Films of piezoelectric and ferroelectric oxides have been widely investigated for various applications, including microelectromechanical systems (MEMS) for printing. Pb(Zr,Ti)O3 is of particular interest due to its excellent piezoelectric properties. Control of the density, crystalline orientation, and compositional uniformity is essential to obtain these properties. In this article, we review recent progress on the fabrication of epitaxial Pb(Zr,Ti)O3films, in which the aforementioned control can be achieved. We discuss the different approaches used for the deposition of the epitaxial piezoelectric layer as well as the achieved degrees of the epitaxy. Furthermore, the integration of these piezoelectric layers in MEMS and the corresponding performance are discussed.

Multi-fingered prosthetic limbs are now capable of performing complex movements, closely simulating those of the lost human arm/hand in amputees. Conveying natural control and perception of such sophisticated robotic limbs requires direct interfacing with the nervous system of the users. Both the brain and transected peripheral nerves have been proposed as appropriate locations for such neural interfaces. In the peripheral nerves, several electrode designs have been used successfully to record motor signals, and through stimulation, used to convey sensation in long-term amputee human volunteers. Here we review the advantages and limitations of peripheral nerve interfaces (PNIs) in relation to the desired characteristics for safety and performance. We compare current PNI electrodes and materials designed to increase recording sensitivity and to achieve selective stimulation of different nerves such as those carrying mechanical sensation and limb position information. Emphasis is placed on novel electrode materials, including biological coatings, conductive polymers, and nanostructured modifications. Successful development of reliable PNIs will not only enable natural control and feel of future robotic prosthetics, but will likely be a centerpiece technology in the development of multiple bionic organs.

Perhaps the greatest challenge of the 21st century is to sustain the developmental needs of the world. The economic growth that occurred in developing countries over the past two decades is unprecedented. Materials science and engineering (MSE) innovations will continue to have a pivotal role as an enabling resource to address sustainable development needs. This article focuses on the opportunities for MSE in five key thematic areas: energy, transportation, housing, materials resources, and health.

Enhanced and confined optical fields near metallic nanostructures, supporting surface plasmon (SP) resonances, make it possible to enhance the interaction of light with tiny amounts of matter, down to the molecular level. Such capability has been extensively exploited in the framework of optical spectroscopy, nonlinear optics, imaging and integrated optics, among others. Here we discuss the use of plasmonics for optical trapping. Plasmon-based trapping addresses key limitations of conventional optical tweezers formed at the focus of a diffraction-limited laser beam. Beyond permitting trapping of smaller objects, down to the true nanometer scale, they enable parallel trapping from a single beam and can be easily integrated on a chip. SP-based trapping opens new perspectives in a wide range of fields from biology to quantum optics.

Atomistic and nanometer scale mechanisms of electrochemical reactions and ionic flows in solids in the nanometer–micron range persist as terra incognito in modern science. While structural and electronic phenomena are now accessible to electron and scanning probe microscopy (SPM) techniques, probing nanoscale electrochemistry requires the capability to probe local ionic currents. Here, we discuss principles and applications of electrochemical strain microscopy (ESM), a technique based on probing minute deformations induced by electric bias applied to an SPM tip. ESM imaging and spectroscopy are illustrated for several energy storage and conversion materials. We further argue that down-scaling of physical device structures based on oxides necessitates ionic and electrochemical effects to be taken into account. Future pathways for ESM development are discussed.

Fundamental aspects of the interactions between cells and biomaterials provide a crucial framework for the design of many systems that interact with the human body. A comprehensive understanding of multifactorial processes may provide an adequate basis for the rational design of implantable devices ranging from nanoparticles for drug delivery and scaffolds for tissue engineering, to artificial organs for augmentation and rehabilitation. Recent progress in the elucidation of cell-biomaterials interactions has been predicated on advances in polymer chemistry, materials engineering, and device microfabrication. The confluence of these developments has stimulated a newfound ability to design soft materials and interfaces with precise chemical, physical, and mechanical properties. While static surfaces can yield insight into the interaction of mammalian cells with medical materials, the study of fundamental cell-biomaterials phenomena will benefit significantly from the ability to present biologically active signals to cells with spatiotemporal control. Specifically, the use of dynamic materials and interfaces can mirror the intrinsic dynamic behavior of living cells. This article highlights recent advances in soft materials design, interfacial engineering, and synthetic polymer networks in the context of producing dynamic materials to study cell-biomaterials interactions. Emerging challenges and future research directions are also discussed.

Many-body potentials were introduced in the early 1980s and have become a workhorse for the simulation of materials, especially metallic systems. The physical motivations for the main classes of the various many-body potentials are summarized, and the advantages of this approach are discussed. Some current examples related to grain growth, stress generation in thin films, shock loading, and nanowire deformation are presented to illustrate the continuing value of these approaches. Finally, some of the approaches that have been introduced in subsequent years are briefly described.

