Fabrication Of Metal Research Articles

Fabrication of large-area metal and semiconductor nanobridge arrays using nanotransfer printing and UV lithography

A new method for the fabrication of large-area metal and semiconductor nanobridge arrays is proposed. The method combines the possibilities offered by the nanotransfer printing technique and by UV lithography. The essence of the method consists in the formation of an array of metal or semiconductor nanostrips “imprinted” into a smooth layer of resist and in subsequent exposure of the resist to UV radiation through an additional mask defining the regions where the suspended nanostrip bridges will be formed during subsequent development of the resist layer. Large-area arrays of Au and Ti/Au nanobridge, 100 nm wide, 25–35 nm thick and 1–4 μm long, with their ends embedded into the SU-8 resist layer, were fabricated. SiGe nanobridge arrays of 18 nm thick and 1 μm long, with their ends embedded into the Shipley 1813 resist layer were fabricated. The proposed method is simple and low-cost, and it does not require using expensive reactive plasma-etching facilities and can be implemented both on solid and polymer substrates on the areas at the excess of 150 cm2.

Conductive woven fabrics made of metallic/modal core yarns: manufacturing techniques and electromagnetic shielding effectiveness

We independently invented the feeding wire device and combined it with the drawing device of the spinning frame to accurately realize the wire in the middle of the core yarn, effectively solve the problem that the wire is easy to expose the fabric surface. Using a degradable and environmentally friendly modal as roving, Cu and SS as conductive yarns, preparing conductive fabrics, and exploring the effect of shielding networks, lamination layer number, lamination angle, and number of metallic wires. When both the warp and weft yarns are composed of conductive core yarns, the conductive woven fabrics with lamination angle of 0° can build a complete conductive network, and the average EMI SE of single-layered conductive woven fabrics is 30 dB. When only the weft yarn is composed of a conductive yarn, varieties of lamination angles and lamination layers improve the EMI SE of the conductive woven fabrics considerably. However, the shielding value of the two metal fabrics is not a multiple of the single metal fabric. Increasing the lamination layers, the thickness of the fabric will increase, and the gas permeability and SSE/t value decrease.

Directed Energy Deposition With Coaxial Wire-Powder Feeding: Melt Pool Temperature and Microstructure

Abstract In this work, we developed a new additive manufacturing paradigm, coaxial wire–powder-fed directed energy deposition (CWP-DED), to enable the fabrication of metals or composites with high manufacturing flexibility and efficiency. Herein, stainless steel (SS) 316L was selected as a representative material to validate the feasibility of CWP-DED process. Effects of feed rates on the melt pool temperature during the CWP-DED process were investigated using experimental and analytical approaches. Thermal contributions of fed wire and powders to the melt pool were involved in the analytical model to predict the melt pool temperature. The experimental results from thermal imaging were also obtained for validation. Besides, we uncovered the evolution of solidification morphology and crystallographic texture with different combinations of wire and powder feed rates. Finally, the microhardness and tensile performance of different as-built parts were tested. The results showed that the powder feed rate played a more dominant role in determining the melt pool temperature than the wire feed rate. Melt pool temperature experienced an initial increase and then decrease with the powder feed rate. A fine microstructure was achieved at a low powder feed rate, producing higher microhardness and larger tensile strength. This paper revealed the relations among process, thermal variation, and microstructure of as-built metallic parts to well understand this novel DED process.

Fabrication of well-intergrown ZIF-8 films via sequential ZnO seed layer overlaying

The fabrication of well-intergrown metal–organic frameworks (MOFs) in film morphology is crucial for various applications such as gas separation and sensing, as it necessitates uniform and controlled mass transport and sorption at the internal pore surfaces. In this work, we report the growth of continuous zeolitic imidazolate framework-8 (ZIF-8) thin films via a secondary solvothermal growth method using a consecutive ZnO seed layer overlaying approach. The primary growth of ZIF-8 crystals on planar substrates occurs through heterogeneous nucleation in solution, followed by overlaying ZnO seed layers via radio frequency (RF) sputtering for secondary growth. We systematically investigate the morphology, crystallinity, and surface properties of the resulting ZIF-8 films. Our results confirm that the seed layer overlaying induces core–shell-like growth on the primary ZIF-8 crystals, promoting conformal growth and interconnection between isolated islands. These findings demonstrate a promising method for synthesizing continuous, well-intergrown MOF films with high surface coverage with various compositions and porosities for numerous applications.

