Orientation-dependent Patterns Research Articles

Shear Wave Ultrasound Inspection of Flaws in Silicon Wafers using Focused Transducers.

Silicon parts can contain micrometer-sized vertical cracks that are challenging to detect. Inspection using high-frequency focused ultrasound has shown promise for detecting defects of this size and geometry. However, implementing focused ultrasound to inspect anisotropic media can prove challenging, given the directional dependence of wave propagation and subsequent focusing behavior. In this work, back surface-breaking defects at various orientations within silicon wafers (0-, 15-, and 45-degrees relative to the [010] crystallographic axis) are experimentally inspected in an immersion tank setup. Using 100 MHz unfocused and focused shear waves, the impact of medium anisotropy on focusing and defect detection is evaluated. The scattering amplitude and defect detection sensitivity results demonstrate orientation-dependent patterns that strongly rely on the use of focused transducers. The defects along the 45-degree orientation reveal two-lobe scattering patterns with maximum amplitudes less than half that of the defects in the 0-degree orientation, which in contrast show a one-lobe scattering pattern. The experimental results are further explored using Finite Element (FE) modeling and ray tracing to visualize the impact of focusing on wave propagation within the silicon. Ray tracing results show that the focused beam profiles for the 45- and 0-degree orientations form a butterfly wing and elliptical focusing profile, respectively, which correspond directly to experimentally found scattering patterns from defects. Additionally, the FE scattering results from unfocused transducers reveal single lobe scattering for both 0- and 45-degree orientations, proving the varying scattering patterns to be driven by the anisotropic focusing behavior.

Nonlinear Lock-In Infrared Microscopy: A Complementary Investigation Technique for the Analysis of Functional Electroceramic Components.

Using lock-in infrared microscopy as a tool for current detection on the micrometer scale in AC-driven specimens in combination with iterative grinding procedure allows preparation of current dominating microstructure regions on well-polished surfaces. This technique is applied successfully on varistor components based on specially doped ZnO-based varistor ceramics. This peculiar electroceramic material exhibits exceptional high nonlinear current-voltage (I-V) characteristics, described by a power law according I~V(α), caused by double Schottky barriers at the grain boundaries. As a novelty the thermographic response is used to evaluate local electrical properties, namely the nonlinearity coefficient α, on basis of higher order harmonics with respect to the basic electrical driving AC-frequency. To correlate the observed electrical properties to the microstructure, the polar crystal orientation of the relevant ZnO grains is determined by combining electron backscatter diffraction and orientation-dependent patterns as a result of a chemical etching procedure. These findings support a modified new model for describing the grain boundary controlled current flow in a varistor microstructure including orientation-dependent barrier properties. Hence, the experimentally observed current direction-dependent behavior can be described consistently.

Orientation-dependent Pattern Formation in a 1.5D Continuum Model of Curved Dislocations

ABSTRACTDislocation pattern formation is a phenomenon where during significant plastic deformation dislocations organize themselves into (meta)stable structures. Modeling such systems is a non-trivial task, because the number of interacting dislocations is high, bringing discrete simulation models to their computational limits. Continuum models, although more efficient, generally do not contain sufficient information for a physically detailed representation of such systems. In this paper we show how a continuum dislocation dynamics theory can be used to model idealized pattern formation. Furthermore, we show how discrete dislocation dynamics (DD) simulations can be used to provide physical input for our continuum model.

Orientation peculiarities of dc Josephson tunneling betweend-wave superconductors with charge density waves

The theory of the stationary Josephson tunnel current Ic was devised for junctions involving superconductors partially gapped by biaxial or unidirectional charge density waves (CDWs) and possessing a superconducting order parameter of d-wave symmetry. Specific calculations were carried out for symmetric junctions between two identical CDW superconducting electrodes and nonsymmetric ones composed of a CDW superconductor and a conventional isotropic s-wave superconductor. Two kinds of superconducting pairing symmetries were studied, namely, that appropriate to cuprates (dx2−y2) and the dxy one. The corresponding calculations were also carried out for the extended s-wave symmetry of the superconducting order parameter. Allowances were made for the directionality of tunneling. In all the cases studied, the dependences of Ic on the angle γ between the chosen crystal direction and the normal to the junction plane were found to be significantly influenced by CDWs. It was shown in particular that the d-wave driven periodicity of Ic(γ) in the CDW-free case is transformed into double-period beatings depending on the parameters of the system. The results of calculations testify that the orientation-dependent patterns Ic(γ) measured for CDW superconductors allow the CDW configuration (unidirectional or checkerboard) and the symmetry of superconducting order parameter to be determined. The predicted effects can be used to indirectly reveal CDWs in underdoped cuprates where pseudogaps are observed. The break-junction technique is an appropriate tool for this purpose.

Further comments on the origin of orientation-dependent patterns obtained in the scanning electron microscope

The contrast effects that occur in the orientation-dependent patterns obtained with the scanning electron microscope by collecting secondary emitted and/or primary back-scattered electrons have been explained in terms of the electron channelling mechanism. Markedly different contrast effects occurred when such patterns were obtained by using the specimen current electrons. In the present work, the latter patterns have been investigated, and it is shown that these contrast effects arise from the channelling of electrons plus signal differentiating effects associated with the additional amplification required.

Studies on the Gamma Ray Irradiation on the Protein

Co/sup 60/ irradiation of proteins was carried out at a rate of 3000 r/ min in vacuo or in an atmosphere of oxygen or nitrogen. The electron spin resonance (ESR) absorption spectra of irradiated bovine and human serum albumin, fibrin, and silk fibroin were determined. It was shown that the free radicals in the irradiated proteins are associated with their cystine or cysteine content. The higher the content of these sulfur-containing amino acids in irradiated proteins, the more their ESR patterns resemble those of cystine and cysteine. Irradiated silk fiber provided a doublet similar to that of glycyl-glycyl-glycine. Such an orientation-dependent pattern could be explained as an unpaired electron localized on the oxygen atom hydrogenbonded to the NH group of the adjacent polypeptide chain. When irradiation was done in the presence of oxygen, the ESR signals of proteins were markedly different from those irradiated in vacuo, the former being attributable to peroxide radicals. Proteins irradiated in the presence of water barely provided a detectable ESR signal. When irradiated albuim or cysteine were dissolved into the solution of native albumin, the titrable SH group decreased, probably due to reaction of sulfhydryl radicals with the SH group. It is concluded that themore » effect of radiation on protein solutions is chiefly, if not entirely, attributable to radicals from the irradiated water, and that the decrease in the SH group of irradiated protein solution can be partly ascribed to free radical reactions. (H.H.D.)« less