| Carbon nanotubes (CNTs) are of great interest in today's research, and more and more researchers are getting interested in what happens when they interact with photons. While a light of certain intensity (usually a laser beam) shining on a carbon nanotube composition, usually two kinds of physical responses will be observed: photoconductivity and photomechanical actuation. Though photoconductivity of single carbon nanotube and thin CNT bundles has been studied thoroughly, photoconductivity of macro scale carbon nanotube devices is expected to have properties different from a single nanotube or thin nanotube bundles, since an interaction of electrodes and nanotube devices is going to play a significant role in the generation of photoconductivity. A study of photoconductivity of unaligned carbon nanotube films has been conducted by our group previously, which has proved some of our expectation of the differences. However, due to fabrication difficulty and structure fragility, the experiment and results about photoconductivity of aligned carbon nanotube fibers introduced in this master's thesis have never been reported before. This novel study will not only further reveal the differences of photoconductivity between macro scale carbon nanotube devices and a single nanotube, but also prove our expectation of the unique properties of aligned carbon nanotube fibers.;In this thesis, the author will describe a fabrication procedure for partially aligned carbon nanotube fibers and the assembly step for the samples, then reason the experimental details. After that, the result will be introduced and labored. For the photocurrent of aligned CNT fibers, a "position effect", a dependency for the frequency of incident light pulse, and a linear photocurrent-intensity curve is observed, which are similar to the responses of unaligned films. But meanwhile, unique properties such as a fast dynamic response, an even faster dynamic response with "flood light exposure", a higher quantum efficiency and a dependency on the polarization of incident light will all be revealed.;These results fit in our previous prediction of the electric mechanism of the photoconductivity of aligned CNT fibers, which is based on electron-hole pair generation and subsequent separation by both the built-in voltage at the electrode-fiber contact and the electrical fields induced by external voltage source and incident light. These results have also demonstrated that the molecular desorption mechanism may not be the dominant origin of the photoconductivity, since the dynamic response we observed is much faster than this process.;Another contribution of this thesis is that we obtained a relatively large quantum efficiency (∼6.4%) using partially aligned carbon nanotube fibers. This demonstrates that carbon nanotubes can be utilized in potential energy conversion devices as photo-detectors or solar cells, which together with the photomechanical applications of CNT structures is suggesting a promising future in research and engineering regarding carbon nanotubes. |
