High-resolution transmission electron microscopy with an electrostatic Zach phase plate

S Hettler,J Zeelen,R R Schröder,M Dries,M Oster,D Gerthsen

doi:10.1088/1367-2630/18/5/053005

Abstract

A new method to control lattice-fringe contrast in high-resolution transmission electron microscopy (HRTEM) images by the implementation of a physical phase plate (PP) is proposed. PPs are commonly used in analogy to Zernike PPs in light microscopy to enhance the phase contrast of weak-phase objects with nm-sized features, which often occur in life science applications. Such objects otherwise require strong defocusing, which leads to a degradation of the instrumental resolution and impedes intuitive image interpretation. The successful application of an electrostatic Zach PP in HRTEM is demonstrated by the investigation of single crystalline Si and Ge samples. The influence of the Zach PP on the image formation process is assessed by analyzing the amplitudes of (111) reflections in power spectra which show a cosine-type dependence on the induced phase shift under certain conditions as predicted by theory.

Highlights

Transmission electron microscopy (TEM) is routinely applied to obtain images with atomic resolution
The phase contrast transfer function (PCTF), which is given by equation (1), describes the transfer of phase information encoded in the object wave below the specimen into image intensity [1]
We demonstrate for the first time that HRTEM lattice fringe imaging can be achieved with an electrostatic Zach phase plate (PP) using single crystalline Si and Ge samples as test objects

Summary

Introduction

Transmission electron microscopy (TEM) is routinely applied to obtain images with atomic resolution. In TEM, an electron-transparent specimen is illuminated by a plane electron wave, whose phase and amplitude is altered upon propagation through the object. The achievable image contrast mainly depends on the structure, thickness and elemental composition of the specimen as well as the chosen imaging parameters. High-resolution (HR) TEM imaging requires very thin objects, which, depending on their properties, may only weakly modify the phase of the electron wave, while the amplitude remains essentially unchanged. Phase contrast of so-called weak-phase objects (WPOs) is only obtained if an additional phase shift (ideally π/2) is generated between the scattered and unscattered part of the object wave. In conventional TEM, the lens aberrations of the imaging system are exploited to generate such a phase shift. The phase contrast transfer function (PCTF), which is given by equation (1), describes the transfer of phase information encoded in the object wave below the specimen into image intensity [1]

Methods

Results

Conclusion