Bio-inspired Surface Structures to Mitigate Interfacial Particle Adhesion and Erosion
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lunar dust↗
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T cell activation and immune synapse organization respond to the microscale mechanics of structured surfaces
Cells have the remarkable ability to sense the mechanical stiffness of their surroundings. This has been studied extensively in the context of cells interacting with planar surfaces, a conceptually elegant model that also has application in biomaterial design. However, physiological interfaces are spatially complex, exhibiting topographical features that are described over multiple scales. This report explores mechanosensing of microstructured elastomer surfaces by CD4 + T cells, key mediators of the adaptive immune response. We show that T cells form complex interactions with elastomer micropillar arrays, extending processes into spaces between structures and forming local areas of contraction and expansion dictated by the layout of microtubules within this interface. Conversely, cytoskeletal reorganization and intracellular signaling are sensitive to the pillar dimensions and flexibility. Unexpectedly, these measures show different responses to substrate rigidity, suggesting competing processes in overall T cell mechanosensing. The results of this study demonstrate that T cells sense the local rigidity of their environment, leading to strategies for biomaterial design.
59 BASIC BIOLOGICAL SCIENCES↗
Crystal Structures, Surface Stability, and Water Adsorption Energies of La-Bastnäsite via Density Functional Theory and Experimental Studies
Bastnasite is a fluoro-carbonate mineral that is the largest source of rare earth elements such as Y, La, and Ce. With increasing demand for REE in many emerging technologies, there is an urgent need for improving the efficiency of ore beneficiation by froth flotation. In order to design improved flotation agents that can selectively bind to the mineral surface, a fundamental understanding of the bulk and surface properties of bastnäsite is essential. Density functional theory calculations using the PBEsol exchange correlation functional and the DFT-D3 dispersion correction reveal that the most stable form of La-bastnäsite is isomorphic to the structure of Ce-bastnäsite belonging to the $P\bar{62}c$ space group, while the Inorganic Crystal Structure Database structure in the $P\bar{62}m$ space group is ca. 11.3 kJ/mol higher in energy per LaFCO 3 formula unit. We report powder X-ray diffraction measurements on synthetic of La-bastnäsite to support these theoretical findings. Six different surfaces are studied by DFT, namely [$10\bar{10}$], [0001], [$10\bar{11}$], [$10\bar{12}$], [$10\bar{14}$] and [$11\bar{22}$]. Among these, the [$10\bar{10}$] surface is the most stable with a surface energy of 0.73 J/m 2 in vacuum and 0.45 J/m 2 in aqueous solution. We predicted the shape of a La-bastnäsite nanoparticle via thermodynamic Wulff construction to be a hexagonal prism with [$10\bar{10}$] and [0001] facets, chiseled at its ends by the [$10\bar{11}$] and [$10\bar{12}$] facets. The average surface energy of the nanoparticle in the gas phase is estimated to be 0.86 J/m 2 , in good agreement with a value of 1.11 J/m 2 measured by calorimetry. The calculated adsorption energy of a water molecule varies widely with the surface plane and specific adsorption sites on a given surface. Moreover, the first layer of water molecules is predicted to adsorb strongly on the La-bastnäsite surface, in agreement with water adsorption calorimetry experiments. Our work provides an important step towards a detailed atomistic understanding of the bastnäsite water interface and designing collector molecules that can bind specifically to bastnäsite.
36 MATERIALS SCIENCE↗
Surface Structure of Reacting Solid Ramjet Fuels
Solid fuel ramjets are a developing technology that will enable extended range for supersonic vehicles. The simplicity of the system in terms of moving parts results in the performance being dictated by the solid fuel combustion processes. The physics near the surface, particularly in the fuel-rich recirculation zone, are challenging to resolve due to flow opacity. Here, regression rate measurements of hydroxyl-terminated polybutadiene from a miniature, portable slab burner are reported. Mass-averaged regression rates agree with correlations from the literature, suggesting that the proper physics in the burner are captured. Synchrotron-based phase-contrast imaging is used to quantify local surface features, including a multiphase froth layer, molten polymer transport, and local regression rate measurements in the recirculation zone. Regression rates near the inlet are less than the mass-averaged values, whereas near the reattachment point the local value exceeds the mass-averaged values. Further, the observed froth layer is as large as 2 mm near the inlet and decreases to sub-millimeter thicknesses near the reattachment point. An analytical heat transfer model is used to quantify the influence of the surface froth layer on the regression rates. Results indicate that the froth layer has an insulating effect and will reduce the local regression rate.
