Surface Orientation Research Articles

Centrifugation-Mediated Crystal Growth of Attractive Colloids for Band Edge Lasing.

Attractive depletion interactions are utilized to organize colloidal particles into crystalline arrays with high crystallinity through spontaneous phase separation. However, uncontrolled nucleation frequently leads to the formation of crystalline grains with varied crystal orientations, which hampers the optical performance of photonic crystals. Here, colloidal crystals have been engineered with uniform orientation and high surface coverage by applying centrifugal force during the depletion-induced assembly of polystyrene particles. The centrifugal force encourages the particles to move toward the bottom surface, which fosters heterogeneous nucleation and supports rapid crystal growth, yielding densely-packed and uniformly-arranged crystal grains with high reflectivity. This study has observed that the nucleation and crystal growth behavior is significantly influenced by the salt concentration. Based on the pair potentials, the transition boundary has been quantitatively analyzed between fluid and crystal phases and identified the threshold for homogeneous nucleation. Utilizing the high-reflectivity colloidal crystals, band-edge lasing is achieved by dissolving the water-soluble dye into the aqueous suspensions. Upon optical excitation, a lasing emission characterized is observed by a narrow spectral width at the short-wavelength band edge. Notably, the laser wavelength can be adjusted by altering the salt concentration or particle diameter, offering a versatile approach to tuning the optical properties.

Near‐surface plastic deformation in polycrystalline SrTiO3 via room‐temperature cyclic Brinell indentation

AbstractDislocations are being used to tune versatile mechanical and functional properties in oxides with most current studies focusing on single crystals. For potentially wider applications, polycrystalline ceramics are of concern, provided that dislocations can be successfully introduced. However, in addition to preexisting pores and flaws, a major barrier for bulk plastic deformation of polycrystalline ceramics lies in the grain boundaries (GBs), which can lead to dislocation pile‐up and cracking at the GBs due to the lack of sufficient independent slip systems in ceramics at room temperature. Here, we use the cyclic Brinell indentation method to circumvent the bulk deformation and focus on near‐surface regions to investigate the plastic deformation of polycrystalline SrTiO3 at room temperature. Dislocation etch‐pit analysis suggests that plastic deformation can be initiated within the grains, at the GBs, and from the GB triple junction pores. The deformability of the individual grains is found to be dependent on the number of cycles, as also independently evidenced on single‐crystal SrTiO3 with representative surface orientations (001), (011), and (111). We also identify a grain‐size‐dependent plastic deformation.

Influence of Copper Surface Orientation on the Hydrogen-Bonded Assembly of 2-Methylbenzimidazole Molecules: A Comparative Study

Influence of Copper Surface Orientation on the Hydrogen-Bonded Assembly of 2-Methylbenzimidazole Molecules: A Comparative Study

Investigation on crystallographic orientation dependent ion transportation in Li3YBr6 superionic conductor for lithium ion battery

Enhancing ionic conductivity in solid electrolytes poses a significant hurdle in advancing all-solid-state batteries. Researchers have explored a variety of materials and techniques to elevate ionic conductivity. Lithium halide-based materials are emerging as a promising option for solid electrolytes due to their capacity for rapid ion conduction and robust electrochemical stability. Various methods, including substitution strategies and defect chemistry, have been deployed to enhance ionic conductivity within lithium halide solid electrolytes. Ionic conductivity is intricately linked to the substructure of migrating ions; therefore, ionic conductivity can be significantly enhanced by the alteration of the substructure. This work focuses on the impact of crystallographic orientation on ionic conductivity. Halide superionic conductor of structure Li3YX6 (X = halogen) has been used for the study. First, the ion transport mechanism in Li3YBr6 (in the C2/c phase) crystal has been examined and sequentially the impact of the crystallographic orientation has been investigated by creating two surfaces of different crystal orientations of pristine Li3YBr6. Findings of the present work show that among two different crystal-oriented surfaces (010) and (100) the (010) crystal-oriented structure Li3YBr6 has remarkable room temperature ionic conductivity (11.8 mS/cm) which is nearly fourteen times higher than that of pristine Li3YBr6 crystal while (100) oriented structure shows a little increment in room temperature ionic conductivity. To examine the mechanism behind this exceptional ionic conductivity in different structures energy barriers along different migration pathways have been evaluated. For the determination of the energy barrier nudged elastic band simulation was carried out. The results demonstrate that the (010) crystal-oriented surface structure possesses the lowest energy barrier, at 0.16 eV, which is 0.10 eV lower than the (100) oriented structure and 0.19 eV less than pristine Li3YBr6 (C2/c). This reduced energy barrier in the (010) crystal-oriented structure can be attributed to the prevalence of the tetrahedron-to-tetrahedron migration pathway.

