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Articles 1 - 30 of 105
Full-Text Articles in Physical Sciences and Mathematics
Structural, Magnetic, And Defect Properties Of Co-Pt-Type Magnetic-Storage Alloys: Density-Functional Theory Study Of Thermal Processing Effects, Aftab Alam, Brent Kraczek, Duane D. Johnson
Structural, Magnetic, And Defect Properties Of Co-Pt-Type Magnetic-Storage Alloys: Density-Functional Theory Study Of Thermal Processing Effects, Aftab Alam, Brent Kraczek, Duane D. Johnson
Duane D. Johnson
Using an optimized-basis Korringa-Kohn-Rostoker-coherent-potential approximation method, we calculate formation enthalpies ΔEf, structural, and magnetic properties of paramagnetic (PM) and ferromagnetic, disordered A1 and ordered L10 CoPt, FePd, and FePt systems that are of interest for high-density magnetic-recording media. To address processing effects, we focus on the point defects that dictate thermal properties and planar defects (e.g., c domain and antiphase boundaries) which can serve as pinning centers for magnetic domains and affect storage properties. We determine bulk Curie (Tc) and order-disorder (To-d) transition temperatures within 4% of observed values, and estimates for nanoparticles. Planar-defect energies γhklx show that the favorable …
Preparation And Characterization Of Pt/Γ-Al2o3 Model Catalyst On Nial Alloy, Zhongfan Zhang, Long Li, Lin-Lin Wang, Sergio I. Sanchez, Ross V. Grieshaber, Qi Wang, Duane D. Johnson, Anatoly I. Frenkel, Ralph G. Nuzzo, Judith C. Yang
Preparation And Characterization Of Pt/Γ-Al2o3 Model Catalyst On Nial Alloy, Zhongfan Zhang, Long Li, Lin-Lin Wang, Sergio I. Sanchez, Ross V. Grieshaber, Qi Wang, Duane D. Johnson, Anatoly I. Frenkel, Ralph G. Nuzzo, Judith C. Yang
Duane D. Johnson
Numerous studies of heterogeneous catalysis systems clearly demonstrate that the metal nanoparticle (NPs)/support interaction is significant in determining the catalytic chemistry. Theoretical simulations have been performed to understand the metal/support interactions [1,2]. For example, theorists discovered that electronic and oxygen defects of γ-Al2O3 anchor the active particles [1]. Platinum NPs dispersed on γ-alumina is one of the most widely used heterogeneous catalysts and Pt performs extremely well as a catalyst for the oxygen-reduction reaction used in fuel cell industries. Hence, we chose Pt/γ-Al2O3 as a model heterogeneous catalyst system to investigate the metal NPs/support interface by electron microscopy methods with …
Interphase Energies Of Hcp Precipitates In Fcc Metals: A Density-Functional Theory Study In Al-Ag, Daniel Finkenstadt, Duane D. Johnson
Interphase Energies Of Hcp Precipitates In Fcc Metals: A Density-Functional Theory Study In Al-Ag, Daniel Finkenstadt, Duane D. Johnson
Duane D. Johnson
Density-functional theory (DFT) calculations of interphase boundary energies relevant to hexagonal-close-packed (hcp) γ-precipitate formation were performed within approximate unit cells that mirror the experimental conditions in face-centered-cubic (fcc) Al-Ag solid solutions. In Al-rich, fcc Al-Ag, γ precipitates are observed to form rapidly with large (300+) aspect ratios even though the Al stacking-fault energy is high (approximately 130 mJ/m2), which should suppress hcp ribbon formation according to standard arguments. Our DFT results show why high-aspect ratio plates occur and why previous estimates based on Wulff construction were orders of magnitude less than observed values. Using DFT, we obtain a Gibbs free-energy …
