Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F17: Organic Interfaces and Adsorption PhenomenaFocus
|
Hide Abstracts |
Sponsoring Units: DMP Chair: Chenggang Tao, Virginia Tech Room: LACC 306A |
Tuesday, March 6, 2018 11:15AM - 11:51AM |
F17.00001: Spin Dependent Chemisorption Interactions at Metal-Organic Semiconductor Interfaces Invited Speaker: Daniel Dougherty Spin dependent electronic structure at interfaces can control spin injection efficiency in spintronic devices. Organic spintronics focused on spin polarized interface state formation due to hybridization between molecular orbitals and metallic band states [1]. This talk will describe observation of spin-polarized hybrid states at metal organic interfaces for organic semiconductor adsorbates with different adsorption interactions. Specific attention is payed to the metal quinolate molecules (Mq3’s) that have been a long-time focus of the organic spintronics community. Spin polarized scanning tunneling microscopy and spectroscopy studies of Mq3’s (where M is either Al or Cr) show hybridization with a magnetic surface state on the Cr(001) surface that varies significantly for the different molecules resulting in either metallic or resistive interface states [2]. Subtle differences in adsorption interactions lead to large differences in the spin-dependent electronic structure at the interface. First principles calculations have provided specific microscopic rationale to the observed diversity of interface states in terms of binding geometry and distances. In addition, the variations can be viewed within the model framework of the Anderson-Newns-Grimley model of chemisorption [3]. This convergence of observation, first-principles computations, and model-based understanding shows that molecular treatment of magnetic electrodes can be a reasonably rational approach to optimizing spin injection in the full range of spintronic applications. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F17.00002: Delocalized Hybrid Band in 2D Molecule-Metal Network Probed by Angle-Resolved Photoemission Spectroscopy Hiroyuki Yamane, Nobuhiro Kosugi The electronic structure of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) monolayer grown on Au(111) has been investigated by means of angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The high-resolution core-level photoemission spectra at the F4TCNQ/Au(111) interface show evidences for the strong charge transfer (CT) from Au to F4TCNQ and for the Au-atom segregation from the underlying Au(111) surface, suggesting a possible origin of the spontaneous formation of the two-dimensional F4TCNQ-Au network. The ARPES experiment reveals a low hole-injection barrier and large CT-induced band dispersion of the F4TCNQ-Au network due to the adatom-mediated intermolecular interaction. These results indicate that strong electron acceptor molecules with metal adtoms can form high hole-mobility molecular layers by controlling the ordered structure and their CT interaction. |
(Author Not Attending)
|
F17.00003: Long-range Coherent Charge Transport in Physisorbed Molecular Layers Leandro Silva, Rafael Furlan de Oliveira, Davi de Camargo, Carlos Cesar Bof Bufon The charge transport in molecular ensembles is intrinsically related to a series of carrier-molecule quantum interactions which result in variety device concepts, such as organic transistors, organic light-emitting diodes, and sensors [1]. At the nanoscale, such interactions are described as either direct tunneling for the 1-10 nm range or activated hopping for longer distances. This work describes the first experimental evidence of long-range (> 10 nm) coherent tunneling occurring for physisorbed small-molecule semiconductors-based vertical junctions. By investigating the charge transport in copper-phthalocyanine (CuPc) thin films, we have identified the sequential tunneling as the long-range charge transport mechanism [2]. Such a sequential coherent process is not only different from the direct tunneling, but intrinsically distinct from the hopping conduction. Consequently, a gradual transition from direct tunneling to sequential tunneling, within the 10-22 nm barrier width, to hopping conduction can be verified. Our results contribute to bridging the gap between molecular and organic electronics. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F17.00004: Compliant Rolling-contact Architectured Materials for Shape Reconfiguration Jonathan Hopkins, Lucas Shaw, Matthew Dotson, Samira Chizari, Yuanping Song The aim of this work is to enable the creation of a new kind of architectured material that consists of a lattice of micro-cams that roll along each other’s surfaces guided by different layers of compliant straps that assure slip-free rolling-contact only motions. These new materials achieve large shape deformations with near-zero stiffness and high precision due to the minimal friction that they generate. They can also be designed to achieve large transmissions or mechanical advantages according to the relative sizes of the cam-shaped bodies within the lattice. This work also introduces a new approach for fabricating such materials that combines two-photon stereolithography with optical tweezers