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by Sara Rothwell Mentor : Bin Liu Advisor: Prof. Dravid August 12, 2008

Nanopatterning of Multiferroic Oxides via “Soft” Electron Beam Lithography. by Sara Rothwell Mentor : Bin Liu Advisor: Prof. Dravid August 12, 2008. VPD Group. NU ANCE Center. Outline. Research questions What are multiferroics? Summer work What is e BL? Results so far… Future work

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by Sara Rothwell Mentor : Bin Liu Advisor: Prof. Dravid August 12, 2008

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  1. Nanopatterning of Multiferroic Oxides via “Soft” Electron Beam Lithography by Sara Rothwell Mentor:Bin Liu Advisor: Prof. Dravid August 12, 2008 VPD Group NUANCE Center

  2. Outline • Research questions • What are multiferroics? • Summer work • What is eBL? • Results so far… • Future work Research questions • Can we create nano-scale multiferroic structures in which ferroelectric and ferromagnetic properties are connected at room temperature? VPD Group NUANCE Center

  3. Multiferroic ceramics • Materials with: • Coupled electric, magnetic and structural order parameters • Simultaneous ferroic properties (i.e. ferroelectric, ferromagnetic, or ferroelastic). • Future applications: • Data storage, communications, sensors, resonators, power control devices… 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 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 • Incorporate magnetic ions into a ferroelectric lattice. O2- Mn3+ Ho3+ VPD Group NUANCE Center

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

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

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

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

  9. BaTiO3 doped with magnetic ions: Mn peaks <112> <211> <111> Dark Orange: 10% Mn Orange: 5% Mn Gold: 1% Mn <200> <202> <220> <201> <210> VPD Group NUANCE Center

  10. Si Substrate Dark Green: 10% Co Green: 1% Co Si Substrate Si Substrate ? Lime: 1% CoFe2O4 Green: 20% CoFe2O4 Dark Green and Indigo: 50% CoFe2O4 Si Substrate ? BTO <101> XRD thin film spectra • Thin films were too thin (10 nm – 50 nm) • Sample size was too small • Samples had too many disconnected grains VPD Group NUANCE Center

  11. XRD Results • CoFe2O4 mixtures: • Peaks are from CoFe2O4 and BaTiO3 spectra, which suggests there are two separate phases mixed together • Will use EDS to verify two separate phases • 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 BaTiO3 lattice • Growth in background intensity with concentration suggests defects increase with concentration Possible double phase multiferroic Possible single phase multiferroic VPD Group NUANCE Center

  12. Multiferroic Applications: Nanostructures • 500 nm dots • 50% CoFe2O4 on silicon substrate VPD Group NUANCE Center

  13. Future Work • In the next two weeks: • Pattern SrTiO3 substrate with dots of CoFe2O4 sol-gel mixtures • Look for epitaxial growth of single crystal dots • Investigate properties of nano-dots using PFM and MFM • 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

  14. Acknowledgements • Bin Liu • Saranya • Prof. Dravid • Prof. Carsello • J. Wang et al. Science299 (2003) 1719. • R. Ramesh; N. Spaldin. Nature Materials 6 (2007) 23. VPD Group NUANCE Center

  15. BaTiO3 doped with magnetic ions: Co peaks VPD Group NUANCE Center

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