Fabrication of dual-gradient microstructure and their effects on the mechanical properties of commercial pure Ti

Commercial pure Ti sheets with an initial wavy profile were rolled and annealed to fabricate heterostructure. Microstructure investigations by electron backscatter diffraction (EBSD) show that a dual-gradient microstructure including gradient grain size and gradient texture is developed, where the average grain size decreases and the split-basal texture gets stronger from the trough zone to the crest zone. Finite element simulations of the rolling process were carried out to investigate the formation mechanism of the dual-gradient microstructure. Uniaxial tension tests were performed to evaluate the mechanical properties, and the digital image correlation (DIC) technique was used to reveal the evolution of local strain during tension. When tensioned along the rolling direction, sheets consisting of both crest and trough zones achieve better elongation compared with the single crest and single trough counterparts. When tensioned along the transverse direction, better elongation is also obtained for the sheets with an initial wavy profile compared with the straight counterparts, which is mainly attributed to the dispersing local strain caused by the gradient texture. The results reported in this study may be inspirational to the design and fabrication of heterostructural hexagonal closed-packed metals.

Facile fabrication of Zr-based metal–organic framework/Ketjen black-carbon nanotubes composite sensor for highly sensitive detection of methyl parathion

A novel methyl parathion (MP) electrochemical sensor was fabricated from the multifunctional composite of Zr-based metal–organic framework (UiO-66) and Ketjen black-carbon nanotubes (KB-CNTs), which achieved the sensitive detection of MP in food samples. For the UiO-66/KB-CNTs composite, Zr-based UiO-66 with Zr-OH groups possessed good affinity for phosphate groups on methyl parathion molecules, which enhanced the selective recognition and enrichment capability towards MP, and KB-CNTs possessed three-dimensional interconnected carbon conductive network with synergistic point-line carbon conductive contact, which showed excellent electrical conductivity. Moreover, KB with pearl chain-like structure and more conductive contact points realized the full contact between KB-CNTs and UiO-66 with Zr-OH groups. The fabricated UiO-66/KB-CNTs/GCE sensor showed good MP detection performance with low limit of detection of 1.53 nM in linear MP concentration range of 0.005–12 µM. Moreover, the fabricated sensor showed good repeatability, reproducibility, and selectivity. A good practical feasibility can be achieved at the UiO-66/KB-CNTs/GCE sensor for the detection of MP in grape juice and apple juice samples (Recovery rate: 96.14–102.93, relative standard deviation: 2.17%-4.95%).

Fabrication of metal–polymer matching layers to improve some ultrasonic transducers for NDT and calibration

This paper investigates the impact of different matching layers on the ultrasonic transducers’ performance. Matching layers are mostly used to solve the acoustic impedance matching problem between the piezoelectric element and the test specimen. To design good matching layers, we merged the metal–polymer and mass–spring systems. Their thickness was also optimized using the quarter-wavelength approach. Silver, alumina, and copper served as mass components, while parylene served as the polymer spring component. This was the first time to use such matching materials with lead zirconate titanate (PZT) transducers. The transducers’ sensitivity increased, the beam diameter broadened, the signal-to-noise ratio reduced, and the echo-height increased. According to the findings, the developed matching layers were extremely efficient in upgrading PZT transducers, making them ideal for a variety of non-destructive ultrasonic applications such as identifying defects in various materials. In addition, the new developed transducers may be useful in calibration.

