L.S. Wielunski

The influence of ion energy on the nitriding behaviour of austenitic stainless steel

Abstract Recent work on austenitic stainless steels has indicated that low energy, high current density nitrogen implantation can result in nitrided layers several micrometers in depth and of considerable hardness. This work was initiated to examine the effects of ion energy during ion implantation at elevated temperatures. Three nitriding methods were considered: plasma immersion ion implantation (PI 3 ), radio frequency (r.f.) plasma nitriding and ion beam nitriding. The structure and nitrogen profile of austenitic stainless steel were examined after the different treatments by a range of analytical techniques including glancing angle X-ray diffraction (GAXD), ultra microhardness indentations (UMIS), glow discharge optical spectroscopy (GDOS) and nuclear reaction analysis (NRA). It was found that similar surface structures can be formed by PI 3 treatments at high energies and ion beam nitriding at low energies. The resultant microstructures, as determined by GAXD, consist primarily of an expanded austenite layer. It appears that the adherent oxide film present on stainless steel must be either removed by sputtering, at low ion energies, or passed through by implantation, at high energies. Subsequent diffusion at elevated temperatures allows the formation of a nitrided layer several micrometers thick in both cases.

Measurement of the micro mechanical properties of sol-gel TiO2 films

Abstract The interest in the use of sol-gel derived films in tribological applications during recent years has increased the interest in the mechanical properties of these films. In this study we compare conventional film processing, firing in a tube furnace, with an alternative method, ion bombardment with medium energy hydrogen ions. In order to understand the behaviour of sol-gel derived titanium dioxide (TiO 2 ) films deposited on glass, we have employed a number of different mechanical testing techniques. An ultra micro indentation system has been employed to measure the hardness and elastic modulus. This technique has been complemented by a bi-axial bending technique in order to fully determine the mechanical properties of the thin films. The results from the bi-axial bending technique have been analyzed using a finite element method in order to determine the stress distribution during the bi-axial loading and therefore to correct for non-uniform sample support. The films have been analyzed using RBS, XRD and AFM in order to examine the structure of the films. A comparison of the behaviour of the sol-gel TiO 2 to PVD deposited aluminium and copper films has also been carried out.

Modification of the mechanical and optical properties of a polycarbonate by 50 keV Ar+ and H+ ion implantation

The effects of 50 keV H+ and Ar+ ions on the mechanical properties and ultraviolet-visible absorption of the polymer CR39 were investigated. It was found that the H+ implantation produced a yellow–brown material with optical properties similar to amorphous hydrogenated carbon, whereas Ar+ implantation produced a material with optical properties more like evaporated amorphous carbon. The mechanical properties of the implanted material were measured using a nanoindentation technique and increases in both the elastic modulus and hardness (maximum sustainable contact pressure) were observed following irradiation with both ion species. Compared to Ar+ implantation, H+ implantation of CR39 was found to produce a more transparent material at an equivalent maximum sustainable contact pressure and therefore H+ ions were found to be more desirable than Ar+ ions for the treatment of CR39 optical components.

The mechanical and structural properties of Ti films prepared by filtered arc deposition

Abstract In this study the development of residual stress of arc deposited Ti films as a function of the energy of deposited atoms was investigated. A comparison with the momentum transfer model for Ti films deposited under substrate bias indicate that the films are in a region characterised by momentum values of 50–150 amu 1 2 eV 1 2 . The compressive stress was found to vary from 1.1 GPa to 0.1 GPa and the range of Ti microhardness was measured to be 6.7–8.7 GPa. The microchardness varied with grain size according the Hall-Petch relationship. The substrate bias was varied and the influence on residual stress, microhardness, preferred orientation, density, surface roughness and topography of the deposited films was investigated.

Mechanical and structural modification of CR-39 polymer surface by 50-keV hydrogen and argon ion implantation

In this study we report hardness changes and structural effects in the polymer Cr-39 following implantation with 50-keV hydrogen and argon ions to doses between 1 × 1015 and 2.8 × 1017 ions/cm2. An increase in hardness (maximum contact pressure) was observed following both H and Ar implantation, with increases by factors of 6.5 and 1.5, respectively. Significant compaction of the ion beam modified layer was also observed for both ion species. These results suggest that the bonding changes induced by H implantation, which is dominated by electronic stopping processes, are more effective at enhancing the hardness of CR-39 than Ar implantation, which has considerable nuclear as well as electronic stopping.

