Nanotwins require little energy to form in metals, but their impact on strength and ductility is dramatic. New mechanisms of strengthening, strain hardening, ductility, and strain-rate sensitivity have been observed in nanowires, films, and bulk materials containing nanoscale twins as the twin-boundary spacing decreases. These mechanisms can act in concert to produce interface-dominated nanomaterials with extreme tensile strength and plastic deformation without breaking. This article reviews recent theoretical and experimental understanding of the physical mechanisms of plasticity in nanotwin-strengthened metals, with a particular focus on the fundamental roles of coherent, incoherent, and defective twin boundaries in plastic deformation of bulk and small-scale cubic systems, and discusses new experimental methods for controlling these deformation mechanisms in nanotwinned metals and alloys.

Femtosecond laser direct writing (FsLDW) in transparent materials is a laser-based precise three-dimensional (3D) micro/nanofabrication method that has shown great potential for applications. The advantages of FsLDW originate in the nonlinear nature of absorption in the multiphoton absorption process. Over the past few years, transparent material micro/nanofabrication using FsLDW has seen several developments in materials and applications. Specifically, two-photon polymerization has been widely used as a precision direct-writing process for fabrication of polymeric 3D micro/nanostructures; internal/surface ablation of polymer 3D structures based on multiphoton absorption has been demonstrated and developed as a promising subtractive manufacturing technique; and femtosecond laser multiphoton modification in glass has been intensively studied for refractive-index change and generation of nanogratings and microvoids. This article describes the latest research on FsLDW in polymers and glasses with specific applications for large-dimension fabrication, microelectromechanical systems, microphotonics, and microfluidics.

Metal–organic frameworks (MOFs) are porous ordered arrays of inorganic clusters connected by organic linkers. The compositional diversity of the metal and ligand, combined with varied connectivity, has yielded more than 20,000 unique structures. Electronic structure theory can provide deep insights into the fundamental chemistry and physics of these hybrid compounds and identify avenues for the design of new multifunctional materials. In this article, a number of recent advances in materials modeling of MOFs are reviewed. We present the methodology for predicting the absolute band energies (ionization potentials) of porous solids as compared to those of standard semiconductors and electrical contacts. We discuss means of controlling the optical bandgaps by chemical modification of the organic and inorganic building blocks. Finally, we outline the principles for achieving electroactive MOFs and the key challenges to be addressed.

Colloidal systems offer ideal conditions to study the nucleation process, both from an experimental viewpoint, due to their relatively large size and long time scales, and from a modeling point of view, due to the tunability of their interactions. In this article, we review recent studies on the process of colloidal crystallization from a microscopic perspective. In particular, we focus on nonclassical pathways to nucleation, where the appearance of solid crystals involves fluctuations of two or more order parameters. Nonclassical behavior is interpreted as a decoupling of positional and orientational symmetry breaking. We then consider how the nucleation pathway determines which polymorph is selected upon nucleation from the melt. The study of nucleation pathways not only sheds new light on the microscopic mechanism of nucleation, but also provides important information regarding its avoidance, suggesting a deep link between crystallization and vitrification.

Surface textures with three-dimensional (3D) architectures demonstrate the ability to control interfacial, optical, chemical, and mechanical properties. Potential applications range from device-scale biomolecule sensing to meter-scale optical or nonwetting coatings. In recent years, capillary forming has become a versatile and scalable approach to creating complex geometries at the nano- and micron scales. Surface tension of a liquid can deform straight pillars and assemble them into 3D architectures with predetermined orientation, where short-range adhesion forces stabilize the final forms. A variety of techniques have been demonstrated for carbon nanotubes and polymer filamentary materials to fabricate useful devices and textures. We discuss these materials and processes as well as the underlying elasto-capillary physics. We indicate the need for new simulation tools to design and engineer elasto-capillary transformations and methods to increase their throughput toward scalable manufacturing.

This article highlights recent advances in analytical electron tomography (AET), the three-dimensional (3D) extension of conventional nanoanalytical techniques, in which electron energy loss, x-ray spectroscopy, and electron diffraction are combined with tomographic acquisition and reconstruction. Examples from the literature illustrate how new 3D information, gleaned from AET, provides insights into not just morphology and composition, but also the electronic, chemical, and optical properties of materials at the nanoscale. We describe how the “multidimensional” nature of AET leads to “big data” sets, how these can be analyzed optimally, and how AET may develop further.

As the characteristic length scale of electronic devices shrinks, so does the required scale for measurement techniques to provide useful feedback during development and fabrication. The current capabilities of atom probe tomography (APT), such as detecting a low number of dopant atoms in nanoscale devices or studying diffusion effects in a nanowire (NW), make this technique important for metrology on the nanoscale. Here we review recent APT investigations applied to transistors (including regions such as gate oxide, channel, source, drain, contacts, etc.), heterogeneous dopant incorporation in NWs, and Pt-based nanoparticles.

