Paulo T. Araujo, University of Alabama
Aaron D. Franklin, Duke University
Yoong Ahm Kim, Chonnam National University
Michael Krueger, University of Freiburg
Symposium Support AIXTRON SE
Oerlikon Leybold Vacuum GmbH
RHK Technology, Inc.
MM2: Carbon Nanotubes Synthesis and Characterization II
Monday PM, December 01, 2014
Hynes, Level 2, Room 200
2:30 AM - *MM2.01
Synthesis and Structural Characterizations of Double- and Triple-Walled Carbon Nanotubes
Hiroyuki Muramatsu 1 Yoong Ahm Kim 2 Morinobu Endo 1 Takuya Hayashi 1
1Shinshu University Nagano Japan2Chonnam National University Gwangju Korea (the Republic of)Show Abstract
Carbon nanotubes show a large variation in the physicochemical properties as a function of the number of layers. Double-walled and triple-walled carbon nanotubes (DWNTs and TWNTs), consisting of two and three concentric nanotubes, have attracted much attention because of their unexplored properties (e.g., optical, electronic, and mechanical properties) caused by a coupling interaction between adjacent layers. Up to now, several methods (e.g., catalytic chemical vapor deposition, thermal treatment of single wall carbon nanotubes (SWNTs) or DWNTs encapsulating fullerenes and other compounds containing carbon elements) have been reported to synthesize DWNTs and TWNTs. However, there are no systematic report on the synthesis and properties of DWNTs and TWNTs due to the complex synthetic technique.
In this talk, I will describe the synthesis of double- and triple walled carbon nanotubes and their structural characterizations. To produce DWNTs, we have used two techniques; catalytic chemical vapor deposition and thermal treatment of SWNTs encapsulating fullerenes. We observed large difference in optical and thermal properties between two types of DWNTs. In addition, the coalescence between adjacent DWNTs by high temperature treatment and boron doping treatment will be described as a tool to create nanotube&’s junctions and also to control the diameter of DWNTs. Finally, the unique structural features of TWNTs will be also described in related with the thermal treatment induced coalescence.
3:30 AM - *MM2.03
Raman Studies on Double and Triple Walled Carbon Nanotubes
Mildred Dresselhaus 1
1MIT Cambridge USAShow Abstract
Although the study of double wall nanotubes has been ongoing for many years, it is only recently that a large advance has occurred through the systematic studies carried out on many tubes and on many optical transitions by Feng Wang at the University of California, Berkeley. The implications of these findings on triple wall carbon nanotubes will be discussed.
4:30 AM - MM2.04
On the Origin of Carbon Nanotube Helicity: Carbon Cap as a Precursor for Symmetry Formation
Avetik R Harutyunyan 1 Rahul Rao 1
1Honda Research Institute USA Inc. Columbus USAShow Abstract
In order to accommodate an increasing demand for carbon nanotubes (CNTs) with desirable characteristics one has to understand the origin of helicity of their structures. Here, through in situ atomic scale microscopy we demonstrate that the formation of carbon nanotube is initiated by the nucleation of the carbon cap. We observe that the nucleation is initiated by the formation of a graphene embryo, which is bound between opposite step-edges on the nickel catalyst surface. The embryo grows larger as the step-edges migrate along the surface, leading to the formation of a curved carbon cap when the steps flow across the edges of adjacent facets. Further motion of the steps away from the catalyst tip with attached rims of carbon cap generates the wall of the nanotube. Density Functional Theory calculations bring further insight into the process, showing that the step flow occurs by surface self diffusion of the nickel atoms via a step-edge attachment-detachment mechanism. Based on the revealed mechanism of carbon cap formation and the fact that it occurs first in the sequence of stages involved in nanotube growth, we suggest the angular distribution of catalyst adjacent facets as a key feature that is responsible for the symmetry of carbon cap and consequently, the helicity of the nanotube. This finding paves a new path towards the controllable growth of carbon nanotubes.
