Universal signal scaling in microwave impedance microscopy

Microwave impedance microscopy (MIM) is an emerging scanning probe technique that measures the local complex dielectric function using near-field microwave. Although it has made significant impacts in diverse fields, a systematic, quantitative understanding of the signal's dependence on various important design parameters is lacking. Here, we show that for a wide range of MIM implementations, given a complex tip-sample admittance change Delta Y, the MIM signal-the amplified change in the reflected microwave amplitude-is - G center dot Delta Y/2Y(0)center dot eta(2)center dot V-in, where eta is the ratio of the microwave voltage at the probe to the incident microwave amplitude, Y-0 is the system admittance, and G is the total voltage gain. For linear circuits, eta is determined by the circuit design and does not depend on V-in. We show that the maximum achievable signal for different designs scales with eta(2) or eta when limited by input power or sample perturbation, respectively. This universal scaling provides guidance on diverse design goals, including maximizing narrow-band signal for imaging and balancing bandwidth and signal strength for spectroscopy.

Automated summary

Microwave impedance microscopy (MIM) is a promising scanning probe technique that measures the local complex dielectric function. This study presents a systematic analysis of the dependence of MIM signal on various important design parameters, providing guidance for different design goals.