Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D32: Focus Session: Controlled Self Assembly and Growth |
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Sponsoring Units: DMP Chair: Hung-Chih Kan, National Chung-Cheng University Room: E142 |
Monday, March 15, 2010 2:30PM - 2:42PM |
D32.00001: Interface Modulation Lithography: Construction of Nanoscale Optical Components by Thermocapillary Forces Mathias Dietzel, Sandra Troian Conventional patterning of nanoscale devices relies on optical projection techniques whose resolution is set by the Rayleigh diffraction criterion. While feature sizes in the sub-100 nm are now possible, this technique is inherently 2D, requires multiple exposure cycles for generating disparate feature sizes, and is limited to flat substrates. Here we discuss development of a new, truly 3D lithographic technique based on control of thermocapillary forces, which is suitable for construction of isolated or collective arrays of optical elements such as planar waveguides or ring resonators. Finite element simulations based on actual experimental systems demonstrate how implementation of various thermal gradient maps can be used to shape and mold nanoscale polymeric films into complex 3D shapes, on demand and in a single step. These simulations provide guiding principles for achieving submicron feature size and pitch while minimizing proximity effects. The simplicity and inherent low cost of this technique, its adaptability to curved substrates, and the variety of thermal distributions possible provides an interesting new method of nanoscale fabrication based on modulation of surface shape. [Preview Abstract] |
Monday, March 15, 2010 2:42PM - 2:54PM |
D32.00002: ABSTRACT WITHDRAWN |
Monday, March 15, 2010 2:54PM - 3:06PM |
D32.00003: Growth of ZnBeMgO films by pulsed laser deposition Neeraj Panwar, Jose Liriano, Venkata S. Puli, Ram S. Katiyar Band gap tailoring of ZnO with Be and Mg co-doping has proven important for the fabrication of a UV detector. For this purpose the deposition of good quality thin films is very essential. We have deposited Zn $_{1-x-y}$Be$_{x}$Mg$_{y}$O (x=0, 0.10; y=0, 0.10, 0.20) films on sapphire substrate by pulsed laser deposition. The films were deposited using a KrF excimer laser ($\lambda $ = 248nm) with 250 mJ energy and repetition rate of 10Hz at a substrate temperature of 650\r{ }C and O$_{2}$ partial pressure 2mTorr. The films were further annealed at 800\r{ }C for 30 min with 200Torr O$_{2}$ pressure. X-ray diffraction studies revealed the polycrystalline nature of the films. For the band gap calculation, UV measurements were carried out and a blueshift was noticed. The cutoff wavelength for the pristine ZnO film was 370 nm which decreased to 240 nm for 10{\%}Be and 20{\%}Mg co-doped film. This value of Zn$_{0.7}$Be$_{0.1}$Mg$_{0.2}$O film lies in the solar blind region and should be useful for the fabrication of solar blind UV detector. Other studies like morphological, Raman and I-V characteristics of these films are in process and will be presented in the meeting. [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:18PM |
D32.00004: Reversible switching of surface texture by hydrogen intercalation Thomas Greber, Thomas Brugger, Haifeng Ma, Marcella Iannuzzi, Simon Berner, Adolf Winkler, J\"urg Hutter, J\"urg Osterwalder The interaction of atomic hydrogen with a single layer of hexagonal boron nitride on rhodium [1] leads to a removal of the $h$-BN surface corrugation within the 3\, nm unit cell. The process is reversible as the hydrogen may be expelled by annealing to about 500\, K whereupon the nano-texture is restored. This effect is traced back to hydrogen intercalation. It is expected to have implications for applications, like the storage of hydrogen, the peeling of sp$^2$-hybridized layers from solid substrates or the control of the wetting angle, to name a few.\\[4pt] [1] Boron Nitride Nanomesh, Corso et al. Science, 303 (2004) 217. [Preview Abstract] |
Monday, March 15, 2010 3:18PM - 3:30PM |
D32.00005: Growth of Single Crystal Fe$_{1-x}$Ga$_{x}$ Thin Films Adam McClure, Paul Rugheimer, H. Li, Y.U. Idzerda Fe$_{1-x}$Ga$_{x}$ alloys are of recent interest because of their magnetostrictive properties. In bulk form these materials display cubic magnetic anisotropy. We have grown single-crystal thin films of Fe$_{1-x}$Ga$_{x}$ of various alloy concentrations using Molecular Beam Epitaxy (MBE). We find that the films display either a conventional (bulk-like) cubic magnetic anisotropy or a uniaxial anisotropy on top of an underlying cubic anisotropy. A Gallium dependent uniaxial anisotropy is introduced by growing the films on GaAs(001) or ZnSe/GaAs(001) substrates. Alternatively, films which show purely cubic magnetic anisotropy have been produced by growing the films on MgO(001) substrates. Thin film Fe$_{1-x}$Ga$_{x}$ alloys can be grown with much higher content of Gallium than bulk while preserving BCC crystal structure. Reflection High Energy Electron Diffraction (RHEED) performed during growth as well as post-growth magnetic anisotropy measurements will be discussed. Growth parameters and a mechanism for the observed uniaxial anisotropy that is consistent with each of the substrates used will be discussed. [Preview Abstract] |
Monday, March 15, 2010 3:30PM - 3:42PM |
