Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session I2: Material Science III |
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Chair: David Allred, Brigham Young University Room: Science Building 246 |
Saturday, October 18, 2014 10:15AM - 10:39AM |
I2.00001: Development of advanced characterization techniques to resolve fundamental materials and device issues in photovoltaics Invited Speaker: Dean Levi Scientists within the National Center for Photovoltaics at the National Renewable Energy Laboratory (NREL) are pursuing critical activities to help accomplish the goal of the U.S. Department of Energy's SunShot Initiative—to make large-scale solar energy systems cost-competitive with other energy sources by 2020. To achieve this goal we must increase the efficiency of PV devices while reducing cost and increasing reliability. As technologies mature, fundamental improvements must be driven increasingly by an in-depth understanding of the relationships between device performance and material properties down to the nanoscale. Solar cell efficiency is often determined by the properties and distribution of the defects and impurities that control doping, recombination, and carrier transport in these devices. Advanced measurement capabilities are crucial to understand the distribution and properties of these defects. In this presentation I will discuss ongoing work at NREL to develop advanced characterization methods that will enable PV scientists to resolve the structural, compositional, optical, and electronic properties of these defects and impurities in established and newly developed PV technologies. [Preview Abstract] |
Saturday, October 18, 2014 10:39AM - 10:51AM |
I2.00002: Two peaks to climb: A multi-critical Ising model Jacob Hansen, Gus Hart Advances in our understanding of materials allow us to push technology and innovation to the next level. Computational research is often the tool that allows for the rapid discovery and screening of new materials. Generalized Ising models are commonly used in modeling these new alloys. The classical Ising model set in a triangular lattice with repulsive nearest neighbor coupling and attractive next nearest coupling is of particular interest because while it exhibits two phase transitions it can still be solved analytically. Our goal is to computationally use this model to test advanced algorithms. This allows for the optimization of these algorithms which would improve the predictive capability of computational materials science. [Preview Abstract] |
Saturday, October 18, 2014 10:51AM - 11:03AM |
I2.00003: Strategies to Accelerate Materials Design Seyedayat Ghazisaeed, Boris Kiefer The 21$^{\mathrm{st}}$ century faces many technological and scientific challenges, and the ability to master these challenges will rely heavily on our ability to design and discover suitable sets of materials. Previous research shows that many electronic, magnetic and optical properties depend strongly on chemistry and the detailed arrangement of the coordinating ligands. In the effort to understand these correlations for d-elements and f-elements, crystal field theory has proven to be particularly useful. The crystal geometry can be determined experimentally for example through x-ray diffraction and the results have been collected and catalogued in databases. In this presentation, we will describe and discuss our efforts to correlate crystal structure databases with crystal field theory, other databases, and first-principle calculations. The goal is to accelerate the identification of sets of promising crystal structures and chemistries to address materials science and engineering challenges in the current century. As an example of the workflow, we consider CrO$_{2}$, and how the coordination environment effects electronic and magnetic properties beyond CrO$_{2}$ in the rutile structure which is known to be half-metallic. [Preview Abstract] |
Saturday, October 18, 2014 11:03AM - 11:15AM |
I2.00004: Gold and Gallium Nanoparticle Growth on Silicon (100) Garett Milton, Samuel Tobler Nanoparticles are used for various applications in today's research. Some researcher's interests involve using the nanoparticles to grow silicon nanowires on a silicon substrate. Before growing nanowires can be accomplished a study must be made of the formation of nanoparticles. Most often the metal used to make the nanoparticles is gold. In this study both gold and gallium were used to make the nanoparticles, by thermal evaporation. The gold and gallium nanoparticles were grown on silicon (100). Between one to three monolayers of material was added to the substrate, with the particle sizes ranging from 0.5 $\mu$m to 3 $\mu$m in diameter. Densities of nanoparticles varied based on the time of growth and on the intensity of the source. The variable sizes were seen with sample temperatures between 700 $^{\circ}$C and 900 $^{\circ}$C measured using a disappearing filament optical pyrometer. The growth process occurred at pressures below 3*10$^{-7}$ Torr. This presentation will summarize the growth process and show the similarities and differences between the two metals. [Preview Abstract] |
Saturday, October 18, 2014 11:15AM - 11:27AM |
I2.00005: Silicon Dioxide Thin Film CVD with Dichlorosilane and Carbon Dioxide Brandon McKeon, Kenneth Hinton, David Allred Silicon dioxide (SiO$_{2})$ is useful in microelectronics and micro-fabrication (MEMS). It has traditionally been deposited through low pressure chemical vapor deposition (LPCVD) at high temperatures (about 900 to 1000 $^{\circ}$C).One method is to take dichlorosilane (DCS) and an oxidizer such as nitrous oxide (N$_{2}$O). Carbon dioxide (CO$_{2})$ is isoelectric and should therefore behave similarly to N$_{2}$O in this reaction. We explored the deposition of SiO$_{2}$ using CO$_{2}$ and DCS via LPCVD at pressures from 600 mTorr to 5 Torr. We also followed standard practices in depositing SiO$_{2}$ using nitrous oxide and DCS to be used as a standard for comparison. We used ellipsometry and energy-dispersive x-ray spectroscopy (EDS) to measure the thickness, refractive index, and chemical composition of each sample and found that all of our samples were silicon rich. We also observed that most of the deposited films were hazy. SiO$_{2}$ deposited with CO$_{2}$ at pressures near 600 mTorr appeared to be more attributable to thermal oxidation than deposition and was the least silicon rich and least hazy. Around 5 Torr is when SiO$_{2}$ deposition with CO$_{2}$ was first successful with a refractive index of 1.6, atomic ratio of Si to O of 40:60, and the most hazy. [Preview Abstract] |
Saturday, October 18, 2014 11:27AM - 11:39AM |
I2.00006: Fabrication of Co/Cu Multilayers with Antiferromagnetic Coupling Nathaniel Vargas, Jessica Gifford, Ji Zhang, Gejian Zhao, Dongrin Kim, Salar Simaie, David Smith, Tingyong Chen Co/Cu magnetic multilayers exhibit giant magnetoresistance (GMR) and are a prototype spintronic device. With proper thickness of Cu, the Co layers can be antiparallel to each other because of the antiferromagnetic (AF) coupling. The GMR value is maximized when the multilayer structure is aligned by an external magnetic field. Thus this point can be utilized to study many spin-dependent phenomena since spin-dependent scattering is optimized at the AF point. In this work, we fabricate the Co/Cu multilayers with AF coupling by varying the Cu and Co thickness using a wedge method by sputtering. Using Fe as a seed layer, the grown Co/Cu multilayers are textured, which is confirmed by transmission electron microscopy (TEM) results. GMR value as large as 63{\%} has been achieved at room temperature. [Preview Abstract] |
Saturday, October 18, 2014 11:39AM - 11:51AM |
I2.00007: High-Aspect-Ratio Metal Microfabrication by Nickel Electroplating of Patterned Carbon Nanotube Forests Dallin Barton, Lawrence Barrett, Steven Noyce, David Allred, Richard Vanfleet, Robert Davis We have developed a process that is able to create metallic MEMS with over 20:1 aspect ratios through nickel electroplating patterned carbon coated carbon nanotube forests. Densities include about 85{\%} bulk nickel (7.3-7.98 g/cm$^{3})$ with an elastic modulus of approximately 42 GPa and a strength of 400 MPa. 7 mN actuation forces were achieved. Applications for a wealth of actuators and similar MEMS devices could be envisioned with this composite material. The process of nickel electroplating carbon nanotube forests will be explained along with material properties testing. [Preview Abstract] |
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