Towards Nanowire-Based Selective Vapor Sensing via Impedance Spectroscopy

The aim of this work is a silicon nanowire-based selective vapor sensing of ammonia (NH
3
) and hydrochloric acid (HCl) via electrical impedance spectroscopy (EIS). Developed highly sensitive silicon sensors could be used for indirect selective analysis of liquid solution composition containing NH
3
and HCl. We use Si nanowires (Si NWs) obtained with cryogenic plasma etching with high aspect ratio providing large adsorption surface area to provide enhanced sensitivity. The NWs are placed on a contact platform and EIS is used to detect the analytes. The development of three different types of sensors based on Si NWs, Si NWs treated with hydrofluoric acid (HF), and Si NWs decorated with silver nanoparticles (Ag NPs) showcases an optimization effort to enhance the sensor's performance. Furthermore, this work proposes a novel approach for interpreting the electrical impedance spectroscopy (EIS) spectra. Instead of analyzing the response solely in terms of impedance or frequency, the proposed approach suggests considering the response in a frequency-resistance F(R) space. This innovative analysis method offers a new perspective for understanding and interpreting the sensor's behavior and response characteristics. By visualizing the response in the F(R) space, it becomes possible to uncover patterns and correlations that might be overlooked by traditional analysis methods.