Incident Electron Beam Energy Research Articles

Low energy ion beam damage of semiconductor surfaces: a detailed study of InSb(100) using electron energy loss spectroscopy

The phonon and plasmon excitations of both n- and p-type InSb(100) have been studied using high resolution electron energy loss spectroscopy (HREELS). The effects of structural damage, induced by low energy ion bombardment, on the conduction band plasmon energy has been monitored as a function of post-bombardment annealing temperature. In all cases, the plasmon energy reaches a maximum of between 55 and 75 meV after annealing to ~ 500 K. This indicates the presence of a large excess of free-carriers in the near-surface region probably due to the presence of defect states including Sb vacancies which would act as donor states. By monitoring the plasmon energy as a function of incident electron beam energy, we exploit the potential of the HREELS technique to probe the free-carrier concentration in semiconductors over a depth range of about 200–2000 Å. The degree and depth of damage induced by the sputtering process is found to be approximately 800–1000 Å into the bulk of the material, corresponding to the formation of an n-type layer in this near-surface region.

Background effects in electron stimulated desorption ion angular distribution (ESDIAD) measurements on Si(111)-(7×7)

The background effect in electron stimulated desorption ion angular distribution (ESDIAD) measurements due to soft x-ray production on Si(111)-(7×7) is investigated. We find that the background intensity from a Si(111)-(7×7) surface varies linearly with incident electron beam energy and current density. It is also found that the elimination of the background effect (by subtraction) plays a crucial role in both quantitative and qualitative interpretations of digital ESDIAD measurements on silicon, as well as to similar measurements on other surfaces.

Electron energy and momentum spectroscopy in solids

We have used (e,2e) coincidence techniques to study electron momentum densities as a function of binding energy and momentum in thin films. The experiment employs symmetric coplanar geometry with incident electron beam energy of 10 keV. The outgoing electrons are retarded to about 100 eV before being dispersed in identical hemispherical analysers and counted in one-dimensional position-sensitive detectors consisting of multichannel plates and resistive anodes. Binding energy spectra are obtained by stepping the incident energy through a predetermined range. In amorphous carbon films 80 A thick, we have obtained electron momentum distributions for binding energies from 0 to 40 eV with momentum as parameter (0, 0.4 and 0.8 atomic units). The results clearly show contributions from the 03C0- and 03C3- bands and demonstrate the usefulness of the method.

Application of X‐ray emission spectrometry (LEEIXS) to the study of insulator surface—molecular characterization of some metallic oxides or compounds

AbstractLow‐energy electron‐induced x‐ray spectrometry (LEEIXS) is a soft and ultrasoft x‐ray emission technique. The wavelength‐dispersive x‐ray spectrometer used is equipped with a cold cathode tube. This device acts as an excitation source by bombarding the sample surface with a quasi‐monoenergetic electron beam, the energy of which is selectable over the range from 0.5–5 keV. The probed depth, depending among other parameters upon the incident electron beam energy and upon the sample nature, typically ranges from 5 to 150–200 nm, the probed area being ∼1 cm2. The capabilities of this technique in the fields of atomic and molecular surface analyses have been shown for a wide range of applications. The aim of this paper is to point out the ability of this technique to solve some problems dealing with the near‐surface analysis of insulating materials and, more particularly, of some metallic oxides.

An electron energy loss study of the surface formate species chemisorbed on Ni(110): Dipole, impact, and resonance scattering for adsorbate covered surfaces