Analysis Of Nonequilibrium Hcp Precipitate Growth In Fcc Matrices: Application To Al–Ag, Daniel Finkenstadt, Duane D. Johnson
Analysis Of Nonequilibrium Hcp Precipitate Growth In Fcc Matrices: Application To Al–Ag, Daniel Finkenstadt, Duane D. Johnson
Duane D. Johnson
Hexagonal-close-packed (hcp) γ-precipitates with large aspect ratios form rapidly in some face-centered cubic (fcc) solid-solutions. No model explains the observed time-dependent increase in aspect ratio, nor irregular intermediate growth shapes. We propose a nonequilibrium process involving trapezoidal offshoots (controlled only by energetics) that governs the growth behavior (kinetics) and yields nonequilibrium structures in agreement with observation. Then, combining nucleation theory and diffusion-limited growth both of secondary nuclei and ledges, we derive a general growth equation for γ-precipitates due to solute-segregation to precipitate–matrix interfaces that includes our modification of the Jones–Trivedi model for thickening to account for the slow growth of …
Optimal Site-Centered Electronic Structure Basis Set From A Displaced-Center Expansion: Improved Results Via A Priori Estimates Of Saddle Points In The Density, Aftab Alam, Duane D. Johnson
Optimal Site-Centered Electronic Structure Basis Set From A Displaced-Center Expansion: Improved Results Via A Priori Estimates Of Saddle Points In The Density, Aftab Alam, Duane D. Johnson
Duane D. Johnson
Site-centered, electronic-structure methods use an expansion inside nonoverlapping “muffin-tin” (MT) spheres plus an interstitial basis set. As the boundary separating the more spherical from nonspherical density between atoms, the “saddle-point” radii (SPR) in the density provide an optimal spherical region for expanding in spherical harmonics, as used in augmented plane wave, muffin-tin orbital, and multiple-scattering [Korringa, Kohn, and Rostoker (KKR)] methods. These MT-SPR guarantee unique, convex Voronoi polyhedra at each site, in distinction to Bader topological cells. We present a numerically fast, two-center expansion to find SPR a priori from overlapping atomic charge densities, valid also for disordered alloys. We …
Surface Geometry Of C60 On Ag(111), H. I. Li, K. Pussi, K. J. Hanna, Lin-Lin Wang, Duane D. Johnson, H.-P. Cheng, H. Shin, S. Curtarolo, W. Moritz, J. A. Smerdon, R. Mcgrath, R. D. Diehl
Surface Geometry Of C60 On Ag(111), H. I. Li, K. Pussi, K. J. Hanna, Lin-Lin Wang, Duane D. Johnson, H.-P. Cheng, H. Shin, S. Curtarolo, W. Moritz, J. A. Smerdon, R. Mcgrath, R. D. Diehl
Duane D. Johnson
The geometry of adsorbed C60 influences its collective properties. We report the first dynamical low-energy electron diffraction study to determine the geometry of a C60 monolayer, Ag(111)−(23√×23√)30°−C60, and related density functional theory calculations. The stable monolayer has C60 molecules in vacancies that result from the displacement of surface atoms. C60 bonds with hexagons down, with their mirror planes parallel to that of the substrate. The results indicate that vacancy structures are the rule rather than the exception for C60 monolayers on close-packed metal surfaces.
