Photothermal modulation of the gap distance in scanning tunneling microscopy

We have employed the photothermal effect to modulate the gap distance in a tunneling microscope. In this approach, optical heating induces the expansion and buckling of laser-illuminated sample surface. The surface displacement can be modulated over a wide frequency range, and its height (typically <1 A-circle) can be varied by changing the illumination intensity and modulation frequency. This novel method provides an alternative means for performing tunneling spectroscopy and microscopy, and for determining work functions of materials