Hexagonal Texture Research Articles

Optical Simulations of Nanotextured All‐Perovskite Tandem Solar Cells

AbstractThis numerical study investigates, how textures at various locations of all‐perovskite tandem solar cells affect their optical performance. For this, hexagonal sinusoidal textures with 750 nm period and aspect ratios (height‐to‐period) of 27% (moderate) and 54% (pronounced) are considered. The optical simulations are performed with the finite element method and an algorithm to correct for the thick glass superstrate. The complex refractive index data of the wide‐bandgap (WBG) and narrow‐bandgap (NBG) perovskites with spectroscopic ellipsometry is determined. Texturing between the glass superstrate and the WBG perovskite top cell has an antireflective effect across the whole wavelength region. In contrast, texturing between the WBG perovskite top cell and the NBG perovskite bottom cell has no additional effect for a moderate texture but leads to light trapping in the NBG perovskite for a pronounced texture. Moderate texturing between the NBG perovskite absorber and the metal back contact leads to light trapping in the NBG perovskite but also excites surface plasmons in the copper back contact. Dielectric interlayers between the NBG perovskite and the metal back contact can reduce the plasmonic absorption losses. Texturing potentially allows to increase the current‐matched short‐circuit current density beyond 17 mA .

Study on the Tribological Properties of Multilayer Concentric Hexagonal Laser Texturing on Rubber Surfaces of Screw Pumps.

Given the friction and drag reduction effects observed in various biological hexagonal structures in nature, a new design was implemented on the rubber surface of the stator of a submersible screw pump. This design featured a multilayer concentric hexagonal groove structure. Furthermore, a composite multilayer hexagonal structure integrating grooves and pits was also developed and applied. This study investigated the influence of groove layer number, groove depth, pit depth, and multilayer hexagonal groove texture arrangement on the rubber surface flow characteristics. Additionally, the pressure field state, the degree of influence on the oil film-bearing capacity, and the biomimetic and hydrodynamic lubrication theories were tested using the finite element analysis method. Tribological experiments were conducted on nanosecond laser-processed rubber textures under simulated liquid lubrication conditions, reflecting actual shale oil well experiments. These experiments aimed to investigate the influence of multilayer hexagonal shape parameters on the tribological characteristics of the stator-rotor friction pair of a submersible screw pump. The results indicated that with a constant overall size, a multilayer hexagonal structure with ~0.1 mm groove depth enhanced the oil film-bearing capacity, providing significant friction and drag reduction. For composite textures, a deeper pit depth within the study area enhanced the oil film-bearing capacity. Furthermore, a gradient arrangement of groove textures featuring wider outer grooves and shallower depth exhibited superior performance in terms of bearing capacity.

Effect of laser surface texturing on the corrosion behaviour and biocompatibility of zinc hydroxyapatite implant material

The demand to optimize pure zinc with adjustable rates of corrosion and biocompatibility has recently increased, and metal matrix composites offer a promising solution. In this study, an optimized Zinc-Hydroxyapatite combination was prepared through a powder metallurgy process, and surface modifications were performed using Laser Surface Texturing. The feasibility of the composite in corrosive and cell culture environments was systematically evaluated through physical and mechanical tests, revealing properties matching those of bone tissue. Three different textures were tested, and textured samples showed better resistance to corrosion and higher cell viability than non-textured ones, with hexagonal texture being the most effective. Contact angle measurements were performed to analyse the sample's hydrophilic nature, which improved with the texturing process. These results suggest that texturing increased the surface area and surface wettability, leading to better biocompatibility results. This study highlights the potential of metal matrix composites for in-vivo conditions and calls for further investigation.

Simulation analysis and experimental study on the friction characteristics of hexagonal texture on the surface of PA66 material

Simulation analysis and experimental study on the friction characteristics of hexagonal texture on the surface of PA66 material

Crystalline and transport characteristics of ferrimagnetic and antiferromagnetic phases in Mn3Ga films

The Mn3Ga material is a promising candidate for memory and computing devices owing to its rich crystalline structures of tunable ferrimagnetic and collinear and non-collinear antiferromagnetic phases. In particular, Mn3Ga with non-collinear antiferromagnetic order exhibits giant anomalous and topological Hall conductivities and is a potential material platform for hosting spin-related quantum phenomena. In this study, we demonstrate Mn3Ga films grown on thermally oxidized Si substrates, with and without the Ta buffer, under different deposition temperatures (Ts). With increasing Ts, the dominant crystalline structure across all Mn3Ga films evolves from a cubic to hybrid tetragonal and hexagonal texture, wherein the crystalline orientation of spins endows the films with in-plane magnetic anisotropy. For Ta/Mn3Ga and Mn3Ga films grown under high Ts, the inhomogeneity in surface energy of the buffer layer results in a non-uniform granular film in the former. Notably, the Mn3Ga films of hexagonal texture exhibit topological Hall signatures. The density functional theory calculations on the hexagonal Mn3Ga phase corroborated with the experimental magnetic, structural, and transport properties. These findings establish an important platform for tailoring Mn3Ga films toward multifunctional applications.

