Nanostructure-Driven Analyte-Interface Electron Transduction: A General Approach to Sensor and Microreactor Design

A concept describing the nanostructure-directed dynamics of acid/base interaction and the balance between physisorption and chemisorption on an extrinsic semiconductor interface is evaluated and compared for n- and p-type semiconductors. The inverse hard/soft acid/base (IHSAB) concept, as it complements the HSAB concept, defines the nature of a dominant physisorption behavior and enables the creation of a matrix of controllable interactions. The technology results in the coupling of Lewis acid/base chemistry with the extrinsic semiconductor majority carriers. Nanoporous silicon layers facilitate the application of nanostructured metal/metal oxides, which provide sensitivity and selectivity for the modified interface. Applied fractional depositions can produce a dominant reversible physisorptive (sensors) or chemisorptive (microreactors) interaction at the semiconductor interface as the nanostructures act as antennas to focus the interaction. The dynamic natures of n- and p-type silicon are evaluated and compared, by focusing on the controlled manipulation of these semiconductors as they are modified with nanostructures and interact with the gas-phase analytes. The observed semiconductor responses correlate well with the temperature dependence of the extrinsic semiconductor, the population of the donor or acceptor levels, and the inherent mobilities of electrons. The response of the modified n-type semiconductors is found to exceed that of comparable p-type systems. The IHSAB concept can be extended to assess the properties of several additional semiconductor interfaces including nanowires. The results obtained not only pertain to sensor and microreactor array design, but also suggest the importance of the dynamic changes created, as the majority charge-carrier concentrations are manipulated and the Fermi energies are modified through chemical interaction.