J. Chevallier

Evidence for atomic mixing induced in metallic bilayers by electronic energy deposition

Abstract High levels of energy deposition by electronic excitations can induce damage creation in some bulk metallic targets as soon as the rate of energy deposition in electronic excitation is higher than a few 10 keV/nm. The present study is aimed at determining whether such excitations can also induce interdiffusion at the interface of metallic bilayers. Ni Ti bilayers were irradiated at 80 K with GeV Pb, Ta and U ions up to a few 10 13 ions/cm 2 . Damage creation and mixing were followed using various methods: electrical resistance, grazing X-ray and neutron reflectometry, X-ray diffraction, electron microscopy and electron energy loss on target cross-sections. A very strong mixing is indeed observed at the Ni Ti interface as a result of electronic energy deposition: the observed mixing efficiency is at least two orders of magnitude higher than that induced by elastic collisions with target nuclei. We finally study the influence of various parameters (irradiation temperature, symetry of the interface) on the mixing efficiency and follow the kinetics of the mixing process.

Atomic mixing induced in metallic bilayers by high electronic excitations

Abstract It has been recently established that high levels of energy deposition in electronic excitations can induce damage creation in a few metallic targets as soon as the linear rate of energy deposition in electronic excitation is of the order of a few 10 keV/nm. The present study is aimed at determining whether high electronic excitations can induce interdiffusion at the interface of metallic bilayers. Ni Ti bilayers were irradiated at 80 K with GeV Ta ions up to a few 1013 ions/cm2. Damage creation and mixing were followed using various methods: X-ray and neutron reflectometry, X-ray diffraction, electron microscopy and electron energy loss on transverse cuts. A very strong mixing is observed at the Ni Ti interface as a result of high electronic excitations.

Effect of ion implantation on thin hard coatings

The surface mechanical properties of thin hard coatings of carbides, nitrides and borides deposited by r.f. sputtering were improved after deposition by ion implantation. The thickness and the stoichiometry of the films were measured by Rutherford backscattering spectrometry and nuclear reaction analysis before and after ion bombardment. The post ion bombardment was achieved with heavy inert ions such as Kr+ and Xe+ with an energy sufficient to penetrate the film and to reach the substrate. Both the film adhesion and the microhardness were consistently improved. In order to achieve a more detailed understanding, Rb+ and Ni+ ions were also used as projectiles, and it was found that these ions were more effective than the inert gas ions.

The dependence of stress in IBAD films on the ion-irradiation energy and flux

Abstract Systematic experimental studies of the stress build-up during e-gun deposition of Ni with simultaneous bombardment by energetic Ar+ ions (IBAD) have been carried out. The ion energy E was varied from 60 to 800 eV, and the ratio of the arrival rates of Ni atoms and Ar+ ions, R J , was varied from 0.5 to 6.4. The Ni-deposition rate was in the range from 0.5 to 2.0 A/s, with all the depositions carried out near room temperature in a chamber with the base pressure of 5 × 10−6 Pa. The film stress was measured by use of profilometry and the application of Stoneys equation. The experimental results were compared with predictions of a simple model proposed by Davis. This model assumes that the compressive stress build-up, due to knock-on implantation of film atoms being proportional to E 1 2 , is balanced by relaxation by collision-cascade-excited atom migration proportional to E 5 3 . To obtain agreement between model and experiment in the investigated ranges of E and R J , an additional model parameter had to be added which takes into account that without irradiation, tensile stresses arise.

Heavy ion channeling

Abstract We discuss recent experiments on heavy ion channeling at high energies. Resonant-capture and loss of electrons has been studied by measurement of the charge state of ions transmitted through a thin Si crystal. The energy loss has been used to define the transverse energy of axially channeled ions and to measure the strength of the resonant processes as a function of transverse energy. We therefore first discuss briefly the average energy loss and the straggling in energy loss for channeled and random penetration. Dielectronic KLL capture (inverse KLL Auger emission) has been measured in the energy range 12–18 A MeV for Br 33+ (He like) ions and the observed dependence of the resonance strength on transverse energy is consistent with the calculated variation of the density of valence electrons seen by the ions. Coherent excitation leading to electron loss has been measured for Si 13+ (H like) ions channeled along a 〈111〉 axis at about 21.7 A MeV, where the energy in the ion rest frame of virtual photons in the 7th harmonic of the axial potential matches the energy of the transition of the bound electron from the ground state to the first excited state. A detailed theoretical discussion of this process is given. The dependence on transverse energy is very strong because the field decreases rapidly with distance from an atomic string. There is good agreement between calculations and experiment, both concerning the dependence of the strength of the resonance on transverse energy and concerning the Stark splitting, which is caused mainly by the zeroth harmonic of the transverse force from 〈111〉 atomic strings.

Study of damage accumulation in sapphire during nitrogen implantation

Abstract The damage structures into α-Al 2 O 3 single crystals produced by 50 keV nitrogen ion implantation were examined as functions of ion implantation parameters (doses, temperature, …) using the Rutherford backscattering channeling technique. Analysis of the profiles for the implanted species are performed on samples implanted with doses ranging from 1 × 10 15 to 8 × 10 17 N + cm 2 at 25°C and 400°C. Ion implantation produces displacement and other damage in the near-surface region and for high fluences (10 17 ) the surface of originally crystalline samples is turned amorphous. Cross section TEM measurements clearly show defects, gas bubbles and amorphous layers in the near-surface regions. Low energy electron induced X-ray spectroscopy method (LEEIXS) confirms that nitrogen remains in the form of gas in the amorphous region.

The influence of ion bombardment on deposition of carbon films

Abstract The possibility of producing hard carbon films with inert ion implantation in the hundred keV region during plasma deposition is discussed. The films showed a distinct improvement in adhesion and microhardness dependent on the energy and dose rates of the implanted ions.

Dielectronic recombination for He-like 79Br ions channeled along the 〈110〉 direction in Ni

Abstract Dielectronic recombination for He-like 79Br has been measured for channeling along a 〈110〉 axis in Ni. The KLL resonance has a FWHM of 14% of the beam energy and an area corresponding to a density of about 6 electrons per atom.

Ion beam induced enhancement of noble metal film adhesion on sapphire

Mesure de ladherence des films de Pt, Pd, Au obtenus par mixage ionique dargon, xenon ou krypton

Influence of ion bombardment on sputtered TiC films

Abstract The influence of heavy ion bombardment of thin sputtered films of TiC was studied. Using a post-deposition bombardment with krypton and xenon ions from a 600 kV ion accelerator on films of the order of 1000 A thick, it was possible to obtain an improvement of up to 50% in the relative microhardness. Rutherford backscattering and nuclear reaction analysis as well as transmission electron microscopy were used to study the effect of the ion bombardment.