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Roger joined the Department in 1983 as a Research Fellow with the SRC (as it was then - interesting how the EPSRC has gained letters over the years) Surrey Ion Beam Centre. He was employed to look after the computing facilities associated with the research group - a single pdp11, about half of the computer "power" in the department in those days.
Before this he had spent 3 years as a post doc at the Naval Postgraduate School in Monterey California, making Molecular Dynamics Studies and Computer Animations, which is still the main area of his research activities. He did his PhD work in the Electronic & Electrical Engineering Department of the University of Salford, on the Mathematical Modelling of Atomic Collisions in Solids.
He was made a Lecturer in the Department in 1986, promoted to Senior Lecturer in 1993 and then to Reader in 1997, reaching the dizzy heights of Professor of Ion Beam Physics in 2002. He is the current Director of the Surrey Ion Beam Centre.
Main area of research is the interaction of energetic ion beams with solids.Current research activities include the use of Molecular Dynamics Simulations to predict the behaviour of cluster and molecular impacts on surfaces. As well as the use of more simple Binary Collisions simulations to predict the effects of energetic particle solid interactions, in particular ion implantation profiles in crystalline solids. Cluster and molecular impacts include fullerene impact induced desorption of molecular solids.Other areas of interest are in automation and control of ion beam analysis equipment. This includes software to automate the collection of data from standard analyses using RBS, PIXE, PIGE, NRA and ERD.He must also take some responsibility for the windows interface to the Data Furnace for the automated and rapid analysis of experimental ion scattering data. Developments in the use of MeV ion beams for Secondary Ion Mass Spectrometry (SIMS) is also of current interest.
Knowledge Transfer Partnership on manufacturable X-Ray detectors with Gresham Scientific Instruments and RMGwilliam, £123,792 awarded June 2004
BioMed Network for High Energy Ion Beams, May '04 - £63,109 - with KJKirkby, GWGrime, SReady, AClough, NSpyrou
Marie Curie Training Network for Application of MeV Ion Beams to Cell Irradiation Jan '05 - £300,000 - with GWGrime, KJKirkby, NJKirkby - part of a £3M EU grant
MeV Ion Nanobeams: Nanotechnology for the 21st Century, Sept '05 - £256,845 - with GWGrime, KJKirkby, AClough, RGwilliam, CJeynes
New Developments in ToF-SIMS Surface Mass Spectrometry with ATR_IR Spectroscopy, Sept '05 - £227,208 - with KJKirkby - part of a £1.9M project with University of Manchester
University of Surrey Ion Beam Centre, March '06 - £2,271,580 - with BSealy, KKirkby, KHomewood, RGwilliam, CJeynes, GGrime
The Non Scaling Fixed Field Alternating Gradient (NS-FFAG) Accelerator, April '07 - £7,489,380 - with 5 other University groups and KJKirkby
Enhancing new developments in ToF-SIMS through researcher exchanges, Oct '07 - £109,825 - with JVickerman and NLockyer
Laser Induced Beams of Radiation and their Applications (LIBRA), Nov '07 - £4,747,342 - with 4 other Universities and KJKirkby
SPIRIT - Support for Public & Industrial Research Using Ion Beam Technology, March '09 - £1,069,314 (FP7 with 7 other centres, total value ~£5.5M)
Ambient Pressure Mass Spectrometry at the Sub Micron Scale (MeV-SIMS), December '11 - £1,278,391 - with NWard and KJKirkby
The proton beam writing (PBW) technique was used to fabricate microfluidic structures in SU-8 resist. A network of the buried channels was fabricated as part of a project to develop functional microfluidic device for neuronal studies and self-powered microfluidics. Protons with energies between 2.5 MeV and 0.75 MeV were used to fabricate the buried channels with a minimum feature size of around 1 ¼m and depths of 40?55 ¼m. Roughness of channels sidewalls was around 2.5 nm rms. Exposure regime and examples of functional networks fabricated using PBW are described. COMSOL Multiphysics® software was used to model the flow characteristics of fluid in the SU-8 microchannels structured by PBW. The results obtained using PBW are compared with the structures fabricated by UV-lithography.
The use of computer simulation to understand the physics of atomic collision phenomenon has escalated in recent years. Even with this proliferation of simulation codes the majority of programs fall into two categories - the event store and the time step models. These models are discussed, and a hybrid formed from the two is described. The best uses of each model is indicated and some examples given. The event store simulations give an accurate method of evaluating range data and the time step models conveniently give information on cascade propogation and nonlinear behaviour. © 1986.
Normal incidence argon-copper sputtering mechanisms have been investigated for ion energies just above threshold. Identical mechanisms operate in both the (111) and (001) surface orientations. Adsorption of an ordered oxygen overlay on the surface does not destroy the ejection processes. Although the mechanisms produce similar ejected atom energy distributions, the processes may be experimentally distinguishable through the angular emission spectrum of the ejected copper atoms.
Carter G, Armour DG, Donnelly SE, Webb R (1978) Energy spike generation and quenching processes in ion bombardment induced amorphization of solids, Radiation Effects 36 (1-2) pp. 1-13
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 centers 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 modeling are also examined.
During the past decade SIMOX (separation by implanted oxygen) has emerged as one of the leading SOI (silicon-on-insulator) technologies. The implantation involves such high doses that sputtering, swelling and the diffusion of excess oxygen within the synthesized layer of SiO2 all contribute to a major oxygen redistribution. The computer program IRIS (implantation of reactive ions into silicon) has been developed to enable fast calculations of these oxygen profiles to be made over a wide range of implantation energies, doses and masking oxide layer thickness. In this paper the model is extended into two dimensions and calculations are performed to simulate high dose implantation through thick patterned masking layers. The resulting oxygen distributions near mask edges are discussed. © 1992.
A single crystal implantation program (CRYSTAL) is used to investigate the behaviour of channelled implants of the major dopant ions (As, P, B) in silicon as a function of the divergence of the incident beam. Many experimental results are currently being published from commercially available implanters which have uncharacterized beam divergences. It is shown that the effects of beam divergence on implant profiles in initially single crystal targets can be substantial and should not be ignored in providing experimental details. A triple peak structure for implant profiles of high energy boron in well-channelled conditions is found to be caused by contributions from a randomized component, a planar channelled component and an axial channelled component. © 1993.
Development of topography in thin (55.5 ¼g cm-2) self-supporting aluminium films, caused by high fluence (
Computer simulations of ion-bombardment events which recrystallize the target demonstrate pit formation at 1.0 keV. Atoms are ejected from the first two target layers in the pit region. The remainder of the pit is created by replacement-collision sequences. Linear-cascade and spike-regime events are dynamically indistinguishable. © 1983 The American Physical Society.
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.
