Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Y30: Nanowires and Nanotubes: Fundamentals and Applications |
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Sponsoring Units: DCMP Chair: Ezequiel Johnston-Halperin, Ohio State University Room: C147/154 |
Friday, March 25, 2011 8:00AM - 8:12AM |
Y30.00001: Apparent Power-Law Behavior of Conductance in Disordered Quasi-One-Dimensional Systems Aleksandr Rodin, Michael Fogler Observation of power-law dependence of conductance on temperature and voltage has been reported for a wide variety of low-dimensional systems(nano-wires, nano-tubes, and conducting polymers). This behavior has been attributed to the Luttinger liquid effects expected in a pure one-dimensional wire. However, the systems studied were neither one-dimensional nor defect-free. Using numerical simulations we show that the power-law behavior can arise from variable-range hopping in an ensemble of non-interacting disordered wires connected in parallel. This power-law behavior holds in restricted ranges of voltage and temperature, typical of experimental situations. Physically, it comes from rare, but highly conducting hopping paths that appear by chance in some members of the ensemble. The power-law exponents and their dependence on system parameters are consistent with the great majority of available empirical data. [Preview Abstract] |
Friday, March 25, 2011 8:12AM - 8:24AM |
Y30.00002: Equilibration of a One-Dimensional Wigner Crystal K.A. Matveev, A.V. Andreev, M. Pustilnik Equilibration of a one-dimensional system of interacting electrons requires processes that change the numbers of left- and right-moving particles. At low temperatures such processes are strongly suppressed, resulting in slow relaxation towards equilibrium. We study this phenomenon in the case of spinless electrons with strong long-range repulsion, when the electrons form a one-dimensional Wigner crystal. We find the relaxation rate by accounting for the umklapp scattering of phonons in the crystal. For the integrable model of particles with inverse-square repulsion, the relaxation rate vanishes. We apply our results to calculation of the correction to the conductance of a long quantum wire due to the equilibration processes. [Preview Abstract] |
Friday, March 25, 2011 8:24AM - 8:36AM |
Y30.00003: STM images of carbon-nanotube quantum dots: Seeing a Wigner molecule of correlated electrons Andrea Secchi, Massimo Rontani The paradigm of few-electron complexes in quantum dots (QDs) relies on the idea that the lowest quantized levels are filled according to Pauli's exclusion principle. If Coulomb repulsion is sufficiently strong to overcome the kinetic energy cost of localization, a different scenario is predicted: a ``Wigner'' molecule (WM) forms, made of electrons frozen in space according to a geometrical pattern. Despite considerable experimental effort, evidence of the WM in semiconductor QDs has been elusive so far. Here we demonstrate theoretically that WMs occur in gate-defined QDs embedded in typical semiconducting carbon nanotubes (CNTs). The unambiguous signatures of the WM state must be searched in the scanning tunneling microscopy (STM) images of the electrons. Through exact diagonalisation (ED) calculations, we unveil the inherent features of the electron molecular states. We show that, like nuclei in a usual molecule, electrons have localized wave functions and hence negligible exchange interactions. ED results for single and double QDs provide a simple interpretation for transport experiments in ultraclean CNTs. [Preview Abstract] |
Friday, March 25, 2011 8:36AM - 8:48AM |
Y30.00004: All-Semiconducting nanotube networks Thin Film Transistors: An insight towards High Performance Printed Nanoelectronics Dheeraj Jain, Nima Rouhi, Katayoun Zand, Peter Burke In this work, we present our progress towards devices fabrication using all semiconducting nanotubes as the starting material. A critical issue is the ink formulation and dependence of electronic properties on the nanotube density after deposition. These are some of the first spin-on, all semiconducting nanotube devices ever made and initial results are quite promising for printed RF electronics. Semiconducting single-walled nanotube (99{\%}) ink was used to deposit nanotube network on