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Full-Text Articles in Physics

Energetics Of Cu Adsorption And Intercalation At Graphite Step Edges, Yong Han, Ann Lii-Rosales, Michael C. Tringides, James W. Evans, Patricia A. Thiel Mar 2019

Energetics Of Cu Adsorption And Intercalation At Graphite Step Edges, Yong Han, Ann Lii-Rosales, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

To assess the energetics of Cu intercalation on defective graphite, the chemical potentials and binding energies for Cu at graphite step edges are calculated for three main configurations: an isolated atom, a chain, and an atom attached to a chain. As expected, for Cu interacting directly with a graphite step edge, the strength of interaction depends on the stability of the step, with Cu binding more strongly at a less-stable step. However, the relationship is reversed when considering binding of a Cu atom attached to a chain. Taken together, these trends mean that if the graphite step is less stable ...


Defect-Mediated, Thermally-Activated Encapsulation Of Metals At The Surface Of Graphite, Yinghui Zhou, Ann Lii-Rosales, Minsung Kim, Mark Wallingford, Dapeng Jing, Michael C. Tringides, Cai-Zhuang Wang, Patricia A. Thiel Feb 2018

Defect-Mediated, Thermally-Activated Encapsulation Of Metals At The Surface Of Graphite, Yinghui Zhou, Ann Lii-Rosales, Minsung Kim, Mark Wallingford, Dapeng Jing, Michael C. Tringides, Cai-Zhuang Wang, Patricia A. Thiel

Chemistry Publications

We show that 3 metals – Dy, Ru, and Cu – can form multilayer intercalated (encapsulated) islands at the graphite (0001) surface if 2 specific conditions are met: Defects are introduced on the graphite terraces to act as entry portals, and the metal deposition temperature is well above ambient. Focusing on Dy as a prototype, we show that surface encapsulation is much different than bulk intercalation, because the encapsulated metal takes the form of bulk-like rafts of multilayer Dy, rather than the dilute, single-layer structure known for the bulk compound. Carbon-covered metallic rafts even form for relatively unreactive metals (Ru and Cu ...


Polar Intermetallics Pr5co2ge3 And Pr7co2ge4 With Planar Hydrocarbon‐Like Metal Clusters, Qisheng Lin, Kaiser Aguirre, Scott M. Saunders, Timothy A. Hackett, Yong Liu, Valentin Taufour, Durga Paudyal, Sergey L. Bud’Ko, Paul C. Canfield, Gordon J. Miller Aug 2017

Polar Intermetallics Pr5co2ge3 And Pr7co2ge4 With Planar Hydrocarbon‐Like Metal Clusters, Qisheng Lin, Kaiser Aguirre, Scott M. Saunders, Timothy A. Hackett, Yong Liu, Valentin Taufour, Durga Paudyal, Sergey L. Bud’Ko, Paul C. Canfield, Gordon J. Miller

Chemistry Publications

Planar hydrocarbon‐like metal clusters may foster new insights linking organic molecules with conjugated π–π bonding interactions and inorganic structures in terms of their bonding characteristics. However, such clusters are uncommon in polar intermetallics. Herein, we report two polar intermetallic phases, Pr5Co2Ge3 and Pr7Co2Ge4, both of which feature such planar metal clusters, namely, ethylene‐like [Co2Ge4] clusters plus the concatenated forms and polyacene‐like [Co2Ge2]n ribbons in Pr5Co2Ge3, and 1,2,4,5‐tetramethylbenzene‐like [Co4Ge6] cluster in Pr7Co2Ge4. Just as in the related planar organic structures, these metal–metalloid species are dominated by covalent bonding interactions. Both ...


Tailoring Nanoscale Morphology Of Polymer: Fullerene Blends Using Electrostatic Field, Moneim Elshobaki, Ryan S. Gebhardt, John Carr, William Lindemann, Wenjie Wang, Eric Grieser, Swaminathan Venkatesan, Evan Ngo, Ujjal Bhattacharjee, Joseph Strzalka, Zhang Jiang, Qiquan Qiao, Jacob W. Petrich, David Vaknin, Sumit Chaudhary Jan 2017

