Recent studies at the Rensselaer Polytechnic Institute have shown that electric field can have a profound effect on individual carbon nanotube ensembles. We have shown that nanotubes can be aligned along the electric field lines, and can also be made to move along the field lines above a critical or threshold electric field. Experiments were repeated with nano-particles such as C-60 (fullerenes) and these effects were not observed, which indicates that the aspect ratio and one-dimensionality of the nanotubes plays a critical role. These observations can foreshadow novel electro-mechanical applications for nanotube elements.
This talk will focus on the directed assembly of multiwalled carbon nanotubes on various substrates into highly organized structures that include vertically and horizontally oriented arrays, ordered fibers and porous membranes. The concept of growing such architectures is based on growth selectivity on certain surfaces compared to others. Selective placement of ordered nanotube arrays is achieved on patterned templates prepared by lithography or oxide templates with well-defined pores. Growth of nanotubes is achieved by chemical vapor deposition (CVD) using hydrocarbon precursors and vapor phase catalyst delivery. The new technique developed in our laboratory allows enormous flexibility in building a large number of complex structures based on nanotube building units. The talk will provide an insight into the creation process of the longest (single walled) nanotube strands. We will also discuss some of our recent efforts in creating nanotube circuits selectively and controllably and on the spatially resolved electronic properties of nanotubes.
Carbon nanotubes have fascinating physical properties. In order to use these novel one-dimensional structures for applications (such as in electronic devices, mechanical reinforcements and nano-electromechanical systems) the structure of nanotubes needs to be tailored and various architectures have to be configured using nanotube building blocks. This paper will focus on the directed and self-assembly of nanotubes on planar substrates into hierarchical structures that include oriented arrays, and ordered bundles. This is achieved by patterning substrates with or without metal catalysts. Growth of nanotubes is typically achieved by chemical vapor deposition (CVD). Various strategies to build two-dimensional and three-dimensional architectures of nanotubes will be described by this method. In addition to creating pristine nanotube arrays on planar substrates, the paper will also cover some of our recent efforts in fabricating nanotube polymer hybrids. Recent efforts and challenges in manipulating nanotube on surfaces and measuring transport properties will be discussed. In conclusion, a perspective will be given on our recent efforts in creating controlled structures with nanotubes and measuring some of their properties.
KEYWORDS: Carbon nanotubes, Field emission displays, Nickel, Scanning electron microscopy, Carbon, Transmission electron microscopy, Diamond, Molybdenum, Electron microscopes, Electronics
Field emission characteristics of carbon nanotubes (CNTs) were investigated in this paper. CNTs were produced by the catalytic decomposition of hydrocarbons--propylene on the nickel films. The SEM images showed that CNTs were quite uniform and disordered; the average diameter is about 50 nm. The measurements were performed in a vacuum chamber at the pressure of 10-7 torr. The results showed the typical voltage-current characteristics, which qualitatively followed the conventional Fowler-Nordheim equation. In conclusion, CNTs appear to be an excellent field emission cathode material with stable and reproducible field emission characteristics and a lower onset field.
The experimental samples, coated with buckyballs and buckytubes respectively, were processed with laser and subsequent quenching. Scanning electron microscopy, transmission electron microscopy, x-ray diffraction and Raman spectroscopy were employed to investigate the treated surfaces. The experimental results showed that diamond particles dispersed in Fe-C alloy system could be obtained by CO2 continuous laser-induced quenching of fullerene coatings on carbon steel s well as on ductile iron. The results also indicated that the treated surfaces, which reached an average macro-hardness of HRC 65-70, contained a great deal of polygonal crystallites on the order of microns and most of them were well-faceted cubic diamonds.
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