33 ADVANCED PROPULSION SYSTEMS↗
Morphological and Surface Structural Changes during Electrochemical Cycling in Li-rich Layered Oxides for Next Generation Li-ion Batteries
Li-rich layered oxides, either as a solid solution or as a nano-composite of layered Li 2 MnO 3 and Li(TM)O 2 (TM=Ni, Co, Mn), draw significant attention as the next-generation cathode materials for high-energy-density Li-ion batteries in electric vehicles. However, there are many issues still unclear, and numerous scientific challenges of these materials that must be overcome to realize their utilization in commercial Li-ion batteries. The first drawback is the irreversible voltage degradation process that limits cycle life. Modified co-precipitation synthesis is introduced to obtain morphology controlled Li-rich material without ammonia addition. This unique design increases meso-structure morphological stability compared with the sample with large secondary particles as proved by Transmission X-ray Microscope. As a result, the voltage decay and capacity loss during long term cycling have been minimized to a large extent. On the other hand, lattice oxygen plays an intriguing role in the electrochemical process of Li-rich material through a reversible redox process as well as an irreversible oxidation with O 2 gas release. To prevent oxygen gas generation, oxygen vacancies have been proposed to form on the surface of the morphology controlled Li-rich layered oxides through the design of a gas-solid interface reaction (GSIR). Dynamic structural changes during the initial two electrochemical cycles of GSIR Li-rich layered oxides are investigated with In operando synchrotron X-ray diffraction (SXRD). Different electrochemical reaction regions dominated by either cations or anions redox are identified in the shifts of the lattice parameters during the first cycle. Changes in lattice parameters, oxygen positions, and microstrain help to explain the lithium de-intercalation mechanism in this class of materials.
Zhang, Minghao↗
Surface structure of neutron stars with high magnetic fields
The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates.
Fushiki, I.↗
A survey of surface structures and subsurface developments for lunar bases
Concepts proposed for lunar-base structures and shelters include those fabricated on earth, fabricated locally using lunar materials, and developed from subsurface features. Early bases may rely on evolutionary growth using Space Station modules and nodes covered with regolith for protection against thermal and radiative stresses. Expandable/inflatable shelters used alone on the surface or in conjunction with subselene (beneath the lunar surface) features and spent portions of the Space Shuttle's fuel tanks offer early alternatives. More mature lunar bases may need larger volumes provided by erectable buildings, hybrid inflatable/rigid spheres, modular concrete buildings using locally derived cement, or larger subselene developments.
Hypes, Warren D.↗
Surface Structure Dependence of the Dry Dehydrogenation of Alcohols on Cu(111) and Cu(110)
The non-oxidative dehydrogenation of alcohols is considered as an important method to produce aldehydes for the chemical industry and hydrogen gas. However, current industrial processes are oxidative, meaning that the aldehydes are formed along with water, which, in addition to being less energy efficient, poses separation problems. Herein the production of aldehydes from methanol and ethanol on clean and dry Cu(111) and Cu(110) surfaces was investigated in order to understand the catalytic anhydrous dehydrogenation of alcohols. We report both ethanol and methanol preferentially react under ultrahigh vacuum conditions at surface defects to yield acetaldehyde and formaldehyde, respectively, in the absence of surface oxygen and water. The amount of alkoxide reaction intermediates measured by scanning tunneling microscopy, and aldehyde and hydrogen products detected by temperature programmed reaction, are increased by inducing more defects in the Cu substrates with Ar ion sputtering. This work also reveals that the Cu model surfaces are not poisoned by the reaction and exhibit 100% selectivity for alcohol dehydrogenation to aldehyde and hydrogen.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Accounting for the Complex Surface Structure in Ellipsometric Studies of the Effects of Magnetron Sputtering Modes on the Growth and Optical Properties of In{sub 2}O{sub 3} Films
The efficiency of invoking additional information on optical transmission in solving the inverse problem of ellipsometry by a minimization method is demonstrated in practice for In{sub 2}O{sub 3} fi doped and nondoped with Sn on Al{sub 2}O{sub 3} (012) substrates. This approach allows the thickness and refractive index of thin films with rough surfaces to be uniquely determined. Solutions of the inverse problem in the framework of one-, two-, and multilayer models are compared. The last provides the best description of the experimental data and the correct parameters of the samples. The dependences of the investigated properties of films produced with different magnetron sputtering modes are found using the above methods and models and do not contradict general concepts about the film formation by this material.
