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0886-F03-14.1

Preparation of (TiTe2)3(Sb2Te3)y(TiTe2)3(Bi2Te3)z Superlattices using the Modulated Elemental Reactants (MER) Technique C. Mortensen1, B. Matelich2, R. Rostek3, B. Schmid1, and D.C. Johnson1 1 Materials Science Institute, University of Oregon, Eugene, OR 97403; 2Department of Natural Sciences, Carroll College, Helena, MT 59601; 3Fraunhofer Institut Physikalische Messtechnik, Freiburg, Germany. Abstract Difficulty in preparing (Bi2Te3)x(Sb2Te3)y superlattices due to interdiffusion of Sb and Bi led to the study of interduffusion barriers. TiTe2 has been explored as an interdiffusion barrier to minimize the interdiffusion of Sb and Bi, as TiTe2 is not soluble in either Bi2Te3 or Sb2Te3. Preparation of (TiTe2)3(Sb2Te3)y(TiTe2)3(Bi2Te3)z superlattices has been achieved with varying x, y and z. The formation of the superlattices was studied as a function of annealing temperature and time. TOF-SIMS depth profiles were used to study the extent of interdiffusion in the samples. Unit cell control was achieved allowing for the preparation of an array of superlattices with varying periods with very good reproducibility. Introduction (Bi2Te3)x(Sb2Te3)y and (Bi2Te3)x(TiTe2)y superlattices have been shown to have decreased thermal conductivity as compared to the state-of-the-art thermoelectric bulk alloys of (Bi2-xTe3)(SbxTe3) [1-3]. In the case of (Bi2Te3)x(Sb2Te3)y, the superlattice material has been shown to have a significantly higher ZT value for a superlattice period of 50 Å[1]. (Bi2Te3)x(Sb2Te3)y superlattices had been previously synthesized by Venkatasubramanian using a low temperature epitaxial growth method. Large scale manufacturability required for widespread use is difficult using epitaxial growth as devices require at least 20 µm of material and typical rates are around 1 µm per hour. The modulated elemental reactants (MER) technique shows promise as being a method in which large scale manufacturing can be achieved to prepare superlattice materials. The MER technique was attempted in the preparation of (Bi2Te3)x(Sb2Te3)y superlattices. Unfortunately crystallization of the (Bi2Te3)x(Sb2Te3)y superlattice competes with interdiffusion of Bi and Sb in the intended superlattice precursor structure [4]. The development of interdiffusion barriers is important to nanoscale materials development as many materials are unstable with respect to interdiffusion. In some instances the barrier layer could enhance properties by acting as a dopant or improving the layering structure of thermoelectric materials. This study examines the effect of interdiffusion barriers in V-VI (Bi2Te3-related) materials for thermoelectric applications. The interdiffusion barrier chosen for the initial studies is TiTe2 as neither Bi2Te3 or Sb2Te3 are soluble in TiTe2. A four component superlattice presents a synthetic challenge as all four components need to be optimized in both composition and thickness to achieve superlattice formation. The absolute amount of the component layers must be controlled to be identical to the amount required