The participant Coster–Kronig preceded Auger transition in the resonant L2,3-M2,3V Auger electron spectrum of Ti metal

The L_2,3-M_2,3V resonant Auger electron spectroscopy (RAES) spectrum of Ti metal measured by Le Fêvre et al. [P. Le Fêvre, J. Danger, H. Magnan, D. Chandesris, J. Jupille, S. Bourgeois, M.-A. Arrio, R. Gotter, A. Verdini, A. Morgante, Phys. Rev. B69 (2004) 155421] is analyzed in the light of relaxation and decay of the resonantly excited L_2,3-hole states. The relaxation time of the resonantly excited L_2,3-hole state to the fully relaxed (screened) one is much shorter than the L_2,3-hole Auger decay time, whereas the participant Coster–Kronig (CK) decay time of the resonantly excited L₂-hole state to the fully relaxed L₃-hole state at the L₂ resonance is as short as the relaxation time of the resonantly excited L₂-hole state to the fully relaxed one. The excited electron is predominantly either rapidly decoupled from the L_2,3-hole decay or annihilated by the participant CK decay. Thus, near the L_2,3 edges the L_2,3-M_2,3V RAES spectral peak appears at constant kinetic energy. The L_2,3-M_2,3V RAES spectrum shows a normal L_2,3-M_2,3V Auger decay profile not modulated by the density of empty d states probed by the resonant excitation. Not only the relaxation time but also the participant CK decay time depends on photon energy because they depend on the density of empty d states probed by the resonant excitation. As a result, the L_2,3 X-ray absorption spectroscopy spectral line broadening depends on photon energy.     

Increase in corrosion resistance of Zn–22Al–2Cu alloy by depositing an Y2O3 film studied by Auger electron spectroscopy

Thin films of Y₂O₃ were deposited on the surface of a zinalco alloy (Zn–22Al–2Cu) in order to modify the surface and increase the corrosion resistance. By means of ion sputtering and surface analysis using Auger electron spectroscopy, in-depth relative elemental intensity profiles were obtained. The growth mechanism of the surface oxides layer is modified by the deposited yttrium oxide film. On samples without film, corrosion progresses mainly at the surface as indicated by the zinc excess, while on samples with film, the growth of the oxides layer occurs at inner points of the film where migrating anions and cations are allowed to find each other. The growth of the corrosion products layer is about nine times smaller in samples with a film of 1600 Å of Y₂O₃ with respect to samples without a film. Migration of aluminum particles is higher than that of zinc particles, producing a surface highly enriched in aluminum.     

Could the GSI decay rate oscillations be observed in a standard electron capture decay experiment?

The electron-capture decay of ¹⁸⁰Re has been investigated to search for oscillations in the decay probability as reported from a recent measurement at GSI, Darmstadt. The production period was kept short compared to the reported oscillation period. No such oscillation was observed, indicating that the reported oscillations would not have been observable in a conventional experiment with radioactive atoms in a solid environment but must have to do with the unique conditions in the GSI experiment where hydrogen-like ions are moving independently in a storage ring and decaying directly by a true two-body decay to a long-lived (ground-)state. Our finding could restrict possible theoretical interpretations of the oscillations.     

On the phase diagram of a two-dimensional electron–hole system

The phase diagram for a system of spatially separated electrons and holes in coupled quantum wells or graphene double layers is studied in the framework of a BCS-like mean-field approach and a Landau expansion in terms of the pairing order parameter. We find a second order transition between an electron–hole plasma and a BCS phase, as well as a first-order transition between the BCS phase and a bosonic Mott phase of tightly bound electron–hole pairs without phase coherence. The electron–hole plasma exists at low and at high densities for weak interaction, the BCS phase at moderate density and the Mott phase at high density and strong interaction.     

