APPLICATIONS OF TECHNOLOGY:
· Phase-contrast apertures for transmission electron microscopes
· Apertures and slits used in electron or ion optics
· Strictly equipotential surfaces in electron or ion-optical instruments
· Mass spectrometry
· Sharply reduces electrostatic charging of phase plates
· High-resolution, high-contrast images of phase objects can be produced without defocusing
· Eliminates patch potentials
· Tolerates heating to a temperature of at least 400 °C
· Allows formation of a native oxide layer no greater than one atom in thickness
An ultra-thin carbon coating of the phase-plate aperture surface developed by Robert Glaeser and his team of Berkeley Lab researchers solves the charging and “patch-potential” effects that degrade phase-plate performance, thus improving the capacity of transmission electron microscopes (TEM) and cryo-TEM microscopy to visualize structures of biological materials. This same technology can be applied to other applications of charged-particle optics, such as mass spectroscopy.
Although phase-plates work better the closer they are to the electron beam, proximity also increases electrostatic charging, thereby degrading performance. The Berkeley Lab technology dramatically reduces the problem by coating the phase-plate apertures with an evaporated carbon film, and maintaining it at 300°C. The amorphous structure of this anti-charging film creates a uniform surface that eliminates the irregular patches of electrostatic potential. In addition, the low-temperature volatility of carbon oxides prevents the formation of a native oxide that is thicker than one atomic layer.
De-focusing, or operating TEMs slightly out-of-focus, is the standard method to achieve higher contrast; however, defocusing naturally corrupts the image at high resolution, an effect that can be only partially reversed by computational processing. Phase-plate apertures boost contrast without defocusing by applying a systematic phase shift to the scattered electrons relative to the unscattered electrons. The effect is to convert phase modulations in the image wave function into amplitude (i.e. intensity) modulations, which can be recorded with a detector that measures the image intensity.
Phase-plate devices hold enormous promise for improved high-resolution transmission electron microscopy (TEM), but their development is hindered by unwanted electrostatic disturbances on the plate. For example, nearly all phase-plate surfaces will develop a native oxide layer, which often is an insulator and thus will charge up when hit by ionizing radiation. In addition, an irregular mosaic in electric potential exists over the surface of any crystalline conductor. This undesirable “patch-potential” is caused by the different facets presented at the surface by different domains of the material. The technology developed by Robert Glaeser and his team overcomes these challenges.
DEVELOPMENT STAGE: Bench scale prototype.
STATUS: Patent pending. Available for licensing or collaborative research.
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REFERENCE NUMBER: WIB-3122