Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session B47: Molecular Assembly on Surfaces |
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Sponsoring Units: DCMP Room: 312 |
Monday, March 14, 2016 11:15AM - 11:27AM |
B47.00001: Supra-molecular networks for CO$_{2}$ capture Jerzy Sadowski, John Kestell Utilizing capabilities of low-energy electron microscopy (LEEM) for non-destructive interrogation of the real-time molecular self-assembly, we have investigated supramolecular systems based on carboxylic acid-metal complexes, such as trimesic and mellitic acid, doped with transition metals. Such 2D networks can act as host systems for transition-metal phthalocyanines (MPc; M $=$ Fe, Ti, Sc). The electrostatic interactions of CO$_{2}$ molecules with transition metal ions can be tuned by controlling the type of TM ion and the size of the pore in the host network. We further applied infrared reflection-absorption spectroscopy (IRRAS) to determine of the molecular orientation of the functional groups and the whole molecule in the 2D monolayers of carboxylic acid. The kinetics and mechanism of the CO2 adsorption/desorption on the 2D molecular network, with and without the TM ion doping, have been also investigated. [Preview Abstract] |
Monday, March 14, 2016 11:27AM - 11:39AM |
B47.00002: Experimental and Computational Comparison of the Self-Assembled Nanostructures of Pentacene Derivatives on Gold Amanda Larson, Ryan Miller, Jun Wang, Karsten Pohl Pentacene derivatives can tailor the standard pentacene molecule for unique properties beneficial to organic photovoltaic devices. Increased solubility, photo-oxidative resistance, thermal stability and tailor-able HOMO-LUMO gaps make novel pentacene derivatives enticing for further study. Scanning tunneling microscopy and density functional theory was used to examine the atomic interface between gold and the pentacene derivatives: 6,13-dichloropentacene (DCP) and 5,6,7-trithiapentacene-13-one (TTPO), electron donors exhibiting self-assembled monolayer structures on gold surfaces. Comparing DCP, TTPO and pentacene highlights the effects of differing substituents to the self-assembled structures. In particular, the unique 3-dimensional angular assembly of TTPO is examined and clarified through use of extensive computation. The lateral arrangement of the molecule is unique, causing the thiol substituent side of the molecule to be angled down towards the gold surface, while the long-axis of TTPO is parallel to the gold surface; distinctive from previously observed pentacene and pentacene derivative assemblies. By understanding the differences in self-assembly of similar molecules, we are developing novel pathways towards molecular control of organic-metal interfaces. [Preview Abstract] |
Monday, March 14, 2016 11:39AM - 11:51AM |
B47.00003: Molecular assembly and organic film growth on complex intermetallic surfaces. Abdullah Al-Mahboob, Hem Raj Sharma, Jerzy T Sadowski, Julian Ledieu, Vincent Fournée, Ronan McGrath We extensively studied the role of molecular symmetry and symmetry/structures of wide ranges of substrate-surfaces from non-periodic to periodic to quasi-crystalline in nucleation, growth and phase transition in films made of organic molecular materials. Recently, most interest in quasicrystals is due to the generalization of aperiodic ordering to several classes of systems. Compared to periodic materials, these provide a closer approximation to an isotropic first Brillouin zone, which is of great importance to the design of new functional materials. Here, we present results obtained from our ongoing study of interface mediated molecular assembly extended on complex intermetallic surfaces with specific examples of C$_{60}$ and Zn-phthalocyanine on quasicrystalline and approximant surfaces. We employed in-situ real-time low-energy electron microscopy (LEEM) for investigation of the processes in assembly and film growth and post-growth STM study and DFT calculations to understand structural details and growth mechanism. [Preview Abstract] |
Monday, March 14, 2016 11:51AM - 12:03PM |
B47.00004: A theoretical and experimental investigation on the adsorption of pentacene on the Cu(322) surface Jeronimo Matos, Michele Sauvage-Simkin, Alessandro Coati, Yves Garreau, Alina Vlad, Kathrin Muller, Azzedine Bendounan, Abdelkader Kara In this study, complementary techniques including density functional theory (DFT), grazing incidence x-ray diffraction (GIXD), and scanning tunneling microscopy (STM) are used to study the surface distortions induced by the adsorption of pentacene on the stepped Cu(322) surface. GIXD measurements are performed for the clean Cu(322) surface and at various coverages of pentacene, up to one monolayer. For the one monolayer case, reciprocal space maps from GIXD measurement suggest the reconstruction of the steps to double the step width and height, with two pentacene molecules present at each terrace. Complementary DFT calculations are carried out, with and without the self-consistent inclusion of vdW interactions, using the optB88-vdW and PBE functionals. Our investigation illustrates a prototype method for conducting future benchmarking studies to assess the accuracy of the current self-consistent vdW functionals when applied to organic molecule adsorption. [Preview Abstract] |
