Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F40: Surfaces, Interfaces, and Thin Films: Molecules on Surfaces |
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Sponsoring Units: DCMP Chair: Daniel Dougherty, North Carolina State University Room: 349 |
Tuesday, March 19, 2013 8:00AM - 8:12AM |
F40.00001: Molecular Ordering in PCBM Monolayer Films on Ag and Au (111): From $\mu $-aerosol deposited glasses to hcp packing Qian Shao, Levan Tskipuri, Janice Reutt-Robey Functionalized C$_{\mathrm{60}}$ and C$_{\mathrm{70}}$ fullerenes are increasingly employed as active components in organic electronic devices. The structure of the PCBM electrode interface is expected to strongly impact charge transfer processes in photovoltaic devices. Here we report molecularly-detailed studies of PCBM ordering at coinage metal surfaces. We have developed a vacuum-compatible liquid delivery source to generate thin films of C$_{\mathrm{60}}$- and C$_{\mathrm{70}}$-$_{\mathrm{\thinspace }}$PCBM from organic solvents. Structure is tracked from the sub-monolayer to multilayer regime on (111)-oriented Ag and Au surfaces with molecular detail by UHV-STM. Glassy morphologies of as-grown films reflect solvent retention. Upon thermal annealing solvent molecules are released and films evolve into ordered packing arrangements that depend upon the PCBM density in the original films. The hcp monolayer phase of C$_{\mathrm{60}}$-and C$_{\mathrm{70}}$-PCBM are newly produced and characterized, indicating the accessibility of new growth phases by $\mu $-aerosol deposition. Acknowledgement: This work was supported by the NSF-MRSEC at the University of Maryland, DMR 0520471. [Preview Abstract] |
Tuesday, March 19, 2013 8:12AM - 8:24AM |
F40.00002: Doping of Grain Boundaries in diF TESADT Transistors Cortney Bougher, Shawn M. Huston, Jeremy W. Ward, Abdul Obaid, Marsha A. Loth, John E. Anthony, Oana D. Jurchescu, Brad R. Conrad We utilize Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) to characterize the dynamics of electronic transport across 2,8-difluoro-5,11-triethylsilylethynyl anthradithiophene (diF TESADT) grain boundaries. We show that the morphology of grain boundaries and the adsorption of atmospheric dopants at these local boundaries have a direct impact on the electrical behavior of diF TESADT in thin film transistor (TFT) devices. Device voltage drops at grain boundaries are characterized as a function of both atmospheric dopants and transition time between dopants. The morphology, including crystallization and packing motifs, of diF TESADT grown on thermally grown SiO$_2$ will be discussed and related to other semiconducting small organic molecules. This work will be put in the context of other, recent advances in small molecule organics. [Preview Abstract] |
Tuesday, March 19, 2013 8:24AM - 8:36AM |
F40.00003: Scanning Tunneling Microscopy investigation of multilayer diF-TES-ADT on Au(111) Shawn Huston, Jiuyang Wang, Marsha Loth, John Anthony, Brad Conrad, Daniel Dougherty Organic thin film transistors (OTFT) partially composed of solution processed 2,8-difluoro-5,11-bis(triethylsilylethynyl)-anthradithiophene (diF-TES-ADT) have shown high performance with hole mobilities up to 1 cm$^{2}$/(V s). Pretreatment of the gold electrodes results in growth of large diF-TES-ADT crystals extending well out into the channel of the OTFT. Without electrode pretreatment, the crystal sizes are small and possess a non-preferred molecular orientation. We have chosen to investigate the reasons for the reduced crystal size of these films on untreated gold electrodes by studying a model system generated by vapor deposition of multilayers of diF-TES-ADT on Au(111). The initial wetting layer forms a highly ordered film such that the anthradithiophene backbone is oriented parallel to the substrate and the unit cell is 1.49 nm x 1.25 nm with an included angle of 56.8$^{\circ}$. The second layer is poorly ordered with only weak evidence of crystallinity in small regions. Growth beyond the second layer appears essentially bulk-like and crystalline with domain sizes that are potentially limited by the disordered bilayer growth. [Preview Abstract] |
