APPLICATIONS OF TECHNOLOGY:
- biological materials
- low atomic number materials
- any specimens requiring reconstruction of the phase of the exit wave
- Visualization of smaller unstained structures than previously possible
- Greater contrast and signal-to-noise ratio than with defocusing
- Compatible with existing electron microscopes
- Less expensive than proposed Zernicke phase plates
Robert Glaeser, Jian Jin, and their colleagues at Berkeley Lab have developed a microfabricated objective aperture for electron microscopes that greatly improves image contrast.
NEW: August 2012 demonstration results available here.
The aperture combines single sideband (SSB) contrast at low spatial frequencies with double sideband (DSB) contrast at high spatial frequencies, thereby optimizing the contrast transfer function (CTF). Unlike proposed devices for Zernike phase contrast, the aperture is relatively inexpensive to manufacture and compatible with most existing electron microscopes.
The aperture is designed to block a half-plane of the electrons at small scattering angles, providing SSB (Foucault) contrast at spatial frequencies where the contrast transfer achieved by defocus is very poor. However, at higher frequencies, i.e., wider scattering angles, the aperture does not block any electrons and thus provides optimal DSB contrast at Scherzer defocus. As a result, the CTF is maximized to 0.5 at low spatial frequencies, and to 0.5 - 1 at moderate to high spatial frequencies. In addition, the Berkeley Lab scientists are optimizing the material used for fabrication and the temperature of the aperture to limit electron charging (contamination).
Applying phase contrast techniques to electron microscopy enables unprecedented visualization of detail in biological and other radiation-sensitive, low atomic number objects without heavy metal staining, which often alters the structures of interest. The Berkeley Lab invention combines SSB contrast at low frequencies and with DSB contrast at higher frequencies, thereby providing the broadest band of high contrast at the least expense.
STATUS: Patent pending. Available for licensing or collaborative research.
DEVELOPMENT STAGE: Testing and refining the prototype. NEW: August 2012 demonstration results available here.
SEE THESE OTHER BERKELEY LAB TECHNOLOGIES IN THIS FIELD:
REFERENCE NUMBER: IB-2851