Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P35: Surface Science of Organic Molecular Solids, Films, and Nanostructures IIFocus
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Sponsoring Units: DMP Chair: Kristen Burson, Hamilton College Room: 298 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P35.00001: Conformations of cyclic silanes control molecular junction conductance Haixing Li, Marc Garner, Zhichun Shangguang, Qianwen Zheng, Yan Chen, Timothy Su, Madhav Neupane, Michael Steigerwald, Shengxiong Xiao, Colin Nuckolls, Gemma Solomon, Latha Venkataraman We examine the impact of ring conformation on the charge transport characteristics of cyclic silicon structures bound to gold electrodes in single molecule junctions. We investigate the conductance properties of cyclic silanes using both the scanning tunneling microscope based break junction technique and density functional theory based ab initio calculations. In contrast with the linear ones, these cyclic silanes yield lower conductance values; calculations reveal that the constrained dihedral geometries occurring within the ring are suboptimal for $\sigma $-orbital delocalization, and therefore, conductance. Due to the weakened $\sigma $-conjugation in the molecule, through-space interactions are found to contribute significantly to the conductance. This work details the vast conformational flexibility in cyclic silanes and the tremendous impact it has on controlling conductance. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P35.00002: Molecular self assembly and chiral recognition of copper octacyanophthalocyanine on Au(111): Interplay of intermolecular and molecule-substrate interactions. Rejaul Sk, Barun Dhara, Joel Miller, Aparna Deshpande Submolecular resolution scanning tunneling microscopy (STM) of copper octacyanophthalocyanine, CuPc(CN)$_{\mathrm{8}}$, at 77 K demonstrates that these achiral molecules form a two dimensional (2D) tetramer-based self-assembly upon evaporation onto an atomically flat Au(111) substrate. They assemble in two different structurally chiral configurations upon adsorption on Au(111). Scanning tunneling spectroscopy (STS),acquired at 77 K, unveils the HOMO and LUMO energy levels of this self-assembly. Voltage dependent STM images show that each molecule in both the structurally chiral configurations individually becomes chiral by breaking the mirror symmetry due to the enhanced intermolecular dipolar coupling interaction at the LUMO energy while the individual molecules remain achiral at the HOMO energy and within the HOMO-LUMO gap. At the LUMO energy, the handedness of the each chiral molecule is decided by the direction of the dipolar coupling interaction in the tetramer unit cell. This preference for LUMO energy indicates that this chirality is purely electronic in nature and it manifests on top of the organizational chirality that is present in the self-assembly independent of the orbital energy. [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P35.00003: Wide-Field Single Molecule Fluorescence Lifetime, Position, and Orientation: Instrumentation and Implementation James Marr, J. Alexander Liddle, Robert Ilic, Muzhou Wang, Marcelo Davanco The combination of super-resolution imaging with single-molecule lifetime determination would allow the collection of structural and environmental detail at the nanoscale. A new class of detector known as a `High-temporal and High-spatial resolution, High-throughput 3-Dimensional' (H33D) detector, allows wide-field imaging with sub-nanosecond timing resolution. We present the detailed characterization of the detector, to understand the underlying structure. This information is used to eliminate artifacts from the sample data and maximize localization accuracy. After initial calibration, a thin polymer film, doped with bright, long-lived fluorescent dye is deposited on wedges of silica atop gold, ITO or hafnium oxide to probe the interaction of a fluorophore with conducting and dielectric materials as a function of distance. The wedge slope is chosen such that lateral localization uncertainty in the x-y plane contributes a sub-nanometer uncertainty in z. In this way, lifetime as a function of distance from and orientation relative to the surface is investigated. The data obtained will help in the understanding of dye/interface interactions. This will minimize localization errors and allow for lifetime changes to be directly linked to distance from and orientation relative to a surface. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P35.00004: Decomposition of energetic molecules by interfacing with a catalytic oxide: opportunities and challenges Fenggong Wang, Roman Tsyshevsky, Anton Zverev, Anatoly Mitrofanov, Maija Kuklja Organic-inorganic interfaces provide both intrigues and opportunities for designing systems that possess properties and functionalities inaccessible by each individual component. In particular, mixing with a photocatalyst may significantly affect the adsorption, decomposition, and photoresponse of organic molecules. Here, we choose the formulation of TiO$_{2}$ and trinitrotoluene (TNT), a highly catalytic oxide and a prominent explosive, as a prototypical example to explore the interaction at the interface on the photosensitivity of energetic materials. We show that, whether or not a catalytic oxide additive can help molecular decompositions under light illumination depends largely on the band alignment between the oxide surface and the energetic molecule. Furthermore, an oxygen vacancy can lead to the electron density transfer from the surface to the energetic molecules, causing an enhancement of the bonding between molecules and surface and a reduction of the molecular decomposition activation barriers. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P35.00005: Thermodynamic and Modeling Study of Cyclopentane on MgO (100), hBN and Graphite Basal Plane Fatema Wahida, Nicholas Strange, John Z. Larese Investigation of the adsorption of cyclopentane on magnesium oxide (100), hexagonal boron nitride and the graphite basal plane was undertaken to explore the role of surface symmetry on the physicochemical properties. This is one portion of a broader study of 2D layers of cyclic organic molecules adsorbed on these scientifically and industrially important substrates. A series of high-resolution volumetric adsorption isotherms over the temperature range of 195-265K were measured on each of the substrates and used to calculate such thermodynamic properties as the heat of adsorption and isosteric heat, differential enthalpy, and differential entropy of adsorption during the layer growth process. The behavior of the two dimensional isothermal compressibility as a function of temperature and coverage was used to identify the locations of layering and potential phase transitions. To gain additional insight into the microscopic details of the adsorption process, classical molecular dynamics simulations were performed using a centralized force field (COMPASS) in tandem with thermodynamic experiments. The results of these modeling studies will be used to aid future quasi- and inelastic neutron scattering experiments aimed at exploring the rotational and translational diffusion and vibrational motion of the single and multilayer molecular films. [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P35.00006: Water adsorption on SrTiO$_3$(001) studied by x-ray standing wave excited photoelectron spectroscopy Jorg Zegenhagen, Vladyslav Solokha, Axel Wilson, David Duncan, Debi Garai, Kurt Hingerl We investigated the nature of water adsorption and in particular the H$_2$O and/or OH$^{-}$ bonding sites on different SrTiO$_3$(001) surfaces using the powerful technique of standing wave excited photoelectron spectroscopy. This allowed us determining whether the H$_2$O adsorption is associative or dissociative and additionally localizing the exact bonding site of the different oxygen species (water oxygen and OH$^{-}$ oxygen species). We deposited water in ultra high vacuum on several differently structured or reconstruction SrTiO3(001) surfaces in the range from $\sim$ 100K to room temperature. Our results provide valuable insight into water adsorption on STO(001) surfaces and its specific catalytic activity in view of water splitting applications. They also help clarify previous conflicting previous results [1,2]. [1] H. Hussain, X. Torrelles, P. Rajput, M. Nicotra, G. Thornton, J. Zegenhagen, J. Phys. Chem. C. 118, 10980 (2014). [2] A.E. Becerra-Toledo, M.R. Castell, L.D. Marks, Surf. Sci. 606 (2012) 762; A.E. Becerra-Toledo, j.a. Enterkin, D.M. Kienzle, L.D. Marks, Surf. Sci. 606 (2012) 791 [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P35.00007: Dynamics of Electronic Excitations at Interfaces Dmitri Kilin Atomistic modeling of broad range of excited state dynamics and charge transfer reactions at metal-to-semiconductor interfaces,[1] supported metal clusters in aqueous environment,[2] as well as in organic-inorganic lead-halide perovskites[3] and laser crystals[4] is performed by a range of methodologies including reduced density operator method, with nonadiabatic coupling being computed on-the-fly along nuclear trajectory.