| Summary: | 博士 === 國立交通大學 === 機械工程系所 === 95 === In the semiconductor industry, silicon devices are being scaled down to smaller dimensions. Carbon nanotubes (CNT) are of particular interest for future nanoelectronic applications, because of their high aspect ratio, small radius of curvature, high chemical stability, and large mechanical strength. Plasma surface treatments are promising techniques in the design and development of new materials because surfaces can be modified without altering the bulk properties of the material. Accordingly, more sensitive surface analysis approaches are being used to obtain more precise information regarding the plasma-treated surface chemistry. An experiment was conducted to elucidated pretreatment, the adsorption (desorption) in plasma surface treatment, the electronic conduction property associated with surface treatments, and the mechanical characteristics of CNTs.
In the pretreatment, CNTs were synthesized by microwave plasma chemical vapor deposition (MPCVD) on Ni/TiN/Si and Ni/TaN/Si systems. The effect of the pretreatment period and flow rate on the growing characteristics of the Ni catalyst layer and the properties of the CNTs was examined. The mechanical response of particle aggregates to the compression of substrates is emphasized. The improvement of the surface performance of the catalyst is using H2 plasma is suggested. Therefore, small agglomerates of catalyst nanoparticles formed on TiN buffer substrates, helping to elucidate the mechanical properties of relatively large pretreated nanoparticles. The deformation behavior of the agglomerates under loaded control-mode nanoindentation was investigated. Nanoparticle testing demonstrated a lower modulus (from 238.9±8.4 to 176.2±6.1 GPa) and hardness (from 17.2±1.6 to 11±0.8 GPa) than those of the Ni film. The effects of the H2 plasma flow rate during pretreatment on the synthesis of CNTs using an MPCVD system are also studied. Raman spectroscopy was employed with a change-coupled detector is used to elucidate the effect of the flow rate on the intensity ratio of G and D bands (ID/IG), which in turn yields the amounts of amorphous carbon and carbonaceous particles in the CNTs.
The effect of CF4/O2 plasma on the surface performance of CNTs in the post-treatment is elucidated. SEM and TEM studies reveal changes in the surface morphologies of CNTs that were exposed to the CF4/O2 plasma. Additionally, the ID/IG ratios reveal that chemical treatment with CF4/O2 plasma for 2 min reduces the degree of disorder. After 10 min, however, the degree of disorder in CNTs is increased. FTIR absorption spectra include peaks that correspond to C-O and C-F stretching vibrations. The TDS results yield adsorption information. XPS datum reveals fluorination in CF4/O2 plasma-treated CNTs and the absence of a significant of physisorbtion on CNTs. This result shows that adding oxygen to the plasma increases the decomposition efficiency.
A CNT bridge on SiO2 that is patterned photolithographically in an electronic device is described. The CNTs grow laterally to the substrate over a Ta vertical growth barrier and connect to the side of the electrode pad. The CF4/O2 post-treated has a higher current-voltage curve than the surface-modified. The typical Schottky contact characteristics at room temperature are discussed. The surface of the CNT interacts with the surrounding plasma, breaking C-C bonds and creating active sites to bond the functional groups (fluorination). C-F binding in the amorphous carbon can be reduced by modifying the CNTs.
A CNT film was studied using nanoindentation equipment (Berkovitch indenter) by varying the loading force. CNT films exhibit features that are associated with toughening against cracks caused by indentation. The quantitative indentation force is utilized to determine the CNTs axial modulus, depending on the Raman shift. The ID/IG ratios of the CNTs films are associated with an increase in the force. Such features follow in part from the fact that CNTs films generally contain some disordered regions.
The experiment on plasma treatments yields information on the formation of the catalyst, the adsorption (desorption) capacity, the electronic conduction and the mechanical behavior in CNTs.
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