Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session N31: Focus Session: Carbon Nanotubes: Sensors and Adsorption |
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Sponsoring Units: DMP Chair: Masa Ishigami, University of Maryland Room: Colorado Convention Center 401 |
Wednesday, March 7, 2007 8:00AM - 8:12AM |
N31.00001: Raman Spectroscopy in Single-Wall and Double-Wall Carbon Nanotube Systems Doped with H$_2$SO$_4$ Eduardo Barros, Antonio Souza Filho, Yoong-Ahm Kim, Hiroyuki Muramatsu, Takuya Hayashi, Riichiro Saito, Moribonu Endo, Mildred Dresselhaus In this work we performed Raman experiments on a mixture of Single-wall and Double-wall carbon nanotubes for different relative concentrations and using different laser energies. Two sets of samples were analyized, one which was exposed to $H_2SO_4$ for 5$~s$ and one which is pristine. The $H_2SO_4$ is known to act as an acceptor for the electrons of graphitic materials. The effect of hole doping on the vibrational and electronic properties of the double and single-wall carbon nanotubes is probed using Resonant Raman scattering with different excitation energies probing different nanotubes. For selected excitation energies, it is possible to probe, at the same time, the inner and outer walls of double-wall nanotubes. The lineshape of the G$'$ band double-wall nanotubes is discussed in terms of the interlayer interaction and the effect of single-wall nanotube contaminants and the H$_2$SO$_4$ doping to the G$'$ band is studied. [Preview Abstract] |
Wednesday, March 7, 2007 8:12AM - 8:24AM |
N31.00002: Evidence of a possible phase transition in ethane adsorbed on purified HiPco Nanotubes Murat Bulut, Dinesh Rawat, Aldo Migone We conducted adsorption measurements for ethane on purified HiPco single-walled carbon nanotubes for coverages in the first layer. In order to obtain the binding energy of ethane, we measured three low-coverage isotherms for temperatures between 220 K and 240 K. The value that we determined, 308 meV, is 1.7 times larger than that obtained for the binding energy of ethane on planar graphite. We measured eight full isotherms between 103 K and 170 K. Evidence of a phase transition in the adsorbed films was investigated by studying temperature dependence of the height of the isotherm substep corresponding to the adsorption of ethane molecules on the external surface of the SWNTs. There is a significant difference in the size of the substeps measured below and above 110 K. This difference suggests that a possible structural phase transition is occurring in the adsorbed film. [Preview Abstract] |
Wednesday, March 7, 2007 8:24AM - 8:36AM |
N31.00003: First Principles Study of Metal Adatom Adsorption on Carbon Nanotubes Kevin T. Chan, Jeffrey B. Neaton, Marvin L. Cohen Recent experiments observed bias-induced mass transport between indium nanoparticles on a carbon nanotube. Ab initio studies later suggested that electromigration in this case can be explained by charge transfer from indium adatoms to the nanotube and small diffusion barriers, and that defects can serve as nucleation sites for nanoparticle formation. Here we use ab initio calculations to explore adhesion, diffusion, and the possibility of mass transport on nanotube surfaces for other metallic species. We will present calculations examining binding energy, binding site, diffusion barriers, and charge transfer for a range of metal adsorbates on surfaces, defects, and vacancies of carbon nanotubes and sheets. Adatom coverage dependence and the role of curvature effects will also be discussed. [Preview Abstract] |
Wednesday, March 7, 2007 8:36AM - 8:48AM |
N31.00004: Accessible surface area in filter deposited, single wall carbon nanotube films Rajib K. Das, Bo Liu, Ryan M. Walczak, Andrew G. Rinzler A convenient process for fabricating thin, homogeneous, transparent films of single wall carbon nanotubes (SWNTs), with potential application as electrodes in organic light emitting diodes and photovoltaic devices, was described in 2004[1]. Among the advantages claimed for such films was the high surface area contact afforded by the nanotubes. Recent measurement of the density for such films shows them to possess nearly 60{\%} of the crystallographic hexagonal close pack density for nominally 1.36 nm diameter SWNTs. Such dense packing does not bode well for infiltration of the films with viscous electro-active polymers by e.g. spin coating. Hence, while the films in principle possess large surface areas, it is not necessarily accessible. To improve this circumstance we have developed a simple, controllable method for modifying the open porosity of the films. We will describe the method and its characterization by imaging, sheet resistance and electrochemical capacitance measurements. [1] Z. Wu et al. Science 305, 1273 (2004) [Preview Abstract] |
