Photoluminescence and Raman Spectra Oscillations Induced by Laser Interference in Annealing-Created Monolayer WS ₂ Bubbles

WS ₂ monolayer crystals have been grown in a large scale by chemical vapor deposition on SiO ₂ (300 nm)/Si substrates, and via high-temperature treatment under protection of Ar or N ₂ gas flow after growth, huge amount of monolayer WS ₂ bubbles have been successfully created in a shape of spherical cap and widely distributed sizes. Optical and fluorescence images reveal obvious interference rings on the monolayer WS ₂ bubbles of large sizes. In line scans and mapping images of photoluminescence (PL) and Raman, oscillatory behaviors have been observed not only for peak intensity but also for peak position and width. It is easy to understand that the oscillatory PL and Raman peak intensities originate from constructive and destructive interference on the bubble's surface, while the oscillatory peak positions and widths are induced by the corresponding enhanced and lowered local heating effects owing to constructive and destructive interference. This is further verified by the absence of oscillation in the position and width when a heat sink layer is applied.