Abstract
Electron backscatter diffraction is a scanning electron microscopy technique used to obtain crystallographic information on materials. It allows the nondestructive mapping of crystal structure, texture, and strain with a lateral and depth resolution on the order of tens of nanometers. Electron backscatter diffraction patterns (EBSPs) are presently acquired using a detector comprising a scintillator coupled to a digital camera, and the crystallographic information obtainable is limited by the conversion of electrons to photons and then back to electrons again. In this article we will report the direct acquisition of energy-filtered EBSPs using a digital complementary metal-oxide-semiconductor hybrid pixel detector, Timepix. We show results from a range of samples with different mass and density, namely diamond, silicon, and GaN. Direct electron detection allows the acquisition of EBSPs at lower (≤5 keV) electron beam energies. This results in a reduction in the depth and lateral extension of the volume of the specimen contributing to the pattern and will lead to a significant improvement in lateral and depth resolution. Direct electron detection together with energy filtering (electrons having energy below a specific value are excluded) also leads to an improvement in spatial resolution but in addition provides an unprecedented increase in the detail in the acquired EBSPs. An increase in contrast and higher-order diffraction features are observed. In addition, excess-deficiency effects appear to be suppressed on energy filtering. This allows the fundamental physics of pattern formation to be interrogated and will enable a change in the use of electron backscatter diffraction (EBSD) for crystal phase identification and the mapping of strain. The enhancement in the contrast in high-pass energy-filtered EBSD patterns is found to be stronger for lighter, less dense materials. The improved contrast for such materials will enable the application of the EBSD technique to be expanded to materials for which conventional EBSD analysis is not presently practicable.
Highlights
In the development and study of new materials, the understanding of their crystal structure plays a crucial rule
In the present work we propose a method for the acquisition of energy-filtered Electron backscatter diffraction patterns (EBSPs) where direct electron detection and energy filtering is achieved using a digital complementary metal-oxide semiconductor (CMOS) hybrid pixel detector, Timepix [25]
Parameters used to define the performance of an imaging detector are the modulation transfer function (MTF), which gives a measure of the spatial frequency response of a detector, and the noise power spectrum (NPS), which describes the spectral component of the noise added to the image by the detection system
Summary
In the development and study of new materials, the understanding of their crystal structure plays a crucial rule. In the present work we propose a method for the acquisition of energy-filtered EBSPs where direct electron detection and energy filtering is achieved using a digital complementary metal-oxide semiconductor (CMOS) hybrid pixel detector, Timepix [25] This approach avoids the use of the phosphor screen and CCD camera combination, and allows energy filtering to be accomplished without any additional hardware: the functionality is implemented in the electronics chip. This allows the acquisition of small-scale details in the EBSP which are not in practice obtainable with existing commercial EBSD systems This may provide routes to, for example, the determination of lattice constant, crystal phase identification, and the mapping of strain with greater sensitivity [6,15].
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