Perfect Surface Research Articles

Adsorption of Cun (n = 1‒4) clusters on CuAl2O4 spinel surface: A DFT study

The interaction of active metal with the support surface is an important factor determines the stability of the catalysts. Periodic density functional theory calculations were performed to investigate the adsorption of Cun (n = 1−4) on the CuAl2O4 (100) and (110) surfaces. The results show that the adsorption energies for single Cu atom adsorbed on CuAl2O4 (100) and (110) surfaces are −4.46 and −3.27 eV, respectively. The adsorption energy for single Cu atom absorbed on the oxygen-defective surface is smaller than on the perfect CuAl2O4 surface. Bader charge and density of states analysis revel that the adsorption of Cu on the spine surface is accompanied by charge transfer. Due to the strong interaction of Cu with the CuAl2O4 (100) and (110) surfaces, the Cu2 and Cu3 prefer dissociative adsorption on the CuAl2O4 surfaces. As indicated by the calculated adsorption energies, growth energies and aggregations energies, the interaction of Cu with CuAl2O4 surface is much stronger than with the γ-Al2O3(110) surface. This result can give reasonable explanations for the experimental phenomenon that Cu supported on the CuAl2O4 spinel show much better stability than on the γ-Al2O3.

Hydrazine adsorption on perfect and defective fcc nickel (100), (110) and (111) surfaces: A dispersion corrected DFT-D2 study

We present density functional theory calculations, with a correction for the long-range interactions, of the adsorption of hydrazine (N2H4) on the Ni (110), (100), and (111) surfaces, both defect-free planes and surfaces containing point defects in the form of adatoms and vacancies. Several low-energy adsorption structures for hydrazine on the perfect and defective surfaces have been identified and compared. The hydrazine molecule is shown to interact with the Ni surfaces mainly through the lone-pair of electrons located on the N atoms, forming either monodentate or bidentate bonds with the surface. The strength of N2H4 adsorption on the perfect surfaces is found to be directly related to their stability, i.e. it adsorbs most strongly onto the least stable (110) surface via both N atoms in a gauche-bridge configuration (Eads = −1.43 eV), followed by adsorption on the (100) where it also binds in gauche-bridge configurations (Eads = −1.27 eV), and most weakly onto the most stable (111) surface via one N–Ni bond in a trans-atop configuration (Eads = −1.18 eV). The creation of defects in the form of Ni adatoms and vacancies provides lower-coordinated Ni sites, allowing stronger hydrazine adsorption. Analysis into the bonding nature of N2H4 onto the Ni surfaces reveals that the adsorption is characterized by strong hybridization between the surface Ni d-states and the N p-orbitals, which is corroborated by electron density accumulation within the newly formed N–Ni bonding regions.

First principles calculation of effect of graphene coating on transmission coefficient of Cu thin film with low surface roughness

In this paper, we calculate the effect of a graphene coating on the transmission coefficient of a Cu thin film with surface disorder. The nonequilibrium coherent potential approximation combined with the linear muffin-tin orbital formulation, which is based on first principles, is applied by assuming that there is surface disorder. The graphene coating mitigates the effect of Cu surface scattering on the transmission coefficient. The weak interaction between Cu and graphene and the upward shift of the Fermi level with respect to the Dirac point improve the transport characteristics by offering more conduction bands. Moreover, graphene-coated Cu with a perfect surface has a completely specular transmission coefficient. The surface disorder decreases the transmission coefficient due to the nonconserved transverse momentum (k) of the scattering wave through the central area of the two-probe system. However, for a graphene coating on a Cu thin film with surface disorder x<3.90%, length l<5.09nm, width 0.25 nm, and thickness 1.23 nm, the transmission coefficient is higher. The increased transmission coefficient due to graphene coating can overcome the diffusive scattering originating from the surface disorder. The coherent potential approximation band structure shows that graphene bands are less affected by Cu surface disorder than Cu bands, which enhances the total conduction by offering additional channels for electrons. Our results demonstrate that graphene is a potential liner material for a Cu thin film with low surface disorder.

P3HT:PC61BM solar cell embedding silver nanostripes for light absorption enhancement

Periodic silver nanostripe arrays are introduced into poly (3-hexylthiophene) and [6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) solar cells to enhance the light absorption in the active materials. The light absorption enhancements were experimentally and numerically investigated. The silver nanostripes with a width, height, and pitch of 82, 50, and 400 nm enhanced the light absorption of P3HT:PC61BM layer by 20%. Numerical calculations revealed not the magnetic resonance that is supported by a perfect absorber configuration but surface plasmon polaritons excited at the boundary between the P3HT:PC61BM layer and aluminum electrode is the dominant mechanism behind its light absorption enhancement.