APTES modified Si/SiO$_{2}$ substrate. Following the nanotube deposition, source and drain electrodes (Pd/Au) were deposited using standard photolithography and E-beam evaporation. The Si wafer was used for back gating and SiO$_{2}$ as the gate dielectric. The impact of density of nanotube was studied for 3 random densities. We also studied the effect of gate length on mobility, and on/off ratio, for devices with different gate lengths (10$\sim $100 $\mu $m). DC characterization of devices shows a high mobility, up to 40 cm$^{2}$/V-s, and good on/off ratio up to the order of 10$^{4}$ in some cases. Since we are using 99{\%} semiconducting ink, a high on/off ratio is expected, which is true in our devices. The on/off ratio of more than 1000 and mobilities up to $\sim $40 cm$^{2}$/V-s were observed in almost all devices. [Preview Abstract] |
Friday, March 25, 2011 8:48AM - 9:00AM |
Y30.00005: Spin-valley blockade and electron valley resonance in carbon-based quantum dots Guido Burkard, Andras Palyi The spin blockade effect in the electric conduction through two semiconductor quantum dots connected in series has allowed the monitoring of spin-breaking effects, notably single-spin rotations induced via external fields in electron spin resonance (ESR) and spin decoherence due to the hyperfine coupling to the nuclear spin environment. Electrons in double quantum dots in carbon nanotubes and graphene comprise a valley isospin in addition to their spin. We show that this can lead to a spin-valley blockade which is sensitive to both spin and valley breaking effects. The hyperfine interaction due to residual $^{13}C$ nuclear spins turns out to be both spin- and valley-breaking, while non-magnetic atomic impurities can lead to pure valley-breaking. We study the magnetic-field dependent leakage current in the spin-valley blockade, also taking into account the spin-orbit interaction in carbon nanotubes. In analogy to ESR, we propose a resonance effect for the valley isospin (electron valley resonance) driven by an oscillatory electric field in a graphene or carbon nanotube quantum dot. References: A. Palyi and G. Burkard, Phys. Rev. B 80, 201404 (2009); Phys. Rev. B 82, 155424 (2010); arXiv: 1010.4338 (2010). [Preview Abstract] |
Friday, March 25, 2011 9:00AM - 9:12AM |
Y30.00006: Single tube electric transport properties of synthesized Titania nanotubes Mohamed Abdelmoula, Latika Menon Titania nanotube arrays fabricated by means of electrochemical anodization is currently the main interest of several research groups due to its promising applications. The high aspect ratio, durability, cheap and scalable fabrication technique make it highly attractive material for efficient solar cell. In this regard extensive research work is being carried out to investigate its properties. In our previous work we were able to find a mechanism for separating a single titania nanotube from the titania nanotube arrays and to measure its electric transport properties using e-beam lithography technique, In this work we investigated the effect of thermal annealing on the transport properties, we studied the effect of different annealing temperatures, heating and cooling rates, and in different gases. As a result, we were able to find the optimal annealing conditions to enhance the transport properties in blank titania nanotube. Under these optimal conditions, we were able to study the effect of coating TNTs with N719 dye and gold nanoparticles on the transport properties. As a result of our work we were able to optimize the treatments for more efficient solar cell fabrication. [Preview Abstract] |
Friday, March 25, 2011 9:12AM - 9:24AM |
Y30.00007: Computer Simulated Cold Welding of Gold Nanowires Edison da Silva, Zenner Pereira Recently cold welding was achieved in gold and silver nanowires (NWs) with diameters in the range of 4 to 10 nm [1]. Since metallic contacts are of great importance in electronic devices, the ability of welding them without temperature change is quite remarkable and of interest. In the present work we use computer simulations to produce cold welding in gold NWs at room temperature. We used molecular dynamics with many body effective potentials based on the embedded-atom method EAM using the LAMMPS code to simulate first the braking of gold NWs, the two produced NWs are then cold welded and similarly as the experiments, the newly welded NWs showed fcc structures as the pristine samples. The structural analysis is done with two independent methods [2] and strain stress curves of the breaking and welding are present. Our computer simulation compare very well with the experiments. \\[4pt] [1] Y. Lu, \textit{et al}. Nature Nanotechnology 5, 218 - 224 (2010) \\[0pt] [2] E. Z. da Silva and Z.S. Pereira, Phys. Rev. B \textbf{81}, 195417 (2010). [Preview Abstract] |
