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Full-Text Articles in Physics

Characteristics Of Sulfur Atoms Adsorbed On Ag(100), Ag(110), And Ag(111) As Probed With Scanning Tunneling Microscopy: Experiment And Theory, Peter M. Spurgeon, Da-Jiang Liu, Holly Walen, Junepyo Oh, Hyun Jin Yang, Yousoo Kim, Patricia A. Thiel May 2019

Characteristics Of Sulfur Atoms Adsorbed On Ag(100), Ag(110), And Ag(111) As Probed With Scanning Tunneling Microscopy: Experiment And Theory, Peter M. Spurgeon, Da-Jiang Liu, Holly Walen, Junepyo Oh, Hyun Jin Yang, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

In this paper, we report that S atoms on Ag(100) and Ag(110) exhibit a distinctive range of appearances in scanning tunneling microscopy (STM) images, depending on the sample bias voltage, VS. Progressing from negative to positive VS, the atomic shape can be described as a round protrusion surrounded by a dark halo (sombrero) in which the central protrusion shrinks, leaving only a round depression. This progression resembles that reported previously for S atoms on Cu(100). We test whether DFT can reproduce these shapes and the transition between them, using a modified version of the Lang–Tersoff–Hamann ...


Mg Assisted Flux Growth And Characterization Of Single Crystalline Sm2co17, Tej Nath Lamichhane, Qisheng Lin, Valentin Taufour, Andriy Palasyuk, Tribhuwan Pandey, David Parker, Sergey L. Bud’Ko, Paul C. Canfield Mar 2019

Mg Assisted Flux Growth And Characterization Of Single Crystalline Sm2co17, Tej Nath Lamichhane, Qisheng Lin, Valentin Taufour, Andriy Palasyuk, Tribhuwan Pandey, David Parker, Sergey L. Bud’Ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

This paper presents details of Mg-assisted flux growth of Sm2Co17 single crystals in a Ta crucible well below the melting temperature of binary Sm2Co17. Both the crushed single crystalline powder x-ray diffraction (XRD) and single crystalline XRD data revealed the Th2Zn17 type rhombohedral(R-3m) crystal structure. Ta atom is found to be statistically replacing the Co-Co dumbbell with its position being at the center of the dumbbell. The Curie temperature of our lightly Mg and Ta doped Sm2Co17 sample is determined to be ∼1100 K using method of generalized Bloch law fitting of easy axis spontaneous magnetization data.


Shedding Light On The Atomic-Scale Structure Of Amorphous Silica–Alumina And Its Brønsted Acid Sites, Frédéric A. Perras, Zichun Wang, Takeshi Kobayashi, Alfons Baiker, Jun Huang, Marek Pruski Jan 2019

Shedding Light On The Atomic-Scale Structure Of Amorphous Silica–Alumina And Its Brønsted Acid Sites, Frédéric A. Perras, Zichun Wang, Takeshi Kobayashi, Alfons Baiker, Jun Huang, Marek Pruski

Ames Laboratory Accepted Manuscripts

In spite of the widespread applications of amorphous silica–aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced 29Si–29Si, 27Al–27Al, and 29Si–27Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein's ...


Effect Of (Poly)Electrolytes On The Interfacial Assembly Of Peg Functionalized Gold Nanoparticles, Srikanth Nayak, Max Fieg, Wenjie Wang, Wei Bu, Surya Mallapragada, David Vaknin Jan 2019

Effect Of (Poly)Electrolytes On The Interfacial Assembly Of Peg Functionalized Gold Nanoparticles, Srikanth Nayak, Max Fieg, Wenjie Wang, Wei Bu, Surya Mallapragada, David Vaknin

Chemical and Biological Engineering Publications

We report on the effect of interpolymer complexes (IPCs) of poly(acrylic acid) (PAA) with poly(ethylene glycol) functionalized Au nanoparticles (PEG-AuNPs) as they assemble at the vapor-liquid interface, using surface sensitive synchrotron X-ray scattering techniques. Depending on the suspension pH, PAA functions both as a weak polyelectrolyte and a hydrogen bond donor, and these two roles affect the interfacial assembly of PEG-AuNPs differently. Above its isoelectric point, we find that PAA leads to the formation of a PEG-AuNPs monolayer at the interface with hexagonal structure. In the presence of high concentration of HCl (i.e., below the isoelectric point ...


