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Electronic structure and surface properties of MgB 2 (0001) upon oxygen adsorption [Electronic structure and surface properties of MgB2: oxygen adsorption on MgB2(0001)]
Here, we use density-functional theory to investigate the bulk and surface properties of MgB 2 . The unique bonding structure of MgB 2 is investigated by Bader's atoms-in-molecules, charge density difference, and occupancy projected band structure analyses. Oxygen adsorption on the charge-depleted surfaces of MgB 2 is studied by a surface potential energy mapping method, reporting a complete map including low-symmetry binding sites. The B-terminated MgB 2 (0001) demonstrates reconstruction of the graphenelike B layer, and the reconstructed geometry exposes a threefold site of the subsurface Mg, making it accessible from the surface. Detailed reconstruction mechanisms are studied by simulated annealing method based on ab initio molecular dynamics and nudged elastic band calculations. The surface clustering of B atoms significantly modifies the B 2p states to occupy low energy valence states. The present paper emphasizes that a thorough understanding of the surface phase may explain an apparent inconsistency in the experimental surface characterization of MgB 2 . Furthermore, these results suggest that the surface passivation can be an important technical challenge when it comes to development of a superconducting device using MgB 2 .
First-principles study of the surface properties of y-LiAlO2: Stability and tritium adsorption
y-LiAlO2 enriched with 6Li isotope exhibits excellent performance under neutron radiation and is used in tritium-producing burnable absorber rods (TPBARs) to produce tritium (T, 3H) in pressurized water reactor (PWR). To better understand the 3H formation and diffusion on the surfaces, the first-principles calculations are performed to study the stability of y-LiAlO2 surface and the 3H adsorption on the surface. By considering all possible symmetrical stoichiometric and nonstoichiometric low-index surfaces, two most stable surfaces, one stoichiometric (100) and one nonstoichiometric (101), were identified. The 3H adsorption and diffusion on the most stable (100) surface were further explored, and the obtained results show that there are four stable sites (three O and one Al atop) for 3H adsorption. The calculated Bader charges of atoms reflect that 3H adsorption on the top of O site is a reduction process, while on the top of Al site is an oxidation one. Under low adsorption coverage of 1/4 per surface unit cell, 3H atoms are adsorbed on the most stable OA atop site. With increasing 3H diffused from bulk to surface, the AlG site is the second choice for 3H adsorption, and then the OB site. The coverage of 2/4 is the most favorable 3H adsorption state due to the counteracted charge transfer. When the coverage is up to 4/4, the interaction between 3H atoms leads to partial formation of T2 molecule that desorbs from surface. Therefore, T2 molecule should be the main product from the perfect surface of y-LiAlO2 at high 3H coverage.
Enhancing the surface properties and functionalization of polymethyl mathacrylate with atomic layer-deposited titanium(IV) oxide
Abstract not provided
Enhanced Surface Properties and Microstructure Evolution of Cr12MoV Using Ultrasonic Surface Rolling Process Combined with Deep Cryogenic Treatment
In this study, the enhanced surface properties and microstructure evolution of quenched and tempered cold work die steel Cr12MoV, which were induced by ultrasonic surface rolling process combined with deep cryogenic treatment (UDCT), were systematically investigated. The results indicated that UDCT had an advantage over conventional ultrasonic surface rolling process (USRP) in improving surface mechanical properties, including smaller surface roughness and smoother machined surface with less cracks and defects; higher surface microindentation hardness with the value of ~ 890 HV (increased by ~ 6.2% compared with USRP); and lower friction coefficient. Such enhancements in surface properties are mainly attributed to the martensitic transformation of retained austenite, the dispersion strengthening of small secondary carbides and the homogenized carbides distribution during UDCT.
