Tuning the response and stability of thin film mesoporous silicon vapor sensors by surface modification

The effect of chemical surface treatment on the sensitivity, specificity, and stability of mesoporous Si thin film vapor sensors is studied. The vapor sensors operate by measurement of Fabry-Perot interference from the porous Si layer, probed using a diode laser operating at a wavelength of 687 nm. Four chemically distinct surface types are each probed with three different analyte vapors: ethanol, methyl ethyl ketone, and n-hexane, all in a carrier gas of pure nitrogen. The four different surface types include the H-terminated, freshly etched material (Si-H), ozone-treated material (Si-ozone), electrochemically methylated material (Si-CH3), and thermally oxidized samples (Si-O-Si). Surface modification has a pronounced effect on the specificity and stability. It is found that the Si-H material is more sensitive to the hydrophobic analyte relative to either the Si-O-Si or Si-ozone samples. Similarly, the Si-CH3 material is more sensitive to the more hydrophobic analyte, although it is found to be much more stable than the Si-H material.