Hexagonal Surface Research Articles

Influence of silanes on the hydration of cement by separating the cement into its individual phases

AbstractCementitious materials can be treated with organosilicon compounds (silanes) to achieve a water‐repellent effect. However, the influence of silanes on cement hydration is still not fully understood. For this reason, we studied the hydration of the main Portland cement phase (C3S ‐ tricalcium silicate) and the interaction with iBTES (isobutyltriethoxysilane), iOTES (isooctyltriethxysilane) and nOTES (n‐octyltriethoxysilane) by isothermal calorimetry and in‐situ X‐ray diffraction (XRD). The results show that C3S hydration is initially retarded and subsequently accelerated by iBTES and iOTES. In addition to the hydration process, the crystal growth of the portlandites (calcium hydroxide) is also affected by the silanes. The XRD results indicate that the portlandites grow significantly more plate‐like. In this context, the influence of the silanes on the portlandite crystallization was therefore also recorded in a special experimental setup. From the scanning electron microscope images it can be shown that all portlandite crystals grown in the presence of silanes have a platelike morphology. This is due to the fact that the hexagonal surfaces of the portlandite are covered by silanes and thus the growth direction of the crystals is affected. The modified portlandite crystals indicate that silanes also influence the microstructure of the cement paste and therefore its chemical and mechanical properties.

Hydrogen and oxygen mixed-termination for nitrogen-vacancy quantum sensors in hexagonal diamond

Controlling the chemical termination of hexagonal diamond surface opens up new possibilities for shallow nitrogen-vacancy (NV) centers in quantum sensing applications. In this work, the H/O/OH mixed terminations on hexagonal diamond (100) surfaces to host NV centers are investigated by first-principles calculations. Results indicate that H–O, O–OH, and H–O–OH mixed surfaces produce positive electron affinity with neither spin noise nor surface-related state. It is concluded that the surface-connected ether bonds should be maintained, and unconnected ether bonds should be avoided, preserving the shallow NV centers unaffected. Based on the surface stability analysis, we further confirm that the H–O surface has a higher possibility to be fabricated. Moreover, we make an intensive study by placing an NV center ∼12 Å from the hexagonal (100) surface, and the results elucidate that the H–O surface has no obvious effect on the defect states of the NV center. Therefore, we identify a combination of surface terminators that is a prospective candidate for NV-based quantum sensors.

Control Synthesis of Metallic Gold Decorated ZnO Nanoparticles for Photocatalytic Degradation of Rhodamine B, Methylene Blue and Eriochrome Black T Dyes

AbstractPure ZnO and metallic gold (Au) decorated ZnO (Au‐ZnO) nanoparticles were prepared by a modified sol‐gel method employing (CTAB, C19H42BrN) as a cationic surfactant. XRD analysis shows the wurtzite hexagonal structure of pure ZnO and confirms the modification in the structure with the decoration of Au metal in ZnO. TEM characterization illustrates the dispersion of metallic gold on the hexagonal surface of ZnO which confirms the result obtained by XRD. The ZnO and Au‐ZnO nanoparticles had negative charge surface values (−16.7 eV) and (−36.6 eV) which enhance an excellent degradation for cationic dyes. Optical studies show that gap energy decreases from 3.19 eV to 3.11 eV upon the decoration of Au on ZnO surface. The decrease in photoluminescence intensity reflects the positive effects of the role of metallic Au on the photodegradation capacity of Au‐ZnO. Photocatalytic results show that Au‐ZnO exhibits a higher efficiencies degradation of 93 % (k=0.016 min−1) in the case of Rhodamine B and 73 % (k=0.001 min−1) of Methylene blue compared to pure ZnO. In the case of Eriochrome Black T, Au‐ZnO presents low degradation efficiency.

First-Principles Study of Adsorption of Pb Atoms on 3C-SiC.

