High-quality Metal Research Articles

Continuous synthesis of high quality metal–organic framework HKUST-1 crystals and composites via aerosol-assisted synthesis

Highly crystalline metal–organic framework (MOF) crystals are desirable for their practical applications and synthesized predominantly using batch processes that are less scalable. More scalable continuous processes for MOF synthesis such as spray-drying and aerosol-assisted synthesis have been recently developed. However, these techniques often resulted in poorly crystalline nanoparticles and their assemblies primarily due to extremely short (sub-second) crystallization time and fast solvent evaporation. Here we report facile continuous aerosol-assisted production of highly crystalline HKUST-1 crystals with relatively narrow size distributions as well as their composites with both inorganic and organic materials exhibiting unique microstructures. Solvents with high donor numbers and low vapor pressures were found desirable to increase both crystallization and solvent evaporation times. Dimethyl sulfoxide (DMSO) was used as a co-solvent with DMF to form phase-pure high quality HKUST-1 crystals revealed by SEM, XRD, and N2 adsorption. Furthermore, alumina nanoparticles and polyethersulfone (PES) polymer were incorporated to create unique microstructures.

Fabrication of ultrathin low-voltage-driven printed organic circuits with anodized gate islands

Abstract Anodization of gate metals can form thin and robust oxide dielectrics of low-voltage-driven organic thin-film transistors (TFTs) for low-cost, flexible electronics. However, anodic oxide dielectrics have rarely been applied to circuit fabrication with complex layouts because separate gate electrode islands cannot be anodized at the same time. To overcome this limitation, we devise a method to simultaneously anodize multiple aluminum gate islands using removable interconnects. The anodic oxide properties, including dielectric constant, film thickness, and leakage current, were thoroughly investigated by varying anodization voltages from 5 to 50 V and a self-assembled monolayer treatment. By printing p-type polymer ink on top of the pattern-grown anodic oxide dielectrics, p-type organic TFTs were fabricated on a 2-μm-thick Parylene substrate. The printed TFTs exhibited subthreshold swing of 200 mV·dec−1, carrier mobility of 0.3 cm2 V−1 s−1, and threshold voltage of 0.17 V on average. Even when the substrate film was crumpled, the TFT characteristics did not substantially changed. Finally, a 3 V differential amplifier with multiple gate islands was successfully demonstrated. These findings suggest that high-quality anodic metal oxide films, when fully incorporated into a low-cost, large-area manufacturing process, can be applied to the fabrication of complex, low-voltage-driven TFT circuits on flexible substrates.

Study of Electrical Behavior of Metal‐Semiconductor Contacts on Exfoliated MoS2 Flakes

While 2D materials have been investigated for their potential applications in nanoelectronic and optoelectronic devices, their functionality is still not fully explored due to lack of proper understanding of metal contacts on these materials. The present work pertains to the study of electrical behavior of different metals such as chromium, silver, nickel, and platinum deposited on to exfoliated MoS2 flakes. Comparative study of different metal contacts to MoS2 shows that Ag/Au exhibits good ohmic behavior with high current injection efficiency and better linearity and symmetry of I–V curves than Cr/Au and Ni/Au contacts. Specific contact resistivity is measured to be 4.54 × 10−4 Ω cm2 using transmission line measurement (TLM) for Ag/MoS2 contacts. Further, taking Ag/Au as ohmic contact, Pt/MoS2 Schottky barrier diode is fabricated with a high rectification ratio of about 900. Barrier height and ideality factor of 0.56 eV and 2.1, respectively are obtained. This study opens up the possibility of having high quality metal contacts on MoS2 with potential applications in nanoscale devices.

Halide-Directed Synthesis of Square Prismatic Ag Nanocrystals by the Polyol Method

Achieving shape control of high-quality metal nanocrystals is a critical challenge in the fabrication of bottom-up plasmonic materials. Here, we synthesize a uniquely anisotropic Ag nanocrystal shape using a modified polyol method. Single-crystalline Ag square prism nanocrystals, which possess two square facets and four rectangular facets, with uniform size distributions and a high yield (≤96%) are generated by the controlled addition of Br– anions during the nucleation and growth process. Br– acts as a reshaping agent for the generation of single-crystalline seed nanoparticles that direct subsequent anisotropic growth in the ⟨100⟩ direction. Nanocrystal growth and shape development are monitored through optical absorption spectroscopy, which reveals the localized surface plasmon resonances of the square prisms. Electrodynamic simulations indicate strong near-field enhancement associated with the high aspect ratio shape and the potential application of these nanocrystals as optical nanoantenna in plasmonic platforms, such as surface-enhanced Raman spectroscopy sensors and optoelectronic junctions.

