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Influence of heat treatment on microstructure, mechanical and corrosion behavior of WE43 alloy fabricated by laser-beam powder bed fusion

Magnesium (Mg) alloys are considered to be a new generation of revolutionary medical metals. Laser-beam powder bed fusion (PBF-LB) is suitable for fabricating metal implants with personalized and complicated structures. However, the as-built part usually exhibits undesirable microstructure and unsatisfactory performance. In this work, WE43 parts were firstly fabricated by PBF-LB and then subjected to heat treatment. Although a high densification rate of 99.91% was achieved using suitable processes, the as-built parts exhibited anisotropic and layered microstructure with heterogeneously precipitated Nd-rich intermetallic. After heat treatment, fine and nano-scaled Mg24Y5 particles were precipitated. Meanwhile, the α-Mg grains underwent recrystallization and turned coarsened slightly, which effectively weakened the texture intensity and reduced the anisotropy. As a consequence, the yield strength and ultimate tensile strength were significantly improved to (250.2  ± 3.5)  MPa and (312  ± 3.7)  MPa, respectively, while the elongation was still maintained at a high level of 15.2%. Furthermore, the homogenized microstructure reduced the tendency of localized corrosion and favored the development of uniform passivation film. Thus, the degradation rate of WE43 parts was decreased by an order of magnitude. Besides, in-vitro cell experiments proved their favorable biocompatibility.

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Towards a new avenue for rapid synthesis of electrocatalytic electrodes via laser-induced hydrothermal reaction for water splitting

Abstract Electrochemical production of hydrogen from water requires the development of electrocatalysts that are active, stable, and low-cost for water splitting. In comparison with conventional powder-based electrode preparation, synthesis of binder-free electrocatalytic integrated electrodes is highly desirable to improve the catalytic activity and long-term stability for large-scale applications of electrocatalysts. Herein, we demonstrate a laser-induced hydrothermal (LIHR) technique to grow NiMoO4 nanosheets on Nickel foam, which is then calcined under H2/Ar mixed gases to prepare the integrated electrode IE-NiMo-LR. This electrode exhibits superior hydrogen evolution reaction performance, requiring overpotentials of 59, 116 and 143 mV to achieve current densities of 100, 500 and 1000 mA cm-2. During the 350 h chronopotentiometry test at current densities of 100 and 500 mA cm-2, the overpotential remained essentially unchanged. In addition, NiFe-layered double hydroxide grown on Ni foam is fabricated with same LIHR method and coupled with IE-NiMo-IR to achieve water splitting. This combination exhibits excellent durability under industrial current density. The energy consumption and production efficiency of LIHR method are systematically compared with conventional hydrothermal method. The LIHR method significantly improved the production rate by over 19 times, while consuming only 27.78% of the total energy required by conventional hydrothermal method to achieve the same production.

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A brief review on the recent development of phonon engineering and manipulation at nanoscales

Phonons are the quantum mechanical descriptions of vibrational modes that manifest themselves in many physical properties of condensed matter systems. As the size of electronic devices continues to decrease below mean free paths of acoustic phonons, the engineering of phonon spectra at the nanoscale becomes an important topic. Phonon manipulation allows for active control and management of heat flow, enabling functions such as regulated heat transport. At the same time, phonon transmission, as a novel signal transmission method, holds great potential to revolutionize modern industry like microelectronics technology, and boasts wide-ranging applications. Unlike fermions such as electrons, polarity regulation is difficult to act on phonons as bosons, making the development of effective phonon modulation methods a daunting task. This work reviews the development of phonon engineering and strategies of phonon manipulation at different scales, reports the latest research progress of nanophononic devices such as thermal rectifiers, thermal transistors, thermal memories, and thermoelectric devices, and analyzes the phonon transport mechanisms involved. Lastly, we survey feasible perspectives and research directions of phonon engineering. Thermoelectric analogies, external field regulation, and acousto-optic co-optimization are expected to become future research hotspots.

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Near-zero-adhesion-enabled intact wafer-scale resist-transfer printing for high-fidelity nanofabrication on arbitrary substrates

Abstract To meet the fast-growing need for broad applications in nanoelectronics, nanophotonics, and flexible optoelectronics, novel processes that can integrate different functional nanostructures onto specific substrates are urgently desired. Existing direct-lithography methods are difficult to use on flexible, nonplanar, and biocompatible surfaces. Therefore, fabrication is usually accomplished by nanotransfer printing. However, large-scale integration of multiscale nanostructures on unconventional substrates is challenging because the fabrication yield and quality are often limited by the resolution, uniformity, adhesivity, and integrity of the nanostructures formed via direct transfer. We propose a resist-based transfer strategy enabled by near-zero adhesion, which we achieved by molecular modification to attain a critical surface energy interval. This approach enabled the intact transfer of wafer-scale, ultrathin-resist nanofilms onto arbitrary substrates with mitigated cracking and wrinkling, thereby facilitating the in-situ fabrication of nanostructures for functional devices. Based on this approach, 3D-stacked multilayer structures with enhanced functionalities, nanoplasmonic structures with ~10-nm resolution, and MoS2-based devices with excellent performance were demonstrated on specific substrates. Collectively, this demonstrated the high stability, reliability, and throughput of our strategy for optical and electronic-device applications.