Changes in the atomic and electronic structure of silicon carbide 3C-SiC (β-SiC), resulting from lead adsorption, were studied within the density functional theory. The aim of the study was to analyze the main mechanisms occurring during the corrosion of this material. Therefore, the investigations focused on process-relevant parameters such as bond lengths, bond energies, Bader charges, and charge density differences. To compare the magnitude of the interactions, the calculations were conducted for three representative surfaces: (100, 110, and 111) with varying degrees of lead coverage. The results indicate that chemisorption occurs, with the strongest binding on the hexagonal surface (111) in interaction with three dangling bonds. The adsorption energy rises with increasing coverage, especially as the surface approaches saturation. As a result of these interactions, atomic bonds on the surface weaken, which affects the dissolution corrosion.

Simplified Nonlinear Dynamic Analysis by Hexagonal Collapse Surface Model of Steel Frame Structure

AbstractBased on the need for effective evaluation of multistorey structures response to seismic loading, this research includes the study of simplified nonlinear dynamic analysis (SNDA) by hexagonal collapse surface model. Existing conventional analysis methods such as FEMA440, restrict the extended use of Nonlinear Static Procedure (NSP) and Nonlinear Dynamic Procedure (NDP) by using the equivalent one‐degree‐of‐freedom (SDOF) model on multi‐degree‐of‐freedom (MDOF) structure. A large error known as Multiple‐Degree‐of Freedom Effects occurs in the elastoplastic behavior. To overcome the limitations of this analysis technique, the understanding of it in the entire structural system due to the influence of the higher‐order vibration modes are investigated, in addition to distinguish the elastoplastic behavior of a structure more precisely. Based on the important collapse mechanisms that are probable to occur during earthquake response, the development of a simplified dynamic analysis technique in which higher‐order vibration mode components were extracted to construct the plastic collapse safety region of a structure. Simplified nonlinear dynamic analysis (SNDA) aims to develop such method whereby multiple vibration mode components are properly considered. Primary and secondary mode of vibrations are generally examined with multiple load patterns corresponding to the condition whereby several independent variables reach maximum concurrently. The formation of hexagonal plastic collapse surface from the probability limit analysis based on proportional load results was discussed. The target for this study is to investigate the competency of this simplified analysis approach in seismic response of structure evaluating techniques.

Fluorine and oxygen terminated hexagonal diamond (100) surfaces for nitrogen-vacancy based quantum sensors

Chemical modification of hexagonal diamond surface is a new and important issue for the negatively charged nitrogen-vacancy (NV) center in quantum sensors. In this work, six types of terminated hexagonal diamond (100) surfaces for shallow NV centers are proposed, and structural and electronic properties are investigated by structure prediction method combined with first-principles calculation. In these structures, only fluorine and oxygen terminated surfaces (F-hex and α-O-hex) have positive electron affinity of 3.00 and 2.85 eV, respectively, no surface-related states and electron spin noise, indicating the F-hex and α-O-hex surfaces could be a promising host of NV center. We make further inspections by placing an NV center ~12 Å below the surfaces, and the results confirm that the surfaces have little effect on the defect states of NV center. Consequently, the F-hex and α-O-hex surfaces are prospective candidates for NV-based quantum sensors.

Square ice formation in CrOCl and graphene confinement

The structure and thermodynamic properties of water in nanoscale confinement environment are greatly involved in the research field of material science and nanotechnology. However, a complete picture of the ordered structure formation and thermodynamics behavior of the confined water inside two parallel nanosheets with different surface atomic arrangement is still lacking. In this paper, by using molecular dynamics (MD) simulations, we study the structural variation and thermodynamics behavior for water molecules confined between two parallel CrOCl with a square surface atomic arrangement and two parallel graphene nanosheets with a hexagonal surface atomic arrangement. Square ice, with a lattice constant 2.1 and 2.0 Å, is observed inside the two parallel CrOCl and graphene nanosheets, respectively. By calculating the configuration entropy of the molecular dipoles St , it is found that, in the CrOCl confinement, St reaches a peak value and then is greatly reduced due to the square ice formation. On the other hand, in the graphene confinement, St continues to grow after the square ice formation and is then reduced after reaching its peak value. Interestingly, it is found that the square ice could be stable at a higher entropy state under the external pressure than the bulk water at ambient condition. By calculating the orientational order parameters M, it shows that the conventional tetrahedral geometry of hydrogen bonding between water molecules breaks due to the square ice formation. By analyzing the average number of hydrogen bonds of water molecules Nh , it is found that the hydrogen bond interaction of the square ice relies on the confinement environment, where Nh is reduced in the CrOCl confinement and increased in the graphene confinement. Probability distribution functions of the dipole orientation angles between the x- or z-axis and the projection of the oxygen atoms of the water molecules are also calculated. It is observed that the square ice structure is paralleled with the x-axis (unit cell axis) in the CrOCl confinement and tilted with the x-axis (the zigzag direction of graphene) at an angle 30° in the graphene confinement. Furthermore, the square ice formation is found to be insensitive to temperature. Our result reveals the peculiar ordered structure and thermodynamics behavior of water in different nanoscale confinement environments.

