We estimate the stiffness of single-walled carbon nanotubes by observing their freestanding roomtemperature vibrations in a transmission electron microscope. The nanotube dimensions and vibration amplitude are measured from electron micrographs, and it is assumed that the vibration modes are driven stochastically and are those of a clamped cantilever. Micrographs of 27 nanotubes in the diameter range 1.0-1.5 nm were measured to yield an average Young's modulus of ͗Y ͘ϭ1.25 TPa. This value is consistent with previous measurements for multiwalled nanotubes, and is higher than the currently accepted value of the in-plane modulus of graphite. ͓S0163-1829͑98͒00144-1͔

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Purification of single‐shell nanotubes is essential if reliable information about their physical and chemical properties is to be obtained. Using the present synthetic techniques, samples typically contain 30% or more amorphous carbon and catalytic metal particle impurities. An extremely simple and efficient method of purification, involving boiling the nanotubes in concentrated nitric acid, is reported. It is demonstrated that this method removes most of the impurities and, unlike some other methods, is not sensitive to the quality of the starting material.

neously and many data points are obtained. We recorded 17 line/time plots under ambient conditions and 18 plots while flooding the sample with nitrogen. Each of the bright lines in Figure 3 was considered to be the time trace of one molecule's fluorescence. Each line was integrated over its width in space to get the total intensity per irradiation time (25 ms). An intensity versus time plot was evaluated using this method. We obtained 113 intensity/ time plots for molecules exposed to ambient air and 124 for molecules exposed to nitrogen.As a result, the fluctuations of the fluorescence intensity of single molecules in ambient air seem to be much more pronounced than of those in nitrogen (Fig. 4). To quantify our observations we analyzed the data with a simple algorithm. First the time interval in which the data are to be analyzed was defined (to avoid analysis of data recorded before the shutter was opened). For each intensity/time plot the mean background was evaluated within preset markers and subtracted from the plot. Then a threshold between 0 % (background level) and 100 % (level of the highest peak) was selected. The program proceeded as shown in Figure

We discuss the oxidation of carbon nanotubes and how it is affected by structure and geometry. While graphite is known to oxidize primarily at defects to create etch pits, nanotubes have additional structural features such as high curvature, helicity, and contain five and seven membered rings which modify the initiation and propagation of oxidation. Oxidation does not necessarily start at the tip of the tubes, and there are pronounced differential oxidation rates between layers which depend on the helicity of the individual shells.