Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B26: Focus Session: Nanotubes and Nanowires: Synthesis and Properties of Nanowires |
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Sponsoring Units: DMP Chair: Grace Jia Lu, University of California-Irvine Room: LACC 501B |
Monday, March 21, 2005 11:15AM - 11:51AM |
B26.00001: Semiconducting and piezoelectric nanoarchitectures of ZnO Invited Speaker: Zhong Lin Wang ZnO is a semiconducting and piezoelectric material. The structure of ZnO can be described as a number of alternating planes composed of tetrahedrally coordinated O$^{2-}$ and Zn$^{2+}$ ions, stacked alternatively along the $c$-axis. The oppositely charged ions produce positively charged (0001)-Zn and negatively charged (000-1)-O polar surfaces, resulting in a normal dipole moment and spontaneous polarization along the $c$-axis. We have synthesized a series of novel nanostructures of ZnO utilizing the effect from the polar surface [1-4]e. The piezoelectric coefficient of a piezoelectric nanobelt has been found to be almost tripled compared to the value of the bulk [5], clearly indicating the exciting applications of piezoelectric ZnO nanobelts for nano-scale electromechanical coupled sensors, transducers, switches and resonators. This presentation will focus on the growth mechanisms and potential applications of piezoelectric nanobelts, nanorings and nanosprings. \newline \newline [1] Z.W. Pan, Z.R. Dai and Z.L. Wang, \textit{Science}, 209 (2001) 1947. [2] X.Y. Kong and Z.L. Wang, \textit{Nano Letters}, 2 (2003) 1625 + cover. [3] Z.L. Wang, X.Y. Kong and J.M. Zuo, \textit{Phys. Rev. Letts}. 91 (2003) 185502. [4] X.Y. Kong, Y. Ding, R.S. Yang, Z.L. Wang, Science, 303 (2004) 1348. [5] M. Zhao, Z.L. Wang, S. X.Mao, Nano Letters, 4 (2004) 587. [6] For details please visit http://www.nanoscience.gatech.edu/zlwang/ [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B26.00002: Magnetoresistive La$_{0.67}$Sr$_{0.33}$MnO$_3$ Nanowires Chao Li, Bo Lei, Chongwu Zhou We report the synthesis of novel La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) nanowires and the observations of intriguing magnetoresistance phenomena. These nanowires were synthesized by depositing an epitaxial shell of LSMO onto MgO nanowires, thereby rendering single-crystalline MgO/LSMO core-shell structures. Transport studies on these nanowires have revealed a remarkable metal-insulator transition at 325 k, accompanied by room-temperature colossal magnetoresistance $\sim $ 10{\%} under a one-Tesla magnetic field. In addition, anisotropic magnetoresistance was observed at room temperature with a 1.4{\%} resistance variation between magnetic fields parallel and perpendicular to the nanowire. Furthermore, polycrystalline LSMO have been obtained by tuning the synthesis condition, leading to a low-field magnetoresistance up to 16 {\%} at 0.06 T. This is attributed to the spin-dependent scattering of polarized electrons at the grain boundaries, with underlying physics similar to the giant magnetoresistance. Our study demonstrates the advantages of one-dimensional magnetic oxide nanowires and may lead to novel applications in the near future. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B26.00003: Magnetite (Fe$_3$O$_4$) Core-Shell Nanowires and Nanotubes: Synthesis and Magnetoresistance Daihua Zhang, Zuqin Liu, Song Han, Chao Li, Bo Lei, Chongwu Zhou Single crystalline magnetite (Fe$_{3}$O$_{4})$ core-shell nanowires and nanotubes have been successfully synthesized using pulsed laser deposition and selective chemical etching techniques. The material composition and stoichoimetric ratio have been carefully examined and confirmed with a variety of characterization techniques. These novel structures have rendered unique opportunities to investigate the transport behavior and spintronic property of Fe$_{3}$O$_{4}$ in its one-dimensional form. Room temperature magnetoresistance of $\sim $1.2{\%} was observed in the as synthesized nanowires under a magnetic field of B = 1.8 T, which has been accounted for the tunneling of spin-polarized electrons across the anti-phase boundaries. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:27PM |
B26.00004: CoZnO diluted magnetic semiconductor nanowires Hao Zhou, Song Han, Tao Tang, Daihua Zhang, Zuqin Liu, Chongwu Zhou We have synthesized a family of cobalt-doped ZnO nanowires using pulsed laser deposition technique, with single-crystalline ZnO nanowires synthesized following the vapor-liquid-solid approach and used as templates. These nanowires are typically 5- 10 micrometers in length and tens of nanometers in diameter. X-ray diffraction was employed to confirm that the doped cobalt atoms replaced the zinc atoms and the lattice constant decreased with increasing cobalt concentration. Electronic transport measurements were performed with individual CoZnO nanowire devices under various magnetic fields and temperatures, and revealed clear semiconductive and magnetic properties. Our experiment opens a new window in the synthesis of low dimensional diluted magnetic semiconductor materials. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 12:39PM |
