R.P. Webb

Simulated annealing analysis of Rutherford backscattering data

The combinatorial optimization simulated annealing algorithm is applied to the analysis of Rutherford backscattering data. The analysis is fully automatic, i.e., it does not require time-consuming human intervention. The algorithm is tested on a complex iron-cobalt silicide spectrum, and all the relevant features are successfully determined. The total analysis time using a PC 486 processor running at 100 MHz is comparable to the data collection time, which opens the way for on-line automatic analysis.

Energy spike generation and quenching processesin ion bombardment induced amorphizationof solids

A detailed analysis of generation and potential recrystallization of amorphous zones resulting from ion irradiation of solid materials is given. The criterion for generation of such spikes is considered to be that sufficient energy is deposited locally to induce melting. Subsequently the heated zone is considered to cool via unperturbed thermal diffusion from an initial temperature distribution of Gaussian form, although the expected ellipsoidal geometry is idealized to spherical symmetry for analytical convenience. Recrystallization is considered to occur via a thermally activated process during spike quenching and criteria for crystallization at both zone boundaries and centres are deduced. These criteria are shown to correspond well to earlier analyses, but other parameters such as substrate temperature and energy deposition density are found to be of considerable importance. Suggestions for more accurate modelling are also examined.

Accurate RBS measurements of the indium content of InGaAs thin films

In x Ga 1~x As been analysed and values of x obtained with an estimated accuracy of ?1% in most cases. The observed variation in two measurements of a set of nine samples with a range of values of x has a mean of 1.000 and a standard deviation of 2.2%. This observed error is not inconsistent (at the 5% signi‐cance level) with the estimated error. The analytical method described is valid for many compound thin ‐lms. 1997 by John Wiley & Sons, Ltd.

Chemical Characterization of Latent Fingerprints by Matrix-Assisted Laser Desorption Ionization, Time-of-Flight Secondary Ion Mass Spectrometry, Mega Electron Volt Secondary Mass Spectrometry, Gas Chromatography/Mass Spectrometry, X-ray Photoelectron Spectroscopy, and Attenuated Total Reflection Fourier Transform Infrared Spectroscopic Imaging: An Intercomparison

The first analytical intercomparison of fingerprint residue using equivalent samples of latent fingerprint residue and characterized by a suite of relevant techniques is presented. This work has never been undertaken, presumably due to the perishable nature of fingerprint residue, the lack of fingerprint standards, and the intradonor variability, which impacts sample reproducibility. For the first time, time-of-flight secondary ion mass spectrometry, high-energy secondary ion mass spectrometry, and X-ray photoelectron spectroscopy are used to target endogenous compounds in fingerprints and a method is presented for establishing their relative abundance in fingerprint residue. Comparison of the newer techniques with the more established gas chromatography/mass spectrometry and attenuated total reflection Fourier transform infrared spectroscopic imaging shows good agreement between the methods, with each method detecting repeatable differences between the donors, with the exception of matrix-assisted laser desorption ionization, for which quantitative analysis has not yet been established. We further comment on the sensitivity, selectivity, and practicability of each of the methods for use in future police casework or academic research.

DIFFICULTIES IN DEDUCING DISORDERING MECHANISMS FROM EXPERIMENTAL STUDIES OF DISORDER-ION FLUENCE FUNCTIONS IN ION IRRADIATION OF SEMICONDUCTORS

Abstract A detailed composite model of amorphousness production during ion irradiation of semiconductors at low temperatures and the stepwise approximation to the disorder density profile for disorder accumulation is presented. Numerical calculations of this and other models are performed and a series of comparisons are made. It is shown that all the models considered can result in numerically similar amorphousness-ion fluence curves and hence that interpretation of experimental data of this kind can be difficult. It is further shown that if in an experimental procedure disordered but not amorphous regions are also analysed then the resulting disorder-fluence curves can be misleading and almost impossible to interpret without further analyses of, for example, dose rate effects or direct observation of defect density.