Anisotropy of nanoscale friction: Influence of lattice structure, temperature, and wear

The anisotropy of nanoscale friction is analyzed for different samples using friction force microscopy under ultrahigh-vacuum conditions with varying scan directions. For both $\mathrm{Mo}{\mathrm{S}}_{2}$ and highly oriented pyrolytic graphite surfaces, our experiments reveal a sixfold symmetry of the friction vector plots in accordance with solutions of the Langevin equation, where the atomic force microscope tip is treated as a point mass elastically driven on the hexagonal surface lattices. In addition, the effect of temperature is analyzed both by experiment and by simulations. In both cases we find that increased temperature not only lowers the absolute friction values but also decreases the friction anisotropy. In contrast, experiments on NaCl cannot be explained on a similar basis. While the square symmetry is clearly revealed in the first measurements, it progressively deteriorates with repeated scanning, which is possibly due to abrasive wear occurring at the interface.

Impact of electron correlations on the k-resolved electronic structure of PdCrO2 revealed by Compton scattering

Delafossite PdCrO2 is an intriguing material which displays nearly-free electron and Mott insulating behaviour in different layers. Both angle-resolved photoemission spectroscopy (ARPES) and Compton scattering measurements have established a hexagonal Fermi surface in the material’s paramagnetic phase. However, the Compton experiment detected an additional structure in the projected occupancy which was originally interpreted as an additional Fermi surface feature not seen by ARPES. Here, we revisit this interpretation of the Compton data. State-of-the-art density functional theory (DFT) with dynamical mean field theory (DMFT), the so-called DFT+DMFT method, predicts the Mott insulating state along with a single hexagonal Fermi surface in excellent agreement with ARPES and Compton. However, DFT+DMFT fails to predict the intensity of the additional spectral weight feature observed in the Compton data. We infer that this discrepancy may arise from the DFT+DMFT not being able to correctly predict certain features in the shape and dispersion of the unoccupied quasiparticle band near the Fermi level. Therefore, a theoretical description beyond our DFT+DMFT model is needed to incorporate vital electron interactions, such as inter-layer electron coupling interactions which for PdCrO2 gives rise to the Kondo-like so-called intertwined excitation.

Perfect absorber with high sensitivity based on hexagonal star graphene surface

Graphene absorbers have attracted wide attention due to their high absorption rate and narrow bandwidth in the terahertz field. In this study, we proposed a dual-band terahertz tunable perfect absorber designed with a hexagonal star ring and a circular ring monolayer graphene metasurface, which exhibits tunable, polarization-insensitive, and high sensitivity characteristics. The graphene absorber was simulated by using the finite element method and validated by using the impedance matching method. Simulation results show that this structure has two perfect absorption peaks at 4.8 and 8.04 THz. The variation of the dielectric layer material was analyzed, and the parameters of the structure and the intrinsic graphene parameters were adjusted to control the absorption efficiency of the dual-band absorption peaks. Simulation results show that the high symmetry of the structure brings incident and polarization-insensitive properties, maintaining absorption higher than 98% over a wide range of incident and azimuth angles. The sensing performance of the device was investigated by varying the ambient refractive index, and the highest sensitivity parameter S of the absorber reached to 2.375 THz/RIU. These results demonstrate that this high-sensitivity sensor has great potential for terahertz imaging and microstructure detection.

