Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J26: Nanotubes and Nanowires: Applications |
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Sponsoring Units: DMP Chair: Chongwu Zhou, USC Room: LACC 501B |
Tuesday, March 22, 2005 11:15AM - 11:27AM |
J26.00001: Carbon Nanotube FETs as Chemical Sensors Jian Zhang, Anthony Boyd, Alexander Tselev, Makarand Paranjape, Paola Barbara Exposure to chemical molecules can greatly change the conductance of carbon nanotube FETs (CNFETs). The underlying sensing mechanisms may involve changes in the properties of the interface between nanotube and electrode [1], as well as the nanotube bulk response to chemical molecules [2]. We fabricate CNFETs by standard photolithographic techniques, both for catalyst and contact patterning [3], and characterize their response, i.e. changes in the threshold voltage and saturated conductance, upon exposure of the whole device to chemical molecules, such as nitrogen dioxide and ammonia. We find that nitrogen dioxide only changes the threshold voltage, whereas ammonia changes both the threshold voltage and the saturated conductance. We plan to protect the carbon-nanotube/electrode interfaces and expose only the carbon nanotube to the same concentration of chemical molecules, to measure the contribution to the response due only to the bulk of the nanotube and distinguish between different sensing mechanisms. This work is supported by the ACS (PRF-39152-G5M) and the NSF (DMR-0239721). [1] V.Derycke, R. Martel, J. Appenzeller and Ph. Avouris, Appl.Phys.Lett., 80, 2773 (2002). [2] J. Kong, etc., Science 287, 622 (2000). [3] A. Tselev, K. Hatton, M. S. Fuhrer, M. Paranjape and P. Barbara, Nanotechnology 15, 1475 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 11:27AM - 11:39AM |
J26.00002: Individual Single Wall Nanotubes for High Sensitivity Gas Detection Bhaskar Nagabhirava$^{1}$, Sharvil Desai$^{2}$, Gamini Sumanasekera$^{2}$, Alex Tchernatinsky$^{2}$, Chakram Jayanthi$^{2}$, Shi-yu Wu$^{2}$, Bruce Alphenaar$^{1}$ We report on the influence of O$_{2}$ adsorption on individual SWNTs, and show that the observed sensitivity is dramatically improved as compared with SWNT thin films or ropes. SWNTs were grown on a SiO$_{2}$ / Si substrate using chemical vapor deposition, and individual nanotubes were located and contacted with Au/Ti electrodes. The resistance of the SWNT devices was then monitored in a sealed chamber under a number of different gas environments. We observe a two order of magnitude decrease in the resistance of a SWNT device following exposure to oxygen. This is much larger than the 10-15{\%} decrease in the resistance that has been observed for SWNT ropes or mats. Theoretical analysis suggests that the O$_{2}$ molecules provide acceptor impurity states to the nanotubes, which shift the Fermi energy towards the valence band. The resulting increase in positive charge carriers leads to the observed conductance increase. We also observe that the resistance of the SWNT decreases substantially when exposed to inorganic vapors, leading to the possibility of using the nanotube device for gas sensing applications. \textit{Supported by the NSF (DMR-0112824 and ECS-0224114), the DoE (DE-FG02-00ER45832), NASA (NCC5-571) and the US Army SMDC (W9113M-04-C-0024)}. [Preview Abstract] |
Tuesday, March 22, 2005 11:39AM - 11:51AM |
J26.00003: Effects of molecular adsorption on electron transport properties of carbon nanotubes Moonsub Shim Highly sensitive response of semiconducting single-walled carbon naotubes (SWNTs) to molecular adsorption provides a simple yet efficient direction in exploiting their unique electrical properties. For example, simultaneous doping and nearly ideal gate efficiencies are achieved with polymer electrolytes. However, highly sensitive responses can also lead to difficulties in interpretation of many observations such as the controversy surrounding whether oxygen adsorption causes doping or changes in the nature of SWNT-metal contacts. Effects of molecular adsorption from oxygen in the ambient surrounding to polymers with varying chemical groups on the electrical properties of SWNTs will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:03PM |
