Conductance Spectroscopy: A Novel Technique for Ultra-Selective Chemical Detection

The present work demonstrated a novel conduction spectroscopic technique for the detection of trace levels of chemicals at room temperature. The technique analyzes the second harmonic current variations of a surface-engineered resistance device. The device was fabricated by growing MoS2 nanosheets decorated with ordered nanoflakes on a Si/SiO2 substrate in a two-terminal device architecture. It was subjected to a dc voltage sweep, with varying concentrations of acetone (25%–100%), and its second harmonic spectra were analyzed against wavenumbers (k). The spectra revealed well-distinguished peaks at k values of ~800, ~1400, ~1700, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 2900~\text {cm}^{-{1}}$ </tex-math></inline-formula> corresponding to O-H bending, C-H bending, C=O stretching, and C-H stretching vibrational modes of the acetone molecule, respectively. The spectra can also be used to identify the nature of the bonds as oxidizing or reducing bonds, based on their effect on the carrier transport, from the direction of the peaks in the spectra. The technique showed unique spectra for NH4OH and 2-propanol, easily distinguishable from acetone. Furthermore, a comparative analysis of acetone peaks at varying concentrations demonstrated phase change to geminal-diol, giving a quantitative estimation of phase-change reactions. The device was highly repeatable, reproducible, and chemically stable for up to 60 days. Thus, the study proposed a novel chemical detection technique utilizing a resistive element to perform bond identification, reaction rates, phase-change studies, and semiconductor characterization with high accuracy. Hence, this technique may be generalized to compete with its optical counterparts by offering a portable system with ultrahigh detection efficiency toward unknown chemicals.