Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U31: Nanotubes, Experiment |
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Sponsoring Units: DCMP Chair: Chris Kendziora, Naval Research Laboratory Room: Baltimore Convention Center 328 |
Thursday, March 16, 2006 8:00AM - 8:12AM |
U31.00001: Controlled Dielectrophoretic Positioning of Carbon Nanotubes Sarbajit Banerjee, Brian White, Limin Huang, Stephen O'Brien, Irving Herman Single-walled carbon nanotubes have been dielectrophoretically aligned between micropatterned electrodes. Use of a limiting resistor enables control over the number of carbon nanotubes deposited in the electrode gap. Further, the electric field between micropatterned electrodes can be perturbed by arrays of metal nanostructures. Simulating electric fields in the presence of metal objects allows us to design electrodes with arrays of metal dots for the precise positioning of nanotubes. Complex network structures can be fabricated using carefully placed metal nanostructures and also by varying the electrode geometry. Crossed-junction nanotube structures have been controllably fabricated by optimization of the electrode geometry, applied electric field, and load resistor. The dielectrophoretically aligned nanotube structures work as functional field-effect transistors. Several approaches to improving the contact resistances will be discussed. The work is supported by the NSEC program of the National Science Foundation under NSF Award Number CHE-0117752 and by NYSTAR. [Preview Abstract] |
Thursday, March 16, 2006 8:12AM - 8:24AM |
U31.00002: Tuning the electrical and mechanical properties of carbon nanotubes interfaced with silicon surfaces using the UHV-STM Peter Albrecht, Joseph Lyding Nanoscale patterning of the Si(100)-2x1:H surface with the UHV-STM [1] is used to selectively modify the Si substrate acting as a semiconducting support for isolated single-walled carbon nanotubes (SWNTs) deposited via dry contact transfer (DCT) [2]. By desorbing H at the SWNT-Si interface, we can mechanically stabilize SWNTs that initially were only weakly coupled to the Si surface and thus highly sensitive to STM tip induced perturbations. Moreover, on the degenerately doped n-type H-Si(100) surface, the presence of negatively charged Si dangling ponds patterned in close proximity to a semiconducting SWNT decreases the magnitude of the substrate voltage required for the onset of filled states conduction through the SWNT. Our results suggest new opportunities for engineering -- on the sub-nm scale -- both the mechanical and electronic properties of SWNTs integrated with semiconductor platforms. [1] J.W. Lyding et al., APL 64, 2010 (1994). [2] P.M. Albrecht and J.W. Lyding, APL 83, 5029 (2003). [Preview Abstract] |
Thursday, March 16, 2006 8:24AM - 8:36AM |
U31.00003: Effect of doping on electro-optical properties of thin carbon nanotube membranes Matthew Garrett, Ilia Ivanov, Bin Zhao, Alex Puretzky, David Geohegan Nanotube membranes can prove to be a practical alternative to the current transparent conductors, such as ITO, that are in touch screen displays and photovoltaic devices. ITO with a transmittance of 80{\%} in the visible spectrum has a resistance of 10ohms/square. Similar transmittance could be obtained only with very thin membranes with nanotube loadings below the percolation threshold and would have very high resistance. Doping of membranes changes transmittance at the S11 and S22 transitions of semiconducting nanotubes, but does not change the transmission in the visible spectrum, while decreasing the resistance. Membranes of different thicknesses have been produced and characterized. Post-production doping of the membranes has been achieved and the change in resistance and in transmission spectrum has been examined. We will discuss effect of donor and acceptor dopants on the conductivity and transmittance of the nanotube membranes. [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 8:48AM |