Kinetics, Energetics, And Size Dependence Of The Transformation From Pt To Ordered Ptsn Intermetallic Nanoparticles, Minda Chen, Yong Han, Tian Wei Goh, Rong Sun, Raghu V. Maligal‐Ganesh, Yuchen Pei, Chia‐ Kuang Tsung, James W. Evans, Wenyu Huang Jan 2019

Kinetics, Energetics, And Size Dependence Of The Transformation From Pt To Ordered Ptsn Intermetallic Nanoparticles, Minda Chen, Yong Han, Tian Wei Goh, Rong Sun, Raghu V. Maligal‐Ganesh, Yuchen Pei, Chia‐ Kuang Tsung, James W. Evans, Wenyu Huang

Chemistry Publications

The outstanding catalytic activity and chemical selectivity of intermetallic compounds make them excellent candidates for heterogeneous catalysis. However, the kinetics of their formation at the nanoscale is poorly understood or characterized, and precise control of their size, shape as well as composition during synthesis remains challenging. Here, using well-defined Pt nanoparticles (5 nm and 14 nm) encapsulated in mesoporous silica, we study the transformation kinetics from monometallic Pt to intermetallic PtSn at different temperatures by a series of time-evolution X-ray diffraction studies. Observations indicate an initial transformation stage mediated by Pt surface-controlled intermixing kinetics, followed by a second stage with ...


Kinetics Of The Γ–Δ Phase Transition In Energetic Nitramine-Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald Jan 2019

Kinetics Of The Γ–Δ Phase Transition In Energetic Nitramine-Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald

Aerospace Engineering Publications

The solid, secondary explosive nitramine-octahydro-1,3,5,7-tetranitro-1,3,5,7 or HMX has four different stable polymorphs which have different molecular conformations, crystalline structures, and densities, making structural phase transitions between these nontrivial. Previous studies of the kinetics of the βδ HMX structural transition found this to happen by a nucleation and growth mechanism, where growth was governed by the heat of fusion, or melting, even though the phase transition temperature is more than 100 K below the melting point. A theory known as virtual melting could easily justify this since the large volume difference in the two ...


The Role Of Anderson’S Rule In Determining Electronic, Optical And Transport Properties Of Transition Metal Dichalcogenide Heterostructures, Ke Xu, Yuanfeng Xu, Bo Peng, Hezhu Shao, Gang Ni, Jing Li, Mingyuan Yao, Hongliang Lu, Heyuan Zhu, Costas M. Soukoulis Nov 2018

The Role Of Anderson’S Rule In Determining Electronic, Optical And Transport Properties Of Transition Metal Dichalcogenide Heterostructures, Ke Xu, Yuanfeng Xu, Bo Peng, Hezhu Shao, Gang Ni, Jing Li, Mingyuan Yao, Hongliang Lu, Heyuan Zhu, Costas M. Soukoulis

Ames Laboratory Accepted Manuscripts

Two-dimensional (2D) transition metal dichalcogenides (TMDs) MX2 (M = Mo, W; X = S, Se, Te) possess unique properties and novel applications in optoelectronics, valleytronics and quantum computation. In this work, we performed first-principles calculations to investigate the electronic, optical and transport properties of the van der Waals (vdW) stacked MX2 heterostructures formed by two individual MX2 monolayers. We found that the so-called Anderson's rule can effectively classify the band structures of heterostructures into three types: straddling, staggered and broken gap. The broken gap is gapless, while the other two types possess direct (straddling, staggered) or indirect (staggered) band gaps. The ...


Temperature Dependence Of The Solid-Liquid Interface Free Energy Of Ni And Al From Molecular Dynamics Simulation Of Nucleation, Yang Sun, Feng Zhang, Huajing Song, Mikhail I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho Nov 2018

Temperature Dependence Of The Solid-Liquid Interface Free Energy Of Ni And Al From Molecular Dynamics Simulation Of Nucleation, Yang Sun, Feng Zhang, Huajing Song, Mikhail I. Mendelev, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

The temperature dependence of the solid-liquid interfacial free energy, γ, is investigated for Al and Ni at the undercooled temperature regime based on a recently developed persistent-embryo method. The atomistic description of the nucleus shape is obtained from molecular dynamics simulations. The computed γ shows a linear dependence on the temperature. The values of γ extrapolated to the melting temperature agree well with previous data obtained by the capillary fluctuation method. Using the temperature dependence of γ, we estimate the nucleation free energy barrier in a wide temperature range from the classical nucleation theory. The obtained data agree very well ...


