Nuclear Backscattering Spectrometry Research Articles

Amorphous hydrogenated carbon films elaborated by plasma-assisted chemical vapour deposition: characterization of composition by nuclear methods

The variation of the stoichiometric composition of amorphous hydrogenated carbon films (a-C:H) deposited onto stainless steel was determined as a function of various elaboration parameters (pressure in the reactor, generator power, gas flow rate), by energetic α particle scattering (elastic recoil detection, nuclear backscattering spectrometry). Whatever the experimental conditions, the films obtained present the following characteristics: a hydrogen-depleted surface layer (∼40nm thick); a deep-lying layer of constant stoichiometry and of variable thickness according to the elaboration parameters. Furthermore, strong hydrogen diffusion inside the substrate is observed. The total hydrogen content decreases when the pressure in the reactor or the generator power increases and it goes through a maximal value when the gas flow rate increases. In the limited range of total hydrogen content studied here, no significant variation of the adhesion properties was found.

Energetic ion scattering analysis and glow discharge optical spectrometry characterization of amorphous hydrogenated carbon films elaborated by PACVD

Amorphous hydrogenated carbon films (a-C:H) were deposited by PACVD on stainless steel substrates. The properties of these films can vary with the elaboration of the conditions, and therefore with the composition. Here, the films were quantitatively determined by energetic alpha particle scattering using two different methods: elastic recoil detection (ERD) for hydrogen analysis; and nuclear backscattering spectrometry (NBS) for carbon and oxygen analysis. Concurrently, the same samples were investigated by glow discharge optical spectrometry (GDOS), a method which gives information on all the elements of the periodic table. Nuclear method investigations showed that the a-C:H films were composed of two layers: the film itself of constant stoichiometry and a hydrogen depleted surface layer. They showed too a strong hydrogen diffusion inside the substrate and the presence of oxygen at the interface. GDOS profiles characterized the film, the film/substrate interface and the substrate. Particularly, Al presence at the interface and in a part of the deep-lying layer of the film was detected. This results from cathode sputtering during the elaboration process.

Physicochemical and tribological characterization of titanium or titanium plus carbon implanted AISI M2 steel

AISI M2 steel samples were implanted with 110 keV titanium ions at fluences ranging from 5 × 10 16 to 4 × 10 17 Ti cm -2. Titanium plus carbon dual implantation was also studied. Titanium distribution profiles were determined using the 48Ti(p,γ) 49V resonant nuclear reaction. The incorporation of carbon and oxygen from residual gases was studied as a function of titanium fluence and residual pressure using nuclear backscattering spectrometry at 5.7 and 7.5 MeV He + ion energies respectively. A competition phenomenon between carbon and oxygen incorporation is pointed out. Analysis of the phases formed was performed using conversion electron Mössbauer spectroscopy. Fe(Ti) solid solution, a-Fe x Ti 100− x and superficial a-Fe-Ti-C amorphous phases were identified. Tribological tests involving a ball (Al 2O 3 or 52100) and disc contact were performed to characterize the friction behaviour of the implanted surface. It is shown that titanium or titanium plus carbon implantation leads to a reduction in the friction coefficient. The wear tracks and debris were examined using scanning electron microscopy and electron microprobe cartography. For the two types of balls a reduction in the wear track width was observed together with oxidation of the wear debris. The tribological improvement observed depends not only on the presence of the superficial a-Fe-Ti-C amorphous layer but also on the surface chemical reaction during the wear process.

Boron implantation into AISI 52100 steel

A 52100 steel substrate was implanted at room temperature with 11B ions of 20, 35 and 50 keV energy at low (5 × 10 16 ions cm -2) and high (2 × 10 17 ions cm -2) fluences. Nuclear backscattering spectrometry using the 11B(γ,γ') reaction at 6.04 MeV was used to determine the boron distribution profiles. Conversion electron Mössbauer spectroscopy was used to analyse the physicochemical alterations of the surface. The high fluence leads to amorphization of the surface. However, the hyperfine field distributions give some indications of the local environment of iron atoms in the perturbed surface. Fe 2B, Fe 3B and Fe 1- x B x phases are distinguished. A small amount of bismuth implanted in front of the boron distribution will act as a tracer for quantifying the alteration in wear produced by boron implantation of 52100 ball bearings. The wear machine is described and some preliminary results are given.

Nuclear reaction analyses of boron nitride films deposited by ion beam based techniques

Abstract Nuclear reaction analysis (NRA) and Rutherford backscattering spectrometry (RBS) measurements were carried out to study the growth mechanisms of boron nitride films deposited at room temperature by reactive ion beam sputter deposition (RIBSD), ion beam assisted deposition (IBAD) and ion beam deposition (IBD) from borazine (B3N3H6). The nuclear reactions 14 N(d , α) 12 C , 10 B(d , α) 8 Be , 11 B(d , α) 9 Be, and H ( 15 N , αγ) 12 C were respectively used to measure the areal concentrations of nitrogen, boron and hydrogen in films deposited on silicon. The calibration of the spectra was made by comparison with standard samples. BNx films analyzed by RBS were deposited on carbon substrates coated in situ with a silicon or an iron layer in order to avoid overlapping of the 11B peak and the carbon plateau. By using complementarily in situ Auger electron spectrometry and ex situ nuclear analyses to determine the respective surface and bulk N-concentrations in the IBAD films, we were able to identify the different phases of the mechanism leading to the nitridation of evaporated boron by nitrogen ions. The composition of RIBSD films is found to depend only on the primary ion energy. In the case of IBD, the H-content decreases with the ion energy, from 19% at 0.5 keV down to 5% at 1.5 keV. In addition, we observed a chemical sputtering process which reduces drastically the deposition yield (i.e. the ratio of deposited atoms to the incident atomic fluence) when the ion energy is increased.

Permalloy stoichiometry by nuclear backscattering

The high mass-resolution capability of nuclear backscattering spectrometry with 4.7 MeV 4He ion beams has been used to study the stoichiometry of thin permalloy (NiFe) films. For film thicknesses ≤, 250 A ̊ , the backscattering signals from isotopes of Ni and Fe are sufficiently resolved to allow accurate determination of stoichiometry; the Ni fraction can be determined to better than ± 1%. Studies of the dependence of NiFe film stoichiometry on deposition method, film thickness and oxygen contamination indicate that NiFe stoichiometry is independent of film thickness and oxygen contamination, but electron-beam evaporation produces films slightly richer in Ni than does sputtering.

Strong metal-support interactions for Pt and Rh on Al 2O 3 and TiO 2: Application of nuclear backscattering spectrometry

The phenomenon of Strong Metal-Support Interactions (SMSI) has been explained previously in terms of a chemical bonding between dispersed metal atoms and cations of certain supports. In this study, planar specimens of Pt Al 2O 3 , Rh Al 2O 3 , Pt TiO 2 , and Rh TiO 2 were heated in hydrogen or oxygen and the resulting changes were observed by the technique of Nuclear Backscattering Spectrometry (together with electron microscopy). Significant and complex diffusion effects were found to occur, being dependent on the particular metal/support combination plus the environment and temperature to which it is exposed. This goes beyond the original mechanistic concept and the results suggest a much wider range of SMSI processes.