Sensitivity improvement of free-standing porous silicon rugate filters for isopropanol vapor detection by applying lateral pressure differences

To improve sensitivity, lateral pressure differences were applied to free-standing porous silicon rugate filters (FPS-RFs) for isopropanol (IPA) vapor detection. The IPA vapor concentration within pores of a 60-cycle FPS-RF used in the research was maximized at a pressure difference of approximately 177 mmH2O, and the highest sensing sensitivity was obtained at the same pressure difference as a result. The reasons for the large difference in sensitivity between the FPS-RFs and the porous silicon rugate filters (PS-RFs) formed on a silicon substrate were also discussed.