A detailed experimental investigation of the KMM + KMN + KNN Auger electron spectrum of Cd from the EC-decay of In

KMM, KMN and KNN Auger electron spectra of ¹¹¹Cd emitted in EC-decay of ¹¹¹In were analyzed at instrumental resolutions of 14 and 21 eV using a combined electrostatic spectrometer. Energies and relative intensities of 26 resolved components were determined and compared with theoretical predictions. For the first time, the predicted intermediate coupling structure of some KMM Auger lines was observed. A structure of the KNN Auger group for Z < 54 was resolved for the first time. Relative intensities of the KMM, KMN and KNN Auger groups were also determined.     

15～600 keV脉冲硬X射线能谱测量

介绍了基于吸收法的脉冲硬X射线能谱测量的基本原理及设计思路,完成了探测器及吸收片的选型,设计了射线准直系统,研究了散射对测量的影响,以12路PIN探测器阵列及铜、铝吸收片为测量核心部件研制了脉冲硬X射线能谱测量系统。实验测量了真空环境下“闪光二号”加速器串级二极管产生的脉冲硬X射线强度,获得了不同衰减程度的实验波形,通过解谱获得了脉冲硬X射线的能谱,光子最高能量约600 keV,平均能量约89.1 keV,与理论计算的结果比较符合。     

The KLL Auger spectrum of neon from the EC-decay of Na

The low energy KLL Auger electrons of neon emitted after EC-decay of ²²Na have been investigated with a 4 eV instrumental resolution using an electrostatic spectrometer and a solid state radioactive source. This is the first experimental investigation of the KLL Auger spectrum of neon from the solid state. Relative intensities and energies of all resolved spectrum components were determined. Measured absolute energy of the dominant KL₂L₃(¹D) transition was found to be 824.5(19) eV, i.e. about 20 eV higher than that obtained in experiments with free Ne atoms. Within the experimental uncertainties, no influence of solid state effects on relative intensities of the KLL transitions was found.     

Mass attenuation coefficient of saccharides for X-rays in the energy range from 8 keV to 32 keV

Mass attenuation coefficients have been measured for mono and disaccharides at photon energies 8.136, 13.596, 17.781, 22.581 and 32.890 keV. The measured values are compared with the computed values obtained using personal computer software package WinXCOM. The agreement between the two is within −5.3% to 3%.     

Coverage effects on the adsorption of sulfur on Co(0 0 0 1): A DFT study

The adsorption of sulfur on Co(0 0 0 1) was studied using density functional theory calculations at coverage from 0.11 ML to 1.0 ML. Calculated results indicate that atomic S favors in hollow sites with bond S–Co dominated at lower coverage and at higher coverage the strong adsorbate S–S interaction leads to the formation of S₂ species. It was shown that the adsorption energy generally increases (gets weaker) with the coverage in a near linear fashion for the most stable configurations. In addition, modification of the surface electronic properties has been discussed and some discrepancy are found between our calculations and the findings of O adsorption on Au(1 1 1) and Pt(1 1 1) surfaces.     

Direct decomposition of nitrogen monoxide over a K-deposited Co(0 0 0 1) surface: Comparison to K-doped cobalt oxide catalysts

The influence of deposited potassium on the oxidation and NO reactivity of a Co(0 0 0 1) surface was studied using X-ray photoelectron spectroscopy. The formation of surface CoO was observed when the clean Co(0 0 0 1) surface was exposed to O₂ at 500 K. In contrast, the Co atoms on the K-deposited Co(0 0 0 1) surface remained at a lower oxidation state, CoO_x (0 < x < 1). No adsorption or dissociation of NO occurred on the CoO/Co(0 0 0 1) surface at 320 K, whereas a NO₂⁻ species formed on the oxidized K/Co(0 0 0 1) surface. This species is considered to be an intermediate in NO decomposition. It was concluded that the role of potassium was (i) to form the NO₂⁻ intermediate, and (ii) to keep the Co surface partially oxidized (CoO_x) as the active site for the dissociation of the NO₂⁻ species.     

Determining the structure of Ru(0 0 0 1) from low-energy electron diffraction of a single terrace

While a perfect hcp (0 0 0 1) surface has threefold symmetry, the diffraction patterns commonly obtained are sixfold symmetric. This apparent change in symmetry occurs because on a stepped surface, the atomic layers on adjacent terraces are rotated by 180°. Here we use a low-energy electron microscope to acquire the threefold diffraction pattern from a single hcp Ru terrace and measure the intensity vs. energy curves for several diffracted beams. By means of multiple scattering calculations fitted to the experimental data with a Pendry R-factor of 0.077, we find that the surface is contracted by 3.5(±0.9)% at 456 K.     

