The global automotive industry is facing challenges in several key areas, including energy, emissions, safety, and affordability. Lightweighting is one of the key strategies used to address these challenges. Maximizing the weight reduction (i.e., minimizing vehicle weight) requires a systems-engineering design optimization and iteration process that combines material properties and manufacturing processes to meet product requirements at the lowest mass and/or cost. Advanced high-strength steels, aluminum and magnesium alloys, and carbon-fiber-reinforced polymers have emerged as important materials for automotive lightweighting. This article presents examples of how coupling materials science with innovative manufacturing processes can provide lightweight solutions in automotive engineering.

Hybrid organic–inorganic perovskites (e.g., CH3NH3PbX3, X represents a halide) have been highlighted for various applications, especially as light absorbers in third-generation photovoltaics. In the pursuit of low-cost and efficient perovskite solar technology, it is crucial to develop a facile method to fabricate conformal, compact perovskite films in an inexpensive and reproducible manner. Here, we report high-quality perovskite films controllably deposited via a facile low-temperature (<150°C) vapor-assisted solution process (VASP). Key steps include deposition of the inorganic framework by solution first, followed by a subsequent in situ reaction between the inorganic species and the desired organic vapor. The VASP approach differs from other conventional solution processing techniques because it retards nucleation and enables vigorous reorganization for film growth, with an absence of solvation, hydration, and undesirable structural transitions. Facilitated by excellent film quality, perovskite materials enable a power-conversion efficiency of ∼16.8% in the planar configuration of a solar cell. This method provides a simple approach to perovskite film preparation and paves the way toward high reproducibility and mass production of high-quality absorber films for solar devices.

Taking the mesoscale to mean length and time scales at which a material’s behavior is too complex to be understood by construction from the atomistic scale, we focus on three-dimensional characterization and modeling of mesoscale responses of polycrystals to thermal and mechanical loading. Both elastic and plastic internal structural responses are now accessible via high-energy x-ray probes. The combination of diffraction experiments and computed tomography, for example, is yielding new insights into how void formation correlates with microstructural features such as grain boundaries and higher-order junctions. The resulting large, combined data sets allow for validation of micromechanical and thermal simulations. As detectors improve in resolution, quantum efficiency, and speed of readout, data rates and data volumes present computational challenges. Spatial resolutions approach one micrometer, while data sets span a cubic millimeter. Examples are given of applications to tensile deformation of copper, grain growth in nickel and titanium, and fatigue cracks in superalloys.

This article reviews the application of nanomaterials for radiation shielding to protect humans from the hazards of radiation in space. The focus is on protection from space radiation, including galactic cosmic radiation (GCR), solar particle events (SPEs), and neutrons generated from the interactions of the GCR and SPEs with the intervening matter. Although the emphasis is on protecting humans, protection of electronics is also considered. There is a significant amount of work in the literature on materials for radiation shielding in terrestrial applications, such as for neutrons from nuclear reactors; however, the space environment poses additional and greater challenges because the incident particles can have high charges and extremely high energies. For materials to be considered for radiation shielding in space, they should perform more than just the radiation-shielding function; hence the emphasis is on multifunctional materials. In space, there is also the need for materials to be very lightweight and capable of surviving temperature extremes and withstanding mechanical loading. Nanomaterials could play a significant role as multifunctional radiation-shielding materials in space.

Transistors with 600 V blocking capability and low switching losses are needed for converting one-phase 230 V mains voltage to lower voltage levels in switch-mode power supplies. The transistors operate as a switch and have to block the system voltage with minimized leakage currents in the OFF-state and have to conduct the current in the ON-state with minimized ON-state resistance. Additionally, any switching losses inside the transistor during the transitions in-between OFF and ON-states need to be minimized for efficient power-converting systems. Efficient high-voltage switching using gallium nitride (GaN)-based power transistors requires excellent material properties in the GaN/AlGaN epitaxial layers in conjunction with optimized process modules and device layout. In the example presented here, GaN buffer compositions and device geometry have been optimized to obtain very low vertical and lateral OFF-state leakage currents at 600 V drain bias and to enable a fast device turn-on with only a minor increase in dynamic ON-state resistance. The developed technology was applied to GaN layers grown on SiC and Si substrates to allow a direct comparison of both static and dynamic device parameters. By implementing a p-type GaN gate, normally OFF operation was realized for 70 mΩ/600 V transistors on both substrates. The new GaN-based devices outperform established Si-based superjunction metal oxide semiconductor field-effect transistors in terms of gate charge and switching energy.

