Magnetic Force Microscopy using Quartz Tuning Fork

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Magnetic Force Microscopy using Quartz Tuning
Fork
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
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Quartz Tuning Fork as a Force Sensor
Quartz Crystal Tuning fork
Micro-machined Cantilever
- optical deflection - laser diode - photo
diode - optical alignment - addition actuator
- Self actuating - Self sensing - No light - No
alignment
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Force Sensitivity of Quartz Tuning Fork
Cantilever
Tuning Fork
f 10 - 100 kHz k 1 - 100 N/m Q 102 10 nm
dithering
f 32 - 100 kHz k 103 - 105 N/m Q 104 (106
in vacuum) lt 1 nm dithering
Force sensitivity ? (Qf/k) 1/2

• Low force sensitivity
• Low thermal noise due to high stiffness
• High resolution by small dithering amplitude

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Previous works MFM using tuning fork
Hal Edwards, et. al. (1997)
Todorovic and Schultz (1998)
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Tuning Fork based Electrostatic force microscopy

• Ferroelectrics
• surface charge in Semiconductor

f 32.768 KHz k 1300 N/m Q 1300
L 2.2 mm, t 190 mm, w 100 mm
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EFM images using Tuning Fork
Surface polarization images of PZT film
poling
Line drawing
dot
7 x 7 mm2
0.9 x 0.9 mm2
4 x 4 mm2
7 x 7 mm2
Y. Seo, et al, Appl. Phys. Lett. 80 4324, (2002).
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Tuning Fork Based Magnetic Force Microscopy
MFM contrast - magnetic force gradient between
tip and sample
Frequency shift
Phase shift
Force gradient
Magnetic force - very weak force (pN)
Lift mode - keep constant gap between tip and
sample (10 nm) - to avoid the
strong short range topographic contrast
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Approach Curve of MFM
Approach Withdraw
Shear force
Attractive force
?f 0.1 Hz
0.01 Hz
1 mHz
high S/N ratio high frequency Sensitivity lt 3
mHz
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Tip Manufacture Electrochemical Etching
- Co or Ni wire
H3PO4
H3PO4
Pt
Co, Ni
D 100 mm
10 mm
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Tip Attachment
-Attach the wire to the tuning fork and make a
tip -Use home-made micromanipulator
Pt
Silver paint
Co, Ni
H3PO4
Tuning fork
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Tip Tuning Fork
epoxy
Co or Ni tip
L 2.2 mm, t 190 mm, w 100 mm spring
constant, k 1300 N/m
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Shear Mode MFM
Advantage of the shear mode MFM

• Perpendicularly
• recorded sample
• longitudinally
• polarized tip
• - monopole approximation

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Magnetic Force Microscopy Images
(a) shear mode, Co tip, perpendicular (b) shear
mode, Co tip, parallel dithering (c) shear mode,
Ni tip (d) tapping mode
100 Mbit / Inch2 hard disk
30 x 30 mm2
30 x 30 mm2
30 x 30 mm2
30 x 30 mm2
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Lift Height Dithering Amplitude
Amplitude (a) dependency
Height (h) dependency
Tip
h
a
Sample
3 x 1 mm2
13 x 3 mm2
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High Resolution Tuning Fork Based MFM
1 Gbit/inch2 hard disk Dithering Amplitude 20
nm lift height 50 nm Spatial resolution 50
nm 2 x 2 mm2
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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).