A Computational Investigation into the Hydrogenation of NO on Water Ice Surfaces to Rationalize the NO:HNO:NOH Disparity in Space

Molecules possessing NO bonds are important precursors in biology; however, in the interstellar medium (ISM), such bonds are observed in relatively low abundance. NO and HNO are two species detected concurrently within the ISM that contain this bond in its simplest form. However, NO is observed to be approximately 200 times more abundant than HNO, which is curious due to the ubiquity of hydrogenated species in the ISM. In the present work, we use computational techniques to determine whether (i) HNO can be formed from NO on cold dust grain surfaces and (ii) if formed, HNO is able to desorb from the surface. Dust grains, which at low (10 K) temperature are primarily coated in water ice, are modeled using both hexagonal and amorphous ice models. A strong thermodynamic driving force is calculated for NO hydrogenation to HNO on the water ice surfaces, suggesting facile formation of HNO. Interestingly, the formation of NOH is also a thermodynamic possibility. Investigation into the reaction kinetics showed no barrier to hydrogenation in either scenario on the hexagonal ice surface; however, on the more astronomically relevant amorphous ice, barriers of 0.53 eV (51 kJ mol–1) and 0.77 eV (74 kJ mol–1) are observed for the formation of HNO and NOH, respectively. Comparison of the adsorption energies showed NO to bind to the surface the weakest (< –0.2 eV/–19 kJ mol–1), followed by HNO (< –0.6 eV/–58 kJ mol–1), and then NOH (< –1.50 eV/–144 kJ mol–1). This suggests that, once formed, HNO is likely to remain adsorbed to the surface, thus accounting for the lower gas phase abundance observed compared to NO. NOH, if formed, will be even less likely to desorb in appreciable amounts and hence remains undetected. Combined, the results suggest that hydrogenated species are possible to be formed from NO on ice surfaces and are likely to remain bound to the surface, supporting the experimental observations.

Crossing the ballistic-ohmic transition via high energy electron irradiation

The delafossite metal ${\mathrm{PtCoO}}_{2}$ is among the highest-purity materials known, with low-temperature mean free path up to 5 $\ensuremath{\mu}\mathrm{m}$ in the best as-grown single crystals. It exhibits a strongly faceted, nearly hexagonal Fermi surface. This property has profound consequences for nonlocal transport within this material, such as in the classic ballistic-regime measurement of bend resistance in mesoscopic squares. Here, we report the results of experiments in which high-energy electron irradiation was used to introduce pointlike disorder into such squares, reducing the mean free path and therefore the strength of the ballistic-regime transport phenomena. We demonstrate that high-energy electron irradiation is a well-controlled technique to cross from nonlocal to local transport behavior and therefore determine the nature and extent of unconventional transport regimes. Using this technique, we confirm the origins of the directional ballistic effects observed in delafossite metals and demonstrate how the strongly faceted Fermi surface both leads to unconventional transport behavior and enhances the length scale over which such effects are important.

Ring-polymer Molecular Dynamics Simulation for the Adsorption of H2 on Ice Clusters (H2 O)n (n=8, 10, and 12).

In the interstellar medium, the H2 adsorption and desorption on the solid water ice are crucial for chemical and physical processes. We have recently investigated the probabilities of H2 sticking on the (H2 O)8 ice, which has quadrilateral surfaces. We have extended the previous work using classical MD and ring-polymer molecular dynamics (RPMD) simulations to the larger ice clusters, (H2 O)10 and (H2 O)12 , which have pentagonal and hexagonal surfaces, respectively. The H2 sticking probabilities decreased as the temperature increased for both cluster cases, whereas the cluster-size-independent profiles were observed. It is thought that the size independence of the probabilities is qualitatively understood from the similar binding energies for all the three cluster systems. Furthermore, the RPMD sticking probabilities are smaller than the classical ones because of the reduction in the binding energies owing to nuclear quantum effects, such as vibrational quantization.

