Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 25 of 25

Full-Text Articles in Physics

Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo Jul 2013

Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo

Patricia A. Thiel

We present a different mechanism to explain the occurrence of long-lived oscillations in diffraction spot intensities during epitaxial growth of metal films on fcc (100) substrates at low temperature. Rather than rely on the common picture of cyclical nucleation and growth to produce the oscillations, the model invokes ‘‘downward funneling’’ deposition dynamics to fourfold-hollow adsorption sites.


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 ...


From Initial To Late Stages Of Epitaxial Thin Film Growth: Stm Analysis And Atomistic Or Coarsegrained Modeling, James W. Evans, Yong Han, Barış Ünal, Maozhi Li, K. J. Caspersen, Dapeng Jing, Anthony R. Layson, C. R. Stoldt, T. Duguet, Patricia A. Thiel Aug 2010

From Initial To Late Stages Of Epitaxial Thin Film Growth: Stm Analysis And Atomistic Or Coarsegrained Modeling, James W. Evans, Yong Han, Barış Ünal, Maozhi Li, K. J. Caspersen, Dapeng Jing, Anthony R. Layson, C. R. Stoldt, T. Duguet, Patricia A. Thiel

Chemistry Conference Papers, Posters and Presentations

Epitaxial thin film growth by vapor deposition or molecular beam epitaxy under ultra‐high vacuum conditions generally occurs in two stages: (i) nucleation and growth of well‐separated islands on the substrate; (ii) subsequent formation of a thicker continuous film with possible kinetic roughening. For homoepitaxial growth, two‐dimensional (2D) monolayer islands are formed during submonolayer deposition. Typically, the presence of a step‐edge barrier inhibits downward transport and leads to the formation of mounds (multilayer stacks of 2D islands) during multilayer growth. For heteroepitaxial growth, islands formed in the initial stages of deposition sometimes have a 2D monolayer structure ...


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 ...


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 ...


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 ...


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 ...


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 ...


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 ...


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 ...


Tribological Properties Of Quasicrystals: Effect Of Aperiodic Versus Periodic Surface Order, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel Jan 2006

Tribological Properties Of Quasicrystals: Effect Of Aperiodic Versus Periodic Surface Order, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel

Chemistry Publications

We investigated the nanoscale tribological properties of a decagonal quasicrystal using a combination of atomic force microscopy and scanning tunneling microscopy in ultrahigh vacuum. This combination permitted a variety of in situ measurements, including atomic-scale structure, friction and adhesion force, tip-sample current, and topography. We found that thiol-passivated tips can be used for reproducible studies of the tip-quasicrystal contact while nonpassivated probes adhere irreversibly to the clean quasicrystalline surface causing permanent modifications. The most remarkable results were obtained on the twofold surface of the Al-Ni-Co decagonal quasicrystal where atoms are arranged periodically along the tenfold axis and aperiodically in the ...


Atomic Scale Coexistence Of Periodic And Quasiperiodic Order In A 2-Fold Al-Ni-Co Decagonal Quasicrystal Surface, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel Jan 2005

Atomic Scale Coexistence Of Periodic And Quasiperiodic Order In A 2-Fold Al-Ni-Co Decagonal Quasicrystal Surface, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel

Chemistry Publications

Decagonal quasicrystals are made of pairs of atomic planes with pentagonal symmetry periodically stacked along a 10-fold axis. We have investigated the atomic structure of the 2-fold surface of a decagonal Al-Ni-Co quasicrystal using scanning tunneling microscopy. The surface consists of terraces separated by steps of heights 1.9, 4.7, 7.8, and 12.6 Å containing rows of atoms parallel to the 10-fold direction with an internal periodicity of 4 Å. The rows are arranged aperiodically, with separations that follow a Fibonacci sequence and inflation symmetry. The results indicate that the surfaces are preferentially Al-terminated and in general ...


Elastic And Inelastic Deformations Of Ethylene-Passivated Tenfold Decagonal Al-Ni-Co Quasicrystal Surfaces, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel Jan 2005

Elastic And Inelastic Deformations Of Ethylene-Passivated Tenfold Decagonal Al-Ni-Co Quasicrystal Surfaces, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel

Chemistry Publications

The adhesion and friction force properties between a tenfold Al‐Ni‐Co decagonal quasicrystal and a titanium nitride (TiN)-coated tip were investigated using an atomic force microscope in ultrahigh vacuum. To suppress the strong chemical adhesion found in the clean quasicrystal surfaces, the sample was exposed to ethylene that formed a protective passivating layer. We show that the deformation mechanism of the tip-substrate junction changes from elastic to inelastic at a threshold pressure of 3.8 to 4.0 GPa. Images of the indentation marks left above the threshold pressure indicate the absence of new steps, and indicate that ...


