Abstract
ABSTRACT This study presents a low‐temperature optical gas sensing platform based on tin dioxide (SnO 2 ) thin films deposited on porous silicon (por‐Si) substrates. The por‐Si scaffold was fabricated electrochemically, followed by SnO 2 deposition via RF magnetron sputtering. Integrating SnO 2 with por‐Si significantly improves gas sensing performance by increasing surface area, enhancing SnO 2 /Si heterojunction effects, and enabling better adsorption kinetics and energy‐efficient operation compared to pristine SnO 2 films. Ellipsometry was used to monitor real‐time thickness and refractive index changes during exposure to water, ethanol, propanol, and ammonia vapors. The sensing behavior strongly depends on molecular size and polarity, with alcohol producing larger optical responses. Additionally, applying an alternating voltage greatly enhanced ammonia adsorption, attributed to NH 4 + ion formation and displacement of surface‐bound water, demonstrating an effective electrical modulation strategy for improving selectivity. Surface morphology and crystal structure were confirmed by AFM, SEM, and XRD, revealing nanocrystalline rutile‐phase SnO 2 with high roughness. UV–vis spectroscopy and contact‐angle measurements indicated hydrophilic and optically responsive surfaces. Density Functional Theory simulations supported experimental findings by providing molecular‐level insight into adsorption mechanisms. The sensing mechanism is based on adsorption‐induced changes in the effective optical thickness and refractive index of the surface layer, enabling surface‐sensitive detection of vapor molecules. These results highlight SnO 2 /por‐Si heterostructures as promising candidates for miniaturized, selective, and low‐power gas sensing applications.