Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session L20: Focus Session: Self-Assembled Organic Overlayers |
Hide Abstracts |
Sponsoring Units: DMP Chair: Philip Cohen, University of Minnesota Room: Morial Convention Center 212 |
Tuesday, March 11, 2008 2:30PM - 3:06PM |
L20.00001: Self-assembly at the liquid/solid interface: from patterns to function Invited Speaker: Self-assembly - the spontaneous organization of molecules into stable, structurally well-defined aggregates - has been put forward as a possible paradigm for generating nanoscale templates under ambient conditions. A very convenient method for the formation of extended two-dimensional (2D) networks is physisorption at the liquid-solid interface. The preparation is relatively simple and scanning tunneling microscopy (STM) allows a detailed investigation of the structural aspects of the 2D patterns. A deep understanding and control of the spatial orientation and packing of molecules in self-assembled systems is indispensable for the development of future nanodevices. We have developed hydrophobic - hydrophylic nanopatterns at electrified surfaces via the self-assembly of amphiphilic molecules. For this purpose we selected 5-hexadecyloxy isophthalic acid: this neutral amphiphile forms hydrogen-bonded rows that are commensurate with the Au(111) surface. Based on the successful adsorption of these amphiphiles, multicomponent architectures have been realized at these electrified surfaces as the result of the potential directed assembly of charged and non-charged molecular systems. Following a slightly different approach, nanoporous two-dimensional networks were formed at the interface between an organic liquid and highly oriented pyrolytic graphite. Pore sizes of more than 5 nm in diameter can be realized. As an alternative approach to make nanoporous two-dimensional networks, molecular defined shape-persistent two-dimensional oligomers, such as molecular spoked wheels, are used. [Preview Abstract] |
Tuesday, March 11, 2008 3:06PM - 3:18PM |
L20.00002: Stress-Induced Striped Domains at the C$_{60}$-Pentacene Interface* Daniel Dougherty, Wei Jin, William Cullen, Gregory Dutton, Janice Reutt-Robey, Steven Robey C$_{60}$:pentacene heterojunctions have been recently employed in functional organic photovoltaic devices [1]. In order to develop a detailed structural understanding of these junctions, we have made STM observations of the growth of pentacene on top of a monolayer film of C$_{60}$ on Ag(111). We observe pattern formation in the first pentacene layer due to the tensile stress arising from interactions with the underlying C$_{60}$. The stress results in a striped pattern of alternating commensurate and incommensurate domains of pentacene with respect to the C$_{60}$ monolayer. The incommensurate domains appear as bright regions 3.6 $\pm $ 0.6 nm in width and are discussed using a 1D Frenkel-Kontorova model. *Supported by the NIST Center of Nanomanufacturing and Metrology and the University of Maryland MRSEC via DMR-05-20471.[1] Yoo et al., Appl. Phys. Lett. 85, 5472 (2004). [Preview Abstract] |
Tuesday, March 11, 2008 3:18PM - 3:30PM |
L20.00003: The growth mechanism of Pentacene-C$_{60}$ heteroepitaxial films A. Al-Mahboob, J.T. Sadowski, Y. Fujikawa, T. Sakurai Pentacene (Pn) and fullerene (C$_{60})$ are of great interest among organic semiconductors as they show highest field-effect hole and electron mobilities respectively. The absorption peak in Pn crystal is located close to maximum of solar visible spectra, making a bipolar Pn-C$_{60}$ diode promising for solar cell application. In order to improve its efficiency to satisfy the requirement for practical application, an in-depth understanding of Pn-C$_{60}$ interface formation is necessary for further optimization. We shall discuss the growth mechanism of Pn-C$_{60}$ heteroepitaxial films on Bi(0001)/Si(111) substrate studied by real time low-energy electron microscopy and complementary scanning tunneling microscopy. A competitive growth between a thin-film phase of Pn having standing-up orientation and a phase with laying-down orientation has been observed. The growth of laying-down phase is suppressed gradually with increasing film thickness. The nucleation of this phase is also suppressed with increasing temperature and the standing up phase without co-presence of laying down phase is achievable at $\sim $75\r{ }C. [Preview Abstract] |
