1
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McDowell BW, Taber BN, Mills JM, Gervasi CF, Honda M, Nazin GV. Modulation of Carbon Nanotube Electronic Structure by Grain Boundary Defects in RbI on Au(111). J Phys Chem Lett 2024; 15:439-446. [PMID: 38189654 DOI: 10.1021/acs.jpclett.3c02974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
The electronic properties of single-walled carbon nanotubes (SWCNTs) are known to be highly sensitive to environmental effects. Here, we use scanning tunneling microscopy and spectroscopy to investigate the electronic properties of SWCNTs deposited on RbI monolayer films grown on Au(111). We find that grain boundary defects in RbI monolayers cause the appearance of spatially confined localized states in the SWCNTs. Our density functional theory calculations show that grain boundary defects in RbI/Au(111) produce a stabilizing electrostatic potential caused by reduced coordination of iodine atoms at the RbI grain boundary. The presented results may offer insights into the performance of devices involving transport through SWCNTs subjected to external electrostatic disorder.
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Affiliation(s)
- Benjamin W McDowell
- Department of Chemistry and Biochemistry, Materials Science Institute, Oregon Center for Optical, Molecular, and Quantum Science, University of Oregon, 1253 University of Oregon, Eugene, Oregon 97403, United States
| | - Benjamen N Taber
- Department of Chemistry and Biochemistry, Materials Science Institute, Oregon Center for Optical, Molecular, and Quantum Science, University of Oregon, 1253 University of Oregon, Eugene, Oregon 97403, United States
| | - Jon M Mills
- Department of Chemistry and Biochemistry, Materials Science Institute, Oregon Center for Optical, Molecular, and Quantum Science, University of Oregon, 1253 University of Oregon, Eugene, Oregon 97403, United States
| | - Christian F Gervasi
- Department of Chemistry and Biochemistry, Materials Science Institute, Oregon Center for Optical, Molecular, and Quantum Science, University of Oregon, 1253 University of Oregon, Eugene, Oregon 97403, United States
| | - Motoaki Honda
- Department of Chemistry and Biochemistry, Materials Science Institute, Oregon Center for Optical, Molecular, and Quantum Science, University of Oregon, 1253 University of Oregon, Eugene, Oregon 97403, United States
| | - George V Nazin
- Department of Chemistry and Biochemistry, Materials Science Institute, Oregon Center for Optical, Molecular, and Quantum Science, University of Oregon, 1253 University of Oregon, Eugene, Oregon 97403, United States
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2
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Deng L, Qiu H, Wang B, Guo Z. Adjustable high-speed and directional diffusion of water nanodroplets confined by graphene sheets. Phys Chem Chem Phys 2023; 25:4266-4275. [PMID: 36688339 DOI: 10.1039/d2cp03421b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Diffusion of confined water is important in nanofluidic and other water transport systems. In this study, the diffusion of water nanodroplets confined by graphene sheets is investigated based on molecular dynamics simulations. We find that the confined water nanodroplets can achieve a high-speed and directional motion. The impact of the size of water nanodroplets and distance of graphene sheets on diffusion is studied. The results show that the diffusion of confined water nanodroplets is adjustable and the speed is about 3 orders of magnitude faster than that of the self-diffusing water molecules in liquid water. Subsequently, the most suitable morphology of confined nanodroplets for rapid movement is found. We also find that the direction of diffusion of confined water nanodroplets is affected by the thermal vibrations of carbon atoms. Finally, the interaction energy and friction coefficient between confined nanodroplets and graphene sheets are analyzed to give an insight into the fast and directional diffusion behaviors of water nanodroplets. Our results reveal that a variation in the structure of interfacial water molecules with the distance of graphene sheets is the key to the rapid movement of confined water nanodroplets. The phenomena reported here can enrich the knowledge of molecular mechanisms for nanoconfined water systems, and may stimulate more ideas for the rapid removal of confined water.