J26.00004: Detection of supported lipid bilayers with carbon nanotube transistors Xinjian Zhou, Jose Moran-Mirabal, Harold Craighead, Paul McEuen Supported lipid bilayers are important synthetic structures that can be used to mimic and study the properties and functions of cellular membranes, as well as to perform various bioassays which involve membrane bound receptors. The fusion of phospholipid vesicles and formation of a supported lipid bilayer can be detected in real time with high sensitivity by carbon nanotube field effect transistors which have been patterned on the same substrate. The properties of different vesicles, such as fusion rates and phospholipid composition can be distinguished by the conductance change of carbon nanotube field effect transistors. Fluorescence is used to verify the formation of a supported lipid bilayer, although the detection scheme is label-free. This demonstrates that electrical detection with carbon nanotubes can provide a powerful tool for study of lipid membranes. [Preview Abstract] |
Tuesday, March 22, 2005 12:03PM - 12:15PM |
J26.00005: Structure and morphology of carbon nanotube AFM probes fabricated by dielectrophoresis Jie Tang, Guang Yang, Qi Zhang, Ben Maynor, Jie Liu, Lu-Chang Qin, Otto Zhou Carbon nanotube probes with diameter of 1$\sim $100 nm and large aspect ratios have been demonstrated both theoretically and experimentally that they are quasi-one-dimensional solids with many unique electronic and mechanical properties. We have recently demonstrated the feasibility of fabricating carbon nanotube AFM probes by a solution based dielectrophoresis process. CNT AFM probes can be readily assembled on the apexes of commercial AFM probes with controlled and predetermined length and orientation. In this talk we discuss the effects of the structure and morphology of the cnt AFM probes, the dispersion and stability of the cnt suspension on the quality and reliability of the cnt probes fabricated. The structure and mechanical stability of the probes were also investigated. [Preview Abstract] |
Tuesday, March 22, 2005 12:15PM - 12:27PM |
J26.00006: Metal-coated carbon nanotube tips for scanning probe microscopy Erhan Yenilmez, Zhifeng Deng, Josh Leu, J.E. Hoffman, Eric Straver, Kathryn A. Moler, Hongjie Dai Metal coating has been introduced in order to improve the resolution and capabilities of carbon nanotube scanning probe microscopy tips. We demonstrate magnetic force microscopy of magnetic recording tracks using Co coated nanotube tips. The resolution achieved is better than 20 nanometers. We also use Au coated nanotube tips to perform electrostatic force microscopy of a cut single nanotube with a narrow gap. The metal coating on nanotubes is found to enable the use of micrometers long nanotubes as scanning probes for topographic imaging of high aspect ratio structures. The metal-coated nanotube tips are shown to significantly decrease the convolution effects from the pyramidal silicon tip in these force microscopy techniques. [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 12:39PM |
J26.00007: Alignment of metal-coated nanotube tips and application in AFM imaging of cells Zhifeng Deng, Erhan Yenilmez, Amy Reilein, Josh Leu, Kathryn A. Moler, Hongjie Dai We demonstrate a reliable method to precisely control the direction of metal-coated nanotubes by exposing them to Ga ions in a Focused Ion Beam. With this method, many metal-coated carbon nanotubes on AFM tips are aligned to a desired direction. Equipped with high aspect-ratio nanotube tips, which are almost perpendicular to the sample surface, we imaged basal cell membrane of polarized Madin Darby Canine Kidney cells in an AFM. Very steep (greater than 80 degree to sample surface) and high (more than 300nm) features in these images illustrate the ability to image high aspect-ratio features with well-aligned nanotube tips. [Preview Abstract] |
Tuesday, March 22, 2005 12:39PM - 12:51PM |