B26.00005: High Performance Ge/Si Core/Shell Nanowire Transistors with High-k Dielectrics Jie Xiang, Wei Lu, Yue Wu, Charles Lieber The growth of semiconductor heterostructures provides the opportunity to improve dramatically transport properties through band structure engineering. In particular, we have observed hole gas formation and confinement in the intrinsic germanium core of epitaxial Ge/Si core/shell nanowire heterostructures. In this talk, we demonstrate the integration of high-k dielectrics with high performance Ge/Si core/shell nanowire field effect transistors. The high-k dielectrics were deposited via atomic layer deposition process, followed by e-beam lithography of local top gates. With this technique, we have obtained a transconductance among the highest in semiconducting nanowire transistors. We have also investigated the transconductance and subthreshold slopes as a function of channel length and temperature to elucidate carrier screening inside the nanowire and oxide/nanowire interface properties. Prospects for integrated ballistic nanowire field-effect transistors will be discussed. [Preview Abstract] |
Monday, March 21, 2005 12:39PM - 12:51PM |
B26.00006: Si nanowire FET arrays: nano-scale logic and electron transport Ezekiel Johnston-Halperin, J.E. Green, R.A. Beckman, B.A. Sheriff, K. Beverly, A. Boukai, Y. Luo, J.R. Heath In the drive to develop an alternative to conventional CMOS-based computing there are a number of technical and scientific hurdles. Reducing individual device size, while critical, will provide limited gains unless concurrent issues such as device pitch and power dissipation are also addressed. Here, we present an integrated scheme for the fabrication of nano-scale circuits that has the potential to integrate logic, memory, and routing at narrow device pitch within a fault-tolerant architecture. The platform for our approach is based on the SNAP technique, which allows for the fabrication of both metal and semiconducting nanowire arrays at 35 nm pitch, aspect ratios of 10$^{6}$, and wire widths down to 10 nm. Using this process, we are able to fabricate arrays of nano-FETs whose size (100 nm by 10 nm) and spacing (35 nm pitch) allow for dramatically reduced circuit densities (down to $\sim $ 10$^{11}$ elements/cm$^{2})$. We present characterization of these arrays as well as the demonstration of a number of implementations including logic arrays and multiplexing. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B26.00007: Electrolyte gating and the charge sensitivity measurements on Si nanowire transistors Jiwoong Park, Yeonghwan Ahn, James Dunning Nanoscale semiconductors can be used as a sensitive charge detector in water because their electrical conductance is strongly affected by the local charge distribution. Here we report conductance measurements on a charge sensor fabricated using individual Si nanowires (SiNWs) with a typical diameter of 20 nm in aqueous environment. First, the conductance of SiNWs was measured with an electrolyte gate. They show good sensor characteristics such as a large transconductance, subthreshold voltage swing and a much reduced noise level. Then a lipid bilayer membrane with different electrical charges and fluorescent dyes were deposited onto the device and manipulated using electric fields and fluorescence quenching while the SiNW conductance was monitored. The DC and AC conductance of SiNWs displays systematic changes according to the polarity and density of electrical charges on the membrane. The sensitivity and temporal resolution of SiNW sensors can be quantitatively decided based on this result. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B26.00008: Surface passivation and high-k dielectrics in Si nano-FETs Jonathan E. Green, E. Johnston-Halperin, K. Beverly, R.A. Beckman, B.A. Sheriff, Y. Luo, J.R. Heath Scaling limitations in contemporary ULSI/VLSI technology have sparked an intense effort to seek alternatives to conventional CMOS-based computing. While much of this effort has consisted of attempts to reduce device size, a more appropriate figure of merit for a scalable architecture is device density. Accordingly, issues such as device pitch and power consumption are also relevant. We have previously demonstrated that SNAP nanowire arrays can simultaneously address both device size (down to 10 nm by 100 nm) and density (pitch down to 35 nm) through the generation of arrays of Si nanowire FETs. However, the concurrent issue of power consumption remains a significant technical problem. One route to increased efficiency is the use of high-k dielectrics (such as HfO$_{2})$ and careful control of the nanowire-dielectric interface. To that end, we explore the impact of various surface passivation schemes, dielectrics, and crystal orientations on SNAP-based nano-FET performance. [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:27PM |
