Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W27: Focus Session: Carbon Nanotubes: Growth and Manipulation |
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Sponsoring Units: DMP Chair: Sami Rosenblatt, Cornell University Room: LACC 501C |
Thursday, March 24, 2005 2:30PM - 2:42PM |
W27.00001: Synthesis of monochiral multiwalled carbon nanotubes Xuedong Bai, Zhi Xu, Enge Wang, Dmitri Golberg So far, it remains a challenge to obtain multiwalled carbon nanotubes (MWCNTs) with the same chirality for all of the shells, i.e., monochiral MWCNTs. Here we report the synthesis of the monochiral MWCNT, with all of the concentric cylinders of a MWCNT exhibiting nearly identical chiral angle, by using microwave plasma assisted CVD method. Among the all kinds of monochiral MWCNTs, several chiral angles are found to be statistically dominant. [Preview Abstract] |
Thursday, March 24, 2005 2:42PM - 2:54PM |
W27.00002: Structural Control of VA-MWNTs by Dual-RF-Plasma CVD Jitendra Menda, Lakshman Vanga, Benjamin Ulmen, Yoke Khin Yap, Zhengwei Pan, Ilia Ivanov, Alex Puretzky, David Geohegan Plasma enhanced CVD is the only known technique for growing vertically-aligned multiwalled carbon nanotubes (VA-MWNTs) at controllable tube densities. These VA-MWNTs are important for electron field emission and sensors. Previously, these VA-MWNTs were grown by a one-plasma approach and have highly distorted structures. Here, we show that dual-RF-plasma enhanced CVD offers unique capability for controlling the graphitic order and diameters of VA-MWNTs. We decoupled two plasmas in a parallel-plate configuration. One of them is applied on the top electrode and responsible for the decomposition of methane gas. Another one is applied on the substrates and initiated a negative dc bias voltage. Ni catalysts are used for the growth. We have examined the effects of catalyst film thickness, growth temperatures, and plasma parameters on the structural properties of VA-MWNTs. High-resolution transmission electron microscopy and Raman spectroscopy indicate that the diameters and graphitic order of VA-MWNTs increased with the increase of the RF power to the top electrode. An increase of substrate biasing also resulted in bigger tube diameters, but decreased when excessive biasing is applied. There is a minimum substrate biasing and RF power required for the growth of VA-MWNTs with enhanced graphitic order. [Preview Abstract] |
Thursday, March 24, 2005 2:54PM - 3:06PM |
W27.00003: Flattened and Coaxial Cable-liked Carbon Nanotubes Wenzhi Li, Zhifeng Ren, Kris Kempa Flattened carbon nanotubes have been occasionally observed in carbon nanotube samples. It was postulated that the flattening of carbon nanotubes was accidentally formed by external mechanical force. In this report, we show batch pure flattened carbon nanotubes synthesized by chemical vapor deposition. Each nanotube is caped at one end with a cylindrical cobalt catalyst particle, which contrasts to the spherically shaped catalyst particles usually found at the tips of carbon nanotubes. The flattened nanotubes may provide the opportunity to investigate how the structure deformation of the nanotubes affects their electronic properties. Another new form of carbon nanotubes, coaxial cable-liked structure, in which a bundle of single-wall carbon nanotubes is wrapped by a multi-wall nanotube, will be presented. The above new structures of carbon nanotubes may shed some light on the understanding of the growth mechanism of carbon nanotubes. [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:18PM |
W27.00004: Bulk Synthesis of Helical Coiled Carbon Nanostructures Wei Wang, Apparao Rao We report a bulk process for preparing helical coiled carbon nanostructures including coiled nanowires and coiled nanotubes on bare quartz substrates. These nanostructures were synthesized at ambient pressure using a thermal chemical vaporization deposition (CVD) process in which xylene and acetylene were used as the primary carbon source. A multi-metal catalyst formed from a mixture of ferrocene and indium isopropoxide served as the seed to initiate the growth of these helical coiled nanostructures. Importantly, no pre-formed substrates are required in our process. The as-synthesized coiled nanowires and nanotubes are pure without the presence of amorphous carbon nanoparticles. Further, by precisely controlling the atomic ratio of In/(Fe+In), coiled nanowires or coiled nanotubes can be synthesized exclusively. The diameters of the as-grown coiled nanowires vary from several tens to several hundreds nanometers, whereas the diameters of the coiled nanotubes are around 20 nm. Structural, electrical and mechanical properties of these nanostructures revealed using SEM, TEM, HR-TEM and AFM. will be presented. [Preview Abstract] |
