Spectroscopic Studies on CVD-grown Monolayer, Bilayer, and Ribbon Structures of WSe2 Flakes

The diverse arrangements of layer stacking introduce intriguing physical properties in two-dimensional layered materials. Understanding the stacking pattern is vitally important for surface engineering and multitudinous applications. From this perspective, we report the spectroscopic investigation of chemical vapor deposition (CVD) grown WSe2 flakes along with their ribbon structures (RS). A qualitative interpretation based on the droplet motion is presented for the synthesis pathway of the WSe2-RS. For more experimental insights, we explore the features of the as-synthesized WSe2 flakes in detail, including monolayer, bilayer, and varying RS using Raman and photoluminescence (PL) spectroscopy. Specifically, the absence of the B1 2g peak in the Raman spectrum and a strong emission at 770.64 nm in the PL spectrum suggest that the monolayer is formed. More intriguingly, a weak PL emission with a broad peak is observed in the RS, confirming that the thickness of the ribbon is larger compared with the monolayer. We also find that the radiative recombination of excitons (A0) in hexagon-shaped flakes is stronger in comparison with triangle-shaped flakes using the exciton (A0) and trion (A(-)) contribution from PL spectra. Thus, this work may open up promising opportunities to deepen our understanding in the synthesis of mixed-dimensional nanostructures and tune of their spectroscopic properties.