2D heterostructures made of transition metal dichalcogenides (TMD) have emerged as potential building blocks for new‐generation 2D electronics due to their interesting physical properties at the ...interfaces. The bandgap, work function, and optical constants are composition dependent, and the spectrum of applications can be expanded by producing alloy‐based heterostructures. Herein, the successful synthesis of monolayer and bilayer lateral heterostructures, based on ternary alloys of MoS2(1−x)Se2x–WS2(1−x)Se2x, is reported by modifying the ratio of the source precursors; the bandgaps of both materials in the heterostructure are continuously tuned in the entire range of chalcogen compositions. Raman and photoluminescence (PL) spatial maps show good intradomain composition homogeneity. Kelvin probe measurements in different heterostructures reveal composition‐dependent band alignments, which can further be affected by unintentional electronic doping during the growth. The fabrication of sequential multijunction lateral heterostructures with three layers of thickness, composed of quaternary and ternary alloys, is also reported. These results greatly expand the available tools kit for optoelectronic applications in the 2D realm.
Monolayer and bilayer lateral heterostructures based on ternary alloys of MoS2(1−x)Se2x–WS2(1−x)Se2x are successfully synthesized, the bandgap of both domains in the heterostructure is continuously tuned in the entire range of chalcogen compositions. Kelvin probe measurements reveal composition‐dependent band alignments. Alloy‐based lateral heterostructures greatly expand the available tools kit for 2D optoelectronic applications.
An experimental study of the configurational thermodynamics for a series of near-eutectic Pt80-x
Cu
x
P20 bulk metallic glass-forming alloys is reported where 14 < x < 27. The undercooled liquid ...alloys exhibit very high fragility that increases as x decreases, resulting in an increasingly sharp glass transition. With decreasing x, the extrapolated Kauzmann temperature of the liquid, TK
, becomes indistinguishable from the conventionally defined glass transition temperature, Tg
. For x < 17, the observed liquid configurational enthalpy vs. T displays a marked discontinuous drop or latent heat at a well-defined freezing temperature, Tgm
. The entropy drop for this first-order liquid/glass transition is approximately two-thirds of the entropy of fusion of the crystallized eutectic alloy. Below Tgm
, the configurational entropy of the frozen glass continues to fall rapidly, approaching that of the crystallized eutectic solid in the low T limit. The so-called Kauzmann paradox, with negative liquid entropy (vs. the crystalline state), is averted and the liquid configurational entropy appears to comply with the third law of thermodynamics. Despite their ultrafragile character, the liquids at x = 14 and 16 are bulk glass formers, yielding fully glassy rods up to 2- and 3-mm diameter on water quenching in thin-wall silica tubes. The low Cu content alloys are definitive examples of glasses that exhibit first-order melting.
The nanoscale crack propagation behavior in the presence of nonlinear disturbance strains is studied by using the phase‐field‐crystal method. The influences of amplitude A and frequency ω on fracture ...mode and crack growth are discussed. The simulation results suggest that the disturbance strains can make fracture mode change between brittle fracture and ductile fracture. When amplitude A is large, increasing frequency ω will lead to the brittle‐to‐ductile transition (BDT). Further increasing ω can make ductile‐to‐brittle transition (DBT) happen. Meanwhile, the value of A can influence the critical frequencies for BDT and DBT. Crack growth is also affected by the disturbance strains. When ω is small, increasing ω or A can accelerate crack growth. When ω is large enough, increasing A will retard it. Through this work, we provide a new way to effectively explore the nanoscale mechanism and behavior of crack propagation.
Epithelial-mesenchymal transition (EMT) is described as the process in which injured renal tubular epithelial cells undergo a phenotype change, acquiring mesenchymal characteristics and morphing into ...fibroblasts. Initially, it was widely thought of as a critical mechanism of fibrogenesis underlying chronic kidney disease. However, evidence that renal tubular epithelial cells can cross the basement membrane and become fibroblasts in the renal interstitium is rare, leading to debate about the existence of EMT. Recent research has demonstrated that after injury, renal tubular epithelial cells acquire mesenchymal characteristics and the ability to produce a variety of profibrotic factors and cytokines, but remain attached to the basement membrane. On this basis, a new concept of "partial epithelial-mesenchymal transition (pEMT)" was proposed to explain the contribution of renal epithelial cells to renal fibrogenesis. In this review, we discuss the concept of pEMT and the most recent findings related to this process, including cell cycle arrest, metabolic alternation of epithelial cells, infiltration of immune cells, epigenetic regulation as well as the novel signaling pathways that mediate this disturbed epithelial-mesenchymal communication. A deeper understanding of the role and the mechanism of pEMT may help in developing novel therapies to prevent and halt fibrosis in kidney disease.
Excitons, quasiparticles of electrons and holes bound by Coulombic attraction, are created transiently by light and play an important role in optoelectronics, photovoltaics and photosynthesis. They ...are also predicted to form spontaneously in a small-gap semiconductor or a semimetal, leading to a Bose–Einstein condensate at low temperature, but there has not been any direct evidence of this effect so far. Here we detect the photoemission signal from spontaneously formed excitons in a debated excitonic insulator candidate, Ta2NiSe5. Our symmetry-selective angle-resolved photoemission spectroscopy reveals a characteristic excitonic feature above the transition temperature, which provides detailed properties of excitons, such as the anisotropic Bohr radius. The present result provides evidence for so-called preformed excitons and guarantees the excitonic insulator nature of Ta2NiSe5 at low temperature.Excitons have been predicted to form spontaneously—without external excitation—in some materials. Low-temperature ARPES measurements on Ta2NiSe5 now provide evidence for such an excitonic insulator and for so-called preformed excitons.
