Device Fabrication of Single-Walled Carbon Nanotube Composites for Electronic Applications

Alternative Title
Chang Jingbo
Chang, Jingbo
Alternative Author(s)
Chang Jingbo
Jae-Ho Kim
일반대학원 분자과학기술학과
The Graduate School, Ajou University
Publication Year
Alternative Abstract
1. We introduced the general background for understanding importance of SWNT emerging applications based on the unique properties of pristine as well as functionalized carbon nanotubes (CNTs). Fabrication, purification, dispersion and applications of caron nanotubes have been demonstrated. Hence, it is impossible to cover previous results, noteworthy works and future real applications. 2. For UV sensor and solar cell applications, ZnO/SWNTs heterostructures have been fabricated at a high density on well-aligned SWNTs by a chemical vapor deposition (CVD) method. Three kinds of novel morphologies, including nanorods, nanoawls and nanonails, were fabricated. Through increasing the lengths of ZnO nanorods, the quenching of an emission peak appears and its intensity increases. This mechanism of photoinduced charge separation and charge transport in a semiconductor ZnO/SWNTs is based on composite heterostructures. It might be possible for these to have applications in photoelectronic devices, such as solar cell, because SWNTs have electron storage property and ZnO/SWNTs as the composite system can transfer electron from ZnO to SWNTs based on different Fermi levels. For further design of novel ZnO/SWNTs architectures, we fabricated aligned ZnO nanorods on the SWNT patterns by CVD without any catalyst. The presence of SWNT patterns can provide scaffolds to selectively grow ZnO nanorods because of electrostatic interaction and lattice match. Photoactive materials consisting of ZnO/SWNTs heterojunctions targeted for optoelectronic applications are investigated in term of photoresponse and photovoltaic effects. The devices based on SWNT/ZnO heterojunction films are fabricated by two step processes: first, a well aligned SWNT monolayer is deposited on an oxide substrate by the Langmuir-Blodgett (LB) technique; then a ZnO film prepared by filtration of ZnO nanowire solution is transferred onto the SWNT film to form SWNT/ZnO junctions. The SWNT/ZnO heterojunction demonstrates faster photoresponse time (2.75 s) up to 18 times and photovoltaic efficiency (1.33 nA) up to 4 times higher than that of only ZnO device. Furthermore, the mechanisms of UV sensitivity enhancement and photovoltaic effects are explained according to the high electron mobility in the SWNT/ZnO heterojunctions. 3. In particular, rational design of nanostructures for desired applications is a key challenge in micro/nanoelectromechanical systems, such as optoelectronic devices and field emitters. Uniform and ordered pyramidal zinc sulfide (ZnS) nanostructure arrays have been fabricated on the SWNT films by chemical vapor deposition without using any metal catalyst. The control of interspatial distance between ZnS nanostructures was achieved by creation of selective growth on the SWNTs in the void with the assistance of a close packed silica particle monolayer as a template. Morphology control of nanostructures plays an important role in the high efficiency of field emission (FE) because of the strong correlation between shapes and functionalities of nanostructures. ZnS nanorod arrays show lower turn-on voltage (3.23 V/μm) and threshold voltage (3.75 V/μm) than that of ZnS pyramids. Comparatively, pyramid nanostructures demonstrate higher stability and FE current density (243.6 μAcm-2 at a macroscopic field of 5.0 Vμm-1). For determination of molecular structure and electronic band structure of SWNTs, surface-enhanced Raman spectroscopy (SERS), which typically employs the strong surface plasmon resonance (SPR), has been used. ZnS nanoparticles anchored on the SWNTs were fabricated by CVD method. The CVD method shows no selectivity for growth of ZnS nanoparticles on types and defects of the SWNTs, and thus ensures the uniform decoration of all SWNTs on the substrate. ZnS nanoparticles with a diameter of 10 nm were decorated on the SWNTs surface with an interparticle distance of about 20 nm. This method provides the possibility to realize the optimal configurations of ZnS nanoparticles on SWNTs for obtaining SERS of SWNTs. Investigations of mechanism reveal that charge transfer (a small amount of excitation electrons) from ZnS nanoparticles to SWNTs weakly affects Raman intensity, and the coupled surface plasmon resonance formed from plenty of excitation electrons on the surface of ZnS nanoparticles contributes to the strong surface enhancement. 4. The development of solution-processable SWNT/polymer composites for electronic devices is essential for applying to organic electronics technology. We describe a simple technique for direct patterning of SWNT/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)(PEDOT-PSS) composite electrodes in large area on a substrate based on solution transfer process by microcontact printing using poly(dimethyl siloxane) (PDMS) stamps. We observed that the crescent shape of ink filled in PDMS channels is the key factor in this method, which assist the formation of parallel patterns with alignment of nanotubes. The role of the PEDOT-PSS in the composite solution is for assisting formation of consecutive patterns, in which the conductive polymer most likely acts as an “inter tube junction bridge” for holding and connecting nanotubes each other on substrates when solvent is evaporating. Various shapes of SWNT/PEDOT-PSS composite patterns, such as line, circle and square, can be easily fabricated with high pattern fidelity and structural integrity. The single parallel line pattern device exhibits high electrical conductivity (0.75×105 S/m) and electronic stability because of alignment of nanotubes and big-size SWNT bundles (~5 nm). The electromechanical study reveals that the composite patterns show ~1% resistance change along SWNT alignment direction and ~5% resistance change along vertical alignment direction after 200 bend cycles. Our approach provides a facile, low-cost method to pattern transparent conductive SWNT/polymer composite electrodes and demonstrates a novel platform for future integration of conducting SWNT/polymer composite patterns for opto-electronic applications. Detection of chemical agents and biological species using nanostructured materials has shown significant progress in recent years. SWNTs are promising candidates due to their high biocompatibilities and the high sensitivity of their band gap energies to the local dielectric or redox environment. To develop label-free, highly sensitive, and reliable biosensor, herein, we fabricated SWNT pattern based Schottky junction devices to measure conductivity change upon immobilizing protein molecules on the sensing area as the dominant mechanism for device response. For the fabrication of biosensor devices, the SWNT/PEDOT-PSS patterns were treated by UV-O3 to induce the metal-to-semiconductor conversion of SWNTs for transistors to enhance Schottky barrier. The devices with enhanced Schottky barrier have shown high sensitivity with 100 pM detection limit for the specific bindings of proteins. This technique is label-free and could be used to probe various protein pairs in real-time with high sensitivity.

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