Seismic exploration in desert area of Tarim basin

Tarim basin is located in northwestern China and is the one of main basins with abundant oil and gas. Due to existence of thick low velocity-reducing layer in desert area of the basin, it is very difficult to gain good seismic datum. The main problem in collecting data include: 1) Bad shot and receiving situation cause very low signalto- noise ratio and low resolution; 2) Undulant hypsography make complicated static correction; 3) Surface deep sand stratum induce absorption and attenuation of seismic wave. To finish the geologic target, we introduce following methods: 1) Enhancing analysis and investigation of surface structure to perfect surface structure model which will serve for choosing better shot points; 2) Exploding under water table to guarantee enough shot energy, and embed the geophone to get the better receiving condition; 3) Selecting bigger diameter of dynamite to form better point explosive response; 4) Surveying the noise wave to design the best acquisition parameters; 5) Calculating better static correction by surface refraction tomography; 6) Applying the compensation of absorbed energy of seismic wave to gain better information. After these methods are introduced, the signal-to-noise ratio and resolution of main prospecting objective in collecting seismic datum are improved obviously and obtain correct geologic interpretation.

First-principles study of the structural and electronic properties of the clean and O-deficient ZnAl2O4(111) surfaces

In this study, the GGA-PBE method was used to study the structural and electronic properties of the ZnAl2O4(111) surface with and without oxygen vacancies. The ZnAl2O4(111) surface has six possible surface terminations called Zn(O2), Zn(Al), Al(Zn), Al(O2), O2(Zn), and O2(Al). The results obtained in this work show that the surface energy, electronic structure and work function of the ZnAl2O4(111) surface depend greatly on the nature of atoms in the top surface layer. The calculated surface energies indicate that the Zn(O2) termination is the most stable surface termination in O-rich and Al-poor environments, while the Al(Zn) termination is the most stable termination in Al-rich and O-poor environments. On the other hand, our results show that the formation of oxygen vacancies can greatly affect the stability of the ZnAl2O4(111) surface. We found that the O-deficient surface is more stable than the perfect surface in the case of O2(Zn) and O2(Al) surface terminations. In the case of other surface termination, the formation energy of VO is positive under both O-rich and O-poor conditions except the case of the Zn(O2) termination under O-poor and Al-rich conditions. Moreover, we found that the formation of oxygen vacancies can greatly affect the stability, electronic structure, and work function of the ZnAl2O4(111) surface.

Understanding HCN heterogeneous adsorption on CaO(1 0 0) surface for the pyrolysis of sludge: A first-principles study and GCMC simulation

Pyrolysis and combustion of the sludge can eliminate the secondary pollution, and achieve the recovery of resource. However, it will produce large amount of nitrogen oxide. HCN is one of the major NOx precursors, and calcium oxide, the dehydrating agent and desulfurizer, have positive effect for HCN emission. Thus, the HCN on the perfect and defect CaO(1 0 0) surface heterogeneous adsorption is investigated through a first-principles calculation and Grand Canonical Monte Carlo simulation. Compared with single molecular model in our previous work, the CaO slab model with periodical boundary conditions has a better effect on describing the solid phase surface. The adsorption of HCN molecule on perfect CaO(1 0 0) surface proves to be chemisorption, and the most stable configuration is H-downward at O top site with the binding energy of −1.09 eV. Furthermore, HCN molecule adsorbs more tightly on to the O vacancy and Ca vacancy surface, and the binding energy increases to −2.76 eV and −2.79 eV, respectively. With the electron population and PDOS analysis, it reveals that the more electrons transfer from defect calcium oxide surface to HCN molecule. In the GCMC results, it is obvious that multiple HCN molecules easily adsorb on Ca vacancy surface. Meanwhile, HCN molecules are inclined to adsorb on the hollow site of the defect CaO(1 0 0) surface. From the isothermal adsorption curves, the adsorption ability decreases with the temperature increasing, and the fitted equation is coincide with the Freundlich isothermal adsorption equation. The variation of adsorption equilibrium constant K in the fitted equation indicates that the Ca vacancy surface is the most activity surface and the temperature increase is negative for the HCN adsorption, conforming to the adsorption rule calculated in the first-principle study. Thus, the point vacancy surface caused by uneven temperature can increase the adsorption ability of HCN on CaO(1 0 0) surface.

