A foundation of the modern technology that uses single-crystal silicon has been the growth of high-quality single-crystal Si ingots with diameters up to 12 inches or larger. For many applications of graphene, large-area high-quality (ideally of single-crystal) material will be enabling. Since the first growth on copper foil a decade ago, inch-sized single-crystal graphene has been achieved. We present here the growth, in 20 minutes, of a graphene film of 5 50 cm 2 dimension with > 99% ultra-highly oriented grains. This growth was achieved by: (i) synthesis of sub-metre-sized single-crystal Cu (111) foil as substrate; (ii) epitaxial growth of graphene islands on the Cu(111) surface; (iii) seamless merging of such graphene islands into a graphene film with high single crystallinity and (iv) the ultrafast growth of graphene film. These achievements were realized by a temperature-driven annealing technique to produce single-crystal Cu(111) from industrial polycrystalline Cu foil and the marvellous effects of a continuous oxygen supply from an adjacent oxide. The as-synthesized graphene film, with very few misoriented grains (if any), has a mobility up to ~ 23,000 cm 2 V -1 s -1 at 4 K and room temperature sheet resistance of ~ 230 □ ⁄ . It is very likely that this approach can be scaled up to achieve exceptionally large and highquality graphene films with single crystallinity, and thus realize various industrial-level applications at a low cost.

Nanothick metallic transition metal dichalcogenides such as VS2 are essential building blocks for constructing next-generation electronic and energy-storage applications, as well as for exploring unique physical issues associated with the dimensionality effect. However, such two-dimensional (2D) layered materials have yet to be achieved through either mechanical exfoliation or bottom-up synthesis. Herein, we report a facile chemical vapor deposition route for direct production of crystalline VS2 nanosheets with sub-10 nm thicknesses and domain sizes of tens of micrometers. The obtained nanosheets feature spontaneous superlattice periodicities and excellent electrical conductivities (∼3 × 103 S cm–1), which has enabled a variety of applications such as contact electrodes for monolayer MoS2 with contact resistances of ∼1/4 to that of Ni/Au metals, and as supercapacitor electrodes in aqueous electrolytes showing specific capacitances as high as 8.6 × 102 F g–1. This work provides fresh insights into the delicate structure–property relationship and the broad application prospects of such metallic 2D materials.

2D metallic transition-metal dichalcogenides (MTMDs) have recently emerged as a new class of materials for the engineering of novel electronic phases, 2D superconductors, magnets, as well as novel electronic applications. However, the mechanical exfoliation route is predominantly used to obtain such metallic 2D flakes, but the batch production remains challenging. Herein, the van der Waals epitaxial growth of monocrystalline, 1T-phase, few-layer metallic VSe nanosheets on an atomically flat mica substrate via a "one-step" chemical vapor deposition method is reported. The thickness of the VSe nanosheets is precisely tuned from several nanometers to several tenths of nanometers. More significantly, the 2D VSe single crystals are found to present an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 10 S m , 1-4 orders of magnitude higher than that of various conductive 2D materials. The thickness-dependent charge-density-wave phase transitions are also examined through low-temperature transport measurements, which reveal that the synthesized 2D metallic 1T-VSe nanosheets should serve as good research platforms for the detecting novel many-body states. These results open a new path for the synthesis and property investigations of nanoscale-thickness 2D MTMDs crystals.

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Fluorescence lifetime imaging microscopy (FLIM) is increasingly used in biomedicine, material science, chemistry, and other related research fields, because of its advantages of high specificity and sensitivity in monitoring cellular microenvironments, studying interaction between proteins, metabolic state, screening drugs and analyzing their efficacy, characterizing novel materials, and diagnosing early cancers. Understandably, there is a large interest in obtaining FLIM data within an acquisition time as short as possible. Consequently, there is currently a technology that advances towards faster and faster FLIM recording. However, the maximum speed of a recording technique is only part of the problem. The acquisition time of a FLIM image is a complex function of many factors. These include the photon rate that can be obtained from the sample, the amount of information a technique extracts from the decay functions, the efficiency at which it determines fluorescence decay parameters from the recorded photons, the demands for the accuracy of these parameters, the number of pixels, and the lateral and axial resolutions that are obtained in biological materials. Starting from a discussion of the parameters which determine the acquisition time, this review will describe existing and emerging FLIM techniques and data analysis algorithms, and analyze their performance and recording speed in biological and biomedical applications.

ZrTe 5 is a newly discovered topological material. Shortly after a single layer ZrTe 5 had been predicted to be a two-dimensional topological insulator, a handful of experiments have been carried out on bulk ZrTe 5 crystals, which however suggest that its bulk form may be a three-dimensional topological Dirac semimetal. We report the first transport study on ultra thin ZrTe 5 flakes down to 10 nm. A significant modulation of the characteristic resistivity maximum in the temperature dependence by thickness has been observed. Remarkably, the metallic behavior, occurring only below about 150 K in bulk, persists to over 320 K for flakes less than 20 nm thick. Furthermore, the resistivity maximum can be greatly tuned by ionic gating. Combined with the Hall resistance, we identify contributions from a semiconducting and a semimetallic bands. The enhancement of the metallic state in thin flakes are consequence of shifting of the energy bands. Our results suggest that the band structure sensitively depends on the film thickness, which may explain the divergent experimental observations on bulk materials.

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