Insights into defect kinetics, mass transport, and electronic structure from spectrum effects in ion-irradiated Bi 2 O 3
Ion-irradiation of α-Bi 2 O 3 induces amorphization, altering mass transport and band structure.
36 MATERIALS SCIENCE↗
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Nonuniversal Scaling Behavior of Conductivity Peak Widths in the Quantum Hall Effect in InGaAs/InAlAs Structures
The longitudinal ρ{sub xx} and Hall ρ{sub xy} resistances were measured in the region of the quantum phase transitions for the quantum Hall effect regime with magnetic fields up to 12 T at temperatures of T = 0.4–30 K in two-dimensional electron systems n-In{sub 0.9}Ga{sub 0.1}As/In{sub 0.81}Al{sub 0.19}As. The nonuniversal scaling behavior of the temperature dependence of the width of the resistance ρ{sub xx} peaks related to the effect of the large-scale random potential and of Landau-level mixing with opposite spin directions was found.
36 MATERIALS SCIENCE↗
Structural and optical effects induced by gamma irradiation on NdPO{sub 4}: X-ray diffraction, spectroscopic and luminescence study
Highlights: • Inorganic NdPO{sub 4} crystal was grown first time using potassium polyphosphate (K{sub 6}P{sub 4}O{sub 13}) flux. • NdPO{sub 4} crystal is insoluble in water, non-hygroscopic and high radiation resistance favoring for actinides host. • Actinide immobilization can be made at 1273 K. • High yield of 1061 nm photon emission. - Abstract: Rare earth orthophosphate (NdPO{sub 4}) monazite single crystals were grown using high temperature flux growth method employing K{sub 6}P{sub 4}O{sub 13} (K{sub 6}) as molten solvent. Their structural parameters were studied using single crystal X-ray diffraction (XRD) method. The grown crystals were examined by SEM and EDX techniques for their homogeniousity and inclusion in the crystals. The influence of gamma irradiation in structural and optical absorption properties were studied by the powder XRD, FTIR and reflectance spectroscopy. The effect of gamma irradiation on luminescence properties was recorded. No significant structural change is observed up to 150 kGy gamma dose. The gamma ray induced charge trap in the crystal was saturated to 40 kGy dose. The luminescence intensity decreases with an increase in the irradiation. The emission of luminescence intensity stabilizes above 40 kGy gamma dose.
36 MATERIALS SCIENCE↗
Taylor expansion of luminosity distance in Szekeres cosmological models: effects of local structures evolution on cosmographic parameters
We consider the Goode-Wainwright representation of the Szekeres cosmological models and calculate the Taylor expansion of the luminosity distance in order to study the effects of the inhomogeneities on cosmographic parameters. Without making a particular choice for the arbitrary functions defining the metric, we Taylor expand up to the second order in redshift for Family I and up to the third order for Family II Szekeres metrics under the hypotesis, based on observation, that local structure formation is over. In a conservative fashion, we also allow for the existence of a non null cosmological constant.
79 ASTRONOMY AND ASTROPHYSICS↗
Effects on crystal structure of CZTS thin films owing to deionized water and sulfurization treatment
To condense the cost and increase the production, using abundantly obtainable non-toxic elements, Cu{sub 2}ZnSnS{sub 4} (CZTS) seem to be a strong contender among the photovoltaic thin film technologies. Cu{sub 2}ZnSnS{sub 4} thin films were fabricated by RF magnetron sputtering system. CZTS were sputtered on Molybdenum (Mo) coated soda lime glass (SLG) using a single target sputtering technique. The sputtering parameters (base pressure, working pressure, Argon (Ar) flow rate, RF power and sputtering time) were kept same for all three types of films. For sulfurization, the temperature used was 500 °C. Finally, As-deposited film was immersed in DIW before undergoing identical sulfurization profile. As-deposited film (Sample A), sulfurized films (Sample B) and sulfurized plus DIW treated (Sample C) were compared in terms of their structural properties by means of X-Ray Diffraction (XRD) measurement and Atomic Force Microscopy (AFM). Sample B and C showed peak of (1 1 2) planes of CZTS which are characteristics of stannite structure. Post deposition treatment on CZTS films proved to be beneficial as evident from the observed enhancement in the crystallinity and grain growth. Significant difference on grain size and area roughness could be observed from the AFM measurement. The roughness of Sample A, B and C increased from 5.007 nm to 20.509 nm and 14.183 nm accordingly. From XRD data secondary phases of Cu{sub x}MoS{sub x} could be observed.
