Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F35: Surface Science of Organic Molecular Solids, Films, and Nanostructures IFocus
|
Hide Abstracts |
Sponsoring Units: DMP Room: 298 |
Tuesday, March 14, 2017 11:15AM - 11:27AM |
F35.00001: Coupling between diffusion and orientation of pentacene molecules on an organic surface Bruno Eckhardt, Paul Rotter, Antonia Morherr, Gregor Witte, Barbara AJ Lechner, David M Chisnall, David J Ward, Andrew P Jardine, John Ellis, William Allison We have used Helium Spin Echo (HeSE) to unveil the intricate motion of pentacene admolecules diffusing on a chemisorbed monolayer of pentacene on Cu(110), a stable, well-ordered organic model surface. HeSE is unique in that it provides access to diffusion on the relevant nm and ps spatial and temporal time scale, respectively, and in not being restricted to low temperatures. The interpretation of the observed scattering data is assisted by Langevin simulations of trajectories on potential energy surfaces extracted from MM3 force fields. We find that the molecules show a strong coupling between the direction of diffusion, the orientation of the adsorbed molecule, and the orientation of the molecules in the monolayer. Specifically, we find that pentacene moves along tracks that are either parallel or perpendicular to the orientation of the molecules on the surface. The molecules are aligned with the direction of motion. The experimental data are explained by admolecule rotation that enables a switching between diffusion directions. The results extend our understanding of diffusion in complex organic systems on the molecular level and highlight the importance of orientation-diffusion coupling for elongated molecules. Rotter et al, Nature Materials 15:397 (2016) [Preview Abstract] |
Tuesday, March 14, 2017 11:27AM - 11:39AM |
F35.00002: Sliding friction levels of molecularly thin organic layers on C60 substrates. Samuel Kenny, Jacqueline Krim Friction at the nanoscale is known to encompass phononic, electrostatic, conduction electronic and magnetic effects [1], and molecularly thin layers sliding on surfaces are exceptionally sensitive to the commensurability of the two materials in contact. The excitation of frustrated translational phonon modes in non-spherical organic monolayers is also closely linked to friction, but the exact role has yet to be established. To explore this topic, we report quartz crystal microbalance measuments of the frictional properties of systems that can be readily modelled: ethanol and related organic molecules sliding on metal substrates in the presence and absence of C60 overlayers. The C60 overlayer acts to spread the adsorbate layers further apart, thus reducing adsorbate-adsorbate interactions while also impacting the interfacial commensurability. [1] J. Krim, Advances in Physics, 61 (2012) pp. 155-323. Work funded by NSF [Preview Abstract] |
Tuesday, March 14, 2017 11:39AM - 11:51AM |
F35.00003: A study of Rolling Mechanism of Single molecule on Metal surface Melihat Madran, alimet özen, zehra akdeniz, sondan durukanoglu ~ We present the results of DFT and molecular dynamic calculations for wheel dimer molecule on corrugated Cu(110) surface. We examined all possible configurations of C$_{44\, }$H$_{26}$ with respect to substrate based on calculations with the vDW-D2 and PBE functional to compare with the experimental results and to better understand the role of van der Waals interactions on the adsorptions of wheel dimer molecule. We also performed molecular dynamic calculations to investigate how the temperature of the system plays roles on the configurations of the molecules on Cu(110) surface. Furthermore, to identify the behavior of molecular motions on corrugated metal surface in the existence of STM tip, we looked deeper into the position of STM tip with respect to central molecular axle during the molecular dynamic simulations. Using the results of MD simulations in the existence of STM tip, we further discussed the position of STM tip for rolling mechanisms of wheel dimer molecule on Cu(110) surface. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:03PM |