J26.00008: Singlewall Carbon Nanotubes as Torsional Springs in a Nanoelectromechanical Device A. R. Hall, S. J. Papadakis, M. R. Falvo, R. Superfine, S. Washburn Nanoelecromechnical devices have been fabricated that utilize 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 repeated deflection with a scanning probe tip. We discuss results of such measurements as well as progress towards high Q oscillator behavior and integrated device arrays. [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J26.00009: Growth of carbon nanofibers on tipless cantilevers: process development and applications in scanning probe microscopy Hongtao Cui, Sergei Kalinin, Xiaojing Yang, Douglas Lowndes Carbon nanofibers (CNFs) are grown on tipless cantilevers as probe tips for scanning probe microscopy. A catalyst dot pattern is formed on the surface of the tipless cantilever using electron beam lithography and CNF growth is performed in a direct-current plasma enhanced chemical vapor deposition reactor. Because the CNF is aligned with the electric field near the edge of the cantilever during growth, it is tilted with respect to the cantilever surface, which compensates partially for the probe tilt introduced when used in scanning probe microscopy. CNFs with different shapes and tip radii can be produced by variation of experimental conditions. The tip geometries of the CNF probes are defined by their catalyst particles, whose magnetic nature also imparts a capability for imaging magnetic samples. We have demonstrated their use in both atomic force and magnetic force surface imaging. These probe tips may provide information on magnetic phenomena at the nanometer scale in connection with the drive for ever-increasing storage density of magnetic hard disks. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J26.00010: Rapid and reproducible fabrication of nanotube/nanowire AFM probes by dielectrophoresis Guang Yang, Jie Tang, Qi Zhang, Ahmet Parhat, Ben Maynor, Jie Liu, Lu-Chang Qin, Otto Zhou Atomic force microscopes (AFM) are commonly used to map the surface structure and topography of different objects and devices. The resolution, sensitivity, and probing depth of an AFM depend on the geometry of the probe. Here, we demonstrate an efficient method to fabricate nanotube/nanowire based AFM tips by dielectrophoresis. Under dielectrophoretic force, the processed CNT bundles can be readily assembled to the apexes of conventional AFM tips with controlled and pre-determined length and orientation. Both the lateral resolution and probing depth have been studied. The fabrication process can also be utilized to assemble other 1-D nanostructures. The research was supported by NASA URETI on Bio Inspired Materials (NCC-1-02037). [Preview Abstract] |
Tuesday, March 22, 2005 1:15PM - 1:27PM |
J26.00011: Room temperature in-situ growth of single Ag2Ga needles on AFM tips Mehdi M. Yazdanpanah, Steven A. Harfenist, Abdelilah Safir, Robert W. Cohn We have found that single metallic nanowires can be grown in various directions, including sticking straight out from the end of a sharp (or for that matter blunt) tips, e.g. atomic force microscope (AFM) tips or even tipless AFM cantilevers. This is done by coating a silicon cantilever with a thin film of silver (with an underlying chrome flash to promote adhesion). Then the tip is dipped in a small drop of melted gallium (at or near room temperature) for 5 minutes. The tip is removed at one micron per second, and a single nanoneedle is found formed on the tip in at least 50{\%} of the experiments. Faceted nanoneedles have been formed from 1 to 20 microns in length and 45 to 300 nm in diameter. In-situ scanning electron microscopy is used to observe the growth and mechanical properties of the needles and transmission electron microscopy shows the needles to be single crystal. Contact and non-contact mode AFM imaging and voltage lithography with these needle-tipped cantilevers is reported. [Preview Abstract] |
Tuesday, March 22, 2005 1:27PM - 1:39PM |
