Symposium Organizers
David B. Geohegan Oak Ridge National Laboratory
John Robertson Cambridge University
Kuei-Hsien Chen Academia Sinica
Jie Liu Duke University
R1: Growth Modelling
Session Chairs
David Geohegan
A. John Hart
Tuesday PM, April 06, 2010
Room 2020 (Moscone West)
9:00 AM - R1.1
Computer Simulation Studies of Carbon Nanotube – Catalyst Particle Interfaces.
Anders Boerjesson 2 , Hakim Amara 3 , Kim Bolton 4 2 , Christophe Bichara 1
2 Department of Physics, Gothenburg University, Gothenburg Sweden, 3 Laboratoire d'Etudes des Microstructures , ONERA-CNRS , Chatillon France, 4 School of Engineering, University of Borås, Borås Sweden, 1 , CINaM CNRS, Marseille France
Show AbstractSelectively growing carbon nanotubes requires an atomic scale understanding of the nanotube – catalyst particle interface, since this is the place where the carbon atoms incorporation takes place. The structure of the catalyst surface [1] as well as its chemical composition [2] seem to be of importance. Using Density Functional Theory calculations [3], we calculate the structure of the interface and adhesion energies of carbon tubes on small particles of pure nickel or nickel carbide. The junctions between single-walled carbon nanotubes and nickel clusters are on the cluster surface, and not at subsurface sites, irrespective of the nanotube chirality, temperature, and whether the docking is gentle or forced. Gentle docking helps to preserve the pristine structure of the SWNT at the metal interface, whereas forced docking may partially dissolve the SWNT in the cluster. We then use these results to fine tune a tight binding model [4, 5], which makes it possible to further investigate the effect of the temperature, chirality and particle size. [1] A. R. Harutyunyan et al., Science, 326, 116-20 (2009).[2] S. Hofmann et al., J. Phys. Chem. C, 113, 1648–1656 (2009); R. Sharma et al. Nano Letters 9, 2, 689-94 (2009); H. Yoshida et al. Nano Letters 8, 7, 2082-6 (2008).[3] A. Börjesson, W. Zhu, H. Amara, C. Bichara and K. Bolton, Nano Letters 9, 3, 1117-20 (2009).[4] H. Amara, C. Bichara and F. Ducastelle, Phys. Rev. Lett., 100, 056105, (2008).[5] H. Amara, J. M. Roussel, C. Bichara, J.-P. Gaspard and F. Ducastelle, Phys. Rev. B 79, 014109 (2009).
9:15 AM - R1.2
Carbon Nanotube Nucleation versus Encapsulation Probed by MD Simulations.
Morgana Ribas 1 , Feng Ding 3 , Perla Balbuena 4 , Boris Yakobson 1 2
1 Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States, 3 Institute of Textile and Clothing, Hong Kong Polytechnic University, Hong Kong China, 4 Department of Chemical Engineering, Texas A&M University, College Station, Texas, United States, 2 Department of Chemistry, Rice University, Houston, Texas, United States
Show AbstractGrowth mechanism of carbon nanotubes (CNT) at the atomic level is far from being completely understood. We still do not know how to fully control CNT growth or even if such control is possible. Which factors and forces decide if the evolving sp2-network of atoms will adhere to the catalyst particle, encapsulating it, or the graphitic cap will lift-off to extend itself into a hollow tube? Such details cannot be studied experimentally, but can be explored by molecular dynamics (MD). We perform a large scale of MD simulations (over 500 simulations) to establish the role of the adhesion strength (Wad) of the graphitic cap to the catalyst and the temperature (and C diffusion rate) in CNT nucleation1. To study the competition of tubular structure vs. encapsulated catalyst as a function of temperature and Wad, we perform MD simulations for a temperature range between 200 K and 1400 K, at 200 K increments. For each temperature we vary Wad from 0 to 0.3 eV/C. Such systematic observations allow us to build a statistically representative map of CNT nucleation and define the conditions for growth or fullerene-like metal encapsulation (catalyst poisoning). Our simulations show that weak Wad, sufficient kinetic energy (high temperature), or fast C diffusion favor catalytic CNT growth. An analysis of these results in light of previous models (curvature energy, thermal decohesion, and requirement of fast C diffusion), shows that below 600 K carbon-diffusion on the catalyst surface limits the growth, but at higher temperature it fully depends on cap lift-off. With an informed set of parameters in which CNT growth is expected to happen, we obtain the longest simulated nanotube structures within reasonable simulation × a significant step towards achieving CNT realistic computational modeling. This study reveals a means of designing metal catalysts for better CNT synthesis, potentially at desirably low temperatures, which is especially important for possible in situ growth for nanoelectronics applications.1 M. A. Ribas, F. Ding, P. B. Balbuena, and B. I. Yakobson J. Chem. Phys., in press.
9:30 AM - **R1.3
In Quest for Chirality Knob in the Nanotube Growth.
Boris Yakobson 1 , Alex Dobrinsky 1 , Feng Ding 1 , Yuanyue Liu 1 , Enrique Munoz 1
1 ME&MS, and Chemistry, Rice University, Houston, Texas, United States
Show AbstractChiral symmetry is definitive for almost all essential properties of carbon nanotubes. To understand the origin of chirality distribution or to possibly control this distribution is a key to tantalizing applications. Proposed view of an arbitrary tube as a base-zigzag type but with a screw dislocation along the axis [1] leads to prediction of simple relationship K ~ Sin(C) between the steady-state growth rate K and the chiral angle C. This trend can indeed be clearly seen as the material abundance distribution in several reported experiments. The mechanism of carbon insertion into the kink area is also supported by the observed stepwise rotation of the growing tube [2], although details are awaiting further investigation. Recently, we have explored the stage of nucleation, when the forming cap can also be seen as a structure with a dislocation. Detailed analysis of caps' topology and their relative energies allows us to evaluate the probabilities of different chiralities, leading to a general form P(C) ~ exp[-A*Cos(C+Co)]. We will discuss how the parameters A and Co can be tuned by the growth conditions, therefore how the preferred chiral type (angle C) can in principle be controlled, and what are thermodynamic limitations of the intriguing possibilities that follow. [1] F. Ding, A.R. Harutyunyan, and B.I. Yakobson, Proc. Natl. Acad. Sci., 106, 2506 (2009); [2] M. Marchand, C. Journet, D. Guillot, J.-M. Benoit, B.I. Yakobson, and S.T. Purcell, Nano Lett., 9, 2961-2966 (2009).
10:00 AM - R1.4
Chirality Selection During Catalytic Nucleation of Carbon Nanotubes.
JinJin Wang 1 , John Robertson 1
1 Electrical Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractWe study the possibility of chirality selection during the catalytic chemical vapor deposition (CVD) of a Single-Walled Carbon Nanotubes (SWNT) by density functional simulations. When nanotubes grow by root growth, the tube's chirality is fixed by the chirality of the initial cap that nucleates on the catalyst cluster surface. We previously studied the energies of caps of different chiralities on a flat, fixed Ni(111) layer [1]. We now consider different caps binding to various planes and apices of a 55 atom cluster of Fe and Ni. Firstly, we find that the caps bind more strongly to these nucleation sites than to the flat (111) layer. A second point is that the cap causes considerable distortion of the metal cluster, while the caps themselves are relatively undistorted. This is because C-C bonds are stronger than Ni-Ni bonds. Of the three high symmetry nucleation sites on the Fe cluster, the binding of (6,5) and (7,5) caps to the pyramidal corner is 2 eV per cap stronger on average than to other sites. Binding energies also depend on the cap diameter, this explains why the pyramid site is less stable for certain caps. For the Ni cluster, there is a strong preference to the zigzag and chiral caps; binding energies for these two caps are generally greater than for armchair caps by 2.5 eV per cap. Lastly, there is strong segregation of carbon atoms to the outside of the cluster, with little dissolution into cluster.1. S Reich, L Li, J Robertson, Chem Phys Lett 421 469 (2006)
10:15 AM - R1.5
Understanding the Growth Transition From Carbon Nanotubes to Carbon Nanofibers.
Ranadeep Bhowmick 1 2 , Brett Cruden 2 , Bruce Clemens 1
1 , Stanford University, Stanford, California, United States, 2 , NASA Ames Research Center, Moffett Field, California, United States
Show AbstractGrowth of carbon nanotubes (CNTs) and nanofibers (CNFs) continues to be an enigma. Though a lot is known about the growth conditions for CNTs and CNFs, the reason that a given growth produces one or the other is still not clear. We propose a new mechanism to explain the formation of CNFs over CNTs. Experimentally; we have observed growth of fibers is favored at conditions of higher pressure or thicker catalyst films. Observation of the impact of pressure on catalyst annealing shows that higher pressure results in the formation of larger particles at the expense of smaller particles, indicative of Ostwald ripening. These larger particles favor the growth of fibers over CNTs. All the prominent catalysts for carbon nanotube growth have extended solid and liquid solubility with carbon, and also form an eutectic at low carbon concentrations. The Gibbs Thompson effect predicts size dependent suppression of melting point. Hence smaller particle exhibit a single liquid phase, conducive to the growth of CNTs. However, larger particles, depending on the growth conditions (temperature and pressure and the extent of carbon dissolution) may exist in a dual solid-liquid phase. The relative concentration of liquid phase increases with increasing carbon dissolution. Beyond a threshold carbon concentration, the dual phase becomes energetically unfavorable, causing the particle to revert to a single solid phase regime by discarding excess carbon. As shown by Helveg, et al., [Nature 427, 426 (2004)] the resulting carbon layers replicate the morphology of the catalyst particle, leading to the characteristic stacked-cone or bamboo morphology of the CNF. TEM investigations validating the above observations and a theoretical model describing the same will be presented.
10:30 AM - R1.6
Material Properties in Codimension > 0: Graphene Edge Properties.
Paulo Branicio 1 , David Srolovitz 1
1 Materials Theory and Simulation Laboratory, Institute of High Performance Computing, Singapore Singapore
Show AbstractWhen materials are very thin in one or more dimensions, their equilibrium shapes are often curved/bent. Such shapes commonly represent a compromise between elastic strain energy and other thermodynamic forces (e.g. related to surface stresses, electrostatic interactions, or adsorption). Examples include ZnO and SnO2 nanobelts, silica/carbonate helicoids, and graphene sheets and nanoribbons. Here, we demonstrate that when the equilibrium shape of a nanomaterial is not flat/straight, important fundamental material properties may be orders of magnitude different from their bulk counterparts. We focus here primarily on the graphene edges. Graphene in three dimensions is a codimension c = 1 material; the codimension is c = D – d = 3 – 2 = 1, where D is the dimensionality of the space in which the material is embedded and d is the dimensionality of the object. By contrast, a flat graphene sheet has c = 2 – 2 = 0. We use the REBO-II interatomic potential to calculate the edge orientation dependence of the edge energy and edge stresses of graphene with c = 0 and c = 1. The edge stress for all edge orientations is compressive with c = 0. Both edge energy and stresses are in reasonable agreement with DFT calculations. The compressive edge stresses in c = 0 lead to edge buckling (out-of-the-plane of the graphene sheet) for all edge orientations (c = 1). The edge buckling in c = 1 reduces all edge energies and dramatically reduces all edge stresses to near zero (more than an order of magnitude drop). We also report the effect of codimension on the free energy and entropy of a graphene sheet and the elastic properties of ZnO nanohelices.
R2: Nanotube Forest Growth
Session Chairs
David Geohegan
A. John Hart
Tuesday PM, April 06, 2010
Room 2020 (Moscone West)
11:15 AM - **R2.1
Making Carbon Nanotube Forests: From Collective Growth Mechanics to Multifunctional Materials.
A. John Hart 1 , Eric Meshot 1 , Mostafa Bedewy 1 , Sameh Tawfick 1 , Erik Polsen 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractWhile carbon nanotubes (CNTs) have been produced industrially in ton-scale quantities for nearly two decades, scalable manufacturing processes that precisely control the structure, length, and alignment of CNTs are needed to realize the exceptional properties of CNTs at larger scales. Specifically, vertically aligned CNT forests are a model system for further understanding what limits the growth of indefinite CNTs, and are building blocks for novel microstructures and multifunctional thin films. First, I will review our current understanding of the limiting mechanisms of CNT forest growth, where interactions among the growing population of CNTs govern their collective growth behavior. We elucidate mechanisms of CNT forest self-organization, steady growth, and termination using a holistic approach combining in situ and ex situ X-ray scattering, measurements of forest mass and height, and chemical analysis of the reaction atmosphere. Second, I will present our recent approaches to synthesis of hybrid polymer-CNT and nanowire-CNT forests, which are amenable to large-scale manufacturing via continuous CVD, rolling, and printing schemes.
11:45 AM - R2.2
Controlled Structure of MWNT by Adjusting Metal-support Interactions in High-surface Area Catalysts.
Veronica Irurzun 1 , James Brown 1 , Daniel Resasco 1
1 CBME, The University of Oklahoma, Norman, Oklahoma, United States
Show AbstractProduction of carbon nanotubes (CNT) with controlled structure has become an important area in the nanotubes field since there are multiple applications in which they could be used, particularly if their structure is known and predictable [1-3]. Uses of CNT range from semiconductors and digital memory to drug delivery in biomedical applications. As well as in polymer applications such as paint, tires, etc. Among the production techniques, CVD (chemical vapor deposition) is not only the least expensive but also the easiest to scale up to be used in industry. In several of our previous studies [4-8] we have shown that the structure of single-walled carbon nanotubes (SWNT), e.g. diameter, chirality, length, can be controlled by varying different conditions either related to the catalyst or to the reaction. However, there are a number of important applications that are more suited for MWNT (multi-walled carbon nanotubes). Therefore, it is important to develop similar degree of control in MWNT growth as that reached with SWNT. In this study, we have investigated the effects of varying in a controlled way the interactions between the active metals and the supports on the resulting CNT morphologies. It is shown that characteristics such as number of walls, diameter, and length, can be changed in a systematic fashion by varying parameters related to the catalyst synthesis and the reaction conditions. Specifically, the catalytic systems investigated are cobalt and cobalt-molybdenum supported on different silicas and aluminas, with special attention to the phenomena that occur on these catalysts during the various steps in the CNT growth, that is pre-calcination and pre-reduction, as well as during contact with the carbonaceous gas feed. References[1] Paradise M., Goswami T. Mater. Design. 2007, 28, 1477. [2] Gojny F.H., Wichmann M.H.G., Fiedler B., Schulte K. Compos. Sci. Technol. 2005, 65, 2300 [3] Merkoçi A., Pumera M., Llopis Xavier, Pérez B., del Valle M., Alegret S. Trac-Trend Anal. Chem. 2005, 24, 9, 826.[4] Resasco D.E., Herrera J.E., Balzano L. J. Nanosci. Nanotechno. 2004, 4, 4, 398.[5] Resasco D.E., Alvarez W.E., Pompeo F., Balzano L., Herrera J.E., Kitiyanan B., Borgna A. J. Nanopart. Res. 2002, 4, 1-2, 131.[6] Alvarez W.E., Pompeo F., Herrera J.E., Balzano L., Resasco D. E. Chem. Mater. 2002, 14, 4, 1853.[7] Monzon, A, Lolli, G. Cosma, S., Sayed-Ali, M. Resasco, D.E., J. Nanosci. Nanotech. 2008, 8, 6141 [8] Irurzun V.M., Tan Y., Resasco D.E., Chem. Mater., 2009, 21, 2238.
12:00 PM - R2.3
Efficient Hydrocarbon Precursors for Rapid and Clean Carbon Nanotube Growth.
Eric Meshot 1 , Desiree Plata 2 , Christopher Reddy 3 , Philip Gschwend 2 , A. John Hart 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, United States
Show AbstractWhile carbon nanotube (CNT) synthesis by thermal chemical vapor deposition (CVD) can be achieved using myriad combinations of carbon-containing precursors and nanoparticle catalysts, there is relatively little mechanistic understanding of how the precursor is incorporated into the CNTs. Identification of efficient CNT growth pathways is essential for cost-effective scaling of CNT synthesis for commercial applications and for understanding of the potential environmental impacts of CNT manufacturing. Using a custom-built apparatus which enables rapid (200 C/s) temperature control of a resistively heated silicon platform, we have successfully decoupled the “preheating” of the gas precursor upstream of the reactor from the local thermal environment of the catalyst. This decoupled technique enables testing of gas species by direct injection without preheating, thus enabling precise quantification of the performance of various hydrocarbons for CNT growth. We identify that thermal decomposition of the typical input reactant mixture (C2H4/H2) creates a mixture of species including various alkanes, alkenes, and alkynes, as well as polycyclic aromatic hydrocarbons (PAHs). These analyses, in concert with real-time measurements of growth kinetics via the forest height, reveal a positive correlation between growth rate and the relative abundance of specific molecules, including acetylene, propyne, and vinylacetylene. By directly delivering these species with the normal growth gases C2H4/H2 in the absence of preheating, we identify that alkynes selectively enhance forest growth (rate and ultimate height) and are thereby a family of efficient precursors for CNT manufacturing. Further, by direct delivery of these molecules to the heated catalyst we achieve efficient CNT growth with a 10-fold reduction in PAH production in the exhausted gas mixture as well as a 55% decrease in energy consumption during synthesis. Finally, we show molecules that have previously been proposed as key precursors to CNT formation, such as methane and benzene, exhibit low conversion efficiencies in our system.
12:15 PM - **R2.4
Preferential Growth of Single-Walled Carbon Nanotubes with Metallic Conductivity.
Avetik Harutyunyan 1
1 materials Science , Honda Research Institute USA Inc., Columbus, Ohio, United States
Show AbstractThe main obstacle that hinders ubiquitous application of carbon nanotubes is our inability to obtain large amount of reasonably homogeneous material. Despite intense research and noticeable achievements in preferential growth of semiconducting SWCNTs there is only a limited understanding of exactly what determines chirality and thereby the electronic structure of grown SWCNT. Our studies reveal that the variation of the noble gas ambient during thermal conditioning of the catalyst, and in combination with oxidative and reductive species, alters the fraction of tubes with metallic conductivity from about 20% of the population to a maximum of 91%. The tubes have been identified based on Raman, photoluminescence and electrical (field effect transistor performance) characterizations. In the meantime, in situ environmental transmission electron microscopy (ETEM) studies reveal that ambient variation leads to differences in both morphology and coarsening behavior of the nanoparticles used to nucleate nanotubes. The relationship between catalyst morphology rearrangements and resulting nanotube electronic structure, will be presented.
12:45 PM - R2.5
Versatile Carbon Hybrid Films Composed of Vertical Carbon Nanotubes Grown on Graphene Film Substrates.
Sang Ouk Kim 1 , Rodney Ruoff 2
1 Department of Materials Science and Engineering, KAIST, Daejeon Korea (the Republic of), 2 Department of Mechanical Engineering and the Texas Materials Institute, The University of Texas at Austin, Austin, Austin, Texas, United States
Show AbstractSubstrate materials for vertical carbon nanotube (CNT) growth have been mostly limited to brittle and flat dielectric oxide materials, such as alumina and silica. An alternative substrate for diverse applications of vertical CNT arrays would (i) be stable at the moderately high temperatures needed for CNT growth, (ii) be mechanically compliant and stretchable for transfer to the widest array of base structures (flexible polymers, non-planar structures, etc.), (iii) allow for the rapid and large-scale fabrication of complex device architectures, and (iv) be electro-conductive with an ohmic contacts with CNT strands for efficient use of input electrical power. In this presentation we will demonstrate versatile carbon hybrid film composed of vertical CNT arrays grown on reduced graphene film substrate, which satisfies all 4 aforementioned requirements. Thin large-area reduced graphene films have been fabricated by deposition from aqueous colloidal suspensions of graphene oxide platelets, decorated them with patterned catalyst particles, and grown CNTs at exceptionally high growth rates and at temperatures that result in the substrate being converted to an electrically conductive graphene-based film. Such carbon hybrid films have excellent flexibility and stretchability, can be readily transferred to any substrate including non-planar surfaces, and were found to have ohmic electrical contacts throughout the junctions in the CNT/metal catalyst/reduced graphene film system. As examples among many possible applications, the carbon hybrid films were readily integrated into a field-emitting device, which demonstrated an excellent performance. (Related articles published: Adv. Mater. in-press; Nano Lett. 9, 1427-1432, 2009; Adv. Mater. 20, 2480-2485, 2008.)
R3: <i>In-situ</i> Growth Studies
Session Chairs
Tuesday PM, April 06, 2010
Room 2020 (Moscone West)
2:30 PM - **R3.1
In-situ Studies on the Role of the Catalyst During Carbon Nanotube CVD.
Stephan Hofmann 1
1 Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractDeterministic control of carbon nanotube growth remains difficult, in particular for single-walled nanotubes, which limits their widespread application. This is largely due to an incomplete understanding of the role of the catalyst. We present environmental transmission electron microscopy (ETEM), in-situ X-ray photoelectron spectroscopy (XPS) and in-situ X-ray diffraction (XRD) experiments analysing the active physical and chemical state of nano-particulate catalysts and their dynamic restructuring during nanotube CVD. We find that for oxide supported Fe and Ni, the active state of the catalyst is a crystalline metallic nanoparticle [1-3]. For these systems, control over nanotube growth is closely linked to catalyst-support interactions [2] and to pre-treatment conditions that prevent excessive coarsening and result in a suitable catalyst phase and topography. On the other hand, we find that nano-particulate zirconia neither reduces to a metal nor forms a carbide while nucleating carbon nanotubes [4]. Such oxide-based catalysts or “metal-free” systems indicate a solely surface-based nanotube formation mechanism and we show that the low reactivity and limited restructuring of oxides allow interesting new possibilities for controlled CNT growth and integration.[1] Hofmann et al., Nano Lett. 7, 602 (2007)[2] Mattevi et al., J. Phys. Chem. C 112, 12207 (2008)[3] Hofmann et al., J. Phys. Chem. C 113, 1648 (2009)[4] Steiner et al., JACS 131, 12144 (2009)
3:00 PM - R3.2
Evolution, Activity, and Lifetime of Alumina-supported Fe Catalyst During Super Growth of Single-walled Carbon Nanotube Carpets: Influence of the Type of Alumina.
Placidus Amama 1 2 , Cary Pint 3 , Seung Min Kim 4 , Eric Stach 4 , Robert Hauge 3 , Benji Maruyama 1
1 RXBN, Air Force Research Laboratory, Dayton, Ohio, United States, 2 University of Dayton Research Institute, University of Dayton, Dayton, Ohio, United States, 3 Richard E. Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, Texas, United States, 4 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractThere has been growing interest in the growth of densely packed, vertically aligned single-walled carbon nanotube (SWNT) carpets by chemical vapor deposition because of their suitability in several important applications. The catalyst commonly used for ‘super growth’ of SWNT carpets is a thin Fe film (<1 nm thick) supported on an alumina film. Although the Fe-alumina catalytic system has been studied extensively, important areas that have not yet been addressed, especially in the context of SWNT carpet growth, are how the type of alumina (deposited by different physical vapor deposition methods) and the transformation sequences of the alumina phases affect the evolution and lifetime of the catalyst. Using AFM, TEM, XPS, and variable angle of incidence spectroscopic ellipsometry, we show that the Ostwald ripening behavior and mass loss of the different alumina-supported catalysts during typical ‘super growth’ conditions corroborate with the lifetime and activity of the catalysts. These results will benefit current efforts aimed at the rational design of catalysts with longer lifetime and enhanced activity for SWNT carpet growth.
3:15 PM - **R3.3
In-situ Measurement of the Effect of Au Doping in Ni Catalysts on the Yield of Tubular Carbon Nanostructures.
Renu Sharma 1 , See Wee Chee 2 , Peter Rez 3 , Jakob Wagner 4 , Michael Treacy 5
1 Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 LE-Center for Solid State Science, Arizona State University, Tempe, Arizona, United States, 3 Center for Nanoscopy, Technical University of Denmark, Kgs. Lyngby Denmark, 4 Dept of Physics, Arizona State University, Tempe, Arizona, United States, 5 Department of Physics, Arizona State University, Tempe, Arizona, United States
Show AbstractDuring the last five years, in-situ observations using environmental transmission microscopy (ETEM) has played a crucial role in revealing atomic level structural transformations occurring during their nucleation and growth. We have combined in-situ and ex-situ measurements to demonstrate the importance of temperature and precursor pressure in controlling the structure and morphology of the CNTs. We have also used the column of the ETEM for site-specific deposition of Fe catalyst particles and revealed the atomic-level structural transformations occurring during nucleation and growth of CNTs. Here we show that the yield of tubular carbon structures can be increased by doping a Ni catalyst with Au, and that their morphology and structure can be controlled by varying the reaction temperature. However, the exact role of Au for catalysis is not well understood.Au/Ni thin films (1–2 nm) with varying composition were co-deposited on perforated Si thin films supported on Mo grids and introduced into the column of a Tecnai F-20 environmental scanning/transmission electron microscope (ESTEM). The sample area of this microscope was used as a cold-wall CVD reactor. After preliminary characterization of as-deposited films, the samples were heated in vacuum up to reaction temperatures (500-650 °C). Acetylene was introduced in the sample region and pressures were kept constant during each experiment but varied between 1–3 mTorr for each individual experiment. Digital videos (15 frames/s) at low and high resolution were recorded at reaction temperatures and under flowing acetylene to measure growth rates and to follow the growth at atomic resolution. We observed increased activity in tubular structure formation for samples with low amounts of Au (~20% nominal composition). Moreover, tubes with herring-bone, stacked rings and multiwalled structure were observed to form depending upon the reaction temperature and pressure. Atomic resolution videos reveal that the graphene layers (the essential topological form of carbon for tubular growth) form at facets of the crystalline catalyst particles. Formation of different structures depended upon the rate of growth, which was in turn controlled by pressure and temperature. Both in-situ and ex-situ analysis of the composition of the catalyst particles, effect of temperature and pressure on the morphology and structural mechanism for the formation of various morphologies observed will be presented.
3:45 PM - R3.4
Fast Fluid Flow and Transport Selectivity in Carbon Nanotube Channels.
Francesco Fornasiero 1 , Jung Bi In 2 , Sangil Kim 6 , Hyung Gyu Park 5 , Costas Grigoropoulos 2 , Alex Noy 1 3 , Bakajin Olgica 6 4
1 Physical and Life Sciences - BBTD, LLNL, Livermore, California, United States, 2 Mechanical Engineering, UC Berkeley, Berkeley, California, United States, 6 , Porifera Inc, Hayward, California, United States, 5 Mechanical and Process Engineering, ETH , Zurich Switzerland, 3 School of Natural Sciences, UC Merced, Merced, California, United States, 4 NSF Center for Biophotonics Science & Technology, UC Davis, Sacramento, California, United States
Show AbstractBy deepening our understanding of novel fluid behavior at nanoscale, nanofluidic research promises significant advances in many technological areas such as chemical and biological sensing, drug delivery, lab-on-chip, and fluid separations. Fundamental understanding of fluid flow under nanoscale confinement requires nanochannels with well-defined and controllable structural properties. In our laboratory, we have fabricated a nanofluidic platform consisting of a silicon nitride membrane with well-aligned, sub 2-nm carbon nanotubes as pores. We have used these membranes to investigate mass transport and selectivity through carbon nanotubes for both pure fluids and mixtures. Measured gas and water transport rates confirm the molecular dynamic predictions of an exceptionally fast fluid flow in carbon nanotube pores. For example, the measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude [1]. Our work on the mass-transport selectivity for single [2] and binary electrolyte solutions through carbon nanotubes suggest that, for dilute solutions, small ions can be selectively excluded by carbon nanotube pores when their open rim is enriched by charged groups. In some cases, ion exclusion can be as high as 98%. The selectivity mechanism for salt rejection/permeation through 1-2 nm carbon-nanotube pores appears to be dominated by electrostatic interactions between the ions and the carboxylic groups at the carbon nanotube rims. By controlling solution pH and, thus, CNT-tip charges, ion transport through CNT pores can be modulated from complete permeation to large exclusion. The observed ion selectivity rules agree with the Donnan membrane equilibrium theory. Steric and hydrodynamic effects are less important [2]. For binary multivalent/monovalent electrolyte solutions with common cation, we observed a negative rejection of the monovalent co-ion at the smallest mole fractions. This effect is stronger for larger multivalent co-ion valences. The measured rejection of binary salt solutions as a function of the salt mole fraction is also consistent with a charge-based exclusion mechanism. Our results on selectivity of ion transport in carbon nanotubes may be important for elucidating many physical, chemical, and biological processes ranging from fluid separation to ion-channel-regulated cellular transport. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
R4: Nanotube Growth and Properties
Session Chairs
Tuesday PM, April 06, 2010
Room 2020 (Moscone West)
4:30 PM - **R4.1
Aligned Arrays of Single Walled Carbon Nanotubes: Materials Aspects of Growth and Implementation in RF Electronics.
John Rogers 1
1 , University of Illinois, Urbana, Illinois, United States
Show AbstractHigh mobilities and other attractive features of single-walled carbon nanotubes (SWNTs), create interest in their use in high speed or unusual (i.e. flexible, stretchable) forms of electronics. Growth strategies that use chemical vapor deposition onto crystalline quartz substrates yield nearly perfectly linear, perfectly aligned, horizontal arrays of individual SWNTs. This talk describes our research in this area, and highlights (1) fundamental theoretical and experiments studies of processes associated with aligned growth, (2) strategies for achieving high density arrays and for removing metallic SWNTs, and (3) device and circuit implementations, including high mobility transistors with GHz switching speeds.
