Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B8: From Single Molecules to Molecular Assemblies on Surfaces I |
Hide Abstracts |
Sponsoring Units: DCMP Room: 006C |
Monday, March 2, 2015 11:15AM - 11:27AM |
B8.00001: Long Range Modification of a Metal Surface Electronic Structure by an Organic Semiconductor Jingying Wang, Daniel Dougherty In an organic spintronic device the interaction between electrode surface and organic semiconductor layer plays an important role in spin injection at this interface. The antiferromagnetic material Cr(001) is known to have a spin-polarized state near Fermi level that could potentially hybridize with organic molecules. Here we report our STM/STS study of electronic structure at interface between an organic semiconductor, PTCDA, and Cr(001) surface. The study shows that the surface state at Fermi level of Cr(001) can be broadened by PTCDA molecules deposited on the surface due to hybridization of PTCDA molecular orbital and conduction sp band of Cr(001). This indirect modification is not only localized at molecular adsorption sites, but also extends several nm to bare surrounding Cr(001) surface and decays with distance away from PTCDA molecules. [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B8.00002: Accurate Energy Level Alignment at Physisorbed Molecule-Metal Interfaces from a Density Functional Theory-Based Approach David A. Egger, Zhenfei Liu, Jeffrey B. Neaton, Leeor Kronik A highly relevant physical quantity for nanostructured molecule-metal interfaces is the energy level alignment of the molecular electronic states with respect to the Fermi level of the metal. Here, we introduce an efficient theoretical method that is based on density functional theory, but in contrast to common approximations fulfills physically motivated criteria for exchange-correlation interactions and can therefore yield quantitatively accurate energy level alignment information for physisorbed metal-molecule interfaces. We validate our approach by a detailed comparison with experimental and theoretical reference data for several prototypical interfaces of this kind: benzene on graphite (0001), and 1,4-benzenediamine, Cu-phthalocyanine, and 3,4,9,10-perylene-tetracarboxylic-dianhydride on Au(111). Our results indicate that obtaining quantitatively accurate energy level alignment information from density functional theory is possible. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B8.00003: Rethinking chemisorption: New insights into the factors controlling the binding energy Marisol Alcantara Ortigoza, Sergey Stolbov Chemisorption of atomic and molecular species on a substrate induces electronic charge redistribution upon which substrate nuclei respond by adjusting their positions. This lattice distortion has been linked to the binding energy E$_{\mathrm{B}}$ of the adsorbed species and attached to the so-called surface relaxation energy, E$_{\mathrm{rx}}$. We have found, however, that for transition metals the energy associated with the mere charge redistribution E$_{\mathrm{elec}}$ is much larger than E$_{\mathrm{rx}}$ and thus both contributions must be considered [1]. In this work, we quantify the electronic and structural perturbation energy E$_{\mathrm{P}}$ brought by various adsorbates on surfaces to understand anomalous adsorbate binding energies, i.e., those in which E$_{\mathrm{P}}$ strongly influences the magnitude of E$_{\mathrm{B}}$. For example, for O adsorption on Au(111), while E$_{\mathrm{rx}}$ is only 0.25 eV, the overall perturbation energy E$_{\mathrm{P}}$ affecting E$_{\mathrm{B}}$(O) is $\sim$ 1 eV [1]. This indicates that E$_{\mathrm{P}}$ cannot be ignored but also that local bonds may not be as weak as portrayed by E$_{\mathrm{B}}$, even though E$_{\mathrm{B}}$ is significantly reduced. We expose cases in which E$_{\mathrm{P}}$ is really dominated by the lattice distortion energy, as well as a rationale for its trends as a function of the substrate and adsorbate. We discuss the implications of the fact that E$_{\mathrm{B}}$ is not always predominately controlled by the bond-strength on heterogeneous catalysis, as well as the applications of the same fact. M. Alc\'{a}ntara Ortigoza and S. Stolbov; ``The Perturbation Energy: The missing key to understand gold `nobleness.' '' Submitted in October 2014 [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B8.00004: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 12:03PM - 12:15PM |
B8.00005: Surface-Mediated Self-Assembly Controlled by Interfacial Charge-Transfer Oliver Monti, Nahid Ilyas, Bret Maughan, Percy Zahl, Rocio Cortes-Rodriguez, Peter Sutter Precise control of molecular self-assembly is desirable and essential to understand electronic structure and dynamics at organic semiconductor interfaces. Self-assembly into ordered supramolecular structures for such pi-conjugated molecules is determined by a subtle balance between surface-molecule and molecule-molecule interactions, and a predictive mechanistic understanding has remained a substantial challenge for most commonly used organic semiconductors. Here we show by a combination of low-temperature scanning tunneling microscopy and two-photon photoemission spectroscopy for the model system of chloro-boron subphthalocyanine on Cu(111) that interfacial charge-transfer results in fundamentally different self-assembly mechanisms for different molecular orientations on the surface. We uncover a novel mechanism that controls thin film growth for an important class of organic semiconductors. We conclude that the adsorption geometry may be exploited in self-assembly to control electronic structure and dynamics at organic semiconductor interfaces. [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B8.00006: Photo-Activation of Single Molecules and Assemblies on Au\textbraceleft 111\textbraceright Yuxi Zhao, Moonhee Kim, Natcha Wattanatorn, Jeffrey Schwartz, Hong Ma, Alex Jen, Paul Weiss Understanding electron transfer at the molecular level is critical to the rational design and performance improvement of organic optoelectronics and photovoltaics. The behavior of photoactive molecules depends critically on their local environment and defects present in the surface. Here, we use a custom-built, laser-assisted scanning tunneling microscope to probe the photocurrent of isolated anthracene derivates on Au\textbraceleft 111\textbraceright . The photocurrent originates from charge-transfer transitions of anthracene into an excited state when illuminated by an evanescent field. The influence of the image potential states on terraces and at defects in the gold surface on photo-induced charge transfer will be discussed. