Heterostructures of Single-Walled Carbon Nanotubes and Carbide Nanorods

Zhang, Yuegang; Ichihashi, Toshinari; Landree, Eric; Nihey, Fumiyuki; Iijima, Sumio

doi:10.1126/science.285.5434.1719

Cited by 395 publications

(235 citation statements)

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“…A crystallized Ti layer should lead to significantly improved contact behaviour, and this is consistent with experimental studies of post-deposition heating which appear to promote TiC formation 22 .…”

Section: Resultssupporting

confidence: 70%

The Role of Oxygen at the Interface between Titanium and Carbon Nanotubes

Felten

Suarez-Martinez

et al. 2009

ChemPhysChem

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[b] ((Dedication, optional)) We study the interface between carbon nanotubes (CNTs) IntroductionCarbon nanotubes appear as a good candidate to replace stateof-the-art inlaid copper interconnects in microprocessors. A key step for integration of CNTs in actual devices is the formation of stable and low-resistance ohmic contacts. Experimental results and calculations seem to agree that Ti and Pd are the best candidates for contacts in carbon nanotube based devices [1][2][3][4][5][6][7][8] . They are superior to conventional metals previously used in electronics such as Au, Al, and Pt which have associated high resistance Schottky barriers. Theoretical studies of pure metals on graphite suggest Ti as the best metal for contacts followed by Pd 5 , yet while low resistance Ohmic contacts have been experimentally reported in the case of Ti [1][2][3] , experimental results give Pd as the best choice due to better reliability and reproducibility 2,6 . One of the reasons invoked for this discrepancy is the high chemical reactivity of Ti compared to the other metals 2,6,9 : in realistic systems titanium oxidation occurs. But until now, no chemical study of the Ti/nanotube interface has been carried out in order to understand the phenomenon, nor supporting theoretical calculations.In this paper, we investigate the growth, electronic structure and chemical composition of Ti atoms on multiwall carbon nanotubes (MWNTs) by transmission electron microscopy (TEM), core levels photoemission spectroscopy (XPS) and density functional calculations. Results and DiscussionEvaporation of Ti on pristine MWCNTs leads to continuous amorphous coverage of the nanotube surface, even for small amounts of evaporated metal. High resolution TEM images in Figure 1 show that the film is continuous from at least 1 nm coverage; unlike for example Pd which shows isolated particle formation.Calculations for small Ti clusters confirm the tendency of Ti to wet the carbon surface. A single Ti atom strongly binds to graphene (2.64 eV), with Ti above a hexagon centre with short Ti-C bonds (2.24 Å), in good agreement with previous studies 10 . We have examined a range of 2D and 3D structures for Ti n on 2 graphene (n=1-4). For each cluster size the most stable structure is planar parallel to the graphene (see Figure 2). This is in contrast to Ti 4 in the gas phase where we find the most stable form is tetrahedral, in agreement with previous Ti cluster calculations 11 . A continuous monolayer of epitaxial Ti forms a buckled layer on average 2.0 Å above the graphitic layer, with Ti-C distances of 2.13 Å or 2.39 Å depending on whether the Ti atom lies above C atoms or hexagon centres respectively. In this case our binding energy is 5.43 eV/Ti atom. Our calculated barrier for Ti diffusion on the graphitic surface is 0.75 eV, as compared to ~0.1eV for Au and Pd. Thus while a simple first order Arhennius type equation with the Debye attempt frequency (10 13 Hz) suggests that isolated Au or Pd atoms on the graphitic surface at room temperature will be moving...

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Section: Resultssupporting

confidence: 70%

The Role of Oxygen at the Interface between Titanium and Carbon Nanotubes

Felten

Suarez-Martinez

et al. 2009

ChemPhysChem

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“…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).…”

mentioning

confidence: 99%

“…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)(2)(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.…”

mentioning

confidence: 99%

Heterojunctions between metals and carbon nanotubes as ultimate nanocontacts

Rodríguez–Manzo

Banhart

Terrones

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

112

100

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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...