Uniting Surface Properties With Hydrodynamic Roughness in Shallow Overland Flow Models
Describing flow resistance from the properties of an underlying surface is a challenge in surface hydrology. Runoff models must specify a resistance formulation or “roughness scheme”—describing the functional relationship between flow resistance and flow depth/velocity—and its parameters. Uncertainty in runoff predictions derives from both the selected roughness scheme (e.g., Darcy Weisbach, Manning's, or laminar flow equations), and its parameterization with a roughness coefficient (e.g., Manning's n). Both choices are informed by model calibration to data, usually discharge, and, if available, velocity. In this study, a Saint Venant Equation-based runoff model is calibrated to discharge and velocity data from 112 rainfall simulator experiments. The results are used to identify the optimal roughness scheme among four widely-used options for each experiment, and to explore whether surface properties can be used to select the optimal roughness scheme and its coefficient. Among the tested roughness schemes, a transitional flow equation provided the best fit to the plurality of experiments. The most suitable roughness scheme for a given experiment was not related to measured surface properties. Regression models predicted the calibrated roughness coefficients with adjusted values between 0.48 and 0.54, depending on the roughness scheme used. Litter cover was the best predictor of the roughness coefficient, followed by soil cover and average canopy gap size. The results suggest that selection of an optimal roughness scheme based on surface properties alone remains difficult, but that once a scheme is selected, roughness coefficients can be estimated from surface properties.
Dispersion controlled by permeable surfaces: surface properties and scaling
Permeable and porous surfaces are common in natural and engineered systems. Flow and transport above such surfaces are significantly affected by the surface properties, e.g. matrix porosity and permeability. However, the relationship between such properties and macroscopic solute transport is largely unknown. In this work, we focus on mass transport in a two-dimensional channel with permeable porous walls under fully developed laminar flow conditions. By means of perturbation theory and asymptotic analysis, we derive the set of upscaled equations describing mass transport in the coupled channel–porous-matrix system and an analytical expression relating the dispersion coefficient with the properties of the surface, namely porosity and permeability. Our analysis shows that their impact on the dispersion coefficient strongly depends on the magnitude of the Péclet number, i.e. on the interplay between diffusive and advective mass transport. Additionally, we demonstrate different scaling behaviours of the dispersion coefficient for thin or thick porous matrices. Our analysis shows the possibility of controlling the dispersion coefficient, i.e. transverse mixing, by either active (i.e. changing the operating conditions) or passive mechanisms (i.e. controlling matrix effective properties) for a given Péclet number. By elucidating the impact of matrix porosity and permeability on solute transport, our upscaled model lays the foundation for the improved understanding, control and design of microporous coatings with targeted macroscopic transport features.
Structure and Sulfur: Tuning the Viscoelastic and Surface Properties of Natural Keratin Fibers
Natural keratin fibers, such as wool, possess a complex hierarchical structure that governs their mechanical properties and surface energy. However, the extent to which these characteristics are influenced by combined contributions of structural variations (e.g., fiber diameter, intermediate filament (IF) packing) and chemical composition (e.g., disulfide bond density) remains poorly understood. In this study, we investigate wool fibers from five sheep breeds (Merino, Polwarth, Cheviot, Eider, and Devon) to elucidate how these factors influence viscoelasticity and surface interactions. Using a multimodal approach integrating interfacial and bulk characterization methods, including inverse gas chromatography (IGC), atomic force microscopy-infrared spectroscopy (AFM-IR), X-ray photoelectron spectroscopy (XPS), uniaxial tensile testing, and synchrotron small-angle X-ray scattering (SAXS), we show that the nanometer-thick 18-methyleicosanoic acid (18-MEA) layer is consistently present across all wool types and plays a key role in governing hydrophobicity and surface heterogeneity. A controlled isothermal treatment at 200 °C, designed to cleave disulfide bonds, results in a nearly 40% reduction in specific surface area across all fiber types, accompanied by a significant decrease in tensile strength and 80% reduction in elongation at break for Merino and Devon wool, but limited influence on the mechanical properties of Eider fibers. Furthermore, rate-dependent tensile testing within the elastic regime reveals distinct viscoelastic responses among the fiber types, suggesting that the sulfur-rich protein matrix surrounding IFs and its structure contribute actively to stress partitioning. Altogether, when combined with conclusions from SAXS measurements of IF spacing, our work offers compelling insights into the role of the keratin-associated protein (KAP) matrix in shaping wool fiber mechanics. Differences in mechanical behavior among wool types, despite similar IF spacing or sulfur content, highlight the importance of matrix composition and cross-linking density, suggesting that the molecular architecture of the KAP network may be a dominant factor in determining fiber performance.