Friday, March 25, 2011 9:24AM - 9:36AM |
Y30.00008: Nanowire FET as a measurement tool: A method for distiguishing molecular configurations using Debye Screening effect Aleksandar Vacic, Jason Criscione, Nitin Rajan, Tarek Fahmy, Mark Reed Silicon nanowires/nanoribbons configured as field effect transistors (FETs) with receptor modified surface can be utilized for sensing of charged biomolecular species due to surface potential modulation upon receptor-ligand binding. However, charged ionic species of the sensing buffers interfere with a sensing process by lowering the effective charge of the bound molecules sensed by an FET. In this work, we exploit the Debye screening effect on the device signal by modulating the ionic strength of the sensing buffer i.e. the Debye length, to distinguish between the different configurations of the receptor-ligand complex. We compare our experimental data with a theoretical model and are able to extract characteristic length parameters of the receptor-ligand system. We will discuss the use of the suggested method for the sensing of conformational changes of biomolecules. References Sorensen M. H., Mortensen N. A., Brandbyge M., Appl. Phys. Lett. 91, 102105 (2007) Stern E., Vacic A., Rajan N. K., et al. Nature Nanotechnology 5, 138 (2010) [Preview Abstract] |
Friday, March 25, 2011 9:36AM - 9:48AM |
Y30.00009: Silicene Nano-Ribbons: Strong Resistance Towards Oxidation due to sp$^{2}$ Hybridization of the Si Valence Orbitals Guy Le Lay, Paola De Padova, Claudio Quaresima, Bruno Olivieri, Paolo Perfetti We have synthesized for the first time silicene, that is, a new silicon allotrope analogous to graphene recently theoretically predicted [1], in the form of a massively parallel array of quantized zigzag nano-ribbons with a common ``magic'' width of 1.6 nm. They display characteristic linear band dispersions similar to the Dirac cones of graphene, in correspondence with their hexagonal arrangement seen in STM imaging [2]. Here we show, through the angle-dependence of REEL spectra taken at the Si L$_{2,3}$ edge, the typical signatures of 2p $\to \quad \pi $* and 2p $\to \quad \sigma $* transitions associated with sp$^{2}$ hybridization of the Si valence orbitals. We further show through high-resolution synchrotron radiation Si 2p core-level spectroscopy measurements that the afore mentioned silicene grating is very resistant toward oxidation. Typically, the oxygen uptake starts at about 10$^{4}$ higher doses than on the clean Si(111)7x7 surface. Indeed, this striking behavior is directly related to the sp$^{2}$ bonding, an additional confirmation of the silicene (i.e., graphene-like) nature of the nano-ribbons. \\[4pt] [1] S. Cahangorov et al., Phys. Rev. Lett., \textbf{102}, 236804 (2009). \\[0pt] [2] P. De Padova et al., Appl. Phys. Lett. \textbf{96}, 261905 (2010). [Preview Abstract] |
Friday, March 25, 2011 9:48AM - 10:00AM |
Y30.00010: Low- Temperature Magneto-conductance In Carbon Nano-tubes Yuichi Ochiai, Atsuro Seino, Michio Kida, Nobuyuki Aoki, Takeshi Nakanishi, Jonathan Bird Angular dependent magneto-resistance (MR) has been studied in Multi- walled carbon nano-tubes (MWNTs). In case of thin MWNTs, the flux cancelation has been observed in the low temperature MR. Based on the theoretical studies on the scattering behaviors in the carbon nano-tube (CNT) and flux cancelation in one dimensional transport in CNT, we can analyze an intrinsic carrier scattering based on our MR result of the angular dependence between the angle of thin MWNT axis in parallel and perpendicular directions to the magnetic fields. Also, we can discuss on the positive MR appeared in the perpendicular field direction into the thin MWNT axis. [Preview Abstract] |
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