Nanopatterning on Reconstructed Ceramic Surfaces
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Nanopatterning on Reconstructed Ceramic Surfaces Shwetha Shetty A1, Vijay B Shenoy1, C. Barry Carter2 and N. Ravishankar1 1 Materials Research Centre, Indian Institute of Science, Bangalore 560 012, India 2 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA ABSTRACT The use of reconstructed ceramic surfaces as templates for nanopatterning has been demonstrated recently. This technique differs from the surface decoration by Au on stepped surfaces of alkali halides which has been a topic of intense research in the past. Some of the intriguing aspects related to the physical origin of the phenomena have been considered here. Based on heterogeneous nucleation of Pt vapor on wedged alumina surfaces, it has been shown that the valley sites are the preferred sites for nucleation. However, the hill sites are decorated by the particles in the present study pointing out to a different physical origin for the formation of the nanoparticles. The role of electrostatic energy reduction on the formation of such nanopatterns is discussed. INTRODUCTION In his classic work, Herring [1] has shown based on the Wulff [2] construction that any given macroscopic surface of a crystal which does not coincide with some portion of the boundary of the equilibrium shape, in other words a high index surface, would always reconstruct into a hill and valley structure which has a lower surface free energy than the original flat surface. The type of surface reconstruction depends on the angle of misorientation of the original high energy surface with the low energy surface. Vicinal surfaces are obtained when the surface normal slightly deviates from the equilibrium surface normal. In this case, the surface adopts a terrace-and-step morphology on annealing. As the angle between the surface normal and the equilibrium surface normal increases, reconstruction results in a hill-and-valley morphology [3]. Such surfaces, which have periodic surface patterns in the nanoscale, can be exploited as templates for growing self organized ordered arrays of nanoparticles or nanowires [4, 5]. α-alumina is one of the important ceramic oxides widely used in microelectronics industry as substrates for thin films of metals, semiconductors and insulators. Several studies have been carried out on the surface morphology of different low index planes of alpha-alumina [3, 6-8]. The m- plane of alumina, {10 1 0} surface, is an unstable surface and it reconstructs in to a hill-and-valley morphology upon annealing at higher temperatures. The two stable facets formed are {10 11 } and { 1 012}. In our earlier work [4], we have shown that the hill-and-valley morphology of the reconstructed m-plane can be use to produce arrays of Pt nanoparticles on it. It was shown that the nucleation from the vapor-phase takes place under undersaturated conditions and the physical origin for this phenomenon differs from the conventional step decoration techniques on alkali halides. It was proposed that the electrostatic energy reduction on the
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