Inner-shell Excitation Research Articles

Scanning Transmission Soft X-Ray Microscopy Probes Topical Drug Delivery of Rapamycin Facilitated by Microneedles.

Scanning Transmission X-ray microscopy (STXM) is a sensitive and selective probe for the penetration of rapamycin which is topically applied to human skin ex vivo and is facilitated by skin treatment with microneedles puncturing the skin. Inner-shell excitation serves as a selective probe for detecting rapamycin by changes in optical density as well as linear combination modeling using reference spectra of the most abundant species. The results indicate that mechanical damage induced by microneedles allows this drug to accumulate in the stratum corneum without reaching the viable skin layers. This is unlike intact skin which shows no drug penetration at all and underscores the mechanical impact of microneedle skin treatment. These results are compared to drug penetration profiles of other drugs highlighting the importance of skin barriers. High spatial resolution studies also indicate that the lipophilic drug rapamycin is observed in corneocytes. Attempts in data evaluation are reported to probe rapamycin also in the lipid layers between the corneocytes, which was not accomplished before. These results are compared to recent results on rapamycin uptake in skin where barrier impairment was induced by pre-treatment with the enzyme trypsin and drug formulations leading to occlusion.

Measurement of coherent vibrational dynamics with X-ray Transient Absorption Spectroscopy simultaneously at the Carbon K- and Chlorine L2,3- edges

X-ray Transient Absorption Spectroscopy (XTAS) is a powerful probe for ultrafast molecular dynamics. The evolution of XTAS signal is controlled by the shapes of potential energy surfaces of the associated core-excited states, which are difficult to directly measure. Here, we study the vibrational dynamics of Raman activated CCl4 with XTAS targeting the C 1s and Cl 2p electrons. The totally symmetric stretching mode leads to concerted elongation or contraction in bond lengths, which in turn induce an experimentally measurable red or blue shift in the X-ray absorption energies associated with inner-shell electron excitations to the valence antibonding levels. The ratios between slopes of different core-excited potential energy surfaces (CEPESs) thereby extracted agree very well with Restricted Open-Shell Kohn-Sham calculations. The other, asymmetric, modes do not measurably contribute to the XTAS signal. The results highlight the ability of XTAS to reveal coherent nuclear dynamics involving < 0.01 Å atomic displacements and also provide direct measurement of forces on CEPESs.

Emission Line Intensity Ratios of Fe xxvi/ xxv/ xxiv in Solar Flares Observed by Hinotori

High-resolution spectra observed by the Solar X-ray spectrometer on board the Hinotori mission are revisited. Flat crystals slightly offset to the satellite spin axis produce automatic spectral scans for emission lines emerging from highly charged iron ions in solar flares every half-spin time period. All the downlinked data of the mission are converted to FITS format and major flare spectral data are revived as IDL save files in ISAS/DARTS. Based on these data sets, single-temperature fits are performed for the emission line complex of highly charged iron ions in the wavelength range of 1.75–1.95 Å and compared with theoretical predictions. Synthetic spectra with single electron temperatures estimated from j/w line-intensity ratios fit fairly well for Fe xxiv and Fe xxiii lines in the wavelength range of 1.85–1.88 Å, while intensity ratios of Fe xxv lines (x, y, z) and the inner-shell excitation line of Fe xxiv (q) to the Fe xxv resonance line (w) have systematic excesses. Empirical relations for the observed line ratios are derived. Ion fractions of Fe+25/Fe+24 estimated by intensity ratios of Lyα/w in the temperature range of log T e =7.25–7.45 are consistent with values in ionization equilibrium, and the remaining excesses of the Fe xxv line ratios may suggest problems with the atomic parameters or atomic modeling.

Photon energy dependence of graphene oxide reduction by soft X-ray irradiation and atomic hydrogen annealing

The effects of soft X-ray irradiation and atomic hydrogen annealing on the reduction of graphene oxide (GO) to obtain graphene were investigated. To clarify the interaction between soft X-rays and GO, soft X-rays of 300 eV and 550 eV were used for C 1s and O 1s inner-shell electron excitation, respectively at the NewSUBARU synchrotron radiation facility. Low-temperature reduction of the GO film was achieved by using soft X-ray at temperatures below 150 °C at 300 eV, and 60 °C at 550 eV. O-related peaks in X-ray photoelectron spectroscopy, such as the C–O–C peak, were smaller at 550 eV than those at 300 eV. This result indicates that excitation of the core–shell electrons of O enhances the reduction of GO. Soft X-rays preferentially break C–C and C–O bonds at 300 and 550 eV, respectively.

