A combined scanning probe microscope

A scanning probe microscope, combining a scanning capacitance microscope with a scanning tunneling microscope (STM) using the same probe and input electronics, has been built. The probe is shielded and its stray capacitance is less than 0.5 fF. As an input stage, a wide-bandwidth current-to-voltage converter has been applied. In the capacitance microscope mode, its phase sensitively measures the current flowing through the probe/sample capacitance. The optimum operating frequency is from 1 to 10 MHz. The achieved signal-to-noise ratio is comparable with microscopes using a videodisk pickup as the capacitance sensor. The same amplifier at reduced bandwidth serves in STM mode. Its sensitivity corresponds to standard microscopes, albeit the input bias current is larger than at good STM input stages. It can be used with tunneling currents larger than 100 pA. (C) 2002 American Institute of Physics.