The paper provides the properties of single crystalline 4H-SiC under helium implantation at temperatures of implantation up to 750 ◦C and fluences in the range 5×1015-1×1017 cm−2. The microstructure evolution was studied by transmission electron microscopy cross- section and X-ray diffraction experiments. The mechanical property changes were investigated by using nanoindentation tests followed by atomic force microscopy observations and by using tribological tests. At elevated temperature of implantation and/or in the low fluence regime at room temperature where only the strained state of SiC is obtained, SiC becomes more resistant to crack formation but no significant change in mechanical properties is seen. At room temperature with increasing fluence the damage accumulation leads to the amorphous state for which a strong degradation of the mechanical properties is observed. At elevated temperature of implantation, amorphization is avoided and a thermally activated saturation of the strain is observed in the near surface region whereas defect accumulation occurs near the maximum of damage. Upon annealing subsequent to room temperature implantation, the near surface strain progressively relaxes while the helium ions agglomerate into platelets around the maximum of strain. These platelets evolve into bubble clusters at temperatures where the vacancies become mobile. Under particular conditions of implantation (high fluence and elevated temperature) the swelling of the surface increases during annealing due to the growth of bubbles and the formation of stacking faults resulting from the migration of interstitials towards the maximum of damage. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Ferromagnetic L10 ordered alloys are extensively studied nowadays as good candidates for high density magnetic storage media due to their high magnetic anisotropy, related to their chemical order anisotropy. Epitaxial thin bilayers NiPt/FePt/MgO(001) have been grown at 700 K and annealed at 800 K and 900 K. At 800 K, the L10 long-range order increases without measurable interdiffusion. At 900 K, the interdiffusion takes place without destroying the L10 long-range order. This surprising observation can be explained by different diffusion mechanisms that are energetically compared using molecular dynamics simulations in CoPt in the second moment tight binding approximation. In addition, the frequencies of the normal modes of vibration have been measured in FePd, CoPt and FePt single crystals using inelastic neutron scattering. The measurements were performed in the L10 ordered structure at 300 K. From a Born-von Karman fit, we have calculated the phonon densities of states. The migration energies in the 3 systems have been estimated using the model developed by Schober et al. (1981). The phonon densities of states have also been used to calculate several thermodynamic quantities as the vibration entropy and the Debye temperature.

L1 0 -ordered FeNiPt 2 ͑001͒ thin films were prepared by the interdiffusion of FePt͑001͒ and NiPt͑001͒ layers codeposited on MgO͑001͒ substrates by molecular beam epitaxy ͑MBE͒. A large uniaxial magnetic anisotropy ͑K u = 9.10 5 J/m 3 ͒ and a reduced magnetic transition temperature ͑T c = 400 K͒ were obtained. Growth at 700 K and a first annealing at 800 K result in a large long-range order parameter reflecting the concentration modulation along the growth direction. This high long-range order parameter is conserved in the FeNiPt 2 layers after interdiffusion at 900 K, contrary to what is expected from a simple vacancy migration process. This experimental observation can be explained either by a 6-jump cycle mechanism or by the alternate diffusion of a double vacancy, which are both favored energetically over a second-nearest-neighbor jump mechanism or the simultaneous diffusion of a double vacancy as shown by quenched molecular dynamics simulations.

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The L10 ordered MPt(001) thin films (M = Fe or Co) are very interesting for perpendicular recording due to their magnetic anisotropy and magneto-optical behaviours. Epitaxial L10-ordered NiPt(001) / FePt(001) bi-layers were co-deposited on MgO(100) substrates by MBE. The L10 order parameter is high with the concentration modulation along the growth direction. Some FeNiPt2(001) thin films were obtained by interdiffusion of the bilayers. The long-range-order parameter is conserved after interdiffusion (S = 0.75 ± 0.06), which can be explained by different mechanisms: a second-neighbour jump, a six-jump cycle, an anti-structural bridge mechanism or an antisite-pair elimination and creation mechanism, a double vacancy or a triple defect diffusion mechanism. Quenched molecular dynamics calculations in the frame of the second moment approximation of the tight binding method have been performed to obtain the energetic paths of the different mechanisms. The secondneighbour vacancy jump, the simultaneous jumps of bivacancies and the triple defect mechanisms can be ruled out for energetic reasons.