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1.
The chemical shift in electron binding energy, magnetic splitting of electron shells, and structures in the valence band are examined for chromium in the 3 + and 6 + oxidation states.The splitting of the Cr 3s energy level is associated with the appearance of a sharp Cr 3d line in the valence band. The relative chemical shift in the Cr 2p32 line between Cr2O3 and K2Cr2O7 is verified in the mixed compound KCr3O8 which contains both types of Cr ions, and the structure of this compound is verified by the X-ray photoelectron spectra. The spin-orbit intensity ratio of the 2p doublet of Cr6+ is 3, instead of the theoretical value of 2, and the spin-orbit splitting is less than for Cr3+. In the 3p level of Cr the relative chemical shift is 3.5 eV whereas for the 2p32 level the shift is only 2.4 eV. The differences in chemical shift and intensity ratio can not be explained.  相似文献   

2.
SCF-Xα SW MO calculations on metal core ion hole states and X-ray emission (XES) and X-ray photoelectron (XPS) transition states of the non- transition metal oxidic clusters MgO610?, AlO45? and SiO44? show relative valence orbital energies to be virtually unaffected by the creation of valence orbital or metal core orbital holes. Accordingly, valence orbital energies derived from XPS and XES are directly comparable and may be correlated to generate empirical MO diagrams. In addition, charge relaxation about the metal core hole is small and valence orbital compositions are little changed in the core hole state. On the other hand, for the transition metal oxidic clusters FeO610?, CrO69? and TiO68? relative valence orbital energies are sharply changed by a metal core orbital or crystal field orbital hole, the energy lowering of an orbital increasing with its degree of metal character. Consequently O 2p nonbonding → M 3d-O 2p antibonding (crystal field) energies are reduced, while M 3d bonding → O 2p nonbonding and M 3d-O 2p antibonding → M 4s,p-O 2p antibonding (conduction band) energies increase. Charge relaxation about the core hole is virtually complete in the transition metal oxides and substantial changes are observed in the composition of those valence orbitals with appreciable M 3d character. This change in composition is greater for e g than for t2g orbitals and increases as the separation of the eg crystal field (CF) orbitals and the O 2p nonbonding orbital set decreases. Based on the hole state MO diagrams the higher energy XPS satellite in TiO2 (at about 13 eV) is assigned to a valence → conduction band transition. The UV PES satellites at 8.2 eV in Cr2O3 and 9.3 eV in FeO are tentatively assigned to similar transitions to conduction band orbitals, although the closeness in energy of the crystal field and O 2p nonbonding orbitals in the valence orbital hole state prevents a definite assignment on energy criteria alone. However the calculations do clearly show that charge transfer transitions of the eg bonding → eg crystal field orbital type would generally occur at lower energy than is consistent with observed satellite structure.A core electron hole has little effect upon relative orbital energies and is only slightly neutralized by valence electron redistribution for MgO and SiO2. For the transition metal oxides a core hole lowers the relative energies of M3d containing orbitals by large amounts, reducing O → M charge transfer and increasing M 3d crystal field → conduction band energies. Large and sometimes overcomplete neutralization of the core hole is observed, increasing from CrO69? to FeO610? to TiO68?. as the O → M charge transfer energy declines.High energy XPS satellites in TiO2 may be assigned to O 2p nonbonding → conduction band transitions while lower energy UV PES satellites in FeO and Cr2O3 arise from crystal field or O 2p nonbonding → conduction band excitations. Our “shake-up” assignment for FeO610?, CrO69? and TiO68? are less than definitive because no procedure has yet been developed to calculate “shake-up” intensities resulting from transitions of the type described. However the results do allow a critical evaluation of earlier qualitative predictions of core and valence hole effects. First, we find that the comparison of hole or valence state ionic systems with equilibrium distance systems of higher nuclear and/or cation charge (e.g. the comparison of the FeO610? Fe 2p core hole state to Co3O4) is dangerous. For example, larger MO distances in the ion states substantially reduce crystal field splittings. Second, core and CF orbital holes sharply reduce O → M charge transfer energies, giving 2eg → 3eg energy separations which are generally too small to match observed satellite energies. Third, highest occupied CF-conduction band energies are only about 4–5 eV in the ground states, but increase to about 7–11 eV in the core and valence hole states of the transition metal oxides studied. The energetic arguments presented thus support the idea of CF and/or O 2p nonbonding → conduction band excitations as assignments for “shake-up” satellites, at least in oxides of metals near the beginning of the transition series.  相似文献   

