Nanostructure‐Directed Physisorption vs Chemisorption at Semiconductor Interfaces: The Inverse of the HSAB Concept

Abstract

A concept, complementary to that of hard and soft acid-base interactions (HSAB-dominant chemisorption) and consistent with dominant physisorption to a semiconductor interface, is presented. We create a matrix of sensitivities and interactions with several basic gases. The concept, based on the reversible interaction of hard-acid surfaces with soft bases, hard-base surfaces with soft acids, or vice versa, corresponds 1) to the inverse of the HSAB concept and 2) to the selection of a combination of semiconductor interface and analyte materials, which can be used to direct a physisorbed vs chemisorbed interaction. The technology, implemented on nanopore coated porous silicon micropores, results in the coupling of acid-base chemistry with the depletion or enhancement of majority carriers in an extrinsic semiconductor. Using the inverse-HSAB (IHSAB) concept, significant and predictable changes in interface sensitivity for a variety of gases can be implemented. Nanostructured metal oxide particle depositions provide selectivity and complement a highly efficient electrical contact to a porous silicon nanopore covered microporous interface. The application of small quantities (much less than a monolayer) of nanostructured metals, metal oxides, and catalysts which focus the physisorbtive and chemisorbtive interactions of the interface, can be made to create a range of notably higher sensitivities for reversible physisorption. This is exemplified by an approach to reversible, sensitive, and selective interface responses. Nanostructured metal oxides developed from electroless gold (Au(x)O), tin (SnO(2)), copper (Cu(x)O), and nickel (NiO) depositions, nanoalumina, and nanotitania are used to demonstrate the IHSAB concept and provide for the detection of gases, including NH(3), PH(3), CO, NO, and H(2)S, in an array-based format to the sub-ppm level.

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

“…[5] The IHSAB concept facilitates designed, highly variable, surface interactions using a diversity of nanostructured fractional oxide depositions that act as antennas to focus the nature of the surface-interface interactions while minimizing the chemical interaction of an acidic or basic analyte with the semiconductor interface. These interactions are understood in terms of electron transfer to (base) or from (acid) the surface of an extrinsic semiconductor, [2] which responds by exhibiting measurable and readily understood changes in conductivity. The concept is applicable to both p-and n-type semiconductors, both of which are ideal for integration with CMOS (complementary metal oxide semiconductor) circuits to transduction interfaces.…”

“…In contrast, the driving principle to promote physisorption represents the inverse (IHSAB) of that necessary to form strong chemical bonds. [2] The driving force is manifest through the interactions 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.…”

“…Here, we expand the correlation of the tenets of acid/base interaction and the properties of extrinsic semiconductors [2][3][4] to encompass n-type systems. We deal here with Lewis acids and bases.…”

“…[1] We have outlined [2] an approach to "nanostructure-directed physisorption versus chemisorption" based on the nanostructure modification of highly sensitive surface layers created utilizing a hybrid nanopore-covered microporous array formed on p-type silicon. Here, we expand the correlation of the tenets of acid/base interaction and the properties of extrinsic semiconductors [2][3][4] to encompass n-type systems.…”

Nanostructure directed interfaces created from nanoparticle island sites deposited to microporous arrays and forming sensor platforms

“…The selective response to each gas is based upon IHSAB theory [2,7,35,67]. A number of papers review the capabilities of porous silicon (PS) sensors [35,47,67,68].…”