Spinel cobalt ferrite (CoFe2O4, CFO) nanoparticles (NPs) are a major focus of fundamental science and technological innovation due to their distinctive mix of magnetic, electrical, and chemical characteristics. CFO NPs have outstanding chemical stability, modest saturation magnetism (∼80 emu/g), a high Curie temperature (∼793 K), and significant magnetocrystalline anisotropy. These characteristics, further improved by cation substitution and surface functionalization, enable a wide range of applications. This review provides a comprehensive analysis of CFO NPs, covering their synthesis methods, physicochemical characterization, surface modifications, and diverse applications. We compare the environmental impact, scalability, yield, and particle size control of a variety of synthesis techniques, including co-precipitation, hydrothermal, sol-gel route, combustion method, microemulsion, thermal decomposition, electrochemical synthesis, polyol method, and green synthesis methods. The sustainable alternative of green synthesis, which employs plant- and microbe-mediated biosynthesis, is becoming increasingly important in the biomedical and environmental sectors. Furthermore, we explore advanced surface functionalization techniques that employ monomeric, inorganic, and polymeric stabilizers to improve the biocompatibility and stability of CFO NPs. The effects of cation substitution (such as transition metals and rare-earth dopants) on the physicochemical and magnetic properties of CFO NPs are examined in detail, addressing challenges like cost and stability in real-world applications. Moreover, the present review provides a detailed discussion correlating structural, morphological, magnetic, dielectric, optical, and electrical properties of CFO with synthesis methods and modifications. The traditional energy storage and conversion applications of CFO are comprehensively discussed. Additionally, the review highlights magnetic applications, biomedical applications (e.g., MRI contrast agents, magnetic hyperthermia, and biosensors), the role of CFO in electronics and optoelectronics, purification and catalysis applications, as well as advances in electromagnetic technologies. Emerging applications, including their roles in quantum computing, nanorobotics, tissue engineering, and bioimaging, are also discussed, emphasizing the cutting-edge potential of CFO NPs in multifunctional technologies. The objective of this review is to critically evaluate recent advancements, challenges, and future research directions to bridge the divide in understanding CFO NPs. This systematic evaluation establishes a strong foundation for researchers, allowing them to investigate novel applications of CFO NPs in both current and emerging technological domains.

The physics and properties of electromagnetic epsilon-near-zero (ENZ) materials have attracted much attention in recent years, especially in the fields of metamaterials, nonlinear optics, subwavelength photonics, and also in many systems supporting strong light–matter interaction. The unique optical properties of the ENZ materials, such as constant phase transmission, strong field enhancement, high tunability, and ultrafast phase transitions, offer novel opportunities for advancing optical communications and data processing, as well as integrated photonic devices. Here, we review the recent advances in theoretical and experimental studies of resonant light–matter interaction in photonic structures with ENZ materials and their applications to linear and nonlinear nanophotonics. We start by discussing briefly the fundamentals of the ENZ physics and experimental realizations of the ENZ materials. We then summarize the most recent advances in the study of ENZ material-based light–matter interaction and their applications in linear and nonlinear optics. Finally, we present our views on the further developments of the ENZ-empowered resonant photonics.

A force field as accurate as quantum mechanics (QMs) and as fast as molecular mechanics (MMs), with which one can simulate a biomolecular system efficiently enough and meaningfully enough to get quantitative insights, is among the most ardent dreams of biophysicists—a dream, nevertheless, not to be fulfilled any time soon. Machine learning force fields (MLFFs) represent a meaningful endeavor in this direction, where differentiable neural functions are parametrized to fit ab initio energies and forces through automatic differentiation. We argue that, as of now, the utility of the MLFF models is no longer bottlenecked by accuracy but primarily by their speed, as well as stability and generalizability—many recent variants, on limited chemical spaces, have long surpassed the chemical accuracy of 1 kcal/mol—the empirical threshold beyond which realistic chemical predictions are possible—though still magnitudes slower than MM. Hoping to kindle exploration and design of faster, albeit perhaps slightly less accurate MLFFs, in this review, we focus our attention on the technical design space (the speed-accuracy trade-off) between MM and ML force fields. After a brief review of the building blocks (from a machine learning-centric point of view) of force fields of either kind, we discuss the desired properties and challenges now faced by the force field development community, survey the efforts to make MM force fields more accurate and ML force fields faster, and envision what the next generation of MLFF might look like.