Several organisms possess a genetic program enabling them to form a mineral, a process termed biomineralization. The structure and composition of biominerals equip the biomineralizing organisms with functionalities that abiotic materials made of the same mineral do not necessarily possess. Even primary organisms such as bacteria are able to produce materials with properties superior to those of human-made equivalents. Magnetotactic bacteria represent a paradigm of such microorganisms. These organisms synthesize a hierarchical one-dimensional magnetic nanostructure based on the alignment of magnetosomes—organelles embedded in a vesicle dedicated to biomineralization and made of magnetic nanoparticles (magnetite (Fe3O4) or greigite (Fe3S4)). This article focuses on factors that play a role in the organization of these magnetosomes. The chains, which are based on aligned particles that have biologically controlled ultrastructure, size, morphology, organization, and orientation, serve as actuators and area means to align the bacteria with the Earth’s magnetic field lines when they swim in search of particular habitats in the aqueous environments they live in.

Dielectric capacitors have been the major enabler for many applications in advanced electronic and electrical power systems because of their capability for ultrafast charging/discharging and ultrahigh power density. The low energy densities of polymer dielectrics used in these capacitors have not been able to meet the ever-increasing demands for compact, reliable, and efficient electrical power systems. Polymer nanocomposites, in which high-dielectric-constant (k) nanofillers are incorporated in the polymer matrix, have been actively pursued. In this article, we begin with two theoretical considerations for concomitantly increasing the dielectric permittivity and breakdown strength of nanocomposites: critical interfacial polarization and local electric-field distribution. In the framework of these considerations, we review recent progress toward polymer nanocomposites with high energy densities based on two approaches: core–shell-structured polymer nanocomposites and dielectric anisotropy. In addition, the potential for the enhanced elastic properties of nanocomposites to improve the dielectric strengths of capacitor films is also discussed.

Three-dimensional (3D) integration has emerged as a potential solution to the wiring limits imposed on chip performance, power dissipation, and packaging form factor beyond the 14 nm technology node. In 3D integrated circuits (ICs), the through-silicon via (TSV) is a critical element connecting die-to-die in the integrated stack structure. The thermal expansion mismatch between copper (Cu) vias and silicon (Si) can induce complex stresses in TSV structures to drive interfacial failure and Cu extrusion, degrading the performance and reliability of 3D interconnects. This article reviews current studies on thermal stresses and their effects on reliability of TSV structures. Recent results from measurements of stress and plasticity characteristics of Cu TSV structures are reviewed, including wafer curvature, micro-Raman spectroscopy, and synchrotron x-ray microdiffraction techniques. The effects of the Cu microstructure on stress and reliability, particularly on via extrusion and the device keep-out zone in TSV structures, are discussed. Based on the analysis of the reliability impact, we explore the potential of material and processing optimization to build reliable TSV structures for 3D ICs.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) such as MoS2, WS2, MoSe2, and WSe2 present an unprecedented excitonic materials family. These materials promise to open up a new age of atomic-scale photonics where devices can be scaled down to the truly atomic level and provide novel functionalities that cannot be obtained with conventional materials systems. Knowledge of the exciton dynamics in these materials is key to the development of the photonic devices. This article reviews recent studies on the excitonic properties of 2D TMDCs and the strategies used to manipulate the exciton dynamics. It also highlights many important scientific questions that remain to be answered for the realization of atomic-scale photonics.

Organ shortage is a severe challenge worldwide. Three-dimensional (3D) printing, a rapidly developing engineering and materials science tool, holds considerable promise in generating implantable organ scaffolds that may reduce or eliminate organ shortage. However, translation of 3D printing into clinical therapies has been astonishingly slow and certainly has not matched the pace of technology development. This review outlines challenges and opportunities for the application of 3D printing in tissue and organ regeneration, with emphasis on in vivo applications of 3D-printed scaffolds. Three-dimensional-printed scaffolds for the regeneration of complex tissues and organs, including bone, cartilage, tooth, and skin, serve as prototypes for 3D printing of other tissues and organs such as the liver, kidney, or heart. The aspiration to reduce or eliminate organ shortage appears to hinge on the translation of 3D bioprinting technologies into preclinical studies and clinical trials. The remaining challenges of cell survival, directed differentiation, angiogenesis, and metabolic exchange are far from trial and need to be addressed. Three-dimensional-printed materials will remain a biomaterials and engineering showcase unless applications in preclinical and clinical models are realized. In balance, 3D printing holds considerable promise in regenerative medicine as a unique approach to address organ shortage.

