Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A52: Surface Adsorption, Dynamics, and Defects |
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Sponsoring Units: DCMP Chair: Daniel Dougherty, North Carolina State University Room: Mile High Ballroom 1E |
Monday, March 2, 2020 8:00AM - 8:12AM |
A52.00001: Quantitative measurements of total yields from electron stimulated desorption of ice Brian Ferrari, Katerina Slavicinska, Chris Bennett Sputtering yields from electron stimulated desorption (ESD) are typically neglected by planetary science models, although mid-energy (200-1000eV) electrons can produce significant sputtering yields. Here, we investigated the total and relative yields from ESD on comet ice analogs in an Ultra-High Vacuum (UHV) chamber with base pressure of 3x10-11 torr. Gas was introduced to the chamber, then condensed on a sample holder, which was then irradiated with an electron source at various energies. A quartz-crystal microbalance (QCM) was used for precise mass desorption measurements, while a quadrupole mass spectrometer (QMS) was used to measure the positive, negative and neutral species that desorbed off the ice. These processes are relevant for various planetary science environments which are subjected to high intensity of electron bombardment, such as the rings of Saturn, Icy Moons, and interstellar ices. The results of our experiments will provide more accurate yields for modeling sputtering from airless bodies. |
Monday, March 2, 2020 8:12AM - 8:24AM |
A52.00002: Investigation of atomic layer deposited amorphous alumina films for the prevention of water-based corrosion of glass Miriam Elisabeth Hiebert, Ethan Hyde, Edward P Vicenzi, Jamie Weaver, Raymond Phaneuf Water is corrosive to a wide range of materials, including silicate glasses, for which contact results in an exchange of modifier ions for protons, swelling of the altered glass, and eventually crack network evolution leading to mechanical failure; this process is referred to commonly as “glass disease”. Atomic layer deposition (ALD) of metal oxide thin films provides a seemingly near-ideal approach toward the protection of silicate glass from water-based corrosion, combining optical, transparency, and potentially high resistance to permeation by water. In this talk I’ll discuss the results of accelerated aging experiments in which ALD alumina-coated silicate glass is immersed in water at elevated temperatures and the rate of ion leaching into the water is monitored as a function of time. We find the application of such films to be capable of slowing water-mediated corrosion by at least an order of magnitude. Finally, I’ll discuss the role of film defects that limit the effectiveness of ALD alumina in preventer water-based corrosion. |
Monday, March 2, 2020 8:24AM - 8:36AM |
A52.00003: Tuning single-atom electron spin resonance in a vector-magnetic field Philip Willke, Aparajita Singa, Xue Zhang, Taner Esat, Christopher Lutz, Andreas J Heinrich, Taeyoung Choi Scanning tunneling microscopy (STM) has been one of highly versatile surface science tools to investigate electronic and magnetic properties of individual atoms and molecules on surfaces. Recently, successful combination of electron spin resonance (ESR) technique and STM has demonstrated electron spin of individual atoms on ultrathin insulating MgO films can be coherently driven. Utilizing a 2D vector magnetic field and the local stray field from the magnetic STM tip, we optimize the ESR signal and characterize the role of the tip field. We demonstrate single atom ESR using the tip-field only, under zero external magnetic field, which promises to make this technique available in many existing STM systems. |
Monday, March 2, 2020 8:36AM - 8:48AM |
A52.00004: Reactive MD simulation on the formation of amorphous sub-nano alumina layer Yuxuan Lu, Devon Romine, Jagaran Acharya, Judy Wu, Ridwan Sakidja In this study, we systematically performed the large-scale classical reactive molecular dynamics (MD) simulations of Atomic Layer Deposition (ALD) processes to model the formation of amorphous alumina sub-nanolayer water. The ALD process used water and (Trimethyl-Aluminum) TMA precursors deposited onto the surface of an aluminum wetting layer. We varied the sizes of the substrate and the concentrations of water/hydroxide precursors with a range of temperature to design the most favorable configurations for the subsequent TMA precursors to add onto. The role of crystallographic orientation of the Al wetting layer was also investigated and compared with the experimental findings. |
Monday, March 2, 2020 8:48AM - 9:00AM |
A52.00005: Quantum-well states and electronic coherence in bimetallic Pb/Ag thin films Chi-Ruei Pan, Woojoo Lee, Chih-Kang Shih, Mei-Yin Chou It has been well established that the presence of quantum-well states in metal thin films plays an essential role in determining the thickness dependence of many physical properties. Here we present first-principles calculations and measurements by angle-resolved photoemission spectroscopy for electronic states in a bimetallic film composed of 10 layers of Pb and 9 layers of Ag in the (111) direction on a Si substrate. It is found that the original quantum-well states in individual Pb and Ag films evolve into new states in the bimetallic film by extending into the additional space, instead of directly coupling with each other as one would have expected. The new set of quantum-well states therefore have modified effective masses and energy values compared with the parent ones. Even though the Pb/Ag interface is incommensurate, the coherence of the electronic states across the whole bimetallic film is verified by supercell configurations with different rotational arrangements in the calculation. The excellent agreement between theory and experiment in the energy dispersion of the quantum-well states confirms the physical picture proposed in this work, which could form the basis in exploring the electronic structure in multiple stacked thin films. |