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“…The lack of complete reaction between the SWNTs and the silicon at 800°C can be explained by the relatively low diffusion rate for Si through SiC. 1,5 The outermost nanotubes in an aggregate or bundle will react readily with the silicon forming a SiC layer around the nanotubes deeper within, preventing silicon from reaching the inner nanotubes at modest annealing temperatures.…”

mentioning

confidence: 99%

Thermally induced decomposition of single-wall carbon nanotubes adsorbed on H/Si(111)

Hunt

Montalti

Chao

et al. 2002

Applied Physics Letters

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The thermally driven reaction of carbon nanotubes with a silicon substrate is studied by photoemission spectroscopy and atomic force microscopy. Carbon nanotubes with a relatively high defect density are observed to decompose under reaction with silicon to form silicon carbide at temperatures ͑650Ϯ10°C͒ substantially lower than the analogous reaction for adsorbed C 60 . The morphology of the resultant silicon carbide islands appears to reflect the morphology of the original nanotubes, suggesting a means by which SiC nanostrutures may be produced. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1530747͔Understanding the interaction of carbon nanotubes with silicon and the resultant formation of silicon carbide at elevated temperatures is of importance due to the need to create well-defined nanotube/semiconductor heterojunctions 1 and the growing interest in fabricating silicon carbide nanorods from carbon nanotube precursors.2-4 Moreover, knowledge of the temperature at which carbide formation occurs is necessary to determine the stability of silicon/carbon nanotube interfaces which would result from integration of carbon nanotubes with silicon-based electronics. Although much effort has been directed toward understanding the interaction and thermal decomposition of C 60 on Si͑111͒ surfaces, 5-11 a closely related system, the inability to evaporate carbon nanotubes makes exploring the interaction of these species with elemental surfaces difficult.In this letter, we report an approach in which nanotubes are deposited on hydrogen passivated Si͑111͒ surfaces in an ambient atmosphere. Hydrogen is subsequently desorbed from beneath the nanotubes in an ultrahigh vacuum ͑UHV͒ environment allowing the study of the nanotube/silicon interface as a function of temperature by photoemission spectroscopy. Desorption of hydrogen from Si͑100͒-2ϫ1-H has previously been observed to occur beneath a C 60 monolayer enabling molecules to bond directly to the silicon surface. 12 We find that defective carbon nanotubes decompose on Si͑111͒ after a short anneal at 650Ϯ10°C, about 150°C ͑Refs. 6 -10͒ lower than the decomposition temperature of C 60 on Si͑111͒-7ϫ7. Ex situ atomic force microscopy ͑AFM͒ indicates that the morphology of silicon carbide islands resulting from nanotube decomposition is governed by initial nanotube geometry, suggesting a route for fabrication of nanometer scale silicon carbide structures.Photoemission experiments were undertaken at Beamline 4.1 of the Synchrotron Radiation Source, Daresbury, UK. Hydrogen passivated Si͑111͒ substrates were produced by conventional techniques and AFM images show large flat terraces, while x-ray photoelectron spectroscopy ͑XPS͒ demonstrated very low levels of residual oxide contamination. Purified single-wall carbon nanotubes ͑SWNTs͒ were supplied by the Sussex Fullerene Group and were placed in suspension by agitating small quantities in acetone in a conventional ultrasonic bath. Several droplets of the sol were cast upon a hydrogen passivated Si͑111͒ sample, and the sample...

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Heterostructures of Single-Walled Carbon Nanotubes and Carbide Nanorods

Cited by 395 publications

References 21 publications

The Role of Oxygen at the Interface between Titanium and Carbon Nanotubes

The Role of Oxygen at the Interface between Titanium and Carbon Nanotubes

Heterojunctions between metals and carbon nanotubes as ultimate nanocontacts

Thermally induced decomposition of single-wall carbon nanotubes adsorbed on H/Si(111)

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