Tailoring Nanoscale Morphology Of Polymer: Fullerene Blends Using Electrostatic Field, Moneim Elshobaki, Ryan S. Gebhardt, John Carr, William Lindemann, Wenjie Wang, Eric Grieser, Swaminathan Venkatesan, Evan Ngo, Ujjal Bhattacharjee, Joseph Strzalka, Zhang Jiang, Qiquan Qiao, Jacob W. Petrich, David Vaknin, Sumit Chaudhary

Chemistry Publications

To tailor the nanomorphology in polymer/fullerene blends, we study the effect of electrostatic field (E-field) on the solidification of poly(3-hexylthiophene-2, 5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) bulk heterojunction (BHJ). In addition to control; wet P3HT:PC60BM thin films were exposed to E-field of Van de Graaff (VDG) generator at three different directions—horizontal (H), tilted (T), and vertical (V)—relative to the plane of the substrate. Surface and bulk characterizations of the field-treated BHJs affirmed that fullerene molecules can easily penetrate the spaghetti-like P3HT and move up and down following the E-field. Using E-field treatment ...


Physical Properties Of Single Crystalline R Mg 2 Cu 9 ( R = Y , Ce − Nd , Gd − Dy , Yb ) And The Search For In-Plane Magnetic Anisotropy In Hexagonal Systems, Tai Kong, William R. Meier, Qisheng Lin, Scott M. Saunders, S. L. Bud’Ko, Rebecca Flint, Paul C. Canfield Jan 2016

Physical Properties Of Single Crystalline R Mg 2 Cu 9 ( R = Y , Ce − Nd , Gd − Dy , Yb ) And The Search For In-Plane Magnetic Anisotropy In Hexagonal Systems, Tai Kong, William R. Meier, Qisheng Lin, Scott M. Saunders, S. L. Bud’Ko, Rebecca Flint, Paul C. Canfield

Chemistry Publications

Single crystals ofRMg2Cu9 (R = Y, Ce-Nd, Gd-Dy, Yb) were grown using a high-temperature solution growth technique and were characterized by measurements of room-temperature x-ray diffraction, temperature-dependent specific heat, and temperature- and field-dependent resistivity and anisotropic magnetization. YMg2Cu9 is a nonlocal- moment-bearing metal with an electronic specific heat coefficient, γ ∼ 15 mJ/mol K2. Yb is divalent and basically non-moment-bearing in YbMg2Cu9. Ce is trivalent in CeMg2Cu9 with two magnetic transitions being observed at 2.1 K and 1.5 K. PrMg2Cu9 does not exhibit any magnetic phase transition down to 0.5 K. The other members being studied (R = Nd ...


Preface: Special Topic On Supramolecular Self-Assembly At Surfaces, Ludwig Bartels, Karl-Heinz Ernst, Hong-Jun Gao, Patricia A. Thiel Jan 2015

Preface: Special Topic On Supramolecular Self-Assembly At Surfaces, Ludwig Bartels, Karl-Heinz Ernst, Hong-Jun Gao, Patricia A. Thiel

Chemistry Publications

Supramolecular self-assembly at surfaces is one of the most exciting and active fields in Surface Science today. Applications can take advantage of two key properties: (i) versatile pattern formation over a broad length scale and (ii) tunability of electronic structure and transport properties, as well as frontier orbital alignment. It provides a new frontier for Chemical Physics as it uniquely combines the versatility of Organic Synthesis and the Physics of Interfaces. The Journal of Chemical Physics is pleased to publish this Special Topic Issue, showcasing recent advances and new directions.


Cu2s3 Complex On Cu(111) As A Candidate For Mass Transport Enhancement, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Christine M. Aikens, Yousoo Kim, Patricia A. Thiel Jan 2015

Cu2s3 Complex On Cu(111) As A Candidate For Mass Transport Enhancement, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Christine M. Aikens, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Sulfur-metal complexes, containing only a few atoms, can open new, highly efficient pathways for transport of metal atoms on surfaces. For example, they can accelerate changes in the shape and size of morphological features, such as two-dimensional nanoclusters, over time. In this study we perform STM under conditions that are designed to specifically isolate such complexes. We find a new, unexpected S-Cu complex on the Cu(111) surface, which we identify as Cu2S3. We propose that Cu2S3 enhances mass transport in this system, which contradicts a previous proposal based on Cu3S3 ...


Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30◦ from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √ 3 times the surface lattice constant, a. Monte Carlo simulations are performed on ...


Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Arich menagerie of structures is identified at 5Kfollowing adsorption of lowcoverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their ...


Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides Dec 2014

Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides

Chemistry Publications

Classically, the onset of nucleation is defined in terms of a critical cluster of the condensed phase, which forms from the gradual aggregation of randomly diffusing adatoms. Experiments in Pb/Si(111) at low temperature have discovered a dramatically different type of nucleation, with perfect crystalline islands emerging “explosively” out of the compressed wetting layer after a critical coverage Θc ¼ 1.22 ML is reached. The unexpectedly high island growth rates, the directional correlations in the growth of neighboring islands and the persistence in time of where mass is added in individual islands, suggest that nucleation is a result ...


Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel Nov 2014

Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel

Chemistry Publications

We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.


Transition Metals On The (0001) Surface Of Graphite: Fundamental Aspects Of Adsorption, Diffusion, And Morphology, David Victor Appy, Huaping Lei, Cai-Zhuang Wang, Michael C. Tringides, Da-Jiang Liu, James W. Evans, Patricia A. Thiel Jan 2014

Transition Metals On The (0001) Surface Of Graphite: Fundamental Aspects Of Adsorption, Diffusion, And Morphology, David Victor Appy, Huaping Lei, Cai-Zhuang Wang, Michael C. Tringides, Da-Jiang Liu, James W. Evans, Patricia A. Thiel

Chemistry Publications

In this article, we review basic information about the interaction of transition metal atoms with the (0001) surface of graphite, especially fundamental phenomena related to growth. Those phenomena involve adatom-surface bonding, diffusion, morphology of metal clusters, interactions with steps and sputter-induced defects, condensation, and desorption. General traits emerge which have not been summarized previously. Some of these features are rather surprising when compared with metal-on-metal adsorption and growth. Opportunities for future work are pointed out.


Search For The Structure Of A Sulfur-Induced Reconstruction On Cu(111), Da-Jiang Liu, Holly L. Walen, Junepyo Oh, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2014

Search For The Structure Of A Sulfur-Induced Reconstruction On Cu(111), Da-Jiang Liu, Holly L. Walen, Junepyo Oh, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

We have carried out an extensive DFT-based search for the structure of the (√43 × √43)R ± 7.5° reconstruction of S on Cu(111), which exhibits a honeycombtype structure in scanning tunneling microscopy (STM). We apply two criteria in this search: The structure must have a reasonably low chemical potential, and it must provide a good match with STM data, both our own and the data published by Wahlström et al. Phys. Rev. B 1999, 60, 10699. The best model has 12 S adatoms and 9 Cu adatoms per unit cell. Local defects within the Cu9S12 framework, consisting of ...


Β-Mn-Type Co8+Xzn12–X As A Defect Cubic Laves Phase: Site Preferences, Magnetism, And Electronic Structure, Weiwei Xie, Srinvasa Timmaiah, Jagat Lamal, Jing Liu, Thomas W. Heitmann, Dante Quirinale, A. I. Goldman, Vitalij K. Pecharsky, Gordon J. Miller Jan 2013

Β-Mn-Type Co8+Xzn12–X As A Defect Cubic Laves Phase: Site Preferences, Magnetism, And Electronic Structure, Weiwei Xie, Srinvasa Timmaiah, Jagat Lamal, Jing Liu, Thomas W. Heitmann, Dante Quirinale, A. I. Goldman, Vitalij K. Pecharsky, Gordon J. Miller

Chemistry Publications

The results of crystallographic analysis, magnetic characterization, and theoretical assessment of β-Mn-type Co–Zn intermetallics prepared using high-temperature methods are presented. These β-Mn Co–Zn phases crystallize in the space group P4132 [Pearson symbol cP20; a = 6.3555(7)–6.3220(7)], and their stoichiometry may be expressed as Co8+xZn12–x [1.7(2) < x < 2.2(2)]. According to a combination of single-crystal X-ray diffraction, neutron powder diffraction, and scanning electron microscopy, atomic site occupancies establish clear preferences for Co atoms in the 8c sites and Zn atoms in the 12d sites, with all additional Co atoms replacing some Zn atoms, a result that can be rationalized by electronic structure calculations. Magnetic measurements and neutron powder diffraction of an equimolar Co:Zn sample confirm ferromagnetism in this phase with a Curie temperature of ∼420 K. Neutron powder diffraction and electronic structure calculations using the local spin density approximation indicate that the spontaneous magnetization of this phase arises exclusively from local moments at the Co atoms. Inspection of the atomic arrangements of Co8+xZn12–x reveals that the β-Mn aristotype may be derived from an ordered defect, cubic Laves phase (MgCu2-type) structure. Structural optimization procedures using the Vienna ab initio simulation package (VASP) and starting ...


