A novel process for the fabrication of ZnO-carbon nanotubes ͑CNT͒ nanocomposites with high uniformity by atomic layer deposition ͑ALD͒ of ZnO on multiwalled carbon nanotubes was reported, and their applications in UV photodetectors were investigated. Two types of photodetectors, p-and n-type, were developed by alternating the ALD reaction cycles. In addition, a schematic model was proposed to explain the p-to n-type conversion of the ZnO-CNTs, which accounts for the amount and surface coverage of ZnO on CNTs.Photodetectors used in the ultraviolet ͑UV͒ region have many applications, including fire prevention, space exploration, and military uses. It is well known that the photon-sensing properties of the metal-oxide-based photodetectors are primarily governed by the oxygen molecule adsorption/desorption behaviors on the metal oxide surface. 1,2 Therefore, constructing a bridge across the gap between surface chemical reactions and efficient electrical signal transduction is a practical method for the fabrication of photodetectors. Recently, combinations of carbon nanotubes ͑CNTs͒ and metal oxides ͑such as SiO 2 , TiO 2 , SnO 2 , and V 2 O 5 ͒ have been attracting considerable attention owing to their superior properties in photocatalyst, lithium battery, and gas sensor applications. [3][4][5][6][7][8][9] ZnO is a multifunctional n-type II-IV semiconducting metal oxide with a wide direct bandgap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature; it has been widely used in applications such as piezoelectronics, solar cells, light-emitting diodes, transparent thin-film transistors, gas sensors, and photodetectors. 1,10-19 It has been reported that ZnO-carbon nanotube ͑CNT͒ nanocomposites exhibit good performance in applications such as electron emitters, nanotransistors, electrochemiluminescence, and sensors because new physical and chemical properties may merge, 20-23 and this might extend the scope of the potential applications of CNTs and cause the ZnO-CNT nanocomposites to be regarded as one of the most promising substances for the fabrication of the nanodevices. Thus far, various processes have been developed to fabricate ZnO-CNT nanocomposites, including electrochemical deposition, 22 pulsed laser deposition, 24 thermal chemical vapor deposition ͑CVD͒, 25,26 covalent coupling, 27 and water-assisted growth. 28 However, the fabrication of ZnO-CNT nanocomposites with the ZnO nanoparticles that have well-controllable sizes and good uniformity remains a challenge.Atomic layer deposition ͑ALD͒ is a CVD technique for the wellcontrolled deposition of the inorganic layers with thicknesses in the nanometer range that has been widely used in the semiconductor industry to induce the growth of high-k dielectric films of the metaloxide-semiconductor field-effect transistors and capacitor layers of dynamic random-access memory. [29][30][31] In addition, the self-limiting gas-solid growth characteristics of the ALD growth facilitate the growth of thin films and ͑or͒ nanoparticles with accurate thicknes...
The emission from ZnO nanorods/poly(3-hexylthiophene) (P3HT) heterostructures with type II band alignment has been investigated. The additional emission due to the formation of the heterojunction around 950 nm has been found and attributed to the type II transition related to the recombination of electrons in conduction band of ZnO and holes in highest occupied molecular orbital band of P3HT. The consistency of excitation power density dependent photoluminescence (PL) spectra with the theoretical prediction offers a firm evidences for the type II transition. In addition, lifetime of P3HT measured by time-resolved PL also strongly supports that the infrared light indeed arises from the type II transition. Our results shown here provide the first direct evidence of the type II band alignment in ZnO nanorods/P3HT heterostructure, which should be very useful for the realization of underpinned mechanism of the developed optoelectronic devices.
Based on the high surface-to-volume ratio of nanorods and high sensitivity of piezoelectric properties of nitride semiconductors, an enzyme-functionalized composite consisting of nanorods and nitride light-emitting devices (LEDs) provides an excellent opportunity for the development of glucose detectors using optical methods. To demonstrate our working principle, a sensing device based on In0.25Ga0.75N/GaN multiple quantum wells and ZnO nanorods has been constructed and exposed to target glucose solutions. The pronounced changes in both emission and Raman scattering spectra under different target glucose concentrations clearly illustrate the feasibility of our newly designed composite for the creation of highly sensitive biosensors with optical detection.
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