Investigation of the microfracture and damage characteristics of dam during impoundment at Sanhekou hydropower station

Dam stability is one of the most important issues in hydraulic engineering. Microfractures and damage commonly occur during impoundment, which might lead to serious dam problems. In this study, based on the engineering background of the Sanhekou hydropower station, microseismic monitoring and numerical simulation were employed to systematically investigate the microfracture and damage characteristics of the dam body. First, the microseismic monitoring system was established to capture the microfractures inside the dam. The results indicated that the rise in water level elevation has a significant effect on the microfracture and damage characteristics of the dam body, especially during the early stage of impoundment. This can be reflected by the variation in the derived source parameters, i.e., the b value, daily energy release, daily apparent stress and daily apparent volume. In addition, the failure mode of the microfractures could be determined by using the ES/EP value of microseismic events and the moment tensor inversion method. The cracking orientation of the failure surfaces could also be determined by the moment tensor inversion method. Subsequently, numerical simulation was conducted where the initial damage of the dam was considered by integrating the microseismic monitoring data. The simulation results suggested that dam deformation under impoundment considering microseismic feedback agrees well with the real field measured results. The stress level of the dam toe was larger than that of the dam heel, and both the dam toe and dam heel were under compression before impoundment. However, with increasing water level elevation, the stress status of the dam heel area changes from compression to tension. The findings in this study will provide a better understanding of the damage and failure mechanism of dams during impoundment, which might be helpful for the design and support of dams in hydropower stations.

Exploring the micromorphological diversity of palynomorphic flora from lesser Himalaya biodiversity hotspot

Palynology, a prominent field in plant systematics and biodiversity studies, plays a vital role in identifying and determining the plant species present in a specific region. The current study was performed to evaluate the micromorphological traits of pollen from flora of Lesser Himalaya. Pollen microstructural variations aid in the identification of species belonging to specific botanical families and various geographic habitats. Flowers of 24 selected species categorized into 16 families were collected, preserved and then acetolysis protocol followed. Pollen was examined under a light and scanning microscopy (LM and SEM) for palynomorph description. The palynomorphs characteristics such as size, shape, exine surface, and aperture orientation, were examined. Status of these plants show that herbs are being dominant (11 species), while shrubs (7 species), climbers (3 species), bulbous plants (2 species), small tree, sedge, weed (1 species each). Pollen shape determined in equatorial view were; spheroidal, sub-prolate, oblate-spheroidal, prolate, spherical and sub-oblate. The variations were seen among pollen types; tricolpate, tricolporate and polyporate in most of the species. Exine stratification was observed mostly scabrate while echinate, cristate-reticulate, granulate, punctate, rugulate-perforate, striate-rugulate, verrucate, cristate-foveolate was visualized in each different species. Palynomorph apertural patterns were observed sunken, furrowed, slightly bulged, scabrate, granulate, slit like, and perforate. The largest polar diameter was measured in Hymenocallis littoralis (138.6 µm) whereas smallest in Parthenium hysterophorus (14.70 µm). Equatorial distance was calculated maximum for Cascabela thevetia (110.1 µm) and minimum for Hibiscus rosa-sinensis (1.7 µm). P/E ratio was calculated largest in Hymenocallis littoralis (1.8) and lowest in Duranta erecta (0.89). The palynomorphs taxonomic characters investigated can be helpful in species level identification and provide a baseline to conduct more systematic research with respect to specific plant families and genera.