5:00 PM - R4.2
Horizontally-aligned, Selectively Grown Single-walled Carbon Nanotubes by CVD.
Cara Beasley 1 , Albert Lin 2 , Bruce Clemens 3 , H.-S. Philip Wong 3
1 Chemistry, Stanford University, Stanford, California, United States, 2 Electical Engineering, Stanford University, Stanford, California, United States, 3 Material Science, Stanford University, Stanford, California, United States
Show AbstractTypical growths of single-walled carbon nanotubes (SWNTs) result in broad distributions of size, nature, and chirality. In particular, statistically random growths produce a mixture with 2/3 semiconducting and 1/3 metallic SWNTs. Applications that demand semiconducting SWNTs require post-processing such as electrical burning or chemical etch to remove the metallic SWNTs. These processes reduce the SWNT density and can damage the remaining semiconducting SWNTs. Applications that require metallic SWNTs can use sorting to enrich the metallic SWNTs or design around the semi-conducting SWNTs. Control of the distribution of SWNT nature by controlling the growth conditions can reduce the need for post-processing and, in general, can lead to a greater ability to tune SWNT properties for a given application. Previous work on CVD growth of SWNTs has shown that many factors, such as carbon source composition, growth temperature, and carbon source temperature affect SWNT growth and can change the distribution of size, character, and chirality of the resulting SWNTs. Exploration of a variety of carbon sources and conditions has demonstrated that the fraction of SWNTs that are semiconducting can be controlled and significantly enhanced. More complex carbon sources also tend to lead to narrower distributions of SWNTs. Optimizing these factors leads to growth procedures that yield more selective distributions of SWNTs. These distributions can then be applied to applications that benefit from non-random ratios of semi-conducting to metallic SWNTs. Here the optimization of growth and source conditions is used to tune the ratio of semi-conducting to metallic tubes, control the diameter distribution, and enrich certain chiralities. These changes in SWNT distributions are investigated using Raman spectroscopy,electrical data is used to verify and help quantify the semi-conductor to metallic ratio changes. Coupling these selective growths with the horizontal alignment achieved by using single crystal quartz as a substrate provides SWNTs for device applications that require less post-processing than SWNTs produced in standard growths.
5:15 PM - R4.3
Zinc Oxide Nanowire and Single Walled Carbon Nanotube Networks for CMOS Devices.
Yan Zhang 1 , Husnu Unalan 1 , Pritesh Hiralal 1 , Sharvari Dalal 1 , Mark Mann 1 , Gehan Amaratunga 1 , Stefano Lagomarsino 2 , William Milne 1 , Matt Cole 1
1 Electrical Engineering Division, Engineering Department, University of Cambridge, Cambridge United Kingdom, 2 , Istituto Fotonica e Nanotecnologie CNR, Rome Italy
Show Abstract Unique properties of one dimensional nanomaterials are being explored through demonstration of various electronic devices [1,2]. Large quantity synthesis and the controlled assembly of the semiconducting nanowires and nanotubes have already been presented for various chemistries [3,4]. Recently, Zinc oxide (ZnO) nanowire and single walled carbon nanotube (SWCNT) networks have been proposed as an alternative to organic and amorphous semiconductors for plastic electronics. Although the mobility of the ZnO and SWCNT networks is lower than that of individual nanowires and nanotubes, they offer the advantages of high transparency and flexibility. A major drawback of using individual nanowires and nanotubes in nano or microelectronic applications is the lack of a manufacturable process to precisely assemble nanowires into small devices. The use of ZnO networks avoids this issue in large area macroelectronic devices because the devices exhibit the average properties of a large number of random individual nanowires and nanotubes. In this work, we have fabricated high-performance p-type SWNT TFTs and n-type ZnO nanowire TFTs by simple stamping processes at room temperature. For the first time, we have demonstrated a hybrid complementary inverter combining SWNT TFTs with ZnO nanowire TFTs. Our inverter can function at ambient conditions and possesses a high gain value. More complicated CMOS circuits utilizing nanotube/nanowire hybrids using our simple approach may be easily fabricated. Therefore, our work opens up new opportunities for quasi 1-D nanomaterial-based CMOS applications requiring low-cost, low-temperature manufacturing on large area flexible substrates.References:[1] Cui, Y. et al.: Science Vol 291 (2001), p. 891.[2] Huang, Y. et al.: Science Vol 294 (2001), p. 1313.[3] Ahn, J.H. et al.: Science Vol 314 (2006), p. 175401757.[4] Yu, G. et al.: Nat. Nanotech. Vol 2 (2007), p. 372.
5:30 PM - R4.4
Massive Aligned Carbon Nanotubes for Beyond-CMOS Electronics.
Chuan Wang 1 , Koungmin Ryu 1 , Alexander Badmaev 1 , Jialu Zhang 1 , Chongwu Zhou 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractMassive aligned carbon nanotubes hold great potential but also face significant integration / assembly challenges for future beyond-silicon nanoelectronics. We report a wafer-scale processing of aligned nanotube devices and integrated circuits, including progress on essential technological components such as wafer-scale synthesis of aligned nanotubes, wafer-scale transfer of nanotubes to silicon wafers, metallic nanotube removal and chemical doping, and defect-tolerant integrated nanotubes circuits. We have achieved synthesis of massive aligned nanotubes on complete 4 inch quartz and sapphire substrates, which were then transferred to 4 inch Si/SiO2 wafers. CMOS analogous fabrication was performed to yield transistors and circuits with features down to 0.5 μm, with high current density ~ 20 μA/μm and good on/off ratios. In addition, chemical doping has been used to build fully integrated complementary inverter with a gain ~ 5, and a defect-tolerant design has been employed for NAND and NOR gates. This full-wafer approach could serve as critical foundation for future integrated nanotube circuits.Another important technology component for nanotube based integrated circuits is to achieve air-stable n-type transistors through metal contact engineering. We demonstrate that by using metal contacts with small work function such as Gadolinium (Gd), the CNTFETs exhibit predominantly n-type behavior since the Fermi level of the metal is aligned with the conduction band of the carbon nanotubes. In order to achieve air stable operation, E-beam evaporated SiO2 was used for passivation and the devices exhibit clear n-type characteristics when measured in air. Further more, stepper and E-beam lithography were used to pattern both p-type (Pd contact) and n-type (Gd contact) devices on the same nanotubes and an integrated air-stable CMOS inverter with a gain of 6 was demonstrated. Rectifying diodes with Pd contact for p side and Gd contact for n side was also demonstrated and their solar-cell response was also studied.
5:45 PM - R4.5
Facile Alignment of Carbon Nanotubes Mediated by Tethered Maghemite Nanoparticles.
Il Tae Kim 1 2 , Nunnery Grady 1 , Karl Jacob 2 , Justin Schwartz 4 , Xiaotao Liu 4 , Rina Tannenbaum 1 3
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Polymer, Textile, and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 4 Mechanical Engineering, Florida State University, Tallahassee, Florida, United States, 3 Chemical Engineering , Technion-Israel Institute of Technology, Haifa Israel
Show Abstract We describe a novel, facile method for the alignment of multi-walled carbon nanotubes (MWNTs) in a magnetic field through the decoration of the MWNTs with monodisperse γ-Fe2O3 magnetic (maghemite) nanoparticles. The tethering of the nanoparticles was achieved by the initial activation of the surface of the MWNTs with carboxylic acid groups, followed by the attachment of the γ-Fe2O3 nanoparticles via their synthesis using a modified sol-gel process. Sodium dodecylbenzene sulfonate (NaDDBS) was introduced into the suspension as a surfactant in order to prevent the formation of an iron oxide 3D network. Various characterization methods were used to confirm the formation of well-defined maghemite nanoparticles, and show that they were tethered to the walls of the MWNTs. The tethered γ-Fe2O3 nanoparticles imparted magnetic characteristics to the MWNTs, which became superparamagnetic. The magnetic carbon nanotubes were oriented parallel to the direction of an externally-applied magnetic field, fact which was made possible by overcoming thermal motion. This alignment exhibited chain-like structures that were generated by the connection of the magnetic carbon nanotubes in line, touching each other in a head-to-tail fashion. This facile alignment of MWNT could promote the enhancement of various properties, e.g. mechanical and electrical properties, of the resulting composites. Moreover, this facile alignment at low magnetic fields, made possible by the magnetization of the carbon nanotubes through the tethering of maghemite nanoparticles, may be applied to a variety of other useful nanofillers, such a glass fibers, clay nanoparticles and cellulose nanowhiskers. Thus this represents a novel strategy that could allow the manipulation of the orientation of nanoscale fillers in a nanocomposite.
R5: Poster Session: Nanotube Composites, Functionalization and Dispersion
Session Chairs
Tuesday PM, April 06, 2010
Exhibition Hall (Moscone West)
6:00 PM - R5.11
Carbon Nanomaterials in Silica Aerogel Matrices.
Christopher Hamilton 1 , Juan Duque 1 , Gautam Gupta 1 , Stephen Doorn 1 , Andrew Dattelbaum 1 , Kimberly DeFriend Obrey 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractSilica aerogels are ultra low-density, high surface area materials that are extremely good thermal insulators and have numerous technical applications. However, their mechanical properties are not ideal, as they are brittle and prone to shattering. Single-walled carbon nanotubes (SWCNTs) and graphene-based materials, such as graphene oxide, on the other hand have extremely high tensile strength and possess novel electronic properties. By introducing SWCNTs or graphene-based materials into aerogel matrices, it is possible to produce composites with the desirable properties of both constituents. We have successfully dispersed SWCNTs and graphene-based materials into silica gels. Subsequent supercritical drying results in monolithic low-density composites having improved mechanical strength. These nanocomposite aerogels have great potential for use in a wide range of applications.
6:00 PM - R5.12
High Performance Titania-wrapped Single-walled Carbon Nanotube Network Thin Films.
Joong Tark Han 1 , Hee Jin Jeong 1 , Seung Yol Jeong 1 , Geon-Woong Lee 1
1 , Korea Electrotechnology Research Institute, Changwon Korea (the Republic of)
Show AbstractSingle-walled carbon nanotube (SWCNT)-based ultrathin network films have been considered as an alternative transparent conducting film (TCF) because the film is prepared in ambient conditions based on a solution process. One of the important requirements for SWCNT-based TCFs is environmental stability such as thermal and thermo-hydrostat stability.In this study, we introduce a simple process to fabricate high performance transparent conducting films with SWCNTs coated noncovalently with ultrathin titania layer by the hydrophobic interaction between nanotube surfaces and acetylacetone (acac) ligands molecules. TiO2 layer having a high electron transporting ability can minimize the increase of junction resistance after hybridization with a binder material. TiO2 coating of SWCNTs was performed by a direct mixing of titanium isopropoxide (TIP) / acac solution with SWCNTs solution in ethanol. Acac has been used as a chelating agent to control the reactivity of a titanium alkoxide. In this study, acac complexing with titanium was utilized to achieve a uniform distribution of TIP/acac sol by hydrophobic interaction with nanotube surfaces. The sheet resistances of the TIP/acac-wrapped SWNT films were gradually increased by increasing the binder content even at 150oC because the bridging acac ligands remain bonded to titanium throughout condensation at low temperature. Acac ligands increase a junction resistance, resulting in gradual increase of the sheet resistance by TIP/acac layer coating on nanotube surfaces. After heating to 300oC, the sheet resistance of the TiO2/acac-wrapped SWNT films drastically decreased by removal of acac ligand molecules above 200oC, while the sheet resistance of the pristine SWCNT film increased on heating by thermal oxidation. Moreover, this work demonstrates that ultrathin and uniform titania layer on SWCNTs prevent from the oxidation of functionalized SWCNTs in atmospheric condition at high temperature, and gives a water protection ability. Moreover, the uniform and thin titania layer formed by hydrophobic interaction promote the selective removal of amorphous carbonaceous materials without an oxidation of SWCNTs on heating at 300oC. Hence it may provide considerable potential in applications such as TCFs, photo-catalysis, sensor electrodes.
6:00 PM - R5.13
Transfer Printing Carbon Nanotube Films to Understand the Effects of Self-assembled Monolayers on the Electrical Properties of Carbon Nanotubes.
Michael Vosgueritchian 1 , Melburne LeMieux 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) are a promising material for next generation electronic devices. In particular they have been shown to be good candidates for sensors, field effect transistors, and as transparent electrodes. Specifically, solution deposition of SWNT films will enable low cost manufacturing and the ability to build these devices on flexible substrates. Despite many recent improvements in solution disposition of these films, there still remain many challenges in controlling the alignment, density, and type of nanotubes within the film. Previously, our group has shown the ability to align and sort SWNTs by spin coating them on a functionalized surface. However, this method does not work on all functionalized surfaces making it difficult to compare surface effects on SWNT films. We address this issue by using a dry transfer printing method to transfer semiconducting rich and aligned SWNT films to several different surfaces that have been reacted to have a self assembled monolayer (SAM), each with a different functional group. Atomic Force Microscopy (AFM) confirms that the density and alignment of the film is maintained. Micro-Raman analysis along with device testing show differences in the electrical properties (on current, mobility, threshold voltage) between the different SAMs, which can be attributed to electron exchange between the SAMs and SWNTs. This shows that it is possible to tune the properties of SWNT films by altering the surface chemistry. In addition, we gain insight on the transport properties of SWNTs on different functionalized surfaces.
6:00 PM - R5.14
Quantitative Metric for Nano-filler Dispersion in Polymer Composites.
Luke Gibbons 1 2 , Peter Lillehei 3 , Jae-Woo Kim 1 , Cheol Park 1 4
1 , National Institute of Aerospace, Hampton, Virginia, United States, 2 Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States, 3 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States, 4 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractThe dispersion quality of nano-inclusions within the matrix material is often overlooked in models relating the effect of nano-scale structures on functional performance of nanocomposites and processing/property relationships for these nanocomposites. This is due in part to the difficulty in visualizing the nano-inclusion and ambiguity in the description of dispersion. Understanding the relationships between the composition of the nano-filler, matrix chemistry, processing methods, and resulting dispersion is necessary for optimization or tailoring of nanocomposite physical properties. A method will be described that incorporates an emerging scanning electron microscopy technique with various image processing procedures to allow for the quantification and validation of dispersion parameters by visualization of conductive nano-fillers deep within insulating polymer matrices. This method makes it possible to quantify the dispersion of various single wall carbon nanotube (SWCNT)-polymer composites as a function of processing conditions, composition of SWCNT, and polymer matrix chemistry.
6:00 PM - R5.15
Dynamic Hydrophobic Behavior of Vertically Aligned Carbon Nanotube Arrays.
Erman Bengu 1 , Beril Baykal 1 , Gokce Kucukayan 2
1 Chemistry, Bilkent University, Ankara Turkey, 2 Nanotechnology Research Center (UNAM), Bilkent University, Ankara Turkey
Show AbstractIn this study, we explored the wetting behavior of water droplets on vertically aligned carbon nanotube arrays (VANTA) of varying film density, film thickness and alignment orientation. These carbon nanotube (CNT) arrays (or forests) were synthesized using a 3 inch tube furnace through chemical vapor deposition (CVD) with a mixture of flowing ethanol, argon, and hydrogen gases at a temperature ranging from 600-750°C. Dilute aqueous solutions (5 mmol l-1) of iron (III) nitrate and aluminum (III) nitrate have been applied on oxidized Si (100) substrates (approximately 10mm X 10mm) in an alternating fashion with the help of a micro-pipette. These nitrate solution treated substrates were allowed to dry at room temperature, and then they were loaded onto a quartz boat and placed into the load-lock of the tube furnace for processing. Some of the CNT forests synthesized in this study, displayed super-hydrophobic behavior upon testing with deionized water, where contact angles (CA) measured were in excess of 150°. Dynamic CA measurement experiments were also conducted. The results indicated that some CNT forest samples preserved their super-hydrophobic character for an extended period of exposure to the water droplet. Some retained a CA above 150° even after 15 minutes of exposure. We investigated the effect of film density, film thickness and orientation on the measured CA and the rate of change in the CA. Table 1 shows the change in the CA for CNT array films synthesized using different process parameters. Our studies indicated an optimum CNT film density and tube length for optimizing the dynamic behavior of these surfaces. Hence, we found that synthesis parameters and catalysis application methodology may significantly affect hydrophobic properties of these CNT forests.
6:00 PM - R5.16
Versatility of Poly-L-Lysine for Carbon Nanotube Network Film Coating.
Debora Lin 1 , Christopher Bettinger 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) have shown promise for use in organic electronic applications including thin film transistors, conducting electrodes, and biosensors. There is a current need to rapidly process SWNTs from solution phase to substrates in order to produce device structures. The use of surfaces covalently functionalized with primary amines has been shown to selectively adsorb semiconducting SWNT. However, this and similar techniques are dependent upon environmentally sensitive surface modification techniques. Hence, we explored the potential of substrates modified with physisorbed polymers as a possible alternative methodology. We hypothesized that rapid surface modification and could be accomplished by adsorption of poly(L-lysine) (PLL). In this work, we detail a rapid and facile method for depositing SWNTs onto various substrate materials using amine-rich PLL. PLL was adsorbed to various substrates including native silicon oxide and glass slides using aqueous solutions of the polyamino acid. Dispersions of SWNT of different chiralities suspended in N-methylpyrrolidinone (NMP) were spin cast on to PLL-treated substrates. SWNT adsorption and alignment were characterized by atomic force microscopy (AFM) while electrical properties of the network were characterized by 2-terminal resistance measurements. Additionally, we investigated the relative chirality of the SWNT networks by micro-Raman spectroscopy. SWNT surface density was strongly dependent upon the adsorbed concentration of PLL on the surface. SWNT density and alignment were also dependent upon spin coating speed and SWNT solution concentration. There is a critical concentration of PLL that induces sufficient SWNT adsorption to form conductive percolating SWNT networks. These networks consisted of mixtures of semiconducting and metallic nanotubes with no detectible selective adsorption. The biocompatibility of the PLL surface treatment also promotes strong cell attachment. We envision these conducting biocompatible SWNT networks could potentially be used as biosensors to investigate cell adhesion mechanics or tissue-device interfaces for neural prosthetics.
6:00 PM - R5.17
Tailoring the Dispersion State of Carbon Nanotubes in Water Using Stimuli-responsive Polymers.
Jaime Grunlan 1 2 , Krishna Etika 2
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Materials Science and Engineering Program, Texas A&M University, College Station, Texas, United States
Show AbstractDespite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use. Stimuli-responsive polymers show conformation changes with applied external stimulus (pH, temperature, light etc.). Two methods for non-covalent stabilization/dispersion of carbon nanotubes are describe here. The first method utilizes the pH-responsive nature of poly(acrylic acid) to disperse carbon nanotubes. The dispersion of nanotubes with weak polyelectrolytes enables the macroscopic properties of aqueous suspensions to be tuned using pH. Microstructural changes as a function of pH were observed with cryo–TEM of aqueous SWNT-filled suspensions. With poly(acrylic acid), nanotube bundling increases with increasing pH and these microstructurally-induced changes are reversible. pH dependent interaction of PAA with carbon nanotubes in water were confirmed by Raman spectroscopy and liquid suspension conductivity. This behavior has significant implications for the processing of carbon nanotubes and tailoring of composite properties. The second method involves the use of thermo-responsive copolymers. Temperature responsive polymers based on poly(N-cyclopropylacrylamide), with varying amounts of pyrene functionality, were used to disperse carbon nanotubes in water. The dispersion state of nanotubes below and above the lower critical solution temperature (LCST) of the polymers was investigated. Such stimuli-controlled dispersion of carbon nanotubes could have a variety of applications in nanoelectronics, sensing, and drug and gene delivery systems.
6:00 PM - R5.19
Fluorination of Single Walled Carbon Nanotubes in Solution Phase.
Ji Eun Park 1 , Hee Cheul Choi 1
1 Chemistry and advanced materials science, Pohang university of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show Abstract Incorporation of heteroatomic moieties into the backbone of single walled carbon nanotubes (SWNTs) is a direct gateway toward the versatile passivation of SWNTs with various active functional groups. Among many candidates, fluorine is of special interest not only because fluorine has been known as a good leaving group which enables further substitution reactions, but more importantly because its strong electronegativity allows facile tuning of the doping level of semiconducting SWNTs. Until now, the fluorination of SWNTs has been available only by gas phase reaction in which toxic fluorine gas should be involved. More seriously, the gas phase fluorination requires long reaction times at high temperature. In this presentation, we will discuss about a newly developed fluorination of SWNTs in solution phase at room temperature. We confirmed the successful fluorination of SWNTs by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The detail proposed mechanism of the fluorination will be also discussed.
6:00 PM - R5.2
Mesoscopic Dynamic Modeling of Impact Resistance of Carbon Nanotube Materials.
William Jacobs 1 , Alexey Volkov 1 , David Nicholson 1 , Leonid Zhigilei 1
1 Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractAn active experimental exploration of the use of carbon nanotube (CNT)-based materials in the design of multifunctional light-weight aerospace structures and thermal protection coatings calls for a better understanding of the nature of the collective behavior of CNTs under conditions of dynamic loading. Recent design of a novel mesoscopic model for CNTs opens up opportunities for computational investigation of the impact resistance of CNT materials. In this presentation we report the results of a series of simulations of high-velocity impact of a spherical projectile on a free-standing thin film composed of a random network of (10,10) CNT bundles (buckypaper). The ballistic threshold and the channels of the energy absorption/redistribution are identified for different impact parameters and related to the structural characteristics of the target material. Atomic-level simulations of individual CNTs and small CNT bundles are used for investigation of the rates of the thermal equilibration and inter-tube energy transfer, providing information required for a reliable parameterization of the mesoscopic model.
6:00 PM - R5.20
Selective Integration of Individual Metallic Single-walled Carbon Nanotubes from Heterogeneous Solutions.
Brian Burg 1 , Julian Schneider 1 , Niklas Schirmer 1 , Dimos Poulikakos 1
1 Department of Mechanical and Process Engineering, ETH Zurich, Zurich Switzerland
Show AbstractOut-of-solution guided assembly of surface-synthesized single-walled carbon nanotubes (SWNTs) on microelectrodes is investigated for electric field frequencies between 0.1 – 200 MHz. The dielectrophoretic separation of metallic from semi-conducting SWNTs is studied by direct electric transport measurements on individually deposited nanotubes, revealing a threshold separation frequency of 200 MHz for a solution conductivity of 250 mS/m. This infers an induced surface conductance of ≈2.5 S/m on semiconducting SWNTs in 1 wt % sodium dodecylbenzenesulfonate (SDBS) surfactant stabilized solution. Of the 22 deposited SWNTs at 200 MHz, 19 (86%) display metallic behavior, whereas at lower frequencies the expected random growth distribution of 2/3 semiconducting tubes prevails. Further, low frequency experiments and multi-physics simulations show that long-range nanotube transport is governed by hydrodynamic effects, while local trapping is dominated by dielectrophoretic forces. This allows a deeper understanding of the underlying dielectrophoretic deposition process in view of nanotube-based electronics and provides the hydrodynamic and electric field framework of dielectrophoresis in low concentration solutions.
6:00 PM - R5.21
Influence of Structural Defects on the Electronic Properties of Carbon Nanotubes Examined by Scanning Tunnelling Microscopy.
Cristina Giusca 1 , S. Ravi Silva 1
1 Advanced Technology Institute, University of Surrey, Guildford United Kingdom
Show AbstractOne of the main potential applications that has been envisaged for carbon nanotubes, due to the availability of both semiconducting and metallic features, is in the field of nanoelectronics. However, their electronic properties are quite often drastically affected by the presence of defects that can develop during nanotubes growth, processing or characterization. Some of these defects such as pentagon-heptagon rings, substitutional impurities, vacancies and dislocations are of topological nature, and can sometimes create on-tube intramolecular junctions, as found by previous scanning tunnelling microscopy (STM) studies. Our recent STM experiments revealed for the first time a much more complicated junction structure, a hybrid single-walled carbon nanotube consisting of a distinct coiled structure located between two straight segments, each of different helicity. The coiled structure has an estimated length of 7 nm and is seamlessly connected to each of the adjacent segments. Based on the atomically resolved images and on the tunnelling spectroscopy data, electronic effects at the interface of the different segments have been examined and the potential of the as-grown defective structures acting as active elements for molecular electronics investigated.In addition to topological defects, structural deformations that result in a radially collapsed state configuration of both single- and double-walled carbon nanotubes as examined by STM will be presented. These experiments bring evidence of changes in fundamental electronic properties of carbon nanotubes, with evidence of metal to semiconductor transitions as a response to the deformation.
6:00 PM - R5.23
Effects of Nitric Acid Treatments on Single-walled Carbon Nanotube Network Devices.
Huiseong Jeong 1 , Ji-Yong Park 1
1 Division of Energy Systems Research, Ajou University, Suwon Korea (the Republic of)
Show AbstractNetworks or thin films of single-walled carbon nanotubes (SWCNTs) are topics of active researches in recent years for applications in electronic devices, and transparent and flexible electronics. Various chemical treatment strategies are often employed to prepare networks of SWCNTs with good electrical characteristics. For example, acids such as nitric acids are often employed to post-treat SWCNTs and their networks. Acids are used to purify SWCNTs by eliminating impurities generated during synthesis. Acids are also shown to enhance the conductivity of networks or films of SWCNTs. There are reports that acid treatments induce hole doping of SWCNTs or reduce contact resistances between SWCNTs. Previous studies are mostly based on the changes of IV characteristics and light absorption properties of devices or bulk samples. Information about local changes occurring during or after acid treatments of SWCNT networks is still lacking and would provide insight on the roles of acid treatments on SWCNT devices. In this presentation, the effects of nitric acid treatments on the device characteristics of SWCNT networks will be discussed. The changes in IV characteristics of SWCNT network devices before and after acid treatments (with nitric acid vapor) are investigated. After exposure to nitric acid vapor at elevated temperature, most devices show increases in current levels and decreases in gate dependences. In order to elucidate the role of nitric acid on SWCNT network device, local electrical characterization tools such as electrostatic force microscopy (EFM) and scanning gate microscopy (SGM) are employed to identify local changes inside SWCNT networks. With EFM and SGM, both local doping effect and enhancements in connectivities among SWCNTs in the networks are found. The local changes inside devices measured with EFM and SGM will be correlated with the whole device characteristics.
6:00 PM - R5.26
True Linear Kinetics of Vertically Aligned Carbon Nanotube Growth Revealed by Spatial Mapping of Alignment.
Mostafa Bedewy 1 , Eric Meshot 1 , Kevin Lyons 1 , Arthur Woll 2 , Anne Juggernauth 1 3 , Sameh Tawfick 1 , A. John Hart 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 , Cornell University, Ithaca, New York, United States, 3 Macromolecular Science and Engineering Research Center, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractOwing to the inherent tortuosity of carbon nanotubes (CNTs) in a vertically aligned array or “forest”, the measured array height does not equal the average length of the constituent individual CNTs. Therefore, even real-time height measurement is not an accurate measure of the genuine growth kinetics. We propose a quantitative methodology that uses high-resolution spatial mapping of alignment to transform real-time measurements of array height to actual CNT length. Alignment is quantified by the Hermans orientation parameter that which is calculated from small-angle X-ray scattering (SAXS) data, enabling spatially-resolved transformation of the height kinetics based on a geometric model. Applying this technique to CNT forests grown by thermal chemical vapor deposition (CVD) from Fe/Al2O3 supported catalyst shows that the true length of CNTs within a forest is significantly greater than the forest height, and that the duration of growth rate deceleration prior to self-termination is overestimated by height measurements. Moreover, this approach transforms the kinetics of CNT forest growth from a sub-linear to a linear relationship with time, highlighting potential for insights into the limiting growth mechanisms of CNTs and other one-dimensional nanostructures.
6:00 PM - R5.27
Nitrogen Implantation and High Temperature Studies of Diamond Nanorods/Nanoflakes Spherule by High Resolution XPS.
Swathi Iyer 1 , Paul Maguire 1
1 School of Electrical and Mechanical Engineering, NIBEC, University of Ulster, Belfast, Belfast, Norther Ireland, United Kingdom
Show AbstractDiamond related nanomaterials such as the diamond nanowires, NCD, UNCD etc have in recent years attracted renewed interest mainly due to very high electrical conductivity, which is reported to be induced by nitrogen during the growth or due to post growth (doping) processes. Reactive ion implantation is one of the many widely acclaimed methods to modify the surface regions of carbon materials. Nitrogen, which acts as a donor can enhance the field emission of the diamond material due to the formation of additional energy levels in the band gap and electrical conductivity channels and also creates changes in the electron affinity levels. For many applications n-type doping is much preferred and nitrogen has been extensively used for n-type semiconductor devices. Novel Diamond nanorod flakes (DNR) structures synthesised by MPECVD were bombarded by low energy (5 keV) nitrogen ions for times between 0 to 20 minutes and subsequently annealed. The changes incurred to the bonding structure upon ion bombardment and thermal treatment was investigated by the in situ high resolution XPS. By controlled ion bombardment and annealing, specific amount of defects can be generated, enabling the system to transform from sp3 C to sp2 C and vice versa. The impact of N-bombardment on DNR structures and their thermal stability were investigated. The C1 component (sp2 C) was up shifted by 0.3 eV due to the N-bombardment defect generation. Increasing bombarding times enhanced the fraction of sp2 CN and sp2 C rather than sp3 C. The increase in the ID/IG ratio and the decrease in the intensity of trans-PA peaks after N-bombardments indicated the incorporation of nitrogen (28 at. %) at the grain boundaries. At elevated temperatures (800 C) the decrease in FWHM of the C 1s and the increase in the sp2 C concentration indicate that the structure is becoming more graphite like. The N 1s splits at higher temperature and this may be due to the re-arrangement of the N bonding states. At higher temperature the broken metastable bonds created by the ion bombardment may be converted to sp2 C, thereby enhancing the population of sp2 C and sp2 CN. The thermal energy drives the defects into the substitution sites in the grain boundaries and the carbon matrix. The complete disappearance of the ν1 and ν3 along with the decrease of ID/IG ratio, with annealing indicates a graphitic transformation.
