We predict a two-dimensional (2D) antiferromagnetic (AFM) boron (designated as M -boron) by using ab initio evolutionary methodology. M -boron is entirely composed of B20 clusters in a hexagonal arrangement. Most strikingly, the highest valence band of M -boron is isolated, strongly localized, and quite flat, which induces spin polarization on either cap of the B20 cluster. This flat band originates from the unpaired electrons of the capping atoms, and is responsible for magnetism. M -boron is thermodynamically metastable and is the first magnetic 2D form of elemental boron.

2D van der Waals materials exhibiting intrinsic magnetic order have attracted enormous interest in the last few years. [1-5] However, despite much progress in the control of their magnetic properties, for example through electrostatic gating or control of the stacking order, [6-9] little is known about the mechanisms governing fundamental magnetic processes in the ultrathin limit. For instance, the extensively studied materials CrI 3 (a semiconductor) and Fe 2 GeTe 3 (a metal) are soft ferromagnets in the bulk crystal form with a remanent magnetization far below the saturation magnetization (a few percent), [10,11] but surprisingly, they become hard ferromagnets when exfoliated to a few atomic layers, with a near squareshaped hysteresis and a large coercive field of H c ≈ 0.1−1 T. [1,12-14] Since hard ferromagnetic properties are crucial to applications, especially as a building block for van der Waals magnetic heterostructures, The recent isolation of 2D van der Waals magnetic materials has uncovered rich physics that often differs from the magnetic behavior of their bulk counterparts. However, the microscopic details of fundamental processes such as the initial magnetization or domain reversal, which govern the magnetic hysteresis, remain largely unknown in the ultrathin limit. Here a widefield nitrogen-vacancy (NV) microscope is employed to directly image these processes in few-layer flakes of the magnetic semiconductor vanadium triiodide (VI 3). Complete and abrupt switching of most flakes is observed at fields H c ≈ 0.5-1 T (at 5 K) independent of thickness. The coercive field decreases as the temperature approaches the Curie temperature (T c ≈ 50 K); however, the switching remains abrupt. The initial magnetization process is then imaged, which reveals thickness-dependent domain wall depinning fields well below H c. These results point to ultrathin VI 3 being a nucleation-type hard ferromagnet, where the coercive field is set by the anisotropy-limited domain wall nucleation field. This work illustrates the power of widefield NV microscopy to investigate magnetization processes in van der Waals ferromagnets, which can be used to elucidate the origin of the hard ferromagnetic properties of other materials and explore field-and current-driven domain wall dynamics.

We propose stable layered structures and ultrathin tubular configurations of titanium oxide (TiO 2 ) nanomaterials on the basis of first-principles calculations within density functional theory. The thinnest TiO 2 nanosheet is characterized by a reconstructed (001) bilayer of rutile TiO 2 , while ultrathin TiO 2 nanotubes can be built by rolling up a TiO 2 NS. These nanotubes are predicted to have high stability, large Young's modulus, and tunable electronic properties. A possible synthetic route toward these nanostructures is also presented.

To monitor the temperature distribution of a cell and its changes under varied conditions is currently a technical challenge. A variety of non-contact methods used for measuring cellular temperature have been developed, where changes of local temperature at cell-level and sub-cell-level are indirectly calculated through the changes in intensity, band-shape, bandwidth, lifetime or polarization anisotropy of the fluorescence spectra recorded from the nano-sized fluorescent materials pre-injected into the target cell. Unfortunately, the optical properties of the fluorescent nano-materials may be affected by complicated intracellular environment, leading to unexpected measurement errors and controversial arguments. Here, we attempted to offer an alternative approach for measuring the absolute increments of local temperature in micro-Testing Zones induced by live cells. In this method, built-in high-performance micro-thermocouple arrays and double-stabilized system with a stability of 10 mK were applied. Increments of local temperature close to adherent human hepatoblastoma (HepG2) cells were continuously recorded for days without stimulus, showing frequent fluctuations within 60 mK and a maximum increment by 285 mK. This method may open a door for real-time recording of the absolute local temperature increments of individual cells, therefore offering valuable information for cell biology and clinical therapy in the field of cancer research.

A high-throughput screening based on first-principles calculations was performed to search for new ternary inorganic electrides. From the available materials database, we identified three new thermodynamically stable materials (Li12Mg3Si4, NaBa2O and Ca5Ga2N4) as potential electrides made by main group elements, in addition to the well known mayenite based electride (C12A7:e − ). Different from those conventional inorganic electrides in which the excess electrons play only the role of anions, the three new materials, resembling the electrides found in simple metals under high pressure, possess mixed ionic and metallic bonding. The interplay between two competing mechanisms, together with the different crystal packing motifs, gives rise to a variety of geometries in anionic electrons, and rich physical phenomena such as ferromagnetism, superconductivity and metal-insulator transition. Our finding here bridges the gap between electrides found at ambient and high pressure conditions.

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