Angular Distributions Of Secondary Electrons Research Articles

Theoretical investigation of the double differential cross section for electron impact ionization of methane molecule

SynopsisWe present theoretical calculations of double differential cross sections (DDCS) for methane molecule. Angular distributions of secondary electrons have been measured after ionizing electron collisions with methane at primary energy of 350 eV using a conventional electron spectrometer. The theoretical model used is the first and second Born approximations with Gamow factor. It is found that these theoretical calculations are successful to describe the post-collision interaction effects due to the Coulomb long-range interaction between the outgoing electrons in the final state.

Double Differential Cross-Section Measurements for Methane Molecule at 350 eV

Double di erential cross-sections have been measured after ionizing electron collisions with methane at primary energy of 350 eV using a conventional electron spectrometer. An electrostatic analyzer was used to measure angular distributions of secondary electrons with energies between 25 eV and 300 eV. Angles of emission were 25◦ to 130◦. It was found that the outgoing electrons belong to one of the two energetically separated groups, either the fast electrons which are scattered mainly in forward direction or the slow electrons which are distributed isotropically into all angles. For higher ejection energies the maxima shifted towards smaller angles as expected from binary type collision.

Monte Carlo simulation of emission site, angular and energy distributions of secondary electrons in silicon at low beam energies

The information about location, energy and angular distribution of secondary electrons emerging from the irradiated sample is very important for the reconstruction of scanning electron microscopy images and to quantify secondary electron potential contrast measurements. In this paper, an original multiple collisions Monte Carlo code is used to calculate the distribution of the emerging sites, the angular distribution of secondary electrons emitted in silicon at 0.5, 1.0, and 7keV beam energy. In particular, the angular distribution, and the secondary electron yield are calculated as function of the surface barrier energy, according to the quantum-mechanical model.

Angular distributions of secondary electrons in fast particle-atom scattering

We present the angular distribution of electrons knocked out from an atom in a fast charge particle collision at small momentum transfer. It is determined not only by dipole but also by quadrupole transitions, the contribution of which can be considerably enhanced as compared to the case of photoionization. There the non-dipole parameters are suppressed as compared to the dipole ones by the parameter \omega R/c << 1, where is the photon energy, R is the ionized shell radius and c is the speed of light. This suppression in fast electron-atom collisions can be considerably reduced: the corresponding expansion parameter \omega R/ \nu << 1 is much bigger than in photoionization, since the speed of the incoming electron is much smaller than c. In formation of the angular distribution it is decisively important that the ionizing field in collision process is longitudinal, while in photoionization - it is transversal. We illustrate the general formulas by concrete results for outer s-, p-, and some nd-subshells of multi-electron noble gas atoms Ar, Kr and Xe, at several transferred momentum values: q=0.0, 0.1, 1.1, 2.1. Even for very small transferred momentum q, i.e. in the so-called optical limit, the deviations from the photoionization case are prominent.

Theoretical and experimental investigations of electron emission in C 6+ + H 2O collisions

Theoretical differential and total cross sections for the direct ionization process of water vapour by 6 MeV/u C 6+ ions are compared to new experimental measurements performed by the dedicated apparatus already used for measuring the energy and angular distributions of secondary electrons emitted from water vapour by fast heavy-ion impact [D. Ohsawa, H. Kawauchi, M. Hirabayashi, Y. Okada, T. Homma, A. Higashi, S. Amano, Y. Hashimoto, F. Soga, Y. Sato, Nucl. Instr. and Meth. B 227 (2005) 431]. In the present work, ab initio calculations have been carried out in the first Born approximation by using an accurate molecular wave function for describing the initial bound state of the target. The calculated cross sections exhibit good agreement with the present experimental measurements and compare relatively well to the existing semi-empirical results over the entire angular and energy ranges investigated here. Free from any adjustable parameter, the proposed theoretical approach describes in detail the complete kinematics of the water molecule ionization process by highly energetic carbon ions, and could therefore be easily used for modelling the heavy charged-particle transport in the biological matter.

