magnetic nanostructures f. j. himpsel, dept. of physics, uw-madison
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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 - PowerPoint PPT PresentationTRANSCRIPT
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
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
In pursuit of the ultimate storage medium
1 Atom per Bit
Writing a Zero
Before
After
Filling all Sites
Natural Occupancy:
50%
After Si Evaporation:
100%
Smaller Bits Less Energy Stored Slower Readout
Use Highly-Parallel Readout
Array of Scanning Probes Array of Shift Registers
( Millipede, IBM Zrich ) ( nm m )
50 nm 10 nm particle
Magnetic Storage Media
600nm
17 Gbits/inch2 commercial
Hundreds of particles per bit
Single particle per bit !
Magnetic ForceMicroscopeImage (IBM)
Perfect Magnetic Particles
Sun, Murray , Weller, Folks, Moser,
Science 287, 1989 (2000)
FePt
Giant Magnetoresistance:
Spin-Polarized Tunneling:
Magnetoelectronics
Spin Currents instead of
Charge Currents
Filtering mechanisms
• Interface: Spin-dependent Reflectivity Quantum Well States
• Bulk: Spin-dependent Mean Free Path Magnetic Doping
Parallel Spin Filters Resistance Low
Opposing Spin Filters Resistance High
GMR and Spin - Dependent Scattering
Minority spins discrete,Majority spins continuous
Spin-polarized Quantum Well States
High Resolution Photoemission
States near the Fermi level
determine magneto-transport
( 3.5 kT = 90 meV )
-10
-8
-6
-4
-2
0
2
4
XK
Ni
En
erg
y R
ela
tiv
e t
o E
F [
eV
]
0.7 0.9 1.1
k|| along [011] [Å-1 ]
Magnetic Doping
Magnetic Impurity Selects Spin Carrier
Fe doped
Why Silicon ? Couple Nano- to MicroelectronicsUtilize Silicon Technology
Storage Media: 1 Particle (Atom) per BitAtomically Precise Tracks
Step Arrays as Templates: 2 - 80 nm
1 Kink in 20 000 Atoms
Emulate Lithography: CaF2 Masks Selective Deposition
Atomic Wires: Exotic Electrons in 1D
One-Dimensional Structures on Silicon
Si(111) 77
Control the step spacing
in units of
2.3 nm = 7 atom rows
Step Step
x - Derivative of the STM Topography
“Illumination from the Left Casting Shadows”
Stepped Silicon
Template
1 Kink in
20 000 Atoms
15 nm
Si(557) Regular Step Spacing
5.73 nm
77 Unit + Triple Step
Si(557)
= 17 Atomic Rows
Stepped Silicon Templates
80 nm15 nm6 nm
triple single bunched
Tobacco Mosaic Virus
CaF2 Mask Selective Adsorption
DPP Molecule
Selective Deposition
via Photolysis of Ferrocene
Troughs converted to Fe wires
Clean Si(557)
+ Gold
Decoration of Steps Atomic Wires2 nm6 nm
Si(557) - Au
Hole Holon + Spinon
EF
Photoelectron
Spin - Charge Separation
in a One-Dimensional Metal
Zacher, Arrigoni, Hanke, and Schrieffer, PRB 57, 6379 (1998)
Spinon
Holon
EF =
Crossing at EF
Si(557)-Au
• Splitting persists at EF
• Electron count is even
Not spin charge separation
EFermi
Two degenerate orbitals ?
Bonding
Antibonding
E2E1
Tailoring the Electronic Structure
Electron count even,
two bands, metallic
Electron count odd,
one band, “gap”
stepped flat
Si(111) - Au
http://uw.physics.wisc.edu/~himpsel