The obtention of quantum-grade rare-earth-doped oxide thin films that can be integrated with optical cavities and microwave resonators is of great interest for the development of scalable quantum devices. Among the different growth methods, chemical vapor deposition (CVD) offers high flexibility and has demonstrated the ability to produce oxide films hosting rare-earth ions with narrow linewidths. However, growing epitaxial films directly on silicon is challenging by CVD due to a native amorphous oxide layer formation at the interface. In this manuscript, we investigate the CVD growth of erbium-doped yttrium oxide (Er:Y2O3) thin films on different substrates, including silicon, sapphire, quartz, or yttria stabilized zirconia (YSZ). Alternatively, growth was also attempted on an epitaxial Y2O3 template layer on Si (111) prepared by molecular beam epitaxy (MBE) in order to circumvent the issue of the amorphous interlayer. We found that the substrate impacts the film morphology and the crystalline orientations, with different textures observed for the CVD film on the MBE-oxide/Si template (111) and epitaxial growth on YSZ (001). In terms of optical properties, Er3+ ions exhibit visible and IR emission features that are comparable for all samples, indicating a high-quality local crystalline environment regardless of the substrate. Our approach opens interesting prospects to integrate such films into scalable devices for optical quantum technologies.

Bound states in the continuum (BICs) have emerged as research hotspots in optics and photonics, offering a new paradigm for achieving extreme field localization and enhancing light–matter interactions. Here, we establish for the first time the intrinsic evolution laws of Fabry–Pérot bound states in the continuum (FP-BICs), revealing that the Q factor is inversely proportional to the square of phase/frequency detuning and to the nonradiative decay rate, enabling directional engineering of FP-BIC resonances. We propose an all-dielectric multilayer film metasurface to create an optical resonator and its perfectly mirrored counterpart, inducing FP-BICs and validating the conclusions. We experimentally demonstrated the evolution of the Q factor with frequency detuning, achieving a maximum Q factor of 610 in the visible. Our work offers novel insights into BICs, promising to inspire exotic phenomena and applications.

The review focuses on architected acoustic metamaterials to manipulate airborne sound waves, with only limited discussions on elastic metamaterials related to solid media. We review the design of acoustic metamaterials and the physical mechanisms underpinning their performance and related manufacturing methodologies, while also examining potential issues and challenges affecting the use of metamaterials in acoustics. The complexities of several metamaterial architectures are discussed. A new classification system is proposed to distinguish metamaterial configurations based on the typology of the channels inside the acoustic meta-atom. Several types of acoustic metamaterials architectures, such as perforated and micro-perforated panels, acoustic foams, resonators, various geometrical paths, and piezoelectric patches, are also discussed. The fundamental acoustic mechanisms of these classes of metamaterials are identified and commented on. The paper also describes the main measurement techniques used for acoustic metamaterials and the physical quantities evaluated, providing a guide to characterize and assess their performance. The fundamental challenges of the current metamaterials designs are discussed, with a focus on the complex synergy between architectural patterns of acoustic metamaterials and their thickness. We clarify the distinction between acoustic and elastic metamaterials, emphasizing the design and applications of materials that manipulate sound waves in fluid media. The paper also offers further comments about the need for practical design tools to allow the use of acoustic metamaterials in real-world applications.