Monday, March 14, 2016 12:03PM - 12:15PM |
B47.00005: Coverage Dependent Assembly of Anthraquinone on Au(111) Brad Conrad, Andrew Deloach, Theodore Einstein, Daniel Dougherty A study of adsorbate-adsorbate and surface state mediated interactions of anthraquinone (AnQ) on Au(111) is presented. We utilize scanning tunneling microscopy (STM) to characterize the coverage dependence of AnQ structure formation. Ordered structures are observed up to a single monolayer (ML) and are found to be strongly dependent on molecular surface density. While the complete ML forms a well-ordered close-packed layer, for a narrow range of sub-ML coverages irregular close-packed islands are observed to coexist with a disordered pore network linking neighboring islands. This network displays a characteristic pore size and at lower coverages, the soliton walls of the herringbone reconstruction are shown to promote formation of distinct pore nanostructures. We will discuss these nanostructure formations in the context of surface mediated and more direct adsorbate interactions. [Preview Abstract] |
Monday, March 14, 2016 12:15PM - 12:27PM |
B47.00006: Self-Assembly of Glycine on Cu (001): The tale of Temperature and Polarity Lifang Xu, Jing Xu, Zheshuai Lin, Sheng Meng, Enge Wang Glycine on Cu(001) is used as an example to illustrate the critical role of molecular polarity and finite temperature effect in self-assembly of bio-molecules at a metal surface. A unified picture for glycine self-assembly on Cu(001) is derived based on full polarity compensation considerations. Temperature plays a non-trivial role: the ground-state structure at 0 K is absent at room temperature, where intermolecular hydrogen bonding overweighs competing molecule-substrate interactions. The unique p(2×4) structure predicted as the most stable structure was confirmed by ab initio molecular dynamics simulations, whose scanning tunneling microscopy images and anisotropic free-electron-like dispersion are in excellent agreement with experiments. Moreover, the rich self-assembling patterns including the heterochiral and homochiral phases, and their interrelationships are entirely governed by the same mechanism. [Preview Abstract] |
Monday, March 14, 2016 12:27PM - 12:39PM |
B47.00007: Interaction of prophyrins with low coordinated sites on the MgO(001) surface Osman Baris Malcioglu, Michel Bockstedte The functionalization of metal oxide surfaces with porphyrins is achieved via site selective linker groups and a specific metal center in the macrocycle. Metal oxide surfaces like MgO(001) have got a rather inert prestine surface and reactive low coordinated sites such as steps and kink-sites. Recently the metallization of H2TPP with Mg via low coordinated sites on MgO(001) has been demonstrated. The underlying mechanisms, however, remain unclear. Here we address this issue. We study the adsorption of H2TPP on MgO(001) and its interaction with low coordinated sites employing ab initio molecular dyanmics simulations. We find that H2TPP is mobile on the surface due to steric hindrance from phenyl rings preventing physisorption of the macrocycle, until a step or kink site is encountered. Upon encountering such a site, H2TPP anchors itself to form a rather stable complex, and spontaneously deprotonates from the macrocycle. We discuss the electronic and structural properties of the adsorbate complex, the intermediate and the metallized porphyrins using (hybrid) TDDFT and many body perturbation theory, identifying various effects that can be used to uniquely identify presence of such complexes. [Preview Abstract] |
Monday, March 14, 2016 12:39PM - 12:51PM |
B47.00008: Molecular lifting, twisting, and curling during metal-assisted polycyclic hydrocarbon dehydrogenation. Davide Curcio, Luca Omiciuolo, Monica Pozzo, Paolo Lacovig, Silvano Lizzit, Naila Jabeen, Luca Petaccia, Dario Alfe, Alessandro Baraldi Through a combined experimental and theoretical approach, we show that coronene molecules adsorbed on Ir(111) undergo major changes in conformation during the dissociation process, which brings the molecules from a flat configuration to graphene, through a series of exotic configurations. The complex reaction path involves the tilting upwards of the molecules, which subsequently experience a rotation with respect to the surface. During the lifting, the C-C strain is initially relieved, while as the dehydrogenation proceeds, the molecules experience a progressive increase in the average interatomic distance, and gradually settle to form peculiar dome shaped nanographenes. This reaction mechanism can provide new insight into the surface assisted break-up mechanism of PAHs, which has been demonstrated to be an effective strategy for the synthesis of low dimensional carbon-based materials. Beside the peculiarity of the reaction pathway, using these processes we envisage the unique possibility of creating new structures with different functionalities by encapsulating single atoms below the carbon dome. [Preview Abstract] |
