RESUMO
Carbon nanotubes incorporating copper are highly sought after for nanoelectronic applications. Indeed, several recent studies have demonstrated the production of copper-tipped nanotubes using the chemical vapor deposition method. Here we present the growth and detailed characterization of such copper-tipped nanotubes. The nanotubes grown were of a 'bamboo-like' structure, consisting of stacked cups of graphene, and were produced by chemical vapor deposition employing iron and copper nanoparticles as a catalyst and metal source respectively. Transmission electron microscopy and electron holography analysis of the tips of these nanotubes revealed a small crystalline iron particle on the inner side of the copper tip, with the nanotube structure encapsulating the iron. This form of growth may allow the formation of similar structures with various other metal-tipped carbon nanotubes to be manufactured.
RESUMO
A method for analysing systems of isolated single-walled carbon nanotubes is of paramount importance if their structural characteristics are to be fully understood and utilized. Here we offer a simple technique for analysing such systems, with unprecedented contrast, using transmission electron microscope imaging of carbon nanotubes suspended over large holes in a silicon nitride grid. The nanotubes are grown directly on the viewing grids, using the chemical vapour deposition process, thus avoiding the use of chemicals or aggressive treatments. This method is simultaneously non-invasive, reusable, allows the analysis of multiple structures based on carbon nanotubes and is quickly implemented.
RESUMO
A polarized microscope was used to study the spreading of mercury droplets on thin silver films. Using the differential interference contrast (DIC) method and semi-quantitative measurements of the optical path difference (OPD), the three-dimensional shape of the liquid droplet that wets the solid surface was constructed with an angle resolution of 1 degrees. The evolution of the droplet shape was determined with a time resolution of 0.04 s. The quantitative results are compared with other wetting-reaction systems. In particular, it is demonstrated that the droplet has a spherical-cup shape during the entire wetting-reaction process.