6:00 PM - R5.28
Comparison of Fitting Procedures in Relating the G′ Band to the Presence of Defects in Carbon Nanotubes.
Szetsen Lee 1 , Jr-Wei Peng 1
1 Chemistry, Chung Yuan University, Chungli Taiwan
Show AbstractPlasma-induced defects in carbon nanotubes (CNTs) have been monitored with micro-Raman spectroscopy. Special attention has been given to the Raman intensity dispersion behavior of the G′ band with two- and three-peak fitting procedures. Similar to the argument for using intensity ratio I(D)/I(G) as a criterion for estimating the defect content on CNT surfaces, this work shows that the intensity ratio dispersion involving the G1′ component from the two-peak fitting procedure and the 2D component from the three-peak fitting procedure, i.e. I(G1′)/I(G) and I(2D)/I(G), is closely related to the presence of defects in CNTs. The dispersion behaviors of other components of the G′ band are also discussed.
6:00 PM - R5.3
Directed Solution Assembly of Nanotube Networks on Polymers Dielectrics for Low Voltage Transistors and Aqueous Chemical Sensors.
Melburne LeMieux 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractThe ability to detect trace amounts of analytes in aqueous environments using portable, low power equipment is important for health diagnostics, environmental monitoring, and national security applications. Because their structure consists entirely of surface atoms, single-walled carbon nanotubes (SWNTs) have been shown to exhibit excellent sensor characteristics. Individual SWNT-based devices currently are not practical for large scale integration. Although random nanotube networks offer an excellent compromise, still, the nature of SWNT network randomness in terms of chirality, tube density, and bundling makes device reproducibility poor, greatly inhibiting SWNT sensors and the understanding of how these elements affect analyte sensitivity and response. Many examples of SWNT devices have been demonstrated for analyte detection, including chemiresistors, chemicapacitors, and chemFETs. Of these, chemFETs offers the most versatility and highest sensitivity. FETs based on semiconducting SWNTs respond to a wider range of analyte interactions than metallic SWNTs because of a reduced density of states near the Fermi level in metallic tubes as compared with the valence band edge of semiconducting tubes. However, depositing a network of semiconducting SWNTs from solution is nontrivial, and controlling the alignment and density of the SWNTs is another critical issue facing SWNT-based sensors. We address these issues by depositing organized, chirality sorted sub-monolayer SWNT networks on polymer dielectrics, and the resulting sensors were used to detect trace concentrations, down to 2 ppb, of dimethyl methylphosphonate (DMMP) and trinitrotoluene (TNT) in aqueous solutions. Importantly, the FET sensors fabricated with aligned, sorted nanotube networks (enriched with semiconductor SWNTs) showed a higher sensitivity to analytes than those fabricated with random, unsorted networks with predominantly metallic charge transport. Finally, the fluidic assembly at room temperature allows for deposition onto plastic surfaces enabling low-voltage operation of the SWNT TFTs and hence operation in aqueous environments.
6:00 PM - R5.30
Influence of Additives on Preparation and Properties on Nanostructured Carbons.
Vinay Bhat 1 , Cristian Contescu 1 , Nidia Gallego 1
1 Carbon Materials Technology Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractPotassium doped and pure nanostructured carbons are prepared from synthetic polymer precursor Poly Furfuryl Alcohol (PFA) using physical activation method to understand the influence of additive on its nanostructure evolution and hydrogen storage property. The study reveals that potassium addition speedup the activation process and helps to improve the surface area and nanopore volume of PFA carbon. In addition, study also shows that the presence of potassium within the carbon structure enhances the hydrogen storage capacity at room temperature. This observation supports long standing speculation that the alkali and alkaline earth metals induce charge transfer effect, which will increase the hydrogen storage capacity near ambient temperature.
6:00 PM - R5.31
Mechanically Robust, Conductive Carbon Nanotube-based Aerogels and Their Composites.
Marcus Worsley 1 , Sergei Kucheyev 1 , Joshua Kuntz 1 , Thomas Han 1 , Octavio Cervantes 1 , Joe Satcher 1 , Alex Hamza 1 , Theodore Baumann 1
1 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractMechanical and electrical properties of porous solids exhibit strongly superlinear dependencies on the material density. Hence, ultralow-density nanoporous materials have notoriously poor mechanical properties. This remains the major factor limiting many potential energy-related applications of these materials. For example, silica aerogels with densities below ~100 mg/cm3 typically have a very low Young’s modulus of ~1 MPa. In this presentation, we will discuss synthesis and characterization of a novel class of robust ultralow-density nanoporous sp2-bonded carbons. These materials, with monolithic densities of ~10 mg/cm3 and above, are made of single-walled carbon nanotubes decorated and interconnected by carbon nanoparticles. Such carbon nanotube-based aerogels exhibit unprecedented properties, including electrical conductivity, high stiffness, fracture toughness, and effective yield stress. In addition, we report the use of these carbon nanotube-based aerogels as scaffolds to fabricate a wide variety of composites with exceptional mechanical and electrical properties. To create the composites, the aerogels were infiltrated with different insulating materials (e.g. polydimethylsiloxane, titania, silica, etc.). The resulting composites had electrical conductivities over 1 Scm-1 and improved stiffness (2-5 times that of the matrix moduli) with as little as 1 vol% nanotube content. These findings will be compared with properties of better studied nanoporous systems (e.g. silica and conventional carbon aerogels) and carbon nanotube composites. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the DOE Office of Energy Efficiency and Renewable Energy.
6:00 PM - R5.32
Role of Marangoni-Bernard Instability on the Formation of Electrical Conductive Network in Amorphous Polymer-carbon Nanotube Nanocomposites Films.
Sang Il Jun 1 , Soon Sik Lee 1 , Hye Min Kim 1 , Cho Hee Park 1 , Sua Choi 1 , Do Young Bae 1 , Heon Sang Lee 1
1 Chemical Engineering, Dong-A University, Busan Korea (the Republic of)
Show AbstractIn order to study Marangoni-Bernard effect on the dispersion of MWCNTs in polymer solutions, we employed various amorphous polymers such as polystyrene, polycarbonate, poly(methyl methacrylate), and poly(styrene-co-acrylonitrile) as well as various organic solvents. We found that the electrical conductivity of amorphous polymer-MWCNT films strongly depends on the Marangoni number. The Marangoni-Bernard instability significantly affects on the formation of electrical network in amorphous polymers-MWCNT solution casting films. The role of enthalpic interaction between polymer and solvent is less significant compared to those of Marangoni-Bernard effect. We anticipate this result would be valuable for understanding the formation of electrical conductive networks in polymers-CNTs nanocomposite films.
6:00 PM - R5.33
Structural Characterization and Application of Carbon Nanoscrolls in Composites.
Debdulal Roy 1 , Eloisa Angeles Tactay 2 , Richard Brown 1 , Steve Spencer 1 , Tony Fry 1 , Martin Milton 1
1 , National Physical Laboratory, Teddington United Kingdom, 2 , University of Cambridge, Cambridge United Kingdom
Show AbstractCarbon nanoscroll is a novel nanostructure of carbon that has been reported recently. Unlike nanotubes and other closed carbon nanostructures, carbon nanoscrolls have very large accessible surface area/weight, up to 2400 m2/gm. This makes it very attractive material for a wide range of applications including reinforcement in composites, solid-state hydrogen storage and electrochemical actuators. In this work we report a simple and scalable method of synthesising carbon nanoscrolls using wet chemical process. Graphite is exfoliated using wet chemical oxidation process followed by reduction using microwave heating in inert atmosphere. Under controlled ultrasonication, graphene is used rolled up to carbon nanoscrolls. The structure and chemistry of the nanostructures have been studied using Raman spectroscopy, XPS, TEM and SEM. New low wave number Raman bands are observed from carbon nanoscrolls and these have been explained in terms of relaxation of Raman selection rules away from the Γ point. Carbon nanoscrolls have also been used to reinforce composites, and 50 to 100 times more reinforcement effects has been demonstrated in poly-vinyl alcohol matrix.
6:00 PM - R5.34
Woven-fabric Textile Nanocomposites: Surprising Enhancement in In-plane, Fiber-dominated Mechanical Properties.
Iti Srivastava 1 , Mohammad Rafiee 1 , Nikhil Koratkar 1
1 Material Science, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractTwo phase nano-composites (e.g. carbon nanotubes embedded in a polymer matrix) have been long known and studied. By contrast study of three-phase nano-composites has not received the same level of attention; the three phases include carbon nanotubes, the polymer matrix and conventional microscale continuous fibers. Recently several groups have investigated three-phase composites involving blends of carbon nanotubes, unidirectional microfibers and epoxy matrices. A key observation from these studies is that while the nanotubes significantly enhance matrix dominated (out-of-plane) properties such as inter-laminar shear strength, they have a minor impact on in-plane properties such as tensile strength and toughness. This is because in-plane tensile properties are dominated by the continuous micro-fibers that run along the length of the composite and consequently the effect of nanotubes as matrix modifiers has a small influence. It should be noted that prior studies with three-phase nanocomposites have focused on unidirectional micro-fibers and woven fabric (i.e. textile) arrangement of micro-fibers has not been investigated in detail. Here we report surprising improvement in tensile strength, toughness and ductility for textile composites with the addition of nanotubes to the matrix. A major improvement in the case of graphite/epoxy textile composites was observed; we report ~200% increase in toughness and ~225% increase in strain-to-break with addition of ~0.05% weight of amine functionalized multiwalled carbon nanotubes to the composite. Similar observations were made for Kevlar/epoxy textile composites. We attribute the differences in the in-plane tensile response of unidirectional vs. textile nano-composites to the geometrical arrangement of the microfibers and the critical role of the pure matrix block in textile systems. In addition to undergoing axial deformation, the pure matrix block in textile composites is also resisting the warping of the unit cell that is induced by the opposite curvature of adjacent fill and warp strands and can therefore degrade rapidly as matrix cracks accumulate under loading. Such degradation of the pure matrix block induces an extension-bending coupling effect in the woven-fabric laminate, which in turn, induces bending stresses in the microfiber strands. These bending stresses in the microfiber strands will augment the axial stresses and therefore accelerate the failure process. As a consequence delay in the pure matrix block’s failure due to the nanotube-induced toughening effect results in a corresponding delay in the ultimate failure of the woven-fabric laminate under in-plane tensile loading. The ability to enhance in-plane microfiber-dominated properties (such as toughness and ductility) of textile composites using nanotube additives is expected to significantly improve their performance, reliability and crashworthiness in a variety of high performance structural applications.
6:00 PM - R5.35
Characterization of Carbon Nano-materials With the Confocal Raman-AFM.
Ute Schmidt 1 , Fernando Vargas 1 , Thomas Dieing 1 , Klaus Weishaupt 1
1 , WITec GmbH, Ulm Germany
Show AbstractCarbon is known to exist in a number of allotropes which range from single crystalline diamond - the hardest of all known materials, to the soft, layer based graphite. The recently discovered carbon nano-materials such as carbon nanotubes [1,2] and graphene [3] play an important role in modern material science due to their light weight, unique electrical and optical properties and mechanical strength. Their functional properties lead more and more to their implementation in modern materials.Both, graphene and carbon nanotubes represent also perfect model systems for fundamental research. Carbon nanotubes have proven to be unique systems for the study of Raman spectra in one-dimensional systems. Although the diameter of single walled carbon nanotubes (SWCNT) is far below the optical resolution limit, its unique optical and spectroscopic properties due to the one-dimensional confinement of electronic and phonon states leads to resonant enhancement of the corresponding photophysical process, thus it provides insight into the photonic and electronic structure of one-dimensional carbon molecules in their bonding environment. Graphene, a one atom layer thick planar sheet of sp2 bound carbon atoms, is a perfect model system for studying Raman spectra in two-dimensional systems.Characteristic Raman spectra for both forms of nano-carbons as well as the influence of the surrounding environment will be discusses.
6:00 PM - R5.39
CNT Gate FETs and Nonvolatile Memories.
Rea Setya 1 , Pik-Yiu Chan 1 , Fuad Alamoody 1 , John Fikiet 1 , Fotios Papadimitrakopoulos 2 , Faquir Jain 1
1 Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Chemistry and IMS, University of Connecticut, Storrs, Connecticut, United States
Show AbstractCarbon nanotubes (CNTs) have been used extensively in the past decade for the fabrication of field-effect transistors (FETs) [Trans et al, Nature, 393, pp 49-52, May 1998], logic circuits [Derycke et al, Nanoletters, Vol 1, 2001], memories [Yang et al, Diamond and Related Materials, 13, pp 1967-1970, 2004] and biomedical applications [Allen et al, Advanced Materials, Vol 19, Issue 11, pp 1439-1451, April 2007] because of their unique physical, mechanical and electronic properties. The unique property of CNTs is their electrical conductivity which can be tailored into either semiconducting or metallic, based on the diameter and chirality of the nanotubes. Most of the published literature in CNTs describes their role as transport channels in FETs [Bachtold et al, Science, 294, 1317 (2001)]. In this work CNTs have been used as a gate for FETs and floating gate for non-volatile memories. The focus of this effort is to alter the work function and hence the threshold of the Si FET by changing the type of CNT used. Recently, CNTs have been separated from metallic and semiconducting. This development assists our investigation in designing sub-22nm Si devices. In terms of processing, vertically-aligned CNTs were deposited by the electrostatic CNT/COO-/Fe3+ interaction using a self assembly technique [Galeska et al, Biomacromolecules, 1, pp 202-207, January 2000]. Briefly, the substrate was first immersed into the Nafion solution, followed by dipping into the ferric chloride solution. The substrate was finally immersed into CNTs dispersed in DMF (dimethylformamide) for 30 minutes. The CNTs were subsequently annealed under high vacuum. AFM characterization was done to investigate the CNT deposition. A much higher surface coverage of CNTs over the substrate was found with this process as compared to the chemical vapor deposition (CVD) method. Height of the nanotube forest was found to be between 8-12 nm. Raman spectroscopy was used and G-band (graphitic band) was observed at 1600 cm-1 indicating the presence of carbon on the silicon substrate. Electrical transfer (Id-Vg) and output (Id-Vds) characteristics of FETs, incorporating solution-assembled vertically-aligned carbon nanotubes, are presented. Modeling of FETs is also discussed. In case of nonvolatile memories, vertical CNTs were deposited on thin layer of oxide as a floating gate to store charge. Shift of 0.5 V (ΔVth ) in the threshold voltage in the drain current-gate voltage (transfer) characteristics was observed in the preliminary data.
6:00 PM - R5.40
RF NEMS Switches Based on Vertical Carbon Nanotubes.
Afshin Ziaei 1 , Michael Charles 1
1 , THALES R& T , Palaiseau France
Show AbstractThe objectives are to demonstrate a reproducible carbon nanotube (CNT) [1] based technology for switching applications and to realize a radio frequency (RF) switch. The final objective is to demonstrate a CNT based switching device working in the range 40-60GHz and fulfilling very demanding requirements: low losses, high isolation, a switching time below 0.1μs, an operation voltage below 30V and high power handling capabilities. The basic innovative idea is to take advantage of the size and of the unique mechanical and electrical properties of CNTs coupled with a one dimensional geometry and of the MEMS technology. We will study the parallel fabrication of switches based on vertically aligned CNTs grown directly on the substrate using a process compatible with integrated circuits. To unable for high power capabilities, we will study the possibility of using an array of CNTs switches to divide the current through an individual switch. In the long term, we will demonstrate that the use of CNTs will lead to a new generation of nano-electro-mechanical-systems (NEMS) with high integration density and low cost for communication networks and other applications requiring ultraminiaturized, lightweight components that operate at low voltage and high speed (>GHz for CNTs due to their geometrical and size properties) and with low power consumption.
6:00 PM - R5.41
Synthesis of Free-standing, Highly Aligned and Transparent Sheets of Silicon Oxide and Silicon Nitrite Ceramic Nanotubes.
Marcio Lima 1 , Xavier Lepro 1 , Ray Baughman 1
1 NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractWe report the synthesis of high aspect ratio, aligned and free-standing ceramic nanotubes made of silicon oxide and silicon nitride by using carbon nanotubes (CNT) sheets as templates. The CNT sheets were directly drawn from spinnable CNT forests (Zhang et al. Science 309, 1215, 2005). The synthesis of the ceramic nanotubes is accomplished by coating the CNTs with the ceramic phases using low temperature (250°C) plasma-enhanced chemical vapor deposition. The CNTs can be uniformly and individually coated by this technique. The deposition can also be performed on the CNT forests. The presence of the ceramic coating do not affect substantially the electrical conductivity of the CNT sheets. The carbon nanotubes can be removed from the interior of the ceramic coatings by oxidation. This process results in the production of transparent, free-standing sheets of ceramic nanotubes. The ceramic nanotubes have an internal diameter of approximately 10 nm and outer diameter between 15 to 100 nm. When in high temperature (1050°C) the silicon nitride nanotube sheets showed a higher mechanical stability than the silicon oxide ones. The ceramic nanotubes show a hydrophilic behavior and can be easily dispersed in water without use of surfactants.
6:00 PM - R5.42
The Development of High Performance Carbon Nanotube Thermal Interface Materials.
Robert Cross 1 , Baratunde Cola 1 , Timothy Fisher 2 , Samuel Graham 1
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Mechanical Engineering , Purdue University, West Lafayette, Indiana, United States
Show AbstractThe development of new thermal interface materials is seen as a key technology in the advancement of thermal management techniques for high powered electronic devices. A new method has been developed to create vertically aligned carbon nanotube (VACNT) thermal interface materials which can be attached to a variety of metalized surfaces. VACNT films were grown on Si substrates using standard CVD processing followed by metallization using Ti/Au. The coated CNTs were then bonded to metalized substrates at 220C. By reducing the adhesion of the VACNTs to the growth substrate during synthesis, the CNTs can be completely transferred from the Si growth substrate and used as a die attach material for electronic components. Thermal resistance measurements using the photoacoustic technique showed thermal resistances as low as 1.7 mm2K/W for bonded VACNT films approximately 20 um in length and 10 mm2K/W for CNTs up to 130 um in length. Tensile testing demonstrated a die attachment strength of 40 N/cm2 at room temperature. Overall, these metalized and bonded VACNT films demonstrate properties which outperform indium based solders and are promising for next generation thermal interface material applications.
6:00 PM - R5.43
Effect of the Carbon Nanotube Molecular Interface on the Photoswitching of Diarylethene Derivatives.
Roger Lake 1 3 , Md. Khalid Ashraf 1 , Nicolas Bruque 1 , Gregory Beran 2 , Jeremy Tan 1 , Thomas Helander 3
1 Electrical Engineering, University of California Riverside, Riverside, California, United States, 3 Computer Science and Engineering, University of California Riverside, Riverside, California, United States, 2 Chemistry, University of California Riverside, Riverside, California, United States
Show AbstractRecently reported conductance measurements of photoswitching molecules bridging CNT contacts are analyzed [1] using density functional theory and non-equilibrium Green functions. The effect on the conductance of the passivation chemistry, the cut angle, the CNT chirality, and the number of molecular bridges is described. In all cases studied, explicit calculations of the electron affinity, ionization potential, and image potential, show that the molecular HOMO provides a weakly coupled conductive channel [2]. Surface states of zigzag CNTs can make the conductance insensitive to the energy level of the molecular HOMO which results in low conductance switching ratios for photoswitching molecules. The origin of the irreversible photoswitching behavior of the diarylethenes connected to CNT leads is analyzed. UV radiation causes the open isomer to close and the conductance to increase. In solution, the closed isomer will open upon visible radiation, but this is not observed when connected to CNT contacts. Also, this behavior is opposite to that observed with gold contacts. We find that the strong coupling of the molecular LUMO to the CNT π-band results in the irreversible switching of the photochromic darylethene derivative molecules. The short lifetime of the molecular LUMO (≤ 30 fs) resulting from the strong coupling indicates that neither the open nor closed form of the molecule can be photoexcited into a charge-neutral excited state for any appreciable length of time. It is likely that this inability to populate the LUMO prevents photoswitching of the closed to open isomer. Analysis of the HOMO and LUMO lifetimes suggests that photoexcitation results in oxidation of the molecules, so that the open to closed switching mechanism is similar to that of electrochemical switching rather than photoexcitation. (1) A. C. Whalley et al., J. Am. Chem. Soc. Comm. 129, 12590 (2007). (2) N. A. Bruque et al., "Conductance of a Conjugated Molecule with Carbon Nanotube Contacts," Phys. Rev. B, 80, 155455 (2009).
6:00 PM - R5.45
Optical Modulation of Microcantilevers by Charge Transfer Between Ru Coordination Complexes and Vertically-aligned SWNTs.
Michael Forney 1 , Jeffrey Alston 1 , Jordan Poler 1
1 , UNC Charlotte, Charlotte, North Carolina, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) have been widely studied because of their superior mechanical properties as well as their ballistic one-dimensional electronic behavior. We hypothesize that vertically-aligned SWNTs (VA-SWNTs) grown on microcantilevers provide an architecture for novel actuators. Actuators based on this architecture could be used for nano-manipulation, release of drugs from a capsule, or nano-valves that are controlled by optical stimulation. By employing optically active Ru coordination complexes that mechanically dock with SWNTs and show evidence of metal-to-ligand charge transfer, we can ‘charge up’ an array of VA-SWNTs. The electrostatic repulsion among the charged SWNTs provides surface stress that will induce microcantilever deflection. Initial COMSOL Multiphysics modeling results for the actuator design are promising and more complex models are currently being studied. Preliminary experiments are being conducted in parallel with the advanced modeling.
6:00 PM - R5.46
Themochemistry of Carbon Nanotubes.
Andrey Levchenko 1 , Alexandra Navrotsky 2
1 , Setaram Inc, Newark, California, United States, 2 Peter A Rock Thermochemistry Laboratory and NEAT ORU, University of California - Davis, Davis, California, United States
Show AbstractOxidation calorimetry at high temperature is shown to be a viable alternative to bomb calorimetry. In oxidation drop calorimetry a compressed pellet is dropped from room temperature into a hot calorimeter (700-800 C) under normal pressure of oxygen or air allowing determination of standard enthalpies of oxidation thus enthalpies of formation. Thermodynamic data for carbon nanotubes (CNTs) are scarce yet important to their characterization, synthesis and processing. Nanomaterials, CNTs in particular, are difficult to deal with using conventional thermal analysis and calorimetry techniques due to low synthesis yield and impurities. Oxidation calorimetry as a suitable tool to study CNTs will be discussed.
6:00 PM - R5.47
Methods for Adjusting the Thermal Conductivity of Carbon Nanotube Felts.
Diana Lewis 1 , Brian White 1 , Tom VanVechten 1 , David Lashmore 1
1 , Nanocomp Technologies, Concord, New Hampshire, United States
Show AbstractThe thermal conductivity of multi-wall CNT non-woven textiles (“felts”) may be altered/tuned by doping and alignment, providing a material capable of exhibiting thermal conductivities varying by more than an order of magnitude (from 2 W/m-K to 65 W/m-K). In the work presented here, CNT felts are produced by using a floating catalyst CVD process to generate a cloud of carbon nanotubes that are deposited on a rotating drum. Boron and C60 have been added during the growth process, incorporating the atoms or molecules into the CNT material. We have shown that increasing boron concentration reduces the thermal conductivity: an addition of 0.66 wt% boron to the felt lowers the thermal conductivity by an order of magnitude over a standard felt. The addition of C60 produces a maximum in the thermal conductivity with a mid-level concentration, doubling the thermal conductivity over the standard felt. The use of other dopants, such as poly(ethylene imine), decreases the bulk thermal conductivity. Alignment of the CNT bundles within the felts using a mechanical drawing process yields an anisotropic material with high single-direction thermal conductivity. A combination of methods could result in felts with thermal conductivities as low as 1 W/m-K or as high as 100 W/m-K. Due to the felt’s low density (0.4 g/cc), the resulting high thermal conductivity materials could be used to produce lightweight thermal straps while the low thermal conductivity material may have applications in high-temperature thermo-electric devices.
6:00 PM - R5.5
Study of Thermal and Mechanical Characteristics of Heterogeneous Nanocomposites With Interfacial Morphology Using ab-initio and Atomistic Methods.
Vikas Samvedi 1 , Vikas Tomar 1
1 School of Aeronautics, Purdue University, West Lafayette, Indiana, United States
Show AbstractStudies on nanocomposites have proven them to be promising options for various applications based on their excellent thermal and mechanical properties, especially at high temperatures. These characteristics of nanocomposites might at times need to be tailored to meet a specific requirement. Interfaces and grain boundaries in such nanocomposites make available the option to obtain the desired properties by making microstructural changes. In the present research, atomistic analyses of nanocomposite interfaces have been correlated and supported with ab-initio calculations based on plane-wave density function theory (DFT). The focus of ab-initio study is to study the mechanical properties of the nanocomposites under the influence of nanoscale diffusion occurring during the formation of interfaces and grain boundaries and correlating it with observed thermal and mechanical properties from atomistic calculations. The configuration restructuring at the interfaces leading to the formation of defects and dislocations with the increase of temperature is analyzed to study the stability and hence, be able to predict the overall thermal and mechanical characteristics of such nanocomposites. Analyses of the effect of straining on the nanocomposite property changes are also performed to study it as a promising means to obtain nanocomposites with tailored properties.
6:00 PM - R5.7
Polystyrene Composites Filled With Multi-wall Carbon Nanotubes and Indium Tin Oxide Nanopowders: Properties, Fabrication, Characterization.
John Boyea 1 , Rosario Gerhardt 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThis research seeks to design and characterize novel polyhedral phase segregated microstructures of polystyrene (PS)-matrix composites filled with multi-walled carbon nanotubes (MWNT) and indium tin oxide (ITO) nanopowders. PS is compression molded with MWNT and ITO separately first. The resulting composites are conducting, and remain optically transparent. Mixtures of MWNT and ITO are then used to form composites in order to optimize their transparency and conductivity. This is achieved by fabricating composites with varying concentrations of fillers. Impedance spectroscopy is used to characterize the electrical properties of the composites. Optical properties are characterized by measuring the transmission of light through the composite in the visible light spectrum using a spectrophotometer. The properties of the fillers used are also characterized which is used in a model to relate them. The main objective of the project is to understand the relationships between the structural, electrical, and optical properties of the composites. The resistivity of PS composites filled with MWNT ranges from 105 to 1013 Ω cm for samples with 0.007 to 0.9 vol% MWNT. The resistivity of PS composites filled with ITO ranges from 107 to 1013 Ω cm for composites with 0.034 to 0.86 vol% ITO. A time dependence on impedance was found for composites filled with MWNT, as time increases there is a decrease in impedance.
6:00 PM - R5.8
Reinforcing Effects of Multi-walled Carbon Nanotubes on Creep Behavior of Aluminum-based Composites.
Hyunjoo Choi 1 , Jaehyuck Shin 1 , Donghyun Bae 1
1 , Yonsei University , Seoul Korea (the Republic of)
Show AbstractReinforcing effects of multi-walled carbon nanotubes (MWNTs) on creep behavior of aluminum-based composites was investigated. The composites were produced by hot rolling the ball-milled mixture of aluminum powders and MWNTs. During the specially controlled milling process, each of MWNTs was uniformly dispersed and embedded within the aluminum powders. Furthermore, the tubes are found to be gradually filled with aluminum atoms as the milling time increases, providing mechanically interlocked strong interface between MWNTs and the matrix. Creep behavior of the composites at high- and low-stress levels was examined in the temperatures ranging from 423 to 523 K. MWNTs may effectively block both thermal diffusion of aluminum atoms and dislocation slips; the composites exhibit significantly reduced thermal diffusivity and remarkably enhanced strength at elevated temperatures. The operative creep mechanism is also suggested, based on the stress exponent and activation energy for creep.
6:00 PM - R5.9
Optimization of CNT/Ni Composite Fabrication for Surface Coating of Microdrill Bit to Improve Wear Resistance.
