Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session Y27: Focus Session: Carbon Nanotubes: Spectroscopies |
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Sponsoring Units: DMP Chair: David Luzzi, University of Pennsylvania Room: LACC 501 C |
Friday, March 25, 2005 11:15AM - 11:27AM |
Y27.00001: Atomically-resolved Imaging of Electrical Bearkdown of Multi-walled Carbon Nanotubes Willi Mickelson, Tom Yuzvinsky, Gavi Begtrup, Adam Fennimore, Andras Kis, Steve Konsek, B.C. Regan, Shaul Aloni, Alex Zettl We report on the controllable electrical breakdown of multi- walled carbon nanotubes (MWCNTs) in air. We see current steps that correspond to the removal of individual walls. This is confirmed by high resolution transmission electron microscopy (HRTEM) of MWCNTs over thin membranes. Using this technique we able to determine how the atomic structure changes the transport through MWCNTs. [Preview Abstract] |
Friday, March 25, 2005 11:27AM - 11:39AM |
Y27.00002: Imaging carbon nanotubes by scanning electron microscopy Dmitriy Dikin, Richard Piner, Rodney Ruoff Scanning electron microscopy (SEM) is used as a primary tool for imaging of nanostructures, including carbon nanotubes. Recent developments of the SEM technique have opened new capabilities for sample analysis at the nanoscale with potential industrial and metrological applications. We will discuss selective imaging of single-walled carbon nanotubes on insulators. The role of the electron beam parameters, effect of surrounding media and substrate, and carbon nanotubes properties on their appearance as seen by an SEM are analysed. The comparison of scanning electron microscopy with atomic force microscopy images will also be presented. Our results support some of the commonly accepted opinions about why such images appear as they do, but mostly contradict them. At the same time our discovery opens new analytical possibilities for applications of an SEM. Funding for this work has been provided by a NASA/MSFC Phase II SBIR, Contract No. NAS8-02102, through a subcontract from Lytec, LLC., and by the NSF NIRT Program, Grant No. 0304506. SEM was done at the Electron Probe Instrumentation Centre at Northwestern University. [Preview Abstract] |
Friday, March 25, 2005 11:39AM - 11:51AM |
Y27.00003: The spin-probe ESR study of single-walled carbon nanotubes at low temperatures Amarjot Dhami, Shrivalli Bhat, Ajay Sharma, S.V. Bhat Single walled carbon nano-tubes (SWNTs) are ESR silent unless they contain ferromagnetic impurities or conduction electrons. A technique that has been widely used to study ESR silent systems is the so-called spin probe ESR, where a free radical, typically a nitroxide radical, is dilutly doped into the system and ESR studied. In this work, we have incorporated the nitroxide radical TEMPO (2.2,6.6-tetramethyl-1-piperidinyloxyl) inside the SWNTs. The ESR spectra were recorded from 5K to 300 K using an X band EPR spectrometer (Bruker ER 200D). The main result of this work is change in dynamics of the probe molecule at 230 K indicated by the appearance of a narrow triplet signal. The ESR measurements were also done on TEMPO in methanol for the comparative studies in the same temperature range, and in the latter observations, no change in spectra was seen around 230K. The origin of the appearance of this narrow triplet at 230 K indicates the possibility of change in some intrinsic property of the carbon nanotube around 230 K, which has been reflected in the motional characteristics of the spin probe. Thus, our studies show that spin probes, which have, till been used widely in biological samples and polymers, can be used for the further studies of carbon nanotubes to investigate their physical properties. [Preview Abstract] |
Friday, March 25, 2005 11:51AM - 12:03PM |
