Paper NS-TuA11
Scanning Microwave Microscopy Imaging in Liquids through Ultra-Thin Membranes

Tuesday, November 8, 2016, 5:40 pm, Room 101D

The growing need in operando imaging of submicron objects immersed in liquids relevant to biomedical or energy applications resulted in a significant effort invested into in situ TEM and SEM. In these techniques, objects of interest are incased inside a chamber equipped with ultra-thin electron-transparent but molecularly-impermeable membrane(s) enabling electron or X-ray probing of the chamber interior. However, local radiation damage and radiolysis induced by high-energy electron or X-ray beams often lead to sample deterioration or adversely affect nanoscale chemical processes. Here, we report a novel concept of in situ near-field scanning microwave microscopy of reactive and biological samples in liquids. Microwaves of a few gigahertz frequencies offer photons of energies ~10 μeV, which ensures non-destructive imaging free from radiolysis and radiation damage associated with use of high-energy electron and X-ray beams. In our approach, the nanoscale objects of interest are separated from ambient by a-few-nanometer-thick dielectric membranes transparent for microwave near-fields. The imaging is performed with microwave near-fields formed at a scanning probe of an atomic force microscope in contact with the ultra-thin membrane. In the proposed approach, a liquid and/or a reactive environment of the object of interest are completely isolated from the probe and the rest of the microscope. We performed a comparative, side-by-side study of imaging capabilities of microwave microscopy and SEM in liquids using the same set of biological and inorganic samples. Sensitivity, spatial resolution, probing depth, and probe-induced effects were evaluated and compared. In particular, we demonstrate in situ real-time imaging of growth of metal dendrites at electrode-liquid electrolyte interface during an electrochemical reaction. The demonstrated spatial resolution of the near-field microwave imaging was ca. 250 nm. The resolution can be improved by optimization of probe and membrane geometry, as well as of the membrane material. Under optimal conditions, a resolution of ca. 50 nm can be achieved for metallic objects with commercially available probes. Such resolution is comparable to that demonstrated by in situ SEM in liquids.

The research was supported in part through Scientific User Facilities Division (ORNL), BES, US DOE, US Civilian Research and Development Foundation, and NIST-CNST/UMD-IREAP Cooperative Agreement.