Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B5: Focus Session: Van der Waals Bonding in Advanced Materials - Surfaces, Growth, and Friction |
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Sponsoring Units: DMP Chair: Jacqueline Krim, North Carolina State University Room: 301 |
Monday, March 18, 2013 11:15AM - 11:51AM |
B5.00001: Exploiting London dispersion forces in nonequilibrium growth of surface-based nanostructures Invited Speaker: Zhenyu Zhang London dispersion force$^{\, }$describes the weak interaction between transient dipoles or multipoles associated with different parts of matter, and accounts for a major part of the attractive van der Waals (vdW) force. It is ubiquitous in nature, yet its importance in various physical and chemical processes just starts to be increasingly recognized. Such advances through definitive quantitative studies are largely enabled by the availability of more accurate descriptions of the weak interactions associated with long-range electron correlation effects within first-principles approaches. The present talk contains two parts, both obtained within the vdW-DF scheme on the theory side. In the first part, we critically assess the binding strengths of different classes of adatoms on ultrathin metal films of varying thicknesses. For inert gas atoms such as Xe, the London dispersion force is found to drastically enhance their adsorption, but the overall binding behavior depends only weakly on the film thickness. In contrast, for atoms with unpaired valence electrons such as H or O, the overall binding is much stronger, and also depends more sensitively on the film thickness, but with a much weaker and (in some cases) repulsive vdW contribution. These results have important implications in our developing a better understanding of atomic and molecular adsorption on different metal substrates. In the second part, we demonstrate unambiguously the decisive role of London dispersion force in non-equilibrium growth of ordered nanostructures on metal substrates using aromatic source molecules. Our multi-scale modeling integrating first-principles calculations with kinetic rate equation analysis shows that a drastic reduction in the growth temperature, from 1000$^{\circ}$C to (250-300)$^{\circ}$C, can be achieved in graphene growth on Cu(111) when the typical carbon source of methane is replaced by benzene or $p$-Terphenyl. The enhanced London dispersion forces effectively prevent easy desorption of the adsorbed molecules, facilitating their dehydrogenation, and promoting subsequent graphene growth at much lower temperatures. These strong predictions are further validated quantitatively in our experimental tests. We also demonstrate that the general trends established above are broadly applicable in graphene growth using other aromatic carbon sources. [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:03PM |
B5.00002: Van der Waals density functional applied to adsorption systems Ikutaro Hamada The van der Waals density functional (vdW-DF) [1] is a promising density functional to describe the van der Waals forces within density functional theory. However, despite the recent efforts [2], there is still room for further improvement, especially for describing molecular adsorption on metal surfaces. I will show that by choosing appropriate exchange and nonlocal correlation functionals, it is possible to calculate geometries and electronic structures for adsorption systems accurately within the framework of vdW-DF. Applicability of the present approach will be illustrated with its applications to graphene/metal [3], fullerene/metal [4], and water/graphene interfaces [5].\\[4pt] [1] M. Dion, H. Rydberg, E. Schr{\"o}der, D. C. Langreth, B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004).\\[0pt] [2] See for e.g., K. Lee, {\'E}. D. Murray, L. Kong, B. I. Lundqvist, D. C. Langreth, Phys. Rev. B 82, 081101(R) (2010).\\[0pt] [3] I. Hamada and M. Otani, Phys. Rev. B 82, 153412 (2010).\\[0pt] [4] I. Hamada and M. Tsukada, Phys. Rev. B 83, 245437 (2011).\\[0pt] [5] I. Hamada (submitted). [Preview Abstract] |
Monday, March 18, 2013 12:03PM - 12:15PM |
B5.00003: Nanotribological Properties of Positively and Negatively charged nanodiamonds as additives to solutions Zijian Liu, Steven Corley, Olga Shenderova, Donald Brenner, Jacqueline Krim Nano-diamond (ND) particles are known to be beneficial for wear and friction reduction when used as additives in liquids,[1] but the fundamental origins of the improvement in tribological properties has not been established. In order to explore this issue, we have investigated the nanotribological properties of ND coated with self-assembled monolayers (SAM) as additives to solutions, employing gold/chrome coated quartz crystal microbalances (QCM). Measurements were performed with the QCM initially immersed in deionized water. ND particles with positively and negatively charged SAM end groups were then added to the water, while the frequency and amplitude of the QCM were monitored. Negative shifts in both the QCM frequency and amplitude were observed when ND with positively charged SAM end groups were added, while positive shifts in both the QCM frequency and amplitude were observed when ND with negatively charged ND end groups were added . The results are consistent with a lubricating effect for the negatively charged ND, but were only observed for sufficiently small negative ND particle size. Experiments on QCM surfaces with differing textures and roughness are in progress, to determine the separate contributing effects of surface roughness charge-water interactions. 1. V. N. Mochalin, et al, Nat. Nanotech. 7, 11--23 (2012) doi:10.1038/nnano.2011.209 [Preview Abstract] |