B26.00009: Scanning Photoconductivity Measurements on Silicon Nanowire FETs Yeonghwan Ahn, James Dunning, Jiwoong Park Optical studies on single nanowires have been of great interest thanks to their potential applications in nanoscale optoelectronics. Here we report optical scanning measurements on photoconductivity of individual Si nanowires (SiNWs) that are fabricated using CVD-grown SiNWs with diameters of 20-30 nm. Their conductance was then monitored while a laser beam (532 nm) was focused on them and raster-scanned by a conventional optical scanning microscope setup. We observe increases in the conductance for more than two orders of magnitude (light intensity $\sim $ 10 kW/cm$^ {2})$ and large polarization anisotropy of 0.9, making the SiNW FET a polarization sensitive, nm-sized light detector. In addition, scanning images of photocurrent at various biases reveal the local energy band profile especially near the electrode contacts. The magnitude and polarity of the photocurrent change depending on gate bias, which can be explained using the depletion band flattening and the conduction mode change in SiNWs. Our results demonstrate that this technique is a powerful tool for studying photo-sensitive nanoscale devices. [Preview Abstract] |
Monday, March 21, 2005 1:27PM - 1:39PM |
B26.00010: Optical Properties of Ge Nanowires Grown on Silicon (100) and (111) Substrates: Nanowire-substrate Heterointerfaces Leonid Tsybeskov, Boris Kamenev, Varun Sharma, Theodore Kamins We report Raman scattering (RS) and photoluminescence (PL) measurements of (111) oriented Ge nanowires (NWs) grown by chemical vapor deposition on (100) and (111) silicon substrates. PL measurements strongly suggest that the observed high internal quantum efficiency emission originates at low-defect density Ge NW -- Si substrate interfaces. A higher level of Si-Ge intermixing and strain has been detected for the Ge NW - (111) Si interface, while NWs grown on (100) Si substrates are relaxed. [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 1:51PM |
B26.00011: InAs Nanowire Josephson Field Effect Transistors Y.-J. Doh, J.A. van Dam, L.P. Kouwenhoven, S. De Franceschi, A.L. Roest, E.P.A.M. Bakkers We have fabricated superconducting nano-junctions using InAs nanowires contacted with Al superconducting electrodes. The diameter of nanowire is about 70 nm with source-drain spacing of 200 nm. Low Ohmic metallic contacts are formed at the interface with typical $R_{N}A$ value of $3\times 10^{-7}$ $\Omega$ cm$^{2}$. Below the superconducting transition temperature $T_{C} =1.1$ K, the devices show clear conductance enhancements below the superconducting gap $2\Delta_{0} = 210$ $\mu$eV, which is explained by multiple Andreev reflection. Near zero-bias voltage, conductance diverges to show supercurrent in V(I) curve. Maximum critical current is about $I_{C} = 130$ nA at T = 30 mK with $I_{C}R_{N}$ product of 60 $\mu$V. Irradiated with microwave, constant voltage plateaus are observed satisfying ac Josephson relation. By applying back-gate voltage, critical currents are suppressed to be zero near pinch-off gate voltage $V_{g}$ = -70 V. Universal conductance fluctuations of nanowire and its corresponding critical current fluctuations are discussed from the viewpoint of truly mesoscopic Josephson field effect transistors. [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B26.00012: Electric Transport in MoSe molecular Nanowires Latha Venkataraman, Yeon Suk Hong, Philip Kim We present results from transport measurements on a new system of metallic one-dimensional (1D) conductors, molybdenum selenide (MoSe) molecular nanowires. These nanowires forms bundles of electrically identical MoSe chains and offer a system in which to investigate charge transport in weakly interacting multiple transport channels. Electrical transport has been measured on small bundles of nanowires whose diameter ranges from 2-16 nm. The measured two-terminal conductance of these wires shows power-law dependence with respect to temperature and bias voltage. The exponents governing the power law dependence are found to vary inversely with wire diameter, which determines the number of conducting channels in the bundles of wires. In addition, the estimated Luttinger Liquid interaction parameter is found to be smaller than that of carbon nanotubes implying stronger repulsive electron-electron interaction in this system. [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B26.00013: Space Radiation Resiliency of Carbon Nanotube and Semiconductor Nanowire Based Nanocircuits Benjamin Jacobs, Mark Englund, Virginia Ayres, Reg Ronningen, Al Zeller, Harry Shaw, Jeanette Benavides, Mihail Petkov, Joshua Halpern, Alan Kogut, Martin Crimp With increasing need for radiation resilient space electronics for the next generation satellites and probes, new materials and electronics utilizing these materials must be examined. We present results of carbon nanotube and gallium nitride nanowire which underwent heavy ion in the form of 86Krypton as well as total ionization dose radiation. Electronic characteristics of the circuits before and after irradiation were taken as well as during radiation. Heavy ion and total dose irradiation of the raw materials, nanotubes and nanowires, and electrospun carbon nanofibers was irradiated as a control. Scanning, transmission, high resolution transmission and atomic force microscopy and Raman spectroscopy of materials was taken. [Preview Abstract] |
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