Gold Nanoclusters Formed by Ion-Implantation into Bi 2 TeO 5
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Gold Nanoclusters Formed by Ion-Implantation into Bi2TeO5 A. Kling1,2, M.F. da Silva1,2, J.C. Soares1,2, P.F.P. Fichtner3, L. Amaral3, F.C. Zawislak3, I. Földvári4 and Á. Péter4 1 Instituto Tecnológico e Nuclear, 2686-953 Sacavém, Portugal 2 Centro de Física Nuclear da Universidade de Lisboa, 1649-003 Lisboa, Portugal 3 Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil 4 Research Laboratory for Crystal Physics, Hungarian Academy of Sciences, 1525 Budapest 114, Hungary ABSTRACT Single crystalline samples of bismuth tellurite (Bi2TeO5) were implanted with 800 keV Au+ ions to a fluence of 1×1016 cm-2 at room temperature. The samples were subjected to heat treatments in two different ambients (air and high vacuum) at temperatures ranging from 400 – 700ºC in a conventional furnace. Strong absorption maxima in the range from 600 – 630 nm in the optical absorption spectra and an intense blue-green color in the samples were observed for annealings performed in air at temperatures between 500 and 700ºC indicating the formation of gold colloids. The average radii of the Au clusters formed were estimated to be in the range of 3-4 nm. Samples annealed under vacuum showed distinct changes in color for different annealing temperatures. Studies using the RBS/channeling technique indicate that no full recrystallization of the samples was achieved under both annealing regimes although heat treatment under vacuum provides a significantly better lattice recovery than for air ambient. INTRODUCTION Bismuth tellurite (Bi2TeO5) is a novel optical material with promising nonlinearoptical properties and orthorhomic structure (space group Abm2) [1,2]. Doping with Fe and Cr introduces interesting photorefractive and photochromic properties [3,4]. On the other hand the formation of noble metal nanoclusters - due to their third-order nonlinear optical properties – are of high technological interest in transparent materials. Ion implantation with subsequent annealing has been already demonstrated to be a highly suitable method for the formation of such clusters, e.g, in LiNbO3 [5], MgO [6], SrTiO3 [6] and other materials. Since only recently single crystals of technologically interesting size became available, investigations on the formation of noble metal colloids in this material are lacking. In addition no knowledge on the behaviour of this material during ion implantation and annealing under different conditions was available. Therefore the optical and structural properties of Au+-implanted bismuth tellurite was studied in this work.
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EXPERIMENTAL DETAILS Single crystalline pure Bi2TeO5 crystals grown at the Research Laboratory for Crystal Physics in Budapest and freshly cleaved along the (100) cleavage plane were implanted with 800 keV Au+ ions at room temperature to a fluence of 1016 cm-2 using the 3.5 MV Tandem accelerator at Porto Alegre. The projected range and straggling for the Au+ ions were calculated using SRIM2000 [7] to be 1130 Å and 420 Å respectively. Annealings where performed in a c
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