Response Simulation and Extraction of Gas Concentrations for Nanostructure Decorated Nano-/Microporous Silicon Interfaces

Sensor and microreactor technology plays a major role in the detection, monitoring, and transformation of materials at interfaces.  We study the dynamics of a matrix of reversible interactions of gas analytes with the majority charge carriers of nanostructure modified extrinsic semiconductor interfaces.  Nanostructures are deposited on highly sensitive surface layers, created by forming an array of nanopore-coated micropores on p- or n- type silicon semiconductors.  The balance of physisorption and chemisorption of the interacting gas analyte on the porous silicon interface is achieved by following the tenants of the developing inverse hard and soft acid/base (IHSAB) interaction model to select metal oxide nanostructures for deposition.  These electronically independent metal oxide catalyst sites are readily modified through in-situ nitridation and sulfidation to create a broad sensing matrix. The resulting relative sensor responses of the modified interfaces to gas analytes are explained by the IHSAB interaction model, rather than simply by a shift in system basicity.  This expanded matrix of observed sensitivities can then be used to predict the relative response of the interface to a variety of gas phase analytes, as well as direct the choice of porous silicon interface modification for enhanced reversible chemical sensing and electron transduction, in the absence of significant chemical bond formation.  The characterization of multiple gas detection, under the guiding model of the IHSAB concept, describes the synergism of two or more analytes simultaneously interacting with an extrinsic semiconductor interface.  We are now extending the application of the porous silicon sensors to the identification of organic solvents by measuring impedance.  Through the use of an equivalent circuit model, we can explore the physical changes of the porous silicon sensor after metal oxide nanostructure depositions and exposure to various organic solvents.