Impact of Geometric and Electronic Factors on Selective Hydro-Deoxygenation of Guaiacol by Surface-Rich Metal/Silica Catalysts

The selective production of hydrocarbons for the chemical industry from biogenic feedstock is a significant challenge when ensuring hydrocarbon and fuel supply, despite the heterogeneity of this feed. In this study, guaiacol, as a surrogate for complex lignin-based biomass resources, is converted by an inert silica carrier material with different d-metal impregnation (Mo, W, Re, Fe, Co, Ni, Cu, Pd, Ag) to reveal the reasons for different product selectivity to hydrogenated and deoxygenated hydrocarbon products. Hydrogen at 15 bar (gauge) and guaiacol are converted on metal/silica catalysts between 250 °C and 400 °C, while the physicochemical catalyst properties are characterized before and after catalytic tests. Volcano plots for the conversion, hydrogenation and deoxygenation products versus the d-band energy, surface atom distance and fouling properties reveal three groups of metals: (i) those that are less active and show high coking (Ag, α-Fe); (ii) those that show high activity for hydrogenation (β-Co, Ni, Pd) and, therefore, preferably yielded cyclohexane, cyclohexanol and 2-methoxycyclohexanol; (iii) those that preferably promote deoxygenation (Mo, W, Re, Cu) and, therefore, promoted the formation of phenol, benzene, anisole and catechol. The results are summarized in a pseudo van Krevelen diagram and interpreted as a complex interdependency from Sabatier’s principle of geometric correspondence of hexagonal metal surface for hydrogenation, electronic correspondence for the activation of hydrogen and electronic correspondence by oxophilicity for deoxygenation from the d-band center model.

Visualization of robust two-dimensional bulk states with suppressed surface state on epitaxial PdCoO2 thin films with bipolar surfaces

Epitaxial thin films of metallic delafossites are a recent topic of intense investigation due to their intriguing electronic states. Using in situ angle-resolved photoemission spectroscopy, we investigated the electronic states of epitaxial ${\mathrm{PdCoO}}_{2}$ thin films with high crystalline quality and bipolar surface with mixed termination. On this characteristic surface, we observed a surprisingly prominent bulklike single hexagonal large Fermi surface with suppressed surface state. Firstly, observation of a sharp Fermi surface relies on the minimized atomic scale disorder in our high-quality film surface. Additionally, the predominantly two-dimensional bulk electronic state with the Fermi group velocity parallel to the plane of ${\mathrm{PdCoO}}_{2}$ is expected to make the near-surface bulklike state less sensitive to the scattering by longer length scale random bipolar surface potentials. Furthermore, the origin of the suppressed surface state can be interpreted by screening of the polarity on the surface, which is qualitatively supported by density functional theory calculation. These findings are invaluable for accelerating the search for exotic functionalities in epitaxial ultrathin films and heterostructures of metallic delafossites.

Band gap opening in graphene by hybridization with Au (001) reconstructed surfaces

Au(001) surfaces exhibit a complex reconstructed structure $[\mathrm{Hex}\ensuremath{-}\mathrm{Au}(001)]$ comprising a hexagonal surface and square bulk lattices, yielding a quasi-one-dimensional corrugated surface. When graphene was grown on this surface, the periodicity of the corrugated surface was predicted to change the electronic structure of graphene, forming bandgaps and new Dirac points. Furthermore, the graphene--Au interface is promising for bandgap generation and spin injection due to band hybridization. Here, we report the angle-resolved photoemission spectroscopy and density functional calculation of graphene on a $\mathrm{Hex}\ensuremath{-}\mathrm{Au}(001)$ surface. The crossing point of the original and replica graphene \ensuremath{\pi} bands showed no bandgap, suggesting that the one-dimensional potential was too small to modify the electronic structure. A bandgap of 0.2 eV was observed at the crossing point of the graphene \ensuremath{\pi} and Au $6sp$ bands, indicating that the bandgap is generated using hybridization of the graphene \ensuremath{\pi} and Au $6sp$ bands. We discussed the hybridization mechanism and concluded that the R30 configuration between graphene and Au and an isolated electronic structure of Au are essential for effective hybridization between graphene and Au. We anticipate that hybridization between graphene \ensuremath{\pi} and Au $6sp$ would result in spin injection into graphene.