Wednesday, March 7, 2007 8:48AM - 9:00AM |
N31.00005: Gas Adsorption on Carbon Nanohorns Aggregates Jeff Wagner, M. Mercedes Calbi We evaluate a simple model of adsorption to predict the possible adsorbed phases of gases on a triangular array of tubes as a function of the distance between the tubes and the external pressure. Specific results are presented for the cases of Ne and CF$_{4}$. In addition, Grand Canonical Monte Carlo simulations are performed for particular choices of the aggregates' geometry. Adsorption isotherms and isosteric heats of adsorption as a function of coverage are obtained. Comparison with experimental results allows us to obtain information on the structure of the aggregates that is then use to predict the adsorption behavior of other gases. [Preview Abstract] |
Wednesday, March 7, 2007 9:00AM - 9:12AM |
N31.00006: Kinetic Selectivity and Competitive Adsorption on Carbon Nanotube Bundles Jared Burde, M. Mercedes Calbi We investigate the kinetics of adsorption of a binary mixture on one-dimensional chains by means of Kinetic Monte Carlo simulations. A competition based on both the binding energies and the adsorption rates is demonstrated. Since the species with smaller binding adsorb faster, it is shown that before reaching equilibrium, that species is the favored one contrary to what eventually happens in equilibrium. Therefore, the weaker binding species can initially reach coverages larger than its equilibrium value, providing evidence of a kinetic selective process that can be exploited for gas separation purposes. [Preview Abstract] |
Wednesday, March 7, 2007 9:12AM - 9:48AM |
N31.00007: Scaffolding Carbon Nanotubes into Single-Molecule Circuitry Invited Speaker: As electronic devices shrink to the nanometer scale, the relative importance of individual chemical bonds becomes larger and larger. Single-walled carbon nanotubes (SWNTs) represent an extreme limit of this rule, as the modification of a single lattice site can dramatically change chemical activity and electronic properties. This presentation will focus on single-site experimentation in which we find, create, and alter point defects in SWNTs. Due to the correspondence between chemical and electronic properties, changes in SWNT device conductance reveal these chemical processes happening in real-time and allow the SWNT sidewall to be deterministically broken, reformed, and conjugated to target species. We routinely functionalize pristine, defect-free SWNTs at one, two, or more sites, and have demonstrated three-terminal devices in which a single-molecule attachment controls the electronic response. [Preview Abstract] |
Wednesday, March 7, 2007 9:48AM - 10:00AM |
N31.00008: Supported Lipid Bilayer/Carbon Nanotube Hybrids Xinjian Zhou, Jose Moran-Mirabal, Harold Craighead, Paul McEuen We form supported lipid bilayers on single-walled carbon nanotubes and use this hybrid structure to probe the properties of lipid membranes and their functional constituents. We first demonstrate membrane continuity and lipid diffusion over the nanotube. A membrane-bound tetanus toxin protein, on the other hand, sees the nanotube as a diffusion barrier whose strength depends on the diameter of the nanotube. Finally, we present results on the electrical detection of specific binding of streptavidin to biotinylated lipids with nanotube field effect transistors. Possible techniques to extract dynamic information about the protein binding events will also be discussed. [Preview Abstract] |
Wednesday, March 7, 2007 10:00AM - 10:12AM |
N31.00009: Carbon nanotube biosensors strongly affected by the biosensitivity of quasi reference electrodes Ethan Minot, Anne Janssens, Iddo Heller, Dirk Heering, Cees Dekker, Serge Lemay Semiconducting carbon nanotubes are extremely sensitive to their electrostatic environment. This property can be utilized to build sensors in liquid environments that detect bio-molecule adsorption in real time via changes in device conductivity. Control of the liquid potential is critical for operation of these sensors, yet nearly all carbon nanotube sensors operating in liquid have employed bare Pt wire to control the liquid potential. We show that the interface voltage between Pt and an electrolyte solution changes by tens of mV upon protein adsorption. This quasi reference electrode biosensitivity can easily mask signals associated with protein adsorption around the carbon nanotube. We demonstrate stable control of the liquid potential using a standard reference electrode, and report signals due entirely to protein adsorption around individual semiconducting NTs. These improved measurements allow us to quantify and differentiate the mechanisms of protein sensing by carbon nanotube devices. [Preview Abstract] |
