Si Nanowire-Based Schottky Sensors for Selective Sensing of NH3 and HCl via Impedance Spectroscopy.

This work is aimed at the development of a highly sensitive silicon (Si)-based sensor allowing for the selective detection and analysis of liquid solution compositions containing ammonia (NH₃) and hydrochloric acid (HCl) in an indirect manner using electrochemical impedance spectroscopy (EIS). For optimization of the performance, we develop three types of sensors based on as-fabricated Si nanowires, nanowires treated with hydrofluoric acid (HF), and nanowires decorated with silver (Ag) nanoparticles. The fabricated sensors exhibit good performance governed by the sensitivity of the nanoscale Schottky barriers at the interface between the golden pads and Si nanowires. The best results on sensitivity are obtained with untreated Si nanowires providing a detection limit at the level of 4 μmol·L^–1 and resistive sensitivities of 0.8% per μmol·L^–1 for HCl and 4 μmol·L^–1, −0.2% per μmol·L^–1 for NH₃, correspondingly. Treatment with HF stimulates the surface oxidation providing higher density of the adsorption sites and found promising for the detection with the analyte content up to 1000 μmol·L^–1. In the end, we study the sensor response upon simultaneous exposure under NH₃ and HCl vapors using developed approach for the EIS data analysis involving characterization of the sensor response with two parametersresistance and EIS frequency corresponding to the change in the operation regime. Due to the use of two parameters simultaneously, this approach is found as a pathway for qualitative analysis of the gas mixture composition using only one sensor. The results of the work shed light on the development of feasible highly sensitive sensors for health monitoring, allowing for selective mixed analytes detection. [ABSTRACT FROM AUTHOR]