M. Hage-Ali

High energy heavy ion irradiation damage in yttrium iron garnet

Abstract We have studied the damage in ferrimagnetic yttrium iron garnet, Y 3 Fe 5 O 12 or YIG, produced by energetic heavy ion bombardment, for which the electronic stopping power is much higher than the nuclear stopping power. Epitaxial thin films of YIG on (111)-Gd 3 Ga 5 O 12 substrates were thus irradiated at room temperature with 50 MeV 32 S, 50 MeV 63 Cu, 235 MeV 84 Kr, and with 59 MeV, 185 MeV and 792 MeV 132 Xe ion beams. The film thicknesses were always smaller than the ion mean projected ranges, in order to avoid implantation effects in the layers. The resulting damage was then studied by high resolution X-ray diffraction, channeling Rutherford backscattering (RBS) spectroscopy and room temperature magnetization measurements. After these ion irradiations, the structural as well as the ferrimagnetic long-range orders are progressively destroyed. X-ray measurements on 84 Kr irradiated samples show the presence of compressive lateral macrostresses in the films due to the coexistence of crystalline and disordered phases. These stresses are partly relaxed away at high fluences, when the amount of disordered phase is high enough (around 45%). Cross section data for this damage process are deduced from the RBS and 300 K saturation magnetization measurements for six different values of the electronic energy loss, between 7 and 27 MeV μm −1 . The damage cross section increases nonlinearly as a function of the electronic stopping power, then seems to level off above 22 MeV μm −1 . However the comparison with previous works indicates that the electronic stopping power might not be the only key-parameter in this process, where the ion beam energy parameters might play some role.

Diamond nuclear radiation detector

Abstract It is shown that natural diamond can be used as a homogeneous conduction counter with near complete charge collection, even over a long period of time. Indeed, polarization effects have been suppressed by making the back contact of the detector injecting under the influence of the applied field in order to compensate for trapped charge carriers. The electric and detection characteristics of these counters have been investigated. Possible application fields are briefly discussed.

Electronic stopping power threshold of damage creation in yttrium iron garnet

Abstract Electronic stopping power threshold of damage creation in yttrium iron garnet (YIG) has been determined by extrapolation using the known model for nuclear and electronic damage creation calibrated by 2 MeV alpha and 510 MeV argon irradiations respectively. This value is equal 4.5

Time-resolved reflectivity and melting depth measurements using pulsed ruby laser on silicon

1.0 keV/nm and its is three times lower than the dE/dx value at which chemical etching appears indicating that electronic stopping power damage can exist at very low value of dE/dx for non radiolytic insulating materials.

Energy loss straggling of protons and He ions in gold from 0.1 to 1.0 MeV/u

Using a pulsed ruby laser (λ=0.69 μm, FWHM=20ns) we have measured the variation of the surface reflectivity during laser irradiation. The melting depth has been measured after repetitive irradiations in order to induce diffusion of dopants to the maximum melt depth. Agreement with thermal model is found. Experimental measurements of time-resolved reflectivity on 1000 Åa-Si onc-Si are explained with the thermal model introducing a low thermal conductivity of 0.002 cal/(cm · s · K) in amorphous silicon.

Reflectance of silicon surfaces after high dose rate molecular ion implantation

Abstract Energy loss straggling of protons (atomic and molecular beams) and He ions in gold has been measured in the region of the stopping power maximum with a high resolution electrostatic analyser. The results are compared with the predictions of Bethe-Livingston and Lindhard-Scharff theories. Contributions from additional stragglings are investigated in solids, where they are of practical interest. Some results for energy loss and straggling of 14N and 16O ions in the range 20 keV/u to 60 keV/u are also given and compared to the velocity proportional theory.

DETERMINATION OF CARBON IN EFG SILICON RIBBONS BY NUCLEAR TECHNIQUES AND SIMS

Abstract Change of reflectivity in the UV to IR range has been measured on crystalline silicon implanted at very high dose rate by a glow discharge process of BF 3 or PF 5 accelerated to 10–50 kV. Partial regrowth of the damage by beam annealing is observed but an amorphous film always remains on the top surface.

Swift heavy ions in magnetic insulators: A damage-cross-section velocity effect

Abstract The edge defined process (EFG) for preparing silicon crystalline sheets is a promising approach to obtain directly the low cost material needed for manufacturing solar cells. The shape of these ribbons is defined by a graphite die, in contact with the molten silicon. Here, we investigated the contamination introduced by graphite by using three different ion beam techniques: (a) SIMS gives the relative evolution of the various elements as a function of depth, but cannot be calibrated in absolute scale; (b) the 12 C( 3 He, p) 14 N resonance at 2.47 MeV allowed us to evaluate the absolute concentration of carbon, as well as its lattice location by using channelling techniques: no dip was visible for carbon; (c) Rutherford backscattering performed with a high resolution electrostatic analyzer showed that the silicon surface peak width (90 A) is the same as on a high quality standard prepared in the same way. Therefore, no supplementary amorphous layer exists on the surface.