Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session E32: Emerging Nanomaterials for Solar Energy Conversion IIFocus
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Sponsoring Units: DCP GERA Chair: Arthur Nozik, NREL Room: 332 |
Tuesday, March 15, 2016 8:00AM - 8:36AM |
E32.00001: The engineering of quantum dots for efficient solar energy capture Invited Speaker: Jeffrey Pietryga Over the past decade, exciting advances have been made in the use of semiconductor nanocrystal quantum dots (QDs) for capture of solar energy, including efficient and inexpensive solar cells based on simple, single-component lead chalcogenide QDs. Such devices take advantage of key advantages offered by QDs, including the ability to control bandgap with particle size, and to alter carrier concentrations using surface modification. Remaining essentially untapped, however, is the much larger potential offered by heterostructured QDs to exhibit new functionality that will enable truly unprecedented device performance. In this talk, I will present recent results from our efforts in application-inspired band-structure engineering of heterostructured QDs. Specifically, I will examine how the selective combination of semiconductor materials in a simple core/shell geometry can result in QDs with radically altered properties optimized for use in applications such as carrier-multiplication-enhanced solar cells, and highly efficient luminescent solar concentrators. I will use these examples to demonstrate the general ability of solution-synthesized nanomaterials to contribute to the overall goal of efficient solar energy capture and conversion in a variety of roles. [Preview Abstract] |
Tuesday, March 15, 2016 8:36AM - 8:48AM |
E32.00002: Are quantum dots spiky balls? James Shepherd, Nadav Geva, Troy Van Voorhis We here propose an alternative view to the ‘spiky ball’ picture of passivated quantum dots. By studying the realistic surface morphology of a dot using atomistic molecular dynamics simulations, paying particular attention to the ligand structure, we find that the ligand shell thickness is substantially reduced by van der Waals packing. This affects the ability of the dot ligands to interdigitate. This is discussed in terms of the available experimental data for the superstructure of quantum dot layers, and related back to the electronic properties of quantum dots. [Preview Abstract] |
Tuesday, March 15, 2016 8:48AM - 9:24AM |
E32.00003: TBA Invited Speaker: Art Nozik |
Tuesday, March 15, 2016 9:24AM - 9:36AM |
E32.00004: Photocatalytic Water-Splitting Characteristic of Electric Reduced Black TiO$_{\mathrm{2}}$ Nanorods Jong-Won Yun, Ki Yeon Ryu, Sunho Kim, Se-Jung Jang, Yong Soo Kim In various reduction methods of TiO$_{\mathrm{2}}$, the electric reduction could apply to anodized TiO$_{\mathrm{2}}$ nanotube. However, it is not suitable to reduce TiO$_{\mathrm{2}}$ nanorods(NRs) grown on fluorine doped tin oxide (FTO) substrate using hydrothermal method, because those are easily peeled off due to lattice mismatching between FTO and TiO$_{\mathrm{2}}$ NRs. In this talk, we will demonstrate electric reduced-black TiO$_{\mathrm{2}}$ NRs with strong adhesion on FTO substrate for an effective visible photocatalyst. To fabricate the reduced-black TiO$_{\mathrm{2}}$ NRs, we firstly deposited TiO$_{\mathrm{2}}$ seed layer on FTO glass using RF-sputtering for mitigating the exfoliation, then grow TiO$_{\mathrm{2\thinspace }}$NRs with hydrothermal method. Finally, TiO$_{\mathrm{2}}$ NRs were reduced with electric bias. The final reduced-black TiO$_{\mathrm{2}}$ NRs exhibit a higher photocurrent density, 0.9 mA/cm$^{\mathrm{2}}$ in comparison with pure-TiO$_{\mathrm{2}}$ NRs. This result indicates that our reduced-black TiO$_{\mathrm{2}}$ NRs has lower bandgap with modified valance band position and enhance the surface reactivity with oxygen defect generation. [Preview Abstract] |
