Review Articles

Covalent organic frameworks are crystalline porous polymers with precisely ordered polygon architectures. In this Review we summarize recent advances in the design principles and synthetic reactions, highlight the current status in structural construction and functionality design, and predict challenging issues and future directions.

Reducing or even eliminating the need for precious-metal catalysts is crucial for the commercialization of clean energy technologies and various important industrial processes. Carbon materials have recently been shown to be cost-effective and efficient metal-free catalysts in clean energy generation and storage, environmental protection and chemical production.

Phosphorene is a 2D material exhibiting remarkable mechanical, electronic and optical properties. In this Review, we survey fabrication techniques and discuss theoretical and experimental findings, exploring phosphorene from its fundamental properties to its implementation in devices.

The energy extrema of an electronic band are referred to as valleys. In 2D materials, two distinguishable valleys can be used to encode information and explore other valleytronic applications.

Field-effect transistors (FETs) with semiconducting channels made from 2D materials are known to have fewer problems with short-channel effects than devices comprising 3D semiconductors. In this Review, a mathematical framework to evaluate the performance of FETs is outlined with a focus on the properties of 2D materials, such as graphene, transition metal dichalcogenides, phosphorene and silicene.

Heavy fermion systems are ideally suited to study strong electronic correlations. These fascinating materials are characterized by a clear separation of the relevant energy scales and may exhibit quantum critical points, non-Fermi-liquid behaviour and unconventional superconductivity coexisting or competing with magnetism.

Thermoelectrics can be used to harvest energy and control temperature. Organic semiconducting materials have thermoelectric performance comparable to many inorganic materials near room temperature. Better understanding of their performance will provide a pathway to new types of conformal thermoelectric modules.

The surface areas of molecular organic cage solids now rival those of metal–organic frameworks. In this Review, the synthesis and structures of various porous organic cages are outlined together with a discussion of the characteristics — such as solubility, polymorphism and modular co-crystallization — that distinguish these cages from their inorganic or hybrid counterparts.

The fascinating wave phenomenon of ‘bound states in the continuum’ spans different material and wave systems, including electron, electromagnetic and mechanical waves. In this Review, we focus on the common physical mechanisms underlying these bound states, whilst also discussing recent experimental realizations, current applications and future opportunities for research.

With a dangling-bond-free surface, two dimensional layered materials (2DLMs) can enable the creation of diverse van der Waals heterostructures (vdWHs) without the conventional constraint of lattice matching or process compatibility. This Review discusses the recent advances in exploring 2DLM vdWHs for future electronics and optoelectronics.

Multiferroic materials exhibit magnetic and ferroelectric order at the same time and provide a way to control magnetism with electric fields. We discuss the mechanisms supporting multiferroicity, multiferroic thin films and heterostructures, the non-equilibrium dynamics of multiferroics, fundamental symmetry issues and the impact of multiferroics on other research areas.

Magnetic skyrmions are quasiparticles that hold promise for future spintronic devices. In this Review, the detection, creation, manipulation and deletion of individual skyrmions in ultrathin films and in multilayers are surveyed, and their control by currents and external fields is discussed.

Applications of liquid-phase transmission electron microscopy (TEM) and cryogenic TEM to investigations of dynamic processes in diverse materials systems — both inorganic and organic — are transforming our understanding of the mechanisms underlying the formation of materials in synthetic, biological and geochemical environments.

Complex mechanisms are responsible for the biomineralization of skeletal tissues and pathological calcification in the cardiovascular system. In this Review, the physiochemical and biomechanical properties of mineralized tissues, both physiologic and pathophysiologic, and analytical methods to elucidate their finer structure are discussed.

Thermomechanical treatments — cold and hot deformation — are established for polycrystalline metals. Their use on metallic glasses to obtain relaxed and rejuvenated states has just begun to be explored, and holds promise for extending the range of available glassy states and gaining access to improved properties.

The clinical translation of biomaterials for tissue engineering reveals their therapeutic performance and relevance, and thus enables the improvement of biomaterials design. In this Review, the design and translation of biomaterials, particularly cartilage and cornea repair, and a new understanding of the interaction between biomaterials and the host immune system are discussed.

To optimize the synthesis of functionally designed nanoparticles, a clear understanding of their formation mechanisms is needed. This Review presents the structural properties of nanoclusters and their role in the prenucleation period, and discusses nonclassical nucleation and growth models, as well as heterogeneous nucleation of multicomponent nanoparticles.

Graphene has now enabled the development of faster and more powerful batteries and supercapacitors. In this Review, we discuss the current status of graphene in energy storage, highlight ongoing research activities and present some solutions for existing challenges.

In this Review, the structure, bonding and defects of half-Heusler compounds are explained in terms of the framework of Zintl (or valence-precise) chemistry. This deeper understanding of the structure and electronic properties of half-Heusler compounds should aid the design of improved thermoelectric materials.

Piezotronics and piezo-phototronics offer new means of implementing adaptive electronics and optoelectronics, taking advantage of the coupling between piezoelectric polarization and semiconductor properties in piezoelectric semiconductor nanomaterials. This Review discusses the recent progress in piezotronics and piezo-phototronics, as well as future research directions.