Exemplary Materials Research Articles

(Invited) Structural Transformations of OER Catalysts during Activation and Operation

Electrocatalysis of the oxygen evolution reaction (OER) plays a pivotal role in the hydrogen economy. Optimizing materials for this reaction presents a significant challenge, as many highly active materials exhibit low stability during activation and/or operation. Therefore, operando methods capable of probing catalyst structure and morphology become key tools for monitoring transformations during operation. These transformations not only determine activity but also influence long-term stability. In this context, high-energy X-rays provide a valuable probe, easily penetrating electrolytes and cell walls, offering unprecedented insight into material behavior. This contribution presents several classes of OER catalysts operating in alkaline and acidic environments, with their structural transformations studied using high-energy synchrotron scattering techniques.Layered double hydroxides (LDH) represent an important class of catalysts functioning in alkaline environments. Notably, NiFe and CoFe serve as exemplary materials due to their high activity and stability. However, in many cases, the structure during the OER reaction differs from the as-prepared materials, undergoing an α-phase to γ-phase transition, where the latter is the active phase. This transition, at times reversible with potential, is challenging to observe without high-energy wide-angle X-ray scattering (WAXS) techniques [1,2]. Another interesting example involves the origin of high activity in spinel-type Co3O4 thin film catalysts, elucidated by high-energy surface X-ray diffraction (HE-SXRD). Here, the superior performance is attributed to the formation of a 3D CoOx(OH)y active phase skin layer during activation, and its thickness defines the final activity [3].In the case of catalysts operating in an acidic environment, RuOx and IrOx are acknowledged as promising materials. While RuOx exhibits high activity, it is prone to instability, whereas IrOx, although stable, demonstrates lower activity and have significantly higher price. A prevailing trend is to create solid solution alloys of Ir and Ru to capitalize on the strengths of both materials [4]. This contribution details structural investigations of a series of IrRu alloys with varying compositions prepared through DC magnetron sputtering. The study investigates the unusual stability of these materials at high current densities using operando WAXS and a custom-built electrolyzer cell [5]. The findings reveal that these alloys undergo Ru dissolution upon activation, forming a thin amorphous IrOx layer that protects the alloy underneath. The stability is defined by this layer, while the activity is mainly determined by the electronic structure of the IrRu alloy core.The examples presented are a reminder that without operando characterization of the materials it is very difficult to ascribe origins of activity and stability, as the ex-situ characterization might be misleading regarding the structure and electronic structure of the active phase.[1] Dionigi, F. et al. In-situ structure and catalytic mechanism of NiFe and CoFe layered double hydroxides during oxygen evolution. Nature Communications, 2020, 11. https://doi.org/10.1038/s41467-020-16237-1[2] Dresp, S. et al., Molecular Understanding of the Impact of Saline Contaminants and Alkaline pH on NiFe Layered Double Hydroxide Oxygen Evolution Catalysts. ACS Catalysis, 2021, 11, 6800–6809. https://doi.org/10.1021/acscatal.1c00773.[3] Wiegmann, T. et al., OperandoIdentification of the Reversible Skin Layer on Co3O4 as a Three-Dimensional Reaction Zone for Oxygen Evolution. ACS Catalysis, 2022, 12, 3256–3268. https://doi.org/10.1021/acscatal.1c05169.[4] Galyamin, D. et al, Unraveling the Most Relevant Features for the Design of Iridium Mixed Oxides with High Activity and Durability for the Oxygen Evolution Reaction in Acidic Media. JACS Au, 2023, 3, 2336–2355. https://doi.org/10.1021/jacsau.3c00247.[5] Moss, A. B. et al., Versatile High Energy X-Ray Transparent Electrolysis Cell for Operando Measurements. Journal of Power Sources, 2023, 562, 232754. https://doi.org/10.1016/j.jpowsour.2023.232754.

