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The first reported NO gas sensor based on a surface photovoltage (SPV) semiconductor device system is fabricated with a metal/SiO 2 (self-ordered hexagonal mesoporous)/Si 3 N 4 /SiO 2 /Si structure (MIS). A size controlled silicate mesoporous film is successfully synthesized by spin coating on a Si 3 N 4 /SiO 2 /Si silicon wafer using poly(ethylene oxide)-poly(propylene oxide)poly(ethylene oxide) (Pluronic P123 = EO 20 PO 70 EO 20 ) triblock copolymers as a template. The characteristics of the mesoporous films were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). The sensing properties of the self-ordered hexagonal mesoporous SPV system have been investigated by repeated exposure to NO gas and air. The changes in the average value and phase of the AC photocurrent (I ph ) have been observed after exposure of the films to 100 ppm NO gas. The response of the alternative photocurrent results from the physical adsorption and chemical interaction between detected NO gases and the self-ordered hexagonal mesoporous film.

Mesoporous silica films with hexagonal (SBA-15) and cubic (SBA-16) mesostructures have been successfully employed to fabricate surface photo voltage (SPV) sensors for NO2 gas. These SPV sensors exhibited better sensitivity (S) in 50 ppm NO2 gas than in 100 ppm NO gas. SPV with SBA-16 film showed better sensitivity in 1 ppm NO2 gas than in 1 ppm NO gas. These phenomena can be explained by the physical adsorption of the target gas into the mesoporous layer, which is regarded as the insulator layer in metal−insulator-semiconductor (MIS) devices.