eV Incident Energy Research Articles

New Data on Autoionizing States of Ne Induced by Low-Energy Electrons from 45 to 64 eV

The lowest single and doubly excited autoionizing states of neon have been studied using a non-monochromatic electron beam and a high-resolution electrostatic analyzer at incident electron energies from 43.37 to 202 (±0.4) eV at three ejection angles, 40°, 90° and 130°. The 2s2p63s(3,1S) and 2s2p63p(3,1P) as well as the 2p43s3p doubly excited states have been observed and their energy determined. The influence of the PCI effect in the energy region of the 2s2p63s(3,1S) states has been investigated. New features in the ejected electron spectra in the low kinetic energy region 3–20 eV at 202 eV incident energy have been observed and assigned.

Non-resonant and resonant X-ray emission at high pressure using a von Hámos setup: the case of FeO

We present a setup exploiting a von Hámos spectrometer in order to study (resonant) X-ray emission of matter exposed to high pressure. The capabilities of this setup are demonstrated for the case of FeO at pressures between 13 GPa and 75 GPa. The setup provides high-quality Kβ 1,3 X-ray emission spectra at high pressures for iron spin state analysis within minutes and iron valence-to-core spectra in less than one hour. Resonant X-ray emission maps can be obtained on a timescale of one hour with 1.0 eV and in approximately 3 hours with 0.2 eV incident energy resolution. Both Kα and Kβ emission can be utilized to gain L-edge and M-edge-like information, respectively, with the option of measuring both simultaneously. The spin state results on FeO between 13 GPa and 75 GPa are in accordance with recent literature. The structural distortion is reflected in both, valence-to-core spectra and resonant X-ray emission maps, which showcase the great potential of the presented setup. The achieved data acquisition times are promising to couple pressure with temperature by laser heating.

Low energy (6-18 eV) electron scattering from condensed thymidine (dT) III: absolute electronic excitation cross sections.

Absolute cross sections (CSs) for electronic excitation by low-energy electron (LEE) scattering, from condensed thymidine (dT) in the 6-18 eV incident energy range, were measured by high-resolution electron energy loss spectroscopy (HREELS). Various electron energy loss (EEL) spectra were acquired using 1 ML of dT condensed on a multilayer film of Ar held at about 20 K under ultra-high vacuum (∼1 × 10-11 Torr). dT is one of the most complex DNA constituents to be studied by HREELS and these spectra provide the first LEE energy-loss data for electronic excitation of a nucleoside. CSs for transitions to the states 13A', 13A'', 23A', 21A', 33A', 23A'', 43A', 33A'', 53A' and 51A' of dT were extracted from the EEL spectra. These states correlate to those previously measured for the thymine moiety. Two broad resonances are observed in the energy dependence of the CSs at around 8 and 10 eV; these energies are close to those found in earlier gas- and solid-phase studies on the interaction of LEEs with dT, thymine and related molecules. A quantitative comparison between the electronic CSs of dT and those of thymine and tetrahydrofuran indicates that no variation is induced in the electronic CSs of thymine upon chemically binding to a deoxyribose group.

Structural properties of protective diamond-like-carbon thin films grown on multilayer graphene

In spite of the versatility of electronic properties of graphene, its fragility and low resistance to damage and external deformations reduce the practical value of this material for many applications. Coating of graphene with a thin layer of hard amorphous carbon is considered as a viable solution to protect the 2D material against accidental scratches and other external damaging impacts. In this study, we investigate the relationship between the deposition condition and quality of diamond-like-carbon (DLC) on top of multilayer graphene by means of molecular dynamics simulations. Deposition of carbon atoms with 70 eV incident energy at 100 K resulted in the highest content of -bonded C atoms. An increase of the number of dangling bonds at the interface between the top graphene layer and the DLC film indicates that decrease of the incident energy reduces the adhesion quality of DLC thin film on graphene. Analysis of radial distribution function indicates that hybridized carbon atoms tend to grow near already existing -atoms. This explains why the quality of the DLC structures grown on graphene have generally a lower content of C atoms compared to those grown directly on diamond. Ring analysis further shows that a DLC structure grown on the -rich structures like graphene contains a higher fraction of disordered ring structures.

