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Phase Plate for High Resolution and High Contrast TEM Images



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Robert Glaeser and Jian Jin at Berkeley Lab along with other researchers have developed a technology for a transmission electron microscope (TEM) phase plate that will have a long lifetime and will consistently produce high quality phase-contrast images of unstained biological materials and low-atomic-number materials. The invention will help realize the goal of phase contrast electron microscopy—converting slight differences in phase, created when electrons pass through a specimen, into meaningful signals that produce an image of unstained, and therefore unaltered, material.

The technology consists of an optical cavity that is placed in the back focal plane of the TEM. A laser outside of the microscope delivers a beam to the cavity from the side, and the cavity focuses the light and builds up its energy by reflecting it multiple times. The electron beam enters the cavity from above, after it has passed through the specimen and the objective lens. Electrons that are not scattered by the specimen pass through the electromagnetic field created by the focused light at the center of the cavity, while scattered electrons pass to the sides of this central point. As a result, the unscattered electrons are shifted in phase relative to the scattered electrons, and a high contrast image is produced.

The device will be compatible with TEMs that are fitted with a transfer lens or objective lens and have the necessary ports and sufficient working space. In addition, the invention does not use a pulsed laser, so that it can be used with non-pulsed as well as pulsed electron microscopes. Moreover, the cavity alleviates the need for expensive, high-power optical beams.

Previous devices for shifting the phase of electrons in TEMs, such as thin carbon-film or magnetic phase plates, have been limited by problems including  (a) inconsistency in the degree of phase shift, which is caused by charging of the phase plate when it is hit by the electron beam; (b) signal loss, as parts of the phase plate block some of the scattered electrons; and (c) rapid “aging,” over days or weeks, which causes previously excellent devices to accumulate a charge that alters the desired phase shift. The Berkeley Lab invention overcomes these problems by using light, which does not result in electron loss or the accumulation of charge.

DEVELOPMENT STAGE: Proof of principle. The next phase is for researchers to develop a prototype.

STATUS: Patent pending. Available for licensing or collaborative research.


Transmission Electron Microscope Phase-contrast Enhancement, IB-2036

Graphene Membranes for Nanometer-scale Lithography and Single Atome Resolution TEM Imaging, IB-2501, 2502


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Last updated: 09/03/2010