Electron Beam Precession Research Articles

Accurate measurement of strain at interfaces in 4D-STEM: A comparison of various methods

Strain analysis by nano-beam electron diffraction allows for measurements of strain with nanometre resolution in a large field of view. This is done by evaluating distances between diffraction discs in diffraction patterns acquired while a focussed electron beam is scanned across the sample in a transmission electron microscope. The bottleneck of this method is a precise determination of diffraction disc positions, which suffers from the inner structure of the discs caused by dynamical diffraction. Electron beam precession is a tool that solves this problem but it is not commonly available in every microscope. Without precession significant progress has been reported recently by using patterned condenser apertures. The pattern of the aperture is reproduced in patterns of the diffraction discs allowing for a more precise position determination. In this report the accuracy of measured strain profiles using patterned apertures is investigated by evaluation of realistic simulations. This is done especially at interfaces between regions with different lattice plane spacing. It is found by evaluation of the simulations that measured strain profiles are more blurred and hence the accuracy at the interface is worse the more patterns are imprinted to the condenser aperture. An explanation of this effect is given and as a proof of principle a solution to this problem is provided applying geometric phase analysis ptychography.

Strain analysis from nano-beam electron diffraction: Influence of specimen tilt and beam convergence

Strain analyses from experimental series of nano-beam electron diffraction (NBED) patterns in scanning transmission electron microscopy are performed for different specimen tilts. Simulations of NBED series are presented for which strain analysis gives results that are in accordance with experiment. This consequently allows to study the relation between measured strain and actual underlying strain. A two-tilt method which can be seen as lowest-order electron beam precession is suggested and experimentally implemented. Strain determination from NBED series with increasing beam convergence is performed in combination with the experimental realization of a probe-forming aperture with a cross inside. It is shown that using standard evaluation techniques, the influence of beam convergence on spatial resolution is lower than the influence of sharp rings around the diffraction disc which occur at interfaces and which are caused by the tails of the intensity distribution of the electron probe.

NiTi Shape Memory Marformed Alloy Studied by Electron Beam Precession TEM Orientation Mapping Method

NiTi Shape Memory Marformed Alloy Studied by Electron Beam Precession TEM Orientation Mapping Method

Orientation and phase mapping in the transmission electron microscope using precession‐assisted diffraction spot recognition: state‐of‐the‐art results

A recently developed technique based on the transmission electron microscope, which makes use of electron beam precession together with spot diffraction pattern recognition now offers the possibility to acquire reliable orientation/phase maps with a spatial resolution down to 2 nm on a field emission gun transmission electron microscope. The technique may be described as precession-assisted crystal orientation mapping in the transmission electron microscope, precession-assisted crystal orientation mapping technique-transmission electron microscope, also known by its product name, ASTAR, and consists in scanning the precessed electron beam in nanoprobe mode over the specimen area, thus producing a collection of precession electron diffraction spot patterns, to be thereafter indexed automatically through template matching. We present a review on several application examples relative to the characterization of microstructure/microtexture of nanocrystalline metals, ceramics, nanoparticles, minerals and organics. The strengths and limitations of the technique are also discussed using several application examples.

Grain Boundary Character Distribution of Nanocrystalline Cu Thin Films Using Stereological Analysis of Transmission Electron Microscope Orientation Maps

Stereological analysis has been coupled with transmission electron microscope (TEM) orientation mapping to investigate the grain boundary character distribution in nanocrystalline copper thin films. The use of the nanosized (<5 nm) beam in the TEM for collecting spot diffraction patterns renders an order of magnitude improvement in spatial resolution compared to the analysis of electron backscatter diffraction patterns in the scanning electron microscope. Electron beam precession is used to reduce dynamical effects and increase the reliability of orientation solutions. The misorientation distribution function shows a strong misorientation texture with a peak at 60°/[111], corresponding to the Σ3 misorientation. The grain boundary plane distribution shows {111} as the most frequently occurring plane, indicating a significant population of coherent twin boundaries. This study demonstrates the use of nanoscale orientation mapping in the TEM to quantify the five-parameter grain boundary distribution in nanocrystalline materials.

Structure solution with automated electron diffraction tomography data: different instrumental approaches

Over the past few years automated electron diffraction tomography has become an established technique for structure solution of nano-crystalline material. The intentional choice of an arbitrary tilt axis and thus, the use of nonoriented diffraction patterns (off-zone acquisition) together with fine equidistant sampling of the reciprocal space result in high quality intensity data sets. Coupling automated electron diffraction tomography with electron beam precession (Vincent & Midgley, 1994) enables sampling of intensities between the static slices of reciprocal space and therefore enhances the quality of intensity data further; relatively complex structures have been solved using 3D electron diffraction intensities extracted from automated electron diffraction tomography data. Automated electron diffraction tomography data was collected initially using a dedicated automated module. In this manuscript we demonstrate that electron diffraction data of comparable quality can be collected using manual technique that mimics the automated process. A rather difficult material, i.e. a low symmetric (triclinic) sodium tetratungstate (Na(2) W(4) O(13) ) including heavy and light scatterers, was selected for testing. In this paper we show, that all collected data sets - automatic and manual, with and without electron beam precession - were able to provide data slightly different but suitable for ab initio structure solution and refinement.