3.
X-ray spectra of Si and SiO2 have been measured accurately with a double crystal spectrometer. The measuredKβ spectrum of silicon element was compared with calculations of the electronic density of states. Observed intensity distribution shows that thep-electrons predominate at the top of the valence band, and somep-like states extend to the middle of the valence band. According to MO calculations the most intensiveKβ line of SiO2 is 4t 2 (100), the 3t 2 (16) line is 17.9 eV lower, and 5t 2 (5) line 6.3 eV higher. In our measurements the energy differences are 13.0 and 4 eV, respectively, and intensities 30% and 3% from the main line.  相似文献   

4.
We perform a dispersion relation type calculation of the I = 0 S-wave amplitude g0+ (t) for the process ππ → KK, in the region from t = 4μ2 to t = (1100 MeV)2. Crossing is imposed by generalizing the newly developed hyperbolic partial-wave relations to our reaction and by imposing them on our amplitude using experimental Kπ phase-shift information as input. Analyticity and unitarity is imposed by generalizing the formalism of BFP [1] for parametrizing partial-wave amplitudes. This readily allows us to impose the experimental ππ → KK cross section. Finally the low energy behaviour is constrained to lie within certain limits recently deduced from fixed-tKπ dispersion relation studies [2] and including the current algebra prediction as a special case. We are able to resolve a previous controversy regarding the sign of Im g0(+) (t).  相似文献   

5.
The energy band structure of mechanically free and compressed LiRbSO4 single crystals is investigated. It is established that the top of the valence band is located at the D point of the Brillouin zone [k = (0.5, 0.5, 0)], the bottom of the conduction band lies at the Γ point, and the minimum direct band gap E g is equal to 5.20 eV. The bottom of the conduction band is predominantly formed by the Li s, Li p, Rb s, and Rb p states hybridized with the S p and O p antibonding states. The pressure coefficients corresponding to the energies of the valence and conduction band states and the band gap E g are determined, and the pressure dependences of the refractive indices n i are analyzed.  相似文献   

6.
7.
Results of measurements of conductivity, Hall and Seebeck coefficients of tellurium doped n-type crystals of platinum antimonide are presented. The Hall coefficient and the Seebeck coefficient undergo sign inversion twice, below and above room temperature. The detailed analysis of the experimental results revealed that below 200 K PtSb2 can be described by a simple conduction and valence band model. The energy gap Eg = (110?0.15 × T) (meV), the electron conductivity mass mnc/m0 = 0.35, acoustic phonon limited electron mobility 〈μan = 3 × 106 T?32 (cm2V · s) and mobility ratio 〈μan/〈μap = 0.4 are determined. However, at higher temperatures a more complicated valence band model is needed to account for the experimental results. The arguments for the existence of subsidiary valleys in the valence band are presented.  相似文献   

8.
The electron distribution in the valence band from single crystals of titanium carbide has been studied by photoelectron spectroscopy with photon energies h?ω = 16.8, 21.2, 40.8 and 1486.6 eV. The most conspicious feature of the electron distribution curves for TiC is a hybridization between the titanium 3d and carbon 2p states at ca. 3–4-eV binding energy, and a single carbon 2s band at ca. 10 eV. By taking into account the strong symmetry and energy dependence of the photoionization crosssections, as well as the surface sensitivity, we have identified strong emission from a carbon 2p band at ? 2.9-eV energy. Our results are compared with several recent energy band structure calculations and other experimental data. Results from pure titanium, which have been used for reference purposes, are also presented.The valence band from single crystals of titanium carbide have been studied by means of photoelectron spectroscopy, with photon energies ranging from 16.8 to 1486.6 eV.By taking into account effects such as the symmetry and energy dependence of the photoionization cross-sections and surface sensitivity, we have found the valence band of titanium carbide to consist of two peaks. The upper part of the valence band at 3–4 eV below the Fermi level consists of a hybridization between Ti 3d and C 2p states. The C 2p states observed in our spectra were mainly excited from a band about 2.9 eV below the Fermi level. The APW5–9, MAPW10 and EPM11 band structure calculations predict a flat band of p-character between the symmetry points X4 and K3, most likely responsible for the majority of C 2p excitations observed. The C 2s states, on the other hand, form a single band centered around ?10.4 eV.The results obtained are consistent with several recent energy band structure calculations5–11, 13 that predict a combined bonding of covalent, ionic and metallic nature.  相似文献   