© 2013 Elsevier Ltd.Aspheric lenses are the most common method for correcting for spherical aberrations but, in microlens production, highly-controlled lens profiles are hard to achieve. We demonstrate a technique for creating bespoke, highly-accurate aspheric or spherical profile silicon microlens moulds, of almost any footprint, using focused ion-beam milling. Along with this, we present a method of removing induced ion-beam damage in silicon, via a hydrofluoric acid etch, helping to recover the surface's optical and chemical properties. In this paper, we demonstrate that our milled and etched moulds have a roughness of 4.0-4.1. nm, meaning they scatter less than 1% of light, down to wavelengths of 51. nm, showing that the moulds are suitable to make lenses that are able to handle light from UV up to infra-red.Using empirical experiments and computer simulations, we show that increasing the ion-dose when milling increases the amount of gallium a hydrofluoric acid etch can remove, by increasing the degree of amorphisation within the surface. For doses above 3000¼C/cm2 this restores previous surface properties, reducing adhesion to the mould, allowing for a cleaner release and enabling higher quality lenses to be made.Our technique is used to make aspheric microlenses of down to 3. ¼m in size, but with a potential to make lenses smaller than 1. ¼m.
A computer program, based on TRIM, has been developed to calculate the spatial density of nuclear energy deposited by incident ion beams as well as the magnitude of mixing caused by the ion. The program divides the collision cascade into spherical subcascades formed by energetic recoils and uses a modified Vineyard model of thermal spike mixing to calculate mixing magnitudes. Good agreement is found with experimental results of Fenn-Tye and Marwick [Nucl. Instr. and Meth. B18 (1987) 236] for the high energy mixing of Pt markers in Pd at 10 K. Mixing efficiencies for low energy ion bombardment are predicted from the model. © 1992.
Ion implantation has frequently been shown to modify the shape of quantum wells following thermal annealing by enhancing the interdiffusion. We have shown that, independent of chemical effects on the interdiffusion, there is a contribution from the vacancies created by the implant. The effects of the diffusion of these vacancies can be modeled using a very simple expression that does not rely on any knowledge of the diffusion coefficients for the vacancies in the material. By comparing the problem to the classic problem of the gambler's ruin, we have shown that implantation into a surface should produce even intermixing of layers at different depths below it, ignoring the effects of vacancy trapping and other depth dependent diffusion processes.
Computer simulation of ion-bombardment events has been extended to coalesce and recrystallise the target, so that the surface damage created when a single ion strikes a metal surface can now be studied directly. Qualitative and quantitative information on pit formation, other surface damage and recoil mixing can be obtained from the model. Many characteristics of the target's final condition are evident before the excess energy has been removed. Small structured and faceted surface pits are found at 1.0 keV ion energy for both low and high energy-density potential functions. Atoms are only sputtered from the first two layers of the pit region. The rest of the pit is formed by atoms displaced laterally or downward, initiating replacement collision sequences. A movie has been produced which presents the temporal development and creation of surface damage, and demonstrates surface reconstruction processes. © 1983.
In this paper, the technique of microscope-spectrophotometry, used to nondestructively characterize the microstructure of ion beam synthesized iron-disilicide layers, is described. The results obtained agree extremely well, in terms of layer thickness and interfacial roughness, with those from Rutherford backscattering. The results also show that it is possible to interpret the measured spectral reflectance data in terms of: 1) defect annealing; 2) iron redistribution; and 3) phase transformations from the ² to the ± phase.
Carbon bombardment of graphite and diamond is investigated by molecular dynamics simulations using a many-body potential to describe the low energy interactions splined to a Molière potential which describes the hard collisions. It is found that no ejection takes place from the perfect graphite {1000} face at bombardment energies of 100 eV and that at normal incidence the yield is below 1% up to 600 eV. At oblique incidence corresponding to the maximum yield angle, the yield can be in excess of ten times that at normal incidence and a much larger proportion of dimer and trimer molecules are ejected. The bulk terminated diamond surfaces are found to be less resistant to erosion than graphite with as much as 23% of material ejected at normal incidence being in the form of dimers. © 1991.
The MIAMI* facility at the University of Huddersfield is one of a number of facilities worldwide that permit the ion irradiation of thin foils in-situ in a transmission electron microscope. MIAMI has been developed with a particular focus on enabling the in-situ implantation of helium and hydrogen into thin electron transparent foils, necessitating ion energies in the range 1 - 10 keV. In addition, however, ions of a variety of species can be provided at energies of up to 100 keV (for singly charged ions), enabling studies to focus on the build up of radiation damage in the absence or presence of implanted gas. This paper reports on a number of ongoing studies being carried out at MIAMI, and also at JANNuS (Orsay, France) and the IVEM / Ion Accelerator Facility (Argonne National Lab, US). This includes recent work on He bubbles in SiC and Cu; the former work concerned with modification to bubble populations by ion and electron beams and the latter project concerned with the formation of bubble super-lattices in metals. A study is also presented consisting of experiments aimed at shedding light on the origins of the dimensional changes known to occur in nuclear graphite under irradiation with either neutrons or ions. Single crystal graphite foils have been irradiated with 60 keV Xe ions in order to create a non-uniform damage profile throughout the foil thickness. This gives rise to varying basal-plane contraction throughout the foil resulting in almost macroscopic (micron scale) deformation of the graphite. These observations are presented and discussed with a view to reconciling them with current understanding of point defect behavior in graphite.*Microscope and Ion Accelerator for Materials Investigations Copyright © Materials Research Society 2014.
Molecular dynamics computer simulations have been used to study the development of ion-induced cascades in the surface region of an initially perfect single crystal metal target. A 16 mm movie has been produced to show the temporal progress of individual cascades. The cascades can then be seen to be formed from a few high energy primary knock-on initiated replacement collision sequences which overlap to form the more usual interpretation of a mature collision cascade. However, it is before the collision cascade has matured, and while the replacement sequences are spreading, that the majority of atoms (>80%) are ejected. These qualitative observations are also upheld more quantitatively in a global average, over many cascades, of the ejection time of each atom. This gives rise to the appearance of a statistical ejection front which propagates radially outwards, from the impact point on the crystal surface, with a well defined velocity. © 1984.
A molecular dynamics multiple interactions simulation computer code has been used to study the near-surface effect of cascade mixing due to ion bombardment. 90% of all moved atoms recoil forward or backward only one layer and 70% of all recoil atoms are displaced to their nearest neighbour positions. A comparison of the computed results and the results predicted from statistical theories indicates that both models would produce similar results if the lower limit in the energy threshold of the statistical theories were decreased sufficiently to include the movement of many more low energy recoils. A further comparison is made between the distributions of recoil-atom displacements at the end of the dynamic regime, and after the damaged crystallite has coalesced. There is a small degree of rearrangement, due to the collapse of collision spikes, but the resultant displacement distributions are similar. © 1983.
Additional, facilities, which are being installed on the 2 MeV Van de Graaff accelerator at the University of Surrey, are described. These include improvements to the microbeam equipment and optical viewing system using an image intensifier, modifications to a 3-axis goniometer to provide batch processing, a goniometer control system and new software for data collection and analysis. © 1985.
SIMS experiments using cluster ions show promising results in de-sorbing intact large molecules from the surface of various materials. The optimum size, shape and energy of the clusters and the material surface has not been studied in any detail. Presented here are the results of a comparative study of gold and carbon clusters of similar total mass and energy, in particular Au4 and C60 clusters and Au5 and C100 clusters are compared and contrasted. The behaviour of the graphite lattice, used as the target substrate material, during the impacts is studied in detail and differences in depth of penetration, damage and energy propagation are reported.