The effect of surface orientation on band alignment and carrier transfer at WS2/CdS interface: Insight from first-principles calculations

Loading of WS2 can greatly improve water splitting H2 generation efficiency of CdS in experiments. Here, we constructed WS2/CdS(100) and WS2/CdS(110) heterostructures with smaller mismatches and explored their interaction energy and band offset by first-principles calculations. Our calculation suggests that the WS2/CdS(100) interface with a stronger binding energy is more active in experiments, while the WS2/CdS(110) interface is metastable. The band alignment between CdS and WS2 is highly dependent on the orientation of the interfaces, and WS2/CdS(100) and WS2/CdS(110) belong to type-I and type-II band alignments, respectively. Therefore, a metal electrode and hole scavenger may be essential in experiments to help WS2/CdS(100) efficiently trap electrons, and a suitable substrate and an appropriate growth temperature are also needed to composite the CdS(110) surface to achieve a higher photocatalytic efficiency. In addition, we performed a detailed analysis of the macroscopic average potential and found that the calculated accuracy of potential difference across the heterostructures due to slab thickness is less than 80 meV at WS2/CdS interfaces. In total, our calculations not only explain the physical reasons for the increased efficiency of WS2/CdS, but also provide a detailed guideline for the design of a more efficient synergistic catalyst.

Surface Segregation Studies in Ternary Noble Metal Alloys: Comparing DFT and Machine Learning with Experimental Data.

Surface segregation, whereby the surface composition of an alloy differs systematically from the bulk, has historically been hard to study, because it requires experimental and modeling methods that span alloy composition space. In this work, we study surface segregation in catalytically relevant noble and platinum-group metal alloys with a focus on three ternary systems: AgAuCu, AuCuPd, and CuPdPt. We develop a data set of 2478 fcc slabs with those compositions including all three low-index crystallographic orientations relaxed with Density Functional Theory using the PBEsol functional with D3 dispersion corrections. We fine-tune a machine learning model on this data and use the model in a series of 1800 Monte Carlo simulations spanning ternary composition space for each surface orientation and ternary chemical system. The results of these simulations are validated against prior experimental surface segregation data collected using composition spread alloy films for AgAuCu and AuCuPd. Our findings reveal that simulations conducted using the (110) orientation most closely match experimentally observed surface segregation trends, and while predicted trends qualitatively match observation, biases in the PBEsol functional limit numeric accuracy. This study advances understanding of surface segregation and the utility of computational studies and highlights the need for further improvements in simulation accuracy.

Heisenberg soft hair on Robinson-Trautman spacetimes

We study 4 dimensional (4d) gravitational waves (GWs) with compact wavefronts, generalizing Robinson-Trautman (RT) solutions in Einstein gravity with an arbitrary cosmological constant. We construct the most general solution of the GWs in the presence of a causal, timelike, or null boundary when the usual tensor modes are turned off. Our solution space besides the shape and topology of the wavefront which is a generic compact, smooth, and orientable 2d surface Σ, is specified by a vector over Σ satisfying the conformal Killing equation and two scalars that are arbitrary functions over the causal boundary, the boundary modes (soft hair). We work out the symplectic form over the solution space using covariant phase space formalism and analyze the boundary symmetries and charges. The algebra of surface charges is a Heisenberg algebra. Only the overall size of the compact wavefront and not the details of its shape appears in the boundary symplectic form and is canonical conjugate to the overall mass of the GW. Hence, the information about the shape of the wavefront can’t be probed by the boundary observer. We construct a boundary energy-momentum tensor and a boundary current, whose conservation yields the RT equation for both asymptotically AdS and flat spacetimes. The latter provides a hydrodynamic description for our RT solutions.

Synergistic Influence of Fibrous Pattern Orientation and Modulus on Cellular Mechanoresponse.

The fibrous extracellular matrix (ECM) is vital for tissue regeneration and impacts implanted device treatments. Previous research on fibrous biomaterials shows varying cellular reactions to surface orientation, often due to unclear interactions between surface topography and substrate elasticity. Our study addresses this gap by achieving the rapid creation of hydrogels with diverse fibrous topographies and varying substrate moduli through a surface printing strategy. Cells exhibit heightened traction force on nanopatterned soft hydrogels, particularly with randomly distributed patterns compared with regular soft hydrogels. Meanwhile, on stiff hydrogels featuring an aligned topography, optimal cellular mechanosensing is observed compared to random topography. Mechanistic investigations highlight that cellular force-sensing and adhesion are influenced by the interplay of pattern deformability and focal adhesion orientation, subsequently mediating stem cell differentiation. Our findings highlight the importance of combining substrate modulus and topography to guide cellular behavior in designing advanced tissue engineering biomaterials.

