Formation of Au-nanocrystals in TiO 2 and SrTiO 3 by ion implantation in restricted volumes
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Formation of Au-nanocrystals in TiO2 and SrTiO3 by ion implantation in restricted volumes 1
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R. Fromknecht , G. Linker , K. Sun , S. Zhu , L.M. Wang , A. van Veen , M.A. van Huis , T. 4 4 4 5 5 Weimann , J. Wang , J. Niemeyer , F. Eichhorn , T. Wang 1 Forschungszentrum Karlsruhe, Institut für Festkörperphysik, Germany 2 The University of Michigan, Dept. of Nucl. Eng. and Rad. Science, USA 3 Interfaculty Reactor Institute, Delft University of Technology, The Netherlands 4 Physikalisch-Technische Bundesanstalt Braunschweig, Germany 5 Forschungszentrum Rossendorf, Institut für Ionenstrahlphysik und Materialforschung, Dresden, Germany ABSTRACT Au-ions were implanted at RT conventionally and through a mask into TiO2- and SrTiO3single crystals with doses in the range from 1x1015Au+/cm2 to 1x1017Au+/cm2, and dose rates of ~1011ions/sec and ~3x1013ions/sec, at an energy of 260keV; some samples subsequently were annealed at temperatures up to 1100K. The Au-atoms precipitated to nanocrystals during implantation with an average particle size of 1.5nm. HRTEM investigations revealed that the Au-nanocrystals, embedded in amorphous TiO2-regions, have a broad size distribution varying from large sizes in the near surface region to smaller sizes at larger depths. In the annealing process a coarsening and a reorientation of the Au-nanocrystals is observed. At 1000K the particle size of the textured Au-implant was evaluated to be ~6nm. Implantation with a high dose rate performed through a metal mask with holes of 120µm diameter and without annealing resulted in an almost equidistant arrangement of the Au-nanocrystals with a narrow size distribution of 2-6nm in TiO2 and 3-5nm in SrTiO3 in the near surface region. Au-ion implantation through an e-beam resist mask (50nm x 50nm holes), with doses ranging from 1x1015Au+/cm2 to 4x1015Au+/cm2 at the low dose rate and annealed at 1000K, lead to a periodic structure of the Au-nanocrystals. The nanocrystal size, evaluated from TEM analysis, in the asimplanted state was ~5nm and after annealing at 1000K sizes of several nanometers to several tens of nanometers were observed.
INTRODUCTION The material properties of matter undergo a dramatic change when the number of atoms in the bulk is decreased to about 100 to 10,000 as in precipitates. Precipitates in the nanometer size regime interact with the surrounding matrix and can cause structural phase transformations, metal insulator transitions, non-linear optical behaviour, or change of melting temperature resulting in many new applications [1-5]. Embedded nanoparticles, formed in an ion implantation process, are usually structurally and thermally stable to high temperatures in contrast to nanoclusters grown by physical methods,such as freestanding particles. Ion implantation has the outstanding advantage that a high energy density (spike) can be deposited in a matrix creating a non-equilibrium process in the very beginning with a high “fictive” temperature of the impact volume. The transfer of kinetic energy leads usuall
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