Monday, March 18, 2013 12:15PM - 12:27PM |
B5.00004: Adhesion in Nanodiamond Particles Vasudeva Rao Aravind, Luke Lutkus, Benjamin Legum Due to their excellent mechanical properties and biologically non-toxic nature, nanodiamonds show great promise for applications in tribology, lubrication, drug delivery, tissue scaffolds and surgical implants. In order to design effective nanocomposites and other biomedical systems exploiting these properties, it is important to understand the properties and mechanisms by which nanodiamonds adhere to other materials, and how they behave at interfaces. In this article, the adhesive force between nanodiamond particles and the silicon scanning probe microscope tip are reported. The adhesive force can be correlated to the purity and functionalization of nanodiamond surface, and the values range from 0.1nN to 2.0nN for the samples studied. It is observed that the lateral forces applied by the scanning probe tip can cause the adhesive forces to increase by an order of magnitude from 0.1 to 2.0nN at regions where the tip experiences maximum contact force. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 12:39PM |
B5.00005: ABSTRACT WITHDRAWN |
Monday, March 18, 2013 12:39PM - 12:51PM |
B5.00006: Adsorption and intercalation of Cs atoms on epitaxial graphene on Ir(111) Predrag Lazic, Marin Petrovic, Iva Srut, Ivo Pletikosic, Milorad Milun, Petar Pervan, Sven Runte, Carsten Busse, Thomas Michely, Damir Sokcevic, Radovan Brako, Nicolae Atodiresei, Jurek Sadowski, Zhi-Hu Pan, Tonica Valla, Marko Kralj From the experimental studies of surface adsorption of Cs atoms and their intercalation under epitaxial graphene on Ir(111) it is known that both - adsorbed and intercalated phase of Cs atoms coexist. However, adsorbed phase is realized as a diluted superlattice adlayer of Cs atom while intercalated phase is a dense Cs layer. The preference for intercalated phase at large Cs layer densities can not be obtained from the DFT calculations with semilocal (GGA) functionals. Only after the van der Waals interaction is taken into account the agreement with experiment is achieved. From the results of calculations it follows that the main energy contribution responsible for the switching of preference from adsorption to intercalation is the graphene delamination energy from the Ir(111) surface which is dominantly of the van der Waals nature. [Preview Abstract] |
Monday, March 18, 2013 12:51PM - 1:03PM |
B5.00007: Structure and Morphology of Copper Phthalocyanine Films on Graphene and Graphite Terry McAfee, Tianshuai Guan, Sean Stewart, Eliot Gann, Jack Rowe, Harald Ade, Daniel Dougherty Indium tin oxide (ITO) is the most widely used anode in organic photovoltaic (OPV) applications. It has several disadvantages, including elemental scarcity and a very rough surface morphology that influences the structure of organic thin film active layers. Alternative transparent conducting anode materials must be identified for use in organic optoelectronic devices. An exciting possibility is the use of graphene since it offers high performance electrical characteristics, good transparency, and a very flat template for high quality film growth. Hard x-ray scattering reveals a ``face-on'' orientation of copper phthalocyanine (CuPc) on graphene, in contrast to its ``edge-on'' orientation on ITO. This is advantageous for solar cells due to enhanced absorption as well as improved charge transport to the anode via pi-pi stacking. Atomic force microscopy shows that CuPc forms large crystalline domains on graphene that should improve carrier mobility, as well as increase the exciton diffusion length leading to improved charge separation. These unique characteristics suggest significantly improvements in the Jsc and FF of CuPc based OPV devices using graphene as an anode material. [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:15PM |
