Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology - Near Field Scanning Optical Microscopy - Electrostatic Force Microscopy - Magnetic Force Microscopy Yongho Seo Near-field Photonics Group Leader Wonho Jhe Director School of Physics and Center for Near-field Atom-photon technology, Seoul Nation University in South Korea

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology NSOM (near-field scanning optical microscopy) EFM (electrostatic force microscopy) MFM (magnetic force microscopy) Scanning Probe Microscope  nano-scale resolution  Slow scanning Optical Microscope :  low resolution  diffraction limit  real time Scanning probe Microscopy Quartz Crystal Resonator probe - self oscillating - self sensing - chip and simple design

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology High Frequency Dithering Probe for Shear Force Detection High frequency (rf) dithering  fast scanning Small dithering amplitude (<< 1 nm)  high lateral resolution Large Signal voltage (> 0.1 V)  high signal to noise ratio High Frequency Quartz Crystal Resonator Thickness Shear mode 2 ~ 100 MHz dithering frequency fast response time ~ 1 ms Bimorph, tuning fork Low dithering frequency 10 ~ 100 kHz Slow response time ~ 100 ms

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Quartz Crystal Resonators High Frequency (rf) Thickness Shear or Extensional mode k = N/m Low Frequency (10 kHz) Flexural Mode k = N/m Z-cut Tuning fork AT-cut QCR BT-cut trident QCR

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology QCR based NSOM Shear mode NSOM - 2 MHz dithering frequency - make a hole to insert optical fiber tip - easy to replace tip - increased the stability - high Q-value > 10 3 Perforated QCR probe

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology QCR probe Feedback Scheme Function Generator induced signal Phase detection Tube scanner high frequency dithering tip Simple design Low cost No lock-in amp

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology High Frequency Dithering Shear Force Microscopy Topographic Image of CD surface Amplitude mode Phase mode Total time : 20 s White dots : dust Large dithering amplitude

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Schematics for high speed NSOM Laser Diode : 650 nm PMT : Optical Signal measurement Reflection mode Near field detection scheme

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Fastest Scanning NSOM Image Near field Scanning Probe Microscopy Image of grating surface in reflection mode Total time : 0.5 s 7x7  m 2 Total time : 0.5 s 7x7  m 2 Total time : 0.5 s 1x1  m 2 Total time : 0.5 s 1x1  m 2

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Electrostatic Force Microscopy L = 2.2 mm, t = 190  m, w = 100  m k = 1300 N/m. The tip is electrically shorted to an electrode. Tuning Fork ( KHz)

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Force Sensitivity of Tuning Fork Force sensitivity  (k/Qf) -1/2 f = kHz k = N/m Q = ~ 10 nm dithering f = kHz k = N/m Q = smaller than 1 nm dithering In this experiment, L = 2.2 mm, t = 190  m, w = 100  m k = 1300 N/m. Q = 1800, f = 32 kHz Si CantileverQuartz Tuning Fork

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology H 3 PO 4 Electrochemical Etching Reduce the diameter of Co and Ni wire Pt Co, Ni D = 100  m10  m

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Make tip and Attach it to the tuning fork -Attach the wire to the tuning fork and make a tip -use home-made micromanipulator Pt Co, Ni H 3 PO 4 Tuning fork Silver paint

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology PZT Thin Film The property requirements of PZT thin films for high quality nano storage devices : ▶ smooth surface roughness ▶ high piezoelectric properties even in the case of very thin films ▶ long term stability and reliability PZT thin films (Zr/Ti = 20/80) by INOSTEK Inc. and Crystalbank

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Electrostatic Force Microscopy Bias voltage applied between the tip and Pt substrate Approach Curve with Bias voltage PZT Pt Tip

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Electrostatic Force Microscopy Minimum Detectable Capacitance due to thermal noise  2 x F Frequency shift due to surface charge

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Electrostatic Force Microscopy 7 x 7  m 2 Tuning Fork based EFM - polarization images 0.9 x 0.9  m 2 After poling of square area Line drawing -long time stable -High resolution (50 nm)

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Electrostatic Force Microscopy Tuning Fork based EFM - polarization images 4 x 4  m 2 7 x 7  m 2

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Magnetic Force Microscopy Frequency shiftPhase 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

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Magnetic Force Microscopy Approach Withdraw Approach Curve high S/N ratio high frequency Sensitivity < 3 mHz Shear force attractive force

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Magnetic Force Microscopy L = 2.2 mm, t = 190  m, w = 100  m spring constant, k = 1300 N/m (smallest one commercially available) Tuning Fork : Co tip attached

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Magnetic Force Microscopy -Perpendicularly recorded sample and longitudinally polarized tip Advantage of the shear mode MFM

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Magnetic Force Microscopy (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  m Mb hard disk

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Magnetic Force Microscopy Tuning Fork based MFM : height and amplitude dependency 3 x 1  m 2 13 x 3  m 2

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Magnetic Force Microscopy 1 Gbit/inch 2 hard disk Dithering Amplitude : 20 nm lift height : 50 nm Spatial resolution : 50 nm 2 x 2  m 2 High resolution Tuning Fork based MFM

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology Atomic Layer of HOPG with trident QCR (1MHz) 160 x160 nm 2 Atomic layer (3Å)

Creative Research Initiatives Seoul National University Center for Near-field Atom-Photon Technology NSOM, EFM, and MFM using Quartz Crystal Resonator In summary, Quartz Crystal Resonator based NSOM, -high resonance frequency, and small dithering amplitude. -facilitates high-speed scanning -obtained atomic scale AFM Tuning fork based EFM and MFM - EFM : obtained with high resolution, for the first time. - MFM : shear mode MFM; improved resolution. - Tuning fork : Force sensitive SPM sensor Published results : Y. Seo, J.H. Park, J.B. Moon and W. Jhe, Appl. Phys. Lett (2000). Y. Seo, Wonho Jhe, Rev. Sci. Instrum. 73 (2002). Published results : Y. Seo, J.H. Park, J.B. Moon and W. Jhe, Appl. Phys. Lett (2000). Y. Seo, Wonho Jhe, Rev. Sci. Instrum. 73 (2002).