Auger decay rates of antiprotonic helium

Auger decay rates of the metastable antiprotonic helium ^3,4He e are calculated. The variational method and solution of coupled differential equations are combined to determine the initial metastable state wave function. Besides metastable states, the calculation reveals specific short-lived states of the antiprotonic helium with an essentially different structure of the wave function. An effect of mixture of the wave functions is taken into account to calculate the decay rate for a few metastable states, which are close in energy to the short-lived ones. This revised version was published online in August 2006 with corrections to the Cover Date.     

RelativisticK—LL Auger transition rates

TheoreticalK—LL Auger transition rates are presented for a large range of the atomic number. These calculations are performed with the relativistic Hartree-Fock-Slater model. A comparison is made with the earlier calculations of Listengarten and of Asaad. TheZ-dependence of severalK—LL lines of Listengarten's calculations is in error. A detailed comparison of the experimental relative intensities with our theoretical calculations is also presented. A satisfactory agreement between the experiments and our theory is obtained forZ>55.     

K-shell Auger rates for multiply-ionized atoms: I. Neon

Theoretical Auger rates for the various terms of electron configurations 1s¹2s²2pⁿ, 1s¹2s⁰2pⁿ and 1s¹2s¹2pⁿ to the final terms after the Auger transitions are presented. The calculations are performed with the Hartree-Fock-Slater model. These rates can be conveniently used in the analyses of Auger-electron spectra produced, in particular, by heavy-ion collisions with neon.     

Band-to-band Auger processes at high carrier concentration

The strong decrease of lifetime in semiconductors under high doping conditions is discussed. The Auger effect should be responsible for it in both p-type and n-type material. Formulas for the begin of decrease are discussed and the appropriate carrier concentrations are calculated for several III–V compounds.     

Time-dependent effective rates for molecular processes

The concept of time-dependent effective rates for molecular processes such as luminescence, introduced in our earlier work, is developed further by obtaining two new results. One is the explicit evaluation of those rates for four initial conditions corresponding to experimentally relevant methods of excitation of the molecule. The other is a proof that the limiting values of those rates for long times or for infinitely fast relaxation are independent of the initial condition. The latter result extends the validity of the rate depression effect (whereby the long time limit of the effective rate is different from its thermalized value) to arbitrary initial conditions.On leave of absence from the Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (permanent address)     

Interatomic Auger processes and the density of states

The correlation between the line shape of Auger peaks and the density of states near the surface has been the subject of recent controversy. In certain cases, it has been possible to obtain the density of states by numerical deconvolution of a KVV peak (Amelio, 1970) or directly using a KLV peak (Cardona et al., 1973). However, the extension of this technique to transition metals (Cu, Zn) has encountered serious difficulties, related to the perturbation created by the presence of localized charges either in the initial or in the final state, although it is not yet clear why this perturbation is strong only in certain cases. The purpose of the present communication is to show a series of results that can throw some light on the abovementioned problem. The main point is that Auger processes of interatomic type, as those occurring in the INS technique of Hagstrum, are free of these perturbations. Recently, the authors have studied the line shape of the Auger peaks of O, C, N and S adsorbed on Cu, Ni and Fe. These results show that only that part of the Auger structure originated by interatomic transitions between substrate and adsorbate atoms can be related to the local density of states (LDOS). The rest of the structure, due to normal intraatomic processes, is dominated by the spectral terms in the final configuration of the ion. This new interpretation allows a separation of perturbation effects and clarifies the contribution of the LDOS to the peak line shape. In this communication, we present the line shape analysis of the L_2,3 VV and KVV Auger peaks of Mg and O in MgO. Due to the strong ionic character of this compound, the L_2,3 VV peak of Mg⁺⁺ is mainly due to interatomic processes between Mg⁺⁺ and O⁼ ions, whereas the KVV peak of O is mainly due to interatomic processes. This analysis shows that good agreement exists between the L_2,3VV Mg⁺⁺ Auger peak and the self-convolution of MgO density of states, whereas the KVV Auger peak of O⁼ is dominated by the spectral terms of the final configuration. Only a small peak in the high energy side of the latter peak can be related to the density of states and could be interpreted as an interatomic transition between two neighboring oxygen ions, in agreement with the interpretation given by others.     

Tracing ultrafast interatomic electronic decay processes in real time and space

Advances in laser pump-probe techniques open the door for observations in real time of ultrafast electronic processes. Particularly attractive is the visualization of interatomic processes where one can follow the energy transfer from one atom to another. The interatomic Coulombic decay (ICD) provides such a process which is abundant in nature. A wave packet propagation method now enables us to trace fully ab initio the electron dynamics of the process in real time and space, taking into account all electrons of the system and their correlations. The evolution of the electronic cloud during the ICD process in NeAr following Ne2s ionization is computed and analyzed. The process takes place on a femtosecond time scale, and a surprisingly strong response is found already in the attosecond regime.     

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.     

Pseudopotential theory of Auger processes in CdSe quantum dots

Auger rates are calculated for CdSe colloidal quantum dots using atomistic empirical pseudopotential wave functions. We predict the dependence of Auger electron cooling on size, on correlation effects (included via configuration interaction), and on the presence of a spectator exciton. Auger multiexciton recombination rates are predicted for biexcitons as well as for triexcitons. The results agree quantitatively with recent measurements and offer new predictions.     

Study of adsorption phenomena on aluminium by interatomic Auger transition spectroscopy: II. CO adsorption onto Al

Adsorption of carbon monoxide on aluminium is studied by the combination of in situ evaporation of Al and the Auger electron spectroscopy. New Auger signals which are attributed to interatomic Auger transitions in Al₄C₃ type AlC bonds are found. It is revealed that two adsorption stages exist in the adsorption process, i.e., that after the formation of the AlC bond takes place, the adsorbed layer consisting of AlC and AlO bonds is formed.     

Study of adsorption phenomena on aluminium by interatomic Auger transition spectroscopy: I. Initial oxidation of Al

The initial oxidation process of aluminium is studied by using the combined molecular beam evaporation and Auger electron spectroscopy under ultra-high vacuum. At the initial stage of oxygen exposure to the clean aluminium at room temperature, the chemisorption of the oxygen atoms on the surface of aluminium is turned out to be dominant from the behaviour of the energy shifted Auger signal of aluminium. Then, the formation of the alumina (Al₂O₃) type bonding is followed, which is concluded from the interatomic Auger signals.     

A combination of Auger and many-phonon processes in nonradiative recombination

The Auger capture coefficient into a trap is calculated taking many-phonon processes into account. For a simple model an enhancement of the Auger capture coefficient is found.     

Effect of interchannel interaction on the neon KLL Auger transition rates

Calculations of neon KLL Auger rates which include the mixing between the final ²S channels are reported. The results are compared with Kelly's recent many-body-perturbation-theory calculations and with absolute rates, obtained from experiments of Gelius et al. and Krause et al.     

Classical interatomic potential for orthorhombic uranium

A classical interatomic potential for uranium metal is derived within the framework of the charge optimized many body (COMB) formalism. The potential is fitted with a database obtained from experiment and density functional theory (DFT) calculations. The potential correctly predicts orthorhombic α-U to be the ground state. Good agreement with experimental values is obtained for the lattice parameters, nearest neighbor distances, and elastic constants. Molecular dynamics simulations also correctly show the anisotropy in the coefficient of thermal expansion and the temperature dependence of the nearest neighbor distances.