Development of a non-contact plasma processing technique to mitigate chemical network defects of fused silica with life enhancement of He-Ne laser device

Surface characteristic as well as bulk properties of optics play a significant role in the performance and the life of the optical device. In this paper a non-contact type plasma processing methodology is adopted to remove sub-micron cracks hidden under surface as generated due to contact mechanical processing. A novel qualitative method is introduced for analysis of sub-micron cracks present at the surface/sub-surface of the optics by using in-situ laser illumination. Raman microscopy is identified for understanding the improvement in chemical structure integrity of the fused silica. Power spectrum density characteristics of fused silica shows 80% reduction in higher spatial wave length after plasma processing which signifies improvement in surface figure. Life of the optical device is enhanced drastically by non-contact plasma processing methodology. The present study proposes a method for futuristic manufacturing of optics for achieving perfect surface structure without affecting surface roughness.

Increasing the accuracy of (U-Th(-Sm))/He dating with 3D grain modelling

Conventional (U-Th(-Sm))/He thermochronology requires accurate determination of the grain shape and dimension for calculation of 4He loss by alpha particle ejection and diffusion. In routine practice, calculations of 4He loss and diffusion are calculated assuming that measured grains approximate symmetric grain shapes with perfectly smooth crystal surfaces. This may introduce uncertainties that are virtually impossible to quantify if grains that do not pass the latter criteria are used. Alternatively, this leads to a selection bias for the analyses of detrital minerals if only grains with perfect crystal surfaces are measured. To address this limitation, we introduce a flexible, open-source numerical approach in Matlab™ to accurately determine the three-dimensional grain shape and numerically model He loss by alpha ejection and diffusion on individual grains. The three-dimensional surface of a mineral grain is interpolated from photomicrographs taken orthogonal to the principal grain axes. He ejection and diffusion is simulated using a coupled Monte Carlo and Brownian motion algorithm. Comparing our approach to high-resolution X-ray microtomography, we demonstrate that our “3D-He” approach improves the accuracy of He loss corrections when mineral grains do not approximate perfect crystal shapes by avoiding constraints inherent to standard manual-analytical approaches. Importantly, this method mitigates any bias introduced by user-dependent grain selection, measurements and assigning grains to a mineral shape for which analytical solutions of He production have been derived. In routine practice, we find that our 3D-He approach improves the accuracy of geometric measures (volume and surface area) and associated sphere-equivalent radii (SER) significantly, reducing the average deviation from true values from ~7–8% (manual-analytical approach) to ~2.5% (3D-He approach). The difference in SER significantly impacts the resulting apatite (U-Th-Sm)/He ages, which may deviate up to 40% when long held at temperatures where He production roughly matches diffusive loss of He. Using the 3D-He approach, the average deviation and overall spread of He loss corrections due to alpha ejection (FT factors) could be reduced from 1.6 ± 4.6% to 0.6 ± 0.8%. In summary, our 3D-He approach is a significant refinement to (U-Th(-Sm))/He age calculation considering relatively low analytical uncertainty in U, Th, Sm and He measurement (~2%). Importantly, our 3D-He approach should mitigate the selection bias introduced through manual grain selection. Toward this end, we discuss additional advantages of our numerical approach to handling broken grains or grains with known parent isotope zonation.

Influence Of Single Linear Surface Defect Orientation To Loading Direction In Nickel Nanowire Using Molecular Dynamics In Large Scale

Abstract The mechanical properties and deformation mechanism of perfect and linear surface defect Ni Nanowires (∼925876 atoms) are investigated using molecular dynamics simulations. The linear surface defects are oriented at 0°, 45°, and 90° to the loading direction. EAM potential is used to model the interactions between Ni atoms. The tensile tests are carried out at temperature of 10 K and strain rate of 109 s-1. The results show that the surface defect oriented at 45° significantly lowers the yields stress (∼ 25%). The Fractographs displays shear type of fracture in perfect, horizontal and 45° surface defect Ni NW and for vertical defect NW, the plastic strain is very less indicating brittle fracture.

The Effectiveness of Using Direct Composite Veneer Template System in Restoring Anterior Teeth

Background: Veneer is one method of dental restoration. Veneers are used to repair tooth deformities, discolorization, diastema, and fractures. One method of veneers is direct composite veneers. However, it is difficult to form a perfect labial surface using this technique.Method: The purpose of this study was to identify the effectiveness of direct composite veneers template. The type of the experiment was quasi-experimental with the post-test only design. The area of interest was the dental practice in Palembang City, with total sample equals to the population of dentists who do the direct composite veneer.Results: The average surgery duration of direct composite veneers using plastic, mica stem, and plastic stem were 46.25, 32.25, and 28.00 minutes respectively. The easiness level of conducting direct composite veneer with a plastic template was 3.35 (normal), 4.20 for mica stem template (easy), and 4.30 (easy) for plastic stem template. The satisfaction level of dentists using the plastic template was 3.50 (ordinary), the mica stem template was 4.30 (satisfied), and the plastic stem template was 4.65 (satisfied).Conclusion: The ANOVA analysis results showed a significant difference between the duration, easiness level, satisfaction level when working on different templates of direct composite veneer. It was concluded that the usage of plastic stem template resulted in fastest, easiest, and the most satisfying outcome.

