Radio Frequency Circuitry for Atomic Force Microscopy up to 100 MHz

Abstract

We developed a control circuitry for non‐contact atomic force microscopy which generates a self‐excited vibration in a cantilever with a frequency up to 100 MHz, and detects its frequency modulation by a novel frequency demodulation technique. The circuitry was tested by applying it to an AFM whose tip vibration was parallel to sample surface. While the self‐excitation loop has only a simple superheterodyne configuration, the excited vibration was as stable as we could obtain a topographic image of Si (111)‐(7×7) surface with frequency feedback. The frequency demodulator is based on IQ (in‐phase and quadrature‐phase) direct frequency conversion to zero Hz intermediate frequency and operations including differentiations, multiplications and a subtraction between these signals. It was implemented as an analog circuit. We obtained an atomic step image in graphite by using this demodulator in frequency regulation feedback.