Thursday, March 24, 2005 3:18PM - 3:30PM |
W27.00005: Synthesis and Electrical Transport Properties of Carbon Nanocoils El Hadi Sadki, Shuuichi Ooi, Hiroyuki Takeya, Kazuto Hirata Since the discovery of carbon nanotubes at the beginning of the last decade, a tremendous progress has been achieved in improving their synthesis techniques, understanding their physical properties, and even their implementation into performing nanodevices. However, another member of the carbon nanostructures family, namely carbon nanocoils (CNC), have surprisingly received little attention, despite their interesting physics and potential applications in nanoelectronics and nano-electromechanical systems (NEMS). Here we report on the synthesis of CNC by chemical vapor deposition (CVD) of carbohydrate gases on specially prepared substrates. In order to explore their electrical transport properties, metallic electrodes have been deposited on selected CNCs by a combination of electron beam lithography and metal lift-off techniques. Attempts to measure their electrical resistivity as a function of temperature and magnetic field will also be presented [Preview Abstract] |
Thursday, March 24, 2005 3:30PM - 3:42PM |
W27.00006: Transfer of Patterned Arrays of Oriented Carbon Nnaotubes by Electron Emission Assisted Sublimation Rashmi Nanjundaswamy, Mei Zhang, Alex Zakhidov, Anvar Zakhidov, Sergey Lee, Mike Sampson Spark light emission was recently reported by us detected above certain threshold electron emission currents from oriented arrays of multiwalled carbon nanotube arrays. We would like to report the unusual phenomenon of mass transfer of patterned and un-patterned arrays of MWNT forests. These transferred NT's retain their alignment and structure on the anode. Both SEM imaging and Raman spectra confirmed this. We have been successful in transferring these nanotubes onto metals such as AL and Cu, on which it is inherently difficult to grow the tubes. We expect this phenomenon to resolve a considerable number of technological problems. These re-deposited tubes are found to be able to emit electrons when in turn used as cathodes that also prove that the nanotubes did not transform to amorphous carbon upon field-induced sublimation. The re-deposition of the tubes was performed using DC as well as AC electric fields. [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 3:54PM |
W27.00007: Precision Cutting of Nanotubes with a Low-Energy Electron Beam Thomas Yuzvinsky, Adam Fennimore, Willi Mickelson, Cristian Esquivias, Alex Zettl We report on a method to locally remove material from carbon and boron nitride nanotubes using the low-energy focused electron beam of a scanning electron microscope (SEM). Using this method, clean, precise cuts can be made into nanotubes, either part-way through (creating hinge-like geometries) or fully through (creating size-selected nanotube segments). The SEM cutting mechanism involves foreign molecular species and differs from electron beam induced knock-on damage in transmission electron microscopy. [Preview Abstract] |
Thursday, March 24, 2005 3:54PM - 4:06PM |
W27.00008: Nanosurgery in Carbon Nanotubes: Efficient Elimination of Pentagon-Heptagon Defects Using Femtosecond Laser Pulses Martin Garcia, Aldo Romero, Felipe Valencia, Mauricio Terrones, Humberto Terrones, Harald Jeschke Using non-adiabatic molecular dynamics simulations we demonstrate that femtosecond laser pulses are able to eliminate pentagon-heptagon defects within carbon nanotubes. We conclude that ultrafast healing of zig-zag and armchair nanotubes can be achieved with pulse durations of 50~fs within a wide range of laser intensities. This nonthermal transition occurs at a relatively low lattice temperature ($\sim$450 K) and is driven by the electronic entropy, which is dramatically increased by the action of the laser pulse, thus causing 5-7-5-7 defects to become unstable at very high electronic temperatures. The intermediate steps of the inverse Stone-Wales-type transformation are qualitatively different from those occurring in thermally driven phenomena. [Preview Abstract] |
Thursday, March 24, 2005 4:06PM - 4:18PM |