Perfect Surface Formation and Emergent Property in Crystalline Battery Materials by Atomistic Crystal Growth Technology

Perfect Surface Formation and Emergent Property in Crystalline Battery Materials by Atomistic Crystal Growth Technology

First principles studies of self-diffusion processes on metallic lithium surfaces

Due to the theoretical high specific capacity (3860 mAh/g) and the low standard electrode potential (-3.040 V vs. standard hydrogen electrode), rechargeable lithium metal batteries are considered as excellent energy storage systems. Unfortunately, security concerns related to dendrite formation during charge/discharge cycles still hinder the commercial use of Li metal-based batteries. Using density functional theory, we have studied the bulk and surface properties of metallic lithium at an atomistic level. In this process, bcc Li(100) proved to be the most stable metallic lithium surface. Subsequently, possible self-diffusion mechanisms on perfect and imperfect Li(100) surfaces were examined. For this purpose, nudged elastic band calculations were performed to characterize the respective diffusion processes and to determine the relevant pre-exponential factors and activation barriers. On the basis of the acquired data, it became possible to derive activation temperatures and reaction rates for the respective processes, which are useful for experimental verification as well as for the implementation in long-scale kinetic Monte Carlo simulations.

Scattering of electromagnetic waves by a perfect electromagnetic conductor half-screen

The diffraction of plane electromagnetic waves by a perfect electromagnetic conductor half-screen is investigated. The total geometrical optics fields are obtained by using the boundary conditions of a perfect electromagnetic conductor surface. A general relation is defined for the scattered fields in terms of waves by soft and hard surfaces. The total scattered field is derived by using this relation. Some numerical simulations are also given.

Preparation and evaluation of famotidine nanosuspension

Famotidine (FM) is a potent H2-receptor antagonist used for the treatment of peptic ulcer. It has a low and variable bioavailability which is attributed to its low water solubility. There are many methods used to increase dissolution rate of drug and in this study, the dissolution of the drug was enhanced by the preparation of nanosuspension. Famotidine nanosuspension was prepared by antisolvent precipitation method, where famotidine dissolved in methanol at room temperature and emptied into water containing different types of stabilizers (single and in combination). The optimum formula (F9) was selected according to particle size (362.8nm) and release profile (80 % of drug release within the 10 minutes) in comparison to pure famotidine powder release. The influence of formulation variables like the type and concentration of stabilizers Polyvinyl pyrrolidone K30, polyvinyl alcohol and poloxamer 188 (PVP K-30, PVA and poloxamer 188) in addition to combination of stabilizers on particle size of drug nanosuspensions were studied. The result showed that single stabilizer (poloxamer 188) has perfect surface affinity and could form a substantial mechanical and thermodynamic barrier at the interface of dug molecule. As the concentration of stabilizer increases the particle size decreases at fixed drug concentration (drug: stabilizer ratio 1:2).

Quantitative assessment and suppression of defect-induced scattering in low-loss mirrors.

In this Letter, defect-induced scattering in 1064nm high-reflection coatings prepared by dual ion beam sputtering and its suppression were investigated by artificial nodules, finite-difference time-domain simulations, angular resolved scattering (ARS) measurements, and planarization technology. After establishing the geometric model of the nodules grown from ϕ 1μm SiO2 microspheres, the far-field scattering of the multiple nodules was determined by intensity superposition. For a nodule density of 100 mm-2, there is good agreement between the simulated and measured ARS. The total scattering is ∼500 ppm for the multilayer coating with artificial nodules, which is more than 10 times that for the coating without nodules. Next, an iterative deposition-etching process was used to planarize the defects, which reduced scattering by almost one order of magnitude. Moreover, detailed characterization of the planarized seeds reveals that the planarization technology is a complex process, and it still does not produce a perfect flat surface. The results showed that there is a pit over each planarized seed in the coating surface, which leads to additional scattering. The possible reasons for the presence of these pits are briefly discussed, and the directions for further research are provided at the end of this Letter.