Computer-simulated energy and angular distributions of sputtered Cu atoms

Abstract The energy and angular distributions of copper atoms ejected by 5 keV incident Ar ions have been simulated using the multiple interaction molecular dynamics technique. Calculations carried out with two independently written computer codes yielded essentially identical results. As in previous simulation studies of low to medium energy sputtering, virtually all ejected atoms came from the first layer or second layer. Two different ion-atom potentials were used in the simulations. Absolute sputtering yields depended strongly on the choice of potential; relative yields and angular distributions were found to be insensitive to the choice of potential. For Ar ions normally incident on the (100), (110), and (111) faces of a fcc Cu crystallite, ejected atoms from the second layer of the crystallite exited preferentially in the forward direction compared to those sputtered from the first layer. The energy spectra of atoms ejected from the second layers were harder than those of the first layer atoms.

Internal energy of molecules ejected due to energetic C60 bombardment.

The early stages of C(60) bombardment of octane and octatetraene crystals are modeled using molecular dynamics simulations with incident energies of 5-20 keV. Using the AIREBO potential, which allows for chemical reactions in hydrocarbon molecules, we are able to investigate how the projectile energy is partitioned into changes in potential and kinetic energy as well as how much energy flows into reacted molecules and internal energy. Several animations have been included to illustrate the bombardment process. The results show that the material near the edge of the crater can be ejected with low internal energies and that ejected molecules maintain their internal energies in the plume, in contrast to a collisional cooling mechanism previously proposed. In addition, a single C(60) bombardment was able to create many free and reacted H atoms which may aid in the ionization of molecules upon subsequent bombardment events.

The injection of inert gas ions into solids: Their trapping and escape

Abstract The title of this symposium and proceedings, and of the other papers presented, reveals not only the general interest in the behaviour of rare gases in solids but some of the technological reasons why knowledge of such behaviour is important. Clearly basic information is required to understand fission gas generation and its consequence for swelling and embrittlement in fission reactors, for understanding and controlling first wall problems in fusion reactors and for attempting to design storage for active gas waste. In all of these areas the rare gas atoms are generated with kinetic energy and may thus interact differently, during their slowing down, with the solid than if they had been introduced more gently (e.g. via diffusion) into the solid. An important method of simulating the behaviour of such energetic rare gas atoms in solids is via external irradiation of the solid with rare gas ions of appropriate species and energies and it is the purpose of this review to evaluate studies of this nature.

THE EFFECTS OF ION-IMPLANTATION ON THE INTERDIFFUSION COEFFICIENTS IN INXGA1-XAS/GAAS QUANTUM-WELL STRUCTURES

Photoluminescence coupled with repetitive thermal annealing has been used to determine the diffusion coefficients for intermixing in InxGa1−xAs/GaAs quantum wells and to study the subsequent effects of ion implantation on the intermixing. It is shown that following ion implantation there is a very fast interdiffusion process, which is independent of the implanted ion and that is thought to be due to the rapid diffusion of interstitials created during the implantation. Following this rapid process, it was found that neither gallium nor krypton ions had any effect on the subsequent interdiffusion coefficient. Following arsenic implantation in addition to the initial damage related process, an enhanced region of interdiffusion was observed with a diffusion coefficient that was an order of magnitude greater than that of an unimplanted control wafer. This enhanced process is thought to be due to the creation of group III vacancies by the arsenic atoms moving onto group V lattice sites. This fast process was pr...

Deactivation of ultrashallow boron implants in preamorphized silicon after nonmelt laser annealing with multiple scans

Electrical activation and redistribution of 500eV boron implants in preamorphized silicon after nonmelt laser annealing at 1150°C and isochronal rapid thermal postannealing are reported. Under the thermal conditions used for a nonmelt laser at 1150°C, a substantial residue of end-of-range defects remained after one laser scan but these were mainly dissolved within ten scans. The authors find dramatic boron deactivation and transient enhanced diffusion after postannealing the one-scan samples, but very little in the five- and ten-scan samples. The results show that end-of-range defect removal during nonmelt laser annealing is an achievable method for the stabilization of highly activated boron profiles in preamorphized silicon.