Surface resistance imaging with a scanning near-field microwave microscope

We describe near-field imaging of sample sheet resistance via frequency shifts in a resonant coaxial scanning microwave microscope. The frequency shifts are related to local sample properties, such as surface resistance and dielectric constant. We use a feedback circuit to track a given resonant frequency, allowing measurements with a sensitivity to frequency shifts as small as two parts in 106 for a 30 ms sampling time. The frequency shifts can be converted to sheet resistance based on a simple model of the system.