(Invited) Metal Oxide Decorated Porous Silicon Interfaces for Sensor Applications: The Question of Water Interaction, Stability, Platform Diversity, Sensitivity, and Selectivity

摘要

Key parameters of a metal oxide nanostructure modified porous silicon (PSi) template that can affect the development and performance of PSi-based sensors are considered. The importance of pore selection and direct in-situ nitrogen functionalization are discussed. Metal oxide (MO_x, M_xO, x≥1) nanostructured island sites, deposited to select, well defined and reproducible micron sized p and n-type silicon pores (0.7-1.5 μ diameter) provide sensitivity and selectivity as they facilitate rapid "Fickian" analyte diffusion to these highly active sites. The metal oxide nanoparticles are trapped by a thin nanopored wall covering preventing their sintering at elevated temperatures. Variable sensitivities of the metal oxide nanostructured sites are well predicted within the recently developed Inverse Hard/Soft-Acid/Base (IHSAB) model. Ready nitrogen functionalization can further provide the conversion of the decorating metal oxides and an oxidized PSi interface from hydrophilic to hydrophobic character. The decrease in water interaction provides enhanced stability. Selectivity in the measurement of multiple gases is possible with a combination of nanostructure based detection matrices, p and n-type charge carrier variation, time dependent diffusion response, and pore structure influenced sensitivity as the range of variable responses is dominated by the molecular electronic structure of the nanostructured island sites as evaluated using the IHSAB concept. Fast Fourier Transfer techniques (pulsed mode operation) can facilitate low analyte consumption and higher analyte selectivity, and provide the ability to assess false positive signals. A new Fermi distribution-based adsorption isotherm is superior to other isotherms in modeling the PSi system.