Journal of Electron Spectroscopy and Related Phenomena最新文献

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.

In the present work, the Hf target was irradiated by tuning the energy (E_p) of synchrotron radiation across the L_i (i = 1–3) edge-energies ranging from 9.6 keV to 14.0 keV in order to measure the cross sections for production of the fluorescent L_k X-rays (k = l, α, η, β_1,6, β₃, β₄, β_2,15, β_5,7, β_9,10, γ_1,5, γ_2,3,6,8, γ₄). These measurements were performed with the aim to check the validity of independent particle approximation (IPA) models at incident photon energies in proximity to the L_i absorption edges of a heavy transition element. The measured cross sections were compared with three sets of values calculated using the X-ray emission rates based on the Dirac-Fock model, the L_i (i = 1–3) sub-shell photoionization cross-sections based on the non-relativistic Hartree-Fock-Slater model and three sets of the fluorescence (ω_i) and Coster-Kronig (f_ji) yields.

The calculated asymmetry parameter ($\beta$) and photoionisation cross sections for eight outermost orbitals ($1e_{1g}$, $3e_{2g}$, $1a_{2u}$, $3e_{1u}$, $1b_{2u}$, $2b_{1u}$, $3a_{1g}$, and $2e_{2g}$) of benzene, in the gas phase, are presented in the range from threshold to 35 eV. The Schwinger Variational Method with Padé approximants was employed to generate the continuum wavefunction of photoelectrons and the dipole matrix transition was computed in the velocity ($V$) and length ($L$) approach of the dipole operator. This operator in $V$ or $L$ form does not affect significantly $\beta$ values in the energy range studied. The cross sections in $V$ form produce lower magnitudes than $L$ and are closer to the measurements. The resonance peaks were observed in the cross sections for some orbitals and their positions were not affected by the dipole approach. Finally, symmetry analysis is done on the partial cross sections to assign the main contributing final state to the resonance feature and also link this to the minimum in the asymmetry parameter. The comparison of our results with other theories has, in general, good qualitative and some quantitative agreement. For some orbitals ($1a_{2u}$, $2b_{1u}$), severe disagreements between theory and experiment are highlighted. Some possible causes for these differences are pointed out. Because of this, we conclude that some asymmetry parameters and PICS for benzene, in ionisation studies, cannot yet be considered as a benchmark and will be necessary further investigation to clarify such discrepancies.

Circular dichroism angle-resolved photoemission spectroscopy (CD-ARPES) receives much attention due to a resolving power of topological and quantum geometrical nature of two-dimensional systems. We propose the Lippmann-Schwinger photoelectron final state, a scattering solution of the lattice model comprising screened short-range potentials at periodically arranged atomic sites, which characterizes the time-reversed low energy electron diffraction (LEED) state well enough to describe the final state effect entailed in CD-ARPES. We find that, through the final state effect, the electron screening length identifies CD-ARPES not only in the qualitative dichroic polarity but also in the quantitative dichroic strength in various graphene systems like the monolayer graphene, the AA-stacking bilayer graphene, and the twisted bilayer graphene especially in a unified fashion. This finding reveals an interplay between electron screening and circular dichroism and enables to extend the spectroscopic expertise of CD-ARPES to a direct probe of the electron screening.