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

High Resolution Image Download MS PowerPoint Slide Vacancy-driven electronic effects in bulk and few-layer hafnium disulfide (HfS 2 ) 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 HfS 2 . 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 HfS 2 .