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Abstract: The results of present paper have shown that sputtering of yttrium iron garnet (Y3Fe5O12) under swift heavy ions in the electronic energy loss regime is non-stoichiometric. Here we are presenting additional experimental results for gadolinium gallium garnet (Gd3Ga5O12) as target. The irradiations were performed with different ions (50Cr (589MeV), 86Kr (195MeV) and 181Ta (400MeV)) impinging perpendicularly to the surface. As earlier, the sputtering yield was determined by collecting the emitted gadolinium and gallium atoms on a thin aluminium foil, placed upstream above the target and analyzing the Al catcher by Rutherford backscattering. Also for Gd3Ga5O12, the emission of Gd and Ga is non-stoichiometric. Sputtering appears above a critical electronic stopping power of Sth =11.6±1.5keV/nm, which is larger than the threshold for track formation, in agreement with other amorphisable materials. In addition, the angular distribution of the sputtered species was measured for Y3Fe5O12 and Gd3Ga5O12 using 200MeV Au ions impinging the surface at 20° relatively to the surface. For the two garnets the ratio of Y/Fe (and Gd/Ga) varies with the angle of emitted species and the stoichiometry seems to be preserved only for an emission perpendicular to the surface. [Copyright &y& Elsevier]

Abstract: Silicon nanocrystals (Si-ncs) embedded in silicon nitride are of great interest for micro and optoelectronic devices such as non-volatile memories and solar cells. Indeed, Si3N4 is a “high-k” dielectric and can replace SiO2 in Si-ncs memories, increasing their performances. On the other hand, Si-ncs embedded in Si3N4 antireflection layer of solar cells can be used as luminescent converters to enhance photovoltaic conversion in the blue region of the spectrum. Controlling Si-ncs characteristics (density, size, surface passivation, etc.) is necessary to the optimisation of both electrical and optical properties of the layers. In this work, we synthesized SiN x :H 50nm thick layers by ECR-PECVD using NH3 and SiH4 gases. Si-ncs are obtained thanks to a Si atom excess in the matrix, controlled by the gas flow ratio. The samples were annealed under Ar flow, first in a RTA furnace at 1000°C during 1min for particles nucleation, and then in a classic furnace, from 700°C to 1100°C, in order to investigate the Si nanostructure evolution. We studied the structural characteristics of Si-ncs population by energy-filtered transmission electron microscopy (EF-TEM). The layers composition was determined by Rutherford back scattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA). Their optical properties were studied by photoluminescence spectroscopy (PL). Results clearly show that structural and optical characteristics of these systems can be controlled by deposition parameters and annealing. [Copyright &y& Elsevier]

Abstract: Single crystals of fluorite (CaF2) were exposed to various swift heavy ions (Ca up to U) of energy 1–11.1MeV per nucleon, covering a large range of electronic stopping power S e between 4.6 and 35.5keV/nm. The irradiated (111) cleaved surfaces were investigated by means of scanning force microscopy in tapping mode. Nanometric hillocks produced by the ion projectiles were analyzed in terms of creation efficiency E eff, diameter and height values, and diameter–height correlation. Hillock formation appears with a low efficiency above a S e threshold of ∼5keV/nm. The mean height of these hillocks is approximately constant (∼1nm) between 5 and 10keV/nm and increases linearly with S e above 10keV/nm reaching 12.5nm for the largest S e value investigated. Similarly, the efficiency grows versus S e achieving 100% for S e >13keV/nm where each projectile produces an individual hillock. Above 13keV/nm, the hillock height and diameter are strongly correlated. The diameter was deduced by graphical deconvolution of the scanning-tip curvature that is determined experimentally for each set of measurements. In the entire S e regime, the mean diameter exhibits a constant value of ∼13nm, which is significantly larger than 6nm wide tracks observed by transmission electron microscopy. [Copyright &y& Elsevier]

Abstract: Single crystals of gadolinium gallium garnet, Gd3Ga5O12 have been irradiated with various swift heavy ions (32S, 52Cr, 63Cu, 86Kr, 128Te, 129Xe, 181Ta, 208Pb, 238U) in the electronic stopping power regime. The extent of the induced damage is extracted from channelling Rutherford backscattering experiments and the corresponding track radii are deduced. At low beam energy (around 1.5MeV/u), the electronic stopping power threshold of damage creation is 7.2±1.2keV/nm while it is 9.3±0.9keV/nm for beam energy around 6MeV/u. The inelastic Thermal Spike model (i-TS) is used in order to calculate the track radii versus (dE/dx)e using λ, the mean diffusion length of the energy deposited on the electrons, as the only fitting parameter model. The i-TS model was extended to some other amorphizable materials like YBa2Cu3O7−δ , GeS and LiNbO3. The results, combined with previous ones extracted from BaFe12O19, Y3Fe5O12, Y3Al5O12 and α-SiO2 quartz data, showed that λ decreases when the band gap energy E g increases. By extrapolation and depending of the material, the damage threshold induced by electronic excitation can appear at beam energy as low as 10−3 to 10−1 MeV/u. [Copyright &y& Elsevier]

The effects of swift heavy ions in insulators, leading e.g. to the appearance of latent tracks, have been extensively studied. In particular, it has been shown that at a fixed value of electronic stopping power the damage cross-section in the yttrium iron garnet (Y3Fe5O12) is larger for low energy ions than for high energy ions. This is the so-called “velocity effect” in the damage creation in the electronic stopping power regime. In order to verify if such a velocity effect also exists for atoms sputtering, the total sputtering yields of yttrium iron garnet (Y3Fe5O12) and gadolinium gallium garnet (Gd3Ga5O12) irradiated at high energy with a lead beam of 19.3 MeV/u, were measured using the catcher technique. The sputtered particles, were collected upon an aluminum foil placed in front of the target and the impurities deposited on the collectors were analysed by Rutherford backscattering. By comparison with previous measurements of the sputtering yield for the same electronic energy loss value at lower velocity, we clearly observed an important velocity effect: the sputtering yield is higher at low velocity than at high velocity. [Copyright &y& Elsevier]

Amorphous carbon nitride (a-CNx) films were grown on silicon substrates by ArF excimer laser ablation of a graphite target in the presence of nitrogen at various gas pressures. By working at elevated pressures (up to 100 Pa), high amounts of nitrogen can be incorporated into the films (N/C≤0.4) which lead to strong enhancement of their field emission properties. This behaviour was demonstrated to be mainly related to changes in the surface roughness of the samples, in connection with the development of graphite-like structures. [Copyright &y& Elsevier]