Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y7: Focus Session: Carbon Nanotubes: Sensor Applications and Gas Absoprtion |
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Sponsoring Units: DMP Chair: Charlie Johnson, University of Pennsylvania Room: 303 |
Friday, March 22, 2013 8:00AM - 8:36AM |
Y7.00001: Parts-per-quadrillion Resolution Molecular Sensor Based on Pristine Carbon Nanotubes Invited Speaker: Gugang Chen Single-walled carbon nanotube (SWNT) is probably the ultimate sensor among nanoscale semiconducting materials since a SWNT consists solely of surface so that every single carbon atom is in direct contact with the environment, allowing optimal interaction with nearby molecules. Ironically the ultrahigh sensitivity of SWNTs is easily compromised by various unintentional contaminants from the device fabrication process as well as the ambient environment. Here we show that applying continuous in situ ultraviolet (UV) light illumination during gas detection could dramatically enhance a SWNT-sensor's performance and for the first time achieve parts-per-quadrillion (PPQ) resolution with detection limit as low as 590 PPQ for nitric oxide detection at room temperature [1]. Gas detections on NO$_{\mathrm{2}}$ and NH$_{\mathrm{3}}$ further showed sensitivities 2 to 3 orders of magnitude better than what previously had reported. The much enhanced performance is apparently aroused from the UV light induced sensor surface cleaning. In addition, aiming for practical applications we illustrate how to address gas selectivity by introducing a gate bias. \\[4pt] [1] G. Chen, T. M. Paronyan, E. M. Pigos, and A. R. Harutyunyan, Scientific Reports 2, 343 (2012). [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 8:48AM |
Y7.00002: Carbon nanotube based photon filter for energetic particle detection David Deglau, Stergios Papadakis, Andrew Monica, Bruce Andrews, Donald Mitchell Energetic particles (EP) ejected from a plasma carry important information about the plasma physics. To study remote plasmas in the heliosphere, space-based sensors must be used. Furthermore, only energetic \textit{neutral} atoms (ENAs) can be analyzed, since charged particle trajectories are curved by the electric and magnetic fields of the heliosphere. Because low power consumption and weight are important for spacecraft, solid-state detectors are used. The challenge with solid-state detectors is their sensitivity to light; in all observational regions of interest, photon counts are several orders of magnitude higher than ENA counts. Current state of the art solid-state detectors use ultra-thin metal or carbon films to block the photons. This sets an energy threshold for the ENAs due to the fact that the ENAs have to penetrate this film. We aim to replace the thin films with carbon nanotube (CNT) mats. The CNT mats have a much lower density while maintaining extremely high photon absorption. Thus the CNT mats will act as an excellent filter for blocking the photons while minimally affecting the ENAs of interest. We will describe the fabrication of the CNT mats and their performance characterization by optical spectroscopy and energetic particle spectroscopy using alpha particles as an ENA simulant. [Preview Abstract] |
Friday, March 22, 2013 8:48AM - 9:00AM |
Y7.00003: Recyclable Buckysponges for De-emulsification and Oil-spill cleaning Mehmet Karakaya, Deepika Saini, Ramakrishna Podila, Apparao M. Rao Here we present a three dimensional, interconnected, carbon nanotube based, spongy material that is capable of efficiently separating oil from water. The buckysponge, as we term it, exhibits superhydrophobicity and oleophilicity. The adopted facile top down approach allows strong control of the porosity and is easily scalable. Due to capillary action combined with its oleophilicity, a buckysponge is capable of selectively absorbing various organic solvents up to 20 times its weight, a value comparable to existing nanosponge materials. This light weight and highly porous material is shown to work with both free and emulsified oil in water. It is not only an ideal candidate for efficient oil removal but also effective in oil recovery. The absorbed oil can be retrieved by reversibly squeezing the buckysponge, or the oil may be burnt to generate heat energy. Notably, the burnt buckysponge shows no damage to its physical structure or its absorptive properties after squeezing or having the oil burnt, and is therefore re-usable. [Preview Abstract] |
Friday, March 22, 2013 9:00AM - 9:12AM |