Detonation spraying behaviour of refractory metals: Case studies for Mo and Ta-based powders

In thermal spraying of refractory metal powders, two major issues need to be solved: particles of materials having high melting temperatures should be heated to reach a semi-molten/molten state or temperatures close to the melting point, while oxidation of the metals should be prevented. It has long been believed that it is rather difficult, if not impossible, to produce high-quality refractory metal coatings by detonation spraying. In this work, we demonstrated the capability of the detonation spraying method to produce tantalum-based and molybdenum coatings of low porosity. Using a computer-controlled detonation spray (CCDS2000) facility, the detonation spraying behaviour of a molybdenum powder and a partially oxidized tantalum powder was studied. Spraying was conducted onto steel substrates using an acetylene-oxygen mixture with O2/C2H2 = 1.1. The spraying process was studied by means of analyzing the splat morphology and calculating the particle temperatures and velocities. According to the X-ray diffraction phase analysis, the metals did not experience oxidation during the deposition. Rather, partial reduction of the oxide phase contained in the Ta-based powder occurred during spraying.

Cu/Cu Barrier Interconnect with Low Resistivity for the Application to the Next-Generation and High-Resolution Display Fabricated Using Microwave-Assisted Sputter

Displays with large size and high resolution are required in many electronic devices such as mobile phones, notebooks, and televisions. In recent times, 8k ultra-high-definition (UHD) display which will be the standards of next-generation display has been developed. While the demand for displays with high-pixel-density is increasing, it is difficult to increase the resolution because of resistor-capacitor (RC) delay issue. The resistance is increased with the display size due to the length of metal lines. When the resolution is increased, the capacitance of metal lines is also increased because of the number of crossings of metal lines. The meaning of RC delay is the signal delay through the circuit wiring as a result of resistance and capacitance effects. This increase induces the severe electrical loads on the gate and data lines. Therefore, controlling these two effects is the major challenge in making high-resolution display. To minimize the effect of the RC delay, many researchers have been studied the variety of materials which can be used in a metal interconnect lines. There are lots of materials such as Al, Mo, W, Cu, and Ti. Among these materials, copper is the most suitable candidate because it has lower resistivity than aluminum, which has been used as conventional interconnect material. Using a material with low resistivity like copper can reduce the RC delay, in other words, increase the electrical signal speed through the metal lines. Although the copper has a resistivity of 1.7 μΩ∙cm, it shows 2.1 ~ 2.3 μΩ∙cm within the thickness of 1 μm when deposited using DC/RF sputtering method. This is due to the fact that it is difficult to deposit high-quality copper film by using the conventional sputtering method. To overcome these problems, we employed microwave-assisted sputter (MWA sputter), providing high-quality copper films having the resistivity of 1.95 μΩ∙cm within the thickness of 1 μm even after formation of the metal lines. The MWA sputtering is an enhanced sputtering method using electron cyclotron resonance (ECR) phenomenon with the induction of microwave into the DC magnetron sputtering. The MWA sputtering has the advantage of generating highly ionized plasma, having low discharge voltage and low working pressure. Therefore, we can deposit high quality copper film by using MWA sputtering, enabling the reducing RC delay for next-generation display. However, when we deposit copper, the barrier metal is always needed because the copper can easily diffuse into adjacent materials. Unless suitable barrier material is used, it can be cause of degradation of device performance. For these reasons, we fabricated Cu/Cu barrier interconnect as a source/drain electrode and observed various properties including calculation of resistivity. In this study, we report a study of properties of copper film deposited by DC sputtering and MWA sputtering using scanning electron microscope (SEM), x-ray diffraction spectroscopy (XRD) and atomic force microscope (AFM). The film stress was calculated before and after the formation of the Cu/Cu barrier metal line because film stress is an important parameter when fabricating electronic devices. Mo and Mo-Ti alloy was used as the copper barrier metal and we developed wet etching condition of Cu/Cu barrier interconnect. After the etching process, we measured etching profile using SEM cross-section image and calculate taper angle. Consequently, we obtained resistivity of Cu/Cu barrier interconnect deposited by DC sputtering and MWA sputtering, respectively. It revealed that Cu/Cu barrier interconnect deposited by MWA sputtering shows the lower resistivity than by DC sputtering. From the experimental results, we confirmed that MWA sputtering method makes it possible to deposit high quality metal films with low resistivity, which gives new opportunities for the design and realization of next-generation displays. Reference [1] Y. Goh, J. Ahn, J.R. Lee, W.W. Park, S.-H K Park and S Jeon. ACS Appl. Mater. Interfaces., 2017, 9 (42), pp 36962-36970

