Atomic-Scale Defects and Edge Engineering of ZrSe ₂ Nanosheets: Correlated Microscopy, Spectroscopy and DFT Study with Implications for Quantum Device Applications

We present a comprehensive study of the atomic-scale electronic behavior of ZrSe₂, focusing on the effects of intrinsic point defects, grain boundaries, and edge configurations. Using a combination of low-temperature scanning tunnelling microscopy/spectroscopy (STM/STS) and density functional theory (DFT), we identify and characterize the spectroscopic fingerprints of various intrinsic point defects, including vacancies, antisites, and interstitials, and reveal how these features perturb the band edges or introduce in-gap states. These defect-induced features are shown to significantly influence the local electronic properties of ZrSe₂. Our analysis of grain boundaries identifies shear-type interfaces that shift the Fermi level without introducing deep in-gap states, thereby preserving the semiconducting character of pristine ZrSe₂. In contrast, the edge configuration has a pronounced effect on the electronic structure, with armchair and zigzag edges exhibiting distinctly different behaviors. While the former is characterized by a prominent peak near the valence band edge, indicating the presence of edge-localized states and a clean semiconducting character, the latter instead introduces a significant density of states at midgap and within the upper half of the bandgap. These findings offer atomic-level insights into the interplay between defects, edge chemistry, and electronic behavior in ZrSe₂, establishing a framework for defect- and edge-state engineering in two-dimensional semiconductors for nanoelectronics and quantum device applications.