D32.00006: Real time growth of bismuth teluride thin films investigated by LEEM Hongwen Liu, N. Fukui, L. Zhang, J.F. Jia, M.W. Chen, T. Hashizume, T. Sakurai, Q.-K. Xue Narrow gap semiconductors such as Bi$_{2}$Te$_{3}$ and Bi$_{2}$Se$_{3}$ have long been considered traditional thermoelectric materials. The very recent discovery of gapless metallic states at their surface characterizes them as a new class of quantum matter, the so-called topological insulators (TIs). To date, the TI materials have mainly been prepared in the form of crystals using melt-growth and suffer from unwanted bulk carriers or extrinsic dopants. In order to overcome this problem, efforts have been made to grow TI thin films. In this work, we use a low energy electron microscope (LEEM), which can reveal film growth processes in real time, to investigate the growth dynamics of Bi$_{2}$Te$_{3}$ films Combined with atomic force microscopy and Raman spectroscopy, we discuss the optimal conditions to obtain high quality Bi$_{2}$Te$_{3}$ films on several substrates. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 3:54PM |
D32.00007: MBE-grown Nd:Y$_x$Al$_y$O solid state laser crystals: Compositional control leading to films of the primary phases YAG, YAP and YAM Raveen Kumaran, Scott Webster, Shawn Penson, Wei Li, Tom Tiedje Solid state laser crystals with planar waveguide geometry are useful for making compact and efficient integrated laser devices. Among the techniques for growing thin film laser crystals, molecular beam epitaxy offers better compositional control due to independently operated elemental sources. By varying the growth temperature and flux ratios of Y, Al and O$_2$, we have grown all the primary phases in the ternary yttrium aluminum oxide system: Y$_3$Al$_5$O$_{12}$ (YAG), YAlO$_3$ (YAP) and Y$_4$Al$_2$O$_9$ (YAM). The films were doped with Nd to make them optically active and the resulting emission spectra consisted of peaks unique to the surrounding host material. The emission spectra were similar to those from bulk crystals indicating that the films were single phase. The Nd emission was also useful for verifying structural and compositional characterization results from x-ray diffraction and x-ray photoelectron spectroscopy. Among the 3 phases, Nd:YAG is the most widely used laser material, with a wavelength corresponding to the strong emission peak at 1064nm. [Preview Abstract] |
Monday, March 15, 2010 3:54PM - 4:06PM |
D32.00008: Surprises in the PLD of LaAlO$_{3}$: non-stoichiometric transfer of material from target to film T.C. Droubay, L. Qiao, M.H. Engelhard, T.C. Kaspar, V. Shutthanandan, S.A. Chambers Despite being composed from two band insulators, the LaAlO$_{3}$/SrTiO$_{3}$(001) interface has been of significant interest due to its electrical conductivity. The conductive interface has been explained as resulting from charge transfer from polar LAO to non-polar STO. Most investigations into this interface have used pulsed laser deposition (PLD) as the deposition method. Contrary to popular assumptions, however, ablation from a LAO target does not necessarily produce congruent (stoichiometric) transfer of material from target to substrate. To determine the atom distribution within the laser plume from an LAO target, films were collected on stationary 2'' Si wafers held at room temperature to eliminate re-evaporation and minimize lateral diffusion. The film composition was then analyzed using both x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). Regardless of the gas pressure in the chamber, we find that the La:Al atom ratio varies as a function of angle in the plane formed by the laser axis and target normal. The La/Al atom ratio peaks at $\sim $1.6 in the on-axis position and approaches unity at a plume angle of 26 off-normal. This ratio is only minimally impacted by the kinetic energy of the ablation species. Growths of epitaxial LAO on STO(001) at 700 \r{ }C reveal a similar trend. These results have significant implications for the mechanism of conductivity of LAO/STO grown by PLD. [Preview Abstract] |
Monday, March 15, 2010 4:06PM - 4:18PM |
D32.00009: Carbon sweating of meta-stable ternary carbides Mikael R{\aa}sander, Erik Lewin, Biplab Sanyal, Mattias Klintenberg, Ulf Jansson, Olle Eriksson Transition metal carbides (TMC) have many attractive and unique physical properties and are nowadays used regularly in many technological applications. In thin films, the TMC can form nanocomposites where nanocrystallites of the carbide are embedded in a carbon matrix. Here we report on a new development where we have investigated meta-stable nanocomposite TMC. By substitutionally dissolving a weak carbide forming metal into a stable monocarbide, the ternary carbide system will become meta-stable and a decomposition into more stable phases will occur. We will show results obtained by density functional theory calculations of meta-stable TMC, where we have alloyed the stable monocarbide TiC with elements from the 3d transition metal series. The stability of the alloyed ternary phase decreases with the amount of alloying metal, which creates a driving force for the release of carbon from the carbide, i.e. the carbide sweats carbon. This mechanism can be controlled by careful tuning of the amount and selection of the alloying metal. These findings are supported by experimental studies on thin films of nanocomposite TMC. [Preview Abstract] |
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