A molecular dynamics simulation has been used to study the times at which atoms are ejected during sputtering events. Plots of the atom ejection time versus distance from the impact point indicate that many sputtering events occur along a roughly circular front that propagates outward at hypersonic speed.
A comparison of the "Magic Formula" as used in the TRIM Monte Carlo simulation program and an analytical approximation to the scattering equation revealed errors in the results of the Magic Formula when used in single precision arithmetic. The errors are not severe but are systematic and could result in accumulation errors. It is shown that the analytical approximation returns a more accurate result in a faster time thus increasing the execution speed of the TRIM program. © 1988.
High resolution Rutherford backscattering has been used to investigate the ion-beam-induced intermixing of silver films deposited onto silicon under increasing fluences of 40 keV Ar+ ions. The onset of atomic mixing in the interface occurs when the Ag layer has been sputtered down to about 300 A
The intermixing of InGaAs/GaAs strained quantum wells following gallium ion implantation was characterised using photoluminescence. It was found that the implanted atoms had no effect of the diffusion coefficient for intermixing when compared to an unimplanted control sample. However, it was seen that the well was broadened by a diffusion length of approximately 37Å during the first anneal, before a photoluminescence measurement could be made. A simulation of the implantation process shows that cascade mixing is not sufficient to account for this and it is suggested that we are observing the diffusion of interstitials created by the implantation. © 1993.
The preferential sputter enrichment or depletion of a species in a binary solid is a well established experimental observation. This composition change is usually found to occur over a depth similar to that of the penetration depth of the sputtering projectile. This paper therefore considers a model for preferential sputtering based upon a preferentially enhanced diffusion of one species over a finite depth in the solid which acts as a continuous atomic supply to the surface. Exact solutions are determined for steady state surface and depth distributions of the composition ratio of the two species for the time dependent behavior of these concentration distributions. The results are compared with models which assume equal diffusion enhancement of both species over both limited and infinite depth and with experimental studies.
Single-crystal silicon has been amorphised by bombardment with Si+, Ge+ or Sn+ ions. After conventional annealing (900° C, 30 min) some disorder remained. The amount was measured by ion channelling and transmission electron microscopy and compared with the quantity of excess interstitials predicted by the Monte Carlo computer program TRIM. Both the predicted and measured integral disorder fell as the atomic weight of the projectile increased. Because lattice strain also leads to a reduction in ion channelling this had to be taken into account when estimating residual damage from back-scattering analysis. The results indicate that there are six scattering centres per interstitial. © 1988 IOP Publishing Ltd.
Medeuov B, Daukeev D, Webb R (1994) Oxygen atom interaction with radiation defects in Nb irradiated by He ions, Vacuum 45 (5) pp. 579-582
The aim of this work is to check the hypothesis regarding the formation of complexes such as an interstitial impurity helium-vacancy cluster. Nb wires uniformly implanted by 24 MeV ±-particles at 320 K are investigated by means of the internal friction technique. It is shown that oxygen atoms occupying interstitial sites in Nb BCCC-structure are trapped during irradiation and after annealing up to T
Aspheric lenses are the most common method for correcting for spherical aberrations but, in microlens production, highly-controlled lens profiles are hard to achieve. We demonstrate a technique for creating bespoke, highly-accurate aspheric or spherical profile silicon microlens moulds, of almost any footprint, using focused ion-beam milling. Along with this, we present a method of removing induced ion-beam damage in silicon, via a hydrofluoric acid etch, helping to recover the surface's optical and chemical properties. In this paper, we demonstrate that our milled and etched moulds have a roughness of 4.0-4.1 nm, meaning they scatter less than 1% of light, down to wavelengths of 51 nm, showing that the moulds are suitable to make lenses that are able to handle light from UV up to infra-red. Using empirical experiments and computer simulations, we show that increasing the ion-dose when milling increases the amount of gallium a hydrofluoric acid etch can remove, by increasing the degree of amorphisation within the surface. For doses above 3000 ¼C/cm(2) this restores previous surface properties, reducing adhesion to the mould, allowing for a cleaner release and enabling higher quality lenses to be made. Our technique is used to make aspheric microlenses of down to 3 ¼m in size, but with a potential to make lenses smaller than 1 ¼m.
We have developed a simple process to fabricate high-TC Josephson junctions by a combination of focused ion beam milling and 100 keV H2+ ion implantation. The resistively shunted junction-like current-voltage characteristics were observed in the temperature range of 48 to 4.2 K. The devices showed clear dc and ac Josephson effects. This technique is very promising in terms of simplicity and flexibility of fabrication and has potential for high-density integration. © 2002 American Institute of Physics.
A band of disorder is observed following the annealing of surface amorphous layers produced by ion bombardment. The depth of the band's centre is just below the original amorphous/crystalline interface. The ion bombardment simulation computer program TRIM.CASCADE has been used in conjunction with ion channelling measurements to predict the areal density of atoms available for the formation of this band of disorder. The variation in the amounts of disorder expected due to changing the implantation parameters: ion dose, ion energy and implantation temperature are reported. The predictions are compared with the published transmission electron microscopy results and electrical measurements of other workers. The implications of this work for the technique of pre-amorphisation are also discussed.
A study is presented of the effect of 5 keV helium ion bombardment on thin (about 2000 Å) aluminium films using proton backscattering, scanning and transmission electron microscopy and ± particle energy loss spectroscopy. Measurements of helium content after irradiation using proton backscattering indicate low below-saturation retention for both room temperature and low temperature implantations (19% and 24% respectively). Electron microscopy examination of the films reveals a severe deformation in the form of coarse and fine-scale wrinkling whose amplitude increases with increasing helium dose. This deformation does not appear to be the result of bubble swelling. An attempt has been made to quantify the wrinkling by measuring the energy loss spectrum of ± particles transmitted through irradiated films and the combination of these measurements with a simple sinusoidal deformation model indicates an increase in film area of up to 20%. © 1982.
LiNbO3 has been implanted with 1.0 MeV 4He+ in order to create a buried layer of crystal lattice damage which acts as the lower boundary of an optical waveguide with the air surface forming the upper boundary. The annealing behaviour of this damage, in the temperature range 20 ° C to 350 ° C, has been studied in vacuo by performing in situ channelling analysis of the disorder during the thermal processing. It is concluded that the minimum annealing temperature required to reduce waveguide attenuation is 150 ± 10 ° C and the optimum is 180 ± 15°C. The results are seen to be in overall agreement with recent optical waveguide measurements. © 1989.
A combined scanning tunnelling/scanning force microscope has been constructed based on a novel design. A single piezoelectric transducer, appropriately shaped, and with appropriately patterned electrodes is used, which acts as flexing element, force sensor, scanner, and height positioner, making the instrument simple and compact. The instrument is described and some results are presented, including characterization of performance. © 1994.
Spatial distributions of ions implanted into crystals can be of a very complex shape with `lobes' due to ions penetrating through open channels in several directions. This paper suggests an analytical model which represents such a distribution as a linear combination of `random' distribution and one or more `channeled' distributions. This study is focused on the algorithm of the separation of ion trajectories into several distributions. The first distribution includes those ions which have undergone predominantly random collisions. The other distributions include those ions which have undergone mainly `weak' collisions and traveled mostly along the main channeling directions. Our binary collision approximation (BCA) simulator is used for generating and analyzing ion trajectories. The spatial moments can be extracted from each separated distribution. It is shown that 2D analytical distributions obtained as a linear combination of distributions derived from these moments and aligned along corresponding channeling direction are in a very good agreement with direct BCA calculations.