Tuesday, March 19, 2013 8:36AM - 8:48AM |
F40.00004: STM and optical investigations of molecules on graphene Ozgun Suzer, Joseph Smerdon, Nathan Guisinger, Jeffrey Guest We describe efforts to understand the structural, electronic and optical properties of an archetypal organic molecular building block for graphene-based nano-optical and photovoltaic devices, presenting UHV STM studies of pentacene (Pn) molecules deposited on graphene that was grown epitaxially on SiC(0001). Isolated electronic states are observed and associated molecular orbitals are resolved; also, a large HOMO-LUMO spacing indicates that we are probing a ``transport gap'' in the monolayer Pn. The electronic properties of this system indicate a de-coupling of the molecules from the graphene and underlying substrate, similar to results obtained for the complementary molecular system, C60 on graphene [Cho, et.al. Nano Letters 12, 3018 (2012)], suggesting a path for developing molecular-scale electronic and optically active devices that are not dominated by substrate interactions. We will also discuss our efforts to correlate these studies with the optical properties of the systems using a UHV STM that incorporates confocal optical microscopy and spectroscopy at the tip-sample junction. [Preview Abstract] |
Tuesday, March 19, 2013 8:48AM - 9:00AM |
F40.00005: ABSTRACT WITHDRAWN |
Tuesday, March 19, 2013 9:00AM - 9:12AM |
F40.00006: Bonding of anthracene derivatives to a Cu (111) surface: a combined STM and DFT study Jonathan Wyrick, Yeming Zhu, Daniel Salib, Connor Holzke, Zhihai Cheng, Ludwig Bartels We compare and contrast three anthracene derivatives whose 9,10 hydrogens are replaced by the elements O, S, and Se respectively that act as ``feet'' binding the molecules to a Cu (111) substrate. DFT calculations are compared with and shed light on STM data for the three molecules. We analyze the three species in terms of their geometric and electronic structure upon adsorption, taking into account the competing effects that the ``feet'' have with the anthracene moiety in their interactions with the underlying Cu surface. [Preview Abstract] |
Tuesday, March 19, 2013 9:12AM - 9:24AM |
F40.00007: Substrate Mediated Short-range and Long-range Adsorption Pattern of CO on Ag(110) Wai-Leung Yim Yim, Thorsten Kluener Substrate-mediated intermolecular interactions were proposed in the literature to explain the adsorption of CO on Ag(110) but the underlying mechanism is yet to be known. Here, short-range and long-range relaxation patterns for CO adsorption on Ag(110) surfaces have been investigated. The relaxation mode can be explained by the interaction of heavy electrons on metal substrates in electron momentum space. We identified two relaxation modes for CO on Ag(110). The long-range relaxation involved a (6$\times$6) commensurate phase, while the short-range relaxation involved an alleviation of Fermi surface nesting along the $\langle$1$\bar{1}$0$\rangle$ direction of the Ag(110) substrate. The symmetry broken ground state structure at high CO coverage can be rationalized, and this structure is consistent with the interpretation of available experimental data. [Preview Abstract] |
Tuesday, March 19, 2013 9:24AM - 9:36AM |
F40.00008: ABSTRACT WITHDRAWN |
Tuesday, March 19, 2013 9:36AM - 9:48AM |
F40.00009: 5,6,7-trithiapentacene-13-one on vicinal gold (788): a STM study Amanda Larson, Jeremiah van Baren, Jeremy Kintigh, Jun Wang, Glen Miller, Karsten Pohl Scanning tunneling microscopy was used to examine the atomic interface between gold and 5,6,7-trithiapentacene-13-one (TTPO), an electron donor of potential interest for photovoltaic applications. TTPO is a polar species of pentacene with centered oxygen and sulfur bridge substituents. TTPO is a thermally and photo-oxidatively robust molecule with a HOMO-LUMO gap of 1.90 eV that can be thermally evaporated onto an electrode. The vicinal gold (788) surface is a well-studied surface on which pentacene molecules and other pentacene derivatives self assemble in long range order. We examined TTPO on gold to gain a better understanding of the structure of photovoltaic interfaces at the nanoscale. [Preview Abstract] |
