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August 2018
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  1. CFNS Seminar @ BNL

    11 am, Building 510, Room 2-160

    Hosted by: Yacine Mehtar-Tani

    I will introduce collinear-drop jet observables which suppress contributions from collinear radiation and systematically probe soft radiation within jets. Such observables are insensitive to collinear radiation and can be designed to be fairly insensitive to process-dependent soft radiation. This enables them to be used for distinguishing quark, gluon, and color neutral jet-initiating particles, for testing the accuracy of the description of soft radiation in Monte Carlo simulations, and for testing methods of predicting hadronization corrections. I will discuss several examples of collinear-drop observables and show how to derive factorization expressions for QCD jets using soft-collinear effective theory (SCET), which enables a resummation of logarithmically enhanced contributions

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  1. Center for Functional Nanomaterials Seminar

    11 am, Bldg 735, Conference Room A, 1st Floor

    Hosted by: Feng Wang (SET) and Dong Su (CFN)

    All-solid-state Li-ion batteries (LIBs) are promising candidates to solve some problems of conventional LIBs with liquid electrolytes. However, large interfacial resistance of Li-ion transfer at the electrode/solid-electrolyte interface causes low power density and prevents practical use. One effective idea to reduce the resistance is in situ fabrication of electrode active materials from parent solid electrolytes. Such in situ formed electrodes were discovered in Li2O-Al2O3-TiO2-P2O5-based solid electrolytes (LATP) [1]. The electrodes are irreversibly formed by decomposing the negative-side electrolytes with the excess Li-ion insertion reaction. However, it was not clear how the electrodes were formed in nanometer scale during the charge-discharge processes. Here, we used electron holography to visualize the electric potential distribution [2,3] and spatially-resolved electron energy loss spectroscopy (SR-EELS) to directly observe the Li distribution and electronic structure changes of Ti and O in the formed electrodes [3-5]. We succeeded in observing the potential changes during the fabrication processes of the in situ formed electrode. We also found from SR-EELS that the inserted Li-ions were distributed in 400 - 700 nm around the negative-side electrolytes, and the Ti was reduced from Ti4+ to Ti3+. Pico-meter scale expansion of O-O distance due to the Li insertion reaction was also visualized. The author will report the detail of those microscopy techniques and their results in the presentation. References [1] Y. Iriyama, C. Yada, T. Abe, Z. Ogumi, K. Kikuchi, Electrochem. Commun., 8 (2006) 1287-1291. [2] K. Yamamoto, Y. Iriyama, T. Asaka, T. Hirayama, H. Fujita, K. Nonaka, K. Miyahara, Y. Sugita, Z. Ogumi, Electorochem. Commun., 20 (2012) 113-116. [3] K. Yamamoto, Y. Iriyama, T. Hirayama, Microscopy 66 (2017) 50-61. (Special issue: Challenges for lithium detection), https://doi.org/10.1093/jmicro/dfw043. (open acce

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  1. SEP

    6

    Thursday

    CFN Colloquium

    "Safe Li-Ion Battery Electrolytes: from Aqueous Electrolytes, Nonflammable Organic Electrolytes, to Solid State Electrolytes"

    Presented by Chunsheng Wang, University of Maryland

    4 pm, Bldg 735, Seminar Room, 2nd Floor

    Thursday, September 6, 2018, 4:00 pm

    Hosted by: Dong Su

    Li-ion batteries are the critical enabling technology for the portable devices, electric vehicles (EV), and renewable energy. However, the safety of current batteries still needs to be improved to satisfy these requirements. We investigated the electrochemical performances of three nonflammable electrolytes: water-in-salt electrolytes, all fluorinated organic electrolytes, and solid state electrolytes. The electrochemical stability window of these electrolytes, interface/interphase stability with anodes and high-voltage cathodes, and the interface/interphase resistance between electrodes and electrolytes were systematically studied. The critical issues limiting the performance of these safe electrolytes will be discussed.

  2. SEP

    13

    Thursday

    CFNS Seminar

    "TBA"

    Presented by Long Pang, LBNL

    4 pm, Building 510, CFNS Seminar Room 2-38

    Thursday, September 13, 2018, 4:00 pm

    Hosted by: Andrey Tarasov

  3. OCT

    4

    Thursday

    CFN Colloquium

    "Superconducting proximity effect in two-dimensional semiconductor-superconductor structures"

    Presented by Javad Habani, Assistant Professor of Physics, New York University, Center for Quantum Phenomena

    4 pm, Bldg 735, CFN, Seminar Room 2nd Floor

    Thursday, October 4, 2018, 4:00 pm

    Hosted by: Mingzhao Liu

    Progress in the emergent field of topological superconductivity relies on synthesis of new material combining superconductivity, low density, and spin-orbit coupling (SOC). Theory indicates that the interface between a one-dimensional semiconductor with strong SOC and a superconductor hosts Majorana-modes with nontrivial topological properties. We discuss the recent developments in epitaxial growth of Al on InAs nanowires was shown to yield a high quality superconductor-semiconductor system with uniformly transparent interfaces and a hard induced gap, indicted by strongly suppressed subgap tunneling conductance. We have developed a two-dimensional (2D) surface InAs quantum wells with epitaxial superconducting Aluminum, yielding a planar system with structural and transport characteristics as good as the epitaxial nanowires. The realization of 2D epitaxial superconductor-semiconductor systems represent a significant advance over wires, allowing extended networks via top-down processing. We present our recent developments in materials synthesis and growth of these density-controlled surface 2D electron-gases and demonstrate Josephson junctions with highly transparent contacts. These developments have lead to unprecedented control over proximity effect in semiconductors where electron densities can be tuned using a gate voltage. We discuss potential applications of this new material system that can serve as a platform for low power circuits, gate-based qubits as well as exploring topological superconductivity for computation.