A comprehensive energy and angular dependent high resolution electron energy loss study of the surface formate species (HCOO), adsorbed on Ni(110) at room temperature, has been carried out. By varying both the primary electron beam energy Ei and the scattering geometry, dipole, impact, and resonance scattering processes have been identified and exploited, to gain information regarding the different vibrational excitations of the HCOO/Ni(110) system. Application of the appropriate dipole and impact scattering selection rules, yields information concerning the HCOO orientation at the surface. It is found that the HCOO bonds to the surface, via the two oxygen atoms, with the C2 axis normal to the surface and with the plane of the HCOO aligned along the close-packed 〈110〉 rows. A dipole active Ni phonon, at 29 meV, observed in specular scattering geometry, is assigned to an S̄ phonon of the clean surface Brillouin zone and clearly indicates that the HCOO is adsorbed with the C–H bond projecting onto a short-bridge site, with the two oxygen atoms occupying effectively on-top sites. Finally, enhancement of the symmetric O–C–O stretch is attributed to a resonant scattering process, centered at an incident electron beam energy, Ei=14 eV, resulting in the formation of a temporary negative ion. On the basis of the energy and angular dependence of the enhancement, the resonant state is related to the so-called σ-shape resonances recently observed in near-edge x-ray absorption spectroscopy studies of HCOO adsorbed on copper surfaces. Overtone and combination bands, some of which are also enhanced by the resonant excitation, are also assigned.

Electron stimulated desorption of positive ions from an adsorbate-covered Si(100) surface

Electron stimulated desorption of positive ions (H +, C +, O +, CO + and CO 2 +) from the (100) surface of a silicon single crystal exposed to NO and CO at room temperature has been observed for electron energies in the range of 0–180 eV. The dependence of the ion yields on the incident electron beam energy shows thresholds in the 18.5–22.5 eV range and features at Si core level excitation energies. The total desorption cross sections for the ionic species are similar and at a value of approximately 10 −18 cm 2.

Pseudo depth profiling by ESCA and X-ray microanalysis: An application to chemical dealumination of Y-zeolites

A combination of electron spectroscopy for chemical analysis (ESCA) and scanning electron microscope X-ray microanalysis techniques is reported, which, when applied to Y zeolites, provides compositional depth profiles and a depth distribution of impurities in materials. The depth profile relies on the fact that ESCA samples down to ∼ 3 nm while variation of the incident electron-beam energy allows X-ray microanalysis to sample depths between ∼ 30 nm and ∼ 5 μm. The technique has been applied to Y zeolites dealuminated with (NH 4) 2SiF 6 and subsequently washed/ion exchanged in various ways. All the samples examined exhibit a decreasing Si Al ratio with increasing depth into the crystallites, showing that the dealumination process is diffusion controlled. Subsequent treatments alter the extent of the dealumination process; for example, washing with 0.1 m HNO 3 (aq) produced substantial further dealumination at all depths.

Electron-stimulated desorption of O+ ions from a gas-covered CdS(0001) surface.

Electron-stimulated desorption of ${\mathrm{O}}^{+}$ ions from a CdS(0001) single-crystal surface exposed to ${\mathrm{O}}_{2}$ and NO has been investigated. Only ${\mathrm{O}}^{+}$ desorption was observed in both cases with a total cross section of \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}17}$ ${\mathrm{cm}}^{2}$. The dependence of the ion yield on the incident electron-beam energy from 0--180 eV exhibits thresholds at both the Cd 4d, 4p, 4s, and the S 3s and 2p core-level binding energies. Evidence is presented which indicates that the ions may originate from multiple states.

An analytical investigation of heterojunctions formed by vacuum deposition

Heterojunctions formed on the surface of the II–VI materials ZnTe, ZnSe, ZnS, CdS, ZnO and Zn 0.22Cd 0.78S have been fabricated by the vacuum deposition of copper chloride. A solid state reaction has been observed to take place at the surface of each of these materials. A detailed study of this reaction has been made by energy dispersive X-ray microanalysis and reflection electron diffraction. For some of the materials a limited reaction was observed to occur at room temperature. A complete reaction was only attained by annealing in the 150°C to 200°C temperature range. The use of a variable incident electron beam energy in X-ray microanalysis as a technique for the detection of heterojunction diffusion and film thickness assessment is demonstrated.

Electron stimulated desorption from GaAs(100) surface

Measurements of electron stimulated desorption of CO+, CO+2 , C+, and O+ have been carried out for a sputter-cleaned and annealed GaAs(100) surface exposed to CO2, O2, and NO at room temperature. The dependence of the ion yields on the incident electron beam energy from 0 to 200 eV exhibits thresholds at the Ga 3d, 3p, and 3s and As 3d and 3p core level binding energies. The total desorption cross section for the ionic species is ∼10−18 cm2.

