Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session D42: Self-Ordering Nanostructures |
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Sponsoring Units: DCMP Chair: Karsten Pohl, University of New Hampshire Room: Colorado Convention Center 505 |
Monday, March 5, 2007 2:30PM - 2:42PM |
D42.00001: Novel mechanisms for self-assembled pattern formation in nanoscopic metal films R. Kalyanaraman, J. Trice, C. Favazza, D. Thomas, R. Sureshkumar Classical hydrodynamic theory of dewetting of spinodally unstable thin films (\emph{Vrij, Disc. farad. Soc. 1966}) predicts a monotonic increase in patterning length scales with increasing film thickness. We verified this effect for nanoscopic Co metal films following melting by ns laser pulses for thickness regime $h\leq h_{c}\sim8\, nm$ (\emph{Favazza et al. Nanotechnology, 2006}). However, a dramatic change is observed beyond this thickness $h_{c}$, with length scales decreasing with increasing $h$. This novel behavior arises from strong thickness dependence of heating by ultrafast laser light resulting in thermocapillary effects, whose magnitude and sign are thickness dependent. We modified the classical theory, according to which the instability occurs when the stabilizing capillary force is overcome by destabilizing attractive long-range interactions, to include thermocapillary effects. The modified theory accurately predicts the experimentally observed trend. This result suggests that a variety of new length scales can be accessed by robust self-assembly via dewetting of metal films under ultrafast light. [Preview Abstract] |
Monday, March 5, 2007 2:42PM - 2:54PM |
D42.00002: Growth and ordering of gas films on a decagonal AlNiCo quasicrystal surface W. Setyawan, R.D. Diehl, N. Ferralis, M.W. Cole, S. Curtarolo The growth and ordering of Ne, Ar, Kr, and Xe films on a decagonal surface of Al$_{73}$Ni$_{10}$Co$_{13}$ quasicrystal are studied with Grand Canonical Monte Carlo using Lennard-Jones interactions. We observe interesting phenomena that can only be attributed to the quasicrystallinity and/or corrugation of the substrate, including structural evolution of the overlayer films from commensurate pentagonal to incommensurate triangular, substrate-induced alignment of the incommensurate films, and density increase in each layer with the largest one observed in the first layer and in the smallest gas. 2D quasicrystalline epitaxial structures of the overlayer form in all the systems only in the monolayer and at low pressure. The final structure of the films is a triangular lattice with a considerable amount of defects except in Xe/QC. Here a first-order transition occurs in the monolayer resulting in an almost perfect triangular lattice. The next layers of Xe/QC have hexagonal close-packed structures. By simulating fictitious gases, we find that the existence of the transition is correlated with the size mismatch between adsorbate and substrate's characteristic lengths. A simple rule is proposed to predict the phenomenon. We extend the theory to other gases/substrates of technological interest. Research is sponsored by NSF and ACS-PRF. [Preview Abstract] |
Monday, March 5, 2007 2:54PM - 3:06PM |
D42.00003: An Addressable Supramolecular Rotary Switch Featuring Distinguishable Positions Embedded In A Two-Dimensional Porphyrin-Based Porous Network Meike Stoehr, Nikolai Wintjes, Hannes Spillmann, Andreas Kiebele, Serpil Boz, Thomas Jung, Fuyong Cheng, Davide Bonifazi, Francois Diederich In recent years, the attempts to build artificial functional devices from single molecules by the ``bottom-up'' approach were strongly in the focus of surface nanoscience. First experiments with molecules manually arranged by the STM tip gave first hints on the powerful possibilities of such a device. Nevertheless, a simple way to produce supramolecular devices parallel in vast amounts has never been shown before. Herein, we report on a highly complex supramolecular device that reminds of a mechanical rotary switch. It is fabricated on a Cu(111) surface following the ``bottom-up'' approach. Self-assembly of a specially designed porphyrin molecule leads to the formation of porous networks featuring chiral cavities which serve as molecular stators for multi-state molecular rotors. By STM, this rotational behavior was analyzed in detail while the energy barrier for rotation was estimated to be 0.28~eV. [Preview Abstract] |
Monday, March 5, 2007 3:06PM - 3:18PM |
D42.00004: Creation of open networks from perylene derivatives Manfred Matena, Meike Stoehr, Markus Wahl, Tomas Samuely, Thomas A. Jung, Lutz H. Gade Self-assembly of molecules on surfaces directed by supramolecular interactions has been widely explored. The perylene derivative (DPDI) we analyzed is modified on the surface in order to achieve self-assemblies. This modification is temperature-induced, thus providing an additional feature to the control of self-assemblies in contrast to usual approaches that make use of molecular properties already inherent to the molecules [1]. Thin films of DPDI were prepared on Cu(111) and investigated with STM. Depending on the coverage before annealing, three different H-bond assemblies are generated, since in a thermally induced reaction the end groups of the molecule are modified and it can then act as both a H-bond donor and acceptor. For a similar perylene derivative (TAPP), an open quadratic assembly is found on Cu(111), which is not based on temperature-induced modification. If both molecules are present on the surface, no intermixing occurs. Instead a separation into two porous networks happens after annealing. [1] M. Stoehr et al., Angew. Chem. Int. Ed. 44 (2005) 7394 [Preview Abstract] |