Y7.00004: Effect of adsorbed monolayers on the conductance of single-walled carbon nanotubes Boris Dzyubenko, Hao-Chun Lee, Oscar Vilches, David Cobden We have studied the effects of adsorbing noble gases He, Ne, Ar, Kr, Xe, and diatomic gases O2, N2 and CO, on the electrical properties of individual suspended single-walled nanotubes, as a function of pressure and temperature. The quantity of gas adsorbed can be determined from the shift in the mechanical resonance frequency of the nanotube. We find that the conductance can be sensitive to small changes in density for all gases and can be measured on a timescale of milliseconds. This opens ways for studying the dynamics of adsorbed atoms/molecules on the surface of a nanotube. For some devices the conductance varies non-monotonically with coverage as a monolayer builds up. The conductance change results at least in part from a very small charge transfer between the adsorbates and nanotube. Measurements below the 2D critical point show sharp features and fluctuations in some devices but not in others. The reason for this is not currently understood. In the nonlinear regime we observe features in the I-V characteristics which occur because electrical currents cause phase transitions on the surface of a nanotube and may lead to stationary nonequilibrium states. [Preview Abstract] |
Friday, March 22, 2013 9:12AM - 9:24AM |
Y7.00005: Toward Quantifying the Electrostatic Transduction Mechanism in Carbon Nanotube Biomolecular Sensors Mitchell Lerner, Nicholas Kybert, Ryan Mendoza, Jennifer Dailey, A.T. Charlie Johnson Despite the great promise of carbon nanotube field-effect transistors (CNT FETs) for applications in chemical and biochemical detection, a quantitative understanding of sensor responses is lacking. To explore the role of electrostatics in sensor transduction, experiments were conducted with a set of similar compounds designed to adsorb onto the CNT FET via a pyrene linker group and take on a set of known charge states under ambient conditions. Acidic and basic species were observed to induce threshold voltage shifts of opposite sign, consistent with gating of the CNT FET by local charges due to protonation or deprotonation of the pyrene compounds by interfacial water. The magnitude of the gate voltage shift was controlled by the distance between the charged group and the CNT. Additionally, functionalization with an uncharged pyrene compound showed a threshold shift ascribed to its molecular dipole moment. This work illustrates a method for producing CNT FETs with controlled values of the turnoff gate voltage, and more generally, these results will inform the development of quantitative models for the response of CNT FET chemical and biochemical sensors. As an example, the results of an experiment detecting biomarkers of Lyme disease will be discussed in the context of this model. [Preview Abstract] |
Friday, March 22, 2013 9:24AM - 9:36AM |
Y7.00006: ABSTRACT WITHDRAWN |
Friday, March 22, 2013 9:36AM - 9:48AM |
Y7.00007: Measurements of adsorbate binding on individual suspended carbon nanotubes Hao Chun Lee, Boris Dzyubenko, Jim Coy, David Cobden, Oscar Vilches By measuring the resonance frequency shift and the conductance change of vibrating suspended single-walled nanotubes at controlled temperature and pressure we can accurately detect the adsorption of gases including He, Ar, Kr, Xe, O2, and N2. The binding energy can then be determined from the low-coverage part of the adsorption isotherms. We find that the adsorption isotherms generally resemble those on graphite but with weaker binding energies, allowing access to behavior at lower two-dimensional (2D) chemical potential than on graphite. For He-4 the binding energy is reduced by as much as a factor of two. For Ar the binding energy on all nanotubes measured is in the range 700 - 800 K, about a third less than that on graphite. This enables us to investigate the 2D critical and triple points of Ar. Puzzlingly, we find that the devices fall into two classes: one with monolayer condensation at lower pressures and sharp 2D liquid-vapor transitions, the other with condensation at higher pressures and lacking sharp transitions even well below the 2D critical point. Possible factors that may be involved are finite-size effects, commensurability, absorption on the inside of nanotubes with holes in them, nanotube bundles containing more than one kind of nanotube and having surface grooves, and amorphous carbon or other contaminants on the surface, though no combination of these factors seems to provide a satisfactory explanation. [Preview Abstract] |
Friday, March 22, 2013 9:48AM - 10:00AM |
Y7.00008: Study of Carbon Dioxide adsorption on Purified HiPco Nanotubes Shree Banjara, Vaiva Krungleviciute, Aldo Migone We have investigated the adsorption characteristics of carbon dioxide on purified HiPco single-walled carbon nanotubes. We measured four full isotherms (starting from zero CO$_{2}$ coverage an ending at the saturated vapor pressure) for temperatures between 150 K and 187 K. While a linear plot of the adsorption isotherms presents initially a relatively broad region of rapid coverage increase with pressure, logarithmic plots of the isotherms are characterized by the absence of any substeps in the data. The equilibration times for each point along the isotherms are much longer than those for other simple adsorbates (e.g., CH$_{4}$ or Ar) on the same sorbent. Results for the effective monolayer capacity as well as values for the isosteric heat of adsorption's dependence on sorbent loading will be presented. [Preview Abstract] |
