Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X21: Surfaces, Interfaces, Solids |
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Sponsoring Units: DCP Chair: George Thurston, Rochester Institute of Technology Room: 302 |
Friday, March 6, 2020 11:15AM - 11:27AM |
X21.00001: Reactive Modeling of Silica Synthesis Roland Faller Reactive Molecular Dynamics can describe complex problems where quantum approaches are too slow and do not properly take into account environmental effects and on the other hand classical molecular dynamics is not capable of describing reactions. ReaxFF is a good moxdel for such systems but it needs to be properly trained for the system at hand. In this study we train a ReaxFF model for silica synthesis as an industrially important question is to characterize silica gels and organo-silicon surface coatings. These are formed by reactive condensation of organo-silicon precursors. The morphologies of silica gels obtained from alkoxysilanes can then be determined using our newly trained models and improved simulation techniques. It is found that the gels obtained from trialkoxysilanes are more loosely bonded, and that the chemistry of the headgroup is important to the gel morphology. We furthermore can describe the chemisorption of alkoxysilanes with organic headgroups to hydroxylated silica surfaces. This approach can also be applied to zeolite synthesis. |
Friday, March 6, 2020 11:27AM - 11:39AM |
X21.00002: Evolution of Amorphous Calcium Sulfate Nanoparticles into Crystalline Phases and Development of Short Range Order Caiyun Jia, James J De Yoreo, Baohong Guan The involvement of amorphous precursors in crystal nucleation remains an important but poorly understood phenomenon in materials science. In particular, the mechanisms by which amorphous precursor evolves to crystalline phase is typically unclear. By maintaining calcium sulfate at a low supersaturation to slow the nucleation rate, we captured amorphous calcium sulfate (ACS) nanoparticles of distinct sizes and shapes, and observed several stages of its evolution. The ACS nanoparticles grow by fusion accompanied by internal structural evolution and gradually develop a layered morphology. Aggregation of the growing ACS particles gives birth to bulk ACS material exhibiting a more compact structure within which crystalline domains form and develop into the gypsum structure. Structural characterization reveals the ACS nanoparticles have a proto-gypsum property ranging from short-range order to medium-range order and that the ACS nanoparticles are hydrous within which elimination of H2O molecules from the first to the second coordination shell of Ca facilitates ions transport and therefore formation of nanocrystalline domains within the amorphous precursors. This finding provides new insights into the evolution of amorphous precursors and their role in multi-stage crystallization. |
Friday, March 6, 2020 11:39AM - 11:51AM |
X21.00003: Using neutral atoms to study in situ damage on organic materials Georgios Stratis, Jordan D. Zesch, Henry Pan, Lauren J. Webb, Mark G Raizen We use helium atoms excited in a metastable state to characterize in real-time damage induced on organic materials due to electron impact. More specifically, we used a self-assembled monolayer of 11-bromo-1-undecanethiol on gold-coated silicon exposed to 30 eV electron beam. After each electron beam exposure, we probed the sample using helium atoms in 3S1 state that is 19.8 eV above the ground state. Once the helium atoms encounter the sample's surface, they de-excite and the excess energy causes electron emission from the surface. By measuring the kinetic energies of the emitted electrons we can determine chemical changes that occurred between each electron beam exposure. Due to the fact that metastable helium atoms barely damage our sample while being probed, this technique ensures that any chemical changes we observe are solely due to the electron beam impact. This project is part of a broader effort to develop a neutral atom microscope. |
Friday, March 6, 2020 11:51AM - 12:03PM |
X21.00004: Quantitatively Accurate Theory to Predict Adsorbed Configurations of Surfactants on Metal Surfaces Sumit Sharma, Xueying Ko We have developed a theoretical model to predict adsorbed configurations of linear surfactant molecules on metal surfaces. Our coarse-grained simulations of adsorption of surfactants show that our theoretical model is quantitatively accurate in predicting adsorbed configurations. We show that depending on the relative interaction strengths of the polar group and the alkyl tails with the metal surface, the linear surfactant molecules either adsorb by lying parallel to the surface to form stripes or adsorb perpendicular to the surface to form a monolayer. In the case of monolayer formation, our theory predicts that adsorbed surfactant molecules will undergo an orientational transition. This orientational transition is seen in simulations and have also been reported in experiments. |
Friday, March 6, 2020 12:03PM - 12:15PM |
X21.00005: Prospects for polarized neutron scattering from substrate molecules prepared via Signal Amplification by Reversible Exchange George Thurston, Michael Kotlarchyk
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Friday, March 6, 2020 12:15PM - 12:27PM |