Molecular dynamics simulations have been carried out to model the implantation of boron into silicon at low energies using boron difluoride. It is shown that at a molecular impact energy of 460 eV the implantation profiles have an orientation dependence with penetration of the boron furthest when the F atoms are aligned perpendicular to the surface. The simulations also predict maximum damage in the surface layer where a peak in the fluorine atoms also occurs. The boron distribution is flatter with a peak which is deeper at 10-15 Å. © 1999 Elsevier Science S.A. All rights reserved.
This paper presents a detailed description of an upgraded silicon surface barrier (SB) detector and analysis of X and gamma radiation and of the spectra given by it. The most frequently used application of these detectors was in measurements and analyses of alpha spectra. However, analysis of spectra gained here presented a silicon surface barrier detector showing possibilities of their wider application in various nuclear techniques and technologies. This specially referes to the feasibility of their use in the conditions that are different from those in laboratories, such as mines, surroundings of nuclear power plants etc. Recorded spectra from 57Co, show that SB detectors are very acceptable in nuclear laboratories for nuclear spectroscopy at room temperatures. On the contrary, field application in nuclear techniques connected with the protection of the environment and counting systems is much wider, and the detector temperature could reach 60 °C. © 1997 Elsevier Science S.A.
The feasibility of using decaborane B10H14, for the manufacture of shallow junctions in Si is investigated by means of molecular dynamics simulations. Bombardment energies of 1, 2, and 4 keV are investigated and the simulations run for up to 7 ps in order to ascertain the implantation profiles of the B atoms, the whereabouts of the H from the impacted molecule and the damage to the lattice. The simulations show that if a small binding energy of the B atom in the Si lattice is assumed then most of the B from the cluster is implanted. The implantation distributions are flatter with depth than those for single B interactions and the surface layers undergo damage and amorphisation in the proximity of the impact. © 1998 American Institute of Physics.
Over the last decade the use of computer simulation in predicting physical phenomena associated with ion beam processing of materials has increased both in use and reliability. This is partly due to the dramatic increase in computer power and decrease in computer cost, but is also being achieved due to an increased understanding of the physical processes occurring. With the increase in computer power has come not just the ability to perform more complex calculations but also the methods for complex data representation in animated form. By animating the results it is much easier to observe collective effects such as acoustic wave propagation at a surface due to, for example, molecule impact.
Latent fingermarks are invisible to the naked eye and normally require the application of a chemical developer followed by an optical imaging step in order to visualize the ridge detail. If the finger deposition is poor, or the fingermark is aged, it can sometimes be difficult to produce an image of sufficient quality for identification. In this work, we show for the first time how mass spectrometry imaging (in this case time-of-flight secondary ion mass spectrometry, ToF-SIMS) can be used to enhance the quality of partially recovered fingermarks. We show three examples of how chemical imaging can be used to obtain enhanced images of fingermarks deposited on aluminium foil, glass and the handle of a hand grenade compared with conventional development techniques.
Ion beam induced luminescence of silica has been recorded in the energy ranges 5-55 key and 0.2-2.8 MeV during excitation with H+, H2+, N+ and N2+, for samples at 77 K. The data reveal that the light is stimulated by electronic energy deposition 0 but the efficiency is a function of the damage retained in the silica. Damage retention is a function of the overlap of nuclear collision and 07 electronic excitation processes during the slowing down of the ion beam so the net effect of these competing features is to produce a maximum in the ion energy dependence of the light production for nitrogen ions (near 42 key), whereas for protons the dependence is a monotonic function of energy as it is dominated by the electronic excitation. Computer modelling of the luminescence production predicts a maximum in the energy dependence which is in agreement with the observations. © 1987 Elsevier Science Publishers B.V.
© 2014 Materials Research Society.The MIAMI? facility at the University of Huddersfield is one of a number of facilities worldwide that permit the ion irradiation of thin foils in-situ in a transmission electron microscope. MIAMI has been developed with a particular focus on enabling the in-situ implantation of helium and hydrogen into thin electron transparent foils, necessitating ion energies in the range 1-10 keV. In addition, however, ions of a variety of species can be provided at energies of up to 100 keV (for singly charged ions), enabling studies to focus on the build up of radiation damage in the absence or presence of implanted gas. This paper reports on a number of ongoing studies being carried out at MIAMI, and also at JANNuS (Orsay, France) and the IVEM/Ion Accelerator Facility (Argonne National Lab, US). This includes recent work on He bubbles in SiC and Cu; the former work concerned with modification to bubble populations by ion and electron beams and the latter project concerned with the formation of bubble super-lattices in metals. A study is also presented consisting of experiments aimed at shedding light on the origins of the dimensional changes known to occur in nuclear graphite under irradiation with either neutrons or ions. Single crystal graphite foils have been irradiated with 60 keV Xe ions in order to create a non-uniform damage profile throughout the foil thickness. This gives rise to varying basal-plane contraction throughout the foil resulting in almost macroscopic (micron scale) deformation of the graphite. These observations are presented and discussed with a view to reconciling them with current understanding of point defect behavior in graphite.?Microscope and Ion Accelerator for Materials Investigations.
Webb RP, Kerford M, Kappes M, Brauchle G (1997) A comparison between fullerene and single particle impacts on graphite, Radiation Effects and Defects in Solids 142 (1-4) pp. 23-26
Gunshot Residue (GSR) is residual material from the discharge of a firearm, which frequently provides crucial information in criminal investigations. Changes in ammunition manufacturing are gradually phasing out the heavy metals on which current forensic GSR analysis is based, and the latest Heavy Metal Free (HMF) primers urgently demand new forensic solutions. Proton scanning microbeam Ion Beam Analysis (IBA), in conjunction with the Scanning Electron Microscope equipped with an Energy Dispersive X-ray Spectrometer (SEM-EDS), can be introduced into forensic analysis to solve both new and old problems, with a procedure entirely commensurate with current forensic practice. Six cartridges producing GSR particles known to be interesting in casework by both experience and the literature were selected for this study. A standard procedure to relocate the same particles previously analysed by SEM-EDS, based on both secondary electron (SE) and X-ray imaging was developed and tested. Elemental Particle Induced X-ray Emission (PIXE) mapping of the emitted X-rays allowed relocation in a scan of 10¼m×10¼m of even a 1¼m GSR particle. The comparison between spectra from the same particle obtained by SEM-EDS and IBA-PIXE showed that the latter is much more sensitive at mid-high energies. Results that are very interesting in a forensic context were obtained with particles from a cartridge containing mercury fulminate in the primer. Particle-induced gamma-ray emission (PIGE) maps of a particles from HMF cartridges allowed identification of Boron and Sodium in particles from hands using the 10B(p,±1³)7Be, 11B(p,p1³)11B and 23Na(p,p1³)23Na reactions, which is extraordinary in a forensic context. The capability for quantitative analysis of elements within individual particles by IBA was also demonstrated, giving the opportunity to begin a new chapter in the research on GSR particles. The integrated procedure that was developed, which makes use of all the IBA signals, has unprecedented characterisation and discrimination power for GSR samples. © 2013 Elsevier Ireland Ltd.