Metamorphic epitaxy offers the possibility of growing devices on wafers composed of different materials that might be larger than the native bulk substrates for a potential cost-reduction of III–V components; this is especially important when native substrates with desired lattice constants are not available. This article reviews the concepts of metamorphic epitaxy of III–V compound semiconductor materials and examines how they have been applied to the development of advanced transistor devices. These metamorphic devices are expected to be a key enabler of future heterogeneous integrated circuits in which Si and III–V devices are monolithically integrated on a wafer scale using complementary metal oxide semiconductor-like process flows.

Conformational changes, and the formation of densely packed ordered aggregates or crystals, are behaviors that profoundly affect the properties of a molecule. Using the example of biological macromolecules, we discuss two types of interactions between these two behaviors. First, we demonstrate that shape change may be driven by crystallization if the gain in crystallization free energy is sufficient to overcome the transition to an unfavorable molecular conformation. Hence, the crystal structures of flexible molecules may be a poor representation of their free-phase atomic arrangements. Second, molecules with conformational variability, such as proteins, may facilitate the nucleation of their crystals by forming dense liquid clusters enriched in domain-swapped or misassembled oligomers. In the clusters, the nucleation barrier is reduced due to the lower surface free energy of the crystal/dense liquid interface, and nucleation is significantly faster.

Industrial ultrafast lasers are a key component of many new industrial manufacturing processes. The virtually athermal nature of the laser–matter interaction process enables high-quality material processing for many different materials with feature size reaching into the nanometer scale. Advances in laser average power and beam-delivery technology have significantly improved the throughput and productivity of real-life industrial and medical applications. In this article, we present key examples of laser processing, including drilling, cutting, and surface processing. In particular, we describe how ultrafast lasers can improve vision in patients, extend battery lifetime, improve the efficiency of solar cells and infrared detectors, or be applied in the printing or microelectronics industries. These examples demonstrate how further developments rely on a combination of laser technology, beam handling and delivery, and laser–matter interaction processes.

Biological surfaces display fascinating topographic patterns such as corrugated blood cells and wrinkled dog skin. These patterns have inspired an emerging technology in materials science and engineering to create self-organized surface patterns by harnessing mechanical instabilities. Compared with patterns generated by conventional lithography, surface instability patterns or so-called ruga patterns are low cost, are easy to fabricate, and can be dynamically controlled by tuning various physical stimuli—offering new opportunities in materials and device engineering across multiple length scales. This article provides a systematic review on the fundamental mechanisms and innovative functions of surface instability patterns by categorizing various modes of instabilities into a quantitatively defined thermodynamic phase diagram, and by highlighting their engineering and biological applications.

The recent decades have seen significant progress in linking the mechanical performance of materials to their underlying microstructure. This article presents an overview of some of these achievements, trends, and challenges. Attention is given to methods initially developed for micromechanics and their gradual evolution toward powerful multiscale methods. Various methods have been proposed for bridging scales in mechanics of materials, all aiming for efficiency and accuracy. Computational homogenization is one of these powerful approaches, now used systematically for the assessment of structure–property relations. Novel solution methods and model reduction techniques provide tools to speed up the structure–property analysis, whereby large-scale computations have been made possible. Truly fast analyses of microstructures may be expected in the near future.

Machining is an important technological process in many areas of industry. The efficiency of machining determines the quality of many industrial products. Machining efficiency and cost depend on the properties, strength, and microstructure of the machining materials. One of the promising ways to increase the reliability and wear resistance of machining tools is the development and use of hierarchical machining materials. In the area of machining materials, designed typically as binder/reinforcement composites, hierarchical structures are realized as lower-scale secondary reinforcements (such as nanoparticles in the binder, or polycrystalline, aggregate-like reinforcements, also at several scale levels). Such materials can ensure better productivity, efficiency, and lower costs of drilling, cutting, grinding, and other technological processes. This article reviews the main groups of hierarchical machining materials and their performance.

Atomic-scale characterization of interfaces in ceramic materials is needed in order to fully understand their electronic, ionic, mechanical, magnetic, and optical properties. The latest development of laser-assisted atom probe tomography (APT), as well as new specimen preparation methods, have opened the realm of ceramics for structural and chemical characterization with high sensitivity and nearly atomic spatial resolution. This article reviews recent APT investigations of interfaces in thin nitride films and thermally grown oxides: TiAlN layers and oxide scales on alumina- and chromia-formers and Zr alloys. The selected examples highlight the role of interfaces in the decomposition of films and in transport processes.

