Design and electron optics performance of a MEMS electrostatic electron monochromator

Abstract

Monochromators are routinely used in Transmission Electron Microscopy and Electron Energy Loss Spectroscopy, to improve both spatial and energy resolution. State-of-the-art monochromators, however, are complex instruments that typically require additional electron optical correctors, limiting their implementation to the high-end, most expensive microscopes. Miniaturized monochromation relying on purely electrostatic fringe fields has recently been proposed as a means to realize a simpler and thereby more cost-effective and easier to operate high-resolution monochromator. Here, we present a design for such a compact, fully electrostatic fringe-field based monochromator. Our design consists of a superposition of an Einzel lens with a series of electrostatic deflectors and is entirely based on dimensions that can be realized with MEMS fabrication technology. Thanks to mild mechanical and electrostatic potential tolerances, the MEMS-fabricated electrodes can be passively aligned and only need seven regular power supplies. We present an analysis of spectral broadening due to diffraction in our monochromator design as well as particle simulations including stochastic Coulomb interactions. This analysis shows that our design can achieve a resolution of 19 meV while maintaining 128 pA of beam current and thus potentially achieve energy filtering comparable to state-of-the-art monochromators. Our MEMS monochromator could therefore bring the application of energy filtering into the domain of SEM and specifically allow higher resolution imaging in chromatic-aberration dominated low-voltage SEM.