Infinite metacyclic subgroups of the mapping class group

For g\geq 2 , let \mathrm{Mod}(S_{g}) be the mapping class group of the closed orientable surface S_{g} of genus g . In this paper, we provide necessary and sufficient conditions for a pair of elements in \mathrm{Mod}(S_{g}) to generate an infinite metacyclic subgroup. In particular, we provide necessary and sufficient conditions under which a pseudo-Anosov mapping class generates an infinite metacyclic subgroup of \mathrm{Mod}(S_{g}) with a nontrivial periodic mapping class. As applications of our main results, we establish the existence of infinite metacyclic subgroups of \mathrm{Mod}(S_{g}) isomorphic to \mathbb{Z}\rtimes\mathbb{Z}_{m} , \mathbb{Z}_{n}\rtimes\mathbb{Z} , and \mathbb{Z}\rtimes\mathbb{Z} . Furthermore, we derive bounds on the order of a nontrivial periodic generator of an infinite metacyclic subgroup of \mathrm{Mod}(S_{g}) that are realized. Finally, we show that the centralizer of an irreducible periodic mapping class F is either \langle F\rangle or \langle F\rangle\times\langle i\rangle , where i is a hyperelliptic involution.

Extending finite free actions of surfaces

AbstractWe prove the existence of finite groups acting freely as orientation‐preserving homeomorphisms on closed orientable surfaces that extend as a group of homeomorphisms of some compact orientable 3‐manifold but that cannot extend to a handlebody. This solves a basic problem in low‐dimensional equivariant topology going back to the work of Reni and Zimmermann in the mid‐1990s.

Synergistic polarization engineering of dielectric towards low-voltage high-mobility solution-processed ultraflexible organic transistors

The emerging wearable skin-like electronics require the ultra-flexible organic transistor to operate at low voltage for electrical safety and energy efficiency and simultaneously enable high field-effect mobility to ensure the carrier migration ability and the switching speed of circuits. However, the currently reported low-voltage organic transistors generally present low mobility, originating from the trade-off between molecular polarity and surface polarity of the dielectrics. In this work, the orientation polarization of the dielectric is enhanced by introducing a flexible quaternary ammonium side chain, and the surface polarity is weakened by the shielding effect of the nonpolar methyl groups on the polar nitrogen atom. The resulting antisolvent QPSU dielectric enables the high-dielectric constant up to 18.8 and the low surface polarity with the polar component of surface energy only at 2.09 mJ/m2. Such a synergistic polarization engineering between orientation polarization and surface polarity makes the solution-processed ultraflexible transistors present the ultralow operational voltage down to −3 V, the ultrahigh charge-carrier mobility up to 8.28 cm2 V−1 s−1 at 1 Hz, excellent cyclic operational stability and long-term air stability. These results combined with the ultrathin thickness of transistor as low as 135 nm, the ultralight mass of 0.5 g/m2, the conformal adherence capability on human skin and 1-μm blade edge, and the strong mechanical robustness with stable electrical properties for 30,000 bending cycles, open up an available strategy to successfully realize low-voltage high-mobility solution-processed organic transistor, and presents the potential application of QPSU dielectric for the next-generation wearable imperceptible skin-like electronics.

Experimental performance characteristics of the daytime radiative cooler at various surface orientations

The daytime radiative cooling technology is becoming crucial with several prospective applications, either as a standalone or in conjunction with conventional cooling systems; however, the dilute cooling flux is a main drawback. The cooling flux can be enhanced by proper surface orientation (direction or azimuth and tilting or inclination), but it has not been studied extensively. Hence, this study describes the radiative cooler's angular and directional-dependent performance. The angular and directional dependent study is essential to emphasize the further development in the radiative coatings' suitable macro-scale geometry. An optimized polymer-particle composite structured daytime radiative cooler has been developed and tested with maximum temperature drop from the ambient as an objective function. The north-facing radiative cooler starts to perform better up to a 30° tilt angle; after that, its performance tends to decrease. The south-facing surfaces have reduced performance due to higher solar flux exposure as well as reduced sky exposure. A flat surface receives the maximum sky exposure since its horizontal placement does not interfere with the earth's objects. A maximum of 10.5 °C temperature drop and an average maximum of 5.5 °C are observed. North-facing tilt up to 30° is recommended in the northern hemisphere and vice-versa for best performance.

