Xenes-based QCM sensors: exploring borophene and silicene for humidity sensing

Borophene and silicene, two novel members of the Xene family, feature high surface reactivity and stability suitable for sensing applications. However, the gas sensing capabilities of these materials in their pristine form have not been systematically investigated. Here we show that borophene- and silicene-based quartz crystal microbalance (QCM) sensors achieve stable and sensitive relative humidity detection and we model their adsorption-desorption mechanisms. Borophene and silicene nanosheets were synthesized via liquid-phase exfoliation and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller surface area analysis. The QCM sensors exhibited sensitivities of 3.2 Hz/%RH and 3.9 Hz/%RH, response/recovery times of 122/65 s and 47/130 s and hysteresis of 1.8% and 3.8% hysteresis for borophene and silicene, respectively. The dominant sensing mechanism was determined to be chemisorption, supported by thermodynamic modeling. These results suggest that 2D borophene and silicene can significantly contribute to sensing applications, especially in environments requiring air stability.