Zinc oxide (ZnO) nanobridge-based sensor platform and functionalization for explosive sensing

Original publisher: Adelphi, MD : U.S. Army Research Laboratory, [2011] OCLC Number: (OCoLC)729377347 Subject: Zinc oxide. Excerpt: ... Figure 11. ( a ) Uncoated ZnO NWs ( b ) NWs protected with parylene-A coating. 3.2 Electrical Measurements The current-voltage ( I-V ) characteristics and ultraviolet ( UV ) response of bare and parylene-A coated devices were measured using an Agilent 4155C. A Mineralight 254-nm, 18.4-W lamp was used for UV excitation. I-V characteristics are presented in figure 12 for the same device d ds before and after parylene-A coating. Measurements were taken with and without UV excitation. Another mechanism for the NB UV response, other than just photocarrier generation, is oxygen adsorption and desorption on the surface. When the device is not exposed to UV, the chemisorbed O molecules on the NW surface form a depletion region, decreasing the NW 2 conductivity. The higher dark current for the parylene coated devices ( compared to the dark current for bare NWs ) could be attributed to the displacement of surface oxygen or the reduction in available O adsorption sites because of the coating. UV exposure generates electron-hole 2-pairs within the NWs, the newly created holes discharge O chemisorbed on the surface. This 2 reduces the surface depletion region and the conductivity within the wire is increased ( 25, 26 ). Figure 12. I-V and UV measurements for a bare and parylene-A coated NBs ( 26 ). 7