Surface Review and Letters

Borophene, a boron analogue of graphene, has been considered as an innovative two-dimensional (2D) material for the scientific and research community. First 2D boron sheet was reported in 2015 by growing it on Ag substrate. Attributable to its exceptional structural, electronic, and spin properties, it has earned enormous exploration interests in the multifaceted fields of material science, nanotechnology and computational physics. Borophene is the newest rising 2D material, which demonstrates various diversified configurations that can be marked by anisotropic and polymorphism. These configurations enabled enhanced tailoring properties of borophene for various applications. This review provides brief discussion on various experimentally synthesized borophene and borophene nanoribbon (BNR), their structural, electronic, and magnetic properties variations along with the width effect. Based upon the type of edges, BNRs are categorized as line edge-BNR (LE-BNR) and zigzag-BNR (ZZ-BNR). Electronic properties of LE-BNR with vacancy defect show semiconductor behavior and ZZ-BNR indicates metallic property. It covers all the structural allotropes, their synthesis, stability and other crucial intrinsic properties, characterization and tailoring of physical properties. Hence, this comprehensive review reported here incorporates the crucial recent experimental and theoretical advances on borophene and BNRs till date. This work also covers recent modifications reported in borophene and BNR to alter their properties as per the demands of various application areas such as nanoelectronic devices, interconnects, biosensors, metal detectors and gas sensors.

Corrosion resistance of A36 carbon steel was assessed in 0.5M H₂SO₄ and HCl media in the presence of specific concentrations of Commiphoramyrrha (CM), Cymbopogon (CP) essential oil extracts and their combined admixture (CMCP). Values from potentiodynamic polarization showed CM extract reacted poorly in both acids at low concentration, but effectively at higher concentrations with optimal performance of 89.76% and 92.83%. CP extract generally performed effectively with inhibition values above 90%. CMCP performed very poorly in H₂SO₄ compared to its performance in HCl which was generally above 80% inhibition efficiency. The oil extracts exhibited mixed-type inhibition effect coupled with dominant anodic shift in corrosion potential and similar anodic slope configuration at all extract concentrations. ATR-FTIR spectra plots showed that most of the identified functional groups within the extract molecules generally adsorbed unto the A36 steel surface. Curves from open circuit potential analysis showed CM extract in H₂SO₄, and CP extract in H₂SO₄ and HCl solution significantly decreased the thermodynamic tendency of A36 steel to degrade. The curves of other extracts displayed significant time and extract concentration dependent active–passive transition behavior. Optical images of the unprotected steel exhibited severe general and localized surface deterioration compared to the inhibited steel with significantly protected morphology. Weight-loss analysis showed the effective protection effect of CP extract in both acids and CMCP in H₂SO₄ is independent of time and concentration from the onset of exposure compared to their remaining counterparts whose performance significantly varies over time and is concentration dependent. X-ray phase identification diagrams and identified patterns list revealed the presence of FeO(OH) on the steel surface without oil extracts while the phase compounds identified in the presence of the extracts are FeNi and Fe₃C.

Macrocyclic compounds have got recognition in modern science and technologies because of their potential applications in energy, catalysis, material science, biochemistry, and pharmaceutical. The most interesting feature of macrocyclic complexes is their adjustable macrocyclic cavity which opens many possibilities for the development of various important fields. Herein, we synthesized two MN₄-macrocyclic complexes (M = Fe(III) and Ni(II) by using template method, and characterized by employing multiple techniques like molar conductance, FTIR, UV–Vis and mass spectra. On the basis of characterization results, a saddle shaped octahedral geometry can be attributed to theses complexes. The “saddle shape” geometry of these complexes is due to the steric repulsions between the benzenoid and amidic moieties on the macrocyclic framework as suggested by theoretical investigations. Further, the electrochemical investigations carried out using cyclic voltammetry in methanol at the Pt electrode indicated that the unusual oxidation state of metal ion could stabilize the macrocyclic framework of the complex. Moreover, these complexes were also evaluated for their antibacterial activities against several pathogens using Gentamycin as standard drug. The results suggested that these complexes did have significant antimicrobial activity.

