The use of metal-oxide nanowires (NWs) for sensing applications has become a highly active area of research in recent years as the high surface to volume ratio of NWs promises increased sensitivity to a target species. There are many challenges to NW sensing. Important considerations include the problem of device formation using cylindrical NWs and sensor selectivity, sensitivity, stability.
High yield fabrication of NW devices and sensors requires alignment of the NWs to previously patterned lithographic features. In this work, directed growth and integration of ZnO nanobridge devices into an electrically accessible three-terminal device structure was achieved using photolithographically pre-patterned carbonized photoresist (C-PR) without the use of a metal catalyst, seed layer, or "pick and place". Electrical measurements of three-terminal field effect NW devices indicate bottom gate modulation of the conductivity of the n-type channel and Schottky type contact between the C-PR and the ZnO nanobridges. We demonstrate that these devices exhibit good ultraviolet (UV) sensitivity and gas phase sensitivity to O2 and humidity.
Device performance can be improved by means of surface functionalization. The selectivity of the device, and reduction of associated false positives can be achieved by variations in the end of a tethered chemical group. In this implementation, all device structures, and the primary levels of functionalization would be constant across a large area. By altering the end group of the chemical bonding structure, multiple detection signals could be monitored and depending on the number of "1" signals (species has been detected) and "0" (no species was detected), the probability that a chemical species is a target molecule (i.e. explosive material) can be determined.