New Microwave Imaging Approach Opens a Nanoscale View on Processes in Liquids

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As important, the low-energy microwaves were too feeble to sever chemical bonds, heat, or interfere in other ways with the process they were being used to capture in images. In contrast, a scanning electron microscope that was used to record the same electroplating process at comparable levels of resolution yielded images showing delamination and other destructive effects of the electron beam.

The team reports similar success in using their AFM-microwave set-up to record images of yeast cells dispersed in water or glycerol. Levels of spatial resolution were comparable to those achieved with a scanning electron microscope, but again, were free of the damage caused by the electron beam.

In their experiments, the team used membranes—made either of silicon dioxide or silicon nitride—that ranged in thickness from 8 nanometers to 50 nanometers. They found, however, that the thinner the membrane the better the resolution—down to tens of nanometers—and the greater the probing depth—up to hundreds of nanometers. “These numbers can be improved further with tuning and development of better electronics,” Kolmakov said.

In addition to studying processes in reactive, toxic, or radioactive environments, the researchers suggest that their microwave-imaging approach might be integrated into “lab-on-a-chip” fluidic devices, where it can be used to sample liquids and gases.

The research was performed at NIST’s Center for Nanoscale Science and Technology and at the Center for Nanophase Materials Sciences, a Department of Energy Office of Science User Facility.

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