Large-Scale Ab Initio Simulations Of Mas Dnp Enhancements Using A Monte Carlo Optimization Strategy, Frederic A. Perras, Marek Pruski Oct 2018

Large-Scale Ab Initio Simulations Of Mas Dnp Enhancements Using A Monte Carlo Optimization Strategy, Frederic A. Perras, Marek Pruski

Ames Laboratory Accepted Manuscripts

Magic-angle-spinning (MAS) dynamic nuclear polarization (DNP) has recently emerged as a powerful technology enabling otherwise unrealistic solid-state NMR experiments. The simulation of DNP processes which might, for example, aid in refining the experimental conditions or the design of better performing polarizing agents, is, however, plagued with significant challenges, often limiting the system size to only 3 spins. Here, we present the first approach to fully ab initio large-scale simulations of MAS DNP enhancements. The Landau-Zener equation is used to treat all interactions concerning electron spins, and the low-order correlations in the Liouville space method is used to accurately treat the ...


Potential Of Mean Force For Two Nanocrystals: Core Geometry And Size, Hydrocarbon Unsaturation, And Universality With Respect To The Force Field, Curt Waltmann, Nathan Horst, Alex Travesset Jul 2018

Potential Of Mean Force For Two Nanocrystals: Core Geometry And Size, Hydrocarbon Unsaturation, And Universality With Respect To The Force Field, Curt Waltmann, Nathan Horst, Alex Travesset

Ames Laboratory Accepted Manuscripts

We present a detailed analysis of the interaction between two nanocrystals capped with ligands consisting of hydrocarbon chains by united atom molecular dynamics simulations. We analyze large cores (up to 10 nm in diameter) and ligands with unsaturated carbon bonds (oleic acid) and we investigate the accuracy of the computed potential of mean force by comparing different force fields. We also analyze the vortices that determine the bonding, including the case of asymmetric nanocrystals, and discuss effects related to the intrinsic anisotropy of the core. Overall our results are in agreement with the predictions of the recently proposed orbifold topological ...


Pore Diameter Dependence Of Catalytic Activity: P-Nitrobenzaldehyde Conversion To An Aldol Product In Amine-Functionalized Mesoporous Silica, Andres Garcia, Igor I. Slowing, James W. Evans Jul 2018

Pore Diameter Dependence Of Catalytic Activity: P-Nitrobenzaldehyde Conversion To An Aldol Product In Amine-Functionalized Mesoporous Silica, Andres Garcia, Igor I. Slowing, James W. Evans

Chemistry Publications

The reaction yield for conversion of p-nitrobenzaldehyde (PNB) to an aldol product in amine-functionalized mesoporous silica nanoparticles (MSN) exhibits a 20-fold enhancement for a modest increase in pore diameter, d. This enhanced catalytic activity is shown to reflect a strong increase in the “passing propensity,” 𝒫, of reactant and product species inside the pores. We find that 𝒫 ≈ 0, corresponding to single-file diffusion, applies for the smallest d which still significantly exceeds the linear dimensions of PNB and the aldol product. However, in this regime of narrow pores, these elongated species must align with each other and with the pore ...


Spatial–Temporal Spectroscopy Characterizations And Electronic Structure Of Methylammonium Perovskites, Zhaoyu Liu, K. C. Bhamu, Liang Luo, Satvik Shah, Joong-Mok Park, Di Cheng, Men Long, Rana Biswas, F. Fungara, Ruth Shinar, Joseph Shinar, Javier Vela, Jigang Wang Jul 2018

Spatial–Temporal Spectroscopy Characterizations And Electronic Structure Of Methylammonium Perovskites, Zhaoyu Liu, K. C. Bhamu, Liang Luo, Satvik Shah, Joong-Mok Park, Di Cheng, Men Long, Rana Biswas, F. Fungara, Ruth Shinar, Joseph Shinar, Javier Vela, Jigang Wang

Chemistry Publications

Using time-resolved laser-scanning confocal microscopy and ultrafast optical pump/THz probe spectroscopy, we measure photoluminescence and THz-conductivity in perovskite micro-crystals and films. Photoluminescence quenching and lifetime variations occur from local heterogeneity. Ultrafast THz-spectra measure sharp quantum transitions from excitonic Rydberg states, providing weakly bound excitons with a binding energy of ~13.5 meV at low temperatures. Ab-initio electronic structure calculations give a direct band gap of 1.64 eV, a dielectric constant ~18, heavy electrons, and light holes, resulting in weakly bound excitons, consistent with the binding energies from experiment. The complementary spectroscopy and simulations reveal fundamental insights into perovskite ...


