Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 1991"

Voigt-based methods for arbitrary-shape static hyperfine parameter distributions in Mössbauer spectroscopy

Abstract: We introduce a powerful approach for obtaining arbitrary-shape static hyperfine parameter distributions from thickness corrected Mossbauer spectra. The distributions are taken to be sums of Gaussian components and the corresponding spectra are shown analytically to be sums of Voigt lines. Three cases are worked out in detail for distributions of: i) center shifts, ii) quadrupole splittings with linear coupling to center shifts, and iii) hyperfine fields with linear couplings to center shifts and quadrupole splittings. The domain of validity of our method is described, with particular attention given to recognizing the presence of dynamic effects. An application of hyperfine field distributions to the spectra of FeNi alloys is given. In all cases, convergence is rapid and unambiguous with only two or three Gaussian components being needed for ideal fits. Adding more components does not destabilize the solution but only results in the same distribution and the same values of all the parameters being obtained. Problems occurring with other methods are eliminated by design — given the intrinsic suitability of an expansion in terms of Gaussians.

Approximations to multiple Coulomb scattering

Abstract: The width of the angular distribution of the multiple Coulomb scattering of relativistic heavy particles can be described by simple formulas. The familiar one, which uses the number of radiation lengths, is accurate to 34% for all Z and can be accurate to 11% if a logarithmic path length correction is included. A fairly simple representation that does not use the radiation length agrees with the predictions of Moliere scattering to 2%.

Empirical formulae for energy loss straggling of ions in matter

Abstract: A detailed survey of the currently available data for the energy loss straggling of hydrogen, helium and heavy ions in matter has been undertaken. An empirical formula based on Chu's calculation has been obtained for the energy loss straggling of hydrogen ions. Using this formula with the effective charge and the scaling of straggling, similar to the scaling of stopping powers, good estimates have been made for He and heavy ions. The empirical formulae represent the available data accurately and permit reliable estimates for combinations of projectile and target where currently no data is available.

The Oxford submicron nuclear microscopy facility

Abstract: This paper describes the unique nuclear microprobe facility now established in the University of Oxford. The system, which uses a dedicated small accelerator, operates on a regular daily basis, therefore the emphasis of the design has been on achieving reliable, high-quality performance while minimising overheads of alignment in the focusing system and off-line data processing. The beam-optical system from the ion source to the final lens is described. The final lens has been specially developed to have negligible sextupole-field contamination which allows submicron operation using simple alignment procedures. The system uses up to three beam lines with specialised target chambers. These are described briefly. The data acquisition system uses distributed processing with a VMEbus 68020 microcomputer system handling collection and on-line sorting of data from up to six detectors, a graphics workstation for operator interfacing and a mainframe computer for archiving and off-line processing of data. The components of the system communicate via Ethernet and a low-failure-rate/highthroughput communications protocol has been developed. The archiving procedures are designed to handle high volumes of data (up to 100 Mb per day) with efficient data compression, transparent recall of recent data and simple restoration of archived data.

Impact of slow gold clusters on various solids: nonlinear effects in secondary ion emission

Abstract: A liquid metal ion source (LMIS) has been installed on a pulsed ion gun built at the IPN. The time of flight (TOF) spectra of the pulsed beam were recorded. With the gold source several cluster ions (up to 10 atoms in the cluster) and doubly charged ions were identified in the ion beam TOF spectra. With a second pulsation, single cluster ions can be selected as projectiles for secondary ion TOF mass spectrometry. We have studied the secondary ion emission (SIE) induced by cluster impact from a variety of targets: organic, CsI, metallic. A large enhancement of yield is observed by comparison to single atomic ion impact (e.g. factor of 30 between Au 3 + and Au + ). The secondary ion yields increase strongly with the number of constituents in the cluster. This effect is not linear. A comparison with other types of clusters and also fission fragments of 252 Cf has been performed. The rate of secondary emission stimulated by cluster is similar to SI yield induced by fission fragments.

Plasma immersion ion implantation for ULSI processing

Abstract: With a high ion-density plasma produced by electron cyclotron resonance (ECR) sources, the space charge region between the plasma and a negatively biased target can sustain a potential difference up to 50 kV, with an implantation flux as high as 10 16 /cm 2 s. Other unique features of this plasma immersion ion implantation (PIII) technique include: no ion mass selection, no beam transport optics, and the ion energy and angular distributions controlled by the plasma gas pressure and the applied bias waveforms. By adding a sputtering electrode into the plasma which is powered by a separate voltage supply (i.e., a triode configuration) the implantation chamber can also be converted into an ion-assisted physical vapor deposition system. In this review paper, we outline the physical mechanisms and operation modes of PIII and discuss applications of PIII's unique features for ultra-large-scale integrated circuit fabrication. Recent successes of using PIII for conformal doping of nonplanar device structures, sub-100-nm p + /n junction formation, backside damage impurities gettering, and selective electroless plating of metal interconnects are presented.

