Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Q30: Nanotubes and Nanowires I: Electronic and Transport Properties |
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Sponsoring Units: DMP Chair: Michael Fuhrer, University of Maryland Room: Morial Convention Center 222 |
Wednesday, March 12, 2008 11:15AM - 11:27AM |
Q30.00001: Correlations in carbon nanotubes: A DMRG approach Alexander Struck, Sebastian A. Reyes, Sebastian Eggert Single wall carbon nanotubes (SWCNT) are a paradigm for studying quasi-one-dimensional systems with strong correlations, both experimentally and theoretically. Considering the strong relevance of SWCNT, it is even more surprising that only few numerical calculations of correlation effects have been attempted. In this talk, we use the density-matrix renormalization group (DMRG) technique to treat a recently formulated one-dimensional tight-binding lattice model, which accounts for both the electron motions around the circumference and along the tube axis. We discuss the influence of interactions of variable strength and range on the electronic structure and the electron density and outline possible finite-size and boundary effects. [Preview Abstract] |
Wednesday, March 12, 2008 11:27AM - 11:39AM |
Q30.00002: First-Principles Electronic Structure Calculations of N$_{2}$H$_{4}$ Adsorbed on Single-Wall Carbon Nanotubes M. Yu, W.Q. Tian, C.S. Jayanthi, S.Y. Wu Recent experiments conducted by Desai \textit{et al.} [1] reveal that single-wall carbon nanotube (SWCNT) networks exposed to N$_{2}$H$_{4}$ vapor at various pressures exhibit considerable drop in resistance with respect to the pristine sample. Experimental findings reveal: (i) n-type behavior for the adsorption of N$_{2}$H$_{4}$/SWCNT, and (ii) the binding of N$_{2}$H$_{4}$ on SWCNT as chemisorption. In the present work, we have performed first-principles electronic structure calculations [2] for the N$_{2}$H$_{4}$ adsorbed on the (14, 0) SWCNT, where several orientations for the N$_{2}$H$_{4}$ molecule were considered. Calculations for the combined system were performed using 3 unit cells with the DFT/GGA and ultra soft pseudo-potentials. Our calculations reveal: (i) the binding of N$_{2}$H$_{4}$ on SWCNT as physisorption, and (ii) the electronic structure of SWCNT to be practically unaltered by the adsorption of N$_{2}$H$_{4}$, suggesting that there will not be a dramatic drop in resistance for N$_{2}$H$_{4}$/SWCNT. This is in disagreement with the experimental findings. To further understand the experimental observations, we will discuss mechanisms that may alter the binding nature of N$_{2}$H$_{4}$ on SWCNT. [1] S. Desai, G. Sumanasekera, et al. (APS, March 2008). [2] G. Kresse and J. Furthmuller, Phys. Rev. B \textbf{54}, 11169 (1996). [Preview Abstract] |
Wednesday, March 12, 2008 11:39AM - 11:51AM |
Q30.00003: First-principles calculations of effects of metallic electrode contacts on transport properties of carbon nanotubes Nobuhiko Kobayashi, Taisuke Ozaki, Kenji Hirose Recently, considerable effort has been devoted to developing carbon nanotube devices. One of the important issues in the developments of carbon nanotube devices is the control of contact effects of the electrodes. To detect electric signals through nanotubes, electrodes must be connected to the nanotubes. Contact with the electrodes sensitively influences their electronic structures and transport properties. Therefore, it is important to discuss the transport properties on the basis of the detailed electronic state calculations that include the effect of contact with the electrodes. We have investigated quantum transport in carbon nanotubes bridged between metallic electrodes. The electronic states are calculated using a numerical atomic orbital basis set in the framework of the density functional theory, and the conductance is calculated using the Green's function method. We have analyzed transport properties of the finite size of carbon nanotubes bridged between metallic electrodes, and discuss the contact effect of the electrodes on the transport properties. We reveal their dependency on the length and the electrode materials. [Preview Abstract] |
Wednesday, March 12, 2008 11:51AM - 12:03PM |
