Inelastic Energy Loss Research Articles

Contribution of Autoionization Processes to the Electronic Stopping Power

It is shown that the excitation of autoionization states during the collisions of keV-energy ions with a solid plays a determining role in the formation of inelastic energy losses and, accordingly, the electronic-stopping cross section Se. It is proposed to estimate the Se values using the relationship between the cross section for autoionization-state excitation and the ionization cross section. For cases where the ionization cross sections are unknown, scaling is used to calculate the ionization cross sections when the L and M shells are excited. The threshold dependence of Se versus the energy of bombarding ions is predicted.

Multiscale simulations of electron and ion dynamics in self-irradiated silicon

The interaction of energetic ions with the electronic and ionic system of target materials is an interesting but challenging multi-scale problem and understanding of the early stages after impact of heavy, initially charged ions is particularly poor. At the same time, energy deposition during these early stages determines later formation of damage cascades. We address the multi-scale character by combining real-time time-dependent density functional theory for electron dynamics with molecular dynamics simulations of damage cascades. Our first-principles simulations prove that core electrons affect electronic stopping and have an unexpected influence on the charge state of the projectile. We show that this effect is absent for light projectiles, but dominates the stopping physics for heavy projectiles. By parameterizing an inelastic energy loss friction term in the molecular dynamics simulations using our first-principles results, we also show a qualitative influence of electronic stopping physics on radiation-damage cascades.

Charmed hadron chemistry in relativistic heavy-ion collisions

We develop for charmed hadron production in relativistic heavy-ion collisions a comprehensive coalescence model that includes an extensive set of s and p-wave hadronic states as well as the strict energy-momentum conservation, which ensures the boost invariance of the coalescence probability and the thermal limit of the produced hadron spectrum. By combining our hadronization scheme with an advanced Langevin-hydrodynamics model that incorporates both elastic and inelastic energy loss of heavy quarks inside the dynamical quark-gluon plasma, we obtain a successful description of the pT-integrated and differential Λc/D0 and Ds/D0 ratios measured at RHIC and the LHC. We find that including the effect of radial flow of the medium is essential for describing the enhanced Λc/D0 ratio observed in relativistic heavy-ion collisions. We also find that the puzzling larger Λc/D0 ratio observed in Au+Au collisions at RHIC than in Pb+Pb collisions at the LHC is due to the interplay between the effects of the QGP radial flow and the charm quark transverse momentum spectrum at hadronization. Our study further suggests that charmed hadrons have larger sizes in medium than in vacuum.

Studying Thermally Reduced Graphene Oxide by X-Ray Photoelectron Spectroscopy

Samples of thermally reduced graphene oxide are studied using differential cross sections for photoelectron inelastic energy losses. We compare different procedures for recovering cross sections from the photoelectron energy spectra resulting from multiple inelastic scattering. It is shown that the cross section for inelastic energy losses (which uniquely characterizes allotropes of carbon) in the sample containing the minimal amount of carbon oxides corresponds the best to pyrolytic graphite.

Dependence of the Energy distribution of Reflected Ions on the Type of the Atomic Potential

The low-energy spectrum of ions reflected from the surface of a solid is calculated theoretically and by means of the computer simulation method. The theory is based on numerical solution of the transport equation by of the method of discrete streams; and computer simulation, on the model of binary collisions and local inelastic energy losses. It is shown that, for small energies of reflected ions, their energy distributions are described by the universal formula containing the only constant. The value of this constant varies weakly when passing from the hard-core potential to the Coulomb one.

Structural and optical band gap modification of Zn2SnO4 thin films after irradiation with swift heavy ions for transparent electrode applications

The structural changes and their effect on optical properties have been studied in Zn2SnO4 thin films irradiated by Ag9+ ions. The irradiation of thin films transforms the mixed crystal structures in to a single diffraction plane. In the XRD, the single peak is the result of atomic jump within the material due to the change in activation energy after irradiation. The XRD and SEM confirmed the modifications of lattice parameters and grains in accordance with the basic requirement of material to be used as transparent conducting oxides. In optical studies, the absorption spectra and Tauc plot confirm the neutralization of free electrons in conduction band minimum which results in an increase in the optical band gap for better transmission in visible range. The results indicate that the swift heavy ions passed from polycrystalline material synergistically with inelastic electronic energy loss to promote the formation of Zn2SnO4 oriented in a single direction and lead to rapid phase transformation.

