Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C25: Chemical Physics at SurfacesLive
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Sponsoring Units: DCP Chair: Martin Bazant, Massachusetts Institute of Technology MIT |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C25.00001: Deep Learning-Assisted Analysis of Anomalous Nanoparticle Diffusion Near the Liquid Cell Surface Reveals the Effect of Electron Beam Dose Rate in TEM Vida Jamali, Cory Hargus, Assaf Ben Moshe, Hyun Dong Ha, Amirali Aghazadeh, Kranthi K Mandadapu, Paul A Alivisatos The motion of nanoparticles near surfaces is of fundamental importance in physics, chemistry, and biology. Liquid cell transmission electron microscopy (LCTEM) is a promising technique for studying motion of nanoparticles with high spatial and temporal resolution. Yet, the lack of understanding of how the electron beam of a transmission electron microscope affects the particle motion has held back advancement in using LCTEM for in situ single nanoparticle and macromolecule tracking at interfaces. Here, we studied the diffusive motion of a model system of gold nanorods dispersed in water and moving near the silicon nitride membrane of a commercial liquid cell in a broad range of electron beam dose rates. Using a convolutional deep neural network model as well as canonical statistical tests, we showed that there is a crossover in diffusive behavior of nanoparticles in LCTEM from fractional Brownian motion at low dose rates, resembling diffusion in a viscoelastic medium, to continuous time random walk at high dose rates, resembling diffusion on an energy landscape with pinning sites. This understanding forms the foundation to use LCTEM for single nanoparticle tracking for a broad range of nanoparticles, interfaces, and liquids. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C25.00002: Absorption and diffusion kinetics of hydrogen in Y5Si3, one-dimensional electride Jinseon Park, Miaofang Chi, Mina Yoon Electrides are ionic compounds in which “free” electrons are confined in a low-dimensional cavity to balance the charge states of the system. The characteristic features of electrides—the existence of large cavities and non–nucleus-bound electrons—make them attractive for various applications, such as gas storage, electron/ion transport, and electrocatalytic processes. The compound Y5Si3 is a 1D electride with excellent catalytic efficiency. In addition, recent studies indicate its reversible hydrogen storage capability. However, the detailed atomistic understanding is far from being complete. Using first-principles density functional theory in combination with global structure search algorithms, we investigate the absorption and diffusion kinetics of hydrogen in the Y5Si3 compound. We identify the 1D cavity as the dominant diffusion channel, where the diffusion process is strongly influenced by the density of hydrogen. Therefore, the fastest kinetics can be achieved at a certain density of hydrogen. Our results provide a better understanding of gas absorption in 1D electrides, and in general their application as efficient ion-transport medium. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C25.00003: Photo-induced oxidation and desorption of CO on Ru(0001) Auguste TETENOIRE, Iñaki JUARISTI, Maite ALDUCIN The oxidation of carbon monoxide (CO) on different transition metal surfaces, including ruthenium, is a benchmark reaction for theoretical and experimental studies of heterogeneous catalysis. Bonn and coworker investigated the photo-induced desorption and oxidation of CO adsorbed on an oxygen pre-covered surface of Ru(0001) with a 800nm femtosecond laser [1]. This experiment predicts that, the electronic excitations created by the laser pulse modify the yield of the reaction by promoting the recombination of carbon monoxide and oxygen atom. Simulations based on the advanced ab-initio molecular dynamics method that includes electronic friction (AIMDEF) and thermostats [2] show that not only the laser-excited electrons matter. It is the electron-phonon synergy that ultimately facilitates the CO oxidation on the surface. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C25.00004: Photoinduced desorption dynamics of CO from Pd(111): a neural network approach Alfredo Serrano-Jiménez, Alberto Sánchez Muzas, Yaolong Zhang, Bin Jiang, Ivor Loncaric, Iñaki JUARISTI, Maite ALDUCIN A novel approach based on a neural network (NN)-generated potential energy surface (PES) is developed to describe the dynamics of the femtosecond laser-induced desorption of CO from Pd(111). Using trajectories computed with (Te,Tl) ab-initio molecular dynamics with electronic friction (AIMDEF)1 as input data, the NN-PES is trained within the embedded atom neural network framework using the atomic configurational energies and forces2. The NN-PES robustness is checked by studying the errors in energies and forces, and also by testing its performance in complex molecular dynamics simulations. The (Te,Tl)-AIMDEF results1 are reproduced with a remarkable level of accuracy. This shows the outstanding performance of the obtained NN-PES that can cover an extensive range of surface temperatures (90-1000 K) and a large amount of degrees of freedom -those corresponding to multiple adsorbates and surface atoms. Application of this NN-PES for future computational tests of the system dynamics under different initial conditions should be straightforward, as well as the utilization of this methodological framework for development of accurate NN-PESs for other complex gas-solid interfaces. