Pattern Formation via a Two-Step Faceting Transition on Vicinal Si(111) Surfaces
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Pattern Formation via a Two-Step Faceting Transition on Vicinal Si(111) Surfaces F.K. Men1, Feng Liu2, P.J. Wang1, C.H. Chen1, D.L. Cheng1, J.L. Lin3, and F.J. Himpsel3 1 Department of Physics, National Chung Cheng University, Chia-Yi, Taiwan, ROC 2 Department of Materials Science, University of Utah, Salt Lake City, UT 84112 3 Department of Physics, University of Wisconsin, Madison, WI 53705
Abstract We demonstrate a self-organized pattern formation on vicinal Si(111) surfaces that are miscut toward the [ 2 11] direction. All the patterns, consisting of a periodic array of alternating (7×7) reconstructed terraces and step-bunched facets, have the same periodicity and facet structure, independent of the miscut angle; while the width of the facets increases linearly with miscut angle. We attribute such unique pattern formation to a surface faceting transition that involves two transition steps: the first step forms a stress-domain structure defining the universal periodicity; the second step forms the low-energy facets controlling the facet width.
Introduction Surface patterning is an important processing step in many device fabrication processes. The continued drive to make devices smaller and smaller has brought up the challenge to pattern surfaces in the nanometer scale where conventional lithographic techniques are no long applicable. Two different routes have been taken toward nanopatterning: one by developing new patterning techniques with nanometer resolution, such as scanning probes, the other by taking advantage of self-organization of surface patterns occurring naturally. The later approach has shown great promises because it offers an economic and parallel process for device fabrication. Surface stress often plays an important role in driving surface structural and morphological ordering, in particular, through the surface stress-induced spontaneous formation of ordered patterns of stress domains [1]. An effective way to create the stress-domain patterns is by step motion and/or by surface faceting transition on vicinal surfaces, as demonstrated on a variety of different materials surfaces, such as the Si(001) [2], Si(111) [3-5], GaAs(001) [6], Au(111) [7], and Pt (001) [8] surfaces. Ideally, one would like to create a desirable surface pattern with controllable length scales. The characteristic length scales of the stress-domain patterns are generally determined by the competition between elastic relaxation energy and domain boundary energy. Therefore, in principle, it should be possible to control the length scales of such patterns by manipulating these energy terms. However, such kind of control is difficult to achieve in real practice. For example, the domain size of a stress domain can be changed by applying external strain [2], but the domain will restore its original size upon relieving the external force. On a vicinal surface, the terrace size can be changed by tuning miscut angle, but different step structures [9,10] and facets [5] usually form at different miscut angles. Here we demonstrate the
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