Equal Thickness Fringes Research Articles

The Edge Sensor of Segmented Mirror Based on Fringes of Equal Thickness

Co-phase and co-focus detection is one of the key technologies for large-aperture segmented mirror telescopes. In this paper, a new edge sensor based on fringes of equal thickness is developed, which can detect each segment’s relative piston, tilt, and tip errors from the interferograms. Based on the co-focus demand for many ground-based seeing limited segmented mirror telescopes, an edge sensor prototype based on such a principle is built and applied in the indoor segmented mirror experiment system in the lab. According to the co-focus requirement of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, many simulations and experiments are carried out for co-focus error detection of the segmented mirror system. Experiment results show that the co-focus accuracy is better than 0.″02 rms, which can meet the co-focus requirements of most large or extremely large segmented mirror astronomical telescopes.

Generation mechanism and motion behavior of sliver defect in single crystal Ni-based superalloy

Sliver is a common but easily neglected defect in single crystal Ni-based superalloy castings. To date, there is still no unified viewpoint on its formation mechanism and generation causes. In this work, the orientation discontinuity and motion behavior of sliver defects were studied through experiments and numerical simulations. The ultrathin wedge-shaped specimen containing the grain boundary of the sliver and the matrix was prepared at the initial position of the sliver defect for the observation of equal thickness fringes. The discontinuity of equal thickness fringes on both sides of the grain boundary was observed through a transmission electron microscope, which directly confirms the abrupt change in the orientation between the sliver and matrix from the nanoscale. The crystal lattices at the smooth area and the bulging area of the grain boundary were found to have unusually different arrangements. The irregular lattice arrangement at the bulging area shows that the grain boundary has experienced high-stress deformation. Statistical results of sliver orientation deviation with a further composition analysis show the micro protuberance of the mold shell has a noticeable inductive effect on the sliver generation. Furthermore, a self-developed three-dimensional phase-field simulation model coupled with the spatial topology algorithm is established to simulate the orientation deflection behavior and orientation deviation threshold of fractured dendrites. The simulation results indicated that there is an upper limit of the cross-section solid fraction at the fracture position for the motion of the fractured dendrites. When the cross-section solid fraction at the fracture position is higher than this upper limit, it will be difficult to produce large deviation slivers due to the structural limitation of surrounding dendrites. This upper limit does not change with the solidification temperature gradient.

Control of strain in subgrains of protein crystals by the introduction of grown-in dislocations.

It is important to reveal the exact cause of poor diffractivity in protein crystals in order to determine the accurate structure of protein molecules. It is shown that there is a large amount of local strain in subgrains of glucose isomerase crystals even though the overall crystal quality is rather high, as shown by clear equal-thickness fringes in X-ray topography. Thus, a large stress is exerted on the subgrains of protein crystals, which could significantly lower the resistance of the crystals to radiation damage. It is also demonstrated that this local strain can be reduced through the introduction of dislocations in the crystal. This suggests that the introduction of dislocations in protein crystals can be effective in enhancing the crystal quality of subgrains of protein crystals. By exploiting this effect, the radiation damage in subgrains could be decreased, leading to the collection of X-ray diffraction data sets with high diffractivity.

Evaluation of crystal quality of thin protein crystals based on the dynamical theory of X-ray diffraction.

Knowledge of X-ray diffraction in macromolecular crystals is important for not only structural analysis of proteins but also diffraction physics. Dynamical diffraction provides evidence of perfect crystals. Until now, clear dynamical diffraction in protein crystals has only been observed in glucose isomerase crystals. We wondered whether there were other protein crystals with high quality that exhibit dynamical diffraction. Here we report the observation of dynamical diffraction in thin ferritin crystals by rocking-curve measurement and imaging techniques such as X-ray topography. It is generally known that in the case of thin crystals it is difficult to distinguish whether dynamical diffraction occurs from only rocking-curve profiles. Therefore, our results clarified that dynamical diffraction occurs in thin protein crystals because fringe contrasts similar to Pendellösung fringes were clearly observed in the X-ray topographic images. For macromolecular crystallography, it is hard to obtain large crystals because they are difficult to crystallize. For thin crystals, dynamical diffraction can be demonstrated by analysis of the equal-thickness fringes observed by X-ray topography.

