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Structural characterisation of advanced silicides
Published in A. G. Cullis, P. A. Midgley, Microscopy of Semiconducting Materials 2003, 2018
H Bender, O Richard, L Nistor, A Gutakovskii, C Stuer, C Detavernier
spectroscopy is a very suitable technique (Howard et a! 1996, De Wolf 1999, Steegen et a! 1999). The lateral resolution is however limited to - 0.7-1.0 r.tm which is far above the needs of modern micro-electronics. Convergent beam electron diffraction (CBED) is the only analytical technique that has enough spatial resolution to directly analyse the stress in very narrow lines (Armigliato et all993, Stuer et al 2001, Stuer 2001). The use of advanced FEG instruments allows beam spots down to I nm. Nevertheless, the needed tilt away from the <Oll>s; directions along which the structures are aligned to [013} (26.6°) or [023} (11.3°) limits the resolution and creates stress gradients within the probed volume that blur the CBED patterns. Therefore the regions with the highest stress, which are actually the most interesting, can often not be analysed. Combination with calculation of the strain with finite element simulation methods can partially overcome this problem. The correspondence between the experimentally determined strain and the simulations is generally good, giving confidence to the simulated values in the high stress regions. The use of energy filtering (Fig. 1Ob) improves the CBED patterns so that cooling to liquid nitrogen is not necessary. The smaller spot sizes at higher beam voltages allow measurements in areas with higher stress (e.g. point 3 on Fig. 10c).
Diffraction
Published in Peter E. J. Flewitt, Robert K. Wild, Physical Methods for Materials Characterisation, 2017
Peter E. J. Flewitt, Robert K. Wild
This class of diffraction patterns was first demonstrated in 1939 by Kossel and Mollenstedt, but their use and application have recently only become widespread following the ability to produce electron beams with a small diameter in the TEM and STEM. The effect has many similarities to Kikuchi diffraction. In convergent beam electron diffraction (CBED), the operating conditions in the microscope are arranged such that the electron beam is focused onto the crystal specimen. Thus, the specimen is traversed by a cone of electron beams. Convergent beam diffraction (CBD) differs from Kikuchi diffraction only in that for the convergent beam the cone of electrons is produced externally while in Kikuchi diffraction the cone of electrons arises from the diffuse scattering within the crystal. The principle is illustrated in Figure 3.72 where the cone of electrons is incident on the specimen surface at the plane BB′, the objective lens then focuses the diffracted beams onto the back focal plane at CC′ and DD′. The ray diagrams for the production of CBD are shown in Figure 3.73 for both the TEM and STEM modes. Here, the second condenser aperture determines the convergence angle and a large number with varying diameters is required. The objective lens focuses the electron beam onto the back focal plane after passing through the specimen. For a more detailed description of the technique, the reader is referred to Steeds (1979) and Tanaka and Terauchi (1985). These patterns display the variation in the intensity of transmitted or diffracted beams as a function of the angle between the incident electron beams and the crystal. These patterns have been given the generic name ‘Tanaka patterns’, and a typical bright-field pattern is shown in Figure 3.74 for a stainless steel specimen. This is essentially a map of the intensity of the direct beam variation with angle, over a range of angles in the general region of the [001] zone axis (Eades 1988).
Influence of transition elements (Zr, V, and Mo) on microstructure and tensile properties of AlSi8Mg casting alloys
Published in Canadian Metallurgical Quarterly, 2023
Zhan Zhang, Anil Arici, Francis Breton, X.-Gant Chen
Conventional metallographic polishing method was used to prepare the samples for microstructure observation. The polished samples were etched by 0.5% HF in deionised water for 35 s to reveal the distribution of dispersoids. A scanning electron microscope (SEM, JSM-6480LV) equipped with an energy dispersive X-ray spectrometer (EDS) was used to analyse the microstructure of these experimental alloys. A transmission electron microscope (TEM, JEM-2100) equipped with an energy dispersive EDS was applied to examine precipitates and dispersoids in detail. TEM foils were prepared in a twin-jet electropolisher using a solution of 30% nitric acid in methanol at −20°C. Convergent-beam electron diffraction (CBED) patterns were used to measure the thicknesses of TEM foils for the calculation of number density of dispersoids and precipitates. An optical image analyzer with CLEMEX JS-2000, PE4.0 software was employed to quantitatively characterise the phase features on optical, SEM and TEM images. For Si particles, 25 optical images with 500× magnifications for each sample were taken, and then the characteristics of the silicon particles in those optical images were statistically analysed using the image analyzer. For intermetallic particles, 25 backscattered SEM images with 500× magnification for each sample were statistically analysed with the image analyzer. The characteristics of needle-like β″-MgSi precipitates, such as the number density and size, were analysed with the methods developed in Ref. [19], and 6–8 TEM bright-field images with 50,000× magnification for each T6 sample were quantitatively analysed.
Many-beam dynamical scattering simulations for scanning and transmission electron microscopy modalities for 2D and 3D quasicrystals
Published in Philosophical Magazine, 2019
Saransh Singh, William C. Lenthe, Marc De Graef
In this section, we present results of dynamical electron scattering simulations for two different electron diffraction modalities: convergent beam electron diffraction (CBED) and electron backscatter diffraction (EBSD). Zone Axis diffraction patterns (ZADP) for quasicrystals have previously been presented in [8,11] and will not be presented for the sake of brevity. For this paper, we use the AlNiCo quasicrystalline phase as an example. The structure of this phase has been refined using 5D crystallography and single crystal x-ray intensity data [28]. The phase has a centrosymmetric 5D space group P10/mmc, quasi-lattice parameters nm , and nm, . For more details about the possible space groups of axial crystals and quasicrystals, the reader is referred to [29]. This phase is locally very similar to the monoclinic CoAl phase with the b-axis as the pseudo-decagonal zone. The refined structure for the approximant phase has been studied in detail in [30].
Dislocation imaging through mapping based on the combination of an electron energy-loss spectroscope with a scanning transmission electron microscope
Published in Philosophical Magazine Letters, 2021
The possible causes for the ZLP broadening and 0.5 eV feature are discussed here. First, we focus on the energies of lattice vibrations. It has been reported that the local vibrational energies of atoms in an edge dislocation core and a perfect crystal area in bcc-Fe are approximately −0.026 and −0.0281 eV, respectively [11]. This means that although the monochromated system used in this study could not resolve phonon peaks, it successfully detected phonon scatterings by dislocations through the ZLP broadening [13]. Second, to explain the 0.5 eV feature, both EELS and local convergent beam electron diffraction (CBED) measurements were conducted at various crystal orientations. It was observed that the 0.5 eV feature was enhanced when the direction of the incident beam was nearly along the zone axis. This suggests that the 0.5 eV feature is influenced by the number of diffracted beams that enter the EESL detector. Further, the 0.5 eV feature is confirmed not to be necessarily related to the FWHM of the ZLP. CBED measurements were conducted to study the unique contrast comprising bright, grey, and dark areas of the dislocation, as shown in Figure 3d. Interestingly, dark lines are formed along with bright ones in some places, indicating that the ‘FWHM’ decreased on one side of the dislocation and increased on the other side. Figure 4 shows the CBED patterns obtained from a perfect area and both sides near a dislocation. We can observe that the rocking curve of a reflection line in the dark-field disk is symmetric with respect to the excitation error w = 0 (the exact Bragg position) in the perfect area but becomes asymmetric about w = 0 due to additional fringes in the reflection line near the dislocation.