F35.00004: Evidence of Near Surface Layer Stabilization by Liquid Multilayer Adsorbed Films Nicholas Strange, J.Z. Larese Molecular adsorption on surfaces is fundamentally important in a variety of scientific and technological processes. Surface adsorption plays a key role in catalysis/catalytic supports, optoelectronic devices, lubrication and adhesion, wetting phenomena, and separations. We present the results of a comprehensive investigation of the first ten members of the homologous series of n-alkanes (methane-decane) adsorbed on the basal plane of hexagonal boron nitride using high-resolution, volumetric adsorption isotherm measurements (more than 30 separate temperatures per molecule). The experimentally determined heats of adsorption vs. carbon chain length follow the well-known ``odd-even'' behavior of the n-alkanes. While this may not be surprising we will illustrate additional potential surface configurations that can lead to an increase in entropy. Potential phase transitions are identified using changes in the 2D-compressibility. In addition, we describe the results of companion molecular dynamics modeling to provide microscopic insight to the wetting behavior as a function of alkane chain length and film thickness. A comparison with the behavior of the same n-alkane set on MgO and graphite will also be included. These studies can serve as the basis for developing accurate, robust models of the potential energy surfaces and can be used for future investigations of the microscopic structure and dynamics of these adsorbed films using neutron/xray diffraction and neutron spectroscopy. [Preview Abstract] |
Tuesday, March 14, 2017 12:03PM - 12:15PM |
F35.00005: Dimethyl Formamide Phase Evolution and Lithium Ethylene Dicarbonate Solvation on Ag(111) Janice Reutt-Robey, Wentao Song The interactions of solvent molecules with electrode surfaces impact many interfacial chemical processes. In this talk, we examine the chemical and 2d structure evolution that follows adsorption of the polar solvent dimethylformamide (DMF) on Ag(111). We further reveal the impact of an organic ionic solute, lithium ethylene dicarbonate, on DMF phase evolution. Complementary STM, XPS and DFT methods characterize DMF dry etching of Ag(111) and concomitant Ag(DMF)$_{\mathrm{2}}$~coordination complex formation. Monolayer phase evolution is tracked from a 2d gas mixture of DMF and Ag(DMF)$_{\mathrm{2}}$~to ordered and nanophase-separated domains of DMF and Ag(DMF)$_{\mathrm{2}}$. A semi-quantitative surface pressure-composition phase diagram, derived from the data, illustrates how these monolayer phases are tuned by surface pressure. The ionic solute, lithium ethylene dicarbonate, shifts the phase equilibria of the solvent film, seeding the formation of ordered DMF domains at reduced surface pressures. Structural models are given for all ordered phases, and the 2d solvation of LEDC is described. [Preview Abstract] |
Tuesday, March 14, 2017 12:15PM - 12:27PM |
F35.00006: Bottom-up design of optoelectronic properties: on-surface synthesis of iron-terpyridine macromolecular complex Agustin Schiffrin, Cornelius Krull, Marina Castelli, Nikhil Medhekar, Yuefeng Yin, Martina Capsoni, Gelareh Farahi, Tanya Roussy, Katherine Cochrane, Sarah Burke, Chen-Guang Wang, Wei Ji Supramolecular chemistry allows for the design of atomically precise materials with tailored (opto)electronic properties. In particular, metal-organic complexes resulting from the coordination of $\pi $-conjugated molecules with metals exhibit electronic properties which can translate in efficient light absorption and photo-induced charge separation. Here, we report the on-surface synthesis of 1D nanostructures based on an iron-terpyridine interaction borrowed from functional complexes used for photovoltaics and catalysis. Thermally activated on-surface conformational changes and molecular and adatom diffusion leads to formation of macromolecular chains via terpyridine-iron coordination. Our low-temperature scanning tunnelling microscopy and spectroscopy, photoelectron spectroscopy and density functional theory studies reveal an unusual poly-iron linkage between ligands accompanied by a metal-to-ligand electron transfer. This results in highest occupied (lowest unoccupied) orbitals dominated by metal (ligand, respectively) states, potentially allowing for efficient visible light absorption and photo-induced electron-hole separation. This novel coordination configuration has not been observed from solution synthesis methods, and is mediated by the constraint the surface provides in this ``bottom-up'' approach. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 1:03PM |