9.
The electronic structures of SrTiO3 crystals doped with Fe3+, Fe4+ and Fe5+ ions have been investigated using the Xα cluster approach. The ground-state eigenvalues show the lower Fe acceptor level, of t2g↓ symmetry, localized inside the SrTiO3 band gap, respectively at 2.8 eV (Fe3+, S = 52), 1.6 eV (Fe4+, S = 1) or 1.1 eV (Fe4+, S = 0) and 1.1 eV (Fe5+, S = 32) above the valence band edge. Other acceptor levels, with eg↓ and eg↑ symmetries, appear inside the gap when the Fe nominal ionicity increases.The theoretical Xα excitation energies of O 2p-Fe 3d transitions confirms the experimental interpretations of acceptor charge transfer bands for the optical absorption spectra of SrTiO3:Fe4+ and SrTiO3:Fe5+ crystals.The large optical excitation energies compared with the thermal transitions are partly due to the O 2p band width.  相似文献   

10.
The energy loss spectrum of low energy (0 < Ep < 200 eV) electrons scattered from W(100) has been experimentally investigated, and mechanisms giving rise to the fine structure analyzed using a dielectric response formalism. The dielectric medium is characterized by available optical data and energy band calculations for tungsten. All of the structure for loss energies, w, less than 18 eV is attributed to intra- and interband transitions involving the bulk valence and conduction bands. The surface and bulk plasmon excitations are observed at w = 21 eV and w = 25.5 eV respectively which is in reasonable agreement with the optical data. A very narrow peak in the density of conduction d-band states apparently functions strongly in well defined excitations involving the 5p32 and 4f tungsten orbitais and the 2s and 2p orbitais of adsorbed oxygen. These conduction band states form a “window” with which to measure the electronic orbital structure of both the substrate and adsorbate during adsorption and reaction. We demonstrate this for the room temperature adsorption of oxygen on W(100) in which we observe the sequential filling of two electronically inequivalent binding states. The stability of the “d-band window” during thermally activated reaction, and the likelihood of its existence in other transition metals makes this an attractive surface sensitive spectroscopy.  相似文献   

11.
Using the light absorption technique in a 132Xe afterglow plasma, we have measured the relative transition probabilities for several xenon lines which have the metastable 6s[32]2 or the resonant 6s[32]1 states as their lowest transition level. Because the transition probabilities of the 8819 Å (6p[52]3 ? 6s[32]2) and 8280 Å (6p[12]0 ? 6s[32]1) lines are relatively well known, we have chosen these as reference lines and have thus been able to determine the absolute values of the transition probabilities for 19 xenon lines corresponding to transitions from 6p, 6p′, 7p, 8p, 9p, 4f and 5f to 6s[32]2, and for four lines corresponding to the transitions 6p?6s[32]1.  相似文献   

12.
The differential cross section of the reaction (γp → pφ) has been measured in the t range 0 ? t ? 0.4 GeV2 and for photon energies from 3.0 to 6.7 GeV. In particular for the small t region the measurement accuracy was better than 10%. We obtained for the slope parameter B in an exponential parametrization of the differential cross section dσ/dt = Ae?Bt values of B ? 6 ± 0.5 GeV?2 which are significantly larger than the slopes obtained by most other experiments at higher t values. This indicates a t dependence of B particularly in the small t region.An energy dependence of the optical point (dσ/dt)t=0, observed in our measurements, has been explained as a kinematic effect due to the VDM relation. A fit of our measurements is in excellent agreement with all other published values of (dσ/dt)t=0(γp → φp), this implies that σtot(φp) must be essentially energy independent in this energy range.Spin density matrix elements of the φ have been evaluated and an analysis of the helicity amplitudes has been carried out. This analysis confirmed s-channel helicity conservation. Moments of spherical harmonics of the KK angular decay distribution have been computed for 10 MeV KK mass-bins from threshold to 1.3 GeV. The mass dependence of the normalized moments is generally smooth. Contributing amplitudes have essentially only even moments. The moment 〈Y20〉/〈Y00〉 changes sign above the φ mass.Differential cross sections for the inelastic φ production γp → φX have been evaluated for the first time both with respect to t?tmin and MK. The integrated inelastic cross sections are comparable in size with the elastic ones. The slopes of the differential cross sections dσ/dt appear to become flatter with increasing MX.  相似文献   

