Ternary Holey Carbon Nanohorn/Potassium Chloride/Polyvinylpyrrolidone Nanohybrid as Sensing Film for Resistive Humidity Sensor

Abstract

The study presents findings on the relative humidity (R.H.) sensing capabilities of a resistive sensor. This sensor utilizes sensing layers composed of a ternary nanohybrid, consisting of holey carbon nanohorn (CNHox), potassium chloride (KCl), and polyvinylpyrrolidone (PVP), with mass ratios of 7/1/2, 6.5/1.5/2, and 6/2/2 (w/w/w). The sensing structure comprises a silicon substrate, a SiO2 layer, and interdigitated transducer (IDT) electrodes. The sensing film is deposited on the sensing structure via the drop-casting method. The sensing layers’ morphology and composition are investigated through Scanning Electron Microscopy (SEM) and RAMAN spectroscopy. The resistance of thin-film sensors based on ternary hybrids increased with exposure to a range of relative humidity (R.H.) levels, from 0% to 100%. The newly designed devices demonstrated a comparable response at room temperature to that of commercial capacitive R.H. sensors, boasting excellent linearity, swift response times, and heightened sensitivity. Notably, the studied sensors outperform others employing CNHox-based sensing layers in terms of sensitivity, as observed through manufacturing and testing processes. It elucidates the sensing mechanisms of each constituent within the ternary hybrid nanocomposites, delving into their chemical and physical properties, electronic characteristics, and affinity for water molecules. Various alternative sensing mechanisms are considered and discussed, including the reduction in holes within CNHox upon interaction with water molecules, proton conduction, and PVP swelling.