The syntheses of FeS2 and Fe3S4 nanomaterials were optimized using a novel facile, surfactant-free, and microwave-assisted, one-pot synthesis method, run under ambient and reasonably mild reaction conditions. Synthetic parameters, such as metal precursor salt identity, reaction time, reaction temperature, metal:sulfur molar ratios, and solvent combinations, were all systematically investigated and optimized. A series of FeS2 (pyrite) samples was initially fabricated using thioacetamide (TAA) as the sulfur precursor to generate a distinctive, uniform octahedra-based morphology. Switching the sulfur precursor from TAA to L-cysteine resulted in a corresponding transformation in not only chemical composition from FeS2 to an iron thiospinel structure, Fe3S4 (otherwise known as greigite), but also an associated morphological evolution from octahedra to nanosheet aggregates. The study of these materials has enabled crucial insights into the formation mechanisms of these materials under a relatively non-conventional microwave-assisted setting. Furthermore, in separate experiments, multi-walled carbon nanotubes (MWNTs) and graphene were added in with underlying metal sulfide species to create conductive Fe–S/MWNT composites and Fe–S/graphene composites, respectively. The method of addition of either MWNTs or graphene was also explored, wherein an ‘ex-situ’ synthetic procedure was found to be the least disruptive means of attachment and immobilization onto iron sulfide co-reagents as a means of preserving the latter’s inherent composition and morphology. The redox acidity for the parent material and associated composites demonstrates the utility of our as-developed synthetic methods for creating motifs relevant for electrochemical applications, such as energy storage.

In recent years, hafnia-based ferroelectrics have attracted enormous attention due to their capability of maintaining ferroelectricity below 10 nm thickness and excellent compatibility with microelectronics flow lines. However, the physical origin of their ferroelectricity is still not fully clear, although it is commonly attributed to a polar Pca21 orthorhombic phase. The high-temperature paraelectric phases (the tetragonal phase or the cubic phase) do not possess a soft mode at the Brillouin zone center, thus the ferroelectric distortion has to be explained in terms of trilinear coupling among three phonon modes in the tetragonal phase. It is necessary to explore new materials with possible ferroelectricity due to the polar Pca21 phase, which in turn should be very helpful in evaluating the microscopic theory for ferroelectric hafnia. In this work, based on the idea of the Materials Genome Engineering, a series of hafnia-like ferroelectrics have been found, exemplified by LaSeCl, LaSeBr, LuOF and YOF, which possess adequate spontaneous polarization values and also relatively favorable free energies for the polar phase. Their common features and individual differences are discussed in detail. In particular, a promising potential ferroelectric material, Pca21 phase LuOF, is predicted and recommended for further experimental synthesis and investigation.

The size dependent interaction of Cu n (n = 1‒5) clusters with pristine and defective (C-vacancy) graphene is studied by employing density functional theory. The computed binding energies are in the range of ∼0.5 eV for pristine graphene and ∼3.5 eV for defective graphene, indicating a much stronger interaction in the later system. The induced spin–orbit coupling interaction, due to the proximity of the Cu n cluster, is studied with non-collinear spin-polarized simulations. The clusters cause a spin splitting in the order of few meV. The resultant low energy bands spin textures are also computed, and a spin–valley coupling in the case of even atom clusters on pristine graphene is predicted, leading to the emergence of a spin lifetime anisotropy. For defective graphene, a complete out-of-plane spin texture and a large spin splitting of 40–100 meV is obtained for Cu n (n = 1, 2, 3, 5) clusters due to local magnetic moment. On the other hand, for Cu4/defective graphene, having no net magnetic moment, the spin–valley coupling prevails close to the band edges.