Cellulose nanocrystals (CNCs) are naturally occurring, structural material building blocks, which exhibit great potential for future multifunctional nanocomposites due to their high bioavailability, low cost, and impressive mechanical properties. Recent research on CNCs has focused on isolation techniques, crystal morphology, mechanical property characterization, and development of hierarchical materials, including CNC thin films and CNC-based nanocomposites. These studies have revealed that the unique conformation, structure, and surface chemistry of CNCs contribute directly to their outstanding mechanical performance and anisotropic features. To better facilitate their applications in hierarchical, bioinspired materials and exploit the inherent benefits of these biological building blocks, interfacial interactions and mechanics of CNCs with various materials, including other nanocrystals, polymer matrices, and small-molecule solvents, must be explored. This review highlights recent work focusing on the interfacial mechanics of CNCs. We discuss the current progress that has advanced our understanding of their behavior, and future challenges that must be addressed in order to fully exploit the potential of CNCs in engineered materials.

Materials synthesis and the functioning of devices often involve liquid media. However, direct visualization of dynamic processes in liquids, especially with high spatial and temporal resolution, has been challenging. For solid materials, advances in aberration-corrected electron microscopy have made observations of atomic-level features a routine practice. Here, we discuss the extent to which one can take advantage of the resolution of modern electron microscopes to image phenomena occurring in liquids. We describe the fundamentals of two different experimental approaches that use closed and open liquid cells. We illustrate the capabilities of each approach by considering processes in batteries and nucleation and growth of nanoparticles from solution. Liquid-cell electron microscopy appears to be duly fulfilling its role and promise for in situ studies of nanoscale processes in liquids, revealing physical and chemical processes that are otherwise difficult to observe.

Recent discoveries have revealed a breakthrough in the photovoltaics (PVs) field using organometallic perovskites as light harvesters in the solar cell. The organometal perovskite arrangement is self-assembled as alternate layers via a simple low-cost procedure. These organometal perovskites promise several benefits not provided by the separate constituents. This overview concentrates on implementing perovskites in PV cells such that the perovskite layers are used as the light harvester as well as the hole-conducting component. Eliminating hole-transport material (HTM) in this solar-cell structure avoids oxidation, reduces costs, and provides better stability and consistent results. Aspects of HTM-free perovskite solar cells discussed in this article include (1) depletion regions, (2) high voltages, (3) panchromatic responses, (4) chemical modifications, and (5) contacts in HTM-free perovskite solar cells. Elimination of HTM could expand possibilities to explore new interfaces in these solar cells, while over the long term, these uniquely structured HTM-free solar cells could offer valuable benefits for future PV and optoelectronics applications.

From the biological/chemical perspective, interface concepts related to the cell surface/synthetic biomaterial interface and the extracellular matrix/biomolecule interface have wide applications in medical and biological technologies. Interfaces also play a significant role in determining structural integrity and mechanical creep and strength properties of biomaterials. Structural arrangement of interfaces combined with interfacial interactions between organic and inorganic phases significantly affects the mechanical properties of biological materials, allowing for a unique combination of seemingly inconsistent properties, such as fracture strength and tensile strength being both high—as opposed to traditional engineering materials, which have high fracture strength linked to low tensile strength and vice versa. While there has been a tremendous amount of work focused on the effects of structural arrangements on biomaterial properties, both experimental and computational studies of the strength, deformation, and viscosity of the interface itself are limited to just a few systems. Even in such studies, the actual interface stress is rarely analyzed, and correlated to the overall material strength or creep properties. This article provides a focused overview of such studies in hard biological materials, followed by a new vision of how the results of interfacial molecular studies could be consistently linked to multiscale, micromechanics-based perceptions of hierarchical biological materials.

