Microwave microscopy of local conductivity – from nano-devices to phase separation in complex materials

Keji Lai
Stanford University

The microscopic electrical properties of novel materials are of fundamental importance in nanoscale science and technology. Using shielded cantilever probes and ultra-sensitive microwave electronics, the local dielectric constant and conductivity at 1GHz can be imaged with a spatial resolution (<100nm) less than one millionth of the free space wavelength. We have demonstrated simultaneous topographic and microwave imaging on semiconductor devices, phase change materials, and graphene in different modalities.

A cryogenic version (2 – 300K) of the microwave microscope has also been implemented to study the emergence of microscopic phase separation in colossal magnetoresistive manganites. With increasing magnetic fields, the filamentary metallic domains percolating through the insulating background align preferentially along certain crystal axes of the substrate, suggesting the anisotropic elastic strain as the dominant physical interaction. The microwave images also reveal drastically different domain structures between the zero-field-cool and field-cool processes, consistent with the macroscopic transport measurements.