Improvement of Hen Egg White Lysozyme Crystal Quality by Control of Dehydration Process

Equal-thickness fringes that are attributed to the Pendellosung effect were clearly observed in the region of a tapered tetragonal hen egg white (HEW) lysozyme crystal with a wedgelike edge, which...

Characterization of grown-in dislocations in high-quality glucose isomerase crystals by synchrotron monochromatic-beam X-ray topography

High quality glucose isomerase (GI) single crystals are grown by using chemical cross-linked seed crystals. The crystal structure is an orthorhombic system in which the molecular arrangement is close to a body-centered cubic (bcc) one. The crystal defects, especially dislocations, in GI crystals are experimentally characterized by synchrotron monochromatic-beam X-ray topography. Two straight dislocations are clearly observed, which originate from the interface between the cross-linked seed crystal and the grown crystal. From the invisibility criterion of the dislocation images, it is experimentally identified that they are close to be of pure edge character with the Burgers vector of [1 1¯ 1] which is typical one in bcc metal crystals. Moreover, bead-like contrasts along the dislocation images and the equal-thickness fringes, related to Pendellösung fringes, at crystal edges are clearly observed, which have never been observed in other protein crystals so far. These contrasts can attributed to the dynamical diffraction effect which has been often observed in high-quality crystals such as Si. Thus it seems that the perfection of GI crystals shown in this paper is extremely high compared with other protein crystals reported so far.

Importance of Determination of Crystal Quality in Protein Crystals when Performing High-Resolution Structural Analysis

We show that the extinction effect explained by the dynamical theory of diffraction must be considered even in the case of protein crystals. Equal-thickness fringes, which are attributed to the Pendellösung effect, were clearly observed in the region of a tapered glucose isomerase crystal with wedge-like edges using X-ray topography carried out with a beam of monochromatic synchrotron radiation. This indicates that the perfection of this glucose isomerase crystal is high enough to produce this dynamical theory-related effect: this surely leads to difficulty in the collection of accurate integrated intensities of diffraction spots for X-ray structural analysis. Therefore, it is important to determine whether the crystal quality of a protein crystal under analysis is adequate to obtain accurate three-dimensional structures of protein molecules for X-ray structural analyses. We show that X-ray diffraction rocking-curve measurements can provide clues for this determination.

Loading effect of a metallic parabolic tip on S0 and A0 lamb waves

The loading effect induced by the contact between a parabolic duralumin tip and a free glass plate is investigated using Lamb waves and an optical heterodyne interferometric probe. The instrument detects 1-MHz impulse symmetric S₀ and antisymmetric A₀ Lamb wave trains launched in 1-mm-thick B270-type glass. Strain-optic modeling is carried out to explain optical measurement through the transparent medium and the loading effect of the tip. Three-wave optical interference modeling is also developed to explain the presence of fringes of equal thickness in C-scans of both modes propagating in a plate that has a 1.1-mrad wedge. Results show that through-glass probing inverts by a factor of -3.1 the signal that is normally returned by the interferometer at a free-air surface for the S₀ Lamb mode. Fringes of equal thickness reveal the spatial extension of the mechanical loading. Through-glass probing on A₀ produces about the same signal as in a free-air measurement configuration. This mode appears to be more appropriate for the evaluation of the loading effect of the tip. For this parabolic tip, we observe an A₀ attenuation of about 50% in the contact area.

