BNL Home
April 2016
Sunday Monday Tuesday Wednesday Thursday Friday Saturday

1

  1. No events scheduled

2

  1. No events scheduled

3

  1. No events scheduled

4

  1. CFN Special Seminar

    11 am, CFN, Bldg 735

    Hosted by: James Dickerson

    Rare-earth (RE) ions play a significant role as the active centers in modern optical technology. The luminescent properties of rare-earth doped materials have attracted great attention for a wide variety of applications including phosphors, lasers, and scintillators. This talk will cover the overview of the spectroscopic evaluation of the following research areas in the UV-Visible (displays, scintillators), Near-IR, and Mid-IR (infrared solid-state laser sources) spectral region using laser-induced fluorescence spectroscopy. The development of RE-activated nitride semiconductor based electroluminescent devices (thin films, nanomaterials) has been of great interest for several optoelectronic applications (e.g. LED's, lasers). Results of photoluminescence properties of RE-doped GaN powders prepared by a Na-flux method will be presented. The development of novel infrared fluorescent materials continues to be of interest for applications in solid-state gain media, infrared sensing, optical taggants, and optical cooling. RE doped crystals with low maximum phonon energies have shown efficient near-IR and mid-IR emissions as well as lasing at room temperature. PbCl2 and PbBr2 based ternary lead halides (e.g. KPb2Cl5, RbPb2Cl5, KPb2Br5, RbPb2Br5) materials have recently emerged as new non-hygroscopic laser hosts with low maximum phonon energies (~138-203 cm-1), which lead to small non-radiative decay rates for trivalent rare earth dopants. In addition, pure and RE activated halide crystals were also investigated to develop efficient scintillators. In this talk, the material synthesis, purification, crystal growth, and spectroscopic characterization of rare-earth activated optical materials will be presented for possible applications in displays, optical cooling, infrared lasers and radiation detectors.

5

  1. No events scheduled

6

  1. No events scheduled

7

  1. No events scheduled

8

  1. No events scheduled

9

  1. No events scheduled

10

  1. No events scheduled

11

  1. Center for Functional Nanomaterials Seminar

    1:30 pm, CFN, Bldg. 735, 1st floor conf. rm. A

    Hosted by: 'Mircea Cotlet'

    Lowest energy electronic excited states (LEES) in transition metal complexes are the states most relevant for practical photophysical and photochemical processes. We investigated relaxation dynamic of two systems – copper chloride dianion with strong Jahn-Teller effect and hexabromoiridate dianion with spin-spin coupling, utilizing 2000 nm near-IR femtosecond (100 fs) pump-probe spectroscopy. In both systems, the Franc- Condon excited states of the transition metal complexes undergo internal conversion to the ground electronic states, but with significantly different lifetimes (55 fs and 360 ps, respectively), despite the fact that the metal-centered states are separated by the same energy gap (~5000 wavenumbers) from the respective ground state. This difference is explained by presence of a conical intersection between the first excited electronic and the ground states in the Cu(II) system due to strong Jahn-Teller linear distortion whereas the involved potential energy surfaces for the Ir(IV) complex are nested directly one above another. Another project under consideration is the ultrafast mechanisms of polyhalomethanes on the example of diiodomethane. This molecule has a tractable number of degrees of freedom, and, therefore, has served in literature as a model system for bond dissociation processes in both gas and condensed phases. In this work we implemented the state-of-the-art ultrafast (~35 fs) transient absorption experiment (supported by the most accurate multireference quantum chemical methods) to understand the UV photodissociation mechanism of methylene iodide molecules. We discovered previously unsuspected photochemical pathway in the UV photochemistry of methylene iodide, in which electronically excited molecules, rather than simply dissociate, undergo direct ~50-fs isomerization through a conical intersection into isomeric species. Host: Mircea Cotlet

12

  1. No events scheduled

13

  1. No events scheduled

14

  1. No events scheduled

15

  1. No events scheduled

16

  1. No events scheduled

17

  1. No events scheduled

18

  1. No events scheduled

19

  1. No events scheduled

20

  1. Center for Functional Nanomaterials Seminar

    1:30 pm, CFN, Bldg. 735, 1st fl. conf. rm.