The omnipresence of polarized light on the surface of the earth, a result of atmospheric scattering, underscores the significance of detecting this light and extracting valuable information regarding the phase and polarization angle. In recent years, there has been a surge in research on polarization-sensitive photodetectors that utilize anisotropic two-dimensional (2D) materials. The essence of these 2D polarization-sensitive photodetectors is rooted in the anisotropic characteristics that arise from the asymmetric crystal lattice of the 2D materials in question. This anisotropy is manifested in both optical and electrical behaviors due to the asymmetrical nature of the crystal structure. This article systematically categorizes anisotropic 2D materials and offers an insightful overview of their crystal structures. It also introduces various optical and electrical characterization techniques designed to elucidate the anisotropic properties of these materials. The focus of the article then shifts to detailing the current state of research in the realm of anisotropic 2D material-based polarization-sensitive photodetectors. It provides a comprehensive description of the working principles behind polarization-sensitive photodetectors with different structural designs, shedding light on the underlying mechanisms that enable their polarization sensitivity. In conclusion, the article summarizes the findings of this review, highlighting the advancements and challenges in the field. Additionally, this review proposes several forward-looking recommendations to guide the future trajectory of research and development in the domain of 2D material-based polarization-sensitive photodetectors.

Metasurface polarization optics, manipulating polarization using metasurfaces composed of subwavelength anisotropic nanostructure array, has enabled a lot of innovative integrated strategies for versatile and on-demand polarization generation, modulation, and detection. Compared with conventional bulky optical elements for polarization control, metasurface polarization optics provides a feasible platform in a subwavelength scale to build ultra-compact and multifunctional polarization devices, greatly shrinking the size of the whole polarized optical system and network. Here, we review the recent progresses of metasurface polarization optics in both classical and quantum regimes, including uniform and spatially varying polarization-manipulating devices. Basic polarization optical elements such as meta-waveplate, meta-polarizer, and resonant meta-devices with polarization singularities provide compact means to generate and modulate uniform polarization beams. Spatial-varying polarization manipulation by employing the pixelation feature of metasurfaces, leading to advanced diffraction and imaging functionalities, such as vectorial holography, classic and quantum polarization imaging, quantum polarization entanglement, quantum interference, and modulation. Substituting conventional polarization optics, metasurface approaches pave the way for on-chip classic or quantum information processing, flourishing advanced applications in displaying, communication, imaging, and computing.

Plasmon-enhanced photo/electrocatalysis using hetero-nanostructures has emerged as a promising approach for boosting the efficiency and selectivity of photo/electrocatalytic reactions. Plasmonic nanostructures (PNSs), with their unique properties including localized surface plasmon resonance (LSPR), play a vital role in enhancing photo/electrocatalytic activities. By leveraging LSPR, PNSs can concentrate incident light, facilitate charge separation, and induce surface reactions, leading to improved catalytic performance. In this review, we provide a comprehensive analysis of the current state of knowledge in this field. We discuss the rational design and synthesis of hetero-nanostructures, focusing on the optimization of composition, size, shape, and interface properties. Furthermore, we explore various combinations of plasmonic sources with semiconductors of diverse morphologies to achieve enhanced photocatalytic activity. The reviewed research encompasses applications in water splitting, removal of organic pollutants, CO2 reduction, and energy conversion. We also address the challenges that need to be overcome, including optimization of materials, reproducibility, stability, band alignment, and understanding plasmon–material interactions in hetero-nanostructures. The review of future perspectives includes the integration of multiple functionalities, the exploration of novel plasmonic materials, and the translation of plasmon-enhanced photo/electrocatalysis into practical applications. The combination of plasmonics and nanotechnology can be used to advance green technologies and address pressing global issues.

Shape-programmable magnetoresponsive soft actuators (SMSAs) are highly desirable for diverse applications in soft robotics and minimally invasive medicine. Current methods face challenges in achieving programmable magnetoresponsive three-dimensional (3D) shapes with non-uniform and continuously adjustable curvatures, which are crucial for the highly effective locomotion of SMSAs. Here, we propose an approach that integrates bioinspired pore design with mechanically guided magnetization, enabling programmable magnetoresponsive complex shapes with non-uniform and continuously adjustable curvatures. Various magnetoresponsive developable and non-developable surfaces, along with biomimetic 3D curved shapes, were prepared. The prepared SMSAs exhibit actuation rates of up to 20 s−1. Furthermore, an inchworm-inspired soft crawling robot capable of steering, navigation, obstacle crossing, and cargo transportation was developed, achieving a locomotion speed of up to 1.2 body lengths per second. This work breaks through the design possibilities for SMSAs, enhances the actuation rates of soft actuators, and advances the application of SMSAs in soft crawling robots.