High-energy Ion Bombardment Research Articles

Prompt and metastable decomposition in 252Cf fission fragment ionization mass spectrometry

High energy ion bombardment of organic compounds in the condensed phase is foundto gice rise to secondary molecular ions in the gas phase containing appreciable internal energy of excitation. This paper presents the results of time-of-flight mass spectrometric studies of the subsequent prompt and metastable decomposition of these excited ions. The implications of the findings on the fragmentation mechanisms involved in heavy particle bombardment mass spectrometry is discussed.

The physical properties of thin Ag films formed under the simultaneous ion implantation in the substrate

A high energy ion bombardment and simultaneous thin film deposition system has been developed. The results of investigations of film conductivity during formation of thin silver films on a silicon oxide substrate are presented. It is concluded that the influence of ion bombardment of the substrate during early stages of thin film nucleation is mainly connected with the accumulation of silicon on the surface as result of preferential loss of oxygen. The transition layer between film and substrate is related to the mixing process induced by ion bombardment.

The characterization of polycrystalline materials using ISS

Some use has been made of low energy ion scattering from single crystals to determine surface crystallography and composition. Descriptions of these applications are given elsewhere in this volume. The ISS method also shows considerable promise for polycrystalline materials whose surfaces are frequently much different from the bulk composition. Engineering materials are often contaminated by impurities, processing aids, and bulk alloying constituents which have segregated at the surface. Low energy ISS allows first monolayer sensitivity not possible with methods such as AES and XPS where analysis is obtained over an average depth governed by penetration and excitation phenomena. Low energy ion scattering also provides minimum destruction to sensitive surfaces whose stoichiometry may be altered by electron stimulated desorption or knock-on effects of high energy ion bombardment. An example of such a surface is the failure surface at a weak boundary layer containing fluorine. Serious quantitation problems exist, caused by uncertain geometric and neutralization effects, but sensitivity factors do not vary to the extent of some other techniques such as SIMS. This paper reviews experimental aspects, advantages, limitations and applications of low energy ion scattering for the surface characterization of polycrystalline materials. Recent and future developments are briefly discussed.

Simultaneous ion implantation and deposition

Ion beams have proved to be a useful tool to modify the properties of solid, particularly in the area of semiconductors. Such methods are, however, now spreading far beyond the field of semiconductor devices into metals and superconductors thereby producing a wide range of beneficial effects. The present paper is devoted to the investigation of simultaneous high-energy ion bombardment and low-energy material deposition. It is demonstrated that such processing can produce effects such as reduced epitaxial temperatures, improved film quality and adhesion and in addition provides the possibility of producing regions with controllable nonuniformities through their thickness.

Growth of lenticular bubbles in relation to blistering and flaking mechanism

Consequences of a theory, which is based on a model of ductile extension of a crack in a material, is presented that explains blistering and flaking which appear after high energy ion bombardment. Distinction in mechanisms between blistering and flaking is clarified theoretically. Comparisons between the theory and experiments show very good correlations with respect to blister size. The relation between blister cover thickness and local bubble swelling is given theoretically, explaining the observations made by transmission electron microscopy.

Optical and luminescent properties of ion-implanted films

It has been shown that band parameters for unimplanted films differ from those for bulk materials. Mechanical stresses and increased concentrations of defects seem to be responsible for this difference. The neighbourhood of the surface and the existence of drain paths for bulk defects determine the activity of the surface as a collector for mobile defects and hence their accumulation and their subsequent combination and annihilation reactions. From this point of view ion-implanted films with radiation-induced defects exhibit specific types of behaviour. For example, low energy ion bombardment (together with the removal of a very thin surface layer by etching) leads to an extensive movement of defects towards the surface and to a purification of the corresponding layer. In a number of cases even structural phase transformations take place within the surface layer, which lead in particular to the creation of surface excitons. High energy ion bombardment does not alter the band parameters of the films at the depth d of ion penetration but distorts the structure at the surface owing to a drain of defects into this layer. At the same time centres of scattering and radiative recombination are effectively induced at the depth d.

Lattice strain in garnet single crystals caused by high-energy heavy ion irradiation

The effect of high-energy heavy ion bombardment on the lattice parameter of single crystal garnets is investigated. Lattice expansion normal to the surface corresponding to lateral compressive strain is observed via x-ray reflection topography and rocking curve analysis using a double-crystal diffractometer. Studied are (111) garnet wafers of differing composition and epitaxial ferrimagnetic iron garnet films on pure and MgZr-substituted (111) Gd3Ga5O12 substrates. Using132Xe and208Pb ions of 1.4MeV/nucleon specific energy, the lattice expansion increases approximately linearly with dose over several orders of magnitude. The specific lattice parameter change is approximately 10−14 per ion per cm2 for132Xe ions. A triple epitaxial film is used to obtain strain depth profiles

Void-Lattice Formation in Natural Fluorite by Electron Irradiation

The production of void lattices in metals as a result of displacement damage associated with high energy and heavy ion bombardment is now well documented. More recently, Murr has shown that a void lattice can be developed in natural (colored) fluorites observed in the transmission electron microscope. These were the first observations of a void lattice in an irradiated nonmetal, and the first, direct observations of color-center aggregates. Clinard, et al. have also recently observed a void lattice (described as a high density of aligned "pores") in neutron irradiated Al2O3 and Y2O3. In this latter work, itwas pointed out that in order that a cavity be formed,a near-stoichiometric ratio of cation and anion vacancies must aggregate. It was reasoned that two other alternatives to explain the pores were cation metal colloids and highpressure anion gas bubbles.Evans has proposed that void lattices result from the presence of a pre-existing impurity lattice, and predicted that the formation of a void lattice should restrict swelling in irradiated materials because it represents a state of saturation.