Robot-Assisted Cold and Warm Incremental Sheet Forming of Aluminum Alloy 6061: A Comparative Study

Incremental sheet forming (ISF) requires no or partial dies for sheet metal fabrication and is widely used for small batch production. In this process, necking is either suppressed or delayed due to the localized nature of tool–sheet contact; hence, more strains than conventional stamping and deep drawing are obtained. In the present study, two variations of ISF, namely cold ISF (CISF) and warm ISF (WISF), are compared. First, FEA modeling is carried out on ABAQUS to reach the forming forces involved in the process. It is found that WISF reduces the forming forces. The temperature for WISF is maintained at 180 °C. Following the simulation analysis, tests are carried out. The forming force in WISF is 55.77% less than that in CISF. The part fabricated by CISF is slightly more substantial than that by WISF; however, more forming depth can be achieved by WISF. There is a more uniform thickness distribution in the case of CISF than in WISF. However, the surface quality of the CISF product is inferior to that of WISF. It is observed that there is reduced forming force, increased formability, and better strain distribution in WISF compared to CISF. However, post-processing heat treatment and surface polishing of the formed parts is required to restore their mechanical properties.

Heat Stress and Noise Exposure Levels in a Manufacturing Plant

This paper analyses skilled workers’ heat stress and noise exposure levels at a pressure vessel manufacturing plant. Measurements were conducted at three partially enclosed workspaces of the plant where hot work and metal fabrications were conducted using a multi-function thermal environment data logger and a sound level recorder. A survey was developed to obtain the field workers’ perceptions of their immediate heat and noise environments. The findings suggested that the heat and noise conditions were generally acceptable. The calculated mean Wet-bulb Globe Temperature (WBGT) indicated that there was only minimal risk of heat stress for the workers. It was also identified that the noise intensities in the sections studied were within the permissible exposure limit for an 8-hour duration specified in the Department of Occupational Safety and Health (DOSH) guideline. Besides, questionnaire survey results showed that the thermal and noise conditions at the workplace were acceptable. The workers perceived their work environment as warm with sensible air movement, moderately humid, free from heat and noise-related injuries, and able to have clear conversations with their co-workers while working.

Fabrication of Ruthenium-Based Transition Metal Nanoparticles/Reduced Graphene Oxide Hybrid Electrocatalysts for Alkaline Water Splitting

Green hydrogen has attracted significant attention as one of the future energy sources because no greenhouse gases are emitted during production and its energy density is much higher than fossil fuels. Precious metals such as platinum (Pt) and iridium (Ir)-based catalysts are commonly used for water splitting catalysts. However, because of high cost of these precious metals, the mass production of green hydrogen is restricted. In this study, water splitting catalysts based on relatively inexpensive ruthenium (Ru), cobalt (Co), and iron (Fe) were synthesized. The metal nanoparticles were anchored on reduced graphene oxide (rGO) by a microwave-assisted process. The nanoparticles were uniformly distributed on the rGO supports with sizes of about 1.5 and 2 nm in Ru/rGO and RuCoFe/rGO, respectively. This promoted the reaction by further increasing the specific surface area of the catalysts. In addition, it was confirmed by EDS mapping results that the nanoparticles were made of RuCoFe alloy. Among the prepared catalysts, Ru/rGO was excellent toward the hydrogen evolution reaction (HER), which required an overpotential of 50 mV to reach a current density of −10 mA cm<sup>−2</sup>. In addition, RuCoFe/rGO, which contained the RuCoFe alloy, was the best for the oxygen evolution reaction (OER), and it required 362 mV at the current density of 10 mA cm<sup>−2</sup>.