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C25.00005: From Order to Disorder of Alkanethiol SAMs on Complex Au (211), (221) and (311) Surfaces: Impact of the Substrate Dimitrios Stefanakis, Vagelis Harmandaris, Georgios Kopidakis, Ioannis N Remediakis We investigate the impact of the substrate on the structural properties and the morphology of alkanethiol self-assembled monolayers (SAMs) on gold, using first principles calculations and atomistic molecular dynamics simulations. We consider hexadecanethiols on Au(211), Au(221) and Au(311) surfaces which contain few-atom wide terraces separated by monoatomic steps similar to the complex Au surfaces used in experiments. The structure of the SAMs is probed via several structural properties including tilt angles, mean C atom heights from the surface, precession angles, gauche defects, gyration tensors and relative shape anisotropy. A clear order to disorder transition is observed by changing the substrate: Well-ordered SAMs on (111) and (211) surfaces become mixed ordered-disordered structures on (311) and fully disordered on (221). The presence of steps on the Au surfaces also results in preferential tilt orientations with long-range order. Our results show that in addition to the expected grafting density dependence, the transition from order to disorder crucially depends on substrate morphology and is related to the atomic structure of the surface. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C25.00006: Attainment of a High Concentration of Salt Ions Near a Metallic or Dielectric Wall in a Salt Solution as a result of Electrical Image Forces Jeffrey Sokoloff, Andy Lau Electrical image potentials near a metallic wall or near a dielectric wall of higher dielectric constant than that of the solution are attractive, and therefore, can concentrate salt ions near the wall. This opens the possibility that they can be used to concentrate salt water, producing brine, and even desalinating salt water. It has recently been observed that near a metallic surface, ions in room temperature ionic liquids precipitate (but not near a nonmetallic surface). A likely reason for why precipitation of ions in salt water, as a result of electrical image forces, has not as yet been observed is the existence of an energy barrier near a solid surface, resulting from the reduction of ion solvation as a result of the large decrease of the dielectric constant of water within 0.75nm and normal to a solid wall. We will explore the conditions under which ions are able to get past this barrier and concentrate at a solid wall, either as a result of thermal activation over the solvation energy potential barrier or as a result of a reduction of this barrier caused by screening due to the ions. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C25.00007: Surface vibrations enhance intramolecular hydrogen tunneling in (some) molecular switches Yair Litman, Mariana Rossi Hydrogen atoms in supported molecular-switch architectures can tunnel close to room temperature, which calls for the inclusion of nuclear quantum effects (NQE) in the calculation of reaction rates even at high temperatures. However, standard computations of NQE that rely on standard parametrized dimensionality-reduced models, quickly become inadequate in these environments. Here, a paradigmatic molecular switch based on porphycene molecules adsorbed on metallic surfaces is addressed by full-dimensional calculations that combine density-functional theory for the electrons with the semi-classical ring-polymer instanton approximation for the nuclei. The double intramolecular hydrogen transfer (DHT) rate can be enhanced by orders of magnitude due to surface fluctuations in the deep tunneling regime [1]. In addition, the origin of an Arrhenius temperature-dependence of the rate below the tunneling crossover temperature, as well as the transition to different regimes, is explained. With these considerations, a simple model is proposed to rationalize the temperature dependence of porphycene DHT rates spanning diverse fcc [110] surfaces. [1] Y. Litman, M. Rossi, Phys. Rev. Lett., accepted (2020) arXiv:2005.13314. |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C25.00008: Cooperative Surface Adsorption and Emergence of Antiferromagnetic-like Order in p-Methyl Benzoic Acid Ramprasath Rajagopal, Onuttom Narayan, Lawrence Ziegler, Shyamsunder Erramilli A remarkable cooperative enhancement of surface concentration at the 2D air-water interface is observed as a function of pH for p-methyl benzoic acid (pMBA) and its conjugate base (pMBA-). Polarization-dependent vibrational sum-frequency generation (SFG) spectroscopy1 of carbonyl and carboxylate stretching modes show that the anomalous enhancement is due to an increase in the number density of both molecular species. This SFG enhancement is observed for a narrow pH range (~0.5) centered at pH 6.3, close to the putative surface pK, and is attributed to a cooperative attractive quantum interaction between pMBA and pMBA-. A 3-state ‘spin’ lattice model successfully reproduces the sharp peak seen in the experiments. A detailed study of mean-field theory and lattice simulations shows the emergence of a highly ordered state analogous to antiferromagnetism. With the appropriate choice of system parameters, surface concentrations as a function of pH undergo either a first or second order transition. This work lays the basis for direct detection of order caused by novel acid-anion interactions that are of considerable recent interest for understanding biological surfactants. |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C25.00009: Probing surface and edge energies of gold using high-symmetry nanoparticles Emmanouil Pervolarakis, Aggeliki Mpoumpaki, Georgios