F35.00007: Tuning the Optoelectronic Properties of Organic Semiconductor Crystals with Monolayer Graphene Templates Invited Speaker: Trisha Andrew Crystal orientation in organic thin films is one of the key parameters that determine interfacial energetics, absorption profile and cross section, exciton diffusion length, exciton dissociation efficiency, and charge collection efficiency. These properties can be effectively tuned using monolayer graphene templates that change the crystal orientation of anisotropically-shaped organic semiconductor crystals. We will discuss the effects of graphene templating on the band edge positions, Fermi levels, surface electrostatic potentials, and optical properties of a small selection of small-molecule semiconductors. Further, the photogenerated charge extraction properties of bare graphene electrodes and their ultimate ramifications on photovoltaic device performance will be discussed. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:15PM |
F35.00008: Temperature Controlled Electrostatic Disorder and Polymorphism in Ultrathin Films of $\alpha $-Sexithiophene Benjamin Hoffman, Sara Jafari, Terry Mcafee, Aubrey Apperson, Brendan O'Connor, Daniel Dougherty Competing phases in well-ordered alpha-sexithiophene ($\alpha $-6T) are shown to contribute to electrostatic disorder observed by differences in surface potential between mono- and bi-layer crystallites. Ultrathin films are of key importance to devices in which charge transport occurs in the first several monolayers nearest to a dielectric interface (e.g. thin film transistors) and complex structures in this regime impact the general electrostatic landscape. This study is comprised of 1.5 ML sample crystals grown via organic molecular beam deposition onto a temperature controlled hexamethyldisilazane (HMDS) passivated SiO$_{2}$ substrate to produce well-ordered layer-by-layer type growth. Sample topography and surface potential were characterized simultaneously using Kelvin Probe Force Microscopy to then isolate contact potential differences by first and second layer $\alpha $-6T regions. Films grown on 70$^{\circ}$ C, 120$^{\circ}$ C substrates are observed to have a bilayer with lower, higher potential than the monolayer, respectively. Resulting interlayer potential differences are a clear source of electrostatic disorder and are explained as subtle shifts in tilt-angles between layers relative to the substrate. These empirical results continue our understanding of how co-existing orientations contribute to the complex electrostatics influencing charge transport. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F35.00009: Effect of polar surfaces on organic molecular crystals Onise Sharia, Roman Tsyshevskiy, Maija Kuklja Polar oxide materials reveal intriguing opportunities in the field of electronics, superconductivity and nanotechnology. While behavior of polar surfaces has been widely studied on oxide materials and oxide-oxide interfaces, manifestations and properties of polar surfaces in molecular crystals are still poorly understood. Here we discover that the polar catastrophe phenomenon, known on oxides, also takes place in molecular materials as illustrated with an example of cyclotetramethylene tetranitramine (HMX) crystals. We show that the surface charge separation is a feasible compensation mechanism to counterbalance the macroscopic dipole moment and remove the electrostatic instability. We discuss the role of surface charge on degradation of polar surfaces, electrical conductivity, optical band-gap closure and surface metallization. [Preview Abstract] |
Tuesday, March 14, 2017 1:27PM - 1:39PM |
F35.00010: Assembly of PCBM Domains on Si(111) from Liquid Solution Raymond Phaneuf, Miriam Cezza In this talk we present the results of investigations aimed at exploring the mechanisms by which small organic molecules self-assemble into domains during phase separation from liquid solutions in the presence of a solid substrate. As an example system we investigated molecular [6,6]-phenyl-C$_{\mathrm{61}}$-butyric acid methyl ester (PCBM), an electron acceptor, in chloroform solution, deposited onto native oxide-covered Si(111) substrates. We find the morphology of PCBM molecule domains varies widely depending on solvent evaporation rate, the presence/absence of a second solute, tn-ZnPc, in the solution, and seemingly the presence/absence of trace impurities. We investigate the role that the solvent evaporation rate plays, and find evidence for spontaneous decomposition at the highest rates, nucleation and growth of crystalline PCBM domains on the substrate for slower rates, and dendritic assembly of domains on the substrate at the slowest rates