Heterojunctions between metals and carbon nanotubes as ultimate nanocontacts

Abstract

We report the controlled formation and characterization of heterojunctions between carbon nanotubes and different metal nanocrystals (Fe, Co, Ni, and FeCo). The heterojunctions are formed from metal-filled multiwall carbon nanotubes (MWNTs) via intense electron beam irradiation at temperatures in the range of 450 -700°C and observed in situ in a transmission electron microscope. Under irradiation, the segregation of metal and carbon atoms occurs, leading to the formation of heterojunctions between metal and graphite. Metallic conductivity of the metal-nanotube junctions was found by using in situ transport measurements in an electron microscope. Density functional calculations show that these structures are mechanically strong, the bonding at the interface is covalent, and the electronic states at and around the Fermi level are delocalized across the entire system. These properties are essential for the application of such heterojunctions as contacts in electronic devices and vital for the fabrication of robust nanotube-metal composite materials.nanoelectronics ͉ interfacial interactions ͉ conductivity ͉ electron microscopy ͉ composites H eterojunctions between different materials are of increasing interest in nanotechnology. For creating devices at the nanoscale, different structures have to be joined so as to obtain junctions with predefined properties. Junctions between carbon nanotubes (CNTs) and metals (1-3) or semiconducting (1, 4) nanowires are highly desirable to exploit the excellent electronic and mechanical properties of CNTs. In electronic devices, conductive contacts between the graphitic network of CNTs and metallic electrodes need to be established to link the nanotubes with each other and their periphery. To date, most results indicate that the properties of such a device are dominated by the electronic behavior at the nanotube-metal contact. For instance, the resistance of the ohmic contact (1, 3, 5) or Schottky barrier effects (6) are influenced by the type of interface between metal and the graphitic structure. In some previous studies, multiwall carbon nanotube (MWNTs) interconnections with metal electrodes only occurred with the outermost wall of MWNTs (7). A robust mechanical connection in such a junction cannot be expected, nor can the inner walls of MWNTs participate considerably in charge transport (5). Therefore, detailed knowledge regarding the nature and strength of bonding as well as the morphology and electrical properties of contacts is important because it is vital to connect all concentric cylinders of a MWNT, across the entire cross-section of the nanotube, to a metal particle. In particular, a covalent nanotube-metal junction would allow one to attach nanotubes firmly to metal pieces, which is useful for achieving well-defined electrical contacts and also for attaching nanotubes firmly to metal supports for the realization of ultrastrong nanotube ropes in mechanical systems.Recent studies have reported examples of graphitic material interfaces with metal particles for Co crysta...

Ion and electron irradiation-induced effects in nanostructured materials

“…The controlled formation of heterojunctions between carbon nanotubes and different metal NCs ͑Fe, Co, Ni, and FeCo͒ was demonstrated. 358 The heterojunctions were formed from metal-filled MWNTs via intense electron beam irradiation in a TEM at elevated temperatures in the range of 450-700°C. Under irradiation, the segregation of metal and carbon atoms occurred, leading to the formation of heterojunctions between metal and graphite, Fig.…”

“…The inset shows a detail of the interface ͑white square͒ after noise filtering, where the bending of the nanotube layers to match the metal lattice is visible, from Ref. 358. ͑f͒ Junction between three MWNTs and a Co particle as made by electron irradiation of a metal-carbon nanotube composite.…”

Preparation and Characterization of Biobased Graphene from Kraft Lignin

“…The formation of CNTs could be attributed to the catalysis of iron particles and the decrease of vacuum degree in quartz tube during the cooling process. The grapheneCNTs system has significant technological advantages due to the combination of individual properties of graphene and CNTs in various applications (Kalita et al 2008;Rodríguez-Manzo et al 2009;Lee et al 2010;Zhang et al 2011).…”

Understanding the Metal-Carbon Interface in FePt Catalyzed Carbon Nanotubes

“…In the most widely used preparation process of chemical vapor deposition (CVD), the choice of transition metal catalyst particles provides a degree of control over the CNT morphology, the production yield, and the growth mode itself (base growth vs. tip growth) [21,22]. Consequently, the interface between the catalyst particle and the CNT is considered to play a key role for the CNT growth [17,[23][24][25][26]. Only few studies deal with the physical properties of these facets which are found to be particularly effective in dissociating the gaseous hydrocarbon feedstock during growth and which typically provide low activation energies for surface diffusion [17,27].…”