Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session D4: Condensed Matter IV |
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Chair: Peter Rez, Arizona State University Room: MU242A |
Friday, October 16, 2015 1:50PM - 2:02PM |
D4.00001: Transient thermoreflectance measurement of gold nanoparticle thermal boundary resistance. Brian Green, Mark Siemens Macroscopic thermal transport is explained by classical thermal diffusion, but as nanostructure length scales approach the phonon mean free path, nanoscale effects emerge such as sensitivity to the presence of surfaces and the onset of ballistic transport. We present experimental measurements in which we time-resolve the cooling dynamics of gold nanospheres, approximately 19 nm in diameter, in a polymer matrix and deposited on a glass substrate. We use the transient thermoreflectance (TTR) method in colinear pump/probe experiments. Excitation and probe signals are generated from an 800 nm near-infrared pulsed laser, with pulse duration about 3 orders of magnitude less than the diffusion time of these structures. The measured thermal dynamics show sub-picosecond heating and a steady cooling decay. Fitting these experimental data with a model of diffusive thermal transport in a stratified, spherical nanostructure, we determine the gold/polymer thermal boundary resistance and compare the result with theoretical models. [Preview Abstract] |
Friday, October 16, 2015 2:02PM - 2:14PM |
D4.00002: Structural Features of Prussian Blue Analogs Michael Boergert, Edwin Fohtung, Heinz Nakotte, Luke Daemen Most Prussian Blue Analogs (PBAs) crystallize in cubic framework structures with alternating C or N octahedrals that contain metal ions. The vast majority of PBAs exhibit negative thermal expansion (NTE), which is of great interest for applications. A full understanding of NTE effects requires detailed knowledge of the structural features of these compounds. This study looks into X-ray diffraction patterns of single-crystalline grains of an exemplary Prussian Blue Analog, taken at the Advanced Photon Source (APS) at Argonne National Laboratory. We collected three-dimensional sets at various temperatures, and the main and lesser peaks of each data set were analyzed. The analysis provides the peak widths, peak shapes (Gaussian or Lorentzian) and peak locations, and the results were used to determine the long- and short-range features of this particular PBA. [Preview Abstract] |
Friday, October 16, 2015 2:14PM - 2:26PM |
D4.00003: Structural properties of SrTiO3 thin films on Semiconductors Nuwanjula Samarasingha, Jaime Moya, Stefan Zollner, Sudeshna Chattopadhyay, Patrick Ponath, Alex Demkov SrTiO3 (STO) films were grown epitaxially on different semiconductor substrates (Si, Ge) with the unit cell rotated by 45 degrees with respect to the underlying substrate lattice. X-ray diffraction (XRD) and X-ray reflectivity (XRR) were utilized to characterize STO on Si, Ge and STO. Structural properties (lattice constant and strain) were obtained using high resolution X-ray diffraction with two types of scans ($\omega $ and $\omega $-2$\theta )$. Most technological applications require thin films of definite thickness with a known density/depth profile. Hence, determination of film thickness and corresponding density profile is very crucial for these technologies. Using a simulation (theoretical model based on Parratt formalism) of the X-ray reflectivity pattern, a highly accurate measurement of thickness, roughness and electron density profile can be obtained. X-ray reflectivity data indicate that the SrTiO3 thin film on Si thickness is approximately 17 nm with 2.9 nm SiO2 layer with a constant electron density. Also, the SrTiO3 thin film on Ge thickness is approximately 19 nm with 1.5 nm GeO2 layer with a varying electron density. We will compare our XRR results with ellipsometry data taken on the same layers. [Preview Abstract] |
Friday, October 16, 2015 2:26PM - 2:38PM |
D4.00004: Multi-scale method for analysis of self-heating in nano-electronic devices Robin Daugherty, Suleman Qazi, Abdul Shaik, Dragica Vasileska Electrons in semiconductor devices under bias gain energy in an electric field and scattering events cause energy exchange with the crystal lattice (where the energy is transported as heat). Due to the nature of these interactions, it is possible for hot spots to form in electronic devices which can be detrimental to device performance. Electrons exchange energy with the lattice in the form of optical and acoustic phonons. The rate of energy exchange due to scattering events is faster for optical phonons than for acoustic phonons, which leads to a concentration of energy into the optical phonon bath. Optical phonons must decay into acoustic phonons before the energy can be dissipated as heat; this decay is slow and results in localized hot spots in active regions of semiconductor devices. The Monte Carlo method is used to solve the Boltzmann transport equation for electrons and the energy balance model is used to calculate the acoustic and optical phonon temperatures to be fed back into the Monte Carlo transport kernel. The electro-thermal device simulator is then self-consistently coupled with a thermal transport solver at the interconnect level. This multi-scale approach gives a good result for the hot spot location and temperature. [Preview Abstract] |
Friday, October 16, 2015 2:38PM - 2:50PM |
D4.00005: Dissipative Mixing of Energy and Spatial Coordinates for Variable Range Hopping in Disordered Organic Semiconductors Tzu-Cheng Wu, David H. Dunlap, Susan R. Atlas, Steve Valone Electron transport of injected charges in disorder organic semiconductor devices is often controlled by a few rate-limiting hops. These hops are facilitated by the interaction between the charge and the surrounding polarizable medium. For strong disorder, variable range hopping considerations result in mixing between the intermolecular hopping distance $R$ and the site energy differences $\Delta\epsilon$. Here we include explicitly relaxation processes described by the Caldeira-Leggett model. We show that because the equilibration time also depends on $R$ and $\Delta\epsilon$, there is an additional $R$-$\Delta\epsilon$ mixing that has not been accounted for previously, offering a possible explanation for the anomalous dependence of mobility on temperature, electric field and hopping site density seen in experiments. [Preview Abstract] |
Friday, October 16, 2015 2:50PM - 3:02PM |
D4.00006: Calibration and validation of the PTW dynamic strength model for Cu using novel feedthrough hydrodynamic instability experiments Sudrishti Gautam, Saul Opie, Elizabeth Fortin, Jenna Lynch, Eric Loomis, Pedro Peralta Hydrodynamic instabilities, e.g., the Rayleigh-Taylor can be used to deduce dynamic material strength at very high pressures and strain rates. The Ritchmyer-Meshkov Instability (RMI) can also be used, since it allows using precise diagnostics such as Transient Imaging Displacement Interferometry due to its slower linear growth rate. Experiments at Los Alamos National Laboratory used RMI to measure strength in polycrystalline copper with a novel approach, whereby the shock is applied directly on the perturbed surface using laser ablation and producing a perturbed shock that propagates through the sample thickness. The Preston-Tonks-Wallace (PTW) model, which is a proven material strength model at very high pressures and strain rates is used along with numerical simulations, to study the effects of initial amplitude and wavelength of the perturbations, dynamic strength of material, stability of the shock front, dynamic evolution of the amplitudes, and velocities of the perturbation imprinted on the back surface by the perturbed shock front. Simulation results obtained from using the PTW models were then compared and validated with experimental results for copper samples tested at pressures $\ge $ 8 GPa. [Preview Abstract] |
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