We present the successful synthesis and characterization of a one-dimensional high-entropy oxide (1D-HEO) exhibiting nanoribbon morphology. These 1D-HEO nanoribbons exhibit high structural stability at elevated temperatures (to 1000°C), elevated pressures (to 12 gigapascals), and long exposure to harsh acid or base chemical environments. Moreover, they exhibit notable mechanical properties, with an excellent modulus of resilience reaching 40 megajoules per cubic meter. High-pressure experiments reveal an intriguing transformation of the 1D-HEO nanoribbons from orthorhombic to cubic structures at 15 gigapascals followed by the formation of fully amorphous HEOs above 30 gigapascals, which are recoverable to ambient conditions. These transformations introduce additional entropy (structural disorder) besides configurational entropy. This finding offers a way to create low-dimensional, resilient, and high-entropy materials.

In this study, Cu/Ni and Cu/Al multilayers, with individual layer thickness varying from 25 nm to 200 nm, and co-sputtered Cu-Ni and Cu-Al single layer films were deposited at room temperature via magnetron sputtering and further annealed from 100 °C to 300 °C. The mechanical and microstructural properties of the as-deposited and annealed samples were characterized by nanoindentation, x-ray diffraction, and scanning electron microscopy. Both multilayer systems exhibit an increase in hardness with increasing annealing temperature. However, the Cu/Ni system shows a gradual and moderate hardness increase (up to 30%) from room temperature to 300 °C, while the Cu/Al system displays a sharp hardness surge (~150%) between 125 °C and 200 °C. The co-sputtered Cu-Ni and Cu-Al samples consistently demonstrate higher hardness than their multilayered counterparts, albeit with distinctly different temperature dependence—the hardness of Cu-Ni increases with annealing temperature while Cu-Al maintains a constant high hardness throughout the entire temperature range. The distinct thermal strengthening mechanisms observed in the two metallic multilayer systems can be ascribed to the formation of solid solutions in Cu/Ni and the precipitation of intermetallic phases in Cu/Al. This study highlights the unique advantage of intermetallic strengthening in metallic multilayer systems.

Strong thermal effect on microstructure and mechanical properties of Ti/Ni multilayer thin films was observed from in situ heating during deposition and subsequent annealing. Films deposited at low-temperature show preferred crystallographic texture for both Ti and Ni layers, with columnar structure extending through the layers. The columnar structure becomes more distinct and complete with the increase of temperature up to 300(degrees)C, and meanwhile, more atomic diffusion and intermixing occur along the Ti/Ni interfaces, promoting the formation of Ti-Ni intermetallic precipitates. High-temperature deposition causes disintegration of the layered structure. Columnar Ti-Ni alloys and further recrystallized alloys were detected with the preferred crystallographic texture. For material strength, an increased hardness trend was observed with increasing deposition temperature even with much larger grain size compared to room temperature case. Furthermore, for multilayer systems deposited under low temperature, post-annealing resulted in higher hardness with minimal microstructure modification, with more strengthening observed in lower deposition temperature case.

Additive manufacturing (AM) has emerged as a crucial technology in recent decades, particularly within the aerospace industry. However, the thermally cyclic nature of these processes introduces significant variations and defects in microstructure, which can adversely affect final part performance and hinder the widespread adoption of the technology. Traditionally, characterization of AM parts has relied on conventional bulk testing methods, which involve analyzing many samples to gather sufficient data for statistical analysis. Unfortunately, these methods are unable to account for local nanoscale variations in material properties caused by the microstructure, as they measure a single averaged property for each tested sample. In this work, we use AM Inconel 718 as a model system in developing a novel approach to correlate nanomechanical properties obtained through nanoindentation with microstructure obtained through electron backscatter diffraction (EBSD). By associating mechanical properties obtained from each indent with the corresponding crystallographic direction, we calculate the weighted average hardness and modulus for each orientation. This enables us to generate inverse pole figure maps depicting the relationship between mechanical properties and crystallographic direction. Our method yields results in good agreement with literature when calculating the part modulus and hardness, while effectively capturing nanoscale variations in properties across the microstructure. The key advantage of this methodology is its capability to rapidly test a single AM part and generate a large dataset for statistical analysis. Complementing existing macroscale characterization techniques, this method can help improve AM part performance prediction and contribute to the wider adoption of AM technologies in the future.