Monday, March 14, 2016 12:51PM - 1:03PM |
B47.00009: \textbf{Predictive Modeling of Metal-Organic Chains with Active Metal Site } Naseem Ud Din, Duy Le, Talat Rahman Creation, stabilization, characterization and control of single atom transition metal (TM) sites may lead to significant advancement of the next-generation catalyst. Motivated by the experimental results of Skomski et al. [1], we have performed density functional theory based calculations of TM-dipyridyltetrazine (DT) chains in which TM atoms are stabilized and separated by the DT molecules. Our calculations show that the formation energies of the chains are high, suggesting that these chains can easily be synthesized and stabilized. Moreover, by calculating the adsorption energies of CO, O$_{\mathrm{2\thinspace }}$and O atom on the metal atom sites of the chains we found that these molecules/atoms strongly bond to TM atoms Mo, Cr, Fe and Co occupying these sites, suggesting that these TM-DT chains are potential candidates for CO oxidation catalyst. Details of reaction pathway (energetic and kinetic) of CO oxidation on the chains will be also presented and discussed. [1] D. Skomski, C.D. Tempas, K.A. Smith, and S.L. Tait, "Redox-Active On-Surface Assembly of Organic Chains with Single-Site Pt(II)," Journal of the American Chemical Society \textbf{136}, 9862-9865 (2014). [Preview Abstract] |
Monday, March 14, 2016 1:03PM - 1:15PM |
B47.00010: \textbf{The impact of functional group on the electronic structure of coordination center} Zahra Hooshmand Gharehbagh, Duy L, Talat S Rahman While 9, 10 dicyano-anthracene (DCA) forms a coordination network on Cu(111) surface with Cu adatom coordinated by three DCA molecules [1], its isomers, 9,10-diisocyano-anthracene forms, surprisingly, molecular rows on the same surface [2]. To understand the impact of functional groups on the electronic structure of the coordination center, we have carried out density functional theory based calculations of the electronic structure of a set of naphthalene molecules with different functional groups (N, CN, NC, NH$_{\mathrm{2}}$, COH, COOH) adsorbed on Cu(111), with and without a Cu adatom. Our results show that while the interaction between the naphthalene backbone and the Cu(111) surface is dominated by van der Waals (vdW) forces, in all cases considered the functional group forms a covalent bond with the Cu (ad)atom (on) of the surface. The calculated differential charge redistribution shows that the strongest covalent bond is formed by the NC group, which differs remarkably from that formed by the CN group, while the vdW interaction is very similar in both cases. These results provide insights into the different surface coordination behavior of molecules with above-mentioned functional groups. 1. Pawin, G., et al., A Surface Coordination Network Based on Substrate-Derived Metal Adatoms with Local Charge Excess. Angewandte Chemie International Edition, 2008. 47(44): p. 8442-8445. 2. L. Bartels, Private communication. [Preview Abstract] |
Monday, March 14, 2016 1:15PM - 1:27PM |
B47.00011: Spin-Polarized Hybridization at the interface between different 8-hydroxyquinolates and the Cr(001) surface Jingying Wang, Andrew Deloach, Daniel B Dougherty Organic materials attract a lot of attention due to their promising applications in spintronic devices. It is realized that spin-polarized metal/organic interfacial hybridization plays an important role to improve efficiency of organic spintronic devices. Hybridized interfacial states help to increase spin injection at the interface. Here we report spin-resolved STM measurements of single tris(8-hydroxyquinolinato) aluminum molecules adsorbed on the antiferromagnetic Cr(001). Our observations show a spin-polarized interface state between Alq3 and Cr(001). Tris(8-hydroxyquinolinato) chromium has also been studied and compared with Alq3, which exhibits different spin-polarized hybridization with the Cr(001) surface state than Alq3. We attribute the differences to different character of molecular orbitals in the two different quinolates. [Preview Abstract] |
Monday, March 14, 2016 1:27PM - 1:39PM |
