Families of metastable misfit layered compounds prepared by modulated elemental precursors and the resulting physical properties

• Main Author: Heideman, Colby Luke, 1979-
• Language: en_US
• Published: University of Oregon 2010
• Subjects: Thin films; Metastable structures; Mobilities; Layered compounds; Elemental precursors; Organic chemistry; Physical chemistry
• Online Access: http://hdl.handle.net/1794/10877

xix, 141 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. === The constant drive to improve material properties has recently led researchers towards metastable nanostructured materials, increasing the need for new synthetic pathways capable of rationally accessing targeted compounds. A method is demonstrated for using physical vapor deposition to create elementally modulated precursors targeting specific compounds. Controlling the modulation length scale of the precursor allows entire families of misfit layered compounds to be synthesized with atomic level control of the structure. Over 100 new misfit layered compounds were synthesized in the [(BiSe) 1.10 ] m (NbSe 2 ) n , [(PbSe) 1.10 ] m (NbSe 2 ) n , [(PbSe) 1.00 ] m (MoSe 2 ) n , and [(SnSe) 1.10 ] m (MoSe 2 ) n , families. The three-dimensional structures of these compounds are examined. These materials are shown to form turbostratically disordered sheets of transition metal dichalcogenide layers interwoven between blocks of rock salt layers. These layers have very small in-plane grain sizes on the order of 10 mn. The interfaces between these layers lack any epitaxial relationship and yet are atomically abrupt and indicate no strain present. The unique metastable structures lead to fascinating properties in these compounds. The turbostratic disorder leads to extremely low thermal conductivity perpendicular to the layering. Thermal conductivities as low as 0.07 W/m/K were measured. Because of the flexible chemistries, a wide range of electrical properties are accessible in these materials, with electrical conductivities ranging from metallic to semiconducting and carrier concentrations ranging from 10 17 to 10 21 cm -3 . Despite the small grain sizes, respectable mobilities have also been measured, up to 21 cm 2 V -1 s -1 . This work consists, in part, of previously published and coauthored material. === Committee in charge: James Hutchison, Chairperson, Chemistry; David Johnson, Advisor, Chemistry; David Tyler, Member, Chemistry; Geraldine Richmond, Member, Chemistry; Richard Taylor, Outside Member, Physics