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Affiliation(s)
- Lijun Deng
- School of Science, Harbin Institute of Technology, ShenZhen, 518055, China.
| | - Hai Qiu
- School of Mechanical Engineering, Jiangsu University of Science and Technology, ZhenJiang, 212003, China
| | - Ben Wang
- School of Science, Harbin Institute of Technology, ShenZhen, 518055, China.
| | - Zaoyang Guo
- School of Science, Harbin Institute of Technology, ShenZhen, 518055, China.
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3
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Sacchi M, Tamtögl A. Water adsorption and dynamics on graphene and other 2D materials: Computational and experimental advances. ADVANCES IN PHYSICS: X 2022; 8:2134051. [PMID: 36816858 PMCID: PMC7614201 DOI: 10.1080/23746149.2022.2134051] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 06/18/2023] Open
Abstract
The interaction of water and surfaces, at molecular level, is of critical importance for understanding processes such as corrosion, friction, catalysis and mass transport. The significant literature on interactions with single crystal metal surfaces should not obscure unknowns in the unique behaviour of ice and the complex relationships between adsorption, diffusion and long-range inter-molecular interactions. Even less is known about the atomic-scale behaviour of water on novel, non-metallic interfaces, in particular on graphene and other 2D materials. In this manuscript, we review recent progress in the characterisation of water adsorption on 2D materials, with a focus on the nano-material graphene and graphitic nanostructures; materials which are of paramount importance for separation technologies, electrochemistry and catalysis, to name a few. The adsorption of water on graphene has also become one of the benchmark systems for modern computational methods, in particular dispersion-corrected density functional theory (DFT). We then review recent experimental and theoretical advances in studying the single-molecular motion of water at surfaces, with a special emphasis on scattering approaches as they allow an unparalleled window of observation to water surface motion, including diffusion, vibration and self-assembly.
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Affiliation(s)
- M. Sacchi
- Department of Chemistry, University of Surrey, Guildford GU2 7XH, UK
| | - A. Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria
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4
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Ivashchenko O. Cryo-SEM and confocal LSM studies of agar gel, nanoparticle hydrocolloid, mineral clays and saline solutions. Sci Rep 2022; 12:9930. [PMID: 35705670 PMCID: PMC9200766 DOI: 10.1038/s41598-022-14230-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Accepted: 06/02/2022] [Indexed: 11/09/2022] Open
Abstract
Cryogenic electron microscopy became a powerful tool to study biological objects. For non-biological objects (solutions, gels, dispersions, clays), the polemic about interpretation of cryogenic microscopy results is still in progress splitting on two contradictive trends: considering structure as a near-real state of the sample or as freezing artefacts. In this study, a microstructure of a range of stable aqueous solutions and dispersions (agar, kaolin, montmorillonite, nanoparticles) was investigated by means of cryo-SEM and confocal LSM in order to compare cryo-fixed and unfrozen structures. Noticed correlation between these two methods for studied systems (agar, kaolin, montmorillonite, NPs) allowed to state that ordered microstructure is an inherent feature of these systems. Some inconsistencies in microstructure dimensions were discussed and prescribed to the differences in the bulk and interface layers. Supposedly, NaCl solutions also possess dynamic (femtosecond level) microstructure of neat water clusters and solvated Na+ and Cl- ions that may have an impact on electrolyte abnormal properties.
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Affiliation(s)
- Olena Ivashchenko
- NanoBioMedical Centre, Adam Mickiewicz University, 61-614, Poznań, Poland.