Colloidal nanocrystal (NC) assemblies are promising for optoelectronic, photovoltaic, and thermoelectric applications. However, using these materials can be challenging in actual devices because they have a limited range of thermal conductivity and elastic modulus, which results in heat dissipation and mechanical robustness challenges. Here, we report thermal transport and mechanical measurements on single-domain colloidal PbS nanocrystal superlattices (NCSLs) that have long-range order as well as measurements on nanocrystal films (NCFs) that are comparatively disordered. Over an NC diameter range of 3.0-6.1 nm, we observe that NCSLs have thermal conductivities and Young's moduli that are up to ∼3 times higher than those of the corresponding NCFs. We also find that these properties are more sensitive to NC diameter in NCSLs relative to NCFs. Our measurements and computational modeling indicate that stronger ligand-ligand interactions due to enhanced ligand interdigitation and alignment in NCSLs account for the improved thermal transport and mechanical properties.

Laser-induced stress waves have been a powerful technique for high strain-rate material characterization. The stress amplitude and duration can be strongly influenced by both laser characteristics and sample configuration. In this study, stress histories of silicon substrates loaded by pico-and nanoseconds laser pulses, with and without confinement of the interaction volume, were investigated. Shorter pulse duration and confinement of the absorbing medium have been found to increase the amplitude of laser-induced stress waves, but they may also alter the stress evolution. Without confinement or at low energy densities the stress wave profile is similar to that of the laser pulse. At high energy densities with confinement shock loading with stretched unloading is observed.

The exoskeletons of crustaceans are essential for providing protection from predators and other environmental threats. Understanding the structure and mechanical behavior of their natural armor could inspire the design of lightweight and high toughness synthetic materials. Most published work has focused on marine crustacea rather than their terrestrial counterparts, which are exposed to a multitude of unique threats. The interest in the terrestrial isopod Armadillidium vulgare (A. vulgare) has grown but the interrelationship between the microstructure, chemical composition, and mechanical properties has not been thoroughly investigated. Thus, this study aims to elucidate missing details concerning this biological mineralized composite. Exoskeleton specimens were fixated to preserve the intrinsic protein structure. We utilize scanning electron microscopy for microstructure analysis, Raman spectroscopy for elemental analysis, and nanoindentation property mapping to achieve mechanical characterization. The naturally fractured A. vulgare exoskeleton cross-section reveals four subregions with the repeating helicoidal 'Bouligand' arrangement most prominent in the endocuticle. The hardness and reduced modulus distributions exhibit a through-thickness exponential gradient with decreasing magnitudes from the outermost to the innermost layers of the exoskeleton. The Raman spectra show a graded spatial distribution of key constituents such as calcium carbonate across the thickness, some of which are consistent with the mechanical property gradient. Potential microstructure, elemental composition, and mechanical property relationships are discussed to explain how the hierarchical structure of this nanolaminate armor protects this species.

Applications of stem cells have been playing significant roles in scientific and clinical settings in the last few decades. The foundation of these approaches is successful cryopreservation of stem cells for future use. However, so far we can only cryopreserve stem cell suspension of small volumes in the order of 1 mL mostly due to the lack of an effective rewarming technique. Rapid and uniform rewarming has been approved to be beneficial, and sometimes, indispensable for the survival of cryopreserved stem cells, inhibiting ice recrystallization or devitrification. Unfortunately, the conventional water bath thawing method failed in providing the rapid and uniform rewarming. The conversion of electromagnetic (EM) energy into heat provides a possible solution to this problem. This chapter will focus on (1) analysis of the combined EM and heat transfer phenomenon in the rewarming of a biospecimen, (2) numerical investigation of the rewarming system, (3) practical setup of an EM resonance system, and (4) test of heating performance with large volume of cells.