Organic–metal and organic–organic interfaces account for the functionality of virtually all organic optoelectronic applications and the energy-level alignment is of particular importance for device performance. Often the energy-level alignment is simply estimated by metal work functions and ionization energies and electron affinities of the organic materials. However, various interfacial effects such as push back, mirror forces (also known as screening), electronic polarization or charge transfer affect the energy-level alignment. We perform x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) measurements on copper-hexadecafluorophthalocyanine (F16CuPc) and titanyl-phthalocyanine (TiOPc) thin films on Ag(111) and use TiOPc bilayers to decouple F16CuPc layers from the metal substrate. Even for our structurally well-characterized model interfaces and by stepwise preparation of vacuum-sublimed samples, a precise assignment of vacuum-level and energy-level shifts remains challenging. Nevertheless, our results provide guidelines for the interpretation of XPS and UPS data of organic–metal and organic–organic interfaces.

High-spin d 7 Co(II) compounds have recently been identified as possible platforms for realizing highly anisotropic and bond-dependent couplings featured in quantum-compass models such as the celebrated Kitaev model. In order to evaluate this potential, we consider all symmetry-allowed contributions to the magnetic exchange for ideal edge-sharing bonds. Though a combination of ab-initio and cluster many-body calculations we conclude that bond-dependent couplings are generally suppressed in favor of Heisenberg exchange for real materials. Consequences for several prominent materials including Na2Co2TeO6 and BaCo2(AsO4)2 are discussed.

The electronic properties of Fe-based superconductors are drastically affected by deformations on their crystal structure introduced by doping and pressure. Here we study single crystals of FeSe 1−x S x and reveal that local crystal deformations such as atomic-scale defects impact the spectral shape of the electronic core level states of the material. By means of scanning tunneling microscopy we image S-doping induced defects as well as diluted dumbbell defects associated with Fe vacancies. We have access to the electronic structure of the samples by means of x-ray photoemission spectroscopy (XPS) and show that the spectral shape of the Se core levels can only be adequately described by considering a principal plus a minor component of the electronic states. We find this result for both pure and S-doped samples, irrespective that in the latter case the material presents extra crystal defects associated to doping with S atoms. We argue that the second component in our XPS spectra is associated with the ubiquitous dumbbell defects in FeSe that are known to entail a significant modification of the electronic clouds of surrounding atoms.

Exploring two dimensional (2D) materials is important for further developing the field of quantum materials. However, progress in 2D material development is limited by difficulties with their production. Specifically, freestanding 2D materials with bulk non-layered structures remain particularly challenging to prepare. Traditionally, chemical or mechanical exfoliation is employed for obtaining freestanding 2D materials, but these methods typically require layered starting materials. Here we put forth a method for obtaining thin layers of β-Bi2O3, which has a three-dimensional covalent structure, by using chemical exfoliation. In this research, Na3Ni2BiO6 was exfoliated with acid and water to obtain β-Bi2O3 nanosheets less than 10 nm in height and over 1 µm in lateral size. Our results open the possibility for further exploring β-Bi2O3 nanosheets to determine whether their properties change from the bulk to the nanoscale. Furthermore, this research may facilitate further progress in obtaining nanosheets of non-layered bulk materials using chemical exfoliation.

The conjugated polymer poly(3-hexylthiophene) (P3HT) p-doped with the strong acceptor tetrafluorotetracyanoquinodimethane (F4TCNQ) is known to undergo ion-pair (IPA) formation, i.e. integer-charge transfer, and, as only recently reported, can form ground state charge-transfer complexes (CPXs) as a competing process, yielding fractional charge transfer. As these fundamental charge-transfer phenomena differently affect doping efficiency and, thus, organic-semiconductor device performance, possible factors governing their occurrence have been under investigation ever since. Here, we focus on the role of a critical dopant concentration deciding over IPA- or CPX-dominated regimes. Employing a broad, multi-technique approach, we compare the doping of P3HT by F4TCNQ and its weaker derivatives F2TCNQ, FTCNQ, and TCNQ, combining experiments with semi-classical modeling. IPA, CPX, and neutral-dopant ratios (estimated from vibrational absorption spectroscopy) together with electron affinity and ionization energy values (deduced from cyclic voltammetry) allow calculating the width of a Gaussian density of states (DOS) relating to the highest occupied molecular orbital in P3HT. While a broader DOS indicates energetic disorder, we use grazing-incidence x-ray diffraction to assess spatial order. Our findings consider the proposal of nucleation driving IPA formation and we hypothesize a certain host-dopant stoichiometry to be key for the formation of a crystalline CPX phase.