    Hosted by: ''Mark Hybertsen''

    Thanks to the fast development of first principles calculations and evolutionary algorithms, computational material design with desired properties is becoming a state-of-the-art research field. It is now possible to predict both the stable compounds and their crystal structures at arbitrary conditions, given just the set of chemical elements. In this talk, I will discuss: 1) a hardness prediction model based on first principles calculation; 2) two potential ultrahard materials, CrB4 and MnB4, by adopting the hardness prediction model, and their crystal structure characterization; 3) topological structure analysis of the mysterious structures of superhard cold-compressed graphite and carbon nanotubes; 4) prediction of novel superconducting magnesium silicides, MgSi2 and MgSi3; and 5) predicted stability of "impossible'' chemical compounds that become stable under high pressure — e.g. MgO3, SiO3, MgSiO6, and MgSi3O12. At the end of the talk, I will also briefly talk about some recent advances of the crystal structure prediction code — USPEX, e.g. crystal structure prediction for complex composition system, surface structure prediction and its reconstruction, and interface structure prediction.

21

  1. No events scheduled

22

  1. Center for Functional Nanomaterials Seminar

    11 am, CFN, Bldg. 735, 1st floor conf. rm.

    Hosted by: 'Mircea Cotlet'

    The nonlinear interaction between intense light and a dispersive medium is inherently frequency-dependent and can significantly vary across optical resonances in a material; therefore it is critical to examine the wavelength dependence of nonlinear parameters when characterizing new materials for nonlinear optical applications. To completely assess the working spectral ranges and nonlinear optical efficiencies of potential materials, a broadband excitation source must be available. I will show that all of the relevant nonlinear optical parameters (second- and third-order susceptibilities, multiphoton absorption coefficients, laser-induced damage thresholds, and phase-matching ranges) that should be considered for potential nonlinear optical applications can be probed with a nonlinear optical characterization technique involving wavelength and intensity dependence. The importance of this work relies on the fact that this technique is not limited to materials with specific physical morphologies, but can be used for any type of sample in question (i.e. monolayer, thin film, powder, or bulk crystal form). Specifically in this presentation, I will present my work on the characterization of nonlinear optical dispersions of novel oxide and chalcogenide semiconductors probed with a broadband picosecond excitation source. The basic theory of nonlinear optics will be described as well as the experimental apparatus for these measurements. A measurement of the two-photon absorption coefficient dispersion in tetrapod ZnO along with a broadband dispersion of the second-order susceptibility χ^((2) ) for Al-doped ZnO thin films will be presented. χ^((2) ) and χ^((3) ) were evaluated for promising infrared quaternary chalcogenides as well as laser-induced damage thresholds and Type-I phase-matching ranges. These nonlinear optical parameters are shown to be strongly correlated to the bandgaps of these chalcogenides. Finally, χ^((2) ) dispersions of monolayer transitio

23

  1. No events scheduled

24

  1. No events scheduled

25

  1. Center for Functional Nanomaterials Seminar

    1:30 pm, Bldg. 735, conf. rm. A, first fl.

    Hosted by: ''Mircea Cotlet''

    Center for Functional Nanomaterials Seminar Interaction between Charge Transfer States in Semiconducting Materials Studied by Magnetic Field Effects Mingxing Li Department of Materials Science and Engineering University of Tennessee-Knoxville, Tennessee Monday, April 25, 2016 1:30 p.m. Bldg. 735 – 1st floor conference room Charge transfer states are interfacial charge pairs residing at the donor–acceptor heterointerface. Experimental evidence shows that they are crucial for the OPV and OLED performances. This presentation reports the experimental studies on the interaction between charge transfer states by using the magnetic field effects. The performance of magnetic field effects, illustrated by the amplitude and line-shape, demonstrates the interactions between intermolecular charge transfer states, between photo-generated charge transfer states and magnetized charge transfer states, and between the intramolecular charge transfer states and d electrons. In addition, this presentation also describes the fundamental studies on organo-metal halide perovskite (OMHP) semiconductors. On one hand, the experimental results based on magnetic field effects indicate the interaction between the electron-hole pairs and free carriers in OMHP, which is crucial for improving the performance of OMHP solar cells. On the other hand, a magneto-electric coupling is found at the interface between OMHP and Co, indicating a possibility for realizing the OMHP-based spintronics application. In summary, this presentation intends to present the recent experimental progress on studying the interaction between charge transfer states in semiconducting materials by taking advantage of magnetic field effects.