Theoretical and experimental investigations of electron emission inHe2++H2Ocollisions

Very recently, Ohsawa et al. have presented a new experimental apparatus for measuring doubly differential cross sections of electron emission from water vapor with fast heavy-ion impact (6-25 MeV). Successful measured energy and angular distributions of secondary electrons were produced for a collision of 6.0 MeV/u He{sup 2+} ions with vapor water [Nucl. Instrum. Methods Phys. Res. B 227, 431 (2005)] and for 10.0 MeV/u He{sup 2+} ions [Phys. Rev. A 72, 062710 (2005)]. The present theoretical work aims to reproduce these very recent measurements as well as more former existing data dedicated to low-energy alpha particles. Doubly, singly differential, and total ionization cross sections have then been studied.

Structures in triply and doubly differential ionization cross sections of atomic hydrogen

The work investigates theoretically triply and doubly differential cross sections for electron- and positron-impact ionization of atomic hydrogen. On the basis of the framework developed by Brauner et al. (1989-91), structures in the triply differential cross section are identified and their contributions to the doubly differential cross section are discussed. A novel structure in the triply differential cross section in the case of positron impact has been found. Results for the energy and angular distributions of secondary electrons are presented and compared with available experimental data. In general, the results are in good agreement with the experiment. Discrepancies between experiment and the theory exist for electrons ejected into the forward direction. It turns out that at low impact energy the angular and energy spectrum of the secondary electrons is strongly influenced by all three two-body interactions involved in the process. In the case of electron impact also exchange effects contribute to the shape and magnitude of the cross section. The authors conclude that triply and doubly differential ionization cross sections depend sensitively on the description of the three-body system.

Angular Distributions of Secondary Electrons Emitted from the Polycrystalline Silver

The angular distributions of secondary electrons (including Auger electrons) of different energies emitted from polycrystalline silver bombarded with primary electrons (E ρ = 1000 and 2500 eV) were measured with a RFA analyzer equipped with an additional collector (acceptance angle 4°). Additionally, the angular distributions of primary electrons of different energies elastically backscattered from the same sample were also investigated by means of a specially constructed rotable RFA analyzer equipped with a channeltron. Tle results obtained show the cosine distribution of secondary and Auger electrons emitted as shown previously in the literature. The angular distributions of electrons backscattered elastically depend on electron energy and are in good agreement with theoretical calculations (Monte Carlo simulation of primary electrons trajectories in solids) proposed by Jablonski.

Monte Carlo Study of Dependence of Secondary Electron Emission from Copper on Incident Angle of keV Primary Electrons

The dependence of secondary electron emission from copper on the incident angle of the keV primary electron is investigated by using Monte Carlo techniques not only for the collision process of the primary electron in material, but also for that of the secondary electron, the `cascade' process. The energy dependence of the secondary electron yield largely changes with the incident angle, while the energy and angular distributions of secondary electrons emitted in vacuum are rather insensitive to the angle, which is consistent with some experimental results. The cascade process reduces the dependence of secondary electron yield on the incident angle, which varies as an inverse cosine of the angle measured from the normal to the surface for high energy, although the effect of the cascade process is smaller than that of the collision process of the primary electron for keV energy.

Secondary-electron velocity spectra and angular distributions from ions penetrating thin solids

