As multifunctional electroactive materials, ferroelectric polymers are unique owing to their exceptionally high dielectric strength (>600 MV/m), high flexibility, and easy and low-temperature fabrication into required shapes. Although polyvinylidene difluoride (PVDF)-based ferroelectric polymers have been known for several decades, recent findings reveal the potential of this class of electroactive polymers (EAPs) to achieve giant electroactive responses by tuning the molecular, nano, and meso-structures. This paper presents these advances, including giant electrocaloric effect, giant electroactuation, and large, hysteresis-free polarization response. New developments in materials benefit applications, such as environmentally benign and potentially highly energy-efficient electrical field controlled solid-state refrigeration, artificial muscles, and high-energy and power density electric energy storage devices. The challenges in developing these materials to realize these applications, and strategies to further improve the responses of EAPs will be also discussed.

From being an unfavorable consequence to finding itself as the intended imaginary part of a non-Hermitian system, loss has truly emerged as more of a friend than a foe in the context of acoustic metasurfaces. With the promising features of sub-wavelength geometries and the rapid advances in manufacturing techniques that can enable their realization, loss becomes a central topic of discussion. Further, the capability of introducing and tailoring loss allows it to serve as a new degree of freedom in passive wavefront shaping devices. In this review, the authors look back at the recent progress in the field of lossy acoustic metasurfaces. The background behind loss in deep sub-wavelength geometries and the instinctive responses to treat them and exploit them are overviewed, followed by more recent works that embrace and tailor their behavior for unconventional applications. The forthcoming years for acoustic metasurfaces thus hold several promising avenues for exploration, with loss as the protagonist.

Photovoltaic organic semiconductors are emerging in many therapeutic applications, including drug delivery and optical control of cell function. However, for their safe use the possible concomitant elicitation of undesired responses in target cells need to be carefully evaluated. Here we describe molecular responses activated by semiconducting polymer nanoparticles based on poly(3-hexyl)thiophene (P3HT) in the model Hydra vulgaris, previously shown to respond to P3HT-NP photostimulation and showed a decrease in the total antioxidant capacity and an increase in the DNA and protein oxidation levels, paving the way to a novel use of photovoltaic devices to control intracellular redox equilibrium.

Continuum modeling approaches are well established in materials science and engineering of metals. They enable the quantitative investigation of diverse questions related to the improved understanding of mechanics and microstructure evolution of various material classes. Applicable to time and length scales relevant in manufacturing and service, continuum modeling approaches are widely used to study engineering-related phenomena such as recrystallization, strain localization, fracture initiation, and phase transformations. However, focusing on individual physical aspects hampers the wider routine use of continuum modeling tools for many engineering applications. With the advent of multi-physics modeling tools developed with the help of and parametrized by (sub-)micrometer-scale simulations and experiments, a huge variety of applications such as hot rolling, bake-hardening, and case-hardening comes within reach for full-field integrated computational materials engineering. Moreover, the integration of experimentally characterized microstructures and the use of user friendly simulation and evaluation tools render powerful modeling approaches feasible for a broad materials science user community. The state of the art and future trends of mechanical, thermodynamic, and kinetic continuum modeling of metallic materials at the grain scale are outlined in this prospective article.

Multiferroic nanostructures have been attracting tremendous attention not only for novel phenomena associated with fundamental physics, but also due to exciting application potentials in future nanoelectronic devices. In this mini-review, we first introduce several fabrication techniques recently developed for single phase and composite multiferroic nanostructures. Then, the topologic vortex domain structures in various ferroic nanostructures, which may bring about additional fundamental discoveries and applications in ultrahigh density recording, are discussed. Particular attention is paid to magnetoelectric effects in multiferroic nanodots, including room temperature electric field induced magnetic domain switching. Finally, existing challenges and new directions, e.g., cross-couplings among multiple functionalities, are prospected. We genuinely hope that this mini-review will arouse the readers' interest in this fascinating field.

This paper discusses the unique patterns evolved through phase separation of a bulk liquid crystal (LC) from the self-assembly of lysozyme induced by evaporation of de-ionized water only. Each domain shows a central dark region surrounded by bright regions (randomly oriented LC droplets). The birefringence intensity reveals three regimes (a slow increase, rapid rise, then saturation) not seen without LC droplets. The textural study exhibits a simple exponential behavior that changes as a function of LC concentration. Furthermore, in the presence of LC, the crack patterns are found to be different near the drop edge than those in the central region.

Lithium (Li)-ion battery cathode materials are typically coated to improve cycling performance, using aqueous-based coating techniques that require filtering, drying, and even sintering of the final product. Here, spherical LiNi0.6Mn0.2Co0.2O2 particles were coated with nano-Al2O3 using the dry mechanofusion method. This method produced a durable, non-porous Al2O3 coating that is retained during slurry making. Mechanofusion coatings significantly improved Li-ion battery cathode cycling at high voltages, enabling high energy densities, while offering inexpensive, scalable, and environmentally friendly solvent-free synthesis. This opens up new possibilities, since, not being limited by synthesis chemistry, mechanofusion can in principle be used to apply any coating material.