Effect of cascade transitions on the polarization of light emitted after electron-impact excitation of Zn by spin-polarized electrons

We investigate the possible effect of cascade transitions from the $(4s5p)\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{0,1,2}$ states to the $(4s5s)\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ state of Zn. The polarization of the light emitted in the subsequent decay to the $(4s4p)\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{0,1,2}$ states has been the subject of recent controversy, with significant disagreement between the experimental data reported by Pravica et al. [Phys. Rev. A 83, 040701 (2011)] and by Clayburn and Gay [Phys. Rev. Lett. 119, 093401 (2017)] in the cascade-free region below $\ensuremath{\approx}7.6$ eV incident energy and relatively good agreement above. The cross sections for excitation of the $(4s5p)\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{0,1,2}$ states, as well as higher-lying triplet states, and the linear polarization of the cascade radiation seem too small to produce a significant alignment of the $(4s5s)\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ state, thereby raising additional questions regarding the origin of the relatively large linear polarizations measured above the cascade threshold.

Excitation of the 2S State of Atomic Hydrogen by Electron Impact

The excitation cross sections of the 2S state of atomic hydrogen at 10 low incident electron energies (10.30 and 54.5 eV) have been calculated using the variational polarized method. Nine partial waves are used to get convergence of cross sections in the above energy range. The maximum of the cross section is 0.137 π a 0 2 at 11.14 eV which is close to the experimental result 0.163 ± 0.2 π a 0 2 at 11.6 ± 0.2 eV. The present results are compared with other calculations, many of them are based on the close-coupling approximation, including the R-matrix method. Differential cross sections at 13.6 eV incident energy have also been calculated. Spin-flip cross sections have been calculated and compared with those obtained using the close-coupling approximation.

Electron collisions with ammonia and formamide in the low- and intermediate-energy ranges

We report an investigation on electron collisions with two nitrogen-containing compounds, namely ammonia (${\mathrm{NH}}_{3}$) and formamide (${\mathrm{NH}}_{2}\mathrm{CHO}$). For ammonia, both theoretical and experimental differential, integral, and momentum-transfer cross sections, as well as calculated grand-total and total absorption cross sections, are reported in the 50--500 eV incident energy range. Calculated results of various cross sections are also reported for energies below 50 eV. Experimentally, angular distributions of the scattered electrons were measured using a crossed electron beam-molecular beam geometry and then converted to absolute differential cross sections using the relative flow technique. Absolute integral and momentum-transfer cross sections for elastic ${e}^{\ensuremath{-}}$-ammonia scattering were also derived from the measured differential cross sections. For formamide, only theoretical cross sections are presented in the 1--500 eV incident energy range. A single-center-expansion technique combined with the method of Pad\'e was used in our calculations. For both targets, our calculated cross sections are compared with the present measured data and with the theoretical and experimental data available in the literature and show generally good agreement. Moreover, for formamide, two shape resonances located at 3.5 eV and 15 eV which correspond to the continuum ${}^{2}{A}^{\ensuremath{'}\ensuremath{'}}$ and ${}^{2}{A}^{\ensuremath{'}}$ scattering symmetries, respectively, are identified. The former can be associated to the ${}^{2}{B}_{1}$ shape resonance in formaldehyde located at around 2.5 eV, whereas the latter can be related to the ${}^{2}E$ resonance in ammonia at about 10 eV. Such correspondence is very interesting and so supports the investigation on electron interaction with small building blocks, instead of with larger biomolecules.

Electron impact excitation of 5p states of rubidium at 20 eV incident energy

The coupled-channel optical method (CCOM) is implemented in this work to study the scattering of electron on rubidium atom at 20 eV. In order to provide a realistic calculation, the continuum effect of the scattering system is accounted by incorporate an ab initio optical potential into the CCOM calculation. The differential cross sections (DCS), as well as the reduced Stokes parameters of 5p excitation are reported and compared to the available experimental and theoretical data.

Ionization of thymine by electron impact: investigation of inner shell orbitals

Triply differential cross section for the ionization of inner orbitals of thymine by electron impact is investigated at low impact energy. Results of first and second Born calculations performed at 250 eV incident energy with coplanar asymmetric geometry are compared with recent experiments. The initial state of the target is described by one single center wavefunction. It is observed that second Born calculations improve substantially the agreement with experiments.

DOPING OF NANO-SIZED DIAMOND LIKE CARBON FILMS AND THEIR CHARACTERIZATION BY MICRO RAMAN SPECTROSCOPY

Capabilities of the rf plasma beam source in deposition of ultra thin diamond like carbon for the hard disk drive applications have been studied. Nano-sized films were doped by nitrogen, hydrogen and silicon and characterized by micro Raman spectroscopy. Projected ranges of incident carbon ions into the magnetic layer as well as growing film were calculated by Monte Carlo simulation. Ion ranges at 100 eV incident energy were around 0.5 nm. With micro Raman spectroscopy is possible to qualitatively determine optimal deposition parameters and to follow changes in the film properties and carbon binding structure in amorphous matrix with hydrogen, nitrogen and silicon doping elements.

