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

- 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

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

Hal Edwards, et. al. (1997) Todorovic and Schultz (1998)

Previous works : MFM using tuning fork

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

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

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

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

H3PO4

H3PO4

- Co or Ni wire

Pt Co, Ni

D = 100 m 10 m

Tip Manufacture Electrochemical Etching

-Attach the wire to the tuning fork and make a tip-Use home-made micromanipulator

Pt

Co, NiH3PO4

Tuning fork

Silver paint

Tip Attachment

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

- Perpendicularly recorded sample -longitudinally polarized tip- monopole approximation

Advantage of the shear mode MFMAdvantage of the shear mode MFM

Shear Mode MFM

(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

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

1 Gbit/inch2 hard diskDithering Amplitude : 20 nmlift height : 50 nmSpatial resolution : 50 nm2 x 2 m2

High Resolution Tuning Fork Based MFM

Summary

•MFM using Tuning Fork

•High resolution.

•low power dissipation at low temperature.

•No laser : dark environment.

•Cryogenic experiment (Vortex in superconductor).