Cooperative strings and glassy interfaces Salez, Thomas; Justin Salez; Kari Dalnoki-Veress ...
Proceedings of the National Academy of Sciences - PNAS,
07/2015, Letnik:
112, Številka:
27
Journal Article
Recenzirano
Odprti dostop
We introduce a minimal theory of glass formation based on the ideas of molecular crowding and resultant string-like cooperative rearrangement, and address the effects of free interfaces. In the bulk ...case, we obtain a scaling expression for the number of particles taking part in cooperative strings, and we recover the AdamâGibbs description of glassy dynamics. Then, by including thermal dilatation, the VogelâFulcherâTammann relation is derived. Moreover, the random and string-like characters of the cooperative rearrangement allow us to predict a temperature-dependent expression for the cooperative length ξ of bulk relaxation. Finally, we explore the influence of sample boundaries when the system size becomes comparable to ξ . The theory is in agreement with measurements of the glass-transition temperature of thin polymer films, and allows quantification of the temperature-dependent thickness h â of the interfacial mobile layer.
The formation of topological defects after a symmetry-breaking phase transition is an overarching phenomenon that encodes the underlying dynamics. The Kibble–Zurek mechanism (KZM) describes these ...non-equilibrium dynamics of second-order phase transitions and predicts a power-law relationship between the cooling rates and the density of topological defects. It has been verified as a successful model in a wide variety of physical systems, including structure formation in the early Universe and condensed-matter materials. However, it is uncertain if the KZM mechanism is also valid for topologically trivial Ising domains, one of the most common and fundamental types of domain in condensed-matter systems. Here we show that the cooling rate dependence of Ising domain density follows the KZM power law in two different three-dimensional structural Ising domains: ferro-rotation domains in NiTiO3 and polar domains in BiTeI. However, although the KZM slope of NiTiO3 agrees with the prediction of the 3D Ising model, the KZM slope of BiTeI exceeds the theoretical limit, providing an example of steepening KZM slope with long-range dipolar interactions. Our results demonstrate the validity of KZM for Ising domains and reveal an enhancement of the power-law exponent for transitions of non-topological quantities with long-range interactions.The Kibble–Zurek mechanism is shown to apply to structural Ising domains in three-dimensional materials. Long-range interactions modify the critical exponents away from theoretical predictions.
Magnetic superconductors are specific materials exhibiting two antagonistic phenomena, superconductivity and magnetism, whose mutual interaction induces various emergent phenomena, such as the ...reentrant superconducting transition associated with the suppression of superconductivity around the magnetic transition temperature (Tm), highlighting the impact of magnetism on superconductivity. In this study, we report the experimental observation of the ferromagnetic order induced by superconducting vortices in the high-critical-temperature (high-Tc) magnetic superconductor EuRbFe4As4. Although the ground state of the Eu2+ moments in EuRbFe4As4 is helimagnetism below Tm, neutron diffraction and magnetization experiments show a ferromagnetic hysteresis of the Eu2+ spin alignment. We demonstrate that the direction of the Eu2+ moments is dominated by the distribution of pinned vortices based on the critical state model. Moreover, we demonstrate the manipulation of spin texture by controlling the direction of superconducting vortices, which can help realize spin manipulation devices using magnetic superconductors.
This paper melds an overview of the history of Reactor Pressure Vessel (RPV) embrittlement research, focusing on predicting ductile-to-brittle transition temperature shifts (ΔT), along with an ...assessment of the current status of these efforts, especially for extended life operation. The 60-year history of RPV research reveals remarkable progress on a very complex and challenging problem that has, for several decades, been a paradigm for a ‘science in service of engineering’ approach to a critical technological challenge. This research has laid the foundation for properly analyzing modestly accelerated materials test reactor (MTR) data to make robust ΔT predictions beyond the current low flux (φ) power reactor surveillance database. We show that most current models, that are accurate at lower fluence (φt), systematically and significantly underpredict ΔT at high φt, largely owing to the currently unaccounted for contribution of late blooming MnNiSi precipitates (MNSPs). We propose a simple empirical approach to predicting ΔT between φt ≈ 4 × 1023 n/m2 (the currently reliable ΔT model limit) and 14 × 1023 n/m2 (for extended life). The method is shown to be empirically robust, and is supported by a microstructurally informed physical model. In addition to quantifying the role of MNSPs, important observations include approximately linear ΔT dependence at high φt (versus the previous ≈ √φt trend at lower φt), and a diminution of the effect of φ. The decreased φ effect at high φt has very important implications for the use of accelerated MTR data to predict service relevant ΔT.
Energy storage with high energy density and low cost has been the subject of a decades-long pursuit. Sodium-ion batteries are well expected because they utilize abundant resources. However, the lack ...of competent cathodes with both large capacities and long cycle lives prevents the commercialization of sodium-ion batteries. Conventional cathodes with hexagonal-P2-type structures suffer from structural degradations when the sodium content falls below 33%, or when the integral anions participate in gas evolution reactions. Here, we show a "pillar-beam" structure for sodium-ion battery cathodes where a few inert potassium ions uphold the layer-structured framework, while the working sodium ions could diffuse freely. The thus-created unorthodox orthogonal-P2 K
Ni
Mn
O
cathode delivers a capacity of 194 mAh/g at 0.1 C, a rate capacity of 84% at 1 C, and an 86% capacity retention after 500 cycles at 1 C. The addition of the potassium ions boosts simultaneously the energy density and the cycle life.
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