Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 58, Number 12
Friday–Saturday, October 18–19, 2013; Denver, Colorado
Session C4: Condensed Matter I |
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Chair: Arthi Jayaraman, University of Colorado - Boulder Room: 281 |
Friday, October 18, 2013 11:00AM - 11:24AM |
C4.00001: Ultrafast nano-optics: accessing structure, function, and dynamics of matter on its natural length and time scales Invited Speaker: Markus Raschke Structure, function, and dynamics of matter are the result of an intricate interplay of its elementary excitations defined on femtosecond time and mesoscopic nanometer length scales. This gives rise to often complex phase behavior in soft matter as well as quantum phases in correlated electron materials with competing atomic scale short-range as well as mesoscopic nanoscale interactions. I will discuss our developments and applications of new nano-optical spectroscopies to study those interactions providing microscopic insight into otherwise difficult to probe processes in soft- and correlated matter. Our approach is based on the combination of plasmonic and optical antenna concepts with ultrafast and shaped laser pulses to achieve precise control of an optical excitation on the nanometer-femtosecond scale. I will introduce the enabling principles based on new regimes of near-field light-matter interaction in terms of impedance matching and optical antenna control of a quantum excitation [Preview Abstract] |
Friday, October 18, 2013 11:24AM - 11:36AM |
C4.00002: Characterization of Order-Disorder Phase Transition Temperature for Select Nanoparticles Greg Sutherland Many metal alloys can form in chemically ordered structures, often resulting in significant changes in properties. The ordered structures are preferred at low temperatures and will go through an order-disorder phase transition at a critical temperature. The formation and stability of these ordered structures in alloy nanoparticles is not well understood but may give insight into the role size plays in phase transitions. To this end we are studying CoPt, AuCu, and FeNiPt alloy nanoparticles. We will focus this presentation on the characterization of these nanoparticles in a Transmission Electron Microscope (TEM) for composition, size, and structure. These nanoparticles are made by co-sputtering the constituents and annealing at different temperatures in various gas mixtures. The nanoparticle samples are prepared for TEM viewing by wedge polishing. We will discuss our results and possible implications. [Preview Abstract] |
Friday, October 18, 2013 11:36AM - 11:48AM |
C4.00003: Non-Specular Reflectance to Determine Surface Roughness Jonathan Schuler, Joshua Marx, R. Steve Turley Extreme ultra-violet (XUV) optics have potential applications in nanoscale photolithography, imaging, astrophysics, and plasma diagnostics. Because the wavelengths can approach atomic dimensions the optics are particularly sensitive to surface roughness. For instance, multilayer mirrors often needs to have their thicknesses and roughnesses controlled to within one nanometer. We have developed a technique to use scattering of XUV light to from rough UOx thin films to determine their surface roughness. From the scattering data, we calculated the reflectance per unit angle of the different materials. We compared the calculated reflectance information to physical optics models of surface scattering to determine details of the surface roughness. We compared these calculations to AFM and SEM characterizations of the same surfaces. By correctly accounting for surface roughness, we improved our determination of the optical constants of these thin films and the predicted performance of XUV optical elements. [Preview Abstract] |
Friday, October 18, 2013 11:48AM - 12:00PM |
C4.00004: Experimental and Theoretical Investigation of Critical Point Energy Shift of Ge Films Grown on Si(100) Substrate due to Strain Nalin Fernando, Ayana Ghosh, Cayla Nelson, Amber Medina, Seth Xu The strain generated due to the thermal expansivity mismatch between the Ge film and Si substrate affects the optical properties of the Ge film resulting in many applications in the field of engineering. The strain which is a function of temperature shifts the critical point energies. The complex pseudo dielectric functions of bulk Ge and Ge films grown on Si(100) were measured using spectroscopic ellipsometry in the 0.76-6.6 eV energy range between 77-700 K to investigate the strain dependence of E$_{\mathrm{1}}$~and E$_{\mathrm{1}}+\Delta_{\mathrm{1}}$~critical point energies (CP). CP energies and related parameters were obtained by analyzing second-derivative spectrum d$^{\mathrm{2}}\varepsilon $/d$^{\mathrm{2}}\omega $~of the ellipsometry data. Using a pseudo-quasi-harmonic model for thermal expansivity proposed by Robert Reeber (Mat. Che. and Phy, 1996) we were able to predict theoretical energy shifts due to the strain on Ge films grown on Si(100) substrate, the predicted energy shifts are in excellent agreement with the ellipsometry results. We will discuss the strain dependence of the CP energies due to the thermal expansivity mismatch of Ge films grown on Si(100) and effect of the temperature to the energy shift upon cooling to lower temperatures. [Preview Abstract] |
Friday, October 18, 2013 12:00PM - 12:12PM |
C4.00005: Generation of spin currents with light and spin Seebeck effect David Ellsworth, Lei Lu, Mingzhong Wu The spin Seebeck effect (SSE) refers to the generation of a spin voltage in a material in the presence of a thermal gradient. This presentation reports on the use of light to induce the SSE. Experiments used a tri-layered sample that consisted of a 5.9-$\mu$m-thick yttrium iron garnet (YIG) film grown on a 0.5-mm-thick gadolinium gallium garnet substrate and capped with a 3.8-nm-thick Pt layer. The sample sat on an aluminum heat sink and was exposed to the light from a 100 W incandescent light bulb. A magnetic field was applied in the plane to bias the YIG film. The light produces a thermal gradient across the sample thickness which produces, through the SSE, a spin current that flows from the YIG/Pt interface into the Pt layer. Via the inverse spin Hall effect, the spin current generates an electric voltage across one of the lateral dimensions of the Pt layer. It was found that the voltage varied with time in sync with the temperature gradient. The voltage amplitude had linear dependence on light intensity and showed sinusoidal dependence when the magnetic field was rotated in the plane for one cycle. The voltage changed its sign as the field switched its polarity. [Preview Abstract] |
Friday, October 18, 2013 12:12PM - 12:24PM |
C4.00006: Molecular Dynamics and the Melting Transition: A Computational Modeling Approach for Building Intuition Derek Ostrom, Gus Hart Even simple models, like Lennard-Jones particles, can show remarkably realistic physics and exhibit important phenomena. Using a Lennard-Jones model and molecular dynamics simulations using a simple Verlet algorithm for generating dynamics, melting/freezing transitions can be observed, ground state structures can be discovered, and the Maxwell-Boltzmann distribution emerges spontaneously. These simulations can be an intuitive starting point for building intuition and spring-boarding to simulations of more complex representations of real materials. [Preview Abstract] |
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