Interface Dynamic Behavior Between a Carbon Nanotube and Metal Electrode

Abstract

The heterointerface between a carbon nanotube (CNT) and a metal is of prime importance for CNT-based nanotechnology.[1] In nanoelectronic circuits, the behavior of every single CNT-based device is highly influenced by the atomic and electronic structures of the contact interface between a nanotube and an electrode. Ohmic CNT/metal contacts of high conductivity are usually prerequisite for the effective performance of an individual device, as well as their interconnections.[2] On the other hand, controlled synthesis of CNTs with desired structures is a crucial step for nanotube integration into nanotechnology. This requires a detailed understanding of the growth mechanism, especially the interactions between C atoms and a catalyst particle at the CNT/metal interface during the catalyst-assisted syntheses. Several hypotheses based on theoretical simulations, [3] postgrowth, or in situ experimental observations [4][5][6][7][8] have been proposed in an attempt to describe catalyzed chemical vapor deposition (CVD). However, some crucial questions related to a CNT/catalyst interface still remain controversial. For example, do C atoms migrate on a metal surface (or metal/graphitic shell interface), [3,5] or diffuse through the body of a catalyst particle? [7,8] Does a metal catalyst convert to an intermediate metal carbide [4,7,8] before segregation of graphitic layers on the catalyst surface? Does a catalyst particle exist in a solid or liquid state during the nanotube growth? Further investigations of a CNT/ metal interface by in situ high-spatial-resolution techniques are required for clarifying these issues. Such studies would also be desirable for the development of new CNT/metal contact designs and schemes that enable robust electrical and mechanical connection between a CNT and a metal electrode.In the present study, a CNT/metal interface was created by connecting an individual multi-walled CNT and a sharp tungsten nanoelectrode inside a high-resolution transmission electron microscope (HRTEM). The details of the interface structural transformations induced by a high current flow and Joule heating were monitored under high spatial resolution (1.7 Å for the microscope used), and the corresponding electrical properties were examined by two-terminal measurements. This in situ study not only brings deeper understanding of the catalytic CNT growth mechanisms and the processes at the CNT/metal electrode interfaces during the current flows, but also attains novel CNT-carbide-metal nanojunctions that exhibit excellent electronic properties and mechanical robustness. Furthermore, unusual CNT wall-thickness changes were demonstrated via preferential fast absorption of CNT core shells into a tungsten electrode.All experiments were carried out in a JEM-3100FEF (JEOL) TEM using a ''Nanofactory Instruments AB'' STM-TEM holder. [9,10] As shown in the schematics of Figure 1, a multiwalled CNT protruding from the edge of a gold wire was approached to a W tip that was delicately driven by a piezo-tube. After the end-to-end physica...

Thermal stability of carbon nanotubes probed by anchored tungsten nanoparticles

“…Only after the particle has been melted (or premelted), it absorbs some carbon shells (indicated by a white arrow in figure 4(b)), implying that the diffusion of C into the W particle starts at a high temperature, close to the melting point of the particle (∼ 3400 K). A similar absorption of CNT shells by a tungsten tip was found to result in the formation of hexagonal α-WC [23]. However, our observation contradicts with some other reports.…”

Distinguishing between Individual Contributions to the Via Resistance in Carbon Nanotubes Based Interconnects

“…24 The formation of metal carbides can significantly reduce the contact resistance at the metal-CNT interface. 19,23 Compared to the vertically aligned CNTs prepared by Bayer et al and Nessim et al, 19,20 we observed a higher value of resistance. We attribute this to the subsequent embedding and planarization processes.…”

“…Potentially, the formation of a thin intermediate carbide layer causes the significantly reduced contact resistance. 23,24 However, as shown by Leroy et al, 24 carbide formation is inhibited as long as oxygen is present. Thus, carbide formation may occur after annealing the sample with the top metallization, only.…”

In Situ TEM of Carbon Nanotubes

“…For the case of Au contacts, the melting threshold was similarly at 10 8 A/cm 2 and the open-end CNTs again led to less resistive contacts [ 88 ]. The authors do not discuss chemical mixing of the materials [ 85 ] or hot-spot migration upon annealing [ 79 ].…”

“…A two-terminal electrical holder was used to follow the dynamics of a MWCNT-W electrode wire contact interface when exposed to a high current density [ 85 ]. The end-to-end contact established was considerably changed as chemical reactions promoted by joule heating took place between the C and W. The formation of the hexagonal phase α-WC was aided further by electromigration leading to visible extensions of mixing and eventual extrusion of excess carbon from the top of the WC segments.…”