Latent track formation induced by high energy heavy ions in superconductive copper oxides

Abstract: Lattice imaging (HREM) of the defects induced by 5.3 GeV Pb ions in YBa 2 Cu 3 O 7−δ ( δ ⩽ 0.1) ceramics provides evidence of latent tracks formation whose influence on the electron transport properties ( R , J c ) has been studied. It is clearly established that the electronic energy loss plays a predominant role in the radiation damage mechanism of 1-2-3 superconductors whenever the energy deposited by inelastic collisions exceeds a threshold value close to 8 MeV μm . A track induced enhancement of the critical magnetization current density is observed at low fluences ( φt ⩽ 3 × 10 11 cm −2 ) but it appears to depend on the value and the orientation of the applied magnetic field with respect to the direction of the tracks.

T-DYN Monte Carlo simulations applied to ion assisted thin film processes

Abstract: The need for computer aided fabrication of modern semiconductor devices calls for reliable algorithms describing complex processes. A number of programs exist for predicting the outcome of several processing steps. In this article we present a new Monte Carlo program, T-DYN, version 2 (1990), which is an extension of the TRIM-CASCADE code. The standard TRIM codes give information about all collisional effects caused by single ions impinging on a virgin target. It does not take into account the target alterations which occur at high dose exposures. A previous TRIM version, TRIM-DYN, takes these alterations into consideration but has the drawback of requiring “super computers” with high operating speed. Process modeling, however, has to be performed in an environment where super computers are normally not available. The new version T-DYN uses different concepts which are more suitable for computer realizations and hence may be operated on advanced personal computers. This makes the program more attractive for applications also by processing engineers. Thin film processing normally involves atom deposition or atom sputter ejection from a surface exposed to some particle fluxes. Thin films are therefore built up or removed. Simulation of thin film processes calls for a code which takes into consideration gradual alterations in the thin film/bulk structure during exposure to the incoming flux. The new T-DYN program can handle energetic ion bombardment and simultaneous deposition of neutral atoms at the surface of the structure. The changes due to previous events are stored and subsequent events will then take into account such updated information. The present paper describes some computational details of the T-DYN program and also presents results obtained.

Mutation breeding by ion implantation

Abstract: Ion implantation as a new mutagenic method has been used in the rice breeding program since 1986, and for mutation breeding of other crops later. It has been shown, in principle and in practice, that this method has many outstanding advantages: lower damage rate; higher mutation rate and wider mutational spectrum. Many new lines of rice with higher yield rate; broader disease resistance; shorter growing period but higher quality have been bred from ion beam induced mutants. Some of these lines have been utilized for the intersubspecies hybridization. Several new lines of cotton, wheat and other crops are now in breeding. Some biophysical effects of ion implantation for crop seeds have been studied.

Morphology of etched pores and microstructures fabricated from nuclear track filters

Abstract: Of the many potent technological applications of nuclear track filters (NTFs), fabrication of micro and ultramicrostructures is one of the most useful spin-offs finding immediate use in a wide range of fields including microelectronics. We report here simple methods of fabrication and morphological investigations on such microstructures and the pores of NTFs. Electrodeposition of copper metal into the etched pores of Makrofol KG, Makrofol N, Kapton-H, and Polyester NTFs with different thickness and porosity has been used to fabricate and reveal the profiles of the structural elements as well as of the pores which act as templates for such structural growths. Some comparative investigations are also presented on non-electrochemical methods of replication.

A particularly fast TRIM version for ion backscattering and high energy ion implantation

Abstract: It was an unresolved problem to theoretically treat the details of RBS spectra, e.g. the influence of double or triple scattering events, or the effects of multiple scattering at glancing incidence or exit angles. The same statement holds true for high energy implantation, if more details than just the main peak are of interest, e.g. the lateral or backward low concentration tails which result from large angle scattering. The present work explains the necessary steps to make the TRIM code even more time efficient: (1) consider only large scattering angles individually; (2) account for the remaining small angle collisions in a global way by (a) subtracting the “partial” nuclear energy loss resulting from these small angle collisions, and (b) adding up the multiple scattering angular spreads caused by such small angle deflections; (3) replacing the “magic” procedure by a fully analytic formula of good precision for large angle scattering at high energies (4) modifying the electronic energy loss subtraction to account for the variation of S e ( E ) along the extended free flight paths; and (5) improving the random number generator to provide in a fast way uncorrelated numbers for billions of ion histories without repetition. In some cases it was possible to increase the program speed by an order of magnitude. Examples of backscattering spectra and high energy range profiles are shown, which could not be obtained by previous existing theories or numerical codes within reasonable computing times.

