Twentieth-century utopian visions of a space-age future have been eclipsed by dystopian fears of climate change and environmental degradation. Avoiding such grim forecasts depends on materials innovation and our ability to predict and plan not only their behaviour but also their sustainable manufacture, use and recyclability.
Materials innovation from quantum to globalIn the long run, what we make will survive and define us. Our modern material culture already marks a dislocation from the past so profound that it will leave a distinct and abrupt imprint of the Anthropocene in geological strata. Here, all the wondrous new materials reported daily in the literature will be lost to posterity, and what remains will be the crudest, most widespread and most telling physical components of modernity: plastics, metal alloys, glass and the modified geological materials of construction, along with human-made radionuclides and the signals of our massive and ongoing perturbations of natural biogeochemical cycles. Sometimes only such a long view can wake us up to our present state.
But those advanced materials invisible to deep time might nonetheless indirectly define this stratigraphic signature. How significantly human activities will transform the global environment — and the geological signal it bequeaths — may depend on our ability, within the next blink of geological time, to innovate away from ecological catastrophe.
Three-dimensional meshes rendered in DNA.
| doi: 10.1038/s41563-022-01350-x | |
Structural materials are critical components for our daily lives and industries. This Comment highlights the emerging concepts in structural materials over the past two decades, particularly the multi-principal element alloys, heterostructured materials and additive manufacturing that enables the fabrication of complex architectures.
Growing designability in structural materialsAlthough never as ‘glamorous’ in the world of materials science as quantum and electronic materials, perovskites or graphene, in many respects structural materials provide the framework for our civilization. The integrity of structural materials ensures the safety of our infrastructure (from buildings to bridges), the basis of our transportation (from automobiles and ships to aerospace), and the critical components for energy and power generation (from pipelines and nuclear pressure vessels to high-temperature power turbines). Over the past two decades there have been many advances in structural materials to enable safer planes, lighter cars, improved infrastructures, more efficient power supplies and the like. However, as many potential applications — such as aerospace, nuclear and hypersonics — call for materials to withstand more extreme environments, there remains the omnipresent quest to develop superior structural materials for the future that can perform at a lighter weight, under higher stresses and in such extreme conditions, including corrosive environments, intense impact loading and at very high or very low temperatures, to support advances in these strategic fields. Implicit in this quest are cost, environmental and sustainability concerns, and strategic issues.
In this Comment, we briefly describe some of the relatively new concepts in structural materials that have emerged over the past two decades and have largely expanded the design space in the field. In many cases, these materials have yet to be ‘used in earnest’, and some are still clearly in the realm of academic research, but they do represent exciting directions with the potential of developing materials with unprecedented mechanical performance.
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Expanding designability of structural materials in the past two decades.
Robert O. Ritchie & Xiaoyu Rayne Zheng
doi: 10.1038/s41563-022-01336-9 | |
Quantum materials show emergent electronic properties and related functions that are profoundly described by quantum mechanics beyond the semi-classical picture of electrons. Here, key developments and progress in the last two decades are surveyed and future challenges outlined.
Quantum materials at the crossroads of strong correlation and topologyThe discovery of high-temperature superconductivity (high-Tc) in copper oxides and the subsequent research fever in the late 1980s and 1990s completely altered the landscape of materials physics research. It became the common understanding that strong electron correlation, namely Coulomb repulsive interaction among the conduction electrons, is an important notion to produce unprecedented and intriguing electronic properties and functions. On the one hand, the semiconductor physics with negligible electron correlation effect has been extensively developed to form the basis for today's semiconductor technology. One of the big outcomes in physics from semiconductor research was the discovery of the quantum Hall effect (QHE) in 1980; for the development of quantum Hall physics, three Nobel prizes have been awarded. In particular, the concept of topology in condensed matter originates in the QHE and is now a fundamental design principle for quantum materials as ignited by the discovery of topological insulators in 2005. Here, defining quantum materials as those that show strongly correlated electrons as well as magnetic, ferroelectric, superconducting and topological orders, we draw on several families of quantum materials to focus on research advances in this highly active and evolving field over the last two decades or so.
The spin textures in k-space and real space with integer topological charges, Chern number and skyrmion number.
| doi: 10.1038/s41563-022-01339-6 | |
The success of silicon photonics is a product of two decades of innovations. This photonic platform is enabling novel research fields and novel applications ranging from remote sensing to ultrahigh-bandwidth communications. The future of silicon photonics depends on our ability to ensure scalability in bandwidth, size and power.