Change in the Energy Losses of Heavy Ions Upon Deceleration in Carbon

When considering the deceleration of heavy ions in matter to a complete stop, it is taken into account that, as the ion path increases, the decrease in energy leads to a change in the ion-energy losses. The process of a decrease in the energy during the propagation of ions through the material is considered on the basis of the previously proposed power-law approximation of the dependence of inelastic ion energy losses on the velocity. The dependence of the energy losses on the ion path is obtained for different initial energies and nuclear charges of ions during their propagation through carbon. The thickness of the material layer in which the energy losses reach their maximum value and also the distance from the carbon target surface to the region of maximum energy losses are determined.

Direct Damage of Deoxyadenosine Monophosphate by Low Energy Electrons Probed by X-Ray Photoelectron Spectroscopy

Low-energy (3-25 eV) electron interactions with multilayers of 2'-deoxyadenosine 5'-monophosphate (dAMP) were probed using X-ray photoelectron spectroscopy (XPS). Understanding how electrons damage the nucleotide dAMP, which is a building block of DNA, can give insight into how the DNA undergoes radiation damage. Chemical modifications to the constituent units of the nucleotide were revealed in situ through monitoring of the O 1s, C 1s, and N 1s elemental transitions. It is shown that direct electron irradiation causes decomposition of both the base and sugar subunits, as well as cleavage of glycosidic and phosphoester bonds. Incident electrons undergo inelastic energy losses, including creation of core-excited resonances above 3-4 eV. In the condensed phase, these resonances decay via autoionization, producing electronically excited targets and <3 eV electrons. The excited states dissociate and the slow (<3 eV) electrons are captured by neighboring molecules, forming molecular shape resonances that can lead to bond rupture. Since the observed chemical changes were similar at all incident electron energies studied, they can be primarily attributed to formation and decay of transient negative ions. Damage enhancements in the energy ranges typical of all scattering resonances are expected, with the damage probability dominated by the low-energy shape resonances.

Contribution of molecular orbital promotion to inelastic energy losses in ion-solid collisions

A model for estimating the contribution of autoionization state formation to inelastic energy losses in collisions of keV-energy ions with solids is proposed. Using the suggested scaling for L and M shell excitation it is possible to estimate the ionization cross sections and the contribution of the ionization processes to the electronic stopping power dE/dx. The model predicts a threshold behavior of dE/dx. In the cases studied the formation of autoionization states gives important contribution to the value of dE/dx.

Probing changes in secondary electron yield from copper electrodes due to surface defects and changes in crystal orientation

There is considerable interest in mitigating secondary electron emission (SEE) from surfaces and electrodes produced by incident electrons, due to the deleterious effects of SEE in vacuum electron devices, accelerators, and other technologies. Since surface conditions are known to affect SEE, here the role played by crystal orientation and a vacancy (which is a simple example of a surface defect) is probed through Monte Carlo simulations. The effect of the lattice imperfection on the frequency-dependent permittivity, which then influences inelastic energy losses, mean free paths, and secondary generation profiles, is obtained on the basis of density-functional theory. The Monte Carlo simulations are in good agreement with previous experimental reports. The results indicate that the secondary electron yield for pure copper is the highest for the 110 orientation and the lowest for the 111 case, with a relatively higher differential predicted between a single vacancy and ideal copper for the 111 orientation. The results underscore the benefit of annealing or reducing inhomogeneities through laser or charged particle beam surface treatments.

Calculation of Ion Reflection from Solids: Computer Simulation and Theory

A computer program is developed to study ion reflection from solid surfaces. The program uses the cutoff Coulomb potential, the binary collision approximation, and the model of local inelastic energy losses. For a fixed ion-target combination, the reflection coefficient is calculated as a function of the ion energy and incidence angle. A reflection theory for the scattering cross section which depends on the transferred energy in accordance with the power law is constructed. Good agreement of the simulation results with the experiment and the theory is obtained.

Simulation of Particle Scattering at Amorphous and Polycrystalline Targets

A procedure for simulating the scattering of atomic particles at amorphous and crystalline targets is described in the binary collision approximation. The influence of thermal vibrations, choice of the potential, and the inclusion of inelastic energy losses are analyzed using the simulation of hydrogen-atom scattering at a tungsten surface as an example. The coefficients of reflection from crystalline, polycrystalline, and amorphous surfaces are compared.

