ORCID Profile
0000-0002-6562-4848
Current Organisation
NIST Material Measurement Laboratory
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Publisher: Elsevier BV
Date: 07-2016
Publisher: Springer Science and Business Media LLC
Date: 11-11-2014
DOI: 10.1557/JMR.2014.316
Publisher: AIP Publishing
Date: 12-05-2014
DOI: 10.1063/1.4878616
Abstract: Stress mapping of micromachined polycrystalline silicon devices with components in various levels of uniaxial tension was performed. Confocal Raman microscopy was used to form two-dimensional maps of Raman spectral shifts, which exhibited variations on the scale of the component and on the scale of the microstructure. Finite element analysis models enabled direct comparison of the spatial variation in the measured shifts to that of the predicted stresses. The experimental shifts and model stresses were found to be linearly related in the uniaxial segment, with a proportionality constant in good agreement with calculations based on an opto-mechanical polycrystalline averaging analysis.
Publisher: Elsevier BV
Date: 10-2018
Publisher: American Physical Society (APS)
Date: 17-12-2015
Publisher: Elsevier BV
Date: 03-2016
Publisher: National Institute of Standards and Technology (NIST)
Date: 27-08-2019
DOI: 10.6028/JRES.124.020
Abstract: Stress measurements in single-crystal and polycrystalline alumina are revisited using a recently developed optical fluorescence energy shift method. The method simultaneously utilizes the R1 and R2 Cr-related ruby line shifts in alumina to determine two components of the stress tensor in crystallographic coordinates, independent of the intended or assumed stress state. Measurements from a range of experimental conditions, including high-pressure, shock, quasi-static, and bulk polycrystals containing thermal expansion anisotropy effects, are analyzed. In many cases, the new analysis suggests stress states and stress magnitudes significantly different from those inferred previously, particularly for shock experiments. An implication is that atomistic models relating stress state to fluorescence shift require significant refinement for use in materials-based residual stress distribution analyses. Conversely, the earliest measurements of fluorescence in polycrystalline alumina are shown to be consistent with recent detailed measurements of stress equilibrium and dispersion.
Publisher: AIP Publishing
Date: 12-2012
DOI: 10.1063/1.4769995
Abstract: Instrumented indentation is a widely used technique to study the mechanical behavior of materials at small length scales. Mechanical tests of bulk materials, microscopic, and spectroscopic studies may be conducted to complement indentation and enable the determination of the kinetics and physics involved in the mechanical deformation of materials at the crystallographic and molecular level, e.g., strain build-up in crystal lattices, phase transformations, and changes in crystallinity or orientation. However, many of these phenomena occurring during indentation can only be observed in their entirety and analyzed in depth under in situ conditions. This paper describes the design, calibration, and operation of an indentation device that is coupled with a Raman microscope to conduct in situ spectroscopic and optical analysis of mechanically deformed regions of Raman-active, transparent bulk material, thin films or fibers under contact loading. The capabilities of the presented device are demonstrated by in situ studies of the indentation-induced phase transformations of Si thin films and modifications of molecular conformations in high density polyethylene films.
Publisher: Elsevier BV
Date: 10-2016
Publisher: National Institute of Standards and Technology (NIST)
Date: 13-12-2017
DOI: 10.6028/JRES.122.043
Abstract: The numerical coefficients linearly relating the effects of stress (including pressure), temperature, and composition to shifts in the energies of the Cr-related fluorescence in alumina (Al2O3) are reviewed. The primary focus is the shift of the R1 and R2 “ruby” fluorescence lines under conditions typical for stress determination in polycrystalline Al2O3. No significant experimental difference in the R1 and R2 responses is observed for hydrostatic stress (or pressure) conditions (average shift coefficient of about 7.6 cm−1/GPa), changes in temperature (about 0.140 cm−1/K), or variations in composition (about 120 cm−1/mass fraction of Cr). There are significant differences in the R1 and R2 responses for nonhydrostatic stress conditions. In particular, for uniaxial stress along the a and c directions in the Al2O3 crystal, the R1 piezospectroscopic tensor coefficients (about 3.0 cm−1/GPa and 1.6 GPa cm−1/GPa, respectively) differ considerably, whereas the R2 coefficients (about 2.6 cm−1/GPa and 2.3 GPa cm−1/GPa, respectively) do not. Measurements of the piezospectroscopic tensor coefficients are shown to have interlaboratory relative consistency of about 4 % extending over 30 years, and are consistent with the scalar high-pressure measurements. Measurements of the temperature coefficients are shown to have interlaboratory relative consistency less than 1 % extending over 60 years. Fluorescence-based measurements of stress in polycrystalline Al2O3, although requiring temperature adjustment, are shown to have a relative uncertainty of about 2.5 %.
Publisher: AIP Publishing
Date: 27-11-2017
DOI: 10.1063/1.5001270
Abstract: The strain field surrounding a spherical indentation in silicon is mapped in two dimensions (2-D) using electron backscatter diffraction (EBSD) cross-correlation and confocal Raman spectroscopy techniques. The 200 mN indentation created a 4 μm diameter residual contact impression in the silicon (001) surface. Maps about 50 μm × 50 μm area with 128 pixels × 128 pixels were generated in several hours, extending, by comparison, assessment of the accuracy of both techniques to mapping multiaxial strain states in 2-D. EBSD measurements showed a residual strain field dominated by in-surface normal and shear strains, with alternating tensile and compressive lobes extending about three to four indentation diameters from the contact and exhibiting two-fold symmetry. Raman measurements showed a residual Raman shift field, dominated by positive shifts, also extending about three to four indentation diameters from the contact but exhibiting four-fold symmetry. The 2-D EBSD results, in combination with a mechanical-spectroscopic analysis, were used to successfully predict the 2-D Raman shift map in scale, symmetry, and shift magnitude. Both techniques should be useful in enhancing the reliability of microelectromechanical systems (MEMS) through identification of the 2-D strain fields in MEMS devices.
Publisher: American Physical Society (APS)
Date: 05-03-2012
Location: United States of America
No related grants have been discovered for Chris Michaels.