[5] A solution for non-equilibrium density of electrons is used for determining the dynamics of formation of surface charge transfer states, computing surface photo-voltage, and rates of energy and charge transfer.[6] An average over long \textit{ab initio} molecular dynamics trajectories provides inhomogeneous broadening of spectral lines.[7] A modification of this methodology helps to evaluate distribution of products in photoassisted reactions.[8] 1. Han, Y., et al. Mol. Phys., 2014.\textbf{ 112}(3-4): p. 474-484. 2. Huang, S., et. al, J. Phys. Chem. Lett., 2014. \textbf{5 }(16): p. 2823-2829 3. Junkman, D., et al., Mater. Res. Soc. Symp. Proc., 2015. \textbf{1776}: p. DOI: 10.1557/opl.2015.782 4. Yao, G., et al., Mol. Phys., 2014. \textbf{11}3(3-4): p. 385-391 5. Kilina, S., et. al. Chem. Rev., 2015.\textbf{ 115}((12)): p. 592--5978 6. Jensen, S.J., et. al, J. Phys. Chem. C, 2016. \textbf{12}0(11): p. 5890-5905. 7. Vogel, D.J. et al., J. Phys. Chem. C, 2015. \textbf{11}9(50): p. 27954-27964. 8. Han, Y., et al., J. Phys. Chem. A, 2015.\textbf{ 119}(44): p. 10838-10848 [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:30PM |
P35.00008: Synthesis of 2D and 1D graphene structures and their magnetic and plasmonic properties Invited Speaker: Changgan Zeng The synthesis of 2D and 1D graphene structures is critical to explore their unique physical properties, including Dirac plasmonics in 2D graphene and spin-polarized edge states in zigzag graphene nanoribbons. We have developed a universal new method to synthesize 2D and 1D graphene structures, and further revealed the exotic magnetic and plasmonic properties of graphene at the quantum level. Our central findings include: 1) Self-assembled synthesis of monolayer graphene from aromatic molecules at low temperatures; 2) One-dimensional self-assembled synthesis of the narrowest zigzag graphene nanoribbons, with the pentacene segments connected by carbon tetragons, which are predicted to serve as definitive spin switches to reverse the spin orientations of the two edge channels; 3) Quantum control of the plasmon excitation and propagation in graphene; 4) Substantial enhancement of quantum coherence in graphene by plasmon coupling. Collectively, these findings help to shed new light on the synthesis of graphene structures with designed patterns and exploration of their emergent quantum properties. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P35.00009: Local electronic structure of atomically-precise graphene nanoribbon heterojunctions Hsin-Zon Tsai, Giang D. Nguyen, Arash A. Omrani, Tomas Marangoni, Meng Wu, Daniel J. Rizzo, Griffin F. Rodgers, Ryan R. Cloke, Rebecca A. Durr, Yuki Sakai, Franklin Liou, Andrew S. Aikawa, James R. Chelikowsky, Steven G. Louie, Felix R. Fischer, Michael F. Crommie Graphene nanoribbons (GNRs) are one-dimensional strips of graphene that exhibit novel electronic and magnetic properties. Bottom-up synthesis of GNRs via self-assembly of molecular precursors yields nanoribbons with atomic-scale structural control, thus allowing precise tuning of properties such as bandgap, edge chirality, and heteroatom doping. Here we report the local electronic structure characterization of bottom-up GNR heterojunctions fabricated from a only single type of molecular precursor. Using this new molecule, bottom-up GNRs were grown that incorporate sacrificial carbonyl groups along their edges. Subsequent thermal annealing of the GNRs after growth was used to induce removal of the carbonyl groups through a bond cleavage process. STM spectroscopy shows that these segments have different electronic properties, thus allowing formation of Type II heterojunctions with atomically well-defined interfaces. Experimental bandedge energy level alignment and wave function distributions are consistent with first principles theoretical simulations for this bottom-up heterojunction system. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P35.00010: Synthesis and Local Characterization of a Porphyrin-based Single-layer Covalent Organic Framework Trinity Joshi, Chen Chen, Hong Li, Huifang Li, Anton D. Chavez, Zahra Pedramrazi, Jean-Luc E. Bredas, William R. Dichtel, Michael F. Crommie Covalent organic frameworks (COFs) form stable 2D networks that have possible applications in areas such as molecular electronics, catalysis, and gas storage. Here we report the synthesis and characterization of a porphyrin-based single layer 2D COF having a square lattice with a core-linker configuration. Our method for synthesizing this COF involves vapor-depositing two different species of molecular precursors onto the surface of a Au(111) crystal: a porphyrin core molecule (5,10,15,20- Tetrakis (4-aminophenyl) porphyrin, or TAP) and a small linker molecule (2,5-dimethoxybenzene-1,4-dicarboxaldehyde, or DMA) that connects the cores. Annealing these molecules on Au(111) causes the core and linker molecules to covalently bond through a Schiff base condensation reaction to form the COF. We have explored the resultant COF local structure and local electronic properties using scanning tunneling microscopy (STM) and spectroscopy (STS). We report an experimental band gap of 1.98eV for this COF system and we observe that the conduction band minimum and valence band maximum states are primarily localized to the porphyrin core. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P35.00011: Evolution of Electronic Localization in Bottom-up Graphene Nanoribbon Heterojunctions Daniel J. Rizzo, Meng Wu, Hsin-Zon Tsai, Tomas Marangoni, Arash A. Omrani, Giang D. Nguyen, Christopher Bronner, Trinity Joshi, Danny Haberer, Ryan R. Cloke, Franklin Liou, Michael F. Crommie, Felix R. Fischer, Steven G. Louie Graphene nanoribbons (GNRs) are narrow semiconducting strips of graphene that are predicted to exhibit novel electronic and magnetic properties. Recent advances in bottom-up synthesis techniques have enabled atomically-precise control over GNR structure and dopant integration, thus allowing fabrication of a variety of different GNR heterojunctions. The ability to reliably fabricate and characterize GNR heterojunctions is a critical first step in the development of sophisticated future device architectures that incorporate bottom-up GNRs. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we have investigated how GNR heterojunction band edge alignment evolves as a function of heterojunction length. We find that a minimum heterojunction length is required to observe electron localization to one side of the of GNR heterojunction interface, and that increased electronic localization is observed as the heterojunction length increases. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P35.00012: Surface Doping of MoS$_{2}$ With Molecular Acceptor Films Daniel Nevola, Alex Bataller, Harold Ade, Kenan Gondogdu, Daniel Dougherty Molecular doping control using small molecule acceptors is an important strategy for controlling the electronic properties of novel van der Waal materials such as graphene and topological insulators. We extend this approach to molybdenum disulfide (MoS$_{2}$), an exciting 2D optoelectronic material in single layer form. We manipulate the valence band photoemission spectrum of MoS$_{2}$ by organic molecular beam deposition of the acceptor tetracyanoquinodimethane (TCNQ). Angle resolved photoelectron spectroscopy shows rigid band shifts due to TCNQ film growth that are consistent with charge transfer to the organic layer from the MoS$_{2}$ substrate. The ability to control Fermi level position in MoS$_{2}$ is important for controlling excited states in optoelectronic applications. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P35.00013: Tunable, Adatom-induced surface conductance drop on InSb(110) Sara Mueller, Steven Tjung, Jacob Repicky, Alexander Keast, Evan Lang, Kevin Werner, Enam Chowdhury, Jay Gupta Understanding atomic defects in III-V semiconductors is crucial for circuit miniaturization and innovation in nanotechnology. With its narrow bandgap and high carrier mobility, Indium Antimonide (InSb) is a desirable candidate for solotronics applications. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we investigate an adatom defect on the InSb(110) surface. The defect presents in three charge states at different tunneling conditions: a bright protrusion in filled-state imaging which corresponds to a positive adatom charge, a deep crater in the neutral charge state, and a depression beyond a threshold condition indicating negative adatom charge. Remarkably, in the crater regime, the lateral size of the depleted area around the adatom extends to more than 50 nm and its apparent depth indicates a suppressed tunneling conductance by 100-fold. We attribute the dramatic change in conductance to filling a charge-transition state that is observed near the conduction band edge in STS. Furthermore, the depletion area can be reliably tuned by changing the local band-bending conditions using electric fields and optical illumination. These results demonstrate that a single adatom can significantly influence the surface conductivity over relatively large distances, which provides opportunities and challenges for future nanoscale electronics. [Preview Abstract] |
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