Abstract
A bewildering number of techniques have been developed for transmission electron microscopy (TEM), involving the use of ever more complex combinations of lens configurations, apertures and detector geometries. In parallel, the developments in the field of ion beam instruments have modernized sample preparation and enabled the preparation of various types of materials. However, the desired final specimen geometry is always almost the same: a thin foil of uniform thickness. Here we will show that judicious design of specimen geometry can make all the difference and that experiments can be carried out on the most basic electron microscope and in the usual imaging modes. We propose two sample preparation methods that allow the formation of controlled moiré patterns for general monocrystalline structures in cross-section and at specific sites. We developed moiré image treatment algorithms using an absolute correction of projection lens distortions of a TEM that allows strain measurements and mapping with a nanometer resolution and 10−4 precision. Imaging and diffraction techniques in other fields may in turn benefit from this technique in perspective.
Highlights
Developments in transmission electron microscopy (TEM) have centered on improving instrumentation and optical configurations
Even dark-field inline holography (DIH) and convergent-beam electron diffraction (CBED) require an imaging energy filter faced with the complexity of the data simulation and interpretation[12,13,16,17]
How can we design the specimen geometry to perform the technique on the most basic conventional TEM: by returning to the moiré imaging phenomenon known from the very beginnings of electron microscopy[18,19]
Summary
The four principle stages of the tripod preparation method are (Fig. 1d): (1) gluing of a cross-sectional sample, cutting a slice, tripod based grinding of the slice butt (A), grinding and polishing of the slice front side (B); (2) grinding and polishing of the slice back side (C) leaving a 300 μm–600 μm-thick lamella with mutually parallel B and C surfaces. For the reconstruction of the geometric phase for the FIB-prepared samples, where the fringe spacing is large, we used a reconstruction method functioning in real space[30] which allows the improvement of the spatial resolution by a factor of 2 with respect to the Fourier method used in GPA6 or DFEH11 It involves several steps: detection of the fringe minimums and maximums, calculation of envelope functions, normalization of the interference pattern to retrieve the cosine function and calculation of the phase image.
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