Today, if you purchase a new transmission electron microscope (TEM), you can specify a choice of objective-lens pole-pieces. Pole-pieces with the smallest pole-gaps exhibit the lowest spherical and chromatic aberrations, and will produce images with better resolution. Unfortunately, these small gaps will have less space for sample tilting, x-ray detectors, or in-situ holders. Conversely, large gap pole-pieces will offer more flexible space for experimental applications but won’t reach the ultimate optical performance.
For instruments in shared microscopy facilities, the pole-piece might then be optimised for one usage scenario (to the detriment of others), or a middle-ground compromise that is optimised for no one. The significant cost of a flagship TEM, perhaps €5M, means that having two instruments side by side is not economical.
Instead, we propose a User Adjustable Pole-piece (UAP) where the pole-piece gap can be adjusted by the TEM operator without the need for engineer support or losing the column vacuum.
This project was initiated in April 2018 to explore the feasibility of constructing an adjustable lens. The research includes studies of the design, construction, and magnetic performance of modern objective lenses.
We have designed a replacement pole-piece for the JEOL architecture of TEM platforms with an initial focus on a 200/300kV design. The pole-gap adjustment is achieved by a sliding concentric mechanism (patent pending). The initial results were submitted to the European Microscopy Congress (EMC) proceedings: Patrick McBean, David O’Mahony and Lewys Jones, “Development of a User Adjustable Pole-piece Gap Objective-lens”, DOI:10.22443/rms.emc2020.322.
This research is part of the “RetroTEM” project supported by a Science Foundation Ireland (SFI) and Royal Society University Research Fellowship (grant no. URF/RI/191637), and the SFI Advanced Materials and BioEngineering Research centre (AMBER).