Communications of the ACM
Well-Aligned and Densely Packed
Metal contacts (gold) connect to highly aligned carbon nanotube patterned films (red) to allow voltage control of their electrical properties.
Credit: Weilu Gao / Rice University
A team of scientists at Rice University and Los Alamos National Laboratory harnessed a spontaneous self-alignment mechanism to produce a thin film with millions of carbon nanotubes aligned and tightly packed, like water pipes on a flatbed truck. The work could lead to computer chips that bend, rather than break.
Making such a chip requires a rapid, simple route to self-organizing tiny carbon tubes into thin films. The team's nanotubes are orders of magnitude better aligned than previously possible. The team's method for creating the film balances forces between the tubes and polymer membrane surfaces to harness a spontaneous self-alignment mechanism.
The researchers describe their work in "Wafer-Scale Monodomain Films of Spontaneously Aligned Single-Walled Carbon Nanotubes," published in the journal Nature Nanotechnology.
Assembly is a key challenge to fabricating flexible computer chips, displays, and other devices from carbon nanotubes. Self-assembly of carbon nanotubes is particularly vital as one looks to integrate multiple devices into useful systems. The researchers harnessed a spontaneous self-alignment mechanism to create a fast way to produce the needed films. The films have applications in imaging, sensing, and security.
Inside an individual carbon nanotube, electrons, phonons, and excitons can travel in only one dimension. This property enables the tube to have electronic, optical, and thermal properties that depend on direction. For example, electrical current can flow along the length of the tube but not perpendicular to it. Tightly bundling millions of tubes together would greatly increase the current-carrying capacity. Despite significant efforts to produce large-scale architectures of aligned nanotubes, results have been limited. In the Nature Nanotechnology study, scientists showed that films greater than a centimeter squared of aligned single-walled carbon nanotubes are possible by combining surfactant chemistry and slow vacuum filtration.
The Nature Nanotechnology article is authored by Xiaowei He, Weilu Gao, Lijuan Xie, Bo Li, Qi Zhang, Sidong Lei, John M. Robinson, Erik H. Hároz, Stephen K. Doorn, Weipeng Wang, Robert Vajtai, Pulickel M. Ajayan, W. Wade Adams, Robert H. Hauge, and Junichiro Kono.
The nanotubes in the resulting films are aligned and tightly packed, with 1 million nanotubes in a cross-sectional area of one square micron (about 1/10,000 the cross-sectional area of a human hair). The method works for nanotubes created using various methods. In addition, the method works with different lengths of nanotubes, meaning film thickness is controllable from a few nanometers to around 100 nanometers. Combining this method with recently developed carbon nanotube sorting techniques allows for highly aligned and chirality-enriched nanotube thin-film devices. The team demonstrated how the films could be used as efficient terahertz polarizers and thin film transistors for optoelectronic applications.
This work was supported by Basic Energy Sciences in the U.S. Department of Energy, Office of Science through grant DE-FG02-06ER46308, and the Robert A. Welch Foundation through grant C-1509. Doorn and Hároz acknowledge support from the Los Alamos National Laboratory Laboratory Directed Research and Development program. Portions of this work were performed at the Center for Integrated Nanotechnologies, an Office of Science user facility operated for the U.S. Department of Energy Office of Science, project C2011B21.
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