The revolution of silicon photonicsOptical research and engineering are undergoing a complete transformation. A decade ago, creating an optical experiment in the lab or an optical prototype, for example, required assembling components such as fibres, lenses, filters and so on. Today, this can be accomplished by sending an optical design to a foundry, where the integrated devices are lithographically defined and fabricated. Hundreds of products are being developed and commercialized based on silicon photonics. Foundries for mass production of silicon photonics are sprouting across the globe, where thousands of optical components are being integrated onto individual chips (Fig. 1).The idea of using silicon photonics for guiding, filtering and manipulating light was first explored in the 1980s, but only in the past two decades, when the need for high-speed and low-power photonics arose, did the field become vibrant as we know it today. Silicon photonics originated from the need to overcome the main bottleneck of computing: increasing the input and output bandwidth of a silicon chip by several orders of magnitude and bringing it to the same level as the data bandwidth that is generated and processed on the chip while consuming minimal power. Light is the ideal candidate for propagating high data rates with low power dissipation, as its frequency is much higher than the material resonances; therefore, its absorption is minimal. While the need for increasing interconnect bandwidth was high, the need for the optical technology to be compatible with the same materials and processes as the microelectronics — into which billions of dollars were already invested — was also high.
A silicon photonics chip.
| doi: 10.1038/s41563-022-01363-6 | |
Organic semiconductors based on molecular or polymeric π-conjugated systems are now used at scale in organic light-emitting diode (OLED) displays and show real promise in thin-film photovoltaics and transistor structures. Here, we address recent progress in understanding and performance for OLEDs and for organic photovoltaics.
Engineering the spin-exchange interaction in organic semiconductorsOrganic semiconductors present a number of fundamental research questions. Their semiconducting properties derive from carbon-based π valence and π* conduction orbitals, but it is a complex question whether or not there is sufficient inter- and intra-molecular contact between π orbitals to provide delocalized band states in the presence of strong Coulomb interactions and the disorder usually found in thin films. Although π bandwidths can be substantial (several eVs intrachain, or several tenths of an eV intermolecular), the Coulomb interactions that are inevitably involved in electronic excitations are much higher than for inorganic semiconductors (organics have typical refractive indices below and dielectric constants around). Thus, photoexcitation of these materials produces stable excitons at room temperature, with a large binding energy of order 0.5 eV (a Frenkel exciton). In contrast, the exciton in gallium arsenide or silicon can be described as a hydrogenic electron–hole state (Mott–Wannier exciton) with a binding energy around 10 meV. A corollary is that the spin-exchange energy is similarly large, pushing the lowest spin-triplet state — typically 0.5 eV — below the singlet state. This sets up a very different parameter space for organic semiconductors, as compared to inorganic semiconductors. Here, control of optoelectronic phenomena and devices calls for the engineering of excitons, by harnessing both Coulomb and spin-exchange interactions.
We address here the design and management of intra- and intermolecular excitons in light-emitting diodes (LEDs) and organic photovoltaics (OPVs), where the electron–hole Coulomb interaction is critical. We do not address progress made in electronic transport as exploited in thin-film transistors, but note that models for improved carrier mobilities and advances in device designs and performance have developed rapidly.
Excitonic-energy-level diagram of organic semiconductors.
Akshay Rao, Alexander James Gillett & Richard Henry Friend
doi: 10.1038/s41563-022-01347-6 | |
Materials and surface sciences have been the driving force in the development of modern-day lithium-ion batteries. This Comment explores this journey while contemplating future challenges, such as interface engineering, sustainability and the importance of obtaining high-quality extensive datasets for enhancing data-driven research.
Material science as a cornerstone driving battery researchClimate change, setting as a major challenge to humanity for the twenty-first century, is a threat that can undermine societal security and prosperity. Thus, the transformation away from fossil-fuel-based energy to a more decarbonized approach is vital to attain environmental sustainability. Policies are being implemented worldwide to promote renewable energy technologies, such as wind energy, bioenergy and solar photovoltaic, with the aim of achieving carbon neutrality by 2050. However, renewables, due to their intermittent nature, are difficult to deploy into the current energy network without parallel innovation in energy storage technologies (ESTs). These ESTs are essential to provide flexibility to energy systems, allowing for better optimization and efficiency gains. They can be classified into mechanical (pumped-storage hydroelectricity and compressed-air energy storage), electrical (supercapacitors and supermagnets), electrochemical (batteries and fuel cells), thermal and chemical. Thermal and chemical storage rely on the use of phase change materials with high heat transfer and chemical molecules (H2) hosting high energy, respectively. Similarly, electrical and electrochemical storage depends on the ability of the materials to store the electric charges on the surface and/or through redox process. In all cases, design of novel functional materials is the key enabler for better device performances or new applications.