Monday, March 2, 2020 9:00AM - 9:12AM |
A52.00006: Investigation of oxidation mechanisms of Pt nanoparticles in water – a molecular dynamics study Karim Gadelrab, Nathan Craig Platinum oxide (PtO) formation has a direct link to nanoparticle passivation as well as Pt dissolution in proton exchange membrane fuel cells (PEMFCs). During potential sweep, place exchange mechanism between Pt and O atoms is first triggered followed by irreversible Pt surface roughening at high potential. In this work, we employ molecular dynamics (MD) to capture atomic level processes of Pt extraction by O atoms from Pt(111) surface. As a benchmarking system, we correlate oxygen coverage with the onset of different Pt surface evolution mechanisms in the presence of water. Local O coordination of Pt atoms, concurrent Pt extraction, and generation of surface vacancies are major factors shaping the final surface structure. In addition, the MD simulation is employed to investigate the oxidation process of Pt nanoparticles. Our results show that in addition to PtO formation on faceted surfaces, Pt atoms desorption into water is a strong function of oxygen coverage. This is particularly true for under-coordinated atoms at edges and corners. The atomistic details described by the MD setup provides valuable insights into Pt-O interaction and stability of Pt nanoparticles in a complex environment. |
Monday, March 2, 2020 9:12AM - 9:24AM |
A52.00007: Atomic Defects of the Hydrogen-Terminated Silicon Surface Imaged with nc-AFM Jeremiah Croshaw, Thomas Dienel, Taleana R Huff, Robert A Wolkow The hydrogen-terminated silicon (H:Si) surface has been shown to be a viable candidate for the development of atom-scale devices1,2; however, the creation of such devices is currently limited by the need for constant user-guided interaction during the fabrication process. Attempts to automate fabrication using deep learning successfully demonstrated the training of a neural network which was able to identify common defects3. Building upon these recent works we present our efforts at creating a comprehensive catalog containing many of the commonly found defects of the H:Si-100(2x1) surface. By imaging the defects using different imaging parameters in STM and two different tip contrasts in non-contact AFM4, we determine the structures of the defects, their likely origins and potential removal, and a path to improved accuracy for their automated detection. A deeper understanding will enable the creation of better defect-free samples for atomic fabrication. |
Monday, March 2, 2020 9:24AM - 9:36AM |
A52.00008: A first-principles study of the physical properties and secondary electron emission of 4d and 5d FCC metal surfaces with and without a vacancy defect Leopoldo Diaz III, Mahdi Sanati, Ravindra P Joshi In this study we have introduced a vacancy defect to the 100, 110, 111 surfaces of the 4d and 5d FCC metals to understand the impact the defect will have on their physical properties and secondary electron emission. We have used density functional theory (DFT) to calculate the formation energy (FE), the work function (WF), and the dielectric constant for each metal surface. To ensure accuracy, the calculations were performed using both the local density approximation (LDA) and the generalized gradient approximation (GGA) exchange correlation functionals. For all the FCC metals we have identified the following trend for the vacancy FE and the WF: φ111 > φ100 > φ110 for surfaces with and without a vacancy. We have also calculated the Q-factor for each of the metals allowing for predictions to be made about the secondary electron yield expected by each metal, including which metal would be best for vacuum or near-vacuum devices. |
Monday, March 2, 2020 9:36AM - 9:48AM |
A52.00009: Probing non-equilibrium dynamics of photoexcited polarons on a metal oxide surface with atomic precision Chaoyu Guo, Xiangzhi Meng, Huixia Fu, Qin Wang, Sheng Meng, Ying Jiang Understanding the non-equilibrium dynamics of photoexcited polarons at atomic scale is of great importance for improving the performance of photocatalytic and solar-energy materials, but remains a grand challenge in experiment so far. Using a pulsed-laser-combined scanning tunneling microscopy and spectroscopy, we succeeded to resolve the photoexcitation and recovery dynamics of single polarons bound to oxygen vacancies on a prototypical photocatalyst, rutile TiO2(110). The visible-light excitation of the defect-derived polarons leads to depletion of the polaron states and delocalized free electrons in conduction band. We found that the formation time of polarons becomes considerably shorter when the polaron is bound to two surface oxygen vacancies than that to one. In contrast, the lifetime of photogenerated free electrons is insensitive to the atomic-scale distribution of the defects but correlated with the averaged defect density within a nanometer-sized area. The results shed new lights on the photocatalytically active sites at the metal oxides surface. |
