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 of a scanning tunneling microscope in front of a gold surface. The transient increase of the tunneling current is measured as a function of the 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 of the tip is responsible for this signal. The expansion has a linear dependence on the incident light intensity with a typical value of the order of 0.1 Å /(mJ/cm2). This result demands a critical inspection of the interpretation of nanostructuring experiments with this technique