Molecular Dynamics Simulation Of The Solid-Liquid Interface Migration In Terbium, Mikhail I. Mendelev, Feng Zhang, H. Song, Yang Sun, Cai-Zhuang Wang, Kai-Ming Ho Jun 2018

Molecular Dynamics Simulation Of The Solid-Liquid Interface Migration In Terbium, Mikhail I. Mendelev, Feng Zhang, H. Song, Yang Sun, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

We developed a Tb embedded atom method potential which properly reproduces the liquid structure obtained from the ab initio molecular dynamics simulation, the hexagonal close packed (hcp)-body-centered cubic (bcc) phase transformation, and melting temperatures. At least three crystal phases [hcp, face-centered cubic (fcc), and bcc] described by this potential can coexist with the liquid phase. Thus, the developed potential provides an excellent test bed for studies of the completive phase nucleation and growth in a single component system. The molecular dynamics simulation showed that all crystal phases can grow from the liquid phase close to their melting temperatures. However ...


Theoretical Prediction Of Crystallization Kinetics Of A Supercooled Lennard-Jones Fluid, K. G. S. H. Gunawardana, Xueyu Song May 2018

Theoretical Prediction Of Crystallization Kinetics Of A Supercooled Lennard-Jones Fluid, K. G. S. H. Gunawardana, Xueyu Song

Chemistry Publications

The first order curvature correction to the crystal-liquid interfacial free energy is calculated using a theoretical model based on the interfacial excess thermodynamic properties. The correction parameter (δ), which is analogous to the Tolman length at a liquid-vapor interface, is found to be 0.48 ± 0.05 for a Lennard-Jones (LJ) fluid. We show that this curvature correction is crucial in predicting the nucleation barrier when the size of the crystal nucleus is small. The thermodynamic driving force (Δμ) corresponding to available simulated nucleation conditions is also calculated by combining the simulated data with a classical density functional theory ...


Local Structure Orders And Glass Forming Ability Of Ni-Nb Liquids, T. Q. Wen, Y. Zhang, Cai-Zhuang Wang, N. Wang, Kai-Ming Ho, Matthew J. Kramer May 2018

Local Structure Orders And Glass Forming Ability Of Ni-Nb Liquids, T. Q. Wen, Y. Zhang, Cai-Zhuang Wang, N. Wang, Kai-Ming Ho, Matthew J. Kramer

Ames Laboratory Accepted Manuscripts

Ab initio molecular dynamics simulations were performed to study the atomistic structures of Ni48Nb52, Ni59.5Nb40.5 and Ni75Nb25 liquids near their melting temperatures. It is found that the total coordination number only changes slightly across the compositions. However, there is significant difference in the chemical ordering. The Cluster Alignment method was used to identify the dominant local structure motifs. It is found that distorted and perfect icosahedral clusters are the most popular motifs around Ni atoms, while Z14, Z15, and Z16 Frank-Kasper polyhedra are dominant around Nb atoms. Among the three compositions, the eutectic composition (Ni59.5Nb40.5) has ...


Csmn4as3: A Layered Tetragonal Transition-Metal Pnictide Compound With An Antiferromagnetic Ground State, Abhishek Pandey, Saroj L. Samal, David C. Johnston Mar 2018

Csmn4as3: A Layered Tetragonal Transition-Metal Pnictide Compound With An Antiferromagnetic Ground State, Abhishek Pandey, Saroj L. Samal, David C. Johnston

Ames Laboratory Accepted Manuscripts

We report the synthesis and properties of a new layered tetragonal ternary compound CsMn4As3 (structure type, KCu4S3; space group, P4/mmm, no.123; and Z = 2). The material is a small band gap semiconductor and exhibits an antiferromagnetic ground state associated with Mn spins. The compound exhibits a signature of a distinct magnetic moment canting event at 150(5) K with a canting angle ≈ 0.3°. Although some features of the magnetic characteristics of this new compound are qualitatively similar to those of the related BaMn2As2, the underlying Mn sublattices of the two materials are quite different. While the ...


