Abstract
An electrical sensor based on porous silicon (PSi) for the detection of various organic molecules in the liquid phase is demonstrated. PSi layers with a thickness of approximate to 4.5m and pore sizes in the range of 30nm were initially synthesized by the electrochemical anodization of a silicon wafer. Anodic oxidation of the mesoporous layers was conducted to passivate the surface and the electrical contacts were created exclusively onto the front porous film. Real-time measurements of conductance were performed at room temperature as a sensing response parameter. The as-fabricated sensors exhibit a sensitive and reversible response upon exposure to polar solvents including ethanol, methanol, acetone, and acetonitrile with a conductance increase. However, an irreversible response was detected upon the addition of non-polar molecules (n-hexane and toluene) with a conductance decrease. The response time covering both infiltration and evaporation times was in the order; acetone<methanol<acetonitrile<ethanol. The response to pure water was extremely slow, due to poor hydrophilicity of the surface. The observed response could be understood in terms of the change in surface charge during solvent infiltration, along with changes in the dielectric constant of the porous layer. The sensor could be reused efficiently for ten cyclic tests for acetone, indicating excellent repeatability of the device.