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Patterned metal systems to periodically modulated nanomultilayered architectures, with crystalline and/or amorphous states, has acted as an effective strategy for tuning desirable mechanical properties. While the spontaneous assembly offers an effective and promising path for constructing nanomultilayers, in high-entropy alloys (HEA) how to trigger such a barrier-free route still faces challenges. In this paper, the enthalpy-difference-guided strategy, incorporating Pt, was employed to induce spinodal decomposition for the barrier-free nanomultilayer structure in refractory HEA systems. Aiming at exploring the elastic and chemical interactions, three HEA films with different degrees of size mismatch δ (Zr-Nb-Ta-Mo-W, Zr-Hf-Nb-Ta-Mo, Zr-Hf-Nb-Cr-Mo systems) were fabricated as model systems. Contributed by differences in ΔH mix and δ , in each HEA film, certain-content Pt can trigger both spinodal decomposition and amorphization behavior, which lead to the barrier-free Pt-rich/Pt-lean nanomultilayers with different topological combinations: crystalline/crystalline and amorphous/amorphous. Compared to model HEAs, such barrier-free nanomultilayers can significantly improve the nanoindentation hardness. In HEA systems, tuning ΔH mix and δ simultaneously can assist the further understanding of the structural arrangements and the progress on the barrier-free nanomultilayered configuration for superior mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

The electric double layer (EDL) has been found to play a critical role in not only electric double-layer capacitors (EDLCs) but also batteries and electrocatalysts. Although the influence of EDLs on the electrochemical behaviors of electrolytes has been extensively investigated, its influence on the electrode itself, particularly the energy storage mechanism, remains unclear. Herein, using popular α-Fe 2 O 3 , we look into the interaction between electrode and EDL and find the energy storage mechanism of an electrode can be tuned by modulating EDL. The EDL, which is mainly influenced by the inner Helmholtz plane (IHP) through the specific adsorption of ions onto the surface of Fe 2 O 3 , determines which ions are present at the interface and how they react with the electrode. Ultimately, the composition and properties of the EDL determine the energy storage mechanism of an Fe 2 O 3 electrode, including conversion reaction, ions insertion, surface redox reaction and pseudocapacitance. Our results not only provide a new understanding on the nature of the EDL but also demonstrate that the EDL should be promoted as a functional "component" which can be designed for achieving the optimum synergy of an electrode-electrolyte interface. [Display omitted] [ABSTRACT FROM AUTHOR]