Damage effects of high energy electrons on metals

In this paper, we present results obtained both experimentally, using in-situ electrical resistivity measurements in the high voltage electron microscope, and theoretically, using molecular dynamics computer simulations. These data give a detailed picture of the mechanisms of atomic displacement in Cu and make it possible to quantitatively predict the production rate of point defects given the incident electron beam energy and direction relative to the crystalline axes. Damage effects are found to be important at energies as low as 100–400 keV. We also review the work that has been carried out on other metals and the effect of temperature on the damage production process.

Three Dimensional Characterization of Interfaces in Semiconductors by Scanning Electron Microscopy

AbstractIn many semiconductor materials problems, structural characterizations must be achieved in both the lateral and vertical dimensions. Although a combination of cross-sectional and planar transmission electron microscopy can provide this information, the sample preparation time is demanding and only relatively small volumes of material are examined. We describe here an alternative approach in which the charge collection (‘CCM’) imaging mode of the scanning electron microscope (SEM) is used. It is shown that, by varying the incident electron beam energy, electricallly active defects at different positions beneath the entrance surface of the material can be imaged and their depth estimated.

Monte Carlo calculation of electron scattering from surface films

The electron backscattering coefficient and reflected energy for surface films on bulk substrates have been computed using the photon-electron Monte Carlo transport code sandyl. The calculations were done for the film/substrate configurations Al/Pt, Ag/Pt, Ag/Al, and Au/Al with incident electron beam energies of 20, 40, 60, and 100 keV at different angles of incidence and various film thicknesses. The backscattering results are compared with available experimental data taken at normal incidence.

Measurement of transition radiation from medium-energy electrons.

The absolute differential production efficiencies (photons/eV sr electron) for x rays emitted from each of three transition radiators were measured for incident electron-beam energies of 17.2, 25, and 54 MeV. The radiators were made of stacks of 1.0-..mu..m-thick foils: 18 foils of beryllium, 18 foils of carbon, and 30 foils of aluminum. The radiation spectra were most intense between 0.5 and 2.5 keV, peaking at 0.8, 1.3, and 1.3 keV, respectively. The angular distribution of the transition radiation from the beryllium-foil stack was measured for the three electron-beam energies and found to agree well with theoretical predictions. Owing to K-shell absorption, the photon-energy spectra from the carbon and aluminum stacks are narrowed. Theoretical calculations, which include both the two-surface interference and photon attenuation in the foil material, agree well with these data. A method of enhancing output using a split-foil stack is considered; cursory experiments with a split stack of Mylar foils showed enhanced emission. The use of transition radiation as a source of x rays for lithographic purposes may be practical.

Electron channeling radiation from diamond.

A series of channeling-radiation experiments for incident electrons of 16.9, 30.5, and 54.5 MeV has been performed, using a type-IIa natural diamond 23 \ensuremath{\mu}m thick. Channeling-radiation transition energies calculated with the standard (Hartree-Fock) potential are in good agreement with the observed results for the (100) and (110) planes as well as for the 〈100〉 axis at all energies, but are in error for the (111) plane. Corrections to the (111) potential due to anisotropic electron distributions which are based upon x-ray-diffraction data result in calculated transition energies that are in better agreement with the observed data; an empirical (111) potential yields calculated transition energies which are in even better agreement with the data. Calculated linewidths are considerably narrower than the observed values; this disagreement probably results from incoherent scattering by crystal defects having an average spacing of approximately 1 \ensuremath{\mu}m. The transition energies are shown to scale as ${\ensuremath{\gamma}}^{5/3}$ for transitions involving states that are localized close to the atomic planes and as ${\ensuremath{\gamma}}^{2}$ for those localized close to the midplane regions. Free-state populations are shown to increase relative to bound-state populations with incident electron-beam energy. Channeling radiation has been shown to constitute a practical source of x-ray photons utilizable at many existing accelerators.

