Session:

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising candidates for applications such as gas sensors, photodetectors, and channel materials in field-effect transistors, thanks to their tunable band structures, reduced leakage current, and high carrier mobility. The patterning of 2D-TMDs is critical in device fabrication, traditionally requiring a complex lithography process. We demonstrate an approach to depositing MoS₂ flakes on SiO₂/Si substrates with a predefined pattern shape, utilizing localized electron irradiation on the surface of SiO₂/Si wafers. Within the regions exposed to low-dose electron irradiation, we successfully achieve area-selective growth of MoS₂ during chemical vapor deposition (CVD) process with selectivity of >0.7. In contrast, negative selectivity with suppressed growth is achieved in heavily irradiated areas of the substrate.

We have investigated the modification of surface potential on SiO₂/Si substrates due to localized electron irradiation using Kelvin probe force microscopy (KPFM) and demonstrated that selective growth takes advantage of the local surface potential difference. The variation of the surface potential is predictable by an analytical model. Raman spectroscopy analysis reveals the adsorption of carbon species due to irradiation, acting as a blocking layer that inhibits MoS₂ growth and contributes to the observed negative selectivity. We will discuss the role of CVD parameters (e.g., precursor flux), surface potential, adsorption of carbon species, and surface topography change observed by atomic force microscopy (AFM) in achieving the desired selectivity in CVD growth of MoS₂. Our findings pave the way for a controllable lithography-free patterned synthesis of 2D-TMD materials, eliminating the need for complex lithography processes and minimizing contamination. This study presents a promising approach to achieving a bottom-up fabrication process for the next-generation TMD-based device fabrication and its further scaling.

Co-Author(s): Edward Naland (National University of Singapore), Silvija Gradecak (National University of Singapore)

Haobo Li

Appearances