The deposition of TiN thin films by nitrogen ion assisted deposition of Ti from a filtered cathodic arc source

Abstract TiN films are synthesised on ambient temperature substrates by condensing Ti+ ions from a filtered cathodic arc source beam under 500 eV N+2 nitrogen ion bombardment. The film stoichiometry was varied from a N:Ti ratio of 0.8 to 1.2 by controlling the relative arrival rates of Ti and nitrogen ions. The compressive stress in 120 nm thick films deposited onto Si was found to decrease from a maximum of 10 GPa under no ion bombardment to a minimum of 6 GPa for an arrival ratio of 1.0. In the absence of ion bombardment the composition of the films was found to depend on the partial pressure of nitrogen over the range 0.6–2 Pa where the N:Ti ratio changed from 0.3 and saturated at approximately 0.8. Collision cascade models are used to describe the evolution of compressive stress as a function of arrival ratio, the damage depth distribution due to Ti+ ions and N+ ions and the composition of the TiN films.

Properties of thin films of tantalum oxide deposited by ion-assisted deposition

Abstract Thin films of Ta 2 O 5 have been deposited by oxygen-electron-beam evaporation using O 2 + ion energies of 100 eV and 1000 eV. A maximum refractive index of 2.14 and an extinction coefficient of 3 × 10 −4 at 633 nm were found under the optimum conditions of 100 eV ion assistance. The film stress was found to change from tensile to compressive under ion assistance and a maximum stress of −0.4 GPa was recorded. The film hardness also increased with the degree of ion assistance from 7.4 GPa for evaporation only to a maximum hardness of 10.3 GPa for films deposited by ion assistance onto Si. A linear relationship was found between the refractive index and the packing density for films deposited using 100 eV O 2 + ions.

Characterization of mechanical properties of VO2 thin films on sapphire and silicon by ultra-microindentation

Abstract Mechanical properties of very thin (100 nm) VO 2 films of the epitaxial (on sapphire) and the polycrystalline (on Si) type were investigated with ultra-microindentation using a spherical diamond indenter of 200 nm in radius with a maximum force of 0.5 or 1.0 mN. The epitaxial films on sapphire exhibited a Meyers hardness ( HM ) of 13 GPa and a composite modulus ( E * ) of 240–260 GPa, with little change for films formed at different substrate temperatures. The polycrystalline films on Si showed a HM of 7–9 GPa and an E * of 140–170 GPa, i.e. with a HM slightly lower than and an E * being almost comparable to that of Si. The values of HM and E * for films on Si reasonably represent the intrinsic mechanical properties of a polycrystalline VO 2 , while the higher values for epitaxial films on sapphire are presumably due to the compressive stress from a lattice mismatch.

Ion-implanted graphitic carbons

Abstract Ion implantation of glassy carbon and other graphitic forms of carbon leads to significantly increased resistance to wear. The effect is observed for a variety of ion species. Nitrogen ion doses as low as 5 × 10 15 ions/cm 2 at 50 keV are effective and the enhancement is related to the damage produced by the incident ions. New and previous data show the importance of ion energy and dose in determining the modified (damaged) zone. The general applicability of implantation as a modification tool for graphite-based carbon is supported by work with highly ordered pyrolytic graphite (HOPG), electrode carbon and carbon fibre. Aspects of possible mechanisms responsible for the enhanced wear resistance are discussed.

MULTIPLE SCATTERING EFFECTS IN DEPTH RESOLUTION OF ELASTIC RECOIL DETECTION

Multiple scattering strongly affects the depth resolution of Elastic Recoil Detection (ERD) experiments in contrast to its small effects in typical Rutherford Backscattering Spectrometry (RBS) measurements. A comparison of experimental ERD and RBS results shows substantial differences in the depth resolution of these two techniques. The effect of multiple scattering is estimated by computer simulations and is compared to experimental results. The effect of sample material is also discussed and it is shown that in high Z materials multiple scattering is dominant and the depth resolution of ERD is often comparable to the measured structure thickness. The effects reported in this paper are of a general nature and are applicable to all ERD type analysis including He and heavy ion ERD and all kind of detection systems.