Niobium wires, outgassed at 2270 K in UHV chamber, were uniformly implanted with 16O+ at 1 MeV and 320 K within the dose range 5×1015-3×1017 cm-2. Internal friction measurements were carried out on computer-controlled inverted torsional pendulum at
The geometric structure of collision cascades developed in solids by energetic ion bombardment is investigated from the view-point of fractal geometry using computer simulated trajectories and defect distributions. The fractal dimension of a collision cascade, as extracted from defect distributions, depends on the effective interaction potential governing the sequence of events in a subcascade, as shown in recent analytical predictions. Possible implications and further work along these lines are suggested. © 1987.
A geometrical theory is presented which divides the collision cascade into energy groups, each with a characteristic anisotropy in the distribution in space of knock-on trajectories. A simplified two group, four (quasi-two-dimensional) component analytical theory is developed. This is used to fit two experimentally determined sputtering yield versus angle of ion incidence relationships; 50 keV argon ion bombardment of gold and 100 keV argon ion bombardment of germanium. The experimental results were obtained using a triple quartz resonator technique. The effect of ion reflection on the measured sputtering yields was estimated by using the Monte Carlo computer simulation TRIM. A good fit to experimental results was obtained and it was demonstrated that models based solely on energy deposition combined with ion reflection are unsatisfactory for high energy (> 10 keV) high mass (> 10 amu) ions. The parameters determined from the fit of theory to experiment are used to determine the characteristic sputtering depths, and the mean ranges of the high and low energy groups for the two sets of experimental data. © 1985.
A modification to the Sigmund formula using calculations of energy deposition instead of correction factors and stopping power is used to compare over 600 experimental results with simulated values. The results indicate that whilst the use of energy deposition yields better general agreement with experimental behaviour, they also show that there is a factor, important in determining the sputtering yield, which appears to relate to the chemical nature of the target. © 1989.
We describe a novel bimorph-type piezoelectric transducer which achieves three-dimensional positioning in a 70 ¼m ×70 ¼m ×10 ¼m volume with applied voltage ranges less than 100 V. This transducer, appropriately shaped and with appropriately patterned electrodes, has been tested by using it as a scanner in a scanning tunneling microscope. Results obtained in this application of the actuator are presented, including characterization of performance.
In this paper we show how the technique of microscope-spectrophotometry (MSP) may be used to characterize SIMOX structures nondestructively. A range of SIMOX materials prepared using various implantation conditions were investigated. The structural parameters elucidated using MSP included: silicon overlayer and buried oxide thicknesses; approximate densities of silicon islands in the buried oxide layer and silicon dioxide islands in the silicon overlayer as appropriate. These results compared favourably with those obtained using XTEM and indicates that MSP is a reliable technique for the nondestructive, three dimensional characterization of complex multi-layer structures. Furthermore, the technique is capable of examining very small areas (1 ¼m) which should enable device structures and local inhomogeneities to be characterized. © 1994.
Photoluminescence coupled with repetitive thermal annealing has been used to determine the diffusion coefficients for intermixing in InxGa 1-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 present until the structure had broadened by about 75 Å when the diffusion coefficient returned to the unimplanted control value. The activation energy for the interdiffusion was measured over the temperature range 1050-750°C and a value of 3.7±0.1 eV was measured. This was found to be independent of the implanted ion.
A numerical analysis of the pressure time equation relating to first order single-step gas release has been performed. This has been done for two configurations of vacuum system, each having a volume into which gas release proceeds linked by a conductance C to a detector volume. The differences between the release function and the observed pressure transient have been characterized by observing the manner in which the maximum release rate Ám, the temperature for maximum release Tm and the leading and trailing 1/e widths We1 and We2 change as a function of the various vacuum system parameters. © 1977.
Carter G, Webb R, Collins R (1978) The accumulation of disorder, subject to saturation and sputter limitation, in ion irradiated solids, Radiation Effects 37 (1-2) pp. 21-32
The depth distribution of disorder and the depth integrated disorder produced by ion irradiation of solids is analyzed theoretically as a function of increasing ion fluence when disorder saturation processes operate at all depths and the solid surface is continuously uniformly eroded by sputtering. The resulting defining equations are evaluated numerically for a Gaussian approximation to the disorder depth function with parameters appropriate to low, equal and high projectile: substrate mass ratio conditions, for several values of sputtering coefficient and effective atom displacement energy. It is shown that the form, if not the magnitude, of the integrated disorder/projectile fluence function is only weakly dependent upon these parameters.
The broadening of a thin (~3 nm) Au marker, sandwiched between two sputtered silicon films deposited on a single crystal silicon substrate, bombarded with 100 keV argon ions has been observed for different angles of incidence using Rutherford backscattering. The results are compared to a theory used to predict the behaviour of the sputtering yield with angle of incidence. It is found that the effect of incomplete collision cascades and anisotropy of the cascade distribution determine the behaviour of the broadening. © 1986.
Recent experimental measurements of craters/defects caused by energetic C60 impacts on graphite have shown how the penetration depth of the C60 increases as a function of velocity. We show here Molecular Dynamics Simulations of C60, C70, C76, C78 and C84 impacts on graphite which are in very close agreement with the experimental findings. By comparison with single atom impacts on the same surface and study of the early cascade propogation we obtain an evidence of long time co-operative, non-linear, effects of the molecular surface interaction which give rise to greater displacement of target atoms than would be expected by just scaling up results from single atom interactions. There is little difference found between different impact sites for the molecules, unlike the single atom impact behaviour.
In a comparative study of size and mass effects in the glancing incidence scattering of hyperthermal ions from a soft surface, He+, Xe+, and C+60 were scattered from highly oriented pyrolitic graphite (HOPG) over an energy range between 200 and 5000 eV. Predominantly neutral scattering products were observed for all projectiles. The corresponding angular and velocity distributions were recorded in the scattering plane. He+ gives rise to broad angular distributions conforming to the predictions of a simple binary collision model. With full widths at half maximum of less than 6 deg at typical collision energies, the angular distributions found for Xe+ and C+60 are very narrow. While Xe+ is always scattered near-specularly independent of collision energy, neutrals resulting from C+60 exit subspecularly - increasingly so the higher the collision energy. The experimental data are discussed in terms of dynamical simulations which indicate that Xe+ collides with a rigid ensemble of six carbon atoms while the fullerene scatters from a larger "moving target." © 1999 American Institute of Physics.
The inherent difficulties in interpreting thermal desorption spectra are discussed. Possible mechanisms which can change the expected form of the evolution spectra are investigated including the possibility of a distribution of activation energies for release of trapped gas and the spatial distribution of the trapped gas. It is shown that the form of the evolution spectra can be quite misleading and unless care is taken the wrong conclusions can be derived. © 1979.
This chapter describes the methods and applications for the use of multi-atom, ionized species, containing 10s to several thousand atoms, for high-flux ion doping and modification of surfaces with sub-keV energies per atom. ?Massive? ion beams are formed using molecular species, liquids and gas clusters. Ion beam systems for such ?massive? ions include the use of novel vaporizer methods, adiabatic cooling, electron beam ionization, and other techniques to provide stable, high-fluence beams. Applications include high-dose ion implantation for ultra-shallow junctions, room-temperature deposition of semiconductor and other layers, smoothing and high-rate etching of surfaces.