4:45 AM - MM2.05
Growth and Characterization of Uniform Carbon Nanotube Arrays on Active Substrates
Qiuhong Zhang 1 Betty Quinton 2 Jacob Lawson 1 James Scofield 2 Neil Merrett 2 Bang-Hung Tsao 2 Kevin Yost 2 Levi Elston 2
1University of Dayton Wright Patterson USA2AFRL Wright Patterson USAShow Abstract
Carbon nanotubes (CNTs) have unique thermal/electrical/mechanical properties and high aspect ratios. Growth of CNTs directly onto reactive material substrates (such as metals, carbon based foam structures etc.) to create a micro-carbon composite layer on the surface has many advantages-the possibilities of eliminating processing steps and resistive junctions, or/and providing a thermally conductive transition layer between materials of varying thermal expansion rates etc. Compared to growing CNTs on conventional inert substrates such as SiO2, direct growth of CNTs onto reactive substrates is significantly more challenging. Namely, control of CNT growth, structure, and morphology has proven difficult due to the diffusion of metallic catalysts into the substrate during CNT synthesis conditions. In this study, uniform CNT layers are successfully grown on copper foil and carbon foam substrates that were pre-coated with an appropriate buffer layer, using the chemical vapor deposition method. SEM images indicated that synthesis method, growth conditions, and most notably substrate surface pre-treatment all influence CNT growth and layer structure/morphology. The SEM image and pull-off testing results revealed that good bonding exists between the CNT layer and substrate material, and interfacial adhesion (0.2-0.5MPa) is affected by the buffer layer thickness. Additionally, the thermal properties of the CNT/substrate structure were evaluated using the laser flash technique and have shown that the CNT layer can reduce thermal resistance when used as a thermal interface material between bonded layers.
5:00 AM - MM2.06
Re-Growth of Carbon Nanotube by Chemical Vapor Deposition and InSitu Scanning Electron Microscope Observation
Huafeng Wang 1 Chisato Yamada 1 Jia Liu 2 Bilu Liu 2 Xiaomin Tu 3 Ming Zheng 3 Chongwu Zhou 2 Yoshikazu Homma 1
1Tokyo University of Science Tokyo Japan2University of Southern California Los Angeles USA3National Institute of Standards and Technology Gaithersburg USAShow Abstract
Carbon seeds like nano-diamond, fullerene fragments and nanotube segments have been used to synthesize carbon nanotubes (CNTs) [1-5]. This new route may produce high purity nanotubes free from metal impurities, which will promote the application of nanotubes. Pretreatment including air oxidation followed by water vapor annealing is proved to be essential. To investigate the process of CNT re-growth so as to better understand it, we conducted re-growth of CNT in conventional chemical vapor deposition (CVD) as well as in the in situ scanning electron microscope. By comparing growth conditions in these two systems, it might be helpful to comprehensively evaluate the influence of experimental parameters on the re-growth of carbon nanotube.
We carefully studied the influences of the experimental parameters on the re-growth of CNT. By varying these parameters, the new pretreatment as well as the growth condition suitable for CVD and in situ system was established, and the re-growth of nanotube from seeds with different chiralities was realized in these two systems. Furthermore, multi-times re-growth of nanotube was also achieved. In situ observation on CNT formation provided a direct evidence for the re-growth of nanotube. According to our experimental results, the efficiency of re-growth was closely related with pretreatment conditions and growth parameters, especially the carbon source. On the basis of these analyses, the growth mechanisms of nanotube synthesized from seed will be discussed.
 Takagi, D. et al. J. Am. Chem. Soc.131, 6922(2009).
 Yu, X. et al. Nano Lett.10, 3343(2010).
 Ibrahim, I. et al. ACS Nano6, 10825(2012).
 Yao, Y. et al. Nano Lett.9, 1673(2009).
 Liu, J. et al. Nat. Commun.3, 1199(2012).
Corresponding Author: Huafeng Wang
Tel: +81-3-5228-8244, Fax: +81-3-5261-1023
5:15 AM - MM2.07
Automated Experimentation Applied to Carbon Nanotube Synthesis
Benji Maruyama 3 Daylond Hooper 2 3 Michael Krein 1 Jason Poleski 1 Pavel Nikolaev 2 3
1Lockheed Martin Advanced Technology Laboratories Cherry Hill USA2UES Inc. Dayton USA3Air Force Research Laboratory WPAFB USAShow Abstract
Carbon nanotubes have an exciting array of applications which span mechanical, electrical, thermal and chemical/sensing. However, full exploitation is slowed by a lack of control over synthesis. Despite the two decades since the explosion of work in the area, progress in controlled production of nanotubes is impeded by our lack of understanding of the fundamental mechanisms of nucleation and growth.
