Optical orientation and shifting of a single multiwalled carbon nanotube

The orientation and shifting of individual carbon nanotubes are extremely important in the assembly of building blocks of nanodevices and in the development of one-dimensional materials for interdisciplinary applications. Here, we report an optical method that is capable of producing the controlled orientation and targeted shifting of single multiwalled carbon nanotubes (MWCNTs) using an optical-fiber nanotip. In a demonstration of this technique, a single MWCNT with an outer diameter of 50 nm and a length of 0.9 µm was first trapped by the nanotip using a laser beam with a wavelength of 980 nm and was then oriented and shifted along the nanotip axis as a result of the interaction of the MWCNT with the optical field output by the nanotip. Various optical powers were applied to characterize the orientation and shifting performance. The orientation and shifting of MWCNTs of various sizes were also demonstrated. The position and orientation of carbon nanotubes in suspension can be controlled using light from an optical fibre with a nanoscale tip. Hongbao Xin and Baojun Li of Sun Yat-Sen University, China, heated and pulled an optical fibre to create a tapered shape, which was then cleaved to form a nanotip about 200 nm in diameter. When 980 nm near-infrared light was launched into the fibre with a power greater than 40 mW, the resulting optical forces were sufficient to overcome Brownian motion and perform trapping and manipulation. In particular, the position of an individual carbon nanotube could be shifted along the fibre axis, and an optically induced torque could realign its orientation. Such optical control could prove useful for high-precision fabrication of carbon–nanotube assemblies.