Edward W. Thomas

Ion bombardment induced photon and Auger emission for surface analysis

Abstract Impact of heavy ions on surfaces induces Auger electron and photon spectra characteristic of the surfaces. In general such spectra are dominated by decay of excited sputtered particles. Auger decays are very fast so decay may sometimes occur while the particle is under the influence of the surface field, leading to complex spectral features. By contrast, radiative decay is slow so that ejected atoms are in free space before photon emission occurs and the spectra are readily recognized by reference to standard tables. We review the present understanding of both types of spectra and consider the circumstances under which they may be useful for determination of surface properties or surface composition.

Auger spectra induced by Ne+ and Ar+ impact on Mg, Al, and Si

Impact of Ne+ and Ar+ at energies of 20–200 keV on targets of Mg, Al, and Si gives rise to an electron spectrum that has sharp atomiclike features superimposed on a continuous background. The continuum is similar to the spectrum observed during electron impact and is generally ascribed to decay of L‐shell vacancies in the matrix. We show, however, that this is not completely correct, that the apparent continuum induced by ion impact extends to higher energies than for electron impact and that this is due to the presence of some hitherto unidentified atomiclike lines. We identify the atomiclike transitions as due to particles sputtered with L‐shell vacancies. A complete modelling of the spectra is performed which accounts quantitatively for all Auger peaks. We conclude that the major features are due to sputtered neutral atoms with a single inner shell vacancy. The electron configurations and energies are Mg0 2p53s23p (50.6 eV), Al0 2p53s23p2 (73.8 eV), and Si0 2p53s23p3 (101.1 eV). These are states where ...

Auger spectra induced by 100‐keV Ar+ impact on Be, Al, and Si

The Auger electron spectrum induced by the impact of 100‐keV Ar+ on metallic aluminum is shown to be consistent with the source of Auger electrons being ejected target particles. The principal spectral line has been identified as being due to ejected Al atoms with a single 2p vacancy. Subsidiary peaks are due to ejected atoms and Al+ ions with one or two 2p vacancies. The ion‐induced Auger spectrum of silicon is similar. By contrast the spectrum induced by Ar+ impact on Be exhibits a rather broad peak characteristic of a K‐shell vacancy and is similar to that induced by the impact of electrons. By considering the lifetime of the Be K‐shell vacancy we conclude that the Auger decay occurs while the Be atoms are either in the solid or interacting with the surface.

The effect of aluminum and boron solid-source doping on recombination in silicon solar cells

The recombination properties of p-type diffusions formed by aluminum diffused into the silicon from an evaporated layer and boron diffused from a B/sub 2/O/sub 3/ layer deposited on the silicon from solid doping sources is investigated. The contactless photoconductivity decay method was used to separate the emitter saturation current density J/sub o/ of the diffusions themselves from the effect of the diffusion process on the bulk lifetime in the substrate. Al diffusions were found to have very high values of J/sub o/, ranging from approximately 66*10/sup -13/ A/cm/sup 2/ at a diffusion temperature of 850 degrees C, to approximately 20*10/sup -13/ A/cm/sup 2/ at 1100 degrees C. However, the detrimental effect of these high J/sub o/ values on cell efficiency can be managed by reducing the coverage fraction of the diffusions. Bulk lifetimes remained high at approximately 2000 mu s after Al diffusion at temperatures from 850 degrees C to 1100 degrees C.<<ETX>>

Auger spectra induced by ion impact on metals

Abstract The Auger electron spectra induced by 20–200 keV Ar + ion impact on Al and Fe are examined and the spectral lines identified. For Al the spectrum is due to sputtered Al and Al + with one or two vacancies in the 2p shell. For Fe there are Doppler broadened lines from Ar plus subsidiary structure from interatomic transitions.

Identification of Auger spectra induced by Ar+ and Kr+ ion impact on transition metals

The production of Auger electrons from Cr, Mn, Fe, and Co by 20–200‐keV Ar, 100‐keV Kr, and 3‐keV electrons has been studied. The metal M23M45M45 and the Argon LMM peaks are clearly identifiable, the latter broadened consistent with electron emission from backscattered Argon ions. Various other features are produced which cannot be due to target or projectile Auger emission. These are believed to result from interatomic transitions between the ions of the beam and those of the target.

ION INDUCED AUGER SPECTROSCOPY

Abstract Auger electron spectra are induced by impact of heavy ions (e.g. Ar + ) on surfaces; it has been suggested that analysis of such spectra would be a useful technique for surface analysis. We have examined the Auger spectra for various projectile-target combinations and present as representative data the spectra for 100 keV Ar + impact on Al, Cr, Mn, Fe and Co. For a projectile incident on a species of higher nuclear charge the spectrum is dominated by Auger lines from the projectile, broadened considerably by the Doppler effect due to the projectiles motion. The spectra are not characteristic of the target and therefore offer no opportunity for surface analysis. For a projectile incident on a target of lower nuclear charge the spectrum is that of the target species but the spectrum is consistent with the source being sputtered excited atoms; the Auger electrons do not come from the surface. We conclude that the ion induced Auger spectra are in general not a convenient method for surface analysis.

The influence of oxygen on backscattering of excited H when H+1, H+2, and H+3 ions at 4–30 keV energy are incident on molybdenum

A study has been made of the Hβ line intensity from excited H atoms scattered off Mo or Cu surfaces. Incident projectiles were 4–30‐keV H+1, H+2, and H+3 ions. The integrated intensity of the atomic line emission increased as the ambient pressure of oxygen in the target chamber was raised from 10−11 to 10−6 Torr. The experimental data suggested that this change of intensity is caused by a reduction in the radiationless deexcitation of atoms by the Auger mechanism. A simplistic model was formulated which predicts the intensity as a function of ambient O2 pressure, projectile beam current density, and energy, but only in the case of H+ ions on Mo. An attempt to extend the model to H+2 ions was not successful. For Cu targets an increase in the intensity as a function of oxygen pressure was also observed. However, no attempt was made to test the model in this case. At an incident angle of 60° coefficients for sputtering of oxygen, Sox, adsorbed on Mo were determined to be 0.0025±0.0004, 0.011, and 0.017, resp...

Using discriminant analysis to identify students at risk

In designing any educational intervention one often needs to determine what factors are related to success and failure in a course, identify students at risk, evaluate the impact of any new program on student performance. In this paper we will discuss the use of discriminant analysis as a technique for addressing all of these issues. Discriminant analysis is a statistical technique designed to investigate the differences between two or more groups of people with respect to several underlying variables. This technique is more appropriate than commonly used educational measures (correlations, regression weights, etc.) because the variable being predicted is categorical. Moreover, this approach results in a unit of analysis, predicted category membership, that is more useful in evaluating instructional interventions.

SIMS analysis using ejected CsX+ ions

Abstract A structure consisting of Ge/Pd/GaAs is analyzed with the SIMS technique using a Cs + probe. Comparison is made between the signals of ejected ions X + and ejected diatomics CsX + . It is proposed that CsX + is formed by an ion molecule reaction between emerging sputtered neutral X and surface Cs + . Depth profiles of Ge, Pd, Ga and As monitored by the species CsX + are shown to be free of matrix effects at interfaces and the species exhibit approximately equal detection efficiencies. Use of the CsX + signals to study an annealed Ge/Pd/GaAs structure clearly shows the segregation of Ge to the GaAs interface.