Trench structure assisted alignment in ultralong and dense carbon nanotube arrays

In the aim towards fulfilling the versatile applications of carbon nanotubes (CNTs) in nanoelectronics, it is vital to control the alignment and orientation of ultralong and dense CNT arrays. Here, we have developed a subtle method to in situ improve the alignment of CNT arrays while maintaining their superior length and high density by introducing strong zipping and gas-guiding effects using trench structures on flat Si/SiO₂ substrates. For CNTs suspended over the trenches, the zipping effect will induce strains into the nanotube body, and thus stretch the slack CNTs, resulting in the taut and straight morphology; for CNT segments sitting on substrate, the straightening is realized by promoting the gas-guiding effect through decelerating the "apparent" elongation rate of the growing CNTs. The improvement could always be observed no matter if the nanotube lies fully suspended across a trench, or is just partially suspended with its middle portion contacting the bottom of the trench. Based on the Raman characterization of individual CNTs and by taking the growth process into account, the improvement mechanism has been elaborately discussed. Our work demonstrates a simple and robust approach to grow aligned CNT architectures for electronic and mechanical applications.