Hexagonal Holes Research Articles

Numerical Investigation of the Optical Properties for Multiple PCF Structures in the THz Regime

This paper presents three different PCF structures including circular, hexagonal, and square holes forming four rings. To investigate various optical properties, simulation has been performed in between 1 THz to 2 THz regimes. Using these PCF structures, the core power fraction (CPF), dispersion, confinement loss (CL), effective material loss (EML), effective area (Aeff), and propagation constant are analyzed. TOPAS is selected as the fiber material for these designed PCF structures. From the analysis, a larger CPF of 97.4% is attained for the square PCF, a small Aeff of 1.65 × 105 μm2, a negligible CL of 5.82 × 10−12 cm−1, and a lower EML of 0.014 cm−1 are obtained for the hexagonal PCF. Besides, a negative dispersion is found for all three PCF structures. However, these PCFs can be fabricated using the prevailing fabrication technologies. Our designed PCFs can be efficiently used in optical signal transmission, also different kinds of analyte sensing can be performed by applying a suitable core structure into these PCFs.

A Single-Component Supramolecular Organic Framework with Efficient Ultralong Phosphorescence

Supramolecular organic frameworks (SOFs), due to the atomically precise integration of the repeated building units, exhibit intriguing properties and consequently potential applications in chemical...

Adsorption of transition metal clusters on Boron-graphdiyne

Layered carbon materials can be useful as supports for catalytic metallic nanoparticles in different applications. Also, doping porous carbons with metal atoms and nanoparticles enhances the hydrogen storage capacity of those materials. We have investigated the adsorption of transition metal atoms and small clusters on boron graphdiyne (BGDY) using density functional theory. This layered material contains uniformly distributed large hexagonal holes that can host the metal clusters. Single V, Co and Pd atoms sit at the hexagon corners, near the B atoms. Their binding energies are large enough to make the systems suitable for single-atom catalysis but atomic diffusion cannot be overlooked. Formation of dimers of those three elements near the hexagon corners is preferred over decoration by two separated atoms. The octahedral structure of the free hexamers is preserved on adsorption of V6 and Co6, but it changes in Pd6. The adsorption sites of the three hexamers are different. The adsorption energies of single atoms, dimers and hexamers on BGDY are substantially larger than those on pristine graphene, and similar to those on graphdiyne, but the larger holes existing in BGDY make this system better tuned for some applications.

Parametric Study on Buckling Behavior of Aluminum Alloy Thin-Walled Lipped Channel Beam with Perforations Subjected to Combined Loading

The objective of the research presented in this paper is to investigate the buckling behavior of a perforated thin-walled lipped channel beam subjected to combined load. A nonlinear finite element method was used to analyze the buckling behavior of the beam. Experimental tests were made to validate the finite element simulation. Three factors with three levels for each factor were chosen to examine their influence on the buckling behavior of the beam and these factors are: the shape of holes, opening ratio and the spacing ratio of. The finite elements outcome was analyzed by using Taguchi method to identify the best set of three-parameter combinations for optimum critical buckling load. The analysis of variance technique (ANOVA) was implemented to determine the contribution of each parameter on buckling strength. Results showed that the mode of buckling failure of the perforated beam is lateral-torsional buckling and the hexagonal hole shape, =1.7 and = 1.3 were the best combination of parameters that gives the best buckling strength. The results also showed that the shape of holes is the most influential on buckling behavior of the perforated beam for this case of loading.

Prediction of superconductivity in bilayer borophenes.