X21.00006: Development of Angle-Dependent Phase Field Crystal Model for Vapor-Liquid-Solid Transitions Zi-Le Wang, Zhi-Rong Liu, Zhi Feng Huang, Duan Wenhui As an efficient and fast-developing continuum modeling approach, the phase field crystal (PFC) method is able to resolve systems on atomic length and diffusive timescales. It can well describe system elasticity, plasticity and other important properties by introducing a free energy functional of a conserved atomic density field. However, what is lacking in majority of PFC models is the interaction or coexistence between vapor and condensed phases, an important factor for many physicochemical processes. Here we present a new PFC model based on the angle-adjustable density field formulation we developed before, which incorporates bond-angle dependence of anisotropic interparticle interactions. The relative stability of vapor, liquid and solid phases, the coexistence and transitions between them, and the corresponding interfacial dynamics can be well described by the model. The pressure-temperature phase diagram for pure substance has been obtained, with results consistent with those of some real material systems. Our new PFC model could serve as an effective tool to model realistic experimental processes such as chemical vapor deposition and vapor-liquid-solid growth. |
Friday, March 6, 2020 12:27PM - 12:39PM |
X21.00007: Combining Optical Tweezers and Laser Induced Nucleation to Get Liquid Phase Separation and Polymorphically Selective Crystals Omar Gowayed, Tasfia Tasnim, Janice Aber, Bruce Allen Garetz, José Fuentes-Rivera A laser-induced phase-separated (LIPS) solution droplet formed by tightly focusing a continuous-wave, near-infrared laser beam at the glass/solution interface of a mm-thick layer of glycine in D2O was irradiated with a single unfocused ns near-IR laser pulse in order to study the effect of nonphotochemical laser-induced nucleation (NPLIN) on the droplet, as well as to help characterize the behavior of the LIPS droplet. This revealed that NPLIN could nucleate crystals within a LIPS droplet and that the LIPS droplet was observed to be more labile to spontaneous nucleation than the control for the first 40 min of relaxation. The resulting crystals were analyzed using powder X-ray diffraction, and 100% of crystals formed within the LIPS droplet induced by NPLIN and by spontaneous nucleation were α-glycine. The results indicate that the LIPS droplet and the surrounding solution are not equilibrium phases of aqueous glycine, but phases in which gradient optical forces have induced a partitioning of large and small solute clusters. |
Friday, March 6, 2020 12:39PM - 12:51PM |
X21.00008: Separation of Carbon Dioxide from Mixed Vapors by Blockage of Methane in Graphene Nanoribbons Silvina Gatica, Hind h Aljaddani
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Friday, March 6, 2020 12:51PM - 1:03PM |
X21.00009: On-surface synthesis of graphene nanostructures on non-metallic substrates Marek Kolmer, Ann-Kristin Steiner, Rafal Zuzak, Lukasz Zajac, Mads Engelund, Szymon Godlewski, Wonhee Ko, Miguel Angel Fuentes-Cabrera, Jingsong Huang, An-Ping Li, Marek Szymonski, Konstantin Amsharov On-surface synthesis of atomically precise carbon-based nanostructures has generated enormous expectations about their potential applications. However, so far selected noble metals have been mostly used as substrates catalyzing the on-surface reactions strongly limiting this perspective. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X21.00010: Anisotropic Ti ionic diffusion giving the anisotropic photo-reactivity in rutile TiO2: A Diffusion Monte Carlo Study Tom Ichibha, Anouar Benali, Kenta Hongo, Ryo Maezono Self-diffusion of Ti interstitials is essential for TiO2 photo-catalysts, because it works for maintaining the surface stoichometry and keeping the photo-reactivity. We revisited ab initio evaluations of the barrier energies along the possible diffusion paths of Ti interstitials in rutile TiO2 bulk using diffusion Monte Carlo method. Our calculation predicted that Ti interstitials diffuse faster in parallel to c-axis, reasonably explaining why rutile TiO2 has a superior photo-activity on (001) surface to (110). Our prediction does not support the previous GGA-DFT works, and this discrepancy can be explained by the poor cancellation of the self-interactions in GGA-DFT. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X21.00011: Unraveling the mechanism of catalytic water oxidation via de novo synthesis of reactive intermediate Alireza Karbakhsh Ravari Artificial photosynthesis has the potential to provide carbon-free fuel. The current systems are limited by the lack of understanding of multi-electron water oxidation catalysts (WOC). Trial and error is the only way that new catalysts are being discovered. A thorough spectroscopic analysis of the prototypical [(tpy)(bpy)Ru(H2O)]2+ -which is the parent complex in the largest family of WOCs- is presented in this study and will give us a clear understanding of dynamics of this catalyst family. This understanding would help to design a catalyst rationally. De novo synthesis of the reactive intermediate with 2,2′-bipyridine-N-oxide, resulted in a hundredfold catalytic activity compare to the parent compound. In situ Raman spectroscopy along with electrolysis of parent and enriched intermediate shed light on the mechanism of the catalysts. Finally, the redox potential of the ligand was shown to be correlated with the rate of O2production. |
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