36 MATERIALS SCIENCE↗
Isotope effects in molecular structures and electronic properties of liquid water via deep potential molecular dynamics based on the SCAN functional
Here, Feynman path-integral deep potential molecular dynamics (PI-DPMD) calculations have been employed to study both light (H 2 O) and heavy water (D 2 O) within the isothermalisobaric ensemble. In particular, the deep neural network is trained based on ab initio data obtained from the strongly constrained and appropriately normed (SCAN) exchange-correlation functional. Because of the lighter mass of hydrogen than deuteron, the properties of light water are more influenced by nuclear quantum effect than those of heavy water. Clear isotope effects are observed and analyzed in terms of hydrogen-bond structure and electronic properties of water that are closely associated with experimental observables. The molecular structures of both liquid H 2 O and D 2 O agree well with the data extracted from scattering experiments. The delicate isotope effects on radial distribution functions and angular distribution functions are well reproduced as well. Our approach demonstrates that deep neural network combined with SCAN functional based ab initio molecular dynamics provides an accurate theoretical tool for modeling water and its isotope effects.
36 MATERIALS SCIENCE↗
Anomalous Hall effect in nanoscale structures of the antiferromagnetic Weyl semimetal Mn 3 Sn at room temperature
The magnetic Weyl semimetallic state in the chiral antiferromagnet Mn 3 Sn has attracted interest for its potential in memory technology. Despite vanishingly small magnetization, the material exhibits large transverse responses that can be electrically manipulated, similar to ferromagnets. Through deposition on heated Si/SiO 2 substrates, we have fabricated polycrystalline Mn 3 Sn films that have coarse surfaces, the thinner of which have a discontinuous structure comprised of grains with diameters of the order of 100 nm. Here we confirm that these grains retain the anomalous Hall effect arising in the time reversal symmetry broken chiral antiferromagnetic phase of Mn 3 Sn at room temperature by serially connecting the grains with an additional conducting layer. These results pave the path for the potential applications of nanoscale Mn 3 Sn systems, which could be useful in the development of energy efficient memory devices.
36 MATERIALS SCIENCE↗
Effects of heat treatments on magneto-structural phase transitions in MnNiSi-FeCoGe alloys
Abstract not provided
Chen, Jing-Han↗
Design of Ternary Nanoalloy Catalysts: Effect of Nanoscale Alloying and Structural Perfection on Electrocatalytic Enhancement
The ability to tune the atomic-scale structural and chemical ordering in nanoalloy catalysts is essential for achieving the ultimate goal of high activity and stability of catalyst by design. This article demonstrates this ability with a ternary nanoalloy of platinum with vanadium and cobalt for oxygen reduction reaction in fuel cells. The strategy is to enable nanoscale alloying and structural perfection through oxidative–reductive thermochemical treatments. The structural manipulation is shown to produce a significant enhancement in the electrocatalytic activity of the ternary nanoalloy catalysts for oxygen reduction reaction. Mass activities as high as 1 A/mg of Pt have been achieved by this strategy based on direct measurements of the kinetic currents from rotating disk electrode data. Using a synchrotron high-energy X-ray diffraction technique coupled with atomic pair function analysis and X-ray absorption fine structure spectroscopy as well as X-ray photoelectron spectroscopy, the atomic-scale structural and chemical ordering in nanoalloy catalysts prepared by the oxidative–reductive thermochemical treatments were examined. A phase transition has been observed, showing an fcc-type structure of the as-prepared and the lower-temperature-treated particles into an fct-type structure for the particles treated at the higher temperature. The results reveal a thermochemically driven evolution of the nanoalloys from a chemically disordered state into chemically ordered state with an enhanced degree of alloying. The increase in the chemical ordering and shrinking of interatomic distances as a result of thermochemical treatment at increased temperature is shown to increase the catalytic activity for oxygen reduction reaction, exhibiting an optimal activity at 600 °C. It is the alloying and structural perfection that allows the optimization of the catalytic performance in a controllable way, highlighting the significant role of atomic-scale structural and chemical ordering in the design of nanoalloy catalysts.
Environmental Molecular Sciences Laboratory↗
Dlx5 Homeodomain: DNA Complex: Structure, Binding and Effect of Mutations Related to Split Hand and Foot Malformation Syndrome
The Dlx5 homeodomain is a transcription factor related to the Drosophila Distal-less gene that is associated with breast and lung cancer, lymphoma, Rett syndrome and osteoporosis in humans. Mutations in the DLX5 gene have been linked to deficiencies in craniofacial and limb development in higher eukaryotes, including Split Hand and Foot Malformation-1 (SHFM-1) in humans. Our characterization of a Dlx5 homeodomain–(CGACTAATTAGTCG) 2 complex by NMR spectroscopy paved the way for determination of its crystal structure at 1.85 Å resolution that enabled rationalization of the effects of disease-related mutations on the protein function. A remarkably subtle mutation, Q186H, is linked to SHFM-1; this change likely affects affinity of DNA binding by disrupting water-mediated interactions with the DNA major groove. A more subtle effect is implicated for the Q178P mutation, which is not in direct contact with the DNA. Our data indicate that these mutations diminish the ability of the Dlx5 homeodomain to recognize and bind target DNAs, and likely destabilize the formation of functional complexes.
