Formation of dense and aligned planar arrangements of Pb nanoparticles at silica/silicon interfaces
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Formation of dense and aligned planar arrangements of Pb nanoparticles at silica/silicon interfaces Flavia P. Luce1, Felipe Kremer1, Dario F. Sanchez1, Zacarias E. Fabrim1,2, Shay Reboh1,2, Fernando C. Zawislak1 and Paulo F. P. Fichtner1,2 1
Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-970, Porto Alegre, Brazil
2
Escola de Engenharia, Universidade Federal do Rio Grande do Sul, 91501-970, Porto Alegre,
Brazil ABSTRACT The ion beam synthesis of Pb nanoparticles (NPs) in silica/silicon films is studied in terms of the combination of a two-step annealing process consisting of a low temperature long time aging treatment followed by a high temperature short time furnace annealing. The samples are analyzed through Rutherford Backscattering Spectrometry and Transmission Electron Microscopy. The aging process leads to the suppression of the classical homogeneous nucleation of metallic Pb NPs in the silica, thus promoting Pb redistribution during the high temperature annealing. This causes the formation of dense bi-dimensional NP arrays located at the silicasilicon interface, presenting small size dispersion. INTRODUCTION The formation of nanoparticles (NPs) via ion beam synthesis (IBS) usually results in a non-homogeneously dispersed NP arrangement located within a certain depth region of the target material. This is a consequence of the stochastic nature of atomic collisions in solids, which generates Gaussian-like ion depth-concentration profiles that influences the NP nucleation and growth processes taking place either during implantation or during subsequent thermal treatments [1-4]. In contrast to this behavior, we have recently demonstrated that the usual IBS process observed for Sn [5] and Pb [6] particles in silica can be avoided by using low temperature aging treatments. The aging process promotes the formation of small, rather thermally stable atomic clusters, which only dissociate at high temperatures when classical nucleation is inhibited. Therefore, the implanted atoms are free to diffuse, either evaporating at the surface or segregating at the silica-silicon interface. This results in the formation of planar and dense arrays of epitaxially aligned NPs. In the present work we focus on the case of silica films implanted with Pb+ ions and extend our previous studies by considering higher implantation fluences. The results obtained demonstrate that for peak Pb concentrations below ≈2.5 at. % the aging treatment is still very effective, preventing the classical nucleation process. EXPERIMENT Pb+ ions were implanted in a 200 nm thick thermally grown silica film on a pristine (001) Si substrate. The implantation energy of 300 keV was selected in order to locate the Pb atoms in the central region of the film. The implantations were performed at room temperature to three
fluences: 0.5x1016, 1x1016 and 2x1016 cm-2. After implantation, the samples were submitted to a combination of two-step thermal treatments: i) an aging treatment performed at 200 °C for 100 h in air; and ii) a subsequent h
