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Yongho Seo
Center for Near-field Atom-photon technology,Seoul Nation University, Rep. of Korea
& Department of Physics, University of Virginia
Kyungho Kim, Hyunjun Jang, Wonho Jhe
School of Physics and Center for Near-field Atom-photon technology,
Seoul Nation University, Rep. of Korea
Magnetic Force Microscopy using Quartz Tuning Fork
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- Self actuating- Self sensing- No light- No alignment
- optical deflection - laser diode - photo diode - optical alignment- addition actuator
Quartz Crystal Tuning fork
Quartz Tuning Fork as a Force Sensor
Micro-machined Cantilever
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Force sensitivity (Qf/k) 1/2
f ~ 10 - 100 kHzk ~ 1 - 100 N/mQ ~ 102 ~ 10 nm dithering
f ~ 32 - 100 kHzk ~ 103 - 105 N/mQ ~ 104 (106 in vacuum)< 1 nm dithering
Cantilever Tuning Fork
Force Sensitivity of Quartz Tuning Fork
• Low force sensitivity• Low thermal noise due to high stiffness• High resolution by small dithering amplitude
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Hal Edwards, et. al. (1997) Todorovic and Schultz (1998)
Previous works : MFM using tuning fork
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f = 32.768 KHz
k = 1300 N/m
Q = 1300
f = 32.768 KHz
k = 1300 N/m
Q = 1300
Tuning Fork based Electrostatic force microscopy
-Ferroelectrics-surface charge in Semiconductor
L = 2.2 mm, t = 190 m, w = 100 m
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7 x 7 m2 0.9 x 0.9 m2
polingpoling Line drawingLine drawing
EFM images using Tuning ForkSurface polarization images of PZT filmSurface polarization images of PZT film
4 x 4 m27 x 7 m2
Y. Seo, et al, Appl. Phys. Lett. 80 4324, (2002).
dotdot
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Frequency shift Phase shift
MFM contrast - magnetic force gradient between tip and sample
Lift mode - keep constant gap between tip and sample (~10 nm) - to avoid the strong short range topographic contrast
Magnetic force - very weak force (~pN)
Force gradient
Tuning Fork Based Magnetic Force Microscopy
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Shear force
Attractive force
Approach Curve of MFM
ApproachWithdraw
high S/N ratiohigh frequency Sensitivity < 3 mHz
f = 0.1 Hz 0.01 Hz 1 mHz
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H3PO4
H3PO4
- Co or Ni wire
Pt Co, Ni
D = 100 m 10 m
Tip Manufacture Electrochemical Etching
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-Attach the wire to the tuning fork and make a tip-Use home-made micromanipulator
Pt
Co, NiH3PO4
Tuning fork
Silver paint
Tip Attachment
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L = 2.2 mm, t = 190 m, w = 100 m spring constant, k = 1300 N/m
Co or Ni tipCo or Ni tip
Tip & Tuning Fork
epoxy
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- Perpendicularly recorded sample -longitudinally polarized tip- monopole approximation
Advantage of the shear mode MFMAdvantage of the shear mode MFM
Shear Mode MFM
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(a) shear mode, Co tip, perpendicular
(b) shear mode, Co tip, parallel dithering
(c) shear mode, Ni tip
(d) tapping mode
(a) shear mode, Co tip, perpendicular
(b) shear mode, Co tip, parallel dithering
(c) shear mode, Ni tip
(d) tapping mode
30 x 30 m2 30 x 30 m2 30 x 30 m2 30 x 30 m2
100 Mbit / Inch2
hard disk
100 Mbit / Inch2
hard disk
Magnetic Force Microscopy Images
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Amplitude (a) dependencyAmplitude (a) dependency
3 x 1 m213 x 3 m2
Lift Height & Dithering Amplitude
Height (h) dependencyHeight (h) dependency
h a
Tip
Sample
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1 Gbit/inch2 hard diskDithering Amplitude : 20 nmlift height : 50 nmSpatial resolution : 50 nm2 x 2 m2
High Resolution Tuning Fork Based MFM
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Summary
•MFM using Tuning Fork
•High resolution.
•low power dissipation at low temperature.
•No laser : dark environment.
•Cryogenic experiment (Vortex in superconductor).