Borophenes and related two-dimensional materials have exhibited many exotic properties, especially for superconductivity, although the superconductivity of single-layer borophene is suppressed by the strains or doping from its substrates. Intriguingly, bilayer (BL) borophenes can be stabilized by appropriate pillar density and hexagonal holes density, rather than being supported by Ag(111) or Cu(111) substrates. Thus, we studied the two most stable structures, namely BL-B8 and BL-B30, stabilized by the above-mentioned two methods. Within density functional theory and Bardeen–Cooper–Schrieffer theory framework, their stability, electron structures, and phonon properties, as well as possible superconductivity are systematically scrutinized. The metallic BL-B8 and BL-B30 exhibit intrinsic superconducting features with superconductivity transition temperatures (Tc) of 11.9 and 4.9 K, respectively. The low frequency (below 400 cm−1) consisting of out-of-plane vibrations of boron atoms plays crucial rule in their superconductivity. In particular, a Kohn anomaly appears at the Γ point in BL-B8, leading to substantial electron–phonon coupling. Here, our findings will provide instructive clues for experimentally determining the superconductivity of borophene and will broaden the two-dimensional superconductor family.

Improving the extraction of sulfur-containing compounds from fuel using surfactant material in a digital baffle reactor

Abstract Extraction desulfurization process (EDP) for dibenzothiophene (DBT) from model light gas oil (LGO) improved using solvent mixture with new surfactant material (sodium thiosulfate) in digital baffle batch reactor (DBBR). Surfactant material was help increase extraction surface through increase dispersion of solvent in LGO. Reactor design was the best designer where negligible region of died zone in the reactor, rotation of fuel beside of wall, because adding the baffle on the wall. The blade design was distributes hexagonal holes that help liquid cross with solvent and this increases mixing and mass transfer DBT from model LGO to solvent. Operational conditions effects on extractive desulfurization process (EDP) it’s found such as solvent mixture (methanol, ethanol and toluene) to LGO model ratio, speed of impeller, extraction temperature, extraction time and effect surfactant were explored. Optimal experimental results represented that the extraction conditions were; (methanol = 10 ml, ethanol = 10 ml, toluene = 10 ml and volume of cocktail solvent equal to 30 ml MET))/model of LGO ratio speed of impeller 450 rpm, extraction time 21 min and extraction temperature 85 °C. Maximum DBT removal from model LGO was obtained at 89.8%, at this operating condition. Higher polarity of DBT was obtained when solvent used 30 ml MET. For removal dibenzothiophene (DBT) from model light gas oil, the results indicate that the extraction desulfurization process is suitable method to improve fuel quality.

Fabrication of a diamond concave microlens array for laser beam homogenization

An ultra-smooth diamond concave microlens array was realized using a chemical reflow process assisted by dry etching technique, which has a great performance for homogenization of light beam. Firstly, photolithography was used to produce a regular hexagonal hole array in the photoresist layer on a diamond substrate. Then, the hole array was reflowed in ethanol solvent vapor atmosphere at 20 ℃ to form the concave spherical structure array. Finally, diamond concave microlens array was formed by transferring photoresist concave structures onto diamond substrate through dry etching technique. The fabricated diamond concave microlens array was characterized, demonstrating a well-uniformity of the surface morphology, high quality imaging and focusing performances. Furthermore, laser beam homogenization was realized by the diamond concave microlens array.

Multi-band and high-sensitivity perfect absorber based on monolayer graphene metamaterial

The Finite Difference Time Domain (FDTD) method is used for the simulation, and a new method based on critical coupling and guided resonance is proposed theoretically and numerically to realize a multi-band ideal absorber (PA) of monolayer graphene. Its physical mechanism can be more perfectly analyzed through impedance matching and coupled mode theory (CMT). Due to the guided resonance (100% transmission or reflection efficiency is obtained through the coupling of the leakage mode and the guided mode under the phase matching condition), the perfect absorber can obtain four perfect absorption peaks. The resonance wavelengths are located at λ1 = 1085.03 nm, λ2 = 1131.48 nm, λ3 = 1187 nm and λ4 = 1365.35 nm, respectively. Their absorption rates are 95.88%, 99.81%, 97.44% and 95.30%. At the same time, we can also see a phenomenon in which the spectral position and value of the absorption peak can be adjusted by changing the relevant geometric parameters in the system (the geometric size, period, and incident angle of the hexagonal air hole absorber). Meanwhile, the structure we designed has certain advantages in the field of similar absorber research by briefly calculating related values of sensing performance. The sensitivity of its four resonance peaks are 46.45, 94.35, 151 and 598.9 nm/RIU, and FOM are 5.445, 11.192, 19.895 and 85.680. So we believe that the research has huge application prospects in terms of sensors, tunable spectrum detection, environmental monitoring and medical diagnosis, modulators and optoelectronic device sensors.

