Bulletin of the American Physical Society
2013 Annual Fall Meeting of the APS Prairie Section
Volume 58, Number 15
Thursday–Saturday, November 7–9, 2013; Columbia, Missouri
Session I1: Condensed Matter Physics V |
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Chair: Paul Miceli, University of Missouri Room: Physics Building 120 |
Saturday, November 9, 2013 10:30AM - 11:06AM |
I1.00001: QSE growth and super-diffusive liquid-like motion in Pb/Si(111) at low temperature Invited Speaker: Michael Tringides QSE are responsible for the formation of uniform height metal islands at low temperatures [1]. For Pb/Si the islands form unusually fast, within a few minutes as low as T $\sim$ 150K. With STM [1] X-ray scattering [2] and LEEM [3] it was found that this is due to the superdiffusive ``liquid-like'' motion of the dense wetting layer that moves collectively with constant speed. Unstable islands transform into stable islands as seen in STM movies with the wetting layer climbing the sides of the unstable islands to complete the next layer. X-ray scattering experiments have shown anomalous coarsening with faster kinetics for growth at higher flux rates [2]. This unusual motion is also directly seen by LEEM with the refilling of an initial vacant circular region generated by a laser pulse, evolving at constant speed x/t instead of the normal x/t$^{1/2}$ diffusive motion (with x the profile edge). An outgoing expanding front is observed whose boundary is the source of material that refills the vacant hole. The combined effect is to observe mass transport over macroscopic distances with unusual long range correlation between the outwards expanding ``source'' and the inward moving ``sink'' (the refilling edge), separated by more than 0.200mm. In collaboration with M. Hupalo, P.Miceli, E. Conrad and M. S. Altman. \\[4pt] [1] M. C. Tringides et al \textit{Physics Today }\textbf{60}, No. 4, 50 (2007).\\[0pt] [2] C. A. Jeffrey et al Phys. Rev. Lett., 96 106105, 2006.\\[0pt] [3] K. L. Man, et al. Phys. Rev. Lett., 11036104--5, 2013. [Preview Abstract] |
Saturday, November 9, 2013 11:06AM - 11:18AM |
I1.00002: Minimum stable height of Ag nano-islands on Si(111)7x7 Yiyao Chen, Michael Gramlich, Shawn Hayden, Paul Miceli The origin of a minimum stable Ag nano-island height of one bi-layer on top of the wetting layer has remained a long-standing mystery in the effort to understand mechanisms that control the growth of supported nanoscale metals. We present the results of synchrotron x-ray scattering studies which demonstrate that the interfacial energy, rather than previously suspected electron confinement effects, is responsible for the minimum island height. In situ measurements of x-ray reflectivity and crystal truncation rods reveal that the Ag nano-islands consume the wetting layer and are, therefore, tri-layers -- an effect that cannot be detected by scanning probe measurements. These experiments lead to an energy ``phase diagram'' that we propose to explain the existence of a minimum island height for supported nanoscale metals. Support from the National Science Foundation under grants DMR-0706278 and DGE-1069091 is gratefully acknowledged. The Advanced Photon Source Sector 6 beam-line at Argonne National Laboratory is supported by the US-DOE under Contract No. W-31-109-Eng-38. [Preview Abstract] |
Saturday, November 9, 2013 11:18AM - 11:30AM |
I1.00003: Temperature Dependent Electrical Characterization of Graphene Flakes Synthesized Using Liquid Phase Exfoliation Baleeswaraiah Muchharla, Mitchell Connolly, Andrew Winchester, Sujoy Ghosh, Swastik Kar, Saikat Talapatra We will report the synthesis and electrical transport properties of graphene flakes synthesized by exfoliating the bulk graphite in isopropyl alcohol. Temperature dependence of the electrical resistivity of thin films made from exfoliated graphene flakes has been studied over a wide range (10K \textless T \textless 300K) of temperature. Temperature dependence of resistance shows a slow linear increase in resistance with decrease in temperature. Electric field effects on charge transport properties e.g. temperature (220K \textless T \textless 275K) dependence of carrier mobilities etc. of exfoliated graphene thin film devices under electrochemically gated environment will also be presented and discussed. [Preview Abstract] |
Saturday, November 9, 2013 11:30AM - 11:42AM |
I1.00004: Interplay between restricted transport and catalytic reaction in nanoporous materials: KMC simulation and analytic theory Andres Garcia, Jing Wang, David Ackerman, James Evans Behavior of catalytic reactions in narrow pores is controlled by a delicate interplay between fluctuations in adsorption-desorption at pore openings, highly restricted diffusion, and reaction. The resulting concentration profiles determined by KMC simulation, showing reactants mainly near pore openings, are not described by standard mean-field reaction-diffusion equations. For simple A$\to $B unimolecular reaction kinetics, the challenge in developing a correct theory is to suitably describe chemical diffusion in mixed-component quasi-single-file systems. This is achieved based on a refined picture of tracer diffusion for finite-length pores. For A$+$B$\to $C$+$D bimolecular and other reactions, there are additional complications in describing spatial correlations in reactant locations which can strongly impact the reaction kinetics. [Preview Abstract] |
