Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J12: Organic Electronic Thin Films |
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Sponsoring Units: DMP DCMP Chair: Renee Diehl, Penn State University Room: 308 |
Tuesday, March 17, 2009 11:15AM - 11:27AM |
J12.00001: Valence band structure in crystalline pentacene thin films Richard Hatch, David Huber, Hartmut H\"ochst Organic semiconductors, such as pentacene (Pn), are beginning to show promise as a low-cost substitute for conventional semiconductors for a variety of electronic devices. The overlap of $\pi $-orbitals in the Pn crystal leads to molecular orbital-derived bands. We used angle-resolved photoemission spectroscopy (ARPES) to reveal the Pn in-plane band structure of the two highest occupied molecular orbital-derived bands in crystalline thin film Pn (grown on a Bi substrate) for various temperatures between 75 K and 300 K. We mapped these two bands in several crystallographic directions with special attention given to the region near the top of the valence band and show, within the limits of our experimental resolution, that temperature does not change the dispersions of these bands. We fit the band structure to a tight binding model and compared our results with recent theoretical predictions[1-2]. We also calculated the in-plane reciprocal effective mass for the $\bar {M}$ point and compared it with the measured mobility. [1] H. Yoshida \textit{et. al.} Phys. Rev. B \textbf{77}, 235205 (2008). [2] G. A. de Wijs \textit{et. al.} Synth. Met. \textbf{139}, 109 (2003). [Preview Abstract] |
Tuesday, March 17, 2009 11:27AM - 11:39AM |
J12.00002: The growth mechanism of anisotropic organic molecular films A. Al-Mahboob, Y. Fujikawa, J.T. Sadowski, Qikun Xue, T. Sakurai The anisotropy in molecular structure and crystal packing may complicate nucleation and growth processes in organic molecular films. The growth mechanism of pentacene (Pn) films has been studied by real time low-energy electron microscopy. Pn is most promising for FET application as it shows the highest field-effect mobility among organic thin-films. We observed delayed nucleation and formation of large grains (as large as 0.5 mm in diameter) on semiconducting $\alpha \surd $3-Bi-Si(111) and on semi-metallic Bi(0001)/Si(111), with a significant delay in film growth after stopping Pn deposition, indicating long diffusion time. This is in contrast to the growth of Pn on SAMs, oxides or wetting layer on clean silicon surfaces. The long diffusion time could be explained by large barrier for Pn nucleation with standing-up orientation from a lying-down diffusing state due to stronger interaction between lying molecules and Bi-treated substrates. [Preview Abstract] |
Tuesday, March 17, 2009 11:39AM - 11:51AM |
J12.00003: Morphology and Crystalline Structure of the Epitaxial Growth of Tetracene Thin Films on H/Si(001)-2x1 Substrate Andrew Tersigni, De-Tong Jiang, Xiaorong Qin Epitaxial growth of tetracene films on H/Si(001)-2x1 surface has been studied systematically using AFM, STM and X-ray diffraction. The surface morphology and in-plane lattice structure observed from AFM and STM are compared with that extracted from the diffraction measurements to reach a consistent description on the in-plane and out-plane lattice parameters of different epitaxial domains, respectively. The influence of the substrate roughness and film coverage to the morphology and underlying lattice structures will be discussed in the light of various characteristics revealed by the multiple structural tools. [Preview Abstract] |
Tuesday, March 17, 2009 11:51AM - 12:03PM |
J12.00004: Structural investigation of pentacene on Ag(111) by density functional theory Fatih Danisman, Ersen Mete, Sinasi Ellialtioglu We have used density functional theory (DFT) calculations based on the projector augmented wave (PAW) method to investigate the initial growth patterns of pentacene (C$_{22}$H$_{14})$ on Ag(111) surface. Here we will report our initial findings and provide a discussion of the results from the point of view of our previous experimental findings. Pentacene prefers to stay planar on Ag(111) surface and aligns perfectly along lattice vector (1,-1,0) without any molecular deformation at a height of 3.74 {\AA}. At 1 ML coverage the separation between the molecular layer and the surface plane extends to 