Tritsaris, Phoebus Rosakis, Ioannis N Remediakis The equilibrium shape of metal particles is the polyhedron that minimizes the total surface energy. Such shapes are routinely modeled using variations of the Wulff construction [1]. At the nanoscale, edge energy becomes important as the fraction of atoms at edges of nanoparticles cannot be neglected. We present a systematic method for calculation of edge energies based on atomistic simulations of high-symmetry nanoparticles. We derive an expression for the total energy of the nanoparticle that includes contributions from bulk, surface and edge atoms. We use this expression to fit the energy of nanoparticles as a function of the number of atoms and derive bulk-, surface- and edge energies. We repeat this procedure for different nanoparticle shapes. For the calculation of total energy, we employ a variety of interatomic potentials and first-principles Density-Functional-Theory (DFT) calculations. Finally, we discuss electronic properties of these nanoparticles in comparison to continuum models [2]. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C25.00010: Visualizing Anionic Electrons in an Electride Qiang Zheng, Tianli Feng, Jordan Hachtel, Jiaqiang Yan, Ryo Ishikawa, Juan Idrobo, Brian Craig Sales, Sokrates T Pantelides, Miaofang Chi Electrides are an unusual family of materials that feature loosely bonded electrons that sit at special interstitial sites and serve as anions. They are attracting increasing attention because of the wide range of exotic physical and chemical properties that are being discovered. Despite the critical role of the anionic electrons in inducing such properties, their presence has not been directly observed experimentally. Here, we visualize the anionic electron density within a prototype one-dimensional electride, Y5Si3, with sub-Ångstrom spatial resolution by utilizing differential phase-contrast imaging in a scanning transmission electron microscope. Our data additionally reveal an unexpected charge variation at different anionic sites. Density-functional-theory simulations show that the presence of trace H impurities, which are challenging to detect by other means, are the cause of the inhomogeneity. The visualization and quantification of charge inhomogeneities in crystals serve as useful input in future theoretical predictions and experimental analysis of exotic properties in electrides and materials beyond. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C25.00011: Non-monotonic thickness-dependent electrocatalytic activity in epitaxial La0.7Sr0.3MnO3 thin films Jegon Lee, Prajwal Adiga, Sang A Lee, Kelsey A. Stoerzinger, Woo Seok Choi The thickness in nanometer-scale has a direct correlation to the electrocatalytic activity of a transition metal oxide thin film. As the thickness increases, the active sites for the electrocatalyst increases as well, until a saturation thickness, defined as the “active depth”. This concept implies the reaction occurs at a depth deeper than conventional “surface” of the thin film. Here, we propose a way to understanding the “active depth” with the atomic-scale precision thickness (t) control of epitaxial La0.7Sr0.3MnO3 (LSMO) thin films using pulsed laser epitaxy. The activity for the oxygen evolution reaction showed a non-monotonous t-dependence. It increased up to t = 23 u.c., and then decreased again. The non-monotonic trend let us identify three t-regions: (1) resistivity-, (2) active depth-, and (3) surface recombination time-dominant regions. While the parameters of (1) and (3) regions were previously reported and well-defined, here we identified the role of active depth for the first time. Using the LSMO t (u.c.)/SrRuO3//Nb:SrTiO3 heterostructures, we could further scrutinize the active depth and electrocatalytic surface of the LSMO layer to be t = 23 u.c. (~ 10 nm). Our study provides an understanding of the fundamental mechanism of electrocatalytic activities. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C25.00012: Understanding localized surface phonons in CsPbI3 nanocrystals using first-principles calculations Ruoxi Yang, Liang Tan Owning to its soft lattices, halide perovskites exhibit unique structural properties including high anharmonicity and dynamical instabilities. |
Monday, March 15, 2021 5:24PM - 5:36PM Live |
C25.00013: The local environment of pentylphosphonic acid molecular layers with mixed azide and OH terminations, examined by X-ray photoemission spectroscopy Esha Mishra, Kenneth Hipp, Andrew S. Olson, Peter A Dowben, Patrick H. Dussault, Rebecca Y. Lai The surface termination of pentylphosphonic acid (PA-C5-R) molecular films with different ratios of PA-C5-N3 (azide termination) and PA-C5-OH (OH termination) was studied by angle resolved X-ray photoemission spectroscopy. Angle resolved X-ray photoemission spectroscopy suggests that the azide, N3, headgroup surface termination decreases with respect to the OH surface termination, as the PA-C5-N3 and PA-C5-OH ratio decreases, very much as is expected. Surprisingly, it is found that the chemical environment around the N3 headgroup changes with changing PA-C5-N3 and PA-C5-OH ratio. We infer from the shift in intensity of the N 1s core level photoemission features to higher binding energies, and away from the N3 photoemission component with the least binding energy, that the N3 is donating more electron charge with higher OH end group concentrations. This tends to suggestion that during the self-assembly growth process, there is weak ordering of the different species rather than strong clustering among the species with different surface terminal groups. |
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