A novel ultrasonic resonance sample tip distance regulation for near field optical microscopy and shear force microscopy

We have developed a novel technique of sample-tip distance regulation by using ultrasonic resonance method to sense the shear force in the nano-Newton range. A piezoelectric quartz fork is driven by its resonance frequency without an additional dither vibrator. By combining the vibration amplitude and phase shift of the fiber tip attached to the quartz fork, the sample-tip distance can be reliably controled at 0-50 nn. The shear force images show that the lateral resolution is better than 50 nm depending of the aperture size of the tip. Being a nonoptical detection mechanism, this method is very promising in the near field scanning optical microscopy, especially in the cases of reflective mode and spectroscopy, as well as being an independent shear force microscope for insulation samples.