A series of GaAs/AlxGa1?xAs MBE structures, in which x ranged from 0.10 to 0.40, was studied using microscope spectrophotometry (MSP). The MSP reflectance measurements were found to be extremely sensitive to compositional variation, with a clear inverse relationship between Al content and reflected intensity, and a sympathetic relationship between composition and dispersion. Theoretical optical models were simulated and fitted to the measured data to give layer dimensions which fitted remarkably well with SIMS data. It is concluded that MSP has great potential for the non-destructive metrology and quality control of simple and complex multilayer structures. © 1994 IOP Publishing Ltd.
The spatial variation of energy deposited in a solid can lead to local variations in sputtering yield at points on the surface neighbouring the point of ion impact. An approximate theory is developed to describe this local sputtering yield variation in terms of the local morphology. It is then shown how, if this local variation merely moderates the standard sputtering yield-projectile incidence angle function by multiplication, an erosion slowness theory can be simply modified and generalized to allow prediction of the time development of sputtered surface morphology. Both transient and steady-state morphologies are explored. © 1981 Chapman and Hall Ltd.
Epitaxial CoSi2 have been layers fabricated by implanting 200 keV cobalt ions, to doses between 1.5×1017 and 7×1017 Co+ cm-2, into (100), (110) and (111) single crystal silicon substrates. The experimental results after implantation are in close agreement with those obtained from computer simulations using single crystal targets. The as implanted structures for the lower doses (1.5×10173×1017 Co+ cm-2) are silicon rich and consist of a mixture of A- and B-type CoSi2 precipitates interwoven by silicon. For the medium doses (4×10175×1017 Co+ cm-2) an epitaxial layer of CoSi2 is formed with any excess cobalt being incorporated in small CoSi inclusions, at the peak of the implanted distribution. For the highest doses (6×10177×1017 Co+ cm-2) preferential sputtering of silicon at the surface of the silicide causes this region to become increasingly rich in cobalt. To accomodate this cobalt excess, grains of CoSi form above the epitaxial CoSi2 layer. As the dose is increased up to 5×1017 Co+ cm-2 the crystallinity of the synthesised layer improves and there is a corresponding decrease in resistivity, after which any further increase in dose causes the crystallinity to deteriorate again and the resistivity to increase. These changes can be correlated with the value of x in CoSix, i.e. when the layer is either rich in cobalt or silicon (2>×>2) the resistivity increases and there is a corresponding deterioration in crystal quality. For all doses, furnace annealing (at 1000°C, 30 min) causes a decrease in resistivity and a corresponding improvement in crystallinity as the ratio of Co:Si approaches the value for the stoichiometric compound (CoSi2). After rapid thermal annealing (RTA) at 1000°C for 5 s. the resistivity and crystal quality of the synthesised layer for the medium dose specimen (5×1017 cm-2) are close to those achieved by conventional furnace annealing. For the higher and lower doses the crystal quality is slightly worse and the resistivity slightly higher than those for analogous samples which have been furnace annealed. © 1991.
Using simple Binary Collision simulations of energetic ion initiated collision cascades, particles are considered to undergo a series of binary collisions with their surroundings. In Molecular Dynamics simulation it is difficult to even define what is meant by a collision as the interaction potentials are infinite in nature and consequently all particles are considered to interact with all other particles. By making a suitable definition of a collision for Molecular Dynamics we are able to compare the temporal behaviour of the number of collisions occurring during the propagation of a collision cascade between the two different calculation schemes. An investigation is made of the number of collisions as a function of time occurring in collision cascades. We compare these results to the time ordered version of MARLOWE. By making further definitions about what makes a many body collision, we further investigate the numbers of many body collisions occurring during a number of collision cascades. © 1995.
A new geometrical theory of sputtering is extended to investigate the behaviour of interface mixing as a function of the angle of ion incidence. It is found that the amount of mixing peaks with the angle of incidence at different angles depending upon the depth of the interface. When the interface is at the surface the mixing parameter behaves as the sputtering yield and maximises around 70 degree , whilst deeper interfaces, around the damage range, have maximum mixing at normal incidence.
Approximately one third of the world's 15000 accelerators are used for tumour therapy and other medical applications [1]. The characteristics of FFAGs make them ideally suited to such applications, as the much smaller magnet size and greater compactness offers considerable cost and operational benefits. In the first stage the work on PAMELA will focus on the optimization of the FFAG design to deliver the specific machine parameters demanded by therapy applications. In this phase of the PAMELA project the effort will concentrate on the design of a semi-scaling type FFAGs to deliver a 450 MeV/u carbon ion beam, including detailed lattice and tracking studies. The second stage will use the existing expertise in the BASROC consortium [2] to undertake a design of the magnets and RF system for PAMELA. An outline of the overall concept of PAMELA will be discussed and the actual status of the work will be presented. ©2007 IEEE.
Recent coaxial impact-collision ion scattering spectroscopy (CAICISS) experiments studying growth kinetics have indicated that 2 keV He ions can be backscattered through 180° from deep - 56 Å - within the target without losing more than a few hundred eV above the kinematic energy loss for 180° scattering. Using simple average stopping data it is difficult to satisfactorily explain how particles can penetrate this deep and come back retaining so much of their initial energy. We use the MARLOWE binary collision code to show that it is indeed possible for particles to be scattered from this deep in the solid and still have sufficient energy to appear in the surface peak. © 1992.
Secondary Ion Mass spectrometry (SIMS) has been generally used in the field of material sciences. In recent years, it has also been applied for molecular imaging of biological samples. Nevertheless, molecular ions derived from the large molecules (more than 1 kDa) were detected with very low sensitivity. Plasma desorption mass spectrometry (PDMS) is known as mass spectrometry for large organic molecule. In PDMS, fission fragments bombard samples and the impact induces molecular ionization by electronic excitation. Large organic molecules are detected by using swift heavy ions in SIMS. In this work, 6 MeV Cu4+ we irradiated angiotensin II, a class of peptides. The intact molecular ions generated by swift heavy ion irradiation were analyzed by time?of?flight (TOF) measurement. The yields are compared with some other probe ions, bismuth or flurane. Swift heavy ion bombardment ionized large organic molecules more effectively than other probes. Therefore, high energy ion can be applied in high resolution molecular imaging.
A molecular dynamics simulation has been used to investigate the sensitivity of atom ejection processes from a single-crystal target to changes in the atom-atom potential function. Four functions, three constructed from the Gibson potentials with Anderman's attractive well, and a fourth specifically developed for this investigation, were investigated in the Cu/Ar+ system over a range of ion energies from 1.0 to 10.0 kev with the KSE-B ion-atom potential. Well depths and widths also were varied. The calculations were done at normal incidence on the fcc (111) crystal orientation. Computed values were compared with experimental data where they exist. Sputtering yields, multimer yield ratios, layer yield ratios, and the ejected atom energy distribution vary systematically with the parameters of the atom-atom potential function. Calculations also were done with the modified Moliere function. Yields and other properties fall exactly into the positions predicted from the Born-Mayer function analysis. Simultaneous analysis of the ejected atom energy distribution and the ion energy dependence of the sputtering yield curve provides information about the parameters of both the wall and well portions of the atom-atom potential function.