Quantum beats in the 3γ annihilation decay of Positronium observed by perturbed angular distribution

We have applied conventional Time Differential Perturbed Angular Correlation (TDPAC) method to observe the anisotropy oscillations in the 3γ annihilation decay of polarized Positronium in a weak magnetic field. The effect, as predicted theoretically and experimentally demonstrated by Barishevsky et al. [V.G. Barishevsky, O.N. Metelitsa, V.V. Tikhomirov, Oscillations of the positronium decay γ-quantum angular distribution in a magnetic field, J. Phys. B: At. Mol. Opt. Phys.22 (1989) 2835], is induced by the coherent admixture of the m = 0 states of ortho-Positronium (o-Ps) and para-Positronium (p-Ps) in interaction with the magnetic field.The following experimental characteristics are to be considered:

(i)

the oscillation frequency corresponds to the difference in energy of the Ps atom levels in magnetic field and is proportional with H²;

(ii)

in a fixed geometry the modulation depth (oscillations amplitude) depends on the mean positron polarization;

(iii)

privileged angles of the polarization vector, magnetic field and detectors are required for optimizing the observed oscillations amplitude.

The normalized difference spectrum function (R(t)) obtained from time spectra measured in vacuum and in different gaseous atmospheres (Ar, H₂, N₂) have the oscillations amplitude constant and we conclude that the Ps atoms are not fully thermalized over a time interval of about 400 ns.The R(t) functions obtained for o-Ps annihilation decays, in dry air or Ar-O mixture, have the oscillations amplitude time dependent due, probably, to the paramagnetism of the Oxygen molecules.     

Investigation of the D Π state of NaK by polarisation labelling spectroscopy

Two-colour polarisation labelling experiments measuring the D-X system of NaK have furnished observations of the D ¹Π state of NaK up to v″ = 42. The last observed level is located 7 cm⁻¹ below the Na(3p ²P_3/2) + K(4s) atomic asymptote, 22247.15 cm⁻¹ above the minimum of the electronic ground state, clearly indicating the dissociation products of this state. The vibrational progressions all exhibit irregular intervals, predominantly because of strong interactions with the nearby d ³Π state, which also dissociates to Na(3p) + K(4s) atoms. The polarisation data have been combined with some resolved fluorescence D-X transitions, and analysed by fitting to spectroscopic parameters and to an analytical potential curve. A full deperturbation treatment has not been attempted, but a ‘robust’ weighting scheme has been used to reduce the influence of levels that cannot be properly represented by a single channel model. Parameters determined in a fit to a potential curve include T_e = 20090.18 ± 0.02 cm⁻¹, well depth 2157.0 ± 0.3 cm⁻¹, R_e = 4.1547 ± 0.0002 Å, with an unweighted root mean square error of 0.12 cm⁻¹ for 959 data.     

Adsorption of nitrogen and ammonia by polycrystalline iron surfaces in the temperature range 80–290 K studied by electron spectroscopy

X-ray and uv induced photoelectron spectroscopy have provided information on the various molecular states of nitrogen formed on polycrystalline iron surfaces from dinitrogen and ammonia. At 85 K two distinct states are observed with N₂(g) which have N(1s) binding energy values of 405.3 and 400.2 eV. These are in equilibrium with N₂(g), are weakly held, and are desorbed on warming to 290 K leaving a nitrogen free surface. The two states are assigned to a molecularly adsorbed

and linear

species the former characterised by an N(1s) value of 400.2 eV and the latter by 405.3 eV. At 290 K nitrogen is adsorbed with a very low sticking probability (?10^?6) giving rise to an N(1s) value of 397.2 eV. This is undoubtedly the dissociatively chemisorbed