Four different vanadium oxide phases [α-vanadium pentoxide (V2O5), β-V2O5, bronze-type vanadium dioxide [VO2(B)], and rutile-type VO2 [VO2(R)])] are investigated from first principles as potential electrode materials for potassium (K) ion batteries. Specifically, insertion energetics and diffusion barriers are computed. These phases are known as promising cathode materials for other types of metal ion batteries. Our results show that the metastable β-V2O5 provides the lowest (strongest) insertion energies for K and the lowest diffusion barriers compared with orthorhombic α-V2O5, VO2(B), and VO2(R). While three of these phases show energetically favorable potassiation and relatively small diffusion barriers, VO2(R) is predicted to be incapable of electrochemical K incorporation.

THz-range dielectric spectroscopy and first-principle-based effective-Hamiltonian molecular dynamics simulations were used to elucidate the dielectric response in the paraelectric phase of (Ba, Sr)TiO3 solid solutions. Our analysis suggests a crossover between two regimes: a higher-temperature regime governed by the soft mode only versus a lower-temperature regime exhibiting a coupled soft mode/central mode dynamics. Interestingly, a single model can be used to adjust the THz dielectric response in the entire range of the paraelectric phase. The central peak cannot be discerned anymore in the dielectric spectra when the rate of underlying thermally activated processes exceeds certain characteristic frequency of the system.

In this work, we showcased a visible-light-assisted reduction of graphene oxide (GO) using N-doped TiO2 photocatalysts. Bench scale capacitive deionization (CDI) experiments determine the optimum working voltage for TiO2–reduced graphene oxide (RGO) nanocomposites as CDI electrodes at 1.8 V. Furthermore, the coupled TiO2 nanoparticles within the as-prepared composite also exhibited photocatalytic ability by removing the humic acid model pollutant. This property is expected to be beneficial as it could relieve the degree of fouling on the electrosorptive surface caused by dissolved organic compounds. In the end, we have demonstrated their potential as a viable desalination water treatment technology in a pilot scale CDI unit.

It is of the uttermost interest to understand the mechanical performance and deformation mechanisms contributing to small-scale plasticity of materials in micro/nanoelectromechanical systems at their service temperatures, which are usually above room temperature. In recent years, high-temperature nanoindentation experiments have emerged as a reliable approach to characterize the deformation behavior of materials at the nano and submicron scale. In this review, we highlight the role of the temperature in nanoindentation response of a wide variety of materials, with a particular focus on the thermally-activated deformation mechanisms in crystalline and non-crystalline materials under the indenter, e.g., dislocation processes, shear transformation zone, and phase transformations. A brief survey of the temperature-dependent nanoindentation elastic modulus, hardness, and creep behavior of materials is also provided. We also discuss experimental methods for correctly measuring the mechanical properties of materials at high temperatures.

Hyperbolic polariton modes are highly appealing for a broad range of applications in nanophotonics, including surfaced enhanced sensing, sub-diffractional imaging, and reconfigurable metasurfaces. Here we show that attenuated total reflectance (ATR) micro-spectroscopy using standard spectroscopic tools can launch hyperbolic polaritons in a Kretschmann–Raether configuration. We measure multiple hyperbolic and dielectric modes within the naturally hyperbolic material hexagonal boron nitride as a function of different isotopic enrichments and flake thickness. This overcomes the technical challenges of measurement approaches based on nanostructuring, or scattering scanning near-field optical microscopy. Ultimately, our ATR approach allows us to compare the optical properties of small-scale materials prepared by different techniques systematically.

The finite element simulations show that non-equibiaxial residual stresses (RS) can shift the load–depth curve from the unstressed curve and cause elliptical remnant indentation in spherical indentation. Thus the relative load change between stressed and unstressed samples and the asymmetry of elliptical remnant indentation were employed as characteristic parameters to evaluate the magnitude and directionality of RS. Through theoretical and numerical analysis, the effects of RS on indentation load and remnant impression as well as the affect mechanism were systematically discussed. Finally, two equations which could provide foundations for establishing spherical indentation method to evaluate non-equibiaxial RS were obtained.

The S-doped BiOBr composite microspheres were successfully prepared through one-pot solvothermal method. The as-prepared samples exhibit higher photocatalytic activity for the degradation of Rhodamine B and phenol under visible light irradiation, attributed to the improvement of the photo-absorption property and the narrow band gap due to the dopants of S element. The higher efficiency for photodegradation of organic pollutant endows this material with a bright perspective in purification of waste water under visible-light irradiation.

