Dresden 2009 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 32: Invited Johnson
DS 32.1: Hauptvortrag
Donnerstag, 26. März 2009, 09:30–10:15, GER 38
Optimizing Electronic Properties of Misfit Layered Compounds — •David Johnson1, Colby Heideman2, Qiyin Lin3, and Clay Mortensen4 — 1University of Oregon, Eugene, Oregon, USA — 2University of Oregon, Eugene, Oregon, USA — 3University of Oregon, Eugene, Oregon, USA — 4University of Oregon, Eugene, Oregon, USA
Misfit layered compounds are naturally occurring nanostructured solids that have been reported to have low thermal conductivities on the order of 0.8 Wm-1K-1 and unoptimized figures of merit ZT as large as 0.3. We have recently reported thermal conductivity in [(PbSe)1.00]m[MoSe2]n and [(PbSe)0.99]m[WSe2]n misfit compounds as low as 0.06 Wm-1K-1. Here we describe annealing treatments of these misfit compounds in fixed chalcogen partial vapour pressures and demonstrate that samples equilibrate with the dominant source of vapour, resulting in controlled carrier concentrations. The thermal stability of these materials allows annealing times and temperatures in excess of 24 hours and 500° C to be used without destroying the layered structure. We present data showing the convergence of electrical properties for isostructural samples on annealing. In addition to control of carrier concentrations, the annealing treatments dramatically improve the carrier mobility. We report electrical resistivity, Seebeck coefficients and carrier concentrations as a function of annealing conditions.