4.14 {\AA} due to intermolecular interactions weakening surface-pentacene attraction. While the first ML remains flat, the molecules on a second full pentacene layer rearrange in a herringbone fashion which is energetically slightly more preferable when compared with a second layer composed of flat lying molecules. With addition of third and fourth layers pentacene molecules continue to maintain the herringbone configuration, with the stability of the herringbone configuration relative to the flat one increasing to 0.13 eV for the 3 ML film, while the first ML always remains flat. Therefore, our calculations indicate bulk-like initial stages for the growth pattern. [Preview Abstract] |
Tuesday, March 17, 2009 12:03PM - 12:15PM |
J12.00005: Magnetic and structural behaviors of transitional metallo-porphines monolayer and bilayer on Ag(111) X.Q. Tian, J.B. Xu Five monolayers and bilayers of transitional metallo-porphine(MP) (Mn, Fe, Co, Ni, Cu) on Ag(111) substrate are investigated by \textit{ab initio }calculation. The strong coupling of FeP and CoP MP/Ag(111) interface leads to magnetic-nonmagnetic transition. The competition mechanism between intermolecular ferromagnetic exchange interaction and coupling of FeP/Ag(111) prevents the magnetic-nonmagnetic transition of interface. The top layer of all 5 bilayers keeps their intrinsic magnetic properties and planar structures, so the bottom layer of the bilayer serves the role of buffer layer. These theoretical results could be used to explain the recent STM and XPS experiments. A new interfacial magnetic competition mechanism has been proposed and hopefully it will influence the construction and design of future molecular spintronics. [Preview Abstract] |
Tuesday, March 17, 2009 12:15PM - 12:27PM |
J12.00006: Quantitative Grain Size Distributions of Magnetic Organic Thin Films Thomas Gredig, K. Paul Gentry, Ivan K. Schuller Many electronic, optical, and magnetic properties of organic thin films depend on the precise morphology of grains. Quantitative grain size distributions of an asymmetric organic molecule are presented and correlated with the magnetic characteristics. Iron phthalocyanine (FePc) thin films are grown on sapphire substrates at varied deposition temperatures to study the effect of grain growth and to experimentally quantify the grain size distributions in organic thin films based on atomic force microscopy images. The data of over 3000 grains for each sample show a pronounced asymmetric growth of grains from a spherical to an elongated needle-like shape. The size along the major axes increases from 35nm to 200nm and is distributed in a different way than the minor axes, which grow from 25nm to 90nm. The dissimilar distributions are attributed to an asymmetric growth rate. Low-temperature hysteresis loops and temperature-dependent magnetization curves for these FePc thin films illustrate the effect of the length of quasi one-dimensional Fe chains on the magnetic properties. [Preview Abstract] |
Tuesday, March 17, 2009 12:27PM - 12:39PM |
J12.00007: The structure of the $\mathrm{C}_{60}$ monolayer on Pb(111) Hsin-I Li, Katharina Franke, Jose Pascual, Renee Diehl Low-energy electron diffraction and scanning tunneling microscopy studies indicate that a monolayer of $\mathrm{C}_{60}$ on Pb(111) forms a modulated structure having an average $\mathrm{C}_{60}$-$\mathrm{C}_{60}$ nearest-neighbor distance of about 10\AA, but a period of about 46\AA. The data were analyzed in the context of the Tkatchenko method$\,^{\dag}$, and the monolayer structure was identified as two coexisting higher-order commensurate structures, namely $(\sqrt{169}\times \sqrt{169})R16.90\,^{\circ}$ and $(\sqrt{169}\times \sqrt{169})R21.31\,^{\circ}$, both with 21 $\mathrm{C}_{60}$ molecules and 169 Pb atoms in their unit cells. This modulated structure has implications for the electronic structure of the $\mathrm{C}_{60}$ film, as measured using scanning tunneling spectroscopy. \newline $\,^{\dag}$A. Tkatchenko, Phys. Rev. B 75, 235411 (2007). [Preview Abstract] |
Tuesday, March 17, 2009 12:39PM - 12:51PM |