13.
Mg Kα ESCA spectra of several α-Zr(PO4)2M2 compounds (M = Li+, Na+, K+, Cs+) have been obtained. Satellite structure is observed at ~7–8 eV from the main P 2s peak (corresponding to ~15–16 eV from the main Zr 3d52 peak). The intensity of the satellite depends on the counter-ion intercalated. For a given counter-ion it is strongly increased by sputtering, the rate of increase being also dependent on the counter-ion. This observation is interpreted mainly in terms of electron-defect formation similar to that involved in the formation of colour centres by radiation damage, and subsequent charge-transfer shake-up of the trapped electrons to the electron-deficient phosphorus or Zr(IV) centres.  相似文献   

14.
Empty electronic states in the sodium tungsten bronze Na23WO3 have been studied by inverse photoemission spectroscopy using a novel narrow-bandpass photon detector. The empty density of states in the t2g(W:5d) band peaks about 3 eV above the Fermi energy, implying an overall t2g bandwidth greater than found in recent bandstructure calculations.  相似文献   

15.
The valence band density of states for PbI2 is determined from X-ray and u.v. induced photoelectron spectra. It is shown that the band derived from Pb 6s states is at 8 eV binding energy and not at the top of the valence bands as suggested by band structure and charge density calculations. A rigid shift in the predominantly iodine 5p derived bands to lower binding energy brings the band structure calculations into essential agreement with experiment. Pb 5d core level binding energies determined here are used to derive core level exciton energies of 0.7 eV from published reflectivity spectra.  相似文献   

16.
The formation of anionic clusters similar to O22?, S22?, Se22? but with higher internuclear distances can be responsible for the more specific forms of interaction required to explain the properties of UO2+x, and many transition metal chalcogenides such as Fe1?xS, Ni1?x,S etc. Resonant structures can lead to clusters of this type even in stoichiometric chalcogenides with NiAs-type structure due to the dp mixing, and low energy differences between metal d- and chalcogen p-bands. The mixed valence effects involved are discussed qualitatively.  相似文献   

17.
XPS data for the valence band, the Pt 4? states, and the Ti 2p states are presented for the intermetallic Pt3Ti. Relative to the Pt valence band, the Pt3Ti band shows a decrease in the density of states just below the Fermi level and a shift of the centroid to higher (binding) energy. Ti 2p and Pt 4? binding energies showed relatively large shifts with respect to the pure metals. These changes in the valence band density of states and core level binding energies are interpreted as arising from hybridization of the d-orbitals in both metals to form strong intermetallic bonds.  相似文献   

18.
The temperature dependence of the fundamental absorption edge in CuGaSe2 single crystals was determined in the temperature range from 15 to 300 K. Above about 120 K the gap energy changes linearly with temperature with dEg/dT = ? (2.1 ± 0.1) eV K?1. The downshift in dEg/dT of the I–III–VI2 compounds compared to their II–VI analogs is discussed accounting for the p-d hybridization of the uppermost valence band.  相似文献   

19.
Hall-effect and magnetoresistance measurements have been carried out in GaAs : Cr as functions of magnetic field strength (B = 0–18kG) and temperature (T = 125–420°K). Independent solutions for the mobilities, μn and μp, and the carrier concentrations, n and p, are obtained from the basic mixed-conductivity equations. These quantities, as well as the intrinsic carrier concentration, ni are then calculated as a function of temperature for one sample, and subsequent analysis yields the following values in the range T = 360–420°K: an acceptor (presumably Cr) energy EA = 0.69±0.02eV (from the valence band); the bandgap energy Eg = Eg0 + αT, with Ego = 1.48±0.02eV, α ? 3.2 × 10?4eV°K; μn = 2700± 100 cm2V sec, decreasing slightly with temperature; = 350± 50 cm2V sec; and an acceptor-to-donor concentration ratio, itNA/ND?8. The electron mobility appears to be limited by neutral impurity scattering, with NA ? 2 × 1016cm?3. Several other samples were also investigated but as a function of temperature only (at B = 0). At room temperature both positive (p-type) and negative (n-type) Hall coefficients were observed.  相似文献   

20.
Hall effect measurements have been carried out over the temperature range 77–500K on p-type GaTe single crystals, grown from the melt. The results indicate that scattering by homopolar optical phonons polarized normally to the layers is largely dominant in GaTe. From the analysis of Hall mobility data, carried out according to the Schmid's model, a phonon energy h?ω = 9.8 meV and the product between the coupling constant and the hole conduction mass along the layers g2mh⊥ = v.205me has been found Finally, an acceptor center, lying at 138 meV from the valence band, displays an hydrogen-like behaviour, with its energy dependent from concentration according to the theory.  相似文献   

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