Neophenomenological strategies in techno-images. Towards the post-metaphysical ontology

The article deals with the deconstruction of “metaphysics of presence”, based on the subject-object duality, in a postsecular/mystical approach. Post-metaphysical ontology, that is described here as negative ontology, needs a neophenomenological tool to be revealed. Characterized by a “wave” structure, beyond the “hard presence”, it can’t be defined as “being” or “non-being”. It is rather a kind of perpetual motion, determined by the trajectory of “photons of light”. This recognition seems to find an appropriate manifestation in a contemporary techno-culture. In the field of media technology (analog film or digital new media art), the negative ontology may be experienced by strategies of neophenomenology, in which “sus- pension” (epoché) gesture would concerns first the “ground” itself, then the aesthetics and narration, constituted by the cognitive/rational act of counsciousness. In other words, the visuality of the techno-image may be a tool of liberation of the perception from a cognitive/rational paradigm, which is closed to experience of what is the Other / the apophatic, wave Reality as it is. What should be underlined, in this proposal neophenomenology is not only the epistemology; the virtual image is directly related to negative ontology. An intuitive, mystical transformation of vision, proposed here, that denudes the discourse of representation, allows us to immerse into pure/“naked” Seeing and pure/“naked” Being. Exemplary materials to the outlined issues are films by Béla Tarr and video installations by Bill Viola.

Effects of external staining on mechanical, optical, and biocompatibility properties of additively manufactured 3Y-TZP ceramic for dental applications

Three mole percent yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramics are exemplary materials for dental restoration due to their high mechanical strength, fracture toughness, chemical endurance, and biocompatibility. Nevertheless, 3Y-TZP ceramics are opaque and their CAD/CAM manufacturing process may cause micro-cracks in conventional clinical practice. In this study, 3Y-TZP ceramic samples were prepared using vat photopolymerization, pre-sintering, external staining, and final high-temperature sintering. The microstructures, mechanical properties, optical properties, and cytotoxicity of the 3Y-TZP ceramic samples were investigated. The results indicate that with increasing Fe3+ concentration of staining solution from 0.1 mol/L to 0.3 mol/L and increasing staining time from 5 s to 30 min, the 3Y-TZP ceramic samples showed a tetragonal crystal structure of zirconia with densely packed grains and a slight increase in grain size. The flexural strength, Vickers hardness, and fracture toughness of 3Y-TZP ceramic samples stained in 0.1–0.3 mol/L Fe3+ solution for 5 s to 3 min were all greater than 665 MPa, 11.9 GPa, and 5 MPa m1/2, respectively, meeting the mechanical requirements for clinical application. Colorimetric analysis revealed a decrease in L* (black-white index) from 90.4 to 81.3, an increase in a* (green-red index) from −1.5 to 3.2, and an increase in b* (blue-yellow index) from 11.6 to 20.3, approximating the commercial VITA 3D-Master Shade Guide chromaticity. Furthermore, the 3Y-TZP ceramic samples exhibited a cell viability of 90% or higher toward L929 cells.

Remarkable improvement in photocatalytic activity of NiO nanoparticles through Ag doping: A kinetics-mechanism & recyclability

Metal oxides are recognized as exemplary materials for photocatalytic dye degradation attributed to their unique characteristics such as tunable electronic structure, prolonged stability, and cost-effectiveness. However, the wide band gap inherent to most of these materials often limits their light absorption to the ultraviolet (UV) region. Consequently, the doping of noble metal nanoparticles into the metal oxide nanostructures has been proposed to significantly improve their light-harvesting ability. This enhancement is primarily ascribed to the localized surface plasmon resonance (LSPR) effect associated with noble metal nanoparticles, which facilitates more effective utilization of light. Thus, in this study, we synthesized silver-doped nickel oxide (Ag:NiO) with varying Ag concentrations (0, 1, 2, 4, 6 wt%) to evaluate their photocatalytic performance. The X-ray diffraction (XRD) spectra revealed that NiO possesses a cubic crystalline structure, and a peak shift to a higher angle was noted for Ag doping, indicative of compressive strain. Further analyses of morphological, vibrational, and absorption properties were conducted through the acquisition of scanning electron microscopy (SEM) images, Raman spectra and UV–Vis absorption spectra, respectively. The photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB) dyes was assessed, revealing that NiO with 4.wt.% Ag doping exhibited enhanced photocatalytic activity, achieving 99% degradation of MB and 90% degradation of RhB. Notably, Ag doping significantly enhances the light absorption capabilities and modifies the electronic structure of the NiO, thereby improving its performance in photocatalytic dye degradation.