U31.00004: Environmental Manipulation of the Electronic Structure of Suspended Carbon Nanotubes A.G. Walsh, Y. Yin, A.N. Vamivakas, S.B. Cronin, M. Tinkham, M.S. Unlu, B.B. Goldberg, A.K. Swan We use tunable resonant Raman spectroscopy to study the effect of changing the dielectric environment on the electronic structure of single wall carbon nanotubes (CNTs) suspended over trenches. The 1D nature of CNTs is responsible for weak intrinsic screening and large Coulomb interactions are anticipated. Two-photon absorption experiments have determined the presence of excitons with large binding energies.[1,2] Therefore, modulation of the surrounding dielectric constant significantly alters the strength of the Coulomb interactions and leads to changes in the exciton binding energy and band-gap renormalization which should be evident in the resulting spectra.[3] Until recently, CNTs were primarily studied in bulk, in suspensions, or coated in surfactants. We measure resonance excitation profiles (REPs) from individual suspended CNTs where the intensity of the Raman peak is plotted vs. excitation energy. We vary the humidity and monitor the shift of the REP peak of the radial breathing mode and the G-Band. We thereby directly measure the relative shift of the renormalized band-edge and exciton binding energy as a function of dielectric constant. [1] Wang, Science, 308, 838 (2005). [2] Maultzsch, arXiv, 0505150 (2005). [3] Perebeinos, PRL, 92, 257402 (2004). [Preview Abstract] |
Thursday, March 16, 2006 8:48AM - 9:00AM |
U31.00005: Capacitance measurements of individual carbon nanotubes Luke A. K. Donev, Shahal Ilani, Paul L. McEuen We present measurements of the capacitance of individual single walled carbon nanotubes. The nanotubes were grown from ethylene at 700$^{\circ}$C using evaporated iron nanoclusters as the catalyst. Electrical contacts and local top gates were patterned using optical lithography and liftoff. The top gate consists of a thin oxide film ($\sim $15 nm, different oxides have been used) covering the nanotube with metal on top. The capacitance was measured between the nanotube and the top gate using a commercially available capacitance bridge. We also measure the transport through the tube and correlate the transport and capacitance measurements. For semiconducting tubes, we measure the difference in capacitance between the conducting state and the state where the charge carriers in the tube are depleted. The measured capacitance per unit length of the nanotube is in reasonable agreement with the geometric capacitance of a metal wire embedded in oxide near a conducting plane. [Preview Abstract] |
Thursday, March 16, 2006 9:00AM - 9:12AM |
U31.00006: Electrical Characterization of Y-junction Carbon Nanotubes of Fish-bone Structure Y. Sun, J. I. Oh, S. Chen, D. Z. Wang, K. Kempa, Z. F. Ren, W. Z. Li, M. J. Naughton Y-junction carbon nanotubes (YCNTs) of fish-bone structure, synthesized by the pyrolysis of methane over cobalt supported on magnesium oxide [1], have been characterized by means of electrical transport measurements. We report both 2- and 4-probe I-V characteristics of YCNTs down to $T$ = 3 K and up to $B$ = 8 T. At 3 K, we found that change in magnetoresistance was about 0.5 {\%} at 8 T, perhaps due to piezoeffect of YCNTs. Also, we report the piezoresistivity of YCNTs directly obtained by an \textit{in situ} STM incorporated into TEM. This piezoresistivity appeared to be substantially bigger than that of straight fish-bone CNTs. In addition, we fabricated some FET-shaped samples with YCNTs whose all 3 branches were contacted by Ti/Au electrodes. We found that there is no rectifying behavior in the fish-bone junctions unlike in similar YCNTs reported in [2]. [1] W. Z. Li, J. G. Wen, Z. F. Ren, Appl. Phys. Lett. \textbf{79}, 1879 (2001). [2] P. R. Bandaru, C. Daraio, S. Jin, A. M. Rao, Nature Mats. \textbf{4}, 663 (2005). [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U31.00007: Resonant Raman spectroscopy analysis of single wall carbon nanotubes treated with high density plasma of different gases. David Mast, Chaminda Jayasinghe, Zhandos Utegulov Single wall carbon nanotubes (SWNTs) have been plasma treated with different gases (Ar, O$_{2}$ and Ar and H$_{2}$ gases mixtures) using an inductively coupled RF plasma system (IC-RFP). The gas pressure was varied from 50mtorr to 315mtorr at 50W plasma power. Microscopic plasma parameters including ion density (n$_{i})$ and electron temperature (T$_{e})$ (thermal energy of electrons) were been determined using a double Langmiur probe in the plasma. Treated SWNTs was been characterized using resonance Raman spectroscopy at 515nm and 633nm laser excitation. It was observed that there was a considerable increase of the D to G-band ratio of treated SWNTs with increasing gas pressures and also that the Breit-Wigner-Fano band (G$_{BWF})$ to G$^{+}$-band ratio was been considerably increased. Further, at 515nm laser excitation the frequency up-shift of the G-band for Ar {\&}(5{\%}) H$_{ 2}$ (gas mixture) plasma treated SWNTs was higher at all pressures than those of other gases. [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 9:36AM |
