N.R. Arista

Energy-angle distribution of low-energy hydrogen ions in thin aluminum and gold foils

Energy and angular distributions of hydrogen ions in thin solid foils of elements with significantly diAerent electronic structures and atomic masses, such as Al and Au, have been measured at 9 keV using the transmission technique. The results are compared with Monte Carlo simulations using a classical scattering approach and an impact-parameter independent electronic energy loss, as well as with a simplified model containing the main physical features. In both cases, the eAect of foil roughness on angular dependence of the energy loss has been included and it has been found to be responsible for the variations observed at small angles. The measured angular distributions have also been compared with standard multiple scattering functions corresponding to Thomas‐Fermi and Lenz‐Jensen potentials and with calculations based on 1=r n power potentials. ” 2000 Elsevier Science B.V. All rights reserved.

Energy loss and angular dispersion of 2-200 keV protons in amorphous silicon

Abstract The energy loss of 2–200 keV protons in thin amorphous silicon foils has been measured for projectiles transmitted in the forward direction and as a function of the exit angle. At the lowest energies, differences of up to 30% with recently published values are observed. Angular effects in the energy loss, at low and high energies, have been investigated. The low-energy results are reproduced by model calculations and Monte Carlo simulations, which indicate that the inelastic energy loss does not show a dependence upon the impact parameter in the low energy region. A fitting formula for the present energy loss values is provided.

Plasmon excitation in single-walled carbon nanotubes probed using charged particles: comparison of calculated and experimental spectra

We study the excitation of plasmons due to the incidence of a fast charged particle that passes through a single-wall carbon nanotube. We use a quantized hydrodynamic model, in which the σ and π electron systems are depicted as two interacting fluids moving on a cylindrical surface. Calculations of the average number of the excited plasmons and the corresponding energy loss probability for the swift electrons are compared with several experimental results for electron energy loss spectra recorded using transmission electron microscopes. We are able to identify the π and σxa0+xa0π plasmon peaks and elucidate the origin of various spectral features observed in different experiments.

Angular dependence of the energy loss of ions in solids: Computer simulations and analysis of models

Abstract The angular dependence of the electronic energy loss of light ions in solids is analyzed in the frame of the binary collision approximation (BCA) using an analytical formalism based on multiple scattering (MS) functions, as well as with Monte Carlo (MC) simulations. These simulations have been performed for different collisional models of ions in the solid. A variation of the mean number of collisions with the observation angle is found, for a frequently used random distribution of interatomic distances, which may originate an angular dependence of the energy loss. Additionally the effect of impact parameter restrictions has been investigated, and again a change in the mean number of collisions with the observation angle has been observed. As this variation depends on the model of the solid and the impact parameter criteria applied, uncertainties in the single collision energy loss appear.

Photoionization of image states around metallic nanotubes

In this work we study a theoretical approach to the ionization of electrons bound in an image state around a metallic nanotube by the impact of photons. In a close analogy to the already studied case of ionization by electron impact [1], we calculate and analyze photoionization cross sections of tubular image states [2] within a first Born approximation. We consider various situations, including different energies and polarizations of the incident photon, ejection directions of the outgoing electron, and angular momenta of the image state.

Excitation of surface plasmons in nanotubes

In this work, we describe the excitation of plasmons in nano-systems of cylindrical symmetry when charged particles impinge on them. In particular, we calculate the average number of plasmons excited by electrons in hollow, metallic tubules, using a Drude model to describe the dielectric function of the material. Based on previous results, which show the equivalence between quantum and classical descriptions of the phenomenon, we are able to evaluate in a simple manner the integrals along penetrating trajectories, perpendicular to the cylinder axis. We study the influence of various parameters on the excitation of the different modes available for such geometry, including the variation of the inner radius of the tube, and the impact parameter of the electron beam. We obtain similarities and differences with the already studied cases of solid wires, and hollow capillaries.

Excitation of hybridized Dirac plasmon polaritons and transition radiation in multi-layer graphene traversed by a fast charged particle

We analyze the energy loss channels for a fast charged particle traversing a multi-layer graphene (MLG) structure with N layers under normal incidence. Focusing on a terahertz (THz) range of frequencies, and assuming equally doped graphene layers with a large enough separation d between them to neglect interlayer electron hopping, we use the Drude model for two-dimensional conductivity of each layer to describe hybridization of graphenes Dirac plasmon polaritons (DPPs). Performing a layer decomposition of ohmic energy losses, which include excitation of hybridized DPPs (HDPPs), we have found for Nxa0=xa03 that the middle HDPP eigenfrequency is not excited in the middle layer due to symmetry constraint, whereas the excitation of the lowest HDPP eigenfrequency produces a Fano resonance in the graphene layer that is first traversed by the charged particle. While the angular distribution of transition radiation emitted in the far field region also shows asymmetry with respect to the traversal order by the incident charged particle at supra-THz frequencies, the integrated radiative energy loss is surprisingly independent of both d and N for Nxa0≤xa05, which is explained by a dominant role of the outer graphene layers in transition radiation. We have further found that the integrated ohmic energy loss in optically thin MLG scales as ∝1/N at sub-THz frequencies, which is explained by exposing the role of dissipative processes in graphene at low frequencies. Finally, prominent peaks are observed at supra-THz frequencies in the integrated ohmic energy loss for MLG structures that are not optically thin. The magnitude of those peaks is found to scale with N for Nxa0≥xa02, while their shape and position replicate the peak in a double-layer graphene (N = 2), which is explained by arguing that plasmon hybridization in such MLG structures is dominated by electromagnetic interaction between the nearest-neighbor graphene layers.

Plasmon decay in the context of the dielectric formalism

We address the problem of quantifying the decay of plasmons excited in the electron gas of a condensed medium. Within the dielectric formalism, we use various methods to define and assess the damping constant γ.

Interference in the plasmon field excited by a diatomic molecule on metallic cylindrical nanostructures

In this work we analyze the fluctuations of the electronic density Δρ and the average number of the excited plasmons, for the case of the diatomic charged molecule traveling near or passing through a metallic nanocylinder at different positions, and compare the results with the case of a single particle.

Photoionization cross section of image potential states around nanotubes

In this paper, we theoretically address the photoemission from image potential states (IPS) around nanotubes. The relevance of this process is related to the fact that this particular kind of IPS has been experimentally detected for carbon nanotubes by means of femtosecond-resolved two-photon photoemission (Zamkov et al 2004 Phys. Rev. Lett. 93 156803). The quantum interaction between the bound electron and the incident radiation field is considered within the dipolar approximation, and the transition matrix for the process is obtained using a first-order Born expansion. For a linearly polarized photon with the polarization vector perpendicular to the nanotube’s axis, electrons are found to be emitted with a polar angle that is determined by the initial parallel momentum of the bound electron.