First-principles study of surface properties of crystalline and amorphous uranium aluminides
Surface energy is a crucial material property required for the modeling of fission gas bubble behavior in nuclear materials. However, there is no information available regarding the surface properties of uranium aluminides. In this work we systematically investigate the surface properties of uranium aluminides (UAl 3 and UAl 4 ) by first-principles density functional theory (DFT) calculations. Specifically, a total of 13 surface orientations with a maximum Miller index (MMI) up to 3 are studied for cubic UAl 3 , while 19 surfaces with a MMI of 2 for orthorhombic UAl 4 . Using the surface energies predicted by DFT, the surface properties of equilibrium single crystal UAl 3 and UAl 4 , including surface area weighted surface energy, dominant surface orientations and surface anisotropy, are obtained from Wulff construction. To understand gas bubble behaviors in amorphous uranium aluminides under irradiation, we study the surface properties of amorphous UAl 3 and UAl 4 . Compared to the crystalline phases, the amorphous phases are found to have lower surface energies due to the reduced number of breaking U-Al bonds close to the surface. The currently obtained surface properties of UAl 3 and UAl 4 can be used for the future modeling of gas bubble behaviors in both crystalline and amorphous uranium aluminide fuels.
First-principles study of the surface properties of uranium carbides
Uranium carbides have attracted renewed interest as advanced nuclear fuels for Generation IV reactors. As an important property required for gas bubble modeling in nuclear fuels, the surface energy of uranium carbides is scarce in literature. In this work, we study the surface properties of uranium carbides by first-principles density functional theory calculations. Surface orientations with maximum Miller index up to 3, 2 and 2 are investigated for UC, U 2 C 3 and α-UC 2 , respectively. By studying the effects of surface termination and chemical potential on surface energy, we identify the factors that determines the surface stability. From the calculated surface energies, the surface properties of uranium carbide single crystals are obtained from Wulff construction, including equilibrium morphology, dominant surface orientation and area weighted surface energy.
Manipulation of fluids in three-dimensional porous photonic structures with patterned surface properties
A three-dimensional porous photonic structure, whose internal pore surfaces can be provided with desired surface properties in a spatially selective manner with arbitrary patterns, and methods for making the same are described. When exposed to a fluid (e.g., via immersion or wicking), the fluid can selectively penetrate the regions of the structure with compatible surface properties. Broad applications, for example in security, encryption and document authentication, as well as in areas such as simple microfluidics and diagnostics, are anticipated.
Manipulation of fluids in three-dimensional porous photonic structures with patterned surface properties
A three-dimensional porous photonic structure, whose internal pore surfaces can be provided with desired surface properties in a spatially selective manner with arbitrary patterns, and methods for making the same are described. When exposed to a fluid (e.g., via immersion or wicking), the fluid can selectively penetrate the regions of the structure with compatible surface properties. Broad applications, for example in security, encryption and document authentication, as well as in areas such as simple microfluidics and diagnostics, are anticipated.
First-Principles Study of Surface Properties of U{sub 3}Si{sub 2} for Accident Tolerant Fuel
Due to the high thermal conductivity and uranium density compared to UO{sub 2} fuel used in current Light Water Reactors (LWRs), U-Si fuels, such as the U{sub 3}Si{sub 2} and U{sub 3}Si{sub 5} compounds, are currently under investigation for the development of accident tolerant fuels (ATF) in response to the Fukushima Daiichi accident in Japan. In order to perform meaningful mesoscale and macroscale fuel performance simulations, fundamental material properties of nuclear fuels should be known. One example is the simulations of fission gas bubble evolution and gas bubble-induced swelling in nuclear fuels using mesoscale methods, such as phase field and rate theory. To properly describe the gas bubble behavior in the fuel, it is crucial to know the surface energies of the fuel. Unfortunately, there is no study of the surface properties of U{sub 3}Si{sub 2} from both experiment and theory. To this end, we systematically investigate the surface properties of U{sub 3}Si{sub 2} using density functional theory (DFT) based first-principles calculations. Of several low index facets, we studied the (001) and (100) surfaces of tetragonal U{sub 3}Si{sub 2} with all the possible