Journal of Electron Spectroscopy and Related Phenomena最新文献

Photoelectron spectroscopy (PES) investigation of two widely used herbicide compounds MCPA and 2,4-D is reported. The GW calculations are shown to offer a good description of their electronic structure. There is excellent agreement between the experimental and theoretical energies of the HOMO states of 2,4-D and MCPA, which are at 8.7 eV and 8.5 eV binding energy, respectively. The low energy tail of the HOMO state extends to about 8 eV. The good agreement between the UPS (ultraviolet photoelectron spectroscopy) spectra and the simulation validates the proposed conformer. The presented gas phase data will help researchers to analyze data from liquid and diluted samples of these herbicide molecules and perform additional theoretical modelling.

We have investigated the laser induced ultrafast dynamics of Gd 4f spins at the surface of Co_xGd_100-x alloys by means of surface-sensitive and time-resolved dichroic resonant Auger spectroscopy. We have observed that the laser induced quenching of Gd 4f magnetic order at the surface of the Co_xGd_100-x alloys occur on a much longer time scale than that previously reported in “bulk sensitive” time-resolved experiments. In parallel, we have characterized the static structural and magnetic properties at the surface and in the bulk of these alloys by combining Physical Property Measurement System (PPMS) magnetometry with X-ray Magnetic Circular Dichroism in absorption spectroscopy (XMCD) and X-Ray Photoelectron spectroscopy (XPS). The PPMS and XMCD measurements give information regarding the composition in the bulk of the alloys. The XPS measurements show non-homogeneous composition at the surface of the alloys with a strongly increased Gd content within the first layers compared to the nominal bulk values. Such larger Gd concentration results in a reduced indirect Gd 4f spin-lattice coupling. It explains the “slower” Gd 4f demagnetization we have observed in our surface-sensitive and time-resolved measurements compared to that previously reported by “bulk-sensitive” measurements.

Model exchange potentials are particularly interesting to account for the indistinguishability between the projectile and target electrons in electron-atom scattering in vacuo and plasma environments. It is well known that their performance is pretty satisfactory in the high energies but also that discrepancies from the results obtained with exact exchange are found toward the zero energy limit. In this article, we examine how well established model exchange potentials based on the free electron gas approach compare to phase shifts calculated considering exchange in exact form. In particular, we show that the Hara and the semiclassical exchange potentials are able to reproduce reference low energy phase shifts through a simple scale transformation, in opposition to the previous approaches where energy dependent corrections to the local momentum were adopted. We provide the scale factors and phase shifts for electron scattering by He, Ne and Ar atoms for $k<$ 1,0 a${}_0^{-1}$. Such scaling factors can be determined reproducing the scattering length and the number of s-wave bound states from exact exchange calculations. We also show that the scaling procedure works for electronic densities that present the physically correct asymptotic behavior. The present results are important to the research field, since they form the basis to construction of scattering models based on optical potential approaches.

Earlier study of exchange-correlation functionals for the calculations of outer-valence ionization potentials of 31 molecules shows that our Density Functional Theory (DFT) method called ∆PBE0(SAOP) performs very well except for the three perhalogenated molecules included in the study. The present work expands the study to 85 molecules including 40 containing halogens. Analysis of a total of 500 vertical ionization potentials (VIPs) confirms that ∆PBE0(SAOP) continues to excel for nonhalogenated molecules with an average absolute deviations (AAD) of 0.19 eV and reveals that the best method for halogenated molecules is ∆mPW1K(SAOP) with an AAD of 0.21 eV.

The analysis of X-ray photoelectron spectra often faces challenges due to the lack of standardization in modeling approaches, background subtraction methods, and computational algorithms within the field of computer science. The interpretation of XPS data significantly relies on the unique expertise and judgment of individual researchers. Therefore, the objective of this study is to highlight the difficulties associated with analytical methods that depend heavily on the discretion of individual scientists, to elucidate the prevailing models and background subtraction techniques, and to suggest improvements to these methodologies. This endeavor aims to enhance the reliability and reproducibility of XPS analysis, thereby contributing to the advancement of research in this area. By utilizing the information criterion as part of a thorough search methodology in Bayesian inference, we show that our sophisticated analytical techniques significantly outperform others in the analysis of actual X-ray photoelectron spectroscopy (XPS) spectra. This improvement is evidenced through enhanced accuracy and reliability in spectral interpretation, underscoring the efficacy of our methods in practical applications of XPS.

Manganese oxides (MnOx) are used as electrode materials in many different energy storage applications such as batteries and supercapacitors. X-ray spectromicroscopy, using near edge X-ray absorption spectra (NEXAFS) for chemical speciation, is a powerful tool to study reduction and oxidation processes in such systems. High quality reference spectra are required for both qualitative identification and quantitative mapping of MnOx species. Here we present accurate, quantitative Mn 2p and O 1s NEXAFS spectra of MnO, MnSO₄, Mn₃O₄, Mn₂O₃, α-MnO₂, β-MnO₂, and KMnO₄, measured using both transmission and total electron yield X-ray absorption techniques. An example of the use of these reference spectra in a study of Zn/MnO₂ batteries is given.

X-ray photoelectron spectroscopy (XPS) is a surface analysis technique for the nondestructive identification of elemental species and chemical states of solid samples, and the measured spectra are affected by not only sample-specific information but also factors dependent on the measurement environment. This feature makes it difficult to analyze the data for the chemical state identification of mixed samples when referring to the data measured with different models or in different environments. In a previous study, Bayesian inference was successfully applied to the analysis of XPS narrow-scan spectra, but the challenge was to apply Bayesian inference to XPS spectra of samples that are nonuniform in the depth direction. We propose a method to infer the layer structure of a sample from XPS spectra by incorporating Bayesian inference into the simulation of electron spectra for surface analysis (SESSA). SESSA can simulate XPS spectra of samples with specified composition and microstructure, and is already in use as a simulator with highly reproducible results. By utilizing the proposed method, one can estimate the layer structure of a sample from XPS data on the basis of the posterior probability distribution. In a typical XPS measurement, wide-scan data are acquired to qualitatively identify elemental species, and narrow-scan data are acquired to the estimate detailed composition and chemical state information of a sample. In this study, we have shown that given wide-scan or narrow-scan data without angle resolution, Bayesian inference can be applied to quantitatively analyze the layer structure information.