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The wetting and capillarity of carbon nanotubes were studied in detail here. Nanotubes are not "super-straws," although they can be wet and filled by substances having low surface tension, such as sulfur, selenium, and cesium, with an upper limit to this tension less than 200 millinewtons per meter. This limit implies that typical pure metals will not be drawn into the inner cavity of nanotubes through capillarity, whereas water and organic solvents will. These results have important implications for the further use of carbon nanotubes in experiments on a nanometer scale.

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We report the formation of a series of metal-containing hydrogenated silicon clusters using an ion trap. Mass analyses reveal that many types of transition metal ions M(+) ( M = Hf, Ta, W, Re, Ir, etc.) react with silane (SiH4) to form dehydrogenated MSi( +)(n) cluster ions ( n = 14, 13, 12, 11, 9, respectively) as an end product, indicating that the metal atom is endohedral and stabilizes the Si polyhedral cage. This finding is confirmed by our ab initio calculation that WSi12 is a W-encapsulating Si12 cage cluster, and is very stable owing to both the electronic and the geometrical shell closures.

Carbon nanotubes can be thought of as cylindrical graphitic micro-crystals with nanometer diameters which are expected to have unique properties.['] Currently multi-shell nanotubes can be made in gram-orders using the carbon arc discharge synthesis method. [', 31 However, the crude sample contains not only nanotubes but also nanoparticles with a weight ratio of about 2:l in the best cases. Therefore the nanotubes must be further purified in order to investigate precisely their properties.Recently we reported the purification of nanotubes by oxidation in air at high temperature (around 750 "C) .L41 In this process the nanoparticles are consumed more rapidly than the nanotubes. However the yields are very small (< 1 %) probably due to the local inhomogeneities in the gas phase oxidation process. To overcome this problem, we have investigated the liquid-phase oxidation of the crude nanotube samples and found that under suitable conditions high yields of opened purified nanotubes can be obtained.In this paper we describe this method which gives yields of the order of 40 % depending on the composition of the crude sample. This method is very useful to obtain gram-quantities of purified nanotubes at one time under well-controlled conditions. By analogy with the gas-phase oxidation referred to earlier,[41 we tried several well-known strong oxidants, such as nitric acid, sulfuric acid, the mixture of both and potassium permanganate. Transmission electron microscopy (TEM) observation revealed that the oxidation was much more homogeneous in solution where the nanotube sample could be well dispersed through sonication and the chemical attack could be uniform. The oxidation by sulfuric and nitric acids is extremely slow and weak. A mixture of the two gives slightly better results.For purification purposes, by far the best oxidant is potassium permanganate in acidic solution. Therefore, for the latter case, the methodology will be described in detail next. 1 .OO g of the core fibrous material is taken from the deposit synthesized by the carbon arc discharge method,[', 31 ground and dispersed in 200 ml of 1 N sulfuric acid. This solution is placed in a two necked flask fitted with a reflux condenser. Separately, 19.8 g (1.5 molar excess in terms of atomic carbon content) of potassium permanganate is dissolved in 200 ml of IN sulfuric acid and placed in a funnel fitted to the side neck of the flask. The flask is heated to 150 "C in an oil bath with vigorous stirring (magnetic stirrer). The potassium permanganate solution is then added drop by drop through the side funnel. The solution is then refluxed for an additional 5 hours. The mixture is then cooled and filtered through a G4 glass filter (pore size 10-16 mm). The filtrate is washed with pure water and then with concentrated hydrochloric acid to remove the manganese(1v) oxide (reduced from the original potassium permanganate) . When all the manganese oxide has been dissolved away, the filtrate is again washed with pure water. The residual filtrate containing the purified n...