The Nanotube (NT) Conference Series

Mon. Invited talkMaterials and device physics aspects of semiconductornanowiresLars SamuelsonLund University, Solid State Physics / the Nanometer Structure Consortium, Box 118,S-221 00 Lund, SwedenContact e-mail: lars.samuelson@ftf.lth.seOne-dimensional materials structures, such as carbon nanotubes and semiconductornanowires, attract much attention for their promise to extend the miniaturization ofelectronic devices and circuits. Top-down fabricated nano-devices tend to have theirproperties dominated by process-induced damage, rendering ultra-small devices notso useful, while bottom-up fabrication methods may allow dimensions on the scaleeven below 10 nm, still with superb device properties. I will in this talk describe ourresearch on catalytically induced growth of semiconductor nanowires. Our methoduses catalytic gold nanoparticles, allowing tight control of diameter as well as positionof where the nanowire grows, with our work completely focused on epitaxiallynucleated nanowires in which the nanowire structure can be seen as a coherent,monolithic extension of the crystalline substrate material. One of the most importantachievements in this field of research is the realization of atomically abruptheterostructures within nanowires, in which the material composition can be alteredwithin only one or a few monolayers, thus allowing 1D heterostructure devices to berealized. This has allowed a variety of quantum devices to be realized, such assingle-electron transistors, resonant tunneling devices as well as memory storagedevices. Another recent field of progress has been the realization of ideally nucleatedIII-V nanowires on Si substrates, cases where we have also been able to reportfunctioning III-V heterostructure device structures grown on Si. Finally, I will describeopportunities to form new kinds of materials based on this technique, such as 3Dcomplex, tree-like nanowire structures.-4-

Mon. Contributed talkNucleation of single-walled carbon nanotubes on catalystparticles: MD and electronic structure calculationsFeng Ding1, Arne Rosén1, Kim Bolton1,21Experimental Physics, School of Physics and Engineering Physics, GöteborgUniversity and Chalmers University of Technology, SE-412 96, Göteborg, Sweden,2School of Engineering, University College of Borås, SE-50190, Borås SwedenContact e-mail: fengding@fy.chalmers.seMetal catalyzed single-walled carbon nanotube (SWNT) nucleation was studied byclassical molecular dynamics (MD) and electronic structure theory. The simulationsrevealed the atomic-level mechanism for SWNT nucleation on metal catalyst particles.The SWNTs nucleate between 800 K and 1400 K, [1] which is the same temperatureinterval used for chemical vapor deposition (CCVD) experiments. Also, in agreementwith experimental results the nucleated SWNT has same diameter with the catalystparticle [2]. The studies also show that a highly supersaturated carbon concentrationin the catalyst particle is needed to initiate the nucleation process. [1] Based on thesimulations a detailed Vapor-Liquid-Solid (VLS) growth model was developed forboth liquid and solid catalyst particles. [1, 3] Furthermore, MD and electronicstructure theory studies indicate that the catalyst particle must be able to maintain anopen end of the growing SWNT in order to be suitable for growth.References:[1] F. Ding, K. Bolton and A. Rosén, J. Phys. Chem. B, 108, 17369-17377 (2004).[2] F. Ding, A. Rosén, and K. Bolton, J. Chem. Phys., 121, 2775-2779 (2004).[3] F. Ding, A. Rosen, and K. Bolton, Chem. Phys. Lett., 393, 309-313 (2004).-5-

Mon. Contributed talkSingle walled carbon nanotube growth fromlithographically defined nanoparticleMasahiko Ishida, Hiroo Hongo, Fumiyuki Nihey, and Yukinori OchiaiNEC Fundamental and Environmental Research LaboratoriesContact e-mail: ishida@ah.jp.nec.comA semiconducting single walled carbon nanotube (SWNT) is an indispensablecomponent of a carbon-nanotube (CNT)-based field-effect transistor (FET). However,for the high-density and high-yield integration of CNTs in devices, many technologicalissues still remain in obtaining only semiconducting SWNTs and in controlling theirindividual position, orientation, diameter, length, and chirality etc. One feasibleapproach is chemical vapor deposition (CVD) from custom-designed catalystparticles because the catalysts are thought to determine the characteristics of CNTs.We demonstrated the top-down control of diameter and position of Fe catalysts bymeans of "lithographically anchored nanoparticle synthesis (LANS*)", and the CNTgrowth from the patterned particles. LANS was able to control the average diameterof Fe particles less than 2nm with the positioning error less than 10nm. CNTs weregrown by the CVD using ethanol and methane. Yield of the CNTs was stronglydependent on the particle size, CVD temperature, preparation procedure of theparticle etc. However, we confirmed that SWNTs were grown from the particles withthe root-growth mode and that their diameters were directly influenced by the particlesize. These results showed the possibility of top-down control of SWNTcharacteristics.*M. Ishida et. al., Jpn. J. Appl. Phys. 43 (2004) L1356.-6-