Asperity contact analysis: coupling effects of normal interference and nanoscale offset by molecular dynamics simulations

This work investigates the offset contact behaviors of nanosized asperity with spherical and non-spherical shapes, aiming to provide a more realistic analysis of asperity contact for rough surfaces. Molecular dynamics models of nanosized asperity are established, using diamond and copper as exemplary materials. Differences between offset and non-offset contacts, as well as spherical and non-spherical asperities are compared through atomic variations including displacement, shear strain and structure. Coupling effects of normal interference and nanoscale offset on asperity contact behaviors are further analyzed. Comparisons between the established models and the microscopic asperity models in contact force-interference dependence are conducted for verification. Results indicate that atoms in central contact region move vertically with smaller shear strains, while those in peripheral region primarily move diagonally outward with larger shear strains due to directional atomic slip motion. Furthermore, the spherical asperity shows higher atomic deformation and contact force compared to the non-spherical asperity for identical interference and offset conditions. Additionally, the shear resistance of single-crystal copper with {100} crystal orientation can be enhanced along the [1 1 0] and [1 − 1 0] directions.

Effects of duty ratio on liquid- and polymer-surface treatment by a unipolar microsecond-pulsed helium atmospheric-pressure plasma jet

Effects of duty ratio of a unipolar microsecond-pulsed helium atmospheric-pressure plasma jet (APPJ) on liquid- and polymer-surface treatments were investigated. In addition, changes in the plasma plume length, gas temperature, excitation temperature, discharge current, absorption power, and optical emission spectra were examined by varying the other operating parameters, such as applied voltage and additive flow of oxygen or water vapor. As an example of liquid sample, de-ionized water (DW) was exposed to an APPJ, and the concentrations of the reactive species generated in the DW were measured as functions of the operating parameters. Polycarbonate, polypropylene, and polymethylmethacrylate were employed as exemplary substrate materials to investigate the effect of plasma treatment on polymeric surfaces. The APPJ treatment increased the surface energy and changed the wetting characteristics of the surface from hydrophobic to hydrophilic. X-ray photoelectron spectroscopy results showed that a short-time plasma treatment with He and/or He/O2, He/H2O affects the surface wettability owing to the introduction of polar groups.

Reversal of spin-polarization near the Fermi level of the Rashba semiconductor BiTeCl

Spin–orbit coupling forms the physical basis for quantum materials with non-trivial topology and potential spintronics applications. The Rashba interaction is a textbook model of spin–orbit interactions, with charge carriers undergoing linear, isotropic spin-splitting in momentum space. Recently, non-centrosymmetric semiconductors in the family BiTeX (X = Cl, Br, I) have been identified as exemplary Rashba materials due to the strong splitting of their bulk bands, yet a detailed investigation of their spin textures, and their relationships to local crystal symmetry, is currently lacking. We perform high-efficiency spin-resolved photoemission spectroscopy to directly image the spin texture of surface states of BiTeCl, and we find dramatic deviations from idealized behavior, including a reversal of the spin-polarization near the Fermi level. We show that this behavior can be described by higher-order contributions to the canonical Rashba model with the surface states localized to individual trilayers of the crystal. Due to the prominence of these effects near the Fermi level, they should have a strong impact on the spin-dependent transport of carriers.

