A digital integrator and scan generator coupled with dynamic scanning for scanning tunneling microscopy

A novel digital integrator circuit has been engineered for constant‐current mode STM feedback control. In contrast to analog integrators that rely on charging or discharging of a capacitor in an amplifier feedback loop, the integrator uses a 16‐bit digital counter that is rapidly incremented or decremented depending on whether the tunneling current is higher or lower than a reference value. The counter drives a digital‐to‐analog converter (DAC) whose output is amplified and used to control the STM Z‐axis scanner. A computer’s parallel input port records the DAC output word at each sampling point, directly giving the digital value of the tip position. The integrator is used in conjunction with a two‐axis 16‐bit scan generator. The Z‐axis feedback reference circuit is used to dynamically control the STM’s lateral scanning rate, and scan rates of 300 μm s−1 are demonstrated. The digital integrator and scan generator facilitate fast switching between different modes of STM operation, allowing glitch‐ and drif...