Tues. Keynote talkOrganic Functionalization of Carbon Nanotubes: Synthesisand ApplicationsMaurizio PratoDipartimento di Scienze Farmaceutiche, University of Trieste, ItalyContact e-mail: prato@units.itCarbon nanotubes (CNT) are of great interest due to their unique electronic, chemical,and mechanical properties for creating new generation electronic devices andnetworks. Advances in production processes have resulted in obtaining CNT withhigh structural perfection: relatively large amounts can now be produced of eithersingle-walled carbon nanotubes (SWNT), or multi-walled carbon nanotubes (MWNTs).However, high molecular weights and strong intertube forces keep CNT together inbundles, making their manipulation, characterization and analytical investigation verydifficult. The organic functionalization offers the great advantage of producing solubleand easy-to-handle CNT. As a consequence, compatibility of CNT with othermaterials, such as polymers, is expected to improve. In addition, once properlyfunctionalized, CNT become soluble in many solvents, so that their solutionproperties can be studied. Many functionalized carbon nanotubes may find usefulapplications in the field of materials science and technology. Also in medicinalchemistry carbon nanotubes are set to play an important role. Their use as drugdelivery scaffolds and substrates for vaccines has been already demonstrated. Withinthis contribution, we will review our most recent achievements in the field of synthesisof functionalized carbon nanotubes and their applications in materials science andmedicinal chemistry.-7-

Tues. Invited talkAlan Windl (abstract not received)-8-

Tues. Invited talkOptical and Transport Properties of Carbon NanotubesVasili Perebeinos, Jerry Tersoff and Phaedon AvourisIBM Research Division, T. J. Watson Research Center, Route 134, Yorktown Heights,NY 10598 USAContact e-mail: tersoff@us.ibm.comCarbon nanotubes (CNTs) have remarkable optical and transport properties, withimportant implications for technology. They have extraordinarily high electron andhole mobilities at low fields, although the mobility saturates at high fields. Wecalculate the electron-phonon scattering and binding in CNTs, within a tight bindingmodel, and calculate mobility using a multi-band Boltzmann treatment [1]. Our resultsfor mobility as a function of temperature, electric field, and nanotube chirality can becaptured by a few simple equations, to provide a broad overview of the transport. Theoptical properties are also unusual, being dominated by excitons even at roomtemperature, with binding energies and oscillator strengths that are orders ofmagnitude larger than those in conventional semiconductors. We find simple scalingrelationships for the exciton size, oscillator strength, and binding energy as a functionthe tube radius, chirality, and the dielectric constant of the embedding material [2].For the optical absorption, we find a phonon sideband 200 meV about the zerophonon line, which provides a signature of the excitonic character [3]. Finally, wecalculate the exciton radiative lifetime, which in turn determines the efficiency. Wepredict an unusual nonmonotonic temperature dependence, due to optically inactiveexciton bands below the optically active exciton.References[1] V. Perebeinos, J. Tersoff, and Ph. Avouris, Phys. Rev. Lett. 94, 086802 (2005).[2] V. Perebeinos, J. Tersoff, and Ph. Avouris, Phys. Rev. Lett. 92, 257402 (2004).[3] V. Perebeinos, J. Tersoff, and Ph. Avouris, Phys. Rev. Lett. 94, 027402 (2005).-9-