species. At a nitrogen pressure of l Torr adsorption is “instantaneous” and the N(1s) value is 397 eV. No evidence for the unstable bridged and linear forms of nitrogen is obtained at 290 K although they may well be precursors to the formation of the strongly chemisorbed nitrogen species. Shifts in the N(1s) binding energy induced by subsequent oxygen adsorption are discussed briefly. At 85 K ammonia adsorbs largely in the molecular form with a broad N(1s) peak centred at about 400 eV but on warming to 290 K this splits to give two peaks one at 397 eV and the other at 400 eV. Interaction at 290 K leads to a dominant peak at 397.2 eV and a subidiary one at 400 eV. Helium (1) spectra support the assignment of the 397.2 eV peak to dissociated species (N, NH) and the 400 eV peak to molecular adsorption. The conclusions with N₂ and NH₃ are substantiated further by comparing the data with results for nitric oxide. The concentration of nitrogen adatom species formed from NO at 290 K and 10^?6 Torr is some ten times that formed from N₂ at 1 Torr and three times that from NH₃ at 10^?6 Torr and the same temperature.     

Anisotropic optical conductivity and electron–hole asymmetry in doped monolayer graphene in the presence of the Rashba coupling

In this study, the optical conductivity of substitutionary doped graphene is investigated in the presence of the Rashba spin orbit coupling (RSOC). Calculations have been performed within the coherent potential approximation (CPA) beyond the Dirac cone approximation. Results of the current study demonstrate that the optical conductivity is increased by increasing the RSOC strength. Meanwhile it was observed that the anisotropy of the band energy results in a considerable anisotropic optical conductivity (AOC) in monolayer graphene. The sign and magnitude of this anisotropic conductivity was shown to be controlled by the external field frequency. It was also shown that the Rashba interaction results in electron–hole asymmetry in monolayer graphene.     

An excitonic model for the electron–hole plasma relaxation in proton-irradiated insulators

The European Physical Journal D - We discuss a Faddeev-like iterative approach which allows one to consistently include the Coulomb potential in strong field phenomena through a Born series. To...     

Autler–Townes spectroscopy of high-lying state by phase conjugate six-wave mixing

An Autler-Townes(AT) spectroscopy based on phase conjugate six-wave mixing(SWM) is proposed to detect AT doublet of high-lying state in a Doppler-broadened cascade four-level system.It is found that the SWM spectrum is dependent strongly on the ratios between the magnitudes of the wave vectors.We discuss how the Doppler broadening affects the SWM spectrum from a time-domain viewpoint and find that,due the atomic motion,the atomic polarizations acquire different phases for atoms with different velocities as time evolves.The Doppler free SWM spectrum can be obtained only when the atomic polarization can be rephasing again at certain time after the interactions of all the incident fields.     

Candidate of the member of three-phonon multiplet observed in the β + +EC decay of 76Br

The decay scheme of ⁷⁶Br is established by the ⁷⁶Br(T _1/2?=?16.2 h) β ^?+?/EC study. The 1791.31 keV level, which was identified initially by Müller et al with ⁷⁶Se(p, p ^′) reaction more than three decades ago, is reconfirmed. However, the spin and parity have not been assigned by Müller et al. Now we consider it reasonable to assign the 1791.31 keV level as a new candidate of the three-phonon multiplet in ⁷⁶Se. In addition, in order to study the deformation of ⁷⁶Se which lies in transitional region between strongly deformed and spherical nuclei, we calculate the total Routhian surfaces (TRS) of positive-parity states by cranking shell model formalism.     

Photoinduced transformations in (As1–xBix)2S3 glass observed by Raman spectroscopy

Raman spectra of (As_1–xBi_x)₂S₃ glass samples with x ≤ 0.2 measured at the excitation with above-bandgap (532 nm) laser light at a relatively low power density (P_exc = 4 kW/cm²) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As_1–xBi_x)₂S₃ glass previously known (x ≤ 0.06). Spectra measured at an increased P_exc (40 kW/cm²) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage-type As₄S₄ units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm⁻¹, which emerge in the Raman spectra of the (As_1–xBi_x)₂S₃ glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As_1–xBi_x)₂S₃ glass surface with formation of units containing arsenate AsO₄³⁻ and sulphate SO₄²⁻ ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.     

