Excited atom emission from metals under ion bombardment

In this paper the available models of excited atom emission from metals under ion bombardment are analysed and a new approach to solving the problem of finding the sputtered atom excitation probability is offered. At distances between a metal and an atom less than some critical distance the ‘metal-sputtered atom’ system is considered adiabatically. At the larger distances interaction between the metal and the atom is considered in terms of a weak perturbation which can excite the valence electron of the atom. The calculations of the probability of sputtered Al and Cu atom excitation and the radiation intensity for a number of spectral lines of these elements have been carried out.     

Tissue molecular ion imaging by gold cluster ion bombardment

The use of gold cluster focused ion beams produced by a liquid metal ion gun in a TOF-SIMS mass spectrometer is shown to dramatically enhance secondary ion emission of phospholipids and peptides. The method has been successfully tested with cells grown onto plastic slips and with mouse brain slices, without any treatment of the samples. Very reliable time-of-flight mass spectra are acquired with a low primary ion dose of a few 10(7) ions, and high lateral resolution molecular ion images are obtained for heavy ions of great biological interest. This approach offers new opportunities in pharmacological and biological research fields by localizing compounds of interest such as drugs or metabolites in tissues.     

Influence of an external electric field on the recovery of stabilized zirconium dioxide under helium ion bombardment

It is shown that the application of an external electric field during helium ion bombardment of yttrium-stabilized zirconium dioxide single crystals may have a substantial influence on the processes accompanying the radiation-stimulated recovery of yttrium-stabilized zirconium dioxide: its n-type conductivity and refractive index may vary, and metallic nanosize inclusions may appear in the yttrium-stabilized zirconium dioxide matrix. Pis’ma Zh. Tekh. Fiz. 25, 72–75 (July 26, 1999)     

Metallurgical applications of ion implantation and ion bombardment

The physical background to the metallurgy of ion implantation is discussed. For instance, the fate of implanted atoms is considered in the content of the precipitation processes which occur as a consequence of exceeding the solubility limit during implantation.The Metallurgical applications of ion implantation and ion bombardment are discussed under the following headings: surface and interfacial energies, surface applications, superconductivity and void formation.     

A mechanism of surface micro-roughening by ion bombardment

The spatial distribution of sputter-etch effects is analysed theoretically under the assumption of random slowing-down of the bombarding ions. When a surface is bombarded at locally oblique incidence the most pronounced sputtering effect is likely to be observed not at the very point of impact, but further downstream. This effect may cause a significant reduction of the local sputtering yield on top of a spike or a ridge, and an increase on the bottom of a groove or a crater. As a consequence, small irregularities on a relatively smooth surface may be enhanced during bombardment. It is concluded that a microscopically flat surface is unstable under high-dose ion bombardment unless atom migration acts as a dominating smoothing effect. Conversely, sharp cones appear to be surprisingly stable under bombardment. Even on a clean surface, cones erode more slowly than a plane surface, provided that their dimensions are of the order of, or less than, the penetration depth of the ions.     

Nonequilibrium structures and decay processes of clusters sputtered by ion bombardment

A phenomenon of fragmentation of clusters sputtered by ion bombardment and containing both stable and metastable states is considered. The suggested kinetic model is based on the competition of three processes: detachment of atoms from metastable and stable states and drift-diffusion transfer from the former to the latter. Major regimes of fragmentation are identified and conclusion is made on the effect of the time of the diffusion transfer on the preexponential factor and fragmentation kinetics equation.     

Characteristic erosion of silica by oblique argon ion beam bombardment

Following previous work on the angular distribution of ejected particles, features of the oblique argon ion beam bombardment of fused silica were elucidated again but from a different aspect. Detailed observations were made of the erosion topographies of fused silica targets obliquely bombarded with partially neutralized argon ion beam at polar angles of 0°, 22.5°, 45° and 67.5° using scanning electron microscopy. The form of the erosion topography changed systematically from isolated circular etch pits at 0° to isolated crescent etch pits at 22.5° and continuous and homogeneous ripple structures at 45°. Scarcely any erosion pattern was found at 67.5°, except for rare band-like structures. Irrespective of the incidence angle of the beam these structures increased in size with total ion dose but their forms remained unchanged. Essentially the same phenomena were observed in the case of sintered SiO₂-5wt.%P₂O₅ and SiO₂-5wt.%B₂O₃ targets in spite of the fact that their surfaces were initially rougher than that of the fused silica target.     

Self-heating effect induced by ion bombardment on polycrystalline Al surface nanostructures evolution

We studied the self-heating effect during ion bombardment process on polycrystalline Al foils. An anisotropic surface morphology evolution has been observed. The adjacent peaks?? fusion along the direction perpendicular to the ion beam projection smoothen the surface. Fusion along the parallel direction has been suppressed due to Ar⁺ ion bombardment. It attributes to the result of the competition between the isotropic thermal effect, due to the self-heating effect by energy exchange between incident ions and Al surface, and the suppression by continuous ion bombardment with a certain incident angle. Varying the incident ion beam angle with the angular range 32°?<????<?82°, the ripple wave vector, ??, is found to be parallel to the ion beam direction, whereas for ?? > 82°, ?? is perpendicular to the beam direction. The critical angle, ?? _c , is close to 82°, which is different from Bradley and Harper??s prediction and attributes to the self-heating effect.     