Tues. Invited talkA Strategy to Select Metallic or Semiconducting CarbonNanotubes from Their MixturesYoung Hee LeeDepartment of Physics, Center for Nanotubes and Nanostructured Composites,Sungkyunkwan Advanced Institute of Nanotechnology,Sungkyunkwan University, Suwon 440-746, R. O. Koreae-mail address: leeyoung@skku.eduCarbon nanotubes have played an important role in leading the nanoscience andnanotechnology due to their peculiar one-dimensional characteristics and potentialapplicabilities in various areas. One important feature is its peculiar electronicstructure that can be metallic and semiconducting depending on the chirality anddiameter of nanotubes.Up to now, it has not been possible to control the chirality ofnanotubes systematically by the conventional synthesis approaches such as arcdischarge, laser ablation, and (high-pressure) chemical vapor deposition methods.Both metallic and semiconducting nanotubes coexist in the grown sample, whichoften hinders device applications with high performance. For instance, application tonanoscale transistors and memories requires nanotubes to be semiconducting forclear gate modulation. Therefore, tailoring the metallicity of nanotubes is highlydesired.One approach is to transform the electronic structures by functionalization using gasadsorbates. We will introduce simple gases such as fluorine and hydrogen gases totransform electronic structures from metallic to semiconducting.[1,2]Another approach is to select either metallic or semiconducting nanotubes from theirmixtures. Several methods of selectiing semiconducting nanotubes from metallicones or vice versa using dielectrophoresis, octadecylamine (ODA), bromination, andDNA have been reported. Our aim is to select semiconducting nanotubes frommetallic ones in large quantity with high yield and more importantly without affectingnanotube properties so that the separated nanotubes could be used directly forvariousapplications.We have found a method for a selective removal of metallic single-walled carbonnanotubes from semiconducting ones by stirring SWNT powder in tetramethylenesulfone (TMS)/chloroform solution with nitronium hexafluoro-antimonate (NO2SbF6:NHFA) and tetrafluoroborate (NO2BF4: NTFB). Positively charged nitronium ions(NO2 ) were intercalated into nanotube bundles, where the intercalation waspromoted also by the counter ions. Nitronium ions selectively attacked the sidewall ofthe metallic SWNTs due to the abundant presence of electron density at the Fermilevel, thus yielding stronger binding energy compared to the counterpartsemiconducting SWNTs. The semiconducting SWNTs were left on the filter afterfiltration, whereas the metallic SWNTs were disintegrated and drained away asamorphous carbons. The effectiveness of selectivity was confirmed by the resonantRaman spectra and absorption spectra.[3] Some other ideas of removing zigzagnanotubes by carbon dioxide gas will be also discussed.[4]- 10 -

[1] K. H. An et al., Amer. Chem. Soc. 125, 3507 (2003); K. H. An et al., Appl. Phys.Lett. 80, 4235; K. A. Park et al., Phys. Rev. B 68, 045429 (2003).[2] K. S. Kim et al. Adv. Mat. 14, 181 (2002); K. A. Park et al., . Phys. Chem.B, to bepublished.[3] K. H. An et al. J. Amer. Chem. Soc. 127, 5196 (2005).[4] K. Y. Seo et al., J. Amer. Chem. Soc. Comm. 125, 13946 (2003).- 11 -

Tues. Contributed talkInfluence of Length on Cytotoxicity of Multi-Walled CarbonNanotubes against Human Acute Monocytic Leukemia CellLine THP-1 in Vitro and Subcutaneous Tissue of Rats inVivoYoshinori Sato1, Atsuro Yokoyama2, Ken-ichiro Shibata2, Yuki Akimoto1, Shin-ichiOgino1, Yoshinobu Nodasaka2, Takao Kohgo2, Kazuchika Tamura2, TsukasaAkasaka2, Motohiro Uo2, Kenich Motomiya1, Balachandran Jeyadevan1, MikioIshiguro3, Rikizo Hatakeyama4, Fumio Watari2, and Kazuyuki Tohji11Graduate School of Environmental Studies, Tohoku University, Aoba 6-6-20,Aramaki, Aoba-ku, Sendai, 980-8579, Japan.2Graduate School of Dental Medicine, Hokkaido University, Kita-ku, Sapporo, 0608586, Japan.3Institute for Materials Research, Tohoku University, Aoba-ku, Sendai, 980-8577,Japan.4Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai, 980-8579,Japan.Contact e-mail: jean.patrick.pinheiro@ife.noCarbon nanotubes (CNTs) are single- or multi-cylindrical graphene structures thatpossess diameters of a few nanometers, while the length can be up to a fewmicrometers. These could have unusual toxicological properties, in that they shareintermediate morphological characteristics of both fibers and nanoparticles. Here, weinvestigated the activation of the human acute monocytic leukemia cell line THP-1 invitro and the response in subcutaneous tissue in vivo to CNTs of different lengths.We used 220 nm and 825 nm long CNT samples for testing, referred to as "220CNTs" and "825-CNTs", respectively. 220-CNTs and 825-CNTs induced humanmonocytes in vitro, although the activity was significantly lower than that of microbiallipopeptide and lipopolysaccharide, and no activity appeared following variation in thelength of CNTs. On the other hand, the degree of inflammatory response insubcutaneous tissue in rats around the 220-CNTs was slight in comparison with thataround the 825-CNTs. These results indicated that the degree of inflammationaround 825-CNTs was stronger than that around 220-CNTs since macrophagescould envelop 220-CNTs more readily than 825-CNTs. However, no severeinflammatory response such as necrosis, degeneration or neutrophil infiltration in vivowas observed around both CNTs examined throughout the experimental period.- 12 -

