Electron-Beam Patterned Monolayer-Protected Gold Nanoparticle Interface Layers on a Chemiresistor Vapor Sensor Array

Abstract

Use of electron-beam induced crosslinking (EBIX) to pattern films of thiolate-monolayer-protected gold-nanoparticles (MPNs) on chemiresistor (CR) vapor sensors is described. MPNs with alkyl, cyanoalkyl, phenoxyalkyl, and hydroxyfluoroalkyl thiolate tail groups were patterned on integrated arrays of interdigital electrodes using electron doses of 500-750 C=cm 2 . The dc resis- tances of solvent cast films of these MPNs decrease and the baseline-normalized changes in resistance to each of five organic vapors increase to different degrees with increasing electron-beam dose. Relative responses patterns from an array of MPN-coated CR sensors for the test vapors change after EBIX patterning and the diversity of responses is diminished, on average, but it is still projected to be sufficient for the discrimination of most of the individual test vapors and binary mixtures. Results are rationalized in terms of expected changes in ligand structures and film properties following EBIX patterning using known models of electronic conduction, and vapor-induced changes of conduction, through MPN films. The implications of the results for creating arrays of densely packed MPN-coated CRs as detectors for microanalytical systems are considered.Index Terms-Chemiresistor, electron beam, nanoparticle, sensor array, vapor sensor.

Materials and Transducers Toward Selective Wireless Gas Sensing

“…113,439 Nevertheless, it is critical to bring attention early to the possible challenges in materials stability. Some researchers provide information about materials instabilities, 317,326,327,412,440,441 serving the sensing community with important data and knowledge that truly facilitate decision-making in the broad area of sensor research.…”

Characterization of Dense Arrays of Chemiresistor Vapor Sensors with Submicrometer Features and Patterned Nanoparticle Interface Layers

“…8 It was argued in that report that these reductions were due primarily to decreases in δ, with changes in β and ε th being possible secondary factors. Without spectroscopic analysis, the nature of the structural changes in the MPN films cannot be determined definitively.…”

“…9 By incorporating a set of MPNs having different thiolate structures in a CR array, each sensor responds to a different extent to a given vapor and the collective response pattern produced permits the discrimination of individual vapors and the components of simple mixtures. 8,12,13 Use of such an array as the detector in a mesoscale or microscale gas chromatograph (μGC) permits the analysis of complex vapor mixtures at low concentrations; 14 the combination of retention times and array response patterns enhances the reliability of analyte determinations.Since the responses of MPN-coated CRs depend on partitioning of vapors into the MPN film, they vary in proportion to the concentration of vapor in the headspace of the sensor. As a result, the amount of sorbed analyte required to produce a given response is proportional to the volume of the film.…”

“…MPNs were prepared using the single-phase method reported by Rowe et al 20 Thiolate monolayers were derived from n-octanethiol (C8), 4-(phenylethynyl)-benzenethiol (DP-A), 6-phenoxyhexane-1-thiol (OPH), methyl-6-mercaptohexanoate (HME), and 7-hydroxy-7,7-bis(trifluoro-methyl)heptane-1-thiol (HFA). 8 Nanoparticle diameters were determined from TEM images, and range from 3.4 nm (DPA) to 4.7 nm (HME) with relative standard deviations (RSD) of 5À23%. Purified MPNs were dissolved in appropriate solvents (toluene for C8, OPH, and DPA, 2-butanone for HME and HFA) at concentrations of 5À6 mg/mL for storage and deposition.…”

“…The films on all four of the sensors in each mono-MPN array were irradiated prior to rinsing with solvents. Since films of HFA MPNs exhibited resistances that varied widely and were typically too high to measure, 8 this material was omitted from the set of mono-MPN arrays examined.…”