Laser-induced spallation is a process in which a stress wave generated from a rapid, high-energy laser pulse initiates the ejection of surface material opposite the surface of laser impingement. Through knowledge of the stress-wave amplitude that causes film separation, the adhesion and interfacial properties of a film-on-substrate system are determined. Some advantages of the laser spallation technique are the noncontact loading, development of large stresses (on the order of GPa), and high strain rates, up to 108/s. The applicability to both relatively thick films, tens of microns, and thin films, tens of nm, make it a unique technique for a wide range of materials and applications. This review combines the available knowledge and experience in laser spallation, as a state-of-the-art measurement tool, in a comprehensive pedagogical publication for the first time. An historical review of adhesion measurement by the laser-induced spallation technique, from its inception in the 1970s through the present day, is provided. An overview of the technique together with the physics governing the laser-induced spallation process, including functions of the absorbing and confining materials, are also discussed. Special attention is given to applications of laser spallation as an adhesion quantification technique in metals, polymers, composites, ceramics, and biological films. A compendium of available experimental parameters is provided that summarizes key laser spallation experiments across these thin-film materials. This review concludes with a future outlook for the laser spallation technique, which approaches its semicentennial anniversary.

Ductility of polymer-supported metal films is important for flexible electronic devices and it is strongly affected by the metal film, polymer substrate, and their interfacial properties. In this paper, the effect of interfacial adhesion and substrate thickness on the metal film ductility was investigated. Mechanical behavior of 500 nm-thick aluminum (Al) films deposited on polyethylene-terephthalate (PET) substrates with thickness of 12, 25, and 50 μm was studied by tensile testing with in-situ electrical resistance measurements and post-mortem scanning electron microscopy. In addition, plasma etching was applied to tailor the PET surface condition before Al film deposition. Subsequently, the Al/PET interfacial adhesion was quantitatively evaluated using the laser spallation approach. The tensile tests showed that plasma etching improved the ductility of the Al films, and that the apparent ductility of the Al film on the 50 μm-thick PET substrate was substantially lower than that on the 12 and 25 μm PET thickness. Laser spallation results revealed that the plasma etching increased the Al/PET interfacial adhesion. The influence of plasma etching and substrate thickness on the Al film ductility can be explained by the interface adhesion and shear lag theory. Plasma etching improves the interfacial adhesion by inducing both chemical and physical changes on the PET surface, and substrate thickness contributes to interface shear stress upon strain localization. The competing effect of the interfacial adhesion and the interfacial shear stress leads to a limiting substrate thickness for the desired ductility at a given tensile strain.

Biocompatibility is an essential requirement for implantable biomaterials, particularly for magnesium (Mg) and its alloys which are being pursued as biodegradable implants. In this study, the influence of corrosion-products layers upon the surface of pure Mg specimens was evaluated through direct contact with simulated body fluid. The immersion of pure Mg specimens was conducted in Dulbecco’s modified Eagle’s medium (DMEM) at physiological conditions over defined time durations (from 24 h to 14 d). Surface morphology, chemical composition, and cross-sectional structure of corrosion layers were examined by means of focused ion beam, scanning electron microscopy, and x-ray diffraction. Results reveal a duplex Mg(OH)2/CaPO4 corrosion layer was produced upon pure Mg as a result of immersion in DMEM, similar to the in vivo surface corrosion films observed on pure Mg in the murine artery. The concentration of Mg in the surface corrosion film decreased with immersion time, from approximately 64 wt% (1 d) to approximately 22 wt% (14 d). Conversely, Ca and P, representing the key constituents in DMEM, were incorporated in corrosion products, resulting in unique surfaces being presented to cells as a function of Mg dissolution. MG63 osteoblast proliferation assay demonstrates comparative cell viability on all corroded surfaces obtained through immersion in DMEM for 1 d, 3 d, 7 d, and 14 d, varying from 90% to 100%. Cell viability on all corroded surfaces was higher than that of bare metal surface (82%), signifying enhanced biocompatibility of corroded surfaces related to the bare metal surface.

