Diffractive electron mirror for use in quantum electron microscopy

Abstract

Periodic atomic structures in thin crystals and artificially fabricated periodic structures in transmission gratings have long been used to coherently split electrons by means of electron diffraction for applications such as interferometry, holography and imaging. Due to their reliance on transmission through matter, however, these methods are prone to electron scattering and absorption and are therefore lossy to some extent. This loss becomes a major issue for quantum electron microscopy (QEM), an interaction-free measurement scheme with electrons as probe particles. QEM relies on single electrons completing many round trips inside an electron resonant cavity, splitting and re-coupling during each round trip, effectively multiplying the probability of loss by the number of round trips. Thus, in one of the designs for QEM, the use of reflective diffraction gratings as lossless electron beam splitters is proposed. In this thesis, diffractive electron mirrors were fabricated by integrating one-dimensional diffraction gratings with tetrode electron mirrors. Optical interference lithography was used to fabricated silicon diffraction gratings with pitches varying from 200 nm to 500 nm. Furthermore, a proof-of-principle experiment to demonstrate their function as electron mirrors inside a scanning electron microscope was developed. It was demonstrated that the constructed tetrode electron mirrors satisfied the requirements of QEM for electron energies up to 3 keV. Finally, in a similar experiment, the fabricated diffractive electron mirrors were tested to demonstrate their function as lossless beam splitters. Preliminary results point to the evidence for electron diffraction, suggesting that diffractive electron mirrors could be used as as lossless electron beam splitters for QEM and other applications.