The interaction of surface orientation and roughness on nanofluid sub-cooled flow boiling

This experimental study examined the subcooled-flow boiling of water-alumina nanofluids with 0.1 vol % concentration. The study aimed to explore how surface roughness, fluid velocity, and surface orientation influenced the subcooled flow boiling heat transfer (SFBHT). A cross-sectional area of 2 × 3 cm2 and a length of 1.20 m are the dimensions of the plexiglass channel in the experimental setup. A copper heater was embedded at the bottom surface of the channel. The results of the experiment revealed that the surface roughness had a positive effect on SFBHT for horizontal channels, and it depended on the surface configuration. The heat flux increases by 233 % and 98.27 % at low and high fluid velocity (0.5 and 0.9 m/s) by changing the surface roughness from 0.65 to 4.4 μm, respectively. The fluid velocity did not have uniform impacts on SFBHT for higher and lower surface temperatures. When altering the fluid velocity from 0.5 m/s to 0.9 m/s, the heat flux experiences significant variations: The overall heat fluxes are 56.52 % and −35.86 % for rough surface at lower and higher surface temperature, respectively. Depending on whether the surfaces were smooth or rough, the SFBHT performance varied due to the surface configuration. The boiling heat transfer (BHT) performance increased for smooth surfaces but decreased for rough surfaces by changing the surface orientation in both negative and positive directions. The overall heat fluxes increase by about 72.84 % and 66.67 % at smooth surface for both positive and negative inclination, respectively. They are about −32.94 % and −29.82 % at rough surface for both positive and negative inclination, too. The rate of surface roughness’ effects on SFBHT reduces by enhancing the surface angles.

The maximum genus of the generalized Petersen Graph, GP (<em>n, k</em>) for the cases <em>k</em> = 1, 2

In Topological graph theory, the maximum genus of graphs has been a fascinating subject. For a simple connected graph G, the maximum genus γM(G) is the largest genus of an orientable surface on which G has a 2-cell embedding. γM(G) has the upper bound, γM(G)≤[β/2], where β(G) denotes the Betti number and G is said to be upper embeddable if the equality holds. In this study, the maximum genus of GP(n, k) is established as γM(GP(n,k))=[(n+1)/2] for k = 1 and k = 2 by proving the upper embeddability of generalized Petersen graph, GP(n, k) for the cases k = 1 and k = 2. The proof is done by obtaining spanning trees T and examining the components in the edge complements GP(n, k)\T for the cases k = 1 and k = 2 of GP(n, k).

Engulfing behavior of vapor bubbles in downward facing heated surface boiling

Boiling of the coolant at the hot surface provides relatively better cooling by absorbing latent heat along with convection heat transfer as compared to heat transfer under single-phase conditions. In boiling, the orientation of heated surface also plays a crucial role. Downward facing boiling is complex than upward facing boiling, as the detachment of the bubble inhibited due to the heater surface orientation. Consequently, the bubble residence time and interaction with other bubbles are different in such boiling conditions. Our experiments on a large downward facing flat surface (100 × 400 mm2) revealed unexplored boiling phenomena. The boiling process is dominated by a complex engulfing phenomenon, which is rarely reported in the past. The engulfing phenomena have been captured using high-speed photography, wherein, at low heat fluxes, it is observed that larger bubbles engulf small bubbles by opening their mouth and swallowing the small bubbles. However, at higher heat fluxes, this phenomenon disappears. A larger vapor blanket is formed due to engulfing of bubbles, which may lead to departure from nucleate boiling. This engulfing behavior depends on the heat flux and subcooling. With the increase in heat flux, it is found that the rate of vapor engulfing increases. We have attempted to explain the science behind such engulfing phenomenon based on the capillary pressure difference. These results are consistent at various subcooling. This research provides new insights into nucleate boiling and may help in developing advanced mathematical models for accurate heat transfer prediction on downward facing nucleate boiling.

