Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X10: Focus Session: Growth, Structure, Dynamics, and Function of Nanostructured Surfaces and Interfaces -- Organic Molecules |
Hide Abstracts |
Sponsoring Units: DMP Chair: Jay Gupta, Ohio State University Room: D221 |
Thursday, March 24, 2011 2:30PM - 2:42PM |
X10.00001: Identification of the Atomic Scale Structures of the Molecule-Metal Interfaces of Single-Molecule Nanowires Firuz Demir, George Kirczenow We show theoretically how inelastic tunneling spectroscopy can identify the atomic scale structures of the molecule-metal interfaces of single-molecule nanowires bridging pairs metal electrodes, and thus resolve a long standing problem that is central to the field of single-molecule nanoelectronics. As an example we consider the propanedithiol (PDT) molecules bridging gold nanocontacts in the recent experiment of Hihath {\em et al.} [Nano Lett. \textbf{8}, 1673 (2008)]. Based on {\em ab initio} density functional and semi-empirical calculations we identify the features observed in the experimental inelastic tunneling spectra of these molecules at phonon energies near 46, 40 and 42 meV as arising from sulfur atoms (that have lost their thiol hydrogen atoms) bonding to the gold contacts in top site, bridge site and mixed bridge-top site geometries respectively. PDT molecules in which the sulfur atoms retain their thiol hydrogen atoms and bond strongly to gold in the top site geometry give rise to an IETS feature in the phonon energy range 54-57 meV. [Preview Abstract] |
Thursday, March 24, 2011 2:42PM - 2:54PM |
X10.00002: The adsorption geometries of C60 monolayer on Ag(111) and Au(111) Renee Diehl, Heekeun Shin, Katariina Pussi C$_{60}$ films on metal surfaces are of particular interest as model van der Waals systems, and for applications such as molecular electronics. The electronic properties of these films are known to depend strongly on their structures and the relative molecular orientations of the C$_{60}$ molecules, yet there are few detailed structure determinations for C$_{60}$ films. When grown at room temperature and annealed to a sufficiently high temperature, C$_{60}$ on Au(111) and Ag(111) form ($2\sqrt{3}\times 2\sqrt{3}$)R30$^{\circ}$ structures with one C$_{60}$ molecule per unit cell. We present a LEED study of their surface geometries, which are similar in some ways, but differ in others. They both form vacancy site structures that are thermally activated, they both form monolayers that are composed of a mixture of hex-down and 6:6 bond down molecules. The details of the 6:6 bond molecule geometries are different on both substrates, and the temperature dependence of the mixture is different. [Preview Abstract] |
Thursday, March 24, 2011 2:54PM - 3:06PM |
X10.00003: Mechanical Properties of a vdW molecular monolayer at a metal surface: Structural Polymorphism leading to facile compression Dezheng Sun, Daeho Kim, Duy Le, {\O}yvind Borck, Kristian Berland, Kwangmoo Kim, Wenhao Lu, Yeming Zhu, Miaomiao Luo, Jon Wyrick, Zhihai Cheng, T.L. Einstein, Talat Rahman, Per Hyldgaard, Ludwig Bartels Intermolecular force plays an important role in self-assembly and surface pattern formation. Anthracene and similar unsubstituted arenes attach to a metallic substrate predominantly through van der Waals interaction leading. In this contribution we present images how anthracene on Cu(111) forms a large number of highly ordered patterns that feature a broad array of structural motifs. Density functional theory modeling including vdW interactions allows us to model the energetic of the pattern formation at high fidelity. Moreover, it allows us to deduce the strain energy associated with films of varying coverage. From this work, we obtain the Young's modulus and Poisson Ratio of a molecular monolayer, which resemble properties conventionally found for porous materials. These patterns are in marked contrast to those found after introduction of functional groups in the molecules, such as carbonyls or thiols. [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:18PM |
X10.00004: Monte Carlo Study of the Fish-like Patterns of Anthracenes on Cu(111) Kwangmoo Kim, T.L. Einstein, Dezheng Sun, Dae-Ho Kim, Ludwig Bartels Using Monte Carlo calculations of the two-dimensional triangular lattice with a 2-component 3-state Potts model, we demonstrate a mechanism for the spontaneous formation of fish-like patterns of anthracene (AC) molecules on Cu(111) by sputtering and annealing, then cooling to $\sim$ 80 K. The two components are an AC on a hollow site and another on a bridge site of Cu(111).\footnote{Dezheng Sun {\it et al.}, Phys.\ Rev.\ B {\bf 82}, xxx(R) (2010).} The liquid crystal model with two separate parts, positional and orientational, only explains a part of the fish-like pattern, not the whole regular pattern. Our model fixes the positional order of AC's into the triangular lattice and the orientational order into three angles as observed in the experiments. The variation of the coverages of AC's is reflected in the change of the ratio of two components in our model. We also try to understand the compression of AC's with the introduction of Gaussian dispersion of AC's about their triangular lattice sites. [Preview Abstract] |