Monday, March 2, 2020 9:48AM - 10:00AM |
A52.00010: TDDFT approach on laser field enhancement by carbon nanotube and photo-decomposition of water Hong Zhang In this presentation, we discuss field enhancement of femtosecond laser by carbon nanotubes and application to accelerating water photo-decomposition. The real-time time-dependent density functional theory (TDDFT) was employed for simulating water photo-decomposition near (8,0) semiconducting carbon nanotube. A short pulse with full-width of half-maximum 10fs was considered. When optical field is perpendicular to the tube axis, we found significant laser field enhancement corresponding to laser-power enhancement by factor 2 with laser wavelength 800 nm, and by factor around 8 with wavelength 400 nm. The enhancement is due to polarizability and wall-curvature of carbon nanotube that helps to reduce threshold power for photo-decomposition of water. |
Monday, March 2, 2020 10:00AM - 10:12AM |
A52.00011: The dissociative adsorption of O2 on the bimetallic Pd3M2 clusters (M= Ag, Au, Co, Cu, Mn, Ni, Pt and Ru) by density functional theory Nusaiba Zaman, Abdelkader Kara We use density functional theory to systematically investigate the adsorption and reactivity of oxygen on the bimetallic Pd3M2 clusters (M = Ag, Au, Co, Cu, Mn, Ni, Pt, and Ru). This is because small bimetallic clusters with high surface area to volume ratio often offers, higher stability, greater selectivity and sometimes superior activity than the pure metal counterparts. We explore different adsorption sites for molecular oxygen, which can be oriented in a vertical or horizontal direction with respect to the cluster, as well as atomic oxygen on these bimetallic Pd3M2 clusters. The reaction path for dissociation of oxygen molecule on these bimetallic clusters is studied using the nudge elastic band method. We will present our result for the calculated energy barriers for O2 dissociation on these bimetallic clusters and how it changes depending on the composition of the bimetallic clusters. Moreover, we will present the effect of O2 adsorption on the electronic properties of these Pd3M2 clusters. Bader charge analysis is performed to probe how the charges are transferred between the molecule and the clusters. |
Monday, March 2, 2020 10:12AM - 10:24AM |
A52.00012: Impact of solvation on the structure and reactivity of the Co3O4(001)/H2O interface: a molecular dynamics study. Stephane Kenmoe, Tim Kox, Eckhard Sphr The spinel Co3O4 has many beneficial properties of potential use in catalysis. In operando, water is always present and alters the properties of the catalysts. To improve these properties and allow a rational design of catalysts, a fundamental understanding of the active crystal facets and their reactivity upon water adsorption is essential. We use ab initio molecular dynamics to understand the effect of water, aqueous solutions and solvation on the structure and reactivity of the Co3O4(001) surface. |
Monday, March 2, 2020 10:24AM - 10:36AM |
A52.00013: Confined Catalysis under 2D silica: A CO Oxidation Study Calley Eads, J. Anibal Boscoboinik, Ashley Head, Dario Stacchiola, Samuel Tenney Open metal surfaces play an active role in heterogeneous catalysis reactions such as the prolific CO oxidation reaction to produce CO2. The addition of a nanostructured film on the metal surface changes the reaction kinetics and dynamics due to confinement effects under the cover. We illustrate the role of porous 2D silica grown on Pd(111) in the model reaction of CO oxidation at the interface of palladium and silica using in situ infrared reflection-absorption spectroscopy (IRRAS), mass spectroscopy (MS) and ambient pressure X-ray photoelectron spectroscopy (APXPS). Our findings suggest that 2D silica more effectively converts CO and O2 to CO2 under industrially-relevant conditions than the bare Pd(111) alone. 2D confinement effects enhance CO2 production even with less CO bound species involved in the reaction. |
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A52.00014: Probing two-dimensional ices with scanning probe microscopy Ye Tian, Runze Ma, Duanyun Cao, Chongqin Zhu, Jinbo Peng, Jing Guo, Ji Chen, Xin-Zheng Li, Joseph S Francisco, Xiao Cheng Zeng, Limei Xu, Enge Wang, Ying Jiang Two-dimensional (2D) water/ices are responsible for a broad spectrum of phenomena in materials science, chemistry, and biology. Particularly, the edges of 2D ice play key roles in the ice growth, melting and catalytic reaction, but atomic-scale structural characterization still remains a big challenge due to the fragileness and high reactivity of the ice edges. Here we report atomic-scale imaging of the edge structures of a 2D bilayer ice grown on Au(111) surface with weakly perturbative non-contact atomic force microscopy (1, 2). We found a new type of edge, aligning along the armchairdirection but reconstructed with 5756-member rings, coexisting with the zigzag edge commonly observed in two-dimensional hexagonal crystals. We were further able to deduce different growth behaviors for the zigzag and armchair edges from the frozen metastable structures at the two edges. In addition, we explore the impact of alkali metal ions on the structure of 2D ice. By changing the concentration of alkali metal ions, various new ice phases can be obtained. Those results reveal new understanding of the stability and growth of 2D ices. |
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