Caroline Sunyong Lee 1 , Jiyoung Roh 1 , Kyubong Jung 1 , Bong-Young Yoo 1 , Sung hoon Ahn 2 , Tae-moo Lee 3
1 Metallurgy Science and Engineering, Hanyang University, Ansan Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of), 3 , Neotis Co. Ltd., Anseong Korea (the Republic of)
Show AbstractRecently, there has been increasing demand in halogen-free PCB (printed circuit board) since environmental regulations ban the use of Pb and Halogen-kinds to be included in PCB. However, Halogen-free PCBs are hard to cut and the improvement in the performance of WC drill bit is urgently needed.[1] To overcome these problems, Carbon Nano Tube (CNT) for surface coating is used to improve wear resistance of WC-microdrill bit. CNT which can be fabricated using various methods, has outstanding physical and chemical properties with much higher strength than that of steel. [2] The optimized fabrication condition for CNT/Ni composite on the surface of WC drill bit was investigated to improve the wear resistance of the micro drill bit. For CNT growth, nickel was used as a catalyst with its thicknesses ranging from 10 to 300 nm. 20nm of SiO2 barrier layer was formed by magnetron sputter to promote formation of Ni islands since forming Ni islands promote formation of high density of CNT growth.[3] Annealing was carried out in Ar atmosphere for 20min up to 740°C to form randomly distributed Ni islands where CNT nucleation can be originated. After that, heat treatment was simply performed to grow CNT in tube furnace for thermal CVD process. 100/400 sccm ratio of CH4 / H2 mixture was used to grow CNT for 30min at 900°C. As a result, bent shapes of CNT with its diameter less than 10 nm were observed. In this study, various parameters, such as growth temperature, growth time and gas flow ratio, were controlled to obtain optimized condition for CNT growth applicable for coating of micro drill bit. After CNT growth, Ni was electroplated to fill the space among CNT with its total thickness to be less than 1 um. The hardness and wear test results of this optimized CNT/Ni composite on the surface of WC drill bit showed higher values than the WC drill bit without coating. Therefore, mechanical properties of micro tool can be improved by surface coating of CNT/Ni composites.REFERENCES[1] L, Fu, “Method and system of automated measurement of micro drill bit wear”, Circuit World (2009), Vol. 35, No. 3, pp. 29-34[2] S.D. Faulkner, “Study of composite joint strength with carbon nanotube reinforcement”, Journal of Materials Science (2009), Vol. 44, No. 11, pp. 2858-2864[3] S.A Moshkalyov, “Carbon nanotubes growth by chemical vapor deposition using thin film nickel catalyst”, Materials Science & Engineering B (2004), Vol. 112, No. 2-3, pp. 147-153
Symposium Organizers
David B. Geohegan Oak Ridge National Laboratory
John Robertson Cambridge University
Kuei-Hsien Chen Academia Sinica
Jie Liu Duke University
R6: Transistors from Aligned Nanotubes
Session Chairs
Pierre Legagneaux
Ken Teo
Wednesday AM, April 07, 2010
Room 2020 (Moscone West)
9:00 AM - **R6.1
Customizing Carbon Nanotube Mat Growth: From Direct Implementation on Device Substrates to Mass Production by Fluidized Bed.
Suguru Noda 1
1 Department of Chemical System Engineering, The University of Tokyo, Tokyo Japan
Show AbstractCarbon nanotubes (CNTs) have attracted much attention owing to their unique one-dimensional structure and properties. Many applications have been proposed and extensively researched, however, the difficulties in their synthesis and implementation limit their practical applications. Catalytic growth on substrates by chemical vapor deposition (CVD) now enables millimeter-thick CNT mats within ten minutes [1,2]. It opens a route of direct CNT device fabrication, however, the process temperature typically as high as 800 degree C often becomes the barrier for it. Lowering the growth temperature is an important approach, and we systematically studied CNT growth by using simple gas mixtures of C2H2/Ar and Co/TiN catalysts for respective temperature and C2H2 partial pressure ranges of 400-600 degree C and 1-200 mTorr [3]. We found that the key for the sustainable CNT growth is to limit the C2H2 pressure correspondingly to the temperature, constructed a model reproducing growth curves, and realized densely-packed CNT mats at 400 degree C. But the approach of low temperature growth suffers from the exponential decrease in growth rates with decreasing temperatures. Here arises an opposite approach, i.e. instant high temperature growth. We prepared line-shaped metal electrodes on glass substrates, supported Fe/Al2O3 catalysts on the electrodes, and grew CNTs by heating the electrodes for 1 second by applying a pulse voltage under a flow of C2H2/Ar [4]. Micrometer-thick CNT mats grew in just 1 second, and Fe catalysts of different thickness yielded CNTs from single-walled to multi-walled. By using line-shaped electrodes and CNT mats as cathodes and cold cathodes, respectively, field emission and cathode luminescence were realized. It should be noted that we never used substrate heaters nor vacuum pumps for CNT growth and that CNT growth was the easiest and fastest among the processes used in the device fabrication.Wet-processing through dispersion and coating is another important route for CNT device fabrication, and mass production of CNTs become the key issue for this route. CNT growth on substrates enables both high growth rate and little catalyst contamination, however, productivity of CNTs is still very small compared with 3D processes using gas-suspended catalysts. We substituted substrates with ceramic beads to enlarge the surface area, and applied the fluidized bed to support Fe/Al2O3 catalysts on the beads, grow CNTs, separate CNTs from the beads, and repeat this cycle only by switching the gas flow while keeping the temperature unchanged [5]. This process now enables continuous production of sub-millimeter-long CNTs.[1] K. Hata, et al., Science 306, 1362 (2004).[2] S. Noda, et al., Jpn. J. Appl. Phys. 46, L399 (2007).[3] S. Noda and T. Shirai, 10th Int. Conf. on the Science and Application of Nanotubes (Nanotubes 2009), A-37 (2009).[4] S. Noda, et al., ibid, A-3 (2009).[5] S. Noda, et al., ibid, CT-05 (2009).
9:30 AM - R6.2
Growth Mechanism of Single-walled Carbon Nanotubes at Low Temperature and Low Pressure CVD Conditions.
Shohei Chiashi 1 , Taiki Inoue 1 , Hiroto Okabe 1 , Junichiro Shiomi 1 , Shigeo Maruyama 1
1 Mechanical Engineering, The University of Tokyo, Tokyo Japan
Show AbstractA control technique of the detailed structures of single-walled carbon nanotubes (SWNTs) is necessary for the fabrication of SWNT electric devices, and understanding the SWNT growth mechanism is important in order to improve growth techniques. On the other hand, for assembly of SWNT devices, the growth technique of SWNTs at low temperature is desired, avoiding thermal damage of the devices. While the quality of SWNTs grown at low temperature is not so high, the metal catalyst is stable at low temperature and it is possible to control the structure of SWNTs by controlling the catalyst. In the present study, we preformed SWNT growth by a catalytic chemical vapor deposition (CVD) method over wide temperature and pressure ranges, using an ultra high vacuum CVD chamber. In particular, we focused on low CVD gas pressure and low temperature conditions, and investigated the SWNT growth mechanism. SWNTs were synthesized using ethanol as the CVD gas. As the catalyst, Co/Mo metal particles deposited on silicon substrates were used. The metal particles reacted with the CVD gas and then SWNTs were grown from the catalyst particles. The ethanol gas pressure ranged from 0.001 to 100 Pa, and the CVD temperature ranged from 400 to 900 C. The yield of SWNTs was assumed to be proportional to the G-band intensity, which was measured by Raman scattering spectroscopy. SWNT samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An optimum CVD temperature existed for a fixed ethanol gas pressure, which decreased with decreasing ethanol gas pressure. We obtained SWNTs even at 500 C, when the ethanol gas pressure was low (less than 0.01 Pa). In this study, the minimum temperature was 450 C at 0.001 Pa. On the other hand, when dimethyl ether (DME) was used as the carbon source, the optimum temperature slightly decreased and the relationship between the optimum CVD temperature and ethanol gas pressure was the same as the case of ethanol. At low temperature, the activity of the catalyst was also low. However, low gas pressure condition moderated the SWNT growth and increased the lifetime of the catalyst.
9:45 AM - R6.3
Compression Mechanics and Energetics of Carbon Nanotube Foam Pillars.
Shelby Hutchens 1 , Lee Hall 2 , Harish Manohara 2 , Julia Greer 1
1 Materials Science, California Institute of Technology, Pasadena, California, United States, 2 , Jet Propulsion Laboratory, Pasadena, California, United States
Show AbstractThe study of carbon nanotube (CNT) forests or turfs as lightweight structural foams has received increasing attention due to the variety of applications they have the potential to fulfill, including energy dissipation and cushioning. CNT foams are inhomogeneous collections of multi-wall nanotubes grown nominally perpendicular to the substrate. We report unique mechanical characteristics of CNT foams having approximately one tenth the density of graphite (≈0.1 g/cm3) grown via a process that creates (1) a density gradient which is lower at the bottom compared to the top and (2) a nominally vertical alignment of CNTs at the macroscale superseded by a more random arrangement at the mesoscale. Specifically, we find that 50-micron diameter cylindrical CNT micro-pillars are capable of sustaining compressive strains in excess of 80% without densifying, while exhibiting foam-like behavior. The deformed morphology exhibits periodic undulations on the surface. Multiwall CNTs have been indirectly shown to have exceptionally high strength, making them lucrative for the creation of low density foams, which have a higher compressibility than typical polymer foams without sacrificing mechanical strengths. Here we show the effect of strain rate on energy dissipation in uniaxial deformation of CNT micro-pillars grown from photolithographically patterned catalyst in terms of typical foam energy-absorption diagrams. We explore the timescales involved in energy absorption and dissipation through dynamic mechanical analysis utilizing steady state harmonic oscillation. We also observe global and local deformation mechanisms responsible for these remarkable mechanical properties visually through the use of in-situ nanomechanical instrument, SEMentor. Through these analyses, we discuss the mechanisms involved in energy dissipation and those giving rise to the unique mechanical properties in these novel materials.
10:00 AM - R6.4
Sound of Carbon Nanotube Assemblies.
Mikhail Kozlov 1 , Carter Haines 1 , Jiyoung Oh 1 , Marcio Lima 1 , Shaoli Fang 1
1 NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractStrong thermo- and photo-acoustic responses have been detected for aligned arrays of multi-walled carbon nanotube (MWNT) forests and solid drawn MWNT sheets. When heated using AC current or a near-IR laser modulated in 100-20,000 Hz range, the nanotube assemblies generated loud, audible sound, with higher sound pressure being detected from MWNT sheets. An evaluation of nonlinear distortions of the thermoacoustic signal revealed highly peculiar behavior of the third and fourth harmonics produced from forests grown on silicon wafers. The peculiarities were especially pronounced for short forests and can be associated with the heat transfer from the MWNT layer to the substrate. For both types of nanotube assemblies, the acoustic signal’s amplitude varied with frequency approximately by the power low fp. The power factor p was found to be an unexpectedly high for short forests probably due to heat loss to the substrate. Observed peculiarities can be used for the characterization of prepared MWNT assemblies. The dependencies can also be helpful for evaluating properties of thermal interfaces, in particular those based on carbon nanotubes.
10:15 AM - R6.5
Rational Development of a NIR-Resonant Nanomaterial for the Thermal Treatment of Cancer.
Andrew Burke 1 , Ravi Singh 1 , David Carroll 2 4 5 , Frank Torti 1 4 , Suzy Torti 3 4
1 Cancer Biology, Wake Forest University School of Medicine, Winston Salem, North Carolina, United States, 2 Physics, Wake Forest University, Winston Salem, North Carolina, United States, 4 Comprehensive Cancer Center, Wake Forest University School of Medicine, Winston Salem, North Carolina, United States, 5 Center for Nanotechnology and Molecular Materials, Wake Forest University, Winston Salem, North Carolina, United States, 3 Biochemistry, Wake Forest University School of Medicine, Winston Salem, North Carolina, United States
Show AbstractThe emergent properties of nano-scale multiwalled carbon nanotubes (MWCNTs) render them an ideal platform for the development of multifunctional agents for the treatment of cancer. We have recently demonstrated that Pluronic-coated MWCNTs are biocompatible and efficiently mediate the thermal destruction of cancer cells in vitro and tumor xenografts in vivo when used in conjunction with tissue-transparent near-infrared laser radiation (1). Encouragingly, the rapid thermal ablation of tumors achieved using this technique translated into long-term survival for treated animals with no evident systemic toxicities.The application of inherently hydrophobic nanomaterials as therapeutic agents in biological systems has necessitated the use of long chain polymer surfactants and/or covalent surface modifications to the nanomaterials themselves to aid in the formation of usable, stable suspensions. As the emergent physical properties of nanomaterials are exquisitely sensitive to interfacial interactions and structural perturbations it is necessary to characterize the effect of these essential modifications on the therapeutic performance of the nanomaterial. In this study we investigate both the role of the polymer surfactant and the covalent functionalization of the nanotube surface in determining treatment efficiency and inherent cytotoxicity. These findings will aid in the development of stable, biocompatible nanomaterials for the thermal treatment of cancer.1.Burke, A., et al. (2009) Long-Term Survival Following a Single Treatment of Kidney Tumors with Multiwalled Carbon Nanotubes and near-Infrared Radiation Proc Natl Acad Sci U S A 106, 12897-12902.
10:30 AM - R6.6
Joule Breakdown and Thermal Dissipation of Carbon Nanotubes With SiO2 Substrate.
Albert Liao 1 3 , Sumit Dutta 1 3 , Zhun-Yong Ong 2 3 , Eric Pop 1 3
1 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 , Micro and Nanotechnology Laboratory, Urbana, Illinois, United States, 2 Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractApplications of single-wall carbon nanotubes (CNTs) require an understanding of how CNTs interface with their environment, dielectric substrate, or electrode contacts. In this study we examine thermal dissipation between CNTs and SiO2, a configuration that is most common in nanotube electronics. While the intrinsic thermal conductivity of CNTs is excellent, thermal dissipation bottlenecks occur at this interface, which are known to degrade performance in transistors, interconnects [1], and heat sinks [2].We use Joule heating and breakdown of CNTs to extract the thermal boundary conductance per unit length, G, with the SiO2 substrate as a function of CNT diameter. We apply an increasing voltage across the CNTs, while monitoring the current. The CNT breakdown temperature (oxidation at ~600 C) is known, and this is correlated with the breakdown power [1] to extract the thermal substrate coupling, G. We took data across 28 CNTs with diameters ranging from 1.1-3.2 nm and extracted thermal coupling G from 0.026-0.59 W/K/m, which displays an increasing trend with larger diameters. In addition, we examined the breakdown location with atomic force microscopy (AFM). We found most CNTs break near the middle, as expected from Joule heating at uniform electric field. However, semiconducting CNTs have uneven field distribution along their length and show breakdown closer to the drain electrode. To further understand our results, we adopt a diffuse mismatch model (DMM) [3] to find the “ideal” limit of CNT thermal energy coupling with its dielectric. We incorporate the full phonon density of states for CNTs and SiO2 obtained from molecular dynamics simulations [4], and we find the contact area consistent with the CNT-SiO2 Van der Waals interaction. The CNT heat capacity and contact area are essential in regulating heat transfer at the interface. The methodology used in this study can also be applied towards finding the thermal energy coupling between other nanomaterials and their 3-dimensional environment.[1] E. Pop et al, J. Appl. Phys. 101, 093710 (2007)[2] M. Panzer et al, J. Heat Transfer, 130, 052401 (2008)[3] E.T. Swartz and R.O. Pohl, Rev. Mod. Phys. 61, 605 (1989)[4] Z.-Y. Ong and E. Pop, http://arxiv.org/abs/0910.2747 (2009)
R7: Solution-Processed Devices
Session Chairs
Pierre Legagneaux
Ken Teo
Wednesday PM, April 07, 2010
Room 2020 (Moscone West)
11:15 AM - **R7.1
Carbon Nanotube Networks: Sorting, Alignment, and Electronic Devices.
Zhenan Bao 1
1 , Stanford University, Stanford, California, United States
Show AbstractFor single walled carbon nanotubes to find use in electronics there is a need to efficiently separate them by electronic type, and align them to ensure optimal and reproducible electronic properties. Here, we report SWNT networks deposited from solution, possessing controllable chirality, density and alignment. Applications of these SNWT networks in thin film transistors, sensors and transparent electrodes will be presented.
11:45 AM - R7.2
Building Highly Organized Two and Three Dimensional Single-walled Carbon Nanotubes-Polymer Hybrid Structures for Smart Composite Systems.
Myung Gwan Hahm 1 , Bo Li 1 , Younglae Kim 2 , Yung Joon Jung 1
1 MIE, Northeastern University, Boston, Massachusetts, United States, 2 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractSingle walled carbon nanotubes (SWNTs) have received increasing attentions as the key transparent electronic material which can be used in multifunctional flexible systems with extraordinary and tunable electrical and optical properties. However, to build integrated and highly functional flexible composite structures with SWNTs, it is required to have abilities to assemble and incorporate SWNTs in desired locations, orientations, and dimensions on/inside of polymer substrates. Here, we demonstrate a design and fabrication of new class of highly organized SWNT network-polymer hybrid composite architectures, which were challenging to make before, by precisely controlling assembly, growth and transfer processes of SWNTs. For this, a novel template guided fluidic assembly process was used to build horizontally organized SWNT network structures in macro/microscale and an oxygen assisted chemical vapor deposition method was employed to create millimeter scale long, highly organized, and vertically aligned SWNT architectures. This was followed by highly controlled polymer casting transfer process of these 2-3 dimensional organized SWNT structures on the surface or inside of selected polymer matrices without disturbing the alignment, pattern and dimension of predesigned SWNT network structures. Using these powerful assembly and transfer techniques, so far we have been able to create diverse and dynamic SWNT-polymer composite architectures such as (i) lateral SWNT line patterns on poly-methyl methacrylate (PMMA) film, (ii) lateral ultra-thin and anisotropic continuous SWNT film on PMMA film, (iii) vertically aligned millimeter long SWNTs placed on the top surface of poly-dimethylsiloxane (PDMS) films, (iv) vertically aligned millimeter scale long SWNTs placed between two PDMS films, and (v) a combination of lateral and vertical SWNTs/polymer architectures giving 3 dimensional SWNT network configurations inside of polymer materials. These multi-dimensional networks of novel SWNTs-polymer hybrid structures open the pathway to build highly organized electrical path way inside of polymer structures. Therefore these structures have immediate and immense implications for the development of SWNT based functional flexible systems such as sensors, interconnect, transparent flexible electrode, and display.
12:00 PM - R7.3
Novel Printing Device Based on Hole Injection between Single Walled Carbon Nanotube and Molecularly Doped Polymer Layers of Arylamine.
Kock-Yee Law 1 , Mandakini Kanungo 1
1 , Xerox Corporation, Webster, New York, United States
Show AbstractCarbon nanotube thin films because of their unique optical and electronic properties coupled with the flexibility and easy patternability are promising candidates for application in low cost, large area flexible displays and optoelectronics. In this work, the hole injection process between single-walled carbon nanotube (SWCNT) thin films and molecularly doped polymer layers of arylamine are studied. Results in bilayer devices showed that SWCNT thin films are efficient hole injectors. The efficiency of the hole injection process was found to be dependent of the surface conductivity of the SWCNT film and the strength of the electric field across the bilayer device. The use of this hole injection process to create a digital electrostatic latent images for novel printing application is discussed.
12:15 PM - R7.4
Single-walled Carbon Nanotube Films for Plastic Solar Cells.
Sungsoo Kim 1 , Xuhua Wang 2 , Jong Hyuk Yim 3 , Soonil Lee 3 , D. Bradley 2 , John deMello 1
1 Chemistry, Imperial College London, London United Kingdom, 2 Physics, Imperial College London, Londong United Kingdom, 3 Division of Energy Systems Research, Ajou University, Suwon Korea (the Democratic People's Republic of)
Show AbstractThere has been an urgent need for new mechanically robust high performance transparent conductors to replace Indium Tin Oxide (ITO), which is the most widely used electrode material, but tends to crack when flexed repeatedly and exhibits substantially reduced conductivities when deposited on plastic instead of glass substrates due to the need for reduced temperature deposition techniques. Recent studies by several research groups have demonstrated that single-walled carbon nanotubes [SWCNTs] are promising candidates for flexible electrodes, but considerable improvements in performance are needed before they become a commercially viable alternative to ITO. In this work, we report that transparent conducting electrodes of Single Walled Carbon Nanotubes (SWCNTs) on glass or plastic substrates were made using spray-coating techniques and used for fabricating efficient, flexible polymer-fullerene bulk hetero-junction solar cells. The spray coated SWCNT films had a typical optical transmittance of over 70% at the wavelength of 550nm, a sheet resistance of ~100 Ω/sq., a work function of 4.81~4.91 eV and a R.M.S. roughness of ~6.0nm for the typical film thickness of around 30-40nm.An interlayer lithography with a minimum processing steps enabled high resolution patterning of spray coated carbon nnaotubesmers at the near micron level and lead to smoother electrodes with an highly transparent intermediate resist layer between the substrate and the CNT layer.Solar cells with a structure of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT:PSS) onto the SWCNT electrodes, followed by a 1:0.7 blend by weight of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric-acid methyl-ester (PCBM)and finally a LiF/Al cathode layer thermally evaporated was fabricated. The device performance fabricated on the SWCNT/glass anodes was identical to the device made on the ITO/glass electrodes. The power conversion efficiency of SWCNT, deposited glass devices under the one sun, was 2.34% while the devices of ITO-coated glass substrates had 2.3% of efficiency. The SWCNT devices had an external quantum efficiency of 73 % compared to 62 % for comparable devices fabricated on ITO-coated glass substrates. Device with an interlayer patterned SWCNT electrode had slightly better device performance with a 2.4% efficiency. Further researches are on-going in order to apply SWCNT electrodes for various optoelectronic applications and at the meantime the conductivity is expected to improve by preferentially selecting metallic SWCNTs and using chemical p-doping methods.
12:30 PM - R7.5
Large Area Electronics Using Carbon Nanotube Composites and Films.
Matt Luke 1 , Thomas Connolly 1 , Richard Smith 1 , Yenny Hernandez 2 , Yurii Gunko 3 , Jonathan Coleman 2 , J David Carey 1
1 Advanced Technology Institute, University of Surrey, Guildford United Kingdom, 2 School of Physics, Trinity College Dublin, Dublin Ireland, 3 School of Chemistry, Trinity College Dublin, Dublin Ireland
Show AbstractCarbon nanotube (CNT) solution based processing and functionalisation has advanced to such a state that a scalable CNT based technology which exploits the excellent inherent electronic properties of the nanotubes is now possible. Two such potential applications include the development of nanocomposite cathodes and films for flexible and transparent electronics. Crucial to the operation of both is an understanding of what controls the current in these structures. We have studied the electron transport properties of functionalised singlewalled carbon nanotubes as a function of nanotube volume fraction in aqueous solutions of PVA based nanocomposites. We find outstanding electron emission with as low as 1% nanotube volume fraction and by varying the CNT concentration improvements in the charge transfer through the composite can be obtained. [1] Transparent films using CNTs have also been developed using pulsed valve methods where both the sheet resistance and optical transmission have been measured as a function of CNT content [2]. In both technologies we have investigated the rate limiting step for transport. For example, at low CNT content we find the rate limit step for emission to be controlled by transport through the composite but at higher content such bulk limited emission is no longer found to be a factor. We generalize our conclusions for other large area CNT based applications and technology.
[1] Thomas Connolly, Richard C. Smith, Yenny Hernandez, Yurii Gun’ko, Jonathan N. Coleman and J. David Carey, Small 5, 826 (2009).
[2] Matt Luke, Richard C Smith and J David Carey, unpublished.
12:45 PM - R7.6
Interfacial Energy Level Alignment at Acid Oxidized Carbon Nanotube - Triphenyldiamine Contacts.
Li Wei Tan 1 , Ross Hatton 2 , Ravi Silva 1 , Cristina Giusca 1
1 Advanced Technology Institude, University of Surrey, Guildford, Surrey, United Kingdom, 2 Chemistry Department, The University of Warwick, Conventry, Conventry, United Kingdom
Show AbstractWe report an ultraviolet photoelectron spectroscopy study of the energetics at the interface between acid oxidized carbon nanotubes and the archetypical molecular N,N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’biphenyl-4,4’diamine(TPD). In this study we have focused on the interface between o-SWCNTs and o-MWCNTs and the archetypal small molecule organic semiconductor TPD. Triphenylamines have been used extensively in studies pertaining to the energetics at metal/organic semiconductor and metal oxide/organic semiconductor interfaces making them good model systems. In the current work we show that there are abrupt vacuum level shift of 0.4eV across both the o-SWCNT/TPD and o-MWCNT/TPD interfaces, the magnitude and direction of which correlates with the difference in work functions such that Fermi level alignment is achieved. Electrical equilibrium is achieved across both interfaces within the experiment time frame due to the formation of an interfacial dipole layer which abruptly shifts the vacuum level at the interface. This is one of the first reports of the electronic structure of carbon nanotube/organic semiconductor interfaces; a system in which the magnitude of the dipole layer formed at the interface upon contact formation is proportional to the difference in work function between the substrate and organic semiconductor overlayer.
R8: Growth for Electronic and Thermal Applications
Session Chairs
Wednesday PM, April 07, 2010
Room 2020 (Moscone West)
2:30 PM - **R8.1
Fabrication of Carbon Nanotube via Interconnects and their Reliability for a High Current Density.
Shintaro Sato 1 , Mizuhisa Nihei 1 , Tadashi Sakai 1 , Yuji Awano 2
1 , MIRAI-Selete, Kanagawa Japan, 2 , Keio University, Yokohama Japan
Show AbstractThe reliability of carbon nanotubes (CNT) via interconnects under the application of high current densities has been investigated. It was found that the electrical contacts between carbon nanotubes and the upper and lower metal lines are important for improving the reliability. The use of chemical mechanical polishing (CMP) processes and optimization of the contact and barrier layers made more CNTs be connected to the metal lines, thus decreasing the current through each nanotube.Such decrease resulted in improving the current tolerance properties of CNT via interconnects.
3:00 PM - R8.2
Surface Reactions During the Catalytic Chemical Vapor Deposition of Carbon Nanotubes.
C. Wirth 1 , Can Zhang 1 , G. Zhong 1 , S. Hofmann 1 , John Robertson 1
1 Engineering Dept, Cambridge University, Cambridge United Kingdom
Show AbstractThe production of mm-high forests of vertically aligned nanotubes allows us to determine the kinetics, and pressure and temperature dependence of their growth. This is important knowledge for the reaction mechanism. For Fe catalysts on Al2O3 support with C2H2 as precursor, we find that reaction varies as pressure to the power of 0.6 over 7 orders of magnitude of pressure, the reaction order of hydrogen is zero, and the activation energy is 0.95 eV. Nanotube growth is often considered to be limited by diffusion through or over the catalyst droplet, but this would not allow a pressure dependence. On the other hand, a pure dependence on diffusion is inconsistent with the known importance of the gas phase and catalyst surface. The proposed mechanism involves a rapid dissociative absorption of acetylene on the catalyst surface to form C atoms as a pre-equilibrium, followed by the rate-determining step of solid-state diffusion of C through or over the catalyst. This mechanism then accounts for all the observations. Acetylene is also identified as the primary growth precursor, so that other feedstocks tend to pass through acetylene as an intermediate species, in hot wall systems.1 C T Wirth et al, ACS Nano (2009)2 G Zhong et al, J Phys Chem C 113 17321 (2009)
3:15 PM - R8.3
Enhancing the Electrical Properties of Carbon Nanotube Wires.
Brian White 1 , Craig Lombard 1 , David Lashmore 1
1 , Nanocomp Technologies, Concord, New Hampshire, United States
Show AbstractCopper wire conductors are universally used throughout various industries because of good electrical conductivity and availability. However, for some applications, where considerations of weight, oxidation resistance, strength and fatigue are concerned, copper wire has serious performance deficiencies. We have the ability to produce wires composed of pure carbon nanotubes (CNTs) on the bulk scale with a density of 0.2 g/cm3. Our as-produced CNT material has a conductivity of 2.5 x 105 to 5 x 105 S/m. A strategy for increasing the conductivity of the nanotube wires is to create a hybrid wire by plying our CNT strands with very small gauge bare copper wire. The resulting hybrid wire has a conductivity greater than 107 S/m, with a weight five times lighter than equivalent gauge copper. This hybrid wire is capable of being insulated by industrial machines with standard polymer insulation. The insulated hybrid wire has potential as a copper replacement in motor/generator windings, wire harnesses, and other applications were weight and performance are crucial.
3:30 PM - R8.4
Performance of Commercial Thermal Interface Materials With Multi-wall Carbon Nanotube Inclusions.
Michael Rosshirt 1 , Christopher Cardenas 1 , Patrick Wilhite 1 , Drazen Fabris 1 , Cary Yang 1
1 Center for Nanostructures, Santa Clara University, Santa Clara, California, United States
Show AbstractThermal management is a fundamental concern in the electronics packaging industry, particularly as heat dissipation demands increase. Thermal interface materials [TIM] are often inserted between contacting surfaces in electronic packages to reduce thermal contact resistance [Rtc] and improve conduction heat transfer. Commercial particle-laden TIM greases have been approaching an upper bound of thermal performance, limited by a maximum volumetric loading of the conductive particle fillers and the inherently low conductivity of the matrix material. Integrating multi-wall carbon nanotubes [CNTs], which possess both a high aspect ratio and high thermal conductivity, with other thermally conducting materials holds great promise as TIM. Composite TIM greases with CNT inclusions may exhibit lower thermal resistance as a result of an increase in more highly conductive percolation paths across the interface. To experimentally quantify the thermal performance of different TIM, we have developed an advanced steady-state TIM testing apparatus based on the ASTM D5470-06 standard. Using the steady-state approach we measure the thermal contact resistance and the ratio of the contact resistance to TIM sample thickness [Rtc/Δt] under constant heat flux and variable pressure. Arctic Silver®5, a commercial particle-filled TIM, was tested as a baseline case and compared to mixtures of Arctic Silver®5 with commercial multi-wall CNTs [CNT/AS], and mixtures of silicone oil with CNTs [CNT/Oil] as the sole conductive particulate filler. The percent weight ratio of CNTs to TIM was varied (0.5% to 2.25% [CNT/AS]; 2.25% to 16% [CNT/Oil]) along with the viscosity of the matrix oil in the CNT/Oil mixtures (200 cSt to 500,000 cSt). The electrical conductivity of a single CNT from the commercially-produced sample was measured and used to approximate the thermal conductivity of an individual CNT at 24 W/m-K.Early Rtc measurements suggest that greater thermal performance is achieved with less viscous composites at lower percent weight loadings of CNTs. Experimental results of CNT/Oil mixtures at a lower loading of CNTs display comparable or reduced bulk thermal resistance values at high packaging pressures (≥ 70 psi) compared to Arctic Silver®5, even with relatively poor thermally conductive commercial CNTs. The goal of this work is to investigate how varying percent weight loadings of CNTs and matrix viscosities affect the bulk thermal performance of the composite TIM grease, and to demonstrate the viability of utilizing CNTs as conductive particle fillers in TIM for electronic packaging.