We present velocity spectra and angular distributions of secondary electrons emitted from cleaned surfaces of thin carbon and gold foils penetrated by H+ (Ep = 0.8 and 1.2 MeV), H2+ (Ep/Mp = 0.8 MeV/u) and C+ (Vp = 2.30− and 2.85 VB). Prominent structures in doubly differential velocity spectra d2n/dEdΩ of secondary electrons (SE) are (1) the “true SE” peak at low electron energies Ee < 10 eV, (2) the binary encounter peak at electron velocities Ve = 2Vp cos θ (observation angle θ), (3) convoy electrons at Ve = Vp (θ = 0°), (4) loss electrons (from ions carrying electrons) at Ve = − Vp at θ = 180° (backward direction!), and (5) low-energy peaks (Ee < 25 eV) resulting from the decay of plasmons. Another collective effect, the directed emission of shock electrons perpendicular to the heavy-ion-induced wake in the electron plasma of the solid, can be observed in angular distributions of secondary electrons. This phenomenon is used to study the refraction of low-energy electrons at solid surfaces. Furthermore, it was found that secondary electron emission from metals and YBaCuO high-temperature superconductors depends on the target temperature.

Ion-induced electron emission from cold metal targets covered by rare gases

The energy and angular distributions of secondary electrons emitted upon ion bombardment of cold metal targets covered by rare gases in different states (two-dimensional gas layer, stationary adsorbed layer or solid film) are examined. The state of noble gas on the metal surface influences the yield of electrons from the metal (bulk electron emission) and from the adsorbed layer. A change of density of surface electrons which become localized near the positions of adsorbed particles is supposed to be responsible for the observed differences in electron emission from the targets covered by physi- or chemisorbed noble-gas layers. This is confirmed by analysis of the reflected ions which has been carried out additionally to the electron measurements.

Surface topography effects on energy-resolved polar angular distributions of electrons induced in heavy ion-Al collisions: Experiments and models

Abstract The influence of the surface topography on the polar angular distributions of secondary electrons emitted in Ar+ (and Xe+)-Al collisions was studied. After each set of experiments, carried out in controlled bombardment conditions, the surface target was viewed by scanning electron microscope. Some models were elaborated to schematize the main structures observed. Under normal incidence, continuum background and Al L23 VV Auger electron polar angular distributions were not modified by the topography and closely followed a cosine law which is that expected from a flat surface for electrons generated inside the crystal. This result was in agreement with the angular distributions calculated taking into account different structured surface models. For Al L23 MM Auger electrons, experimental angular distributions as a function of the emission polar angle Θ, either were near a constant law or followed a decreasing law depending on the irradiation conditions. The N(Θ) curves calculated from the models sh...

Angular distributions of secondary electrons emitted in Ar +-Polycrystalline al collisions

Polar angular distributions of secondary electrons emitted from 40 keV Ar +-polycrystalline Al collisions were studied for both Al L 23 Auger electrons and continuum background electrons. For the latter the angular distributions closely follow a cosine law due to the attenuation of the electron flux inside the crystal as a consequence of the inelastic electron mean free path. Such a result gives evidence for an isotropic “source” for these electrons. For Auger electrons, structures superimposed on the monotonic decreasing law, appeared. Their positions are linked to the incident ion beam direction. The experimental L 23M 1M 23 Auger electron angular distributions seem to be an argument in favour of an emission inside the solid or close to the surface (≲ 2 Å).

Angular distributions of secondary electrons emitted in Ar +-polycrystalline Al collisions

Polar angular distributions of secondary electrons emitted from 40 keV Ar+-polycrystalline Al collisions were studied for both Al L23 Auger electrons and continuum background electrons. For the latter the angular distributions closely follow a cosine law due to the attenuation of the electron flux inside the crystal as a consequence of the inelastic electron mean free path. Such a result gives evidence for an isotropic “source” for these electrons. For Auger electrons, structures superimposed on the monotonic decreasing law, appeared. Their positions are linked to the incident ion beam direction. The experimental L23M1M23 Auger electron angular distributions seem to be an argument in favour of an emission inside the solid or close to the surface (≲ 2 A).

