Various methods have been developed for growing well-aligned CNTs based on variant alignment mechanisms such as 'overcrowding growth', 'template hindrance growth' and 'electric field induced growth'. Compared to other methods, electric field induced growth has been considered to be a more effective and controllable method for producing well-aligned single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Interestingly, while the alignment of CNTs became more controllable and repeatable with the assistance of an electric field, it was also shown that for CNTs grown in an electric field, the diameter uniformity and the crystallinity of graphite sheets of CNTs were clearly improved. This led Chinese researchers to develop an electric-field-induced method to not only improve CNT uniformity but also to create a new approach to control the microstructure of CNTs.
The study of very thin structural foams for cushioning and energy dissipation is, now more than ever, of primary importance in the engineering world, for example for the protection of electronic gadgets (such as MP3 players, cell phones, PDAs, etc.) from microimpacts due to accidental drops, as well as in the security area, for mitigation of explosive loading in macro scales. The advancement in the controlled growth of carbon nanotubes and other nanostructures has allowed researchers to create improved systems designed accurately for specific engineering applications.
Back in 2005, Dr. Pu-Chun Ke conducted an experimental study ("Coating Single-Walled Carbon Nanotubes with Phospholipids") where he discovered a very efficient method of solubilizing nanotubes using lysophospholipids, or the so-called single-tailed phospholipids. The solubility provided by lysophospholipid LPC is at least one order of magnitude better than that provided by SDS, a routine surfactant people use to solubilize nanomaterials in aqueous solutions. Ke and his colleagues showed that superior solubility was due to the formation of lipid 'striations' coated on the nanotubes. The underling principle of this superior solubility of nanotubes by lysophospholipids is supramolecular assembly, a topic of common interest to researchers in nanoscience, chemistry, materials, and biophysics. New results obtained during recent follow-up research provide useful insight on the binding mechanism of amphiphiles and one-dimensional nanostructures. This knowledge may facilitate the bottom-up design of supramolecular assembly, nanotechnology, nanotoxicology, and gene and drug delivery.
Anthrax is an acute infectious disease caused by the bacteria Bacillus anthracis and is highly lethal in some forms. Anthrax spores can and have been used in biological warfare. "Weaponizing" the spores requires a process to make an aerosol form of anthrax so that they easily can enter the lungs. Inhalation is the most lethal form of anthrax infection. Consequently there has been significant interest in the surface structure and characteristics of anthrax spores as related to their binding by molecular species. The investigation of such binding is obviously important to the development of countermeasure technologies for the detection and decontamination of anthrax spores. A group of researchers at Clemson University have come up with an agent that clings to the anthrax spores to make their inhalation into the lungs difficult.
Individual carbon nanotubes (CNTs) of different structural and thus electronic characteristics can be joined to build up three-terminal logic devices. However, today this can only be achieved using highly sophisticated nanomanipulation processes. The direct growth of intrinsic functional CNT elements such as Y-shaped CNTS (YCNTs) and helical CNTs (HCNTs) can be considered as an important alternative. YCNTs already have proven to show rapid and nonlinear transistor action without the need for external gating, while HCNTs could be used as inductive elements offering rapid signal processing. Additionally, HCNTs have shown operational functionality as high sensitivity force and mass sensors and are of great interest for nanoelectromechanical systems (NEMS). A research group in Spain now reports that sulfur may be used as a highly efficient additive in chemical vapor deposition (CVD) processes, allowing enhanced selectivity in the synthesis of helical and Y-shaped CNTs.
The ubiquitous static friction (stiction) and adhesion forces comprise a major obstacle in the manipulation of matter at the nanoscale. In order to realize the potential of nanotubes and nanowires as components in electronic devices or other microsystems, methods for reliable pick-and-place assembly must be established. A major obstacle here is the delicate balance required between the adhesion forces acting between the object to be manipulated, and the surface and the manipulation tool, respectively. A group od Danish and UK researchers found that self-assembled organic nanofibers, which are otherwise totally impossible to remove from any normal surface, can be lifted straight off from a nanotube forest. It means that the notorious stickiness of even the most soft and fragile materials, which immobilizes them and prevent handling, is a problem that now can be solved.
The photoconductivity of carbon nanotubes (CNTs) has been studied theoretically in a nanotube p?n junction, a single SWNT transistor, and thin SWNT films. While individual nanotubes generate discrete fine peaks in optical absorption and emission, macroscopic structures consisting of many CNTs gathered together also demonstrate interesting optical behavior. For example, a millimeter-long bundle of aligned multi-walled nanotubes (MWNTs) emits polarized incandescent light by electrical current heating, and recently researchers in China have made multi-walled nanotubes (SWNT) bundles giving higher brightness emission at lower voltage compared with conventional tungsten filaments. Recent achievements in fabricating self-assembled centimeter-long bundles of CNTs have greatly facilitated study on the macroscopic behavior of these bundle structures. Preliminary results such as an optical polarizer and a light bulb based on CNT macrobundles have been reported.
Carbon nanotubes (CNTs) are considered the most promising material for field emitters and a practical example are CNTs as electron emitters for field emission displays (FED). CNT emitters are generally fabricated by indirect growth methods such as screen-printing and electrophoresis. These methods show advantages in lowering the coating temperature and scale-up of the substrate size, but the direction of CNTs cannot be well controlled and a post-treatment process is generally necessary to enhance the performance of CNT emitters. In contrast to the indirect method, chemical vapor deposition (CVD) is a common technique for growing nanotubes directly on the substrate with the assistance of metallic catalysts. With the CVD method, CNTs can be grown at desired locations with a specified direction. However,most synthesis technologies such as conventional thermal CVD or plasma enhanced CVD are performed at temperatures over 500 C, which may restrict the application of CNTs on plastic substrates. Therefore, lowering the growth temperature for CNTs is one of the important directions for facilitating CNT applications.