The influence of annealing time on microstructure, morphological, electrical and mechanical properties of La1.9Ce0.1CuO4 (LCCO) superconducting films has been studied. Single-phase LCCO thin films were prepared by pulsed-laser deposition on SrTiO3 substrate with varying annealing time. Microstructure and morphology of the LCCO films were investigated using x-ray diffraction and atomic force microscopy. Temperature dependence of electrical resistance of the LCCO films was determined by four-point method. Hardness and elastic modulus of the LCCO films were characterized by depth sensing nanoindentation technique. Results show that annealing time mainly affects the hardness and elastic modulus of the LCCO films through Cu-rich particles and the crystallite size. However, the influence of Cu-rich particles is much less remarkable than that of the crystallite size.

Residual stresses in multilayer thin films are of substantial importance to the service life of advanced engineering systems. In this investigation, the residual stresses in magnetron sputtered Cu/Ni multilayer thin films were characterized using x-ray diffraction (XRD) and the sin2ψ method. The influence of layer thickness on residual stress was explored for films with alternating Ni and Cu layers with equal layer thicknesses ranging from 10 nm to 100 nm. To address peak broadening and overlapping, the Gaussian Mixture Model (GMM) and Expectation Maximization (EM) algorithm were employed, and the peak position was determined using the Center of Gravity (CoG) method. Results showed tensile residual stress in both the Cu and Ni layers and a prominent layer thickness dependence. The stress in the Ni layers increased from roughly 880 MPa to 1550 MPa with decreasing layer thickness from 100 nm to 10 nm. In the Cu layers, the stress remained relatively constant at ~250 MPa and then substantially decreased for the 10 nm thickness. The findings confirm that the XRD-based approach can be applied for residual stress measurement in nanoscale multilayer thin films, provided that peak broadening and overlapping issues are addressed. Furthermore, the residual stress in metal multilayers is strongly dependent on layer thickness.

This work investigated the effect of sodium (Na) and potassium (K) ions permeation on optical properties of vanadium dioxide (VO2) deposited on three different glass substrates: silica-soda-lime (SL), silica-potash-soda (PS) and fused quartz (FQ), respectively. The VO2 thin films were prepared by reactive magnetron sputtering. Microstructure and compositions were determined by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Morphology of the films was characterized by atomic force microscopy (AFM), and the optical properties of the films, including refractive index and extinction coefficient, were characterized by spectroscopic ellipsometry (SE). Results show that the optical properties of the VO2 films grown on different substrates exhibited different dispersion trends at room temperature, which could be attributed to the penetration of Na and K ions. In addition, the influence of temperature on the optical properties of VO2 thin films was also studied by varying temperature ellipsometry. Below the phase transition temperature, the peak of the refractive index showed a clear blue shift with increasing temperature; above the phase transition temperature, the peak of refractive index also showed a blue shift, which was different from the trend below the phase transition temperature. This phenomenon indicates that the VO2 film has undergone a phase change. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Mechanics of Additive and Advanced Manufacturing, Volume 9 of the Proceedings of the 2017 SEM Annual Conference & Exposition on Experimental and

Previous work showed that pulse-laser irradiation can strengthen metal multilayer thin films through intermetallic formation and the degree of strengthening is a function of laser pulse energy. In this work, the effect of individual layer thickness (λ) and total multilayer thickness (h) on the resulting microstructure and mechanical strength of laser-treated Ti/Ni multilayers was further investigated. Experiments were carried out on fourλ/hcombinations using individual layer thickness of 20 nm and 50 nm, and total multilayer thickness of 500 nm and1μm, respectively. Obvious intermetallic strengthening was observed in the 500 nm thick multilayers, especially with the 20 nm layer thickness, but not in the 1μm thick multilayers. Further, the multilayer surface morphology after laser treatment was observed to be dominated by competition between laser-induced optical interference and thermal melting, with the former leading to ripple or cross-hatched patterns and the latter leading to melted surfaces with pores and cracks.