W27.00009: Oxidative Process for Cutting Single-Walled Carbon Nanotubes Jonah Shaver, Kirk Ziegler, Zhenning Gu, Zheyi Chen, Erica Flor, Candace Chan, Robert Hauge, Richard Smalley Cut single-walled carbon nanotubes (SWNTs) are needed for many applications. An efficient way to produce bulk amounts of cut SWNTs is a two step process consisting of sidewall damage and oxidative exploitation. In these experiments sidewall damage is introduced by ozonation in a perfluoropolyether (PFPE) while monitoring the degree of functionalization with in-situ Raman spectroscopy. Use of PFPE allows for a high degree of sidewall functionalization at room temperature, mainly in the form of epoxides. These damaged SWNTs are exposed to piranha (4:1 96%H2SO4:H2O2) for one hour and then quenched. The piranha exposed samples are then functionalized with alkyl groups and spin cast on mica for length analysis. The cut samples are found to have significantly shorter lengths while maintaining a relatively high carbon yield. [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:30PM |
W27.00010: Modeling a Carbon Nanotube Field Emitter Vacuum Triode Douglas Clauss, Ben Yu-Kuang Hu, Alper Buldum Carbon nanotubes hold the promise of diverse applications in many emerging fields. In particular, the low-voltage field emission capabilities of nanotubes make them prime candidates for nanoscale amplifiers. Towards this goal, we model a carbon nanotube as the cathode of a field emission vacuum triode, in which the gate of the triode is a nanoscale metallic aperture. We use a relaxation algorithm to numerically solve Laplace’s equation for the electrostatic fields within the device. We utilize these fields, together with the electronic stucture of the nanotube, to calculate the $I$-$V$ characteristics of the triode as a function of gate voltage and emitter-aperture distance. We also discuss the feasibility of the fabrication of this device. [Preview Abstract] |
Thursday, March 24, 2005 4:30PM - 4:42PM |
W27.00011: Modulation of Field Electron Emission from Carbon Nanotubes by Double layer Charging Anvar Zakhidov, Rashmi Nanjundaswamy, Ray Baughman, Sergey Lee, Ali Aliev Field emission from carbon nanotubes is well known phenomenon. In this work we present a novel method of modulating the current densities and threshold voltages. We studied field emission characteristics of HIPCO Single Walled Nanotube (SWNT) paper charged in NaCl electrolyte. The charge injection was by double layer electro chemical doping and it showed significant change in the threshold electric fields and the current densities. This was attributed mostly to a change in the work function and partially due to the change in the field enhancement factor beta. The turn on field (for 1microA of emission current) was seen to change from 1.04 V/micron to 0.82 V/micron for the negatively charged paper (Na ions) and similarly on the positively charged (Cl ions) it increased from 1.01 V/micron to 2.1 V/micron. Calculated values of the work function were compared with values from Kelvin Probe measurements. The work function values showed a significant decrease in the negatively charged samples and a sharp increase in the positively charged samples as compared to the uncharged ones. Experiments were repeated by varying the charging time from 2000 sec to 3 hrs with the current being kept constant. [Preview Abstract] |
Thursday, March 24, 2005 4:42PM - 4:54PM |
W27.00012: CNT Twisted Yarns as Low Threshold Cold Electron Sources for Displays. Alexander Zakhidov, Rashmy Nanjundaswamy, Mei Zhang, Sergey Lee, Ray Baughman, Alexander Obraztsov, Anvar Zakhidov Carbon nanotubes are known as best field emitters of electrons, which emit at low threshold electric fields of E$_{thr} \quad \sim $ 1-3 V/$\mu $m with typical, stable current densities of J $\sim $ 100 mA/cm$^{2}$. Our team has recently created strong CNT fibers, yarns and ribbons by dry twist-spinning from oriented arrays of long MWCNTs prepared by CVD [1]. Here we show that such twisted yarns (TY) of typical diameters of 10 $\mu $m show phenomenally low E$_{thr}<$0.5 V/$\mu $m with very high J and steep I-V curves. If used as cathode for phosphorescent screens the horizontally placed CNT TY FE show rather bright and uniform light emission. The high luminosity lamp and also numeric displays prototypes are created and their properties described. The mechanism of low threshold E$_{thr}$ and high J is discussed in terms of high porosity structure and linear geometry of CNT TY. [1] M. Zhang, Ken Atkinson, Ray Baughman, Science (2004) [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:06PM |