J12.00008: The structures of a C$_{60}$ monolayer on Al(111) Heekeun Shin, Hsin-I Li, Katariina Pussi, Renee Diehl The interfaces of C$_{60}$ films with metal surfaces are of particular interest for molecular electronics applications. 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, C$_{60}$ on Al(111) forms a (2$\surd $3x2$\surd $3)R30\r{ } structure with one C$_{60}$ molecule per unit cell, which upon heating converts to a 6x6 structure with 3 C$_{60}$ molecules per unit cell. We present a LEED study of the transition between these structures, a LEED I(E) analysis of the 6x6 structure, and characterization of the adsorption of rare gases onto the surface of the 6x6 C$_{60}$ film. This research is supported by NSF-DMR-0505160 and the Academy of Finland. [Preview Abstract] |
Tuesday, March 17, 2009 12:51PM - 1:03PM |
J12.00009: The Adsorption of C$_{60}$ fullerene molecules on Nanostructured Au (111) Xin Zhang, Quanmin Guo, Richard Palmer The sub-monolayer growth of C$_{60}$ molecules on the Au (111) surface has been studied using STM in ultra high vacuum. The C$_{60}$ molecules tend to form close-packed layers due to a strong inter-molecular interaction. However, within the close-packed layer, there are finer, secondary structures that are specific to each of all the three C$_{60}$/Au interfacial structures ((2$\surd $3$\times $2$\surd $3)R30\r{ }, in-phase (R0\r{ }) and R14\r{ }) observed [1]. This is a consequence of the molecule-substrate interaction and our findings demonstrate a much more complex structural variation at the molecule-substrate interface than previously assumed. Furthermore, within the R14\r{ } C$_{60}$ layer, slightly darker molecules (30 pm lower) aligned along the \~{a}11-2\~{o} direction with a $\sim $6 nm spacing are observed and these molecules are arranged in a reasonably well-ordered two-dimensional lattice. C$_{60}$ molecules are also found to decorate the elbow sites of the herringbone reconstructed Au(111) even at room, and when fullerenes are deposited to arrays of fabricated monolayer gold stripes (gold-fingers) [2], the molecules show step-specific attachment where the step edges with the (111) micro-facet are preferentially populated.\\[0pt] [1] X. Zhang, F. Yin, R. E. Palmer and Q. Guo, \textit{Surf. Sci.} 602 (2008) 885-892.\\[0pt] [2] Q. Guo, F. Yin and R. E. Palmer, \textit{Small} 1 (2005) 76-79. [Preview Abstract] |
Tuesday, March 17, 2009 1:03PM - 1:15PM |
J12.00010: Towards 2-D Conjugated Organic Polymers; Br-TTA molecules on Cu(111) J.A. Lipton-Duffin, M.C. Gallagher, J.L. Brusso, D.F. Perepichka, F. Rosei We report on recent experiments using an Ullmann surface polymerization approach to synthesize 2-d polymers on flat metal surfaces in UHV. We previously demonstrated the utility of this technique to perform the surface confined synthesis of individual conjugated polyphenylene chains the Cu(110) surface [1]. In the present work we extend this technique to deposit multidendate Br-TTA monomers onto a Cu(111) surface. The evaporation of Br–TTA monomers at room temperature leads to the formation of flat 2-d islands at submonolayer coverage. We use STM and XPS to investigate the structural and chemical characteristics of these structures. Upon annealing (500K) many of the islands restructure to form highly ordered 2-d nanostructures. These structures are quite robust and are stable up to temperatures of 800K at which point the TTA desorbs.\\[3pt] [1] Lipton-Duffin, Ivasenko, Perepichka and Rosei, in preparation. [Preview Abstract] |
Tuesday, March 17, 2009 1:15PM - 1:27PM |
J12.00011: Interactions of sulfur with graphite Ko Munakata, Theodore Geballe, Malcolm Beasley Possible evidence for very high temperature superconductivity at the interface of sulfur and graphite in composite materials has been reported in the literature [1]. To examine better this possibility, we are studying the interfacial electronic properties of thin UHV deposited layers of sulfur and other overlayers on graphite and few-layer graphene by means of in-situ UPS and XPS. The results of this study and its implications for the possibility of superconductivity will be presented. [1] S. Moehlecke, Y. Kopelevich, and M. B. Maple, Phys. Rev. B 69, 134519 (2004). [Preview Abstract] |
Tuesday, March 17, 2009 1:27PM - 1:39PM |
