The Library
Atomic and electronic structure of random and ordered 2D alloys
Tools
Xia, Xue (2020) Atomic and electronic structure of random and ordered 2D alloys. PhD thesis, University of Warwick.
|
PDF
WRAP_Theses_Xia_2020.pdf - Submitted Version - Requires a PDF viewer. Download (21Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b3717703
Abstract
Recently, transition metal dichalcogenides (TMDs) have attracted increasing research interest as promising two-dimensional materials for a range of electronic and optoelectronic applications and for the fundamental science that can be studied in them. This interest stretches beyond the properties of pure TMD materials, with an increasing number of reports on doped-TMD and TMD alloys to increase the functionality of these materials. For example, by substituting or alloying the metals or chalcogens of the TMDs, it is possible to tune their electronic structure.
In this thesis, single crystals of pure TMDs and of TMD alloys have been synthesised via chemical vapor transport (CVT). Techniques for the fabrication of van der Waals stacks with artificial sequences have been developed, specifically to allow the direct measurement of atomic and electronic structure in the alloys and to correlate these properties to optical spectroscopy measurements.
The atomic structure of Mo1-xWxS2 alloys are visualised by annular dark field (ADF) scanning transmission electron microscopy (STEM). Statistical analysis of the images allows the atomic distributions to be compared to those from Monte Carlo simulations and first principles calculations. Mo1-xWxS2 alloys show random distributions as expected from thermodynamic considerations. The evolution of the band structure of the Mo1-xWxS2 alloys is determined by angle-resolved photoemission spectroscopy (ARPES) measurements and compared to first principles calculations. Combined, these results demonstrate that TMD alloying is a powerful approach for band structure engineering.
In contrast to the Mo1-xWxS2 alloys, short-range ordering is found in Nb0.1W0.9S2, with the Nb atoms forming atomic lines along one of the equivalent crystallographic directions. This ordering is confirmed by quantitative statistical analysis through the Warren-Cowley short-range order (SRO) parameters. Meanwhile, density function theory (DFT) calculations have been applied to explain this ordering, revealing this structure results from a combination of thermodynamic and kinetic considerations.
Item Type: | Thesis (PhD) | ||||
---|---|---|---|---|---|
Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Transition metals, Transition metal compounds, Chalcogenides, Two-dimensional materials, Crystals -- Electric properties, Alloys -- Structure, Atomic structure, Electronic structure | ||||
Official Date: | September 2020 | ||||
Dates: |
|
||||
Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Wilson, Neil R. ; Sanchez Fuentes, Ana | ||||
Sponsors: | University of Warwick. Department of Physics | ||||
Format of File: | |||||
Extent: | xviii, 163 leaves : illustrations | ||||
Language: | eng |
Request changes or add full text files to a record
Repository staff actions (login required)
View Item |
Downloads
Downloads per month over past year