Ion irradiation of polymers

Abstract: The keV-MeV ion irradiation of polymers produces deep changes in their physical and chemical properties associated with the breaking and rearrangement of original bonds. The modification of chain structure occurs within a well defined ion fluence range which depends on the ion linear energy transfer as well as on the target parameters. At low ion fluences (≈1014 ions/cm2) crosslinks between chains and chain-scissions are detected with a chemical yield in the range 0.05–0.3, depending on the ion mass. With increasing ion fluence (1015 ions/cm 2) the original polymer structure is heavily modified and the irradiated films exhibit properties close to those of hydrogenated amorphous carbon. At very high fluences (≈1016 ions/cm 2) graphitization of the material occurs.

Ion-induced damage and amorphization in Si

Abstract: Ion-induced damage growth in high-energy, self-ion irradiated Si was studied using electron microscopy and Rutherford backscattering spectrometry. The results show that there is a marked variation in the rate of damage growth, as well as the damage morphology, along the path of the ion. Near the ion end-of-range (eor), damage increases monotonically with ion fluence until a buried amorphous layer is formed, while damage growth saturates at a low level in the region ahead. Damage growth remains saturated ahead of the eor until expansion of the buried amorphous layer encroaches into the region. The morphology of the damage in the saturated region is shown to consist predominantly of simple defect clusters such as the divacancy. A homogeneous nucleation and growth model, presented to account for damage saturation, is shown to also predict the dose-rate dependence of the saturation level. Mechanisms are identified which contribute to the unconstrained damage growth observed near the eor prior to amorphization, and subsequently at the interface of the buried amorphous layer. The effects of an imbalance in the generation rates of interstitials and vacancies on damage growth in the eor region are discussed. This imbalance is shown to arise either as a result of added atoms during implantation or spatial separation of the Frenkel defect pairs created during ion impact. A local, uniaxial strain field in the interfacial region of the amorphous layer is identified, and the possibility of its contribution to growth at that location is discussed.

MeV-ion-induced damage in Si and its annealing

Abstract: The interactions between buried defects and impurities formed by MeV ion implantation in Si have been investigated from the following aspects: First, the interactions between the O atoms in CZ Si and the defects introduced during annealing after implantation with various ions, such as B, C, F, Si, P, Ge and As, are discussed by clarifying the amount, nature, morphology and depth distribution of the generated defects. Generally, oxygen atoms are gettered in two different regions of implanted layers. A shallow O peak appears in regions near the surface (between 0.5 and 1.5 μm deep), where no visible defect band exists. A deep peak of O is observed at locations where severe defects exist. These results are explained by considering ion mass, mismatch stress and point defects generated along individual ion tracks. Second, the effect of additional C and F implantation on density reduction and on changes in the configuration of defects formed by individual P and B implantation is reported. Under optimum implantation conditions, an effective suppression of elongated defect formation is observed after annealing at temperatures above 800 ° C. The results are discussed on the basis of interactions between implantation-induced interstitials (which are responsible for secondary defect formation) and implanted C and F atoms.

A photoelectron-ion multiple coincidence technique applied to core ionization of molecules

Abstract: We describe a multiple coincidence technique designed for the measurement of the fragmentation of molecules after inner-shell excitation. The apparatus has been carefully calibrated and optimized for high mass resolution and high detection efficiencies, while maintaining low discrimination against energetic particles. The enhanced counting rates which result allow the determination of detailed information concerning the fragmentation processes.

Production of and studies with secondary radioactive ion beams at LISE

Abstract: The doubly achromatic spectrometer LISE, installed at GANIL, has delivered secondary radioactive beams for the past 6 years. Essentially, it consists of two dipole magnets selecting (in A/Z) and refocussing (achromatically) the projectile-like fragment beams emitted at 0°. Important features of LISE and selected experimental results will be discussed. LISE was substantially upgraded, recently, by adding a Wien filter, providing secondary radioactive beams of still increased intensity and isotopic purity.