Starting from polydisperse diatomaceous earth (DE), we proposed an efficient separation method for obtaining different morphologies of biosilica from diatoms. DE is a very low-cost source of silica containing all the differently nanostructured elements. By a glucose gradient/dialysis, three types of biosilica morphologies were achieved: rods, valves, and clusters. We fully characterized the diatom fractions and we used them to produce fluorescent biosilica platforms (“tabs”). These supports exhibited good resistance in water, ethanol, and soft scraping. A preliminary biologic application by testing Saos-2 proliferation was also performed to check osteoblasts-like cells biologic attitude for this scaffolds with tunable nanostructure.

Axial compression was conducted on micro-pillars, in which polycrystalline Cu thin films were sandwiched between CrN and Si. Plastic flow of Cu was achieved, when the Cu films are inclined either at 90° or 45° with respect to the pillar axis. The texture of Cu films was altered by changing the template on which film growth occurred. The Cu microstructure was further altered by post-deposition annealing. The flow stress shows little dependence on the film texture in the as-deposited state. However, annealing influences the flow stress of confined Cu films significantly. The implications on strain gradient plasticity models are discussed.

Deformation twinning has been frequently observed in body-centered cubic (BCC) high entropy alloys (HEAs), however, the underlying mechanism remains elusive. We perform molecular dynamics simulations on a representative BCC HEA nanopillar under high-symmetry compression, describe atomic details of deformation twinning, and propose a mechanism of twin nucleation from the surface. We find that twinned regions are formed by partial dislocations and that chemical heterogeneity can reduce local fault energy and promote stacking faults and twins. These results help to understand the propensity for stacking fault formation and twinning in HEAs and may guide the design of novel HEAs through control of active twinning mechanisms.

There has been increasing interest in so-called phononic materials, which can support surface modes known as surface phonon polaritons, consisting of electromagnetic waves coupled to lattice vibrations at the surface of a polar material. While such excitations have a variety of desirable features, they are limited to the spectral range between a material's longitudinal and transverse optical phonon frequencies. In this work, we demonstrate that for materials whose free-carrier concentrations can be controlled, hybrid plasmonic/phononic modes can be supported across a range of frequencies including those generally forbidden by purely phononic materials.

The photothermal experiments on the incident light angle dependence are carried out using simulated solar light on thin films of both iron oxides (Fe3O4 and Fe3O4@Cu2-xS) and porphyrin compounds (chlorophyll and chlorophyllin). Fe3O4 and Fe3O4@Cu2-xS are synthesized using various solution methods that produce mono-dispersed nanoparticles on the order of 10 nm. Chlorophyll is extracted from fresh spinach and chlorophyllin sodium copper is a commercial product. These photothermal (PT) materials are dispersed in polymethyl methacrylate (PMMA) solutions and deposited on glass substrates via spin coating that result in clear and transparent thin films. The iron-oxide based thin films show distinctive absorption spectra; Fe3O4 exhibits a strong peak near UV and gradually decreases into the visible and NIR regions; the absorption of Fe3O4@Cu2-xS is similar in the UV region but shows a broad absorption in the NIR region. Both chlorophyll and chlorophyllin are characterized with absorption peaks near UV and NIR showing a “U”-shaped spectrum, ideally required for efficient solar harvest and high transparency in energy-efficient single-pane window applications. Upon coating of the transparent PT films on the window inner surfaces, solar irradiation induces the photothermal effect, consequently raising the film temperature. In this fashion, the thermal loss through the window can be significantly lowered by reducing the temperature difference between the window inner surface and the room interior, based on a new concept of so-called optical thermal insulation (OTI) without any intervention medium, such as air/argon, as required in the glazing technologies. Single-panes are therefore possible to replace double- or triple panes. As OTI is inevitably affected by seasonal and daily sunlight changes, an incident light angle dependence of the photothermal effect is crucial in both thin film and window designs. It is found that the heating curves reach their maxima at small angles of incidence while the photothermal effect is considerably reduced at large angles. This angle dependence is well explained by light reflection by the thin film surface, however, deviated from what is predicted by the Fresnel's law, attributable to non-ideal surfaces of the substrates. The angle dependence data provide an important reference for OTI that window exposure to the sun is greater at winter solstice while that is considerably reduced in the summer. This conclusion indicates much enhanced solar harvesting and heat conversion via optically insulated windows in the winter season, resulting in much lower U-factors.

Among the commercially common transparent conducting oxides (TCOs) are fluorine-doped tin oxide (FTO) and indium-doped tin oxide (ITO), neither of which meets all criteria for the optimal TCO. Despite its superior chemical stability and being composed of abundant elements, FTO suffers from high surface roughness compared to ITO. Here, we introduce a path to substantially decrease the surface roughness of FTO, while preserving most of its original advantages, by depositing an SnO2 coating on top of the FTO layer using pulsed laser deposition. Such an enhancement may allow future use of FTO in devices that use now the more expensive, less stable ITO, which contains relatively rare indium.