Tuesday, March 11, 2008 3:30PM - 3:42PM |
L20.00004: Self-Limiting C$_{60}$-Pentacene Network on Ag(111) Wei Jin, Daniel Dougherty, Gregory Dutton, William Cullen, Steven Robey, Janice Reutt-Robey During Scanning Tunneling Microscopy investigations of C$_{60}$:Pentacene (Pc) interfaces on Ag(111), we identified a new network structure. This binary arrangement forms readily by sequential deposition: Pc, of $\sim $0.3 mL coverage, is first evaporated onto the Ag(111), forming a 2-D gas. Subsequent C$_{60}$ deposition produces a network, consisting of chains of close-packed C$_{60}$ molecules, spaced by C$_{60}$ molecules. The characteristic 1 x 2.5 nm$^{2}$ pores are sized to accommodate Pc molecules. Spontaneous formation of this structure from an iniital Pc coverage ranging from 0.3 to 0.6 mL, indicates a self-limiting assembly process. Drawing upon topographic and Z(V) measurements, we propose a structural model and describe molecular mechanisms that could cause this self-limiting behavior. [Preview Abstract] |
Tuesday, March 11, 2008 3:42PM - 3:54PM |
L20.00005: Guest-host interaction of C$_{60}$ adsorbed on an ordered layer of phthalocyanine derivatives Tomas Samuely, Meike Stoehr, Nikolai Wintjes, Thomas A. Jung, Marco Haas, Shi-Xia Liu, Silvio Decurtins Symmetrically substituted phthalocyanines (Pcs) with eight peripheral di-(tert-butyl)phenoxy (DTPO) groups self-organize on noble metal substrates. The rotational degrees of freedom, specific for the DTPO substituents, allow a bowl-like conformation of the Pc derivatives and thus, hosting of the C$_{60}$ molecules in two clearly distinguishable binding sites. Moreover, controlled manipulation of the C$_{60}$ by the STM tip enables switching from one site to the other. Since Pcs are well-known electron donors and C$_{60}$ molecules are good acceptors, it can be conceived as a system with two morphologically different donor-acceptor complexes, individually addressable by an STM tip. Preliminary STS analysis shows vast differences in the electronic properties. Exploration of such a system is of great interest because of its similarity to fundamental biological processes (photosynthesis, respiration), as well as its potential for application in energy storage, conversion, nanoelectronics, etc. [Preview Abstract] |
Tuesday, March 11, 2008 3:54PM - 4:06PM |
L20.00006: Scanning Tunneling Microscopy Investigation of Ordered Iron Phthalocyanine Molecules on Ag(111) Ken Park, Kedar Manandhar, S. Ma, Jan Hrbek A well-ordered, molecular thin films (about 0.5 monolayers) of iron phthalocyanine (FePc) on Ag(111) has been investigated using a scanning tunneling microscopy. The room temperature deposition, followed by 30 minutes of annealing up to 475 K results in well-ordered islands of FePc molecules which form a two-dimensional, oblique lattice. The overlayer lattice vectors \textbf{a}$_{1}$ and \textbf{b}$_{1 }$are 16.2 {\AA} each with the angle of 80\r{ } between the lattice vectors. The FePc overlayer lattice is commensurate to the substrate lattice with the relationship of \textbf{a}$_{1}$ = 6\textbf{a} - \textbf{b} and \textbf{b}$_{1}$ = -\textbf{a} + 6\textbf{b}, with \textbf{a} and \textbf{b} are the Ag(111) lattice vectors. Furthermore, FePc molecules at the opposite corners within the unit cell align their isoindole rings at each other, significantly increasing the nearest and the next-nearest neighbor distances in the overlayer. The commensurate overlayer lattice structure and the distinct molecular orientation within the unit cell are attributed to the molecule-surface interaction via the Fe 3d$_{xz,yz}$ and Ag 4d$_{xz,yz}$ orbitals. [Preview Abstract] |
Tuesday, March 11, 2008 4:06PM - 4:18PM |