Quantitative Prediction Of Twinning Stress In Fcc Alloys: Application To Cu-Al, Sandeep A. Kibey, Lin-Lin Wang, J. B. Liu, H. T. Johnson, H. Sehitoglu, Duane D. Johnson
Quantitative Prediction Of Twinning Stress In Fcc Alloys: Application To Cu-Al, Sandeep A. Kibey, Lin-Lin Wang, J. B. Liu, H. T. Johnson, H. Sehitoglu, Duane D. Johnson
Duane D. Johnson
Twinning is one of most prevalent deformation mechanisms in materials. Having established a quantitative theory to predict onset twinning stress τcrit in fcc elemental metals from their generalized planar-fault-energy (GPFE) surface, we exemplify its use in alloys where the Suzuki effect (i.e., solute energetically favors residing at and near planar faults) is operative; specifically, we apply it in Cu-xAl (x is 0, 5, and 8.3 at. %) in comparison with experimental data. We compute the GPFE via density-functional theory, and we predict the solute dependence of the GPFE and τcrit, in agreement with measured values. We show that τcrit correlates …
Bcc-To-Hcp Transformation Pathways For Iron Versus Hydrostatic Pressure: Coupled Shuffle And Shear Modes, J. B. Liu, Duane D. Johnson
Bcc-To-Hcp Transformation Pathways For Iron Versus Hydrostatic Pressure: Coupled Shuffle And Shear Modes, J. B. Liu, Duane D. Johnson
Duane D. Johnson
Using density-functional theory, we calculate the potential-energy surface (PES), minimum-energy pathway (MEP), and transition state (TS) versus hydrostatic pressure σhyd for the reconstructive transformation in Fe from body-centered cubic (bcc) to hexagonal closed-packed (hcp). At fixed σhyd, the PES is described by coupled shear (ϵ) and shuffle (η) modes and is determined from structurally minimized hcp-bcc energy differences at a set of (η,ϵ). We fit the PES using symmetry-adapted polynomials, permitting the MEP to be found analytically. The MEP is continuous and fully explains the transformation and its associated magnetization and volume discontinuity at TS. We show that σhyd (while …
Sum Frequency Generation Vibrational Spectroscopy Of Pyridine Hydrogenation On Platinum Nanoparticles, Kaitlin M. Bratlie, Kyriakos Komvopoulos, Gabor A. Somorjai
Sum Frequency Generation Vibrational Spectroscopy Of Pyridine Hydrogenation On Platinum Nanoparticles, Kaitlin M. Bratlie, Kyriakos Komvopoulos, Gabor A. Somorjai
Kaitlin M. Bratlie
Pyridine hydrogenation in the presence of a surface monolayer consisting of cubic Pt nanoparticles stabilized by tetradecyltrimethylammonium bromide (TTAB) was investigated by sum frequency generation (SFG) vibrational spectroscopy using total internal reflection (TIR) geometry. TIR-SFG spectra analysis revealed that a pyridinium cation (C5H5NH+) forms during pyridine hydrogenation on the Pt nanoparticle surface, and the NH group in the C5H5NH+ cation becomes more hydrogen bound with the increase of the temperature. In addition, the surface coverage of the cation decreases with the increase of the temperature. An important contribution of this study is the in situ identification of reaction intermediates adsorbed …
Low-Energy Antiphase Boundaries, Degenerate Superstructures, And Phase Stability In Frustrated Fcc Ising Model And Ag-Au Alloys, Nikolai A. Zarkevich, Teck L. Tan, Lin-Lin Wang, Duane D. Johnson
Low-Energy Antiphase Boundaries, Degenerate Superstructures, And Phase Stability In Frustrated Fcc Ising Model And Ag-Au Alloys, Nikolai A. Zarkevich, Teck L. Tan, Lin-Lin Wang, Duane D. Johnson
Duane D. Johnson
An Ising model exhibits zero-energy antiphase boundaries (APBs) and frustration on close-packed face-centered cubic (fcc) and triangular lattices. The frustration results in degenerate structures and chains of long-period superstructures forming a quasicontinuous ground-state “hull” in the formation energy versus composition (c) diagram. In alloys, a nonzero but small APB energy yields a c-dependent reduction in this degeneracy that affects the phase diagram topology and range of the two-phase coexistence. Using density functional theory combined with cluster expansions (CEs), we study Ag-Au alloys as a prototype and find the effective cluster interactions (dominated by nearest-neighbor pairs), predict energetics of millions of …
Grain Growth And Texture Development In Lithium Fluoride Thin Films, Hakkwan Kim, Alexander H. King
Grain Growth And Texture Development In Lithium Fluoride Thin Films, Hakkwan Kim, Alexander H. King
Alexander H. King
We have studied grain-growth and texture development in polycrystalline lithium fluoride thin films using dark-field transmission electron microscopy. We demonstrate that we can isolate the size distribution of 〈111〉 surface normal grains from the overall size distribution, based on simple and plausible assumptions about the texture. The {111} texture formation and surface morphology were also observed by x-ray diffraction and atomic force microscopy, respectively. The grain-size distributions become clearly bimodal as the annealing time increases, and we deduce that the short-time size distributions are also a sum of two overlapping peaks. The smaller grain-size peak in the distribution corresponds to …
Predicting Enthalpies Of Molecular Substances: Application To Libh4, Nikolai A. Zarkevich, Duane D. Johnson
Predicting Enthalpies Of Molecular Substances: Application To Libh4, Nikolai A. Zarkevich, Duane D. Johnson
Duane D. Johnson
For molecular substances exhibiting harmonic and nonharmonic vibrations, we present a first-principles approach to predict enthalpy differences between phases at finite temperatures, including solid-solid and melting. We apply it to the complex hydride LiBH4. Using ab initio molecular dynamics, we predict a structure for the high-T solid phase of lithium borohydride, and we propose an approximation to account for nonharmonic vibrations. We then predict the enthalpy changes for solid-solid transition, melting, and an H-storage reaction, all in agreement with experiment.