Even though charge transport in semiconducting polymers is of relevance for a number of potential applications in (opto-)electronic devices, the fundamental mechanism of how charges are transported through organic polymers that are typically characterized by a complex nanostructure is still open. One of the challenges which we address here, is how to gain controllable experimental access to charge transport at the sub-100 nm lengthscale. To this end charge transport in single poly(diketopyrrolopyrrole-terthiophene) fiber transistors, employing two different solid gate dielectrics, a hybrid Al2O3/self-assembled monolayer and hexagonal boron nitride, is investigated in the sub-50 nm regime using electron-beam contact patterning. The electrical characteristics exhibit near ideal behavior at room temperature which demonstrates the general feasibility of the nanoscale contacting approach, even though the channels are only a few nanometers in width. At low temperatures, we observe nonlinear behavior in the current–voltage characteristics in the form of Coulomb diamonds which can be explained by the formation of an array of multiple quantum dots at cryogenic temperatures.

Chemical modifications such as intercalation can be used to modify surface properties or to further functionalize the surface states of topological insulators (TIs). Using ambient pressure x-ray photoelectron spectroscopy, we report copper migration in CuxBi2Se3 , which occurs on a timescale of hours to days after initial surface cleaving. The increase in near-surface copper proceeds along with the oxidation of the sample surface and large changes in the selenium content. These complex changes are further modeled with core-level spectroscopy simulations, which suggest a composition gradient near the surface which develops with oxygen exposure. Our results shed light on a new phenomenon that must be considered for intercalated TIs—and intercalated materials in general—that surface chemical composition can change when specimens are exposed to ambient conditions.

Inkjet printing technique provides a low-cost way for large-area construction of the patterned organic semiconductors toward integrated organic electronics. However, because of a lack of control over the wetting and dewetting dynamics of organic inks, inkjet-printed organic semiconductor crystals (OSCCs) are frequently plagued by the ‘coffee ring’ effect and uncontrollable growth process, leading to an uneven crystal morphology and disordered orientation. Here, we report a universal microchannel-assisted inkjet printing (MA-IJP) method for patterning of OSCC arrays with ordered crystallographic orientation. The micro-sized channel template not only provides a unidirectional capillary force to guide the wetting process of organic inks, but also confines the evaporation-induced dewetting behavior, enabling the long-range ordered growth of OSCCs. The patterned 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) crystals present one-dimensional structures with a pure (010) crystallographic orientation. The 7 × 7 discrete organic field-effect transistor array made from the patterned C8-BTBT crystals exhibits a high average mobility up to 3.23 cm2 V−1 s−1 with a maximum mobility of 5.36 cm2 V−1 s−1. Given the good generality of the patterning process and high quality of the obtained OSCC crystal array, it is anticipated that our MA-IJP approach will constitute a major step toward integrated electronic and optoelectronic devices.

The application of engineering tools and techniques to studying women’s health, including biomaterials-based approaches, is a research field experiencing robust growth. Biomaterials are natural or synthetic materials used to repair or replace damaged tissues or organs or replicate an organ’s physiological function. However, in addition to in vivo applications, there has been substantial recent interest in biomaterials for in vitro systems. Such artificial tissues and organs are employed in drug discovery, functional cell biological investigations, and basic research that would be ethically impossible to conduct in living women. This Roadmap is a collection of 11 sections written by leading and up-and-coming experts in this field who review and discuss four aspects of biomaterials for women’s health. These include conditions that disproportionately but not exclusively affect women (e.g. breast cancer), conditions unique to female reproductive organs, in both non-pregnant and pregnant states, and sex differences in non-reproductive tissues (e.g. the cardiovascular system). There is a strong need to develop this exciting field, with the potential to materially influence women’s lives worldwide.

