keV Energy Regime Research Articles

Effect of phosphorus ion implantation on electrical conductivity and local lattice distortions in diamond

In this work, phosphorus ions have been implanted with various doses at an energy 100 keV on single crystal (100) diamond. We try to understand the local lattice distortions (disorder) induced in the implanted layer post annealing (at 850 °C) as a result of ion impact with the help of out-of-plane as well as in-plane XRD techniques and its corresponding effect on the electrical conductivity in diamond crystal. While a low dose of 1014cm−2 increases the lattice parameter along the out-of-plane direction and leads to formation of isolated point defects (mostly interstitials) in the lattice without introducing much disorder, a moderate dose of 1015cm−2 initiates the process of clustering of these defects in the implanted/defected layer. An out-of-plane tensile strain that is present in low dose case is eventually released with moderate dose implantations. With high doses of phosphorus in diamond, the crystallinity in the implanted layer drops, the damage propagates to the extent that it forms small amorphous pockets within this defected layer; although the lattice is not completely amorphous as it still retains the long range order as confirmed from X-ray absorption results. Our data indicate that the electrical transport in diamond is mainly due to substitutional phosphorus when implanted at low dose of 1014cm−2 and also highlights that damage or ‘localized amorphization’ takes place at a critical implantation dose of 1016cm−2 and therefore the critical phosphorus ion dose of 1015cm−2 (in 100 keV energy regime) i.e. a damage threshold of 8 × 1021vacancies/cm3 is the limit beyond which chances of amorphization is prevalent and the electronic properties in diamond are solely due to sp3 bond breakage.

Attractive scenario for light dark matter direct detection

Direct detection of light dark matter (DM), below the GeV scale, through electron recoil can be efficient if DM has a velocity well above the virial value of $v\sim 10^{-3}$. We point out that if there is a long range attractive force sourced by bulk ordinary matter, i.e. baryons or electrons, DM can be accelerated towards the Earth and reach velocities $v\sim 0.1$ near the Earth's surface. In this "attractive scenario," all DM will be boosted to high velocities by the time it reaches direct detection apparatuses in laboratories. Furthermore, the attractive force leads to an enhanced DM number density at the Earth facilitating DM detection even more. We elucidate the implications of this scenario for electron recoil direct detection experiments and find parameters that could lead to potential signals, while being consistent with stellar cooling and other bounds. Our scenario can potentially explain the recent excess in electron recoil signals reported by the XENON1T experiment in the $\sim$ keV energy regime as well as the hint for non-standard stellar cooling.

Single-collision scattering of keV-energy Kr ions off a polycrystalline Cu surface

In the keV-energy regime, the scattering of krypton ions off a copper sample has been studied. In addition to the broad energy spectrum arising from multiple-collision scattering, the energy distributions of the backscattered ions exhibit prominent peaks at energies where single-collision (SC) scattering peaks are expected. Such SC peaks were shown to be absent in Sn – Mo/Ru scattering, systems of similar mass ratio and thus similar kinetics. The present Kr on Cu results allow for a comparison to a simulation package as SRIM. An important difference found between the present experiment and the predictions of SRIM is that the SC contribution is observed to decrease with scattering angle, whereas SRIM predicts this contribution to be constant. The intensity of the experimental SC peaks, though much weaker than in the SRIM simulations, may be used as markers to improve SRIM in its description of low-energy heavy particle scattering off surfaces.

Energy-angle correlation correction algorithm for monochromatic computed tomography based on Thomson scattering X-ray source