to first 3D print the micro-cams with straight flexure straps and to then use the optical forces to deform the flexure straps by rolling the bodies together. The materials introduced would impact numerous applications (i.e., high precision, large-range bears to guide microscopy stages, optical mounts, or nano-positioners, actuator couplings that alter the stroke, resolution, or load capacity of the actuators to which they are attached, and airfoils that can reconfigure their shape for improving flight maneuverability). |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F17.00005: n-Alkanethiols directly grown on a bare Si(111) surface: from disordered to ordered transition Chia-Hao Chen, Lo Yueh Chang, Yen-Chien Kuo, Hung Wei Shiu We observed the growth phase transition of n-alkanethiols (AT), CH3(CH2)n-1SH, n = 4 ~16, directly implanted on a bare Si(111) surface, forming an AT monolayer. These monolayers were characterized with static water-contact angle, high-resolution X-ray photoelectron spectroscopy, near-edge X-ray fine-structure spectroscopy and grazing-angle reflection absorption Fourier-transform infrared spectroscopy. The integrated spectral results indicated that the implanted n-AT molecules formed a self-oriented and densely packed monolayer through formation of an S-Si bond. With the number of carbons in the alkyl chain at six or more, namely beginning at hexanethiol, the molecular monolayer began to develop an orientation-ordered structure, which is clearly shorter than for AT monolayers on Au and Ag. This result implies that, with a stronger molecule-substrate interaction, an ordered molecular monolayer can form with a short chain. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F17.00006: Molecule assembly structure and tilt geometry evaluation of 5,6,7-trithiapentacene-13-one (TTPO) / Pentacene-Quinone on Au(111) with NC-AFM Amanda Larson, Percy Zahl, Karsten Pohl Using non-contact atomic force microscopy (NC-AFM) the 3D molecular structure, tilt and assembly details of a new pentacene-based organic semiconductor, 5,6,7-trithiapentacene-13-one (TTPO) adsorbed on Au(111) were determined. 3D AFM force maps of individually resolved molecular orbitals were acquired to visualize the complete adsorption structure. Robust, thermally stable, and highly inert to photo-oxidation, TTPO is a very promising organic semiconductor. When adsorbed on a gold electrode, scanning tunneling microscopy (STM) experiments and first-principle computation reveal a novel 3-D angular assembly of the TTPO molecules, with the long axis of the molecule parallel to the gold surface, distinctive from any previously observed pentacene and pentacene derivative assemblies. NC-AFM is potentially the only technique capable of directly resolving the 3D angular arrangement of the individual adsorbed molecule and by evaluating consecutively acquired constant height force maps, we were able to directly measure the 3D structure and tilt of small TTPO and Pentacene-Quinone byproduct assemblies on Au (111). The molecule tilt was evaluated to 11±1°. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F17.00007: Lognormal Distribution of Pore Areas for AQ on Au(111) Theodore Einstein, Andrew DeLoach, Brad Conrad, Daniel Dougherty, Rajesh Sathiyanarayanan For anthraquinone (AQ) on Au rather than Cu(111), we find no giant honeycomb network or chain formation, just small hubs of three AQ pairs [1]. This behavior is shown to be consistent with the explanation of the giant regular network on Cu in terms of surface states populating close-shell 2D orbitals [2]. For higher coverage large irregular vacancy pores have a lognormal area distribution indicative of multiplicative noise, in contrast to less-skewed distributions found for capture-zone areas. Lognormal distributions have also been found for county-like secondary administrative units in a minority of countries, e.g. ilceler in Turkey and gemeenten in Netherlands [3]. |
(Author Not Attending)
|
F17.00008: Abstract Withdrawn
|
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F17.00009: Effect of Substrate Wetting on the Morphology and Dynamics of Phase Separating Multi-Component Mixtures Abheeti Goyal, Federico Toschi, Paul Van der Schoot We numerically study the structural evolution due to demixing of multi-component fluids in thin films on a substrate. More specifically, we explore the surface-directed spinodal decomposition of multi-component mixtures by means of Free Energy Lattice Boltzmann simulations in order to have explicit control over the free energy landscape and the equation of state of the system. We investigate the effect of composition, film thickness and substrate wetting on the phase morphology and the mechanism of growth in the vicinity of the substrate. We find that in binary mixtures the phase morphology and averaged size of the structural domains in the vicinity of the substrate varies greatly due to preferential wetting of the substrate in both the parallel and perpendicular directions. We also discuss how the model can be extended to include an arbitrary number of fluid components. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F17.00010: Solvent Effects on the Adsorption of Polyvinylpyrrolidone on Ag Surfaces Tonnam Balankura, Kristen Fichthorn The shape-control mechanism in metal nanocrystal syntheses relies heavily on the adsorption of structure-directing agents or capping molecules on metal surfaces. The solvent environment can influence the thermodynamics of adsorption and consequently influence the nanocrystal’s morphology. Here, we examine the effect of ethylene glycol solvent on the adsorption thermodynamics of polyvinylpyrrolidone (PVP) on Ag surfaces, where we use molecular dynamics simulation to calculate the binding free energy and entropy change due to adsorption. This interface is commonly observed in the solution-phase synthesis of Ag nanocrystals. Our calculations show that (a) solvent lowers the binding free energies of the adsorbing molecules, and (b) adsorption of PVP is entropically favorable in solvent due to the displacement of adsorbed solvent molecules by the binding PVP molecule. Our study underscores the importance of explicitly including solvent in theoretical models for molecular adsorption. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F17.00011: Methodology to Optimize Biologically Inspired Algorithms for an Efficient Global Structure Search of TiO2 Nanoparticles Eric Inclan, Mina Yoon Biologically inspired optimization algorithms have been successfully applied to a variety of materials optimization problems, but their adaptation, and tuning to these problems is often ad-hoc. This work studies two popular algorithms, particle swarm and differential evolution, to determine how various tuning parameter values affect their relative performance in identifying configurations of TiO2 nanoparticles. Empirical probability density distributions are created for the convergence rate of each algorithm and the energies of the meta-stable structures they identify. Their sample size is determined using non-parametric tests (Kolmogorov-Smirnov 2-Sample, and Anderson-Darling k-Sample) and the convergence rates of the statistics themselves. The mode of each distribution is used to generate a Pareto Front (PF) of the algorithm’s performance. Each algorithm is tuned until the PF converges, and a surrogate-model-aided inverse-design of tuning parameters is used to accelerate convergence, and tests such as kernel principal component analysis are used to identify correlations in order to provide tuning recommendations and guidelines. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F17.00012: Adsorption Studies of Benzoic Acid on Single Walled Carbon Nanotubes Shifan Li, Milinda Wasala, Iskinder Arsano, X. F. Zang, Mesfin Tsige, Xingmao Ma, Saikat Talapatra Carbon based nanostructures, specifically carbon nanotubes due to their unique surface adsorption properties can become the choice materials for removal of toxic chemicals from water. In this study, we will present our investigations on adsorption of benzoic acid on single walled carbon nanotubes (SWNT) synthesized by direct thermal decomposition of ferrocene (Fe(C5H5)2). The analysis of the adsorption isotherms of benzoic acid and its conjugate base on these carbon nanotubes indicate that the adsorption capacity of both benzoic acid and benzoate on them are significantly higher than those reported previously on other carbon based adsorbents. We also find that these SWNTs provide better adsorption capacity than commercially available multiwalled carbon nanotubes (MWNT) with different functionalization. We attributed this to the smaller nanotube sizes (diameters) of SWNT which gives rise to stronger surface potentials. A detailed discussion of these experimental results along with analysis and comparison of results obtained from Molecular Dynamics (MD) simulation on similar system will be presented. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F17.00013: Molecular Dynamics of Benzoic Acid Adsorption on Carboxylated Carbon Nanotubes Iskinder Arsano, Shifan Li, Milinda Wasala, Mesfin Tsige, Xingmao Ma, Saikat Talapatra We investigate, through molecular dynamics computer simulation, the adsorption behavior of single-walled carbon nanotube relative to degree of surface carboxylation. A model contaminant species in the form of benzoic acid is uniformly distributed in water creating a solution that is then allowed to adsorb on the tube. We control for tube chirality in two sets of starting systems. An iterative manual replacement of depleted regions was used to guarantee creation of at least one adsorption shell in each system. Aggregation trends in the adsorption shell reveal that uniformity of adsorption correlates well with amount of surface modification. We also assess the competitive adsorption between water and benzoic acid structurally by use of density, orientation, and hydrogen bonding analyses, and dynamically through diffusion calculations. Furthermore, limitations in the current simulation setup direct toward the usefulness of dissociation based analysis as gleaned from a corresponding experimental work that indicates charge-assisted hydrogen bonding might underlie an enhanced benzoic acid adsorption on carboxylated carbon nanotubes relative to the observed behavior on neat counterparts. |
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