New materials for thin-film phase-plates

TL;DR

This paper introduces a novel aluminium metal-based Zernike phase-plate for TEM, demonstrating improved stability and reduced charging compared to traditional carbon plates, with potential for enhanced imaging performance.

Contribution

It presents the first production and testing of metal (aluminium) phase-plates for TEM, including cryo-deposition techniques to create amorphous metal films with improved durability and reduced distortions.

Findings

Aluminium phase-plates show no charging and high stability.

Cryo-deposited metal-films are amorphous and reduce distortions.

Metal-films exhibit lower electron-scattering and longer durability.

Abstract

Previous Zernike phase-plates, for transmission-electron-microscopy (TEM) have always been made out of carbon. A critical constraint on those phase-plates is their fast degradation during use. Here, a Zernike phase-plate consisting out of metal is produced and tested for the first time. For the new aluminium phase-plate, no charging like for the carbon phase-plate is observed. Under conditions of use, the stability of the aluminium phase-plate, is excellent. For both materials, a distortion in the image's Fourier-transformation is observed, when inserting the thin-film into the beam at the back-focal-plane. This distortion is a negative, spatial-frequency dependent phase-shift, that is not equal to a focus-change. A phase-shift and an increase of contrast, is observed for the tested phase-plates. Different types of self-sustaining metal-films are produced with a technique, invented by Janbroers et al. All metal-films, produced at room-temperature, exhibit a polycrystalline structure, while carbon-films are amorphous. However, a high crystallinity is unfavored, causing distortions in the image and an increase of electron-scattering in the phase-plate, due to diffraction. Using cryo-deposition, metal-films are obtained that combine an amorphous structure with beneficial properties of metals such as lower charging and prolonged durability. Investigations with TEM, show a great potential of those cryo-films as material for Zernike phase-plates. Thickness-measurements are successfully carried out with atomic-force-mycroscopy at step-edges between the thin-film and its substrate. For this, a technique for the preparation of very narrow step-edges is developed here.