3:45 PM - R8.5
Predicting the Phonon Properties and Thermal Conductivity of Carbon Nanotubes Using the Spectral Energy Density.
John Thomas 1 , Joseph Turney 1 , Alan McGaughey 1 , Cristina Amon 1 2
1 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Mechanical Engineering, University of Toronto, Toronto, Ontario, Canada
Show AbstractWe present a fast, accurate, and straightforward technique for predicting phonon dispersion relations, lifetimes, and thermal conductivities directly from the velocities of the atoms in a crystal using the spectral energy density. This procedure naturally incorporates the full anharmonicity of the atomic interactions into the lifetime prediction. It can also be used investigate the role of non-periodic interactions between phonons and non-bonded molecules near the solid surface on thermal transport. We use this procedure to examine phonon transport and scattering in empty and water-filled carbon nanotubes (CNTs). Next, we compare the fully-anharmonic phonon properties to those obtained from third-order anharmonic lattice dynamics calculations. Our findings indicate that, even at room temperature, neglecting higher-order scattering events in a CNT leads to an overestimation of the acoustic phonon mode lifetimes and the CNT length required to obtain fully-diffusive phonon transport. We then use the spectral energy density to identify how interactions with confined water molecules shift the phonon frequencies, lower the phonon lifetimes, and reduce the CNT thermal conductivity.The CNT thermal conductivities predicted using the fully-anharmonic phonon properties are in excellent agreement with what we predict using a direct application of the Fourier law in an MD simulation. The number of atoms and simulation runtime required to predict the spectral energy density, however, are both at least one order-of-magnitude smaller than required by MD-based techniques that predict only the thermal conductivity. Thus, although applied here to classical MD simulation, the spectral energy density technique can be used to predict fully-anharmonic phonon properties using atomic velocities obtained from ab initio MD simulations driven by density functional theory (DFT) calculations.
R9: Water Scale Growth and Applications
Session Chairs
Wednesday PM, April 07, 2010
Room 2020 (Moscone West)
4:30 PM - **R9.1
Technology for 300mm Wafer Scale Growth of Carbon Nanotubes.
Ken Teo 1
1 , AIXTRON, Swavesey, Cambridgeshire, United Kingdom
Show AbstractThe integration of carbon nanotubes (CNT) on silicon-based substrates/devices require its deposition over a variety of wafer sizes, including the current production size of 300mm diameter wafers. This presentation discusses the development and scaling of CNT deposition equipment at AIXTRON. The horizontal flow and vertical flow techniques are compared. The simulation and measurement of gas flow and thermal distribution of the reactor are presented. Plasma enhanced chemical vapour deposition of cnt is discussed and techniques for obtaining improved plasma stability are explained. The use of a pre-heater is also characterised using mass spectroscopy.Finally, various growth results (SWNT, MWNT, VACNF, cvd graphene) achieved are shown and a 300mm wafer with CNT will be displayed.
5:00 PM - R9.2
Spinnable Carbon Nanotube Forests Grown on Thin, Flexible Metallic Substrates.
Xavier Lepro Chavez 1 , Marcio Lima 1 , Ray Baughman 1
1 Alan G. Mac Diarmid NanoTech Institute BE 26 , The University of Texas at Dallas, Richardson, Texas, United States
Show AbstractWe report by first time a successful growth of yarn-spinnable and sheet-drawable carbon nanotube (CNT) forests on highly flexible, inexpensive stainless steel sheets, instead of the conventionally used polished silicon wafers. The controllable growth of spinnable carbon nanotube forest is challenging since minor changes in the synthesis/substrate conditions can produce unspinnable forests instead of spinnable ones. We call the property of CNT forests to self-assemble in dry state drawability. The forests obtained on metallic substrates show similar good drawability to the one of those grown on Si based substrates (Zhang et al. Science 306, 1358, 2004). However, this new process has the additional advantage of having drawable CNT forests directly grown on flexible substrates, cheaper than conventional Si wafers, which can potentiate the technological application of the aligned CNT sheets and yarns obtained from them as structural materials, transparent electrodes, actuators and others (Zhang et al. Science 309, 1215, 2005 and Aliev et al. Science 323, 1575, 2009). Due to the flexibility of the substrate, we have been able to increase the effective area of synthesis in the reactor, producing forests up to 16 cm width by means of bending the substrate to fit in the tubular quartz CVD reactor of 7 cm in diameter. Robustness of our method is shown by the growth of these drawable CNT forests on either a single or both faces of stainless steel foils by a single thermal chemical vapor deposition at atmospheric pressure. Besides direct applications of such CNT forests in electronic, thermal, biological and electrochemical fields, we anticipate that this approach can enable the mass production of drawable CNTs forests in a continuous and economical way.
5:15 PM - R9.3
Mechanical and Electrical Properties of Pristine and Modified Carbon Nanotube Yarns.
Luke Gibbons 1 2 , Jae-Woo Kim 1 , Nathan Elowe 3 , Godfrey Sauti 1 , Jin Ho Kang 1 , Sharon Lowther 4 , Gail Jefferson 1 , Cheol Park 1 5 , Peter Lillehei 4
1 , National Institute of Aerospace, Hampton, Virginia, United States, 2 Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States, 3 Mechanical Engineering, Tufts University, Medford, Massachusetts, United States, 4 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States, 5 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractCarbon nanotube (CNT) based yarns have been investigated for their applicability as electrical interconnects, sensors, actuators, antennas, and other applications requiring tailored mechanical and electrical properties. Pristine and modified CNT yarns have the potential to incorporate the unique and extraordinary properties of single nanotubes into systems that function on a larger scale. This objectives of this work are to understand the structure-function relationship of CNT yarns and determine their tailorability and suitability for use in multifunctional composites and electrical applications. The CNT yarns studied were fabricated through different methods and have undergone various modifications to tailor their mechanical and electrical properties. Damage mechanisms were observed by outfitting a scanning electron microscope with a tensile and compression module in order to capture images and videos as the CNT yarns experienced various degrees of mechanical deformation and failure. The mechanical properties, electrical properties, surface energies, and damage mechanisms of the pristine yarns, as well as the effect of various modifications, such as metal coatings and acid treatments, on the resulting material characteristics will be presented.
5:30 PM - R9.4
Post-production Processing of Carbon Nanotube Yarns.
Mark Schauer 1 , David Lashmore 1 , Diana Lewis 1 , Benjamin Lewis 1 , Erick Tolle 1 , David Degtiarov 1
1 , Nanocomp Technologies, Concord, New Hampshire, United States
Show AbstractThe strength and electrical conductivity of Carbon Nanotube (CNT) yarns is dramatically affected by the handling of the material after the nanotubes are produced. Our nanotube production process involving Chemical Vapor Deposition (CVD) using the floating catalyst method produces a mass of entangled bundles of single-walled nanotubes in a gas suspension. Simply collecting and spinning this material produces a yarn with strength and electrical conductivity far less than the properties of the individual nanotubes due to the poor alignment of the bundles on the microscopic scale. We have developed methods of aligning the CNT material that are analogous to the techniques used in the textile industry for spinning staple yarns, but modified to be appropriate for nano-scale material. The result is a dramatic improvement in strength and electrical conductivity of our CNT yarns.
5:45 PM - R9.5
Double-layered Carbon Nanotube Array With Super-hydrophobicity Synthesized by One-step Chemical Vapor Deposition.
Yingying Zhang 1 , Liliana Stan 1 , Stephen Doorn 1 , Han Htoon 1 , Quanxi Jia 1
1 , Los Alamos National lab, Los Alamos, New Mexico, United States
Show AbstractSince the landmark paper on carbon nanotubes by Iijima in 1991, carbon nanotubes (CNTs) continue to be a subject of scientific research and development. There have been many reports on the growth and application of vertical aligned CNT arrays. At the same time, the surfaces of CNT arrays, with a nanoscale surface roughness derived from the nanotube tips, have attracted much research interests as well. Here, we report a novel phenomenon of CNTs which is related to the growth and the surface morphology of layered CNT arrays. In an effort to synthesize longer CNT arrays, we observed the growth of unexpected double-layered CNT arrays by a single step CVD process. The deactivation and reactivation of catalyst particles may be the cause of such a growth process. Even more interestingly, after removal of the top layer, we observed novel morphology difference between the top and the bottom CNT layers. The surface of the bottom CNT layer, which shows hierarchical structures, exhibits super-hydrophobic properties and excellent self-cleaning abilities.
R10: Poster Session: Growth, Devices and Electrical Properties
Session Chairs
Thursday AM, April 08, 2010
Salon Level (Marriott)
9:00 PM - R10.1
Double-walled Carbon Nanotubes-incorporated Bulk Heterojunction Solar Cells.
A.A. Damitha Adikaari 1 , Simon Henley 1 , Maxim Shkunov 1 , S. Ravi Silva 1
1 Advanced Technology Institute, University of Surrey, Guildford, Surrey, United Kingdom
Show AbstractWe report the effects of incorporating double walled carbon nanotubes in the active layer of polythiophene/fullerene derivative bulk heterojunction solar cells fabricated on indium tin oxide coated glass substrates. Design of organic photovoltaic devices is limited by the low exciton diffusion lengths of organic photoactive materials and carbon nanotubes are investigated here for possible enhancement of charge dissociation/transport within the active layer. Larger diameter (>30 nm) multiwall carbon nanotubes in active layers of bulk heterojunction systems prove to decrease shunt resistances and lower the open circuit voltages of the devices, mainly due to active layer thicknesses of two to four times the diameter of nanotubes. Here, double walled nanotubes are utilised due to their smaller diameters compared to multi wall nanotubes, and we present the performance comparison with reference polythiophene/fullerene derivative bulk heterojunction devices. Importantly, these devices were part fabricated and characterised under atmospheric conditions. The reference devices show efficiencies close to 3.5 %, with short circuit current densities ~8.0 mA/cm2 at the typical open circuit voltage of 0.6 V for regioregular poly(3-hexylthiophene)/ [6,6]-phenyl C71 butyric acid methyl ester system, with nanotube incorporated device efficiencies heavily depending on the loading of nanotubes. With metallic behaviour dominant rather than semiconducting, double walled carbon nanotubes with their thinner diameters allow incorporation the nanotubes in the active layer of bulk heterojunction organic photovoltaic devices, with minimum leakage effects.
9:00 PM - R10.10
Anomalous Dissipation in Single-walled Carbon Nanotube Resonators.
Peter Greaney 1 , Jeffrey Grossman 1 , Giovanna Lani 2 3 , Giancarlo Cicero 3
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Ecole Polytechnique, 91128 Palaiseau cedex France, 3 INFM and Physics Department, Polytechnic of Torino, Torino Italy
Show AbstractWe observe transient anomalous dissipation during the ring-down of the flexural modes in single-walled carbon nanotube (CNT) resonators, during which the quality factor of the mode can be reduced by more that 95% for tens of picoseconds. The anomalous dissipation depends on the CNT temperature and the energy in the mode, and remarkably increasing the excitation energy in the resonator causes it to decay to zero faster. This phenomenon is analogous to the Mpemba effect in the freezing of water, and like with the Mpemba effect the background temperature in the system does not uniquely define its dissipative state.
9:00 PM - R10.12
Silicon Coated Multi-walled Carbon Nanotubes for Lithium Ion Battery Anode With High Power.
Jaehwan Ha 1 , Kichun Kil 2 , Hyungkyu Han 1 , Moon-Seok Kwon 3 , Young-Min Choi 3 , Hansu Kim 3 , Yoon Chang Kim 4 , Dong Sik Zang 4 , Ungyu Paik 1 2
1 Division of Materials Science Engineering, Hanyang University, Seoul Korea (the Republic of), 2 Department of Energy Engineering, Hanyang University, Seoul Korea (the Republic of), 3 Energy Lab., Samsung Advanced Institute of Technology, Samsung Electronics Co. Ltd., Suwon Korea (the Republic of), 4 Corporate Research & Development Center, Samsung SDI Co. Ltd., Yongin, Kyeonggi-Do Korea (the Republic of)
Show AbstractWe have designed a new electrode configuration, consisting of silicon coated multi-walled carbon nanotubes for lithium ion battery anode with high power. Silicon was coated on the multi-walled carbon nanotubes by thermal CVD process. Multi-walled carbon nanotubes play roles as both efficient electron conducting pathways and enhanced mechanical supports. The electrochemical properties of our designed silicon coated multi-walled carbon nanotubes were evaluated by fabrication of 2016 coin-type half cells. From the electrochemical properties, our designed electrodes show a high discharge capacity of 2760 mAh/g and columbic efficiency of 94% at a rate of 100mA/g. In addition, they show a discharge capacity of 2500 mAh/g and a columbic efficiency of 93% at a rate of 600mA/g.
9:00 PM - R10.13
Monolithic Fabrication and Field Emission Studies of Carbon Nanotubes and Diamond Film.
Deepak Varshney 1 , Brad Weiner 1 , Gerardo Morell 1
1 , University of Pueto Rico, San Juan, Puerto Rico, United States
Show AbstractSolid state field emission devices are limited by the type and quality of their interfaces.Although, both, carbon nanotubes and doped diamond films have been identified as good field emissionmaterials individually, their monolithic integration can simultaneously exploit their best features, and thusappears to be very promising. Doped diamond provides a robust material in good adhesion with the metallicsubstrate, while carbon nanotubes provide local field enhancement for low turn on fields. MonolithicCNT/diamond structures were fabricated and tested for their field emission properties and long termstability. Multilateral characterizations - including Raman, XPS, SEM, EELS, TEM - were employed toelucidate the compositional and structural properties of the monolithic high performance field emitting devicesobtained. In this presentation we discuss the growth mechanism, the seamless integration of CNTs indiamond, the Fowler-Nordheim parameters and their interpretation, and the stability tests performed.
9:00 PM - R10.14
Electrical Properties of Nanotube Polymer Composites.
Enis Tuncer 1 , Georgios Polizos 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractMaterials with tailored electrical properties are needed for electrotechnology. Carbon nanotubes provide flexible solutions in applications such that at low nanotube concentrations low electrical resistivity materials can be fabricated. Several carbon nanotube samples were prepared using polymethyl methacrylate as matrix. Electrical properties of the nanotube composites were measured using an impedance technique between 20-300K at different frequencies. We report the influence of nanotube concentration on electrical resistivity of the composite and polymer structure.
9:00 PM - R10.15
Tunability of Carbon Nanotubes Resistance Deposited by Inkjet Printing at Low Temperature.
Sebastien Pacchini 1 2 , Veronique Conedera 1 2 , Fabien Mesnilgrente 1 2 , Norbert Fabre 1 2 , Emmanuel Flahaut 3 2 , Mircea Dragoman 4 , Robert Plana 1 2
1 , CNRS-LAAS, Toulouse, Haute Garonne, France, 2 , University of Toulouse, Toulouse, Haute Garonne, France, 3 , CNRS-CIRIMAT, Toulouse, Haute Garonne, France, 4 Physics Dept, University of Bucharest, Bucharest Romania
Show AbstractInkjet printing technology is experiencing an increasingly central role in large consumer electronics manufacturing as selective transfer process. In recent years its use has been broadening also to prototyping of circuits in microwave range. Current and future electronics systems and in particular the radio frequency (RF) ones, demand multiple functionalities (reconfigurability, tenability) with guaranteeing at the same time miniaturization, reliability and temperature stability. Carbon nanotubes (CNTs) have demonstrated superior properties, such as exceptional stiffness, remarkable thermal conductivity.This paper describes the development carried out in this direction by combining inkjet printing technology with CNTs inks in order to obtain thin film layers with tunable electrical properties. The results were obtained by measuring the I –V curve and the electrical impedance from DC up to 100 MHz.For this purpose, double walled carbon nanotubes (DWCNTs) with diameter about of 2 nm were prepared by catalytic chemical vapour deposition (CCVD). In order to produce stable CNTs ink, different solvent (ethylene-glycol and water) were investigated in order avoid the use of any surfactant. Furthermore, the modification of carbon nanotubes surface was purposed by surface oxidation in order to decrease the CNTs wettability and thus decrease the sedimentation.CNTs were deposited by a process based on the inkjet printing technology using Altadrop® equipment. The inkjet printing process was taken into account, as such: the effects of substrate heating, surface hydrophilicity of silicon oxide and the jetting process to make the uniform networks of dropped CNTs. Here, the low temperature allows not to degrade the electronic systems and to process on flexible substrate in near future. To evaluate the impact of the jetting process, the number of overwrites, the number of drops and different kinds of CNTs were investigated. Thin films were printed on silicon oxide in between the slots of a coplanar waveguides transmission line (CPW-TLs), commonly used in microwave application.The measurements results confirmed that the DC resistance of the CNTs line was proportionally changed according to the linewidth, the number of overwrites and the number of drops. The resistance could be reduced from 1 MΩ to 6 KΩ as a function of jetting parameters. For the low resistance of CNTs line (6 KΩ), DC resistance was measured at different bias (0 to 20 V) and presented a tunability of 20 %. Next, the impedance of CNTs films was measured to identify the electrical properties. The results demonstrated that impedance was reduced from 400 to 5 KΩ at 100 KHz.In conclusion, a range of DC resistance and impedance as function of jetting process, design and the bias condition have been demonstrated. These results open the way to a new class of multifunctional and multiscale material for microelectronics high frequency application with low temperature process.
9:00 PM - R10.16
Enhanced Irreversibility Field and Critical Current Density in Superconducting NbC Integrated With Aligned Carbon Nanotubes.
Guifu Zou 1 , Hongmei Luo 1 , Scott Baily 1 , Yingying Zhang 1 , Jie Xiong 1 , Junyi Zhai 1 , Eve Bauer 1
1 , Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractWe report a novel chemical solution approach to integrate the superconducting NbC with oriented carbon nanotubes (CNTs). The composite NbC:CNTs shows improved irreversibility field (~ 5 T at 4.2 K), far greater than reported 1.2 T at 4.2 K. In addition, very high critical current densities at 6 K are achieved 105 Acm-2 at 3 T. To the best our knowledge, both the irreversibility field and the critical current density of the NbC are the highest reported in the literature. We believe that the aligned CNTs play a key role in the enhancement of pinning of vortex lines to increase the performance of superconducting NbC. Our results suggest that the incorporation of CNTs into superconductors has potential for high-field applications.
9:00 PM - R10.17
Wafer-scale Meniscus Alignment of Single-walled Carbon Nanotubes.
Joshua Wood 1 2 , Vineet Nazareth 1 2 , Joseph Lyding 1 2
1 Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractMaking single-walled carbon nanotubes (SWNTs) a possible next-generation transistor nanotechnology requires control of their chirality, length, placement, and alignment. We develop a method for controlled placement and alignment of SWNTs using mechanical meniscus action. In this technique, we suspend surfactant-coated SWNTs in aqueous solution and place the solution between two surfaces of differing hydrophobicity. By capillary action and different hydrophobic character, a meniscus forms between the surfaces. We drag this meniscus across the bottom substrate, causing contact angle hysteresis, forcing SWNTs towards the moving contact line by convective transport [1]. Since SWNT surfactants screen electrostatic interactions, the imparted drag force mechanically torques the SWNTs, causing alignment in the meniscus drag direction. Alignment critically depends on the meniscus velocity and the substrate’s contact angle. We find that more hydrophobic surfaces promote better alignment, and lower meniscus velocities allow SWNTs to pin and torque on the substrate. From Monte Carlo simulations, we can determine optimal SWNT alignment parameters for experiment. On the H-passivated Si(111) surface, our SWNTs align with at an angle of 4.35±37.94° relative to the meniscus direction, indicating good alignment. To prevent misalignment and generalize the technique to hydrophilic surfaces, we dispense SWNT solution with a capillary tube, whose capillary forces shift the receding contact angle into the hydrophobic regime. We place SWNTs in densities of up to ~30 SWNTs/μm^2, with the density exponentially dependent on the number of meniscus passes. Capillary-based meniscus confinement further prevents stray SWNT placement. In comparison to aligning SWNTs during growth or by dielectrophoresis, our technique aligns SWNTs on a large-scale while controlling SWNT density and taking advantage of chirally pure SWNTs. We are developing SWNT field-effect transistors and crossbar memory structures using this wafer-scalable alignment technique.[1] P. G. de Gennes, Rev. Mod. Phys. 57, 827 (1985).
9:00 PM - R10.18
Single-walled Carbon Nanotube Film-silicon Junctions.
Ashkan Behnam 1 , Nischal Arkali Radhakrishna 1 , Jason Johnson 1 , Ant Ural 1
1 Electrical & Computer Engineering , University of Florida, Gainesville, Florida, United States
Show AbstractSingle-walled carbon nanotube (CNT) films have been suggested for applications such as thin film transistors, flexible microelectronics, optoelectronic and photovoltaic devices, and chemical sensors, because they are transparent, conductive, and flexible, have uniform physical and electronic properties, and can be mass produced in a cost effective manner. For applications such as solar cells and photodetectors, the interface between the CNT film and the substrate plays a significant role in determining the transport mechanisms and device characteristics. As a result, understanding and controlling the interface properties is an important task for optimizing device operation and improving reliability.In this talk, we fabricate and experimentally characterize the junction formed between the CNT film and both n-type and p-type Si. The fabrication process steps include preparing CNT films by vacuum filtration, transferring them onto Si substrates, patterning them by photolithography and reactive ion etching, and finally depositing contact metals for probing. We also fabricate metal control samples, in which the CNT film is replaced with a Ti/Au metal stack for comparison. We characterize these devices by measuring their dark and photo I-V and C-V characteristics as a function of temperature and electric field and analyzing the results in the light of transport mechanisms, such as thermionic emission, drift-diffusion, and tunneling. Our dark I-V measurements on devices with various dimensions reveal that the CNT film forms a Schottky contact with an average barrier height of 0.44 +/- 0.03 eV and 0.6 +/- 0.02 eV (including the effect of Schottky barrier lowering) on p-type and n-type Si, respectively. Assuming no Fermi level pinning, both of these values correspond to a work function of about 4.65 eV for the CNT film, which is in agreement with previous experiments. Average extracted ideality factors and series resistances (normalized with area) for the CNT film-Si junctions are 1.025 +/- 0.01, 4.5 +/- 0.9 Ω.cm2 for n-type Si and 1.03 +/- 0.02, 10.3 +/- 3.5 Ω.cm2 for p-type Si substrates. We also employ a simple model to study the effect of non-homogeneity on local variations in the barrier heights. Furthermore, photocurrent measurements on CNT film-Si junctions at reverse bias result in a responsivity and normalized photo to dark current ratio (NPDR) of 0.197 A/W and 7.11*10^4 mW-1, respectively, at a bias of 3 volts. C-V measurements are performed not only on MS Schottky barriers, but also on devices that had intentional thin layers of oxide with various thicknesses between the CNT film and Si. CNT film workfunction values obtained from these measurements verify the values obtained from I-V measurements. These results extract the important electrical and optoelectronic parameters of CNT film-Si junctions and facilitate the application of CNT films as Schottky electrodes in conventional semiconductor electronic and optoelectronic devices.
9:00 PM - R10.19
Electrical Properties of Pd-contacted Single-walled Carbon Nanotubes: A Scanning Probe Microscopy Study.
Oleg Kononenko 1 , S. Bozhko 2 , V. Matveev 1 , V. Volkov 1 , A. Firsov 1 , D. Matveev 2 , Yu Kasumov 1 , I. Khodos 1
1 , Institute of Microelectronics Technology and High Purity Materials, RAS, Chernogolovka, Moscow region, Russian Federation, 2 , Institute of Solid State Physics, RAS, Chernogolovka, Moscow region, Russian Federation
Show AbstractPd is widely used in producing electrodes to single-walled carbon nanotubes (SWNT). However up to now its ability to form ohmic contacts to SWNTs was not employed in scanning probe microscopy (SPM). Here we present a study of SWNTs with Pd electrodes by SPM using Pd-coated tips. SWNTs were selectively grown on oxidized silicon substrates by low pressure CVD method. Pd electrodes were prepared to SWNTs to fabricate two terminal structures for SWNTs resistance measurements. It is shown that SPM Kelvin mode is a reliable technique for SWNT detection on insulating substrate. Contact potential difference between Pd electrode and SWNT is measured using the Kelvin mode.
9:00 PM - R10.2
The Possibility of High-performance n-type Carbon Nanotube Devices by Fullerene Functionalization: A First-principles Study.
Yong-Hoon Kim 1
1 Materials Science & Engineering, University of Seoul, Seoul Korea (the Republic of)
Show AbstractThe successive appearance of low-dimensional carbon materials, such as zero-dimensional [60]fullerene (C60), one-dimensional carbon nanotubes (CNTs), and two-dimensional graphenes, have been an inexhaustible source for the study of novel scientific principles and the search of advanced technological applications. Recently, about a decade after the discovery of the first C60-CNT hybrid form, carbon nanopeapod, a new hybrid C60-CNT nanostructure termed as "carbon nanobud" has been synthesized [1]. Extending our earlier study of polymerized C60 nanowires [2], we here apply a first-principles computational approach [3] to consider the C60 functionalization of CNTs as a scheme to engineer the CNT-metal contacts to produce reliable high-performance n-type CNT devices. References:[1] A.G. Nasibulin, et al., Nat. Nanotechnol. 2, 156 (2007).[2] G. I. Lee, J. K. Kang, and Y.-H. Kim, J. Phys. Chem. C 112, 7029 (2008).[3] Y.-H. Kim et al., Phys. Rev. Lett. 94, 156801 (2005).
9:00 PM - R10.20
Characterization of Electronic Property and Defects in Carbon Nanotubes by Voltage-contrast Scanning Electron Microscopy.
Aravind Vijayaraghavan 1 2 , Christoph Maquardt 1 , Simone Dehm 1 , Frank Hennrich 1 , Frank Hennrich 1 , Ralph Krupke 1
1 Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe Germany, 2 Chemical Engineering, Massachusetts Institute of Technology, Boston, Massachusetts, United States
Show AbstractSingle-wall carbon nanotubes have a wide range of electronic properties, from metallic to semiconducting. In addition, their properties and performance can be affected or tuned by defects. The large-scale, parallel screening and characterization of electronic properties and defects in carbon nanotubes, using a new technique called voltage-contrast scanning electron microscopy, will be presented here.The secondary electron yield during scanning electron microscopy depends not only on intrinsic material properties but also surface potentials. Carbon nanotubes in their device configuration show variations in potential profile along their length, depending on whether they are metallic or semiconducting and if they are in their On or Off states. This is reflected in a secondary electron contrast variation, and we show how this can be used to distinguish metallic and semiconducting nanotubes in an SEM, for the first time.[1] The presence of defects along the length of a nanotube can cause abrupt changes in the potential distribution and this can be used to locate and characterize defects.[2] Defects can be either structural or purely electronic, and the typical signatures of various kinds of defects in the secondary electron contrast image will be presented.[1]A. Vijayaraghavan, S. Blatt, C. Marquardt, S. Dehm, R. Wahi, F. Hennrich, R. Krupke, Nano Research 2008, 1, 321.[2]A. Vijayaraghavan, C. W. Marquardt, S. Dehm, F. Hennrich, R. Krupke, Carbon, 2009 In Press.
9:00 PM - R10.21
High Electron Gain from Forests of Multi-Walled Carbon Nanotubes.
Mario Michan 1 , Alireza Nojeh 1
1 Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia, Canada
Show AbstractCarbon nanotubes are attractive candidates for electron field-emitters due to their high aspect ratio, mechanical stability, and electrical conductivity. It has previously been shown that an electron beam hitting the tip of a carbon nanotube biased near the threshold of field-emission can stimulate the emission of a large number of electrons from the nanotube tip. Here we report on similar experiments on arrays of free-standing multi-walled carbon nanotubes (nanotube forests) interacting with a scanning electron microscope beam. Electron gains of up to 19000 were obtained. This can enable applications such as electron detection and multiplication, and vacuum transistors.
9:00 PM - R10.23
Resistances of Individual Bundles and Bundle Junctions in Carbon Nanotube Transparent Conductors Measured by Electric Force Microscopy.
