Bulletin of the American Physical Society
2018 Annual Meeting of the APS Four Corners Section
Volume 63, Number 16
Friday–Saturday, October 12–13, 2018; University of Utah, Salt Lake City, Utah
Session L02: CMP + Materials 8: Structure/Materials General |
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Chair: Heinz Nakotte, New Mexico State University Room: JFB 102 |
Saturday, October 13, 2018 11:20AM - 11:44AM |
L02.00001: Group representation theory and crystal-structure determination Invited Speaker: Branton J Campbell Group-representation theory (GRT) is a bedrock layer of modern chemistry and physics. Its reach includes any physical or mathematical system that exhibits any kind of symmetry, even the universe itself, and provides a unique parameter set for describing order parameters that break the parent symmetries of a system. In the field of chemical and materials physics, GRT has long been an essential tool for understanding band structures and spectroscopic data, and for classifying continuous phase transitions. Here, we'll present GRT as the ideal basis for the experimental determination of atomic structures arising from symmetry loss in a crystal. The scope includes all types of commensurate and incommensurate order parameters (e.g. atomic displacements, magnetic moments, molecular/polyhedral rotations, compositional site orderings, lattice strains, thermal ellipsoids) at diffraction-relevant length scales. |
Saturday, October 13, 2018 11:44AM - 11:56AM |
L02.00002: Optical Characterization of Stressed Aluminum Kaylee Rellaford, Shawn Averett, Alex Farnsworth, Scott Smith, Emma Carlsen, James Patterson The characterization of the effects of stress on materials is a field of inherent interest. Nondestructive evaluation (NDE) methods have been developed to assess damage before any major failures. Current NDE methods have several limitations such as expense and the need for highly-trained operators. To eliminate some of these limitations we have found an optical technique, second harmonic generation (SHG), can be used to characterize mechanical and chemical stress in aluminum. In optical surface SHG, one input light is converted to produce a SHG response at half the wavelength after interaction with the sample surface. In our work, we measured the SHG response before and after mechanical and chemical stress on 2024 and 5083 series aluminum samples. We monitored the SHG change of 2024 samples after we used tensile loading to induce mechanical stress. We found the SHG response decreases with increasing deformation. We also used an oven at 175 °C to speed up the chemical stress in 5083 samples. We monitored SHG response to the amount of chemical stress and found it to be directly correlated. These results suggest that we have a promising new method that could compliment current nondestructive testing |
Saturday, October 13, 2018 11:56AM - 12:08PM |
L02.00003: Selective Solar Absorber Development for Water Heating Applications Corey Collatz The goal of this research is to create and optimize a thin film material that receives solar radiation with minimal heat loss to the atmosphere to generate steam for performing work on other systems. Each thin film made in the developmental process is a combination of codeposited silicon dioxide and molybdenum that has the intent of having a high solar absorbance and low thermal emittance. The process of making these thin selective absorbers is done by a technique known as sputtering. We will present characterization data and corresponding trends with increased molybdenum that have been obtained through scanning electron microscope imaging, energy dispersive x-ray spectroscopy, ultraviolet-visible light spectrophotometry, and thermal emissivity readings. The water heating experiment requires minimal optical concentration and the use of cost-effective materials. Progress towards generating steam with our apparatus will also be presented. |
Saturday, October 13, 2018 12:08PM - 12:20PM |
L02.00004: Keeping Squares Square John Christensen, Gus L.W. Hart, Wiley S Morgan, Rodney Forcade First principles calculations for materials use ~25% of the world’s supercomputing resources. We propose a method for reducing the computational cost for these types of calculations without losing accuracy. Because crystalline structures and their properties are symmetric, it is only necessary to compute their properties at symmetrically unique points. Others have utilized these symmetric properties to create grids of symmetrically unique points. However these grids are restricted to integer divisions of the lattice vectors that define the crystal. Our method explores all possible grids that have the same symmetries of the crystal. By utilizing all the symmetries of a crystalline structure, a material’s properties can be computed more efficiently, reducing the amount of computation needed to predict new materials. |
Saturday, October 13, 2018 12:20PM - 12:32PM |
L02.00005: Mechanically Robust Ultra-Black Kevin Laughlin, Robert Davis, Richard Vanfleet Detectors such as astronomical cameras, infrared sensors, etc. could all be improved by reducing the amount of stray light that hits the sensors. This can be accomplished by using an ultra-black material to absorb stray light. Vertically aligned carbon nanotubes (VACNT) are the darkest material discovered so far, and if they could be used they would reduce the amount of stray light for these detectors to a minimum. Unfortunately VACNTs are difficult to grow on most surfaces, and they are very fragile which makes them difficult to transfer to a surface after they are grown. One solution has been to use a spray on ultra-black material, but this film is an order of magnitude less absorptive than the VACNTs. By using VACNT that are strengthened on one side, they can become robust enough to be transferred onto a flexible substrate, which could then be cut and placed onto any desired surface. I have developed a mechanically robust VACNT structure that retains its ultra-high absorption by reinforcing one side of the VACNT structure with amorphous carbon. This VACNT structure is then released from the substrate by pealing it off with double sided sticky tape. The absorbance was measured over a wide range of wavelengths using an integrating sphere and a spectrometer. |
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