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B8.00007: Anchoring and Bending of Pentacene on Aluminum (001) Guido Fratesi, Anu Baby, Shital R. Vaidya, Laerte L. Patera, Cristina Africh, Luca Floreano, Gian Paolo Brivio We study the structural, electronic, and spectroscopic properties of pentacene adsorbed on Al(001) surface, combining density functional theory (DFT) methods including van der Waals interactions with x-ray photoemission (XPS), near-edge x-ray absorption fine structure (NEXAFS), and scanning tunneling microscopy (STM). We find a major change of the molecular backbone resulting into a peculiar V-shape bending, due to the direct anchoring of the two central carbons atop two Al atoms underneath. In the most stable adsorption configuration, pentacene is oriented with the long axis parallel to the substrate [110] direction, where such anchoring is favored by optimally matched interatomic distances. Remarkably, due to the generally low degree of order, we measure by STM a significant portion of molecules oriented along the [100] direction, which also display the same V-shape conformation, as driven by the link of the central carbon atoms of pentacene to a pair of slightly displaced Al atoms. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B8.00008: Pentacene thin films on flat and vicinal Au(111) surfaces M. Fatih Danisman, Ersen Mete, Erol Albayrak Here we present a structural study of pentacene thin films on flat and vicinal Au(111) surfaces by He atom diffraction measurements and dispersion corrected density functional theory (DFT) calculations. Though experimentally investigated parameter space was limited, no significant difference between the films prepared by different deposition energies was observed. Completion of monolayer coverage was confirmed by simultaneous helium scattering and quartz crystal resonance frequency shift measurements during pentacene film growth on the gold electrode of a quartz resonator. Monolayer films were found to adopt a (6x3) unit cell which was also observed for pentacene monolayers on Ag(1 1 1). However no ordered multilayer film structure could be observed which is in contrast with the previous Ag(1 1 1) studies. DFT calculations were performed with and without dispersion correction. Adsorption site of isolated pentacene molecules, crystal and electronic structure of monolayers and multilayers (up to 4 ML) were studied. The most stable monolayer structure was found to be the (6x3) unit cell in agreement with the experimental findings. [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B8.00009: The self-assembly of 5,6,7-trithiapentacene-13-one molecules on gold: from low-coverage molecular chains to monolayer coverage Amanda Larson, Jian-Ming Tang, Karsten Pohl Understanding electronic devices down to the atomic scale is essential for the development of novel organic molecule based nanotechnologies. 5,6,7-trithiapentacene-13-one (TTPO) is a promising organic semiconductor with potential applications in high temperature photovoltaic devices. Scanning tunneling microscopy (STM) of TTPO on the close-packed stepped Au (788) surface reveals interesting nanoscale surface structures ranging from molecular chains at low coverage to an ordered self-assembled monolayer. Density functional theory (DFT) calculations have been used to further probe this unique 3-D angular assembly, where the long-axis of TTPO is parallel to the gold surface, distinctive from previously observed pentacene and pentacene derivative assemblies on surfaces. It is the lateral arrangement of the underlying pentacene backbone of the molecule that is unique, causing the thiol substituent side of the molecule to be angled down towards the gold surface, with the oxygen angled away. Combining imaging with density functional theory calculations allows for classification of these self-assembled structures with particular interest being directed toward the interaction between TTPO and gold at this organic-metallic interface. Understanding of the structure of such interfaces can potentially guide nanoscale modifications for improved electrical transport and energy-conversion efficiency in future devices. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B8.00010: Layer resolved evolution of $\alpha$-sexithiophene films: Correlation between PEEM and optical reflectance Ebrahim Ghanbari, Thorsten Wagner, Peter Zeppenfeld $\alpha$-sexithiophene ($\alpha$-6T) is a well-known organic dye pigment which represents a model system to study the photo-physical properties of $\pi$-conjugated molecules. We apply a combination of Differential Reflectance Spectroscopy (DRS) and Photo Electron Emission Microscopy (PEEM) to follow the growth of $\alpha$-6T on Ag(111) surfaces in real time. The deposition of the molecules changes the density of states at the surface as well as the actual photoelectron emission barrier. Therefore, the lateral variation of the electron yield can be used to follow the growth of layers and 3D crystallites. Upon opening of the shutter, the PEEM intensity rises uniformly across the entire field of view (145 $\mu$m) until the first layer is closed. The following drop of the electron yield is terminated when the wetting layer is completed and the nucleation of 3D islands sets in. The DRS and the PEEM are synchronized and both signals are recorded simultaneously. The evolution of different features in the normalized differential optical reflectance can be attributed to the formation of the first layer, the second layer, the nucleation and growth of 3D crystallites. Therefore, we can make a direct correlation between the PEEM and the transients of the spectral reflectance. [Preview Abstract] |
