TIME-RESOLVED MEASUREMENTS OF THE RESPONSE OF A STM TIP UPON ILLUMINATION WITH A NANOSECOND LASER-PULSE

Nanosecond laser pulses are used to illuminate the very end of a tip o f a scanning tunneling microscope in front of a gold surface. The tran sient increase of the tunneling current is measured as a function of t he pulse energy density, tip retraction amplitude, polarization of the incident light, and bias voltage. The transient signal has a typical timescale of ms. Thus it can be concluded that the thermal expansion o f the tip is responsible for this signal. The expansion has a linear d ependence on the incident light intensity with a typical value of the order of 0.1 Angstrom/(mJ/cm(2)). This result demands a critical inspe ction of the interpretation of nanostructuring experiments with this t echnique.