Microwave impedance microscopy of nanostructured carbon

Microwave impedance microscopy (MIM) is a scanning probe technique that measures local changes in tip-sample admittance. The imaginary part of the reported change is calibrated with finite element simulations and physical measurements of a standard capacitive sample, and thereafter the output ?Y is given a reference value in siemens. Simulations also provide a means of extracting sample conductivity and permittivity from admittance, a procedure verified by comparing the estimated permittivity of polytetrafluoroethlyene (PTFE) to the accepted value. Finally, the well-known effective medium approximation of Bruggeman is considered as a means of estimating the volume fractions of the constituents in inhomogeneous two-phase systems. Specifically, we consider the estimation of porosity in nanostructured carbons often used in charge storage devices, such as carbide derived carbon (CDC) and onion-like carbon (OLC).