Direct Growth of Multi-Layer Graphene on Quartz Glass for High-Performance Broadband Neutral Density Filter Applications

2D layered materials, such as graphene, transition metal dichalcogenides, and hexagonal boron nitride (h-BN), cover a broadband in the electromagnetic spectrum with wavelengths ranging from hundred nanometers to millimeters. Their applications in photonic and optoelectronic nano-devices have been demonstrated frequently, while they still need to be extended to daily life related fields. Herein, this work demonstrates a brand new application of multi-layer graphene directly grown on quartz glass as broadband neutral density filters (NDFs). The graphene-based NDFs present nearly wavelength-independent transmittances over a wavelength range of 400-2500 nm, affording great optical attenuation capacity in the long-exposure photography. This work further shows that, MoX2 (X = S, Se) and h-BN directly grown on quartz glass can serve as optical cut-off filters with different absorption edges located in the visible and deep-ultraviolet ranges, respectively. The results are hereby expected to promote macroscopic optical applications of 2D layered materials and their heterostructures in high-performance multi-functional optical filters.