Posterminaries: More Or Less Modern, Alexander H. King
Posterminaries: More Or Less Modern, Alexander H. King
Alexander H. King
It is yet another sign that I am aging. More and more often when young researchers hand me a written report of their research, I find myself criticizing their introductory section: “You need to start your literature survey with the original papers on this topic. Go and read…” followed by a citation to some classic of the learned literature.
Platinum Nanoparticle Shape Effects On Benzene Hydrogenation Selectivity, Kaitlin M. Bratlie, Hyunjoo Lee, Kyriakos Komvopoulos, Peidong Yang, Gabor A. Somorjai
Platinum Nanoparticle Shape Effects On Benzene Hydrogenation Selectivity, Kaitlin M. Bratlie, Hyunjoo Lee, Kyriakos Komvopoulos, Peidong Yang, Gabor A. Somorjai
Kaitlin M. Bratlie
Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-HâââPt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for …
Control Of Porosity In Fluoride Thin Films Prepared By Vapor Deposition, Alexander H. King
Control Of Porosity In Fluoride Thin Films Prepared By Vapor Deposition, Alexander H. King
Alexander H. King
We have measured the porosity in thin films of lithium fluoride (LiF), magnesium fluoride (MgF2), barium fluoride (BaF2), and calcium fluoride (CaF2) as a function of the substrate temperature for films deposited by thermal evaporation onto glass substrates. The amount of porosity in the thin films was measured using an atomic force microscope and a quartz crystal thickness monitor. The porosity was very sensitive to the substrate temperature and decreased as the substrate temperature increased. Consistent behavior was observed among all of the materials in this study.
Posterminaries: Full Circle, Alexander H. King
Posterminaries: Full Circle, Alexander H. King
Alexander H. King
A few years ago, I was walking near the old Union Station in Pittsburgh with a colleague only slightly younger than myself, when we happened upon some large-scale relics of the steel industry displayed for public viewing. “You don’t see too many of those in public parking lots,” I offered. “Um… what is it?” was the response. I suppose I was just a little surprised that a prominent materials scientist did not recognize a Bessemer converter—arguably the principal source of wealth during the U.S. industrial revolution—but this conversation took place back when steel was in decline, and many university Materials …
Density Functional Study Of Structural Trends For Late-Transition-Metal 13-Atom Clusters, Lin-Lin Wang, Duane D. Johnson
Density Functional Study Of Structural Trends For Late-Transition-Metal 13-Atom Clusters, Lin-Lin Wang, Duane D. Johnson
Duane D. Johnson
Because reactivity increases as particle size decreases and competition between numerous structures are possible, which affects catalytic and magnetic properties, we study the structural trends of late-transition-metal 13-atom clusters using density functional theory within the generalized gradient approximation to exchange-correlation functional. We consider open structural motifs, such as bilayer and cubic (recently found to have lower energy), and find new bilayer candidates that are even lower in energy. To study the influence of d-orbital filling on structural trends, we focus on Pt, Pd, and Rh clusters and find several new, low-energy structures for Pt13 and Pd13 from searches using a …
A Sum Frequency Generation Vibrational Spectroscopic Study Of The Adsorption And Reactions Of C6 Hydrocarbons At High Pressures On Pt(100), Kaitlin M. Bratlie, Gabor A. Somorjai
A Sum Frequency Generation Vibrational Spectroscopic Study Of The Adsorption And Reactions Of C6 Hydrocarbons At High Pressures On Pt(100), Kaitlin M. Bratlie, Gabor A. Somorjai
Kaitlin M. Bratlie
Sum frequency generation (SFG) vibrational spectroscopy was used to investigate the adsorption geometries and surface reactions of various C6 hydrocarbons (n-hexane, 2-methylpentane, 3-methylpentane, and 1-hexene) on Pt(100). At 300 K and in the presence of excess hydrogen, n-hexane, 3-methylpentane, and 2-methylpentane adsorb molecularly on Pt(100) mostly in “flat-lying” conformations. Upon heating the metal surface to 450 K, the molecules underwent dehydrogenation to form new surface species in “standing-up” conformations, such as hexylidyne and metallacyclic species.