DOPING OF NANO-SIZED DIAMOND LIKE CARBON FILMS AND THEIR CHARACTERIZATION BY MICRO RAMAN SPECTROSCOPY

Capabilities of the rf plasma beam source in deposition of ultra thin diamond like carbon for the hard disk drive applications have been studied. Nano-sized films were doped by nitrogen, hydrogen and silicon and characterized by micro Raman spectroscopy. Projected ranges of incident carbon ions into the magnetic layer as well as growing film were calculated by Monte Carlo simulation. Ion ranges at 100 eV incident energy were around 0.5 nm. With micro Raman spectroscopy is possible to qualitatively determine optimal deposition parameters and to follow changes in the film properties and carbon binding structure in amorphous matrix with hydrogen, nitrogen and silicon doping elements.

Dissociative excitation and fragmentation of S8 by electron impact

The vacuum-ultraviolet emission spectrum from 136 nm to 168 nm following the dissociative excitation of a predominantly S(8) target by electron impact at 100 eV incident energy was measured. The relative cross sections for the dominant multiplets at 138.9, 142.9, 147.9, and 166.7 nm are presented. Excitation functions are shown for electron-impact energies from below threshold to 360 eV for the two most prominent emissions at 142.5 nm and 147.4 nm. Five thresholds are clearly apparent in both excitation functions. For the four highest energy channels, the energy separation between the adjacent thresholds is approximately constant and the cross sections reduce regularly as the threshold energies increase. We suggest possible fragmentation pathways of the dissociating S(8) molecule that reproduce the energies of our observed thresholds.

Atomic-Scale Investigation of the Ti/Al(001) Interface: A Molecular Dynamics Simulation

The intermixing characteristics of Ti thin film deposited on Al(001) substrate at atomic level were investigated by molecular dynamics simulation. The intermixing at Ti/Al(001) interface was limited within only the topmost layer of the Al(001) substrate at 300 K with 0.1 eV incident energy of a Ti atom. The mixing characteristics for Ti/Al(001) such as layer coverage function and mixing length were significantly different from those of the transition metals (TM; Fe, Co, and Ni)/Al(001) systems. The different intermixing behavior can be explained in terms of local acceleration and incorporation energy barrier.

Angle-differential Stokes parameters for spin-polarized electron-impact excitation of the Hg6s6p3P1state at25-eV scattering energy

Results of spin-resolved angle-differential Stokes parameters from electron-photon coincidence studies of electron-impact excitation of the 6s6p {sup 3}P{sub 1} state of mercury, resulting in 254 nm radiation, are presented. Due to the intermediate-coupling nature of the excited state, the wave function of this state has a small singlet part. With increasing scattering energy, the influence of exchange scattering decreases, so that direct scattering via the singlet part can become relevant. Recent angle-integrated Stokes-parameter measurements indicated that exchange is still important for the 254 nm line (6s6p {sup 3}P{sub 1}->6s{sup 2} {sup 1}S{sub 0}) up to at least 50 eV incident energy [Juettemann et al., Phys. Rev. A 79, 042712 (2009)]. At energies above 15 eV, however, cascade effects complicate a detailed comparison of these angle-integrated results with theoretical calculations. The angle-differential Stokes parameters presented here are unaffected by cascade effects due to the coincidence technique and thus allow for an analysis of the discrepancies observed by Juettemann et al. and also by Srivastava et al. [Phys. Rev. A 80, 022718 (2009)]. Comparison of the experimental data with theoretical predictions reveals that the description of the initial target state and the excited state in intermediate coupling have a significant influence onmore » the overall agreement.« less

Triple differential cross sections for the electron-impact ionization of helium at 102 eV incident energy

We examine the time-dependent close-coupling (TDCC) approach to electron-impact single ionization of helium and study the convergence properties of our method. As an example, we compare our calculations to recent measurements of the triple differential cross sections from He after 102 eV electron impact, made for asymmetric electron energies and a variety of electron geometries. We find that our calculations compare well to the measurements and to convergent close-coupling calculations.