Y27.00004: Thermal Conductivity of Single Wall Carbon Nanotube (SWNT) Epoxy Composites M.B. Bryning, D.E. Milkie, M.F. Islam, J.M Kikkawa, A.G. Yodh Pristine SWNTs were dispersed in epoxy to create composites. Our dispersion procedure achieved fairly uniform SWNT distributions without introducing stabilizing agents that could affect composite performance. We measured thermal and electrical conductivity of the resulting composites. Thermal conductivity increased continuously with increasing SWNT concentration, exhibiting an enhancement of about 30{\%} at a volume fraction of $\sim $0.01. In similar composites made with surfactant stabilized SWNTs, the thermal enhancement was weaker; volume fractions of $\sim $0.03 were needed to achieve a 30{\%} increase. We contrast these findings with electrical measurements on the same samples, which show a percolation-like behavior with a sharp insulator-conductor transition. This work has been partially supported by the NSF through MRSEC grant DMR-0079909 and DMR-0203378, by DARPA/ONR grant N00015-01-1- 0831, and by NASA through grant NAG8-2172. [Preview Abstract] |
Friday, March 25, 2005 12:03PM - 12:15PM |
Y27.00005: Formation of long-lived image states around carbon nanotubes. Mikhail Zamkov, N. Woody, B. Shan, H. Chakraborty, Z. Chan, U. Thumm, P. Richard The long-lived electronic states with wave functions enclosing a carbon nanotube (NT) were observed in two-color time-resolved photoemission experiments. These cylindrical ``electronic rings'' constitute a new class of surface image states due to their quantized angular motion. The electron rotation about the axis of the nanotube gives rise to a centrifugal force that virtually detaches the electron charge-cloud from the tube's body. This isolation results in enhanced lifetimes that were measured to be one order of magnitude longer than those of image states forming above metal surfaces. The experiments were performed using the high-purity ($>$ 95{\%}) samples of individual multi walled NTs. Our current efforts are aimed towards the observation of these ``exotic'' states around the isolated double walled NTs as well as in bundles of single walled NTs. [Preview Abstract] |
Friday, March 25, 2005 12:15PM - 12:27PM |
Y27.00006: Collective electronic excitations in single wall carbon nanotubes Ricardo Perez, William Que Collective electronic excitations in single wall carbon nanotubes are studied theoretically, using a tight-binding model. Our results suggest that a new theoretical explanation is possible for the controversial nondispersive modes discovered in the electron energy-loss spectroscopy experiment of Pichler et al. on bulk carbon nanotube samples. These modes have been attributed by Pichler et al. to interband excitations between localized states polarized perpendicular to the nanotube axis. This interpretation has been challenged by a theorist Bose [2] who attributed the modes to optical plasmons carrying nonzero angular momenta. Both interpretations suffer from difficulties. We find that the nondispersive modes could be due to collective electronic modes in chiral carbon nanotubes, while the observed dispersive mode should be due to collective electronic modes in armchair and zigzag carbon nanotubes. Momentum-dependent electron energy-loss experiments on individual carbon nanotubes should be able to confirm or disprove this interpretation decisively. [1] T. Pichler et al., PRL 80, 4729 (1998). [2] S. M. Bose, Phys. Lett. A 289, 255 (2001). [Preview Abstract] |
Friday, March 25, 2005 12:27PM - 12:39PM |
Y27.00007: Accurate determination of the atomic structure of multiwalled carbon nanotubes by electron diffraction Zejian Liu, Lu-Chang Qin We report a new method that allows direct, systematic and accurate determination of the atomic structure of multiwalled carbon nanotubes by analyzing the scattering intensities on the non-equatorial layer lines in the electron diffraction pattern. As an example to illustrate the method, we will present complete structure determination of a quadruple-walled carbon nanotube. It was determined that the chiral indices of the four shells were: [32,1], [26,24], [39,25], and [64,2]. All are semiconducting in this case. We also found that the inter-tubular distance varied from 0.36 nm to 0.5 nm with a mean value of 0.42 nm. [Preview Abstract] |
Friday, March 25, 2005 12:39PM - 12:51PM |
