Emergent behavior can be achieved in composites by interfacing different materials at the nano- or mesoscales. Integrating different materials on a single platform or forming composite provides a new design paradigm to yield enhanced or novel functionalities that cannot be obtained in individual constituents. Nanocomposites, in particular, have been model systems for enhancing interface effects on physical properties because they provide reduced dimensionality or enlarged interfacial areas. To fabricate technologically relevant multifunctional materials, one needs to understand and control the interactions in different materials by manipulating interfaces at the nano- or mesoscales. This issue of MRS Bulletin focuses on nanocomposites, with an emphasis on approaches to the design and control of the functionalities of composite materials through controlled synthesis and advanced characterization in concert with simulation and modeling.

Multiferroic magnetoelectric nanostructures with coupled magnetization and electric polarization across their interfaces have stimulated intense research activities over the past decade. Such interface-based magnetoelectric coupling can be exploited to significantly improve the performance of many devices such as memories, tunable radio-frequency/microwave devices, and magnetic sensors. In this article, we introduce a number of current or developing technologies and discuss their limitations. We describe how the use of magnetoelectric nanostructures can overcome these limitations to optimize device performance. We also present challenges that need to be addressed in pursuing practical applications of magnetoelectric devices.

Complex oxides provide an ideal playground for exploring the interplay among the fundamental degrees of freedom: structural (lattice), electronic (orbital and charge), and magnetic (spin). In thin films and heterostructures, new states of matter can emerge as a consequence of such interactions. Over the past decade, the ability to synthesize self-assembled nanocomposite thin films of metal oxides has provided another pathway for creating new interfaces and, thus, new physical phenomena. In this article, we describe examples of such materials systems explored to date and highlight the fascinating multifunctional properties achieved. These include enhanced flux pinning in superconductors, strain-enhanced ferroelectricity, strain- and charge-coupled magnetoelectrics, tunable magnetotransport, novel electrical/ionic transport, memristors, and tunable dielectrics.

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.

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.

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.

To meet the challenge of precise nanoscale arrangement of emitter and plasmonic nanoantenna, synthesis and assembly methods continue to evolve in accuracy and reproducibility. This article reviews some of the many strategies being developed for “soft” chemical approaches to precision integration and assembly. We also discuss investigations of the Purcell effect, emission directionality control, and near-unity collection efficiency of photons, emitter–emitter coupling, and higher-order emission processes that have been most deeply explored using individual-emitter– (or several-emitter–) nanoantenna pairs fabricated using traditional lithographic methods or dynamically and controllably manipulated using scanning probe methods. Importantly, these results along with theoretical analyses inspire and motivate continued advancements in large-scale synthesis and assembly. We emphasize assembly approaches that have been used to create nanosemiconductor–nanometal hybrids and, in particular, those that have afforded specific plasmonic effects on excitonic properties. We also review direct-synthesis and chemical-linker strategies to creating discrete, though less spatially extended, semiconductor–metal interactions.