High-precision orientation mapping from spherical harmonic transform indexing of electron backscatter diffraction patterns.

The angular precision of crystal orientation determination by cross-correlating dynamically simulated electron diffraction patterns with experimental patterns via spherical harmonic analysis is investigated. The best precision found in this study is 0.016°, which approaches the level reported in the literature for other high-precision electron backscatter diffraction implementations.

L's approach: illumination pattern estimation technique for optical microscopy.

We propose a novel solution to the correction of illumination nonuniformity without removing the imaging sample. Calibration of the spatial illumination pattern in reflectance microscopy is challenging due to the fact that the illumination source is colocated with the objective lens and therefore cannot be observed directly. Our proposed methodology overcomes this by collecting three spatially translated images in a strategic way.

Quasi-periodic events in crystal plasticity and the self-organized avalanche oscillator.

When external stresses in a system--physical, social or virtual--are relieved through impulsive events, it is natural to focus on the attributes of these avalanches. However, during the quiescent periods between them, stresses may be relieved through competing processes, such as slowly flowing water between earthquakes or thermally activated dislocation flow between plastic bursts in crystals. Such smooth responses can in turn have marked effects on the avalanche properties.

Stencil mask methodology for the parallelized production of microscale mechanical test samples.

A new methodology to parallelize the production of micromechanical test samples from bulk materials is reported. This methodology has been developed to produce samples with typical gage dimensions on the order of 20-200 μm, and also to minimize the reliance on conventional focused ion beam fabrication methods. The fabrication technique uses standard microelectronic process methods such as photolithography and deep-reactive ion etching to create high aspect ratio patterned templates-stencil masks-from a silicon wafer.

Electron channeling: a problem for x-ray microanalysis in materials science.

Electron channeling effects can create measurable signal intensity variations in all product signals that result from the scattering of the electron beam within a crystalline specimen. Of particular interest to the X-ray microanalyst are any variations that occur within the characteristic X-ray signal that are not directly related to a specimen composition variation. Many studies have documented the effect of crystallographic orientation on the local X-ray yield; however, the vast majority of these studies were carried out on thin foil specimens examined in transmission.

Scale-free intermittent flow in crystal plasticity.

Under stress, crystals irreversibly deform through complex dislocation processes that intermittently change the microscopic material shape through isolated slip events. These underlying processes can be revealed in the statistics of the discrete changes. Through ultraprecise nanoscale measurements on nickel microcrystals, we directly determined the size of discrete slip events.

Sample dimensions influence strength and crystal plasticity.

When a crystal deforms plastically, phenomena such as dislocation storage, multiplication, motion, pinning, and nucleation occur over the submicron-to-nanometer scale. Here we report measurements of plastic yielding for single crystals of micrometer-sized dimensions for three different types of metals. We find that within the tests, the overall sample dimensions artificially limit the length scales available for plastic processes.