L20.00007: Self-assembly of functionalized fullerenes on strained metallic interfaces. Bogdan Diaconescu, Mikael Jazdzyk, Glen Miller, Karsten Pohl The process of growing ordered arrays of molecules or nanometer sized clusters with tailorable properties on the dislocation networks of strained metallic thin films requires a detailed understanding of the nucleation processes and film-molecule and intermolecular interactions. We compare two different self-assembly mechanisms of functionalized fullerenes on strained metallic films of Ag on Ru(0001). We found that by controlling the molecular coverage and/or the strain in the thin film, various interactions can dominate the self-assembly process, thus resulting in a richness of structures with controllable properties. At low molecular coverage on 1 monolayer Ag films on Ru(0001), ordered triangular arrays of clusters, 4.9 nm apart, with a tunable number of molecules can be grown. This process is driven by strain relaxation in the metal film, as confirmed by 2D Frenkel-Kontorova models, and was found to be a general one working for various functionalized molecules. At higher molecular coverage and different Ag film thickness, the intermolecular interaction becomes dominant and the symmetry and unit cell size of the self-assembled monolayer are a consequence of the molecular structure and functionality. Both these processes are generally applicable to many functionalized C60 molecules thus opening avenues towards complex self-assembled structures based on lock and key type approach. [Preview Abstract] |
Tuesday, March 11, 2008 4:18PM - 4:30PM |
L20.00008: Morphology of thin organic semiconductor layers on vicinal (0001) sapphire surface Gvido Bratina, Primo\v{z} Rebernik Ribic Morphology of pentacene, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), rubrene, and N,N$'$-diphenyl-N,N$'$-bis(3-methylphenyl)-1,1$'$-diphenyl-4,4$'$-diamine (TPD) layers grown on vicinal (0001) sapphire surface was examined by non-contact atomic force microscopy ex situ. The layer thickness ranged from a submonolayer coverage to up to four molecular layers. Pentacene was found to nucleate at the nm-size sapphire steps, and continues to grow on the terraces in a layer-plus-island growth mode. PTCDA nucleates randomly at room temperature, while at 135$^{\circ}$C and low coverage the molecules aggregate at the steps. At increased coverage the island growth proceeds in the directions determined by the intermolecular interactions and not along the steps. Rubrene and TPD nucleate in 3D islands that evolve over time by ripening. TPD nucleates along the steps and also ripening proceeds along the steps. The rate of ripening of rubrene islands is one order of magnitude slower than the rate of ripening of TPD. We associate this difference to the wealth of rotational degrees of freedom in TPD molecules as opposed to only twisting degree of the tetracene backbone in rubrene. [Preview Abstract] |
Tuesday, March 11, 2008 4:30PM - 4:42PM |
L20.00009: Organic Vapor-Liquid-Solid Deposition for Controlled Growth of Organic Semiconductor Films. David Patrick, Brad Johnson Thin films of low molecular weight organic semiconductors (OS) are drawing much attention for their potential use in a range of different applications. Because the optical and electronic properties of OS films are extremely sensitive to structural imperfections, domain size, and crystallographic orientation, preparation of high quality thin films with controlled microstructural organization under technologically favorable conditions has long been a bottleneck toward practical applications and better controlled fundamental studies. Here we describe an approach for fabricating OS films that comes close to achieving these demanding objectives. The main advance is the combined use of atmospheric pressure vapor-phase deposition into a thermotropic liquid crystal (LC) solvent, which is applied as a thin coating onto a supporting substrate, providing an organized fluid environment in which OS crystals nucleate and grow. The technique produces relatively large crystals, enables control over crystallographic orientation, growth habit, and size, and involves near ambient conditions compatible with a variety of substrates and inexpensive processing conditions. Results will be presented for the model compounds tetracene and pentacene. [Preview Abstract] |
Tuesday, March 11, 2008 4:42PM - 4:54PM |
