There is presently a critical need for a viable approach to form ultrathin, high-quality layers of oxides such as Al₂O₃ on MoS₂ and related two-dimensional transition-metal chalcogenides. Atomic layer deposition (ALD), which is, in principle, the most suitable technique, has been problematic in this case as a result of the low reactivity of these substrates when free of strain, impurities, and defects. Lewis acid-base chemistry provides a possible solution, and the present work employs ab initio theory to examine the feasibility of adsorbing strongly Lewis-acidic Al reagents on MoS₂. The investigation focuses on small Al precursor molecules that are able to adsorb at high coverages and, therefore, to produce a dense and uniform layer of Al(OH)₃ when reacted with H₂O, which is highly desirable for initiating ALD growth. Of those species considered, it is found that Al(CH₃)₃, the most widely used reagent for ALD of Al₂O₃, is actually the least favorable in terms of its interaction with the MoS₂ basal plane. Other, more Lewis-acidic reagents are found to adsorb somewhat more strongly in the critical first step of the growth process and, therefore, to be potentially more useful for initiating ALD growth. The coverage dependence of the adsorption energy and geometry and the effects of AlX₃ polymerization are also considered, and practical suggestions are given for how such species can be incorporated into an ALD process.

中文翻译：

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路易斯酸在MoS2上的吸附与Al2O3原子层沉积有关的理论研究

目前，迫切需要一种可行的方法来在MoS ₂和相关的二维过渡金属硫属元素化物上形成超薄的高质量氧化物层，例如Al ₂ O ₃。原则上，最合适的技术是原子层沉积（ALD），在这种情况下存在问题，这是因为这些基材在没有应变，杂质和缺陷的情况下反应性较低。路易斯酸碱化学提供了一种可能的解决方案，并且本研究采用从头算的理论来研究将路易斯酸性Al试剂强力吸附在MoS ₂上的可行性。。研究集中在能够以高覆盖率吸附并因此在与H ₂ O反应时产生致密且均匀的Al（OH）₃层的小的Al前驱物分子上，这对于启动ALD生长是非常理想的。认为是这些物种的，发现使Al（CH ₃）₃，最广泛使用的试剂的Al为ALD ₂ ö ₃，实际上是在与MOS其相互作用而言最不利的₂基面。发现其他更多的路易斯酸性试剂在生长过程的关键第一步中会更强地吸附，因此可能对于启动ALD生长更有用。还考虑了吸附能和几何形状的覆盖率依赖性以及AlX ₃聚合反应的影响，并就如何将此类物质引入ALD工艺提供了实用建议。