Reactive gas-timing GLAD TiO2 nanorod films: Structural and electronic properties and MEMS-based NO2 gas sensing

TiO 2 nanorod thin films were fabricated using conventional glancing angle deposition (CONV-GLAD) and reactive gas-timing glancing angle deposition (RGT-GLAD) with controlled Ar:O 2 gas-timing sequences to investigate their structural, optical, electronic, and gas-sensing properties. SEM analysis confirmed the formation of well-defined nanorod architectures with an average thickness of ∼300 nm, while GIXRD revealed a phase transformation from a predominantly amorphous or poorly ordered structure to crystalline anatase for the RGT-GLAD films after annealing at 450 °C, with improved crystallinity after annealing. Optical measurements showed high visible transmittance and variations in optical bandgap depending on the gas-timing conditions. XPS analysis demonstrated that RGT-GLAD modifies the surface composition and oxygen-related chemical states, while UPS revealed corresponding variations in work function. These results indicate that the Ar:O 2 gas-timing sequence influences the surface and electronic properties of the TiO 2 nanorod films. Gas-sensing evaluations toward NO 2 (0.1–1.0 ppm) using MEMS-based sensors revealed that RGT-GLAD-modified TiO 2 nanorods exhibit enhanced NO 2 responses compared with the CONV-GLAD film. In particular, the RGT-GLAD 20:20 condition showed the highest response among the investigated conditions and good short-term repeatability at 0.1 ppm NO 2 . Overall, this work demonstrates that RGT-GLAD with controlled Ar:O 2 gas-timing is an effective strategy for tailoring the structural and electronic properties of TiO 2 nanorods, leading to enhance NO 2 gas-sensing performance and highlighting its potential for NO 2 gas-sensing applications.