ABSTRACT
A novel local vapor transport technique via induction heating is presented to enable selective, localized synthesis and self-assembly of nanowires, providing a simple and fast method for the direct integration of nanowires into functional devices. The single-crystalline zinc oxide (ZnO) nanowires are grown locally across the silicon-on-insulator microelectrodes within minutes, and the enhancement of gas sensing of ZnO nanowires is demonstrated under ultraviolet (UV) illumination at room temperature. Experiments indicate that when suspended nanowires are exposed to UV light, a twelve-fold increase in conductance and a near five-fold improvement in oxygen response are measured. Furthermore, the UV-enhanced transient responses exhibit a two-level photocurrent decay attributed to carrier recombination and oxygen readsorption. As such, the local vapor transport synthesis and UV-enhanced sensing scheme could provide a promising approach for the construction of miniaturized and highly responsive nanowire-based gas sensors.
ABSTRACT
Titanium dioxide (TiO(2)) is one of the most widely studied and important materials for catalysis, photovoltaics, and surface science applications, but the ability to consistently control the relative exposure of higher surface energy facets during synthesis remains challenging. Here, we present the repeatable synthesis of highly reactive, rutile {001} or {101} facets on broad, sword-shaped TiO(2) nanostructures rapidly synthesized in minutes. Growth occurs along planes of lower surface energy, repeatedly yielding nanostructures with large, high energy facets. The quantitative photocatalytic reactivity of the nanoswords, demonstrated by the photoreduction of silver, is over an order of magnitude higher than reference low energy TiO(2){110} substrates. Therefore, the higher surface energy dominated TiO(2) nanoswords are ideal structures for characterizing the physicochemical properties of rutile TiO(2), and may be used to enhance a variety of catalytic, optical, and clean-technology applications.
ABSTRACT
We show both gas pressure and species sensing capabilities based on the electrothermal effect of a multiwalled carbon nanotube (MWCNT). Upon exposure to gaseous environments, the resistance of a heated MWCNT is found to change following the conductive heat-transfer variances of gas molecules. To realize this mechanism, a suspended MWCNT is constructed by synthesis and assembly in localized chemical vapor deposition that is accomplished within seconds via real-time electrical feedback control. Vacuum pressure sensitivity and gas species differentiability are observed and analyzed. Such MWCNT electrothermal sensors are compact, fast and reversible in responses, and fully integratable with microelectronics.