Investigation of functionalization effect of carbon nanotubes as supercapacitor electrode material on hydrogen evolution side-reaction by scanning electrochemical microscopy

It is indeed particularly important in aqueous supercapacitors to avoid any gas evolution due to safety concerns. Nevertheless, limited research has been concentrated on those side reactions, but with more focus on the advancement of the intrinsic electrochemical properties of supercapacitor electrode materials. Herein, we report for the first time to apply high-resolution scanning electrochemical microscopy (SECM) in elucidating hydrogen evolution side reaction occurred during the charge process of supercapacitor electrodes. By taking CNTs functionalized with or without oxygen groups as the exemplary electrode materials, at first we applied conventional analytical methods to demonstrate their difference in supercapapcitor behavior. Subsequently, SECM was specifically introduced to investigate the local reactivity and conductivity of the CNT samples at submicrometer scale. Prominently, SECM was demonstrated to be capable of in-depth understanding the type of side reactions taken placeon the CNT surfaces. This report offers a new avenue to extend SECM application into assessment of supercapacitor safety performance.

Insights into Low Thermal Conductivity in Inorganic Materials for Thermoelectrics.

Efficient manipulation of thermal conductivity and fundamental understanding of the microscopic mechanisms of phonon scattering in crystalline solids are crucial to achieve high thermoelectric performance. Thermoelectric energy conversion directly and reversibly converts between heat and electricity and is a promising renewable technology to generate electricity by recovering waste heat and improve solid-state refrigeration. However, a unique challenge in thermal transport needs to be addressed to achieve high thermoelectric performance: the requirement of crystalline materials with ultralow lattice thermal conductivity (κL). A plethora of strategies have been developed to lower κL in crystalline solids by means of nanostructural modifications, introduction of intrinsic or extrinsic phonon scattering centers with tailored shape and dimension, and manipulation of defects and disorder. Recently, intrinsic local lattice distortion and lattice anharmonicity originating from various mechanisms such as rattling, bonding heterogeneity, and ferroelectric instability have found popularity. In this Perspective, we outline the role of manipulation of chemical bonding and structural chemistry on thermal transport in various high-performance thermoelectric materials. We first briefly outline the fundamental aspects of κL and discuss the current status of the popular phonon scattering mechanisms in brief. Then we discuss emerging new ideas with examples of crystal structure and lattice dynamics in exemplary materials. Finally, we present an outlook for focus areas of experimental and theoretical challenges, possible new directions, and integrations of novel techniques to achieve low κL in order to realize high-performance thermoelectric materials.

Theoretical Methods for Excitonic Physics in 2D Materials

In this Perspective article, the reader is introduced to several theoretical methods of determining the exciton wave functions and the corresponding eigenenergies. The methods covered are either analytical, semianalytical, or numeric. All the details associated with the different methods are made explicit, thus allowing newcomers to do research on their own, without experiencing a steep learning curve. The Perspective starts with a variational method and ends with a simple semianalytical approach to solve the Bethe–Salpeter equation (BSE) in gapped 2D materials. For the first methods addressed in this Perspective, the authors focus on a single layer of hexagonal boron nitride (hBN) and of transition metal dichalcogenide (TMD), as these are exemplary materials in the field of 2D excitons. For explaining the Bethe–Salpeter method, the biased bilayer graphene, which presents a tunable bandgap is chosen. The system has the right amount of complexity (without being excessive). This allows the presentation of the solution in a context that can be easily generalized to more complex systems or to apply it to simpler models.

Transparent, Photothermal, and Icephobic Surfaces via Layer-by-Layer Assembly.

