Journal of Electron Spectroscopy and Related Phenomena最新文献

We have studied the absolute double differential cross section (DDCS) of electrons ejected from the methane molecule (CH${}_4$) under the impact of highly charged fast projectile ions. The energy and angular distributions of electrons have been measured in interactions with 70 MeV Si${}^{12+}$ ions. These DDCS data together with the derived single differential cross sections and the total cross section (TCS) have been compared with predictions of the continuum distorted wave-eikonal initial state model using different approaches for the molecular orbitals. It has been found that the theories overestimate the measured DDCS values at low ejection energies, which may indicate shortcomings of the model in the case of strong perturbation. At the same time, applying the model to a previous measurement using fast C ions having a lower perturbation strength, excellent agreements have been obtained with the experimental data. Considering the scaling properties, the available TCS data have been plotted with a scaled parameter, namely the perturbation strength, q/v (where q= charge state, v=velocity of the projectile). The KLL Auger e-emission as well as the KLL hyper-satellite peaks are analyzed for different emission angles. The double K-vacancy production shows a considerable enhancement i.e. 37% of the single production cross section which is consistent with some of the recent experiments on K-ionization using x-ray techniques.

The application of a potential model to the analysis of differences between the Auger parameters of InSb and the elemental materials yields a value $1.82\pm 0.07\AA$ for the core hole screening distance in InSb. It also yields a value of 0.22 ± 0.49 e for the charge transfer in InSb. Shifts in the Auger parameters of elements between their metallic states and in a compound semiconductor are interpreted using a novel method based on quantifying atomic core potential, as a quantum mechanical observable, in terms of its dependence on the valence charge and the number of atomic core holes. The core hole screening distance is $\sim 30\%$ larger than half the interatomic distance between the nearest neighbors and, by the equivalent cores model, is expected to be the screening radius of Sn and Te impurities in InSb.

The radiative and Auger decay of K-shell hole states of argon ions with configuration 1s2s^m2pⁿ3 s²3p⁶ (m=0–2; n = 0–6) are studied theoretically using the flexible atomic code. The effect of L-shell spectator vacancies on the competition of filling the K, L₁, and L₂₃ vacancies is discussed for the first time. We find the K or L₁ vacancy is preferred to be filled first when there is 0 or 1 vacancy in the L₂₃ shell, but the L₂₃ vacancy becomes the priority when the number of the L₂₃ vacancies is larger than 2, and the total branching ratio of the L₂₃ vacancy is as high as 66.98%, 74.66%, and 80.95% when the L₂₃ shell has 4 vacancies and there are 2, 1 and 0 vacancies in the L₁ shell, respectively. In addition, the natural widths of the K, L₁, and L₂₃ vacancies with different L-shell vacancy distributions are also calculated. The results show that they all first increase and then decrease with the number of L₂₃ vacancies. It is expected that the present study will be useful for the qualitative analysis of the decay processes of multiple hole states, the understanding of ion yields and the production of satellites in x-ray and Auger spectra.

The magnetic circular X-ray dichroism (XMCD) in X-ray absorption spectroscopy (XAS) is extensively used to monitor the response of a magnetic system to an external perturbation. Application of a static external electric field to control its magnetic properties may just lead to a charge rearrangement or to a steady electric current dependent on the geometry. As it is demonstrated, the first situation can be handled with minor modifications of the standard well established schemes to calculate XAS and XMCD spectra. For the second case, however, more advanced schemes have to be used that account for the steady-state out-of-equilibrium situation. It is shown, that this can indeed be achieved by making use of the Keldysh non-equilibrium Green function formalism that allows in particular to express the X-ray absorption coefficient in terms of the corresponding greater Green function $G^{>}\left(E\right)$. As an alternative approach, a bi-linear response formalism is presented that can be used to calculate the modification of the XMCD spectra due to the electric field directly.

The second derivative mode of peak analysis in electron energy loss spectroscopy (EELS) in a Transmission Electron Microscope (TEM) has been quantitatively evaluated in terms of the accuracy of the method. This includes a demonstration of the importance of the second derivative peak width, the second order dependency of the accuracy upon that peak width and effect of high frequency noise in the spectra. It is shown that while the second derivative method is an efficacious and powerful mode of analysis, there are limitations in terms of the number of significant digits in both the spectral values and derived electronic quantities. The case of uranium N_4,5 spectral peaks and the 5f population is presented as an example, with UO₂ X-ray Absorption Spectroscopy used as a benchmark.

