Nanostructure-directed chemical sensing: The IHSAB principle and the dynamics of acid/base-interface interaction

Abstract

SummaryNanostructure-decorated n-type semiconductor interfaces are studied in order to develop chemical sensing with nanostructured materials. We couple the tenets of acid/base chemistry with the majority charge carriers of an extrinsic semiconductor. Nanostructured islands are deposited in a process that does not require self-assembly in order to direct a dominant electron-transduction process that forms the basis for reversible chemical sensing in the absence of chemical-bond formation. Gaseous analyte interactions on a metal-oxide-decorated n-type porous silicon interface show a dynamic electron transduction to and from the interface depending upon the relative strength of the gas and metal oxides. The dynamic interaction of NO with TiO2, SnO2, NiO, CuxO, and AuxO (x >> 1), in order of decreasing acidity, demonstrates this effect. Interactions with the metal-oxide-decorated interface can be modified by the in situ nitridation of the oxide nanoparticles, enhancing the basicity of the decorated interface. This process changes the interaction of the interface with the analyte. The observed change to the more basic oxinitrides does not represent a simple increase in surface basicity but appears to involve a change in molecular electronic structure, which is well explained by using the recently developed IHSAB model. The optical pumping of a TiO2 and TiO2− xNx decorated interface demonstrates a significant enhancement in the ability to sense NH3 and NO2. Comparisons to traditional metal-oxide sensors are also discussed.

Light Enhanced Electron Transduction and Amplified Sensing at a Nanostructure Modified Semiconductor Interface

“…The conversion to TiO 2‐ x N x creates a more basic site that does not compete nearly as effectively with the acidic NO 2 for electrons. In addition, the more basic TiO 2‐ x N x fractional deposition contributes electrons more effectively than can TiO 2 4, 8, 11. When the decorated sensor is exposed to a low level of “white light”, its enhanced basicity, which also translates to visible light absorption, results in an enhanced electron transfer from TiO 2‐ x N x to NO 2 .…”

Nanostructure-Directed Chemical Sensing: The IHSAB Principle and the Effect of Nitrogen and Sulfur Functionalization on Metal Oxide Decorated Interface Response

“…In support of this argument, initial results obtained for the nitridation of NiO lead to a decrease in response for NO; however, as would be predicted by the IHSAB model, the reversible response for interaction with NH 3 increases [ 16 ]. The simplicity of the in situ nitridation process [ 10 , 16 , 18 , 19 , 20 ] can provide an important means of enhancing interface modification and selection.…”

“…Within this framework, the creation of novel, highly active, micro-/nano-structured porous extrinsic semiconductor interfaces, their ability to provide readily accessible significant light harvesting surface areas [ 7 ] and their ability to be transformed with select nanostructure interactions [ 1 , 2 , 3 ] provide new avenues for sensing based on energy transfer and transduction [ 8 ]. Nanopore coated, microporous arrays not only enable enhanced Fickian diffusion [ 9 ] to active sites, but also, the nanopores provide a “phase matching” region with which modifying nanostructured materials can be made to interact in a controlled manner to promote a distinct and controllable, wide ranging and variable interface sensitivity [ 10 ].…”

“…As primarily acidic metal oxides, the nanostructures focus the interaction and coupling with the majority charge carrier concentration of an extrinsic p - or n -type semiconductor, directing an electron transduction process. We have now found that these metal oxide nanostructures can be readily functionalized, in situ , to create what appear to be metal oxynitride [ 10 , 12 ] and oxysulfide [ 13 ] sites. The semiconductor interfaces can also be modified, as they are treated with nanostructured photocatalysts to provide a light-enhanced sensing efficiency.…”

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

“…Second, once deposited, the nanostructures can be readily functionalized, in-situ, predictably changing their interaction with a given analyte. This is exemplified as we convert the metal oxides to oxynitrides or as we functionalize the nanostructured metal oxides with S-H z (CH x ) y (z=0,1) groups [9,31,33,34]. The important consideration is that the nanostructured sites are easily modified.…”