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Oxygen vacancy boosting Fenton reaction in bone scaffold towards fighting bacterial infection

Abstract Bacterial infection is the major issue after artificial bone transplantation due to the absence of antibacterial function of bone scaffold, which seriously causes the transplant failure and even amputation in severe cases. In this study, oxygen vacancy defects Fe-doped TiO2 (OV-FeTiO2) nanoparticles were synthesized by nano TiO2 and Fe3O4 via high-energy ball milling, which was then incorporated into polycaprolactone/polyglycolic acid (PCLGA) biodegradable polymer matrix to construct composite bone scaffold with good antibacterial activities by selective laser sintering (SLS). The results indicated that oxygen vacancy (OV) defects were introduced into the core/shell-structured OV-FeTiO2 nanoparticles through multiple welding and breaking during the high-energy ball milling, which facilitated the adsorption of hydrogen peroxide (H2O2) in the bacterial infection microenvironment at the bone transplant site. The accumulated H2O2 could amplify the Fenton reaction efficiency to induce more hydroxyl radicals (·OH), thereby resulting in more bacterial deaths through ·OH-mediated oxidative damage. This antibacterial strategy had more effective broad-spectrum antibacterial properties against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). In addition, the PCLGA/OV-FeTiO2 scaffold possessed mechanical properties that match those of human cancellous bone and good biocompatibility including cell attachment, proliferation and osteogenic differentiation.

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Characterization, preparation, and reuse of metallic powders for laser powder bed fusion: a review

Laser powder bed fusion (L-PBF) has attracted significant attention in both the industry and academic fields since its inception, providing unprecedented advantages to fabricate complex-shaped metallic components. The printing quality and performance of L-PBF alloys are influenced by numerous variables consisting of feedstock powders, manufacturing process, and post-treatment. As the starting materials, metallic powders play a critical role in influencing the fabrication cost, printing consistency, and properties. Given their deterministic roles, the present review aims to retrospect the recent progress on metallic powders for L-PBF including characterization, preparation, and reuse. The powder characterization mainly serves for printing consistency while powder preparation and reuse are introduced to reduce the fabrication costs. Various powder characterization and preparation methods are presented in the beginning by analyzing the measurement principles, advantages, and limitations. Subsequently, the effect of powder reuse on the powder characteristics and mechanical performance of L-PBF parts is analyzed, focusing on steels, nickel-based superalloys, titanium and titanium alloys, and aluminum alloys. The evolution trends of powders and L-PBF parts vary depending on specific alloy systems, which makes the proposal of a unified reuse protocol infeasible. Finally, perspectives are presented to cater to the increased applications of L-PBF technologies for future investigations. The present state-of-the-art work can pave the way for the broad industrial applications of L-PBF by enhancing printing consistency and reducing the total costs from the perspective of powders.

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Advances in memristor based artificial neuron fabrication-materials, models, and applications

Spiking neural network (SNN), widely known as the third-generation neural network, has been frequently investigated due to its excellent spatiotemporal information processing capability, high biological plausibility, and low energy consumption characteristics. Analogous to the working mechanism of human brain, the SNN system transmits information through the spiking action of neurons. Therefore, artificial neurons are critical building blocks for constructing SNN in hardware. Memristors are drawing growing attention due to low consumption, high speed, and nonlinearity characteristics, which are recently introduced to mimic the functions of biological neurons. Researchers have proposed multifarious memristive materials including organic materials, inorganic materials, or even two-dimensional materials. Taking advantage of the unique electrical behavior of these materials, several neuron models are successfully implemented, such as Hodgkin–Huxley model, leaky integrate-and-fire model and integrate-and-fire model. In this review, the recent reports of artificial neurons based on memristive devices are discussed. In addition, we highlight the models and applications through combining artificial neuronal devices with sensors or other electronic devices. Finally, the future challenges and outlooks of memristor-based artificial neurons are discussed, and the development of hardware implementation of brain-like intelligence system based on SNN is also prospected.

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