Tuesday, March 15, 2016 9:36AM - 10:12AM |
E32.00005: TBA Invited Speaker: Xiaogang Peng |
Tuesday, March 15, 2016 10:12AM - 10:24AM |
E32.00006: High Pressure Synthesis of Rhombohedral Delafossite Structured $\alpha $-AgGaO$_{\mathrm{2}}$ Meysam Akhtar, MADHU MENON, MAHENDRA SUNKARA, GAMINI SUMANASEKERA, ANDRIY DURYGIN, JACEK JASINSKI In this work, we demonstrate for the first time the high pressure synthesis of $\alpha $-AgGaO$_{\mathrm{2}}$ via a solid state reaction of Ag$_{\mathrm{2}}$O and Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$. Synthesis experiments were carried out at pressures and temperatures up to 10 GPa and 600 \textdegree C, respectively, using a resistively-heated diamond anvil cell. Electron diffraction confirmed the rhombohedral delafossite crystal structure of the synthesized AgGaO$_{\mathrm{2}}$ and its corresponding lattice parameters of a $=$ 2.99 {\AA} and c $=$ 18.43 {\AA}. The vibrational modes analysis was also conducted using a combination of ab initio density functional theory (DFT) and Raman spectroscopy. This analysis yielded good agreement between the calculated Raman-active modes and experimental Raman data. Finally, the application of the GGA $+ \quad U$ formalism-based on DFT to calculate the electronic band structure of $\alpha $-AgGaO$_{\mathrm{2}}$ provided a more realistic theoretical band gap value than those reported previously. [Preview Abstract] |
Tuesday, March 15, 2016 10:24AM - 10:36AM |
E32.00007: Competitive Adsorption of Carbon Dioxide/Methane in Coal: First-Principles Quantum Mechanical Investigations Yingdi Liu, Sanwu Wang Sequestration of CO$_{\mathrm{2}}$ into geological formations has been suggested to mitigate the effect of the increasing of the atmospheric CO$_{\mathrm{2}}$ concentration on global warming. Coalbeds are investigated as one of the attractive storage sites since the cost of CO$_{\mathrm{2}}$ sequestration can be offset by the enhanced coalbed methane (ECBM) recovery. Extensive experimental studies have been performed for the competitive adsorption of CO$_{\mathrm{2}}$/CH$_{\mathrm{4}}$ into coalbeds. However, the atomic-level understanding for the interaction between the adsorbate (CO$_{\mathrm{2}}$/CH$_{\mathrm{4}})$ and the adsorbent (coal) has not been fully explored. We report first-principles density-functional calculations for the competitive adsorption between CO$_{\mathrm{2}}$/CH$_{\mathrm{4}}$ in the coal network. In particular, we report results of atomic structures, bonding characteristics, energetics, as well as electronic structures of the CO$_{\mathrm{2}}$/CH$_{\mathrm{4}}$-coal systems. [Preview Abstract] |
Tuesday, March 15, 2016 10:36AM - 10:48AM |
E32.00008: Gentlest Ascent Dynamics for Calculating First Excited State and Exploring Energy Landscape of Kohn-Sham Density Functionals Chen Li, Jianfeng Lu, Weitao Yang We develop the gentlest ascent dynamics (GAD) for Kohn-Sham density functional theory to search for the index-$1$ saddle points (\textit{i.e.}, the stationary points with one and only one energy descending direction) on the energy landscape of the Kohn-Sham density functionals. These stationary solutions correspond to excited states in the ground state functionals. As shown by various examples, the first excited states of many chemical systems are given by these index-$1$ saddle points. Our novel approach provides an alternative, more robust way to obtain these excited states, compared with the widely used $\Delta$SCF approach. The method can be easily generalized to target higher index saddle points. Our results also reveal the physical interest and relevance of studying the Kohn-Sham energy landscape. [Preview Abstract] |
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