Monday, March 2, 2015 1:15PM - 1:27PM |
B8.00011: Spatially-resolved molecular Quantum Dots at the Surface of a Gated Graphene Device Hsin-Zon Tsai, Sebastian Wickenburg, Jiong Lu, Arash A. Omrani, Sinisa Coh, Han Sae Jung, Dillon Wong, Johannes Lischner, Ramin Khajeh, Alexander Riss, Aaron J. Bradley, Erik Piatti, Alex Zettl, Steven G. Louie, Marvin L. Cohen, Michael F. Crommie The ability to modify the electronic properties of monolayer graphene via charge-donating or charge-accepting molecules creates new opportunities for fabricating nano-scale hybrid devices. Understanding the charge transfer process at the single molecule level is essential for tuning the electronic and magnetic characteristics of such hybrid devices. We have used scanning tunneling microscopy (STM) to locally probe how different molecular assemblies (including single molecules, molecular chains, and 2D molecular islands) exchange charge with a graphene substrate as the device backgate voltage is varied. Different molecular configurations exhibit substantially different charging behavior - some are permanently charged while others can be controllably ionized using the device backgate. Electrostatic interactions lead to charge heterogeneity at the molecular level. Single-chemical-bond-resolved atomic force microscopy allows us to correlate chemical structure and adsorption geometry of the molecules with their electronic properties. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B8.00012: Tailored Organic Molecular Growth on Silicon Studied by STM and DFT* Sean Wagner, Bing Huang, Changwon Park, Jiagui Feng, Mina Yoon, Pengpeng Zhang Control of highly ordered organic molecular thin films with extended $\pi$ systems is currently of intense interest for integrating molecules into modern electronics due to their tunable nature. Selection of molecules and substrates can lead to desired transport properties such as charge transfer, charge injection, exciton diffusion, etc., at the hetero-interface, which is crucial to the development of organic and molecular electronics. Combining scanning tunneling microscopy and density functional theory, we show that by appropriately choosing the coordinated transition-metal ion in metal phthalocyanine, the strength of the molecule-substrate interaction can be tailored, allowing for the molecular ordering and orientation at the hetero-interface with the silicon substrate to be tuned accordingly. This mechanism provides new control over the delicately balanced molecule-substrate and intermolecular interactions, offering a route towards well-ordered organic molecular growth. *Experimental work is funded by the U. S. DOE Office of Science Early Career Research Program (DE-SC0006400) through the Office of Basic Energy Sciences. Theory work conducted at Oak Ridge National Laboratory is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 2:15PM |
B8.00013: Bonding at the Metal-Organic Interface Invited Speaker: Eva Zurek We present the results of density functional theory calculations that account for dispersion, which systematically study the perturbations of the electronic structure of various organic molecules physisorbed or weakly chemisorbed to the (111) surfaces of the coinage metal surfaces copper, silver and gold. The molecules considered include: benzene, substituted benzenes, 4-fluorostyrene, tetraphenyl porphyrin, a quinonoid zwitterion, croconic acid and rhodizonic acid. We have employed a frontier orbital perspective to analyze the bonding between the substrate and the adsorbate, studied the charge redistribution at the organic-metal interface, and analyzed how this affects the self-assembly. Our theoretical studies have helped to explain the experimental observations of STM (scanning tunneling microscopy) groups by showing that: tetraphenyl-porphyrin forms attractive networks on the Ag(111) surface and repulsive ones on Cu(111) because of the larger amount of charge transfer on Cu(111); the 10 D dipole of a quinonoid zwitterion changes substantially upon adsorption to the coinage metal surfaces Cu(111), Ag(111) and Au(111) as a result of donation of charge from the molecular HOMO to the surface and back donation to the LUMO; the charge transfer which occurs between the quinonoid zwitterion and Au(111) has been studied as a function of surface coverage; 4-fluorostyrene molecules form clusters of ``magic'' sizes that depend on the metal surface and can be understood in terms of a balance between attractive H-bonding and van der Waals interactions as well as Coulomb repulsion between the molecules; the topological organic ferroelectric molecule croconic acid forms chiral honeycomb networks on the Ag(111) surface. Moreover, our calculations have illustrated that classic activating groups generally increase and prototypical deactivating groups decrease the amount and direction of charge transferred from a substituted benzene derivative to the Cu(111) and Ag(111) surfaces. The effect of functionalization on the binding site preferences of benzenes substituted with various activating and deactivating functional groups has been explored. [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