Space missions have unique requirements for payloads of electronics, sensors, instruments, and other components in terms of mass, footprint, power consumption, and resistance to various types of radiation. Nanomaterials offer the potential for future radiation-hardened or radiation-immune electronics. Gas-sensing needs in planetary exploration and crew-cabin air-quality monitoring are currently being met by bulky instruments. Routine health checkups of astronauts and testing of water in space habitats are being done on a delayed basis by bringing samples back to Earth. Instead, nanomaterials can be used to construct ultrasmall, postage-stamp-sized gas/vapor sensors with selective discrimination and also lab-on-a-chip biosensors for water-quality monitoring and crew health monitoring.

The mobile revolution has enabled broad applications with a faster response, small form factors, and more data bandwidth, sensing, and processing power. The industry is pursuing three-dimensional (3D) stacked integrated circuits (ICs) in order to provide higher density interconnects between chips and/or functional blocks, which translates to enhanced system performance. These value propositions are attractive, especially for wireless applications, and will likely lead to further growth of this sector. Recent progress has been reported for development of IC stacking technologies, specifically for wireless applications. However, for full high volume deployment of 3D stacked ICs, a number of technical challenges remain, including many opportunities to be addressed by material enhancements. This article reviews the state-of-the-art technology solutions used for 3D IC stacking and highlights the material properties and remaining technology challenges required to meet the demanding specifications for high volume manufacturing of consumer devices. In particular, it focuses on the electrical (dielectrics and metallic) properties of the interconnects, the thermal and mechanical properties of the integrated components, and the ultimate component level/board level reliability characteristics.

Three-dimensional powder printing (3DP) is attractive for the direct fabrication of bioceramic implants and scaffolds from a computer aided design file for bone tissue engineering by localized deposition of a reactive binder liquid onto thin powder layers. This article reviews recent findings on novel material developments for the three-dimensional (3D) printing process using either sintering regimes or cement setting reactions. Customized ceramic implants can be fabricated by 3DP using computer tomography data obtained from a patient, whereas further drug modification of such implants can be achieved either in situ or post-printing. The excellent biological in vitro and in vivo behavior of 3D-printed bioceramics together with processing at ambient conditions may give the opportunity to directly produce cell-seeded patient-specific implants for accelerated and enhanced bone regeneration in the future.

Graphene is not the only prominent example of two-dimensional (2D) materials. Due to their interesting combination of high mechanical strength and optical transparency, direct bandgap and atomic scale thickness transition-metal dichalcogenides (TMDCs) are an example of other materials that are now vying for the attention of the materials research community. In this article, the current state of quantum-theoretical calculations of the electronic and mechanical properties of semiconducting TMDC materials are presented. In particular, the intriguing interplay between external parameters (electric field, strain) and band structure, as well as the basic properties of heterostructures formed by vertical stacking of different 2D TMDCs are reviewed. Electrical measurements of MoS2, WS2, and WSe2 and their heterostructures, starting from simple field-effect transistors to more demanding logic circuits, high-frequency transistors, and memory devices, are also presented.

The materials characterization universe is as large and multifaceted as the materials and engineering fields combined. Many methods have evolved over decades, or even centuries, from quite rudimentary tools to extremely sophisticated instruments. Measurement and testing of materials span properties from mechanical, to electrical, to thermal; materials classes from metals, to semiconductors, to insulators, with ceramics, polymers, and composites somewhere in between; scales from atomic through nano-, micro-, meso-, and macroscopic; and times spanning picoseconds to years in practice, to eons in simulation. The technical context of a materials measurement ranges from fundamental science, often with no immediately transparent connection, to future engineering applications, to quite practical “real-world” field tests that can predict performance and—one hopes—prevent component failure. Materials measurement methods have grown out of distinct disciplinary homes: physics, chemistry, metallurgy, and, more recently, biology and environmental science. Drawing from the broad expanse of materials characterization techniques, we offer a perspective on that breadth and cite examples that are illustrative of the crucial role such techniques have played and are playing in the technologies of today.

Biomineralization is the matrix-directed calcification of tissue in living organisms. The deposition of different polymorphs of calcium phosphate or calcium carbonate is a highly regulated process. It may involve cell-controlled mechanisms with vesicular delivery of inorganic material to the extracellular matrix and cell-independent processes mediated by dedicated matrix proteins. These proteins promote the formation of microscopic crystals of defined size and shape, which combine to form bio-inorganic materials with unique properties. Successful biomineralization is correlated with structural elements, such as matrix proteins involved in the nucleation process. Circular dichroism (CD) is a spectroscopic technique for the determination of a secondary structure of proteins and has therefore been applied for studying numerous biomineralization promoter proteins. This article reviews and compares CD data on matrix proteins from different contexts, such as eggs, seashells, and teeth. It highlights the potential of CD for secondary structure determination and quantification and points out pitfalls that may lead to misinterpretation of CD spectra. The data suggest that most biomineralization promoter proteins contain domains of different secondary structure with predominantly unordered conformation. However, they may acquire a higher degree of order initiated by environmental factors such as pH, presence of cations, or charged surfaces.

