탄소나노튜브와 나노복합체의 광반응 특성 연구와 미래 나노소자에의 응용

Abstract

Carbon nanotube (CNTs), due to excellent electrical and optical properties and chemical stability, has been experimentally researched by many groups for application at various field such as sensor, solar cell and display. For potential application of CNTs, an investigation on their fundamental characteristics on CNTs should be conducted along with application of CNTs. To progress of investigating on characteristics of CNTs, three-dimensional (3-D) CNTs and CNTs based nanomaterial/composite were fabricated and applied for future nanodevice. Chapter I introduces a brief history of research on the basic properties of carbon nanotubes and the objective of this research. Chapter II includes a fabrication of three-dimensional SWNT (3-D SWNT) networks, and a study on infrared (IR) photoresponse for 3-D SWNT networks and on applications of them in future nanodevices. In a study on infrared (IR) photoresponse for SWNTs, two fundamental models have been formulated to explain the origin of the photoresponse in the electrical conductivity of SWNT films for an illumination of infrared (IR): the interband transition model (band model) and the bolometric model. However, the photoresponse of SWNTs has generated considerable debate, with various studies leading to different interpretations of the origin of photoconductivity. 3-D SWNT networks suspended between SiO2 pillars grown on flat quartz were fabricated to suggest the origin of the photoresponse of SWNTs. From the measurements of photoconductivity of our samples under three conditions using a continuous Xe lamp, one IR laser pulse, and a repeated IR laser pulse, it was demonstrated that two response modes coexist. And, gas sensors and field emission device were fabricated and compared with devices based on SWNTs film to confirm structural benefit on applications of 3-D SWNTs in future nanodevices. Chapter III describes the applications of CNTs and CNTs based nanomaterial/composite. First, conductivity properties of SWNTs upon the encapsulation of organic materials were investigated. N-type and p-type doped SWNTs were formed via encapsulation of tetrathiafulvalene (TTF) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) inside SWNTs, respectively. Raman, near-infrared and X-ray photoelectron spectrometer were used to confirm encapsulation. From measurements of the current-voltage curves in a vacuum chamber, it was revealed that current of TTF-encapsulated SWNT decreased and TCNQ-encapsulated SWNT increased comparing with that of pristine SWNT. This was resulted from electron-donating character for TTF and electron-withdrawing character for TCNQ inside SWNTs, presenting a possibility of modulating doping level of SWNTs. Second, a study on the wettability of SWNTs film synthesized on flat and textured Si substrates was conducted. The contact angle of water was measured on SWNT films formed on flat and textured Si substrates. The latter consisted of nanoscale SWNTs and microscale Si, and they showed superhydrophobic properties in which the water contact angle was around 161°. A direct surface treatment to that sample increased the contact angle to 174°. The reversible wettability of the SWNT film formed on the textured Si substrate was confirmed through the oxidation process using an acid mixture of nitric and sulfuric acids and a successive reduction procedure via heating treatment in an NH3 environment. Third, the application of SWNTs on In2S3/In2O3 photoelectrochemical cells (PECs) was reported. Simple solution methods, such as spray-coating and chemical bath deposition, were used to assemble each layer in the PECs. Pristine SWNTs, semiconducting SWNTs and metallic SWNTs were applied to the PECs, and their solar performances, incident photon to charge carrier efficiency, and electro-impedance spectra were measured. Field emission is also measured to explain the enhanced electric field of each cell. Chapter IV finally show a possibility of CNTs and CNTs based nanomaterial/composite as the next generation structures for investigation on their fundamental characteristics and improved application in future nanodevices.