3D printing of fine-grained aluminum alloys through extrusion-based additive manufacturing: Microstructure and property characterization

• A new extrusion-based solid-state metal additive manufacturing method was developed. • The new method enables direct deposition of fine-grained aluminum alloy without melting. • The new method uses off-the-shelf metal rods rather than pricy powders as feedstock. • The printing process was completed in an open-air environment, avoiding costly inert or vacuum conditions. • The printed 6061 aluminum alloys yield the strength and ductility comparable to wrought 6061 aluminum alloys. Additive manufacturing (AM) has the potential to transform manufacturing by enabling previously unthinkable products, digital inventory and delivery, and distributed manufacturing. Here we presented an extrusion-based metal AM method (refer to “SoftTouch” deposition in the filed patent) that is suitable for making the metal feedstock flowable prior to the deposition through dynamic recrystallization induced grain refinement at elevated temperatures. The flowable metal was extruded out of the printer head like a paste for building dense metal parts with fine equiaxed grains and wrought mechanical properties. Off-the-shelf metal rods were used as feedstock and the printing process was completed in an open-air environment, avoiding pricy powders and costly inert or vacuum conditions. The resulting multi-layer deposited 6061 aluminum alloys yield the strength and ductility comparable to wrought 6061 aluminum alloys after the same T6 heat treatment. The extrusion-based metal AM method can also be advanced as green manufacturing technologies for fabricating novel alloys and composites, adding novel features to existing parts, repairing damaged metal parts, and welding advanced metals for supporting sustainable manufacturing, in addition to being developed into a cost-effective manufacturing process for the fabrication of dense metal of complex structural forms.

Impact of process anneals on high-k/β-Ga2O3 interfaces and capacitance

Gallium oxide (β-Ga2O3) is becoming a popular material for high power electronic devices due to its wide bandgap and ease of processing. In this work, β-Ga2O3 substrates received various annealing treatments before atomic layer deposition of HfO2 and subsequent fabrication of metal–oxide–semiconductor (MOS) capacitors. Annealing of β-Ga2O3 with forming gas or nitrogen produced degraded capacitance–voltage (C–V) behavior compared to a β-Ga2O3 control sample with no annealing. A sample annealed with pure oxygen had improved C–V characteristics relative to the control sample, with a higher maximum capacitance and smaller flat-band voltage shift, indicating that oxygen annealing improved the C–V behavior. X-ray photoelectron spectroscopy also suggested a reduction in the oxygen vacancy concentration after O2 annealing at 450 °C, which supports the improved C–V characteristics and indicates that O2 annealing of β-Ga2O3 may lead to better MOS device performance.

Microstructure and high temperature properties of tungsten processed via electron beam melting additive manufacturing

There is considerable interest in the adoption of additive manufacturing for processing refractory metals. The layer-wise fabrication approach enables opportunities for producing complex geometries which cannot be otherwise be achieved via powder metallurgy. However, the processing science is still in its nascent stages and structure–property relations are relatively unexplored. Fundamental research is needed to further develop the technology and enable the fabrication of refractory metals for high temperature applications. Here we focus on the processing of pure tungsten using electron beam melting additive manufacturing. Experimentally we develop a suitable processing window for achieving high density crack free material. Microstructural analysis reveals that the microstructure generally consists of a columnar structure with a 111 build direction fiber preference, although, fiber switching was observed. Process induced deformation is believed to drive the formation of subgrains whose boundaries exhibit a high dislocation density. High temperature tensile testing reveals that the material exhibits excellent properties closer to that of annealed tungsten. Significant mechanical anisotropy was observed to be present which is likely driven by strong crystallographic texture.

Metal doped BiOCl nano-architectures (M-BiOCl, M = Ni, Mo, Cd, Co) for efficient visible light photocatalytic and antibacterial behaviour