Heterogeneous gas–solid catalyst reactions occur at the atomic level, and understanding and controlling complex catalytic reactions at this level is crucial for the development of improved processes and materials. There are postulations that single atoms and very small clusters can act as primary active sites in chemical reactions. Early applications of our novel aberration-corrected (AC) environmental (scanning) transmission electron microscope (E(S)TEM) with single-atom resolution are described. This instrument combines, for the first time, controlled operating temperatures and a continuous gas environment around the sample with full AC STEM capabilities for real-time in situ analysis and visualization of single atoms and clusters in nanoparticle catalysis. ESTEM imaging and analysis in controlled gas and temperature environments can provide unique insights into catalytic reaction pathways that may involve metastable intermediate states. Benefits include new knowledge and more environmentally friendly technological processes for health care and renewable energy as well as improved or replacement mainstream technologies in the chemical and energy industries.

This article reviews current progress in research in ferroelectric switching phenomena using in situ electron microscopy. We focus on state-of-the-art instrumentation, analytical methods, experimental procedures, and image contrast mechanisms. Particular emphasis is on ferroelectric domain and domain wall structures that determine ferroelectric behaviors. The applicability of in situ microscopy to studying a wide range of switching phenomena, such as domain nucleation, domain wall motion, and domain wall pinning by various types of defects, in ferroelectric thin films is demonstrated. The underlying physics of these dynamic processes is also discussed.

The ongoing pursuit of multifunctional soft materials that can impact a wide range of technological challenges, ranging from information processing to energy storage and transducing devices, has resulted in the development of hybrid materials composed of nanoparticles (NPs) dispersed in polymers. Beyond the simple preparation of composites that have the additive value of the individual components, this review discusses recent work and trends in composites that exhibit novel synergistic or emergent properties arising from combining the components. In particular, we highlight recent examples of composites in which NP assembly within polymers leads to enhancement or changes of the NP properties and how introducing NPs into a polymer can cause significant changes in the polymer’s intrinsic properties.

The physics underlying operation of cold (room-temperature) ionic-liquid emitter sources for use in propulsion shows that such thrusters are advantaged relative to all other “rockets” because of the direct scaling of power with emitter array density. Nanomaterials and their integration through nano- and microfabrication can propel these charged-particle sources to the forefront and open up new applications including mass-efficient in-orbit satellite propulsion and high-thrust-density deep-space exploration. Analyses of electrostatic, fluid-dynamic, and electrochemical limits all suggest that arrays of such ionic-liquid thrusters can reach thrust densities beyond most in-space propulsion concepts, with a limit on nanoporous thruster packing density of ∼1 μm due to ionic-liquid viscous flow and electrochemistry. Nanoengineered materials and manufacturing schemes are suggested for the implementation of microfabricated and nanostructured thruster arrays.

Learning from nature and starting from the lotus leaf, we have used a four-step strategy to develop a superwetting system ranging from two-dimensional interfaces to nanochannels and fibers. First, we explored unique superwetting properties in nature from lotus leaves, mosquito eyes, strider legs, rose petals, rice leaves, and butterfly wings, to fish scales, spider silks, and cacti. Second, we investigated the correlation between the multiscale structures and superwettability. Third, we designed target molecules to prepare bioinspired functional materials with promising applications, such as self-cleaning coatings, water/oil separation, water collection, and energy conversion. Finally, by combining two complementary properties and achieving reversible switching between them, we were able to develop bioinspired smart interfacial materials with superwettability.

With the electronics packaging industry shifting increasingly to three-dimensional packaging, microbumps have been adopted as the vertical interconnects between chips. Consequently, solder volumes have decreased dramatically, and the solder thickness has reduced to a range between a few and 10 microns. The solder volume of a microbump is approximately two orders of magnitude smaller than a traditional flip-chip joint. In contrast, the thickness of the under-bump metallization (UBM) remains almost the same as that in flip-chip solder joints. Therefore, many issues concerning materials and reliability of microbumps arise. This article reviews the challenges related to microbump materials for vertical interconnects, including transformation of solder joints into intermetallic (IMC) joints, necking or voiding induced by side wetting/diffusion on the circumference of the UBM, formation of porous Cu3Sn IMCs, early electromigration failures caused by specific orientations of Sn grains, and precipitation of plate-like Ag3Sn IMCs. An alternative way of fabricating vertical interconnects using direct Cu-to-Cu bonding is also discussed.