Tailoring Au Films at the Atomic Scale with an Electron Beam Tweezer.

A thin, clean pristine Au film created in a transmission electron microscope chamber was tailored by an electron beam. Various kinds of nanopatterns, including hexagonal holes and dumbbell-like patterns, were fabricated by different doses of the electron beam. A high-quality series of in situ images were recorded to explore the irradiation mechanism. The electron-matter collision enabled the electron beam to act as a tweezer to arrange atoms into a specified pattern.

Axially Chiral Cage-Like B38+ and B382+: New Aromatic Members of the Borospherene Family

The successive discoveries of the cage-like D2d B40−/0 and C3/C2 B39− mark the onset of borospherene chemistry. Based on extensive global minimum searches and first-principles theory calculations, we predict herein the possible existence of the axially chiral cage-like C2 B38+ (1/1′) and C2 B382+ (3/3′) which are novel aromatic members of the borospherene family featuring a B21 boron triple-chain on the waist and four B6 hexagonal holes on the cage surface. Detailed bonding analyses show that the B38+ (1) and B382+ (3) possess 12 and 11 delocalized π bonds over a σ-skeleton, respectively, following the universal bonding pattern of σ + π double delocalization of the borospherene family. Extensive molecular dynamics simulations indicate that both B38+ (1) and B382+ (3) are dynamically stable at 700 K. The IR, Raman, and UV–vis spectra of these cluster cations are computationally simulated to facilitate their future spectral characterizations.

B36 nanoflake supported nickel as an efficient single-atom catalyst for oxygen reduction reaction: A first-principles study

We introduced the newly-designed bowl-shaped B36 cluster supported single atom catalysts in which the atomic transition metal (TM) can be captured by the electron-deficient hexagonal hole of B36. Among all tested TM@B36 candidates (TM = Ti-Cu, Rh, Ru, Pd, Ir), the Ni@B36 is screened out as a promising catalyst for the 4e− water formation process with an extremely low overpotential of 0.29 V.

Complex internal faults of MgZn2 in Mg[sbnd]Zn binary alloy

Complex internal planar faults in the MgZn2 phase of a binary Mg6Zn alloy were thoroughly studied using transmission electron microscopy. Two staking faults lying on {101¯0}MgZn2 and {213¯0}MgZn2 planes were observed, with the latter one found to be able to be densely arranged in the whole MgZn2 phase, resulting in a new structure with a monoclinic structure, a = 1.71 nm, b = 2.12 nm, c = 4.05 nm, and β = 116°. Subsequently, stacking faults, stacking fault boundary as well as the evolved twin boundaries lead to many additional diffraction spots and even hexagonal diffraction holes in the corresponding SAED patterns.

Buckling Behavior of Aluminum Alloy Thin-Walled Beam with Holes under Compression Loading

Thin-walled members are increasingly used in structural applications, especially in light structures like in constructions and aircraft structures because of their high strength-to-weight ratio. Perforations are often made on these structures for reducing weight and to facilitate the services and maintenance works like in aircraft wing ribs. This type of structures suffers from buckling phenomena due to its dimensions, and this suffering increases with the presence of holes in it. This study investigated experimentally and numerically the buckling behavior of aluminum alloy 6061-O thin-walled lipped channel beam with specific holes subjected to compression load. A nonlinear finite elements analysis was used to obtain the buckling loads of the beams. Experimental tests were done to validate the finite element results. Three factors namely; shape of holes, opening ratio D/Do and the spacing ratio S/Do were chosen to study their effects on the buckling strength of the channel beams. Finite elements results were obtained by using Taguchi method to identify the best combination of the three parameters for optimum critical buckling load, whereas determining the contribution of each parameter on buckling strength was implemented by using the analysis of variance technique (ANOVA) method. Results showed that the combination of parameters that gives the best buckling strength is the hexagonal hole shape, D/Do=1.7 and S/Do= 1.3 and the opening ratio (or size of holes) is the most effective on buckling behavior.