Herein, we report the fabrication of well-crystalline metal (Ni, Mo, Cd and Co) doped BiOCl nanoscale photocatalytic material (M-BiOCl; M = Ni, Mo, Cd, and Co) by employing the solvothermal synthetic route. It was found that Ni doping results in remarkable improvement in photocatalytic and antibacterial behavior of BiOCl. The morphological investigation of typical samples by the FE-SEM revealed that undoped BiOCl shows closely stacked thick discs like morphology, while doping with different metals resulted into nanosheet (Ni, Cd), nanoflowers (Mo) and nanodiscs (Co) like morphologies. Interestingly, doping of Ni metal led to a substantial transformation into large size nanosheets with (010) prominent facet and increased surface area (41.927 m2/g) along with improved porous structure. Similarly, HR-TEM confirmed the formation of extended nanosheet like growth having dimensions ∼287.16 × 179.14 nm for Ni-BiOCl photocatalyst along with nano-pores morphology that might serve as active sites during photocatalysis or antibacterial activity. Moreover, the inclusion of Ni into BiOCl nanostructure brings the band gap (Eg) shifted to 2.85 eV from 3.54 eV (pure BiOCl), while all other metal doped nanostructure exhibited nearly similar Eg. Meanwhile, the photo-induced charge carriers recombination behaviour analysed by photoluminescence (PL) analysis shows diminished peak intensity for Ni-BiOCl as compared to pure BiOCl that can be directly correlated with minimum recombination of electron-hole during photocatalysis thus contributing for its excellent photocatalysis performance. In addition, we observed the excellent photocatalytic antibacterial activity of Ni-BiOCl against S. aureus bacteria under the visible light.

Homogeneous Metastable Hexagonal Phase Iridium Enhances Hydrogen Evolution Catalysis.

Catalytic reactions are surface-sensitive processes. Fabrication of homogeneous metastable metals can be used to promote phase-dependent catalytic performance; however, this has been a challenging task. Herein, homogeneous metastable hexagonal close-packed (hcp) Ir is epitaxially grown onto metastable phase hcp Ni, as demonstrated using spherical aberration electron microscopy. The as-fabricated metastable hcp Ir exhibits high intrinsic activity for the alkaline hydrogen evolution reaction (HER). In particular, metastable hcp Ir delivers a low overpotential of 17mV at 10mA cm-2 and presents a high specific activity of 8.55mA cm-2 and a high turnover frequency of 38.26 s-1 at -0.07V versus the reversible hydrogen electrode. Owing to its epitaxially grown structure, metastable hcp Ir is highly stable. Theoretical calculations reveal that metastable hcp Ir promotes H2 O adsorption and fast H2 O dissociation, which contributes to its remarkable HER activity. Findings can elucidate the crystal phase-controlled synthesis of advanced noble metal nanomaterials for the fundamental catalytic applications.

In Situ Fabrication of Metal–Organic Framework Thin Films with Enhanced Pervaporation Performance

AbstractThe intrinsic porosity in the periodic structures of metal–organic frameworks (MOFs) endows them with a great potential for membrane separation. However, facile fabrication of crystalline MOF membranes has been challenging and limited to few materials for economic and environmental considerations. Herein, a continuous Zr‐MOF thin film with a thickness of ≈180 nm has been fabricated via in situ recrystallization of MOF nanoparticles on the porous support under formic acid vapor. Owing to the inherent microporosity and the well‐established hydrophilicity during membrane fabrication, the MOF thin films exhibit excellent pervaporation performance with separation factors of 2630, 501 and fluxes of 1.45, 1.41 kg m−2 h−1) for n‐butanol dehydration and methanol/methyl tert‐butyl ether (MeOH/MTBE) separation, respectively. The structural stability of the film has been further confirmed by its steady performance in the 10‐day pervaporation test. This in situ recrystallization method induced by a trace amount of acid vapor with no extra ingredients opens a new avenue for the facile membrane fabrication of various MOF materials to feasibly realize their versatile potential as membrane materials.