Residual gas and ion-beam analysis of ion-irradiated polymers☆

Abstract: In order to understand the ion-polymer interactions which lead to improved polymer-surface properties of ion-irradiated polymers, we have measured both the gases evolved from the polymers Teflon and Kapton during irradiation and the change in the composition of Kapton after irradiation. Ion beams of helium, nitrogen and silicon in the energy range 0.2 to 2.0 MeV were used to irradiate the targets. The primary residual gases observed were CF and CF3 from Teflon and H2, CO, and CO2 from Kapton. Teflon appeared to decompose by fragmentation of its molecular chain. Ion beam analysis of the ion-irradiated Kapton was carried out by Rutherford backscattering (RBS), by elastic recoil detection analysis (ERDA), and by nuclear reaction analysis (NRA). The results from these analyses show that the heavy-ion irradiation creates a complex depth dependence in the composition of the target. Radiolysis and radiation induced chemical reactions during the ion irradiation are discussed.

The A1200 projectile fragment separator

Abstract: A beam analysis device, the A1200, has been constructed at the National Superconducting Cyclotron Laboratory (NSCL) for routine cyclotron beam analysis. This device can also be used to separate radioactive beams produced by projectile fragmentation. Since the A1200 begins the K1200 cyclotron beam lines, radioactive ions can be delivered to any experimental device. The details of the mechanical and optical designs are presented. In addition some of the planned experiments with the separated radioactive beams are discussed.

Quantitative pixe microanalysis of fluid inclusions based on a layered yield model

Abstract: The PIXE microanalysis of geological material using the proton microprobe often involves the treatment of layered or complex three-dimensional samples. While many problems remain intractable, some specific cases lend themselves to quantitative analysis. In addition to thick targets, the two sample geometries that have been treated quantitatively at the CSIRO are fluid inclusions and mineral grains in polished thin sections. The analysis of synthetic targets of known thickness layers has been used to assess the accuracy of this calculation. Also, the effects of inclusion geometry and uncertainties in depth and thickness, on the deduced concentrations in the fluid, have been investigated. The method was applied to the in situ microanalysis of fluid inclusions in quartz. Direct optical measurements of depth and thickness were used, and the quartz matrix was analyzed separately. For many inclusions, the observed Cl K α K β ratio was used as a direct measure of inclusion depth. The results compared well with analyses obtained by the bulk crush-leach method.

High-energy ion implantation for ULSI

Abstract: The “well engineering” of a retrograde twin well formed by high-energy ion implantation for 0.5 μm CMOS is demonstrated to be quite useful in improving many device characteristics, such as leakage current reduction, soft-error immunity, low latchup susceptibility, smaller device isolation dimensions, etc. In forming a heavily doped buried layer by high-energy ion implantation, a drastic reduction in leakage current has been found. This would be caused by gettering of impurities or mudefects by secondary defects which are induced either by implantation of dopant itself (“self-gettering”) or by an additional implantation of oxygen, carbon or fluorine (“proximity gettering”).

PIGME fluorine determination using a nuclear microprobe with application to glass inclusions

Abstract: Fluorine quantitative microanalysis was performed on geological samples, using the 19 F (p, p ′ γ) 19 F reaction, with a 30 (μm proton microbeam at an energy of 3.4 MeV. We have detailed the analytical procedure and the calibration method in relation to a large range of fluorine concentrations in natural glasses and some minerals. This procedure was applied to study the fluorine distribution in melt inclusions trapped in minerals of different origins. The potential of this nuclear microanalysis method is discussed.

Range parameters study of medium-heavy ions implanted into light substrates

Abstract: Carbon films were implanted with Cs, Xe, Sn, Rb, Kr, Ga and Cu and boron films with Bi, Pb, Au, Yb, Cs and Rb ions in an energy range of 10 to 300 keV. Range parameters were determined using the Rutherford backscattering technique. The experimental results are 20–40% higher than the theoretical predictions by Ziegler, Biersack and Littmark. Good agreement is achieved only when inelastic effects are included in the nuclear stopping regime. These features are also observed when previously published range parameter data for medium-heavy ions implanted into Be films are analyzed.

Sputtering of Tungsten by Carbon

Abstract: The sputtering of tungsten by carbon is investigated experimentally and by computer simulation. The erosion and deposition is studied as a function of the fluence of the incident carbon at 1 and 6 keV and for different angles of incidence. Both, experimental data and computer simulation show a transition from net carbon deposition to net erosion as the angle of incidence exeeds values of 40°.

Microstructure of ultrahigh dose nitrogen-implanted iron and stainless steel

Abstract: Nitrogen ion implantation of pure Fe and AISI 304 stainless steel to doses as high as 1 × 1019N2+/cm2 while the target is held at elevated temperatures between 100 and 600° C leads to layers of various N-containing phases as identified by conversion electron Mossbauer spectroscopy and X-ray diffraction. Very thick layers, compared to the ballistic implantation depth, containing γ'-Fe4N can be produced by holding the Fe targets near 400° C while even thicker layers containing either ϵ-(Fe, Cr, Ni)+2+xN, γ-phase high N solid solution, or mixed α-phase/γ-CrN can be produced in 304 stainless steel depending on the dose and provided the average temperature during implantation is near or above 400° C. Nearly complete retention of the implanted dose is observed in 304 SS.