First-Principles Prediction Of Phase-Segregating Alloy Phase Diagrams And A Rapid Design Estimate Of Their Transition Temperatures, Nikolai A. Zarkevich, Teck L. Tan, Duane D. Johnson
First-Principles Prediction Of Phase-Segregating Alloy Phase Diagrams And A Rapid Design Estimate Of Their Transition Temperatures, Nikolai A. Zarkevich, Teck L. Tan, Duane D. Johnson
Nikolai A. Zarkevich
We calculate the transition temperature versus concentration (Tc vs c) phase diagrams of several phase-segregating alloys [fcc Ca-Sr, Au-Pt, and Rh-(Pd,Cu,Ag,Au)] using a multiscale method combining first-principles calculations and Monte Carlo via the cluster expansion (CE). We study Pd-Rh, with its well-known high-T miscibility gap, to verify the method’s reliability. We predict that Ca-Sr segregates at low temperatures. We then show that a rapid estimate of Tc is obtained from enthalpies analytically derived from a CE, and, using thermodynamic integration, we determine under what circumstances this mean-field estimate is accurate compared to Monte Carlo results. Also, we discuss how an …
Thermal Effects On Mechanical Grinding-Induced Surface Texture In Tetragonal Piezoelectrics, Wonyoung Chang, Alexander H. King, Keith J. Bowman
Thermal Effects On Mechanical Grinding-Induced Surface Texture In Tetragonal Piezoelectrics, Wonyoung Chang, Alexander H. King, Keith J. Bowman
Alexander H. King
The effect of temperature on grinding-induced texture in tetragonal lead zirconate titanate (PZT) and lead titanate (PT) has been investigated using in situ x-ray diffraction (XRD) with an area detector. In contrast with previous results on electrical poling, mechanically-ground PT and soft PZT materials retain strong ferroelastic textures during thermal cycling, even after excursions to temperatures slightly above the Curie temperature. The relationship between the residual stresses in the surface region, caused by grinding, and those resulting from domain wall motion is elucidated by in situ texture measurements obtained during thermal cycling.
How Surface Stresses Lead To Size-Dependent Mechanics Of Tensile Deformation In Nanowires, M. Ravi Shankar, Alexander H. King
How Surface Stresses Lead To Size-Dependent Mechanics Of Tensile Deformation In Nanowires, M. Ravi Shankar, Alexander H. King
Alexander H. King
It has been proposed that surface and interface stresses can modify the elastic behavior in nanomaterials such as nanowires. The authors show that surface stresses modify the tensile response of nanowires only when nonlinear elastic effects become important leading to cross terms between the applied stress and the surface stress. These effects are only significant when the radius of the nanowire is of the order of a few nanometers. The resulting alteration of tensile stiffness, though effected in part by the nonlinear elastic modulus, is particularly wrought by a modification of the stress state in the deformed nanowire.