A DFT study of the transition metal promotion effect on ethylene chemisorption on Co(0 0 0 1)

Transition metals are often introduced to a catalyst as promoters to improve catalytic performance. In this work, we study the promotion effect of transition metals on Co, the preferred catalytic metal for Fischer–Tropsch synthesis because of its good compromise of activity, selectivity and stability, for ethylene chemisorption using density functional theory (DFT) calculations, aiming to provide some insight into improving the α-olefin selectivity. In order to obtain the general trend of influence on ethylene chemisorption, twelve transition metals (Zr, Mn, Re, Ru, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au) are calculated. We find that the late transition metals (e.g. Pd and Cu) can decrease ethylene chemisorption energy. These results suggest that the addition of the late transition metals may improve α-olefin selectivity. Electronic structure analyses (both charge density distributions and density of states) are also performed and the understanding of calculated results is presented.     

3 to 15 keV Ar+ induced Auger electron emission from Si and Ar

Ar⁺ induced Auger electrons from Si and Ar were investigated at bombardment energies between 3–15 keV and target currents of a few μA. The Auger electron yields were compared with secondary ion yields of Si and Ar by simultaneous SIMS-AES measurements. In the ion induced Auger spectra of Si five Auger peaks and in the Ar spectra three Auger peaks were observed. The ion induced Auger electron yield of Si and Ar were found to be strongly dependent upon the primary ion energy. “Bulk like” and “atomic like” Auger transitions of ion induced Auger electrons of Si were observed.     

The structure and lattice dynamics of RbBr(1 0 0) and RbI(1 0 0) single crystal surfaces: A tensor low energy electron diffraction analysis

The structure and lattice dynamics of RbBr(1 0 0) and RbI(1 0 0) single crystal surfaces cleaved under UHV conditions were investigated by means of low energy electron diffraction (LEED) at temperatures of 156 K and 183 K, respectively. Since RbBr and RbI are insulators the experiments were carried out with a microchannel plate LEED system at very low primary currents (5 nA). For both materials four different diffraction orders could be observed. Diffraction patterns were recorded over an energy range from 30 eV to 220 eV in increments of 2 eV and I(V) curves for each spot were extracted. The I(V) curves were analyzed using the tensor LEED approach. For both alkali halide substrates surface structures of (1 × 1) periodicity close to the truncated bulk structure were found. For RbBr, the first interlayer distance is reduced by about 2.2%, where the Rb⁺ cations in the topmost layer are shifted inwards by 0.06(3) Å, and the anions also exhibit an inward shift which is however smaller (0.04(3) Å). The root mean square vibrational amplitudes are enlarged by a factor of 1.3 for Rb⁺ and 1.25 for Br⁻, respectively. For RbI(1 0 0) the cations of the topmost layer are shifted inwards by 0.07(3) Å and the anions outwards by 0.02(1) Å. The vibrational amplitudes of the ions are not enlarged as for RbBr but close to the corresponding bulk values.     

Analysis of the rotational spectrum of pyruvonitrile up to 324 GHz

The room-temperature rotational spectrum of pyruvonitrile (acetyl cyanide, CH₃COCN) was measured up to 324 GHz, and additional measurements were also made in supersonic expansion in the region 7-19 GHz. The available data sets for the A and E torsional sublevels were extended to over 1200 transitions, J = 65 and K_a = 38 for the ground vibrational state, and to comparable numbers of transitions for first excited states of the methyl torsional mode ν₁₈, and the in-plane CCN bending mode ν₁₂. The collected experimental measurements were fitted with several different computer programs for dealing with the effects of methyl torsional motion on the rotational spectrum and many spectroscopic constants have been determined. The experimental results are discussed in detail and are augmented by ab initio computations. Stark effect measurements in supersonic expansion were used to precisely determine the electric dipole moment of pyruvonitrile, ∣μ_a∣ = 2.462(2) D, ∣μ_b∣ = 2.442(2) D, μ_tot = 3.468(2) D. Pyruvonitrile, as an 8-atom molecule with a sizable dipole moment, is a possible candidate for astrophysical detection and the present work provides the laboratory data necessary for that purpose.     

