Investigating the Influence of Nanoarchitecture and Atoms/Unit Area on Constituent Structure and Transport Properties of Nanolaminate Heterostructures
Datum
2020-09-24
Autor:innen
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Verlag
University of Oregon
Zusammenfassung
At the thin film limit, interface interactions between constituents become increasingly important. This dissertation focuses on exploring thin films with the goal of preparing novel compounds, understanding interactions between layers, and examining the formation mechanism of these materials. All of the materials in this work were prepared by the low temperature modulated elemental reactants (MER) synthesis method which enables the preparation of metastable compounds with unique nanoarchitectures via designed elemental precursors. Synthesis and characterization of heterostructures and single- phase compounds were facilitated by a unique XRF data treatment which related measured XRF signal to atoms/Å2 with sub-monolayer sensitivity. The ability to precisely deposit elemental layers into specific sequences and measure the absolute amount of material in each layer was foundational for this work, which is split into two sections: 1. Investigating the influence of nanoarchitecture on properties and 2. Preparing novel
compounds with targeted properties.
The influence of nanoarchitecture on observed properties was investigated by preparing series of compounds with systematic changes in the repeating unit structure (i.e. number of each constituent or arrangement of the constituent layers). Both [(SnSe)1+d]m[TiSe2]n and [(PbSe)1+d]m[TiSe2]n heterostructures were studied. There are strong interactions between the two constituents as a result of charge donation from the SnSe/PbSe layer to the TiSe2 layer. The charge donation results in a novel conducting material at the interface, which can be composed of two or three layers depending on the nanoarchitecture and has transport properties that differ from the material’s bulk counterparts. These materials demonstrate complex temperature dependent transport properties which are dominated by variable range hopping from the novel interfacial material at low temperatures and the non-interfacial layers at high temperatures.
A series of novel Mn- containing materials were prepared as a result of a synergistic theoretical and experimental collaboration. First, a DFT “island” based approach was used to predict kinetically stable heterostructures. After the identification of these potentially stable phases, heterostructures containing various layering schemes of these phases were prepared via the MER method. This symbiotic relationship lead to the synthesis of an interfacially-stabilized ferromagnetic (Pb2MnSe3)0.6VSe2 compound.
This dissertation includes previously published and unpublished coauthored material.
Beschreibung
Schlagwörter
heterostructures, metastable, nanoarchitecture, structure-property relationship, thin films