59 BASIC BIOLOGICAL SCIENCES↗
A detailed study of the nuclear dependence of the EMC effect and short-range correlations
Because nucleons are closely packed in medium-to-heavy nuclei, one expects to observe density-dependent effects in their structure. Such effects can be seen in the nucleon momentum distribution in the form of a significant high-momentum tail related to the short-range interaction between nucleons, generating high-momentum short-range correlations (SRCs). High nuclear densities also imply overlap between neighboring nucleons, leading to the possible modification of their internal quark structure, which may contribute to the EMC effect. Recent Jefferson Lab experiments provided detailed information on both SRC contributions [1] and the EMC effect [2] in a range of light and heavy nuclei. We examine these results and previous data to make a detailed comparison of the A dependence of SRCs and nuclear quark distributions, along with a detailed comparison of the nuclear dependence of these two effects. We also examine the correlation between these effects, first studied in [3], in the context of different pictures of the underlying connection between these observables [4]. \\[4pt] [1] N. Fomin, et al., PRL 108 (2012) 092502\\[0pt] [2] J. Seely, et al., PRL 103 (2009) 202301\\[0pt] [3] L. Weinstein, et al., PRL 106 (2011) 052301\\[0pt] [4] J. Arrington, et al., arXiv:1206.6364 (2012)
Arrington, John↗
Experimental study of crystallization fouling by calcium carbonate: Effects of surface structure and material
We report mitigation of crystallization fouling on heat transfer surface is crucial for developing highly efficient desalination techniques, because the tenacious and porous crystal layer can drastically deteriorate system efficiency. Surface modification is a potential approach to decrease scale formation and promote crystal removal, but some of the mechanisms between crystallization and substrate properties are still not fully understood. In this study, we use dual-angle microscopic visualization and image processing to quantify three-dimensional crystallization behavior and analyze the impact of surface structure and material. The transition of crystal size and distance with roughness and wettability are identified from statistical analysis. The determination of crystal porosity and effective thermal conductivity is enabled by visualized geometry and measured deposition mass. This study shed lights on potential strategies of surface modification to mitigate scaling in desalination by enhancing scale removal and localizing crystal growth.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Understanding the doping effects on the structural and electrical properties of ultrathin carbon nanotube networks
Similar to other semiconductor technology, doping of carbon nanotube (CNT) thin film is of great significance for performance improvement or modification. However, it still remains a challenge to seek a stable and effective dopant. In this paper, we unitize several spectroscopic techniques and electrical characterizations under various conditions to investigate the effects of typical dopants and related methods. Nitric acid (HNO{sub 3}) solution, I{sub 2} vapor, and CuI nanoparticles are used to modify a series of ultrathin CNT networks. Although efficient charge transfer is achieved initially after doping, HNO{sub 3} is not applicable because it suffers from severe reliability problems in structural and electrical properties, and it also causes a number of undesired structural defects. I{sub 2} vapor doping at 150 °C can form some stable C-I bonding structures, resulting in relatively more stable but less efficient electrical performances. CuI nanoparticles seem to be an ideal dopant. Photonic curing enables the manipulation of CuI, which not only results in the construction of novel CNT-CuI hybrid structures but also encourages the deepest level of charge transfer doping. The excellent reliability as well as processing feasibility identify the bright perspective of CNT-CuI hybrid film for practical applications.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Temperature dependence of the photo-induced inverse spin Hall effect in Au/InP hybrid structures
Photo-induced Inverse Spin Hall Effect (ISHE) measurements on Au/InP hybrid structures are performed over a temperature range of 45 to 300 K. Dependence of the spin current density on the degree of circular polarization and also on the angle of incidence of laser beam confirms the ISHE origin of measured signal. The magnitude of ISHE increases with sample cooling. A numerical model based on the spin relaxation of non-equilibrium spin-polarized electrons is proposed for predicting the temperature dependence of ISHE. Our results indicate that the proposed device can be used as a spin photodetector over a wide temperature range.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Isotope effects on the structural transformation and relaxation of deeply supercooled water
Herein, we have examined the structure of supercooled liquid D 2 O as a function of temperature between 185 and 255 K using pulsed laser heating to rapidly heat and cool the sample on a nanosecond timescale. The liquid structure can be represented as a linear combination of two structural motifs, with a transition between them described by a logistic function centered at 218 K with a width of 10 K. The relaxation to a metastable state, which occurred prior to crystallization, exhibited nonexponential kinetics with a rate that was dependent on the initial structural configuration. When the temperature is scaled by the temperature of maximum density, which is an isostructural point of the isotopologues, the structural transition and the non-equilibrium relaxation kinetics of D 2 O agree remarkably well with those for H 2 O.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Localized High Concentration Electrolyte and Its Effects on Polysulfide Structure in Solution