Energy spectra of secondary electrons emitted from metal surfaces under bombardment with high energy noble gas ions

The investigation of the energy distribution of electrons released from metal targets by high energy ion bombardment showed an unexpected fine structure of monoenergetic electrons, which could be attributed to the decay of highly excited auto-ion-izing states of the bombarding gas atoms. A comparison with spectra reported in literature revealed a rather good agreement with respect to the position of the lines on the energy scale. The measurements proved the practicability of the experimental method for such an investigation and will be applied by us in the future with greater refinements of electrons and data processing.

イオン注入時に生じる表面汚染層のＥＳＣＡ測定

Surface contamination of silicon produced by ion implantation is examined by ESCA and IMA, and following results are disclosed. The contaminant film thickness can be evaluated by using ESCA. Deposition rate of the film increases with increase of ion current density and partial pressure of hydrocarbons in the vacuum system, and decrease of ion energy and substrate temperature. The contaminant film is very tenacious. Heat treatment in air can remove the film, but heat treatment in vacuum cannot. Surface contamination produced by ion implantation is formed by polymerization of hydrocarbon molecules, mainly originated from diffusion pump oil, caused by high energy ion bombardment.

Study of Radiation Damage in Silicon with the Scanning Electron Microscope

HIGH energy ion bombardment of silicon causes the formation of disordered regions in the lattice, which overlap on continued irradiation to form a complete amorphous layer1. When the irradiated material is annealed at temperatures above 600° C, this amorphous layer recrystallizes either in an epitaxial or polycrystalline manner, depending on ion type, dose, energy and so on.

Spectral analysis of light emitted from metallic targets bombarded by high energy ions

Results of the spectral analysis of light emitted from metallic targets by bombardment of high-energy ions are presented. Line spectra of target materials and incident ions have been detected while continuous radiation has not been observed. The effect of nonradiative processes near the surface on the character of the obtained spectra is discussed and a model of the generation of an excited particle by binary collision between the incident ion and the surface atom is presented.

Thermal release of rare gases implanted in metal targets by high-energy ion bombardment

Results of thermal gas release from copper, silver, and gold targets bombarded with krypton and xenon ions of energies between 20 and 450 keV will be presented. The influence of bombardment doses is shown. The desorption carried out under high-vacuum conditions was examined with the tracer technique, and the fractional release was determined as a function of temperature, energy, and dose. Depth distributions were studied using a corrosion film technique, and the correlation between such distributions and the gas release was investigated. The results are compared with earlier work, and an attempt to elucidate inert-gas diffusion in copper is described.

Kinetic Emission of Electrons from Monocrystalline Targets

This paper develops a single-collision theory of the emission of electrons from a metal surface subjected to high-energy ion bombardment, which gives reasonable agreement with the data of Carlston, Magnuson, Mahadevan, and Harrison, in the 1 to 10-keV energy range. The model is based upon a Thomas-Fermi-Firsov energy-transfer calculation which has been modified to include an explicit dependence upon lattice orientation. Orientation effects appear naturally, and orientation-dependent cross sections are not required, but the distribution of possible impact parameters for a particular crystal orientation is of central importance. The theory has been used to determine semiempirical interaction potentials between the moving particle and a lattice atom. These potentials are more similar to Abrahamson's atom-atom potentials than to the Gibson potentials used in radiation-damage studies.

Secondary Electron Emissions from Metal Surface by High-Energy Ion and Neutral Atom Bombardments

To obtain ${\ensuremath{\gamma}}_{e}$ for ${\mathrm{H}}_{2}^{+}$ ion bombardment on metal targets, an expression for the secondary electron emission coefficient by fast positive ion bombardment is obtained after adopting a method of calculation similar to that employed by Sternglass. It is shown that the experimental values of ${\ensuremath{\gamma}}_{e}$ for ${\mathrm{H}}_{2}^{+}$ ion bombardment agree with the calculated values provided it is assumed that inside the target a hydrogen molecular ion is dissociated into a proton and a hydrogen atom, each having half the energy of the molecular ion. The dissociation cross section of a hydrogen molecular ion inside the target may be given by ${\ensuremath{\sigma}}_{d}=K\ensuremath{\surd}T$, where $K=1.2$, ${\ensuremath{\sigma}}_{d}$ is expressed in units of ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$, and $T$ is in Mev.The secondary electron emission coefficient ${\ensuremath{\gamma}}_{e}$ for high-energy hydrogen atom bombardment on a metal surface is also calculated and compared with experimental data. In the calculation, a neutral beam of hydrogen atoms is treated inside the target as composed of protons and electrons in addition to hydrogen atoms. Each of these three kinds of particles are capable of producing internal secondaries.A fair agreement between the calculated and observed values of ${\ensuremath{\gamma}}_{e}$ for ${\mathrm{H}}^{+}$, ${\mathrm{D}}^{+}$, ${\mathrm{H}}_{2}^{+}$, and ${\mathrm{H}}^{0}$ bombardments has been obtained.

Electron Emission from Metals under High-Energy Hydrogen Ion Bombardment

Measurements of the electron emission from Mg, Al, Fe, Ni, Au, and Pb surfaces bombarded by atomic (H1+) and molecular (H2+) hydrogen ions with energies from 0.7 to 2.0 Mev showed a diminishing emission with ion energy and little dependence on either atomic number or on the field intensity at the metal surface. Measurements of this type are of interest in connection with the mechanism of high voltage discharges in vacuum. The expected variation of secondary emission with angle of incidence and with conditioning was found. The emission ratios are compared with measurements by others at lower ion energies.