Cover Feature: Vibrationally Resolved Inner‐Shell Photoexcitation of the Molecular Anion C2− (ChemPhysChem 11/2023)

The Cover Feature The cover illustrates the application of the photon-ion merged-beams method to vibrationally-resolved inner-shell excitation of carbon dimer anions by synchrotron radiation. Cover design by Elisa Monte. More information can be found in the Research Article by Stefan Schippers, Pierre-Michel Hillenbrand, Alexander Perry-Sassmannshausen and coworkers.

Benchmark of GW Methods for Core-Level Binding Energies.

The GW approximation has recently gained increasing attention as a viable method for the computation of deep core-level binding energies as measured by X-ray photoelectron spectroscopy. We present a comprehensive benchmark study of different GW methodologies (starting point optimized, partial and full eigenvalue-self-consistent, Hedin shift, and renormalized singles) for molecular inner-shell excitations. We demonstrate that all methods yield a unique solution and apply them to the CORE65 benchmark set and ethyl trifluoroacetate. Three GW schemes clearly outperform the other methods for absolute core-level energies with a mean absolute error of 0.3 eV with respect to experiment. These are partial eigenvalue self-consistency, in which the eigenvalues are only updated in the Green's function, single-shot GW calculations based on an optimized hybrid functional starting point, and a Hedin shift in the Green's function. While all methods reproduce the experimental relative binding energies well, the eigenvalue self-consistent schemes and the Hedin shift yield with mean absolute errors <0.2 eV the best results.

Generalized oscillator strength of the core-excited states of molecular nitrogen studied by nonresonant inelastic x-ray scattering

Fast electron impact was used to study the generalized oscillator strengths of the inner-shell excitations in atoms and molecules previously. In this work, a nonresonant inelastic x-ray scattering technique is extended to determine the generalized oscillator strengths of $(1{\ensuremath{\sigma}}_{g}\ensuremath{\rightarrow}1{\ensuremath{\pi}}_{g})+(1{\ensuremath{\sigma}}_{u}\ensuremath{\rightarrow}1{\ensuremath{\pi}}_{g})$ inner-shell excitations of molecular nitrogen in the squared momentum transfer range of 0.86 to 14.40 a.u. at a photon energy of about 10 keV and an energy resolution of about 1.3 eV. The present generalized oscillator strength strictly follows the first Born approximation and thus provides a rigorous test to the previously calculated results and the experimental ones measured by the electron energy loss spectroscopy. The presently extrapolated optical oscillator strength at zero momentum transfer is in accord with most experimental results and the theoretical data with the correlation effect considered carefully. This work indicates that the nonresonant inelastic x-ray scattering technique is a powerful tool to study the core excitation mechanism in atoms and molecules.

Probing the delocalized core-hole via inner-shell excitation in N2

The dispute about whether the 1s core-hole is localized on one atom or delocalized over both in a homonuclear diatomic molecule has continued for decades, which has been extensively studied by the photoelectron and electron–ion coincidence spectroscopies. For N2, if the 1s core-hole is delocalized, the K-shell excitation into the 1π g orbital should split into two components, i.e., the dipole-allowed transition from the ungerade 1σ u state and the dipole-forbidden transition from the gerade 1σ g state. However, only the dipole-allowed transition has been observed up to now. Here, we report the inner-shell electron energy loss spectra of N2 at different scattering angles with an incident electron energy of 1500 eV and an energy resolution of 65 meV. The vibrational structures of both the dipole-allowed and dipole-forbidden states of N2 have been identified at different momentum transfers. The splitting between the and states with the reverse symmetry is determined to be 67 ± 7 meV. Moreover, the momentum transfer dependence behavior of the transition intensity ratio agrees with the theoretical predictions, as increasing to a maximum and then decreasing. The experimental observations clearly show that the inner most electrons can be described by 1σ g and 1σ u , which indicates that the inner-shell 1s core-hole of N2 is delocalized over two N atoms based on the excitation process.

