Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K26: Insulator: Growth, Structure, Properties, and Defects |
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Sponsoring Units: DCMP Chair: Bharat Jalan, University of Minnesota Room: 325 |
Wednesday, March 16, 2016 8:00AM - 8:12AM |
K26.00001: Nanocrystal Ghosting: Extensive radiation damage in MgO induced by low-energy electrons William Sawyer, Zachery Frankenfield, Kenneth Kane Radiation damage in magnesium oxide has been an ongoing source of investigation. Early work was motivated by its simple cubic structure and its excellent electrical insulating properties over a wide range of temperatures and mechanical conditions. The goal was to determine its suitability as an electrical insulator in radiation intense environments including nuclear reactors and proposed nuclear fusion devices. During this period experimental results for irradiation of MgO using electrons with energies less than 500 keV produced very limited damage. These results, supported by theoretical arguments, lead to the conclusion that MgO was relatively impervious to damage from electrons with energies below this threshold. More recently its excellent insulating properties and relative mechanical stability combined with an increased interest in nanomaterials applications have created renewed interest in MgO. In this paper direct evidence is presented for extensive radiation damage in MgO nanocrystals from intense irradiation by electrons (2 x 10 $^{4\, }$electrons/nm$^{2}$ sec) with beam energies between 120 keV and 60 keV. [Preview Abstract] |
Wednesday, March 16, 2016 8:12AM - 8:24AM |
K26.00002: Point defects in yttria-stabilized zirconia C. Stephen Hellberg, Noam Bernstein, Steven C. Erwin The densification that occurs during sintering of certain ceramics has been observed to occur more rapidly and at lower temperatures when a weak external electric field is applied.$^1$ We compute the formation energies of point defects in yttria-stabilized zirconia using first principles density functional theory. We examine interstitials, vacancies, and vacancy complexes including Schottky defects in a Y$_2$Zr$_{14}$O$_{31}$ computational cell, which corresponds to approximately 7 mol\% yttria stabilized zirconia. We relate our results to recent experimental work on electric-field-assisted sintering in yttria-stabilized zirconia, showing how how the expansion of lattice constants observed in diffraction measurements results from increasing defect densities. ~ 1. Raj, R., Cologna, M., and Francis, J. S.~C. Influence of Externally Imposed and Internally Generated Electrical Fields on Grain Growth, Diffusional Creep, Sintering and Related Phenomena in Ceramics. {\em Journal of the American Ceramic Society}{ \bf 94}, 1941 (2011). [Preview Abstract] |
Wednesday, March 16, 2016 8:24AM - 8:36AM |
K26.00003: Investigation of Defect Structure to Determine the Primary Photorefractive Centers Responsible for Enhanced Beam Coupling in KNbO3:Fe Dean Evans, Sergey Basun A series of experiments are used to determine the location of the energy levels of various Fe centers and associated defect centers in KNbO$_{\mathrm{3}}$:Fe, as well as conclude which centers are the primary photorefractive centers. In particular, the methods include electron paramagnetic resonance, optical absorption spectroscopy, electric conductivity, and beam coupling. A correlated study using data acquired with these techniques has been performed on as-grown (unreduced) and reduced KNbO$_{\mathrm{3}}$:Fe crystals, which identified which Fe centers were reduced and which ones were not. Conditions for an increased electron source population (improved beam coupling performance) was determined and compared to beam coupling results for pure electron, pure hole, and electron-hole competition processes. [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 8:48AM |
K26.00004: Raman and Fluorescence Study of Erbium-Doped Laser-Induced Crystals-in-Glass Brian Knorr, Keith Veenhuizen, Adam Stone, Himanshu Jain, Volkmar Dierolf Laser induced crystallization of glasses is a spatially selective process which has the potential to produce photonic integrated circuits in a glass matrix. Low temperature Combined Excitation Emission Spectroscopy in Er:LaBGeO$_5$ show that erbium incorporates at predominantly one majority site in both glass-ceramics and laser-induced crystals-in-glass, but that other minority sites also exist. The energy levels of the majority site were quantified. The fluorescence characteristics of the erbium ions in any site in the laser-induced crystals were found to be only weakly influenced by the irradiation conditions during growth. On the other hand, a hidden parameter, potentially boron deficiency-related defects, resulted in a significant change in the incorporation behavior of the erbium ions. Simultaneous scanning confocal Raman and fluorescence spectroscopy showed that the energies of the Raman modes are shifted, and the erbium fluorescence intensity varies, in a non-uniform manner, despite the host glass being homogeneously doped, across the cross-sections of laser-induced crystals in glass. These fluctuations within the Raman and fluorescence are spatially correlated, implying that different erbium sites form preferentially at different locations in the crystal cross-section. [Preview Abstract] |