Monday, March 5, 2007 3:18PM - 3:30PM |
D42.00005: Statistical Mechanics of Pore Self-Ordering in Porous Alumina Arief Budiman, Daniel Lo Porous alumina has been used as natural templates in forming various ordered nanostructures and has also a potential as catalysts or molecular sieves. Optoelectronic applications typically require a perfect spatial pore ordering, while chemical applications demand less ordering. More recently, pore self-ordering has also been observed in other material systems. A general framework to understand the self- ordering is still lacking. We will focus on the filled hexagonal lattice of pores in porous alumina and describe their pore-ordering by their elastic interaction and their configurational entropy using cluster variation method. Phase diagrams describing the location of ordered and disordered phases as functions of interpore distance, surface tension, and temperature are obtained. [Preview Abstract] |
Monday, March 5, 2007 3:30PM - 3:42PM |
D42.00006: Characterization of molecular linkages of Zeolite microcrystal assembly Heeju Lee, Jin Seon Park, Kyung Byung Yoon, Hyunjung Kim We have measured x-ray reflectivity curves of silicalite-1 microcrystal (MC) monolayers on Si wafers using two different types of molecular linkages, namely, through chloropropyl (CP) groups and through CP/polyethylene imine/CP groups. While the scanning electron microscope images of the two MC monolayers are indistinguishable of molecular linkage between the monolayers and the substrate, their reflectivity curves are distinctively different, despite the fact that the thicknesses of the molecular linkage layers ($\sim $1-2 nm) are negligibly small compared to the thicknesses of MC monolayers ($\sim $320 nm). We demonstrated that x-ray reflectivity is a very useful tool for the characterization of very thin layers of molecular linkages existing between much thicker MC monolayers and the substrate. [Preview Abstract] |
Monday, March 5, 2007 3:42PM - 3:54PM |
D42.00007: Determination of the hyperpolarizability components of hemicyanine dyes by measuring the anisotropic fluorescence and second harmonic of the dyes uniformly aligned within zeolite channels Doseok Kim, Taekyu Shim, Myounghee Lee, Bumku Rhee, Hyeonsik Cheong, Hyunsung Kim, Kyungbyung Yoon Unidirectional ensemble of hemicyanine molecules was prepared by inserting the molecules into the vertical channels of a uniformly-oriented zeolite (silicalite-1) film grown on a glass substrate. Fluorescence from this sample excited with light polarized along the vertical channel was 50 times larger than that excited with light polarized orthogonal to the vertical channel direction. This vertically aligned hemicyanine dyes were used to determine the ratio of the molecular hyperpolarizability components $\beta_{zxx}$/$\beta_{zzz}$ of hemicyanine. [Preview Abstract] |
Monday, March 5, 2007 3:54PM - 4:06PM |
D42.00008: Orientational Order and Hyperpolarizability of Nonlinear Chromophore Molecules Supported in Amphiphilic 4-Helix Bundle Peptides Grazia Gonella, Andrey Tronin, Michael J. Therien, Hai-Lung Dai, J. Kent Blasie The designed nonlinear optical chromophore, (Polypyridyl)Ruthenium-(Porphinato)Zinc(II) (Ru-PZn), incorporated in a monolayer of amphiphilic 4-helix bundle peptides which is used to provide control of the chromophore orientational order on a silica substrate, has been examined by optical Second Harmonic Generation (SHG). The single monolayer of the H6H20 AP0 [1] peptide covalently attached to an alkylated silica surface with thiol end groups can be used to host and support Ru-PZn cofactor. It has been found that the cofactor's hyperpolarizability tensor is dominated by its component along the conjugation axis as suggested by Karki et al. for similar systems [2]. The tilt angle of the principal symmetry axis of the chromophore molecule from the surface normal has been determined as well as the absolute magnitude of the molecular nonlinear polarizability through comparison with a quartz crystal.\\ \\ 1. Strzalka, J. et al., Nano Lett. (2006) in press\\ 2. Karki, L. et al., J. Am. Chem. Soc. 120 (1998), 2606 [Preview Abstract] |
Monday, March 5, 2007 4:06PM - 4:18PM |
D42.00009: \textit{Ab initio }simulations of alkyl-terminated Si(001) surfaces. Giancarlo Cicero Self assembled monolayers (SAMs) are ordered molecular assemblies formed by the adsorption of an active surfactant on a solid surface. The interest in the area of self-assembly, and specifically in SAMs, stems partially from their perceived relevance to science and technology. In contrast to ultrathin films made by, for example, chemical vapour deposition, SAMs are highly ordered and oriented and can incorporate a wide range of groups both in the molecular chain and at the chain termination. Therefore, a variety of surfaces with specific interactions can be produced with fine chemical control. In particular, SAM are used in cantilever based detection, as the first step towards the realization of surfaces with specific sensing properties. Understanding how the surface stress and the mechanical properties of a cantilever change upon functionalization is fundamental to achieve accurate quantitative analysis. Here we present \textit{ab initio }simulations of SAM formation on Si(001) surface to make contact with some recent experimental results [1], in which well packed and ordered alkyl-terminated silicon surfaces were obtained. We will show how the Si(001) surface stress and its mechanical properties (elastic constants) change when organic molecules are attached to it. In particular we will discuss the effect of increasing the surface coverage and the length of the alkyl chain used for the functionalization process. [1] Cerofolini G. F. \textit{Semicond. Sci. Technol. }\textbf{18}, 423-429 (2003). [Preview Abstract] |