Dimensional Crossover and Enhanced Thermoelectric Efficiency Due to Broken Symmetry in Graphene Antidot Lattices

Graphene antidot lattices (GALs) are two-dimensional (2D) monolayers with periodically placed holes in otherwise pristine graphene. We investigate the electronic properties of symmetric and asymmetric GAL structures having hexagonal holes, and show that anisotropic 2D GALs can display a dimensional crossover such that effectively one-dimensional (1D) electronic structures can be realized in two-dimensions around the charge neutrality point. We investigate the transport and thermoelectric properties of these 2D GALs by using non-equilibrium Green function (NEGF) method. Dimensional crossover manifests itself as transmission plateaus, a characteristic feature of 1D systems, and enhancement of thermoelectric efficiency, where thermoelectric figure of merit, $zT$, can be as high as 0.9 at room temperature. We also study the transport properties in the presence of Anderson disorder and find that mean free paths of effectively 1D electrons of anisotropic configuration are much longer than their isotropic counterparts. We further argue that dimensional crossover due to broken symmetry and enhancement of thermoelectric efficiency can be nanostructuring strategy virtually for all 2D materials.

Hydrothermal formation of controllable hexagonal holes and Er2O3/Er2O3-RGO particles on silicon wafers toward superhydrophobic surfaces

In this work, controllable hexagonal holes and distributed Er2O3/Er2O3- graphene particles are fabricated on silicon wafers using a straightforward, hydrofluoric, acid-free, and strong alkali-free hydrothermal method. As long as erbium nitrate hydrate and urea coexist in the reaction mixture, silicon wafers can be synthesized successfully using controllable hexagonal hole structures that are regulated by hydrothermal temperature and the addition of graphene oxide and hexadecyl trimethyl ammonium bromide to the reaction mixture. Correspondingly, the wettability of these silicon wafers also is controllable due to the structure that can be changed from hydrophilic (89.3°) to superhydrophobic (153.1°). In short, this work not only provides a simple and nontoxic approach for preparing hexagonal hole structured silicon wafers, but also produces superhydrophobic silicon wafers that potentially can be applied for corrosion-resistant coatings, oil-water separation, and other fields.

Borophene with Large Holes.

In two-dimensional (2D) borophene, the structural transition from triangular lattice to hexagonal lattice with an increase in vacancy concentration is a basic principle of constructing various borophene isomers. Here, by performing an extensive structural search of 4239 borophene isomers with both hexagonal holes (HHs) and large holes (LHs), we show that the structural transformation from triangular lattice to borophene with large holes is energetically more favorable. Borophene isomers with LHs are more stable than those with only HHs at high vacancy concentrations (>20%) and are just slightly less stable than those with only HHs at low vacancy concentrations. This discovery greatly expands the family of 2D borophene and opens a route for synthesizing new borophene isomers.

