Thin Film van der Waals Heterostructures containing MoSe2 from Modulated Elemental Precursors

Transition metal dichalcogenides (TMDs) are naturally occurring layered materials that have attracted immense research interest due to their high degree of chemical tunability. In particular, MoSe2 has been the focus of significant investigation stemming from reports that it converts to a direct band gap semiconductor material at ultralow dimensions. Yet, as more and more is learned about increasingly thin MoSe2, efforts are now aimed at imparting the novel functionality of MoSe2 into van der Waals heterostructures. This dissertation focuses on synthesis and characterization of novel MoSe2-based nanolaminate structures that have been self assembled from modulated elemental precursors. The first section describes a new treatment of x-ray fluorescence spectroscopy data and its use as a powerful probe for determining the absolute composition per unit area of a thin film with sub-monolayer accuracy. While this has widespread application in the thin film world, it is particularly useful for MER synthesis in the calibration of modulated elemental precursors. In order to crystallize a target structure, it is imperative to deposit the correct number of atoms, which is now possible with greater precision. The second section shows the importance of rotational (i.e. “turbostratic”) disorder on lowering cross-plane thermal conductivity in two systems—MoSe2 and the (SnSe2)1(MoSe2)1.32 heterostructure. The binary systems exhibits ultralow thermal conductivity that rivals that of WSe2, yet some interlayer atomic registry was noted in TEM images. By interleaving layers of MoSe2 with SnSe2—which also possesses hexagonal symmetry, but has a significantly larger basal plane—the cross-plane thermal iv conductivity was depressed to the lowest reported value in the literature for a fully dense solid. The final section presents the synthesis and characterization of a new, ternary phase of Bi|Mo|Se. The structure consists of alternating layers of a “puckered” rock salt BiSe lattice and nanosheets of MoSe2. Notably, the MoSe2 sublattice consists of a mixture of the semiconducting 2H phase (~60%) and the metallic 1T phase (~40%). This is the result of electron injection from the BiSe into the conduction band of the MoSe2, which is known to undergo a rearrangement upon reduction. This dissertation includes previously published and unpublished coauthored materials.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Department of Chemistry and Biochemistry

Grantor dc:publisher

University of Oregon

Year dc:date.issued

2019

Author dc:creator

• Hadland, Erik

Advisor dc:contributor.advisor

• Boettcher, Shannon

• Materials
• Solid state

Statement dc:rights

• All Rights Reserved.

Language dc:language.iso

en_US

Handle dc:identifier.uri

https://hdl.handle.net/1794/24520

OAI record oai:identifier

https://scholarsbank.uoregon.edu/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ascholarsbank.uoregon.edu%3A1794%2F24520