Halogenated MXenes have been experimentally demonstrated to be promising two-dimensional materials for a wide range of applicability. However, their physicochemical properties are largely unknown at the atomic level. In this study, we applied density functional theory (DFT) to theoretically investigate the halogenation effects on the structural, electronic, and mechanical characteristics of Ti3C2, which is the most studied MXene material. Three atomic configurations with different adsorption sites for four kinds of halogen terminals (fluorine, chlorine, bromine, and iodine) were considered. Our DFT results reveal that the adsorption site of terminals has a considerable impact on the properties of MXene. This can be ascribed to the different coordination environments of the surface Ti atoms, which change d-orbital splitting configurations of surface Ti atoms and the stabilities of systems. According to the density of states, crystal orbital Hamilton population, and charge analyses, all the considered halogenated MXenes are metallic. The electronic and mechanical properties of the halogenated MXenes are strongly dependent on the electronegativity of the halogen terminal group. The Ti–F bond has more ionic characteristics, which causes Ti3C2F2 mechanically behave in a more ductile manner. Our DFT results, therefore, suggest that the physicochemical properties of MXenes can be tuned for practical applications by selecting specific halogen terminal groups.

Motivated to understand phonon spectrum renormalization in the ground state of the half-filled Su–Schrieffer–Heeger model, we use the Born–Oppenheimer approximation together with the harmonic approximation to evaluate semi-analytically the all-to-all real-space ionic force constants generated through both linear and quadratic electron-phonon coupling. We then compute the renormalized phonon spectrum and the corresponding lattice zero-point energy (ZPE) as a function of the lattice dimerization. Crucially, the latter is included in the system’s total energy, and thus has a direct effect on the equilibrium dimerization. We find that inclusion of a small quadratic coupling leads to very significant changes in the predicted equilibrium dimerization, calling into question the use of the linear approximation for this model. We also argue that inclusion of the ZPE is key for systems with comparable lattice and electronic energies, and/or for finite size chains. Our method can be straightforwardly generalized to study similar problems in higher dimensions.

Recent years have witnessed the emergence of indoor photovoltaic (PV) devices with the rapid development of the Internet of things technology field. Among the candidates for indoor PVs, halide perovskites are attracting enormous attention due to their outstanding optoelectronic properties suitable for indoor light harvesting. Here we investigated the indoor PV properties of CH3NH3PbI3-based devices using Spiro-OMeTAD and P3HT as the hole transport layers. The Spiro-OMeTAD-based devices show a consistently higher power conversion efficiency under indoor illumination and 1 sun, with the champion devices showing a power conversion efficiency of 21.0% and 30.1% for the forward and reverse scan under 1000 lux warm white LED illumination. Fewer trap states and higher carrier lifetime were revealed for Spiro-OMeTAD based devices compared to P3HT. The best-performed Spiro-OMeTAD-based devices are used to self-power a wearable motion sensor, which could detect human motion in real-time, to create a primary sensor system with independent power management. By attaching the Spiro-OMeTAD indoor PV device to the strain sensor, the sensor exhibits an accurate and sensitive response with finger bending movements with good repeatability and negligible degradation of mechanical stability, which indicates the success of sensor powering with the indoor PV device.

An innovative method is proposed to determine the most important magnetic properties of bioapplication-oriented magnetic nanomaterials exploiting the connection between hysteresis loop and frequency spectrum of magnetization. Owing to conceptual and practical simplicity, the method may result in a substantial advance in the optimization of magnetic nanomaterials for use in precision medicine. The techniques of frequency analysis of the magnetization currently applied to nanomaterials both in vitro and in vivo usually give a limited, qualitative picture of the effects of the active biological environment, and have to be complemented by direct measurement of the hysteresis loop. We show that the very same techniques can be used to convey all the information needed by present-day biomedical applications without the necessity of doing conventional magnetic measurements in the same experimental conditions. The spectral harmonics obtained analysing the response of a magnetic tracer in frequency, as in magnetic particle spectroscopy/imaging, are demonstrated to lead to a precise reconstruction of the hysteresis loop, whose most important parameters (loop’s area, magnetic remanence and coercive field) are directly obtained through transformation formulas based on simple manipulation of the harmonics amplitudes and phases. The validity of the method is experimentally verified on various magnetic nanomaterials for bioapplications submitted to ac magnetic fields of different amplitude, frequency and waveform. In all cases, the experimental data taken in the frequency domain exactly reproduce the magnetic properties obtained from conventional magnetic measurements.