Influence of bio-inspired surface texture of additively manufactured 17-4 PH stainless steel adherends on the strength of adhesively bonded joints

The bonding potential of as-printed additively manufactured stainless steel is largely unknown, and the use of additional hierarchical bio-inspired surface texture has not yet been explored or characterized. In this study, it is demonstrated with the use of Selective Laser Melting (SLM) that a hierarchy of three surface features at different length scales can greatly improve the shear strength of metal-metal adhesive joints. The intrinsic stochastic texture of the SLM as-printed surface showed a high contact angle and a mixed failure with a dominance of adhesive failure. However, enhancing the as-printed surface with the Tree Frog (TF) and Fish Scale (FS) bio-inspired textures produced super-wetting surfaces, significantly improving the shear strength due to the synergistic effect of mechanical interlocking and physical adsorption adhesion mechanisms, resulting in mixed failure. The results indicated that the interfacial bonding performance was in line with the super-wetting behavior and was higher for the samples with a hierarchy of three surface features. The highest increase in bond strength was found for the tree frog hierarchical hexagonal texture (+70% compared to the as-printed texture). In contrast, abrasion of the as-printed surface with P1000-grit paper significantly reduced the surface roughness and increased the water contact angle, resulting in the lowest shear strength.

Effect of bionic hexagonal texture on squeezing films inside soft contacts with high adhesion and high friction.

To understand the mechanisms of high friction and high adhesion in bioinspired textured surfaces under wet conditions, the evolution behavior of squeezing films across lubricated interfaces is experimentally investigated using optical interferometry. The results show that the splitting of the continuous large-scaled liquid film into numerous isolated micro zones is an important function of the hexagonal texture. Both the orientation and the size of the hexagonal texture have noticeable effects on the drainage rate: either downscaling the hexagonal texture or orienting the texture with two sides of each micro-hexagon parallel to the inclining direction could accelerate the draining process. While the draining process is completed, residual micro-droplets turn out to be entrapped within the contact regions of single hexagonal micro-pillars. The entrapped micro-droplets gradually shrink as the hexagonal texture downsizes. Moreover, a novel geometrical shape for the micro-pillared texture is proposed to improve the drainage efficiency.

Effect of Different Etching Time on Fabrication of an Optoelectronic Device Based on GaN/Psi

Gallium nitride (GaN)/porous silicon (PSi) film was prepared using a pulsed laser deposition method and 1064 nm Nd: YAG laser for optoelectronic applications and a series of Psi substrates were fabricated using a photoelectrochemical etching method assisted by laser at different etching times for 2.5–15 min at 2.5 min intervals. X-ray diffraction, room-temperature photoluminescence, atomic force microscopy and field emission scanning electron microscopy images, and electrical characteristics in the prepared GaN on the Psi film were investigated. The optimum Psi substrate was obtained under the following conditions: 10 min, 10 mA/cm2, and 24% hydrofluoric acid. The substrate exhibited two highly cubic crystalline structures at (200) and (400) orientations and yellow visible band photoluminescence, and homogeneous pores formed over the entire surface. The pores had steep oval shapes and were accompanied by small dark pores that appeared topographically and morphologically. The GaN/Psi film fabricated through PLD exhibited a high and hexagonal crystallographic texture in the (002) plane. Spectroscopic properties results revealed that the photoluminescence emission of the deposited nano-GaN films was in the ultraviolet band (374 nm) related to GaN material and in the near-infrared band (730 nm) related to the Psi substrate. The topographical and morphological results of the GaN films confirmed that the deposited film contained spherical grains with an average diameter of 51.8 nm and surface roughness of 4.8 nm. The GaN/Psi surface showed a cauliflower-like morphology, and the built-in voltage decreased from 3.4 to 2.7 eV after deposition. The fabricated GaN/Psi film exhibited good electrical characteristics.

