Enhancement of Raman and Photoluminescence Intensity of Monolayer MoS₂ Using Engineered Substrates via Grayscale Electron-Beam Lithography

The properties of two-dimensional (2D) materials are heavily influenced by their dielectric environment. Nanoscale variations in thickness and trench depth of the substrate are often used to vary the optical properties, which involve testing multiple substrates. In this study, we develop grayscale electron-beam lithography (g-EBL) to vary substrate thicknesses (staircase structure) or trenches of different depths (holey structure) on the same SiO 2 /Si substrate. Monolayer MoS 2 transferred onto these structures shows variations in Raman and photoluminescence (PL) intensities, consistent with the multireflection model (MRM). In holey structures, we observe a PL (Raman) enhancement of over 150 (90) times compared with the MoS 2 placed directly on the substrate. Raman peak shifts are systematically analyzed using the MRM model, which considers trench-depth-dependent power absorption with implications for thermal conductivity measurements and thermal engineering applications. Our fabrication technique is also useful for creating photonic/phononic band gap crystals with varying depths, designing diffractive optical elements, and developing micro/nanoelectromechanical systems (M/NEMS).