Liquid-Like Thermal Conduction In Intercalated Layered Crystalline Solids, B. Li, H. Wang, Y. Kawakita, Q. Zhang, M. Feygenson, H. L. Yu, D. Wu, K. Ohara, T. Kikuchi, K. Shibata, T. Yamada, X. K. Ning, Y. Chen, J. Q. He, David Vaknin, R. Q. Wu, K. Nakajima, M. G. Kanatzidis Mar 2018

Liquid-Like Thermal Conduction In Intercalated Layered Crystalline Solids, B. Li, H. Wang, Y. Kawakita, Q. Zhang, M. Feygenson, H. L. Yu, D. Wu, K. Ohara, T. Kikuchi, K. Shibata, T. Yamada, X. K. Ning, Y. Chen, J. Q. He, David Vaknin, R. Q. Wu, K. Nakajima, M. G. Kanatzidis

Ames Laboratory Accepted Manuscripts

As a generic property, all substances transfer heat through microscopic collisions of constituent particles1. A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations2,3. As a result, a solid is usually thermally more conductive than a liquid. In canonical viewpoints, such a difference also serves as the dynamic signature distinguishing a solid from a liquid. Here, we report liquid-like thermal conduction observed in the crystalline AgCrSe2. The transverse acoustic phonons are completely suppressed by the ultrafast dynamic disorder while the longitudinal acoustic phonons are strongly scattered but survive, and are thus ...


Characterization Of Pharmaceutical Cocrystals And Salts By Dynamic Nuclear Polarization-Enhanced Solid-State Nmr Spectroscopy, Li Zhao, Michael P. Hanrahan, Genetech, Inc., Aaron J. Rossini Feb 2018

Characterization Of Pharmaceutical Cocrystals And Salts By Dynamic Nuclear Polarization-Enhanced Solid-State Nmr Spectroscopy, Li Zhao, Michael P. Hanrahan, Genetech, Inc., Aaron J. Rossini

Ames Laboratory Accepted Manuscripts

Multicomponent solids such as cocrystals have emerged as a way to control and engineer the stability, solubility, and manufacturability of solid active pharmaceutical ingredients (APIs). Cocrystals are typically formed by solution- or solid-phase reactions of APIs with suitable cocrystal coformers, which are often weak acids. One key structural question about a given multicomponent solid is whether it should be classified as a salt, where the basic API is protonated by the acid, or as a cocrystal, where the API and coformer remain neutral and engage in hydrogen bonding interactions. It has previously been demonstrated that solid-state NMR spectroscopy is a ...


Uncovering The Origin Of Divergence In The Csm(Cro4)2 (M = La, Pr, Nd, Sm, Eu; Am) Family Through Examination Of The Chemical Bonding In A Molecular Cluster And By Band Structure Analysis, Shane S. Galley, Alexandra A. Arico, Tsung-Han Lee, Xiaoyu Deng, Yong-Xin Yao, Joseph M. Sperling, Vanessa Proust, Julia S. Storbeck, Vladimir Dobrosavljevic, Jennifer N. Neu, Theo Siegrist, Ryan E. Baumbach, Thomas E. Albrecht-Schmitt, Nikolas Kaltsoyannis, Nicola Lanata Feb 2018

Uncovering The Origin Of Divergence In The Csm(Cro4)2 (M = La, Pr, Nd, Sm, Eu; Am) Family Through Examination Of The Chemical Bonding In A Molecular Cluster And By Band Structure Analysis, Shane S. Galley, Alexandra A. Arico, Tsung-Han Lee, Xiaoyu Deng, Yong-Xin Yao, Joseph M. Sperling, Vanessa Proust, Julia S. Storbeck, Vladimir Dobrosavljevic, Jennifer N. Neu, Theo Siegrist, Ryan E. Baumbach, Thomas E. Albrecht-Schmitt, Nikolas Kaltsoyannis, Nicola Lanata

Ames Laboratory Accepted Manuscripts

A series of f-block chromates, CsM(CrO4)(2) (M = La, Pr, Nd, Sm, Eu; Am), were prepared revealing notable differences between the Am-III derivatives and their lanthanide analogs. While all compounds form similar layered structures, the americium compound exhibits polymorphism and adopts both a structure isomorphous with the early lanthanides as well as one that possesses lower symmetry. Both polymorphs are dark red and possess band gaps that are smaller than the Ln(III) compounds. In order to probe the origin of these differences, the electronic structure of alpha-CsSm(CrO4)(2), alpha-CsEu(CrO4)(2), and alpha-CsAm(CrO4)(2) were studied ...


