Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y16: Focus Session: Carbon Nanotubes, Graphene, & Related Materials: Chemical Properties and Sensing |
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Sponsoring Units: DMP Chair: Michael Fuhrer, Monash University Room: 101AB |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y16.00001: Measurement of electronic perturbations in the surface of a carbon nanotube by adsorbed atoms and molecules David Cobden, Boris Dzyubenko, Hao-chun Lee, Oscar Vilches The physisorption of atoms and molecules onto a surface such as carbon involves small hybridization with the substrate electron states which have not previously been accessible to experiments. Suspended single-walled carbon nanotube devices are a good system for studying the electronic perturbations, as they combine a perfect carbon surface with single-atom mass sensing capability and single-electron-transistor sensitivity. By monitoring both the conductance and the adsorbed mass, derived from the mechanical frequency shift, in equilibrium with the vapor, we are able to detect for the first time the very small charge transfer from adsorbates to the surface. It is found to be of a similar magnitude for all gases tested (4He, Ar, Kr, Xe, N2, CO and O2), and depends on coverage and temperature. Although it is only 10$^{\mathrm{-5}}$ -- 10$^{\mathrm{-3}}$ e per atom, at gate voltages near threshold it can produce a large change in conductance. It can thus be used to sense tiny amounts of adsorbates and to explore the phase transitions of atoms on a cylinder. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y16.00002: Argon Adsorption on Open Carbon Nanohorns Angel Calvillo, Brice Russell, Aldo Migone, Sumio Iijima, Masako Yudasaka We have measured adsorption isotherms for argon adsorbed on a 0.1692 g sample of chemically-opened carbon nanohorns. Two clear substeps are visible in the adsorption data, corresponding to groups of stronger binding sites (lower pressure substep) and weaker binding sites (higher pressure substep). We have measured adsorption at five different temperatures in the range between 70 and 90 K. The chemically-opened nanohorns have the space at the interior of the individual nanohorns accessible to adsorbates. Consequently, higher loadings are obtained on these samples compared to those for unopened (as-produced) nanohorns. Results for the kinetics of adsorption, the effective specific surface area, and the isosteric heat of adsorption as a function of sorbent loading will be presented and compared to results from other studies on nanohorns. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y16.00003: Computer simulations of Ne and CO$_2$ adsorbed in carbon nanohorns Silvina Gatica, Adam Scrivener We compute the equilibrium properties of Ne and CO$_2$ adsorbed on carbon nanohorns. We modeled the nanohorns as an arrangement of nanometer-size cones composed of carbon atoms. Our method of calculation is the Grand Canonical Monte Carlo technique, where the substrate is considered rigid. We calculate the adsorption isotherms for various temperatures (18K-50K for Ne and 147K - 200K for CO$_2$). We also calculate the isosteric heat of adsorption and compare with available experimental results. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 8:48AM |
Y16.00004: Ethane Adsorption on Carbon Nanohorns Brice Russell, Aldo Migone, Sumio Iijima, Masako Yudasaka We have measured adsorption isotherms for ethane adsorbed on as-produced single-walled carbon nanohorns. Measurements have been completed for nine temperatures between 123.66 K and 221.32 K. The kinetics of adsorption will be compared to results previously obtained for ethane adsorption on purified HiPco single-walled carbon nanotubes. On nanotubes it was found that equilibration times for ethane decreased with increasing sorbent loading (coverage). By contrast, for adsorption on the as-produced nanohorns, equilibration times increased with increasing sorbent loading. The kinetic results for sorbent mass loading will be compared to an expression with only one rate-controlling mechanism. The point-B method was used to determine monolayer completion values at each temperature. Results will also be presented for the isosteric heat values, which were determined for the full range of loadings covered by the isotherms. [Preview Abstract] |
Friday, March 6, 2015 8:48AM - 9:00AM |
Y16.00005: Transport and Optical Investigations of Substitutional and Trapped Nitrogen in Carbon Nanotubes Ali Qajar, Danhao Ma, Ramakrishnan Rajagopalan, Kofi Adu, Gamini Sumanasekera Multiwall carbon nanotubes that contain nitrogen were synthesized using acetonitrile as the precursor and ferrocene as the catalysis. X-ray photoelectron spectroscopy detected $\sim$ 2 atomic{\%} nitrogen in the carbon nanotubes with $\sim$ 1 atomic{\%} of the nitrogen as substitutionally doped in the carbon nanotubes skeletal structure and 1 atomic{\%} present as gaseous nitrogen trapped inside the nanotubes. Investigation of the temperature dependent transport properties (thermoelectric power and resistivity) and the phonon modes of the CNTs and the trapped gaseous nitrogen are used to further substantiate the XPS results. High pressure adsorption of CO$_{2}$ at room temperature also confirmed no porosity accessible for CO$_{2}$ molecules. Transmission electron microscopy (TEM) showed presence of corrugations and wisps in the carbon nanotubes framework attributed to the curvature induced by nitrogen atoms. [Preview Abstract] |
Friday, March 6, 2015 9:00AM - 9:12AM |
