RESUMO
The inverted resistance method was used in this study to extend the bulk resistivity of [Formula: see text] to a regime where the surface conduction overwhelms the bulk. Remarkably, regardless of the large off-stoichiometric growth conditions (inducing disorder by samarium vacancies, boron interstitials, etc.), the bulk resistivity shows an intrinsic thermally activated behavior that changes â¼7-10 orders of magnitude, suggesting that [Formula: see text] is an ideal insulator that is immune to disorder.
Assuntos
Compostos de Boro/química , Samário/química , Condutividade Elétrica , Condutividade TérmicaRESUMO
The performance of arrays of small, densely integrated chemiresistor (CR) vapor sensors with electron-beam patterned interface layers of thiolate-monolayer-protected gold nanoparticles (MPNs) is explored. Each CR in the array consists of a 100-µm(2) interdigital electrode separated from adjacent devices by 4 µm. Initial studies involved four separate arrays, each containing four CRs coated with one of four different MPNs, which were calibrated with five vapors before and after MPN-film patterning. MPNs derived from n-octanethiol (C8), 4-(phenylethynyl)-benzenethiol (DPA), 6-phenoxyhexane-1-thiol (OPH), and methyl-6-mercaptohexanoate (HME) were tested. Parallel calibrations of MPN-coated thickness-shear-mode resonators (TSMR) were used to derive partition coefficients of unpatterned films and to assess transducer-dependent factors affecting responses. A 600-µm(2) 4-CR array with four different patterned MPN interface layers, in which the MPN derived from 7-hydroxy-7,7-bis(trifluoro-methyl)heptane-1-thiol (HFA) was substituted for HME, was then characterized. This is the smallest multi-MPN array yet reported. Reductions in the diversity of the collective response patterns are observed with the patterned films, but projected vapor discrimination rates remain high. The use of such arrays as ultralow-dead-volume detectors in microscale gas chromatographic analyzers is discussed.
