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.

We describe a reversible response matrix and the dynamic interplay, as a moderately acidic NO 2 analyte interacts at room temperature with a TiO 2 , SnO x , Cu x O (x = 1,2), and A x O (x 1) metal oxide nanostructure deposited n-type nanopore coated microporous porous silicon (PS) interface. A significant variable response matrix is measured and the dynamic nature of analyte-interface processes characterizing the semiconductor-analyte interaction as NO 2 couples to the decorated semiconductor majority charge carriers. The competition for electrons between NO 2 and the TiO 2 decorated PS interface leads to distinct variations in sensor response as a function of increased TiO 2 concentration and displays a time variance as the extraction of electrons by NO 2 reaches a limiting charge carrier depletion and the decorated PS surface becomes electron withdrawing. This dynamic reversal is also demonstrated by distinct time-dependent PS interface responses to NO 2 and NO where the degree of electron extraction reaches a maximum and is again countered by the depleted n-type PS. Electron depleted SnO x and Au x O treated PS interfaces display a significant remnant effect as the decorated surface can become electron withdrawing for extended periods, forming a stronger acid and extracting electrons from NO 2. Exposure to NH 3 also demonstrates the remnant effects of depletion.We have outlined 1 an approach to "nanostructure directed electron transduction vs. chemisorption" on a sensor/microreactor interface. The fractional deposition of nanostructured metal oxide islands is used to modify sensitive surface layers created utilizing a hybrid nanopore covered microporous matrix formed on "p-or n-type" silicon. The core of this approach is the Inverse Hard / Soft acid / base (Table I) interaction model (IHSAB). This model provides a general approach to optimally design sensors with improved and variable sensitivity and conversion efficiency for a variety of gases, in an array-based format, 5 by correlating the tenants of acid/base interaction and the properties of extrinsic semiconductors. [1][2][3][4] In the present study, we demonstrate not only the variable surface sensitivities that are introduced by the playoff between the untreated extrinsic semiconductor interface and the matrix of fractionally deposited nanostructured islands, but also the dynamic time-dependent response that exemplifies the manner in which these nanostructure decorated interfaces interact with the analyte NO 2 , striking at the heart of the competitive electron dynamics that characterizes these systems.The IHSAB principle correlates with a basis in directed electron transduction with minimized chemisorption,and is in complement to the HSAB principle for hard/soft acid/base interactions first put forth by Pearson et al. 6 and later correlated with density functional theory (DFT) 7,8 and Chemical Reaction Theory 9 by Pearson, Parr, 7,8 Cohen et al. 9 and others. 10 In contrast to the HSAB principle which outlines a means to form strong ionic or covalent b...

Metal-oxide nanostructure-decorated extrinsic semiconductor interfaces modified through in situ nitridation greatly expand the range of sensor interface response. Select metal-oxide sites, deposited to an n-type nanopore-coated microporous interface, direct a dominant electron-transduction process for reversible chemical sensing, which minimizes chemical-bond formation. The oxides are modified to decrease their Lewis acidity through a weak interaction to form metal oxynitride sites. Conductometric and X-ray photoelectron spectroscopy measurements demonstrate that in situ treatment changes the reversible interaction with the analytes NH3 and NO. The sensor range is extended, which creates a distinct new family of responses determined by the Lewis acidity/basicity of a given analyte relative to that of the nanostructures chosen to decorate the interface. The analyte response, broadened in a substantial and predictable way by nitridation, is explained by the recently developing inverse hard/soft acid/base model (IHSAB) of reversible electron transduction.

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Silicon oxide nanostructures which span the range from hydrophilic to hydrophobic have been synthesized. The surface chemistry of these silicon-based nanostructures was analyzed using a combination of x-ray photoelectron spectroscopy, reflectance infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The dominant oxidation state for the nanostructured oxides shifts from an average oxidation state of +III to a combination of +II and +III oxidation states. A correlation of the ability to adsorb water with variations in the surface Si:O ratios was observed showing a transition from hydrophilic to hydrophobic character.