Abstract
We present a short review and novel approach for the construction of conductometric sensors demonstrating considerably higher sensitivities than traditional metal oxide sensors. Sensor platforms do not require film-based technology, operate at room temperature, and can be obtained without the use of time consuming self-assembly processes. A combined nanopore coated micro-porous array, is deposited with nanostructure directing acidic metal oxide island sites which vary in their Lewis acidity, decorate the micropores, and control an electron transduction process. The interaction of analytes with these island sites varies in a predictable manner and can be modified through in-situ functionalization of their Lewis acidity through formation of the oxynittrides or oxysulfides. Microporesallow rapid Fickian diffusion of the analytes to the active nanostructured island sites whose reversible interaction with the analyte dominates the sensor response. We require only that the island sites be deposited at sufficiently low concentration so as not to interact electronically with each other. Highly accurate repeat placement of the nanostructured island depositions is not required. The nanoporous walls of the microarray act as a phase match for the deposition of a diversity of nanostructures that are selected for deposition from a variety of solution-based sources and the forgiving deposition process requires a minimum of energy consumption and time. Comparisons to a variety of metal oxide systems are considered. Observed sensitivities and the sensor system reversibility can be predicted from the recently developing IHSAB model.
Highlights
Because the requirements for the detection, monitoring, and transformation of environmental constituents are increasing at a significant rate developing sensor interfaces must be sensitive to low level exposures and have fast response times [1]
Conductometric gas sensors can be made to consist of a sensitive interface layer decorated by nanostructure island sites
In some cases thick films are used, doped with noble metals or various nanoshapes designed to effect grain boundaries [13,14,15,16,17,18,19,20]. These metal oxide sensors must be heated to elevated temperatures that range from 100 to 600°C depending on the analyte [13,21,22,23]
Summary
Because the requirements for the detection, monitoring, and transformation of environmental constituents are increasing at a significant rate developing sensor interfaces must be sensitive to low level exposures and have fast response times [1]. We describe a conductometric gas sensor that can be made to consist of an designed sensitive hybrid nano/microporous interface transformed through the introduction of select nanostructures This hybrid structure facilitates rapid Fickian [24,25] diffusion into a microporous framework whose nanoporous wall covering serves to provide a phase match for the selectively deposited nanostructures. The novel sensor core concept forces nanostructure island site directing analyte- interface physisorption (rather than chemisorption) at a doped and metal oxide decorated semiconductor interface and provides a sensitive means of transferring electrons that are detected. Understanding the character of an analyte on an extrinsic semiconductor interface (p or n-type) provides a sensitive and controllable means of transferring electrons that are detected by monitoring the resistivity (conductivity) of the semiconductor This approach is relatively simple to follow and implement [25]. Test devices have been built and characterized providing complementarity with, and a significant superiority to
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