Icing and frosting on transparent surfaces compromise visibility on various optical equipment and transparent infrastructures. It remains challenging to fabricate energy‐saving coatings for harvesting solar energy while maintaining high transparency. Here, transparent, photothermic, and icephobic composite surfaces composed of photothermal nanomaterials and polyelectrolytes via layer‐by‐layer assembly are designed and constructed. The positively‐charged polypyrrole nanoparticles and negatively‐charged poly(acrylic acid) are assembled as exemplary materials via electrostatic attractions. The optically transparent photothermal coatings are successfully fabricated and exhibited photothermal capabilities and light‐transmittance performance. Among the various coatings applied, the seven‐bilayer coating can increase the temperature by 35 °C under 1.9‐sun illumination, maintaining high transmittance (>60%) of visible light. With sunlight illumination at subzero temperatures (> −35 °C), the coatings show pronounced capabilities to inhibit freezing, melt accumulated frost, and decrease ice adhesion. Precisely, the icephobic surfaces remain free of frost at −35 °C as long as sunlight illumination is present; the accumulated frost melts rapidly within 300 s. The ice adhesion strength decreases to ≈0 kPa as the melted water acts as a lubricant. Furthermore, the negatively‐charged graphene oxide and positively‐charged poly(diallyldimethylammonium chloride) show their material diversity applicable in the coating fabrication.

Recent Advances in Layered Double Hydroxide-Based Electrochemical and Optical Sensors.

Layered double hydroxides (LDHs) have attracted considerable attention as promising materials for electrochemical and optical sensors owing to their excellent catalytic properties, facile synthesis strategies, highly tunable morphology, and versatile hosting ability. LDH-based electrochemical sensors are affordable alternatives to traditional precious-metal-based sensors, as LDHs can be synthesized from abundant inorganic precursors. LDH-modified probes can directly catalyze or host catalytic compounds that facilitate analyte redox reactions, detected as changes in the probe’s current, voltage, or resistance. The porous and lamellar structure of LDHs allows rapid analyte diffusion and abundant active sites for enhanced sensor sensitivity. LDHs can be composed of conductive materials such as reduced graphene oxide (rGO) or metal nanoparticles for improved catalytic activity and analyte selectivity. As optical sensors, LDHs provide a spacious, stable structure for synergistic guest–host interactions. LDHs can immobilize fluorophores, chemiluminescence reactants, and other spectroscopically active materials to reduce the aggregation and dissolution of the embedded sensor molecules, yielding enhanced optical responses and increased probe reusability. This review discusses standard LDH synthesis methods and overviews the different electrochemical and optical analysis techniques. Furthermore, the designs and modifications of exemplary LDHs and LDH composite materials are analyzed, focusing on the analytical performance of LDH-based sensors for key biomarkers and pollutants, including glucose, dopamine (DA), H2O2, metal ions, nitrogen-based toxins, and other organic compounds.

FINISHING AND POLISHING OF DIRECT COMPOSITE RESTORATIONS - A REVIEW

Contemporary cosmetic dentists are expected to create realistic and seamless restorations that mimic natural tooth structures. Recent advancements in composite resin systems have improved the practitioners ability to deliver optimal results using chair-side techniques. Many times, the form and function is achieved but the surface of these restorations is not smooth. This might lead to rough or uneven surfaces which over time invite microbial flora leading to an inevitable failure of the restoration. To avoid such failures and to satisfy this patient-driven demand for aesthetic restorations, the use of exemplary finishing and polishing materials is required. These techniques of finishing and polishing helps to achieve the proper form and function of the restoration along with pleasing aesthetics and the maintenance of proper periodontal and gingival health. This article aims to briefly outline finishing and polishing of composite restorations.

