Leandro Araujo

Structural and vibrational properties of Co nanoparticles formed by ion implantation

This work was financially supported by the Australian Synchrotron and the Australian Research Council. ChemMatCARS Sector 15 is principally supported by the National Science Foundation/Department of Energy under Grant No. NSF/CHE-0822838. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Swift heavy-ion irradiation-induced shape and structural transformation in cobalt nanoparticles

This work was financially supported by the Australian Synchrotron and the Australian Research Council with access to equipment provided by the Australian Nanofabrication Facility. ChemMatCARS Sector 15 is principally supported by the NSF/ DOE under Grant No. NSF/CHE–0822838.

Structural modification of swift heavy ion irradiated amorphous Ge layers

Swift heavy ion (SHI) irradiation of amorphous Si (a-Si) at non-perpendicular incidence leads to non-saturable plastic flow. The positive direction of flow suggests that a liquid phase of similar density to that of the amorphous solid must exist and accordingly a-Si behaves like a conventional glass under SHI irradiation. For room-temperature irradiation of a-Si, plastic flow is accompanied by swelling due to the formation of voids and a porous structure. For this paper, we have investigated the influence of SHI irradiation at room temperature on amorphous Ge (a-Ge), the latter produced by ion implantation of crystalline Ge substrates. Like a-Si, positive plastic flow is apparent, demonstrating that liquid polymorphism is common to these two semiconductors. Porosity is also observed, again confined to the amorphous phase and the result of electronic energy deposition. Enhanced plastic flow coupled with a volume expansion is clearly responsible for the structural modification of both a-Si and a-Ge irradiated at room temperature with swift heavy ions.

Pt nanocrystals formed by ion implantation: a defect-mediated nucleation process

The influence of ion irradiation of SiO2 on the size of metal nanocrystals (NCs) formed by ion implantation has been investigated. Thin SiO2 films were irradiated with high-energy Ge ions then implanted with Pt ions. Without Ge irradiation, the largest Pt NCs were observed beyond the Pt projected range. With irradiation, Ge-induced structural modification of the SiO2 layer yielded a decrease in Pt NC size with increasing Ge fluence at such depths. A defect-mediated NC nucleation mechanism is proposed and a simple yet effective means of modifying and controlling the Pt NC size is demonstrated.

Formation and structural characterization of Ni nanoparticles embedded in SiO2

This work was financially supported by the Australian Synchrotron and the Australian Research Council with access to equipment provided by the Australian Nanofabrication Facility.

Nano-porosity in GaSb induced by swift heavy ion irradiation

Nano-porous structures form in GaSb after ion irradiation with 185 MeV Au ions. The porous layer formation is governed by the dominant electronic energy loss at this energy regime. The porous layer morphology differs significantly from that previously reported for low-energy, ion-irradiated GaSb. Prior to the onset of porosity, positron annihilation lifetime spectroscopy indicates the formation of small vacancy clusters in single ion impacts, while transmission electron microscopy reveals fragmentation of the GaSb into nanocrystallites embedded in an amorphous matrix. Following this fragmentation process, macroscopic porosity forms, presumably within the amorphous phase.

The influence of annealing conditions on the growth and structure of embedded Pt nanocrystals

We thank the Australian Synchrotron Research Program and the Australian Research Council for financial support.

Random stopping power and energy straggling of 16O ions into amorphous Si target

Abstract In the present contribution, we report results on random stopping power and range straggling of 16 O ions into amorphous Si target. The measurements were performed in a 300 keV–13.5 MeV energy interval by using the Rutherford backscattering technique together with a marker system. The present stopping results were compared with the TRIM predictions based on the Ziegler, Biersack and Littmark calculations, the theoretical values being always higher than the experimental ones. On the other hand, the calculated straggling data are compared with the Bohr predictions. For low energies, the calculated values over-estimate the experimental ones. For energies larger than 2 MeV, the experimental results became larger than the Bohr predictions. However, with increasing energies, the experimental results approach the Bohr values, and above 12 MeV a quite good theoretical experimental agreement was found.

Swift heavy ion irradiation of Pt nanocrystals: I. shape transformation and dissolution

We report on the effects of swift heavy ion irradiation of embedded Pt nanocrystals (NCs), which change from spheres to prolate spheroids to rods upon irradiation. Using a broad range of ion irradiation energies and NC mean sizes we demonstrate that the elongation and dissolution processes are energy and size dependent, attaining comparable levels of shape transformation and dissolution upon a given energy density deposited in the matrix. The NC shape transformation remains operative despite discontinuous ion tracks in the matrix and exhibits a constant threshold size for elongation. In contrast, for ion irradiations in which the ion tracks are continuous, the threshold size for elongation is clearly energy dependent.

Lift-off protocols for thin films for use in EXAFS experiments

Lift-off protocols for thin films for improved extended X-ray absorption fine structure (EXAFS) measurements are presented. Using wet chemical etching of the substrate or the interlayer between the thin film and the substrate, stand-alone high-quality micrometer-thin films are obtained. Protocols for the single-crystalline semiconductors GeSi, InGaAs, InGaP, InP and GaAs, the amorphous semiconductors GaAs, GeSi and InP and the dielectric materials SiO2 and Si3N4 are presented. The removal of the substrate and the ability to stack the thin films yield benefits for EXAFS experiments in transmission as well as in fluorescence mode. Several cases are presented where this improved sample preparation procedure results in higher-quality EXAFS data compared with conventional sample preparation methods. This lift-off procedure can also be advantageous for other experimental techniques (e.g. small-angle X-ray scattering) that benefit from removing undesired contributions from the substrate.