Sensors based on macroporous silicon (M-PSI) have demonstrated the ability to detect the presence of certain chemical and biological materials. The devices utilize silicon sensing membranes with deep trench structures (macropores) formed by electrochemical etching to depths up to 100μm. The sensor structure is unique in that it exploits the vertical dimension of the planar silicon substrate, utilizing the large internal surface area of the membrane as the active sensing region. Upon exposure to organic solvents (i.e. ethanol, acetone, benzene) the devices exhibit a characteristic impedance signature. Discrimination is achieved by recognizing a specific response characteristic, or by placing appropriate probe materials to provide an electrically detectable signal upon exposure to the target substance. M-PSi sensing devices have demonstrated an electrical response to DNA hybridization and shown discrimination between binding and non-binding events. The size of the pores in the sensing elements can host larger molecules such as proteins, which extends the use of the devices to other fields of biotechnology. The sensors have been designed and fabricated in array configurations. A flexible electronics interface platform has been developed to accommodate the use of the sensors for a variety of applications.
Nanocrystalline (nc)-Si/amorphous (a)-SiO2 superlattices (SLs) have been studied by transmission electron microscopy, Auger elemental microanalysis (AEM), Raman spectroscopy and optical reflection spectroscopy. Recrystallized Si/SiO2 SL is extremely stable under high temperature annealing (up to 1100 degree(s)C) and aggressive wet thermal oxidation: AEM and Raman spectroscopy of folded acoustic phonons show no changes in periodicity in the growth direction and the abruptness of the nc-Si/a-SiO2 interfaces. Furthermore, Raman spectroscopy in the optical phonon range indicates that the annealing decreases the defect density in the Si nanocrystals, possibly due to Si-Si bond rearrangement accompanied by surface reconstruction and surface defect passivation by oxygen.
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