Superlubricity is a sliding regime with almost vanishing friction sustained under stringent material conditions. This remarkable phenomenon was first found between surfaces with incommensurate lattice structures, and later extended to materials with weak shear, as in many two-dimensional layered materials. Such materials, however, face great challenges that limit their applications, including the difficulty to scale up to meet the needs of many practical implementations and low durability stemming from the intrinsic structural weakness. Overcoming these limitations hinges on new design and fabrication of advanced superlubricating materials. Here, we report on the realization of macroscale ultradurable superlubricity on passivated transition-metal diborides (TMB 2) following an unconventional design principle that first construct materials with strong anti-wear ability then create superlubricity via effective surface passivation. TMB 2 possess superior mechanical strength and durability, along with the ability to activate in-situ load-induced passivation layers via tribochemical actions at the surface. The resultant passivated TMB 2 exhibits characteristic superlubricating and ultradurable friction coefficient (0.002) and wear rate (10−19 m3/N·m). These findings introduce a fresh approach toward rational design and implementation of superlubricating materials, opening a new avenue for versatile applications at large (up to industrial) scales. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract The improvement of comprehensive properties including hardness, toughness, wear, and corrosion resistance in the transition-metal carbides/nitrides (TMC(N)) films, especially avoiding the trade-off between the hardness and toughness, is strongly required for various applications. Herein, we provide a new strategy, by activating solid-state dewetting during layered deposition, to accomplish the self-assembly of ordered TaC@Ta core–shell-like nanocomposite film consisting of TaC nanocrystallines encapsulated with thin pseudocrystal Ta tissues (∼1.5 nm). The novel core−shell-like structure can simultaneously achieve superhardness (∼45.1 GPa) mainly dominated by the Orowan strengthening mechanism and high toughness attributed to the indenter-induced phase transformation from the pseudocrystal to body-centered cubic α-Ta, together with drastically enhanced wear and corrosion resistance. Furthermore, thin pseudocrystal Ta encapsulated layer (∼1.5 nm) in the TaC@Ta core–shell-like structure helps for promoting the formation of lubricious TaO x Magnéli phase during sliding, thereby further dropping the coefficient of friction relative to TaC monolayer. Apparently, solid-state dewetting may provide a new route to construct ordered TMC(N)@TM core–shell-like nanocomposite structure capable of combining superhardness, high toughness, low friction, and superior wear and corrosion resistance. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The development of next-generation programmable metasurfaces urgently requires phase change materials with dielectric-metallic transition (DMT-PCMs). Although DMT-PCMs in the infrared have been reported, DMT-PCMs in the visible spectrum are yet to be designed, limiting the nanophotonic applications of conventional programmable metasurfaces to the infrared band. Herein, we find that stoichiometric germanium monotelluride solid solutions, Ge 1- x M x Te (M = Sn, Sb, Pb, and Bi), have excellent DMT performance throughout the whole visible spectrum, and they can be used as versatile material platforms for fabricating programmable metasurfaces. As a proof-of-concept, the DMT performance of stoichiometric Ge 0.9 Sn 0.1 Te solid solution is significantly superior to that of commonly studied non-stoichiometric PCMs (e.g., Ge 2 Sb 2 Te 5 , Sb 2 Te 3). Through a combination of experiments and first-principle calculations, we demonstrate that the high DMT performance of Ge 0.9 Sn 0.1 Te derives from the unique bonding structure of the crystalline state with non-stoichiometric vacancy-free, high atomic number, and weak Sn-Te bonds, which is not present in conventional PCMs. Furthermore, using ultrashort-pulse lasers, we show that the crystalline Ge 0.9 Sn 0.1 Te can be arbitrarily written, erased, and modified at the subwavelength level. The resonance peaks and colors of the Ge 0.9 Sn 0.1 Te-based grating metasurface can be continuously modulated over the whole visible spectrum. These results suggest that the DMT material platforms can be used to fabricate programmable metasurfaces. Therefore, this work presents a coherent report on the physical origin, material design, and photonic devices of DMT in the visible spectrum, which may extend the applications of programmable metasurfaces from the infrared band to the visible spectrum and inspire more researches. [Display omitted] [ABSTRACT FROM AUTHOR]

The high-hardness nature of transition metal nitrides (TMN) has been widely exploited for industrial applications ranging from wear-resistance and cutting tools to scratch-resistant films. To design TMN-based films displaying a further improved toughness and a reduced friction represent urgent challenges. Up to now, creating a nanocomposite structure by introducing a very small content of the metal phase has been considered as a common strategy to enhance hardness and toughness. Herein, we present a new approach to incorporate few solute Ag atoms (∼1.5 at.%) into NbN film to form a Nb-Ag-N solid solution structure, achieving enhanced hardness and toughness, coupled with improved wear-resistance ability and remarkable drop in coefficient of friction (CoF). Hardness and toughness enhancement as well as the tribochemistry actuated by solute Ag have been investigated by combined experimental and density functional theory (DFT) analyses. Results show that the hardness enhancement induced by solute Ag stems from the combination of variation in microstructure and increment in bulk modulus B and C 44 . DFT calculations and electronic structure analyses further reveal that the presence of hybridizations between Ag 5s, 4d orbitals and N p-electrons is responsible for increment in B and C 44 ; furthermore, the appearance of additional Ag e g states contributes to the improved toughness. Additionally, solute Ag can activate self-oxidation by forming Ag 2 O + Nb 2 O 5 at the surface, which is beneficial for the formation of silver niobate (AgNbO 3 ) during the sliding, thereby triggering the falling of the CoF at only 1.5 at.% Ag. Incorporation of few solute Ag atoms into TMN may provide a new strategy to improve the comprehensive properties including hardness, toughness, friction and wear-resistance. [ABSTRACT FROM AUTHOR]