W27.00013: Fractal Effect Induced Giant Field Enhancement in Carbon Nanotubes and ZnO Nanowires Grown on Carbon Cloth Jianyu Huang, Krzysztof Kempa, Sung-Ho Jo, Shuo Chen, Zhifeng Ren Recently we have observed an extremely strong field emission from carbon nanotubes and ZnO nanowires grown on carbon cloth, with the field enhancement factor of up to 40,000. In this work we study the origins of this effect, by investigating field emission from individual carbon nanotubes grown on carbon cloth, in a transmission electron microscope equipped with a piezo-driven scanning tunneling microscopy probe. Microscopic analysis reveals a fractal structure of some of the nanotubes, characterized by an order of magnitude smaller nanotubes branching-off the tips of bigger nanotubes (or carbon fibers). The fractal structure of the emitters implies that the field enhancement factor is a product of the field enhancement factors of individual fractal units. This explains the observed giant field enhancement. [Preview Abstract] |
Thursday, March 24, 2005 5:06PM - 5:18PM |
W27.00014: Electron Field Emission from Nanostructured Carbon Materials Sanju Gupta Fabricating small structures has almost become fashionable and the rationale is that reducing one or more dimensions below some critical length changes the systems' physical properties drastically, where nanocrystalline diamond (n-D) and carbon nanotubes (CNTs) in the class of advanced carbon materials serve model examples. Emission of electrons at room temperature - cold electron emitters - are of vital importance for a variety of vacuum microelectronic devices - electron microscopes, photo multipliers, X-ray generators, lamps, and flat panel displays and microwave cathodes. Electron emitters may lead to otherwise difficult to obtain advantages in performance and/or design. This is the driving force to investigate the carbon-related materials as cold cathodes. In this talk, the performance of various forms of carbon in thin film form including diamond, n-D, and vertically aligned CNTs as cold cathodes for their potential use in field emission displays (FEDs) in terms of$ I-V$ characteristics and corresponding spatial imaging will be presented. Physics based models such as, NEA, surface modification, geometric enhancement, and microstructure alteration due to particle bombardment, and doping, will be described to support the experimental observations of electron field enhancement (low turn-on voltage, high current and emission site density) and its reliability from the abovementioned carbon-related materials. Other vacuum device applications such as thermionic power generators will be mentioned briefly. [Preview Abstract] |
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W27.00015: Significant Effects of Confinement and Catalysis in Formation of Tabular Structures from Peapod Structures Haibin Su, R. Nielsen, Adri van Duin, William Goddard III A large number of experimental and theoretical studies have been reported on buckyballs-containing nanotubes (a.k.a. peapod) structures since the discovery of these materials. It was observed that self- assembled buckyballs with nearly uniform centre-to-centre distances and resemble a nanoscopic peapod. The endofullerenes coalesce into longer capsules by either the electron irradiation or thermal annealing. We applied the recently developed Reactive Force Field (ReaxFF) to study the growth dynamic process starting from C$_{60}$-buckyball/nanotube peapod structures. We found that the space confinement provided by the single wall nanotube encapsulating the buckyballs, is of critical importance on the coalescence reaction. Furthermore, we also simulated the effects of a Ni-particles on the coalescence process and found a significant reduction on the reaction initiation temperature in the presence of these catalysts. One related quantity is the energy barrier of forming a 4-member ring between adjacent buckyballs. We chose both corannulenes (C$_{20}$H$_{10})$ and C$_{60}$ to compute this energy barrier from quantum mechanic and ReaxFF. The good agreement between these two methods encouraged us to investigate the effect of catalysis on this energy barrier. It turned out that this barrier is lowered by 40{\%} with the aid of catalysis. The piece of research work can help the community to gain better understanding of the complicated growth process in fullerene systems. [Preview Abstract] |
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