Control circuit for a scanning tunneling microscope

A control circuit was designed to control a piezoelectric tube scanner having the standard single inner-electrode quartered outer-electrode configuration. The control circuit allows both analog and digital feedback. The circuit was tested using two 12 bit A/D-D/A converters DAS 1602 to control the scanner of the scanning tunneling microscope. With the complete system in operation but in the absence of tunneling current, the electrometer exhibits a current noise under 3 pA rms and a response time of 30 μs to a step input current. Images of a commercial holographic grating covered with gold running the instrument in the digital feedback were obtained to calibrate the instrument and verify proper control operation. The control circuit and the electrometer turned out to be about an order of magnitude less expensive than commercially available control circuits and low noise current amplifiers of similar performance.