J26.00012: Composite Nanowire-Based Probes for Magnetic Resonance Force Microscopy Mladen Barbic, Axel Scherer We will present a nanowire-based methodology for the fabrication of ultra-high sensitivity and resolution probes for atomic resolution magnetic resonance force microscopy (MRFM). The fabrication technique combines electrochemical deposition of multi-functional metals into nanoporous polycarbonate membranes and chemically selective electroless deposition of optical nanoreflector onto the nanowire. The completed composite nanowire structure contains all the required elements for ultra-high sensitivity and resolution MRFM sensor with: (a) magnetic nanowire segment providing atomic resolution magnetic field imaging gradients as well as large force gradients for high sensitivity, (b) noble metal enhanced nanowire segment providing efficient scattering cross-section from a sub-wavelength source for optical readout of nanowire vibration, and (c) non-magnetic/non-plasmonic nanowire segment providing the cantilever structure for sensitive mechanical detection of magnetic resonance. [Preview Abstract] |
Tuesday, March 22, 2005 1:39PM - 1:51PM |
J26.00013: Scanning Probe Microscopy of Semiconducting Nanowires A.C. Bleszynski, R.M. Westervelt, F.A. Zwanenburg, J.A. van Dam, S. De Franceschi, L.P. Kouwenhoven, A.L. Roest, E.P.A.M. Bakkers A liquid He cooled scanning probe microscope (SPM) with a conducting tip has been used to image conduction through InAs and InP nanowires. The nanowires, grown using a vapor-liquid-solid technique, have diameters between 50 nm and 100 nm and resistances on the order of 10 k$\Omega $. Ti/Al electrodes were defined using e-beam lithography to form source and drain contacts with a spacing of 1 to 3 $\mu $m. The charged SPM tip is scanned in an area above the nanowire; the resulting change in nanowire conductance is recorded to form the image. These conductance images are used to study the behavior of electrons in the nanowire on a local scale. [Preview Abstract] |
Tuesday, March 22, 2005 1:51PM - 2:03PM |
J26.00014: Photoconductivity, High-resolution AFM, and Scanning Conductance Microscopy of Porphyrin Nanorods Alexander D. Schwab, Lauren L. Comfort, John Iannacone, Jaclyn O'Pella, Julio C. de Paula, Walter F. Smith, Deirdre E. Smith, Danvers E. Johnston, Alan T. Johnson, James Hone We have shown$^{1}$ that the diacid form of the porphyrin tetrakis(4-sulfonatophenyl) porphine (TPPS$_{4})$ self assembles into nanorods with well-defined height and width. Upon illumination, their conductivity grows over hundreds of seconds. They also produce a zero-bias photocurrent with trainable polarity.$^{2}$ We present measurements as a function of illumination wavelength and intensity, which support a model of charge hopping along paths of previously photoionized porphyrin molecules. We also give results from Scanning Conductance Microscopy experiments; these are designed to clarify the role of the contacts in the DC measurements. Our high-resolution AFM images support the model of a hollow tube$^{3}$, which collapses on contact with the substrate. $^{1}$A.D. Schwab \textit{et al.}, J. Phys. Chem. B \textbf{107}, 11339 (2003). $^{2}$A.D. Schwab \textit{et al.}, Nano Letters \textbf{4}, 1261 (2004). $^{3}$S.C.M. Gandini, E.L. Gelamo, R. Itri, and M. Tabak, Biophys. J. \textbf{85}, 1259 (2003). [Preview Abstract] |
Tuesday, March 22, 2005 2:03PM - 2:15PM |
J26.00015: Integration of carbon nanotubes into atomic resolution UHV-STM lithography and nanofabrication schemes on H-passivated Si(100) surfaces Peter Albrecht, Joseph Lyding Nanoscale patterning of the Si(100)-2x1:H surface with the UHV-STM [1] is leveraged to chemically modify the Si substrate acting as a pristine semiconducting support for isolated single-walled carbon nanotubes (SWCNTs). By intercepting an isolated SWCNT with a sub-5-nm-wide pattern of Si dangling bonds [2], we can reproducibly strengthen the SWCNT-Si interaction which is directly manifested as an enhanced mechanical stability of the SWCNT in the presence of the rastered STM tip and a concomitant topographic depression. Spatially-resolved tunneling conductance maps have been generated for individual SWCNTs spanning both depassivated and unperturbed domains on the Si(100)-2x1:H surface. We have also demonstrated the controlled manipulation of SWCNTs with the STM tip, including the reversible actuation of a 13-nm-long segment intentionally cut from a longer SWCNT and the splitting of two SWCNTs originally in wall-to-wall contact. [1] J.W. Lyding et al., APL 64, 2010 (1994). [2] P.M. Albrecht and J.W. Lyding, Superlattice Microst. 34, 407 (2003). [Preview Abstract] |
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