Inorganic semiconductors such as silicon, gallium arsenide, and gallium nitride provide, by far, the most well-established routes to high performance electronics/optoelectronics. Although these materials are intrinsically rigid and brittle, when exploited in strategic geometrical designs guided by mechanics modeling, they can be combined with elastomeric supports to yield integrated devices that offer linear elastic responses to large strain (∼100%) deformations. The result is an electronics/optoelectronics technology that offers the performance of conventional wafer-based systems, but with the mechanics of a rubberband. This article summarizes the key enabling concepts in materials, mechanics, and assembly and illustrates them through representative applications, ranging from electronic “eyeball” cameras to advanced surgical devices and “epidermal” electronic monitoring systems.

Plasmonic metal nanoparticles have the ability to act as nanoscale antennas for visible and near-IR (infrared) light, leading to increased electromagnetic fields at their surface. As a result, Raman scattering and/or fluorescence from nearby molecules can be enhanced by many orders of magnitude. However, imaging how these molecules interact with the enhanced fields at the surface of noble metal nanoparticles is a challenge due to the diffraction limit of light. In this article, we review super-resolution imaging of plasmonic hot spots using two all-optical readouts, surface-enhanced Raman scattering and surface-enhanced fluorescence, which are used to locate and track single or a few molecules on the surface of nanoscale-roughened metals. These super-resolution imaging techniques allow localization of the emission centroid of an emitter to better than 5 nm and allow mapping of the electromagnetic field enhancement experienced by molecules at the nanoparticle surface.

Self-folding of thin films is a more deterministic form of self-assembly wherein structures curve or fold up either spontaneously on release from the substrate or in response to specific stimuli. From an intellectual standpoint, the study of the self-folding of thin films at small size scales is motivated by the observation that a large number of naturally occurring materials such as leaves and tissues show curved, wrinkled, or folded micro- and nanoscale geometries. From a technological standpoint, such a self-assembly methodology is important since it can be used to transform the precision of existing planar patterning methods, such as electron-beam lithography, to the third dimension. Also, the self-folding of graphene promises a means to create a variety of three-dimensional carbon-based micro- and nanostructures. Finally, stimuli responsive self-folding can be used to realize chemomechanical and tether-free actuation at small size scales. Here, we review theoretical and experimental aspects of the self-folding of metallic, semiconducting, and polymeric films.

Identifying constituent atoms in materials is the ultimate goal for all analytical techniques. Here, we describe the successful achievement of single atom spectroscopy in nanostructured carbon-based materials using a scanning transmission electron microscope equipped with electron energy-loss spectroscopy. The chemical analyis of individual metallofullerene molecules can be successfully performed without massive beam damage. Atom-by-atom spectroscopy of the edge carbon atoms in single layer graphene is also discussed.

The exceptional properties of graphene originate from its two-dimensional polymeric structure of sp2-bonded carbon. This feature also causes graphene to grow on metal substrates through mechanisms that are strikingly different from those of conventional heteroepitaxy. We provide here a brief review of graphene growth on metals, a subject with a rich history even before the recent explosion of interest in graphene. The current activities related to graphene growth on metals have been motivated by the need to develop low-cost, scalable processes for graphene synthesis and to understand how graphene–metal interfaces behave in devices. In this article, we examine the current state of the art, emphasizing the basic processes that distinguish graphene growth from normal crystal growth.

Atomic force microscopy (AFM)-based impedance spectroscopy provides localized impedance information of materials and interfaces at the nanoscale by utilizing the conductive AFM tip as a moving electrode to detect current response as a function of time and frequency under controlled environments. This capability enables AFM-based nanoscale impedance measurements to play a unique role in enhancing our understanding of many electronic and electrochemical devices. This article introduces the central concepts of AFM-based impedance measurement and reviews recent examples applying this technique to a variety of functional materials systems, in particular focusing on fuel cells, lithium-ion batteries, photoactive biomembranes, as well as other application examples.

The recording of neural signals with microelectrodes that are implanted into the cortex of the brain is potentially useful for a range of clinical applications. However, the widespread use of such neural interfaces has so far been stifled because existing intracortical electrode systems rarely allow for consistent long-term recording of neural activity. This limitation is usually attributed to scar formation and neuron death near the surface of the implanted electrode. It has been proposed that the mechanical property mismatch between existing electrode materials and the brain tissue is a significant contributor to these events. To alleviate this problem, we utilized the architecture of the sea cucumber dermis as a blueprint to engineer a new class of mechanically adaptive materials as substrates for “smart” intracortical electrodes. We demonstrated that these originally rigid polymer nanocomposites soften considerably upon exposure to emulated physiological and in vivo conditions. The adaptive nature of these bioinspired materials makes them useful as a basis for electrodes that are sufficiently stiff to be easily implanted and subsequently soften to better match the stiffness of the brain. Initial histological evaluations suggest that mechanically adaptive neural prosthetics can more rapidly stabilize neural cell populations at the device interface than rigid systems, which bodes well for improving the functionality of intracortical devices.

