Aluminum hydride (AlH3), and the complex aluminum hydrides (e.g., M3AlH6, MAlH5, M2AlH7, M(AlH4)n), make up a fascinating class of materials that have received considerable attention over the past 60 years for their use as explosives, reducing agents, solid rocket propellants, as well as a hydrogen source for portable power systems. The recent renaissance in hydrogen storage research, particularly for automotive applications, has generated renewed interest in aluminum-based hydrides due to their capacity to store up to 11 wt% hydrogen with volumetric capacities up to 150 g H2/L (more than twice that of liquid hydrogen). In addition, hydrogen can be released from these materials by low temperature thermolysis (<100°C), making them well-suited for proton exchange membrane fuel cells and other low temperature applications. This article covers recent research on aluminum-based hydrides, including crystal structures, thermodynamics, kinetics, hydrogenation conditions, and regeneration methods.

The successful development of quantum computers is dependent on identifying quantum systems to function as qubits. Paramagnetic states of point defects in semiconductors or insulators have been shown to provide an effective implementation, with the nitrogen-vacancy center in diamond being a prominent example. The spin-1 ground state of this center can be initialized, manipulated, and read out at room temperature. Identifying defects with similar properties in other materials would add flexibility in device design and possibly lead to superior performance or greater functionality. A systematic search for defect-based qubits has been initiated, starting from a list of physical criteria that such centers and their hosts should satisfy. First-principles calculations of atomic and electronic structure are essential in supporting this quest: They provide a deeper understanding of defects that are already being exploited and allow efficient exploration of new materials systems and “defects by design.”

This article reports the search for nonflammable, stable electrolytes based on ionic liquid (IL) compounds, able to effectively improve the needed safety and reliability of lithium batteries. The most significant results are reviewed with the aim of elucidating critical aspects governing the properties of IL electrolytes, including (1) transport properties affecting ionic conductivity and the cycling rate of battery systems, (2) electrochemical/chemical stability toward most conventional electrode materials, and (3) thermal properties determining the range of applicability. Both liquid and polymer electrolytes, adopting ILs as the main component or as an additive to standard electrolyte solutions, are considered. Very promising results, in terms of battery prototype performances in scaled-up configurations, demonstrate the validity of the use of ILs for practical applications. Even though further improvements are necessary, particularly at high current density operations in both lithium-metal and lithium-ion systems, the realization of safer, high-performance batteries based on IL electrolytes is certainly possible. It can be concluded that ILs represent a viable solution to disappointing compromises between energy density and acceptable safety features in lithium batteries.

Quantum wells created from nanostructured transition metal oxides offer unique possibilities for creating and manipulating quantum states of matter, including novel superconductors, high Curie temperature magnets, controllable metal-insulator transitions, and new topological states. This article explores what is known and conjectured about confined electronic states in oxide quantum wells. Theoretical challenges are reviewed, along with issues arising in the creation of oxide quantum wells. Examples from the current experimental state of the art are summarized, open questions are discussed, and prospects for the future are outlined. The key roles of epitaxial strain and proximity effects are emphasized.

This article reviews the principles of magnetic field-directed self-assembly (MFDSA) of magnetic nanoparticles (MNPs), along with recent studies that advance the fundamental understanding and potential capabilities of MNP MFDSA. This technology could eventually find application in manufacturing novel materials and components for biomedicine, energy, optics, functional composites, and microfluidics. In MFDSA, an externally applied field drives the assembly of MNPs. Uniform fields can create complex chains of MNPs, while inhomogeneous fields (such as those created by permanent magnets) apply attractive forces to MNPs that pull them toward the region of strongest field strength. Thus, MNPs can be self-organized as well as directed into user-designed patterns by controlling the external field arrangement. Because of its biocompatibility, nanoscale resolution, and low cost, MFDSA is a highly versatile technique that could enable high volume nanomanufacturing of MNPs into complex, finished materials.

The traditional paradigm for obtaining a quantitative measurement in point-of-care (POC) assays may not be adequate for extremely resource-limited environments, such as remote villages in the developing world. In standard quantitative POC assays, sample volume and assay time must be controlled. Furthermore, thermally stable assay reagents, a power supply, and an electronic reader must be available. Arranging all of these variables in a single assay results in systems that are too complicated, expensive, and user-intensive for extremely resource-limited environments. This overview describes new approaches in various areas of materials science that are beginning to redefine how quantitative POC assays are achieved, with a focus on approaches that use paper as the platform for the assays. Such approaches should have an immediate impact in the developing world, but also may transform quantitative POC assays in a variety of other settings, where quantitative information about the health of people, plants, animals, and the environment would help individuals better assess and manage their lives.