Preparation and evaluation of famotidine nanosuspension

Famotidine (FM) is a potent H2-receptor antagonist used for the treatment of peptic ulcer. It has a low and variable bioavailability which is attributed to its low water solubility. There are many methods used to increase dissolution rate of drug and in this study, the dissolution of the drug was enhanced by the preparation of nanosuspension. Famotidine nanosuspension was prepared by antisolvent precipitation method, where famotidine dissolved in methanol at room temperature and emptied into water containing different types of stabilizers (single and in combination). The optimum formula (F9) was selected according to particle size (362.8nm) and release profile (80 % of drug release within the 10 minutes) in comparison to pure famotidine powder release. The influence of formulation variables like the type and concentration of stabilizers Polyvinyl pyrrolidone K30, polyvinyl alcohol and poloxamer 188 (PVP K-30, PVA and poloxamer 188) in addition to combination of stabilizers on particle size of drug nanosuspensions were studied. The result showed that single stabilizer (poloxamer 188) has perfect surface affinity and could form a substantial mechanical and thermodynamic barrier at the interface of dug molecule. As the concentration of stabilizer increases the particle size decreases at fixed drug concentration (drug: stabilizer ratio 1:2).

Preparation and evaluation of famotidine nanosuspension

Famotidine (FM) is a potent H2-receptor antagonist used for the treatment of peptic ulcer. It has a low and variable bioavailability which is attributed to its low water solubility. There are many methods used to increase dissolution rate of drug and in this study, the dissolution of the drug was enhanced by the preparation of nanosuspension. Famotidine nanosuspension was prepared by antisolvent precipitation method, where famotidine dissolved in methanol at room temperature and emptied into water containing different types of stabilizers (single and in combination). The optimum formula (F9) was selected according to particle size (362.8nm) and release profile (80 % of drug release within the 10 minutes) in comparison to pure famotidine powder release. The influence of formulation variables like the type and concentration of stabilizers Polyvinyl pyrrolidone K30, polyvinyl alcohol and poloxamer 188 (PVP K-30, PVA and poloxamer 188) in addition to combination of stabilizers on particle size of drug nanosuspensions were studied. The result showed that single stabilizer (poloxamer 188) has perfect surface affinity and could form a substantial mechanical and thermodynamic barrier at the interface of dug molecule. As the concentration of stabilizer increases the particle size decreases at fixed drug concentration (drug: stabilizer ratio 1:2).

A computational study on linear and bent adsorption of CO2 on different surfaces for its photoreduction

The adsorption of CO2 on the surface of heterogeneous catalysts is crucial for the subsequent photoreduction reactions. As the direct one-electron reduction of CO2 is extraordinarily difficult because of the –1.9 V reduction potential, adsorption induced CO2 bending to form CO2δ− is considered one efficient approach to decrease the overpotential of the intermediate formation during CO2 reduction. However, it is still unclear what material and surface are in favor of the formation of adsorption-induced bending of CO2, which is important for the design of active surfaces. Here we perform the first principle study on the adsorption of CO2 on the surface of some typical photocatalysts and co-catalysts. It is found that the CO2 bending upon adsorption can only occur on certain crystal surfaces of some materials, even on the perfect surface without any defects. If the exposed crystal surface has a linear metal-oxygen-metal (MOM) structure, the carbonate-like configuration upon CO2 adsorption may be easier to be formed than that on the other exposed surfaces. TiO2 (001), CeO2 (111), CeO2 (110) and MgO (100) seem more attractive among all the surfaces under study, as the bent CO2 configuration on these two surfaces are more stable than the linear one. Moreover, the barrier that CO2 changes from linear configuration to bent is relatively small. Our results are in good agreement with the experimental results that TiO2 (001) and MgO (100) exhibit high photocatalytic activity.

DFT study on the influence of sulfur on the hydrophobicity of pyrite surfaces in the process of oxidation

Using the first-principles method of density functional theory (DFT) and the plane-wave ultra-soft pseudopotential method, the adsorption process of water on a perfect pyrite surface and a surface with an adsorbed sulfur atom was calculated and simulated. The mechanistic role of sulfur formed during pyrite surface oxidation in the hydrophobicity of pyrite surfaces was explored. The simulation results showed that compared with the perfect pyrite surface, the surface with an adsorbed sulfur atom had an absorption energy that went from a negative to a positive value. The strong FeS covalent bond was formed first between the surface pyrite iron atom and the adsorbed sulfur atom. Following this, a weak SO bond was formed between the sulfur and oxygen atoms of the water molecule. The adsorption of H2O on the pyrite surface was hindered by the generation of sulfur so that the surface with an adsorbed sulfur atom became hydrophilic. The simulation results are consistent with the results of wetting heat. The influence of sulfur adsorption on pyrite hydrophobicity was mechanistically revealed from the view of quantum chemistry.