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
An investigation concerning the tautness of suspended carbon nanotubes (CNTs) grown using the chemical vapor deposition (CVD) method is presented. The suspended nanotubes were analyzed with both a transmission electron microscope (TEM) and a high-resolution scanning electron microscope (HR-SEM). The HR-SEM and TEM investigations revealed that the interaction between CNTs among themselves as well as with the surface on which they are grown is a primary cause for the tautness of suspended tubes. Specifically, the tube-tube and tube-surface dynamics cause adjoining tubes to create a "zipper-effect", thereby straightening and tightening them. Suspended CNTs cling to each other and to as much of the surface as possible and thus minimize their total energy, creating taut, suspended structures. This effect can be so strong so as to force wide tubes to buckle, with no other external force involved. The implications of this study include all forms of alignment processes of nanotubes using the CVD method. The results presented here provide the groundwork for the capability of fine-tuning the control of CNT network formation using substrate mechanical features.
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.