Temperature Dependence Of Island Growth Shapes During Submonolayer Deposition Of Ag On Ag(111), Eric Cox, Maozhi Li, Po-Wen Chung, C. Ghosh, T. S. Rahman, Cynthia J. Jenks, James W. Evans, Patricia A. Thiel Jan 2005

Temperature Dependence Of Island Growth Shapes During Submonolayer Deposition Of Ag On Ag(111), Eric Cox, Maozhi Li, Po-Wen Chung, C. Ghosh, T. S. Rahman, Cynthia J. Jenks, James W. Evans, Patricia A. Thiel

Chemistry Publications

Growth shapes of Ag islands formed on Ag(111) during submonolayer deposition at different temperatures were studied with scanning tunneling microscopy, and analyzed via kinetic Monte Carlo simulation of a suitable atomistic lattice-gas model. Distinct shape transitions can be observed, from dendrites with triangular envelopes at low temperatures (below 140 K) to more isotropic fat fractal islands at intermediate temperatures, and then to distorted hexagonal shapes with longer Bsteps and shorter A steps at higher temperatures (above 170 K). In contrast, the equilibrium island shapes in this system are almost perfect hexagons displaying a near-sixfold symmetry. Modeling reveals that the ...


Sensing Dipole Fields At Atomic Steps With Combined Scanning Tunneling And Force Microscopy, Jeong Young Park, G. M. Sacha, M. Enachescu, D. F. Ogletree, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel, J. J. Sáenz, M. Salmeron Jan 2005

Sensing Dipole Fields At Atomic Steps With Combined Scanning Tunneling And Force Microscopy, Jeong Young Park, G. M. Sacha, M. Enachescu, D. F. Ogletree, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel, J. J. Sáenz, M. Salmeron

Chemistry Publications

The electric field of dipoles localized at the atomic steps of metal surfaces due to the Smoluchowski effect were measured from the electrostatic force exerted on the biased tip of a scanning tunneling microscope. By varying the tip-sample bias the contribution of the step dipole was separated from changes in the force due to van der Waals and polarization forces. Combined with electrostatic calculations, the method was used to determine the local dipole moment in steps of different heights on Au(111) and on the twofold surface of an Al-Ni-Co decagonal quasicrystal.


Surface Structures Of Approximant Phases In The Al-Pd-Mn System, V. Fournée, A. R. Ross, Thomas A. Lograsso, James W. Anderegg, C. Dong, Matthew J. Kramer, I. R. Fisher, Paul C. Canfield, Patricia A. Thiel Jan 2002

Surface Structures Of Approximant Phases In The Al-Pd-Mn System, V. Fournée, A. R. Ross, Thomas A. Lograsso, James W. Anderegg, C. Dong, Matthew J. Kramer, I. R. Fisher, Paul C. Canfield, Patricia A. Thiel

Chemistry Publications

We present a study of the surface of the ξ′-Al-Pd-Mn approximant phase based upon scanning tunneling microscopy and low-energy electron diffraction. Several structures are observed on two different samples grown either by the Bridgman technique or by a self-flux method, and which contain various degrees of disorder. We also describe some other complex crystalline phases that are sometimes observed on the fivefold surface of Al-Pd-Mn quasicrystalline samples after the sputter-annealing cleaning process under ultrahigh vacuum conditions. This includes the T approximant phase resulting from surface decomposition after a high-temperature annealing.


Evolution Of Two-Dimensional Wormlike Nanoclusters On Metal Surfaces, Woei Wu Pai, John F. Wendelken, C. R. Stoldt, Patricia A. Thiel, James W. Evans, Da-Jiang Liu Apr 2001

Evolution Of Two-Dimensional Wormlike Nanoclusters On Metal Surfaces, Woei Wu Pai, John F. Wendelken, C. R. Stoldt, Patricia A. Thiel, James W. Evans, Da-Jiang Liu

Chemistry Publications

A pinch-off phenomenon is discovered in the evolution of 2D wormlike nanoclusters formed in homoepitaxial adlayers. This feature is shown to distinguish mass transport via periphery diffusion from other mechanisms. Continuum modeling of such evolution accurately describes experimental observations, particularly if one incorporates the anisotropy in step-edge line tension.