Communication: Structure, Formation, And Equilibration Of Ensembles Of Ag-S Complexes On An Ag Surface, Selena M. Russell, Yousoo Kim, Da-Jiang Liu, James W. Evans, Patricia A. Thiel Jan 2013

Communication: Structure, Formation, And Equilibration Of Ensembles Of Ag-S Complexes On An Ag Surface, Selena M. Russell, Yousoo Kim, Da-Jiang Liu, James W. Evans, Patricia A. Thiel

Chemistry Publications

We have utilized conditions of very low temperature (4.7 K) and very low sulfur coverage to isolate and identify Ag-S complexes that exist on the Ag(111) surface. The experimental conditions are such that the complexes form at temperatures above the temperature of observation. These complexes can be regarded as polymeric chains of varying length, with an Ag4S pyramid at the core of each monomeric unit. Steps may catalyze the formation of the chains and this mechanism may be reflected in the chain length distribution.


Anisotropic Coarsening: One-Dimensional Decay Of Ag Islands On Ag(110), Yong Han, Selena M. Russell, Anthony R. Layson, Holly L. Walen, Chad D. Yuen, Patricia A. Thiel, James W. Evans Jan 2013

Anisotropic Coarsening: One-Dimensional Decay Of Ag Islands On Ag(110), Yong Han, Selena M. Russell, Anthony R. Layson, Holly L. Walen, Chad D. Yuen, Patricia A. Thiel, James W. Evans

Chemistry Publications

Scanning tunneling microscopy studies show that coarsening of arrays of rectangular single-layer Ag islands on Ag(110) at 220 K and below occurs by one-dimensional (1D) decay of narrower islands, which maintain roughly constant width in the 〈001〉 direction. Adatoms mainly detach from the island ends with 〈001〉 step edges. 1D decay derives from the absence of corner rounding diffusion from 〈001〉 to 〈1̅ 10〉 edges and from inhibited nucleation of new layers on 〈1̅ 10〉 edges. In contrast, rounding from 〈1̅ 10〉 to 〈001〉 edges is active. The island decay rate exhibits an unexpectedly low effective Arrhenius energy due ...


Creating Nanoscale Ag Patterns On The Si(111)–(√3 × √3)R30°-Ag Surface Via Guided Self-Assembly, Alex Belianinov, Barış Ünal, Michael C. Tringides, Patricia A. Thiel Jul 2012

Creating Nanoscale Ag Patterns On The Si(111)–(√3 × √3)R30°-Ag Surface Via Guided Self-Assembly, Alex Belianinov, Barış Ünal, Michael C. Tringides, Patricia A. Thiel

Chemistry Publications

Patterns of Ag nanostructures can be created on the Si(111)–(√3 × √3)R30°-Ag surface, using a simple two-step process in ultrahigh vacuum. First, patterns are created using the tip of a scanning tunneling microscope. Second, Ag is deposited at room temperature. The Ag diffuses over long distances on the surface and selectively aggregates at the patterned regions. The size of the Ag features is ∼3–4 nm.


Growth Morphology And Thermal Stability Of Metal Islands On Graphene, Xiaojie Liu, Myron Hupalo, Cai-Zhuang Wang, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, Michael C. Tringides Jan 2012

Growth Morphology And Thermal Stability Of Metal Islands On Graphene, Xiaojie Liu, Myron Hupalo, Cai-Zhuang Wang, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, Michael C. Tringides

Chemistry Publications

We performed an experiment to study the thermal stability of metal on graphene. We show that Fe, Gd, Dy, and Eu on graphene exhibit island growth morphology. The 3D islands of Fe, Gd, and Dy show a small decrease in island density and an increase in the height/width aspect ratio upon thermal annealing. By contrast, coarsening of Eu islands to a close flat film is observed after annealing to 365 K. By investigating the fundamental interactions (i.e., adsorption energies and diffusion barriers) between the metal adatoms and graphene using ab initio calculations, we predict that most of the ...


