Nanocrystalline Porous Silicon Layers.Porous silicon is a nanocrystalline material that is generated by etching of bulk crystalline silicon in aqueous hydrofluoric acid (HF).It is of interest for its luminescence,[l] electroluminescence,[2] biolomedical,and sensor properties.[3] The open pore structure and large specific surface area (a few hundred m~2 per cm~3,corresponding to about a thousand times the surface of the polished silicon wafer) make porous Si a convenient material for sensitive detection of liquid and gaseous analytes.The ability to electrochemically tune the pore diameters[4] and to chemically modify the surface[5,6] provides control over the size and type of molecules adsorbed.
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