Y16.00006: Spectroscopic Investigations into the Redox Sorting of Carbon Nanotubes Jason Streit, Hui Gui, Jeffery Fagan, Angela Hight Walker, Chongwu Zhou, Ming Zheng Charge-transfer reactions have been shown to alter the electronic structure of single-wall carbon nanotubes (SWCNTs) in a bandgap-dependent fashion. Such electronic modification shows great promise for chiral selective separations. This study investigates the role of redox chemistry in the aqueous two-phase extraction of SWCNTs. We demonstrate a multi-step oxidative extraction procedure to successfully separate SWCNTs both by semiconducting bandgap and metallicity. We propose that electron transfer between redox molecules and the nanotubes induces reorganization of the surfactant coating layer, which in turn affects the partitioning of the SWCNTs between the two different aqueous polymer phases. Spectroscopic measurements are applied to probe surfactant structure reorganization in different redox environments. We suggest that redox-induced modulation of the surfactant coating is a generally observed phenomenon in many different nanotube sorting processes which can be further controlled to improve separation reproducibility and purity. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y16.00007: Rotations and vibrations of water molecule inside the fullerene cage: infrared study of H$_2$O@C$_{60}$ Toomas Room, A. Shugai, U. Nagel, S. Mamone, A. Krachmalnicoff, R.J. Whitby, M.H. Levitt, T. Nishida, Y. Murata, Xuegong Lei, Yongjun Li, N.J. Turro Water is the second molecule after hydrogen what has been trapped inside the cage of a C$_{60}$ molecule by the molucular surgery method [Kurotobi and Murata, Science {\bf 333}, 613 (2011)]. We studied isolated water molecule isotopologs H$_2$O, D$_2$O, and HDO in the solid phase at cryogenic temperatures using IR spectroscopy. The water molecule rotation transitions were observed in the THz [Beduz et al., PNAS {\bf 109}, 12894 (2012)] and vibration-rotation transitions in the mid-IR range. The slow conversion between para and ortho water allowed us to record the time evolution of spectra and to separate ortho and para absorption lines of water. The similarity of the rotation spectrum of caged water to water in the gas phase indicates that water is free to rotate in the C$_{60}$ cage even at temperature as low as 3\,K. However, spectral lines show a splitting of about 0.5 meV what is not compatible with the icosahedral symmetry of C$_{60}$. Different models (e.g. crystal field effects in solid C$_{60}$, C$_{60}$ cage distortions) will be discussed. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y16.00008: Adsorption of Ar on individual carbon nanotubes, graphene, and graphite Boris Dzyubenko, Joshua Kahn, Oscar Vilches, David Cobden We compare and contrast results of adsorption measurements of Ar on single-walled carbon nanotubes, graphene, and graphite. Adsorption isotherms on individual suspended nanotubes were obtained using both the mechanical resonance frequency shift (sensitive to mass adsorption) and the electrical conductance. Isotherms on graphene mounted on hexagonal boron nitride were obtained using only the conductance. New volumetric adsorption isotherms on bulk exfoliated graphite were also obtained, paying special attention to the very low coverage region (less than 2{\%} of a monolayer). This allowed us to compare the degree of heterogeneity on the three substrate types, the binding energies, and the van der Waals 2D parameters. Research supported by NSF DMR 1206208. [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y16.00009: Ortho-para conversion of endohedral water in the fullerene C$_{60}$ at cryogenic temperatures Anna Shugai, U. Nagel, T. R{\~o}{\~o}m, S. Mamone, M. Concistr{\`e}, B. Meier, A. Krachmalnicoff, R.J. Whitby, M.H. Levitt, Xuegong Lei, Yongjun Li, N.J. Turro Water displays the phenomenon of spin isomerism in which the two proton spins either couple to form a triplet (ortho water, $I=1$) or a singlet nuclear spin state (para water, $I=0$). Here we study the interconversion of para and ortho water. The exact mechanism of this process is still not fully understood. In order to minimize interactions between molecules we use a sample where a single H$_2$O is trapped in the C$_{60}$ molecular cage (H$_2$O@C$_{60}$) and H$_2$O@C$_{60}$ is crystallized. H$_2$O@C$_{60}$ has long-lived ortho state [Beduz et al., PNAS {\bf 109}, 12894 (2012)] and ortho-para conversion kinetics is non-exponential at LHeT [Mamone et al, J.Chem.Phys. {\bf 140}, 194306, (2014)]. We studied mixtures of H$_2$O@C$_{60}$, D$_2$O@C$_{60}$ and C$_{60}$ using IR absorption, NMR and dielectric measurements. We saw the speeding up of the interconversion with the growth of H$_2$O@C$_{60}$ concentration in C$_{60}$ or when D$_2$O@C$_{60}$ was added. At some temperatures the kinetics is exponential. Models are discussed in order to explain the $T$ and concentration dependence of ortho-para interconversion kinetics. [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y16.00010: Effect of intercalated molecules on graphene sensing behavior Tao Sun, Kyoungmin Min, Narayana Aluru The physical mechanism of graphene humidity sensor based upon capacitance measurement is explored by atomic/ab-initio simulations. Our simulations show that molecules intercalated between graphene and substrate (HfO2) can have large influence on graphene sensing behavior. We find that oxygen vacancies on the surface of the substrate can induce an N-type doping in graphene, while oxygen molecules entering between the substrate and graphene will fill the vacancies and eliminate the N-type doping effect. We also observe thatwater molecules trapped at the interfacial layer can change the interlayer distance, thus changing the measured capacitance. Our simulations uncover the effect of intercalated molecules, which is helpful to better understand the operation process of graphene sensing devices. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y16.00011: Determining the thermal noise floor of graphene biosensors Michael Crosser, Morgan Brown, Ethan Minot The use of graphene field-effect transistors (GFETs) as biosensors in aqueous environments is fundamentally limited by voltage noise. In many GFET devices, noise is dominated by the fluctuating occupancy of charge traps in the substrate. Fabrication techniques have been found to reduce this substrate effect, but thermally-driven charge transfer across the graphene liquid interface has yet to be quantified and addressed. In this report we present the first characterization of this noise source. We show that the power spectral density of this noise scales inversely with frequency and inversely with interface area. Our results are in quantitative agreement with recent measurements of voltage noise in clean, suspended graphene. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y16.00012: Spatial Self-Phase Modulation in Graphene and Graphene Oxide Water Suspensions Yanan Wang, Zhuan Zhu, Xiaoxiang Wang, Da Lin, Dong Liu, Xufeng Zhou, Zhiming Wang, Jiming Bao With promising potential in photonic and optoelectronic applications, nonlinear optical properties of graphene based materials have attracted enormous interest. In this work, we observed spatial self-phase modulation (SSPM) of propagating laser beams in both graphene and graphene oxide (GO) water suspensions. The formation and temporal evolution of far-field diffraction rings have been investigated systematically. It is found that alignment of graphene or GO flakes is controlled by water convection rather than the polarization of laser. We further discovered that SSPM can be mainly attributed to the thermo-optic effect of water instead of graphene or GO. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y16.00013: Asymmetric behavior in electrowetting of electrolyte solutions on graphene at the nanoscale: A molecular dynamics simulation Fereshte Taherian Tabasi, Nico van der Vegt Using molecular dynamics simulations, electrowetting of aqueous solutions on graphene are studied. By doping the surface with the positive or negative charges, the counter-ions are adsorbed at the solid-liquid interface, and the co-ions are repelled from the interface, leading to the decrease of the solid-liquid surface tension and therefore the contact angle (known as electrowetting). Our simulation results show that at zero surface charge density, water molecules at the interface (located between the surface and first ionic layer) are mainly oriented parallel to the surface. However due to the smaller size of the hydrogen than the oxygen, there is a slight tendency of the water dipole moment to orient into the surface. On the charged surfaces, the orientation polarization of the interfacial water molecules are shown to be stronger on the negative surfaces than the positive ones. Such asymmetric orientation polarization of water leads to different screening of the graphene surface charge and therefore different contact angles of the solution on surfaces with opposite charges. Simulations results show more spreading of the liquid on the positively charged surfaces than the negative ones. [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y16.00014: Ionic transport across atomically-thin graphene membranes Lauren Cantley, Scott Bunch Graphene is an attractive material for applications in single molecule sensing and molecular sieving, in part due to its atomic thinness, strength and barrier properties. In this study, we examine ionic transport across a suspended single-layer graphene membrane separating two reservoirs of aqueous ionic solution. Molecularly sized, sub-nm pore(s) are introduced by chemical etching, which allow for only proton transport across the graphene membrane. The pore is further opened and ionic conductance measurements are carried out to further investigate and characterize ionic transport across sub-nm and nm-scale pores. [Preview Abstract] |
Friday, March 6, 2015 10:48AM - 11:00AM |
Y16.00015: Synthesis, characterization and application of highly crystalline sp$^{2}$ -- bonded boron nitride aerogels Thang Pham, Anna Goldstein, Marcus Worsley, Leta Woo, William Mickelson, Alex Zettl Aerogels have much potential in both research and industrial applications due to high surface area, low density and fine pore size distribution. Here we report a versatile synthesis and thorough structure characterization of three-dimensional aerogels composed of highly crystalline sp$^{2}$ -- bonded BN layers formed by carbothermal reaction. The structure, crystallinity and bonding of the as-prepared BN aerogels were elucidated by x-ray diffraction, nuclear magnetic resonance of $^{11}$B, transmission electron microscopy (TEAM) and resonant soft x-ray scattering. The macroscopic roughness of the aerogel's surface causes it to be superhydrophobic with a contact angle of 155 $\pm$ 3$^{\circ}$ and high oil uptake (up to 1500 wt{\%}). The used BN aerogel can be regenerated by different heat treatments and still maintain the crystalline porous structure and adsorption capacity. The highly crystalline, chemically pure, thermally stable and porous sp$^{2}$ -- boron nitride aerogel is an ideal host for liquids, gases and other nanomaterials. [Preview Abstract] |
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