Global constraints from RHIC and LHC on transport properties of QCD fluids in CUJET/CIBJET framework * * Supported by the National Science Foundation (PHY-1352368), IOPP of CCNU Wuhan China, the computations in this study were performed on IU's Big Red II clusters, supported in part by the Lilly Endowment, Inc., through its support for the Indiana University Pervasive Technology Institute,

We report results of a comprehensive global analysis of nuclear collision data from RHIC (0.2 ATeV), LHC1 (2.76 ATeV), and recent LHC2 (5.02 ATeV) energies using the updated CUJET framework. The framework consistently combines viscous hydrodynamic fields predicted by VISHNU2+1 (validated with soft GeV bulk observables) and the DGLV theory of jet elastic and inelastic energy loss generalized to QGP fluids with an sQGMP color structure, including effective semi-QGP color electric quark and gluon as well as emergent color magnetic monopole degrees of freedom constrained by lattice QCD data. We vary the two control parameters of the model (the maximum value of the running QCD coupling, , and the ratio of color magnetic to electric screening scales) and calculate the global compared with available jet fragment observables ( ). A global minimum is found with and . Using CIBJET, the event-by-event (ebe) generalization of the CUJET framework, we show that ebe fluctuations in the initial conditions do not significantly alter our conclusions (except for ). An important theoretical advantage of the CUJET and CIBJET frameworks is not only its global consistency with jet fragment observables at RHIC and LHC and with non-perturbative lattice QCD data, but also its internal consistency of the constrained jet transport coefficient, , with the near-perfect fluid viscosity to entropy ratio ( ) property of QCD fluids near needed to account for the low GeV flow observables. Predictions for future tests at LHC with 5.44 ATeV Xe + Xe and 5.02 ATeV Pb + Pb are also presented.

Electron transport and negative streamers in liquid xenon

In this work we investigate electron transport, transition from an electron avalanche into a negative streamer, and propagation of negative streamers in liquid xenon. Our standard Monte Carlo code, initially developed for dilute neutral gases, is generalized and extended to consider the transport processes of electrons in liquids by accounting for the coherent and other liquid scattering effects. The code is validated through a series of benchmark calculations for the Percus–Yevick model, and the results of the simulations agree very well with those predicted by a multi term solution of Boltzmann’s equation and other Monte Carlo simulations. Electron transport coefficients, including mean energy, drift velocity, diffusion tensor, and the first Townsend coefficient, are calculated for liquid xenon and compared to the available measurements. It is found that our Monte Carlo method reproduces both the experimental and theoretical drift velocities and characteristic energies very well. In particular, we discuss the occurrence of negative differential conductivity in the E/n0 profile of the drift velocity by considering the spatially-resolved swarm data and energy distribution functions. Calculated transport coefficients are then used as an input in fluid simulations of negative streamers, which are realized in a 1.5 dimensional setup. Various scenarios of representing the inelastic energy losses in liquid xenon, ranging from the case where the energy losses to electronic excitations are neglected, to the case where some particular excitations are taken into account, and to the case where all electronic excitations are included, are discussed in light of the available spectroscopy and photoconductivity experiments. We focus on the way in which electron transport coefficients and streamer properties are influenced by representation of the inelastic energy losses, highlighting the need for the correct representation of the elementary scattering processes in the modeling of liquid discharges.

Excitation of Autoionization States and Electronic Stopping Powers at Collisions of Slow Ions with a Solid

It has been shown that the excitation of autoionization states at collisions of keV ions with a solid is decisive for inelastic energy loss and, correspondingly, the electronic stopping power dE/dx. It has been proposed to estimate the electronic stopping power dE/dx using the relation of cross sections for the excitation of autoionization states to ionization cross sections. When ionization cross sections are unknown, scaling is used to calculate ionization cross sections at the excitation of the L and M shells. A threshold dependence of the electronic stopping power dE/dx on the energy of bombarding ions has been predicted.

On the Interrelation of Processes Leading to Inelastic Energy Losses by Ions

Inelastic energy losses can be presented as two components determined by processes of the ionization of target atoms and the charge exchange of ions. These components are interrelated. The interrelation is determined by the value of the average ion charge. The energy losses during the ionization of a target atom are calculated using a parameter which characterize the effect of states of excited atoms. The difference between inelastic energy losses in gaseous and solid targets is explained.