Michael Rowell 1 , Mark Topink 1 2 , Sondra Hellstrom 3 , David Goldhaber-Gordon 2 , Zhenan Bao 3 , Michael McGehee 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Physics, Stanford University, Stanford, California, United States, 3 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractCarbon nanotube thin films are promising candidates for low cost transparent electrodes for solar cells and macroelectronics. Current transmittance/resistance performance, however, is more than an order of magnitude worse than traditional doped metal oxides and two orders of magnitude worse than what we predict from single tube properties. Electrical transport in these films is complicated by intertube resistance and a tortuous, bundled morphology which varies greatly with different processing techniques. Within and between bundles, transport is further complicated by the mixture of depleted semiconducting tubes and metallic tubes that are below the percolation threshold. Here, we show scanned probe measurements of bundles in various geometries which elucidate these resistances. We use electric force microscopy (EFM) to measure the potential of single bundles and bundle junctions isolated using a novel method of atomic force microscope (AFM) scratch lithography. For junctions between crossing bundles ranging from 10 to 30 nm in diameter, the contact resistance decreases with bundle size and ranges from 25 to 2 kOhm, which is significantly lower than expected from previous measurements of individual tube junctions or previous estimates of bundle junctions. We also measure contact resistances of 10 to 15 kOhm-um for adjacent bundles parallel to one another which is high relative to the effective junction resistance of crossed bundles and limits the conductivity of large ropes comprised of multiple bundles. Doping with thionyl chloride is seen to reduce both the crossed and parallel junction resistances by a factor of 3. These measurements show that tubes in the interior of bundles are likely active in the electrical conduction and that there is a trade-off between bundle diameter and junction resistance. Consequently, films with markedly different morphologies can have similar sheet resistances, as is often observed. The more important morphological parameter is the number of junctions/bundle. These insights suggest new methods for improving film performance through morphology control.
9:00 PM - R10.24
Wafer-scale Fabrication of Separated Carbon Nanotube Thin-film Transistors for Display Applications.
Jialu Zhang 1 , Chuan Wang 1 , Alexander Badmaev 1 , Chongwu Zhou 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractPre-separated, semiconductive enriched carbon nanotubes hold great potential for thin-film transistors and display applications due to their high mobility, high percentage of semiconductive nanotubes, and room-temperature processing compatibility. Here in this paper, we report our progress on wafer-scale processing of separated nanotube thin-film transistors (SN-TFTs) for display applications, including key technology components such as wafer-scale assembly of high-density, uniform separated nanotube networks, high-yield fabrication of devices with superior performance, and demonstration of organic light-emitting diode (OLED) switching controlled by a SN-TFT. Based on separated nanotubes with 95% semiconductive nanotubes, we have achieved solution-based assembly of separated nanotube thin films on complete 3 inch Si/SiO2 wafers, and further carried out wafer-scale fabrication to produce transistors with high yield (> 98%), small sheet resistance (~ 25 kΩ/sq), high current density (~ 10 μA/μm), and superior mobility (~ 52 cm2V-1s-1). Moreover, on/off ratios of > 10^4 are achieved in devices with channel length L > 20μm. In addition, OLED control circuit has been demonstrated with the SN-TFT, and the modulation in the output light intensity exceeds 10^4. Our approach can be easily scaled to large areas and could serve as critical foundation for future nanotube-based display electronics.
9:00 PM - R10.25
Electric-field Alignment and Growth Mechanisms of Horizontal and Vertical Carbon Nanotubes by Plasma Enhanced Chemical Vapour Deposition.
M. Cole 1 , M. Mann 1 , W. Milne 1
1 Department of Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractInvestigations have been carried out to elucidate the growth and alignment mechanisms of individual, horizontal and vertical, carbon nanotubes (CNTs) synthesised by plasma enhanced chemical vapour deposition (PE-CVD) in an NH3 / C2H2 atmosphere. Horizontal alignment was considered via two approaches; photolithographically defined electrodes, and a new proof-of-concept horizontal PE-CVD reactor. In both instances CNT alignment was achieved via locally derived electric-fields (E-fields). We have shown that, in the case of pre-patterned electrodes, DC E-fields greater than; 0.2 V/μm in situ, and 2.0 V/μm post-synthesis, are necessary. Preliminary studies on the viability of horizontal alignment through means of a new proof-of-concept horizontal PE-CVD reactor have been considered. This new reactor has been characterised using a Langmuir probe approach. An analytical model is proposed relating the aligning E-field sheath width within the plasma to the cathode bias, reactor pressure and plasma power. The estimated sheath widths, electron temperatures and electron densities all show good agreement with previously reported data. For individual vertically aligned CNTs the surface diffusion activation energies for Ni and Fe catalyst nano-particles were estimated to be 0.60±0.15 eV/atom and 0.44±0.17 eV/atom respectively. Typical surface diffusion coefficients of 1.8x10-9 m2/s for Ni and 0.83x10-9 m2/s for Fe, have been found. Data suggest a (sub)surface diffusion mechanism (where carbon diffusion occurs within the first few atomic layers of the catalyst) with a (sub)surface-to-bulk diffusion transition approximately occurring at the catalysts geometrically corrected melting temperature.
9:00 PM - R10.26
Enhanced Semiconducting Characteristic of Single-walled Carbon Nanotube Network Thin-film Transistors by Transport Channel Stripping.
Min-Ho Jeong 1 3 , Eun-Suk Choi 1 3 , Kunhak Lee 1 3 , ChaeHyun Lim 2 3 , Seung-Beck Lee 1 2 3
1 Department of Electronic Engineering, Hanyang University, Seoul Korea (the Republic of), 3 Institute of Nano Science and Technology, Hanyang University, Seoul Korea (the Republic of), 2 Department of Nanoscale Semiconductor Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractRecent reports on the performance of nanotube based thin-film transistors (TFTs) have shown promise for the realization of flexible and transparent TFTs.[1] However, SCNTF as the semiconducting transport channels are known to form leakage current paths due to the 1/3 of the nanotubes having metallic characteristics. Moreover, due to strong van der Waals interaction between carbon nanotubes in solution, they easily form bundles during synthesis, purification and thin-film preparation which contains metallic nanotubes resulting in higher leakage currents then the TFTs fabricated by nanotubes grown directly on the substrate. Pimparkar et al, have recently demonstrated that reducing the channel width by introducing a cut along the channel length, or “striping”[2], it was possible to reduce the density of metallic paths. This helps to increase Ion /Ioff without large reduction in Ion. Also increasing the channel length helps to enhance semiconducting characteristics.[3] Here, we report here, the field-effect transport characteristics of SCNTFs depending on transport channel aspect ratio and number of strips. We fabricated SCNTF-TFTs with various channel aspect ratio and the number of strips to reduce the metallic path percolation in SCNTF channels. Low contact resistace of our device showed that the resistance of the device was dominated by SCNTFs, not between the SCNTF- contact metal interface. SCNTF transistors with higher channel aspect ratio showed increased Ion/Ioff of up to 246%. The reduction of Ioff was attributed to the reduced probability of metallic paths forming between the source and drain and the reduction in Ion was attributed to the longer channel length. We also observed introducing more strips into the channel increased Ion/Ioff up to 859% by reduction of leakage paths. The existence of strips in the channel region efficiently reduces the number of metallic conducting paths existing between source and drain, which are the major cause of leakage in nanotube based TFTs. It was found that increasing the number of strips was more effective at increasing Ion/Ioff than increasing the channel length.This work was supported by the Korea Science and Engineering Foundation(KOSEF) grant funded by the Korea government (MEST) (No.R01-2007-000-10898-0) and partially by the Seoul R&BD Program (10919).[1] E. S. Snow, et al, Appl. Phys. Lett, 82, 2145 (2003) [2] N. Pimparkar, et al, Nano. Res. 2, 167 (2009) [3] C. Lim, et al, J. Korean. Phys. Soc. 53, 2039 (2008)
9:00 PM - R10.27
The Electromagnetic Shielding Property of Multiwalled Carbon Canotubes/Iron Oxide Composite Filled In Epoxy.
Yao-Cheng Lai 1
1 Material Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractAs the wireless communication is universal, the electromagnetic wave (EM wave) spreads worldwide. The contamination of EM wave is harmful to the electrical devices, the data accuracy, and the health of creatures. The best solution is electromagnetic absorption to consume EM wave. Three kinds of mechanisms of absorption are dielectric loss, magnetic loss, resistive loss. The composite of multiwalled carbon nanotubes (MWCNTs) and polymer has shown that it consumes the EM wave by resistive loss. The efficiency of the resistive absorption is limited by the reflection caused by impedance mismatch, which comes from the high conductivity and the low permeability. To match the impedance, attach the magnetic particle on the MWCNTs to increase the permeability. We show that Fe2O3/MWCNTs and Fe3O4/MWCNTs, which are added into the epoxy, successfully increase the electromagnetic shielding efficiency. Decrease the impedance as increase the permeability. It point out a new concept to make electromagnetic absorption material.
9:00 PM - R10.28
Carbon Nanofiber Supercapacitors With Large Areal Capacitances.
James McDonough 1 , Jang Wook Choi 1 , Yuan Yang 1 , Fabio La Mantia 1 , Yuegang Zhang 2 , Yi Cui 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractWe develop supercapacitor (SC) devices with large per-area capacitances by utilizing three dimensional (3D) porous substrates. Carbon nanofibers (CNFs) functioning as active SC electrodes are grown on 3D nickel foam. The 3D porous substrates facilitate a mass loading of active electrodes and per-area capacitance as large as 60 mg/cm^2 and 1.2 F/cm^2, respectively. We optimize supercapacitor performance by developing an annealing-free CNF growth process that minimizes undesirable nickel carbide formation. Superior per-area capacitances described here suggest that 3D porous substrates are useful in various energy storage devices where per-area performance is critical.
9:00 PM - R10.29
Electrical and Mechanical Properties of Carbon Nanotube Turfs after Thermocompression Bonding to Dissimilar Substrates.
Anqi Qiu 1 , Melinda Lopez 1 , Aikaterini Bellou 1 , David Bahr 1
1 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show AbstractCarbon nanotubes, often grown at elevated temperatures on semiconductor substrates, can be grown in vertically aligned arrays (turfs) and then subsequently transferred to metallized substrates. This allows the use of these turfs on substrates such as polyimde or other substrates that would not be suitable for direct growth. A series of turfs consisting of multiwalled nanotubes with diameters on the order of 15 nn, were grown on patterned substrates using Fe based catalyst to form turfs on the order of 100 microns tall and with lateral dimensions between 20 and 200 microns. The turfs were grown by chemical vapor deposition via tip growth, coated with a 50 nm thick Au layer, and then subsequently transferred to Au coated Kapton polyimide substrates by applying pressures on the order of 1 MPa and temperatures less than 450 K. The mechanical properties of these turfs were measured using nanoindentation, and the effective elastic modulus of the free surface (that which was initial in contact with the Si substrate during growth) was approximately 10 MPa, statistically indistinguishable from the region of the turf containing the catalyst layer. The electrical properties of the Au coated and uncoated surfaces was examined using electrical contract resistance measurements during nanoindentation, and clear evidence of both the onset of contact and a measurable decrease in electrical resistance in the gold coated system was observed. This system was then stretched laterally, as might occur during use on flexible electronics or during thermal expansion of a substrate, and the resulting electrical properties were found to be related to the areal density, rather than volumetric density, of the tubes, suggesting that electrical resistivity was negligibly influenced by tube-tube contacts and instead dominated by the contact resistance of each tube with the metallized substrate.
9:00 PM - R10.3
Realization of Highly Controllable Electrolysis Process by Application of Carbon Nano-tubes in Field Effect Transistors.
Jalal Naghsh Nilchi 1 , Seyed-Shamsoddin Mohajerzadeh 1
1 Thin Films and NanoElectronoics Lab., School of Electrical and Computer Engineering, University of Tehran, Tehran, Tehran, Iran (the Islamic Republic of)
Show AbstractWe have proposed, fabricated and tested a novel structure of Field-Effect Transistor (FET) combined with Carbon Nano-Tubes (CNT) to control the process of electrolysis. Our proposed device includes a conventional n-channel MOSFET but with the selective growth of Carbon Nano-Tubes in the drain region of it. MOSFET is made according to Standard NMOS Fabrication flow chart using the advantage of self-aligned process. Since the CNT growth is done in plasma and high temperature environment, we observed that the impurities escaped from the silicon and polycrystalline silicon and MOSFET does not work anymore. So we deposited a thick layer of chromium (200nm) on the whole structure as a passivating layer and just left the drain region of the MOSFET exposed, using the conventional photolithography. Afterward we deposited and patterned a thin layer of nickel (10nm) as the catalyst of CNT growth. The CNTs are grown in a DC-PECVD system. Following this step, we etched away the chromium layer completely. After the growth, the transistors needed an annealing treatment in Argon chamber at 500oC for 5 hours to retrieve their electrical behavior. We believe this happens because the atomic hydrogen can pass through the chromium layer and passivate the impurities and annealing in Argon chamber give them enough energy to leave the silicon.In this structure, the CNT collection is used as one-side electrode of electrolysis and the MOSFET acts as the current controller. We tested the structure to electrolyze some kinds of liquid such as a mixture of water and salt and observed a well-controlled electrolysis current-voltage characteristics. We related the result to enhancement in effective area achieved by application of CNTs in drain region. We investigated the effect of CNT collection area on the electrolysis process and this investigation approved our assumption.
9:00 PM - R10.30
Electronic Enhancement of Heat Transport in Carbon Nanotube Thermal Interface Materials.
Stephen Hodson 1 2 , Xianfan Xu 1 2 , Timothy Fisher 1 2
1 School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractVertically oriented carbon nanotube (CNT) arrays are of interest as thermal interface materials (TIMs) between two mating solids for their high thermal conductivity to transport heat efficiently. However, when contact sizes between a nanotube and another material (e.g., at a CNT-Cu interface) are relatively small there is exists a major impediment to heat flow at the true heterogenous material interface in which ballistic phonon effects can substantially decrease conductance. This paper investigates an approach to circumvent the phonon ‘bottleneck’ by altering the charge density in the nanotubes via exposure to electron-donating and withdrawing molecular species, tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE), respectively. The process is intended to increase the electronic contribution to thermal conductivity at a CNT-substrate interface by opening electron channels for the transport of heat. A transient photoacoustic (PA) method is used to measure the thermal interface resistance of one-sided, doped CNT TIMs at room temperature and pressure. With respect to undoped CNT TIMs, we report a 26% and 43% decrease in thermal interface resistance for CNT TIMs doped with TTF and TCNE, respectively.
9:00 PM - R10.31
Growth Mechanism and Kinetic Study of Vertically Aligned Super Long Carbon Nanotube Arrays via in situ Observation.
Wondong Cho 1 3 , Vesseline Shanov 1 3 , Mark Schulz 2 3
1 Chemical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio, United States, 3 Nanoworld Lab., University of Cincinnati, Cincinnati, Ohio, United States, 2 Mechanical Engineering, University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractThe CVD growth mechanism and kinetics of vertically aligned super long multi-wall carbon nanotube (SLCNT) were investigated by a novel in situ technique using high speed digital camera. We have developed a new engineered catalyst system that was able to prolong the catalyst lifetime, thus resulting in super long CNT arrays. The performance of our catalyst system revealed that the growth length was in the range from a few µm to 18 mm, depending on the growth time. The catalyst lifetime was over 900 min and varies with the deposition temperature and the concentration of the carbon precursor (C2H4). The kinetics of CVD grown CNT arrays has been studied by many research groups using in situ observation that is suitable for short arrays (below few mm). We developed technique that let us obtain very clear in situ image of the growing SLCNT arrays throughout the whole period of deposition time that varied from a few seconds to several hours. This technique was used to obtain kinetic curves at deposition temperatures from 730 oC to 840 oC. The growth rates were found to be constant with time until the activity of catalyst was terminated, and their values decreased with lowering the deposition temperature. Simultaneously, the life time of the catalyst increased with decreasing of the deposition temperature. Finally, activation energy of 250 kJ/mol was calculated from the obtained kinetic curves, which falls within the values of previously reported data. Keywords: Carbon Nanotube, Growth Mechanism, KineticsContact information : Wondong Cho -
[email protected]9:00 PM - R10.33
In situ Synchrotron X-ray Diffraction Study of Metal Electrodeposition on Carbon Micro- Nano-fiber Surfaces for Multi-functionalization.
Shuangqi Song 1 , Karen Taniguchi 1 , Hao Xing 1 , Zhonghou Cai 2 , Li Sun 1
1 Mechanical Engineering, University of Houston, Houston, Texas, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractOne of the biggest challenges for carbon based materials application is to tailor their physicochemical properties and assemble them into suitable architectures in a cost-effective and reproducible fashion. Based on electrochemical synthesis, room temperature deposition of metals on individual carbon microfiber and assembled carbon nanofiber sheets can be realized. . This process can significantly improve carbon materials electrical and thermal conductivity and more importantly, stimulate nanofiber alignment in external magnetic field. To reveal the nucleation, grow and grain stability of Nickel deposits on single microfiber, micro x-ray fluorescence and diffraction studies have been carried out at Argonne National Lab’s Advanced Photon Source using beamline 2-ID-D. By using a specially designed electrochemical cell, synchrotron micro-beam techniques provide in situ structural and compositional characterization capabilities. Studies show that the nucleation and grain growth of Ni on carbon surface strongly depends on the applied over potentials: instantaneous nucleation and growth process dominate at lower over-potential (-300mV) and the nucleation and growth become progressive at higher overpotential (-950mV). When varying the deposition overpotential, the stable Ni grain size is found to ranges from 45nm to 80 nm determined by the Sherrer Equation. The size distribution can also be determined by the controlled overpotential. Also the metal nuclei stability of the metal deposit is found to strongly depend on their size and can be controlled during the electrodeposition process. With better understanding of the nucleation and growth mechanism of metals on the carbon surfaces; mechanical, electrical, thermal and catalytic behaviors of carbon fibers can be further improved thus lead to large-scale engineering applications of carbon based materials in lightning strike prevention, electromagnetic shielding, vibration/acoustic noise reduction, reinforced composites, catalyst substrates, supercapacitors and bio/chemical sensors.
9:00 PM - R10.34
Growth of Carbon Nanotubes on Diamond Substrates by Microwave Plasma and Thermal Chemical Vapor Deposition Methods.
Betty Quinton 1 , Chakrapani Varanasi 2 , Jack Burke 2 , Breanna Ruter-Schoppman 1 , William Lanter 3 , Haiyan Wang 4 , Jared Petry 1 , John Bulmer 1 , Lyle Brunke 2 , James Scoffield 1 , Paul Barnes 1
1 , Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 , University of Dayton Research Institute , Dayton, Ohio, United States, 3 , Innovative Scientific Solutions Incorporated , Dayton, Ohio, United States, 4 Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractCarbon nanotube (CNT) and diamond are two allotropic forms of carbon that have good thermal conductivity properties. By growing CNTs on diamond substrates, an unique thermal interface material system can be produced for thermal management-applications. While CNTs can be grown by different methods with different catalysts, the quality of CNTs on diamond substrates could be different because of defects and the bonding strength between the substrate and CNTs. CNTs were grown by using two different methods on diamond substrates; microwave plasma enhanced chemical vapor deposition (MPECVD) and thermal chemical vapor deposition (TCVD). First, the diamond/ silicon substrate was sputtered with either iron or nickel thin film, each at 10nm. For TCVD the growth is carried out using a horizontal tube furnace at a pressure of 90 Torr, and a temperature of 800C. For MPECVD method, the diamond substrate coated with metal catalysts went through pretreatment in MPECVD chamber first. Raman spectroscopy was used to evaluate final CNT growth quality by comparing its D-Peak to G-Peak ratio (D/G ratio). A scanning electron microscopy and a transmission electron microscopy were used to study the microstructures of CNTs. For TCVD, a D/G ratio of ~0.3 was noted indicating high quality of CNTs. For MPECVD, CNTs with a D/G ratios of ~0.6 were obtained. Additional details of growth methods and their effect on the CNTs morphology/quality will be presented.
9:00 PM - R10.35
Controlled Growth of Vertically Aligned Single-walled Carbon Nanotubes.
Daniel Engstrom 1 , Antonio Lombardo 2 , Christian Koenig 3 , Andrea Ferrari 2 , Peter Boggild 1 , William Milne 2 , Hyung Park 3 , Ken Teo 4
1 Department of Micro- and Nanotechnology, Technical University of Denmark, Lyngby Denmark, 2 Centre for Advanced Photonics and Electronics, University of Cambridge, Cambridge United Kingdom, 3 Institute of Energy Technology, ETH, Zürich Switzerland, 4 , Aixtron Ltd., Cambridge United Kingdom
Show AbstractSingle-walled carbon nanotubes (SWNTs) have generated much interest since they were discovered by scientists at NEC and IBM in 1993. Their outstanding electrical, thermal, and mechanical properties have led to many proposed applications, few of which have yet been realized as commercial products. In recent years growth of vertically aligned SWNTs with unique mechanical and thermal properties has been reported . Using SWNTs as a structural material in applications such as heat sinks and water purification membranes requires good control of growth rates and SWNTs quality over large surfaces.We report growth of vertically aligned single walled carbon nanotubes from a Mo-Fe bimetallic catalyst. The carbon nanotube growth speed and quality were investigated as a function of anneal pressure, growth pressure, anneal temperature, and growth temperature using hydrogen and acetylene as precursors. The growth rate was determined from electron micrograph images whereas the level of graphitization I(D)/I(G) was determined by Raman spectroscopy. The investigation showed a maximum growth rate at 750 C and for 40 mbar whereas the lowest level of graphitization occurred at higher temperatures and lower pressures. Growth rates were found to be as high as 50µm/min resulting in SWNT films with a thickness of more than 500 µm. The Raman studies showed that the graphitization I(D)/I(G) depended heavily on both the growth pressure and growth temperature with a minimum of I(D)/I(G) = 0.1. Raman spectroscopy also revealed that the SWNT film consisted of nanotubes with a diameter distribution from 0.8 nm to 1.5 nm with the largest concentration around 1.3 nm.
9:00 PM - R10.36
Ab-initio Study of Catalytic Boron Nitride Nanotube Synthesis.
Sampsa Riikonen 1 , Adam Foster 2 , Arkady Krasheninnikov 1 3 , Risto Nieminen 1
1 Department of Applied Physics, Helsinki University of Technology, Espoo Finland, 2 Department of Physics, Tampere University of Technology, Tampere Finland, 3 Materials Physics Division, University of Helsinki, Helsinki Finland
Show AbstractStructure of boron nitride nanotubes (BNNTs) is analogous to carbon nanotubes (CNTS), with the difference that carbon-carbon bonds have been substituted with boron-nitrogen bonds [Golberg, et. al., Advanced Materials 19 2413 (2007)]. Similar to their carbon cousins, BNNTs posses impressive mechanical properties (for example, Young's modulus is of the order of terapascals), while some of the BNNT properties are even more attractive than those of their carbon counterparts: CNTs are either conducting or semiconducting, while BNNTs are always semiconducting, allowing to produce semiconducting nanotubes only. Boron nitride is also chemically very inert and resistant to oxidation, making it more attractive for applications such as shielding and coating; iron nanoparticles encapsulated into boron nitride nanotubes have been produced very recently resulting in oxidation resistance and preservation of magnetism [Narita et. al., J Electron Microscopy 55 123 (2006)]. Despite these and many other promising properties, BNNTs have received little attention, when compared to CNTs. This is because their synthesis has proven to be very difficult.We have studied boron and nitrogen chemistry and bonding on two very different catalyst metals, namely iron and magnesium. Iron is a very traditional catalyst, used widely in the CVD synthesis of carbon nanotubes. The same CVD methods used to produce CNTs do not work for BNNTs, although some results have been obtained using boride catalysts and in those cases, boron seems to come from the catalyst particle itself [Gleize et. al., J of Materials Science 29 1575 (1994)].Magnesium might seem a rather odd choice for a catalyst, but it seems to play an important role in state of the art method for producing BNNTs [Tang et. al., Chem. Commun. 1290-1291 (2002)]. In this synthesis boric oxide and ammonia are reacted in the presence of magnesium.By studying the energetics and bonding of the smallest molecules that might results from placing boron and nitrogen on the catalyst (i.e. N2, B2 and BN), we look at situations where the desired BN bond is stabilized, leading eventually to nanotube formation. Our findings indicate that on iron, BNNT synthesis is spoiled by the B2 formation (boron tends to form clusters with iron), while on magnesium, BN and B2 bonds compete as the most stable end product. We explain these findings based on the coordination of atoms and on the electronic structure of the adsorbed molecule and the catalyst.
9:00 PM - R10.38
Novel Phase Transitions of Atomic Monolayer on the Surface of a Single Nanotube.
Zenghui Wang 1 , Jiang Wei 1 , Erik Fredrickson 1 , J. Dash 1 , David Cobden 1 , Oscar Vilches 1
1 , University of Washington, Seattle, Washington, United States
Show AbstractMonolayer of gas atoms are formed on the surface of an individual suspended nanotube. Using the nanotube itself as a vibrating nanobalance and monitoring the resonance frequency, the density of the adsorbed atomic layer can be determined as temperature and pressure are varied. Discontinuities in the density are identified as individual phase transitions, by comparing to the known behavior of respective gases adsorbed on 2-Dimensional (2D) graphitic surfaces. Besides the similarity to the phase behavior of adsorbates on 2-D substrate, some important contrasts exist. The weaker binding energy resulting from less carbon atoms interacting with each adsorbate atom has a few interesting consequences, including higher equilibrium pressure of the corresponding phases transitions on the nanotube surface, lower isosteric heat, and different wetting behavior. The curvature of the surface breaks the isotropy of the substrate surface and offers more available adsorption area per carbon atom. The cylindrical boundary condition imposes new requirements on the formation of commensurate phase. And the formation of twisted pair of nanotubes offers the possibility to study the 1-D atomic chain adsorbed in the grooves between the nanotubes.
9:00 PM - R10.39
Synthesis and Characterization of High-density Horizontally Well-aligned Single-wall Carbon Nanotubes.
Yuehai Yang 1 , Wenzhi Li 1
1 Physics, Florida International University, Miami, Florida, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) have been demonstrated as active elements in sensors, optoelectronic devices, transparent conductors, and thin film electronics. Thin films consisting of high density randomly-oriented SWNTs enable the fabrication of high current-output devices. However the resistance at the tube–tube contacts that are inherent in the networks may limit charge transport efficiency and other applications. To avoid this problem, high-density horizontally aligned SWNT thin film is desirable. In this work, horizontal arrays of well-aligned SWNTs were synthesized on quartz surface by using chemical vapor deposition (CVD) on metal catalyst deposited by electron beam evaporation. The annealing effect on the alignment of the SWNTs was studied. The atomic force microscopy (AFM) characterization shows that our CNTs have small diameters ranging from 0.6 to 1.0 nm, with the high density > 20 SWNTs / μm. The density vs. length diagram shows a clear exponential tendency, which implys that the degeneration of the metal catalysts follows the decaying pattern with a length half-life of 6.6 μm. This work was supported by the National Science Foundation under grant DMR-0548061
9:00 PM - R10.40
The Size Effect of Catalyst on the Growth of Helical Carbon Nanofibers at 300°C.
Xin Jiang 1 , Junhai Xia 1 , Chunlin Jia 2
1 Institute of Materials Engineering, University of Siegen, Siegen Germany, 2 Institute for Solid State Physics, Research Center Jülich, Jülich Germany
Show AbstractThe size effect of catalyst on the growth of helical carbon nanofibers at 300°C.J. H. Xia and X. Jiang*Institute of Materials Engineering, University of Siegen, Paul-Bonatz-Str. 9-11, 57076 Siegen, GermanyC. L. JiaInstitute of Solid State Research and Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons, Research Centre Jülich, D-52425 Jülich, GermanyAbstractCu catalyzed carbon nanofibers are investigated by means of transmission electron microscopy. Straight and helical carbon nanofibers are observed to connect to the catalyst particles of octahedron or triangular prism in the samples prepared using the same processing conditions. Statistic analysis leads to evidence that the morphology of the nanofibers depends on the size of the catalyst particles. Small size of catalyst particles favours formation of the helical fibers, while large size of catalysts results in the straight fibers. Based on the observed results, growth and morphology formation of the carbon nanofibers are discussed. The growth model in which the rotating catalysts catalyze the growth of the carbon nanostructure in a helical way is proposed.*Corresponding author:
[email protected] (Prof. X. Jiang)
9:00 PM - R10.41
Fabrication and Electrical Characterization of Large-area Vertically-aligned Carbon Nanoneedles.
Jia Yun 1 , Rui Wang 2 , Mei Zhu 2 , Minghui Hong 2 , T.L. John Thong 1 2 , Carl Thompson 1 3 , Wee Kiong Choi 1 2
1 Advanced Materials for Micro- and Nano-Systems, Singapore-MIT Alliance, Singapore Singapore, 2 Electrical and Computer Engineering, National University of Singapore, Singapore Singapore, 3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe demonstrate a new technique for fabrication of periodic arrays of carbon nanoneedles and use them to characterize field emission as a function of their spacing and aspect ratio. Laser interference lithography is used for fabrication of precisely located periodic arrays of inverted nanopyramids in silicon surfaces. The nanopyramids are then used to define the position of nickel (Ni) catalysts for growth of carbon nanofibers (CNFs). Associated with this method of CNF growth, we observed a splitting of the Ni catalyst during growth, with the upper catalyst diameter ~5nm, and the bottom catalyst diameter ~100nm. We have synthesized large-area vertically-aligned carbon nanofibers (VACNFs) with different interfiber-distance-to-fiber-height ratio and fiber aspect ratio. The field emission properties of these VACNFS show that the field emission performance of VACNF arrays is optimized when the interfiber-distance-to-fiber-height ratio is equal to 1.