B5.00008: Atomic Friction Studies of Nitrogen and Oxygen Uptake on Magnetic substrates by means of the Quartz Crystal Microbalance Technique Zachary Fredricks, Keeley Stevens, Jacqueline Krim In the study of friction at the nanoscale, phononic, electrostatic, conduction electron and magnetic effects all contribute to the dissipation mechanisms [1]. Magnetic contributions have been alluded to in past studies, but remain poorly characterized. We will report here our efforts to detect magnetic friction for sliding adsorbed films on various magnetic films substrates in the presence and absence of an external field. Using a quartz crystal microbalance (QCM), we record the sliding friction of liquid monolayers of nitrogen, a diamagnetic material, as well as liquid oxygen, a paramagnetic material, on nickel alloy and graphene/nickel surfaces. In the prior literature, these systems have been reported to exhibit sensitivity to external fields.\\[4pt] [1] I. Altfeder and J. Krim, J. Appl. Phys. (2012) \\[0pt] [2] Highland et al., PRL (2006) [Preview Abstract] |
Monday, March 18, 2013 1:15PM - 1:27PM |
B5.00009: Developing of van der Waals parameters for graphitic carbon-water interaction using ab initio methods Yanbin Wu, Narayana Aluru In this study, graphitic carbon-water van der Waals interaction parameters are developed entirely from first-principle calculation data. First, the M{\o}ller-Plesset perturbation theory of the 2nd order (MP2) method is employed to compute the polycyclic aromatic hydrocarbon-water interaction energies. The proper size of basis sets is utilized in the MP2 calculations and the energy component analysis is performed to extrapolate to infinite-sized graphene limit. Then, graphitic carbon-water interaction parameters are developed based on the MP2 results from this work and the ab initio data available in the literature from other methods such as random-phase approximation (RPA), diffusion Monte Carlo (DMC), density functional theory-symmetry-adapted perturbation theory (DFT-SAPT) and couple cluster treatment with single and double excitations and perturbative triples (CCSD(T)). We evaluate the accuracy of the interaction parameters by predicting water contact angle on graphite and compare it with experimental data. The interaction parameters based on RPA, DFT-SAPT and corrected DMC data predict contact angles which agree well with experiments, while the parameters based on MP2 and CCSD(T) data have the tendency to underestimate the contact angle. [Preview Abstract] |
Monday, March 18, 2013 1:27PM - 1:39PM |
B5.00010: Field-effect modulation of water adsorption on the TiO$_2$ (110) surface from van der Waals density functional theory Abraham Hmiel, Yongqiang Xue The interaction of water and the titanium dioxide surface has been identified as a target problem across many possible fields of application of electrochemical devices and sensors, as the surface chemistry at the interface is not well-understood. This work applies self-consistent van der Waals density functional theory and the effective screening medium theory\footnote{M. Otani, O. Sugino Phys. Rev. B \textbf{73}, 115407 (2006)} to study the surface chemistry and wetting of H$_2$O on nanostructured TiO$_2$ surfaces. Water-TiO$_2$ substrate interactions are probed from the monomer limit up to monolayer coverage under an external electric field in a charged capacitor model. We illustrate the competitive effect between the electric field and the descriptions of the hydrogen bonding induced by the application of the van der Waals functional by analyzing the energetics, charge partitioning, and bonding at the interface. [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 1:51PM |
B5.00011: Thermodynamic Stability and Structure of Oxidized Cu(110) Surfaces: The Critical Role of non-Local Interactions Joseph Bamidele, Jan Brndiar, Ivan Stich, Lev Kantorovitch Thermodynamic stability of oxidized Cu(110) surface is studied using DFT techniques. At high oxygen exposures standard techniques predict more phases to be quasi-isoenergetic, whereas experiments observe only the $c$(6 $\times$ 2) phase at high oxygen exposures clearly indicating this phase to be the ground-state separated by considerable energy differences from other candidates. We show that this surface system is stabilized by a delicate coexistence and balance of chemi- and physi-sorption. Agreement with experiments is only achieved if the van der Waals interaction between the surface templates is accounted for in DFT thermodynamics. Moreover, van der Waals stabilization of the surface structure is anticipated to be a general feature present also in the cases of other related surfaces. [Preview Abstract] |
Monday, March 18, 2013 1:51PM - 2:03PM |
B5.00012: A Density Functional Theory Examination of the Local Conformational Energetics of Normal and Epigenetically Modified Duplex DNA Tahir Yusufaly, Wilma Olson We report density functional theory calculations of various local regions of duplex DNA, including hydrogen bonded base pairs, stacked nearest-neighbor bases, and sugar-phosphate backbones. Special attention is given to the methylation of 5-cytosine, an epigenetic modification believed to play a key role in eukaryotic gene regulation. Energetically stable molecular conformations are identified and their elastic properties analyzed. Our results are compared with previous ab initio studies and high-resolution crystalline structural data. [Preview Abstract] |
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