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 ...


Interfacial Self-Assembly Of Polyelectrolyte-Capped Gold Nanoparticles, Honghu Zhang, Srikanth Nayak, Wenjie Wang, Surya K Mallapragada, David Vaknin Oct 2017

Interfacial Self-Assembly Of Polyelectrolyte-Capped Gold Nanoparticles, Honghu Zhang, Srikanth Nayak, Wenjie Wang, Surya K Mallapragada, David Vaknin

Ames Laboratory Accepted Manuscripts

We report on pH- and salt-responsive assembly of nanoparticles capped with polyelectrolytes at vapor–liquid interfaces. Two types of alkylthiol-terminated poly(acrylic acid) (PAAs, varying in length) are synthesized and used to functionalize gold nanoparticles (AuNPs) to mimic similar assembly effects of single-stranded DNA-capped AuNPs using synthetic polyelectrolytes. Using surface-sensitive X-ray scattering techniques, including grazing incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR), we demonstrate that PAA-AuNPs spontaneously migrate to the vapor–liquid interfaces and form Gibbs monolayers by decreasing the pH of the suspension. The Gibbs monoalyers show chainlike structures of monoparticle thickness. The pH-induced self-assembly is attributed ...


Off-Axis Electron Holography Of Bacterial Cells And Magnetic Nanoparticles In Liquid, Tanya Prozorov, Trevor Alemeida, András Kovács, Rafal E. Dunin-Borkowski Oct 2017

Off-Axis Electron Holography Of Bacterial Cells And Magnetic Nanoparticles In Liquid, Tanya Prozorov, Trevor Alemeida, András Kovács, Rafal E. Dunin-Borkowski

Ames Laboratory Accepted Manuscripts

The mapping of electrostatic potentials and magnetic fields in liquids using electron holography has been considered to be unrealistic. Here, we show that hydrated cells of Magnetospirillum magneticum strain AMB-1 and assemblies of magnetic nanoparticles can be studied using off-axis electron holography in a fluid cell specimen holder within the transmission electron microscope. Considering that the holographic object and reference wave both pass through liquid, the recorded electron holograms show sufficient interference fringe contrast to permit reconstruction of the phase shift of the electron wave and mapping of the magnetic induction from bacterial magnetite nanocrystals. We assess the challenges of ...


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 ...


Crystal Structure, Homogeneity Range And Electronic Structure Of Rhombohedral Γ-Mn5al8, Srinivasa Thimmaiah, Zachary Tener, Tej N. Lamichhane, Paul C. Canfield, Gordon J. Miller Jul 2017

Crystal Structure, Homogeneity Range And Electronic Structure Of Rhombohedral Γ-Mn5al8, Srinivasa Thimmaiah, Zachary Tener, Tej N. Lamichhane, Paul C. Canfield, Gordon J. Miller

Chemistry Publications

The γ-region of the Mn–Al phase diagram between 45 and 70 at.% Al was re-investigated by a combination of powder and single crystal X-ray diffraction as well as EDS analysis to establish the distribution of Mn and Al atoms. Single crystals of γ-Mn5–x Al8+x were grown using Sn-flux at 650 °C. The crystal structure, atomic coordinates and site occupancy parameters of γ-Mn5−x Al8+x phases were refined from single crystal X-ray data. The γ-Mn5-x Al8+x phase adopts the rhombohedral Cr5Al8-type structure rather than a cubic γ-brass structure. The refined compositions from two crystals extracted ...