Copper metal and its alloys are the most used in the industries because it holds excellent conductivity and natural corrosion protectiveness against air/moisture. However, copper undergoes degradation in presence of aggressive 3.5% NaCl. Protective coating is one of the practical methods to safeguard copper metal. In this study, 2-amino-4-methyl-pyridine (AMP) was coated as self-assembled monolayer method (SAM) with different immersion periods (12 h/24 h) and investigated the corrosion potential against 3.5% NaCl medium. Chemical composition of AMP/SAM/Cu was characterized using Fourier-transform infrared (FT-IR) spectroscopy and morphological analysis using atomic force microscopy (AFM) techniques. AMP’s corrosion inhibition potential were evaluated via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDS) analyses. Quantum chemical calculations and molecular dynamics (MD) simulations explained the stronger adsorption of AMP over copper metal surface via self-assembly method. The corrosion analysis revealed that AMP’s SAM formation (24 h immersion) enhances the corrosion protection of Cu metal, which is mainly due to the uniform thin adhesive compact layer formation and blocks incoming corrosive chloride ions. EIS investigation evident that AMP forms an adhesive layer over the copper surface and prevents the diffusion of aggressive corrosive medium, while PP studies revealed that AMP acts via the mixed mode of corrosion inhibition mechanism. AMP’s significant inhibition efficiency 90% was confirmed via PP analysis. AFM analysis enabled the morphology image of AMP’s shielding over Cu surface and the molecular modeling investigation supported well for the Cu–N (from AMP) bond formation.

The interaction of accelerated helium atoms with the atomic-smooth surface of tun+gsten single crystals was investigated using the low-temperature field-ion microscope, equipped with the source of helium atoms with an energy of 5 keV together with the techniques of molecular dynamics. It was observed the effect of the surface channeling of fast atoms of a target along the surface steps which occurs as a result of the collision cascade induced by the incident projectile. A substantial part of these displaced atoms in the target gains momentum oriented along the < 111 > close-packed crystallographic directions. The fine morphology of the trajectory of an excited tungsten atom reveals the transverse oscillations of the W atom normally to the < 111 > surface atomic step. The rate of the kinetic energy loss during the surface channeling of fast tungsten atoms does not exceed 0.4 eV/Å. This provides relatively large displaced surface atom ranges along the close-packed atomic steps. The found out results can be regarded as a special case of the correlation mechanism of the radiation-induced surface mass transfer.

Crane hooks are used to ensure the safe transportation of loads to be lifted in load lifting and handling systems. In this study, special hooks for cranes designed to open and close the doors of warehouse zones used for ship cargo and cargo transport, and their responses under 60,000 N static loading conditions are numerically and experimentally analyzed. In the experimental study, ST37 structural steel and Weldox700 high-strength steel were used to manufacture the hook. Experimental data collected under static loading conditions of the component was measured via strain gauges sensors. It was concluded that the results of structural numerical analysis with the Finite Element Method (FEM) using ANSYS 2019 R3 analysis program with experimental data are in harmony with the results of experimental measurements. In addition, the maximum values of stress of the hook manufactured with Weldox700 and ST37 steels under the stress static loading conditions are obtained as 60 MPa and 57.3 MPa, respectively. In the numerical analysis results, stress value was obtained as 61.21 MPa. Compared to the analysis results based on experiments and FEM, numerical analysis results showed that fudge factors in ST37 and Weldox700 steels are 1.8% and 6%, respectively. This result confirms that experimental and mathematical data were in harmony with each other and reliable.

The effect of tea extract (TE) concentration on the inhibition efficiency and the corrosion behavior of HP13Cr stainless steel in 3.5 wt.% NaCl solutions has been investigated. It was found that the inhibition efficiency was influenced significantly by the addition of different concentration of TE. With the concentration of TE increased from 0.1 g/L to 0.3 g/L, the intermolecular interactions among the TE molecules were mainly characterized by attraction, and the coverage of the inhibition film was increased. However, when the concentration of TE was increased to 0.4 and 0.5 g/L, the intermolecular interactions among the TE molecules were mainly characterized by repulsion, which can result in the desorption of the covered TE molecules and the coverage of the inhibition film was decreased obviously. Therefore, the inhibition efficiency was reduced and the corrosion of HP13Cr was aggravated. The intermolecular interactions of TE are calculated, and the influencing mechanisms of the TE concentration on the inhibition efficiency and corrosion behavior are also discussed.

