Quantitative microwave evanescent microscopy

We have developed a scanning evanescent microwave microscope with shielded tip geometry allowing quantitative characterization of the electrical imped ance of insulating and conducting materials. By modeling the tip-sample cap acitance, quantitative estimates of the sample (both dielectric and conduct ing) electrical impedance (real and imaginary) and tip-sample separation ca n be made. Measurements of the tip-sample capacitance versus tip-sample sep aration have been made and agree with estimated values. Also, the slope of the tip-sample capacitance with respect to the tip-sample distance is calcu lated to implement tip-sample distance regulation for dielectric materials. (C) 1999 American Institute of Physics. [S0003-6951(99)04245-X].