Inner-shell excitation in the YbF molecule and its impact on laser cooling

The YbF molecule is a sensitive system for measuring the electron’s electric dipole moment. The precision of this measurement can be improved by direct laser cooling of the molecules to ultracold temperature. However, low-lying electronic states arising from excitation of a 4f electron may hinder laser cooling. One set of these “4f hole” states lies below the A2Π1/2 excited state used for laser cooling, and radiative decay to these intermediate levels, even with branching ratios as small as 10−5, can be a hindrance. Other 4f hole states lie very close to the A2Π1/2 state, and a perturbation results in states of mixed character that are involved in the laser cooling cycle. This perturbation may enhance the loss of molecules to states outside of the laser cooling cycle. We model the perturbation of the A2Π1/2 state to determine the strength of the coupling between the states, the de-perturbed potential energy curves, and the radiative branching ratios to various vibrational levels of the ground state, X2Σ+. We use electronic structure calculations to characterize the 4f hole states and the strengths of transitions between these states and the A2Π1/2 and X2Σ+ states. We identify a leak out of the cooling cycle with a branching ratio of roughly 5×10−4, dominated by the contribution of the ground state configuration in a 4f hole state. Finally, we assess the impact of these results for laser cooling of YbF and molecules with similar structure.

Electron Wave Packet Interference in Atomic Inner-Shell Excitation.

We report the observation of quantum interference between electron wave packets launched from the inner-shell 4d orbital of the Xe atom. Using pairs of femtosecond radiation wave packets from a synchrotron light source, we obtain time-domain interferograms for the inner-shell excitations. This approach enables the experimental verification and control of the quantum interference between the electron wave packets. Furthermore, the femtosecond Auger decay of the inner-shell excited state is tracked. To the best of our knowledge, this is the first observation of wave packet interference in an atomic inner-shell process, and also the first time-resolved experiment on few-femtosecond Auger decay using a synchrotron light source.

Performance of BL07A at NewSUBARU with installation of a new multi-layered-mirror monochromator.

Soft X-rays excite the inner shells of materials more efficiently than any other form of light. The investigation of synchrotron radiation (SR) processes using inner-shell excitation requires the beamline to supply a single-color and high-photon-flux light in the soft X-ray region. A new integrated computing multi-layered-mirror (MLM) monochromator was installed at beamline 07A (BL07A) of NewSUBARU, which has a 3 m undulator as a light source for irradiation experiments with high-photon-flux monochromatic light. The MLM monochromator has a high reflectivity index in the soft X-ray region; it eliminates unnecessary harmonic light from the undulator and lowers the temperature of the irradiated sample surfaces. The monochromator can be operated in a high vacuum, and three different mirror pairs are available for different experimental energy ranges; they can be exchanged without exposing the monochromator to the atmosphere. Measurements of the photon current of a photodiode on the sample stage indicated that the photon flux of the monochromatic beam was more than 1014 photons s-1 cm-2 in the energy range 80-400 eV and 1013 photons s-1 cm-2 in the energy range 400-800 eV. Thus, BL07A is capable of performing SR-stimulated process experiments.

Laser-induced inner-shell excitations through direct electron re-collision versus indirect collision

The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having "drifted away" from the original parent ion.