In vivo evaluation of antithrombogenicity for ion implanted silicone rubber using indium-111-tropolone platelets

Abstract: H2+, N2+, O2+, and Ne+ ion implantations into silicone rods were performed at 150 keV with doses ranging from 1 × 1017 to 3 × 1017 ions/cm2 to improve antithrombogenicity. The antithrombogenicity was tested by the superior vena cava (SVC) indwelling method for two days in rats with 111In-tropolone platelets and by the inferior vena cava (IVC) indwelling method for periods of one to seven weeks in dogs. Results of the SVC indwelling method showed that platelet accumulation on H2+ and O2+ implanted specimens decreased. In particular 1 × 1017 O2+/cm2 implantation caused both accumulation onto specimens and a decrease of the SVC. Macroscopic views of the ion implanted IVC specimens in dogs revealed little thrombus formation. It is concluded that ion implantation into silicone rod is a useful technique to improve its antithrombogenicity.

H - formation in grazing collisions of fast protons with an Al(111) surface

Abstract: We have investigated fractions of negative hydrogen atoms after the interaction of fast protons with energies ranging from 1–30 keV with a clean Al(111) surface under grazing angles of incidence. The observed H − fractions are generally small ( − formation in grazing surface scattering proceeds in a two-step process of single-electron transfer.

Interactions of energetic particles and clusters with solids

Abstract: Ion beams are being applied for surface modifications of materials in a variety of different ways: ion implantation, ion beam mixing, sputtering, and particle or cluster beam assisted deposition. Fundamental to all of these processes is the deposition of a large amount of energy, generally some keV, in a localized area. This can lead to the production of defects, atomic mixing, disordering and in some cases, amorphization. Recent results of molecular dynamics computer simulations of energetic displacement cascades in Cu and Ni with energies up to 5 keV suggest that thermal spikes play an important role in these processes. Specifically, it will be shown that many aspects of defect production, atomic mixing and cascade collapse can be understood as a consequence of local melting of the cascade core. Included in this discussion will be the possible role of electron-phonon coupling in thermal spike dynamics. The interaction of energetic clusters of atoms with solid surfaces has also been studied by molecular dynamics simulations. This process is of interest because a large amount of energy can be deposited in a small region and possibly without creating point defects in the substrate or implanting cluster atoms. The simulations reveal that the dynamics of the collision process are strongly dependent on cluster size and energy. Different regimes where defect production, local melting and plastic flow dominate will be discussed.

Studies of γ-ray background with a low level germanium spectrometer

Abstract: A germanium spectrometer was constructed with the intention of achieving high sensitivity at low level background and large sample capacity (about 10 1). To suppress the contribution of radon, the sample chamber can be evacuated. A proportional chamber veto shield reduces the total background (65–2680 keV) by a factor of 13.3. Its residual background, unaffected by cosmic rays, as measured in a deep salt mine, is about 46% of that obtained during normal operation at 15 meter water equivalent (m.w.e.) in the veto mode. The achieved sensitivity for nondestructive γ-ray spectroscopy reaches below mBq/kg corresponding to 10−10 g/g for uranium and thorium.

Ion cluster beam deposition of thin films

Abstract: The idea of using energized ionized clusters of atoms to control the quality of thin film deposition is due to Takagi and his associates at Kyoto University. They have worked to develop and demonstrate the benefits of bringing selected energy and momentum to the surface of a growing solid film without involving any other atomic species than that desired in the film. This technique is related to other ion assisted deposition methods, many of which involve bombardment of a growing film with rare gas ions of selectable energy and current density to improve film density and texture. The ionized cluster beam (ICB) concept involves the supersonic expansion of the atomic vapor of the material of interest from a crucible with a small exit aperture. Species from the expansion (atoms, dimers and larger atomic clusters which may form) are subsequently electron impact ionized and accelerated to a selected energy to bombard the surface of a growing film. ICB has been thought to involve clusters as large as 500 to 1000 atoms. Very high quality films, some of them epitaxial metals on silicon, have been formed with an ICB apparatus. This article reviews the present status of ICB. Based on recent measurements, the number of large clusters is so small that it seems very unlikely they have a dominant influence on the properties of deposited films. The high quality of ICB films seems instead to be due to ion assisted processes involving atomic ions or perhaps ions of quite small clusters.