Quantum anomalous Hall effect in two-dimensional magnetic insulator heterojunctions

Recent years have witnessed tremendous success in the discovery of topological states of matter. Particularly, sophisticated theoretical methods in time-reversal-invariant topological phases have been developed, leading to the comprehensive search of crystal database and the prediction of thousands of topological materials. In contrast, the discovery of magnetic topological phases that break time reversal is still limited to several exemplary materials because the coexistence of magnetism and topological electronic band structure is rare in a single compound. To overcome this challenge, we propose an alternative approach to realize the quantum anomalous Hall (QAH) effect, a typical example of magnetic topological phase, via engineering two-dimensional (2D) magnetic van der Waals heterojunctions. Instead of a single magnetic topological material, we search for the combinations of two 2D (typically trivial) magnetic insulator compounds with specific band alignment so that they can together form a type-III broken-gap heterojunction with topologically non-trivial band structure. By combining the data-driven materials search, first-principles calculations, and the symmetry-based analytical models, we identify eight type-III broken-gap heterojunctions consisting of 2D ferromagnetic insulators in the MXY compound family as a set of candidates for the QAH effect. In particular, we directly calculate the topological invariant (Chern number) and chiral edge states in the MnNF/MnNCl heterojunction with ferromagnetic stacking. This work illustrates how data-driven material science can be combined with symmetry-based physical principles to guide the search for heterojunction-based quantum materials hosting the QAH effect and other exotic quantum states in general.

Interfacing Neurons with Nanostructured Electrodes Modulates Synaptic Circuit Features.

Understanding neural physiopathology requires advances in nanotechnology-based interfaces, engineered to monitor the functional state of mammalian nervous cells. Such interfaces typically contain nanometer-size features for stimulation and recording as in cell-non-invasive extracellular microelectrode arrays. In such devices, it turns crucial to understand specific interactions of neural cells with physicochemical features of electrodes, which could be designed to optimize performance. Herein, versatile flexible nanostructured electrodes covered by arrays of metallic nanowires are fabricated and used to investigate the role of chemical composition and nanotopography on rat brain cells in vitro. By using Au and Ni as exemplary materials, nanostructure and chemical composition are demonstrated to play major roles in the interaction of neural cells with electrodes. Nanostructured devices are interfaced to rat embryonic cortical cells and postnatal hippocampal neurons forming synaptic circuits. It is shown that Au-based electrodes behave similarly to controls. Contrarily, Ni-based nanostructured electrodes increase cell survival, boost neuronal differentiation, and reduce glial cells with respect to flat counterparts. Nonetheless, Au-based electrodes perform superiorly compared to Ni-based ones. Under electrical stimulation, Au-based nanostructured substrates evoke intracellular calcium dynamics compatible with neural networks activation. These studies highlight the opportunity for these electrodes to excite a silent neural network by direct neuronal membranes depolarization.

Differential volumetric analysis combined with monitoring of differential ultra-sound travel time, an approach for tracing fine-structural compression behaviour of solids: a study on MgO / periclase and polyethylene / PE up to 1.5 GPa at room temperature

The study addresses the topic of fine-structural compression behaviour of solids. MgO / periclase and polyethylene / PE are studied as exemplary materials by volumetric and ultra-sound techniques at room temperature up to 1.5 GPa. The experiments conducted with a high-pressure device of the piston cylinder type rely on: (a) measurements of the piston displacement performed under continuously changing uniaxial load in combination with (b) simultaneous monitoring of the travel time of ultra sound. Both methods base on differential technique implying that all data are of relative nature. The volume-density relation (Δρ = Mconst / ΔV) is the fundamental relation which provides information on compressional as well as on acoustic behaviour of the sample. It serves, additionally, as mutual control of the observations. The data evaluation bases on the method of difference calculation: the data obtained from a run with sample [sample + (vessel + piston assembly)] are subtracted from those of a calibration run [(vessel + piston assembly)]. In most cases the differences retrieved are small and may be presented best in form of derivatives with respect to pressure. The compression behaviour of MgO under hydrostatic conditions is reported to be quasi-linear up to about 2 GPa. Under the uniaxial load exerted by the piston cylinder apparatus MgO reveals a compression behaviour characterized by two volumetric anomalies at 400 and at 1000 MPa. The ultrasonic measurements suggest that shear plays an important role. Comparative measurements on the visco-elastic material polyethylene corroborate that interpretation.

