Electrostatic field imaged in 3D around an electron nano-emitter

The strong and spatially extended electrostatic fields in electron field emission and atom probe tomography are difficult to measure due to the double requirement of resolution and field of view. The new research describes an experimental setup that can measure electrostatic fields in 3-D with nanometer resolution and micrometer field of view around the sharp tip of an electron nano-emitter.

Wu et al. measured the electron beam deflection around an electron nano-emitter using differential phase contrast in scanning transmission electron microscopy. Using a method based on the inverse Abel transform and assuming axial symmetry of the nano-emitter, they reconstructed a slice of the 3-D electrostatic field from a single projection measurement of electron beam deflection with differential phase contrast. The experimental results are in quantitative agreement with simulations based on a finite element numerical Maxwell equation solver.

A tungsten nano-emitter was created for the experiment with standard electro-chemical etching and plasma etching in an ultra-high vacuum chamber.

The new technique improves over previous methods by providing no reference wave distortion, making for a straightforward interpretation of the data. The technique also allows for a balance of field of view with resolution as well as an easily calibrated signal. The researchers believe their technique can be used in future studies of fields around tips of other shapes, provided that tilt series data acquisition is feasible.

Source: “Determination of 3D electrostatic field at an electron nano-emitter,” by Mingjian Wu, Alexander Tafel, Peter Hommelhoff, and Erdmann Spiecker, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5055227 .