A circuit for measuring the gap voltage of a scanning tunneling microscope on a nanosecond time scale

We demonstrate a new circuit design for fast measurements of the voltage drop across the gap of a scanning tunneling microscope (STM) based on the simultaneous operation of two different amplifiers. The first is a fast instrumentation amplifier, sensing directly the voltage drop across the tunneling barrier, the second is a medium speed current amplifier with an overall gain of 10 8 V/A , suitable for normal STM operation. We obtained a time resolution of 10 ns measuring the plasma ignition under a STM tip during illumination with an intense 10 ns laser pulse. Possible applications include the study of STM point contacts.