Showing papers by "Rodney S. Ruoff published in 1999"

Tailoring graphite with the goal of achieving single sheets

Abstract: We demonstrate the tailoring of highly oriented pyrolytic graphite (HOPG) to obtain uniformly sized islands of up to several microns in size. There has already been some research on manipulating individual sheets on HOPG surfaces with scanning probe microscope tips; such sheets were obtained either accidentally or with a less controllable indenting technique. Here we present a different approach, which is more reliable and controllable. The HOPG surface was first patterned to create an array of small graphite islands by reactive ion etching of the HOPG surface with an oxygen plasma. These islands were then manipulated with an atomic force microscope tip. Carbon nanotubes represent a promising material for nanotechnology and can be considered as a graphene sheet rolled into a seamless cylinder. While carbon nanotubes are synthesized successfully with laser ablation, carbon arc, or chemical vapour deposition techniques, we speculate that it might be possible, by the controlled fabrication of graphene sheets, to form nanotubes or other novel motifs of use for nanotechnology.

Three-dimensional manipulation of carbon nanotubes under a scanning electron microscope

Abstract: Carbon nanotubes are manipulated in three dimensions inside a scanning electron microscope (SEM). A custom piezoelectric vacuum manipulator achieves positional resolutions comparable to scanning probe microscopes, with the ability to manipulate objects along one rotational and three linear degrees of freedom. This prototypical device can probe, select and handle nanometre-scale objects such as carbon nanotubes in order to explore and correlate their mechanical and electrical properties. Under real-time SEM inspection, carbon nanotubes are stressed while monitoring their conductivity, and nanotubes are attached to commercial atomic force microscope (AFM) tips such that the forces applied to the tubes can be measured from the cantilevers' deflections. The manipulator functions both as a research tool for investigating properties of carbon nanotubes and other nanoscale objects without surface restrictions, and as a rudimentary building device for larger nanotube assemblies. This capability to select and manipulate nanoscale components and to examine directly their suitability as construction materials during various phases of the construction process will play an important role in enabling the technology of assembling mechanical and electronic devices from prefabricated components.

Predictions of Enhanced Chemical Reactivity at Regions of Local Conformational Strain on Carbon Nanotubes: Kinky Chemistry

Abstract: Simulations that model the effects of conformational strain on the chemical reactivity of single-walled carbon nanotubes suggest a method for significantly enhancing their reactivity locally by controlled deformations. The chemisorption of hydrogen atoms is predicted to be enhanced by as much as 1.6 eV at regions of high conformational deformation, suggesting that local reactivity will be significantly enhanced. Analysis of the local electronic density of states suggests the introduction of radical p orbital character to the sites that are locally deformed, consistent with the heightened reactivity and large pyramidalization angles at these sites. Preliminary experimental data consistent with this predicted heightened reactivity is also presented.

Patterning of highly oriented pyrolytic graphite by oxygen plasma etching

Abstract: Patterning of highly oriented pyrolytic graphite (HOPG) was demonstrated by oxygen plasma etching of lithographically patterned substrates. Periodic arrays of islands, or holes of several microns on an edge, were obtained on freshly cleaved HOPG surfaces which had been prepared with SiO2 mask stops and then oxygen plasma etched. The etching process is described, including a study of etch rate as a function of rf power, and morphology was characterized with scanning electron microscopy.

Calorimetric Studies of Solvates of C60 and C70 with Aromatic Solvents

Abstract: To improve the understanding of the solution properties of C60 and C70 in aromatic solvents, binary systems of C60 and C70 with benzene, toluene, 1,2- and 1,3-dimethylbenzene, 1,2,4- and 1,3,5-trimethylbenzene, bromobenzene, and 1,2- and 1,3-dichlorobenzene were studied using differential scanning calorimetry, solution calorimetry, and thermogravimetry. Solid solvates with different compositions were identified in many of the systems. The solvates were characterized by composition and by the temperature and the enthalpy of the incongruent melting transition. Enthalpies of solution of C60 in toluene, 1,2-dimethylbenzene, 1,2- and 1,3-dichlorobenzene, and 1,2,4-trimethylbenzene and of C70 in 1,2-dimethylbenzene and in 1,2- and 1,3-dichlorobenzene were determined. The formation−incongruent melting of solid solvates causes maxima in the temperature−solubility curves of fullerenes in aromatic solvents. Trends in solubility behavior of fullerenes were discussed in terms of thermodynamics of solution and solvate...

Scanning electron microscopy study of carbon nanotubes heated at high temperatures in air

Abstract: Multiwalled carbon nanotubes (MWNTs) were dispersed in 2-butanol and dropped onto a V-ridge, lithographically patterned Si substrate that was coated with a thin layer of gold. These MWNTs were shown by scanning electron microscopy (SEM) to conform to the V-ridge surface topology at room temperature, which is thus useful for introducing kinks (at the apex of the V-ridge and the bottom of the trenches between V ridges). The substrate-supported MWNTs were then heated in air at temperatures from 673 to 1173 K for varying exposure times and were monitored with SEM. A 122 kJ mol−1 activation energy for complete oxidation was obtained, and preferential oxidation at kink sites was observed on some MWNTs at high temperatures. The dominant mode of oxidation was either thinning of the walls of the MWNTs or sequential oxidation of the component tubes in bundles. Some MWNTs, which at room temperature conformed to the V-ridge surface topology, detached (“sprang” away) from the substrate surface, demonstrating that the ...

Nanostressing and mechanochemistry

Abstract: Experimental evidence supporting the heightened chemical reactivity of highly conformationally strained carbon sites in multi-walled carbon nanotubes is reported. The strain is introduced by two methods, van der Waals attractions to nonplanar surfaces and ultrasonic cavitation. Oxidative acid attack was observed in both cases, in the former by etching of the nanotubes' kinked sites, and in the latter by peptide coupling to polystyrene spheres that are large enough to be visible by SEM imaging. A novel single-axis straining stage for nanometre-scale objects is also described.