Q30.00004: Effect of Phase-Breaking Events on Electron Transport in Single-Wall Nanotubes Thushari Jayasekera, Pavan Pillalamarri, J.W. Mintmire, Vincent Meunier Existing ballistic models for electron transport in single wall nanotube systems will break down as the size of the device becomes longer than the phase coherence length of electrons in the system. V. Krstic, \textit{et al.} observed experimentally that the current in a SWNT system can be regarded as a combination of a coherent part and a non-coherent part. We analyze this problem in detail following Buttiker's dephasing model. We investigate the effect of phase-breaking events on the electron transport in two-terminal single wall carbon nanotube systems, and discuss about more possible applications. [Preview Abstract] |
Wednesday, March 12, 2008 12:03PM - 12:15PM |
Q30.00005: Local Gating in Carbon Nanotubes Joseph Sulpizio, Charis Quay, David Goldhaber-Gordon Single Wall Carbon Nanotubes (SWNTs) exhibit a host of remarkable physical properties. Their unique electronic structure suggests that SWNTs are ideal for studying the rich physics of one-dimensional (1D) quantum systems. Local gating enables the creation of tunable structures where such phenomena can be experimentally studied. We have fabricated locally-gated SWNT devices and have performed low-temperature electronic transport measurements. We present our recent data and discuss the results in the context of 1D mesoscopic systems. [Preview Abstract] |
Wednesday, March 12, 2008 12:15PM - 12:27PM |
Q30.00006: Distinguishing the mechanisms of transistor-like switching in single-walled carbon nanotubes (SWCNTs) Steven Hunt, Brett Goldsmith, Philip G. Collins One of four mechanisms usually dominates the conductance switching of SWCNTs in field effect transistor geometries. In semiconducting SWCNTs, both the bandstructure and the Schottky barriers present at the SWCNT-electrode interface are sensitive to local electric fields. Disorder, too, leads to field sensitivity through SWCNT-SWCNT junctions and SWCNT defect sites. These four mechanisms can be distinguished by scanning gate microscopy, in which the local gating characteristics of interfaces, defects, and pristine sidewall can each be independently measured. We will demonstrate this separation and, in particular, focus on the gate sensitivity of sidewall defects produced by point functionalization. Scanning gate microscopy of SWCNTs before and after chemical attack allows us to visualize the electronic contributions of localized disorder and rank its contribution to three-terminal device characteristics. [Preview Abstract] |
Wednesday, March 12, 2008 12:27PM - 12:39PM |
Q30.00007: Probing Vapor Phase Analytes with Single Walled Carbon Nanotube Biopolymer Hybrid Devices. Samuel Khamis, Michelle Chen, A.T. Charlie Johnson Covalent and non-covalent functionalization schemes have been investigated in order to tune the chemical affinity of Single Walled Carbon Nanotube (SWNT) Field Effect Transistors (FET's). Non- covalent means are preferable since they have minimal impact on the electronic structure of pristine nanotubes. We present work involving the non-covalent adsorption of both ss-DNA and ss-RNA strands to SWNT FET's in order to obtain a class of devices that respond electrically to the presence of gaseous odors. ~We present a database representing measurements of hundreds of such devices, involving ten different sequences of ss-DNA, two different sequences of ss-RNA, and five different chemical vapors. We show that these responses are determined by the sequence of the adsorbed species of biopolymer, and we explore the performance limits of these devices. [Preview Abstract] |
Wednesday, March 12, 2008 12:39PM - 12:51PM |
Q30.00008: Selective Chemical Functionalization for the Fabrication of Single-Walled Carbon Nanotube Devices George Tulevski, Ali Afzali, Phaedon Avouris, James Hannon Single-Walled Carbon Nanotubes (SWCNTs) have attracted enormous interest due to their excellent electronic properties. The integration of SWCNTs into technologically relevant architectures is limited by the processing techniques available to address numerous integration challenges such as selective placement, doping and separation by electronic type. This talk will focus on using chemical methods to address the separation challenge by selectively functionalizing the metallic SWCNTs to fabricate field-affect transistors consisting of multiple SWCNTs. The process begins with a large-scale, low-loss purification of SWCNTs using a density step-gradient to allow for characterization of SWCNTs in large quantities. Once the material is purified, functionalized diazonium salts are used to selectively react with the metallic SWCNTs. Multiple SWCNT devices are then prepared and result in dramatically improved switching behavior. Methods to exploit the selective functionalization as a means of physically separating the material will also be discussed. [Preview Abstract] |