terminations. Since all the studied surfaces are not stoichiometric, we also investigated the effect of elemental chemical potentials on the formation of surface. We systematically investigate the surface properties of U{sub 3}Si{sub 2} using density functional theory calculations. Of several low-index facets, the (001) and (100) surfaces show similar averaged surface energies calculated using even number of layers. At the high Si chemical potential, the Si-terminated U{sub 3}Si{sub 2}(100) and U{sub 3}Si{sub 2}(001) surfaces show lower energies than those of the U-terminated surfaces, with U,Si-terminated U{sub 3}Si{sub 2}(001) as the most stable surface. The surface energies of all non-stoichiometric U{sub 3}Si{sub 2} are linearly dependent on the Si chemical potential. The surface energies of U-terminated surfaces decrease as Si potential decreases. The U{sub 2}-terminated U{sub 3}Si{sub 2}(100) surface becomes that the most stable surface at U-rich side. Based on the current results, an averaged surface energy of U{sub 3}Si{sub 2}, i.e., 1.45 J/m{sup 2}, is recommended for the description of the rounded facets of gas bubbles in U{sub 3}Si{sub 2} by mesoscale simulations. (authors)
Role of defects on the surface properties of HfC
HfC has shown promise as a material for field emission due to the low work function of the (100) surface and a high melting point. Recently, HfC tips have exhibited unexpected failure after field emission at 2200K. Characterization of the HfC tips identified faceting of the parabolic tip dominated by coexisting (100) and (111) surfaces. To investigate this phenomenon, we used density functional theory (DFT) simulations to identify the role of defects and impurities (Ta, N, O) on HfC surface properties. Carbon vacancies increased the surface energy of the (100) surface from 2.35 J/m 2 to 4.75 J/m 2 and decreased the surface energy of the carbon terminated (111) surface from 8.75 J/m2 to 3.48 J/m 2 . Once 60% of the carbon on the (100) surface have been removed the hafnium terminated (111) surface becomes the lowest energy surface, suggesting that carbon depletion may cause these surfaces to coexist. The addition of Ta and N impurities to the surface are energetically favorable and decrease the work function, making them candidate impurities for improving field emission at high temperatures. Overall, DFT simulations have demonstrated the importance of understanding the role of defects on the surface structure and properties of HfC.
Silver nanowire/polyaniline composite transparent electrode with improved surface properties
Highlights: • AgNWs/PANI transparent electrode was prepared by layer-by-layer coating method. • The surface roughness of the electrode reached to 6.5 nm (root mean square). • The electrode had reasonable sheet resistance (25 Ω/□) and transmittance (83.5%). - Abstract: Silver nanowires (AgNWs) are as potential candidates to replace indium tin oxide (ITO) in transparent electrodes because of their preferred conducting and optical properties. However, their rough surface properties are not favorable for the fabrication of optoelectronic devices, such as displays and thin-film solar cells. In the present investigation, AgNWs/polyaniline composite transparent electrodes with better surface properties were successfully prepared. AgNWs were incorporated into polyaniline:polystyrene sulfonate (PANI:PSS) by layer-by-layer coating and mechanical pressing. PANI:PSS decreased the surface roughness of the AgNWs electrode by filling the gap of the random AgNWs network. The transparent composite electrode had decreased surface roughness (root mean square 6.5 nm) with reasonable sheet resistance (25 Ω/□) and transmittance (83.5%)
Formation and Acid–Base Surface Properties of Highly Dispersed η-Al{sub 2}O{sub 3} Nanopowders
Highly dispersed η-Al{sub 2}O{sub 3}-based nanopowders have been prepared via glycine–nitrate combustion followed by heat treatment in air. The resultant materials have been characterized by X-ray diffraction, Fourier transform IR spectroscopy, scanning electron microscopy, simultaneous thermal analysis, and other techniques. We have optimized the glycine-to-nitrate ratio (G/N = 0.2) and found heat treatment conditions for combustion products (isothermal holding at a temperature of 700°C for 6 h) that allow one to obtain single- phase nanocrystalline η-Al{sub 2}O{sub 3} powders with an average particle size of 5 ± 1 nm and specific surface area of 54 ± 5 m{sup 2}/g. The acid–base surface properties of the η-Al{sub 2}O{sub 3} nanopowder have been analyzed using pyridine sorption–desorption processes as an example. The specific concentrations of weak, intermediate, and strong Lewis acid centers on the surface of the η-Al{sub 2}O{sub 3} nanocrystals have been shown to markedly exceed those on the surface of commercially available γ-Al{sub 2}O{sub 3} (A-64). The synthesized nanopowders can thus be used as effective supports of acid catalysts.