This article reviews atomic-resolution in situ electron microscopy studies of two-dimensional materials such as graphene, hexagonal boron nitride, and metal dichalcogenides with a focus on defect structures. Electron irradiation allows defect formation and atomic-resolution imaging at the same time by the same electron beam. Two-dimensional hexagonal lattices show unique mechanisms of defect reconstruction that do not appear in other materials. The combination of thermal annealing and irradiation, both adjustable in the electron microscope, sets a balance between equilibrium and nonequilibrium and allows for the generation of new structures and morphologies.

Lumbar intervertebral disc (IVD) degeneration is the leading cause of lower back pain. While lumbar IVDs have low cellularity and limited capacity of regeneration, they bear high mechanical loads. Accelerated disc degeneration may happen because of undue cell stimulation, and cell nutrition also seems to be particularly influent in the disc. Cell nutrition depends on exchange of oxygen, glucose, and lactate between the periphery and the various regions of the IVD, which in turn depends on mechanical deformations. The mechanical regulation of disc cell nutrition, known as indirect mechanotransduction, is difficult to study in vivo or in vitro. This review reports on an important alternative in the form of numerical methods, which are based on the ability of poromechanical models to be coupled to solute transport-reaction models. Models need to address intricate nonlinear and time-dependent phenomena, but have allowed for important mechanisms to be proposed, complementing current knowledge gained from in vivo or in vitro observations.

Organic–inorganic perovskites have emerged as one of the most promising materials for future optoelectronics applications, most notably photovoltaics. The achievement of high-efficiency solar cells has been possible mainly through the understanding of the perovskite formation during the solution deposition of thin films. Vacuum deposition methods have also been developed and have intrinsic advantages over solution-based processing, including control over the film thickness and composition, low-temperature processing, and the possibility of preparing multilayer structures. This article summarizes the latest advances in the vacuum deposition of hybrid perovskites, with an emphasis on the application to photovoltaics. Methods for the deposition of perovskite thin films and the performances of the correspondent solar cells are reviewed.

The making of composites has served as a working principle of achieving material properties beyond those of their homogeneous counterparts. The classical effective-medium theory models the constituent phases with local properties drawn from the corresponding bulk values, whose applicability becomes questionable when the characteristic size of individual domains in a composite shrinks to nanometer scale, and the interactions between domains induced by interfacial and size effects become important or even dominant. These unique features of nanocomposites have enabled engineering of extraordinary thermoelectric materials with synergistic effects among their constituents in recent years. For other applications requiring high thermal conductivity, however, interfacial and size effects on thermal transport in nanocomposites are not favorable, although certain practical applications often call for the composite approach. Therefore, understanding nanoscale transport in nanocomposites can help determine appropriate strategies for enhancing the thermal performance for different applications. We review the emerging principles of heat and charge transport in nanocomposites and provide working examples from both thermoelectrics and general thermal engineering.

Certain biocomposites exploit the combination of soft and hard elements to achieve high strength and toughness. In nacre, found inside certain seashells or on the surface of pearls, hard layers of micron-scale thickness are glued together by thin layers of soft proteins to realize remarkable strength and toughness. In spider webs, stiffer radial threads are connected by softer spiral threads to produce a light and resistant structure. In the exoskeleton of lobsters, organic fibers form a chiral structure in an inorganic matrix. This article reviews progress in the understanding of the mechanical superiority of such soft-hard biocomposites. In particular, simple physical views are presented that allow an intuitive understanding of how their remarkable structures contribute to enhancing their fracture resistance in the presence of cracks, and how such structures are physically optimized in terms of mechanical properties. Such fundamental insights could be useful as guiding principles for developing artificial, reinforced materials.

Recent successes with the fabrication of high-performance GaN-based heterostructures on silicon substrates have made this technology very promising. However, epitaxial growth of GaN on Si is challenging. This article presents some of the challenges of epitaxial growth of GaN-on-Si substrates focusing on basic aspects that are pertinent to consider for power electronics.

Catalytic nanomaterials play a major role in chemical conversions and energy transformations. Understanding how materials control and regulate surface reactions is a major objective for fundamental research on heterogeneous catalysts. In situ environmental transmission electron microscopy (ETEM) is a powerful technique for revealing the atomic structures of materials at elevated temperatures in the presence of reactive gases. This approach can allow the structure–reactivity relations underlying catalyst functionality to be investigated. Thus far, ETEM has been limited by the absence of in situ measurements of gas-phase catalytic products. To overcome this deficiency, operando TEM techniques are being developed that combine atomic characterization with the simultaneous measurement of catalytic products. This article provides a short review of the current status and major developments in the application of ETEM to gas-phase catalysis over the past 10 years.