Laser Com-Texture on Ti6Al4V Surface for Lubricant Transportation to Improve Tribological Properties

Abstract Artificial joint materials often wear out due to poor lubrication, affecting their service life. A compound texture (com-texture) was prepared, to improve the spreading of lubricant at the friction interface and reduce the friction and wear of artificial joint pairs UHMWPE and Ti6Al4V. The com-texture was divided into rough and smooth parts on the surface. The rough area was a hexagonal convex texture with a texture ratio of 66%, and it was covered with a recoagulated layer left by laser processing to absorb and transport lubricant to the friction interface. The smooth area was a convex texture with a texture ratio of 85%, which was the friction contact area. The texture morphology of the rough region was characterized by SEM and laser focusing microscope. It was found that the edge of the texture was covered with recondensed mountains after laser processing and corroded micro-nano pits, which helped to prepare super-hydrophilic surfaces. Besides, the flow law of simulated body fluid (SBF) on a textured surface was explored, and the motion process was recorded by a high-speed camera. The results showed that the com-texture could transport SBF to the friction region smoothly and quickly. The friction test results indicated that the structure had improved tribological properties.

Laser hexagonal texture on surface of Ti6Al4V for the improvement of fluid spreadability and tribological properties

The joint capsule removal after artificial joint replacement surgery have led to improper lubrication, causing the pair to wear out quickly and reducing the joint lifespan. In this paper, laser processing and chemical corrosion were used to prepare a hexagonal convex texture on the surface of titanium alloy (Ti6Al4V). After etching and laser polishing, SEM images indicated the presence of secondary micro-nano textures in the grooves around the hexagonal texture, and the formation of anatase oxides on the surface, resulting in an increase of the surface energy and a very small contact angle (CA). The surfaces’ CA increases with the texture ratio, and the surface is super-hydrophilic when the texture ratio is less than 0.84. Furthermore, the effect of texture parameters and directions are studied by using UHMWPE and Ti6Al4V as friction pairs and simulated body fluid as lubricant. The COF is 0.068 with 0.84 area ratio, which is 51.4% lower than the original surface. The wear rate of UHMWPE on the textured surface decreases by 74.5% after two hours of tribological testing. In addition, high speed camera images and calculation results proved that creating grooves can promote fluid distribution on the textured surface. The surface texture on titanium alloy results in a significant COF and wear reduction, extending the service life of artificial joints.

Effect of surface line/regular hexagonal texture on tribological performance of cemented carbide tool for machining Ti-6Al-4V alloys

Effect of surface line/regular hexagonal texture on tribological performance of cemented carbide tool for machining Ti-6Al-4V alloys

Structure, Optical and Electrical Properties of the High Doped ZnO Thin Films Deposited By RF Magnetron Sputtering of Powder Target in Methane Ambient

The ZnO thin films were deposited by RF-magnetron sputtering of ZnO powder target using pure argon, argon with hydrogen and argon with methane as reactive gas. Surface morphology and crystalline structure of the films were studied by SEM, XRD and XRR techniques. Chemical composition and optical properties were investigated by SIMS, Raman scattering spectroscopy (RSS), PL spectroscopy and spectral ellipsometry. Electrical measurements were performed on the ZnO films deposited on SiO2-Si and silicon wafers n- and p-type with Ni contacts by TLM, IV, CV characteristics, admittance spectroscopy, Van der Pauw and Hall methods. It was found that growth morphology, crystalline structure, optical and electrical properties of the films are strongly affected by adding methane to argon during the deposition process. Adding of methane resulted in a destruction of hexagonal phase texture and considerable increase a size of ZnO nanocrystallites (from 50 nm for argon to 200 nm for argon/methane working gas). SIMS measurements demonstrated that methane promoted hydrogen incorporation into the ZnO film that was more than an order of magnitude larger in comparison with adding molecular hydrogen in the gas mixture at the same concentration. Adding of methane resulted in a high energy shift of near band edge ultraviolet photoluminescence band, quenching of deep level emission in the visible spectral range and increase of optical band gap from 3.24 to 3.45 eV. The strongest effect of methane has been found for electrical resistivity that reduced by 3 orders of magnitude in comparison with films deposited in pure argon. Additionally, electrical conductance of the ZnO film deposited at high methane concentration does not depend on measurement temperature. Hall method with combination with Van der Pauw resistivity measurements shows: strong n-type doping of the film; donor concentration more than 1020 cm-3 slightly depending on methane concentration; maximum electron mobility about 7 cm2/V s. The direct comparison of resistivity and donor concentration of the films deposited using methane and molecular hydrogen as doping precursors has demonstrated that doping efficiency of methane is about an order of magnitude larger than that of molecular hydrogen under similar deposition conditions. On the other hand, methane addition in working gas resulted in an intensity decrease of the E2L (100 cm-1) and E2H (438 cm-1) lines in the RSS that can be associated with some disturbance of the ZnO structure. Additionally a peak at 71 cm-1 was observed in some films that can be related to the metallic Zn. The possible mechanisms of the ZnO film formation, nature of the doping and electron transport mechanisms will be discussed.