Saturday, November 9, 2013 11:42AM - 11:54AM |
I1.00005: Effect of metal and semiconducting nanoparticles on the fluorescence of Dy$^{3+}$ doped lead and bismuth borate glasses Saisudha Mallur, Stewart Ferrell, P.K. Babu The rapid development of laser research has led to increased theoretical and experimental investigations of fluorescence of rare-earth ions in heavy metal oxide glasses. These glasses containing metallic and semiconducting nanoparticles are very promising systems because the nanoparticles may induce favorable changes in the rare earth ion's fluorescence properties. We prepared Dy$^{3+}$ doped lead and bismuth borate glasses containing Ag, CdSe and ZnSe nanoparticles. Glasses are made through the normal melt quench method. AgNO$_{3}$ or powders of the semiconducting compounds are added as precursor materials. Glasses obtained through this process contain Ag atoms or molecules of the semiconducting compounds uniformly distributed within the glass system. These are then subjected to a controlled annealing near the glass transition temperature. During this annealing process, Ag atoms or CdSe/ZnSe molecules thermally diffuse and coalesce to form nanoparticles. The sizes of these nanoparticles can be varied by varying the annealing times as confirmed by the TEM. Fluorescence spectra of Dy$^{3+}$ show noticeable changes as a function of annealing times. Variations in the fluorescence spectra are believed to arise from the strong interaction between Dy$^{3+}$ ions and the nanoparticles. [Preview Abstract] |
Saturday, November 9, 2013 11:54AM - 12:06PM |
I1.00006: Supported shock waves in hydroxyl-terminated polybutadiene melts: A large-scale molecular dynamics study Markus Froehlich, Thomas Sewell, Donald Thompson Hydroxyl-terminated polybutadiene (HTPB) melts subjected to supported shock loading were studied by non-reactive all-atom molecular dynamics (MD) simulations to investigate their responses to shock wave passage. An efficient Monte Carlo/MD technique was developed to generate multi-million-atom systems of well-equilibrated linear polymers with chain lengths $n=$ 64, 128, or 256 backbone carbons. Explicit shock wave simulations, performed using a reverse-ballistic method, were carried out for all three chain lengths with a shock strength of 8.6 GPa, and for the $n=$ 128 system with four different shock strengths ranging from 2.8 to 12.5 GPa. All MD simulations were done using LAMMPS and the OPLS-AA force field with the Lennard-Jones potential replaced by the Buckingham exp-6 potential. Spatial and temporal resolution of the shock response was obtained by analyzing the simulation data in a reference frame centered on the shock front, which traverses the sample with constant speed. Structural properties, global scaling behaviors, and vibrational spectra of the unshocked polymers are in good agreement with literature data. Results for the shocked material indicate a shock-induced transition to a glass-like state based on residual shear stresses and increases of structural relaxation times by several orders of magnitude. Vibrational spectra for the shocked states exhibit considerable broadening and blue shifting. [Preview Abstract] |
Saturday, November 9, 2013 12:06PM - 12:18PM |
I1.00007: Fluorescence Enhancement and Single Molecule Fluorescence Detection on Nanogap Embedded Plasmonic Gratings fabricated using HD-DVD Avinash Pathak, Sagnik Basuray, Joseph Mathai, Drew Menke, Keshab Gangopadhyay, Peter Cornish, Shubhra Gangopadhyay A novel method for producing silver plasmonic gratings for surface plasmon resonance (SPR) based coupling of light has been developed which utilizes soft lithography technique using PDMS stamping of grating from HDDVDs. Further, 20nm wide nano-gaps are formed on the stamp wherein an extreme field concentration occurs leading to enhancements of 118 times with respect to glass. The gratings with nanogaps were used for single molecule studies, with an immobilized layer of tagged DNA molecule. Enhancement with epifluorescence on gratings when compared to total internal reflection microscopy (TIRF) on quartz slides is up to 40 times on nanogaps. Further, single molecule Forster resonance energy transfer imaging used to study the dynamics of DNA performed on the gratings shows intensity enhancement by 10 times on nanogaps in comparison to TIRF on quartz. Finally, in order to improve the reproducibility of the nanogaps, a glancing angle deposition method (GLAD) is coupled with the existing technique in order to form nanogaps. We are thus also able to produce extremely sharp tip regions on these grating structures which further enhance the coupling efficiencies due to a field concentration within these hotspot regions. The layered structure is able to produce height dependent enhancement giving a 3-dimentional view of micromolar concentration of dye on the surface. In conclusion, a method of fabricating plasmonic substrates has been developed which can be utilized for sensing or observation of single molecule interactions using epifluorescence. [Preview Abstract] |
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