High-energy x-ray (HEX) scattering is a sensitive and powerful tool to nondestructively probe the atomic and mesoscale structures of battery materials under synthesis and operational conditions. The penetration power of HEXs enables the use of large, practical samples and realistic environments, allowing researchers to explore the inner workings of batteries in both laboratory and commercial formats. This article highlights the capability and versatility of HEX techniques, particularly from synchrotron sources, to elucidate materials synthesis processes and thermal instability mechanisms in situ, to understand (dis)charging mechanisms in operando under a variety of cycling conditions, and to spatially resolve electrode/electrolyte responses to highlight connections between inhomogeneity and performance. Such studies have increased our understanding of the fundamental mechanisms underlying battery performance. By deepening our understanding of the linkages between microstructure and overall performance, HEXs represent a powerful tool for validating existing batteries and shortening battery-development timelines.

Motivated by low cost, low toxicity, mechanical flexibility, and conformability over complex shapes, organic semiconductors are currently being actively investigated as thermoelectric (TE) materials to replace the costly, brittle, and non-eco-friendly inorganic TEs for near-ambient-temperature applications. Metal–organic frameworks (MOFs) share many of the attractive features of organic polymers, including solution processability and low thermal conductivity. A potential advantage of MOFs and MOFs with guest molecules (Guest@MOFs) is their synthetic and structural versatility, which allows both the electronic and geometric structure to be tuned through the choice of metal, ligand, and guest molecules. This could solve the long-standing challenge of finding stable, high-TE-performance n-type organic semiconductors, as well as promote high charge mobility via the long-range crystalline order inherent in these materials. In this article, we review recent advances in the synthesis of MOF and Guest@MOF TEs and discuss how the Seebeck coefficient, electrical conductivity, and thermal conductivity could be tuned to further optimize TE performance.

There is increasing interest in the use of additive manufacturing (AM) for Ni-based superalloys due to their various applications in the aerospace and power-generation sectors. Ni-based superalloys are known to have a complex chemistry, with over a dozen alloying elements in most alloys, enabling them to achieve outstanding high-temperature mechanical performance as well as oxidation resistance when processed using conventional routes (e.g., casting and forging). Nonetheless, this complex chemistry results in the formation of various phases that could affect their processability using AM, resulting in cracking. Furthermore, due to the directional solidification and rapid cooling associated with AM processes, the alloys experience significant anisotropy due to the epitaxially grown microstructure, as well as the residual stresses that can sometimes be difficult to mitigate using thermal postprocessing techniques. This article highlights the outstanding issues in Ni-based superalloys AM processing, with special emphasis on defect formation mechanisms, process optimization, and residual stress development.

The epitaxial integration of III–V optoelectronic devices on silicon will be the enabling technology for full-scale deployment of silicon photonics and the key to improving communication systems. Silicon photonics also offer new opportunities for the realization of ultracompact and fully integrated sensing systems operating in the mid-infrared (MIR) regime of the spectrum. In this article, we review recent developments, through several approaches, in the direct metamorphic epitaxial growth of various III–V materials-based lasers on silicon substrates. We show that GaAs-based 1.3-μm III–V quantum dot lasers and GaSb-based MIR quantum-well lasers grown on silicon substrates can operate with low threshold current density and high operating temperature, which hold promise for the future.

Three-dimensional (3D) scanning transmission electron microscopy (STEM) has become one of the primary tools for analytical characterization in materials science and also finds increasing use in the life sciences. A number of different recording schemes exist for the acquisition of 3D data using STEM, each capturing different spatial frequencies and, thus, different information about the shape of a specimen. In this article, we present and compare different sampling approaches based on images with both large and small depth of field. We highlight the latest contribution to 3D data acquisition, the combined tilt, and focal series. This recording scheme combines the advantages of tilt series-based tomography with 3D data acquisition using a focal series and is particularly beneficial for imaging specimens with a thickness of 1 µm or greater.

As a relatively new class of hierarchically structured materials, nanotwinned (NT) metals exhibit an exceptional combination of high strength, good ductility, large fracture toughness, remarkable fatigue resistance, and creep stability. This article reviews current studies on fracture, fatigue, and creep of NT metals, with an emphasis on the fundamental deformation and failure mechanisms. We focus on the complex interactions among cracks, dislocations, and twin boundaries, the influence of microstructure, twin size, and twinning/detwinning on damage evolution, and the contribution of nanoscale twins to fatigue and creep under indentation and irradiation conditions. The article also includes critical discussions on the effects of twin thickness and grain size on the fracture toughness, fatigue resistance, and creep stability of NT metals.