Evaluation of the possibility of using the laser-induced thermocapillary effect for photothermal spectroscopy

A new approach to the photothermal spectroscopy of solids and liquids is proposed on the basis of the thermocapillary effect, which arises when a laser beam excites a layer of liquid several hundreds of millimeters thick lying on a solid surface. The method uses the measurement of the diameter of a thermocapillary response or the counting of the number of fringes of equal thickness observed in the light reflected from a thermocapillary depression. The detectability threshold and the resolution of the method correspond to absorbed optical powers of, respectively, 500 and 100 μW in the first case and 500 and 10 μW in the second case.

Retrieval of spatial shot-noise in the full dynamic range of calibrated CCD cameras

The pixel by pixel calibration of a scientific CCD camera allows Poissonian statistics of the spatial fluctuations of an uniform enlightening to be retrieved in the full range of the camera dynamic. The procedure works efficiently for thermal as well as for laser sources, provided that the wavelength and the coherence properties of the source are chosen in order to avoid the formation of equal thickness fringes in the chip (etaloning effect). Calibration allows also the comparison at the shot noise level of images recorded at different places on the chip.

Dynamic observation of dislocation-free plastic deformation in gold thin foils

Ductile fracture of metals produces a thin foil portion, which is observable by transmission electron microscopy, at the fractured edge. The thin foil portion shows unusual deformation microstructure, which contains no dislocations, but contains vacancy-type point defect clusters at extraordinarily high density. Dynamic observation of the deformation process revealed that these defect clusters are produced in the portion of local heavy deformation; however, no dislocation motion was observed during the course of the heavy plastic deformation, constituting direct evidence that the unusual deformation microstructure is produced by plastic deformation without dislocations. Also, the deformation was found to involve 14% elastic deformation, indicating that the dislocation-free plastic deformation occurs under an extraordinarily high internal stress level of more than 10 GPa, which is comparable to the ideal strength of metals. Furthermore, during the dislocation-free plastic deformation, equal-thickness fringes were found to disappear temporarily, suggesting that instability of crystalline state under extraordinarily high internal stress level is a key factor for the mechanism of dislocation-free plastic deformation.

Quantitative determination of the spatial coherence from the visibility of equal-thickness fringes.

Spatial coherence of the undulator radiation in the horizontal direction is measured by a wedge-shaped crystal interferometer. The Borrmann effect, the effect of the angular divergence of the incidence and the wavefront matching of the collimating asymmetric diffractions with the interferometer are discussed to estimate the coherence factor. The spatial coherence length of 145 microm is experimentally determined, which is enhanced by the collimators about 100 times more than expected from the source size.

Quantitative intensity measurement of equal thickness fringes in Si and MgO crystal images with an energy-filtering transmission electron microscope using an imaging plate.

Quantitative measurement of intensity profiles of equal thickness fringes has been carried out in Si and MgO crystal images with an energy-filtering transmission electron microscope using an imaging plate. The crystals have a 90 degrees wedge-shape with [110] surfaces for Si and with [100] surfaces for MgO, and are observed under the exact axial incidence of a 200 keV electron beam along the [100] axis for Si and along the [110] axis for MgO. The intensities are measured in bright field and 022 and 040 dark field images for Si, and in bright field and 111, 002, 220, 113, 222, and 004 dark field images for MgO, with and without an energy slit having +/- 5 eV energy width for incident electrons. The intensity profiles obtained from the images are presented as standard experimental data for calculation of electron diffraction intensities. A few simulation programs for high-resolution transmission electron microscopy are checked by comparing the calculated diffraction intensities with the experimental data. The complex potential suitable for matching the data is discussed.

Measuring the Surface Defects of a Fabry-Perot Étalon

A simple method for mapping the surface defects of a Fabry-Perot étalon is described. Images of the fringes of equal thickness are acquired as the plate separation is altered in a stepwise manner. This information is processed to yield a map of the location of the surface defects, and can be further used to estimate the effect of varying plate reflectance on the instrument function.