A stoichiometry-driven phase transition from rocksalt to “nitrogen-rich” structure exists in group-IVB transition metal nitride films. As this phase transition is critical in controlling the film properties it has attracted numerous studies. However, researchers are still divided with regard to the structural identity of this “nitrogen-rich” phase, not to mention detailed exploration of the phase transition mechanisms. In this study, we confirmed that the “nitrogen-rich” phase in hafnium nitride (HfN x ) films had a cubic Th 3 P 4 structure of space group symmetry of I- 43 d (220), namely c -Hf 3 N 4 . The confirmation was obtained by combining the first-principle calculations with a series of experiments: Selected Area Electron Diffraction, High Resolution Transmission Electron Microscopy, Raman, Gracing Incident X-ray Diffraction and X-ray Photoelectron Spectroscopy. The mechanisms of the phase transition were elucidated through calculations on enthalpy of formation ( EOF ). The experimental results agree well with the theoretical calculations. We conclude that with increasing nitrogen, phase transition takes place from rocksalt ( δ -HfN) to c -Hf 3 N 4 through three stages of structural evolution: δ -HfN (containing Hf vacancies) → mixture of ( δ -HfN + c -Hf 3 N 4 ) → c -Hf 3 N 4 . The driving force of the phase transition is energy minimization. The three stages of structural evolution are explained by comparing the EOF of the δ -HfN and c -Hf 3 N 4 phases. As the phase transition takes place, the hafnium nitride film morphs from a conductive and opaque metal into an insulating and transparent semiconductor. [ABSTRACT FROM AUTHOR]

Although point defects are found to exist commonly in non-stoichiometric group-IVB transition metal nitrides, the identification of primary point defects still causes some disagreement. The formation mechanism and influence of primary point defects on electronic structures are not yet well explored. This study finds that the types and formation mechanism of primary point defects in rocksalt hafnium nitride (δ-HfN x ) films can be identified by a combination of first-principles calculations and grazing incidence X-ray diffraction, Raman and high-resolution transmission electron microscopy experiments. It is shown that the primary point defects in sub- and over-stoichiometric δ-HfN x films are N and Hf vacancies, respectively, which arise preferentially because they are thermodynamically more stable than other types of point defects, such as interstitials and antisites, because they have much lower formation energy and equilibrium formation enthalpy. Furthermore, it is found that the formation of N and Hf vacancies have an important role in changing electronic structures. N vacancies act as donor-like defects and can add extra free electrons to the conduction band at a rate of an electron per N vacancy, while Hf vacancies serve as acceptor-like defects and efficiently reduce free electrons at a rate of two electrons per Hf vacancy. Additionally, the formation of N vacancies can induce two new interband absorption bands centered at ∼0.81 and ∼2.27 eV, while the incorporation of Hf vacancies create an additional interband absorption band at ∼3.75 eV. These new insights are demonstrated by good agreement between calculations and experiments. [ABSTRACT FROM AUTHOR]

Full-color multi-level transmittance-modulated films have important applications in many emerging fields, such as decorative smart windows and camouflage laser-protection windows. However, the existing transmission-modulated films cannot obtain rich colors due to the limitation of selective absorption. Although the traditional selective reflection-enhanced Fabry-Perot (FP) cavity has rich colors, it cannot obtain the transmission-modulated properties due to the use of a metal reflective layer. Herein, we design an asymmetric FP cavity with a pair of high- and low-activation energy chalcogenide phase change materials as the reflective layer (named as "PCM pair" FP cavity), achieving a combination of full color and multi-level transmittance modulation in a thin film. This is attributed to the "PCM pair" having the coupling effect of selective reflection enhancement and gradient absorption that traditional FP cavities do not have. According to simulations and experiments of ITO/"PCM pair" ("PCM pair" = GeTe/Sb 2 Te 3), we prove that the gradient absorption is attributed to the multi-stage change of "PCM pair" from amorphous to crystalline state. This increases carrier absorption and induces additional interface absorption, thus resulting in four-level transmittance modulation. The selective reflectivity enhancement is due to light interference effect between "PCM pair" and ITO with different thicknesses, which realizes full-color modulations. Based on new insights into the activation energy, we propose the design principles of "PCM pair" and present a materials map. Therefore, this study provides the new FP cavity and candidate materials for the problem that the color and transmittance modulation cannot be integrated in a thin film. [Display omitted] [ABSTRACT FROM AUTHOR]