Downcycling in automobile recycling process: A thermodynamic assessment

Current metal recycling techniques for end-of-life vehicles (ELV) are based on mechanical treatments to mainly recover steel, aluminum, copper, and zinc alloys. Such techniques facilitate compliance with the ELV European Directive (2000/53/EC) target of achieving recyclability quotes of up to 85%. However, a vehicle can use more than 60 metals, some of them considered critical by international institutions, which end up downcycled as part of alloys or ultimately in landfills. This paper undertakes an assessment of the downcycling degree of minor metals in conventional vehicles using a SEAT Leon III model as a case study. Downcycling is assessed from a thermodynamic point of view using thermodynamic rarity, an indicator that is used as a weighting factor for the metals used in the car. The thermodynamic rarity of metals is a function of the quality of the minerals from which they stem, considering their relative abundance in Nature and the energy intensity required to extract and process them. The results demonstrated that, even if the quantity of downcycled metals only represents 4.5% of the total metal weight of the vehicle, in rarity terms, this figure increases to approximately 27%. This indicates that an important portion of high-quality metals becomes functionally lost. The most downcycled vehicle subsystems are in order: (1) accessories, (2) electrical and electronic equipment, (3) exhaust system, and (4) engine. Further, the most downcycled parts are: speed sensor, control unit, antenna amplifier, airbag circuit, temperature and rain sensors, front pipe, particle filter, and turbo parts.

Laser induced breakdown spectroscopy for multielement analysis of powdered materials used in additive technologies

ABSTRACTAdditive manufacturing technologies utilizing metal parts production with layer by layer printing are of high demand for different fields of science and technology. Analytical chemistry is challenged to provide multielemental quantitative analysis of any metal powders within a few minutes and onsite to fulfil the requirements for high quality metal parts production. Powder materials utilized in additive technologies were quantitatively analyzed by laser induced breakdown spectroscopy for the first time. Laser induced breakdown spectroscopy mapping of loose metal powder attached to the double-sided adhesive tape provided high reproducibility of measurements even for powder mixtures with large difference of particles densities (tungsten carbide particles in nickel alloy powder). Laser induced breakdown spectroscopy analytical capabilities were estimated for tungsten and carbon analysis by calibration curve construction and accuracy estimation by leave-one-out cross-validation procedure. Laser induced breakdown spectroscopy and X-ray fluorescence spectroscopy techniques comparison revealed better results for laser induced breakdown spectroscopy analysis. Improved accuracy of analysis and capability to quantify light elements (carbon, etc.) demonstrated the potential of laser induced breakdown spectroscopy as a promising technique for express onsite multielement analysis of powder materials utilized in additive technologies.

Import Substitution in Medicine on the Basis of Russian Precision Alloys

The possibility of import substitution by using Russian precision alloys developed at Bardin Central Research Institute of Ferrous Metallurgy in medical applications is considered. In many cases, Russian products outperform their imported counterparts. In practice, import substitution will call for close cooperation of Russian producers of medical equipment with the developers and manufacturers of high-quality metals.

Fundamentals and Prospects of the Development of Reduction Steelmaking

The laws of direct iron reduction by solid carbon are revealed. They open up fresh opportunities for the development of high-tech processes and the manufacture of high-purity and high-quality metal products at a substantial decrease in the gas yield and gas release to atmosphere. The existing (traditional and new) metallurgical technologies are based on the use of hot reducing gases (HRGs) according to the generally accepted scientific basis of an autocatalytic-adsorption mechanism. The use of the HRG potential at a level of 0.4–0.42 corresponds to HRG consumption of 2500–3000 m3/t per unit metal. The gas release to atmosphere is significant for such high HRG consumption, which complicates the worldwide ecological problem.

Large-Area Direct Laser-Shock Imprinting of a 3D Biomimic Hierarchical Metal Surface for Triboelectric Nanogenerators.

