Since the manufacture of the first commercial electron microscope more than 70 years ago, instrument developers have sought to improve resolution by designing ever-better electromagnetic lenses. However, the best resolution ever obtained is still about 25 times poorer than the theoretical diffraction limit.
Further improvement in lens performance faces ever-decreasing gains, because of the way higher and higher order aberrations begin to dominate the lens correction process, and because energy spread in the electron source and instabilities in the power supplies sabotage the extreme requirements for coherent interference.
Because it is a lensless technology, the Phase Focus Virtual Lens® unshackles the image formation process from the constraints of conventional electron optics. Its incorporation into a commercial electron microscope can already deliver resolution superior to that of the conventional lens by a factor of five, confirming that this disruptive approach can overcome the lens-defined resolution limit over an unlimited field of view.
Beyond resolution improvement, the Virtual Lens eliminates the extreme experimental challenges of electron holography, making quantitative electron phase microscopy available to all users for applications including:
- “Magnetic Microscopy” (visualisation and analysis of electro-magnetic phenomena and magnetic domains in, e.g., superconductors and recording media);
- Analysis and measurement of electric fields in p-n junctions; specimen thickness; dislocations and strain fields; and inner potential in semiconductors
- Imaging of biological specimens (effectively transparent to electrons) without the need for damaging heavy metals stains.
Quantitative phase imaging of 261nm diameter latex spheres obtained using a Virtual Lens add-on to a commercial transmission electron microscope (TEM) operating at 200 keV. The Virtual Lens phase image, superimposed on the conventional TEM image (left), is colour-coded to show successive 360° “phase contours” introduced by phase delays sustained by the electron beam as it passes through the specimen. This phase information is unwrapped in the grey-scale image (centre), and the profile taken across the spheres (right) shows excellent dimensional and geometrical agreement with shape and size of the specimen.