Chemical sensing with lithium molybdenum selenide nanowire films.

摘要

In this dissertation, we show that thin films of LiMo3Se 3 nanowires undergo a change of their electrical resistance when exposed to vapors of solvents. The resistance changes depend on the thickness of the films, on the polarity of the analytes and on their concentration. Our results suggest that LiMo3Se3 could be employed in new types of sensitive chemical sensors.; In order to study the mechanism of the sensors, QCM (quartz crystal microbalance) and AFM (atomic force microscopy) measurements were performed on nanowire films. These measurements showed that the temporal and steady state resistance changes of the films are time dependent following the adsorption of molecules on the nanowire films. AFM profile scans demonstrate that analyte vapors cause a swelling of the films. The positive response in resistance of nanowire films when exposed to solvent vapors can be explained by assuming that coating of the nanowire bundles with analyte molecules reduces the interwire-charge transport in the films.; Two approaches were used to tailor the selectivity of the LiMo3 Se3 nanowire film sensor towards polar or non polar solvent vapors, one of which is by adding Lil receptors and the other is by replacing Li cations with quartery ammonium ions. Lithium iodide increases the response of the films to both polar and non-polar analytes. CTA (Cetyltrimethylammonium) increases the response of the films to non-polar analytes but reduces the response to polar analytes.; Efforts to fabricate LiMo3Se3 nanowire based sensors that can be readily applied to aqueous medium were also made. We systematically investigated the sensitivity and selectivity of LiMo3Se 3 nanowire sensors, a potential ISFET (Ion Selective Field Effect Transistor) device, to several metal ions. The evaluation shows that LiMo3Se 3 nanowire films can respond to metal cations with a positive resistance change.; Finally, we fabricated a Au-LiMo3Se3 nanowire composite-based sensor that can be readily used in aqueous medium. The detection limit for L-cysteine can be as low as 1-10 ppm. In these sensors, LiMo3Se 3 nanowires seem to mainly act as signal transducers, while gold seems to serve as a receptor to L-cysteine.