Nanostructure and morphology modified porous silicon sensors

Abstract

The ability to control and transform the morphology and optical properties of porous silicon (PS) interface arrays can have important implications for displays and sensors. The optoelectronic properties and interaction sensing capabilities of PS can be varied as a function of pore size and pore morphology as dictated by the manipulation of a surface structure which can be controlled with current density, the solution composition of the electrochemical etches used to prepare the pores, and careful post etch surface treatments. These treatments influence the time dependent photoluminescence (PL) emission from PS. The variation of surface structure as it effects the PL from these PS pore arrays is outlined and discussed within the framework of detailed molecular electronic structure calculations which model the excited state structure giving rise to the UV-visible PL emission from PS. Applications varying from displays to sensors to micro-reactors will be considered. Porous silicon interfaces have also been transformed within the framework of nanotechnology to create highly efficient sensors displaying a rapid, reversible, sensitive, and selective response to HCl, NH₃, CO, and NO down to the ppb level. Photoluminescence induced metallization is used to obtain a highly efficient, <20&Omega;, electrical contact to the sensor, allowing operation at a bias voltage of 1-10mV. The introduction of gold and tin-based nanostructures to a micro/nanoporous PS array selectively modifies its impedance response to considerably improve the detection of the NH₃, CO, and NO. Through FFT analysis, a gas response can be acquired and filtered on a drifting baseline, further improving sensitivity. New nanoscale exclusive techniques have been developed for the rapid formation of highly efficient TiO_2-xN_x nanophotocatalysts, operative and tunable throughout the visible wavelength region, to be used in conjunction with porous silicon hybrid nanopore coated micropores to form novel and efficient solar pumped sensor arrays.