Tuesday, March 19, 2013 9:48AM - 10:00AM |
F40.00010: DFT based modeling of C60/Dichloropentacene on stepped Au surfaces Jun Wang, Jian-Ming Tang, Karsten Pohl The co-assembly of functionalized pentacenes (electron-donor materials) and fullerenes (electron-acceptor materials) on metal substrates provides a model for studying the structural and electronic properties for novel organic photovoltaic (OPV) heterojunctions [1]. Our previous STM experimental results show C$_{60}$ to form molecular chains on an intact single-domain, brick-wall structured 6,13-dichloropentacene (DCP) monolayer adsorbed on stepped Au(788) [2]. Here, we have included a stepped gold substrate in DFT calculations for the geometric and electronic structure of this interacting three-component system. Our calculations show that C$_{60}$ molecular chain prefer to absorb on top of the DCP molecules on the upper step edge. We calculate the dipole moments for various C$_{60}$ configurations. The stepped gold substrate interaction shows a major influence on this unique molecular chain formation. [1] J. Wang, I. Kaur, B. Diaconescu, J.-M. Tang, G. P. Miller, and K. Pohl, ACS Nano 5 (2011) 1792. [2] J. Wang, J.-M. Tang, G. P. Miller, and K. Pohl, in preparation. [Preview Abstract] |
Tuesday, March 19, 2013 10:00AM - 10:12AM |
F40.00011: First Principles Study of the Electronic Structure of Organic Adsorbates on Cleaved GaP Surfaces Min Yu, Peter Doak, Jeffrey Neaton We report a first principles calculations of structural, electronic, and spectroscopic properties of organic molecules, such as ethylene and benzene, adsorbed on cleaved GaP (110) surface to assess their potential to allow controlled coupling and to modify charge transport between light absorbing semiconductors and catalysts for applications in artificial photosynthesis. We compute adsorbate geometries, binding energetics, surface band structures, constant current scanning tunneling microscopy images, and electronic energy level alignment of organic molecules on GaP surfaces using density functional theory and many-body perturbation theory within the GW approximation. We quantify the impact of coverage, interface dipoles, hybridization, and nonlocal polarization effects on level alignment, and validate our understanding through direct comparison recent measurements. Work supported by JCAP and computational resources provided by NERSC. [Preview Abstract] |
Tuesday, March 19, 2013 10:12AM - 10:24AM |
F40.00012: Low Temperature STM Study of Single-Molecule Attachment to GaP(110) Aaron Bradley, M.M. Ugeda, M. Yu, K.L. Meaker, J. Neaton, G. Moore, I. Sharp, M.F. Crommie Engineering efficient artificial photosystems for catalytic and photovoltaic (PV) purposes is a major challenge for the development of viable solar fuel generators. One possible route toward this goal is to employ molecular catalysts covalently attached to semiconductor light absorbers through molecular linkages. The effect of such linkage on local electronic structure, however, remains an important question. Scanning tunneling microscopy (STM) is a useful tool for answering this question since it enables characterization of molecular interfaces at the atomic level. Here we describe our progress at measuring the structural and electronic properties of single organic molecules adsorbed to a p-doped GaP(110) surface. Low temperature STM was used to explore the surface chemistry and reactivity of GaP(110) by exposing UHV-cleaved GaP surfaces to sub-monolayer coverages of ethylene (C2H4) and iodobenzene (IC6H6), the latter being a candidate linker for connecting catalysts and PV molecules to semiconducting light absorbers. Our high-resolution STM images in combination with DFT calculations provide guidance for future attachment strategies involving improved molecule/semiconductor interfaces. [Preview Abstract] |
Tuesday, March 19, 2013 10:24AM - 10:36AM |
