Development of Low Voltage/ Low Dose Electron Holography to Reveal 3D Dynamics of Soft Matter at Atomic Resolution
DescriptionIn the late 1950s Richard Feynman pointed outthat ‘It would be very easy to make an analysis of any complicated chemical substance; all one would have to do would be to look at it and see where the atoms are.’  In principle, the latest generation aberration-corrected transmission electron microscopes (TEMs) could achieve this goalbut there are two bottlenecks that hinder the final step towards Feynman’s challenge. Firstly, TEM always provides only 2D projected images. Secondly, in order to achieve a resolution around 1 Å with single atom sensitivity, the electron dose rate need to be sufficiently large (104–105eÅ-2s-1). With such large dose rate the electron beam can induce surfaces alterations or even bulk modifications, in particular, for electron beam sensitive (soft) materials such as nm size particles, organic materials, proteins or macro-molecules. In principle one can reduce the radiation damage at low temperature using cryo-electron microscopy. But cryo-EM has the major drawback that, at low temperature, the shape of the protein may be deformed and the dynamics information is lost. However recently it has been shown that by keeping the energy of the electron beam below a critical voltage and simultaneously keeping the electron dose below a certain threshold the damage of the sample can be substantially reduced or even totally avoided. In this proposal, we intend to develop both theory and methodology of low dose electron holography for observing the dynamics of soft materials such as MoS22D materials and single Oleic acid molecules at atomic resolution. The main improvement of this new type of electron holography is based on two concepts. Firstly, the total electron dose is distributed over many images obtained at different defocus values from which the electron hologram is then reconstructed. Secondly, in contrast to the current tomographic methods that require projections from several directions, the 3D structural information of the nano-object is then extracted from this one hologram obtained from only one viewing direction.The development of this proposal will be done in close cooperation with several professors [2, 3, 4] . This project aims at pushing the spatial 3D resolution for nano-materials up to the single atom scale but with a time resolution of few ten seconds at this moment. The time resolution can be pushed further to micro-and even nano-seconds by the combination with a self-designed ultrafast electron microscope  . The role of each collaborator is clearly stated in reference.
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