B47.00012: Adsorption of thiophene on Pt, Pd, Au, and Rh(100) surfaces with the role of the van der Waals' interaction Walter Malone, Jeronimo Matos, Abdelkader Kara We explore the adsorption of thiophene (C4H4S) on Pt(100), Au(100), Pd(100), and Rh(100) surfaces using density functional theory with and without self-consistent van der Waals interactions (vdWs). The six functionals we use are PBE, optB86b-vdW, optB88-vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2. We examine a variety of adsorption sites with the molecule's plane both parallel and perpendicular to the surface. In the case of parallel adsorption the highest binding energy occurs when the molecule is centered over a hollow site with the sulfur atom near an atop site. The highest adsorption energy for perpendicular configurations is achieved when the sulfur atom lies over a bridge site and the carbon atoms near hollow sites. We find that for thiophene on the coinage metals the vdW functionals predict higher adsorption energies than those predicted by the PBE functional. On the other hand, for thiophene on the reactive transition metal substrates only optB86b-vdW, optB88-vdW, and optPBE-vdW result in an enhancement in the adsorption energy over the PBE value. We also explore some of the electronic properties of the system including charge transfer and change in the work function. Our results indicate that adsorption characteristics depends heavily on the functional used and geometry. [Preview Abstract] |
Monday, March 14, 2016 1:39PM - 1:51PM |
B47.00013: Manipulating the dipole layer of polar organic molecules on metal surfaces via different charge-transfer channels Meng-Kai Lin, Yasuo Nakayama, Ying-Jie Zhuang, Chin-Yung Wang, Tun-Wen Pi, Hisao Ishii, S.-J. Tang The key properties of organic films such as energy level alignment (ELA), work functions, and injection barriers are closely linked to this dipole layer. Using angle resolved photoemission spectroscopy (ARPES), we systemically investigate the coverage-dependent work functions and spectra line shapes of occupied molecular orbital states of a polar molecule, chloroaluminium phthalocyanine (ClAlPc), grown on Ag(111) to show that the orientations of the first ClAlPc layer can be manipulated via the molecule deposition rate and post annealing, causing ELA at organic-metal interface to differ for about 0.3 eV between Cl-up and Cl-down configuration. Moreover, by comparing the experimental results with the calculations based on both gas-phase model and realistic model of ClAlPc on Ag(111) , we evidence that the different orientations of ClAlPc dipole layers lead to different charge-transfer channels between ClAlPc and Ag, a key factor that controls the ELA at organic-metal interface. [Preview Abstract] |
Monday, March 14, 2016 1:51PM - 2:03PM |
B47.00014: Coulomb blockade and charge ordering in a few layers of TTF-TCNQ investigated by low-temperature STM/STS Seokmin Jeon, Petro Maksymovych In contrast to the vast effort on bulk crystal phases of the prototypical organic charge-transfer complex, TTF-TCNQ, study of low-dimensional phases has been limited to monolayer phases on substrates. In this state, however, none of the physics of the bulk phase is observed owing to the overwhelming effect of the substrate. We investigate the molecular structure and electronic properties of a few layers of TTF-TCNQ grown on Au(111) and Ag(111) using STM/STS at 4.3 K. By decoupling the molecular electronic state from the metal surface, we have made the first observation of the effect of confinement on the electronic properties of TTF-TCNQ. STS reveals a plethora of sharp features due to molecular orbitals, each influenced by charge-transfer between the molecules. We hypothesize the existence of a Mott-insulator state in 3-layer islands, with a Coulomb gap of \textasciitilde 1 eV. In contrast, the corresponding bulk phase is a Peierls insulator with a gap of \textasciitilde 20 meV. The root cause of the nanoscale phase is traced to simultaneous electron confinement and structural frustration, which dramatically modify the energy balance of self-ionization allowing for integer charge transfer. These studies open broad opportunities to explore correlated electron physics in molecular systems. [Preview Abstract] |
Monday, March 14, 2016 2:03PM - 2:15PM |
B47.00015: The evolution of phases and electronic states in potassium doped coronene film Chaoqiang Xu, Xudong Xiao Alkali-metal-doped hydrocarbon materials have been found to exhibit improved superconductivity transition temperature Tc relative to the traditional organic superconductors. However, theoretical attempts to understand the superconductivity mechanism in this class of materials are still hindered by the limited experimental information available. In our study, we employed scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) to detect both the structures and the electronic properties of the doped hydrocarbon films at molecular scale. By gradually increasing potassium doping level, the evolution of structures and electronic properties in potassium doped coronene film was then investigated. Particularly, a splitting of the lowest unoccupied molecular orbital (LUMO) state was observed when the LUMO was brought to the Fermi level, giving direct evidence of electronic correlation effect in this system. Our results should contribute to a better understanding of the interaction between coronene molecules and potassium atoms and may shed some light to understand the superconductivity properties of this system. [Preview Abstract] |
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