26

  1. Center for Functional Nanomaterials Seminar

    11 am, CFN, Bldg. 735, 2nd Fl. Seminar Room

    Hosted by: 'Deyu Lu'

    Center for Functional Nanomaterials Special Seminar Disordered water phases from ambient to ultrahigh pressure Roberto Car Princeton University Tuesday, April 26, 2016 11:00 a.m. CFN, Bldg. 735, 2nd floor Seminar Room The unusual properties of water, including the thermodynamic anomalies of the liquid, the existence of more than one amorphous ice form, and the abnormal mobilities of the water ions, derive from the tetrahedral network of hydrogen bonds that hold the molecules together. Under applied pressure the topology of the network changes but local tetrahedrality is preserved as the system explores a variety of different phases until at extreme pressure the molecules dissociate into ions and the hydrogen bonds collapse. Modern ab-initio simulations provide a unifying picture of these processes. In this talk, I will review recent progress in these studies stressing connections between theory, simulation, and experiment. Bio Roberto Car of Princeton University is Ralph W. Dornte professor for chemistry with a simultaneous appointment at the Material Sciences Institute of the university. He is a professor in the Theory Department, of the Fritz Haber Institute of the Max Planck Society. His research focus is theory and numerical simulation (classical and quantum) of condensed and molecular systems. He studied physics and attained a doctorate in 1971 in nuclear technology at the Politecnico di Milano. After being professor for physics at SISSA in Trieste (1984-1991), and at University of Geneva (1991-1999) he joined Princeton University in 1999. In 2007, a birthday symposium was held at ICTP. He received the Aneesur Rahman prize in computational physics. The Aneesur Rahman Prize is the highest honor given by the American Physical Society for work in computational physics.

27

  1. No events scheduled

28

  1. Center for Functional Nanomaterials Seminar

    11 am, Building 735, Conf. Rm. A.

    Hosted by: 'Gregory Doerk'

    Center for Functional Nanomaterials Seminar Batteries with high specific energy and energy density higher than that of state-of-the-art Li-ion batteries are considered critical for mass adoption of electric automobiles. Metal-oxygen batteries, Li- and Na-O2 batteries in particular, offer the highest theoretical specific energy among all known battery types. Li2O2 and NaO2, the discharge products in Li- and Na-O2 batteries respectively, are both electronic insulators. Therefore, electrochemical deposition of Li2O2 and NaO2 might lead to battery electrode passivation and to low actual specific energy. I will present experimental results backed by theoretical calculations that suggest the capacity limitations in these batteries can be overcome by enabling solution-mediated electrochemical deposition of Li2O2 and NaO2. This mechanism leads to a higher specific energy than that limited by electrode passivation. We have identified design rules for selecting electrolyte solvents that favor this alternate pathway and enable high specific energy metal-air batteries. I will also discuss our work on dendrite-resistant composite Li-ion conducting membranes which find applications in Li-ion and other lithium battery chemistries that would benefit from using a lithium anode.

29

  1. No events scheduled

30

  1. No events scheduled

  1. MAY

    19

    Thursday

    CFN Colloquium

    "Manipulating Light on Chip"

    Presented by Michal Lipson, Cornell University, Ithaca, NY

    11 am, CFN, Bldg 735, Seminar Room, 2nd Floor

    Thursday, May 19, 2016, 11:00 am

    Hosted by: ''Chuck Black''

    Photonics on chip could enable a platform for monolithic integration of optics and microelectronics for applications of optical interconnects in which high data streams are required in a small footprint. This approach could alleviate some of the current bottlenecks in traditional microelectronics. In this talk I will review the challenges and achievement in the field of Silicon Nanophotonics and present our recent results. Using highly confined photonic structures, much smaller than the wavelength of light, we have demonstrated ultra-compact passive and active silicon photonic components that enhance the electro-optical, mechanical and non-linear properties of Silicon. Based on the ability to dynamically modulate light on the same time scale as the time of flight we have demonstrated novel GHz structures for a variety of applications including all-optical synchronized RF oscillators and optical isolators on a silicon chip. Michal Lipson is an Associate Professor at the School of Electrical and Computer Engineering at Cornell University, Ithaca NY. Her research focuses on novel on-chip Nanophotonics devices. She has pioneered several of the critical building blocks for silicon photonics including the GHz silicon modulators. Professor Lipson's honors and awards include 2010 Macarthur fellow, NYAS Blavatnik award, OSA Fellow, IBM Faculty Award, and NSF Early Career Award. More information on Professor Lipson can be found at nanophotonics.ece.cornell.edu.

  2. JUN

    2

    Thursday

    CFN Colloquium

    "TBD"

    Presented by Dr. James Tour, Rice University

    11 am, CFN, Bldg 735, Seminar Room, 2nd Floor

    Thursday, June 2, 2016, 11:00 am

    Hosted by: Dmitri Zakharov

    TBD