Journal of Electron Spectroscopy and Related Phenomena最新文献

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.

The vertical, valence ionization energies of some [12]circulenes (C₄₈H₂₄) topoisomers have been calculated as free molecules in the gas phase using high-level ab initio coupled-cluster method: EOM-DLPNO-CCSD. Their valence electronic structures depend on molecular topology. We have used calculated vertical, valence ionization energies to simulate their UV photoelectron spectra (UPS). HOMO-LUMO bandgaps and the influence of molecular topology on the spectra were also studied. Our results indicate the presence and importance of stabilizing intramolecular π-π stacking interactions and molecular distortion (via strain energy) on electronic structures and UPS spectra. For example, the HOMO ionization energy increases along the sequence: infinitene<Möbius<Kekulene. The results presented may help in identification and analysis of photoelectron spectra of circulenes which can not be obtained in the gas phase, but rather as adsorbed molecules on metal surface.

We present a theoretical study for electron and positron-impact ionization of water molecule by using the three-body formalism of distorted-wave approximation. In this approximation, the final state contains one-Coulomb, two-Coulomb, and three-Coulomb distortion due to pairwise Coulombic interactions, respectively. In the entrance channel, the initial state is a product of two wavefunctions: the first one for the incident electron/positron described by a Coulomb wave and the second one for the ten bound electrons. The molecular wavefunction for these bound electrons of $H_{2}O$ are described by the linear combination of atomic orbitals. We investigate the angular distribution of the triple differential cross section (TDCS) for single ionization of the outer orbitals $1b_1,3a_1,1b_2$, and $2a_1$. The structure with two peaks around the binary and recoil region are clearly observed for $1b_1$, $3a_1$, and $1b_2$ orbitals. At the same time, a single peak in the binary region with no recoil peak is found for the $2a_1$ orbital. The present TDCS results are compared with available experimental and theoretical findings. Fair agreement regarding the structure of angular profile of the TDCS is observed for all orbitals except $2a_1$. Finally, an enhanced TDCS have been found for positron impact compared to the electron impact.

We investigate in the present paper the doubly excited ${}^1{P}^o$ states in the C${}^{4+}$ ion. We report highly accurate results of their energy positions in the energy spectrum, their lifetimes and the x-ray photon energies required to populate them and observe their autoionization. The results were obtained by using our B-spline based spectral approach combined with the complex rotation method that has proven its effectiveness in the detection of the doubly excited states in the O${}^{6+}$ [1] and Li${}^{+}$ [2] ions. We also report in the paper the first results on the characterization and identification of the states that share similar angular correlation pattern, which allows their classification into distinct resonance series.