Spin-resolved electron-impact excitation of the6s6p(J=1)states in mercury

Results of angle-integrated Stokes-parameter measurements for spin-polarized electron-impact excitation of the $6s6p$ $(J=1)$ states in mercury, resulting in 185 and 254 nm radiations, are presented. Due to the intermediate-coupling nature of the two states, exchange effects are visible in both excitation processes. However, their influence on the excitation of the 185 nm line $({^{1}P}_{1}\ensuremath{\rightarrow}{^{1}S}_{0})$ is significant only for energies very close to the excitation threshold of 6.7 eV, whereas exchange is still relevant for the 254 nm line $({^{3}P}_{1}\ensuremath{\rightarrow}{^{1}S}_{0})$ up to at least 50 eV incident energy. Comparison of the experimental data with theoretical predictions reveals a considerable improvement obtained through a fully relativistic 36-state Dirac $R$-matrix (close-coupling) model over a previous 5-state semirelativistic Breit-Pauli $R$-matrix approach. The experimental results at energies above 15 eV for the 254 nm line are likely dominated by cascade effects.

Dissociative excitation ofH2Sby electron impact

Vacuum-ultraviolet emissions following the dissociative excitation of ${\text{H}}_{2}\text{S}$ by electron impact at 100 eV incident energy have been measured. The absolute photoemission cross sections are presented over the wavelength range from 94 to 170 nm and the H, SI, or SII transitions producing the features identified. The measured cross section of the Lyman-$\ensuremath{\alpha}$ emission at 121.6 nm for an electron-impact energy of 100 eV is $(9.79\ifmmode\pm\else\textpm\fi{}0.67)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\text{ }{\text{cm}}^{2}$. Excitation functions of the dominant H and SI emission lines are shown for electron-impact energies from threshold to 300 eV. We study the near-threshold region of the excitation functions and use the measured threshold energies to identify the dominant fragmentation channels.

Emission cross sections for electron-impact excitation of zinc atoms

Experimental and theoretical studies of the electron-impact excitation of the $(4s4p)\text{ }{^{1,3}P}_{1}$, $(4s5s)\text{ }{^{3}S}_{1}$, and $(4s4d)\text{ }^{1,3}D$ states of zinc atoms are reported. Relative emission cross sections were measured from the excitation thresholds to 50 eV incident energy. Theoretical angle-integrated and emission cross sections were obtained using the convergent close-coupling and $B$-spline $R$-matrix methods. The measured data were normalized to theory and are discussed in terms of electron spin and correlation effects. The studies highlight the significance of both channel coupling to the continuum and the inner $3d$-shell electrons.

Ion production by positron impact on H2O

The energy distributions of positrons scattered around 0° from H2O have been measured in coincidence with the remnant ions (H2O+, OH+ and H+) at 100 eV and 153 eV incident energies. The maxima of the distributions (d2σ/dE+dΩ) associated with the production of OH+ and H+ are about 5–10 times smaller than that for H2O+. At both incident energies, a small shoulder has been observed at ∼28 eV in the energy loss spectra associated with H2O+ production possibly arising from a shake-up band associated with the 2a1 orbital. The branching ratios for the H+ and HO+ fragments are also presented.

Comparative study of electron-impact C(1s) core-excitation processes in C 2 and C 2N 2 molecules

Distorted-wave approximation (DWA) is applied to study core-orbital excitations in C 2and C 2N 2 molecules by electron impact. More specifically, we report calculated integral cross sections (ICS) for the X 1 Σ g + → 1 , 3 Π u ( 1 s σ u → 1 p π g ) and X 1 Σ g + → 1 , 3 Π g ( 1 s σ g → 1 p π g ) transitions in the C 2, and X 1 Σ g + → 1 , 3 Π g ( 2 s σ g → 2 p π g ) and X 1 Σ g + → 1 , 3 Π u ( 2 s σ u → 2 p π g ) transitions in the C 2N 2 molecules in the 300–800 eV incident energy range. The comparison of the calculated ICS of these targets with the corresponding data for C 2H 2 presented. Comparison is also made for the theoretical RI(3:1) ratios of these targets which are calculated by dividing the ICS for triplet transitions by the corresponding results for singlet transitions. The similarities and differences of these results, particularly the presence of the shape resonances at near excitation thresholds, are discussed. The influence of the atomic (localized) and molecular (delocalized) characters of the core orbitals on the core-excitation processes is also investigated. In addition, generalized oscillator strengths for the singlet core-orbital transitions are calculated at incident energy of 1290 eV for C 2 and C 2N 2. A comparison with the existing theoretical and experimental data for C 2H 2 is also presented.