Berkeley Lab

New directions in phase contrast microscopy

By Brooke Kuei

Phase contrast electron microscopy, a form of microscopy that takes advantage of interference between scattered and unscattered waves, has recently seen significant advances due to new instrumentation and computation algorithms. Today’s afternoon symposium titled New Directions in Phase Contrast Microscopy featured the many different and creative ways in which microscopists have been improving phase contrast microscopy.

For example, Benjamin McMorran from the University of Oregon described a nanofabricated diffraction grating that enabled STEM-holography. Using this technique, he was able to image amorphous carbon and nanomagnetic domains in a magnetic thin film. On the other hand, Stewart Koppell from Stanford University talked about innovative electron optic schemes that have the potential to improve resolution. One idea was to use a multi-pass filter which causes electrons to be trapped in a re-imaging cavity such that they pass through the sample multiple times. The signal gained from multiple passes is more than the damage caused, making this an efficient technique for improving resolution while also minimizing damage. Yet another way in which researchers are improving resolution in phase microscopy was presented by Laura Waller from UC Berkeley, who leverages computation to replace expensive and bulky optics. For example, gigapixel imaging methods enabled a live view of cancer cells dividing and multiple scattering models allowed for 3D imaging of strongly scattering embryos, and even a full worm. While the methods presented by Waller today were applied to optical microscopy, ongoing efforts to transfer them to electron microscopy are underway.