Thursday, March 24, 2011 3:18PM - 3:30PM |
X10.00005: Self-assembly of metal phthalocyanines modulated by different substrates Wende Xiao, Yuhang Jiang, Jichun Lian, Liwei Liu, Zhihai Cheng, Li Gao, Shixuan Du, Hongjun Gao The self-assembly of organic molecules on solid surfaces has made tremendous progresses due to potential applications in organic nano-devices. Among the organic molecular building blocks, metal phthalocyanines (MPcs) have been attracting considerable interests because of their novel electronic and magnetic properties. The self-assembly and physical properties of MPcs on various surfaces have been investigated by scanning tunneling microscopy and spectroscopy (STM/STS). In this presentation, we will report on the self-assembly of iron phthalocyanine (FePc), manganese phthalocyanine (MnPc) and nickel phthalocyanine (NiPc) on Pb(111) and monolayer graphene (MG) epitaxy on Ru (0001) by means of low temperature (LT) STM. Highly ordered close-packed islands with square lattice are observed for all three kinds of MPcs growth on Pb(111), whereas regular dislocation lines are formed in the molecular islands of FePc on Pb(111). We find that the Kondo resonance of MnPc on Pb(111) is strongly location-dependant. For FePc, MnPc and NiPc growth on MG, dispersive single molecules, dispersive molecular lines and small patches of Kagome lattice are observed, respectively. [Preview Abstract] |
Thursday, March 24, 2011 3:30PM - 3:42PM |
X10.00006: Structural and electronic properties of polymer-silicon semiconductor heterojunctions using hybrid functionals Joseph Turnbull, Wenchang Lu, Jerry Bernholc Combining organic and inorganic components to form semiconductor heterostructures provides the basis for an enormous number of potential optoelectronic device designs. We report here on the use of hybrid-DFT calculations to study the structural and electronic properties of semiconductor interfaces between silicon and pi-conjugated polymers. Using large supercells and exact-exchange-corrected hybrid functionals, we explore different attachment motifs for polymer monolayers, as well as the role of screening, in particular in the context of predicting semiconductor band-offsets. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X10.00007: Tuning Structural and Mechanical Properties of Two-Dimensional Molecular Crystals: The Roles of Carbon Side Chains H.-J. Gao, H.Y. Cun, Y.L. Wang, S.X. Du, L. Zhang, L.Z. Zhang, W.A. Hofer, S.J. Pennycook Organic-molecule based flexible electronics has been of significant interest due to its potential to challenge conventional silicon-based technologies. The crucial properties of these devices rely on the largely invariant physical properties of organic compounds or films when they are mechanically deformed. In this present work, by choosing quinacridone with flexible carbon chains as a model system, we developed a theoretical scheme to evaluate the contributions of various interactions to the molecular self-assembly process and find that such a process should be considered as a collective interaction between molecules and substrates rather than from the viewpoint of an isolated molecule. Importantly, the data provide insight into the origin and an estimate of the magnitude of the Young's modulus of the molecular film, which suggests that the elastic properties of molecular films can be tuned through control of side chain length. [Preview Abstract] |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X10.00008: Formation of Molecular Networks: Tailored Quantum Boxes and Behavior of Adsorbed CO in Them Jon Wyrick, Dezheng Sun, Dae-Ho Kim, Zhihai Cheng, Wenhao Lu, Yeming Zhu, Miaomiao Luo, Yong Su Kim, Eli Rotenberg, Kwangmoo Kim, T.L. Einstein, Ludwig Bartels We show that the behavior of CO adsorbed into the pores of large regular networks on Cu(111) is significantly affected by their nano-scale lateral confinement and that formation of the networks themselves is directed by the Shockley surface state. Saturation coverages of CO are found to exhibit persistent dislocation lines; at lower coverages their mobility increases. Individual CO within the pores titrate