1-(4-Bromo-2-fluoro­benz­yl)pyridinium bis­(2-thioxo-1,3-dithiole-4,5-dithiol­ato)nickelate(III)

The title compound, (C12H10BrFN)[Ni(C3S5)2], is an ion-pair complex consisting of N-(2-fluoro-4-bromo­benz­yl)pyridinium cations and [Ni(dmit)2]− anions (dmit = 2-thioxo-1,3-dithiole-4,5-dithiol­ate). In the anion, the NiIII ion exhibits a square-planar coordination involving four S atoms from two dmit ligands. In the crystal structure, weak S⋯S [3.474 (3), 3.478 (3) and 3.547 (3) Å] and S⋯π [S⋯centroid distances = 3.360 (3), 3.378 (2), 3.537 (2) and 3.681 (3) Å] inter­actions and C—H⋯F hydrogen bonds lead to a three-dimensional supra­molecular network

Triaqua­bis(1H-imidazole)bis­[μ2-2-(oxalo­amino)benzoato(3−)]dicopper(II)calcium(II) hepta­hydrate

In the title heterotrinuclear coordination compound, [CaCu2(C9H4NO5)2(C3H4N2)2(H2O)3]·7H2O, the Ca2+ cation is in a penta­gonal–bipyramidal geometry and bridges two (1H-imidazole)[2-(oxaloamino)benzoato(3−)]copper(II) units in its equatorial plane. Each CuII atom has a normal square-planar geometry. The mol­ecule has approximate local (non-crystallographic) mirror symmetry and 23 classical hydrogen bonds are found in the crystal structure

Minimizing the diffusivity difference between vacancies and interstitials in multi-principal element alloys.

Interstitial atoms usually diffuse much faster than vacancies, which is often the root cause for the ineffective recombination of point defects in metals under irradiation. Here, via ab initio modeling of single-defect diffusion behavior in the equiatomic NiCoCrFe(Pd) alloy, we demonstrate an alloy design strategy that can reduce the diffusivity difference between the two types of point defects. The two diffusivities become almost equal after substituting the NiCoCrFe base alloy with Pd. The underlying mechanism is that Pd, with a much larger atomic size (hence larger compressibility) than the rest of the constituents, not only heightens the activation energy barrier (Ea) for interstitial motion by narrowing the diffusion channels but simultaneously also reduces Ea for vacancies due to less energy penalty required for bond length change between the initial and the saddle states. Our findings have a broad implication that the dynamics of point defects can be manipulated by taking advantage of the atomic size disparity, to facilitate point-defect annihilation that suppresses void formation and swelling, thereby improving radiation tolerance

Evolution of Interlayer Coupling in Twisted MoS2 Bilayers

Van der Waals (vdW) coupling is emerging as a powerful method to engineer and tailor physical properties of atomically thin two-dimensional (2D) materials. In graphene/graphene and graphene/boron-nitride structures it leads to interesting physical phenomena ranging from new van Hove singularities1-4 and Fermi velocity renormalization5, 6 to unconventional quantum Hall effects7 and Hofstadter's butterfly pattern8-12. 2D transition metal dichalcogenides (TMDCs), another system of predominantly vdW-coupled atomically thin layers13, 14, can also exhibit interesting but different coupling phenomena because TMDCs can be direct or indirect bandgap semiconductors15, 16. Here, we present the first study on the evolution of interlayer coupling with twist angles in as-grown MoS2 bilayers. We find that an indirect bandgap emerges in bilayers with any stacking configuration, but the bandgap size varies appreciably with the twist angle: it shows the largest redshift for AA- and AB-stacked bilayers, and a significantly smaller but constant redshift for all other twist angles. The vibration frequency of the out-of-plane phonon in MoS2 shows similar twist angle dependence. Our observations, together with ab initio calculations, reveal that this evolution of interlayer coupling originates from the repulsive steric effects, which leads to different interlayer separations between the two MoS2 layers in different stacking configurations

Growth and applications of two-dimensional single crystals

Two-dimensional (2D) materials have received extensive research attentions over the past two decades due to their intriguing physical properties (such as the ultrahigh mobility and strong light-matter interaction at atomic thickness) and a broad range of potential applications (especially in the fields of electronics and optoelectronics). The growth of single-crystal 2D materials is the prerequisite to realize 2D-based high-performance applications. In this review, we aim to provide an in-depth analysis of the state-of-the-art technology for the growth and applications of 2D materials, with particular emphasis on single crystals. We first summarize the major growth strategies for monolayer 2D single crystals. Following that, we discuss the growth of multilayer single crystals, including the control of thickness, stacking sequence, and heterostructure composition. Then we highlight the exploration of 2D single crystals in electronic and optoelectronic devices. Finally, a perspective is given to outline the research opportunities and the remaining challenges in this field