Bulletin of the American Physical Society
75th Annual Meeting of the Southeastern Section of APS
Volume 53, Number 13
Thursday–Saturday, October 30–November 1 2008; Raleigh, North Carolina
Session KB: Forefront Materials Physics III |
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Chair: David Aspnes, North Carolina State University Room: Holiday Inn Brownstone Washington |
Friday, October 31, 2008 3:45PM - 4:15PM |
KB.00001: Magnetocapacitance and the physics of solid state interfaces Invited Speaker: When Herbert Kroemer stated in his Nobel address [1] that ``the interface is the device,'' he was implicitly acknowledging the importance of understanding the physics of interfaces. If interfaces are to have character traits, then ``impedance'' (or complex capacitance) would be a commonly used descriptor. In this talk I will discuss the use of magnetic fields to probe the ``character'' of a variety of interfaces including planar capacitor structures with magnetic electrodes, simple metal/semiconductor contacts (Schottky barriers) and the interface-dominated competition on microscopic length scales between ferromagnetic metallic and charge-ordered insulating phases in complex oxides. I will show that seeking experimental answers to surprisingly simple questions often leads to striking results that seriously challenge theoretical understanding. Perhaps Herbert Kroemer should have said, ``the interface is the device with a magnetic personality that continually surprises.'' \\[3pt] [1] Herbert Kroemer, ``Quasielectric fields and band offsets: teaching electron s new tricks,'' Nobel Lecture, December 8, 2000: [Preview Abstract] |
Friday, October 31, 2008 4:15PM - 4:45PM |
KB.00002: Microstructure and Transport properties of epitaxial VO$_{2}$ thin films on TiO$_{2}$ substrates Invited Speaker: Vanadium oxides are paradigms of strongly correlated oxides and have attracted attention because of the metal insulator transitions (MIT) that several of the oxides and sub-oxides exhibit. In particular, VO2 has a metal--semiconductor transition at 340 K. This transition in VO2 combines the properties of a pure Mott Hubbard electronic transition with those of a Peierls structural transition. The Mott transition is responsible for the extreme speed of the optical switching that has been observed (faster than 100 fs). Understanding this transition and how to control it remains a challenge for both theory and experimental physics. We used a novel deposition technique, Reactive Bias Target Ion Beam Deposition, to grow 40 nm epitaxial VO2 thin films on rutile TiO2 substrates with various crystal orientations. X-ray diffraction (XRD) was used to explore the epitaxy of VO2 and we found that all VO2 thin films on TiO2 substrates showed tetragonal symmetry at room temperature due to the constrain from rutile substrates. We also characterized the metal-insulator transition of VO2 films as the function of the crystal orientation of rutile TiO2. We also characterized the anisotropy of VO2 thin films. In collaboration with Kevin West and Stuart Wolf, University of Virginia. [Preview Abstract] |
Friday, October 31, 2008 4:45PM - 5:15PM |
KB.00003: A surface-driven approach to the synthesis of basic building blocks for the design of complex Si-Ge-Mn nanostructures Invited Speaker: The combination of Silicon and Germanium with Manganese is highly desirable for the development of novel spintronics devices. We will describe a surface-driven approach to the tailored synthesis of basic building blocks for the design of complex Si-Ge-Mn nanostructures. The goals are to incorporate Mn as delta-doped layers in a Si matrix, and to magnetically dope Ge-quantum dots. These processes are studied with STM and photoelectron spectroscopy. The Si(100)(2x1) surface functions as a template and Mn-nanowires are formed which run perpendicular to the Si-dimer rows. The bonding sites of the Mn-adatoms, the wire length and spatial distribution are interpreted within the framework of recent theoretical predictions. The bonding of Mn-adatoms changes with temperature: at 500 K the adatoms move into sub-surface sites, higher temperatures initiate silicide formation, which is controlled by the Si- surface atom mobility. In a next step we deposited a Ge-overlayer on the Mn-wires, and used voltage dependent STM analysis to separate the Ge and Mn contributions. In the low-adatom-mobility regime the Mn-wires are preserved. The low temperature growth therefore offers a pathway to create buried nanostructures in controlled manner. The formation of Mn-doped Ge-quantum dots is approached by the deposition of Mn on the Ge-QDs at 273 K. On both surfaces, the Ge(100) wetting layer and the Ge (105) facet of the QDs, the Mn adatoms form nanoclusters. On the Ge(105) facet the flat clusters are aligned with respect to the reconstruction, and the wetting layer surface is considerably roughenend. Annealing of the surface structures to initiate a diffusion of Mn into the Ge-QD bulk is investigated as a means to achieve local doping. However, the annealing process leads to a highly complex response which is extremely sensitive to temperature. While these processes are by no means currently understood, we will offer a first qualitative interpretation of the observed reactions. [Preview Abstract] |
Friday, October 31, 2008 5:15PM - 5:45PM |
KB.00004: Metal Clusters as Superatoms and Nanostructures Invited Speaker: Atomic nanoclusters are agglomerates of a discrete number of atoms, from a few to thousands, forming a bridge between small molecules and crystalline materials. By studying the properties of size-resolved clusters, the evolution of finite systems can be traced as a function of the precisely known number of atoms. In addition, nanoclusters can serve as model sensors and as potential building blocks for novel materials. In many metallic clusters, size-quantized electronic levels give rise to a striking shell structure pattern, akin to that of atoms and nuclei, which controls particle stabilities, shapes, and other physical and chemical properties. The talk will touch upon shell effects, collective excitations (plasmons), fast electron-hole recombination (escaping the phonon bottleneck), the determination of work functions, and the possibility of strengthened pairing. [Preview Abstract] |
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