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Defect and terrace characterization of PtSn₄ using scanning tunneling microscopy and spectroscopy Warner, Ashley Nicole


Topological materials are a newly discovered class of matter where protected gapless states arise within the material band structure. Of these materials is PtSn₄, a topological semimetal with experimentally confirmed Dirac nodal arcs in its band structure. It exhibits extremely large magnetoresistance and a high residual resistivity ratio which is indicative of efficient electron transport. There are many material characteristics responsible for excellent carrier mobility such as a topological surface state or low density defects to name a few. Since materials can exhibit high mobility without being topological, it is unknown how much of the assumed high mobility of PtSn₄ is dependent on its topological features versus something else entirely. Scanning tunneling microscopy and spectroscopy is a surface sensitive technique that allows for the imaging of a conductive surface at an atomic resolution via quantum tunneling. It is an excellent tool for studying imperfect crystal lattices due to defects, characterizing cleaving terraces of materials and probing both occupied and unoccupied electron states. In this thesis, scanning tunneling microscopy and spectroscopy is used to explore PtSn₄ in detail. The structure of the pristine lattice is defined and the three different possible terrace steps are identified using differing spectroscopies as well as comparing terrace step edge heights to distances within the unit cell. One of the main goals was to explore the intrinsic defect density of the material and provide clarity to the cause of the high residual resistivity ratio. Five different types of defects are documented in both topographic and spectroscopic detail. The lattice site origins of each defect is discussed in hopes to provide a strong basis for future exploration.

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