Entropy of Conduction Electrons from Transport Experiments

The entropy of conduction electrons was evaluated utilizing the thermodynamic definition of the Seebeck coefficient as a tool. This analysis was applied to two different kinds of scientific questions that can—if at all—be only partially addressed by other methods. These are the field-dependence of meta-magnetic phase transitions and the electronic structure in strongly disordered materials, such as alloys. We showed that the electronic entropy change in meta-magnetic transitions is not constant with the applied magnetic field, as is usually assumed. Furthermore, we traced the evolution of the electronic entropy with respect to the chemical composition of an alloy series. Insights about the strength and kind of interactions appearing in the exemplary materials can be identified in the experiments.

Ionic liquid–assisted hydrothermal synthesis of Ta2O5 nanoparticles for lithium-ion battery applications

Ta2O5 nanoparticles (NPs) are one of the exemplary anode materials for a lithium-ion battery which undergoes the conversion-type electrochemical reaction with extrinsic pseudocapacitance. Ta2O5 NPs have been synthesized using the ionic liquid–assisted hydrothermal method. The prepared mesoporous Ta2O5 NPs were characterized using XRD, Raman, TEM, and BET surface area analysis. XRD pattern of prepared Ta2O5 NPs exhibited an orthorhombic crystal structure with an average crystallite size of 30 nm. The BET specific surface area and average pore diameter of Ta2O5 NPs were found to be 23.11 m2/g and 21 nm respectively. TEM images showed the particle-like structure with an average particle size of 25 nm. Ta2O5 NPs show excellent performance with a reversible capacity of 190 mAh g−1 even after 150 cycles at C/10 current rate. Therefore, Ta2O5 NPs could be the prospective contestant as a anode material for the lithium-ion battery.

Theory of second-order excitonic nonlinearities in transition metal dichalcogenides

Single layers of transition metal dichalcogenides exhibit tightly bound excitons with large oscillator strength making them to promising materials for future optoelectronic applications. Despite that the linear response of these ultrathin materials is extensively studied, a profound understanding of the excitonic second-order nonlinear optical response, including trigonal warping and Berry curvature effects, is lacking so far. To bridge this gap, in this paper we report a microscopic model for the second-order nonlinear susceptibility tensor of these materials. Based on a $kp$ description of the underlying many-particle Hamiltonian we are able to address excitonic features as well as trigonal warping effects, spin-valley coupling, and also Berry curvature to the susceptibility tensor. We present explicit calculation of the latter for the exemplary materials ${\mathrm{MoS}}_{2}$ and ${\mathrm{WS}}_{2}$ on silicon substrate and encapsulated in hBN. For instance we predict resonant susceptibility for second-harmonic generation $0.5--1.3\phantom{\rule{4pt}{0ex}}\mathrm{nm}/\mathrm{V}$ and double-resonant susceptibility $10--30\phantom{\rule{4pt}{0ex}}\mathrm{n}\mathrm{m}/\mathrm{V}$ for the difference and sum-frequency generation processes. Our results are in good agreement with available experimental findings in the literature.

Design of Architectured Materials Based on Mechanically Driven Structural and Compositional Patterning

Providing materials with an inner architecture that improves their mechanical and physical properties is a potent approach to materials design. Herein, the possibilities of such architecturing by means of severe plastic deformation (SPD) are discussed. Compositional and structural patterns caused by SPD processing can potentially improve the mechanical characteristics and physical properties of exemplary materials considered. The message to convey is that SPD opens up new opportunities with regard to producing materials with a multiscale structure. This can be achieved by virtue of the following effects associated with SPD: extreme grain refinement, whose level is governed by strain distribution; controlled self‐organization of the structure of multiphase materials; and anomalously fast mass transfer, which leads to the formation of new phases and various “reaction–diffusion” patterns. Furthermore, combining SPD with conventional metal forming, differential heat treatment, or 3D printing offers additional possibilities, which are considered in this article.