Thiourea (Th)-doped CdO thin films were deposited on glass and crystalline p-type Si (100) substrates for various Th doping concentrations (0.3, 0.5 and 0.7 at.%) using spin coating method. Some structural parameters, such as the crystallite size, lattice constant, dislocation density (δ) and strain in the films were obtained from XRD analysis in which the polycrystalline structure with cubic nature and (111) preferential orientation was confirmed. CdO thin film has not shown any change in crystal phase after Th doping. The optical study emerged that the Th doping caused important changes in the transmittance, absorbance and reflectance spectra. The optical transmittance above 80% range from 720 nm to 800 nm is obtained for 0.3% Th-doped CdO thin films. The rectifying behavior increases with increasing Th content in CdO while Th-doped CdO/p-Si heterojunction exhibits low rectifying character.

Many researchers have attempted to join Aluminum Matrix Composites (AMCs) using traditional fusion welding processes resulting in the formation of porosity, segregation, coarse microstructure, brittle intermetallic compounds and corrosion of ceramic particles. Friction Stir Processing (FSP) is the latest solid-state technique to achieve the homogeneous dispersion of reinforcement particles in the friction stir processed zone of AMCs [M. Shamanian, E. Bahrami, H. Edris and M. R. Nasresfahani, Surf. Rev. Lett. 25 (2018) 1950010]. The most widely used reinforcing material since the inception of FSP is inorganic (metallic) powders such as silicon carbide, titanium alloy, graphene, iron, stainless steel, nitrides and oxides, and fewer works have been reported on organic powders (i.e. bioprocessing using agro-waste powders) such as fly ash, palm kernel shell ash, coconut shell ash and rice husk ash [O. M. Ikumapayi, E. T. Akinlabi, S. K. Pal and J. D. Majumdar, Procedia Manuf. 35 (2019) 935]. In this work, the effect of FSP on the changes in metallurgical characterization and mechanical properties of AA7075/(3, 6 and 9) vol.% ZrB₂ in situ AMCs was observed. After performing FSP, the AMCs were characterized using Scanning Electron Microscope and the mechanical properties such as Ultimate Tensile Strength and microhardness on the processed zone of the AMCs were calculated. The effect of FSP on AA7075/ (3, 6 and 9) vol.% ZrB₂ in situ AMCs was investigated. The fracture morphologies on the processed surface of the AMCs were evaluated.

Disparate industry bodies across the planet use pallets for storing large and heavy objects. Pallets provide an assurance of safe handling of material (cargo) and storage of material in a damage-free environment. In this work, an attempt has been made to analyze and investigate making pallets out of ULTEM 9805 using the latest additive techniques (FDM). The maximum deflections and von Mises stresses are analyzed for the disparate boundary conditions indicating the possible alternatives or loads to be used. Study of surface (morphology) and characteristics was done in order to establish the relationship between pallet surface and its application. The factors of load, maximum and minimum values, ascertained in each stage are 168.15, 522.22, 215.31 and 316.79 kPa as well as 18.77, 6.7, 1.2 and 35.84 kPa for the floor, rack, forklift and conveyor load supports, respectively. A cross-hatched design causes a rise in capacity of the shear factor owing to the length of the span being in correlation with rectilinear fill. The filament of surface, made of ULTEM 9805, exhibits a level of roughness of 43.14 μm on the pallet surface indicating better holding capacity and grip. A 9^∘ peak shift is comprehended with respect to XRD, indicating a compressive residual factor measured at 76.47 MPa.

Fiber metal laminates (FML) are used in outer covering of the fuselage skin structure. The thrust force and the torque generated during drilling process affect the quality of the holes on the structure. The magnitude of cutting forces is controlled by optimizing the drilling process parameters. In this study, the influence of drilling parameters such as spindle speed, feed rate and the weight percentage of layered double hydroxides (LDH) in the binder epoxy on the thrust force and torque during drilling operation was studied. The experiments were designed based on Taguchi’s L₉ orthogonal array. The Gray Relational Analysis was used as multi-objective optimization tool for finding the optimal combination of process parameters. The spindle speed was identified as the most influencing process parameter to affect the drill quality in the FMLs. SEM images taken on the drilled specimens for the best and worst input parameter settings were compared and discussed. The regression models were generated to predict the output response values within the range of actual experiments.