Why are the band-like states suppressed in the M3–M4,5M4,5 super Coster–Kronig electron spectrum of Cu metal compared to those in the L3–M4,5M4,5 Auger electron spectrum?

The relative spectral intensity of the band-like two M_4,5-hole state to the atomic-like localized one is much suppressed in the coincidence M₃–M_4,5M_4,5 super Coster–Kronig (sCK) electron spectrum of Cu metal compared to the one in the coincidence L₃–M_4,5M_4,5 Auger electron spectroscopy (AES) spectrum. The M₃-hole lifetime width of Cu metal is calculated by an ab initio atomic many-body theory (the extended relaxed core random phase approximation with exchange). The calculated M₃-hole lifetime width of Cu metal agrees well with the experimental one. The M₃–M_4,5M_4,5 sCK decay width of Cu metal decreases much with delocalization of the two M_4,5 holes in the sCK final state, whereas the Auger decay width is fairly independent of localization and delocalization of the two M_4,5 holes in the Auger final state. Thus, the relative spectral intensity of the band-like state is much suppressed in the coincidence M₃–M_4,5M_4,5 sCK-electron spectrum of Cu metal compared to the one in the coincidence L₃–M_4,5M_4,5 AES spectrum.     

The influence of electron–phonon interaction on the OSL decay curve shape

The significance of the electron–phonon interaction for optically stimulated luminescence (OSL) process in quartz is demonstrated. OSL variation with temperature has been investigated for four samples of natural quartz. Changes of the OSL decay rate have been observed for all components of the OSL signal. The scale and tendency of these changes are comparable with outcomes of computer simulations carried out for the model composed of two deep electron traps, one shallow trap and one recombination centre, taking into account the electron–phonon interactions.     

Fine structure of the emission spectrum of a two-dimensional electron–hole liquid in SiGe/Si quantum wells

The fine structure of the emission spectrum of a quasi-two-dimensional electron–hole liquid in shallow SiGe/Si quantum wells is observed experimentally. This fine structure is explained by the occurrence of steps in the density of states resulting from the coexistence of light and heavy holes in the liquid phase and by the interaction of charge carriers with charge-density oscillations in the liquid.     

Percolation and the electron–electron interaction in an array of antidots

A square lattice of microcontacts with a period of 1 μm in a dense low-mobility two-dimensional electron gas is studied experimentally and numerically. At the variation of the gate voltage V _g , the conductivity of the array varies by five orders of magnitude in the temperature range T from 1.4 to 77 K in good agreement with the formula σ(V _g ) = (V _g ?V _g ^* (T))^β with β = 4. The saturation of σ(T) at low temperatures is absent because of the electron–electron interaction. A random-lattice model with a phenomenological potential in microcontacts reproduces the dependence σ(T, V _g ) and makes it possible to determine the fraction of microcontacts x(V _g , T) with conductances higher than σ. It is found that the dependence x(V _g ) is nonlinear and the critical exponent in the formula σ ∝ ? (x - 1/2) ^t in the range 1.3 < t(T, V _g ) < β.     

Formation of hydrogen atom in 2s state in proton–sodium inelastic scattering

The inelastic collision of protons with sodium atoms are treated for the first time within the framework of the coupledstatic and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels(elastic and hydrogen formation in 2s state) are open. In each case, the calculations are carried out for seven values of the total angular momentum l(0≤ l≤ 6). The target is described using the Clementi Roetti wave functions within the framework of the one valence electron model. We use Lipmann–Swinger equation to solve the derived equations of the problem, then apply an iterative numerical method to obtain the code of computer to calculate iterative partial cross-sections. This can be done through calculating the reactance matrix at different values of considered energies to obtain the transition matrix that gives partial and total cross sections. The present results for total hydrogen(2s state)formation cross sections are in agreement with results of other available ones in wide range of incident energy.