Energy Pathways And Directionality In Deformation Twinning, S. Kibey, J. B. Liu, Duane D. Johnson, H. Sehitoglu
Energy Pathways And Directionality In Deformation Twinning, S. Kibey, J. B. Liu, Duane D. Johnson, H. Sehitoglu
Duane D. Johnson
We present ab initiodensity functional theory calculations of twinning energy pathways for two opposite twinning modes, (111)[112¯] and (111)[1¯1¯2], in fcc materials to examine the directional nature of twinning which cannot be explained by classical twin nucleationmodels or the “twinnability” criterion. By accounting for these energy pathways in a multiscale model, we quantitatively predict the critical twinning stress for the (111)[1¯1¯2] mode to be substantially higher compared to the favorable (111)[112¯] mode (whose predicted stresses are in agreement with experiment), thus, ruling out twinning in the (111)[1¯1¯2] mode.
Posterminaries: After Nabarro, Alexander H. King
Posterminaries: After Nabarro, Alexander H. King
Alexander H. King
With the passing of Frank Nabarro in July of this year, we have lost one of the founding fathers of materials science. His name appears in many of the textbooks from which we train our students today, and also on the spines of several volumes on dislocation theory, including his classic monograph on the subject. He rightly stands among the gods of our field. Ninety years old at his death, he was a sprightly dancer at the frontiers of knowledge, right up to the end.
Semicrystalline Thermoplastic Elastomeric Polyolefins: Advances Through Catalyst Development And Macromolecular Design, Atsushi Hotta, Eric W. Cochran, Janne Ruokolainen, Vikram Khann, Glenn H. Fredrickson, Edward J. Kramer, Yong-Woo Shin, Fumihiko Shimizu, Anna E. Cherian, Phillip D. Hustad, Jeffrey M. Rose, Geoffrey W. Coates
Semicrystalline Thermoplastic Elastomeric Polyolefins: Advances Through Catalyst Development And Macromolecular Design, Atsushi Hotta, Eric W. Cochran, Janne Ruokolainen, Vikram Khann, Glenn H. Fredrickson, Edward J. Kramer, Yong-Woo Shin, Fumihiko Shimizu, Anna E. Cherian, Phillip D. Hustad, Jeffrey M. Rose, Geoffrey W. Coates
Eric W. Cochran
We report the design, synthesis, morphology, phase behavior, and mechanical properties of semicrystalline, polyolefin-based block copolymers. By using living, stereoselective insertion polymerization catalysts, syndiotactic polypropylene-block-poly(ethylene-co-propylene)-block-syndiotactic polypropylene and isotactic poly propylene-block-regioirregular poly propylene-block- isotactic polypropylene triblock copolymers were synthesized. The volume fraction and composition of the blocks, as well as the overall size of the macromolecules, were controlled by sequential synthesis of each block of the polymers. These triblock copolymers, with semicrystalline end-blocks and mid-segments with low glass-transition temperatures, show significant potential as thermoplastic elastomers. They have low Young's moduli, large strains at break, and better than 90% elastic recovery at …
Hydrogen And Deuterium Exchange On Pt(111) And Its Poisoning By Carbon Monoxide Studied By Surface Sensitive High-Pressure Techniques, Max Montano, Kaitlin M. Bratlie, Miquel Salmeron, Gabor A. Somorjai
Hydrogen And Deuterium Exchange On Pt(111) And Its Poisoning By Carbon Monoxide Studied By Surface Sensitive High-Pressure Techniques, Max Montano, Kaitlin M. Bratlie, Miquel Salmeron, Gabor A. Somorjai
Kaitlin M. Bratlie
Catalytic hydrogen/deuterium exchange on a platinum (111) single crystal and its poisoning with carbon monoxide was studied using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), sum frequency generation vibrational spectroscopy (SFG), and mass spectrometry under reaction conditions at pressures in the mTorr to atmospheric range. At 298 K and in the presence of 200 mTorr of hydrogen and 20 mTorr of deuterium the surface is catalytically active, producing HD with activation energy of 5.3 kcal/mol. Addition of 5 mTorr of CO stops the reaction completely. In situ STM images reveal an ordered surface structure of chemisorbed CO. At 353 …
Sum Frequency Generation Vibrational Spectroscopic And High-Pressure Scanning Tunneling Microscopic Studies Of Benzene Hydrogenation On Pt(111), Kaitlin M. Bratlie, Max O. Montano, Lucio D. Flores, Matti Paajanen, Gabor A. Somorjai
Sum Frequency Generation Vibrational Spectroscopic And High-Pressure Scanning Tunneling Microscopic Studies Of Benzene Hydrogenation On Pt(111), Kaitlin M. Bratlie, Max O. Montano, Lucio D. Flores, Matti Paajanen, Gabor A. Somorjai
Kaitlin M. Bratlie
Sum frequency generation (SFG) vibrational spectroscopy and high-pressure scanning tunneling microscopy (HP-STM) have been used in combination for the first time to study a catalytic reaction. These techniques have been able to identify surface intermediates in situ during benzene hydrogenation on a Pt(111) single-crystal surface at Torr pressures.