Anisotropic Cu2O nanostructures: A promising remediation for per- and polyfluoroalkyl substances

Copper oxide (Cu2O) exhibits exceptional optical properties and phase stability at the nanoscale level making it highly desirable in nanotechnology applications. Its unique and distinctive properties make it highly feasible for diverse applications, which include environmental remediation, energy conversion, and catalysis. In this study, we tailor the surface and facet orientation of Cu2O nanoparticles to enhance their efficacy in addressing environmental contaminants such as per- and polyfluorinated substances (PFAS). By adjusting the ratios of the precursor and capping agent, we have synthesized Cu2O nanocubes (NCs) and octahedra (Oh) with average sizes of 450 nm and 650 nm, respectively. The time-dependent UV–Vis interaction studies revealed significant redshifts in absorption spectra upon the addition of Cu2O NCs and Oh to the PFAS solutions, indicative of the changes in the surroundings upon the interaction. FT-IR spectra further confirmed the sorption of PFAS on Cu2O nanostructures with stronger adsorption observed for longer-chain PFAS due to enhanced hydrophobic interactions. XPS analysis further provided insights into the surface composition changes after post-interaction, indicating the presence of PFAS on Cu2O nanostructures. The zeta potential analysis supported the role of electrostatic interactions in PFAS removal. Our results demonstrate that Cu2O Oh exhibits superior PFAS adsorption compared to Cu2O NCs, which is attributed to the exposed facets of a copper atom having a positive surface charge and facilitating electrostatic interactions. Specifically, Cu-terminated (110) or (111) surfaces exhibit enhanced sorption capacity, while the reduced reactivity of Cu-terminated Cu2O (100) surfaces is linked to high energy barrier holes at the surface region. Overall, this study elucidates the interaction mechanisms between Cu2O nanostructures and PFAS which underscores the significance of surface engineering for optimizing their performance in environmental remediation strategies.

Closed orientable surfaces and fold Gauss maps

This paper describes how the elliptic and hyperbolic regions of a surface are related to stable Gauss maps on closed orientable surfaces immersed in three-dimensional space. We will show that for certain connected, closed, orientable surfaces containing a finite number of embedded circles that delineate two distinct types of regions, if all regions of one type are homeomorphic to a cylinder, then there exists an immersion f:M→R3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f: M \\rightarrow \\mathbb {R}^3$$\\end{document} for which the Gauss map is a fold Gauss map.

Self-Assembly of Hierarchical High-χ Fluorinated Block Copolymers with an Orthogonal Smectic-within-Lamellae 3 nm Sublattice and Vertical Surface Orientation.

Hierarchical structure-within-structure assemblies offer a route toward increasingly complex and multifunctional materials while pushing the limits of block copolymer self-assembly. We present a detailed study of the self-assembly of a series of fluorinated high-χ block copolymers (BCPs) prepared via postmodification of a single poly(styrene)-block-poly(glycidyl methacrylate) (S-b-G) parent polymer with the fluorinated alkylthiol pendent groups containing 1, 6, or 8 fluorinated carbons (termed trifluoro-ethanethiol (TFET), perfluoro-octylthiol (PFOT), and perfluoro-decylthiol (PFDT), respectively). Bulk X-ray scattering of thermally annealed samples demonstrates hierarchical molecular assembly with phase separation between the two blocks and within the fluorinated block. The degree of ordering within the fluorinated block is highly sensitive to synthetic variation; a lamellar sublattice was formed for S-b-GPFOT and S-b-GPFDT. Thermal analyses of S-b-GPFOT reveal that the fluorinated block exhibits liquid crystal-like ordering. The complex thin-film self-assembly behavior of an S-b-GPFOT polymer was investigated using real-space (atomic force microscopy and scanning electron microscopy) and reciprocal-space (resonant soft X-ray scattering (RSoXS), grazing incidence small- and wide-angle scattering) measurements. After thermal annealing in nitrogen or vacuum, films thicker than 1.5 times the primary lattice spacing exhibit a 90-degree grain boundary, exposing a thin layer of vertical lamellae at the free interface, while exhibiting horizontal lamellae on the preferential (polystyrene brush) substrate. RSoXS measurements reveal the near-perfect orthogonality between the primary and sublattice orientations, demonstrating hierarchical patterning at the nanoscale.