Ultra-shallow B and BF 2 implants in silicon pre-amorphised with Ge have been activated using a scanning non-melt laser. The implants were activated either by using 1 or 10 laser scans. Isochronal 60s post-laser annealing between 700-1000°C were then undertaken to study the deactivation and reactivation of the B. Both B and BF2 samples were implanted with a dose of 1×10 15 B cm -2 at an effective energy of 500eV. The presence of F from the BF 2 implants, which is superimposed over the boron profile increases the sheet resistance of the initial fabricated junction (from 600-700 ohms/sq from B implants only to 750-1100 ohms/sq for BF2 implants). Fluorine also changes the deactivation and reactivation behaviour of the boron during the post-anneals by increasing the amount of deactivation of the boron. © 2006 Materials Research Society.
Ultra low energy boron implants (0.2 to 3 keV) have been carried out on Si (100) at doses between 1×1014cm-2 and 1×1015cm-2 using xRLEAP. The samples were annealed at temperatures between 900 °C and 1050 °C. The atomic profiles of these samples was measured using SIMS. Monte Carlo and diffusion simulations were performed using the SSupreme code. Comparisons between the simulations and experimental measurements show interesting differences these are discussed.
It is well known that energetic impacts of Sb and Sb2 ions on gold substrates give rise to high energy density collision cascades and potentially very high sputtering yields. A large component of the sputtering mechanism is due to the presence of a thermal spike which causes prolonged ejection of material with thermal energies. This phenomenon is investigated using molecular dynamics simulations. The energy dissipation mechanisms and the effects of molecular orientation are investigated. The overall sputtering yields are compared to experimental measurements.
A scanning tunneling microscope has been built together with the necessary controlling electronics. Currently this is used at atmospheric pressure but is capable of use under vacuum with minor modifications. Trials of the system, and subsequent adjustments, have taken place using highly oriented pyrolitic graphite and gold evaporated on silicon samples. Good and versatile control of tunneling current was achieved. We report on the design, development, construction, and evaluation of the instrument. Preliminary results illustrating reproducible topographical images are presented and discussed. Gap-versus-bias voltage and gap-versus-tunneling current characteristics are also presented and discussed.
This paper examines some simple growth models of surface morphology on the atomistic scale from a single point nucleation source. Cellular Automata and Monte Carlo simulations are described and compared for growth from a point source. They are then applied to demonstrate the growth of spiral morphology from a screw dislocation. The shape of the spiral is shown to be dependant both on the parameters used in the models and the type of algorithm chosen.
Individual impacts have been observed on quartz surfaces resulting from very low dose (typically 1010 to 1011 ions cm-2) energetic ion bombardment (species: Pb, Ni, O, Si, Ar, In, energy: 30 keV to 0.73 GeV). The work was undertaken in part to test a hypothesis drawn from earlier work that the change in surface topography around the ion track at the surface arises from a change in density brought about by radiation damage. The earlier work led us to predict that, whilst craters are seen from impacts on amorphous SiO2 (a-SiO2) due to an increase in density, we should see asperities on single crystal quartz due to a reduction in density. We also expected that the effect would be much larger in the case of quartz as the density change is much greater. The results reported here certainly support this hypothesis in general. Bombardment regimes have been chosen to enable us to compare directly with earlier measurements on a-SiO2, also to compare predominantly (near surface) electronic stopping with predominantly nuclear stopping regimes. In all cases, the areal density of asperities is less than that expected if every ion impact resulted in an observable effect and there is a great variation in asperity size.
Analysis using MeV ion beams is a thin film characterisation technique invented some 50 years ago which has recently had the benefit of a number of important advances. This review will cover damage profiling in crystals including studies of defects in semiconductors, surface studies, and depth profiling with sputtering. But it will concentrate on thin film depth profiling using Rutherford backscattering, particle induced X-ray emission and related techniques in the deliberately synergistic way that has only recently become possible. In this review of these new developments, we will show how this integrated approach, which we might call ?total IBA?, has given the technique great analytical power.
Some recent developments in computational models of atomic collision studies are described and the relative merits of the binary collision and molecular dynamics approaches are discussed. © 1992.
The control of implanted depth distributions by preamorphising silicon results in the production of defects in sensitive regions of devices fabricated in this fashion. The most stable - and therefore the most troublesome - defects are the dislocation loops that form at the original amorphous/crystalline interface on annealing. Our models suggest that the dislocation loops evolve from atoms injected into the underlying crystalline region during the amorphising implant. The idea was tested by annihilating these excess atoms with excess vacancies produced during the formation of a deep buried amorphous layer as our model predicted. No dislocation loops were then observed in this region. © 1989.
Multiple interaction computer simulations of bombardment cascades have been used to study the surface damage created by an ion. Qualitative information on the temporal evolution of the dynamic cascade is obtained from an animated movie of the process. A comparison is made between the final damage states of high energy-density trajectories. A number of ion-atom potential functions have been investigated over a wide range of ion energies. Only superficial differences are found. © 1984.
P+/N Shallow junctions formation for 0.18 technology by low-energy implantation of boron atoms into Si using decaborane is demonstrated by molecular dynamics simulations. The simulations also show that some H is also implanted, although the amount is less than B. Transient enhanced diffusion appears to be limited .
There are at least 3 known fast techniques for calculating the range profiles of ions implanted into layered structures which utalise the implantation profiles of the ions in bulk material of the individual layers. A fourth model - Layer - is introduced. These models are discussed and compared with experimental results, Monte Carlo calculations and each other. All models perform well in most layered materials where the stopping powers differ only slightly between the layers, but some perform better then others when there are large differences in stopping powers between layers. Layer is found to behave very well in most circumstances. © 1988.
Molecular dynamics simulations of energetic particle interactions with silicon and graphite crystal surfaces are discussed. The simulations can be used to describe the physical state of the surface after such interactions and the dynamic development of the resulting surface damage can be examined. We demonstrate in the case of atomic impact at energies {greater-than or approximate} a few hundred eV, that craters can form on silicon while bumps are formed on graphite. Impact of C60 molecules is also discussed. On graphite, hexagonal surface waves propagate from the impact point and surface bonds remain unbroken at energies H a few hundred eV. The interactions with silicon surfaces at impact energies of H few eV depend crucially on the form of the potential. At keV energies the C60 molecule disintegrates and a large crater forms near the impact point. © 1995.
This report is an attempt to assess the validity of the binary collisions approximation by comparing TRIM and molecular dynamics in calculating the backscattering of carbon ions off a graphite surface. The TRIM calculations were performed for an amorphous target with smooth surface. In the molecular dynamics calculations, a recently available semi-empirical many body potential by Tersoff was used. The calculations were made for a perfect crystal at zero temperature, consisting of 1342 atoms in five layers. The probability of reflection was calculated as a function of energy and angle of incidence of the projectile. Compared with the binary collisions calculations, molecular dynamics predicts a significantly higher backscattering probability. For instance, at normal incidence TRIM shows less than one per cent reflection in the whole energy range up to 1 keV, whereas in molecular dynamics the reflection yield peaks around 20 eV with more than 40% reflection. The case of a head-on collision with a surface at normal incidence is discussed in detail. © 1993.
