Highly Sensitive ppb Level Methanol Sensor by Tuning C:O Ratio of rGO-TiO2 Nanotube Hybrid Structure

In this paper, ppb level methanol sensing by a hybrid gas sensor device based on reduced graphene oxide (rGO) and TiO
₂
nanotubes is reported. Tuning of carbon to oxygen ratio, in rGO layers, was found to be very effective in modulating the sensor response. The C:O ratio was tuned by varying the voltage (11-31V) during the electro-deposition of rGO (on top of the TiO
₂
nanotube matrix) and was confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. Due to variations in the C:O ratio in rGO, the barrier height of rGO-TiO
₂
nanotube junctions and etch hole dimension on rGO layer were varied. Judicious optimization of these two pivotal parameters resulted in the sensor device (for rGO deposition voltage of 16 V), capable of detecting ppb level (up to 62 ppb) methanol efficiently. The sensor showed ~16%, ~59%, and ~94% response magnitude for 62 ppb, 1 ppm, and 200 ppm concentrations, respectively. A comprehensive discussion elucidating the role of rGO-TiO
₂
NTs junctions (with a tunable C:O ratio) has also been presented correlating the experimental findings.