A Physical Modeling of TiO2 Nanotube Array-Based Capacitive Vapor Sensor

A physical model was developed to estimate the capacitance and capacitive response of electrochemically grown ordered and self-organized TiO2 nanotube array based sandwich structured vapor sensor device (Au/TiO2 nanotube /Ti). Nanotubes were modeled in hexagonal grid geometry considering its structural and morphological parameters. Five different capacitances, i.e., capacitance due to TiO2 solid (Cn), free space in bulk (Cf), Au/TiO2 junction (Cju), Ti/TiO2 junction (Cjd), and internal capacitances between two adjacent nanotubes (Cz) were formulated, simplified, and represented in a complex capacitive network. Equivalent device capacitance (Ceq) was calculated by solving the charge-voltage equations through matrix method. Simulated capacitance (Ceq) and capacitive response (R C) of Au/TiO2 nanotube /Ti device towards different organic vapors were compared with practically measured values obtained by impedance analysis method.