| Porous Si has been considered for many applications such as biosensing, bioscreening and drug delivery. A major limitation of this material is its instability towards oxidation in air and aqueous media. A variety of organic functional groups is grafted onto porous Si via electrochemical modification to passivate the surface. The stability of modified samples is studied in air, aqueous, and nonaqueous environments. Methyl endcapping method is developed to increase the stability of previously modified surface.; It has been reported that absorption of analytes into porous Si layer can induce changes of optical features such as Fabry-Perot fringes in the reflectance spectrum, and a variety of chemical and biological sensors based on this mechanism has been developed. However, using this methodology, porous Si by itself is not expected to detect noncondensible gases such as H2. In this thesis, a porous Si-based interferometric sensor of H2 is reported, using Pd deposit as a hydrogen trap. The optical H2 sensor is safe, sensitive, reliable, selective, and reproducible, displays a short response time, and operates at room temperature.; Surface enhanced Raman scattering (SERS) on silver-plated porous Si (Ag-PS) is explored in this thesis. Roughened silver film containing dendritic structures is synthesized by immersion plating on porous Si to form a stable and SERS-active substrate. A simple acid pretreatment is found to dramatically reduce the background signal, resulting in a low and flat baseline. SERS of rhodamine 6G, adenine, and erythrosin B are studied at concentrations ranging from 0.1 nM to 1 muM. Some interesting anion effects on SERS of rhodamine 6G are observed. The detection limit of adenine with the present experimental setup is found to be 1 nM. Ag-PS samples that have been stored in air for 10 days still display high sensitivity. This technique is suitable for in situ preparation of SERS-active substrates in the field, and amenable to mass production and integration with well-developed silicon microfabrication technologies. |