J12.00012: Surface and trapped charge characterization of epitaxial oxides for applications in graphene electronics$^{1}$ Blake Riddick, Brad Conrad, William Minshew, William Cullen, Ellen Williams, Tassilo Heeg, Darrell Schlom Trapped charges have been shown to play an important role in the transport properties of graphene supported on SiO$_{2}$, and surface roughness may also play a role. Alternative substrate materials, Sc$_{2}$O$_{3}$ ($\varepsilon \sim $ 14, $n\sim $ 1.9) and Gd$_{2}$O$_{3}$ ($\varepsilon \sim $ 22, $n\sim $ 2) were grown epitaxially by molecular beam epitaxy on Si(111) over a range of thicknesses from 2 nm to 100 nm. AFM measurements yield rms roughness, and correlation function analysis reveals the nature of the long range order. For Sc$_{2}$O$_{3}$, the roughness is strongly thickness dependent, with root-mean-square height 0.26 nm$^{2}$ for a 20 nm thick film and 0.55 nm$^{2}$ for a 65 nm thick film; however, the correlation exponent (2$H\sim $ 1) and correlation length ($\xi \sim $ 20 nm) are the same. The roughness characterization for the full range of thicknesses of both oxides will be presented. In addition, frequency-dependent CV measurements are underway to determine the trapped charge densities. [1] supported by a NRI supplement to the UMD-NSF-MRSEC grant {\#} DMR 0520471. [Preview Abstract] |
Tuesday, March 17, 2009 1:39PM - 1:51PM |
J12.00013: Morphology of hydrocarbon films on decagonal Al-Ni-Co quasicrystalline surfaces Wahyu Setyawan, Renee D. Diehl, Majid Karimi, Stefano Curtarolo Lubricants can affect quasicrystalline coatings by modifying commensurability. We present simulation studies of physically adsorbed hydrocarbons on a decagonal surface of a Al-Ni-Co quasicrystal. We use the Grand Canonical Monte Carlo technique with novel embedded-atom-method potentials fitted to {\it ab initio} calculations and standard hydrocarbons interactions. Methane forms pentagonal structure, benzene monolayer adsorbs in hexagonal domains with 5 orientational degeneracies induced by the substrate, propane forms pentagonal domains with significant disorder, hexane and octane monolayers shows linear ordering. The results support the potential use of quasicrystals as low friction coatings. [Preview Abstract] |
Tuesday, March 17, 2009 1:51PM - 2:03PM |
J12.00014: First principles study of aromatic molecules on Copper substrates Andrea Ferretti, Arrigo Calzolari, Rosa Di Felice, Alice Ruini, Elisa Molinari Conjugated molecules and oligomers have attracted large attention in the last years due to their interesting electronic and transport properties. The interaction of these molecules with metallic surfaces is attractive both for the properties of the metal-organic interface and for the possibility of tuning the crystal structure of the films using the surface as a template. In the present work we focus on an ab initio investigation based on density functional theory of pentacene adsorbed on Copper surface. We also compare with the case of the DPDI molecule adsorbed on the same substrate. We address structural and electronic properties, and we relate our results to experimental data, STM, XSW, and angle resolved photoemission spectroscopy in particular. Our theoretical findings show a flat adsorption geometry for both pentacene and DPDI molecules. For what concerns the electronic structure, a strong rehybridization of the molecular electron states is found in the range of the occupied $\pi$ states. These results lead to an interpretation of the adsorption mechanism of pentacene in terms of a coupling intermediate between the physi- and the chemi-sorption regimes. [Preview Abstract] |
Tuesday, March 17, 2009 2:03PM - 2:15PM |
J12.00015: Highly Sensitive Molecular Sensing on Optimally Modified Graphene Monolayers John Russell, Petr Kral We develop a methodology of molecular sensing on optimally modified graphene monolayers. The idea is to modify the monolayers by atomistic (substitution) doping or by covalent binding of short charged ligands at selected positions in such a way that the created local electric fields form selective molecular nests for inorganic, organic and biological molecules [1]. We show by molecular dynamics simulations the nesting of small organic molecules and peptides on modified graphene ribbons. The nested molecules can be detected by electronic, optical or vibrational means [2]. The method is highly sensitive and, at low temperatures, it can even distinguish the configurations of the nested molecules.\\[3pt] [1] B. Wang and P. Kr\'{a}l, Small 3, 580 (2007).\\[0pt] [2] J. Russell and P. Kr\'{a}l, in preparation. [Preview Abstract] |
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