A new approach for 3D reconstruction from bright field TEM imaging: Beam precession assisted electron tomography

The successful combination of electron beam precession and bright field electron tomography for 3D reconstruction is reported. Beam precession is demonstrated to be a powerful technique to reduce the contrast artifacts due to diffraction and curvature in thin foils. Taking advantage of these benefits, Precession assisted electron tomography has been applied to reconstruct the morphology of Sn precipitates embedded in an Al matrix, from a tilt series acquired in a range from +49° to -61° at intervals of 2° and with a precession angle of 0.6° in bright field mode. The combination of electron tomography and beam precession in conventional TEM mode is proposed as an alternative procedure to obtain 3D reconstructions of nano-objects without a scanning system or a high angle annular dark field detector.

Elucidating Gating Effects for Hydrogen Sorption in MFU‐4‐Type Triazolate‐Based Metal–Organic Frameworks Featuring Different Pore Sizes

A highly porous member of isoreticular MFU-4-type frameworks, [Zn(5)Cl(4)(BTDD)(3)] (MFU-4l(arge)) (H(2)-BTDD=bis(1H-1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo[1,4]dioxin), has been synthesized using ZnCl(2) and H(2)-BTDD in N,N-dimethylformamide as a solvent. MFU-4l represents the first example of MFU-4-type frameworks featuring large pore apertures of 9.1 Å. Here, MFU-4l serves as a reference compound to evaluate the origin of unique and specific gas-sorption properties of MFU-4, reported previously. The latter framework features narrow-sized pores of 2.5 Å that allow passage of sufficiently small molecules only (such as hydrogen or water), whereas molecules with larger kinetic diameters (e.g., argon or nitrogen) are excluded from uptake. The crystal structure of MFU-4l has been solved ab initio by direct methods from 3D electron-diffraction data acquired from a single nanosized crystal through automated electron diffraction tomography (ADT) in combination with electron-beam precession. Independently, it has been solved using powder X-ray diffraction. Thermogravimetric analysis (TGA) and variable-temperature X-ray powder diffraction (XRPD) experiments carried out on MFU-4l indicate that it is stable up to 500 °C (N(2) atmosphere) and up to 350 °C in air. The framework adsorbs 4 wt % hydrogen at 20 bar and 77 K, which is twice the amount compared to MFU-4. The isosteric heat of adsorption starts for low surface coverage at 5 kJ mol(-1) and decreases to 3.5 kJ mol(-1) at higher H(2) uptake. In contrast, MFU-4 possesses a nearly constant isosteric heat of adsorption of ca. 7 kJ mol(-1) over a wide range of surface coverage. Moreover, MFU-4 exhibits a H(2) desorption maximum at 71 K, which is the highest temperature ever measured for hydrogen physisorbed on metal-organic frameworks (MOFs).

Precession technique and electron diffractometry as new tools for crystal structure analysis and chemical bonding determination

We have developed a new fast electron diffractometer working with high dynamic range and linearity for crystal structure determinations. Electron diffraction (ED) patterns can be scanned serially in front of a Faraday cage detector; the total measurement time for several hundred ED reflections can be tens of seconds having high statistical accuracy for all measured intensities (1–2%). This new tool can be installed to any type of TEM without any column modification and is linked to a specially developed electron beam precession “Spinning Star” system. Precession of the electron beam (Vincent–Midgley technique) reduces dynamical effects allowing also use of accurate intensities for crystal structure analysis. We describe the technical characteristics of this new tool together with the first experimental results. Accurate measurement of electron diffraction intensities by electron diffractometer opens new possibilities not only for revealing unknown structures, but also for electrostatic potential determination and chemical bonding investigation. As an example, we present detailed atomic bonding information of CaF 2 as revealed for the first time by precise electron diffractometry.

Some effects in field electron emission from a YBa 2Cu 3O 7 − x superconductor

Field electron emission from YBa 2Cu 3O 7 − x ceramic samples was studied. For superconducting samples the emission localization effect was observed. Depending on the electric field strength and emitter temperature the transition from the localized spot to the surrounding ring appears. The effect of electron beam precession was also observed. The feasible mechanism of the appearance of the above effects may be connected with the existence of electron pairs in high- T c superconductors.