared with X-ray transition energies.
Abstract: The core lines and valence bands of LiF, BeO, BN and graphite have been studied by the ESCA technique. The energy differences between inner levels and valence bands are compared with X-ray transition energies. The changes in binding energy for the Bels level when going from metal to oxide and fluoride are compared with X-ray spectroscopic data and with a study of the disintegration constant in electron capture of 7Be in the same compounds.
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TL;DR: In this paper, the self-interaction correction (SIC) of any density functional for the ground-state energy is discussed. But the exact density functional is strictly selfinteraction-free (i.e., orbitals demonstrably do not selfinteract), but many approximations to it, including the local spin-density (LSD) approximation for exchange and correlation, are not.
Abstract: The exact density functional for the ground-state energy is strictly self-interaction-free (i.e., orbitals demonstrably do not self-interact), but many approximations to it, including the local-spin-density (LSD) approximation for exchange and correlation, are not. We present two related methods for the self-interaction correction (SIC) of any density functional for the energy; correction of the self-consistent one-electron potenial follows naturally from the variational principle. Both methods are sanctioned by the Hohenberg-Kohn theorem. Although the first method introduces an orbital-dependent single-particle potential, the second involves a local potential as in the Kohn-Sham scheme. We apply the first method to LSD and show that it properly conserves the number content of the exchange-correlation hole, while substantially improving the description of its shape. We apply this method to a number of physical problems, where the uncorrected LSD approach produces systematic errors. We find systematic improvements, qualitative as well as quantitative, from this simple correction. Benefits of SIC in atomic calculations include (i) improved values for the total energy and for the separate exchange and correlation pieces of it, (ii) accurate binding energies of negative ions, which are wrongly unstable in LSD, (iii) more accurate electron densities, (iv) orbital eigenvalues that closely approximate physical removal energies, including relaxation, and (v) correct longrange behavior of the potential and density. It appears that SIC can also remedy the LSD underestimate of the band gaps in insulators (as shown by numerical calculations for the rare-gas solids and CuCl), and the LSD overestimate of the cohesive energies of transition metals. The LSD spin splitting in atomic Ni and $s\ensuremath{-}d$ interconfigurational energies of transition elements are almost unchanged by SIC. We also discuss the admissibility of fractional occupation numbers, and present a parametrization of the electron-gas correlation energy at any density, based on the recent results of Ceperley and Alder.
16,027 citations
TL;DR: In this paper, the dopant-free electron and hole carrier-selective heterocontacts using alkali metal fluorides and metal oxides, respectively, in combination with passivating intrinsic amorphous silicon interlayers, were successfully developed and implemented.
Abstract: A salient characteristic of solar cells is their ability to subject photo-generated electrons and holes to pathways of asymmetrical conductivity—‘assisting’ them towards their respective contacts. All commercially available crystalline silicon (c-Si) solar cells achieve this by making use of doping in either near-surface regions or overlying silicon-based films. Despite being commonplace, this approach is hindered by several optoelectronic losses and technological limitations specific to doped silicon. A progressive approach to circumvent these issues involves the replacement of doped-silicon contacts with alternative materials which can also form ‘carrier-selective’ interfaces on c-Si. Here we successfully develop and implement dopant-free electron and hole carrier-selective heterocontacts using alkali metal fluorides and metal oxides, respectively, in combination with passivating intrinsic amorphous silicon interlayers, resulting in power conversion efficiencies approaching 20%. Furthermore, the simplified architectures inherent to this approach allow cell fabrication in only seven low-temperature (≤200 ∘C), lithography-free steps. This is a marked improvement on conventional doped-silicon high-efficiency processes, and highlights potential improvements on both sides of the cost-to-performance ratio for c-Si photovoltaics. The use of doped-silicon contacts in silicon solar cells adds cost and complexity to the fabrication process. These issues can now be circumvented by using dopant-free carrier-selective interfaces on silicon, realized by alkali metal fluorides and metal oxides.
443 citations
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TL;DR: In this article, the binding energies of calibration lines suitable for solid and for gaseous samples have been determined for different X-radiation, sample thickness and material, and experiments indicated that in calibrating relative to a surface layer, the carbon line from the hydrocarbon contamination layer can be used as well as a line from a thick layer of a noble metal on a part of the sample.