The mainstream commercialization of colloidal quantum dots (QDs) for light-emitting applications has begun: Sony televisions emitting QD-enhanced colors are now on sale. The bright and uniquely size-tunable colors of solution-processable semiconducting QDs highlight the potential of electroluminescent QD light-emitting devices (QLEDs) for use in energy-efficient, high-color-quality thin-film display and solid-state lighting applications. Indeed, this year’s report of record-efficiency electrically driven QLEDs rivaling the most efficient molecular organic LEDs, together with the emergence of full-color QLED displays, foreshadow QD technologies that will transcend the optically excited QD-enhanced products already available. In this article, we discuss the key advantages of using QDs as luminophores in LEDs and outline the 19-year evolution of four types of QLEDs that have seen efficiencies rise from less than 0.01% to 18%. With an emphasis on the latest advances, we identify the key scientific and technological challenges facing the commercialization of QLEDs. A quantitative analysis, based on published small-scale synthetic procedures, allows us to estimate the material costs of QDs typical in light-emitting applications when produced in large quantities and to assess their commercial viability.

Surfaces that display liquid contact angles greater than 150° along with low contact angle hysteresis for liquids with both high and low surface tension values are known as superomniphobic surfaces. Such surfaces are of interest for a diverse array of applications, including self-cleaning surfaces, nonfouling surfaces, stain-free clothing, spill-resistant protective wear, drag reduction, and fingerprint-resistant surfaces. Recently, significant advances have been made in understanding the criteria required to design superomniphobic surfaces. In this article, we discuss the roles of surface energy, roughness, re-entrant texture, and hierarchical structure in fabricating superomniphobic surfaces. We also provide a review of different superomniphobic surfaces reported recently in the literature and emphasize the need for mechanical, chemical, and radiation durability of superomniphobic surfaces for practical applications. Finally, we conclude with a discussion of the unresolved challenges in developing durable superomniphobic surfaces that define the scope for further improvements in the field.

Advances in nanotechnology have enabled the opportunity to fabricate nanoscale optical devices and chip-scale systems in diamond that can generate, manipulate, and store optical signals at the single-photon level. In particular, nanophotonics has emerged as a powerful interface between optical elements such as optical fibers and lenses, and solid-state quantum objects such as luminescent color centers in diamond that can be used effectively to manipulate quantum information. While quantum science and technology has been the main driving force behind recent interest in diamond nanophotonics, such a platform would have many applications that go well beyond the quantum realm. For example, diamond’s transparency over a wide wavelength range, large third-order nonlinearity, and excellent thermal properties are of great interest for the implementation of frequency combs and integrated Raman lasers. Diamond is also an inert material that makes it well suited for biological applications and for devices that must operate in harsh environments.

In suspensions of magnetic nanoparticles in appropriate carrier liquids—commonly called ferrofluids—an external magnetic field can control the fluid properties such as viscosity. This article provides an overview of the properties and general makeup of ferrofluids, as well as classical fluid dynamics. Some of the applications of ferrofluids are also described.

Supercapacitors are nowadays considered to be one of the most important electrochemical storage devices. These devices display high power and extraordinary cycle life, and they are currently used in an increasing number of applications. However, in order to further increase the applications of supercapacitors, an increase in their energy capacity appears to be necessary. Moreover, the development of safe and environmentally friendly supercapacitors is also required. In this article, we illustrate the contributions ionic liquids (ILs) might play in the development of high energy and safe supercapacitors. First, the use of ILs as electrolytes in supercapacitors is considered, and the advantages as well as challenges related to the use of this kind of electrolyte are analyzed. Next, the interaction between ILs and electrode materials is taken into account, with particular attention paid to inactive components of supercapacitor electrodes. The introduction of natural cellulose as a binder is used as an example of the contribution ILs might provide to the development of environmentally friendly supercapacitors.

Quantum dots (QDs) have inspired researchers to develop innovative optoelectronics applications, and especially the current advances in light-emitting diode (LED) displays have attained production level technology. The most challenging issues in developing practical QD displays are the design of highly efficient and stable nanostructures and control of the interfaces between the nanostructures and device components. This article highlights applications of both color-converting and current-driven QD-LEDs, with emphasis on the synthesis of materials specifically tailored for display applications and fabrication techniques that improve device performance, such as cross-linking and transfer-printing of nanocrystal thin films.