To this end, we have developed a method, Automated Rapid Experimentation and in-situ Spectroscopy (ARES) which speeds the rate of experimentation by 100 times. We are also exploring experimental parameter space autonomously, using the same artificial intelligence and machine learning approaches used in advanced robotics. Our intent is to integrate computation and simulation explicitly into our closed-loop experimentation system to direct the path of exploration, yielding faster results with better fidelity than conventional approaches. We use this to determine the conditions which discriminate between single wall and multiwall carbon nanotube synthesis.
5:30 AM - MM2.08
SWNT and MWNT from a Polymeric Electrospun Nanofiber Precursor
John D Lennhoff 1
1Physical Sciences, Inc. Andover USAShow Abstract
CNT&’s are expected to revolutionize a range of technologies because of their unique mechanical and electrical properties. Using nanotubes in structural materials holds significant promise due to their extremely high modulus and tensile strength, however their cost, production rate and integration into a fiber form severely limit the current structural application opportunities. We report the investigation of the formation of carbon nanotubes from a polymeric precursor using an electrospinning production process. This CNT formation concept is based upon modeling studies performed by Sinnot. Reactive Empirical Bond order calculations show that for small diameter carbon fibers, less than about 60 nm, the SWNT and MWNT phases are thermodynamically favored relative to an amorphous or planar graphitic nanofiber structure. We have developed a novel process using continuous electrospun polyacrylonitrile (PAN) nanofibers as precursors to continuous SWNT and MWNT. The process for converting PAN nanofibers to SWNT's and MWNT's follows the process for typical carbon fiber manufacture. The PAN nanofibers, of 10 to 100 nm in diameter, are crosslinked by heating in air and then decomposed to carbon via simple pyrolysis in inert atmosphere. The pyrolyzed carbon nanofibers are then annealed to form the more energetically favorable SWNT or MWNT phase, depending upon the precursor diameter. We will discuss the process and characterization data.
5:45 AM - MM2.09
Force-Modulated Growth of Carbon Nanotubes
Mostafa Bedewy 1 Nick Dee 1 A. John Hart 1
1Massachusetts Institute of Technology Cambridge USAShow Abstract
Literature abounds with examples of mechanochemistry, in which chemical reactions are shown to be influenced by mechanical loads acting on the reacting surfaces/volumes. These mechanochemical effects promise to direct the reaction pathways of chemical synthesis processes, enabling unprecedented control of the produced structures. We study the effect of externally applied mechanical forces on the collective growth of aligned carbon nanotube (CNT) "forests" by chemical vapor deposition (CVD). Previous work on CNT growth under mechanical pressure showed that the final forest height decreased with applying compressive stresses, but did not measure growth kinetics. Motivated by these results, we use a custom-built cold-wall CVD reactor to apply measurable axial loads in situ during forest growth, while recording the growth kinetics in real-time. Compressive forces in the range of 0.2 to 20 grams are applied by a probe pushing on millimeter-size CNT forests growing on a resistively heated substrate from a mixture of ethylene, acetylene, hydrogen and helium at atmospheric pressure. The real-time growth kinetics are determined by measuring the forest height increase using a feedback loop controlled actuator that moves the probe vertically upwards to maintain a constant force during growth. Results show that a mechanical force influences both the growth kinetics and the resulting forest morphology. The maximum growth rate is found to be inversely related to the applied compressive force. These findings highlight the importance of studying mechanochemistry of CVD, in which the process activation energy at the catalyst is modulated by the mechanical stresses. The exact influence of mechanical stresses on the kinetics and energetics of CNT growth provides insights into the internal mechanical feedback within a growing forest, comprising billions of CNTs per square centimeter each having diameter-dependent growth rates. If the kinetics of CNTs subjected to compressive forces is slowed down, while the kinetics of those CNTs subjected to tensile loads is accelerated, a homogenizing effect ensues, which eventually leads to reducing the growth rate mismatch and contributes towards the coordinated forest growth at a single collective growth rate. Hence, understanding these collective mechanochemical effects is key to engineering the morphology of functional aligned CNT ensembles.