A Molecular Debye-Hückel Theory And Its Applications To Electrolyte Solutions: The Size Asymmetric Case, Tiejen Xiao, Xueyu Song Mar 2017

A Molecular Debye-Hückel Theory And Its Applications To Electrolyte Solutions: The Size Asymmetric Case, Tiejen Xiao, Xueyu Song

Chemistry Publications

A molecular Debye-Hückel theory for electrolyte solutions with size asymmetry is developed, where the dielectric response of an electrolyte solution is described by a linear combination of Debye-Hückel-like response modes. As the size asymmetry of an electrolyte solution leads to a charge imbalanced border zone around a solute, the dielectric response to the solute is characterized by two types of charge sources, namely, a bare solute charge and a charge distribution due to size asymmetry. These two kinds of charge sources are screened by the solvent differently, our theory presents a method to calculate the mean electric potential as well ...


Tracer Counterpermeation Analysis Of Diffusivity In Finite-Length Nanopores With And Without Single-File Dynamics, David Ackerman, James W. Evans Jan 2017

Tracer Counterpermeation Analysis Of Diffusivity In Finite-Length Nanopores With And Without Single-File Dynamics, David Ackerman, James W. Evans

Physics and Astronomy Publications

We perform a tracer counterpermeation (TCP) analysis for a stochastic model of diffusive transport through a narrow linear pore where passing of species within the pore is inhibited or even excluded (single-file diffusion). TCP involves differently labeled but otherwise identical particles from two decoupled infinite reservoirs adsorbing into opposite ends of the pore, and desorbing from either end. In addition to transient behavior, we assess steady-state concentration profiles, spatial correlations, particle number fluctuations, and diffusion fluxes through the pore. From the profiles and fluxes, we determine a generalized tracer diffusion coefficient Dtr(x), at various positions x within the pore ...


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 ...


Enhancement Of The Superconducting Gap By Nesting In Cakfe4as4: A New High Temperature Superconductor, Daixiang Mou, Tai Kong, William R. Meier, Felix Lochner, Lin-Lin Wang, Qisheng Lin, Yun Wu, S. L. Bud’Ko, Ilya Eremin, Duane D. Johnson, Paul C. Canfield, Adam Kaminski Dec 2016

Enhancement Of The Superconducting Gap By Nesting In Cakfe4as4: A New High Temperature Superconductor, Daixiang Mou, Tai Kong, William R. Meier, Felix Lochner, Lin-Lin Wang, Qisheng Lin, Yun Wu, S. L. Bud’Ko, Ilya Eremin, Duane D. Johnson, Paul C. Canfield, Adam Kaminski

Chemistry Publications

We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe4As4. In contrast to the related CaFe2As2 compounds, CaKFe4As4 has a high Tc of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the ...


Point Island Models For Nucleation And Growth Of Supported Nanoclusters During Surface Deposition, Yong Han, Émilie Gaudry, Tiago J. Oliveira, James W. Evans Dec 2016

Point Island Models For Nucleation And Growth Of Supported Nanoclusters During Surface Deposition, Yong Han, Émilie Gaudry, Tiago J. Oliveira, James W. Evans

Physics and Astronomy Publications

Point island models (PIMs) are presented for the formation of supported nanoclusters (or islands) during deposition on flat crystalline substrates at lower submonolayer coverages. These models treat islands as occupying a single adsorption site, although carrying a label to track their size (i.e., they suppress island structure). However, they are particularly effective in describing the island size and spatial distributions. In fact, these PIMs provide fundamental insight into the key features for homogeneous nucleation and growth processes on surfaces. PIMs are also versatile being readily adapted to treat both diffusion-limited and attachment-limited growth and also a variety of other ...


Capture Zone Area Distributions For Nucleation And Growth Of Islands During Submonolayer Deposition, Yong Han, Maozhi Li, James W. Evans Dec 2016

Capture Zone Area Distributions For Nucleation And Growth Of Islands During Submonolayer Deposition, Yong Han, Maozhi Li, James W. Evans

Physics and Astronomy Publications

A fundamental evolution equation is developed to describe the distribution of areas of capture zones (CZs) associated with islands formed by homogeneous nucleation and growth during submonolayer deposition on perfect flat surfaces. This equation involves various quantities which characterize subtle spatial aspects of the nucleation process. These quantities in turn depend on the complex stochastic geometry of the CZ tessellation of the surface, and their detailed form determines the CZ area distribution (CZD) including its asymptotic features. For small CZ areas, behavior of the CZD reflects the critical island size, i. For large CZ areas, it may reflect the probability ...