Ternary Oxidized Carbon Nanohorns/ TiO2/PVP Nanohybrid as Sensitive Layer for Chemoresistive Humidity Sensor

The relative humidity (RH) sensing response of a chemoresistive sensor using a novel ternary hybrid nanocomposite film as sensing element is presented. The sensitive layer was obtained using drop-casting technique for depositing a thin film of nanocomposite between the electrodes of an interdigitated structure. The sensing support structure consists of interdigitated (IDT) dual-comb structure made of Si and covered by a SiO₂ layer of 1 µm thickness. The interdigitated electrode structure is made of a chromium adhesion layer (10 nm thickness) and a gold layer (100 nm thickness).

The sensing capability of the novel thin film based on a ternary hybrid made of oxidized carbon nanohorns – titanium dioxide – polyvinylpyrrolidone (CNHox/TiO₂/PVP) nanocomposite was investigated by applying a direct current with known intensity between the two electrodes of the sensing structure, and measuring the resulting voltage difference, while varying the RH from 0% to 100% in humid nitrogen atmosphere. The ternary hybrid-based thin film's resistance increases when the sensors were exposed to relative humidity ranging from 0–100%. It was found that performances of the new chemoresistive sensor are consistent with those of the capacitive commercial sensor used as benchmark throughout the moisture monitoring experiment.

Raman spectroscopy has been used to provide information about the composition of the sensing layer, as well as about potential interactions between constituents. Several sensing mechanisms were considered and discussed, based on the interaction of water molecules with each component of the ternary nanohybrid. The sensing results obtained lead to the conclusion that the synergic effect of p-type semiconductor behavior of CNHox and the PVP swelling process plays a pivotal role for the overall resistance decrease of the sensitive film.