The development of safe, efficient, and economic hydrogen storage technologies is key for implementation of a hydrogen-based energy economy. In the search for high-hydrogen content materials, attention in the past decade has shifted to amides and borohydrides, two representative solid-state chemical sorption materials with high hydrogen capacities that had not been previously explored for hydrogen storage. A large number of new amide and borohydride systems have recently been developed that expand the material scope for hydrogen storage. This article reviews the current progress in amides and borohydrides with emphases on material design and kinetic improvement.

A quantum computer will have computational power beyond that of conventional computers, which can be exploited for solving important and complex problems, such as predicting the conformations of large biological molecules. Materials play a major role in this emerging technology, as they can enable sophisticated operations, such as control over single degrees of freedom and their quantum states, as well as preservation and coherent transfer of these states between distant nodes. Here we assess the potential of semiconductor nanowires grown from the bottom-up as a materials platform for a quantum computer. We review recent experiments in which small bandgap nanowires are used to manipulate single spins in quantum dots and experiments on Majorana fermions, which are quasiparticles relevant for topological quantum computing.

Recent advances in understanding electronic charge transport in organic semiconductors are motivated by the fast growth of organic electronics. In particular, organic single crystals provide an ideal test bed for systematic studies of charge transport, with rapid progress in single-crystal-based field-effect transistors in the past few years. Charge densities induced in crystals by the field-effect have been in the low limit regime (1010 cm–2 to 1013 cm–2) mainly due to the difficulties of boosting gate dielectric capacitance. Consequently, the transport physics of organic crystals in the high-charge-density regime has not been systematically explored. With the emergence of the electrolyte gating technique, ultrahigh charge densities (1013 cm–2 to 1015 cm–2) can be achieved. In this article, we first discuss the general methodologies of applying electrolyte gating to organic crystals. We then review several recent research highlights, including the maximization of charge density and improvement of carrier mobility, enhanced understanding of the mobility-charge density relationship, and observations of ambipolar transport and a novel conductivity peak that occurs only at high charge densities. These recent achievements are extremely important for ongoing efforts to realize novel transport behavior in organic crystals, such as superconductivity and the insulator-to-metal transition.

We provide a review of the main aspects related to surface-enhanced Raman scattering (SERS) enhancement factors (EFs), from their origins to the important issue of their practical quantification. The discussion also focuses on correcting some long-held misconceptions regarding the EFs in SERS, which still persist through the literature. We explain the main topics in simple terms, aiming at clarification of basic concepts rather than an in-depth overview of the already existing literature.

Directional textured surfaces help butterflies to shed water from their wings, pitcher plants to capture prey, and water striders and certain beetles and spiders to walk on water. Inspired by natural directional surfaces, researchers have developed a myriad of synthetic surfaces with precisely tuned physicochemical properties to regulate wettable adhesion. Anisotropic surfaces are of great value to the energy and biomedical fields for applications such as directional syringes, microprocessor cooling, high-efficiency hydropower turbines, and nanoscale digital fluidics. We summarize experimental and theoretical approaches to the design, synthesis, and characterization of engineered surfaces demonstrating anisotropic wetting properties.

Oxide thin films and interfaces exhibit a variety of novel magnetic phenomena, which are unknown in well-crystallized bulk material. The origin of these phenomena must be sought in the changes in electronic structure due to broken symmetry, strain, and electronic or atomic reconstruction, including oxygen and cation defects. These effects are first discussed in magnetically ordered 3d oxide thin films and heterostructures, wherein a metal-insulator transition up on changing film thickness may influence the magnetism. In heterojunctions, the interface magnetic order can be modified, and exchange bias may appear. A high-temperature ferromagnetic-like response in dilute and undoped oxide films appears to be associated with defects near the substrate interface. A two-dimensional electron gas emerges at interfaces of a polar oxide and SrTiO3, where electronic reconstruction brings electrons into the bottom of the Ti d band; ferromagnetism then emerges as a result of localized or delocalized d states in the presence of atomic defects.

Cellulose is one of the most abundant organic materials on earth, and cellulose paper is ubiquitous in our daily life. Re-engineering cellulose fibers at the nanoscale will allow this renewable material to be applied to advanced energy storage systems and optoelectronic devices. In this article, we examine the recent development of nanofibrillated cellulose and discuss how the integration of other nanomaterials leads to a wide range of applications. The unique properties of nanofibrillated cellulose enable multi-scale structuring of the functional composites, which can be tailored to develop new concepts of energy and electronic devices. Tapping into the nanostructured materials offered by nature can offer many opportunities that will take nanotechnology research to a new level.