Au/TiO₂ Nanotube/Ti Chemicapacitive Devices: An Approach for Optimal Gas Sensing

Frequency-tuned selectivity enhancement of Mg@ZnO–TiO2 nanoflake-based heterojunction sensor devices

“…The device capacitance is proportional to the effective dielectric, C air/VOC ∝ ε reff , where ε reff is the effective dielectric constant. 14 A significant capacitive change was evident in the present study, and the effective dielectric variation was significant due to presence of VOCs at the volume of the void region of the ZnO–TiO 2 nanostructure. In addition, the catalytic effect of Mg induced VOC molecules at the inner and outer surface of nanoflakes and subsequent fast dissociation of VOCs at the surfaces also contribute to improving the sensor response.…”

“…The response time ( τ res ) is the time it takes for the sensor to reach 90% of the saturated response, while the time to recover 90% of the saturated response during desorption is defined as the recovery time ( τ rec ). 14 The response times for 2-butanone, acetone, 2-propanol, ethanol, and methanol were 29, 66, 32, 30, and 31 s, respectively, whereas the recovery times for the same were 19, 19, 3, 17, and 16 s, respectively. The long-term stability of the Mg@ZnO–TiO 2 sensor towards air and 100 ppm of 2-butanone, acetone, 2-propanol, ethanol, and methanol is shown in Fig.…”

“…The sensor showed a good response (61%), linearity, and response time (178 s) at 250 ppm concentrations. Chowdhury et al 14 demonstrated a TiO 2 nanotube array in capacitive mode. Their further study identified that the exposure of 2-butanone, acetone, 2-propanol, ethanol, and methanol shifted the resonant frequency from 2.2 kHz in air to 2.1, 1.5, 0.84, 0.52, and 0.4 kHz, respectively.…”

“…However, the depletion width ( λ D ) variation in the presence of VOCs with respect to air at both ZnO and TiO 2 could be correlated as per eqn (10). 14 where L D is the Debye length, qV s is the barrier height, k is the Boltzman constant, and T is the temperature in kelvin. Oxidation of the VOCs at the Mg@ZnO–TiO 2 interfaces and the hydrocarbon by-products are shown in eqn (11)–(15).…”

Synthesis and characterization of Co3O4 spinel nanowall: understanding the growth mechanism and properties

“…In addition to all resistive mode of gas sensing measurements, it also offers a corresponding capacitive mode of measurements where the capacitance of the porous oxide layer can be exploited. Nanowall growth on a conducting substrate surface (which can act as a bottom electrode) and subsequent selective deposition of a top electrode can serve this purpose [15]. In addition to resistive sensing, capacitive changes between the substrate surface and top electrode also can be obtained which can provide the requires information, which may successfully address the most challenging issue the 'selectivity' of any gas sensor.…”