the surface state, providing crucial information for understanding formation of the network as a result of optimization of the number N of electrons bound within each pore. Determination of N is based on quinone-coverage-dependent UPS data and an analysis of states of particles in a pore-shaped box (verified by CO's titration); a wide range of possible pore shapes and sizes has been considered. [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X10.00009: Origin of the Giant Honeycomb Network of Quinones on Cu(111) T.L. Einstein, Kwangmoo Kim, Jon Wyrick, Zhihai Cheng, Ludwig Bartels, Kristian Berland, Per Hyldgaard We discuss the factors that lead to the amazing regular giant honeycomb network formed by quinones on Cu(111). Using a related lattice gas model with many characteristic energies, we can reproduce many experimental features. These models require a long-range attraction, which can be attributed to indirect interactions mediated by the Shockley surface state of Cu(111). However, Wyrick's preceding talk gave evidence that the network self-selects for the size of the pore rather than for the periodicity of the superstructure, suggesting that confined states are the key ingredient. We discuss this phenomenon in terms of the magic numbers of 2D quantum dots. We also report calculations of the effects of anthraquinones (AQ) in modifying the surface states by considering a superlattice of AQ chains with various separations. We discuss implications of these results for tuning the electronic states and, thence, superstructures. [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X10.00010: Tunneling and Time-Reversal Invariance in the Diffusion of Polyatomic Molecules at a Metal Surface Zhihai Cheng, Eric Chu, Dezheng Sun, Daeho Kim, Yeming Zhu, MiaoMiao Luo, Greg Pawin, Kin Wong, Ki-Young Kwon, Robert Carp, Michael Marsella, Ludwig Bartels Rectangular molecules with 1 or 2 oxygen substrate linkers attached to each of their long sides diffuse in a uniaxial fashion, despite the threefold symmetry of the Cu(111) substrate. They achieve this by sequential placement of their substrate linkers and are hence dubbed ``molecular walkers''. VT-STM monitoring of their motion reveals a striking difference between the diffusion prefactors of the quadrupedal and bipedal species, with the latter being very low. DFT modeling of the diffusion barrier and WBK-based estimation of the potential for tunneling suggest that this discrepancy lies in the prevalence of tunneling for species, whose motion is only blocked by a barrier affecting one of their substrate linkers. In contrast, if the diffusion barrier affects two substrate linkers simultaneously, tunneling will not occur and conventional prefactors are observed. This finding may actually have far-reaching implications for the modeling of molecular motion in general, as it highlights that blocking of a single atoms is insufficient for confinement of molecular motion. We also investigated an asymmetric ``molecular walkers'', showing a symmetric diffusion in agreement with time-reversal invariance despite a saw-tooth shape of the diffusion barrier experienced. [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X10.00011: Hydrogen Bonding Controls the Dynamics of Catechol Adsorbed on a TiO$_{2}$(110) Surface Ulrike Diebold, Shao-Chun Li, Li-Na Chu, Xue-Qing Gong Direct studies of how organic molecules diffuse on metal oxide surfaces can provide insights into catalysis and molecular assembly processes. We studied individual catechol molecules, C$_{6}$H$_{4}$(OH)$_{2}$, on a rutile TiO$_{2}$(110) surface with scanning tunnelingmicroscopy. Surface hydroxyls enhanced the diffusivity of adsorbed catecholates. The capture and release of a proton caused individual molecules to switch between mobile and immobile states within a measurement period of minutes. Density functional theory calculations showed that the transfer of hydrogen from surface hydroxyls to the molecule and its interaction with surface hydroxyls substantially lowered the activation barrier for rotational motion across the surface. Hydrogen bonding can play an essential role in the initial stages of the dynamics of molecular assembly. [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 4:54PM |