U31.00008: Measurements of 1/f Noise in Carbon Nanotube Devices Masa Ishigami, W. X. Yan, J.H. Chen, M. S. Fuhrer, E. D. Williams We have measured the low frequency noise of field effect transistors made from individual single-walled carbon nanotubes in an ultra high vacuum environment. We will compare Hooge’s constants measured in oxygen, argon, air, and ultra high vacuum, and propose a possible solution for reducing noise in nanotube devices. Furthermore, the utility of noise amplitude in carbon nanotube devices for chemical specific sensing will be discussed. [Preview Abstract] |
Thursday, March 16, 2006 9:36AM - 9:48AM |
U31.00009: Temperature dependence of mean free length of electrons in single walled carbon nanotubes Meninder Purewal, Aniruddh Ravi, Byung Hee Hong, Joshua Small, Bhupesh Chandra, James Hone, Philip Kim We have measured how single walled carbon nanotube resistance scales with channel length. Multiple two-terminal devices of varying source-drain separation are fabricated on isolated ultra-long ($>$1 mm) SWNTs grown by chemical vapor deposition. Pd electrodes provide low resistance contacts to the SWNTs. The resistance of SWNT devices are investigated in length scales ranging from 100 nm to 200 $\mu $m, from which the 1-dimensional resistivity is extracted. The temperature dependence of the electron mean free path obtained from the resistivity values indicate that in the majority of metallic SWNT devices the electron transport is ballistic up to $\sim $ 500 nm at room temperature and $\sim $ 10 $\mu $m at 1.6K. [Preview Abstract] |
Thursday, March 16, 2006 9:48AM - 10:00AM |
U31.00010: Field Enhanced Thermionic Electron Emission from Oxide Coated Carbon Nanotubes Christopher Day, Feng Jin, Yan Liu, Scott Little We have created a novel nanostructure by coating carbon nanotubes with a thin functional oxide layer. The structure was fabricated by sputter deposition of a thin film of oxide materials on aligned carbon nanotubes, which were grown on a tungsten substrate with plasma enhanced chemical vapor deposition. This structure combines the low work function of the oxide coating with a high field enhancement factor introduced by carbon nanotubes and we have demonstrated that it can be used as a highly efficient electron source. A field enhancement factor as high as 2000 was observed and thermionic electron emission current at least an order of magnitude higher than the emission from a conventional oxide cathode was obtained. [Preview Abstract] |
Thursday, March 16, 2006 10:00AM - 10:12AM |
U31.00011: Low-temperature conductive tip scanning measurements of single walled carbon nanotubes. Matthew Prior, Alexander Makarovski, Alexei Zhukov, Gleb Finkelstein We have built a low-temperature atomic force microscope (AFM) that fits inside a 38 mm bore cryostat. The scanning probe is attached to a quartz tuning fork, and a frequency shift is used as the feedback signal. By using a conductive tip we can locally tunnel into single walled carbon nanotubes grown on a non-conducting (SiO2) substrate. The nanotubes are contacted by a metal grid *electrode* evaporated on top of the sample. The tip is used as a second, movable contact. We measure the nanotube conduction as a function of the tip position and the gate voltage. [Preview Abstract] |
Thursday, March 16, 2006 10:12AM - 10:24AM |
U31.00012: Local Density of States in Nanoscale Systems Measured by Electrostatic Force Microscopy Cristian Staii, Douglas R. Strachan, Dawn A. Bonnell, Alan T. Johnson, Jonathan E. Spanier We use Electrostatic Force Microscopy (EFM) to measure the local density of states (LDOS) in carbon nanotubes and semiconducting nanowires. A voltage biased EFM cantilever, driven at its resonant frequency is used to perturb the local charge density in these systems. The recorded change in the oscillation phase is proportional to the LDOS of the sample. We monitor the phase change as a function of both the tip voltage and cantilever oscillation amplitude for a fixed cantilever position above the sample. We also show that this is a general electrostatic method that can be used to measure the band gap and LDOS of both conducting and insulating nanoscale systems with no need for electrical contacts. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U31.00013: Nanotorsional Actuator Devices Built on Individual Singlewall Carbon Nanotubes A. R. Hall, M. R. Falvo, R. Superfine, S. Washburn Nanoelecromechnical devices have been fabricated comprising an individual singlewall carbon nanotube as a torsional spring for a fully suspended, lithographed metal platform. The torsional properties of the structure were measured through electrostatic deflections. We discuss the mechanical properties of the oscillator and the electrical response of the nanotube during deflections. [Preview Abstract] |
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