Nanoscale Editing of Multi and Single Layer Tungsten Disulfide via Gas-Assisted Focused Electron Beam Induced Etching for Device Prototyping

Focused electron beam induced etching (FEBIE) with XeF₂ (xenon difluoride) precursor is conducted on multi-layer exfoliated WS₂ (tungsten disulfide) and monolayer WS₂ grown by chemical vapor deposition (CVD). The films are characterized by atomic force microscopy (AFM) and Raman and photoluminescence (PL) spectroscopy post-etching. The etch rates/efficiencies are reported as a function of electron beam energy, current, dwell time, and XeF₂ pressure. Bulk film Raman spectra are unchanged post-FEBIE, indicating minimal subsurface damage. Monolayer WS₂ shows a decrease in Raman and PL intensity post-FEBIE, with a dose-to-clear of ≈2 nC µm⁻². The study reveals regimes affected by the various mass transport contributions such as refresh time and the ratio of electrons/XeF₂. Spontaneous etching was discovered during FEBIE of large patterned areas due to the long frame/refresh times. Density functional theory and ab initio molecular dynamics simulations compares desorption of SF_x and WF_x molecules from pristine WS₂ basal planes and pore edges, revealing the spontaneous etching is consistent with etching of partially etched monolayers during each frame. Single-line etching width of 21 nm, and patterning flakes into 100 nm wide channels are demonstrated. This work demonstrates the possibility of editing WS₂ flakes into electronic devices of arbitrary dimensions for semiconductor applications.