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5
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Tamtögl A, Bahn E, Sacchi M, Zhu J, Ward DJ, Jardine AP, Jenkins SJ, Fouquet P, Ellis J, Allison W. Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene. Nat Commun 2021; 12:3120. [PMID: 34035257 PMCID: PMC8149658 DOI: 10.1038/s41467-021-23226-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 04/16/2021] [Indexed: 02/04/2023] Open
Abstract
The interfacial behaviour of water remains a central question to fields as diverse as protein folding, friction and ice formation. While the properties of water at interfaces differ from those in the bulk, major gaps in our knowledge limit our understanding at the molecular level. Information concerning the microscopic motion of water comes mostly from computation and, on an atomic scale, is largely unexplored by experiment. Here, we provide a detailed insight into the behaviour of water monomers on a graphene surface. The motion displays remarkably strong signatures of cooperative behaviour due to repulsive forces between the monomers, enhancing the monomer lifetime ( ≈ 3 s at 125 K) in a free-gas phase that precedes the nucleation of ice islands and, in turn, provides the opportunity for our experiments to be performed. Our results give a molecular perspective on a kinetic barrier to ice nucleation, providing routes to understand and control the processes involved in ice formation.
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Affiliation(s)
- Anton Tamtögl
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria.
| | - Emanuel Bahn
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany
| | - Marco Sacchi
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
- Department of Chemistry, University of Surrey, Guildford, UK.
| | - Jianding Zhu
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - David J Ward
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | | | - Stephen J Jenkins
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | | | - John Ellis
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - William Allison
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
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6
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Jiang L, Wang S, Liu D, Zhang W, Lu G, Liu Y, Zhao J. Change in Convection Mixing Properties with Salinity and Temperature: CO 2 Storage Application. Polymers (Basel) 2020; 12:polym12092084. [PMID: 32937738 PMCID: PMC7570007 DOI: 10.3390/polym12092084] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 09/01/2020] [Accepted: 09/03/2020] [Indexed: 11/16/2022] Open
Abstract
In this study, we visualised CO2-brine, density-driven convection in a Hele-Shaw cell. Several experiments were conducted to analyse the effects of the salinity and temperature. The salinity and temperature of fluids were selected according to the storage site. By using charge coupled device (CCD) technology, convection finger formation and development were obtained through direct imaging and processing. The process can be divided into three stages: diffusion-dominated, convection-dominated and shutdown stages. Fingers were formed along the boundary at the onset time, reflecting the startup of convection mixing. Fingers formed, moved and aggregated with adjacent fingers during the convection-dominated stage. The relative migration of brine-saturated CO2 and brine enhanced the mass transfer. The effects of salinity and temperature on finger formation, number, and migration were analysed. Increasing the salinity accelerated finger formation but suppressed finger movement, and the onset time was inversely related to the salinity. However, the effect of temperature on convection is complex. The dissolved CO2 mass was investigated by calculating the CO2 mass fraction in brine during convection mixing. The results show that convection mixing greatly enhanced mass transfer. The study has implications for predicting the CO2 dissolution trapping time and accumulation for the geological storage of CO2.
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Affiliation(s)
| | | | | | | | | | - Yu Liu
- Correspondence: (Y.L.); (J.Z.)
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7
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Abstract
The diffusion of water molecules and clusters across the surfaces of materials is important to a wide range of processes. Interestingly, experiments have shown that on certain substrates, water dimers can diffuse more rapidly than water monomers. Whilst explanations for anomalously fast diffusion have been presented for specific systems, the general underlying physical principles are not yet established. We investigate this through a systematic ab initio study of water monomer and dimer diffusion on a range of surfaces. Calculations reveal different mechanisms for fast water dimer diffusion, which is found to be more widespread than previously anticipated. The key factors affecting diffusion are the balance of water-water versus water-surface bonding and the ease with which hydrogen-bond exchange can occur (either through a classical over-the-barrier process or through quantum-mechanical tunnelling). We anticipate that the insights gained will be useful for understanding future experiments on the diffusion and clustering of hydrogen-bonded adsorbates. The experimental observation that water dimers diffuse more rapidly than monomers across materials’ surfaces is yet to be clarified. Here the authors show by ab initio calculations classical and quantum mechanical mechanisms for faster water dimer diffusion on a broad range of metal and non-metal surfaces.
