Large-angle convergent-beam electron diffraction patterns via conditional generative adversarial networks.

The accuracy of electron density distribution analysis using large-angle convergent-beam electron diffraction (LACBED) patterns is evaluated for different convergence angles. An orbital ordered state of FeCr2O4 is used as an example of the analysis. Ideal orbital-ordered and non-ordered states are simulated by using orbital scattering factors. LACBED patterns calculated for the orbital-ordered state were used as hypothetical experimental data sets. Electron density distribution of the Fe 3d orbitals has been successfully reconstructed with a higher accuracy from LACBED patterns with convergence angles larger than 15.2 mrad, which is 4 times as large as that for conventional convergent-beam electron diffraction patterns. Excitation of particular Bloch waves with the aid of LACBED patterns has a key role in the accurate analysis of electron density distributions.

The characterization of the Burgers vector of dislocations from large-angle convergent-beam electron diffraction (LACBED) patterns is now a well-established method. The method has already been applied to relatively large and isolated dislocation loops in semiconductors. Nevertheless, some severe experimental difficulties are encountered with small dislocation loops. By using a 2 microm selected-area aperture and a carbon contamination point to mark the loop of interest, we were able to characterize both the plane and the Burgers vector of dislocation loops of a few tens of nanometres in size present in Al-Cu-Mg alloys.

Conventional methods of convergent beam electron diffraction (CBED) use a fully converged probe focused on the specimen in the object plane resulting in the formation of a CBED pattern in the diffraction plane. Large angle CBED (LACBED) uses a converged but defocused probe resulting in the formation of ‘shadow images’ of the illuminated sample area in the diffraction plane. Hence, low-spatial resolution image information and high-angular resolution diffraction information are superimposed in LACBED patterns which enables the simultaneous observation of crystal defects and their effect on the diffraction pattern. In recent years LACBED has been used successfully for the investigation of a variety of crystal defects, such as stacking faults, interfaces and dislocations. In this paper the contrast from coherent precipitates and decorated dislocations in LACBED patterns has been investigated. Computer simulated LACBED contrast from decorated dislocations and coherent precipitates is compared with experimental observations.

A new method using Large Angle Convergent Beam Electron Diffraction (LACBED) patterns is proposed to measure accurately the grain boundary misorientation. The LACBED patterns which are obtained with a defocused convergent electron beam having a convergence semi-angle in the range 1 to 5o contain very sharp deficiency lines. Due to the good quality of the LACBED patterns, these sharp deficiency lines can be used to measure with great accuracy the grain boundary misorientation. In addition, since the LACBED method is a defocus mode method, the patterns contain at the same time information on the reciprocal space (the deficiency lines typical of the crystal orientation of the two grains on each side of the grain boundary) and on the real space (the image of the grain boundary). We describe a method which allows the identification of the misorientation from these LACBED patterns. The main point to consider is the accuracy which is about 0.05o. It is much better than the one obtained from other conventional methods used to measure this misorientation.

Surface relaxation of strained heterostructures revealed by Bragg line splitting in LACBED patterns

Convergent-beam electron diffraction in the high-voltage electron microscope with continuously variable reference voltage for lenses and alignments

CBED and LACBED: characterization of antiphase boundaries

Reasonably good images of dislocations in LACBED patterns and effects of dislocation strain fields on the Bragg lines

Determination of the orientation of a stacking fault by large-angle convergent-beam electron diffraction (LACBED)

Analysis of extended defects in melt-grown GaSe single crystals by convergent-beam electron diffraction techniques

Decorated and undecorated dislocations in γ-TiAl have been studied by conventional transmission electron microscopy using diffraction contrast and by large-angle convergent-beam electron diffraction (LACBED). The results of the Burgers vector determination for undecorated and decorated dislocations using the different techniques have been compared. For the decorated dislocations the contrast from the decorating particles and the underlying dislocation have been separated and the misfit introduced by the precipitates has been determined. Computer simulations of the contrast from decorated dislocations in LACBED patterns have been performed. The rules governing the dislocation contrast in LACBED patterns have been discussed and extended to the case of decorated dislocations. A new fringe-counting rule to determine the Burgers vectors of dislocations decorated by misfitting precipitates has been proposed. Remarkably good agreement of the computer-simulated LACBED contrast with experimental observations has been achieved.

Convergent-beam electron diffraction (CBED) techniques have been applied to the study of silicon layers grown laterally on partially oxidized silicon wafers by liquid-phase epitaxy. Energy filtering of the electrons in the microscope provides CBED patterns from cross-sectional and plan-view specimens of large thickness with improved contrast and angular resolution. Cross-sections from the interfacial regions show a splitting or a broadening of the rocking profile of lines in CBED patterns. Strains at the Si–SiO2 interfaces are deduced from the patterns and related to relaxation effects in the special geometry of the cross-sectional specimens. Inference to bulk systems reveals that the Si lattice is in a state of tetragonal distortion close to the Si/SiO2 interface. Large-angle CBED patterns from plan-view specimens reveal a bending of Si layers relative to the substrate. Examples in the study of lateral coalescence of Si layers are demonstrated, such as the reversal of bending of the layers at th...