The long-term success of an orthopedic implant largely depends on the extent of its osseointegration in the surrounding bone. During recent decades, there have been several attempts to develop porous structures and coatings in order to maximize the bone ingrowth on prosthesis surfaces. Innovative additive manufacturing technologies, such as electron beam melting (EBM), which are based upon building components by adding layers of material rather than by removing material from a raw shape, can provide a breakthrough solution, both to overcome the major limitations of the actual technologies and to significantly enhance the performance of porous scaffolds. This article reviews the latest developments in EBM technology applied to the preparation of highly biocompatible porous materials such as Trabecular Titanium and the production of orthopedic prostheses with enhanced characteristics.

The ability to pattern materials in three dimensions is crucial for structural, optical, electronic, and energy applications. Three-dimensional printing allows one to design and rapidly fabricate materials in complex shapes without the need for expensive tooling, dies, or lithographic masks. A growing palette of printable materials, coupled with the ability to programmably control mesoscale architecture, open new avenues for creating designer materials with unprecedented performance.

Modern materials design is largely based on composite structures aimed at a synergistic integration of multiple components with a diverse range of properties. Biologically grown minerals provide an intriguing example of sophisticated organic–inorganic nanocomposite structures resulting in excellent mechanical characteristics. Among the mineral phases utilized by living organisms to generate hard tissues, calcium carbonate—especially the calcite polymorph—is ubiquitous and has been studied intensively. Biogenic calcite crystals often show hierarchical organization spanning multiple length scales, and the occluded organic phases are now known to be intimately associated with the mineral host. Here, we discuss the internal micro- and nanostructure of two selected types of calcite biominerals—the sea urchin spine and prismatic single crystals extracted from mollusk shells. This article highlights recent advances in translating the key principles of biological mineralization into design strategies for synthetic materials and presents analogies between biogenic and synthetic calcite single crystals.

To overcome various concerns due to scaling-down device size in future large-scale integration (LSI), it is indispensable to introduce a new concept of heterogeneous three-dimensional (3D) integration in which various kinds of device chips with different sizes, devices, and materials are vertically stacked. To achieve such heterogeneous 3D integration, the key technology of self-assembly and electrostatic (SAE) bonding has been developed. The heterogeneous 3D integration technology with the SAE bonding method has enabled 3D heterogeneous stacking of different types of chips such as the compound semiconductor device chip, photonic device chip, and spintronic device chip on complementary metal oxide semiconductor chips. A 3D image sensor with extremely fast processing speed and a 3D microprocessor with a self-test and self-repair function for future automatic driving vehicles are typical examples of heterogeneous 3D LSIs which we fabricated by the SAE bonding method.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) consist of over 40 compounds. Complex metal TMDs assume the 1T phase where the transition-metal atom coordination is octahedral. The 2H phase is stable in semiconducting TMDs where the coordination of metal atoms is trigonal prismatic. Stability issues have hampered the study of interesting phenomena in two-dimensional 1T phase TMDs. Phase conversion in TMDs involves transformation by chemistry at room temperature and pressure. It is possible to convert 2H phase 2D TMDs to the 1T phase or locally pattern the 1T phase on the 2H phase. The chemically converted 1T phase 2D TMDs exhibit interesting properties that are being exploited for catalysis, source and drain electrodes in field-effect transistors, and energy storage. We summarize the key properties of 2D 1T phase TMDs and their applications as electrodes for energy and electronics.

Major advances have been made over the past 30 years in the development of an integrated computational materials design (ICMD) technology. The hierarchical structure of its methods, tools, and supporting fundamental materials databases is reviewed here, with an emphasis on successful applications of CALPHAD (calculation of phase diagrams)-based tools as an example of ICMD, expressing mechanistic understanding in quantitative form to support science-based materials engineering. Opportunities are identified for rapid expansion of CALPHAD databases, as well as a major restructuring of materials education.

Carbon nanotubes (CNTs) have captured the imagination of the research community because of their many superior properties. In the nearly 25 years since their novelty was recognized, however, progress toward their utility as superlightweight structural materials, especially for aerospace applications, has been disappointing. Recent advancements have revived some of the anticipation for the touted systems payoffs. The purpose of this article is to examine how close CNTs have come to fulfilling expectations for lightweight aerospace structures in the two decades since the initial report stimulated intense interest in this material. This article also proposes areas of study to bridge knowledge gaps that can realize the potential for these CNT composites to be part of the lightweight structures technology suite for aerospace use.