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8
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Tamtögl A, Sacchi M, Avidor N, Calvo-Almazán I, Townsend PSM, Bremholm M, Hofmann P, Ellis J, Allison W. Nanoscopic diffusion of water on a topological insulator. Nat Commun 2020; 11:278. [PMID: 31937778 PMCID: PMC6959239 DOI: 10.1038/s41467-019-14064-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 12/13/2019] [Indexed: 11/12/2022] Open
Abstract
The microscopic motion of water is a central question, but gaining experimental information about the interfacial dynamics of water in fields such as catalysis, biophysics and nanotribology is challenging due to its ultrafast motion, and the complex interplay of inter-molecular and molecule-surface interactions. Here we present an experimental and computational study of the nanoscale-nanosecond motion of water at the surface of a topological insulator (TI), Bi[Formula: see text]Te[Formula: see text]. Understanding the chemistry and motion of molecules on TI surfaces, while considered a key to design and manufacturing for future applications, has hitherto been hardly addressed experimentally. By combining helium spin-echo spectroscopy and density functional theory calculations, we are able to obtain a general insight into the diffusion of water on Bi[Formula: see text]Te[Formula: see text]. Instead of Brownian motion, we find an activated jump diffusion mechanism. Signatures of correlated motion suggest unusual repulsive interactions between the water molecules. From the lineshape broadening we determine the diffusion coefficient, the diffusion energy and the pre-exponential factor.
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Affiliation(s)
- Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010, Graz, Austria.
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK.
| | - Marco Sacchi
- Department of Chemistry, University of Surrey, Guildford, GU2 7XH, UK
| | - Nadav Avidor
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
| | - Irene Calvo-Almazán
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
- Material Science Division, Argonne National Laboratory, Argonne, 60439, IL, USA
| | - Peter S M Townsend
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
- Department of Chemistry and Chemical Biology, Rutgers University, 123 Bevier Road, Piscataway, NJ, 08854, USA
| | - Martin Bremholm
- Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, 8000, Aarhus, Denmark
| | - Philip Hofmann
- Department of Physics and Astronomy, Interdisciplinary Nanoscience Center (iNANO), Aarhus University, 8000, Aarhus C, Denmark
| | - John Ellis
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
| | - William Allison
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge, CB3 0HE, UK
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9
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Doležal J, Merino P, Redondo J, Ondič L, Cahlík A, Švec M. Charge Carrier Injection Electroluminescence with CO-Functionalized Tips on Single Molecular Emitters. NANO LETTERS 2019; 19:8605-8611. [PMID: 31738569 PMCID: PMC7116301 DOI: 10.1021/acs.nanolett.9b03180] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force, and light detection capabilities. The role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), using metal and CO-metal tips. CO-functionalization is found to have an impact on the resolution and contrast of the photon maps due to the localized overlap of the p-orbitals on the tip with the molecular orbitals of the emitter. The possibility of using the same CO-functionalized tip for tip-enhanced photon detection and high resolution atomic force is demonstrated. We study the electroluminescence of ZnPc, induced by charge carrier injection at sufficiently high bias voltages. We propose that the distinct level alignment of the ZnPc frontier orbitals with the Au(111) and Ag(111) Fermi levels governs the primary excitation mechanisms as the injection of electrons and holes from the tip into the molecule, respectively. These findings put forward the importance of the tip status in the photon maps and contribute to a better understanding of the photophysics of organic molecules on surfaces.