Monday, March 5, 2007 4:18PM - 4:30PM |
D42.00010: Structure and morphology of (111) textured Au/Co/Au trilayers grown on glass by MBE. Divine Kumah, J.R. Skuza, A. Cebollada, C. Clevaro, J.M. Garcia Martin, R.A. Lukaszew, Roy Clarke A complete structural and morphological study as a function of Co thickness is presented in a series of Au/Co/Au trilayers grown by MBE on glass substrates. A combined AFM, RHEED, SAXRR and XRD characterization allows determining the optimum deposition conditions that lead to the fabrication of highly textured, flat and continuous layered structures. Development of (111) texture upon annealing the Au layer grown on glass is followed in situ using RHEED. High crystalline quality is confirmed by XRD measurements. A simultaneous in-plane and out-of-plane Co lattice expansion is observed for the thinnest Co layers, converging to bulk values for thickest films. The roughness of the Co layer extracted from the SAXRR data is similar to that of the Au buffer layer, indicative of a conformal growth. [Preview Abstract] |
Monday, March 5, 2007 4:30PM - 4:42PM |
D42.00011: Silicon-on-insulator for symmetry-converted growth Y. Fujikawa, Y. Yamada-Takamura, G. Yoshikawa, T. Ono, M. Esashi, P. Zhang, M. G. Lagally, T. Sakurai Because of its well-established processability, good electronic-transport properties, and ability to form a stable insulating oxide, silicon will remain the essential semiconductor for fabrication of electronic devices. Most device fabrication uses Si(001) and hence most of fundamental research, including heteroepitaxy and integration, has focused on Si(001), a square lattice. Materials having 3- or 6-fold symmetries, a major and important class with key properties, have intrinsic difficulty in their growth on Si(001) because the symmetry mismatch induces polycrystallization at the interface and degrades the film quality. We present a general solution for this long-standing problem that allows maintaining the Si(001) bulk material for those aspects of device fabrication that require it while making possible the growth of 3-fold symmetric structures. We utilize silicon-on-insulator (SOI) in which Si(111) is bonded to Si (001). A 14 nm-thick Si(111) template layer is bonded to Si(001) via the buried oxide. Using the surface preparation method recently developed for the Si(001)-SOI surface, this SOI structure provides a uniform Si(111)-7x7 clean surface. Wurtzite GaN is grown directly on this SOI structure, forming of uniform N-polar film. [Preview Abstract] |
Monday, March 5, 2007 4:42PM - 4:54PM |
D42.00012: Nanotube Formation from Self-Bending Nanofilms Driven by Atomic-scale Surface Stress Imbalance Ji Zang, Minghuang Huang, Feng Liu We present a novel mechanism for fabricating nanotubes by self-bending of nanofilms under intrinsic surface stress imbalance due to surface reconstruction. A freestanding Si nanofilm may spontaneously bend itself into a nanotube without external stress load, and a bilayer SiGe nanofilm may bend into a nanotube with Ge as the inner layer, opposite of the normal bending configuration defined by misfit strain. Such rolled-up nanotubes can accommodate a high level of strain, even beyond the magnitude of lattice mismatch, greatly modifying the tube electronic and optoelectronic properties. [Preview Abstract] |
Monday, March 5, 2007 4:54PM - 5:06PM |
D42.00013: Formation of metallic periodic nanostructures by spontaneous oscillation in self-organized electrocrystallization Mu Wang, Ruwen Peng, Guobin Ma, Xiping Hao, Naiben Ming A unique electrodeposition system is designed to self-organize metallic periodic nanostructures on the surface of solid substrate, which consists of an ultrathin electrolyte layer about 300 nm in thickness. In this system the metal electrodeposits (copper, cobalt, zinc and silver) are formed robustly on the solid substrate (silicon wafer or glass plate), possess considerably low branching rate, and usually cover with periodic metal/metal oxide nano-nodules. Both potentiostatic and galvanostatic modes can be applied to generate such structures. Following issues are focused in this presentation: (1) The mechanism for the formation of the periodic nanostructures on the filaments; (2) The experimental conditions to control the periodicity of these periodic spatio-temporal structures; (3) The electric properties of this nano-nodules chains. \newline References: \newline [1] Yu-Yan Weng, et al. Phys. Rev. E 73, 051601 (2006) \newline [2] Yuan Wang, Yu Cao, Mu Wang, et al., Phys. Rev. E, 69, 021607 (2004) \newline [3] M. Zhang, et al., Adv. Mater. 16, 409 (2004) \newline [4] S. Zhong, Y. Wang, Mu Wanget al., Phys. Rev. E, 67, 061601 (2003) [Preview Abstract] |
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