Journal Article Schottky barrier defect engineering monolayer MoS2 sulfur vacancies 2D materials Fermi-level pinning Published Erratum Review all-van-der-Waals contacts band alignment contact resistance electrical transport electronic devices electronic structure modulation electronics field-effect transistors heterostructures in situ defect healing logic inverters metal-semiconductor contacts molecule treatment transistors van der Waals contacts van der Waals interfaces van der Waals semimetals work function