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Nanoscale Epitaxial Films of Cu 2 O 2-x An attempt to make cubic CuO Wolter Siemons

Nanoscale Epitaxial Films of Cu 2 O 2-x An attempt to make cubic CuO Wolter Siemons. MRS Spring meeting HH4.9: Novel materials Wednesday, April 19 th 2006, 4:30pm. People and funding. At Stanford University : Wolter Siemons , Gertjan Koster, Hideki Yamamoto,

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Nanoscale Epitaxial Films of Cu 2 O 2-x An attempt to make cubic CuO Wolter Siemons

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  1. Nanoscale Epitaxial Films of Cu2O2-xAn attempt to make cubic CuOWolter Siemons MRS Spring meeting HH4.9: Novel materials Wednesday, April 19th 2006, 4:30pm

  2. People and funding At Stanford University: Wolter Siemons, Gertjan Koster, Hideki Yamamoto, Bob Hammond, Ted Geballe, Paul Grant, Malcolm Beasley At University of Twente: Guus Rijnders and Dave Blank This research is funded by EPRI, DoE, and NanoNed MRS Spring meeting

  3. Motivation • Model system related to High-Tc cuprates • Expected to be 3D system, compared to the 2D planes • Increased superfluid density (raising Tc?) • Exploration of doping methods • More general: Exploration epitaxial stabilization MRS Spring meeting

  4. Material specifics • CuO (tenorite) naturally has a monoclinic unit cell • Charge transfer system (Mott-Hubbard), insulating in undoped form Growth parameters: • Grown in 10-5 Torr O2 pressure with 600 W atomic oxygen source • Various substrates at 500-600oC • Can be grown both with MBE and PLD MRS Spring meeting

  5. Proxy structure O O Cu Cu (111) CuO -Tenorite (100) CuO - MgO Average bond length: 1.92 A (Shorter than cuprates) Average bond length: 2.10 A • Stabilized Cu2O2 by epitaxy on TiO2 terminated SrTiO3 substrates MRS Spring meeting

  6. RHEED • CuO, like MgO and NiO, grows epitaxially on SrTiO3 • Grows 45 degrees rotated with respect to substrate • After critical thickness (~25-30A) structure changes to tenorite • Critical thickness depends on temperature, substrate, and oxidation conditions MRS Spring meeting

  7. X-ray Photoelectron Diffraction q Along SrTiO3 110 MRS Spring meeting

  8. Instability • Structure wants to change to tenorite structure • Taking sample out of vacuum might have this effect, and certainly does this going beyond the critical thickness MRS Spring meeting

  9. In situ XPS from Cu to CuO In situ technique to avoid degradation of the material Detailed studies of the XPS Cu 2p multiplet structure have been used to estimate the charge transfer energy (D) MRS Spring meeting

  10. XPS shifts Different chemical environment Okada and Kotani, J. Elec. Spec. and Rel. Phen. 52, 312 (1990) MRS Spring meeting

  11. Future experiments • Determine the out of plane lattice constant (through simulation of XPD) • Doping of CuO: chemical, charge transfer overlayers and field effect • Determination (with Kapitulnik and Xia) of the magnetic properties, with the help of a sagnac interferometer, by measuring Kerr rotation (could be done in situ) MRS Spring meeting

  12. Work by other groups Critical thickness and instability make it very hard to analyze the material. XRD, TEM, etc. almost impossible. Catana, Locquet, Paik, and Schuller, PRB 46, 15477 (1992) MRS Spring meeting

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