Vacancy-Driven Electronic Effects in Few-Layer HfS 2 Probed by Scanning Tunneling Microscopy and Spectroscopy

Vacancy-driven electronic effects in bulk and few-layer hafnium disulfide (HfS2) were investigated using scanning tunneling microscopy/spectroscopy and density functional theory simulations. Fermi level variations associated with sulfur vacancies were observed in spectroscopic data carried out on both bulk and nanoflakes of HfS2. Atomically resolved imaging revealed structural sulfur vacancies, which locally induce a pronounced shift in the Fermi level. Stoichiometric regions exhibit p-type semiconducting behavior, whereas defective regions display clear n-type doping. A noticeable reduction in the average band gap was also observed near sulfur vacancies, decreasing from 1.28 to 1.19 eV in bulk material. Finally, a thickness-dependent evolution of the electronic band gap was observed, ranging from 1.48 eV for the 3-layer to 1.28 eV for bulk HfS2.