Friday, March 22, 2013 10:00AM - 10:12AM |
Y7.00009: Protein coronas of Graphene and Carbon Nanotubes Ramakrishna Podila, Pu Chun Ke, Jared Brown, Apparao Rao We explored the effects of protein coating on the optical and vibrational properties of single-walled carbon nanotubes (SWCNTs) and bi- and few layer graphene nanosheets using micro-Raman spectroscopy, UV-visible absorption and electron microscopy. We found that bovine serum albumin (BSA) forms a hard corona on the surfaces of both graphene and SWCNTs. Our results suggest that the BSA hard corona acted as a weak acceptor to facilitate charge transfer from the carbon nanostructures. Notably, we observed that charge transfer occurred only in the case of SWNTs possibly due to their sharp and discrete electronic density of states. On the contrary, we find that graphene did not show a similar charge transfer due to its continuous energy dispersion. Furthermore, the nanostructures induced significant changes in the secondary structure of the BSA by relaxing their external ?-helices. These results are expected to guide controlled nanostructure-biomolecule interactions and prove beneficial in developing benign nanomaterials. [Preview Abstract] |
Friday, March 22, 2013 10:12AM - 10:24AM |
Y7.00010: Optimization of a carbon nanotube field emission electron gun for applications in mass spectrometry Adrian Southard, Stephanie Getty, Daniel Glavin, Gregory Hidrobo, Steven Feng, Nicholas Costen, Carl Kotecki Field emission electron guns composed of carbon nanotube (CNT) pillar arrays make a low power, robust field emission source with turn-on fields as low as 1.8 Volts/$\mu $m. Fowler-Nordheim fits to the current-voltage data exhibit field enhancement factors of greater than 1000. Scaling of a carbon nanotube field emission electron gun to an aspect ratio of 2 mm x 40 mm using MEMS fabrication techniques has increased emitted current by two orders of magnitude beyond previous designs up to a current of 0.7 mA. Enhanced sensitivity from a time-of-flight mass spectrometer compatible with such a source was also obtained. Finite difference simulations (SIMION) of emission from CNT pillar arrays indicate that the field enhancement factors measured in the experiments can't be explained by emission from smooth pillars and must be due to emission from CNTs that protrude from the top of the pillar. SIMION simulations also explain why much of the emitted current is absorbed by the extraction grid using the current geometry and provide methods for improving electron beam transmission through the addition of a second grid. Simulations of electron beam focusing also demonstrate how the addition of a second grid could enable better focusing of the electron beam. [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 10:36AM |
Y7.00011: Neon and Xenon adsorption on opened carbon nanohorns Carl Ziegler, Vaiva Krungleviciute, Aldo Migone, Masako Yudasaka, Sumio Iijima Adsorption isotherms were measured for neon adsorbed on opened (oxidized) carbon nanohorn aggregates. The isotherms were performed at eleven different temperatures between 19 to 40 K. Two distinct substeps are present in logarithmic plots of the adsorption data. The two substeps correspond to high and low binding energy sites present in the nanohorn aggregates. The values of the isosteric heat as a function of substrate loading was calculated; it shows features corresponding to the two adsorption isotherm substeps. The results for neon will be compared to those from ongoing measurements for xenon adsorbed on the same sample of open carbon nanohorn aggregates as well as to a previous study of neon on closed carbon nanohorns. [Preview Abstract] |
Friday, March 22, 2013 10:36AM - 10:48AM |
Y7.00012: Phase transition of adsorbed noble gas on suspended graphene Zaiyao Fei, Hao-Chun Lee, Boris Dzyubenko, Sanfeng Wu, David Cobden Suspended graphene sheets are simultaneously 2D nanomechanical resonators, hosts to massless Dirac electrons, and 2D substrates for adsorption. Adsorption is expected to modulate the mechanical and elctrical properties in a number of ways. We therefore aim to investigate the effects of equilibrium adsorbates on the vibrational resonances and on the conductance. Beginning with noble gases on non-suspended graphene exfoliated on SiO2, for argon we have seen a gradual change in the conductance as a function of vapor pressure at temperatures below the 2D critical point (54 K), indicating gradual formation of a monolayer over a wide chemical potential range (although we have also seen signs of a sharp monolayer phase transition in a least one sample). The mechanism of conductance modulation is a topic of interest. The large broadening of the expected 2D vapor-liquid step is likely to be due to inhomogeneous binding caused by charge disorder, roughness, and other properties of the SiO2 substrate. We are developing pristine suspended graphene devices to eliminate these complications. [Preview Abstract] |
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