Oxides hold great promise as new and improved materials for thermal-barrier coating applications. The rich variety of structures and compositions of the materials in this class, and the ease with which they can be doped, allow the exploration of various mechanisms for lowering thermal conductivity. In this article, we review recent progress in identifying specific oxides with low thermal conductivity from both theoretical and experimental perspectives. We explore the mechanisms of lowering thermal conductivity, such as introducing structural/chemical disorder, increasing material density, increasing the number of atoms in the primitive cell, and exploiting the structural anisotropy. We conclude that further systematic exploration of oxide crystal structures and chemistries are likely to result in even further improved thermal-barrier coatings.

Recent advances in stretchable electronics have seen the emergence of new technologies, and intensive efforts are being dedicated to embed some form of “intelligence” in various types of surfaces. However, the primary challenge in the field of stretchable electronics has been the development of stretchable or elastic electrical wiring that is both highly conductive and highly stretchable. Another challenge has been the development of manufacturing processes for integrating active device components as non-stretchable regions with electrical wiring as stretchable regions; the rigid/stretchable interfaces of these components require both high conductivity and high mechanical stability. In this article, we review the fabrication of carbon-nanotube-based elastic conductors with high electrical conductivity and mechanical stretchability as a representative example of stretchable organic integrated circuit electronics. Furthermore, we demonstrate the development of rubber-like stretchable integrated circuits for large-area human/machine interfaces. The fabrication process described in this article exploits the advantages of integrating a variety of electrical functional materials, ranging from rigid and semi-rigid elastomers to gels, with electronic circuits. The stretchable devices can be spread over a wide range of surfaces, including free surface curvatures and movable parts, thereby significantly increasing the scope of application of stretchable electrical and electronic circuits.

Materials scientists today employ essentially the entire periodic table in creating modern technology. In an age of sharply increasing usage, it is reasonable to wonder about the supplies of these elemental building blocks. In this article, we review current and prospective supply and demand for a variety of metals. Although data are often sparse, available information suggests that current practices are likely to lead to scarcity for some metals in the not-too-distant future. We conclude by discussing policies that, if adopted, might defuse some of these concerns.

Coulson’s bond order is a chemically intuitive quantity that measures the difference in the occupation of bonding and anti-bonding orbitals. Both empirical and rigorously derived bond order expressions have evolved in the course of time and proven very useful for atomistic modeling of materials. The latest generation of empirical formulations has recently been augmented by screening-function approaches. Using friction and wear of diamond and diamond-like carbon as examples, we demonstrate that such a screened bond order scheme allows for a faithful description of dynamical bond-breaking processes in materials far from equilibrium. The rigorous bond order expansions are obtained by systematic coarse-graining of the tight binding approximation and form a bridge between the electronic structure and the atomistic modeling hierarchies. They have enabled bottom-up derivations of bond order potentials for covalently bonded semiconductors, transition metals, and multicomponent intermetallics. The recently developed magnetic bond order potential gives a correct description of both directional covalent bonds and magnetic interactions in iron and is able to correctly predict the stability of bulk Fe polymorphs as well as the intricate properties of dislocation cores. The bond order schemes hence represent a family of reliable and powerful models that can be applied in large-scale simulations of complex processes involving fracture, wear, and plasticity.

This article reviews recent progress in understanding the resistive switching (RS) behavior and improvements in device performance of RS metal oxide (MO) thin-film systems and devices. The diverse RS MO materials are classified according to their switching mechanisms and characteristics. For each category, some representative materials are selected, and their characteristics are discussed. In addition, other factors such as the device structure, which also plays a crucial role in determining the device properties, are discussed as well. When applied in a real circuit (e.g., in a crossbar structure), there are device features/characteristics that need to be considered, including the bias polarity for switching, the current-voltage relationship, reliability, and scaling issues. Since nonvolatile RS in many MO materials is primarily associated with localized conduction channels, understanding the nature and the dynamic change of the current path structure is crucial and therefore is reviewed at length here. Guidelines for the choice of materials and access devices and their fabrication methods will also be provided. Finally, this review concludes with the outlook and challenges of MO-based resistance change devices for semiconductor memories.

Piezoelectric microelectromechanical systems (MEMS) have been proven to be an attractive technology for harvesting small magnitudes of energy from ambient vibrations. This technology promises to eliminate the need for replacing chemical batteries or complex wiring in microsensors/microsystems, moving us closer toward battery-less autonomous sensors systems and networks. To achieve this goal, a fully assembled energy harvester the size of a US quarter dollar coin (diameter = 24.26 mm, thickness = 1.75 mm) should be able to robustly generate about 100 μW of continuous power from ambient vibrations. In addition, the cost of the device should be sufficiently low for mass scale deployment. At the present time, most of the devices reported in the literature do not meet these requirements. This article reviews the current state of the art with respect to the key challenges such as high power density and wide bandwidth of operation. This article also describes improvements in piezoelectric materials and resonator structure design, which are believed to be the solutions to these challenges. Epitaxial growth and grain texturing of piezoelectric materials is being developed to achieve much higher energy conversion efficiency. For embedded medical systems, lead-free piezoelectric thin films are being developed, and MEMS processes for these new classes of materials are being investigated. Nonlinear resonating beams for wide bandwidth resonance are also being developed to enable more robust operation of energy harvesters.