Ongoing efforts in triboelectric nanogenerators (TENGs) focus on enhancing power generation, but obstacles concerning the economical and cost-effective production of TENGs continue to prevail. Micro-/nanostructure engineering of polymer surfaces has been dominantly utilized for boosting the contact triboelectrification, with deposited metal electrodes for collecting the scavenged energy. Nevertheless, this state-of-the-art approach is limited by the vague potential for producing 3D hierarchical surface structures with conformable coverage of high-quality metal. Laser-shock imprinting (LSI) is emerging as a potentially scalable approach for directly surface patterning of a wide range of metals with 3D nanoscale structures by design, benefiting from the ultrahigh-strain-rate forming process. Here, a TENG device is demonstrated with LSI-processed biomimetic hierarchically structured metal electrodes for efficient harvesting of water-drop energy in the environment. Mimicking and transferring hierarchical microstructures from natural templates, such as leaves, into these water-TENG devices is effective regarding repelling water drops from the device surface, since surface hydrophobicity from these biomicrostructures maximizes the TENG output. Among various leaves' microstructures, hierarchical microstructures from dried bamboo leaves are preferable regarding maximizing power output, which is attributed to their unique structures, containing both dense nanostructures and microscale features, compared with other types of leaves. Also, the triboelectric output is significantly improved by closely mimicking the hydrophobic nature of the leaves in the LSI-processed metal surface after functionalizing it with low-surface-energy self-assembled-monolayers. The approach opens doors to new manufacturable TENG technologies for economically feasible and ecologically friendly production of functional devices with directly patterned 3D biomimic metallic surfaces in energy, electronics, and sensor applications.

Low temperature and rapid formation of high quality metal oxide thin film via a hydroxide-assisted energy conservation strategy

We develop a universal hydroxide-assisted strategy for the low thermal budget efficient fabrication of high quality metal oxide thin films.

Numerical and experimental analysis of product development by composite metal foil manufacturing

The paper presents a new additive manufacturing process for the production of high quality metal parts and is termed as composite metal foil manufacturing (CMFM). It is a blend of laminated object manufacturing (LOM) and soldering/brazing strategies. A calculated model of a machine in view of the new process has been outlined and its parts accepted for usefulness either by experimentation or recreations. The product development has two stages – the principles of LOM for cutting and stacking of foils and brazing for joining. The process consists of a fibre laser to cut the metal foils, a paste dispenser for depositing the paste, a roller to make the paste of layer between the foils smooth, two thickness sensors to measure the thickness of the part being built and two heated plates to apply heat to the part. In this paper, results of investigations on the sub-processes; laser cutting, final joining and transient thermal analysis are shown.

Numerical and experimental analysis of product development by composite metal foil manufacturing

The paper presents a new additive manufacturing process for the production of high quality metal parts and is termed as composite metal foil manufacturing (CMFM). It is a blend of laminated object manufacturing (LOM) and soldering/brazing strategies. A calculated model of a machine in view of the new process has been outlined and its parts accepted for usefulness either by experimentation or recreations. The product development has two stages – the principles of LOM for cutting and stacking of foils and brazing for joining. The process consists of a fibre laser to cut the metal foils, a paste dispenser for depositing the paste, a roller to make the paste of layer between the foils smooth, two thickness sensors to measure the thickness of the part being built and two heated plates to apply heat to the part. In this paper, results of investigations on the sub-processes; laser cutting, final joining and transient thermal analysis are shown.

Extremely flat metal films implemented by surface roughness transfer for flexible electronics.

We present an innovative approach to fabricate an extremely flat (EF) metal film which was done by depositing metal on an extremely flat mother substrate, then detaching the metal from the substrate. The detached flexible metal films had a roughness that was within 2% of the roughness of the mother substrate, so EFs with Ra < 1 nm could be fabricated using the surface roughness transfer method. With quantitative analysis using in situ synchrotron XPS, it was concluded that the chemical reaction of oxygen atoms with the metal film played a critical role in designing a peel-off system to get extremely flat metal films from the mother substrate. The OLED was successfully implemented on the metal film. The OLED's luminance could be increased from 15 142 to 17 100 cd m−2 at 25 mA m−2 by replacing the glass substrate with an EF copper (Cu) substrate, due to the enhanced heat dissipation during the operation. This novel method can be very useful for mass production of large scale, low-cost and high quality metal films using roll-to-roll process.

Catalytic metal-induced crystallization of sol–gel metal oxides for high-efficiency flexible perovskite solar cells

A novel c-MIC mechanism is discovered, enabling solution-based fabrication of high-quality metal oxide films at low temperatures.