Tribological Performance of Nickel-Plated Regular Hexagonal Texture on a Brass Surface Under Boundary Lubrication

Abstract A novel bio-inspired nickel-plated regular hexagonal texture (NPRHT) was proposed and fabricated by photolithography combined with electroless nickel plating to improve the tribological performance of a shaft/bushing bearing under boundary lubrication. The friction coefficient, wear loss, and wear resistance mechanism of the NPRHT that was fabricated on the brass surface were investigated under line contact sliding. It is found that the nickel-plated textured samples show a lower friction coefficient than the non-textured samples with a maximum reduction of 43.6% at a sliding speed of 0.02 m/s. The wear rate coefficient of the nickel-plated textured sample decreases by 42.86% compared with that of the non-textured sample. The energy dispersive spectrometry and X-ray photoelectron spectroscopy analysis confirm that the nickel element is transferred from the nickel-plated textured area to the brass zone, resulting in the formation of a Ni/Cu alloy, NiO and Ni2O3 successively. These three films can improve lubricity, repair wear defects, and protect surfaces from oxidation. The experimental results show that the NPRHT provides a novel strategy to manage the friction and wear of shaft/bushing bearings under boundary lubrication.

Fabrication and characterization of Au/n-ZnO/p-Si/Al sandwich device with Sol–gel spin coating method

ZnO thin films with the n-type properties were obtained on the p-Si substrates for multi-layered sandwich device depositing by sol–gel method. Au and Al were conducted on two side of hetero-junction by PVD technique. From X-ray diffraction pattern, a strong (002) direction is observed, which means the film is hexagonal texture. Cross-section image from the scanning electron microscope demonstrated that the coated ZnO films had ~ 427 nm thickness. Electrical behavior of the device was characterized by applying voltage versus current. High purity Au and Al metals were vacuum evaporated to make Schottky and Ohmic contacts onto the device. Au/n-ZnO/p-Si/Al architecture exhibited a rectification behavior. According to Thermionic emission mechanism theory, barrier height and ideality factor of device were found as 1.4 and 0.54 eV, respectively. The series resistance values were obtained from dV/d(lnI) versus I and H(I) versus I graphs as 43.6 Ω and 229.9 Ω, respectively.

The size effect of hexagonal texture on tribological properties under mixed lubrication

PurposeThe purpose of this study is to elucidate the size effect (groove width, unit length and area density) of the hexagonal texture on tribological properties under lubrication.Design/methodology/approachThe tribological properties of nine hexagonal textures with different hexagon lengths and groove widths have been investigated under mixed lubrication to elucidate the size effect.FindingsOverall, the friction coefficient decreases as the groove width increases within the examined range, whereas the hexagon length shows an optimal value around 3 mm. In particular, one hexagonal texture (3 × 3 mm) exhibits lower friction coefficients and less wear losses than the others. Interestingly, two hexagonal textures of similar area density (1 × 1 mm and 3 × 3 mm) yield the worst and best tribological performances, respectively, which can be explained by the simulated distribution of equivalent stress.Originality/valueThe tribological properties of nine hexagonal textures are examined under lubrication. The 3 × 3 texture exhibits lower friction coefficient and wear loss than the others. Two textures of similar area density yield the worst and best tribological performances. The results agree with the simulated distribution of equivalent stress.

Numerical simulation and experimental investigation of tribological performance on bionic hexagonal textured surface

The numerical models for hexagonal textures of two orientations (θ = 0° and 90°) have been established by using MATLAB and the corresponding specimens have been fabricated by laser texturing. The tribological performance has been examined both theoretically and experimentally to investigate the effects of geometrical characteristics and operating conditions. Overall, the experiments have verified the trends identified from the simulation and both show that the textured surface of θ = 90° demonstrates better friction behavior than that of θ = 0°. Moreover, the hexagonal textured surface with the area density of 25% can reduce friction coefficient up to 41%, compared to the control of smooth surface.