High Island Densities And Long Range Repulsive Interactions: Fe On Epitaxial Graphene, Steven Michael Binz, Myron Hupalo, Xiaojie Liu, Cai-Zhuang Wang, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, E. H. Conrad, Michael C. Tringides Jan 2012

High Island Densities And Long Range Repulsive Interactions: Fe On Epitaxial Graphene, Steven Michael Binz, Myron Hupalo, Xiaojie Liu, Cai-Zhuang Wang, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, E. H. Conrad, Michael C. Tringides

Chemistry Publications

The understanding of metal nucleation on graphene is essential for promising future applications, especially of magnetic metals which can be used in spintronics or computer storage media. A common method to study the grown morphology is to measure the nucleated island density n as a function of growth parameters. Surprisingly, the growth of Fe on graphene is found to be unusual because it does not follow classical nucleation: n is unexpectedtly high, it increases continuously with the deposited amount θ and shows no temperature dependence. These unusual results indicate the presence of long range repulsive interactions. Kinetic Monte Carlo simulations ...


Destabilization Of Ag Nanoislands On Ag(100) By Adsorbed Sulfur, Mingmin Shen, Selena M. Russell, Da-Jiang Liu, Patricia A. Thiel Jan 2011

Destabilization Of Ag Nanoislands On Ag(100) By Adsorbed Sulfur, Mingmin Shen, Selena M. Russell, Da-Jiang Liu, Patricia A. Thiel

Chemistry Publications

Sulfur accelerates coarsening of Ag nanoislands on Ag(100) at 300 K, and this effect is enhanced with increasing sulfur coverage over a range spanning a few hundredths of a monolayer, to nearly 0.25 monolayers. We propose that acceleration of coarsening in this system is tied to the formation of AgS2 clusters primarily at step edges. These clusters can transport Ag more efficiently than can Ag adatoms (due to a lower diffusion barrier and comparable formation energy). The mobility of isolated sulfur on Ag(100) is very low so that formation of the complex is kinetically limited at ...


Fe-Fe Adatom Interaction And Growth Morphology On Graphene, Xiaojie Liu, Cai-Zhuang Wang, Myron Hupalo, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, Michael C. Tringides Jan 2011

Fe-Fe Adatom Interaction And Growth Morphology On Graphene, Xiaojie Liu, Cai-Zhuang Wang, Myron Hupalo, Wen-Cai Lu, Patricia A. Thiel, Kai-Ming Ho, Michael C. Tringides

Chemistry Publications

The nucleation and growth of Fe on graphene is highly unusual. A constantly increasing island density indicates the presence of strong, predominantly repulsive, adatom interactions. We study these interactions by first-principles calculations to identify their origin. We find that the interactions consist of a short-range attraction and longer-range repulsion. We show that electric dipole-dipole interaction can contribute only part of the repulsive force (∼30%) between Fe adatoms, and the repulsion due to the elastic interaction is small. We suggest that the dominant contribution to the repulsive energy would originate from the indirect (or RKKY) interactions mediated through the delocalized electrons ...


Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel Jan 2010

Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

H2S forms a rich variety of structures on Ag(111) at low temperature and submonolayer coverage. The molecules decorate step edges, exist as isolated entities on terraces, and aggregate into clusters and islands, under various conditions. One type of island exhibits a (×)R25.3° unit cell. Typically, molecules in the clusters and islands are separated by about 0.4 nm, the same as the S–S separation in crystalline H2S. Density functional theory indicates that hydrogen-bonded clusters contain two types of molecules. One is very similar to an isolated adsorbed H2S molecule, with both ...


Adsorbate-Enhanced Transport Of Metals On Metal Surfaces: Oxygen And Sulfur On Coinage Metals, Patricia A. Thiel, Mingmin Shen, Da-Jiang Liu, James W. Evans Jan 2010

Adsorbate-Enhanced Transport Of Metals On Metal Surfaces: Oxygen And Sulfur On Coinage Metals, Patricia A. Thiel, Mingmin Shen, Da-Jiang Liu, James W. Evans

Chemistry Publications

Coarsening (i.e., ripening) of single-atom-high, metal homoepitaxial islands provides a useful window on the mechanism and kinetics of mass transport at metal surfaces. This article focuses on this type of coarsening on the surfaces of coinage metals (Cu, Ag, Au), both clean and with an adsorbed chalcogen (O, S) present. For the clean surfaces, three aspects are summarized: (1) the balance between the two major mechanisms—Ostwald ripening (the most commonly anticipated mechanism) and Smoluchowski ripening—and how that balance depends on island size; (2) the nature of the mass transport agents, which are metal adatoms in almost all ...


