Auger kinetic energies and electronic relaxation phenomena in atoms and solids

A semi-empirical theory has been developed to calculate the kinetic energy of Auger electrons resulting from radiationless transitions in both free atoms and metals. Experimental electron binding energies and calculated two-electron interaction and relaxation energies are used. Relaxation energies are determined by means of hyper-Hartree—Fock hole-state calculations. To account for extra-atomic relaxation phenomena in metals, it is assumed that conductionband electrons occupy free-atom-like screening orbitais. The relationship of the present theory to recent work of Shirley et al., Larkins, Kim et al. and Watson et al. is discussed. The dependence of the Auger cross-relaxation energy on the ionicity of compounds is briefly discussed.     

Line shape analysis and relaxation energies in the MVV Auger spectra of zinc and zinc oxide

The oxidation of polycrystalline zinc has been studied by recording the evolution of the line shape of the corresponding Auger spectra. The fine structure of the surface-sensitive low energy M₁ VV and M₂₃VV (V = 4s ? 3d valence band) lines in pure zinc has been analyzed and a new feature involving the 4s band tentatively identified. In the course of oxidation the main peaks broaden and shift to lower energies. This behaviour is explained in terms of increase of the 3d band width and decrease in the extraatomic relaxation energies. The extraatomic relaxation is found to decrease in the oxide by ~3.8 eV. A derivation of Auger intra and Extraatomic energies involving basically experimental data is presented. These values are compared to theoretical evaluations and their connection with photoemission dynamical relaxation data is discussed.     

Energy parameter and the free-atom behavior of Auger spectra

The L₃M₄₅M₄₅ spectra of V and Cr do not exhibit free atom behavior, in sharp contrast to those of Cu and Zn. An energy difference parameter, Δ ?, derived entirely from observable energies, has been introduced to correlate with the extent of electron localization and free-atom behavior in Auger transitions.     

Calculation of Al and Si KLV Auger energies and intensities

KLV Auger spectra of Al and Si were measured with the electron-beam excitation method. A new semi-empirical method for calculating the kinetic energies of these spectra originated from inner and valence shells is proposed. In this method, the measured energy of a Kβ X-ray satellite emitted from a K¹L¹ doubly ionized state and a calculated Hartree-Fock-Slater type potential acting between inner shells, i.e. K and L shells, for an isolated atom were used. The absolute kinetic energies of the Al and Si KLV Auger spectra were simply but accurately estimated without any complicated multiplet calculations involving the interaction potential between the L and V shells.     

Extra-atomic electronic cross-relaxation energies in KL2,3L2,3 Auger transitions in small sodium clusters from SCF-Xα-SW calculations

The self-consistent-field-Xα-scattered-wave method is used to calculate extra-atomic electronic cross-relaxation energies R_C^ea involved in KL_2,3L_2,3 Auger transitions in a series of small sodium clusters. R_C^ea is shown to increase with increasing dimension of the cluster. The R_C^ea value for Na₁₅ already closely approaches the metallic value. It is felt that the present calculational method will also be useful in determining relaxation energies in chemisorption systems.     

Auger relaxation processes in semiconductor nanocrystals and quantum wells

Auger recombination rates in mesoscopic semiconductor structures have been studied as a function of energy band parameters and heterostructure size. It is shown that nonthreshold Auger processes stimulated by the presence of heteroboundaries become the dominant nonradiative recombination channel in nanometer size semiconductor structures. The size dependence of luminescence quantum yields in nanostructures and microcrystals are discussed. Auger-like collisions of electrons and heavy holes are shown to serve as “accelerators” of thermalization processes in semiconductor quantum dots.     

Auger and other characteristic energies in secondary electron spectra from Al surfaces

The energy spectra of secondary electrons back-scattered from clean, oxygen covered, and Cu covered Al surfaces have been determined. The data support the previous suggestion that Auger electrons can experience both characteristic energy loss and absorption phenomena. From the experimental results it was not possible to determine whether densities of states of electrons in the valence band affected the Al L_2,3 VV Auger spectrum. This portion of the spectrum was greatly changed by oxygen absorption on the Al surface, but little affected by less than a monolayer of Cu. Conversely, characteristic loss spectra were less sensitive to oxygen on the surface, but were highly sensitive to the presence of copper at even less than monolayer coverage. A correlation between characteristic loss and “true” secondary spectra from clean surfaces was established and possible reasons for the correlation are discussed.     

