Humidity sensing properties of CNT–OD–VETP nanocomposite films

In this study, the blend of orange dye (OD), C17H17N5O2 (5 wt%), vinyl-ethynyl-trimethyl-piperidole (VETP), C12H19NO, (5 wt%) and carbon nanotube (CNT) powder (10 wt%) in a mixture of distilled water (80 wt%) and spirit were drop-casted on glass substrates with pre-deposited surface-type silver electrodes to fabricate CNT–OD–VETP nanocomposite thin films. In the process of thin films deposition, 2 V DC was applied to Ag electrodes. The thicknesses of the CNT–OD–VETP films were in the range of 10–15 μm. The I–V characteristics of the surface-type Ag/CNT–OD–VETP/Ag samples showed rectification behavior. The effect of humidity on the electrical properties of the nanocomposite films was investigated by measurement of the capacitance and dissipation of the samples at two different frequencies of the applied voltage: 120 Hz and 1 kHz. The resistance of the samples was determined from values of dissipation. It was observed that at 120 Hz and 1 kHz, under humidity of up to 90% RH, the capacitance of the cell increased by 7.4×103 and 740 times and resistance decreased by 2.3×104 and 3.8×104 times, accordingly, with respect to 40% RH conditions. The average response and recovery times of the films were obtained by capacitance-time measurements to evaluate the dynamics of the water vapor absorption and desorption processes. The experimental results have been supported by the simulation of the capacitance–humidity relationship. It is assumed that the humidity response of the cell is associated with diffusion of water vapors and doping of the semiconductor nanocomposite by water molecules.