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7 September 2018 Investigation of mechanical torque applied by electron vortex beams in a liquid cell
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Abstract
Electron beams carrying orbital angular momentum (OAM), or electron vortex beams (EVBs), can be produced in a Transmission Electron Microscope (TEM) with forked diffraction gratings.1,2 Just as optical vortex beams can be used to trap and rotate particles, EVBs have been reported to transfer their OAM to a nanoparticle on a dry substrate and cause it to spin.3,4 However the results have not been reproduced, perhaps due to contact friction. It has been suggested that a more dramatic effect could be observed by imaging particles levitated in an optical trap or in a liquid environment. 3,5,6 To reproduce these results and demonstrate a more pronounced response, we are performing experiments to transfer OAM from an EVB to a nanoparticle suspended in a fluid. TEM liquid cells consist of a liquid sample sealed against the vacuum of the standard TEM column between two electron-transparent windows. These cells have enabled the study of liquid samples at nanometer to atomic resolution and have applications in the study of microfluidics, electrochemical processes, and biological samples. Electron vortex beams could provide a useful new tool to manipulate nanoparticles and liquids themselves inside such cells. Here we describe an experimental investigation of EVB-induced rotation in a liquid and show that initial results are inconclusive. A theoretical consideration using the fluctuation-dissipation theorem suggests that, unlike in an optical trap, viscous forces and rotational Brownian motion may overwhelm the subtle torqueing effect the EVB has on the particle.
Conference Presentation
© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Alice Greenberg, Hannah DeVyldere, Jordan Pierce, and Benjamin McMorran "Investigation of mechanical torque applied by electron vortex beams in a liquid cell", Proc. SPIE 10723, Optical Trapping and Optical Micromanipulation XV, 107231O (7 September 2018); https://doi.org/10.1117/12.2323187
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