Wednesday, March 16, 2016 8:48AM - 9:00AM |
K26.00005: Excitons and band edge alignment in CdSe/CdS core-shell nanocrystals: ab initio Danylo Zherebetskyy, Lin-Wang Wang Quantum confinement is a foundational nanoscience concept that allows tuning electronic properties of quantum dots. Core-shell quantum dots are promising nanoparticles and found applications as light-emitting optoelectronic devices and biomarkers [1] due to their robustness and tunability of both core and shell. The fluorescent quantum yield of these quantum dots can achieve 100{\%} [2] even at room temperature [3]. However, to understand many phenomena of carrier dynamics, photoluminescence efficient and Auger effects, fine electronic structures of the exciton are needed. Here, using large scale electronic structure calculations based on charge patching method, we have investigated the exciton binding energy, band alignment between core and shell, charge separation between electron and hole. We will discuss how these can be tuned by changing the core/shell dimensions. 1. Shirasaki Y., Supran G., Bawendi M., Bulovi\'{c} V. Nature Photonics 7, 13 (2013). 2. Javaux C. et al, Nature Nanotech. 8, 206 (2013) 3. Achieved in Alivisatos lab (2014). [Preview Abstract] |
Wednesday, March 16, 2016 9:00AM - 9:12AM |
K26.00006: Photocreation and hyperbolic decay of Sb$^{\mathrm{2+}}$ in Sn$_{\mathrm{2}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$:Sb. Sergey Basun, Larry Halliburton, Serguey Odoulov, Alexandr Shumelyuk, Alexander Grabar, Dean Evans In Sn$_{\mathrm{2}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$:Sb, photorecharging of Sb$^{\mathrm{3+}}$ ions to Sb$^{\mathrm{2+}}$ causes a new interesting phenomenon -- photo-sensitizing of photorefraction.[1,2] The decay of the optically produced Sb$^{\mathrm{2+}}$ ions was directly measured through EPR and was found to have a hyperbolic character: \textasciitilde 1/(t/$\tau +$1) with an activation energy of 0.42 eV. This decay character and a very similar activation energy were also found in photorefraction and optically induced absorption experiments. The observed hyperbolic decay was explained through the set of rate equations that takes into account the EPR result: only Sb$^{\mathrm{3+}}$ ions are present in Sn$_{\mathrm{2}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$:Sb in thermal equilibrium. The long-wavelength onset of the EPR-measured Sb$^{\mathrm{2+}}$ ``photocreation'' spectrum together with the activation energy of the Sb$^{\mathrm{2+}}$ decay allowed to firmly locate the position of the Sb$^{\mathrm{2+/3+}}$ electron level in the bandgap of Sn$_{\mathrm{2}}$P$_{\mathrm{2}}$S$_{\mathrm{6}}$: 0.42 eV below the conduction band bottom. [1] D. R. Evans, A. Shuymelyuk, G. Cook, S. Odoulov. Opt. Lett. 36, 454 (2011). [2] Y. Skrypka, A. Shumelyuk, S. Odoulov, S. Basun, D. Evans, Opt. Comm. 356, 208 (2015). [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:24AM |
K26.00007: Surface Analysis of sp$^{\mathrm{2}}$ Carbon in Ag and Al Covetic Alloys* H M Iftekhar Jaim, Daniel P. Cole, Lourdes G. Salamanca-Riba Ag, Al-6061 and Al-7075 were doped with carbon by an electrocharging assisted process where high electric current is applied to the molten metal containing particles of activated carbon. This process gives rise to epitaxial growth of graphene nanoribbons (GNR) and carbon nanostructures within the metal matrix. Alloys produced with such technique are named Covetics. Al-6061 and Al-7075 covetics have shown superior mechanical, electrical and anti-corrosion properties. The nanostructured carbon incorporation has been confirmed by XPS, Raman, and TEM studies. Here, we present detailed surface characterization of the carbon nanostructures in these new alloys. Raman and EELS mapping of carbon nanostructure were carried out to identify the nature of bonding, strain and defect characteristics. Mostly, crystalline GNR or graphene sheets were found to create networks with sp2 character, under compressive strain with high concentration of defects. AFM and KPFM showed contrast in phases and potentials for ribbon like features. Incorporation of sp2 carbon in metals is an initial step for the integration of carbon nanostructures for future applications requiring high strength and conductivity. [Preview Abstract] |