Wednesday, March 7, 2007 10:12AM - 10:24AM |
N31.00010: Theoretical Investigation on Alcohol Sensing of Glycine-Coated Carbon Nanotubes Tao Jiang, Gary Kussow, Young-Kyun Kwon It has been observed that single walled carbon nanotube field effect transistors (SWNT-FET) coated with glycine can be used as alcohol sensors. The original semiconducting glycine-coated SWNT-FET have been changed to be metalic in the presence of alcohol. Using {\em ab initio} density functional theory, we compute the structural and electronic properties of carbon nanotubes coated with glycine in the absence or in the presence of alcohol (Isopropanol) to investigate alcohol sensing mechanism. To demonstrate specificity of such glycine-coated SWNT-FETs on alcohol, we also study those properties in the presence of other molecules, such as acetone and water. Furthermore, we investigate the effect of an external fields on glycine-coated SWNT with IPA, and indentify the gate-electric-field screening in SWNT-FET to be a major role for alcohol sensing. [Preview Abstract] |
Wednesday, March 7, 2007 10:24AM - 10:36AM |
N31.00011: Detection of Individual Gas Molecules Absorbed on Graphene Andre Geim, Kostya Novoselov, Fred Schedin, Sergey Morozov, Da Jiang, Ernie Hill The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason for this is fluctuations due to thermal motion of charges and defects which lead to intrinsic noise exceeding the sought-after signal from individual molecules usually by many orders of magnitude. We describe micron-size sensors made from graphene, which are able to detect individual events when gas molecules attach to graphene's surface at room temperature. The absorbed molecules change the local carrier concentration by one electron, which leads to clear step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material, which makes it a promising candidate not only for ultra-sensitive chemical detectors but also for other applications where local probes sensitive to external charge or magnetic field are required. [Preview Abstract] |
Wednesday, March 7, 2007 10:36AM - 10:48AM |
N31.00012: Elucidating the mechanism of bio-sensing with carbon nanotube devices in solution. Iddo Heller, Anne Janssens, Ethan Minot, Hendrik Heering, Serge Lemay, Cees Dekker We address the mechanism of electronic sensing with carbon nanotube field-effect transistors in solution. It has been demonstrated that the electrostatic interaction of proteins with single-walled carbon nanotube (SWNT) devices can strongly modulate the transport properties. The exact nature of this electrostatic interaction however remains ill-defined. Recent reports suggest that protein adsorption at the metal-SWNT contact interface plays a more dominant role than adsorption along the bulk of the SWNT. We will report on scanned probe experiments that demonstrate that sensing is not only localized at the contacts. Furthermore, through protein adsorption experiments we show that the effect of either bulk or contact adsorption can dominate depending on the electrolyte gate potential. Because protein adsorption at bulk and contacts can have opposite effects on device conductivity, the two mechanisms can even cancel each other out. This makes it crucial to carefully choose the operating gate potential for protein sensing experiments where the device conductivity is monitored over time. [Preview Abstract] |
Wednesday, March 7, 2007 10:48AM - 11:00AM |
N31.00013: Light-assisted oxidation of carbon nanohorns for enhancing bio-compatibility Minfang Zhang, Masako Yudasaka, Kumiko Ajima, Sumio Iijima Single-wall carbon nanohorn (SWNH) has a structure similar to single-wall carbon nanotubes but with a larger diameters (2-5 nm) and shorter lengths (40-50 nm), and about 2000 of them assembled to form a spherical aggregate with a diameter of about 100 nm. For various applications of SWNHs, the chemical modification is the crucial issue. To chemically modify SWNHs, the --COOH groups at the holes edges are useful. We show in this report that --COOH groups are formed abundantly when SWNHs were oxidized with H$_{2}$O$_{2}$ under the light irradiation (Xe lamp). SWNHox thus obtained well dispersed by themselves in water, which was even more enhanced by attaching proteins to SWNHox. The modification with proteins effectively enhance the bio-compatibility of SWNHox, which was confirmed through in vitro assay using the mammalian cells. [Preview Abstract] |
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