Microstructure control of Bi0.4Sb1.6Te3 thermoelectric material by pulse-current sintering under cyclic uniaxial pressure

The effect of the sintering holding time on the microstructure and thermoelectric properties of Bi0.4Sb1.6Te3 prepared by pulse-current sintering under cyclic uniaxial pressure was investigated. The sintering was performed at 400 °C under a cyclic pressure of 0 MPa and 100 MPa, and the holding time was varied from 0 to 60 min. The microstructure of samples, including grain size, hexagonal c-plane texture, and high-angle grain boundary, changed with holding time, that is, grain size and c-plane texture were enhanced and the high-angle grain boundary was reduced with increasing holding time. The thermoelectric properties changed corresponding to the change in the microstructures. The Seebeck coefficient was independent of the sintering parameters and had a value of approximately 200 μV/K. Nevertheless, electrical resistivity decreased with holding time because of the increase in the c-plane texture. As a result, the power factor was enhanced with increasing holding time. In contrast, thermal conductivity was insensitive with the holding time and had almost constant value. As a result, a dimensionless figure of merit of approximately 1 at 300 K was achieved with a large power factor of 4.3 × 10−3 W/K2m. Therefore, in the PCS-cyclic process, the holding time is an important sintering parameter for controlling the microstructure and electrical properties of Bi0.4Sb1.6Te3 thermoelectric materials.

Bionic Coupling of Hardness Gradient to Surface Texture for Improved Anti-wear Properties

This work investigates the potential of combining hardness gradient with surface texture (an example of bionic coupling) to improve anti-wear properties. The bionic coupling of hardness gradient and Hexagonal Texture (HT) was achieved by laser heat treatment on steel specimens with pre-engraved hexagonal surface texture. The successful establishment of decreasing hardness from surface to internal bulk was verified by hardness measurements along the depth of cross-sectioned specimens and correlated with the observations from metallurgical microscopy. The tribological performance of bionic coupling specimens (HT-L) was examined under dry contact condition, together with respective control specimens of individual bionic features, e.g. HT-H (of similar surface hardness generated by conventional heat treatment but without hardness gradient) and SS-L (of smooth surface treated by the same laser processing as for HT-L). It is found that HT-L not only exhibits lower friction coefficient and less friction fluctuation than HT-H and SS-L, but also demonstrates a >50% reduction of wear loss compared to HT-H and SS-L (0.0343 g for HT-L vs. 0.0723 g for HT-H, P<0.001; 0.0343 g for HT-L vs. 0.0817 g for SS-L, P<0.001). Corroboratively, observations with scanning electron microscopy revealed a relatively smooth surface for worn HT-L specimen, contrasting with the rugged and grooved surfaces of worn HT-H and SS-L specimens. These results indicate that the bionic coupling of hardness gradient to hexagonal texture can indeed improve anti-wear properties, affording a new strategy to wear and friction management.

Structural, morphological and optical studies of ripple-structured ZnO thin films

Ripple-structured ZnO thin films were prepared on Si (100) substrate by sol–gel spin-coating method with different heating rates during preheating process and finally sintered at 500 °C for 2 h in ambient condition. The structural, morphological and photoluminescence (PL) properties of the nanostructured films were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and PL spectroscopy. XRD analysis revealed that films have hexagonal wurtzite structure and texture coefficient increases along (002) plane with preheating rate. The faster heating rate produced higher crystallization and larger average crystallite size. The AFM and SEM images indicate that all the films have uniformly distributed ripple structure with skeletal branches. The number of ripples increases, while the rms roughness, amplitude and correlation length of the ripple structure decrease with preheating rates. The PL spectra show the presence of different defects in the structure. The ultraviolet emission improved with the heating rate which indicates its better crystallinity.

Toxicity evaluation of pH dependent stable Achyranthes aspera herbal gold nanoparticles

Nanoparticles have gained substantial attention for the control of various diseases. However, any adverse effect of herbal gold nanoparticles (HGNPs) on animals including human being has not been investigated in details. The objectives of current study are to assess the cytotoxicity of HGNPs synthesized by using leaf extract of Achyranthes aspera, and long epoch stability. The protocol deals with stability of HGNPs in pH dependent manner. Visually, HGNPs formation is characterized by colour change of extract from dark brown to dark purple after adding gold chloride solution (1 mM). The 100 μg/ml HGNPs concentration has been found nontoxic to the cultured spleenocyte cells. Spectrophotometric analysis of nanoparticles solution gave a peak at 540 nm which corresponds to surface plasmon resonance absorption band. As per scanning electron microscopy and Transmission electron microscopy (TEM), size of HGNPs are in the range of 50–80 nm (average size 70 nm) with spherical morphology. TEM-selected area electron diffraction observation showed hexagonal texture. HGNPs showed substantial stability at higher temperature (85 °C), pH 10 and salt concentration (5 M). The zeta potential value of HGNPs is −35.9 mV at temperature 25 °C, pH 10 showing its good quality with better stability in comparison to pH 6 and pH 7. The findings advocate that the protocol for the synthesis of HGNPs is easy and quick with good quality and long epoch stability at pH 10. Moreover, non-toxic dose could be widely applicable for human health as a potential nano-medicine in the future to cure diseases.