Wednesday, March 16, 2016 9:24AM - 9:36AM |
K26.00008: Direct visualization of atomically precise nitrogen-doped graphene nanoribbons. Hong-Liang Lu, Yi Zhang, Yanfang Zhang, Geng Li, Jianchen Lu, Xiao Lin, Shixuan Du, Reinhard Berger, Xinliang Feng, Klaus Mullen, Hong-Jun Gao We have fabricated atomically precise nitrogen-doped chevron-type graphene nanoribbons by using the on-surface synthesis technique combined with the nitrogen substitution of the precursors. Scanning tunneling microscopy and spectroscopy indicate that the well-defined nanoribbons tend to align with the neighbors side-by-side with a band gap of 1.02 eV, which is in good agreement with the density functional theory calculation result. The influence of the high precursor coverage on the quality of the nanoribbons is also studied. We find that graphene nanoribbons with sufficient aspect ratios can only be fabricated at sub-monolayer precursor coverage. This work provides a way to construct atomically precise nitrogen-doped graphene nanoribbons. [Preview Abstract] |
Wednesday, March 16, 2016 9:36AM - 9:48AM |
K26.00009: First-principle study on substrate-induced structures of bismuth adsorption on graphene. Shih-Yang Lin, Shen-Lin chang, Hsin-Hsien Chen, Shu-Hsuan Su, Jung-Chun Huang, Ming-Fa Lin The geometric and electronic properties of Bi-adsorbed monolayer graphene, enriched by the strong effect of substrate, are investigated by the first-principles calculations. The six-layered substrate, corrugated buffer layer, and slightly deformed monolayer graphene are all simulated. Adatom arrangements are optimized through detailed analyses on adsorption energies and ground-state energies of various adsorption sites, revealing a hexagonal array of Bi atoms dominated by the interactions between buffer layer and monolayer graphene. The increasing temperature can overcome a \textasciitilde 50 meV energy barrier and induce triangular and rectangular nanoclusters. The most stable and the metastable structures agree with the scanning tunneling microscopy measurements. The density of states exhibits a finite value at the Fermi level, a dip at low energy, and a shoulder at \textasciitilde -0.8 eV, as observed in the experimental measurements of tunneling conductance. [Preview Abstract] |
Wednesday, March 16, 2016 9:48AM - 10:00AM |
K26.00010: Atomic-scale investigation of grain boundary motion in graphene Dongwook Kim, Youngkuk Kim, Jisoon Ihm, Euijoon Yoon, Gun-Do Lee Grain boundaries (GBs) in graphene can migrate when irradiated by electron beams from a transmission electron microscope (TEM). Here, we present an ab initio study on the atomic scale mechanism for the GB motion with misorientation angle of 30° in graphene. From total energy calculations and energy barrier calculations, we find that a Stone--Wales(SW)-type transformation can occur more easily near GBs than in pristine graphene due to a reduced energy barrier. There are other cases of migration which can be understood by other type of transformation, named “evaporation of a carbon dimer”. We also find that a mismatch in the crystalline orientation at GBs can drive the evaporation of a carbon dimer easily by greatly reducing the corresponding overall energy barrier. After evaporation of the carbon dimer, the GBs can be stabilized through a series of SW-type transformations that result in GB motion. The GB motion induced by evaporation of the dimer is in excellent agreement with recent TEM experiments. [Preview Abstract] |
Wednesday, March 16, 2016 10:00AM - 10:12AM |
K26.00011: Ripplocations: A Novel Defect in Layered Materials Jacob Gruber, Andrew Lang, Justin Griggs, Garritt Tucker, Michel Barsoum Recently, a new defect, the ripplocation, the mechanical buckling of a single atomic layer, was proposed to explain the behavior of two dimensional materials. Leveraging atomistic simulations, this concept is extended to bulk layered materials. Unlike dislocations, ripplocations do not possess a Burgers vector and do not have polarity. In graphite, ripplocations are attracted both to vacancies, where they can annihilate, and other ripplocations, forming larger complexes and eventually kink boundaries. While some ripplocation behavior can be described by dislocation complexes, the failure of these models to explain core interactions suggests that ripplocations are a fundamentally new class of defect. Furthermore, TEM examination of nanoindented Ti$_3$SiC$_2$, where dislocation theory does not provide a complete description of behavior, reveals the presence of defects with no Burgers vector and with rotation and strain fields similar to those predicted in simulation, suggesting the presences of buckled basal planes. Ripplocations have profound implications for the deformation of plastically anisotropic solids, including graphite, layered silicates and the MAX phases. [Preview Abstract] |
