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Magnetic Nanostructures F. J. Himpsel, Dept. of Physics, UW-Madison

Magnetic Nanostructures F. J. Himpsel, Dept. of Physics, UW-Madison. Limits of Data Storage Magnetoelectronics One-Dimensional Structures on Silicon. SSSC Meeting, Irvine, Oct. 4, 2001. All of the information ... accumulated in all the books

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Magnetic Nanostructures F. J. Himpsel, Dept. of Physics, UW-Madison

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  1. Magnetic Nanostructures F. J. Himpsel, Dept. of Physics, UW-Madison • Limits of Data Storage • Magnetoelectronics • One-Dimensional Structures on Silicon SSSC Meeting, Irvine, Oct. 4, 2001

  2. All of the information ... accumulated in all the books in the world can be written … in a cube of material 1/200 inch wide. Use 125 atoms to store one bit. Richard Feynman Caltech, December 29th, 1959

  3. In pursuit of the ultimate storage medium 1 Atom per Bit

  4. Writing a Zero Before After

  5. Filling all Sites Natural Occupancy:  50% After Si Evaporation:  100%

  6. Smaller Bits  Less Energy Stored  Slower Readout Use Highly-Parallel Readout Array of Scanning Probes Array of Shift Registers ( Millipede, IBM Zrich ) ( nm m )

  7. Magnetic Storage Media 600 nm 17 Gbits/inch2 commercial Hundreds of particles per bit Single particle per bit ! Magnetic Force Microscope Image (IBM) 50 nm 10 nm particle

  8. Perfect Magnetic Particles FePt Sun, Murray , Weller, Folks, Moser, Science 287, 1989 (2000)

  9. Magnetoelectronics Spin Currents instead of Charge Currents Giant Magnetoresistance: Spin-Polarized Tunneling:

  10. GMR and Spin - Dependent Scattering Parallel Spin Filters  Resistance Low Opposing Spin Filters  Resistance High • Filtering mechanisms • Interface: Spin-dependent Reflectivity Quantum Well States • Bulk: Spin-dependent Mean Free Path  Magnetic Doping

  11. Spin-polarized Quantum Well States Minority spins discrete, Majority spins continuous

  12. High Resolution Photoemission Ni Energy Relative to EF [eV] 0.7 0.9 1.1 k|| along [011] [Å-1 ] States near the Fermi level determine magneto-transport (  3.5 kT = 90 meV )

  13. Magnetic Doping Fe doped Magnetic Impurity Selects Spin Carrier

  14. One-Dimensional Structures on Silicon • Why Silicon ?Couple Nano- to Microelectronics • Utilize Silicon Technology • Storage Media: 1 Particle (Atom) per Bit • Atomically Precise Tracks • Step Arrays as Templates:2 - 80 nm • 1 Kink in 20000 Atoms • Emulate Lithography: CaF2 Masks • Selective Deposition • Atomic Wires: Exotic Electrons in 1D

  15. Step Step Si(111) 77 Control the step spacing in units of 2.3 nm = 7 atom rows x - Derivative of the STM Topography “Illumination from the Left Casting Shadows”

  16. Stepped Silicon Template 1 Kink in 20000 Atoms 15 nm

  17. Si(557) Regular Step Spacing 5.73 nm

  18. Si(557) 77 Unit + Triple Step = 17 Atomic Rows

  19. Stepped Silicon Templates triple single bunched 6 nm 15 nm 80 nm Tobacco Mosaic Virus

  20. CaF2 Mask Selective Adsorption DPP Molecule

  21. Selective Deposition via Photolysis of Ferrocene Troughs converted to Fe wires

  22. Clean Si(557) 6 nm Decoration of Steps  Atomic Wires 2 nm + Gold

  23. Si(557) - Au

  24. Spin - Charge Separation in a One-Dimensional Metal EF = Spinon Holon Zacher, Arrigoni, Hanke, and Schrieffer, PRB 57, 6379 (1998) Photoelectron EF Hole  Holon + Spinon Crossing at EF

  25. Si(557)-Au Antibonding E1 E2 Bonding • Splitting persists at EF • Electron count is even •  Not spin charge separation EFermi Two degenerate orbitals ?

  26. Tailoring the Electronic Structure stepped flat Electron counteven, two bands, metallic Electron countodd, one band, “gap”

  27. Si(111) - Au http://uw.physics.wisc.edu/~himpsel

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