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CONFOCAL SPECTROMICROSCOPY OF AMORPHOUS AND NANOCRYSTALLINE TUNGSTEN OXIDE FILMS

CONFOCAL SPECTROMICROSCOPY OF AMORPHOUS AND NANOCRYSTALLINE TUNGSTEN OXIDE FILMS A. Kuzmin , R. Kalendarev, A. Kursitis, J. Purans E-mail: a.kuzmin@cfi.lu.lv. NCM-10, Praha (Czech Republic), September 18-22, 2006 . State-of-the-Art.

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CONFOCAL SPECTROMICROSCOPY OF AMORPHOUS AND NANOCRYSTALLINE TUNGSTEN OXIDE FILMS

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  1. CONFOCAL SPECTROMICROSCOPY OF AMORPHOUS AND NANOCRYSTALLINE TUNGSTEN OXIDE FILMS A. Kuzmin, R. Kalendarev, A. Kursitis, J. Purans E-mail: a.kuzmin@cfi.lu.lv NCM-10, Praha (Czech Republic), September 18-22, 2006.

  2. State-of-the-Art • “Blu-ray” disks, having capacity of more than 25 GB per recording layer,use a 405 nm laser, focussed through a high numerical aperture (NA=0.8-1.0) objective lens to a spot size of about 300 nm. • The most frequently used rewritable phase change recording materials, belong to the group of semiconductor chalcogenides. • For example: ternary GeSbTe and quaternary AgInSbTe alloys. • Other materials - tungsten oxides: - a reversible photoredox reaction under two-wavelength laser excitation of tungsten oxide in air • J.M. Osman, R.J. Bussjager, F. Nash, J. Chaiken, R.M. Villarica, Appl. Phys. A 66 (1998) 223. • - heat treatment of WO3/metal thin-film bilayered structures • Y. Takeda, N. Kato, T. Fukano, A. Takeichi, T. Motohiro, S. Kawai, J. Appl. Phys. 96 (2004) 2417. • - rewritable electrically selective multi-layered optical recording disk, based on the electrochromic behaviour of WO3 • R. Sato, N. Ishii, N. Kawamura, H. Tokumaru, in: Proc. 3rd European Symp. • on Phase Change and Ovonic Sci., Balzers, Liechtenstein, September 04-07, 2004. • - write-once optical recording was demonstrated in WO2 film • T. Aoki, T. Matsushita, A. Suzuki, K. Tanabe, M. Okuda, Thin Solid Films 509 (2006) 107.

  3. Present work goal • To demonstrate the possible use of WO3 & AWO4 thin films for write-once phase change optical recording. • To propose the multilayer AWO4 phase-change media structure based on Raman scattering detection of the highest frequency stretching W-O mode.

  4. 3D scanning confocal microscope with spectrometer "Nanofinder-S" produced by SOLAR TII, Ltd. • Simultaneous / Multifunctional Analysis: • Optical and Confocal Microscopy • Raman Spectroscopy • Luminescence Spectroscopy • 0D, 1D, 2D & 3D High-speed Imaging and Spectroscopy

  5. "Nanofinder-S" modular optical layout He-Cd 441.6 nm 50 mW

  6. Commercial Compact Disk Imaging in Confocal Mode CD-ROM CD-R CD-RW Track pitch = 1.6 µm Track pitch = 1.6 µm Track pitch = 1.6 µm Images size: 2024 µm

  7. N S S N Thin Film Preparation by DC Magnetron co-Sputtering Metallic targets: W (99.95%) Ni (99.0%) Zn (99.9%) Substrates: Si, glass Sputter gas: Ar (80%) + O2 (20%) Total gas pressure: 6.7 Pa Discharge power: 100 W Sputter Gas SUBSTRATE Plasma Glow Metallic Target / Cathode Magnets

  8. W O Crystalline Structure of WO3 WO3: [WO6] Well known electrochromic material based on valence change of tungsten ions: W6+ (transparent)  W5+ (blue)

  9. Crystalline Structure of AWO4 (A = Ni, Zn ) A W O AWO4: [AO6] & [WO6] Tungstates are known as scintillators and Raman shifters.

  10. * A. Kuzmin, J. Purans, E. Cazzanelli, C. Vinegoni, G. Mariotto, J. Appl. Phys. 84 (1998) 5515. a-W6+O3 W(6-y)+ c-W6+O3 Optical Recording in t.f.-WO3 Confocal images: 274 m × 333 m 15 mW 25 mW 50 mW O-W-O stretching modes O-W-O & W=O stretching modes

  11. O-W-O stretching modes Optical Recording in t.f.-NiWO4 25 mW 50 mW 15 mW Confocal images: 134 m × 167 m 700°C * A. Kuzmin, J. Purans, R. Kalendarev, D. Pailharey, Y. Mathey, Electrochim. Acta 46 (2001) 2233.

  12. Optical Recording in t.f.-ZnWO4 O-W-O stretching modes 700°C W-O-W bending modes 50 mW

  13. W6+O3-x & AW6+O4-x (A = Ni, Zn) • Formation of metastable color centers W6+ W(6-y)+ • short term life time in air • Crystallization to WO3 / AWO4 • long term life time • good thermal stability Change in reflectivity (10-20%) Change in phase & reflectivity Multilayer phase-change media structure based on Raman scattering detection Possible Mechanismsof Optical Recording in Tungsten Oxides

  14. Raman signal 1 1,..., n Dielectric layer Dielectric layer Phase-change A1WO4-x layer Phase-change A1WO4-x layer Dielectric layer Dielectric layer ... ... n-layers n-layers Phase-change AnWO4-x layer Phase-change AnWO4-x layer Dielectric layer Dielectric layer Metallic mirror layer Metallic mirror layer Substrate Substrate Sequential Writing Parallel Reading Multilayer write-oncephase-change media structure based on Raman scattering detection AWO4 band gap ~ 3.0-3.8 eV

  15. Thank you ! For more information look at the Internet: http://www.cfi.lu.lv/exafs This work was supported by the Latvian Government Research Grants and National Research Program in Materials Science.

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