Control of Ga-oxide interlayer growth and Ga diffusion in SiO2/GaN stacks for high-quality GaN-based metal–oxide–semiconductor devices with improved gate dielectric reliability

A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal–oxide–semiconductor (MOS) devices was developed. The direct chemical vapor deposition of SiO2 films on GaN substrates forming Ga-oxide interlayers was carried out to fabricate SiO2/GaOx/GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state densities below 1010 cm−2 eV−1 were obtained by postdeposition annealing, Ga diffusion into overlying SiO2 layers severely degraded the dielectric breakdown characteristics. However, this problem was found to be solved by rapid thermal processing, leading to the superior performance of the GaN-MOS devices in terms of interface quality, insulating property, and gate dielectric reliability.

Particle size characterisation of metals powders for Additive Manufacturing using a microwave sensor

The production of high-value and high-quality metal parts with complex interior structures is enabled by the use of Additive Manufacturing (AM) techniques, which use metal powders with repeatable characteristics. Of these characteristics, particle size distribution is a key factor. This paper describes a particle size sensor based on a microwave cavity. It works on the principle that the magnetic permeability of metallic powders at microwave frequencies depends strongly on the particle size distribution of the powder owing to the classical skin effect. The sensor's capability is demonstrated by measurement of the permeability of a range of Ti6Al4V alloy powders with different particle size distributions. Permeability is shown to be congruent generally with the existing theory. The reduced imaginary permeability compared with the theoretical case observed for larger particle sizes is shown to be consistent with simulation. The method is also demonstrated to be highly precise, able to detect changes of <0.1μm for particles of average radii of approximately 11.7μm. Increases in sensitivity are possible by optimising the sensor design so that it operates in the regime where the permeability changes most rapidly as a function of particle size.

Ultrafast laser-enabled 3D metal printing: A solution to fabricate arbitrary submicron metal structures

3D metal printing has become one of the critical manufacturing methods in recent years that enables a variety of applications across different disciplines, e.g. aerospace and medicine. In this work, we present a high-throughput 3D metal printing method based on a programmable femtosecond light sheet and electrodeposition, achieving submicron resolution in both lateral and axial directions. The light sheet, for parallel material removal, is generated by spatially and temporally focusing the ultrafast laser in the processing plane, which is in conjugation with a digital micromirror device (DMD), thereby allowing fast pattern generation in synchronization with laser pulses. High quality metal layers are formed successively via electrodeposition processes. Accordingly, 3D metal printing is realized by repeating the steps of (1) forming structural/sacrificial layers; and (2) laser micromachining. In the experiments, we demonstrate fast metal printing of various complex 3D structures within tens of laser pulses over an area of 100×60μm2. Compared with the existing sequential metal printing techniques, the new method has substantially improved both the throughput and resolution by a factor of ∼100 times.

Shape-Uniform, High-Quality Monolayered MoS2 Crystals for Gate-Tunable Photoluminescence.

Two-dimensional molybdenum disulfide (MoS2) has recently drawn major attention due to its promising applications in electronics and optoelectronics. Chemical vapor deposition (CVD) is a scalable method to produce large-area MoS2 monolayers, yet it is challenging to achieve shape-uniform, high-quality monolayered MoS2 grains as random, diverse crystallographic orientations and various shapes are produced in the same CVD process. Here, we report the growth of high-quality MoS2 monolayers with uniform triangular shapes dominating (up to 89%) over other shapes on both SiO2/Si and sapphire substrates. The new confined-space CVD process prevents contamination and helps regulate the Mo/S ratio during the deposition. The as-grown triangular MoS2 monolayers exhibit grain sizes up to 150 μm and possess better crystalline properties and lighter n-type doping concentration than those of the monolayers grown by common CVD methods. The corresponding field effect transistor devices show high electron mobilities of 50-60 cm2 V-1 s-1 and positive threshold voltages of 21-35 V. This mild n-type behavior makes it possible to regulate the formation of excitons by back-gate voltage due to the interaction of excitons with free charge carriers in the MoS2 channel. As a result, gate-tunable photoluminescence (PL) effect, which is rarely achievable for MoS2 samples prepared by common CVD or mechanical exfoliation, is demonstrated. This study provides a simple versatile approach to fabricating monolayered crystals of MoS2 and other high-quality transition metal dichalcogenides and could lead to new optoelectronic devices based on gate-tunable PL effect.