A. Traverse

Progress report on Aramis, the 2 MV tandem at Orsay

Abstract Aramis is a home built multipurpose 2 MV electrostatic tandem accelerator. A large variety of ions are available for high energy implantation. Characterization possibilities are also quite large in the Van de Graaff mode owing to the Penning positive ion source in the terminal. A second beam line is now available that sends the beam into the target chamber of the 200 kV medium current implanter. We will provide a progress report on the machine and present some results regarding in situ studies of multilayer mixing and implanted silicide layers

Structure and magnetism of well defined cobalt nanoparticles embedded in a niobium matrix

Our recent studies on Co-clusters embedded in various matrices reveal that the co-deposition technique (simultaneous deposition of two beams : one for the pre-formed clusters and one for the matrix atoms) is a powerful tool to prepare magnetic nanostructures with any couple of materials even though they are miscible. We study, both sharply related, structure and magnetism of the Co/Nb system. Because such a heterogeneous system needs to be described at different scales, we used microscopic and macroscopic techniques but also local selective absorption ones. We conclude that our clusters are 3 nm diameter f.c.c truncated octahedrons with a pure cobalt core and a solid solution between Co and Nb located at the interface which could be responsible for the magnetically inactive monolayers we found. The use of a very diluted Co/Nb film, further lithographed, would allow us to achieve a pattern of microsquid devices in view to study the magnetic dynamics of a single-Co cluster.

A characterization of titanium anodic oxides by X-ray absorption spectroscopy and grazing X-ray diffraction

Abstract Thin oxide layers obtained by electrochemical oxidation of titanium were studied using grazing X-ray diffraction (GXRD) and X-ray absorption spectroscopy (XAS). In the precursor state the layers, with thicknesses ranging from 15 to 105 nm, appeared to be amorphous by GXRD whereas a short-range order is detected via XAS with a first O shell and a second Ti shell, rather similar to those of crystallized anatase. Subsequent treatments of the layers such as aging under polarization or thermal annealing led to ordering on a larger scale and to crystallization in the anatase form.

Specific behaviour of CdTe ion implantation damage

Abstract In order to study the damage produced as a function of both the chemical nature of the ion and the implantation energy, [111] CdTe single crystals were implanted with 150 keV Mn and 50, 100 and 200 keV P ions. Analysis of the damage was carried out by Rutherford backscattering spectrometry and ion channeling measurements using 4He beams at different energies. These measurements show that the disorder induced by ion implantation in CdTe exhibits specific features: (i) saturation of damage without reaching the amorphous state; (ii) existence of an almost undamaged near-surface region. In fact, whatever the implantation conditions, the normalized channeling yield (which is a measure of the integrated disorder) reaches the value of 0.6–0.7 at saturation and the low damaged layer depth is about 40 nm thick. The channeling measurements are consistent with a previous study in which the residual damage was identified as small-sized dislocation loops mainly located beyond the ion projected range R P . These results are interpreted as indicating a high mobility of defects in CdTe together with a high efficiency of the surface in their recombination process, and the role played by the dislocation-loop-induced stress.

Ion channeling study of P implantation damage in CdTe

Abstract Phosphorus implantation was performed on single-crystal samples of [111] CdTe at incident energies of 50, 100 and 200 keV, with fluences up to 4×1016 P cm 2 . All implants were done at room temperature with current densities below 0.2 μA/cm2. In order to investigate the damage produced, Rutherford backscattering of 4He particles in channeling condition was done in situ at several energies. The dependence of the dechanneling upon the incident 4He beam energy allowed us to characterize the nature of the implantation induced defects. We describe the evolution of the damage resulting from P implantation in CdTe as a function of fluence and implantation energy. In order to understand the nature of the damage, 100 keV P implantations were also monitored with in situ transmission electron muscopy (TEM).

Structural study of the Al/Ni interface in ultrathin polycrystalline multilayers

Several Al–Ni multilayers were prepared where the Ni thickness was varied in order to (i) detect Ni diffusion in Al and Al diffusion in Ni and (ii) determine the compounds that form at the interface during deposition at room temperature. X-ray absorption spectroscopy was carried out at the K edge of Ni to identify the local atomic arrangement around this atom. Magnetic measurements allowed the detection of pure Ni among nonmagnetic AlxNi1−x compounds. At the Al/Ni interface, Ni diffuses in Al whereas no Al diffusion in Ni was observed at the Ni/Al interface. Ni diffusion in Al results in the formation of a disordered aluminide over a thickness of about 1.7 nm, then pure Ni growth takes place in the form of islands.

Structural and electronic modifications in ion beam treated yttrium oxide

Abstract Disorder induced by ion beam treatments (irradiation with energetic Au ions or Zr implantation) in the Y 2 O 3 ceramic has been studied. By combining several experimental techniques, we obtained information on electronic distributions and on atomic rearrangements around each species of the matrix. Three types of defects have been investigated. They are the intrinsic defects: on the oxygen and Y sublattices, and an extrinsic defect: the implanted impurity, here Zr, a cation greedy of oxygen. No amorphisation was reached under the experimental beam conditions used here. The whole matrix remained well crystallized, despite the fact that the final disorder around the impurity, located on a substitutional site, was rather large. Oxygen desorption occurred on the ion beam treated depth. We found that (i) oxygen vacancies appeared to be ordered and (ii) there was a competition between energy deposition via atomic collisions which induced O desorption and chemical effects due to Zr implantation which retained O.

An overview of the ion beam mixing rates in Pd/Si bilayers versus the temperature and deposited energy

Abstract Pd/Si bilayers prepared by electron gun evaporation of Pd on Si substrates were irradiated with different ions and incident energies in order to vary the deposited energy in form of nuclear collisions, Fd, in the range 2.8–6.2 keV nm . Considering mixing rates measured in the range 0.05–1.1 keV nm taken from the literature, we provide an overview of mixing rates dependence on deposited energy on a range covering two orders of magnitude. Temperature dependence of mixing rates have also been measured in the 80–573 K range in order to deduce the critical temperatures and activation energies. The phase formation process (Pd2Si and PdSi) is also discussed.

Copper clusters made by implantation in aluminium nitride

Abstract Copper has been implanted in AIN at 80 and 300 K with an average concentration around 14%. X-ray absorption spectroscopy performed at the K edge of Cu on as-implanted samples and on samples annealed at 800°C for 1 and 5 h show that Cu precipitated in the host matrix even for implantations performed at low temperature. Analysis of the spectra allows the average size of the clusters to be deduced. These crystalline entities grow with dense planes of each phase parallel to each other, as shown from previous transmission electron microscopy experiments. The initial implantation fluence together with the subsequent annealing times and temperatures appear to be easy tools to monitor the cluster size.

An ion beam mixing model for compound formation: the case of Pd/Si

Abstract The squared thickness of the mixed layer in the case of ion-beam-irradiated Pd/Si displays a quadratic dependence on the fluence below a critical value Φ c and a linear dependence above Φ c . A qualitative interpretation of such a behavior has been provided in terms of a formation-controlled process below Φ c and a diffusion-controlled process above Φ c . In this paper, we give a short presentation of a model associating Ficks law and a chemical driving force in order to simulate the chemical reaction at the irradiated boundary leading to the formation of Pd 2 Si. The mixing rate above Φ c is enhanced as compared to the one due to collisional processes only. In the particular case of Pd/Si, we have used this model to account for the experimental mixing rates measured above Φ c at 300 K on a wide range of the density of energy deposited in nuclear collisions from 0.01 to 6 keV/nm.