Bulletin of the American Physical Society
2005 Joint Spring Meeting Ohio Section of APS and the Southern Ohio Section of AAPT
Friday–Saturday, April 8–9, 2005; Dayton, OH
Session D6: Nanotechnology |
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Chair: Michael Marciniak Room: SC 107 |
Saturday, April 9, 2005 8:00AM - 8:12AM |
D6.00001: Field Enhanced Thermionic Emission from a New Cathode Using Oxide Coated Carbon Nanotubes Feng Jin, Chris Day We report field enhanced thermionic emission from a new type of cathode based on oxide coated carbon nanotubes. This cathode consists of a metal substrate with carbon nanotubes grown on its surface using plasma enhanced chemical vapor deposition. The carbon nanotubes are further coated with thermionic emission materials (BaO, SrO, and CaO). These oxides are coated by magnetron sputter deposition and spin coating techniques. The emission current density from this cathode is at least an order of magnitude higher than from a conventional thermionic cathode coated with the same emission materials operated at the same temperature. This strong emission current is attributed to the field enhancement effect. Field enhancement is usually negligible for conventional thermionic cathodes; however, in this case the high aspect ratio of carbon nanotubes induces significant field enhanced thermionic emission. We present comparisons of some early experimental results for three different cathodes: 1) a oxide coated carbon nanotube cathode, 2) a conventional oxide cathode, and 3) an uncoated carbon nanotube cathode. [Preview Abstract] |
Saturday, April 9, 2005 8:12AM - 8:24AM |
D6.00002: Novel Gapped Quantum Wire Trinanjan Datta, Erica W. Carlson High quality state of the art quantum wires (QWRs) can be fabricated by the novel Cleaved Edge Overgrowth (CEO) technique, proposed by (Pfeiffer et al, 1990). Transverse quantization in these QWRs leads to a succession of nested energy bands. With the lowest two successive energy levels occupied, gapped phases are possible including, e.g., an intersubband charge density wave (ICDW) and a Cooper phase with strong superconducting fluctuations (Starykh et al, 2000). Due to the possibility of density reorganization, in which it becomes favorable for the two lowest subbands to match their densities, the ICDW is usually the most likely state. Recently, by exploiting the valley degeneracy in AlAs, a single QWR has been fabricated with two degenerate nonoverlapping bands separated in k space by half an Umklapp vector (Moser et al 2004). For low densities the structure is able to access a multiple subband regime that is not subject to the density reorganizing ICDW, leaving a Cooper phase to flourish. Using Abelian bosonization, we explore the relevant interaction terms for this system, including Umklapp assisted Cooper scattering and discuss the phase diagram. [Preview Abstract] |
Saturday, April 9, 2005 8:24AM - 8:36AM |
D6.00003: Fano quadrupole resonance in an Aharonov-Bohm ring Eric Hedin, Arkady Satanin, Yong Joe We examine new effects arising from the collision of Fano dipoles seen in the transmission through an Aharonov-Bohm (AB) ring. An exact solvable model is developed in which the effect of coupling between two quantum dots in one arm of the AB ring is studied. A detailed investigation of the collision of Fano dipole resonances and the formation of a unique coupled object called a Fano quadrupole is carried out. The behavior of the zeros and poles of the transmission amplitude as a function of magnetic field through the ring is investigated. To control the transmission zeros and resonances, the coupling between the quantum dots is varied. It is shown that in the weak coupling regime, the zeros of the transmission amplitude independently orbit their respective poles in the complex energy plane as a function of magnetic flux. In the strong coupling regime, the zeros are shown to move in a common orbit around both poles, indicating the formation of the coupled Fano quadrupole. We briefly discuss possible applications of these effects for the realization of a quantum transistor and the use of nano-devices for quantum computing. *Supported by the Indiana 21st Century Research and Technology Fund [Preview Abstract] |
Saturday, April 9, 2005 8:36AM - 8:48AM |
D6.00004: Scanning Probe Microscopy and Microwave Characterization of Nanostructured Ferroelectric Barium Strontium Titanate Thin-Films Fabricated by Pulsed Laser Deposition Angela Campbell, Guru Subramanyam, Rand Biggers, Bonnie Riehl A series of nanostructured ferroelectric thin-films of barium strontium titanate were fabricated using a pulsed laser deposition system with real-time in-situ process control. Pulsed laser deposition parameters were optimized for growth of tunable, low-loss nanostructured thin-films for use in the development of high frequency tunable microwave devices. Thin-films were grown at identical temperatures and energy densities as oxygen ambient pressures were varied from 19 mT through 1 T. Structural and electrical characterization were performed using contact-mode AFM and surface potential imaging. Microwave characterization was performed using coplanar waveguide lines and resonators to characterize the frequency dependent dielectric properties ($\varepsilon _{r}$ and tan $\delta )$. Contact-mode AFM showed an increase in grain size with increase in oxygen ambient pressure from 38-75 mT. Surface potential imaging demonstrated that X patterns written by applying a voltage to thin-films with an AFM tip in contact mode are electrically switchable. Microwave characterization showed that thin-films grown at 75mT oxygen partial pressure yielded the most stable films in terms of tunability and loss-tangent over a wide frequency range. [Preview Abstract] |
Saturday, April 9, 2005 8:48AM - 9:00AM |
D6.00005: Highly ordered FePd magnetic thin films Rosa Lukaszew, Cesar Clavero, Mukut Mitra, Alfonso Cebollada The study of magnetic materials constrained to very small sizes is important under both fundamental and applied points of view. One of the challenges that the magneto-recording industry currently faces is that the ever increasing demands for higher storage density is reaching fundamental limitations such as the super-paramagnetic limit (i.e. thermal fluctuations can ``flip'' the magnetization in the nano-magnets). One possibility to overcome this problem is to use nano-magnets made of materials that exhibit high magnetic anisotropy. Highly ordered L1o alloys of FePd and FePt exhibit such strong perpendicular anisotropy. We are currently studying highly ordered FePd and FePt thin films deposited on MgO substrates. We have studied the deposition conditions and post-deposition treatments that allowed us to obtain significant highly ordered phase. We will present our correlated XRD, magneto-optical as well as AFM/MFM studies on highly ordered FePd thin films. We will also show systematic studies on films of varying thickness in the 5-30 nm range. In particular we will show how different capping materials (i.e. Pd versus MgO) have an important effect on the magnetic and magneto-optical properties of the films. [Preview Abstract] |
Saturday, April 9, 2005 9:00AM - 9:12AM |
D6.00006: Numerical Simulations in Quantum-dot Cellular Automata Devices Ioan Sturzu, Travis Barclay, Mahfuza Khatun Fault tolerance simulations for Quantum-dot Cellular Automata (QCA) devices will be presented. A Full basis quantum calculation and Intercellular Hartree Approximation have been implemented using an extended Hubbard model. We have studied manufacturing as well as operational defects for wires and shift registers. Cell defects have been simulated by uniform and normal distributions. Results show temperature dependence of the breakdown displacement factor. A comparison of the results for uniform and normal distribution will be shown. [Preview Abstract] |
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