Electron‐stimulated desorption from hydrogen exposed palladium 〈100〉

Measurements of electron‐stimulated desorption (ESD) of H+ have been carried out for a sputter‐cleaned and annealed palladium 〈100〉 surface exposed to hydrogen at low temperature. The dependence of the H+ yield on the energy of the incident electron beam energy from 15 to 400 eV exhibits thresholds for hydrogen desorption at the Pd 4p, 4s, and 3d core level binding energies. In addition, a low energy threshold is observed near 23 eV. The temperature dependence of the ESD signal has also been measured and shows that the H+ yield drops nearly two orders of magnitude upon warming from 130 to 250 K.

High kinetic energy N+ ions from decay of doubly ionized N2

N+ ions from the process e+N2→N22++3e→N+ +N++3e have been searched for by a coincidence method in which N+ ions were detected at 90° to crossed N2 and pulsed electron beams. Measurements were made for incident electron beam energies of 100, 150, and 300 eV. At electron energies of 150 and 300 eV, a comparison of calculated accidental and measured coincidence time-of-flight distributions indicates the presence of N+ ions with kinetic energies in the region from 5 to 14 eV from the double ionization process above.

Electrodisintegration ofHe3

The continuum spectra of $^{3}\mathrm{He}$ have been measured up to excitation energies of 40 MeV by means of inelastic electron scattering. Incident electron beam energies between 60 and 120 MeV were used, corresponding to a momentum transfer range of 0.3 ${\mathrm{fm}}^{\ensuremath{-}1}$ to 1.1 ${\mathrm{fm}}^{\ensuremath{-}1}$. Scattered electrons were observed at two angles, 92.6\ifmmode^\circ\else\textdegree\fi{} and 127.7\ifmmode^\circ\else\textdegree\fi{}. The radiation corrected spectra and the form factors are presented, and compared with calculations based on a zero-range approximation. In this model, the sharp rise from the $p+d$ threshold previously reported may be identified as a $^{2}S\ensuremath{\rightarrow}^{2}S$ Coulomb monopole transition.NUCLEAR REACTIONS $^{3}\mathrm{He}(e, {e}^{\ensuremath{'}})$, ${E}_{x}=0\ensuremath{-}40$ MeV; measured $\ensuremath{\sigma}(E; \ensuremath{\theta})$; $\ensuremath{\theta}=92.6\ifmmode^\circ\else\textdegree\fi{} \mathrm{and} 127.7\ifmmode^\circ\else\textdegree\fi{}$. Comparison between radiation-corrected spectra and zero-range model calculations; multipole decomposition.

Backscattering of 10-100 keV electrons from thick targets

Experimental measurements of backscattering as a function of incident electron beam energy, angle of beam incidence and atomic number of scatterer, together with energy spectra of backscattered electrons, are discussed within the framework of a simple, qualitative theory. A semi-empirical expression for the variation of backscattering coefficient with angle of beam incidence is derived. Spectra integrated over energy and angle of take off also tabulated from experimental measurements for several elements. The use of the experimental data to derive backscattering corrections for X-ray elemental analysis, particularly at non-normal incidence, is briefly described.

Measurement of inclusive hadron electroproduction from hydrogen and deuterium

We report on the inclusive electroproduction of hadrons from nucleon targets. The incident electron beam energy is 19.5 GeV. We detect scattered electrons corresponding to exchanged virtual photons in the range $\ensuremath{-}0.25>{q}^{2}>\ensuremath{-}3.00$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ and $12<s<30$ ${\mathrm{GeV}}^{2}$. In coincidence we detect most hadrons which go in the forward (virtual photon) direction in the virtual-photon-nucleon c.m. system. The cross section for producing these hadrons is studied as a function of azimuthal angle, transverse momentum squared,and a longitudinal-momentum-related variable. Data are presented for proton, deuteron, and neutron targets, and are largely consistent with the data in real photoproduction ${q}^{2}=0$. Notable differences are that in electroproduction the transverse momentum distributions are somewhat broader, and the forward hadrons are less charge- and less charge- and less charge- and isospin-symmetric. The data are generally consistent with expectations of parton models.