The necessity for compact and relatively low cost x-ray sources with monochromaticity, continuous tunability of x-ray energy, high spatial coherence, straightforward polarization control, and high brightness has led to the rapid development of Thomson scattering x-ray sources. To meet the requirement of in-situ monochromatic computed tomography (CT) for large-scale and/or high-attenuation materials based on this type of x-ray source, there is an increasing demand for effective algorithms to correct the energy-angle correlation. In this paper, we take advantage of the parametrization of the x-ray attenuation coefficient to resolve this problem. The linear attenuation coefficient of a material can be decomposed into a linear combination of the energy-dependent photoelectric and Compton cross-sections in the keV energy regime without K-edge discontinuities, and the line integrals of the decomposition coefficients of the above two parts can be determined by performing two spectrally different measurements. After that, the line integral of the linear attenuation coefficient of an imaging object at a certain interested energy can be derived through the above parametrization formula, and monochromatic CT can be reconstructed at this energy using traditional reconstruction methods, e.g., filtered back projection or algebraic reconstruction technique. Not only can monochromatic CT be realized, but also the distributions of the effective atomic number and electron density of the imaging object can be retrieved at the expense of dual-energy CT scan. Simulation results validate our proposal and will be shown in this paper. Our results will further expand the scope of application for Thomson scattering x-ray sources.

X-ray spectroscopy for chemistry in the 2-4 keV energy regime at the XMaS beamline: ionic liquids, Rh and Pd catalysts in gas and liquid environments, and Cl contamination in γ-Al2O3.

The 2-4 keV energy range provides a rich window into many facets of materials science and chemistry. Within this window, P, S, Cl, K and Ca K-edges may be found along with the L-edges of industrially important elements from Y through to Sn. Yet, compared with those that cater for energies above ca. 4-5 keV, there are relatively few resources available for X-ray spectroscopy below these energies. In addition, in situ or operando studies become to varying degrees more challenging than at higher X-ray energies due to restrictions imposed by the lower energies of the X-rays upon the design and construction of appropriate sample environments. The XMaS beamline at the ESRF has recently made efforts to extend its operational energy range to include this softer end of the X-ray spectrum. In this report the resulting performance of this resource for X-ray spectroscopy is detailed with specific attention drawn to: understanding electrostatic and charge transfer effects at the S K-edge in ionic liquids; quantification of dilution limits at the Cl K- and Rh L3-edges and structural equilibria in solution; in vacuum deposition and reduction of [Rh(I)(CO)2Cl]2 to γ-Al2O3; contamination of γ-Al2O3 by Cl and its potential role in determining the chemical character of supported Rh catalysts; and the development of chlorinated Pd catalysts in `green' solvent systems. Sample environments thus far developed are also presented, characterized and their overall performance evaluated.

Monochromatic computed tomography with a compact laser-driven X-ray source

A laser-driven electron-storage ring can produce nearly monochromatic, tunable X-rays in the keV energy regime by inverse Compton scattering. The small footprint, relative low cost and excellent beam quality provide the prospect for valuable preclinical use in radiography and tomography. The monochromaticity of the beam prevents beam hardening effects that are a serious problem in quantitative determination of absorption coefficients. These values are important e.g. for osteoporosis risk assessment. Here, we report quantitative computed tomography (CT) measurements using a laser-driven compact electron-storage ring X-ray source. The experimental results obtained for quantitative CT measurements on mass absorption coefficients in a phantom sample are compared to results from a rotating anode X-ray tube generator at various peak voltages. The findings confirm that a laser-driven electron-storage ring X-ray source can indeed yield much higher CT image quality, particularly if quantitative aspects of computed tomographic imaging are considered.

X-ray laser spectroscopy with an electron beam ion trap at the free electron laser LCLS

We present a first laser spectroscopy experiment in the keV energy regime, performed at the Free-Electron Laser LCLS at Stanford. An electron beam ion trap was used to provide a target of highly charged O, F and Fe ions. The resonant fluorescence spectra obtained for various transitions were calibrated to simultaneously measured Lyman lines of hydrogenic ions.