Variation Of Growth Morphology With Chemical Composition Of Terraces: Ag On A Twofold Surface Of A Decagonal Al-Cu-Co Quasicrystal, T. Duguet, Barış Ünal, Yong Han, James W. Evans, J. Ledieu, Cynthia J. Jenks, J.-M. Dubois, V. Fournée, Patricia A. Thiel Jan 2010

Variation Of Growth Morphology With Chemical Composition Of Terraces: Ag On A Twofold Surface Of A Decagonal Al-Cu-Co Quasicrystal, T. Duguet, Barış Ünal, Yong Han, James W. Evans, J. Ledieu, Cynthia J. Jenks, J.-M. Dubois, V. Fournée, Patricia A. Thiel

Chemistry Publications

Growth of Ag thin films on the twofold surface of a decagonal Al-Cu-Co quasicrystal is characterized by scanning tunneling microscopy, at different temperatures, and for coverages ranging from submonolayer to 11 monolayers. From prior work, three types of clean surface terraces are known to exist. By correlation with a bulk structural model, the major difference between them lies in their transition-metal (TM) content, two being aluminum-rich (0 and 15 at. % TM) and one being TM-rich (40–50 at. % TM). The present article focuses on understanding the difference between Ag film morphologies on these terminations, in terms of their chemical content ...


Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, Barış Ünal, Alex Belianinov, Patricia A. Thiel, Michael C. Tringides Jan 2010

Lattice Expansion In Islands Stabilized By Electron Confinement: Ag On Si(111)-7×7, Barış Ünal, Alex Belianinov, Patricia A. Thiel, Michael C. Tringides

Chemistry Publications

Ag on Si(111)-7×7 was one of the first systems where height selection of metal islands was attributed to electron confinement, i.e., stabilization of selected heights through a quantum size effect (QSE). However, it has been puzzling how the requisite electron standing waves can form, because the Fermi level EF (along the growth [111] direction) is within the gap for bulk Ag. With detailed experiments over a wide coverage and temperature range, we show that a large increase of 12% is present in the interlayer spacing within the bilayer islands. This can shift EF below ...


Formation And Coarsening Of Ag(110) Bilayer Islands On Nial(110): Stm Analysis And Atomistic Lattice-Gas Modeling, Yong Han, Barış Ünal, Dapeng Jing, Feili Qin, Cynthia J. Jenks, Da-Jiang Liu, Patricia A. Thiel, James W. Evans Jan 2010

Formation And Coarsening Of Ag(110) Bilayer Islands On Nial(110): Stm Analysis And Atomistic Lattice-Gas Modeling, Yong Han, Barış Ünal, Dapeng Jing, Feili Qin, Cynthia J. Jenks, Da-Jiang Liu, Patricia A. Thiel, James W. Evans

Chemistry Publications

Scanning tunneling microscopy analysis of the initial stages of film growth during deposition of Ag on NiAl(110) reveals facile formation of bilayer Ag(110) islands at temperatures of 130 K and above. Annealing subsequent to deposition at 130 K induces coarsening of the bilayer island distribution. The thermodynamic driving force for bilayer island formation reflects a lower relative surface energy for films of even layer thicknesses. This feature derives from quantum size effects due to electron confinement in the Ag film. The kinetics of island formation and relaxation is controlled by terrace and edge-diffusion barriers, detachment barriers, interlayer diffusion ...