Comment On “Structural Stability Of Complex Hydrides: Libh4 Revisited”, Duane D. Johnson, Nikolai A. Zarkevich
Comment On “Structural Stability Of Complex Hydrides: Libh4 Revisited”, Duane D. Johnson, Nikolai A. Zarkevich
Duane D. Johnson
A Comment on the Letter by Zbigniew Łodziana and Tejs Vegge, Phys. Rev. Lett. 93, 145501 (2004).
Structure Effects Of Benzene Hydrogenation Studied With Sum Frequency Generation Vibrational Spectroscopy And Kinetics On Pt(111) And Pt(100) Single-Crystal Surfaces, Kaitlin M. Bratlie, Christopher J. Kliewer, Gabor A. Somorjai
Structure Effects Of Benzene Hydrogenation Studied With Sum Frequency Generation Vibrational Spectroscopy And Kinetics On Pt(111) And Pt(100) Single-Crystal Surfaces, Kaitlin M. Bratlie, Christopher J. Kliewer, Gabor A. Somorjai
Kaitlin M. Bratlie
Sum frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have identified at least two reaction pathways for benzene hydrogenation on the Pt(100) and Pt(111) single-crystal surfaces at Torr pressures. Kinetic studies at low temperatures (310-370 K) show that benzene hydrogenation does not proceed through cyclohexene. A Langmuir-Hinshelwood-type rate law for the low-temperature reaction pathway is identified. The rate-determining step for this pathway is the addition of the first hydrogen atom to adsorbed benzene for both single-crystal surfaces, which is verified by the spectroscopic observation of adsorbed benzene at low temperatures on both the Pt(100) and Pt(111) …
Posterminaries: The Scales Of Judgement, Alexander H. King
Posterminaries: The Scales Of Judgement, Alexander H. King
Alexander H. King
Materials scientists are generally well-versed in physics, and physics, above all, is a science of measurements. The first instinct of a physicist is to parse a problem in terms of its measurables in the dimensions of mass, length, and time, and it is the shifting of attention down the scale of length that particularly characterizes our present times as the Nano Age.
Dynamics Of Surface Catalyzed Reactions; The Roles Of Surface Defects, Surface Diffusion, And Hot Electrons, Gabor Somorjai, Kaitlin Bratlie, Max Montano, Jeong Park
Dynamics Of Surface Catalyzed Reactions; The Roles Of Surface Defects, Surface Diffusion, And Hot Electrons, Gabor Somorjai, Kaitlin Bratlie, Max Montano, Jeong Park
Kaitlin M. Bratlie
The mechanism that controls bond breaking at transition metal surfaces has been studied with sum frequency generation (SFG), scanning tunneling microscopy (STM), and catalytic nanodiodes operating under the highpressure conditions. The combination of these techniques permits us to understand the role of surface defects, surface diffusion, and hot electrons in dynamics of surface catalyzed reactions. Sum frequency generation vibrational spectroscopy and kinetic measurements were performed under 1.5 Torr of cyclohexene hydrogenation/dehydrogenation in the presence and absence of H2 and over the temperature range 300-500 K on the Pt(100) and Pt(111) surfaces. The structure specificity of the Pt(100) and Pt(111) surfaces …