Nanotube surface arrays: Weaving, bending, and assembling on patterned silicon

The fabrication of ordered arrays of oriented and bent carbon nanotube on a patterned silicon surface with a micron scale spacing extending over millimeter size surface areas, was presented. A combination of multistep purification and oxidation procedures were used to generate bundles containing 3-20 nanotubes of high purity. The patterned surface was composed of alternating hydrophilic and hydrophobic stripes. The results suggest that the patterning is controlled by the hydrodynamic behavior of a fluid front and orientation and bending mechanisms are facilitated by the pinned carbon nanotubes trapped by the liquid-solid-vapor contact line.open849

High-resolution Raman microscopy of curled carbon nanotubes

The use of confocal Raman imaging spectroscopy and atomic force microscopy for identifying conditions of carbon nanotubes with bent nanotube bundles in the bent state was described. It was found that the tangential G mode on Raman spectra systemically shifts downward upon nanotube bending. The frequency shifts observed in the nanotubes were due to tensile strain of the bending nanotube arrays, which resulted in the loosening of C-C bonds in the outer walls. It was speculated that the frequency shift in Raman spectra was used for fast monitoring of the bending state of the standing carbon nanotube in gas and fluid flow nanosensors.open282

Selective Deposition and Alignment of Single-Walled Carbon Nanotubes Assisted by Dielectrophoresis: From Thin Films to Individual Nanotubes

Dielectrophoresis has been used in the controlled deposition of single-walled carbon nanotubes (SWNTs) with the focus on the alignment of nanotube thin films and their applications in the last decade. In this paper, we extend the research from the selective deposition of SWNT thin films to the alignment of small nanotube bundles and individual nanotubes. Electrodes with “teeth”-like patterns are fabricated to study the influence of the electrode width on the deposition and alignment of SWNTs. The entire fabrication process is compatible with optical lithography-based techniques. Therefore, the fabrication cost is low, and the resulting devices are inexpensive. A series of SWNT solutions is prepared with concentrations ranging from 0.0125 to 0.2 mg/ml. The alignment of SWNT thin films, small bundles, and individual nanotubes is achieved under the optimized experimental conditions. The electrical properties of these samples are characterized; the linear current–voltage plots prove that the aligned SWNTs are mainly metallic nanotubes. The microscopy inspection of the samples demonstrates that the alignment of small nanotube bundles and individual nanotubes can only be achieved using narrow electrodes and low-concentration solutions. Our investigation shows that it is possible to deposit a controlled amount of SWNTs in desirable locations using dielectrophoresis

Combing and bending of carbon nanotube arrays with confined microfluidic flow on patterned surfaces

Ordered arrays of carbon nanotubes in bent and straight states were prepared using "wet" deposition of nanotube solutions on a patterned surface. This approach provided a means for the formation of highly oriented and textured nanotube arrays of different types. Moreover, under certain conditions, nanotube loops of different shapes were formed on amine-terminated silicon surface stripes. Atomic force microscopy observations indicated that the majority of the deposited nanotubes (up to 90%) are uniformly oriented and up to 40% of aligned nanotubes are folded into different nanoscale shapes (open and closed loops with 200-300 nm radius of curvature). We suggested that the dewetting of the SAM-confined liquid film was responsible for the alignment of carbon nanotubes and for the formation of the looped nanotubes. The instability of a receding contact line caused water microdroplets behind the dewetting film, which could serve as nuclei for nanotube trapping. The nanotubes pinned to the functionalized surface can be trapped by these drying microdroplets and bent along their shrinking circumference. In addition, highly packed ordered arrays of carbon nanotubes were formed by casting from solution on tilted patterned substrates. The preparation of the ordered arrays of uniform nanotube loops or woven nanotube stripes may be useful in microelectronic and microelectromechanical devices, where tunable electronic and surface properties result from different nanotube shapes, locations, and orientations.close727

Carbon nanotube arrays encapsulated into freely suspended flexible films

The incorporation of carbon nanotubes (CNT) in the freely suspended layer-by-layer (LbL) membranes by using the micropatterned LbL surface as a template for nanotube assembly was presented. The micropatterned surface composed of alternating open-protected areas was formed by the microcontact printing followed by CNTs selective absorption onto the LbL multilayers. Stable dispersion of CNTs in aqueous solution was prepared by oxidation in nitric acid, filtration, and taking supernatant after high-speed centrifugation. It was observed that the removal of the protective polymer layer exposed electrostatically active surface areas, allowing further deposition of LbL multilayers resulting in carbon nanotube arrays sandwiched between LbL films.close383

Ultrathin PFPE film systems fabricated by covalent assembly: An application to tribology

10.1007/s11249-011-9895-2Tribology Letters452371-37