The synthesis of refractory materials usually relies on high-temperature conditions to drive diffusion-limited solid-state reactions. These reactions result in thermodynamically stable products that are rarely amenable to low-temperature topochemical transformations that postsynthetically modify subtle structural features. Here, we show that topochemical deintercalation of Al from MoAlB single crystals, achieved by room-temperature reaction with NaOH, occurs in a stepwise manner to produce several metastable Mo-Al-B intergrowth phases and a two-dimensional MoB (MBene) monolayer, which is a boride analogue to graphene-like MXene carbides and nitrides. A high-resolution microscopic investigation reveals that stacking faults form in MoAlB as Al is deintercalated and that the stacking fault density increases as more Al is removed. Within nanoscale regions containing high densities of stacking faults, four previously unreported Mo-Al-B (MAB) intergrowth phases were identified, including Mo2AlB2, Mo3Al2B3, Mo4Al3B4, and Mo6Al5B6. One of these deintercalation products, Mo2AlB2, is identified as the likely MAB-phase precursor that is needed to achieve a high-yield synthesis of two-dimensional MoB, a highly targeted two-dimensional MBene. Microscopic evidence of an isolated MoB monolayer is shown, demonstrating the feasibility of using room-temperature metastable-phase engineering and deintercalation to access two-dimensional MBenes.

中文翻译：

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MoAlB 中 Al 的拓扑化学脱嵌：逐步蚀刻路径、层状共生结构和二维 MBene

耐火材料的合成通常依赖于高温条件来驱动扩散受限的固态反应。这些反应产生热力学稳定的产物，这些产物很少适合低温拓扑化学转化，这些转化后合成后会改变微妙的结构特征。在这里，我们展示了通过室温与 NaOH 反应实现的 MoAlB 单晶中 Al 的拓扑化学脱嵌，以逐步的方式产生几个亚稳态 Mo-Al-B 共生相和二维 MoB（MBene）单层，它是类似石墨烯的 MXene 碳化物和氮化物的硼化物类似物。高分辨率显微研究表明，随着 Al 的脱嵌，在 MoAlB 中会形成堆垛层错，并且随着更多的 Al 被去除，堆垛层错密度增加。在含有高密度堆垛层错的纳米级区域内，发现了四种以前未报道的 Mo-Al-B (MAB) 共生相，包括 Mo2AlB2、Mo3Al2B3、Mo4Al3B4 和 Mo6Al5B6。其中一种脱嵌产物 Mo2AlB2 被确定为可能的 MAB 相前体，这是实现二维 MoB（一种高度靶向的二维 MBene）的高产合成所需的。显示了孤立的 MoB 单层的显微证据，证明了使用室温亚稳相工程和脱嵌来获得二维 MBenes 的可行性。被确定为可能是实现二维 MoB 高产合成所需的 MAB 相前体，这是一种高度靶向的二维 MBene。显示了孤立的 MoB 单层的显微证据，证明了使用室温亚稳相工程和脱嵌来获得二维 MBenes 的可行性。被确定为可能是实现二维 MoB 高产合成所需的 MAB 相前体，这是一种高度靶向的二维 MBene。显示了孤立的 MoB 单层的显微证据，证明了使用室温亚稳相工程和脱嵌来获得二维 MBenes 的可行性。