Wednesday, March 12, 2008 12:51PM - 1:03PM |
Q30.00009: Electric Field Modulation of Thermoelectric Transport in Carbon Nanotubes and Graphene in the Quantum Transport Limit Yuri M. Zuev, Philip Kim Mesoscopic thermoelectric power (TEP) measurements of nanometer scaled graphitic systems such as single walled carbon nanotubes (SWNTs) and graphene are reported. Highly transparent electrical contact was made to SWNTs using Pd electrodes. TEP was measured in-situ using a microfabricated heater and thermometers. Electrical conduction and TEP were observed at low temperature where both quantities were modulated by the gate voltage. At low temperatures, coherent quantum electric transport was observed as the conductance displayed oscillatory Fabry-Perot type interference. Simultaneously measured TEP provided corresponding oscillatory features. Deviations of the low temperature TEP gate dependence from the semiclassical Mott relation allows us to gain insight into the quantum transport regime in this one dimensional conductor. We compare these results with TEP measurements of the two dimensional graphitic conductor, graphene. [Preview Abstract] |
Wednesday, March 12, 2008 1:03PM - 1:15PM |
Q30.00010: Thermal Conductivity of Single-Wall and Multi-Wall Carbon Nanotubes Nihar Pradhan, Huanan Duan, Jianyu Liang, Germano Iannacchione One-dimensional materials, such as nanotubes, and their composites attract interest due to their potential use in applications as well as model systems for understanding low-dimensional physics. There is a need for detailed measurements of the specific heat ($c_p$) and thermal conductivity ($\kappa$) in order to guide theoretical efforts. This talk presents $c_p$ and $\kappa$ using an ac-calorimetric technique for single-wall (SW) and multi-wall (MW) carbon nanotubes (CNT) in a composite sample+cell arrangement. From $300$ to $400$~K, $c_p$ exhibits a linear behavior for both nanotubes. However, $\kappa$ for MWCNT and SWCNT with the heat flow perpendicular to the nanotube long-axis is bulk-like in behavior until $\approx 370$~K, thereafter decreasing with increasing temperature, indicating the onset of phonon-phonon scattering. For samples where the heat flow is parallel to the nanotube long-axis, $\kappa$ for the MWCNT sample is consistent with ballistic phonon transport. [Preview Abstract] |
Wednesday, March 12, 2008 1:15PM - 1:27PM |
Q30.00011: Efficient excitation energy transfer in single-walled carbon nanotube/porphyrin complexes John P. Casey, Sergei M. Bachilo, R. Bruce Weisman A novel method for generating single-walled carbon nanotube (SWNT) excited states by energy transfer from porphyrin molecules is presented. Addition of SWNTs to a series of micelle suspended porphyrins results in efficient quenching of porphyrin fluorescence. Analysis of concentration-dependent porphyrin quenching reveals that intermolecular energy transfer is associated with complex formation. Two-dimensional excitation/emission spectroscopy demonstrates that photoexcitation of porphyrin absorption bands results in characteristic near-IR SWNT photoluminescence. The porphyrin/SWNT hybrid displays significantly shifted absorption and emission transitions as a result of strong electronic coupling between these two pi-conjugated systems. These interactions allow controllable tuning of SWNT transition energies. Complexation of SWNTs with organic photosensitizing molecules provides uniform excitation of a wide range of nanotube species in polydisperse samples using a convenient single excitation wavelength. [Preview Abstract] |
Wednesday, March 12, 2008 1:27PM - 1:39PM |
Q30.00012: Heat Treatments In Situ and Noise Reduction in Metallic Single-Walled Carbon Nanotubes (SWCNTs) Alexander Kane, Philip Collins As fabricated, small diameter metallic SWCNTs have anomalously high contact resistances and noise amplitudes. High temperature treatments have been found to decrease both the resistance and noise through undetermined mechanisms. This work investigates this high temperature processing through in situ measurements in a UHV environment, focusing on small metallic SWCNTs contacted by Ti, Pt, or Pd electrodes. The role of the contact resistance and contaminants in the device fluctuations or noise is studied. The two mechanisms affect device noise differently, with the net effect that room temperature noise decreases can be more than proportional to resistance decreases. Annealing temperatures for improving device performance are determined for all three contact metals. [Preview Abstract] |