First-principles dynamics treatment of light emission in collisions between alkali-metal atoms and noble-gas atoms at10keV

Collision-induced light emission during the interaction of an alkali-metal atom and a noble-gas atom is treated within a first-principles, or direct, dynamics approach that calculates a time-dependent electric dipole for the whole system, and spectral emission cross sections from its Fourier transform. These cross sections are very sensitive to excited diatomic potentials and a source of information on their shape. The coupling between electronic transitions and nuclear motions is treated with atomic pseudopotentials and an electronic density matrix coupled to trajectories for the nuclei. A recently implemented pseudopotential parametrization scheme is used here for the ground and excited states of the LiHe system, and to calculate state-to-state dipole moments. To verify the accuracy of our new parameters, we recalculate the integral cross sections for the LiHe system in the keV energy regime and obtain agreement with other results from theory and experiment. We further present results for the emission spectrum from $10\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ $\mathrm{Li}(2s)+\mathrm{He}$ collisions, and compare them to experimental values available in the region of light emitted at $300--900\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

Photoelectron spectroscopy with hard X-rays

The use of hard X-ray synchrotron radiation as the primary excitation for photoelectron spectroscopy has recently attracted great interest. At HASYLAB, a dedicated instrument for experiments in the photon energy range 2.3–10 keV (electron energies up to 7.5 keV) has been in operation for several years. The overall energy resolution is source limited to about 0.4 eV, which is well suited for most core level studies. Scientific work using this instrument has so far focused on the near-threshold excitation of inner-shell Auger transitions and the electronic properties of buried structures and interfaces. Here, general aspects of photoelectron spectroscopy using X-rays in the keV energy regime are discussed and some applications are presented.

Projectile neutralization in large-angle back-scattering of slow Fq+, Neq+ and Arq+ incident on RbI([formula omitted

The scattering of multi-charged ions (MCI) from the [100] surface of a RbI single crystal has been studied using a 120° back-scattering technique in the keV energy regime. Scattered charge-state distributions were measured as a function of the polar incidence angle and the target azimuthal orientation. Preliminary results indicate that “quasi-binary” collisions associated with scattering from a Rb or I site can be clearly distinguished for each scattered final charge state. The charge-state distribution and the relative Rb/I binary collision yields for scattered ions are found to depend on both the beam incidence angle and the target azimuthal orientation. The preliminary RbI(100) results are discussed in the context of earlier experimental and theoretical studies of MCI scattering on a Au(110) surface.

Fraunhofer diffraction of atomic matter waves: electron transfer studies with a laser cooled target.

We have constructed an apparatus combining the experimental techniques of cold target recoil ion momentum spectroscopy and a laser cooled target. We measure angle differential cross sections in Li(+)+Na-->Li+Na(+) electron transfer collisions in the keV energy regime with a momentum resolution of 0.12 a.u. yielding an order of magnitude better angular resolution than previous measurements. We resolve Fraunhofer-type diffraction patterns in the differential cross sections. Good agreement with predictions of the semiclassical impact parameter method is obtained.

Quantitative calibration of intense (α, α) elastic scattering resonances for 12C at 5.50–5.80 MeV and for 16O at 7.30–7.65 MeV

Extremely strong (α, α) elastic scattering resonances — more than 100 times the Rutherford value — occur in 16O at 7.35–7.65 keV and in 12C at 5.50–5.80 MeV, thus allowing the normal RBS technique to be extended to low-Z components, such as oxygen and carbon. Both resonances have been calibrated over the appropriate 300 keV energy regime with an overall accuracy of ±4%. Some recent examples of their use in profiling oxygen and carbon in various substrates are given.

Molecular treatment of electron capture in atomic collisions in the meV- to keV-energy regime: Collisions of C5+ ions with H atoms and the effect of core electrons.