F40.00013: Interplay between dynamics of molecule and surface plasmons in scanning tunneling microscope-induced light emission Kuniyuki Miwa, Mamoru Sakaue, Hideaki Kasai Scanning tunneling microscope (STM)-induced light emission spectroscopy of molecules has unique advantage to investigate the luminescence properties of molecules with the atomic-scale spatial resolution. Recently, many attempts have been made to control the molecular luminescence by using the intense electromagnetic field generated by surface plasmons localized near the tip-substrate gap region. In this study, the nonequilibrium Green's function method are utilized to investigate effects of coupling between an exciton composed by electron and hole in the molecule and the surface plasmons on the luminescence properties of the molecule and the surface plasmons. It is found that the luminescence intensities of the molecule are suppressed due to the re-absorption of the surface plasmons by the molecule. Molecular absorption and enhancement by molecular electronic and vibrational modes lead to dip and peak structures in the luminescence spectra of the surface plasmons. Corresponding structures can be seen in a recent experiment. Moreover we found that the re-absorption by the surface plasmons plays important roles in determining the luminescence spectral profiles. We will discuss the detailed mechanisms of variation in these luminescence spectral profiles. [Preview Abstract] |
Tuesday, March 19, 2013 10:36AM - 10:48AM |
F40.00014: In-situ spectro-microscopy on organic films: Mn-Phthalocyanine on Ag(100) Abdullah Al-Mahboob, Jerzy T. Sadowski, Elio Vescovo Metal phthalocyanines are attracting significant attention, owing to their potential for applications in chemical sensors, solar cells and organic magnets. As the electronic properties of molecular films are determined by their crystallinity and molecular packing, the optimization of film quality is important for improving the performance of organic devices. Here, we present the results of in situ low-energy electron microscopy / photoemission electron microscopy (LEEM/PEEM) studies of incorporation-limited growth [1] of manganese-phthalocyanine (MnPc) on Ag(100) surfaces. MnPc thin films were grown on both, bulk Ag(100) surface and thin Ag(100)/Fe(100) films, where substrate spin-polarized electronic states can be modified through tuning the thickness of the Ag film [2]. We also discuss the electronic structure and magnetic ordering in MnPc thin films, investigated by angle- and spin-resolved photoemission spectroscopy. \\[4pt] [1] Al-Mahboob et al., Phys. Rev. B 82, 235421 (2010).\\[0pt] [2] E. Vescovo et al., Phys. Rev. B 51, 12418 (1995). [Preview Abstract] |
Tuesday, March 19, 2013 10:48AM - 11:00AM |
F40.00015: Adsorption structure analysis of co-adsorption dye-sensitized solar cells by the NEXAFS and XPS Mitsunori Honda, Masatoshi Yanagida, Liyuan Han Adsorption structures of N719 dye alone and a N719$+$D131 co-adsorption system on a TiO$_{2}$ electrode were studied with the objective of increasing the efficiencies of dye-sensitized solar cells (DSCs). However, adsorption structure of isothiocyanate (R-N$=$C$=$S) in the alone and co-adsorption system was not completely understood because the surface morphology about nanocrystalline TiO$_{2\, }$is complex. Therefore, we have investigated the adsorption structure on nanocrystalline TiO$_{2}$ surface using the Sulfur K absorption edge (S K-edge) and core level (S 1s) in details by using the near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS), respectively. To consider the co-adsorption effect on DSCs, we analyze the depth profiling by the angle dependent NEXAFS spectroscopy and the chemical state on top of surface by the XPS analysis. As the results, we can determine the electronic structure around S atom in R-N$=$C$=$S in N719 on nanocrystalline TiO$_{2}$ surface. We clarify the adsorption structure of alone and co-adsorption system from the S K-edge NEXAFS and S 1s XPS analysis. I will talk about these results in my presentation. [Preview Abstract] |
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