Wednesday, March 12, 2008 1:39PM - 1:51PM |
Q30.00013: Dependence of the Raman G' band intensity on metallicity of single-wall carbon nanotubes Ki Kang Kim, Jin Sung Park, Sung Jin Kim, Hong Zhang Geng, Kay Hyeok An, Cheol-Min Yang, Kentaro Sato, Riichiro Saito, Young Hee Lee We report the peculiar behavior of the G'-band Raman intensity, which is dependent on the metallicity of single-wall carbon nanotubes (SWCNTs). In the metallic SWCNTs, the G'-band intensity was enhanced relative to the G-band intensity, while the G'-band intensity was suppressed in the semiconducting SWCNTs. Resonance Raman spectroscopy (using laser energies of E$_{laser }$= 2.41 eV, 1.96 eV, 1.58 eV, and 1.165 eV) showed these features on the metal-enriched and semiconducting-enriched SWCNTs samples that had been selectively separated by the nitronium ions. The metallicity dependence was explained theoretically by calculating the resonance Raman intensity within the extended tight-binding calculations. The calculated results confirm that the G'-band intensity of the metallic SWCNTs is stronger than that for the semiconducting SWCNTs because the electron-phonon matrix elements for the TO phonon at the K point is larger for metallic SWCNTs and the resonance window for E$_{33}^{S}$ is larger than that for E$_{11}^{M}$. [Preview Abstract] |
Wednesday, March 12, 2008 1:51PM - 2:03PM |
Q30.00014: Stability of finite single-walled carbon nanotubes adsorbed on Si(001) Walter Orellana The stability and bonding properties of capped single-walled carbon nanotubes (CNTs) adsorbed on the Si(001) surface are studied using ab initio methods. Supercell calculations of finite CNTs on surface avoid the commensurability condition that an infinite CNT-surface system requires, providing a realistic description of bond formations. We consider capped armchair (5,5) and zigzag (9,0) CNTs with lengths of about 24~\AA, adsorbed parallel and perpendicular to the Si-dimer direction of Si(001). At the equilibrium geometry we observe the formation of C-Si covalent bonds throughout the CNT-surface interface with binding energies ranging from 0.4 to 0.6~eV per C-Si bond. These bonds only form when nearest-neighbor C and Si atoms are closer than 2.15~\AA. Our results show a preferential direction for the CNT adsorption along the Si dimers, where the zigzag CNT is find to be the most stable. We also find that the stability of the adsorbed CNTs depends to a major extend on the C-Si bond length instead of the numbers of bonds throughout the nanotube-surface interface. [Preview Abstract] |
Wednesday, March 12, 2008 2:03PM - 2:15PM |
Q30.00015: Brownian Dynamics Simulations of Single-Wall Carbon Nanotube (SWNT) Separation by Type using Dielectrophoresis Manuel J. Mendes, Noe Alvarez, Howard Schmidt, Matteo Pasquali We theoretically investigate the separation of individualized metallic and semiconducting SWNTs in a dielectrophoretic (DEP) flow device. The SWNTs motion is simulated by a Brownian Dynamics (BD) algorithm including the translational and rotational effects of hydrodynamic, Brownian, dielectrophoretic, and electrophoretic forces. The device geometry is chosen to be a coaxial cylinder, because it yields effective flow throughput, and all fields can be described analytically. We construct a flow-DEP phase map, showing different regimes depending on the relative magnitudes of the forces in play. The BD code is combined with an optimization algorithm that searches for the conditions which maximize the separation performance. The optimization results show that a 99{\%} performance can be achieved with typical SWNT parameters by operating in a region of the phase map where metallic SWNTs orient with the electric field, whereas the semiconducting SWNTs flow align. We show spectroscopic measurements of experimental tests which demonstrate metallic vs. semiconductor separation at frequencies in the MHz range. These results reveal crucial knowledge on the influence of the surfactant on the SWNTs effective conductivity. [Preview Abstract] |
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