Lithium–sulfur batteries (LiSB) are a promising next-generation lithium energy storage technology that offers a multifold improvement over the traditional lithium-ion battery. However, the LiSB still faces the unresolved issue of the polysulfide shuttle effect. This phenomenon arises from the dissolution of sulfur intermediate reduction products into the electrolyte, which then causes a cascade of issues throughout the battery. Many mitigation strategies have been proposed to counteract this effect including the use of novel electrolyte compositions. Recently, there has been increased focus on the use of hydrofluorinated ethers as a major constituent of an electrolyte for lithium batteries. Previous studies have reported that the presence of these species create localized high concentration electrolytes (LHCE) which can have many advantages resulting in improved battery performance. Here, we report on how the inclusion of a hydrofluorinated ether BTFE (bis(2,2,2-trifluoroethyl) ether) modifies the general properties of a LiSB electrolyte and the structure of dissolved polysulfide species in the electrolyte. Here, we found that the inclusion of BTFE does not modify the primary solvation structure of Li + directly but actively participates in secondary solvation shells. With a high concentration of BTFE, the LHCE formation is observed by the presence of clusters of non-BTFE molecules. The structure of polysulfide species in solution was modified by the BTFE in the same way. Much of the primary solvation structure was kept, but the presence of BTFE increased polysulfide–polysulfide clustering. These results indicate that the polysulfide solubility will be limited due to the promotion of clustering.
25 ENERGY STORAGE↗
Size effects on the structural, electronic, and optical properties of (5,0) finite-length carbon nanotube: An ab-initio electronic structure study
We use density functional computations to study the zero temperature structural, electronic, magnetic, and optical properties of (5,0) finite carbon nanotubes (FCNT), with length in the range of 4–44 Å. It is found that the structural and electronic properties of (5,0) FCNTs, in the ground state, converge at a length of about 30 Å, while the excited state properties exhibit long-range edge effects. We discuss that curvature effects enhance energy gap of FCNTs, in contrast to the known trend in the periodic limit. It is seen that compensation of curvature effects in two special small sizes may give rise to spontaneous magnetization. The obtained cohesive energies provide some insights into the effects of environment on the growth of FCNTs. The second-order difference of the total energies reveals an important magic size of about 15 Å. The optical and dynamical magnetic responses of the FCNTs to polarized electromagnetic pulses are studied by time dependent density functional theory. The results show that the static and dynamic magnetic properties mainly come from the edge carbon atoms. The optical absorption properties are described in terms of local field effects and characterized by Casida linear response method.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Structural basis for effectiveness of siderophore-conjugated monocarbams against clinically relevant strains of Pseudomonas aeruginosa
Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes nosocomial infections for which there are limited treatment options. Penicillin-binding protein PBP3, a key therapeutic target, is an essential enzyme responsible for the final steps of peptidoglycan synthesis and is covalently inactivated by {beta}-lactam antibiotics. Here we disclose the first high resolution cocrystal structures of the P. aeruginosa PBP3 with both novel and marketed {beta}-lactams. These structures reveal a conformational rearrangement of Tyr532 and Phe533 and a ligand-induced conformational change of Tyr409 and Arg489. The well-known affinity of the monobactam aztreonam for P. aeruginosa PBP3 is due to a distinct hydrophobic aromatic wall composed of Tyr503, Tyr532, and Phe533 interacting with the gem-dimethyl group. The structure of MC-1, a new siderophore-conjugated monocarbam complexed with PBP3 provides molecular insights for lead optimization. Importantly, we have identified a novel conformation that is distinct to the high-molecular-weight class B PBP subfamily, which is identifiable by common features such as a hydrophobic aromatic wall formed by Tyr503, Tyr532, and Phe533 and the structural flexibility of Tyr409 flanked by two glycine residues. This is also the first example of a siderophore-conjugated triazolone-linked monocarbam complexed with any PBP. Energetic analysis of tightly and loosely held computed hydration sites indicates protein desolvation effects contribute significantly to PBP3 binding, and analysis of hydration site energies allows rank ordering of the second-order acylation rate constants. Taken together, these structural, biochemical, and computational studies provide a molecular basis for recognition of P. aeruginosa PBP3 and open avenues for future design of inhibitors of this class of PBPs.
59 BASIC BIOLOGICAL SCIENCES↗