Electron-capture processes in collisions of ${\mathrm{C}}^{5+}$ ions with H atoms are investigated theoretically by using quantum-mechanical and semiclassical molecular-orbital methods in the collision-energy range from meV/amu to keV/amu. Atomic-type electron-translation factors are appropriately incorporated to ensure correct scattering boundary conditions. Total capture cross sections have a broad minimum at 0.4 keV/amu that is caused by the change of major contributors. The dominant capture channels in the triplet manifold are ${\mathrm{C}}^{4+}$(1s4s) below 0.1 keV/amu and ${\mathrm{C}}^{4+}$(1s4p), ${\mathrm{C}}^{4+}$(1s4d), and ${\mathrm{C}}^{4+}$(1s3p) above that energy. In the singlet manifold, below 0.5 keV/amu, the dominant channel is ${\mathrm{C}}^{4+}$(1s4s), as in the triplet manifold. However, above that energy the ${\mathrm{C}}^{4+}$(1s4f), ${\mathrm{C}}^{4+}$(1s4d), ${\mathrm{C}}^{4+}$(1s3p), and ${\mathrm{C}}^{4+}$(1s3d) channels become important. The present results for the total capture cross section is in excellent accord with the measurements by Phaneuf et al. [Phys. Rev. A 26, 1892 (1982)] and Crandall, Phaneuf, and Meyer [Phys. Rev. A 19, 504 (1979)] over the entire energy region studied. The effect of core electrons on the capture process is examined by using data from the present (${\mathrm{C}}^{5+}$+H) system and the previously studied (${\mathrm{N}}^{5+}$+H) and (${\mathrm{B}}^{5+}$+H) systems, and some remarks on the role of core electrons are made on the basis of an argument concerning the overlap of electronic charge distribution.

Electron capture in Ar++H

Electron capture in ${\mathrm{Ar}}^{+}$${(\mathrm{}}^{2}$P)${+\mathrm{H}}_{2}$(X ${\mathrm{}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathrm{g}}$) collisions in the keV energy regime has been studied theoretically. The molecular-orbital expansion method was used within a semiclassical formalism and an electron translation factor correction was incorporated to the first order in the magnitude of the relative velocity V. The molecular wave function and eigenenergy were obtained using the diatoms-in-molecules (DIM) method. We have examined the effect of the orientation of the target ${\mathrm{H}}_{2}$ molecule on the electron-capture mechanism within the sudden adiabatic approximation. Since \ensuremath{\pi} symmetry arising from the p orbital of the ${\mathrm{Ar}}^{+}$ ion is involved in this system, a strong influence on the probability of the molecular orientation was found in all energies studied. As the collision energy increases, the \ensuremath{\Pi}-symmetry state in the initial channel becomes more important through the rotational coupling to the electron-capture mechanism, while at lower energies the \ensuremath{\Sigma}-symmetry state in the initial channel is the dominant source for the electron capture through strong radial coupling. Agreement of the present theory with measurements is good, but marked disagreement is seen with the atomic-orbital calculation.

Charge transfer in ion-molecule collisions at keV energy regime: Study of H++H

Charge transfer in H/sup +/+H/sub 2/(X/sup 1/..sigma../sub g/; v = 0) collisions has been studied theoretically at energies from 0.2 to 20 keV with use of a molecular-state--expansion method incorporating electron translation factors. Two-state semiclassical close-coupling calculations have been performed to investigate the ion-molecule collision dynamics. The molecular states, used as the expansion basis, have been obtained by using the diatoms-in-molecules (DIM) method as functions of the internuclear distance R and two molecular orientation angles theta and phi. The effect of orientation of the target molecule on the charge-transfer mechanism has been examined and the charge-transfer cross section is found to be very sensitive to the molecular orientation at energies below 0.5 keV or above 10 keV. Between these energies, however, the orientation effect was small (due to accidental near-degeneracy of the probability from different theta). Our results are in good agreement with experimental measurements in the energy range where they are available.

Heavy ion neutralization behaviour in the 30–130 keV energy regime

Charged fractions of Li, B, C, N, F and Ne in the range of 30–130 keV backscattered from Au surfaces have been measured using a high resolution solid state detector. Li shows the highest charged fraction followed by F, B, Ne, N and C. These results are compared with existing theoretical predictions. A reduced velocity scaling, derived from capture and loss processes in the bulk, seems to unify N, B, Li and perhaps C. An exponential relationship, appropriate to near surface neutralization, appears to account for all ions except Ne. The semiempirical approach of Zaidins for describing the heavier ion charged fractions agrees reasonably well with the measured values for Ne, N and C but differs by a large amountfor Li, B and F.