Y27.00008: Telling the chiral indices of carbon nanotubes from electron diffraction Lu-Chang Qin, Zejian Liu We report a newly developed one-step method that allows direct reading of the chiral indices [u,v], which specify the perimeter vector of a carbon nanotube, from an electron diffraction pattern of the nanotube. We will present a systematic procedure for the actual use of this method. With the chiral indices of a carbon nanotube determined, its atomic structure such as diameter and helicity and its electronic properties such as being metallic or semiconducting are readily obtained. We have examined a large number of individual single-walled carbon nanotubes to study the distribution of the atomic structure of nanotubes in a sample material produced by arc-discharge. Some selected examples will be presented to illustrate the applications of this method. [Preview Abstract] |
Friday, March 25, 2005 12:51PM - 1:03PM |
Y27.00009: Pressure effect on multiwalled carbon nanotubes (MWCNT) up to 25 GPa probed by X-ray Raman scattering Malcolm Nicol, Ravhi Kumar, Andrew Cornelius, Michael Pravica, Michael Hu X-ray Raman scattering (XRS) is a sensitive bulk probe that yields information about the local structure of systems and compounds in the soft x-ray regime. The availability of high energy synchrotron radiation has allowed combining this method with different sample environmental conditions such as extreme pressures and temperatures. Here we present the C k-edge measurements under pressure to investigate the bonding changes of multi walled carbon nanotubes (MWCNT) up to 25 GPa. The results show that the MWCNT transform to a superhard phase similar to diamond around 15 GPa. Further compression results in a structural collapse leading to an amorphous state. [Preview Abstract] |
Friday, March 25, 2005 1:03PM - 1:15PM |
Y27.00010: The Neutron Scattering Length Density of Carbon Nanotubes Howard Wang, Gregory Christopherson, Tom Xu, Derek L. Ho, Erik K. Hobbie Contrast matching experiments have been carried out to obtain the neutron scattering length density (SLD) of carbon nanotubes (CNT). The quantitative variation of SLDs of CNTs from various sources and with various processing histories is related to their structure characteristics and elemental impurity. The neutron SLD is particularly sensitive to the inclusion of hydrogen in CNT samples. [Preview Abstract] |
Friday, March 25, 2005 1:15PM - 1:27PM |
Y27.00011: Single-wall nanohorn structure and distribution of incorporated materials Alan Maigne, Alexandre Gloter, Kumiko Ajima, Katsuyuki Murata, Masako Yudasaka, Christian Colliex, Sumio Iijima Single-wall carbon nanohorns (SWNHs) are unique spherical-aggregates of single-wall carbon quasi-nanotubes. So far, the observable area has been limited to the aggregate surfaces. We studied core-region structure with TEM using thickness measurement method, EELS, and EDS, and found that carbon density was uniform over the whole aggregate. This result allows to modelize the core-region and to clarify previous models of SWNHs. We used same tools to investigate the incorporation of materials such as fullerenes or platinium compounds. We found that particles can even be incorporated in the core-region and that their distribution in the aggregate depends on their concentration. The information available with these models should be useful in the study of SWNH applications to, for example, drug delivery system. [Preview Abstract] |
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Y27.00012: Drugs incorporation in single-wall carbon nanohorns Kumiko Ajima, Masako Yudasaka, Alan Maigne, Tatsuya Murakami, Kiyotaka Shiba, Sumio Iijima To apply single-wall carbon nanohorns (SWNHs) as drug carriers in drug delivery systems, we have been studying the drug incorporation inside SWNHs. We incorporated several drugs in SWNHs (DR@SWNHs) at room temperature by liquid-phase methods, such as Nano-Titration and Nano-Precipitation. Whether DR was inside or outside of SWNHs was judged by X-ray diffraction, and the elements of DR inside SWNHs were identified by energy dispersive X-ray spectroscopy. The release of DR in phosphate-buffered saline was measured with atomic absorption spectroscopy, which indicated slow and fast release processes. The biological integrity of the released DR was studied with cultured cells. These results indicate that SWNHs will be useful for drug carriers. [Preview Abstract] |
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