L20.00010: Structure and adsorption mechanisms of thiol self-assembled monolayers on GaAs (001) surfaces Oleksandr Voznyy, Jan J. Dubowski Self-assembly of organic molecules on solid substrates attracts a lot of interest from both fundamental and practical perspectives. Particularly, alkanethiol SAMs on GaAs surfaces can be used, e.g., for surface passivation, bio- and chemical sensing, molecular electronics and nanolithography. However, the progress of the investigation of this material system is hindered by problems of reproducibility of SAMs growth due to insufficient understanding of the deposition process on the atomic level and a lack of experimental characterization techniques. In this work, we present the results of ab initio modeling of thiol SAMs on GaAs (001) surface which helps to resolve the SAM structure, chemistry of bonding to substrate, adsorption kinetics and energetics. We also compare the GaAs case to a prototypical system of thiols on Au and discuss differences the semiconductor surface brings to the process. [Preview Abstract] |
Tuesday, March 11, 2008 4:54PM - 5:06PM |
L20.00011: Self-assembly of long chain alkanes and their derivatives on graphite Teng Yang, Savas Berber, David Tom\'anek, Jun-Fu Liu, Glen P. Miller We combine scanning tunneling microscopy (STM) measurements with {\em ab initio} calculations to study the self-assembly of long chain alkanes and related alcohol and carboxylic acid molecules on graphite. For each system, we identify the optimum adsorption geometry and explain the energetic origin of the domain formation observed in the STM images. Our results for the hierarchy of adsorbate-adsorbate and adsorbate-substrate interactions provide a quantitative basis to understand the ordering of long chain alkanes in self-assembled monolayers and ways to modify it using alcohol and acid functional groups. [Preview Abstract] |
Tuesday, March 11, 2008 5:06PM - 5:18PM |
L20.00012: Theoretical Modelling of Self-Assembly of Molecular Networks Manuela Mura, Natalia Martsinovich, Lev Kantorovich The phenomenon of self-assembly of atomic and molecular superstructures on crystal surfaces has attracted an increasing interest in nanotechnology. Self-organised nano-templates where the self-assembled monolayer traps other molecules with selected functional properties, can be used as building blocks for larger nanoscale structures. These superstructures can form chiral domains ranging from 1D chains to 2D monolayers. In particular, there have been many scanning tunneling microscopy (STM)studies of self-assembly of melamine, perylene tetra-carboxylic di-imide(PTCDI) or perylene tetra-carboxylic di-anhydride (PTCDA) molecules on the Au(111). STM images of these networks do not reveal the exact details of the intermolecular bonding and process of network growth. It is therefore the task of theory to determine the exact atomic structure of these networks. We present a theoretical study of self-assembly of molecular networks based on different molecules by using a systematic approach to build molecular superstructures. The energies of these structures are calculated using the density-functional theory SIESTA code. The theoretically predicted monolayer structures are in very good agreement with the results of STM measurements. [Preview Abstract] |
Tuesday, March 11, 2008 5:18PM - 5:30PM |
L20.00013: Polymerization of a perylene derivative on a metal surface Manfred Matena, Jorge Lobo-Checa, Meike Stoehr, Kathrin Mueller, Thomas A. Jung, Till Riehm, Lutz H. Gade By utilizing the concepts of supramolecular chemistry, impressive results for molecular self-assembly on surfaces have been presented. Mostly, non-covalent interactions like metal coordination, hydrogen bonding or dipolar coupling are exploited to create supramolecular patterns. One approach to influence these structures relies mainly on the sophisticated design of the molecular functional groups. Thus it makes use of properties already inherent to the molecules. In our work we have chosen a different concept. A thermally-induced surface-assisted reaction was used to modify the endgroups of a perylene derivative (TAPP) and thereby, the molecular interactions are altered. TAPP was found to form a closed-packed assembly on Cu(111), whereas the molecular interactions are based upon vdW-forces. After annealing at 150\r{ }C, a rectangular network is obtained which is commensurate to the underlying Cu surface. In this case the organic molecules coordinate to Cu atoms through the lone pairs of their nitrogen atoms. A second annealing step at temperatures $>$240\r{ }C modifies the molecule on the surface and leads to covalently linked polyaromatic chains. [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