Ultrawide band gap materials have numerous potential applications in deep ultraviolet optoelectronics, as well as next-generation high-power and radio frequency electronics. Through the first-principles calculations based on density functional theory calculations, we demonstrate that the As2O3 bulk and monolayer structures have excellent energetic, mechanical, and thermal stabilities. The bulk and monolayer of As2O3 come in two distinct structures, namely st1-As2O3, and st2-As2O3. We show that the st1-As2O3 and st2-As2O3 monolayer and bilayer could be mechanically exfoliated from their bulk material and found that the cleavage energy values are significantly lower than those reported for similarly layered materials. By performing Perdew–Burke–Ernzerhof (PBE) and Heyd–Scuseria–Ernzerhof (HSE06) band structure calculations, we found that the bulk and monolayers of As2O3 structures exhibit wide (PBE) and ultra-wide (HSE06) indirect band gaps. We further evaluate the As2O3 layered thickness-dependent band gaps and found that band gap decreases uniformly as the number of st1-As2O3 and st2-As2O3 layers increases. Our findings demonstrate the potential of the As2O3 structures for the future design of ultra-wide band gap semiconductor electronic devices.

The incorporation of inorganic nanofillers into polymeric matrices represents an effective strategy for the development of smart coatings for corrosion protection of metallic substrates. In this work, wet-jet milling exfoliation was used to massively produce few-layer hexagonal boron nitride (h-BN) flakes as a corrosion-protection pigment in polyisobutylene (PIB)-based composite coatings for marine applications. This approach represents an innovative advance in the application of two-dimensional (2D) material-based composites as corrosion protection systems at the industrial scale. Although rarely used as an organic coating, PIB was selected as a ground-breaking polymeric matrix for our h-BN-based composite coating thanks to its excellent barrier properties. The optimization of the coating indicates that 5 wt.% is the most effective h-BN content, yielding a corrosion rate of the protected structural steel as low as 7.4 × 10−6 mm yr−1. The 2D morphology and hydrophobicity of the h-BN flakes, together with the capability of PIB to act as a physical barrier against corrosive species, are the main reasons behind the excellent anticorrosion performance of our composite coating.

In recent years, a great deal of effort has been undertaken with regards to treatment of pathologies at the level of the central nervous system (CNS). Here, the presence of the blood-brain barrier acts as an obstacle to the delivery of potentially effective drugs and makes accessibility to, and treatment of, the CNS one of the most significant challenges in medicine. In this Roadmap article, we present the status of the timeliest developments in the field, and identify the outstanding challenges and opportunities that exist. The format of the Roadmap, whereby experts in each discipline share their viewpoint and present their vision, reflects the dynamic and multidisciplinary nature of this research area, and is intended to generate dialogue and collaboration across traditional subject areas. It is stressed here that this article is not intended to act as a comprehensive review article, but rather an up-to-date and forward-looking summary of research methodologies pertaining to the treatment of pathologies at the level of the CNS.

The complex magnetic ordering of parent compounds of most unconventional superconductors is crucial for the understanding of high-temperature superconductivity (SC). Within this framework, we have performed temperature-dependent magnetotransport experiments on a single crystal of SmFeAsO, a parent compound of iron pnictide superconductors. We observe multiple features in the measured transport properties at temperatures below the antiferromagnetic (AFM) ordering of Sm, T