Scanning Probe Microscopy Using Quartz Crystal Resonator

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Creative Research InitiativesSeoul National UniversityCenter for Near-field Atom-Photon Technology

Yongho Seo

Wonho Jhe

School of Physics and Center for Near-field Atom-photon technology,

Seoul Nation University in South Korea

Scanning Probe Microscopy Using Quartz Crystal Resonator

High Frequency (rf)Thickness Sheark = 105 - 106 N/m

High Speed

Low Frequency (32 kHz)Flexural Mode k = 103 - 104 N/mHigh force sensitivity

Z-cut Tuning fork

AT-cut QCRZ-cut trident QCR

QCRs as a Force Sensor

High Frequency (1 MHz)Extensional mode k = 105 - 106 N/m

High resolution

-Shear mode - 2 MHz dithering frequency- make a hole to insert optical fiber tip- easy to replace tip- increased the stability- high Q-value > 103

High Speed NSOM

Optical image of Grating

Total time : 0.5 s

7x7 m2

Optical image of Grating

Total time : 0.5 s

7x7 m2

Fastest Scanning NSOM Image

Topography of CD

Total time : 20 s

Topography of CD

Total time : 20 s

Y. Seo, et. al, Appl. Phys. Lett. 77 4274 (2000).

Slowly diffusing micro-spheres in water

Scanning time 25 s, 5 x 4 m2

0 min.

Continuous Images usingHigh Speed Shear Force

Microscope

3 min.6 min.9 min.12 min

Y. Seo and W. Jhe, Rev. Sci. Instrum. 73, 2057 (2002)

f = 32.768 KHz

k = 1300 N/m

f = 32.768 KHz

k = 1300 N/m

Tuning Fork Based Electrostatic force microscopy

-Ferroelectrics-surface charge in Semiconductor

L = 2.2 mm, t = 190 m, w = 100 m k = 1300 N/m.Q = 1800, f = 32 kHz

minimum detectable force = (k/Qf) 1/2

f = 10 - 100 kHzk = 1 - 100 N/mQ = 102 - 103 ~ 10 nm dithering

f = 10 - 100 kHzk = 103 - 105 N/mQ = 103 - 105 < 1 nm dithering

Si Cantilever Quartz Tuning Fork

Force Sensitivity of Quartz Tuning Fork

• Long range electrostatic force• Short range shear force• keep constant gap between tip and sample (~10 nm)• to avoid the strong short range topographic contrast

Lift mode

- 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

Co, NiH3PO4

Tuning fork

Silver paint

Tip Attachment

• for high quality nano storage devices : • high ferroelectric properties • long term stability and reliability

PZT (100 nm) / Pt electrode layer / Si substratePZT (100 nm) / Pt electrode layer / Si substrate

Ferroelectric PZT Thin Film

Bias voltage applied between the tip and Pt substrate

Approach Curve in EFM

7 x 7 m2 0.9 x 0.9 m2

polarization polingpolarization poling Line drawingLine drawing

long time stable

(10 hr)

long time stable

(10 hr)High resolution (50 nm)

narrow line width

High resolution (50 nm)

narrow line width

Poling and Drawing by EFM

Tuning Fork based EFM - polarization imagesTuning Fork based EFM - polarization images

4 x 4 m2 7 x 7 m2

Patterning and Imaging by EFM

Y. Seo, et al, Appl. Phys. Lett. 80 4324, (2002).

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

ApproachWithdraw

high S/N ratiohigh frequency Sensitivity < 3 mHz

Shear force

attractive force

Approach Curve of MFM

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

- 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

Sample

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

High Resolution Tuning Fork Based MFM

160 x160 nm2

Atomic layer (3Å)

Atomic Layer of HOPG With Trident QCR (1MHz)

True Atomic resolution AFM in air

• Mica

• Ambient condition

• Non-contact AFM

• Dithering Amp: 0.1 nm

• Triangular structure

• k = 50,000 N/m

• Trident QCR, 1MHz

• Piezoelectric detection

• Corrugation : 0.3 Å

1nm x 1nm, 51 s

2nm x 2nm, 51 s

1nm x 1nm 13 s

2nm x 2nm, 13 s

Summary

•AT-cut QCR : High speed NSOM

•Tuning fork : High force sensitivity MFM, EFM

•Trident QCR : Atomic resolution AFM in air

Thank you !!!

Near field Group ResearchersYongho Seo, Ho Jin Cho, Moon Hun Hong, Jun Mo An, Sung Jin Jang,

Hwan Sung Choi, Kyeong Ho Kim,Professor

Wonho Jhe

Scanning Probe Microscopy Using Quartz Crystal Resonator

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