Strong temperature and thickness dependent mechanical properties of Ti/Ni multilayer thin films have been observed with layer thickness from 200 nm to 6 nm and annealing temperature from room temperature to 500 °C. The as-deposited case follows the traditional trend of dislocation mediated-strengthening to grain boundary mediated-softening with decreasing layer thickness. Initial thermal strengthening of multilayers is achieved by annealing induced grain boundary relaxation. This strengthening is found to increase with decreasing layer thickness and increasing annealing temperature. Further strengthening could be achieved due to solid solution of diffused atoms and Ti-Ni intermetallic precipitates for multilayers with thin layer, while obvious softening has been observed for multilayers with thick layer due to recrystallization and grain growth.

A systematic study was performed on mechanical and microstructural properties of Ti/Ni multilayers with layer thickness from 200nm to 6nm and annealing temperature from room temperature to 500°C. Based on the observed hardness evolution, a coupled layer-thickness and annealing-temperature dependent strengthening mechanism map is proposed. For as-deposited films, the deformation behavior follows the traditional trend of dislocation mediated strengthening to grain boundary mediated softening with decreasing layer thickness. For annealed films, grain boundary relaxation is considered to be the initial strengthening mechanism with higher activation temperature required for thicker layers. Under further annealing, solid solution hardening, intermetallic precipitation hardening, and fully intermixed alloy structure continue to strengthen the thin layered films, while recrystallization and grain-growth lead to the eventual softening of thick layered films. For the films with intermediate layer thickness, a strong orientation dependent hardness behavior is exhibited under high temperature annealing due to mechanism switch from grain growth softening to intermetallic precipitation hardening when changing the loading orientation from perpendicular to parallel to the layer interfaces.

In this study, a multilayer thin film of ITO/VO2/TiO2 was investigated for simultaneous control of the solar and thermal spectra with potential application as an energy-efficient coating for windows in built environments. The functions for these layers were: low emissivity, thermochromism, and anti-reflectance in the visible region. Films were deposited using reactive magnetron sputtering and characterized with scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis–NIR spectrophotometry, and Fourier transform infrared spectroscopy. The results demonstrate that relatively high luminous transmittance, low emissivity, and favorable thermochromism can be achieved for a film with a transition temperature centered at 52°C with a hysteresis width of 18°C. This shows that an advancement of the previous state of the art can be made by restricting the Scherrer grain size of the VO2 layer to 92nm.

The in vitro degradation of magnesium (Mg) alloys containing low levels of strontium (Sr, 0.05, 0.1 and 0.2 wt%), with and without addition of zinc (Zn, 0.5 and 1.0 wt%), was studied for potential use in orthopaedics for fracture treatment. Alloying Mg with Sr was selected as a promising strategy to utilise the biological effect of Sr in inducing accelerated bone tissue growth. The influence of controlled alloying upon degradation rate was studied via electrochemical measurements and immersion tests in minimum essential medium (MEM). Immersion testing revealed a comparable degradation rate of the alloys tested herein, indicating no detrimental effect of Sr on degradation. Cytotoxicity experiments on primary mouse osteoblasts indicated good biocompatibility and enhanced proliferation of osteoblasts for all the tested Mg alloys. Potentiodynamic polarisation testing further confirmed that addition of low-levels of Sr had a minor influence on cathodic kinetics, with a slight inhibition of anodic kinetics. In contrast, the addition of Zn as a ternary element moderated both anodic and cathodic kinetics of Mg-Sr alloys.