Hydrogen trapping efficiency of Li decorated porous boron fullerene B38: The first-principles study

The demand for clean renewable energy is urgent in current. The hydrogen application is difficult mainly due to the ratively low capacity in the storage medium. In this work, the adsorption and desorption of the hydrogen molecules by the Li atoms decorated B38 cage are studied by the density functional theory. The calculated largest binding energy of one Li atom (2.68 eV and 2.58 eV) is upon the hexagonal hole of the B38 cage, which is much larger than the experimental cohesive energy of bulk Li (1.63 eV). Each Li atom in the outside of the B38 cage can adsorb up to four H2 molecules. The Ead of B38(Li-nH2)4 decreases from the 0.22 eV for n = 1 to the 0.11 eV for n = 4. The B38(Li–4H2)4 structure achieves the 6.85 wt% hydrogen gravimetric density, which is higher than the goal of 5.5 wt% before 2017 set by the United States Department of Energy. The almost the same partial density of states for the fifth H2 molecule as that of the isolated H2 molecule, the longer 4.5 Å distance between the fifth H2 molecule and the Li atom, together with the small NBO charges all reveal the weak electronic field around the Li+, which can interpret the weak H2 adsorption mechanism. Finally, the B38Li4 structure can easily release 9H2 molecules at 373 K known from the molecular dynamic simulation and practically trap about 1.08H2 molecules at 373 K/3 atom condition calculated by the grand partition function. Thus, its reversible practical HGD of B38Li4-14.34H2 is 6.18 wt%, which is almost the same value as the theoretical 6.85 wt% for B38(Li–4H2)4. Our studies will be the strong theory basis for the future application in hydrogen storage material development.

Theoretical model to determine the effective thermal conductivity coefficient of first clad region in photonic crystal fiber with the hexagonal hole structure

To study the thermal effects on devices with a porous area, the effective thermal conductivity of the porous area must be determined. The factors that impress the value of the heat transfer coefficient are 1-Type of material, 2-Structure geometry, and 3- heat flow direction with respect to the porous object. In this paper, a theoretical model is developed to determine the Thermal Conductivity Coefficient of the hole region of Photonic Crystal Fiber (PCF) using the thermal resistance networks method. This model was applied to the PCF with the hexagonal structure, and the effect of the hole size and hole distance is studied on the Thermal Conductivity Coefficient of the proposed structure. The presented method can be expanding to all photonic crystal fibers with different hole structures. In that case, the value of the heat transfer coefficient will depend on the arbitrarily selected cell.

Low‐Energy Facets on CdS Allomorph Junctions with Optimal Phase Ratio to Boost Charge Directional Transfer for Photocatalytic H2 Fuel Evolution

Low-energy facets on CdS allomorph junctions with optimal phase ratio are designed to boost charge directional transfer for photocatalytic H2 fuel evolution. Fermi energy level difference between low-energy facets as driving force promotes electrons directional transfer to hexagonal CdS(102) facet and holes to cubic CdS(111) facet. The optimal allomorphs CdS presents superior photocatalytic H2 evolution rate of 32.95 mmol g-1 h-1 with release in a large amount of visible H2 bubbles, which is much higher than single-phase CdS with high-energy facets and even supports noble metal photocatalysts. This scientific perspective on low-energy facets of allomorph junctions with optimal phase ratio breaks the long-held view of pursuing high-energy crystal surfaces, which will break the understanding on surface structure crystal facet engineering of photocatalytic materials.

Effect of Two-Dimensional Re-Entrant Honeycomb Configuration on Elastoplastic Performance of Perforated Steel Plate

Perforated steel plates with regularly shaped holes are already widely employed as steel dampers, which dissipate seismic energy through plastic deformation of steel. As a typical auxetic structure, two-dimensional (2D) re-entrant honeycomb configurations have characteristics of large deformation and good energy absorption. However, research on the effects of these configurations on the mechanical performance of steel is limited. This paper investigated the auxetic properties of perforated steel plates with re-entrant hexagon holes. Repetitive units are controlled by three parameters, hole ratio, re-entrant angle, and chamfer radius. Elastoplastic behavior and damage under large deformation were studied via tension tests and finite element (FE) analysis based on a micromechanics-based ductile fracture model. The effects of different parameters on mechanical properties of configurations were analyzed and discussed. The static performance of the perforated steel plates obtained in this study provides a good basis for its further dynamic study under large deformation.