APPLICATION OF NUCLEAR ANALYTICAL TECHNIQUES IN CHARACTERIZATION OF SEVERAL SAMPLE MATRICES

The existence of elements in major, minor, and even in trace levels could have a significant impact on human health, environmental, industry, or other life sciences. Results of characterization from several matrices of samples could become as valuable and important information since a lot of important decisions regarding public health, environmental protection, and international trade is based on those results. Characterization of several matrices of samples requires excellence, reliable, and complies with ideal criteria as an analytical method. In recent years, nuclear analytical techniques become one of the analytical techniques that could meet the challenge of capability in characterization various matrices of samples and have been proven to be suitable and applicable in a broad range of applications. Nuclear analytical techniques deal with nuclear excitations, electron inner-shell excitations, nuclear reactions, and/or nuclear decay. These techniques are selective with high sensitivity, non-destructive, simultaneous, and limit detection microgram until nanogram level. In this paper, the role and contribution of nuclear analytical techniques used for BATAN research, especially neutron activation analysis (NAA), particle-induced X-ray emission (PIXE), and X-ray Fluorescence (XRF) in the characterization of various matrices of geological, pharmacy, biology and environmental samples were discussed. The comparison with other methods was also carried out. The validations of results were conducted by analysis of standard reference material (SRM). Discussion related optimization of parameter measurement and similar efforts were also presented. The results of this research are hopefully could show and emphasize the significant role of NAT in the characterization of several matrices of samples in contribution and support the life sciences and public welfare.

Theoretical calculations of the mean escape depth of secondary electron emission from compound semiconductor materials

We have performed a systematic Monte Carlo simulation of primary and secondary electron trajectories to predicate the mean escape depth of secondary electron emission for six compound semiconductors, i.e., TiN, VN, GaAs, InAs, InSb, and PbS. Mott's cross section is used for the description of electron elastic scattering in the simulation model, and the full-Penn's dielectric function approach is adopted for the modeling of electron inelastic scattering, where the energy loss function obtained with the optical data is contributed from phonon excitation, interband transition of the loosely bound valance electrons, and inner-shell electron excitations. We have calculated the excitation depth distribution function, emission depth distribution function, and their combining effect in probability depth distribution function at different primary energies for the excited and emitted secondary electrons in these materials. The calculation leads to the primary energy dependence of mean escape depth whose values are found in the range of 0.4–1.4 nm for these materials.

Effect of the Breit interaction on inner-shell electron-impact excitation and subsequent radiative decay of highly charged berylliumlike ions

Effect of the Breit interaction on inner-shell electron-impact excitation and subsequent radiative decay of highly charged berylliumlike ions

On the determination of stopping cross-sections in ion scattering in solids and deviations from standard models

When atomic particles traverse solids they suffer energy losses due to elastic scattering from nuclei and excitation of electron–hole pairs. These are referred to as nuclear and electronic stoppings respectively. In this paper we discuss methods of determining energy losses and ‘stopping’ cross-sections in ion transmission through thin films, as well as in large angle and grazing backscattering from surfaces. This is done on the basis of deterministic simulations of ion scattering by following ion trajectories as they pass through the solid and sample regions of different electron densities depending on the distance from atomic nuclei. The ab initio calculated electron densities in the crystal are used to determine the stopping power, as predicted by the free electron gas model, and including a threshold value for d electron excitation. We discuss some aspects that are not included in standard descriptions based on the use of free electron models and averaged effective electron densities. In this context, we point out the possibility of inelastic processes involving inner-shell excitations, and briefly summarise main findings.

Theoretical models of stopping and ionization of metallic targets and oxydes bombarded by H2 + molecules

SynopsisWe study the vicinage effects in the interaction of H2 + projectiles with C, Al, Si, Al2O3 and SiO2 targets considering the excitation of inner shells. On one side we extend the use of the semiclassical impact-parameter model for the excitation of atomic shells, considering quantum corrections and the role of target screening in the vicinage effects. On the other hand, we adapt our extended wave packet model (EWPM) [3] to the calculation of stopping ratios and ionization cross sections for correlated ions. Lindhard model is used to evaluate valence electrons contributions.

Vibrational effects in the photo-ion yield spectrum of the SiH2+ molecular ion following 2p inner-shell excitation

We report on complementary theoretical and laboratory investigations of the 2p ion yield cross sections for the molecular-ion series SiHn+ (n = 1, 2, 3), in the 95-108 eV photon energy range, below the L-shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatised synchrotron radiation in a merged-beam configuration. The experimental spectra are compared with total photoabsorption cross-sectional profiles calculated using an ab initio configuration interaction method inclusive of spin-orbit coupling and the vibrational dynamics. The experimental results show vibrationally resolved resonances for SiH2+ in the 98-102 eV range. The calculations indicate twenty four core-excited states below the energy of 102 eV, of which only four contribute significantly to the observed spectrum. These states correspond to the excitation of an atomic-like 2p electron to the SiH2+ (5a1) valence orbital.

