Two-dimensional (2D) transition-metal borides (TMBs) are especially expected to exhibit excellent performance in various fields among electricity, superconductivity, magnetism, mechanics, biotechnology, battery, and catalysis. However, the synthesis of ultrathin TMB single crystals with ultrahigh phase purity was deemed extremely challenging and has not been realized till date. That is because TMBs have the most kinds of crystal structures among inorganic compounds, which possess generous phase structures with similar formation energies compared with other transition-metal compounds, attributing to the metalloid and electron-deficient characteristics of boron. Herein, for the first time, we demonstrate a chemical potential-modulated strategy to realize the precise synthesis of various ultrahigh-phase-purity (approximately 100%) ultrathin TMB single crystals, and the precision in the phase formation energy can reach as low as 0.01 eV per atom. The ultrathin MoB₂ single crystals exhibit an ultrahigh Young’s modulus of 517 GPa compared to other 2D materials. Our work establishes a chemical potential-modulated strategy to synthesize ultrathin single crystals with ultrahigh phase purity, especially those with similar formation energies, and undoubtedly provides excellent platforms for their extensive research and applications.

中文翻译：

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超薄过渡金属硼化物单晶的化学势调制超高相纯度生长

二维（2D）过渡金属硼化物（TMBs）尤其有望在电学、超导、磁学、力学、生物技术、电池和催化等各个领域表现出优异的性能。然而，超高相纯度的超薄TMB单晶的合成被认为极具挑战性，迄今为止尚未实现。这是因为 TMB 在无机化合物中具有最多种类的晶体结构，与其他过渡金属化合物相比，TMB 具有丰富的相结构和相似的形成能，这归因于硼的类金属和缺电子特性。在此，第一次，我们展示了一种化学势调制策略来实现各种超高相纯度（约 100%）超薄 TMB 单晶的精确合成，相形成能量的精度可低至每个原子 0.01 eV。超薄 MoB_{与其他二维材料相比， 2}单晶表现出 517 GPa 的超高杨氏模量。我们的工作建立了一种化学势调制策略来合成具有超高相纯度的超薄单晶，尤其是那些具有相似形成能的超薄单晶，无疑为它们的广泛研究和应用提供了极好的平台。