Food-chain process from a new phase to practical electrode material.
| doi: 10.1038/s41563-022-01342-x | |
Metal–organic frameworks, porous coordination network materials constructed with metal ions and organic molecules, have grown over the past 20 years into an innovative chemistry that has contributed to solutions for the problems faced by humanity in the environment, resources, energy and health.
The development of molecule-based porous material families and their future prospectsGases are essential substances that are closely related to functions in the environment, energy applications and life activities. Many types of porous materials, including carbons, clays and minerals, and silicates (such as zeolites and mesoporous silica), have been utilized in everyday life applications related to gas sciences and technologies. There was a need for advanced porous materials that outperform conventional materials for gas storage, separation and conversion. Since the early nineteenth century, coordination polymers (CPs), which are constructed from metal ions and bridging ligands, have been studied with a focus on their crystal structures. In the late 1990s, CPs with stable permanent porosity that exhibit gas adsorption were discovered. This meant that the organic components could be modularly designed for chosen pore shapes and functionalities. Since this discovery, CPs have exploded as porous materials collectively called porous coordination polymers or metal–organic frameworks (MOFs). MOFs are highly designable in structure and functionality due to their rich coordination geometry and the variety of functional organic molecules, which enable a wide degree of structural and chemical control at synthesis. Their high porosity and surface area distinguish MOFs from conventional porous materials. The chemistry of MOFs has spilled over into the creation of more molecule-based porous materials, which have been actively studied, such as covalent–organic frameworks, polymers of intrinsic microporosity, and porous molecular solids.
Major MOF discoveries and developments over the past 20 years.
Satoshi Horike & Susumu Kitagawa
doi: 10.1038/s41563-022-01346-7 | |
Soft matter has evolved considerably since it became recognized as a unified field. This has been driven by new experimental, numerical and theoretical methods to probe soft matter, and by new ways of formulating soft materials. These advances have driven a revolution in knowledge and expansion into biological and active matter.
Soft materials evolution and revolutionThe study of soft matter is a relatively young discipline, with the field itself becoming recognized as a unified research field only about 40 years ago, although many materials now commonly considered as part of soft matter have a much longer history of study. The first 20 years of soft-matter research was focused mainly on the definition of the field and the development of many of its foundational principles. The past 20 years has seen an explosion of new topics with the concomitant growth and broadening of soft matter as a discipline. Advances in soft matter have been driven by both new experimental and theoretical methods to study soft materials and by development of new ways of making soft matter (Fig. 1). In addition, the study of soft matter has extended to new topics of increasing sophistication. Importantly, advances in our fundamental understanding of soft matter have been complemented by new and valuable technological applications that directly benefit society. We review this evolution of soft matter in this Comment.
An overview of advances in soft matter.
| doi: 10.1038/s41563-022-01356-5 | |
Semi-synthetic goldilocks material design integrates the tunable characteristics of synthetic materials and the refined complexity of natural components, enabling for the progress of biomaterials across length scales. Accelerated translational success may thus be possible for more personalized and accessible products.
Ascendancy of semi-synthetic biomaterials from design towards democratizationOver the past 20 years, the biomaterial repertoire has expanded rapidly alongside progress in synthetic biology and our deepening understanding of biological systems across many length scales. Refined synthetic strategies reach new levels of biomimicry, and novel methods to engineer naturally derived materials increasingly blur the lines between synthetic and natural approaches. This confluence of advances has given rise to a‘goldilocks’design class of biomaterials: optimized blends that aim to unite the benefits of both the synthetic and the natural. Synthetic components are often more controllable, modular and easily characterized, while natural materials are often more familiar to the host system, better able to replicate native complexity, and allow for personalized variability. Such hybrid designs are now becoming increasingly accessible and scalable, and have begun to gain translational traction (Fig. 1).
Goldilocks semi-synthetic biomaterials optimally blend synthetic and natural components.
Alessondra T. Speidel, Christopher L. Grigsby & Molly M. Stevens
doi: 10.1038/s41563-022-01348-5 | |