Decoration of ZnO surface with tiny sulfide-based nanoparticles for improve photocatalytic degradation efficiency

Modifying wide band gap ZnO nanoparticles surface by combine narrow bandgap semiconductors is a novel route to promote the ZnO to diverse applications. Herein, different metal sulfides (CdS, Ag2S and Bi2S3) were decorated on ZnO surface using facile a chemical route for photocatalytic application. Crystal structure, surface morphology and optical changes for the surface modified ZnO were studied by using various characterization techniques. The XRD spectra exhibited mixed phase of decorated metal sulfide nanoparticles along with strong pattens of hexagonal structure ZnO. The SEM images were confirmed that tiny CdS, Ag2S and Bi2S3 sulfide nanoparticles are well decorated on ZnO hexagonal rods surface. Band gap of the ZnO was tuned into visible region by modifying the surface by the sulfide nanoparticles. Textile industry-based crystal violet (CV) dye was used as a model pollutant to evaluate the photocatalytic activity of sulfides decorated well-crystalline ZnO photocatalysts under natural sunlight. Among the three catalysts, the Ag2S decorated ZnO achieved greatest photodegradation efficiency of 94.1% for degradation of the CV dye with rate constant value of 0.050. The highest catalytic activity may be related to Ag2S acting a significant part in reducing bandgap and boosting hole, superoxide radical, and hydroxyl radical formation, which inhibits recombination, hence enhancing the photocatalyst's efficacy, activity, and also stability.

Micromorphology and texture of niobium coating electrodeposited in NaCl—KCl—CsCl molten salt system

A low-toxicity and environment-friendly NaCl—KCl—CsCl—K2NbF7 system was used to prepare Nb coatings on Mo substrates. The effects of temperature, current density and electrodeposition time on the micromorphologies and textures of the electrodeposited Nb coatings were studied. The results showed that Nb coatings obtained at 30—70 mA/cm2 in the temperature range of 700—750 °C were continuous and compact, with a hardness range of 2.16—2.45 GPa. As the columnar crystals grew with time, the preferential growth orientations of the Nb coatings changed from 〈200〉 to 〈211〉 and then became disordered. With increasing polarization, the morphologies of the Nb coatings changed from hexagonal star-like surface to conical or pyramid-like surface.

Yttrium doped ZnO nanofillers reinforced epoxy coating for anticorrosion application

In the present study, synthesized pure and Yttrium (0.5, 1.0, 1.5, 2.0 and 2.5 mM) doped Zinc Oxide (YZO) nanoparticles by chemical precipitation method. X-ray diffractogram asserts the hexagonal wurtzite structure of ZnO nanoparticles. The average crystallite size was found to be 22–17 nm. The hexagonal shape, surface morphology, particle size and elemental composition of the samples were analyzed by FESEM, HRTEM and EDAX. The anticorrosive property of nanoscopic size (17 nm) YZO/epoxy nanocomposite was studied by electrochemical impedance spectroscopy (EIS) technique in both neutral and acidic media. Epoxy/YZO nanocomposites were prepared using different loadings (0.05, 0.10 and 0.15 wt%) of yttrium doped ZnO nanoparticles. The results obtained confirm that 0.10 wt% is the optimum concentration to get superior anticorrosion activity Epoxy/YZO nanocomposites were applied on mild steel substrates. The acquisition of yttrium doped ZnO nanofillers into the plain epoxy coating materially increased the charge transfer resistance Rct by 3.5 times in oxalic acid solution as against epoxy/ZnO coating. This encapsulates that the YZO nanoparticles are a potential anti-corrosive filler in coat on mild steel.

Wettability and biological responses of titanium surface's biomimetic hexagonal microstructure.

In this research, an experiment was conducted on how the surface wettability and biocompatibility of staplers' titanium nails impact the healing of gastrointestinal tissue. Firstly, the bionic hexagonal structure was prepared on the surface of Ti metal by laser processing technology, and the laser textured titanium samples were observed by scanning electron microscope. Then, the liquid-solid contact angle-measuring instrument was used to characterize the wettability of titanium samples. Finally, cells were cultured on the surface of different titanium samples, CCK8 assay and qRT-PCR were carried out to investigate cell adhesion and collagen secretion on the surface of different samples. The results showed that the bionic hexagonal surface increased the surface roughness, reduced the liquid-solid contact angle, and promoted the adhesion and collagen secretion of fibroblasts. The increased wettability provided a better growth environment for cell growth. Microtexture is an important factor affecting the behavior of cells and its size parameters regulate cell gene expression, which is worthy of further study.