9:00 PM - R10.42
Atomic Layer Growth and Applications of Aligned TiO2/MWCNT Array.
Yu-Hsien Lin 1 , Sheng-Yi Lu 1 , Meng-Yen Tsai 2 , Chiung-Wen Tang 1 , Chih-Chieh Wang 1 , Der-Hsien Lien 1 , Hsin-Fu Kuo 1 , Wen-Kuang Hsu 1 , Chi-Chung Kei 2
1 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan, 2 Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu Taiwan
Show AbstractPhotocatalytic decompose organic contaminants via TiO2 nanoparticles is well known and practical to water treatment and semiconductor industry as well as our usual life. In general, TiO2 nanoparticles are usually dispersed on filter and decompose efficiency is always limited by the contact area of filter. To enlarge the reacting area, we coat TiO2 on MWCNT array via atomic layer deposition (ALD) and specific area is raised due to the high aspect ratio of TiO2/MWCNT (shell/core) structure. Super capacitor (SC) is very critical to provide a fast response charge tank for electrical vehicle. We suppose TiO2/MWCNT array is also applicable as one of the candidates. Dielectric constant of TiO2 is large (85@1MHz) and high aspect ratio of TiO2/MWCNT array support a good reasons of our new device in SC.
9:00 PM - R10.43
Engineering of Catalyst Particle Size Toward Diameter Specified Growth of SWNTs.
Kang-Hee Choi 1 , Jin-Ju Kim 1 , Goo-Hwan Jeong 1
1 Department of Advanced Materials Science and Engineering, Kangwon National University, Chuncheon Korea (the Republic of)
Show AbstractSingle-walled carbon nanotubes (SWNTs) have been widely studied due to their outstanding properties and potential applications in many areas. Since their electronic, physical and optical properties are decided by their diameter and chirality, a number of researches to control the diameter or chirality has been dedicated so far. More specifically, owing to their correlation between tube diameter and catalyst size, a lot of experimental and theoretical works have focused to more clarify the size relations between them and great progress is recently undergoing. To sum up briefly, the diameter coincidence between tube and catalytic particles is not necessarily in SWNTs cases but the size window of catalytic particles yielding thin or thick SWNTs seems to present. In order to achieve diameter specified growth of SWNTs, more efforts should be concentrated on the above mentioned issue including the exact clarification of catalyst behavior during growth process. According to this background, we investigated the catalyst particle size effect on SWNTs’ diameter systematically. We used spin-coated ferritin molecules with optimized conditions to get monodispersed catalytic nanoparticles on substrates. In addition, the size of the catalytic iron nanoparticles was controlled by high temperature annealing under argon atmosphere. The proportionality between annealing time and particle size reduction gave reliability of the treatments. Silicon with thermal oxide and ST-cut quartz wafers were used as growth substrates and their growth results such as tube diameter distribution, density and yield were compared. AFM was mainly used for diameter estimation. Especially, the horizontally aligned SWNTs on the quartz substrates were transferred onto the patterned slit substrates which make quite effective to get RBM signals of Raman spectroscopy. We believe the obtained results contribute to not only size control of nanoparticle but also diameter specified growth of SWNTs.
9:00 PM - R10.44
Vertical Aligned CNT Growth on Metals for Direct Use With Electrical Conductance.
Jin-Ju Kim 1 , Byeong-Joo Lee 1 , Goo-Hwan Jeong 1
1 Department of Advanced Materials Science and Engineering, Kangwon National University, Chuncheon Korea (the Republic of)
Show AbstractCarbon nanotubes (CNT) have been attracted much attention since they have been expected to be used in various areas by virtue of their outstanding physical, electrical, and chemical properties. Among the various applications, such as electron emission sources, device interconnects, and energy storage fields, vertically standing CNT on metal substrates are definitely beneficial because they can maintain robust mechanical stability and high conductivity between CNT and metal interfaces. At present, CNT have been used as paste form with organic binder or used as powder form by direct spaying of CNT suspension. For electrochemical applications such as supercapacitors or secondary ion batteries, however, the rates of ion exchange through the entangled CNT structures are questionable and the device reliability in terms of long term performance would not enough to be guaranteed at present. Thus, the approach using vertically aligned (VA) CNT on metal electrodes have been proposed recently especially in the electrochemical applications of CNT. Here, we report direct growth of VACNT on Cu foils using thermal chemical vapor deposition (CVD) and show the feasibility of the VACNT as anode materials in lithium ion batteries. The VCNT growth was performed at 725 C with acetylene and hydrogen mixtures. The length of VCNT was controlled by changing the growth time and process control. The diameter of the VCNT grown was much smaller than that of usual multi walled CNT which is good for higher take up of lithium ion. Coin cell battery systems with the VACNT anode were made and high capacitance of the cell was observed. Furthermore, we have investigated the effect of VACNT structures on electrochemical performance by modifying the VACNT structures through plasma treatment just after growth. Both the electrochemical properties and the filling mechanisms of the systems will also be compared.
9:00 PM - R10.45
Controlled, Surface-confined Oxygen-doping of Carbon Nanotubes: Effects on Network Devices.
Justin Opatkiewicz 1 , Melburne LeMieux 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractSolution deposition of single walled carbon nanotubes (SWNTs) has been shown to produce high quality semiconducting nanotube networks (sc-SWNTnts) when deposited on amine-functionalized surfaces. It is believed that the amine not only separates the SWNTs by chirality, but also dopes the network. Likewise, it is well documented that SWNTs become p-doped in the presence of oxygen in air. In this study, oxygen-containing self-assembled monolayers (SAMs) are utilized to simultaneously examine their sorting and doping ability on the SWNTnts. By controlling the density of the SAM on the surface, a direct correlation between oxygen exposure and SWNT doping can be determined. Atomic Force Microscopy was used to analyze network density whereas µ-Raman spectroscopy was used to determine sorting efficiency. Pre-sorted networks from amine surfaces were transferred onto oxygenated SAM surfaces and then examined to decouple sorting and doping effects. Understanding the doping effect of the oxygen functional groups on the SWNTnts can allow for further optimization of network device performance.
9:00 PM - R10.46
The First Principles Study of the Chemical Bonds Between the Defective or Functionalized CNT and Various Metal Elements.
Mina Park 1 , Byung-Hyun Kim 1 4 , Gunn Kim 2 , Kwang-Ryeol Lee 1 , Sang Hak Kim 3 , Do Seok Han 3
1 Computational Science Center, Korea Institution of Science and Technology, Seoul Korea (the Republic of), 4 Department of Materials Science and Engineering, Hanyang University, Seoul Korea (the Republic of), 2 FPRD and Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 3 Eiwang Research Center, Hyundai Motors Company, Eiwang Korea (the Republic of)
Show AbstractIntroduction of CNTs into a metal matrix has been considered to improve the mechanical properties of the metal matrix. However, the binding energies between metals and pristine CNTs wall are known to be so small that the interfacial slip between CNTs and the matrix occurs at a relatively low external stress. The interfacial strength between CNTs and metal matrix is thus one of the key factors for successful development of the CNT–metal composites. For this reason, application of defective or functionalized CNTs has attracted great attention in order to enhance the interfacial strength of nanocomposites.In the present work, we design the various hybrid structures of the single wall CNT/metal complexes and characterize the interaction between single wall CNTs and various metals such as Cu, Al, Co and Ni with the first principle methods. The calculations were mainly performed using the SIESTA code based on the density functional theory. First, differences in the binding energies or electronic structures of the CNT/metal complexes with the topological defects, such as the Stone-Wales and vacancy, were compared. Second, the characteristics of functionalized CNTs with various surface functional groups, such as –O, –COOH, –OH, –NO and –NH2 interacting with metals were investigated. We have found that the binding energy can be enhanced by the surface functional group including oxygen since the oxygen atom can mediate and reinforce the interaction between carbon and metal. The binding energy is also greatly increased when it is absorbed on the defects of CNTs. These results strongly support the recent experimental work which suggested the oxygen on the interface playing an important role in the excellent mechanical properties of the CNT-Cu composite.
9:00 PM - R10.47
Direct Growth of Carbon Nanotubes on C-MEMS Platform as Electrode Materials for On-chip Supercapacitors.
Wei Chen 1 , Majid Beidaghi 1 , Wenzhi Li 2 , Chunlei Wang 1
1 Department of Mechanics and Materials Engineering, Florida International University, Miami, Florida, United States, 2 Department of Physics, Florida International University, Miami, Florida, United States
Show AbstractOn-chip supercapacitors are the highly desired power supply for portable electronics since they may exhibit higher power densities, faster charge/discharge capability and longer cycle lifetime. However, how to increase the total energy of an on-chip supercapacitor on a limited footprint is a big challenge. Increasing the surface area by introducing carbonaceous nanostructures on the small footprint is a promising method to solve the low energy-density problem of on-chip supercapacitors. In this work, we develop a facile method to conformal deposit catalyst nanoparticles on the surface of 3D C-MEMS and grow carbon nanotube (CNTs) directly by Chemical Vapor Deposition process. SEM investigation shows that the nanotubes are distributed uniformly and densely on the surface of carbon posts. Cyclic voltammetry shows that the CNTs/C-MEMS composites exhibits typical double-layer capacitor behavior and has a high specific capacitance per gravimetry. We attribute this improvement to the excellent electronic properties and high surface area of CNTs. After 300 cycles of charge/discharge, the capacity maintains over 90% of initial capacitance. The minimizing contact resistance between carbon posts and nanotubes may facilitate good cyclability of the on-chip supercapacitors.
9:00 PM - R10.49
ESR Evidence for Disordered Magnetic Phase from Sub-nanometer Carbon Nanotubes Embedded in Zeolite Nanochannels.
Srinivasa Rao Singamaneni 1 , Andre Stesmans 1 , Jasper V Noyen 2 , Bert Sels 2
1 , Department of Physics and INPAC-Institute for Nanoscale Physics and Chemistry, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium, Leuven Belgium, 2 , Department of M2S, Centre for Surface Science and Catalysis, KU Leuven, Leuven, Belgium. , Leuven Belgium
Show Abstract Impressive research efforts have been devoted to study the properties of carbon nanotubes (CNTs) for possible application in electrical devices as interconnects and in transistors. The electronic and magnetic properties of sub-nanometer CNTs are expected to be drastically different from those of large-sized (10-100 nm) CNTs because of the strong admixing of σ-pi unoccupied electronic orbitals due to curvature effects. To date, it appears no attention has been paid to investigate the nature and dynamics of magnetic species in confined sub-nanometer metal free and aligned CNTs formed in zeolite. Recent theoretical electron spin resonance (ESR) studies predict that single walled (SW) CNTs are expected to show a two peak ESR spectrum (fine structure) due to spin-charge separation, while multi-walled (MW) CNTs are expected to exhibit an asymmetric ESR signal due to strong Rashba type spin-orbit coupling. To observe these features experimentally, it is suggested to work with clean systems, free from metallic catalytic impurities, comprised of isolated carbon nanotubes with no inter-tube interaction, and at sub-one Kelvin temperatures.According to previous suggestions though, it would constitute inherently a much appropriate system to verify theoretical predictions. This concerns the subject of the present work where the nature of magnetic species in clean ultra–small CNTs grown in nano channels of zeolites is probed by multi frequency ESR. This study provides evidence for the occurrence of low temperature ferromagnetic/spin-glass behavior in aligned arrays of sub-nanometer SWCNTs confined in zeolite nano-channels, owing to sp2-type non-bonding carbon associated localized states with density of ≈3 × 1019 /g. Features related to the much anticipated conduction electron spin resonance (CESR) are not detected down to 1.5 K. In the paramagnetic phase, the ESR linewidth is found to be weakly dependent on microwave frequency. The ESR signal observed arises from the localized paramagnetic moments of carbon. While various forms of hydrogen-adsorbed defects were suggested as origin of the localized magnetic moments, no hyperfine structure was apparent in our ESR spectra, which can be taken as negative evidence for the hydrogen-adsorbed defects as origin of the magnetic moment. Thermal treatment in H2 treatment turned out to be unsuccessful in passivating the C–related defects, leaving unaffected the low temperature magnetic features. Still no CESR could be detected. As possible reason for the absence of CESR from SWCNTs grown in zeolite nanochannels, we speculate that either the Luttinger liquid phase broadens the CESR beyond the ESR detection limit or the itinerant spins are trapped at defect states, essentially meaning that the number of metallic nanotubes present is insufficient to enable detection.
9:00 PM - R10.5
Structure-electronic Property Relationship of Electron Beam Induced Deposited (EBID) Carbon - Multiwalled Carbon Nanotube (MWNT)- Metal Interface.
Dhaval Kulkarni 1 , Srikanth Singamaneni 1 , Konrad Rykaczewski 2 , Andrei Fedorov 2 , Vladimir Tsukruk 1
1 School of Material Science and Engineering and School of Polymer,Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Woddruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractOne of the significant bottlenecks in the miniaturization of electronic devices is the large resistivity of copper based interconnects due to grain and boundary scattering of electrons and electromigration effects as they approach the nanoscale. Owing to their exceptional electrical and thermal properties, carbon nanotubes have been proposed to be promising candidates for nanoscale interconnects. Multi-walled carbon nanotubes (MWNTs), which can support current densities as high as 107 A/cm2, are excellent candidates as future interconnects. However, their application as interconnects is hindered by the large contact resistance (few GΩs) with the metal electrode underneath. Electron beam induced deposition (EBID) of amorphous carbon at the MWNT-metal interface and its subsequent graphitization results in lowering the resistance. Here, we employ atomic force microscopy, conductive force microscopy, and confocal Raman microscopy to understand the changes in the structure, phase and electrical properties of the EBID-made carbon-MWNT-metal interface during the thermal and electrical annealing. The ratio of the graphitic(G) band to disorder(D) band in the Raman spectra of EBID-carbon deposit revealed that the maximum graphitization was achieved by annealing at 300 oC. Conductive force microscopy measurements reveal the changes in the interconnect resistance with various degrees of graphitization which is in agreement with the macroscopic electrical characteristics. Our results clearly demonstrate that the EBID made graphitized carbon deposit is a promising approach to achieve MWNT-metal interfaces with significantly (few orders of magnitude) lower electrical resistance.
9:00 PM - R10.6
Single Walled Carbon Nanotube-based Tactile Pressure Sensors.
Chaehyun Lim 1 3 , Kangwon Choi 2 3 , Min-Ho Jeong 2 3 , Kunhak Lee 2 3 , Eun-Suk Choi 2 3 , Seung-Beck Lee 1 2 3
1 Department of Nanoscale semiconductor engineering, Hanyang University, Seoul Korea (the Republic of), 3 Institute of Nano science and technology, Hanyang University, Seoul Korea (the Republic of), 2 Department of electronic engineering, Hanyang university, Seoul Korea (the Republic of)
Show AbstractIn this report, we have proposed and demonstrated a Carbon Nanotube (CNT) thin- film tactile pressure sensor. It uses the piezoresistive properties of CNT thin-films, that is the effect of conductivity change caused by the mechanical modulation of individual CNT lattice structure, and the change in CNT-CNT interconnection characteristics due to strain. We investigated the electrical properties of the CNT thin-films, when parallel or perpendicular force was applied to the strip type CNT thin-films. We found that the parallel force resulted in higher conduction changes than when perpendicular force was applied.From this result, we have designed a unit tactile pressure sensor cell structure whereby a PDMS membrane was used to centralize the perpendicular pressure to the free-standing CNT thin-film active sensing element. The sensing element comprises of 100×120μm2-patterned CNT thin-film embedded on a thin PDMS film. The tactile pressure applied to the PDMS film was transferred to the sensing element as lateral strain, stretching the CNT thin-film sensing element patterns resulting in increased resistance. We have tested various CNT active sensing layer dimension in order to enhance the sensitivity (ΔR/R0) to applied tactile pressure. We found that the pressure detection range may be controlled by modulating PDMS layer thickness and active sensing layer dimension. After repeated application of tactile pressure, we found that the CNT tactile pressure sensor showed good reproducibility with only a small decrease in sensor sensitivity after several thousand times operation.
9:00 PM - R10.7
Simulations of Pressurized Water Flow Through Carbon Nanotubes.
Samantha Shaw 1 , David Faux 1
1 Physics, University of Surrey, Guildford United Kingdom
Show AbstractRecently there has been increased interest in the behaviour of water molecules within confined nano-sized spaces, for example, in the study of drug-delivery systems, cements, zeolites and polymeric materials. Water/carbon nanotubes (CNT) systems not only provide a relatively simple case study [1] but also have potential applications for fluid piping, desalination and drug delivery. A greater understanding of the molecular interaction between water and CNTs is required.Classical molecular dynamics (MD) simulations are used to investigate the flow of water molecules within the confined space of flexible single-walled CNTs. A sequence of different MD ensembles is used to achieve a set of water baths at pressures ranging from 2 – 12 GPa. The simulation cell consists of four CNTs in a bundle and placed adjacent to the bath of water molecules. The flexible single point charge model of Wu et al [2] is used for the water-water potentials, while the CNTs are modelled using the Tersoff potential [3]. The water-carbon interactions are modelled using a Lennard-Jones potential, optimised for carbon and oxygen by Werder et al [4].The flow of the water molecules is simulated as a function of pressure, temperature and CNT diameter. The minimum pressure required to facilitate water entry is presented, along with the change in flow dynamics throughout the pressure range. The effect of temperature on the flow characteristics is presented for pressures at either end of the pressure range.The structure and radial density distribution of nano-confined water are presented for nanotubes with diameters from 0.95nm to 1.67nm. The water molecules are found to undergo restructuring due to their confinement, with detail molecular arrangement dependent on CNT diameter. The flow dynamics depends on the water position within the CNT. In the case of the smallest CNT, 0.95nm a single chain of water molecules is found. In the case of the 1.4nm CNT, the water molecules form a single chain down the centre of the CNT, surrounded by a helical arrangement of water. This diameter-dependent structuring is in agreement with Thomas and McGaughey [5] for the smaller nanotube diameters. Their findings showed a tendency to an almost bulk like state at diameters greater than 1.39 nm whereas the present results indicate two separate structures (the single chain and the surrounding helical structure similar to that of the ice nanotubes simulated by Maniwa et al [6]) for the larger CNTs.References[1] Berezhkovskii, Hummer, Phys. Rev. Lett, 89,0645303, (2002)[2] Wu et al, The Journal of Chemical Physics, 124, 024503 (2006)[3] Tersoff, Phys. Rev. Lett. (Dec 1988)[4] Werder et al Journal of Physical Chemistry B, (Feb 2003)[5] Thomas and McGaughey, Phs Rev Lett, 102, 184502 (2009)[6] Maniwa et al, Nature Materials, Vol 6, (Feb 2007)
9:00 PM - R10.8
Underwater Sound Generation Using Carbon Nanotube Films.
Ali Aliev 1 , Marcio Lima 1 , Shaoli Fang 1 , Ray Baughman 1
1 NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractFor the first time, we have studied and demonstrated the underwater thermoacoustic generation of sound using various carbon nanotube assemblies and packaging. Resistively heated thin carbon nanotube sheet (20 μm), directly immersed into liquid (water, methanol, ethanol), produces wide-band acoustic wave emission on doubled frequency. Due to non-resonance sound generation the emission spectrum of MWNT sheet is smooth and continuous in wide frequency range, 1-10^5 Hz. By proper design and encapsulation, there is potential for high-power, low-frequency and wide-band generation of continuous wave, pulsed, or modulated output. Advantages and disadvantages of this source technology are discussed.
9:00 PM - R10.9
Enhanced Long-term Stability of Carbon Nanotube-based Field Emitters Fabricated by Spray Method.
Hee Jin Jeong 1 , Hae Deuk Jeong 1 , Seung Yol Jeong 1 , Joong Tark Han 1 , Geon-Woong Lee 1
1 , Korea Electrotechnology Research Institute, Changwon Korea (the Republic of)
Show AbstractThin multiwalled carbon nanotube (t-MWNTs)-based field emitters with long term stability are fabricated by using a spray method. Tetraethylorthosilicate (TEOS) sol as a binder was mixed withdispersed solution of t-MWNTs to enhance the adhesion of t-MWNTs on the cathode substrate. Due to the poor intermolecular interaction of TEOS to the CNTs, the TEOS was precipitated during spray coating, and finally tightly adhered to cathode electrode when heat treatment at 150 C for 1 hour was performed. Stable emission for long time of CNT emitters is attributed from the TEOS binder which has no organic materials compared to other silane binders such as methyltrimethoxysilane and phenyltrimethoxysilane. Excellent field emission characteristics were exhibited, with a large field enhancement factor and low turn-on voltage, comparable to those of CNT emitters fabricated by a screen printing of CNT paste. Therefore, t-MWNTs/TEOS hybrid films could be utilized as an alternative for an efficient and reliable field emitters.
Symposium Organizers
David B. Geohegan Oak Ridge National Laboratory
John Robertson Cambridge University
Kuei-Hsien Chen Academia Sinica
Jie Liu Duke University
R11: Separation of Nanotubes
Session Chairs
Thursday AM, April 08, 2010
Room 2020 (Moscone West)
9:00 AM - **R11.1
High Efficiency Metal-semiconductor Separation of SWCNTs.
Hiromichi Kataura 1 2 , Takeshi Tanaka 1 , Yasumitsu Miyata 1 , Shunjiro Fujii 1 , Daisuke Nishide 1 2 , Kazuhiro Yanagi 2 3 , Ye Feng 1 2 4 , Kiyoto Matsuishi 4 , Yutaka Maniwa 2 3
1 Nanotechnology Research Institute, AIST, Tsukuba, Ibaraki, Japan, 2 JST, CREST, Kawaguchi Japan, 3 Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo, Japan, 4 Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, Japan
Show AbstractIt is well known that there are two electronic types of single-wall carbon nanotube (SWCNT), metal and semiconductor, depending on their wrapping structures. Because no synthesis methods can produce single electronic type, metal-semiconductor separation is indispensable for practical applications of SWCNTs, such as thin film transistors and transparent conducting films. After the great works by Arnold et al.[1], now we can obtain high-purity (up to 99 %) metallic and semiconducting SWCNTs by using density gradient ultracentrifugation (DGU). Although DGU realized high purity separation, we have to reduce time and cost of the separation for the industrial applications. Recently, we found that the agarose gel can be used for the separation of SWCNTs [2]. We demonstrated that SWCNTs dispersed in agarose gel with sodium dodecyl sulfate as surfactant could be separated into two distinct potions each of which contains metal and semiconductor, respectively by electrophoresis, permeation, diffusion, and centrifugation [3]. Now the separation method was improved and the continuous separation was achieved. Separation purity is sufficiently high and separation yield is almost 100% that is much higher than that of DGU method. In this presentation, we will show our recent progress in the separation and improvements in the device applications using semiconductor enriched SWCNTs.
References
[1] M.S. Arnold et al., Nat. Nanotechnol. 1 (2006) 60.
[2] Takeshi Tanaka et al. Appl. Phys. Express 1 (2008) 114001.
[3] Takeshi Tanaka et al., Nano Lett. 9 (2009) 1497.
9:30 AM - R11.2
Large-scale Integration of Single-chirality Carbon Nanotube and Graphene Devices.
Aravind Vijayaraghavan 1 2 , Frank Hennrich 1 , Christoph Marquardt 1 , Ninette Stuerzl 1 , Michael Engel 1 , Marc Ganzhorn 1 , Simone Dehm 1 , Ralph Krupke 1
1 Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe Germany, 2 Chemical Engineering, Massachusetts Institute of Technology, Boston, Massachusetts, United States
Show AbstractSingle-wall carbon nanotubes have a wide range of electronic applications, however, they face two major hurdles. One is the ‘polydispersity problem’, resulting for the large variation in properties and performance across different chiralities. The second involves large-scale directed assembly of individual nanotubes into functional devices. Graphene too faces this hurdle. Here I present our advancements in overcoming these two challenges.Recently, various sorting techniques have come to the fore to yield single-chirality (monodisperse) or electronically-sorted carbon nanotube suspensions. Here, we use a chirality selective polymer to yield monodisperse nanotube solutions.[1] Efforts are underway to similarly sort graphene by number of layers, and initial success has been reported.We have previously shown that single-wall carbon nanotubes can be integrated into large-scale arrays of functional devices using A/C dielectrophoresis.[2] The process is self-limiting to one nanotube per device. The nanotubes from monodisperse suspensions are integrated by dielectrophoresis into large-scale single-chirality device arrays for the first time.[3] I will also present similar large-scale assembly of graphene flakes and nanoribbons by dielectrophoresis.[4][1]F. Hennrich, S. Lebedkin, M. M. Kappes, Physica Status Solidi (B) 2008, 245, 1951.[2]A. Vijayaraghavan, S. Blatt, D. Weissenberger, M. Oron-Carl, F. Hennrich, D. Gerthsen, H. Hahn, R. Krupke, Nano Lett. 2007, 7, 1556.[3]A. Vijayaraghavan, F. Hennrich, N. Stürzl, M. Engel, M. Ganzhorn, C. Marquardt, S. Dehm, R. Krupke, ACS Nano 2009, In Press.[4]A. Vijayaraghavan, S. Dehm, C. Sciascia, A. Lombardo, A. Bonetti, A. C. Ferrari, R. Krupke, ACS Nano 2009, 3, 1729–1734.
9:45 AM - R11.3
Influence of Electrostatics on Separation of and Electronic Properties of Solution Deposited Carbon Nanotube Networks.
Justin Opatkiewicz 1 , Melburne LeMieux 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractSolution deposition of single walled carbon nanotubes (SWNTs) onto self-assembled monolayers (SAMs) containing amine functional groups has been found to produce high quality semiconducting network devices (SWNTnts). When these aminated surfaces were exposed to varying pH solutions, the resulting NT networks were altered. We have previously shown that the chirality, density, and alignment of these networks were highly dependent on the pH exposure. Further analysis has shown that device performance of SWNTnts can be altered, quite drastically, by this pH treatment. Atomic Force Microscopy (AFM) was used to observe variation in the density of CNTs adsorbed on the surface while µ-Raman spectroscopy was used to determine the efficiency of sorting and SWNT chirality. Electrode deposition and device testing was used to determine the influence of the pH treatment on thin film transistor (TFT) performance. As an additional study, primary, secondary, tertiary, and quarternary amine surfaces were examined to analyze the influence of the amine structure on SWNT adsorption. When the interaction between the amine and SWNTs can be better understood and characterized, this surface sorting technique can be optimized for better TFTs.
10:00 AM - R11.4
Solution Processed Self Sorted Carbon Nanotubes for Transistors and Conductive Films.
Soumendra Barman 1 , Melburne LeMieux 1 , Jae Yeon Baek 1 , Zhenan Bao 1
1 Department of Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractSingle walled carbon nanotubes (SWNTs) posses great potential for applications ranging from sensors, flexible computing networks and and transparent conducting electrodes. However, these next generation electrical devices can only be enabled if the separation of nanotubes by chirality is controlled. Here, we work towards this goal by utilizing the surface sorting separation technique we have developed for the fabrication a range of solution assembled sub-monolayer SWNT thin film transistors (SWNT-TFTs) and conducting films. This is done modifying the solution processing conditions and self assembled monolayer functionalities in an effort to understand and tune the interactions leading to chirality selectivity. UV-vis-NIR spectroscopy, Raman spectroscopy, atomic force microscopy and semiconductor parameter analysis were used to characterize the results. The role of SWNT concentration, nanotube length and diameter and defect density are discussed. Knowledge gained from understanding the mechanism for surface self sorting is critical for the fabrication of devices and could be important for the integration of carbon nanotubes into large scale electronics.
10:15 AM - R11.5
Direct Determination of the Semiconducting/Metallic Character of Single-wall Carbon Nanotubes via Electric Force Microscopy.
Bernardo Neves 1 2 , Ana Paula Barboza 1 , Ana Paula Pereira 1 , Helio Chacham 1
1 Physics, UFMG, Belo Horizonte Brazil, 2 Chemistry, Indiana University, Bloomington, Indiana, United States
Show AbstractSingle Wall Carbon Nanotubes (SWNTs) can either be metallic or semiconducting depending on their chirality and diameter. The vast amount of proposed (and accomplished) SWNT devices strongly depends on such metallic/semiconducting nature. Therefore, it is highly desirable to investigate the electrical properties of individual nanotubes, which has been achieved via optical and electrical techniques. The majority of electrical characterization studies have addressed SWNT conductivity and used transport measurements to distinguish metallic from semiconducting nanotubes. There is also a fair amount of works, which employed Electric Force Microscopy (EFM) techniques to investigate electrical properties of SWNTs. Some of these studies focused their attention to defects, conductance and charging effects. Only a few works dealt with the identification of metallic and semiconducting SWNTs using EFM. Such studies, however, employed sophisticated (albeit elegant) experimental setups (using DC or AC excitations) to accomplish this task, which, nevertheless, may not be easily available. The present work brings a new perspective to the process of SWNT characterization, widening its availability, by showing that conventional EFM imaging (using a DC biased tip) directly resolves semiconducting from metallic SWNTs on any as-grown sample (without the need of any further processing). Specifically, metallic nanotubes always present a characteristic “V-shaped” EFM line profile across the nanotube, while semiconducting nanotubes present a “W-shaped” profile. In addition, the effects of SWNT length and diameter on the EFM data were also investigated. Even though these parameters affect differently metallic and semiconducting SWNTs, it is shown that the EFM line profile across a nanotube (i.e., the plane EFM image) is a robust method for absolute determination of the SWNT metallicity. The accuracy of such “metal” or “semiconductor” SWNT direct labeling is further confirmed via Raman spectroscopy and charge injection experiments.