Auger parameter of hafnium in elemental hafnium and in hafnium oxide

X-ray photoelectron spectroscopy has been used to determine the Auger parameters in elemental hafnium and in hafnium oxide (HfO₂). The zirconium L_α line has been used as a source of excitation to study the 3d core levels of hafnium, the 1s core level of oxygen, and the X-ray excited MNN Auger region of hafnium and KVV Auger region of oxygen. The Auger parameters for hafnium and oxygen have been determined from these spectral data. In case of oxygen, the Auger parameter has been compared with the corresponding value in water. The change in the Auger parameter is observed to be negative for hafnium and positive for oxygen. We have shown that the opposite signs of the Auger parameters in binary systems can be utilized to determine the direction of charge transfer between the constituents. This is consistent with the chemical shift due to charge transfer. This chemical shift in the core level has been evaluated by subtracting the relaxation shift from the experimentally observed core level shift. It is found to be positive for the 3d_5/2 core level of hafnium in the oxide indicating a charge transfer from hafnium to oxygen in the oxide. The observations are consistent with Pauling’s electronegativity criterion.     

On the relation between XPS and AES relaxation energies in metals

XPS (R₁) and AES cross-relaxation (R_c) energies are calculated by means of a Pseudopotential linear-response electron-gas method using norm-conserving Pseudopotentials, including intraatomic non-linearity contributions. The results are compared with excited atom model calculations and with self-consistent local density results from the literature. It is pointed out that deviations from the linear response rule R_c = 2R₁ are largely due to a shrinking of the core in the presence of the spectator hole. The remainder is due to non-linear response of the electron-gas.     

C~+离子内壳激发共振态1s2s(~3S)2p~3的Auger能量和Auger分支率(英文)

利用精确的鞍点变分波函数和鞍点复数转动方法,计算了C⁺离子五电子原子系统内壳激发共振态1s2s（³S）2p^32,4P°,^2,4D°的俄歇能量和俄歇分支率,考察了俄歇跃迁的收敛性,对300 keV C⁺离子和CH₄气体碰撞实验产生的高分辨率俄歇电子谱进行了标定,并指出这些类硼C⁺离子的内壳激发共振态对253～273 eV范围的实验谱线有重要贡献.本文计算结果与实验数据符合得很好.     

C+离子内壳激发共振态1s2s(3S)2p3的Auger能量和Auger分支率

利用精确的鞍点变分波函数和鞍点复数转动方法,计算了C+离子五电子原子系统内壳激发共振态1s2s(3S)2p3 2,4Po, 2,4Do 的俄歇能量和俄歇分支率,考察了俄歇跃迁的收敛性,对300-keV C+离子和CH4气体碰撞实验产生的高分辨率俄歇电子谱进行了标定,并指出这些类硼C+离子的内壳激发共振态对253-273eV范围的实验谱线有重要贡献. 本文计算结果与实验数据符合得很好.     

Single orbital relaxation energies accompanying core ionization in first row atoms and an investigation of the basis set dependence of computed single orbital relaxation energies for CO

Single orbital relaxation energies have been computed in the ΔSCF formalism for CO as a function of basis set. Investigations have been made of the orbital relaxation energy terms for first row atoms and correlation diagrams are presented for component relaxation terms on going from the atoms to the molecules in the particular cases of CO, N₂ and NO.     

Saddle-point energies and Monte Carlo simulation of the long-range order relaxation in CoPt

We present atomic-scale computer simulations in equiatomic L1₀-CoPt where Molecular Dynamics and Monte Carlo techniques have both been applied to study the vacancy-atom exchange and kinetics relaxation. The atomic potential is determined using a Tight-Binding formalism within the Second-Moment Approximation. It is used to evaluate the different saddle-point energies involved in a vacancy-atom exchange between nearest-neighbour sites. The potential and the saddle-point energies have been used to simulate the relaxation of the long-range order in CoPt using a Monte Carlo technique. A vacancy migration energy of 0.73±0.15 eV and an order-disorder transition temperature of 935 K have been found.     

On the relaxation of the order parameter in the BCS model

The relaxation of the nonequilibrium order parameter (wave function of pairs) of a “pure” superconductor is considered for the homogeneous case. The relaxation is due to the electron-phonon interaction. The orderparameter relaxation time is shown to be much longer than the time interval between electron-electron collisions. This relation is explained by the smallness of the superconducting transition temperature compared to both the Fermi energy and the Debye energy in the BCS model.     

Electron capture and intra-band relaxation by means of Auger processes in colloidal semiconductor nanocrystals

The electron relaxation dynamics in combination with LO phonon-assisted electron capture and intra-dot Auger scattering processes in a spherical quantum dot embedded in non-polar matrix is presented theoretically. The electron capture efficiency is investigated as a function of the lattice temperature and quantum dot radius for a deferent injected electron concentration, taking into account the confinement effect of the polar optical phonons in spherical quantum dots. Exact numerical calculations for the phonon-assisted electron capture rate as well as for the Auger scattering rate in colloidal CdSe quantum dot have been carried out. These calculations are consistent with experiment.     

Temperature dependence of the relaxation time of the superconducting order parameter

We have measured the temperature dependences of the relaxation time of the superconducting order parameter and of the equilibrium energy gap close to the transition temperature in very clean films of aluminum. The results are only consistent with the temperature and energy gap dependence predicted by Schmid and Schön. We also show that the magnitude and mean free path dependence of the electron inelastic collision time is in good agreement with calculations.