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Affiliation(s)
- Jiří Doležal
- Institute of Physics, Czech Academy of Sciences, Praha, Czech Republic
| | - Pablo Merino
- Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, E28049, Madrid, Spain
- Instituto de Física Fundamental, CSIC, Serrano 121, E28006, Madrid, Spain
| | - Jesus Redondo
- Institute of Physics, Czech Academy of Sciences, Praha, Czech Republic
| | - Lukáš Ondič
- Institute of Physics, Czech Academy of Sciences, Praha, Czech Republic
| | - Aleš Cahlík
- Institute of Physics, Czech Academy of Sciences, Praha, Czech Republic
- Regional Center for Advanced Materials and Technologies, Olomouc, Czech Republic
| | - Martin Švec
- Institute of Physics, Czech Academy of Sciences, Praha, Czech Republic
- Regional Center for Advanced Materials and Technologies, Olomouc, Czech Republic
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10
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Bertram C, Fang W, Pedevilla P, Michaelides A, Morgenstern K. Anomalously Low Barrier for Water Dimer Diffusion on Cu(111). NANO LETTERS 2019; 19:3049-3056. [PMID: 30947502 DOI: 10.1021/acs.nanolett.9b00392] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
A molecular-scale description of water and ice is important in fields as diverse as atmospheric chemistry, astrophysics, and biology. Despite a detailed understanding of water and ice structures on a multitude of surfaces, relatively little is known about the kinetics of water motion on surfaces. Here, we report a detailed study on the diffusion of water monomers and the formation and diffusion of water dimers through a combination of time-lapse low-temperature scanning tunnelling microscopy experiments and first-principles electronic structure calculations on the atomically flat Cu(111) surface. On the basis of an unprecedented long-time study of individual water monomers and dimers over days, we establish rates and mechanisms of water monomer and dimer diffusion. Interestingly, we find that the monomer and the dimer diffusion barriers are similar, despite the significantly larger adsorption energy of the dimer. This is thus a violation of the rule of thumb that relates diffusion barriers to adsorption energies, an effect that arises because of the directional and flexible hydrogen bond within the dimer. This flexibility during diffusion should also be relevant for larger water clusters and other hydrogen-bonded adsorbates. Our study stresses that a molecular-scale understanding of the initial stages of ice nanocluster formation is not possible on the basis of static structure investigations alone.
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Affiliation(s)
- Cord Bertram
- Physical Chemistry I, Department of Chemistry and Biochemistry , Ruhr-Universität Bochum , D-44780 Bochum , Germany
- Faculty of Physics , University of Duisburg-Essen , Lotharstraße 1 , D-47057 Duisburg , Germany
| | - Wei Fang
- Thomas Young Centre, London Centre for Nanotechnology, London WC1E 6BT , U.K
- Department of Physics and Astronomy , University College London , London WC1E 6BT , U.K
- Laboratory of Physical Chemistry , ETH Zurich , CH-8093 Zurich , Switzerland
| | - Phillipp Pedevilla
- Thomas Young Centre, London Centre for Nanotechnology, London WC1E 6BT , U.K
- Department of Physics and Astronomy , University College London , London WC1E 6BT , U.K
| | - Angelos Michaelides
- Thomas Young Centre, London Centre for Nanotechnology, London WC1E 6BT , U.K
- Department of Physics and Astronomy , University College London , London WC1E 6BT , U.K
| | - Karina Morgenstern
- Physical Chemistry I, Department of Chemistry and Biochemistry , Ruhr-Universität Bochum , D-44780 Bochum , Germany
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11
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Quantifying the dynamic density driven convection in high permeability packed beds. Magn Reson Imaging 2017; 39:168-174. [PMID: 28315390 DOI: 10.1016/j.mri.2017.03.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 03/09/2017] [Accepted: 03/11/2017] [Indexed: 10/20/2022]
Abstract
The density driven convection phenomenon is expected to have a significant and positive role in CO2 geological storage capacity and safety. The onset and development of density-driven convective on the core scale is critical to understand the mass transfer mechanism. In this paper, laboratory experiments were conducted to investigate the density-driven convective in a vertical tube. The deuterium oxide (D2O)/manganese chloride (MnCl2) water solution in water or brine were as an analog for CO2-rich brine in original brine. Experiments are repeated with variations in permeability to vary the characteristic Rayleigh number. Based on the MRI technology, the intensity images showed the interface clearly, reflecting the transition from diffusion to convective. With the echo-multi-slice pulse sequence method, the intensity images can be obtained as 2min 8s. For the denser fluid pairs, fingers appeared, propagated, coalesced and multi-fingers formed. The finger growth rate of the convective was visualized as three distinct periods: rising, stable and declining. Detailed information regarding the wave number, wave length, onset time and mixing time as functions of Rayleigh number are developed.
