Native Oxide MoO₂- MoSe₂ Heterostructure-Based Self-Powered Gas Sensor for Selective NO₂ and H₂ Detection

A single-step chemical vapor deposition method is reported to synthesize native oxide metal -semiconductor MoO₂-MoSe₂ heterostructure flakes for self-powered gas sensing. Two types of flakes, S1 and S2, with distinct compositions, are analyzed using Raman, photoluminescence spectroscopy, Atomic Force Microscopy, X-ray and UV Photoelectron Spectroscopy, and High-Resolution Transmission Electron Microscopy (HRTEM). TEM and Energy Dispersive Spectroscopy (EDS) mapping confirm a clear interface and compositional gradation in the heterostructures. Sample S1, predominantly MoO₂ and highly metallic, exhibits minimal photoresponse but shows selective H₂ detection at room temperature. In contrast, S2, with a top-down MoO₂-MoSe₂ structure, demonstrates broadband optical photoresponse and high sensitivity toward NO₂ with a detection limit of 10 ppm. The enhanced performance at low (few mili volts) or zero bias is attributed to photocarriers generated at the heterojunction and NO₂/MoSe₂/MoO₂ interface-driven interactions under visible light exposure. The response is further found to be enhanced significantly in the presence of humidity, making it suitable for detection in humid environments. This interface engineering strategy enables the development of room-temperature, self-powered gas sensors with high selectivity and sensitivity, paving the way for future nanoelectronic and MEMS-integrable sensing devices.