Structural and magnetic properties of BCC Fe/Co (0 0 1) superlattices

In thin layered Fe/Co (0 0 1), grown on MgO (0 0 1), both Fe and Co crystallize in the body-centered cubic (BCC) structure, as seen in a series of superlattices where the layer thickness of the components is varied from two to twelve atomic monolayers. These superlattices have novel magnetic properties as observed by magnetization and polarized neutron reflectivity measurements. There is a significant enhancement of the magnetic moments of both Fe and Co at the interfaces. Furthermore, the easy axis of the system changes from [1 0 0] for films of low cobalt content to [1 1 0] for a Co content exceeding 33%. No indication of a uniaxial anisotropy component is found in any of the samples. The first anisotropy constant (K₁) of BCC Co is found to be negative with an estimated magnitude of 110 kJ/m³ at 10 K. In all cases, the magnetic moments of Fe and Co have parallel alignment.     

The effect of defects on the hydrogenation in Mg (0 0 0 1) surface

Density-functional theory was presented to investigate the hydrogen dissociation on a pure, Pt-doped, vacancy and oxide Mg(0 0 0 1) surface. Our results show that the energy barriers are 1.05, 0.39, 0.93 and 1.33 eV for H₂ dissociation on the pure, Pt-doped, vacancy and oxide Mg surface, respectively. The calculation results imply that the initial dissociation of H₂ is enhanced significantly for the Pt-doped Mg(0 0 0 1) surface, negligible for the vacancy model and weekend for the oxide model. The density of state results shows that, following the dissociation reaction coordinate, the H–H interactions are weeker for the Pt-doped model while interactions become stronger for the oxide model. It is suggested that the dissociation process is facilitated when Pt atom acts as catalyst and oxide overlayers delay hydrogen adsorption on the Mg layer. The present study will help us understand the defect role being played for the improvement or opposition effect in absorption kinetics of H₂ on the Mg(0 0 0 1) surface.     

Nonlinear magnetoelastic effects in ultrathin epitaxial FCC Co(0 0 1) films:: an ab initio study

Those linear and nonlinear magnetoelastic coupling coefficients which determine the magnetostrictive stress and the strain-induced out-of-plane magnetic anisotropy in epitaxially grown FCC Co(0 0 1) films are calculated by the ab initio density functional electron theory. The nonlinear couplings have a strong effect on the change Δσ₁^m of the in-plane magnetostrictive stress resulting from a change of the magnetization direction from [0 1 0] to [1 0 0], but a negligibly small effect on the out-of-plane anisotropy e_MCA. The calculations confirm the experimental result that the measured out-of-plane anisotropy cannot be totally attributed to volume magnetoelastic effects. Estimates are given for the nonlinear magnetoelastic coupling coefficients m₁^γ,2 and m₂^γ,2.     

Monte carlo simulations of low-energy (<10eV) electron transmission and reflection experiments: application to solid xenon

A Monte Carlo method is developed for simulating low-energy (< 10 eV) electron-impact transmission and reflection experiments. This method is applied to test the results obtained with various electron transport models which have recently been proposed for the interpretation of these experiments on thin solid xenon films. Particular attention is given to the critical examination of the adequacy of the assumption of isotropy of the collisions which is generally used in these models to calculate the various electron transport parameters, such as the elastic and inelastic electron scattering mean free paths. The simulation is also used to predict both the variation of the electron current transmitted through the films with the incident angle of the electron beam and the angular distribution of the reflected electrons.     

Coincidence mass spectrometry study of double ionization of anthracene by 70 eV electron impact

The European Physical Journal D - To improve the quality of optical imaging, this paper proposes a ghost imaging method based on multi-frequency fusion. First, filter is used to decompose the...     

Exchange coupling of Co/Cr(0 0 1) superlattices for in-plane and perpendicular anisotropy

We have investigated the exchange coupling of Co/Cr(0 0 1) superlattices by polar and longitudinal magneto-optical Kerr effect measurements, by varying both the Co and Cr film thicknesses. At a Co thickness of ≈10 Å a nearly perpendicular anisotropy is found with antiferromagnetic order in the range of 5–15 Å of Cr thickness. For these superlattices the magnetization curve starting from remanence to saturation is characterized by a surface spin-flip transition at low field, followed by domain wall nucleation and motion, and finally by a coherent spin rotation with increasing field. Antiferromagnetic coupling is also observed for superlattices with thicker Co layers and with in-plane magnetic anisotropy.