MM3: Poster Session I: Carbon Nanotubes Synthesis and Characterization
Monday PM, December 01, 2014
Hynes, Level 1, Hall B
9:00 AM - MM3.01
Anomalous Structure of Tellurium Encapsulated within Confined Nanospaces of Carbon Nanotubes, and Relation between Carbon Nanotube Diameter and the Structure
Keita Kobayashi 1 Hidehiro Yasuda 1
1Osaka University Ibataki JapanShow Abstract
In the inner spaces of cylindrical hollow nanomaterials such as carbon nanotubes (CNTs), some kind of materials are encapsulated having anomalous structure by comparison with the bulk materials due to the confined nanospaces. For example, sulfur (S) is encapsulated within inner space of CNTs of less than 1 nm in inner diameters as one dimensional liner or zigzag structure, while S crystal has a orthorhombic structure at atmospheric pressure. Especially, although bulk S is insulator, the one dimensional S in the CNTs are expected to exhibit metallic conductivity. Since insulator-metal phase transition of bulk S has been observed only under ultra-high-pressure conditions (P>90 GPa), encapsulation of materials into the confined nanospace is expected to induce appearance of not only anomalous structure but also properties, which appear at ultimate state, of the materials even at atmospheric pressure.
In this study, we encapsulated tellurium (Te) in CNTs of various inner diameters. Our aims were to prepare anomalous phase of Te at ordinary pressure and to clarify the relation between CNT diameter and the crystal structure of encapsulated Te. As a result, we found that Te exists as ordinary phase when encapsulated within CNTs of greater than ~2 nm in diameter. In contrast, in CNTs of less than ~2 nm in diameter, the encapsulated Te had an unknown structure that could not be indexed to known tellurium phases, including high-pressure phases, Te oxides, and Te hydroxides. Here, we describe the unknown structure of Te discovered by transmission electron microscopy and Raman spectroscopy, as well as the relation between CNT diameter and the crystal structure of encapsulated Te.
9:00 AM - MM3.02
Growth Mechanism of Single-Walled Carbon Nanotubes from Pt Catalysts by Alcohol Catalytic CVD
Takahiro Maruyama 1 Hiroki Kondo 2 Akinari Kozawa 2 Takahiro Saida 1 Shigeya Naritsuka 2 Sumio Iijima 2
1Meijo University Nagoya Japan2Meijo University Nagoya JapanShow Abstract
Single-walled carbon nanotubes (SWNTs) have been anticipated for application in various electronic devices. To fabricate SWNT devices in a conventional LSI process, it is important to grow SWNTs at low temperatures under high vacuum. So far, using Pt as a catalyst, we have attained SWNT growth under an ethanol pressure of 1x10-1 Pa . However, the mechanism of SWNT growth from Pt catalysts have not been clarified. In this study, we investigated the growth process of SWNTs from Pt.
After deposition of Pt catalyst on the SiO2/Si substrates, SWNT growth was carried out using the alcohol catalytic chemical vapor deposition (ACCVD) in a high vacuum. For fabrication of Pt catalysts, we used both EB and pulsed arc plasma (PAP) depositions to control the catalyst particle size. The grown SWNTs were characterized by FE-SEM, TEM and Raman spectroscopy.
Average particle size of Pt catalysts prepared by the EB deposition was smaller than that by the PAP deposition, but most of Pt particle sizes were below 3 nm in both methods. Irrespective of the catalyst particle size, the diameter distribution of SWNTs were almost same and the average diameter was below 1.0 nm, when the growth temperature was 700 0C. TEM and Raman results showed that most of SWNTs grown from Pt particles whose sizes were larger than the SWNT diameters. In addition, compared with Co catalysts, the SWNT growth from Pt endured for longer time under the same growth temperature, although the growth rate was lower. This indicates that growth process of SWNTs is different between Pt and Co catalysts, and the surface diffusion process on the catalyst particle would play an important role in the SWNT growth from Pt. Based on the experimental results, we will discuss the growth mechanism of SWNTs from Pt.
 T. Maruyama et al. Mater. Express 1 (2011) 267.
9:00 AM - MM3.03
Synthesis and Study of Carbon Nanotubes by the Spray Pyrolysis Method Using Different Carbon Sources
Beatriz Ortega Garcia 1 Oxana V Kharissova 1 F. Servando Aguirre T. 2
1UANL Monterrey Mexico2CIMAV Monterrey MexicoShow Abstract