Nanoimprint lithography-based replication techniques for fabrication of metal and polymer biomimetic nanostructures for biosensor surface functionalization

Nanostructuring is a promising and successful approach to tailor functional layers and to improve the characteristics of biosensors such as signal transmission and tighter cell-surface coupling. One of the major objectives in biosensing and tissue engineering is the development of interfaces that mimic the natural environment of biosystems composed of extracellular matrix biomolecules. Nevertheless, effective techniques to reconstruct the random distribution of these biomolecules are still not well established. For this reason, the presented work demonstrates different methods based on nanoimprint lithography to replicate randomly distributed natural nanostructures with complex geometries into different polymers and metals. The fidelity of the replicated nanostructures has been evaluated by atomic force microscopy and the attributes of the fabrication processes have been discussed. Finally, different replication techniques have been combined for the biomimetic nanostructuring of the dielectric passivation layer as well the metal electrode surface to develop novel whole-surface-nanostructured microelectrode arrays.

High Performance H2−Mn Regenerative Fuel Cells through an Improved Positive Electrode Morphology

The effective scaling-up of redox flow batteries (RFBs) can be facilitated upon lowering the capital costs. The application of ubiquitous manganese along with hydrogen (known as H2−Mn regenerative fuel cells (RFC)) is seen as an effective solution for this purpose. Here, we aim to evaluate different positive electrodes so as to improve the key performance metrics of the H2/Mn RFC, namely electrolyte utilization, energy efficiency, and peak power densities. Commercially available carbon paper and graphite felt are used to show that the latter provides better key performance indicators (KPIs), which is consistent with the results reported for standard all-vanadium RFBs in the literature. Even better KPIs are obtained when an in-house carbon catalyst layer (CCL) is employed in combination with graphite felt electrodes (e.g., more than 80% energy efficiency, >0.5 W cm−2 peak power density and electrolyte utilization of 20 Ah L−1 for felt and carbon metal fabric (CMF), prepared by means of electrospinning and carbonization, in comparison with about 75% energy efficiency 0.45 W cm−2 peak power density and 11 Ah L−1 electrolyte utilization for felt on its own). It is envisaged that if the electrochemical performance of CCLs can be optimized then it could open up new opportunities for the commercial exploitation of H2−Mn systems.

Friction Behavior between Carbon Fiber Plain Weave and Metal Semi-Cylinder Tool

The deformations that occur during composite forming processes are governed by the friction between the fabrics and tooling material on the mesoscopic level. The effect of normal load and multi-plies on the frictional behavior of the carbon plain weave is investigated by simulating the friction between the fabric and metal semi-cylinder tool by using the experimental method. The periodic wavy friction-displacement curve between the metal tool and fabric is caused by the interwoven structure of the fabric. Both the increase in the normal load and the number of layers cause an increase in the real contact area during friction, leading to an increase in the friction force. The real contact area is calculated based on the Hertzian contact model and the self-designed testing method. The friction force values obtained from multiplying the real contact area with shear strength are closely aligned with the measured results.

Centimeter-Scale Two-Dimensional Metallenes for High-Efficiency Electrocatalysis and Sensing

Two-dimensional (2D) metals have received considerable attention in recent years because of their fascinating physical and chemical properties, as well as potential applications in electrocatalysis, sensors, plasmonics, etc. However, the fabrication of 2D metals, especially atomically thin ones with large lateral size, remains a significant challenge because of the strong and isotropic metallic bonds. Here, we use Pt as a model system and demonstrate a general way to fabricate freestanding, high-quality 2D metals with giant aspect ratios (as large as ∼107) and controllable thickness down to 1 nm via a combination of room-temperature physical deposition and chemical etching. The cool deposition could suppress the Volmer–Webber growth mode, resulting in the formation of continuous ultrathin Pt with smooth surface and high conductivity. Moreover, the ultrathin 2D Pt exhibit outstanding hydrogen evolution reaction activity with a mass activity of 8.06 mA μg–1 at 0.06 V, ∼18 times higher than that of the commercial Pt/C catalyst. Additionally, the freestanding Pt-based strain sensor exhibits a high gauge factor of up to ∼4643, which is 3 orders of magnitude higher than that of conventional constantan wire-based strain gauges. Our studies pave the way for further developing wafer-scale 2D metal-based devices for various applications.