Rapid Anisotropic Photoconductive Response of ZnO-Coated Aligned Carbon Nanotube Sheets

Abstract

We investigate the rapid and anisotropic UV-induced photoconductive response of hybrid thin films comprising zinc oxide (ZnO) nanowires (NWs) directly grown on horizontally aligned (HA-) carbon nanotube (CNT) sheets. The films exhibit anisotropic photoconductivity; along the CNTs, conductivity is dominated by the CNTs and the photoconductive gain is lower, whereas perpendicular to the CNTs the photoconductive gain is higher because transport is influenced by ZnO nanoclusters bridging CNT-CNT contacts. Because of the distributed electrical contact provided by the large number of ZnO NWs on top of the HACNT film, this hybrid nanoarchitecture has a significantly greater photocurrent than reported for single ZnO NW-based devices at comparable UV illumination intensity. Moreover, the hybrid architecture where a thin basal film of ZnO ohmically contacts metallic CNTs enables rapid transport of photogenerated electrons from ZnO to CNTs, resulting in sub-second photoresponse upon pulsed illumination. The built-in potential generated across ZnO-CNT heterojunctions competes with the externally applied bias to control the photocurrent amplitude and direction. By tuning the anisotropic conductivity of the CNT network and the morphology of the ZnO or potentially other nanostructured coatings, this material architecture may be engineered in the future to realize high-performance optical and chemical sensors.

Durable and scalable icephobic surfaces: similarities and distinctions from superhydrophobic surfaces

“…171 The radicals formed subsequently initiate chain-growth polymerization of the monomers adsorbed at the surface of the substrate. Among the large number of monomers investigated, perfluorodecylacrylate (PFDA), 166,[172][173][174] heptadecafluorodecylmethacrylate (HFDMA), 175 perfluoroalkylethylmethacrylate (PFEMA) 157 and hexafluoropropylene oxide (HFPO) 169,170 are particularly important for development of low surface energy polymers.…”

“…169 Hydrophobization of the CNT forest induces a WCA increase from 841 to 1611, while the only noticeable CNT morphology change was an increase in diameter along their 2 mm height. The iCVD of fluorocarbon polymers has also been successfully applied to various porous substrates, including nonwoven fabrics 157,174 or mesh and filter paper, 175 to confer on them superhydrophobic properties with no alteration of their porosity. More impressively, iCVD of PFDA has also been reported to uniformly coat the nanometer size pores of a 10 mm thick membrane.…”

Energy-Efficient Hydrogenated Zinc Oxide Nanoflakes for High-Performance Self-Powered Ultraviolet Photodetector

“…Recently, it has been realized that heterostructure system induce internal built-in electric field, which plays a significant role in generating an internal driving force to prevent the recombination of photo induced electron-hole pairs. [2][3][4][5][6][7] Thus, these photodetectors are commonly known as "self-powered", which has recently drawn a great research attention. 2,4 Among UV photodetector materials, zinc oxide (ZnO) is one of the most investigated materials that includes characteristics such as wide direct band gap (3.37 eV), large exciton binding energy (60 meV) at room temperature, piezoelectricity and pyroelectricity etc.…”

Significant Enhancement of Infrared Photodetector Sensitivity Using a Semiconducting Single‐Walled Carbon Nanotube/C60 Phototransistor

“…Improvements in photosensitivity have been made by attaching polymers to enhance exciton dissociation, suggesting that photoinduced carrier collection renders the device more sensitive than utilizing bolometric effect. Other groups have fabricated photodetectors by combining SWNTs with other nanostructures . However, these devices have generally used SWNTs as a carrier transporting layer rather than as an active light absorbing/carrier generating layer.…”