Low-voltage coherent electron microscopy based on a highly coherent electron source built from a nanoemitter

Abstract

It has been a general trend to develop low-voltage electron microscopes due to their high imaging contrast of samples and low radiation damage. Atomic-lattice-resolved transmission electron microscopes with voltages as low as 15–40 kV have been demonstrated. However, achieving an atomic resolution at voltages lower than 10 kV is extremely difficult. An alternative approach is a coherent imaging or phase retrieval imaging, which requires a sufficiently coherent source, an adequately small illumination area on the sample, the detection of high-angle diffraction patterns with a sufficient signal-to-noise ratio, and an appropriate theoretical reconstruction algorithm. This study proposes several transmission-type schemes to achieve coherent imaging of thin materials (less than 5 nm thick) with atomic resolution at voltages lower than 10 kV. Experimental schemes of both lens-less and lens-containing designs and preliminary results based on a highly coherent single-atom electron source are presented. The image plate is designed to be retractable to record the transmission patterns at different positions along the beam propagation direction. In addition, the authors proposed reflection-type coherent electron imaging schemes as novel methods for characterizing surface atomic and electronic structures of materials. The ultimate goal is to achieve high-contrast and high-spatial-resolution imaging of thin materials, such as two-dimensional materials, or molecules, such as organic or biological molecules, under low-dose conditions.