Wednesday, March 16, 2016 10:12AM - 10:24AM |
K26.00012: Spin chains and electron transfer at stepped silicon surfaces Steven Erwin, Julian Aulbach, Ralph Claessen, Joerg Schaefer Stepped silicon surfaces oriented between Si(111) and Si(001) show unusual behavior when submonolayer amounts of gold are adsorbed: they self-assemble to form arrays of steps with virtually perfect structural order. Known examples include Si(553), Si(557), and Si(775). For the first two of these there is, in addition, strong theoretical and experimental evidence that the silicon step edges are spin polarized, raising the possibility of a magnetically ordered ground state at a silicon surface. The situation is different, however, for Si(775): theory and experiment both show that spin polarization does not occur. Here we use density-functional theory and scanning tunneling microscopy to develop a physically transparent picture explaining the formation of these 'spin chains' on the family of Si(hhk)-Au surfaces. Specifically, we explain why spin chains form on particular silicon (hhk) orientations but not on others. Finally, we use this understanding to propose strategies for using surface chemistry to control the formation or suppression of spin chains on Si(hhk)-Au surfaces. [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K26.00013: Film Growth on Nanoporous Substrate Xue Zhang, James Joy, Chenwei Zhao, J.M. Xu, James Valles Self-ordered nanoporous anodic aluminum oxide (AAO) provides an easy way to fabricate nano structured material, such as nano wires and nano particles. We employ AAO as substrates and focus on the thermally evaporated film growth on the surface of the substrate. With various materials deposited onto the substrate, we find the films show different structures, e,g. ordered array of nano particles for Lead and nanohoneycomb structure for Silver. We relate the differing behaviors to the difference of surface energy and diffusion constant. To verify this, the effect of substrate temperature on the film growth has been explored and the structure of the film has been successfully changed through the process. [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K26.00014: Thermal Expansion of ScF$_{\mathrm{3}}$. R. Bhandia, A. Grockowiak, T. Siegrist, T. Besara, S.W. Tozer, G.M. Schmiedeshoff ScF$_{\mathrm{3}}$ is an insulator, has a cubic crystal structure, and exhibits negative thermal expansion over a very wide temperature range. We will present and discuss thermal expansion measurements made with capacitive and fiber-Bragg-grating dilatometers. Work at Occidental College is supported by the National Science Foundation under DMR- 1408598. A portion of this work was funded by the US Department of Energy NNSA SSAA DE-NA0001979, and performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida. [Preview Abstract] |
Wednesday, March 16, 2016 10:48AM - 11:00AM |
K26.00015: Electronic and optical properties of co-doped BaTi O$_{\mathrm{3}}$ with fluorine and nitrogen: A first-principles study. Jawad Alsaei, Pual Tangney, Arash Mostofi Ferroelectric oxides such as BaTi O$_{\mathrm{3}}$ (BTO) are very good candidates for tunable dielectric devices. Tailoring the electronic and optical properties of these materials is usually achieved through means of strain engineering and compositional variations. In this work, we use first-principles calculations to study the effect of the co-substitution of F and N in BTO on its electronic and optical properties. Our simulations suggest that the optical properties are very sensitive to the atomic configuration of the dopant atoms. Our simulations show that the most energetically favorable configuration is that in which the F and N atoms form linear parallel chains of F-Ti-N motif that tend to cluster with each other. This configuration induces a large birefringence that can be further enhanced by means of biaxial strain. Our results shed more light on this particular type of anionic doping that has been rarely studied in the literature~\cite{Rao2013JPhysConMa}. \begin{thebibliography}{1} \bibitem{Rao2013JPhysConMa} Kumar, N., Pan, J., Aysha, N., Waghmare, U. V., Sundaresan, A., and Rao, C. (2013) Journal of Physics: Condensed Matter 25(34), 345901. \end{thebibliography} [Preview Abstract] |
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