The special properties of molecular dynamics multiple interaction simulations make it possible to analyse in detail the spatio-temporal history of every atom within a fixed region of a target during ion irradiation. When the positions of each particle are analysed, with respect to all other atoms, a radial distribution function is readily obtainable. These distributions can give detailed information as to the degree of damage, up to amorphisation, and can determine an effective temperature of a collision cascade. It is found that at least 2% of the trajectories for 5 keV Ar ion normal incidence irradiation of a Cu target give rise to extensive (> 1000 atomic volumes) amorphous regions which can later be recrystallised. Comparison with the energy deposition distribution indicates above average surface deposited energy density in these cases and consequently a higher effective cascade temperature. © 1985.
A study has been made to explore impact-induced desorption of C 60 fullerenes embedded in a benzene matrix as a model of matrix assisted secondary ion mass spectrometry. A fullerene concentration of about 0.5% was incorporated in a coarse-grained benzene target and then struck by a 5 keV fullerene projectile. The response of the benzene target was compared with a pure benzene target to observe the effects of the embedded molecules on the matrix. Three different trajectories were investigated. In the first, a single sputtered fullerene was ejected joined to a carbon atom from the projectile. In the second, an undamaged C60 was ejected, and in the third, no intact fullerenes were ejected. In all three cases, 4-6 fullerenes were pushed above the initial surface but were relocated into the crater rim, enriching the surface layer with the heavier and more strongly bound component. It is observed that the sputtered fullerenes are ejected with a number of matrix molecules, and that there is a small decrease in the internal energy of the ejected fullerene that corresponds to the gradual separation of the surrounding matrix molecules from the larger molecule. This evaporative cooling may provide a potential benefit to Matrix Assisted SIMS. Copyright © 2010 John Wiley & Sons, Ltd
Ion beam damage combined with nanoscale focused-ion-beam direct milling was used to create manufacturable superconductor-normal-superconductor type (SNS) Josephson junctions in 100-nm-thick MgB2 with TC of 38 K. The junctions show nonhysteretic current-voltage characteristics between 36 and 4.2 K. Experimental evidence for the dc and ac Josephson effects in MgB 2 metal-masked ion damage junctions are presented. This technique is particularly useful for prototyping devices due to its simplicity and flexibility of fabrication and has a great potential for high-density integration. © 2002 American Institute of Physics.
The surface topographic development by sputter erosion of a solid resulting from spatially non-uniform projectile bombardment is considered theoretically. It is shown that whilst formal prediction of time-dependent surface geometry is possible, analytic solution of the defining equations is generally unachievable, although an approximate treatment may be made for the case of a Gaussian flux distribution profile and an initially plane surface. It is shown that profile perturbations resulting from erosion rate-projectile incidence angle variations can assume importance when erosion crater depths become of similar order to projectile beam width. This behaviour is also revealed by computer simulation of the erosion process and a sand blasting experimental analogue study. © 1979 Chapman and Hall Ltd.
A new protocol using time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been developed to identify the deposition order of a fingerprint overlapping an ink line on paper. By taking line scans of fragment ions characteristic of the ink molecules (m/z 358.2 and 372.2) where the fingerprint and ink overlap and by calculating the normalised standard deviation of the intensity variation across the line scan, it is possible to determine whether or not a fingerprint is above ink on a paper substrate. The protocol adopted works for a selection of fingerprints from four donors tested here and for a fingerprint that was aged for six months; for one donor, the very faint fingerprints could not be visualized using either standard procedures (ninhydrin development) or SIMS and therefore the protocol correctly gives an inconclusive result.
Ion beam analysis comprises of a group of analytical techniques tackling the elemental composition of thin films by probing them with MeV ions. These techniques exploit information from photons and particles that come from the interaction of the MeV ions with the sample surface. Secondary ions, yet another species ensuing from such interactions can also be analysed providing information on molecular composition. The only ion beam analysis technique addressing the molecular composition is MeV SIMS, enabling detection and imaging of organic matter. The molecular detection and imaging of organic material is dominated by other surface sensitive techniques, such as TOF SIMS, providing a strong competition to MeV SIMS. In a pursuit to fully exploit the advantages of MeV SIMS in the field, the possibility to extract MeV ions into the air can also be utilised, thus offering the potential for application of ambient based MeV SIMS.
In this work, a fully ambient MeV SIMS setup is introduced and commissioned at the University of Surrey Ion Beam Centre, and termed ?Ambient Pressure MeV SIMS?. The aims of this thesis are to optimise AP MeV SIMS for detection and imaging of organic species, as well as to explore potential applications for the technique. The complex optimisation of AP MeV SIMS described in this work encounters many parameters influencing either the electronic sputtering or gas dynamic of secondary ions. A great volume of the optimisation process has addressed the issue of an immense background contribution by investigation of its identity and origin. Moreover, the atmosphere encompassing the sampling area was investigated and the effect of different angles and types of a sheath gas directing the sample was tested.
The following work of this thesis demonstrates the application assessment of AP MeV SIMS. Here results of analysis of amino acids, explosives and synthetic organic pigments are presented. Finally, a description of a feasibility study on merging of AP MeV SIMS and HIPIXE with a purpose of simultaneous molecular and elemental imaging under ambient conditions is given.
One of the greatest challenges in silicon photonics has been to induce light emission in silicon, with the ultimate vision is to have fully silicon-based photonics emitters or lasers which can operate by both optical and electrical pumping.
Comprehensive photoluminescence (PL) and electroluminescence (EL) studies are conducted on dislocation engineering light emitting diode structures based on silicon implanted (Si:B) with Ce, Eu, and Yb rare-earth (RE) ions. The PL and EL results show very bright luminescence intensity and dramatic red shifting in luminescence peaks which shows a possible novel phenomenon of RE energy transition modification. The modification is attributed to the direct transition from Si conduction band edge to RE manifolds? (_^2)F?_(7/2)^ , ?(_^2)F?_(5/2)^ for ?Ce?^(3+), ?(_^7)F?_j^ (j=0 to 4) for ?Eu?^(3+), ?(_^2)F?_(5/2)^ and ?(_^2)F?_(7/2)^ for ?Yb?^(3+).
The emissions are shifted from the conventional lowest internal energy transition in ?Ce?^(3+) from around blue spectrum at ~350 nm (due to (_^2)D_(3/2)^ excited state to the ?(_^2)F?_(7/2)^ , ?(_^2)F?_(5/2)^ transitions) to ~1.35 µm in Si:B&Ce. For ?Eu?^(3+) the emission is shifted from around the red spectrum at ~600 nm (due to (_^5)D_0^ excited state to the ?(_^7)F?_j^ transitions, j=0 to 4) to ~ 1.40 µm in Si:B&Eu and for ?Yb?^(3+) is shifted from slightly beyond the visible region at ~980 nm (due to ?(_^2)F?_(5/2)^ excited state to the ?(_^2)F?_(7/2)^ transition) to ~ 1.43 µm in Si:B&Yb samples. The new shifting of luminescence peak into NIR region is very important for optical communication in making LEDs and lasers.