Dynamic Interaction of NO2 with a Nanostructure Modified Porous Silicon Matrix: Acidity, Sensor Response, and the Competition for Donor Level Electrons

Abstract

We describe a reversible response matrix and the dynamic interplay, as a moderately acidic NO2 analyte interacts at room temperature with a TiO2, SnOx, CuxO (x = 1,2), and AxO (x ≫ 1) metal oxide nanostructure deposited n-type nanopore coated microporous porous silicon (PS) interface. A significant variable response matrix is measured and the dynamic nature of analyte-interface processes characterizing the semiconductor-analyte interaction as NO2 couples to the decorated semiconductor majority charge carriers. The competition for electrons between NO2 and the TiO2 decorated PS interface leads to distinct variations in sensor response as a function of increased TiO2 concentration and displays a time variance as the extraction of electrons by NO2 reaches a limiting charge carrier depletion and the decorated PS surface becomes electron withdrawing. This dynamic reversal is also demonstrated by distinct time-dependent PS interface responses to NO2 and NO where the degree of electron extraction reaches a maximum and is again countered by the depleted n-type PS. Electron depleted SnOx and AuxO treated PS interfaces display a significant remnant effect as the decorated surface can become electron withdrawing for extended periods, forming a stronger acid and extracting electrons from NO2. Exposure to NH3 also demonstrates the remnant effects of depletion.