studied. [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F35.00011: Molecular Patterning and Directed Self-Assembly of Gold Nanoparticles on GaAs Tianhan Liu, Timothy Keiper, Xiaolei Wang, Guang Yang, Daniel Hallinan, Jianhua Zhao, Peng Xiong The ability to organize Au NPs into ordered structures on solid-state substrates, especially semiconductors, holds great promise for controlled fabrication of nanoplasmonic devices. Here, we report on the development of a process for the formation and micro/nano patterning of self-assembled monolayer (SAM) of thiol molecules on GaAs, and the utilization of the molecular SAMs for the directed self-assembly of Au NPs. An ammonium polysulfide treatment of the GaAs substrate results in a sulfur-passivated oxide-free surface, which enables the formation of thiol molecule SAM via solution-based assembly. Furthermore, micro- and nano-scale patterns of thiol SAMs are created directly on the passivated GaAs surfaces by micro-contact printing and dip-pen nanolithography respectively. SAM patterns of different thiol molecules on GaAs are then used for Au NP assembly by leaving the substrate in the Au NP solution (13 nm 0.47 mM Au NPs in DI water) for 24 hours. 4-Aminothiophenol (ATP) SAM patterns result in highly specific Au NP assembly with clearly defined boundaries. The results are consistent with an assembly process driven by electrostatic interaction between the negatively charged Au NPs in an aqueous solution and positively charged~ATP molecules on the GaAs substrate. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F35.00012: Nucleation and Growth Kinetics in Solution-Processed Organic Molecular Crystalline Thin Films. David Patrick, Brad Johnson, Cyrus Schaaf, Michael Jenkins, Linnea Bavik We report in-situ, real-time observation of early stage nucleation and growth kinetics in submonolayer crystalline films of the organic semiconductor tetracene grown in ultrathin liquid solvent layers. Films are prepared using a vapor-liquid-solid deposition technique in which tetracene monomers are delivered at a constant rate via a vapor-phase flux to a substrate coated with a sub-micron thick layer of an organic liquid solvent, causing crystals to nucleate and grow. ~~Using fluorescence videomicroscopy we follow the formation and growth of individual crystals, including simultaneous mapping of spatial variations in monomer concentration and depletion zones. A unified theoretical treatment accurately describing the time- and flux-dependent nucleation rate, limiting nucleation density, steady-state growth rates, and crystal spacing statistics is developed by modifying the Walton relation to account for the presence of the liquid solvent, with the critical nucleus size treated as a concentration-dependent variable. We discuss the differences between molecular crystallization in quasi-2D liquid films, versus traditional growth on a bare substrate in vacuum by physical vapor deposition (PVD). [Preview Abstract] |
Tuesday, March 14, 2017 2:03PM - 2:15PM |
F35.00013: Simultaneous and coordinated rotational switching of all molecular rotors in a network Yuan Zhang, Heath Kersell, Roman Stefak, Jorge Echeverria, Violeta Iancu, Gayani Perera, Yang Li, Aparna Desahpande, Kai-Felix Brown, Christian Joachim, Gwenael Rapenne, Saw-Wai Hla A range of artificial molecular systems has been created that can exhibit controlled linear and rotational motion. To further develop such systems, a key step is adding communication between molecules in a network. Here, we show that a two-dimensional array of dipolar molecular rotors can undergo simultaneous rotational switching when applying an electric field from the tip of a scanning tunnelling microscope. Several hundred rotors made from porphyrin-based double-decker complexes can be simultaneously rotated in a hexagonal rotor network on a Cu(111) surface by applying biases above 1 V at 80 K. The phenomenon is observed only in a hexagonal rotor network due to the degenerated ground-state dipole rotational energy barrier of the system. Defects are essential to increase electric torque on the rotor network and to stabilize the switched rotor domains. At low biases and low initial rotator angles, slight reorientations of individual rotors occur, resulting in the rotator arms pointing in different directions. Analysis reveals that the rotator arm directions are coordinated to minimize energy via crosstalk through dipolar interactions. DE-FG02-02ER46012 [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700