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12
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Antczak G, Kamiński W, Sabik A, Zaum C, Morgenstern K. Complex Surface Diffusion Mechanisms of Cobalt Phthalocyanine Molecules on Ag(100). J Am Chem Soc 2015; 137:14920-9. [PMID: 26584143 DOI: 10.1021/jacs.5b08001] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
We used time-lapsed scanning tunneling microscopy between 43 and 50 K and density functional theory (DFT) to explore the basic surface diffusion steps of cobalt phthalocyanine (CoPc) molecules on the Ag(100) surface. We show that the CoPc molecules translate and rotate on the surface in the same temperature range. Both processes are associated with similar activation energies; however, the translation is more frequently observed. Our DFT calculations provide the activation energies for the translation of the CoPc molecule between the nearest hollow sites and the rotation at both the hollow and the bridge sites. The activation energies are only consistent with the experimental findings, if the surface diffusion mechanism involves a combined translational and rotational molecular motion. Additionally, two channels of motion are identified: the first provides only a channel for translation, while the second provides a channel for both the translation and the rotation. The existence of the two channels explains a higher rate for the translation determined in experiment.
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Affiliation(s)
- Grażyna Antczak
- Institute of Experimental Physics, University of Wrocław , Wrocław, Poland
| | - Wojciech Kamiński
- Institute of Experimental Physics, University of Wrocław , Wrocław, Poland
| | - Agata Sabik
- Institute of Experimental Physics, University of Wrocław , Wrocław, Poland
| | | | - Karina Morgenstern
- Chair for Physical Chemistry I, Ruhr-Universität Bochum , Bochum, Germany
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13
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Abstract
The adsorption and reactions of water on surfaces has attracted great interest, as water is involved in many physical and chemical processes at interfaces. On metal surfaces, the adsorption energy of water is comparable to the hydrogen bond strength in water. Therefore, the delicate balance between the water-water and the water-metal interaction strength determines the stability of water structures. In such systems, kinetic effects play an important role and many metastable states can form with long lifetimes, such that the most stable state may not reached. This has led to difficulties in the theoretical prediction of water structures as well as to some controversial results. The direct imaging using scanning tunneling microscopy (STM) in ultrahigh vacuum at low temperatures offers a reliable means of understanding the local structure and reaction of water molecules, in particular when interpreted in conjunction with density functional theory calculations. In this Account, a selection of recent STM results on the water adsorption and dissociation on close-packed metal surfaces is reviewed, with a particular focus on Ru(0001). The Ru(0001) surface is one where water adsorbs intact in a metastable state at low temperatures and where partially dissociated layers are formed at temperatures above ∼150 K. First, we will describe the structure of intact water clusters starting with the monomer up to the monolayer. We show that icelike wetting layers do not occur on close-packed metal surfaces but instead hydrogen bonded layers in the form of a mixture of pentagonal, hexagonal, and heptagonal molecular rings are observed. Second, we will discuss the dissociation mechanism of water on Ru(0001). We demonstrate that water adsorption changes from dissociative to molecular as a function of the oxygen preadsorbed on Ru. Finally, we briefly review recent STM experiments on bulk ice (Ih and Ic) and water adsorption on insulating thin films. We conclude with an outlook illustrating the manipulation capabilities of STM in respect to probe the proton and hydrogen dynamics in water clusters.
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Affiliation(s)
- Sabine Maier
- Department
of Physics, University of Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Miquel Salmeron
- Materials
Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, United States
- Materials
Science and Engineering Department, University of California, Berkeley, California 94720, United States
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