Neoclassical Diffusion of Radiation‐Belt Electrons Across Very Low L‐Shells

AbstractIn the presence of drift‐shell splitting intrinsic to the International Geomagnetic Reference Field magnetic field model, pitch angle scattering from Coulomb collisions experienced by radiation‐belt electrons in the upper atmosphere and ionosphere produces extra radial diffusion, a form of neoclassical diffusion. The strength of the neoclassical radial diffusion at L &lt; 1.2 exceeds that expected there from radial‐diffusion mechanisms traditionally considered and decreases with increasing L‐shell. In this work we construct a numerical model for this coupled (radial and pitch angle) collisional diffusion process and apply it to simulate raw count‐rate data observed aboard the Gemini spacecraft for several years after the 1962 Starfish nuclear detonation. The data show apparent lifetimes 10–100 times as long as would have been expected from collisional pitch angle diffusion and Coulomb drag alone. Our model reproduces apparent lifetimes for &gt;0.5‐MeV electrons in the region 1.14 &lt; L &lt; 1.26 to within a factor of 2 (comparable to the uncertainty quoted for the observations). We conclude that neoclassical radial diffusion (resulting from drift‐shell splitting intrinsic to International Geomagnetic Reference Field's azimuthal asymmetries) mitigates the decay expected from collisional pitch angle diffusion and inelastic energy loss alone and thus contributes importantly to the long apparent lifetimes observed at these low L‐shells.

Study of Defects Produced by Displacement Cascades in Tantalum Monocarbide

We used the binary collision approximation code Marlowe to simulate displacement cascades in tantalum monocarbide. We investigated the damage production, the spatial configurations of the resulting defects, and the vacancy clustering. Statistics over 5000 cascades were accumulated, and primaries with kinetic energies up to 20 keV were launched from lattice sites. Elastic collisions between atoms were modeled by the universal Ziegler–Biersack–Littmark, Moliere, and Born–Mayer potentials. The Lindhard–Scharff–Schiott theory was used to account for the inelastic energy losses. Principal components analysis was utilized to evaluate the volume of the damaged zone. Analysis of the simulation results shows that no more than 40% of the displaced Ta and C atoms constitute permanent damage. The number of surviving tantalum Frenkel pairs is about twice the carbon one. The cascade volume distributions deviate from a Gaussian distribution showing high degree of dispersion. Only small vacancy clusters are observed within the investigated range of the primary energies, and 33% of the produced vacancies are considered as isolated point defects in 20 keV cascade.

Elucidation of ALD MgZnO deposition processes using low energy ion scattering

Low energy ion scattering (LEIS) provides an analytical tool for probing the surface composition and structure on the angstrom to nanometer scale. These length scales are central to the growth and processing of ultrathin films produced by atomic layer deposition (ALD). Here, the authors present the application of LEIS to the elucidation of ALD deposition processes and in particular how it provides information about growth parameters including the growth per cycle (GPC), the nature of the film–substrate interfaces, and adatom incorporation into the growing film. The deposition of varying thickness zinc oxide films and the composition of magnesium-doped zinc oxide films are used as model systems. LEIS has been used to investigate the GPC of ZnO using two approaches, namely, static and dynamic measurements. The static approach exploits inelastic energy loss processes to estimate the GPC of different thicknesses of ZnO films. The dynamic approach measures the GPC via a combination of LEIS surface analysis and sputter depth profiling. The measurement of GPC using these two methods is compared with spectroscopic ellipsometry. The adatom incorporation of Mg into the ZnO matrix is measured using a dynamic LEIS process, and the variation of Mg incorporation is discussed as a function of the varying ALD cycle fractions of Mg and ZnO used to deposit MgxZn1-xO films in the range of 0 &amp;lt; x &amp;lt; 1.

A didactic proposal about Rutherford backscattering spectrometry with theoretic, experimental, simulation and application activities

Rutherford backscattering spectrometry is a nuclear analysis technique widely used for materials science investigation. Despite the strict technical requirements to perform the data acquisition, the interpretation of a spectrum is within the reach of general physics students. The main phenomena occurring during a collision between helium ions—with energy of a few MeV—and matter are: elastic nuclear collision, elastic scattering, and, in the case of non-surface collision, ion stopping. To interpret these phenomena, we use classical physics models: material point elastic collision, unscreened Coulomb scattering, and inelastic energy loss of ions with electrons, respectively. We present the educational proposal for Rutherford backscattering spectrometry, within the framework of the model of educational reconstruction, following a rationale that links basic physics concepts with quantities for spectra analysis. This contribution offers the opportunity to design didactic specific interventions suitable for undergraduate and secondary school students.