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Crystal diffraction is a well-established technique for high-resolution structural analysis of material science and biological samples. However, the recovered structure is a result of averaging over all the unit cells in the crystal, which smears out the imperfections, atomic defects, or asymmetries and chiral properties of the individual molecules. We propose Bragg holography, where a nano-crystal is imaged at a defocus distance allowing separation of the diffracted beams, without turning them into peaks. The presence of a reference wave gives rise to a Bragg hologram, which can be reconstructed by conventional holographic reconstruction algorithms. The recovered complex-valued wavefront contains the complete information about the atomic distribution in the crystal, including defects. Bragg holography is demonstrated for gold nano-crystals, and its feasibility for biological nano-crystals is shown., source:https://www.sciencedirect.com/science/article/pii/S030439912100156X

In this report, we applied annular bright-field (ABF) and annular dark-field (ADF) low-energy (30 keV) scanning transmission electron microscopy (STEM) imaging to a vitreous ice-embedded biological macromolecule, T4 phage, to investigate the applicability of these methods for morphological investigation and sample screening. Multiple camera lengths were examined to find the optimal acceptance angle for both modes. Image clarity differed substantially between the modes, with the presence of ice also strongly influencing the quality of acquired micrographs. In ADF mode, the proper discrimination of electrons scattered by the specimen from those scattered by the background ice was found to be difficult owing to the severe overlap of the scattered electrons. The resulting micrographs lacked clarity, and the ice-embedded phage particles could only be discerned after post-processing image adjustment. However, in ABF mode, despite similar overlapping of the scattered electrons, it was possible to assess the morphology and intactness of the specimen in the embedding ice, suggesting that this mode may find utility in low-energy cryo-STEM imaging methods., source:https://academic.oup.com/jmicro/advance-article/doi/10.1093/jmicro/dfac056/6767311

In this work, we have explored the factors which govern mean free path values obtained from off-axis electron holography measurements. Firstly, we explore the topic from a theoretical perspective, and show that the mean amplitude reconstructed from off-axis holograms is due to the coherent portion of the direct, central object-transmitted beam only – it is not affected by the presence or absence of other scattered beams. Secondly, we present a detailed experimental study which compares mean free path values obtained from hologram sideband, centreband, EELS, and TEM measurements as a function of optical collection angle and energy-loss-filtering. These results confirm that the coherent portion of the direct beam defines the mean amplitude, and additionally show that the coherent portion corresponds to the conventional energy-filtered signal (with threshold 5 eV in this work). Finally, we present summary measurements from a selection of different materials, and compare the results against a simple electron scattering model. This study reinforces the claim that the mean amplitude is defined by the energy-filtered direct beam, and confirms that the contributions of elastic and inelastic scattering to the total mean free path are broadly in line with theoretical expectations for these different materials. These results in aggregate indicate that neither experimental collection angles nor enhanced sensitivity to low-loss phonon scattering affect the mean amplitude signal arising from off-axis holography reconstructions, nor the associated mean free path values which are derived from this mean amplitude., source:https://www.sciencedirect.com/science/article/pii/S0968432822001421?via%3Dihub

In this report, we applied annular bright-field (ABF) and annular dark-field (ADF) low-energy (30 keV) scanning transmission electron microscopy (STEM) imaging to a vitreous ice-embedded biological macromolecule, T4 phage, to investigate the applicability of these methods for morphological investigation and sample screening. Multiple camera lengths were examined to find the optimal acceptance angle for both modes. Image clarity differed substantially between the modes, with the presence of ice also strongly influencing the quality of acquired micrographs. In ADF mode, the proper discrimination of electrons scattered by the specimen from those scattered by the background ice was found to be difficult owing to the severe overlap of the scattered electrons. The resulting micrographs lacked clarity, and the ice-embedded phage particles could only be discerned after post-processing image adjustment. However, in ABF mode, despite similar overlapping of the scattered electrons, it was possible to assess the morphology and intactness of the specimen in the embedding ice, suggesting that this mode may find utility in low-energy cryo-STEM imaging methods., source:https://academic.oup.com/jmicro/advance-article/doi/10.1093/jmicro/dfac056/6767311

In this work, we have explored the factors which govern mean free path values obtained from off-axis electron holography measurements. Firstly, we explore the topic from a theoretical perspective, and show that the mean amplitude reconstructed from off-axis holograms is due to the coherent portion of the direct, central object-transmitted beam only – it is not affected by the presence or absence of other scattered beams. Secondly, we present a detailed experimental study which compares mean free path values obtained from hologram sideband, centreband, EELS, and TEM measurements as a function of optical collection angle and energy-loss-filtering. These results confirm that the coherent portion of the direct beam defines the mean amplitude, and additionally show that the coherent portion corresponds to the conventional energy-filtered signal (with threshold 5 eV in this work). Finally, we present summary measurements from a selection of different materials, and compare the results against a simple electron scattering model. This study reinforces the claim that the mean amplitude is defined by the energy-filtered direct beam, and confirms that the contributions of elastic and inelastic scattering to the total mean free path are broadly in line with theoretical expectations for these different materials. These results in aggregate indicate that neither experimental collection angles nor enhanced sensitivity to low-loss phonon scattering affect the mean amplitude signal arising from off-axis holography reconstructions, nor the associated mean free path values which are derived from this mean amplitude., source:https://www.sciencedirect.com/science/article/pii/S0968432822001421?via%3Dihub

The mean free path governing the scattering of high-energy electrons in cadmium telluride (CdTe) has been measured and analyzed using off-axis electron holography (OEH). In the first part of the study, the total mean free path value was determined via acquisition and aggregation of a large off-axis holography dataset at 300 kV and room temperature, yielding the value [See formula in full text]. This is significantly shorter than some previously reported values obtained via different experimental techniques and theoretical calculations. To confirm the validity of the measurement and to understand the underlying physical scattering processes, the study was extended to systematically investigate the role of electron energy loss, electron scattering angle, and specimen temperature in the overall holography measurement. This allowed the observed mean free path value to be clearly decomposed into terms of electronic (inelastic) and nuclear (elastic) scattering processes in the material and enabled direct measurement of the relevant contributions. Specifically, the determined attenuation coefficients were [See formula] (full details in the main text). With appropriate consideration of the relevant scattering mechanisms, the mean free path value determined here from off-axis holography measurements is consistent with prior experimental measurements from other techniques and theoretical calculations. These insights and measurements should be of future value for quantitative holography and electron beam scattering experiments in CdTe., source:https://aip.scitation.org/doi/full/10.1063/5.0036989