In order to reduce the carbon emissions of fuel vehicles, hydrogen has received extensive attention as a new clean energy. In this paper, a packed-bed microreactor for hydrogen production from methanol steam is designed for use in hydrogen fuel cells. By considering the heating gas velocity in the heating tubes, the inlet temperature of the microreactor, the size and number of heating tubes, inlet pressure, pellet porosity and thermal conductivity, parameters such as methanol conversion rates and hydrogen concentration were evaluated. First, the rate at which the gas is heated has a great influence on the reaction results. Choosing a larger heating gas velocity leads to an increase in the temperature inside the microreactor, thereby increasing the CH₃OH conversion, resulting in a higher H₂ concentration at the outlet. Changing the inlet temperature of the microreactor affects the reaction speed, but has little effect on the H₂ concentration at the outlet. By studying the radius and number of heating tubes, we selected three different sets of data to compare the conversion rate of reactants and the concentration of products, and finally determined the optimal parameters as R = 4 mm and N = 8. Second, the inlet pressure has little effect on the H₂ concentration at the outlet, but has a significant effect on the reaction speed. Particle porosity has no effect on the reaction results. Finally, the larger the thermal conductivity, the higher the temperature in the microreactor, which is more conducive to the reaction.

Laser-induced periodic surface structures (LIPSS, ripples) are generated on CVD nano-crystalline diamond (NCD) films by femtosecond laser irradiation in air (pulse duration 200 fs and central wavelength 1040 nm). The experimental conditions (laser fluence and spatial spot overlap) are optimized to obtain a 3 × 3 mm² area covered with homogenous LIPSS. Then, the influence of LIPSS on the frictional performance of NCD films is investigated by dry reciprocating ball-on-disc tests, where ZrO₂ ceramic balls are used as counterparts. The results show that the friction behavior is very sensitive to the orientation of nano-structured ripples in LIPSS. The frictional coefficient can be greatly reduced when the sliding direction is parallel to the orientation of the nano-structured ripples, indicating potential benefit of LIPSS on NCD films for frictional applications.

Increase in the demand for high-performance and lightweight structural materials in the automobile and aircraft industries may inspire a strong tendency to develop fiber metal laminates (FMLs). In this work, the FML composites are fabricated using different stacking sequences of glass/carbon fibers, aluminum wire mesh, BaSO₄ filler and epoxy resin. Six different combinations of composites with different stacking sequences and wire mesh angles are fabricated using the hand-lay technique. Dynamic mechanical analysis (DMA), ballistic and wear experiments were used to investigate the fabricated composites’ performance. The FML6 Al wire mesh with BaSO₄ filler increases the storage modulus by 16.12% and enhances the energy absorption capacity by 3.19%. From the ballistic, the carbon fiber composite (FML3) shows 4.47% improvement compared to the glass fiber composite (FML1) for the same 90^∘ wire mesh orientation.

The chemical composition, crystalline structure and optical properties of un-doped ZnO (UZO) and indium (6%)-doped ZnO (IZO) thin films grown on Si substrate were studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL) techniques. The results are complementary and confirm each other. The surface is cleaned using checked ultra-high vacuum (UHV) treatment (argon ion sputtering followed by successive heating). For IZO, the XPS analysis displays that the indium incorporates in the ZnO matrix to form the In-O-Zn-type chemical bonds. The PL of UZO reveals structural defects, including oxygen interstitial (O_i), oxygen vacancies (V_O), zinc vacancies (V_Zn) and interstitial zinc (Zn_i), and they decrease with the In doping and UHV treatment. For IZO, the PL measurements show the great interest of UHV treatment to stimulate the incorporation of indium into the ZnO matrix. There is an increase in the UV emission intensity and improvement of its physical structure. The In (6%) doping of ZnO is convenient to compensate the zinc vacancies (V_Zn), eliminate Zn_i and V_O, and ensure the structural homogeneity of IZO film. All the detected peaks of the XRD patterns are matched to the wurtzite crystalline structure for both UZO and IZO thin films grown mainly along the (002) orientation plane.