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1166-N02-02

Interdiffusion of Bi and Sb in Superlattices Built from Blocks of Bi2Te3, Sb2Te3 and TiTe2 Clay D. Mortensen and David C. Johnson Department of Chemistry and Materials Science Institute, 1253 University of Oregon, Eugene, Oregon 97403, U.S.A. ABSTRACT The reaction kinetics of [(Ti-Te)]x[(Sb-Te)]y, [(Bi-Te)]x[(Sb-Te)]y, [(Ti-Te)]w[(Bi-Te)]x and [(Ti-Te)]w[(Bi-Te)]x[(Ti-Te)]y[(Sb-Te)]z precursors as a function of annealing temperature and time was probed using x-ray diffraction techniques to define the parameters required to form superlattice structures. [(TiTe2)1.36]x[Sb2Te3]y and [(TiTe2)1.36]x[Bi2Te3]y superlattices were observed to form while [(Bi-Te)]x[(Sb-Te)]y precursors yielded only Bi2-xSbxTe3 alloys. This behavior was correlated with the miscibility/immiscibility of the constituents of the targeted superlattices. For the three component system, Bi and Sb were observed to interdiffuse through the Ti-Te layer over the range of Ti-Te thicknesses explored, resulting in formation of (BixSb1x)2Te3 alloys within the superlattice structure. When the Bi2Te3 and Sb2Te3 thicknesses were equal, symmetric [{(TiTe2)}1.36]w[(Bi0.5Sb0.5)2Te3]y superlattices were formed. INTRODUCTION Over the past 30 years, nanostructured (A)x(B)y superlattices have allowed researchers to tune physical properties including magnetism1 and thermal conductivity2 and design new semiconductor structures with enhanced performance for applications.3 Increasing the complexity by adding a third component in an (A)x(B)y(C)z pattern has resulted in exciting breakthroughs including increased polarization enhancement in ferroelectric materials,4,5 delta doping of semiconductors,6 high mobility semiconductor heterostructures,7 and tuning of optoelectronic properties.8 not achievable with (A)x(B)y superlattices. Three component superlattice structures have been prepared with a variety of epitaxial growth techniques (atomic layer deposition, pulsed laser deposition, chemical vapor deposition, and molecular beam epitaxy) to sequentially deposit the three superlattice components, but it is frequently difficult to find suitable growth conditions. Molecular beam epitaxy is generally limited by the need for epitaxial relationships and limited and often conflicting growth conditions. Low temperatures are desired to limit losses due to the high vapor pressure of some elements and to limit interdiffusion of the elements. High temperatures are necessary to obtain sufficient surface mobility. As the number of components increase, the lack of favorable growth conditions and epitaxial relationships limits the material combinations that can be explored for the discovery of unprecedented novel properties.9,10 Recently Harris and coworkers reported a new solid-phase growth technique that used self assembly of preconfigured reactants to prepare a series of [(Bi2Te3)]x[(TiTe2)1.36]y materials having a 36% lattice mismatch between the a-b planes of the components.11,12 In this paper, we examine the reaction kinetics of [(Ti-Te)]x[(Sb-Te)]y, [(Bi-Te)]x[(Sb-Te)]y,