X10.00012: Reversible rectification in sub-monolayer molecular heterojunctions Joe Smerdon, Chris Giebink, Matthias Bode, Nathan Guisinger, Jeffrey Guest Pentacene and C$_{60}$ are archetypal molecules for optically active acceptor-donor heterojunctions and have been used as the active materials in bilayer solar cells. We will discuss UHV STM and STS measurements on these bi-molecular films deposited sequentially to form heterojunctions on Cu(111). It is observed that rectification can be detected at the single-junction limit, and that the direction of rectification flips in accordance with the polarity of the heterojunction. The morphology of heterolayers will also be discussed. It is found that the density of a Pn monolayer can be affected by choice of growth conditions, and in turn can affect the overall morphology of the heterolayer and the rectification behavior of the heterojunctions. We will also briefly discuss progress towards probing the photophysical behavior of these systems. The correlation of atomic-scale structure and electronic behavior at the single-junction limit has important implications for applications of such heterojunctions, such as solar cells or OLEDs. [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:06PM |
X10.00013: Molecular self-assembly of dichloropentacene and C$_{60}$ for a model organic solar cell heterojunction Jun Wang, Amanda Brown, Irvinder Kaur, Jian-Ming Tang, Glen Miller, Karsten Pohl Organic molecular self-assembly is a bottom-up approach to create molecular architectures that are suitable for a variety of applications including functional materials and molecular electronics. Specifically, the co-assembly of functionalized acenes (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 heterojunctions. Previously, we have fabricated a persistent self-assembled monolayer composed of single-domain 6,13-dichloropentacene (DCP) over large areas on the stepped Au(788) surface. Here we present the subsequent growth of C$_{60}$ on a DCP monolayer covered gold surface by STM investigation and ab-initio calculations. After mild annealing C$_{60}$ molecules are forced to the Au(788) step edges forming very long C$_{60}$ chains, in contrast to the short C$_{60}$ chains reported on bare vicinal gold steps. These final structure formations are attributed to the delicate intermolecular interactions and molecule-substrate interactions. [Preview Abstract] |
Thursday, March 24, 2011 5:06PM - 5:18PM |
X10.00014: BEEM Study of Interface Properties in PVDF-graphite Heterojunctions Le Zhang, Clay Upton, Andrei Sokolov Since the prediction of giant electroresistance, tunnel junctions with ferroelectric (FE) barrier attract significant experimental and theoretical attention due to potential application as non-volatile data storage devices. The ferroelectric polymer, polyvinylidene fluoride (PVDF), is of particular interest thanks to its outstanding electromechanical, dielectric, and mechanical properties. However, direct experimental study of organic FE interface properties as a function of its polarization is extremely challenging. We employ ballistic electron emission microscope (BEEM) technique for nanometer size characterization of P(VDF-TrFE)/HOPG heterostructure. This method offers STM scale of spatial resolution and is immune to the contact quality of top electrode. By comparing the voltage dependence of ballistic current for different polarization states, we observe the change in tunnel barrier properties as the sign of FE polarization reverses.~High-quality thin films of PVDF were fabricated using a Langmuir-Blodgett (LB) technique. Results will be also compared with thermally evaporated PVDF film and its isomorphic analog, polyethylene. [Preview Abstract] |
Thursday, March 24, 2011 5:18PM - 5:30PM |
X10.00015: Reverse self assembly: (111)-oriented gold crystallization at thiol monolayer templates Ahmet Uysal, Benjamin Stripe, Pulak Dutta, Binhua Lin, Mati Meron Certain microorganisms can reduce gold ions from aqueous solutions to form gold nano/micro particles in a controlled way [1]. Understanding how biomolecules control the crystallization process may result in cheap and environment-friendly techniques in many different applications, including organic-inorganic hybrid molecular technologies and shape controlled gold nanoparticle production. To better understand the organic-inorganic interactions, we studied the crystallization of gold under octadecanethiol monolayers at the air-water interface. We used synchrotron x-rays in the grazing incidence geometry to determine the orientation of the gold crystals as well as the organic monolayer structure \textit{in situ}. These x-rays also act as the gold reducing agent in this experiment. We see that the (111) faces of gold crystals are parallel to the monolayer surface. The monolayer structure changes with time and becomes commensurate with the gold (111) face, similar to a $\sqrt 3 \times \sqrt 3 $ self-assembled monolayer of thiol on gold. \\[4pt] [1] K. B. Narayanan, and N. Sakthivel, Advances in Colloid and Interface Science 156, 1 (2010). [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