Showing papers by "Rodney S. Ruoff published in 2001"

Mechanics of C60 in nanotubes

Abstract: A modeling study of C60 in nanotubes is presented, with focus on a new approach. We report on the elastic properties, energetics, and certain tribological issues, for C60 inside (n, n) nanotubes, with n ranging from 5 to 10. A new combined molecular dynamics/continuum approach with account of both the nonbonded and bonded interactions was used. The elastic properties of the nanotube were analytically derived on the basis of the Tersoff-Brenner potential. The derived Young's modulus is consistent with experimental values. We have computed the case where the C60 has zero initial velocity and is “sucked” into the (10, 10) or (9, 9) tubes due to the sharp force gradient present from the deep attractive potential at the tube inlet; C60 then oscillates back and forth inside the (10, 10) and (9, 9) nanotubes. C60 seems to make a perfect nanobearing system when in the (10, 10) tube. In a separate modeling study, C60 was fired on axis at high velocity (from 400 up to 1600 m/s) toward the six different armchair nan...

Structural Analysis of Collapsed, and Twisted and Collapsed, Multiwalled Carbon Nanotubes by Atomic Force Microscopy.

Abstract: A fully collapsed multiwalled carbon nanotube (MWCNT1) section and a different twisted and fully collapsed MWCNT were observed with tapping-mode atomic force microscopy. The collapsed section of MWCNT1 was significantly more flexible than the uncollapsed sections, and advanced 120 nm within 1 month. The collapse of MWCNT1 was most likely initiated by its interaction with the surface, and possibly a water meniscus. The ability of carbon nanotubes to radially deform under the influence of surface interactions is in striking contrast with their extremely high axial rigidity.

Locked twist in multiwalled carbon-nanotube ribbons

Abstract: Twisted multiwalled carbon-nanotube (MWCNT) ribbons were observed with transmission electron microscopy Particularly one cantilevered MWCNT ribbon had a twist present in the freestanding segment An energetics analysis was presented supporting the hypothesis that twists in MWCNT ribbons are stabilized through more favorable atomic registry between neighboring layers in the twisted state

Structure and mechanical flexibility of carbon nanotube ribbons: An atomic-force microscopy study

Abstract: Collapsed multiwalled carbon nanotube (MWCNT) sections and segments (carbon nanotube ribbons) on surfaces were observed by atomic-force microscopy. The collapsed form of these MWCNTs allowed the determination of the layer number and the inner and outer diameters for their uncollapsed form. The results show that such carbon nanotube ribbons are extremely flexible and readily conform to the underlying substrate morphology. The formation of the collapsed form of these nanotubes is consistent with recent theoretical analysis on the mechanics of nanotubes.

Ternary system of C60 and C70 with 1,2-dimethylbenzene

Abstract: Differential scanning calorimetry, X-ray, and solubility measurements were used to study phase equilibria in the ternary system C60-C70-1,2-dimethylbenzene up to the boiling point of the solvent. Formation of the two ternary phases was confirmed. Partial solubilities of C60 and C70 were measured and calculated.

An empirical study of etching for the fabrication of nanoscale imprinters

Abstract: One of the greatest challenges facing nanotechnology is the ability to selectively place nanoscale entities in specific locations and subsequently interconnect these devices. Several methods have been proposed and the relative strengths of each technique will become apparent in time. One method that has received considerable attention in recent years is nanoimprint or nanostamp lithography. These techniques have shown resolution down to 10 nm, can be applied over large areas, are relatively inexpensive, and have several variations to accommodate different processing tasks. One common challenge in nanoimprint or nanostamp lithography is the fabrication of the imprinter or stamp. The features on the imprinter are usually fabricated using e-beam lithography and then etched. The etching step is often the determining factor in the quality of the imprinter. We have evaluated etching of 50 nm and 250 nm features in silicon and silicon dioxide using 16 different etching recipes. The features have been etched down approximately 200 nm resulting in an aspect ratio of 4 to 1 for the 50 nm features. The primary evaluation criteria is the anisotropy of the etch with the goal of achieving vertical sidewalls. In this paper, we present the 16 different etching recipes, the chamber conditions for three different reactors, and qualitative evaluations based upon SEM micrographs of each etch. For this work, we will concentrate on the nanoscale etching of SiO/sub 2/. Several etching recipes are shown to be able to produce near-vertical walls for 50 nm features etched down 200 nm.