Electronic Structure Of Quasicrystalline Surfaces: Effects Of Surface Preparation And Bulk Structure, V. Fournée, P. J. Pinhero, J. W. Anderegg, Thomas A. Lograsso, A. R. Ross, Paul C. Canfield, I. R. Fisher, Patricia A. Thiel Dec 2000

Electronic Structure Of Quasicrystalline Surfaces: Effects Of Surface Preparation And Bulk Structure, V. Fournée, P. J. Pinhero, J. W. Anderegg, Thomas A. Lograsso, A. R. Ross, Paul C. Canfield, I. R. Fisher, Patricia A. Thiel

Chemistry Publications

We elucidate the nature of the surface electronic properties of quasicrystalline Al-Pd-Mn. We do this by using photoelectron and Auger electron spectroscopies, and by making a variety of comparisons—across types of bulk samples, and across methods of surface preparation. The main conclusions are these: (i) The narrow Mn 2p3/2core-level line observed in the icosahedral phase is a fingerprint of a suppression in the density of states (a pseudogap) at the Fermi level and is not unique to the quasicrystalline phase. It is also independent of the symmetry of the quasicrystalline surface. The Auger line shape is ...


Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel Oct 1998

Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel

Chemistry Publications

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below ∼700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for ...


Fivefold Surface Of Quasicrystalline Alpdmn: Structure Determination Using Low-Energy-Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, P. J. Pinhero, Cynthia J. Jenks, James W. Anderegg, C.-M. Zhang, Patricia A. Thiel Apr 1998

Fivefold Surface Of Quasicrystalline Alpdmn: Structure Determination Using Low-Energy-Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, P. J. Pinhero, Cynthia J. Jenks, James W. Anderegg, C.-M. Zhang, Patricia A. Thiel

Chemistry Publications

The atomic structure of the fivefold symmetric quasicrystal surface of icosahedral AlPdMn has been investigated by means of a dynamical low-energy-electron diffraction (LEED) analysis. Approximations were developed to make the structure of an aperiodic, quasicrystalline surface region accessible to LEED theory. A mix of several closely similar, relaxed, bulklike lattice terminations is favored, all of which have a dense Al-rich layer on top followed by a layer with a composition of about 50% Al and 50% Pd. The interlayer spacing between these two topmost layers is contracted from the bulk value by 0.1 Å, to a final value of ...


Structural Analysis Of The Fivefold Symmetric Surface Of The Al70pd21mn9 Quasicrystal By Low Energy Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, Cynthia J. Jenks, C.-M. Zhang, Patricia A. Thiel Jan 1997

Structural Analysis Of The Fivefold Symmetric Surface Of The Al70pd21mn9 Quasicrystal By Low Energy Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, Cynthia J. Jenks, C.-M. Zhang, Patricia A. Thiel

Chemistry Publications

The atomic structure of the fivefold symmetric quasicrystal surface of Al70Pd21Mn9 was investigated by means of a dynamical low energy electron-diffraction analysis. Approximations are developed to address the high structural complexity of quasicrystals, yielding average layer-by-layer structural and compositional information. A mix of several relaxed bulklike terminations is found, consistently favoring dense Al-rich outermost atomic layers. These results can be understood in terms of principles known to govern surface structures of simpler, crystalline metals.


Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch Sep 1996

Photoelectron Spectra Of An Al70pd21mn9 Quasicrystal And The Cubic Alloy Al60pd25mn15, Cynthia J. Jenks, S.-L. Chang, James W. Anderegg, Patricia A. Thiel, David W. Lynch

Chemistry Publications

Photoelectron spectra of a fivefold quasicrystalline alloy Al70Pd21Mn9 and a related cubic alloy Al60Pd25Mn15 reveal two noteworthy features. The first is that the Pd 3dlines fall at binding energies which are 2.2 eV higher than in pure Pd. A similar shift is observed for Pd in other alloys. The second noteworthy feature is that the Mn 2p3/2 line is very sharp in the quasicrystal. Fitting the experimental peaks with a Doniach-Sunjic line shpae suggests that the position and density of Mn states near EFis very ...


Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo Mar 1990

Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo

Chemistry Publications

We present a different mechanism to explain the occurrence of long-lived oscillations in diffraction spot intensities during epitaxial growth of metal films on fcc (100) substrates at low temperature. Rather than rely on the common picture of cyclical nucleation and growth to produce the oscillations, the model invokes ‘‘downward funneling’’ deposition dynamics to fourfold-hollow adsorption sites.