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TL;DR: In this article, a review of the experimental measurements which are used to establish the wavelength of this line on an absolute angstrom basis is given, and the recommended wavelength values are listed in \AA{}* units together with probable errors; corresponding energies are given in keV.
Abstract: Inconsistencies in accepted values (in x units) of x-ray reference lines have recently been demonstrated, although all are supposedly based on "good" calcite crystals. Factors supporting the selection of the W $K{\ensuremath{\alpha}}_{1}$ line as the X-Ray Wavelength Standard are critically discussed. A review is given of the experimental measurements which are used to establish the wavelength of this line on an absolute angstrom basis. Its value is $\ensuremath{\lambda}$ W $K{\ensuremath{\alpha}}_{1}=(0.2090100\ifmmode\pm\else\textpm\fi{}5 \mathrm{ppm})$ \AA{}. This may be used to define a new unit, denoted by \AA{}*, such that the W $K{\ensuremath{\alpha}}_{1}$ wavelength is exactly 0.2090100 \AA{}*; hence 1\AA{}*=1\AA{}\ifmmode\pm\else\textpm\fi{}5 ppm. The wavelengths of the Ag $K{\ensuremath{\alpha}}_{1}$, Mo $K{\ensuremath{\alpha}}_{1}$, Cu $K{\ensuremath{\alpha}}_{1}$, and the Cr $K{\ensuremath{\alpha}}_{2}$ have been established as secondary standards with probable error of approximately one part per million. Sixty-one additional x-ray lines have been used as reference values in a comprehensive review and reevaluation of more than 2700 emission and absorption wavelengths. The recommended wavelength values are listed in \AA{}* units together with probable errors; corresponding energies are given in keV. A second table lists the wavelengths in numerical order, and likewise includes their energies in keV.
1,467 citations
TL;DR: The position and shape of the energy bands of the following transition metals have been studied by ESCA: Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au as mentioned in this paper.
Abstract: The position and shape of the energy bands of the following transition metals have been studied by ESCA: Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au. The Fermi levels of the metals with unfilled d-bands are found in the high-energy flanks of the valence band spectra. For the noble metals the Fermi level is shifted toward higher energies. These observations are in general accordance with the overlap of d- and sp-bands in transition metals. An increase in band width is noted between corresponding elements in each series of transition metals. A comparison is drawn between band widths obtained in the present study and those deduced from cohesive energy data. An observed splitting in some of the bands seems to be much too large to be attributable to spin-orbit interaction. Core electron lines are recorded for the purpose of obtaining an energy calibration, estimating the contribution to the observed band spectra from inelastically scattered electrons, and checking the chemical state of the sample. The photoexcitation process and the energy losses of the electrons due to single-particle and plasmon excitations are discussed.
169 citations
TL;DR: In this article, an analysis is presented of two variants of the superposition of spectra of boron and nitrogen of hexagonal BN into one energy diagram of electron composition in the crystal BN hex.
80 citations
TL;DR: In this article, the chemical binding and properties of the two isoelectronic series N2, CO, BF, a 14-electron series, and C2, BeO, LiF, a 12-electric series are discussed in terms of the molecular charge distributions and the forces which they exert on the nuclei.
Abstract: The chemical binding and properties of the two isoelectronic series N2, CO, BF, a 14‐electron series, and C2, BeO, LiF, a 12‐electron series, are discussed in terms of the molecular charge distributions and the forces which they exert on the nuclei. It is found that the formation of the chemical bond in the 14‐electron series results in a transfer of charge from the bonding to the nonbonded regions of both nuclei in the molecule, the amount transferred increasing with the increasing asymmetry of the nuclear potential field. The larger and more diffuse nonbonded charge increase on B in BF as compared to that on C in CO suggests that BF may be superior to CO in its ability to act as a ligand in metal complexes. The increasing asymmetry of the potential field in the 12‐electron series results in a parallel increase in the asymmetry of the molecular charge distributions. Unlike the 14‐electron series, the charge transfer in BeO and LiF is unidirectional. The Δρ(e, η) or density difference contour maps [ρ(mole...
65 citations
01 Jan 1968
65 citations