Islands And Holes As Measures Of Mass Balance In Growth Of The (√3×√3)R30° Phase Of Ag On Si(111), Alex Belianinov, Barış Ünal, Ning Lu, Min Ji, Kai-Ming Ho, Cai-Zhuang Wang, Michael C. Tringides, Patricia A. Thiel Jan 2010

Islands And Holes As Measures Of Mass Balance In Growth Of The (√3×√3)R30° Phase Of Ag On Si(111), Alex Belianinov, Barış Ünal, Ning Lu, Min Ji, Kai-Ming Ho, Cai-Zhuang Wang, Michael C. Tringides, Patricia A. Thiel

Chemistry Publications

It is well known that conversion of Si(111)-(7×7) into the (√3×√3)R30° phase of adsorbed Ag requires a change in the Si density, and causes formation of islands and holes at the surface. By mass balance, the ratio of areas of islands and holes (RIH) should be approximately 1. However, we find that the ratio is significantly higher, depending on preparation conditions. A possible explanation would be that there are different types of (√3×√3)R30° structures. However, neither scanning tunneling microscopy nor density-functional theory (implemented as a genetic algorithm search) supports this explanation. We ...


Nanoscale “Quantum” Islands On Metal Substrates: Microscopy Studies And Electronic Structure Analyses, Yong Han, Barış Ünal, Dapeng Jing, Patricia A. Thiel, James W. Evans Jan 2010

Nanoscale “Quantum” Islands On Metal Substrates: Microscopy Studies And Electronic Structure Analyses, Yong Han, Barış Ünal, Dapeng Jing, Patricia A. Thiel, James W. Evans

Chemistry Publications

Confinement of electrons can occur in metal islands or in continuous films grown heteroepitaxially upon a substrate of a different metal or on a metallic alloy. Associated quantum size effects (QSE) can produce a significant height-dependence of the surface free energy for nanoscale thicknesses of up to 10–20 layers. This may suffice to induce height selection during film growth. Scanning STM analysis has revealed remarkable flat-topped or mesa-like island and film morphologies in various systems. We discuss in detail observations of QSE and associated film growth behavior for Pb/Cu(111), Ag/Fe(100), and Cu/fcc-Fe/Cu(100 ...


Periodic Step Arrays On The Aperiodic I-Al-Pd-Mn Quasicrystal Surface At High Temperature, Y. Sato, Barış Ünal, Thomas A. Lograsso, Patricia A. Thiel, A. K. Schmid, T. Duden, N. C. Bartelt, K. F. Mccarty Jan 2010

Periodic Step Arrays On The Aperiodic I-Al-Pd-Mn Quasicrystal Surface At High Temperature, Y. Sato, Barış Ünal, Thomas A. Lograsso, Patricia A. Thiel, A. K. Schmid, T. Duden, N. C. Bartelt, K. F. Mccarty

Chemistry Publications

We have observed the configuration and motion of surface steps on the aperiodic icosahedral (i-) Al-Pd-Mn quasicrystal using low-energy electron microscopy and scanning tunneling microscopy. As the quasicrystal is cooled from high temperature, bulk vacancies migrate to the surface causing the surface to be etched. Surprisingly, this etching occurs by two types of steps with different heights moving in different directions with different velocities. The steady-state surface morphology is a uniformly spaced rhomboidal step network. This network requires that the layer stacking near the surface deviates from the bulk quasicrystal stacking.


Twofold Surface Of The Decagonal Al-Cu-Co Quasicrystal, T. Duguet, Barış Ünal, M. C. De Weerd, J. Ledieu, R. A. Ribeiro, Paul C. Canfield, S. Deloudi, W. Steurer, Cynthia J. Jenks, J.-M. Dubois, V. Fournée, Patricia A. Thiel Jan 2009

Twofold Surface Of The Decagonal Al-Cu-Co Quasicrystal, T. Duguet, Barış Ünal, M. C. De Weerd, J. Ledieu, R. A. Ribeiro, Paul C. Canfield, S. Deloudi, W. Steurer, Cynthia J. Jenks, J.-M. Dubois, V. Fournée, Patricia A. Thiel

Chemistry Publications

We have investigated the atomic structure of the twofold surface of the decagonal Al-Cu-Co quasicrystal using scanning tunneling microscopy and low-energy electron diffraction. We have found that most of the surface features can be interpreted using the bulk-structure model proposed by Deloudi and Steurer (S. Deloudi, Ph.D. thesis, ETH, Zürich, 2008). The surface consists of terraces separated by steps of various heights. Step heights and steps sequences match with the thickness and the stacking sequence of blocks of layers separated by gaps in the model. These blocks of layers define possible surface terminations consisting of periodic atomic rows which ...