Energy-resolved angular distributions of secondary electrons emitted from (111) Al target bombarded by different inert gas ions

Energy-resolved angular distributions of secondary electrons emitted from (111) Al targets bombarded by noble gas ions (Ne +, Ar +, Kr +, Xe +) are studied. These experimental results show an anisotropy less than 10%; they are compared with two theoretical models which apply to continuum background electrons and Auger electrons, respectively. These models take into account the multiple scattering effects of the electrons inside the crystal and their passage through the surface and furthermore, for the Auger electrons, the matrix elements of the corresponding transition. For Kr + and Xe + ions the experimental angular distributions are in reasonable agreement with the calculated curves. For Ne + and Ar + ions experimental results disagree with calculated profiles both for Auger electrons and for continuum background electrons. The analysis of these results lead to presumptive evidence of a preferential ejection of electrons along the [110] directions.

Energy-resolved angular distributions of secondary electrons emitted from (111) Al target bombarded by different inert gas ions

Energy-resolved angular distributions of secondary electrons emitted from (111) Al target bombarded by different inert gas ions

Energy and angular distributions of secondary electrons from 5-100-keV-proton collisions with hydrogen and nitrogen molecules

Cross sections for the ejection of electrons from hydrogen and nitrogen by protons have been measured as a function of the energy and angle of ejection of the electrons at incident proton energies of 5-70 keV and 100 keV for hydrogen. The range of angles measured was 10-160\ifmmode^\circ\else\textdegree\fi{} and the electron energy range was 1.5-300 eV. The doubly differential cross sections were also integrated over angle, over electron energy, or over both to obtain singly differential and total cross sections for electron production. Average electron energies were also calculated from the data. The angular distributions of electrons are peaked in the forward direction but become more isotropic as the proton energy decreases. Nitrogen yields a more isotropic distribution than hydrogen. In this range of proton energies the cross sections integrated over angle are found to fall off approximately exponentially with electron energy, and a simple empirical equation has been found that describes the singly differential and total cross sections within a factor of 2 for several targets. A theoretical interpretation of this result in terms of the molecular promotion model is given in which Meyerhof's method of calculating cross sections for $K$-shell excitation is applied for the first time to the ionization of outer shells of atoms.

Diffraction effects in the angular distribution of secondary electrons emitted under ionic bombardment of a (111) surface of silver: Experimental results and theoretical model

The angular distributions of secondary electrons emitted from a (111)Ag target, when bombarded by rare gas ions, are presented. A theoretical model based upon multiple scattering effects using the Low Energy Electron Diffraction (LEED) formalism is proposed. The calculated curves are in good agreement with experimental results within the electron energy range we have investigated (10 < E < 100 eV).

Angular distributions for the charged components in a cascade shower induced by 350 MeV electrons

The angular distributions of secondary electrons contained in a cascade shower are studied by using a streamer chamber∗∗∗∗This study was partly supported by the grant-in-aid for scientific research from the Ministry of Education, Japan.. The primary electrons with energy of about 350 MeV are incident on a lead converter of various thickness. The angular data are analyzed for the number of electrons in a shower, and for the converter thickness. The obtained distributions show a systematic agreement with the Monte-Carlo calculations presented by Messel and Crawford.

Angular and energetic distributions of secondary electrons emitted by solid targets under ionic bombardment

Abstract The energy distributions of secondary electrons emitted by targets bombarded with ions in the range 10–100 keV, are studied. The energy spectra show an intensive peak at 2 eV. Beyond, in the experiments performed on light elements (Z ≤ 30) we observe an Auger peak relating to the creation of a hole on the fxst atomic energy level situated below the valence band (KVV, L23 VV and M23 VV transitions) accompanied by two or three peaks corresponding to excitation of surface plasmons. Energy spectra obtained from phosphorus and sulphur compounds reveal Auger electrons corresponding to L23(P) VV (or L23(S) VV) and L23(P) MIV-V(Ga) V (or L23(P) NIV-V(In) V) transitions; moreover peaks due to plasmon excitations and d band excitations can be distinguished. The fnst results obtained from some alloys show Auger spectra, characteristic of the different elements which compose the alloy. An anisotropy in the energy angular distribution of secondary electrons emitted from copper single crystal is observed.