K-shell photoabsorption and photoionization of trace elements

Context. This is the final report of a three-paper series on the K-shell photoabsorption and photoionization of trace elements (low cosmic abundance), namely F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu, and Zn. K lines and edges from such elements are observed in the X-ray spectra of supernova remnants, galaxy clusters, and accreting black holes and neutron stars, their diagnostic potential being limited by poor atomic data.Aims. We here complete the previously reported radiative datasets with new photoabsorption and photoionization cross sections for isoelectronic sequences with electron number 19 ≤N≤ 26. We also describe the access to and integrity and usability of the whole resulting atomic database.Methods. Target representations were obtained with the atomic structure code AUTOSTRUCTURE. Where possible, cross sections for ground-configuration states were computed with the Breit–PauliR-matrix method (BPRM) in either intermediate orLScoupling including damping (radiative and Auger) effects; otherwise and more generally, they were generated in the isolated-resonance approximation with AUTOSTRUCTURE.Results. Cross sections were computed with BPRM only for the K (N= 19) and Ca (N= 20) isoelectronic sequences, the latter inLScoupling. For the remaining sequences (21 ≤N≤ 26), AUTOSTRUCTURE was run inLS-coupling mode taking into account damping effects. Comparisons between these two methods for K-like ZnXIIand Ca-like ZnXIshow that to ensure reasonable accuracy, theLScalculations must be performed taking into account the non-fine-structure relativistic corrections. The original data structures of the BPRM and AUTOSTRUCTURE output files, namely photoabsorption and total and partial photoionization cross sections, are maintained but supplemented with files detailing the target (NT-electron system, whereNT=N− 1) representations and photon states (N-electron system).Conclusions. We conclude that because of the large target size, the photoionization of ions withN&gt; 20 involving inner-shell excitations rapidly leads to untractable BPRM calculations, and is then more effectively treated in the isolated resonance approximation with AUTOSTRUCTURE. This latter approximation by no means involves small calculations as Auger damping must be explicitly specified in the intricate decay routes.

Evolution of L -shell photoabsorption of the molecular-ion series SiHn+ ( n=1,2,3 ): Experimental and theoretical studies

We report on complementary laboratory and theoretical investigations of the $2p$ photoexcitation cross sections for the molecular-ion series $\mathrm{Si}{{\mathrm{H}}_{n}}^{+}$ ($n=1,2,3$) near the $L$-shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatized synchrotron radiation in a merged-beam configuration. For all three molecular ions, the $\mathrm{S}{\mathrm{i}}^{2+}$ decay channel appeared dominant, suggesting similar electronic and nuclear relaxation patterns involving resonant Auger and dissociation processes, respectively. The total yields of the $\mathrm{S}{\mathrm{i}}^{2+}$ products were recorded and put on absolute cross-section scales by comparison with the spectrum of the $\mathrm{S}{\mathrm{i}}^{+}$ parent atomic ion. Interpretation of the experimental spectra ensued from a comparison with total photoabsorption cross-sectional profiles calculated using ab initio configuration interaction theoretical methods inclusive of vibrational dynamics and contributions from inner-shell excitations in both ground and valence-excited electronic states. The spectra, while broadly similar for all three molecular ions, moved towards lower energies as the number of screening hydrogen atoms increased from one to three. They featured a wide and shallow region below $\ensuremath{\sim}107\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ due to $2p\ensuremath{\rightarrow}{\ensuremath{\sigma}}^{*}$ transitions to dissociative states, and intense and broadened peaks in the $\ensuremath{\sim}107--113\ensuremath{-}\mathrm{eV}$ region merging into sharp Rydberg series due to $2p\ensuremath{\rightarrow}n\ensuremath{\delta},n\ensuremath{\pi}$ transitions converging on the ${L}_{\mathrm{II},\mathrm{III}}$ limits above $\ensuremath{\sim}113\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. This overall spectral shape is broadly replicated by theory in each case, but the level of agreement does not extend to individual resonance structures. In addition to the fundamental interest, the work should also prove useful for the understanding and modeling of astronomical and laboratory plasma sources where silicon hydride molecular species play significant roles.