Scanning Tunneling Microscopy and Spectroscopy of Pt-based Transition Metal Dichalcogenides*

Recent studies of 2-dimensional layered materials have shown that group-10 transition metal dichalcogenides (TMDs) are host to numerous advantageous properties, with demonstrated potential for applications in high-performance nanoelectronics, strain gauges, broadband optoelectronics, electrocatalysis and ultra-sensitive gas sensing. An advantage is low synthesis temperature, which significantly broadens the processes by using substrates that the growth is compatible with. The electronic band structures of these materials are greatly influenced by their physical attributes, namely factors such as thickness and the presence of defects. Here we utilise scanning tunneling microscopy and spectroscopy (STM/S) to structurally and electronically characterise platinum-based TMDs. Low-temperature STM is used to get atomically resolved images and probe the local density of states (LDOS) for all Pt-based TMDs. For PtS₂ we obtained the first STM images and determined a lattice constant of ~0.36 nm. Investigation of PtSe₂ allowed us to correlate crystal size to the observed changes in the bandgap. Notably, we also confirmed the presence, and explored the influence, of edge states. Through the study of PtTe₂, STM/S resulted in distinguishing and characterising of 5 different types of point defects that are present on, and in the vicinity of, the surface of PtTe₂. The nature of these defects and their electrical influence within the films were probed and determined by controlling the tip-sample bias. Prior to the STM investigation, Raman and X-ray photoelectron spectroscopy (XPS) were performed to confirm a successful synthesis of TMDs.