Self-Assembly Carbon Nanotubes And Their Manipulation With Optical Tweezers

Carbon nanotubes (CNTs) have in recent years attracted increasing interest for their extraordinary physical and chemical characters in nanoscience and nanotechnology. It is a key work to assembly and to align CNTs in assembling CNTs-based nano-electric devices. In this thesis, chemical assembling and physical manipulations of CNTs including multi-walled and single-walled carbon nanotubes (MWNTs, SWNTs) were explored.First, the surface of the SWNTs was chemically modified by function groups such as–COOH, -SH and–COCl. These active chemical groups can make SWNTs to be self-assembled onto the chemically modified surfaces of gold and silicon substrate to form a dandified SWNTs film. Samples were checked by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) and Transmition Electron Microscope (TEM). Repeated experiments showed that most of SWNTs were horizontally not vertically bonded onto the surface of the substrates. The density of the SWNTs film was proportional to the reaction time and concentration of the SWNTs solution. And the density of the SWNTs film also was related to the characters of SWNTs and substrate. Using similar method of chemical self-assembly, we covalently bonded SWNTs with polystyrene nano-spheres (PS), C60 and liposome molecules, which indicate that the chemical function-groups on the chemical etched SWNTs can be used as the basic unites to react with other nano-materials in assembling bio- or gas- sensors.In experiment, we developed a droplet evaporation method to self-assembly SWNTs into different regular patterns including ramified-fractal patterns, ring patterns and fingering patterns on silicon and glass surfaces for the first time. The formations of these patterns were discussed theoretically based on Diffusion-Limited Aggregation (DLA) model and Marangoni Effect.Self-assembly is fitting to process a large amount of CNTs simultaneously,but it is not able to manipulate of individual carbon nanotube bundles (CNTBs) or carbon nanotubes (CNTs). Optical tweezers is a powerful tool to manipulate CNTBs or CNTs. We analyzed the optical trapping of SWNTs in nano-scale using electromagnetic model. We studied two different phenomena of assembling nano-scale SWNTs into a ring pattern by optical tweezers, which were explained by thermal effect of the laser beam. These results indicate that optical tweezers is a powerful tool to manipulate CNTs in nano-scale.In addition, we used optical tweezers to multi-dimensionally manipulate CNTBs including multi-walled and single-walled carbon nanotube bundles (MWNTBs and SWNTBs). CNTB in the optical trap can rotate by itself until its long axis is originated with the propagation direction of the laser beam. By adjusting trapping depth, optical tweezers can trap CNTB with a certain of length vertically or horizontally (the long axial of CNTBs is along or vertical to the propagation direction of the laser beam). The trapped CNTB can be moved to any wanted position in the solution. Fixing of the trapped CNTB can be realized by decreasing the trapping depth to get desired patterns. In order to get more exact controls of origination of the tapped CNTB, we developed three other methods to align CNTB. One is to insert a slide glass between two convex lenses of the beam expander. By adjusting the angle between the glass and the central axial of the laser beam, the slant angle of the trapped CNTB in the optical trap can be adjusted due to the asymmetric power redistribution of the focused laser beam. The second method is to adjust the shape of the focused laser beam from circular shape into line-shape. CNTB can orientate its long axial in the line-shaped optical trap. The arbitrary positioned CNTB can rotate until its long axial is aligned with the line-shaped optical trap. The trapped CNTB in the line-shaped optical trap can be manipulated freely. The third method is to adjust the polarization of the laser into perfect line polarization. The arbitrary positioned CNTB can rotate until its long axial orientate with the polarization direction of the laser beam in the optical trap. Theoretical explanation was given qualitatively. These results about the orientation of CNTBs in the optical trap are meaningful for assembling CNTs into useful nano-scale electronic devices like optical controlled carbon nanotubes tweezers.Finally, rotations of CNTB in the optical trap were also studied in experiment. Because of the absorption of photon energy by CNTB, a temperature lattice field near the optical trap can be formed. The induced solution convection in the focus can lead the trapped CNTB to rotate randomly in some different ways. It is found that the CNTB with a curved structure can be rotated if it is vertical trapped. The curved structure provides the rotation torque for rotation. Rotation direction depends on the exact curved structure not the solution convection. If MWNTB is vertically trapped in the circular polarized optical trap, it can be rotated due to the adsorption of the photon momentum. These results will promote the applications of CNTs in micro-mechanics.