Intensity Measurement of Equal-Thickness Fringes in TEM Images of Wedge-Shaped GaAs and InP Crystals by a Slow-Scan CCD Camera

Intensity Measurement of Equal-Thickness Fringes in TEM Images of Wedge-Shaped GaAs and InP Crystals by a Slow-Scan CCD Camera

A new type of displacement fringe associated with martensitic transformation in transmission electron microscopy

Abstract A new interference fringe type in transmission electron microscopy has been studied. These fringes are observed in a thin martensite plate or bainite plate embedded in a matrix crystal. They have the characteristics of equal-thickness fringes and follow the thickness contours of the martensite or bainite plate. It has been clarified that the displacement caused by lattice shearing on martensitic transformation is responsible for these fringes. The thickness periodicity of fringes has been deduced to be dependent on the amount of the transformation shear, the direction of the shear and the vector of the operating reflection. It also depends weakly on the deviation from the exact diffracting condition. These fringes may be useful for the deduction of the morphology of martensite or bainite plates. They also provide the means of direct measurement of the transformation shear strain.

Observation of lattice relaxation at the GaAsP/GaAs interface beyond the critical thickness by transmission electron microscopy

The lattice relaxation at the GaAs1−xPx/GaAs interface is observed using thickness fringe images in transmission electron microscopy. The bending of the equal thickness fringes observed near the interface is explained, assuming that crystal planes are inclined near the interface and that the inclination has a maximum at the interface. The magnitudes of inclination and the thickness of the strained region are estimated for various phosphorous composition and the GaAsP thickness. The lattice relaxation mechanisms for GaAsP on GaAs is described. It is indicated from the thickness fringe observation that the lattice relaxation occurs gradually beyond the critical thickness.

Crystallinity of InGaPAs epitaxial layers revealed in equal thickness fringes in transmission electron microscopy

Crystallinity of InGaPAs layers grown on GaAs substrates by liquid phase epitaxy has been examined by observing equal thickness fringes in transmission electron microscopy. Even InGaPAs layers within the theoretically immiscible composition region are found to be of one phase without compositional fluctuation. Phase separation, which can theoretically occur, is not found. However, crystallinity is generally inferior, and this inferiority increases as the epitaxial layer grows. The substrate-induced stabilization effect seems to produce high quality crystals in the immiscible region only in the initial stage of epitaxial growth. It is also found that immiscibility affects InGaPAs layers grown on GaAs substrates to a greater extent than those grown on InP substrates.

Effects of strain on the electron diffraction contrast at III-V compound heterostructure interfaces

Abstract Electron diffraction contrast effects which arise at III-V compound heterostructure boundaries with small mismatches due to small differences in the diffraction conditions on either side of the boundary are discussed in detail. These effects can be characterized by a change in the deviation parameter s and give rise to δ fringes when the boundary is tilted with respect to the electron beam and also to a displacement of equal thickness fringes. Observations of the latter phenomenon require a well defined sample geometry and layers of known composition. δ fringe profiles are evaluated by comparison with theoretical profiles computed on the basis of equations from the two-beam dynamical theory for superposed crystals. The mismatch value extracted by this method agrees with the value expected for a GaAlAs/GaAs boundary provided that a relative change in crystal orientation at the boundary is allowed for rather than a simple tetragonal distortion perpendicular to the interface. The case of a GaInAsP/I...

Quasicrystal structure in Al─Cu─Fe annealed alloy

Abstract Powder X-ray diffraction, electron diffraction and electron microscopic experiments, including high-resolution electron microscopy, have revealed that the Al─Cu─Fe icosahedral phase has a higher degree of structural perfection than other known icosahedral phases. This icosahedral phase exhibits clear equal thickness fringes in bright and dark-field images and also sharp diffraction spots with small Bragg angles, both of which have not been observed in other icosahedral phases. A scaling rule by the golden mean τ along the fivefold, threefold and twofold axes was found in reciprocal space of this icosahedral phase. In the high-resolution electron micrographs observed along the twofold axis, this scaling rule was also recognized to be present in real space. This fact suggests that the Al─Cu─Fe icosahedral phase belongs to a different class of icosahedral phase from the one to which belong other icosahedral phases having a scaling rule of τ3.