Local Defect-Engineering in Monolayer MoS2 through Sulfur Vacancies Controlling with Dip-Pen Nanolithography

Molybdenum disulfide (MoS₂) is a promising layered semiconductor material that can overcome the limitations of conventional silicon-based devices. MoS₂ has a unique characteristic in which the band gap changes depending on the thickness; Monolayer MoS₂ has a direct band gap of about 1.8 eV, while multilayer MoS₂ has an indirect band gap of about 1.3 eV. Therefore, MoS₂ has potential applications in various fields such as optoelectronics, sensors, and catalysis. However, the electrical and optical properties of monolayer MoS₂ are sensitive to defects on its surface. Sulfur vacancies are the most prevalent defects in MoS₂ and they work as electron donors and trap sites. Thus, they create mid-gap states influencing the band structure and the Fermi level of monolayer MoS₂. The charge state and the local environment of the sulfur vacancies can either improve or deteriorate the electrical conductivity, the photoluminescence intensity, and the catalytic activity of monolayer MoS₂. Thus, it is crucial to control the sulfur vacancies in monolayer MoS₂ to optimize its electrical characteristics and device performance. In this study, we propose a method for local defect engineering in monolayer MoS₂. The proposed method controls sulfur vacancies through dip-pen nanolithography (DPN), a tip-based lithography technique that enables direct deposition of molecules or ions onto specific regions of the substrate surface.