This work focuses on the EXAFS investigation of the local environment of lead and iron sorbed onto volcanic ash materials previously studied using XANES technique. Different compounds found in the composition of volcanic ash were used as the models in the EXAFS fitting procedure of the experimental EXAFS spectra collected at the Fe K edge and Pb L3 edge in the Fe- and Pb-sorbed volcanic ash samples. The results showed two types of interactions involving in the adsorption process of both samples. The first is related to iron or lead absorber with oxygen atoms in the first coordination shell. The second interaction occurred between the absorbers (Fe or Pb) and the backscatters (Fe or Pb) in the second shell. The local environment of the iron-sorbed element may have a cubic geometry with different crystallographic sites related to oxygen and iron atoms. On the other hand, the lead-sorbed element may be in orthorhombic geometry with different sites related to oxygen atoms and lead atoms. The adsorption mechanisms involved in the process of iron and lead sorption are ion exchange with probable chemisorption for iron and microprecipitation for lead.

Spectroptychography is being used to realize a significant improvement in the spatial resolution of x-ray spectromicroscopy, allowing chemical microanalysis at finer spatial scales. The chemical sensitivity of near edge X-ray absorption fine structure (NEXAFS) is familiar to most researchers who use x-ray spectromicroscopy for chemical microanalysis. However, the additional phase information available through ptychography provides additional and tantalizing data, and potentially additional chemical information. This paper explores the chemical information available in phase for a system of silicon dioxide nanospheres.

The F, C, O, and N elemental distribution maps at the exfoliated surfaces of Cu plate after peeling the fluoropolymers from Fluorinated ethylene propylene (FEP)/Cu and Perfluoroalkoxyalkane (PFA)/Cu pieces which were bonded by plasma treatment including amino acid were performed by microscopic synchrotron radiation (SR)　spectroscopic imaging measurements. The spatial elemental distribution pattern of exfoliated Cu after peeling PFA/Cu piece was not detectable by scanning electron microscopy with energy dispersive X-ray spectroscopy imaging alone, was revealed by SR-based soft X-ray microspectroscopy. We also obtained the microprobe X-ray fluorescence spectra and microprobe near-edge X-ray absorption fine structure spectra. Based on these measurement results, it is considered that the delamination of FEP/Cu piece mainly caused by resin failure, while the delamination of PFA/Cu is caused by interfacial delamination in addition to resin failure. The Hard X-ray photoelectron spectroscopy was also performed to confirm that the bonding via nitrogen is formed. Our SR-based analyses provided confirmation that fluoropolymers and Cu plates are bonded by N-mediated chemical bonding. The present study insists that the technique and plasma bonding process reported are expected to contribute to the development of new devices and systems consisting of fluoropolymers and metals.

Calcium plays an important role in the physiology of bacterial cells and as a free soluble form inside the cells, it is tightly regulated at a low concentration. However, much higher amounts of stored calcium exist within cells and can be remobilized at diverse occasions. As a consequence, there has been a variety of techniques developed to quantitatively map the different forms of Ca in cells. Here we show how scanning transmission x-ray microscopy (STXM), a synchrotron-based microscopy technique, conducted in the soft x-ray range at the Ca L_2,3 edges (340–360 eV) offers an original and informative quantitative view of different Ca reservoirs in bacterial cells at a spatial resolution better than 100 nm. To illustrate this, we analyzed mutants of the cyanobacterium Synechococcus elongatus PCC 7942, overexpressing different versions of a gene called ccyA from two phylogenetically distant cyanobacteria: Gloeomargarita lithophora and Synechococcus sp. PCC 6312. This gene is diagnostic of the capability of some cyanobacteria to form intracellular amorphous calcium carbonate (iACC) but its function remains unknown. Here we show that the overexpression of the ccyA gene in the iACC non-forming cyanobacterium S. elongatus PCC 7942 results in an increased Ca content, especially in some Ca-rich cells. Moreover, we show that STXM can discriminate four different reservoirs of Ca in cyanobacteria and provides quantitative assessment of their relative importance.

Dissociative electron attachment (DEA) to 1-chloroanthracene and 9-chloroanthracene was investigated under gas-phase conditions. In both compounds, the elimination of the chlorine anion is the dominant channel for the dissociation of molecular negative ions (NIs). The second most intense channel leads to the formation of molecular anions (Mˉ). The autodetachment lifetime of Mˉ was measured to be about 170 μs for both compounds. The widths of the Mˉ peaks indicate that molecular anions are formed via two resonances: at thermal electron energies and through a shape resonance at the energy of ∼0.5 eV. Adiabatic electron affinities were estimated in the framework of the simple Arrhenius model to be 0.86 eV for both molecules, the values being close to the theoretical predictions by DFT method of 0.90 eV and 0.93 eV for 1-chloroanthracene and 9-chloroanthracene respectively. Metastable negative ions are observed in the DEA spectra of both molecules, which testifies that the elimination of chlorine anions from molecular NIs appears on a time scale of several microseconds.