Tues. Contributed talkReference standard for carbonaceous impuritymeasurements in carbon nanotubesPavel Nikolaev, Sivaram Arepalli1. G.B.Tech / NASA JSC 2. ERC / NASA JSCContact e-mail: pasha.nikolaev1@jsc.nasa.govNear-infrared spectroscopy is a convenient tool for measuring nanotube / non-tubularcarbon impurities ratios in carbon nanotube samples1. These measurements arebased on separation of contributions from nanotubes and impurities to the nearinfrared absorption. In the current work we produced a reference standard for NIRmeasurements using purified laser nanotubes. The sample was oxidized slowly in athermal gravimetry analyzer (TGA) in 2 % oxygen atmosphere. In these conditions,the sample oxidized in several steps, which were attributed to carbonaceousimpurities, nanotubes and graphitic shells based on TEM and Raman observations.Stopping oxidation at 625 oC (this temperature is sample-specific) allowed us toproduce a sample with well-defined ratio of nanotubes, graphite and metal catalyst.Since carbonaceous impurities no longer glue nanotubes and particles together,further dispersion and centrifuging allowed us to remove particles (verified by IC PMS) and produce pure nanotube sample. This sample was used as a referencestandard to determine relative contributions of nanotubes and impurities to NIRabsorption in p-plasmon background and Van-Hove peak areas. We will also discussa refinement of this technique for samples with varying diameter distributions, thattakes into account energy dependence of absorption.1. M. E. Itkis, et al. Nano Lett, 3, 309 (2003)- 13 -

Tues. Contributed talkMagnetic properties of metal phosphide nanoparticlesperiodically inserted in carbon nanotubesVincent Jourdain (a), John Robertson (a), Ed Simpson (b), Takeshi Kasama (b),Rafal Dunin-Borkowski (b), Matthieu Paillet (c), Philippe Poncharal (c), Ahmed Zahab(c), Patrick Bernier (c), Etienne Snoeck (d), Annick Loiseau (e)(a) Department of Engineering, University of Cambridge,(b) Department of Materials Science, University of Cambridge,(c) GDPC, Université Montpellier II,(d) CEMES, Toulouse, France,(e) LEM, CNRS-ONERA, Châtillon, FranceContact e-mail: vjj24@cam.ac.ukUnderstanding the growth mechanism of carbon nanotubes and controlling theirmorphology and insertion still remain important challenges. The possibility to fill theirinner channel with foreign materials also opens the way to the design of new hybridmaterials with novel or enhanced properties, in terms of electron charge/spintransport or magnetic storage. We showed that the use of phosphorus as a cocatalyst enables to modify the kinetic equilibrium between the growth elementarysteps of multiwall nanotubes (MWNT) and to induce a mechanism of sequentialcatalytic growth. Such a mechanism produces nanotube-based filaments periodicallyinserted with catalyst nanoparticles. The periodically inserted nanoparticles are nickel,cobalt or iron phosphides. We will present our work devoted to the control of themagnetic properties of the inserted metal phosphide nanoparticles and theircharacterisation by local techniques (MFM and electron holography).- 14 -

Wed. Plenary talkMass Production, Applications and StructuralControllability of Carbon Nanotubes by Catalytic CVD(CCVD) MethodMorinobu EndoFaculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano-shi 380-8553,JapanContact e-mail: endo@endomoribu.shinshu-u.ac.jpMulti walled carbon nanotubes (MWNTs) have been successfully produced by largescale production system based on CVD method using Fe catalyst [1,2]. Thediameters are in the range of several 10 nm or less and have provided differentmechanical as well as electronic properties than those of conventional carbons. Thecommercially available NT's have been applied and contributing to lithium ion batterytechnology, sporting goods, NT based carbon composite for advanced audio speakercones. It is also expected to be applied as a micro-catheter (inner diameter 0.43mm,outer diameter 0.53mm) made by resin/high-purity NT composite with enhancedmechanical properties (easier to handle) and extremely reduced thrombogenicity [3].Based on the present CCVD process, controllable growth of double-walled carbonnanotubes (DWNTs) has been established, because it is expected that DWNTs areexpected to have striking new electronic and mechanical properties, which is alsovery promising for specified applications. Here, we fabricate a paper-like material thatconsists of hexagonally packed bundles of clean, coaxial carbon nanotubes whosedouble walls vary little in diameter [1,2,4]. Also demonstrated are the coalescence ofDWNTs [5], and a novel structure consisting of flattened tubules containing twoSWNTs (bicable) [5].It is envisaged that carbon nanotubes will take an important place in the developmentof emerging technologies in near future.The author would like to thank Prof

VI NT’05 contributions In the spirit of the NT Conference series, oral presentation