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by Sara Rothwell Mentor : Bin Liu Advisor: Prof. Dravid July 2, 2008

Nanopatterning of Multiferroic Oxides via “Soft” Electron Beam Lithography. by Sara Rothwell Mentor : Bin Liu Advisor: Prof. Dravid July 2, 2008. R. Ramesh; N. Spaldin. Nature Materials 6 (2007) 23. VPD Group. NU ANCE Center. Outline. What are multiferroics? Summer work

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by Sara Rothwell Mentor : Bin Liu Advisor: Prof. Dravid July 2, 2008

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  1. Nanopatterning of Multiferroic Oxides via “Soft” Electron Beam Lithography by Sara Rothwell Mentor:Bin Liu Advisor: Prof. Dravid July 2, 2008 R. Ramesh; N. Spaldin. Nature Materials6 (2007) 23. VPD Group NUANCE Center

  2. Outline • What are multiferroics? • Summer work • What is eBL? • Results so far… • Future work Research questions • Can we create synthetic multiferroics on the nano scale in which ferroelectric and ferromagnetic properties are connected at room temperature? • How do multiferroic properties change when patterned on the nanoscale? J. Wang et al. Science299 (2003)1721. VPD Group NUANCE Center

  3. Multiferroic ceramics Diamagnetic • Materials with: • Coupled electric, magnetic and structural order parameters • Simultaneous ferroic properties (i.e. ferroelectric, ferromagnetic, or ferroelastic). • Conflict between ferroelectric and ferromagnetic crystal structure • Future applications: • Data storage, communications, sensors, resonators, and power control devices. Ferromagnetic Anti-Ferromagnetic “Weak” or canted Ferromagnetic J. Wang et al. Science299 (2003)1721. Nan C-W; Bichurin, M.I. et al. J. Appl. Phys.103 (2008). VPD Group NUANCE Center

  4. Multiferroics cont… • Naturally occurring single phase multiferroics: BiFeO3, hexagonal HoMnO3 • BiFeO3 is ferroelectric and anti- ferromagnetic at room temperature • Possible synthetic multiferroics: • Combination of two phases: • Ferroelectric BaTiO3 and ferromagnetic Fe3O4 or CoFe2O4 combined in hetero- structures or epitaxial thin films • Magnetic phase dispersed in a ferroelectric • Dope BaTiO3 with magnetic Mn, Fe, or Co ion O2- Mn3+ Ho3+ J. Wang et al. Science299 (2003) 1719. VPD Group NUANCE Center

  5. Summer Work • Mix CoFe2O4 and BaTiO3 sol-gels in ratios • Make powder samples and thin films to find out phase content using X-ray diffraction • Make nano-dots using eBL and find properties • Dope BaTiO3 with magnetic Mn, Fe, or Co ion • Make powder samples and thin films to find out phase content using X-ray diffraction • Make nano-dots using eBL and find properties VPD Group NUANCE Center

  6. “Soft” Electron Beam Lithography Double layer of photoresist Nanopatterning of resist With electron beam Sol-gel applied to nanopatterned surface. Spin the sample to distribute sol-gel evenly Lift off photoresist Heat treatment • Advantages • Sol-gel is a low cost, room temperature fabrication method for metal oxides • Double layer creates a controlled undercut • Site specificity Tao Sun et al. Appl. Phys. Lett.89 (2006) 163117. VPD Group NUANCE Center

  7. XRD Powder Results: CoFe2O4 mixtures BTO <101> <110> Purple: 90% CoFe2O4 Blue: 50% CoFe2O4Green: 20% CoFe2O4 CFO <311> CFO <220> BTO <001> <100> BTO <112> <211> CFO <440> CFO <400> BTO <200> CFO <511> BTO <202> <220> BTO <201><210> BTO <111> CFO <422> VPD Group NUANCE Center

  8. XRD thin film: CoFe2O4 mixtures Si Substrate Si Substrate ? Lime: 1% CoFe2O4 Green: 20% CoFe2O4 Dark Green and Indigo: 50% CoFe2O4 VPD Group NUANCE Center

  9. XRD Powder Results:BaTiO3 doped with magnetic ions <001> <100> <101> <110> <111> <200> <201> <210> <112> <211> <202> <220> VPD Group NUANCE Center

  10. BaTiO3 doped with magnetic ions <112> <211> <111> <200> <202> <220> <201> <210> VPD Group NUANCE Center

  11. XRD thin film: BaTiO3 doped with Co ions Si Substrate Dark Green: 10% Co Green: 1% Co Si Substrate ? BTO <101> VPD Group NUANCE Center

  12. XRD Results • CoFe2O4 mixtures: • Peaks are from primarily CoFe2O4 and BaTiO3 spectra, which suggests there are two separate phases mixed together • Will use EDS to verify two separate phases • Possible double-phase multiferroic • BaTiO3 with magnetic ions: • Peaks are all from BaTiO3 spectrum • Peaks shift with dopant concentration indicating some change in lattice constants • Suggests full incorporation of magnetic ions into the BaTiO3 crystal lattice • Possible singe phase multiferroic VPD Group NUANCE Center

  13. Nanodots • 50% CoFe2O4 on silicon substrate • 500 nm dots VPD Group NUANCE Center

  14. Future Work • In the next two weeks: • Pattern SrTiO2 substrate with dots of CoFe2O4 sol-gel mixtures • Look for epitaxial growth of single crystal dots • Investigate properties of nano-dots using PFM • Make a sol-gel combining CoFe2O4 and BaTiO3 sources in a single sample • Find XRD powder spectra • Finish taking XRD powder spectra for CoFe2O4 mixtures • … and beyond • Use ICP to verify doped BaTiO3 composition • Use XPS to verify composition of thin films • Continue to pattern nano-structures using eBL and test magnetic and electrical properties VPD Group NUANCE Center

  15. Acknowledgements • Bin Liu • Saranya • Prof. Dravid • Prof. Carsello VPD Group NUANCE Center

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