The structure of a new metastable Al-Ge phase recrystallized at 300°C from amorphous films with equiatomic composition deposited on to NaCl substrates cooled with liquid nitrogen was determined by convergent beam electron diffraction (CBED). The micron-sized crystals were tetragonal with space group 14/mcm, lattice parameters a = 6.13 Å and c = 4.92 Å, and composition Al0·9 Ge0·9. The structure was the C16 type with nominal AB 2 composition, although there was no evidence for preferential location of Ge on either A or B sites. The A atoms occupied 4(a) sites, and the B atoms were located on 8(h) sites with x = 0·158. Conditional Patterson transforms parallel to the c axis were calculated from kinematic intensities measured in focused large-angle CBED patterns. The contour maps showed clear peaks from A-B and B-B interatomic vectors. Dynamical perturbations reduced peak visibility but did not affect peak positions. The x parameter for B atoms was refined from the quasi-kinematic intensities of first-order Laue zone reflections diffracted from Bloch states localized on B atom strings in conventional CBED patterns.

Large angle convergent beam electron diffraction (LACBED) patterns recorded of trenches in silicon devices were compared with simulated LACBED patterns to determine the strain in the structure. Displacement fields stemming from stress simulations of a 2D device simulator (TSUPREM IV) were used as an input for the LACBED simulations. The LACBED far-fields are very well reproduced by the simulations whereas the near-fields close to the interfaces show that the device simulator overestimates the strain.

At present, operating temperature of solid oxide fuel cells (SOFCs) is as high as 800-1000 ° C due to requirement of sufficient oxide ion conductivity of electrolyte material. Under such high temperature operation, there remain problems of reliability, durability and limitation of materials. Development of electrolyte oxide which exhibits enough ionic conductivity at temperatures between 400-600 ºC should be required to solve the problems, resulting in development of so-called intermediate temperature SOFC (IT-SOFC). One of the probable methods to decrease the operation temperature is employing proton conducting oxide as electrolyte instead of oxide ion conducting oxide since lower energy is required for light proton transportation. Among proton conducting oxides, BaCe1−x Y x O3-δ shows the highest proton conductivity. Not only for practical application but also for elucidation of high proton conduction mechanism, information on accurate crystal structure of BaCe1−x Y x O3-δ is essential. So far, it has been reported that crystal structures of BaCe1-x Y x O3-δ are orthorhombic distorted perovskite and monoclinic distorted one for x=0.00-0.10 and x=0.15-0.20, respectively, at room temperature. The crystal structures have mainly been analyzed with Rietveld analyses of powder X-ray diffraction or neutron diffraction patterns. However, space groups employed for Rietveld analyses were not experimentally evidenced ones but assumed to be Pnma (No. 62) and I2/m (No. 12) for orthorhombic and monoclinic phase, respectively, in the most studies reported so far. In this study, we have clarified the space group of BaCe0.80Y0.20O3- δ by convergent beam electron diffraction. In addition, Rietveld analyses of powder X-ray diffraction and neutron diffraction patterns of BaCe0.80Y0.20O3- δ have been examined to elucidate minute crystal structure. BaCe0.80Y0.20O3-δ was prepared with Pechini method, with starting materials of BaCO3, CeO2 and Y2O3. BaCO3 was dissolved with citric acid. CeO2 and Y2O3 were dissolved with dilute HNO3 containing H2O2. After addition of ethylene glycol to mixed solution with stoichiometric cation composition, the solution was heated at 300 °C and burned to resin. The resin was calcined at 700 °C for 24 hour in air, followed by uniaxially pressing into pellets. The pellets were sintered at 1300~1400 °C for 10 hour in air. The obtained phase was revealed to be a single phase of monoclinic distorted perovskite structure with a=6.239 Å, b=8.740 Å, c=6.249 Å and β=91.06 º by X-ray diffraction measurement. Convergent beam electron diffraction (CBED) patterns were obtained at room temperature by using energy filtered TEM (JEOL Co., Ltd.: JEM-2010FEF) with operating voltage of 100 kV. X-ray diffraction pattern was obtained with RINT-2500 (Rigaku Co., Ltd.: CuKα, 50 kV, 250 mA). TOF neutron diffraction measurement was carried out using superHRPD at J-PARC. The Rietveld refinements for X-ray diffraction pattern and neutron diffraction one were carried out using RIETAN-FP [1] and Z-Rietveld [2], respectively. Figure attached shows zero-order Laue zone reflections of CBED pattern of BaCe0.80Y0.20O3-δ from [001] azimuth. The observation of the disc identified as 0k0 with odd k denied I-lattice. Space group of I2/m was also denied from A2-type dynamical extinction indicated by arrows, indicating existence of screw axis or glide plane. Combining various CBED patterns from various azimuths, space group of BaCe0.80Y0.20O3-δ was concluded to be P21/m (No. 11), which was a subgroup of Pnma (No. 62) of BaCeO3 [3]. It can be explained that substitution of Y and/or generation of oxide ion vacancy decreased crystal symmetry of BaCeO3. The both X-ray diffraction pattern and the neutron diffraction pattern could successfully be refined by Rietveld analysis with structure model of both I2/m and P21/m. This indicates that accurate space group cannot be clarified by only Rietveld analysis of powder diffraction patterns. The tilts of octahedrons of perovskite were represented as “a + b - c -“ and “a 0 b - c -“ for P21/m and I2/m, respectively [3]. It can be speculated that tilt angle according to a-axis in P21/m phase is so small that diffraction patterns of BaCe0.80Y0.20O3- δ can be refined by Rietveld analysis with space group of both I2/m and P21/m. [1] F. Izumi and K. Momma, Solid State Phenom., 130 (2007) 15. [2] R. O-Tomiyasu et. al. J. Appl. Cryst., 45 (2012) 299. [3] C. J. Howard and H. T. Stokes, Acta Cryst. B54 (1998) 782. Figure 1