36 MATERIALS SCIENCE↗
Fan-shaped coma, orientation of rotation axis, and surface structure of a cometary nucleus. I - Test of a model on four comets
Pronounced anisotropy in the outgassing from comets, especially from short-period ones, appears to be a factor responsible for the frequent occurrence of a fan-shaped coma, extending in the general direction of the sun. It is suggested that the pattern of deviations from the sunward direction contains information on the orientation of the spin axis and on the time lag in the sublimation process, which in turn provides insight into the nature of the nuclear surface. A simple model of a spherical rotating nucleus is formulated and a trial-and-error technique is devised to determine the axis-orientation constants and a lag angle, a measure of the time lag in units of the rotation period. The method is applied to the comets Encke, Tempel 2, Borrelly, and Schwassmann-Wachmann 3.
Sekanina, Z.↗
Near surface structure of ultrathin epitaxial Ru films on graphene/amorphous SiO 2 revealed by azimuthal RHEED
Ru has been considered as an alternative metallic candidate for future local interconnects. The 2D reciprocal space map constructed from the azimuthal reflection high-energy electron diffraction patterns reveals that ultrathin Ru(0001) is epitaxially grown on transferred graphene on amorphous SiO 2 through quasi-van der Waals interaction. The in-plane and out-of-plane lattice constants are measured from streaks’ separation and intensity modulations along streaks, respectively. Weak and broad rings indicate that a low density of nanoscale polycrystals exist on the surface. In this work, The intensities of 00 and non-00 diffraction spots vs. azimuthal angles in the 2D map show a few degrees out-of-plane and in-plane angular misorientations among grains, respectively. As the film thickness decreases these angular misorientations increase. Transmission electron microscopy carried out in this study also provides precise values of lattice constant and sub-grain sizes in the films. These findings show that ultrathin Ru film is epitaxial but not exactly single crystalline.
36 MATERIALS SCIENCE↗
Surface Structure, Morphology, and Stability of Li(Ni 1/3 Mn 1/3 Co1/3)O 2 Cathode Material
Layered Li(Ni 1-x-y Mn x Co y )O 2 (NMC) oxides are promising cathode materials capable of addressing some of the challenges associated with next-generation energy storage devices. In particular, improved energy densities, longer cycle-life, and improved safety characteristics with respect to current technologies are needed. However, sufficient knowledge on the atomic-scale processes governing these metrics in working cells is still lacking. Herein, Density Functional Theory (DFT) is employed to predict the stability of several low-index surfaces of Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 (NMC111) as a function of Li and O chemical potentials. Predicted particle shapes are compared with those of single crystal NMCs synthesized under different conditions. The most stable surfaces for stoichiometric NMC111 are predicted to be the non-polar (104), the polar (012) and (001), and the reconstructed, polar (110) surfaces. Results indicate that intermediate spin Co 3+ ions lower the (104) surface energy. Furthermore, it was found that removing oxygen from the (012) surface was easier than from the (104) surface, suggesting a facet dependence on surface-oxygen vacancy formation. In conclusion, these results give important insights into design criteria for the rational control of synthesis parameters as well as establish a foundation on which future, mechanistic studies of NMC surface instabilities can be developed.
25 ENERGY STORAGE↗
Optimizing structured surfaces for diffractive waveguides
We introduce universal diffractive waveguide designs that can match the performance of conventional dielectric waveguides and achieve various functionalities. Optimized using deep learning, diffractive waveguides can be cascaded to form any desired length and are comprised of transmissive diffractive surfaces that permit the propagation of desired modes with low loss and high mode purity. In addition to guiding the targeted modes through cascaded diffractive units, we also developed various waveguide components and introduced bent diffractive waveguides, rotating the direction of mode propagation, as well as spatial and spectral mode filtering and mode splitting diffractive waveguide designs, and mode-specific polarization control. This framework was experimentally validated in the terahertz spectrum to selectively pass certain spatial modes while rejecting others. Without the need for material dispersion engineering diffractive waveguides can be scaled to operate at different wavelengths, including visible and infrared spectrum, covering potential applications in, e.g., telecommunications, imaging, sensing and spectroscopy.
Applied optics↗
X-Ray Spectroscopic Investigation of Chlorinated Graphene: Surface Structure and Electronic Effects
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solar (photovoltaic), electrodes - solar, charge t↗
Changes in local surface structure and Sr depletion in Fe-implanted SrTiO[subscript 3] (001)
Abstract not provided
Lobacheva, O.↗