R12: Optical Properties of Nanotubes
Session Chairs
Thursday PM, April 08, 2010
Room 2020 (Moscone West)
11:00 AM - **R12.1
Phonon-assisted Electroluminescence from Metallic Carbon Nanotubes and Graphene.
Ralph Krupke 1
1 Institut für Nanotechnologie, Karlsruhe Institute of Technology, Karlsruhe Germany
Show AbstractWe report on light emission from biased metallic single wall carbon nanotubes (SWNT), multi wall carbon nanotube (MWNT) and few layer graphene (FLG) devices. SWNT devices were assembled from tubes with different diameters ranging from 0.7-1.5 nm. They emit light in the visible spectrum with peaks at 1.4 eV and 1.8 eV. Similar peaks are observed with MWNT and FLG devices. We propose that the light emission is due to phonon assisted radiative decay from populated π band states at the M point to the Fermi level at the K point. Since for most carbon nanotubes as well as for graphene, the energy of unoccupied states at the M point is close to 1.6 eV, we consider the observation of two emission peaks at ~1.6 ± ~0.2 eV as evidence for radiative decay under emission or absorption of optical phonons, respectively.
11:30 AM - R12.2
Dissociation of Carbon Nanotube Excitons at Heterojunction Interfaces.
Michael Arnold 1 , Dominick Bindl 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractSemiconducting single-walled carbon nanotubes are intriguing optical absorbers for photovoltaic solar cells and photodetectors because of their outstanding charge transport characteristics, solution-processability, near- and mid-infrared tunable optical band gaps, and strong optical absorptivity> 1E5 cm-1. However, despite their intriguing properties, carbon nanotubes have had restricted impact as the optically absorptive materials of photosensitive devices [1]. On the nanoscale, single (one) nanotube-based photodetectors have been fabricated but have diminutive absolute absorbance. A potentially more scalable approach to carbon nanotube optoelectronics and photodetectors is to utilize thin films consisting of many nanotubes that enable more substantial absorptance over larger areas. However, devices based on bulk films of many nanotubes have been hindered by the large exciton binding energy in nanotubes > 0.1 eV. Without a mechanism for overcoming this binding energy (dissociation), the potential energy stored in photogenerated excitons cannot be harvested for non-thermal energy harvesting- (e.g. solar photovoltaics) or photodetector- applications.Several studies have reported on exciton dissociation and subsequent charge transfer at carbon nanotube/semiconductor heterojunctions with conflicting results as to what materials form type-I (straddling gap) versus type-II (staggered gap) heterojunctions with carbon nanotubes [see ref. 1 and ref. within]. Here, we have systematically studied the dissociation of photogenerated excitons in carbon nanotubes that are in contact with a range of semiconductors of varying energetics. These semiconductors include organic electron acceptors such as fullerene and perylene derivatives; organic electron donors including polyacenes, phthalocyanine, and conjugated semiconducting polymers; and, solution-processed inorganic semiconductors such as ZnO and TiO2.The dissociation of excitons at the heterojunction interfaces between semiconducting carbon nanotubes and the aforementioned semiconductors has been characterized using spectrally resolved photocurrent spectroscopy, surface photovoltage spectroscopy, and phototransistor device-test geometries. We have found that the phototransistor measurements are sensitive to photocurrent arising from both dissociated electron/hole pairs and photoconductive bolometric (heat-induced) changes in resistivity. However, by measuring photocurrent and photovoltage spectra at zero-applied bias, the thermally induced photoconductivity effects can be eliminated. The results from the various heterojunctions are quantitatively compared with the previous results of Arnold and coworkers [2] in which the internal quantum efficiency of exciton dissociation at polymer wrapped carbon nanotube / C60 interfaces was shown to be > 40%.1. Ph Avouris, M Freitag, V Perebeinos Nature Photonics (2008). 2. MS Arnold, JD Zimmerman, SR Forrest, et al. Nano Lett. (2009).
11:45 AM - R12.3
Electroluminescence from Schottky Diodes Based on Perfectly Aligned Arrays of Single Walled Carbon Nanotubes.
Xinning Ho 1 , Lina Ye 1 , Jana Zaumseil 2 , Slava Rotkin 3 , Frank Du 1 , Simon Dunham 1 , John Rogers 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States, 3 , Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractNear infra red electroluminescence is observed from Schottky diodes based on perfectly aligned arrays of single walled carbon nanotubes (SWNTs). The devices each involve hundreds of SWNTs grown on crystalline quartz substrates, contacted on one end by palladium and on the other by calcium electrodes. Under appropriate bias conditions, emission spots from each of the individual semiconducting SWNTs can be observed near the calcium-SWNT interface. Similar Schottky diodes based on single semiconducting-SWNTs and resistors based on single metallic-SWNTs are studied to yield insights into the details of the behaviors of the array devices. Electrolyte gating transistors with analogous designs enables determination of the majority carrier type at various gate and drain biases. Collectively, the results establish the operation of a class of SWNT based light emitting diode (LEDs).
12:00 PM - R12.4
In situ Measurements of Growth Kinetics and Density Variations in SWNT Arrays: Flux Effects Induced by Pulsed CVD.
Jeremy Jackson 2 1 , Alex Puretzky 1 2 , Gyula Eres 2 , Karren More 3 , Chris Rouleau 1 2 , David Geohegan 1 2
2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Shared Research Equipment User Facility, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractControl over the density, purity, and uniformity of vertically-aligned nanotube arrays (VANTAs) are factors currently limiting applicability of these unique nanotube architectures. Here, pulsed feedstock gas introduction during chemical vapor deposition was used to probe the dependence of VANTA density on feedstock flux. Operating at low pressures and fast gas flows for fast response times, C2H2 gas pulses from a pulsed valve were injected into fast propagating jets of Ar/H2 inside a high temperature CVD reactor to probe the onset times for nucleation, measure early growth kinetics, understand the origin of alignment of VANTA growth from evaporated metal film multilayers, and study the influence of variable feedstock flux on individual nanotube and VANTA properties. Using time-resolved reflectivity from growing VANTAs, both the height of the arrays vs. time (based on interference fringes) and the optical extinction coefficients of the arrays were simultaneously estimated. Fabry-Perot fringes were fitted using an effective medium approximation to estimate the evolution of the complex index of refraction, roughness of the top layer of the array, and array length throughout growth runs performed under different feedstock fluxes. The density of the arrays was found to vary dramatically with feedstock flux. High resolution transmission electron microscopy of sectioned arrays was performed to confirm this hypothesis. Z-contrast STEM was used to directly measure density variations for comparison with the optical measurements. In addition, the onset time for nucleation was measured for both CW and pulsed CVD fluxes and correlated with both the initial (maximum) growth rate and the resulting density of the arrays. Instantaneous growth rates for single pulses were varied from 0.02 μm/s up to extremely high rates of 7 μm/s depending on the feedstock supply. The pulsed and CW CVD conditions employed resulted in nearly exclusively SWNT growth, with high flux pulsed growth conditions result in a narrowing and shifting of the SWNT diameter distribution toward large (~3.8 nm) diameters. Repeatedly stopping and renucleating growth using gas pulses results in the synthesis of segmented SWNT arrays separated by “horizontal” bands which reveal evidence for the origin of alignment in the array, renucleation fractions, and the nature of the density variation within the array. The density variation within each pulsed (t < 1s) growth period indicates that different catalyst nanoparticles respond differently to the changing feedstock flux within each pulse, some shutting down, and then renucleating on successive pulses. Nanotubes were found to renucleate effectively after hundreds of growth interruptions, with small-diameter SWNTs showing little evidence of wall defects under HRTEM. Synthesis science sponsored by the U.S. Dept. of Energy Office of Science, BES, DMSE. Characterization facilities at CNMS and ShaRE sponsored by DOE-BES, DSUF.
12:15 PM - R12.5
Narrow and Intense Resonances in SERS Spectra of Single Wall Carbon Nanotubes.
Alex Puretzky 1 , David Geohegan 1 , Chris Rouleau 1
1 , ORNL, Oak Ridge, Tennessee, United States
Show AbstractHere we report the discovery of very narrow Raman lines in SERS spectra of the low frequency region of SWNTs - in some cases almost 10 times narrower compared to those measured and predicted theoretically for individual SWNTs. In this study, the disordered top layer of as-synthesized vertically aligned carbon nanotube arrays (VANTAs) was investigated. SWNTs in this layer served as templates for deposition of variably-spaced gold nanoparticles, creating numerous “hot spots” that generated very intense single lines of individual SWNTs in the low frequency region (10-300 cm-1) of the Raman spectra. Minimum linewidths of 0.3 cm-1 and maximum SERS-to-Raman intensity ratio of ~ 2000 were observed. The corresponding electronic resonances were studied and assigned using tunable laser excitation. Interesting new features were observed in this low frequency region. Pairs of lines with identical SERS excitation profiles were observed and interpreted as the longitudinal-acoustic and radial breathing modes of same nanotube. Furthermore, SERS lines in previously unexplored very low (14-30 cm-1) frequency region were measured and tentatively assigned to the ring modes of SWNTs. Their origin and implications for new opportunities in SERS-based carbon nanotube spectroscopy will be discussed. This research at the Center for Nanophase Materials was supported by the DOE BES Scientific User Facilities Division. Samples resulted from research sponsored by the BES Division of Materials Sciences and Engineering.
12:30 PM - R12.6
Photoluminescence Sidebands for Evaluating Nanotube Aggregation.
Yuan Chen 1 , Li Wei 1 , Yanhui Yang 1
1 , Nanyang Technological University, Singapore Singapore
Show AbstractEfficient dispersion of individual single walled carbon nanotubes (SWCNTs) is one of the major obstacles for many nanotube fundamental studies and practical applications, such as nano-composites, electronic devices, bio-imaging, biosensors and drug-delivery. Developing sensitive characterization methodologies, which can proficiently monitor the aggregation of SWCNTs, are strongly desired. Aggregation of SWCNTs has a profound impact on their optical properties; in particularly, photoluminescence emission (PLE). In this study, two SWCNT samples enriched with (6, 5) and (7, 5) chiral structures were utilized to establish the correlation between PLE sidebands (the transverse sideband E12,21, the phonon coupled sidebands E22+G,G' and the E33→E11 emission band) and nanotube aggregation. SWCNT samples containing different amounts and sizes of bundles were obtained by centrifuging surfactant dispersed SWCNTs at various centrifugation forces. Dialysis is also used to achieve the controlled re-bundling of nanotubes in our experiments. Our results demonstrated that the intensity ratios between PL sidebands and the main E22→E11 PL peak are more sensitive toward the aggregation of SWCNTs than other commonly used methods, such as optical absorption spectroscopy and atomic force microscope. Furthermore, this PL sideband based analytical method is applicable to different dispersion conditions involving various surfactants and solvents, which make it an attractive methodology for monitoring the nanotube aggregation in various applications.
12:45 PM - R12.7
Stable and Responsive Fluorescent Carbon Nanotube Silica Gels.
Gautam Gupta 1 , Juan Duque 2 , Stephen Doorn 2 , Andrew Dattelbaum 1
1 CINT, Los Alamos National Lab., Los Alamos, New Mexico, United States, 2 Chemistry, Los Alamos National Lab., Los Alamos, New Mexico, United States
Show AbstractCarbon nanotubes show a promising future in the fields of sensing,optics, nanotechnology, electronics, and materials science. In order to harness these unique properties for device applications, there is a need to develop a stable solid platform that incorporate nanotubes with ease while maintaining their unique properties. Here we report a general route to prepare silica nanocomposite gels doped with fluorescent single walled carbon nanotubes (SWNT). We show that tetramethylorthosilicate (TMOS) vapors can be used to gel an aqueous solution of surfactant wrapped SWNT while maintaining fluorescence from the semiconducting nanotubes.Initial exposure of aqueous SWNT solutions to TMOS vapors resulted in an acidification of the solution prior to gelation that caused a 30% decrease in the emission signal from sodium dodecylsulfate (SDS)wrapped SWNT. However, addition of buffer to the SDS/SWNT solution or selection of a surfactant, which forms a more rigid micelle such as sodium deoxycholate, allows one to prepare nanocomposites with little to no loss of the fluorescence signal observed in solution. Further,exposure of encapsulated SWNT to small aromatic molecules demonstrates that the surfactant-wrapped SWNT can interact with the surrounding environment. We show that nanocomposites prepared from unbuffered SDS/SWNT encapsulated in silica were found to be completely accessible to small molecules, while nanocomposites prepared from buffered-SDS/SWNT or DOC/SWNT are relatively unaffected by exposure to external stimuli. These results suggest that there is a balance between maximizing emission intensity and environmental sensitivity of surfactant-wrapped single walled carbon nanotubes.
R13: Nanotube Devices and Field Emission
Session Chairs
Thursday PM, April 08, 2010
Room 2020 (Moscone West)
2:30 PM - **R13.1
Aligned Carbon Nanotube Arrays: Alignment Mechanisms and Field Emission Properites.
Kaili Jiang 1
1 Dept. of Physics, Tsinghua University, Beijing China
Show AbstractThe properties and synthesis methods of vertically-aligned carbon nanotube arrays will be presented. Field emission properties and alignment methods will be reviewed.
3:00 PM - R13.2
Optically Controlled Carbon Nanotube Cathodes for X-ray and Microwave Electron Tubes.
Pierre Legagneux 1 , Nicolas Le Sech 1 , Pierrick Guiset 1 , Laurent Gangloff 1 , Stephane Xavier 1 , Jean-Philippe Schnell 1 , Costel Cojocaru 1 , Didier Pribat 1 , Kenneth Teo 2 , John Robertson 2 , William Milne 2
1 Nanocarb, Thales-Ecole Polytechnique, Palaiseau France, 2 Electrical Engineering Division, University of Cambridge, Cambridge United Kingdom
Show AbstractCompared to thermoionic cathodes used in most electron tubes, carbon nanotube (CNT) based cathodes enable to easily modulate the emitted electron beam. This can be performed using an integrated or external extraction grid. This can also be performed using the optical control of a CNT photocathode [1].This photocathode is an array of vertically aligned multi-walled CNTs, each CNT being associated to a semiconducting p-i-n photodiode. The p-i-n element acts as an optically controlled current source that imposes the current that can be emitted by the CNT emitter. The envisaged applications are 3D X-ray imaging using computed tomography and microwave amplification for satellite telecommunication.Computed tomography enables the reconstruction of a 3D image of an object by collecting many 2D projection images. Using multiple X-ray sources and a 2D X-ray sensor, low cost, light and efficient stationary scanners can be fabricated. CNT based cathodes are currently studied because they operate at room temperature and enable pulsed operation. However the control of the emission through a control circuit is complicated, especially if the cathode is biased at high voltage (50 to 200 kV). CNT photocathodes are particularly attractive for this application because the laser source is electrically insulated from the cathode and also because the emission current is proportional to the laser power. To demonstrate this approach, we will present the performances of a CNT photocathode based on silicon p–i–n photodiodes and multi-walled CNTs. The CNTs have been grown by plasma enhanced chemical vapour deposition using C2H2 and NH3 gases. Using a 650 nm laser, a 1 mm diameter photocathode delivers 0.8 mA and exhibits an ION/IOFF ratio above 20. Moreover, the electron beam can be modulated at frequencies up to 300 MHz.The second application relates to microwave amplifiers and particularly to the large bandwidth travelling wave tubes (TWTs) which are used on satellites for telecommunication. These TWTs are based on thermoionic cathodes that emit a continuous electron beam. The post modulation of the beam that is required to amplify the microwave signal takes roughly half of the tube length. The use of a photocathode directly delivering a modulated electron beam would enable the fabrication of light, compact and highly efficient amplifiers. For this purpose, we are currently studying CNT photocathodes based on GaInAs p-i-n photodiodes operating at 1.55 µm. To prevent dopant diffusion during CNT growth, we have developed a new water-based growth process where H2O is employed (instead of NH3). The growth temperature is then reduced to 550-600°C. First experiments concerning the operation of a CNT photocathode operating in the GHz range will be presented.This work was partially funded by the EC through the NMP project Canape and the French ANR projects Spiders and PhotoCat.[1] L. Hudanski et al, Nanotechnology 19, 105201 (2008).
3:15 PM - R13.3
Significant Enhancement of the Capacitance of Carbon Nanotube Based Supercapacitors, Using Argon Irradiation.
Mark Hoefer 1 , Prabhakar Bandaru 1
1 Materials Science Program, Mechanical Engineering department, UC, San Diego, La Jolla, California, United States
Show AbstractCarbon nanotubes (CNTs) have been proposed for electrodes in electrochemical capacitors (ECCs)/supercapacitors primarily due to their large surface area and abundance of reaction sites with the possibility of large charge storage capacity and capacitance (C). In this paper, we specifically probe the total CNT capacitance (CT), through voltammetric techniques, and suggest ways in which it can be improved. We focus on the accurate characterization and analysis of the electrostatic/double layer (Cdl) and faradaic/pseudo-capacitive (Cp) components of the CT. It should be noted that Cdl arises primarily due to charge separation across the electrode/electrolyte interface while Cp requires adsorption of electroactive species coupled with charge transfer. We then suggest methods aimed at increasing Cdl and Cp, based on the controlled introduction of defects into the CNTs through argon irradiation. A monotonic increase in Cp with increased argon exposure, with an ~ 50% rise at a given scan rate e.g., ~ 255 μF/cm2 enhanced to ~ 395 μF/cm2 at 5 mV/s. A further enhancement of Cp by 30-60%, at any given concentration, was seen due to the argon, presumably due to the creation of additional electroactive defects and reactive sites. The Cp increase was correlated to the decreased Tuinstra-Koenig correlation length through Raman spectroscopy. An ~ 200% increase in Cdl , e.g., ~ 3 μF/cm2 enhanced to ~ 10 μF/cm2 at 0.5 mM, and ~ 23 μF/cm2 enhanced to ~ 58 μF/cm2 at 10 mM. In summary, the strategy of artificial introduction of defects may be able to harness the electrical conductivity of the CNTs along with an enhanced effective specific surface area. We have consequently obtained superior power densities ~ 1000 W/kg along with energy densities ~ 10 Wh/kg.
3:30 PM - R13.4
Carbon Nanotube-silicon Composite Films as High Capacity Anode for Lithium Ion Batteries.
Li-Feng Cui 1 , Liangbing Hu 1 , Yi Cui 1
1 Materials Science & Engineering, Stanford University, Stanford, California, United States
Show AbstractSilicon is an attractive alloy-type anode material for lithium ion batteries because of its highest known capacity (4,200 mAh/g). However silicon’s large volume change upon lithium insertion and extraction, which causes pulverization and capacity fading, has limited its applications. In this talk I will present a novel study using carbon nanotube-silicon (CNT-Si) composite films as high capacity anode material. CNT-Si composite films up to 6 μm in thickness were synthesized by SiH4 chemical vapor deposition (CVD) on pure CNT films. The composite film has a structure similar to the steel bar reinforced concrete, where CNT network inside the film functions as mechanical support and provide good flexibility and strength. This composite film is also very conductive due to the existence of infiltrated CNT network. It can be made on a stainless steel mesh or free standing and used as anode electrodes. This composite film has a high specific charge storage capacity (~2000 mAh/g) and a good cycling life, much superior to pure sputtered-on silicon film with similar thickness. We attribute the great performance to the good flexibility and conductivity of the composite film, which can maintain structural integrity upon repeated lithium insertion and extraction. Scanning electron micrographs show that the composite film are still connected by CNT network even small breaking or cracks appear in the film after cycling. The composite film can even “ripple up” to release the strain of volume expansion during lithium insertion.
R14: Thin-Film Devices I
Session Chairs
Kaili Jiang
John Robertson
Thursday PM, April 08, 2010
Room 2020 (Moscone West)
4:30 PM - **R14.1
Patterned CVD Growth of Single-walled Carbon Nanotubes for a Thin-film Transistor.
Shigeo Maruyama 1 , Rong Xiang 1 , Shinya Aikawa 1 2 , Erik Einarsson 1 3 , Shohei Chiashi 1 , Junichiro Shiomi 1
1 Department of Mechanical Engineering, The University of Tokyo, Tokyo Japan, 2 Department of Electrical Engineering, Tokyo University of Science, Tokyo Japan, 3 GCOE for Mechanical Systems Innovation, The University of Tokyo, Tokyo Japan
Show AbstractTwo different patterned growth techniques of single-walled carbon nanotubes (SWNTs) based on dip-coating catalyst-loading process and alocohol CVD (ACCDV) method [1] are explored for a simple manufacturing of thin-film nanotube transistor. The first approach is the conventional concept of using SiO2 patterned Si substrates. Using a dip-coating method [2] followd by alcohol CVD growth, high-quality vertically aligned SWNTs (VA-SWNT) [3,4] patterns can be easily obtained. This results the 3D carbon nanotube structures [5]. Apart from the sintering of catalyst into Si at high temperature, the difference in surface wettability between Si and SiO2 also plays an important role in this selective growth, which leads us to a novel method of patterning the growth on chemically modified surfaces. The more elaborate and precise patterned growth is based on the controll of wettability of substates [6]. Surface wettability strongly affects the deposition of catalyst in dip-coating process. By functionalizing the silicon surface using a conventional self-assembled monolayer (SAM) and then selectively removing the SAM by ultraviolet (UV) light, the catalyst can be dip-coated onto only the hydrophilic areas of the substrate. This method can simplify fabrication without sacrificing the resolution in the case of using conventional UV photolithography. Furthermore, by utilizing an electron beam instead of UV, the line width of an SWNT pattern can be easily reduced to 50 nm. Since the electron beam strength of magnified imaging in scanning electron microscope (SEM) is just enough for this SAM removal, patterned region can be easily located and visualized under a SEM [6]. Employing this pattering method, we fabricated a CNT-FET with an as-grown SWNT as its gate channel and as Si substrate as a back-gate. The I-V characteristics for various devices will be discussed. References: [1] S. Maruyama, R. Kojima, Y. Miyauchi, S. Chiashi and M. Kohno, Chem. Phys. Lett., 360 (2002) 229.[2] Y. Murakami, Y. Miyauchi, S. Chiashi and S. Maruyama, Chem. Phys. Lett., 377 (2003) 49.[3] Y. Murakami, S. Chiashi, Y. Miyauchi, M. Hu, M. Ogura, T. Okubo, S. Maruyama, Chem. Phys. Lett., 385 (2004) 298.[4] S. Maruyama, E. Einarsson, Y. Murakami and T. Edamura, Chem. Phys. Lett., 403 (2005) 320.[5] R. Xiang, E. Einarsson, H. Okabe, S. Chiashi, J. Shiomi, Jpn. J. Appl. Phys., (2009), in press.[6] R. Xiang, T. Wu, E. Einarsson, Y. Suzuki, Y. Murakami, J. Shiomi, S. Maruyama, J. Am. Chem. Soc., 131 (2009) 10344.
5:00 PM - R14.2
A Novel Direct Deposition System Based on the Gas-phase CVD Growth of SWCNTs for Film Electronics.
Takeshi Saito 1 2 , Shigekazu Ohmori 1 , Fumiyuki Nihey 1 , Bikau Shukla 1 , Motoo Yumura 1 , Sumio Iijima 1
1 Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki Japan, 2 , JST-PRESTO, Saitama Japan
Show AbstractSWCNTs possess extraordinary electronic properties with chemical stability, which could make them promising for various electronics applications such as transparent conductive films (TCFs) and thin film transistors (TFTs). Although manufacturing devices using single SWCNT is expensive and suffers from irreproducibility problems, a thin film constructed by the network of SWCNTs can perform variety of basic electronic functions reproducibly by ensemble averaging over a large number of SWCNTs with low-cost. So far the thin film of SWCNTs for TCFs and TFTs has generally prepared by wet process using dispersion of SWCNTs, but that is not as easy as it sounds. Once SWCNTs are mixed in solvents, they tend to bundle together, requiring surfactants to keep them dispersed. However, surfactants give an impediment to the electronic conductivity and some additional processes of acid treatments are needed for their removal. It is well known that such acid treatments of SWCNTs can degradate their electrical conductivity and chemical stability due to induced defects. Thus the process for preparing homogeneous thin films of SWCNT networks without surfactants and wet dispersion process is eagerly anticipated. Recently we have reported the novel gas-phase CVD growth process of SWCNTs with precise diameter controllability, so-called enhanced direct injection pyrolytic synthesis (eDIPS)[1], in which controlling the supply of carbon sources can selectively tuned the diameter of SWCNTs at any point within the range of 0.8 nm to 2.0 nm. In this work, we have evoluted this smart growth process into the direct depositing system of SWCNT thin films. Performances of deposited films as TCFs or TFTs have been characterized: The sheet resistance of less than 500 ohm/sq with over 85% transmittance in SWCNT films with 1.4 nm diameter, and FET performance with on/off ratio of 10^2 in SWCNT films with 0.9 nm diameter have been demonstrated.Reference[1] T. Saito, et. al., J. Nanosci. Nanotech., 8, 6153 (2008).
5:15 PM - R14.3
Controllable Patterning and CVD Growth of Carbon Nanotubes with Direct Parallel Writing of Catalyst Ink using Dip-Pen Nanolithography.
Irma Kuljanishvili 1 , Dimitriy Dikin 2 , Sergey Rozhok 3 , Scott Mayle 1 , Venkat Chandrasekhar 1
1 Physics & Astronomy, Northwestern University, Evanston, Illinois, United States, 2 Mechanical Engineering , Northwestern University, Evanston, Illinois, United States, 3 , NanoInk Inc, , Skokie, Illinois, United States
Show AbstractCarbon nanotubes (CNTs) are one of the most attractive building blocks for constructing nanoscale devices due to their unique structural, mechanical, electrical, thermal, and optical properties. Much interest has been generated around patterning and synthesis of high quality single wall carbon nanotubes (SWCNTs) into desired architectures. We will report on our recently developed method [1] undertaken to achieve delivering catalyst nanoparticles onto the substrates at predefined locations via direct writing approach. We applied the Dip Pen Nanolithography (DPN) approach to pattern molecular catalyst in selective locations on the substrate and developed a successful recipe for the subsequent CVD growth to produce high quality SWCNTs into scalable array geometries. Key parameters for successful implementation of this technology into devices or circuit architectures will be discussed. We will present our results on parallel patterning performed with multipen cantilever arrays that allows for large area patterning. Synthesis and characterization of as-grown CNTs on the substrate and in suspended geometries will also be discussed. [1] I. Kuljanishvili, D. A. Dikin, S. Rozhok, S. Mayle, V. Chandrasekhar “Controllable Patterning and CVD Growth of Isolated Carbon Nanotubes with Direct Parallel Writing of Catalyst Using Dip-Pen Nanolithography” (in press)DOI: 10.1002/smll.200900841Support by DOD, Army Research Office
5:30 PM - R14.4
Excimer Laser-based Purification of Single-walled Carbon Nanotubes.
Katherine Hurst 1 , Elisabeth Mansfield 1 , Anne Dillon 2 , John Lehman 1
1 , National Institute of Standards and Technology, Boulder, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractBulk purified carbon nanotube (CNT) material is essential for the realization of CNT applications including incorporating them into various composite materials. We have developed a laser-based purification technique for bulk single-walled carbon nanotubes (SWCNTs) that selectively reduces carbon impurities from as-produced material.(1) Photochemical changes are characterized by Raman spectroscopy, and responsivity measurements of nanotube coated pyroelectric detectors. Differences in the reactivity of SWCNTs, graphite and amorphous carbon are compared by using quartz crystal microbalance. This method of in-situ measurement reduces our uncertainty that is attributable to environmental variables, such as relative humidity and temperature. We consider the influence of irradiance, ambient atmosphere and the wavelength of incident photons. At 248 nm, near the resonance of the π plasmon, the interaction of laser light and carbon nanotube material exhibits a relatively high absorptivity. We discuss the importance of the SWCNT surface plasmon in the reduction of carbon impurities. (1) K. E. Hurst, A. C. Dillon, S. Yang, and J. H. Lehman J. Phys. Chem. C. 16296-16300 (112) 2008.
5:45 PM - R14.5
Growth of High Density Vertically-aligned Forests of Carbon Nanotubes on Metallic Supports.
C. Esconjauregui 1 , B. Bayer 1 , M. Fouquet 1 , C. Wirth 1 , S. Hofmann 1 , John Robertson 1
1 , Cambridge University, Cambridge United Kingdom
Show AbstractThe future use of carbon nanotubes as vias and interconnects in VLSI integrated circuits requires their growth at high density on conducting substrates. The growth of high density, vertically aligned mats of nanotubes has been achieved by many groups, but this traditionally uses the Fe or CoMo catalysts on Al2O3 or SiO2 supports, in other words insulating supports which is incompatible with its desired use. The role of the support oxide is to have a low surface energy, which helps the metal catalyst to form high-density nuclei by de-wetting, from which the nanotubes grow. But if the support is a metal, this occurs badly. We find that various plasma pre-treatments of the catalysts will allow efficient growth of high density (1E12 /cm2) nanotube forests on TiN and similar substrates, a factor of 100 improvement, but still not enough. The process occurs by inducing root growth. S Esconjauregui, et al, App Phys Lett 95 173115 (2009)