Proposals for producing novel periodic structures on silicon by ion bombardment sputtering

It is proposed, and confirmed analytically, that if multiple ion fluxes are incident simultaneously, at different oblique polar angles but at the same Azimuthal angle, on to a target, then the individual ripple patterns generated by sputtering are superimposed to produce novel surface structures. It is also shown that multiple focused ion fluxes incident on to rotating targets can produce circular novel patterns.     

Effect of ion bombardment on thin hafnium nitride films

The use of ion bombardment in the modification of the surface mechanical properties of hafnium nitride has been investigated. Initially the deposition rate and the composition of the films prepared under different conditions of bias potential, partial pressure of N₂ and substrate temperature during r.f. sputtering were analyzed by Rutherford backscattering spectrometry and ¹⁴N(d, ∝)¹²C nuclear reaction. The concentration of hafnium in the film was dependent on both the substrate temperature and the partial pressure of N₂ during sputtering. Films bombarded with 500 keV Kr⁺ ions at different doses (10¹⁵-10¹⁷ ions cm^-2) indicate only moderate changes in the microhardness compared with similar studies of TiN films. However, the HfN films showed a greater improvement in adhesion compared with TiN films at lower ion doses. Ion channeling studies on single-crystal stainless steel substrates did not show any evidence of ion-induced mixing or recoil implantation of hafnium into the substrate. Preliminary measurements of the sputtering yield at high energies indicate that the modifications in microhardness and adhesion of the films may be explained by possible recoil implantation of some nitrogen into the substrate.     

Proposals for producing novel periodic structures by ion bombardment sputtering

It is proposed, and confirmed analytically that if multiple ion fluxes are incident simultaneously, all at the same oblique polar angle but at different azimuthal angles, on to a target then the individual ripple patterns generated by sputtering are superimposed to produce novel surface structures. It is also shown that single focused ion fluxes incident on to rotating targets can produce circular ripple patterns.     

Introduction of helium into metals by magnetron sputtering deposition method

High concentration helium, up to 16 at.%, was introduced into Ti films through magnetron sputtering method in a He/Ar complex atmosphere. The introduced helium distributes homogeneously in the films and mainly forms small helium bubbles. Helium thermodesorption experiments were carried out, from which it was found that the thermodesorption properties of the introduced ⁴He are similar to those of radiogenic ³He in titanium tritides. Titanium alloy films containing helium were also prepared through this way and a comparison of thermodesorption properties was made between them and Ti–He films.     

Lattice disorder in alumina single crystals produced by ion bombardment

The effect of 40 keV Kr ion bombardment of Al₂O₃ single crystals has been investigated using a Rutherford backscattering-channelling (RBC) technique. Curves of lattice disorder were found to be sigmoidal; the disorder increasing slowly up to a fluence of 1 × 10¹⁵ ions cm^–2 and then accelerating to a saturation level at 1 × 10¹⁶ ions cm^–2. These doses are about 100 times higher than comparable values found for elemental and III–V semiconductor compounds. The number of displaced atoms per incident ion estimated for an ion dose of 3 ×10¹⁴ ions cm^–2 was found to be less than that calculated using Sigmund's equation. This difference is discussed in terms of defect recombination and re-ordering during bombardment. Measurements taken from the RBC random spectra before and after each bombardment have indicated that the stoichiometry of the alumina crystals did not alter even at the highest bombardment fluences used.     

Biomedical aspects of ion bombardment of polyethylene

Press-moulded ultra-high molecular weight polyethylene (UHMWPE) samples were subjected to ion bombardment and effects of the modification studied. Helium, nitrogen, argon and silver ions of energy 65–150 keV and fluences in the range of 1 × 10¹⁴ to 3 × 10¹⁶/cm² were applied. The consequences of the modification were studied with FT-IR, Raman and AFM techniques, contact angle measurements, bacteriostaticity and thrombogeneity tests. Surface layer oxidation, graphitization and changes to the surface geometry lead to increase of the surface energy. Modified surface exhibits bacteriostatic properties particularly for higher ion fluences. Aggregation of blood platelets on polymer surface subjected to ion bombardment is limited.     

Structure modifications of vertically grown carbon nanotubes by plasma ion bombardment

We report the structural modifications of vertically grown carbon nanotubes (VCNT) by plasma ion bombardments. The VCNT were grown by thermal chemical vapor deposition (CVD) using acetylene feedstock with iron catalyst and alumina supporting layers on silicon substrate. The plasma ion bombardments were performed using DC plasma enhanced CVD with parallel electrodes configuration. As a result, the height of the as-grown VCNT decreased with increasing applied bias voltages, plasma powers and working pressures. In addition, we observed the aggregated morphologies of the VCNT top surface after the plasma treatments which would be useful for field emission display and energy storage applications.     

Silicide formation by Ar+ ion bombardment of Pd/Si

Palladium films, 45 nm thick, evaporated on to Si(111) were irradiated to various doses with 78 keV Ar⁺ ions to promote silicide formation. Rutherford backscattering spectroscopy (RBS) shows that intermixing has occurred across the Pd/Si interface at room temperature. The mixing behaviour is increased with dose which coincides well with the theoretical model of cascade mixing. The absence of deep RBS tails for palladium and the small area of this for silicon spectra indicate that short-range mixing occurs. From the calculated damage profiles computed with TRIM code, the dominant diffusion species is found to be silicon atoms in the Pd/Si system. It is also found that the initial compound formed by Ar⁺ irradiation is Pd₂Si which increases with dose. At a dose of 1×10¹⁶ Ar⁺ cm^–2, a 48 nm thickness of Pd₂Si was formed by ion-beam mixing at room temperature.