Department of Applied Physics, Eindhoven University of Technology, P. O. Box 513, 5600 MB, Eindhoven, The Netherlands.
Phys Chem Chem Phys. 2018 Jun 20;20(24):16861-16875. doi: 10.1039/c8cp00210j.
In this study, we investigate the reactions involving Atomic Layer Deposition (ALD) of 2D-MoS2 from the heteroleptic precursor Mo(NMe2)2(NtBu)2 and H2S as the co-reagent on a SiO2(0001) surface by means of density functional theory (DFT). All dominant reaction pathways from the early stage of adsorption of each ALD reagent to the formation of bulk-like Mo and S at the surface are identified. In the metal pulse, proton transfer from terminal OH groups on the SiO2 to the physisorbed metal precursor increases the Lewis acidity of Mo and Lewis basicity of O, which gives rise to the chemical adsorption of the metal precursor. Proton transfer from the surface to the dimethylamido ligands leads to the formation and desorption of dimethylamine. In contrast, the formation and desorption of tert-butylamine is not energetically favorable. The tert-butylimido ligand can only be partially protonated in the metal pulse. In the sulphur pulse, co-adsorption and dissociation of H2S molecules give rise to the formation and desorption of tert-butylamine. Through the calculated activation energies, the cooperation between H2S molecules ('cooperative' mechanism) is shown to have a profound influence on the formation and desorption of tert-butylamine, which are crucial steps in the initial ALD deposition of 2D-MoS2 on SiO2. The cyclic ALD reactions give rise to the formation of a buffer layer which might have important consequences for the electrical and optical properties on the 2D layer formed in the subsequent homodeposition.
在这项研究中，我们通过密度泛函理论（DFT）研究了在 SiO2(0001) 表面上，由异核配体前体 Mo(NMe2)2(NtBu)2 和 H2S 作为共试剂进行二维 MoS2 的原子层沉积（ALD）的反应。确定了从每个 ALD 试剂吸附的早期到表面上形成块状 Mo 和 S 的所有主要反应途径。在金属脉冲中，来自 SiO2 末端 OH 基团的质子转移到物理吸附的金属前体中，增加了 Mo 的路易斯酸度和 O 的路易斯碱度，从而导致金属前体的化学吸附。来自表面的质子转移导致二甲基酰胺配体的形成和脱附。相比之下，叔丁基胺的形成和脱附在能量上是不利的。在金属脉冲中，叔丁基亚氨基配体只能部分质子化。在硫脉冲中，H2S 分子的共吸附和离解导致叔丁基胺的形成和脱附。通过计算的活化能，H2S 分子之间的协同作用（“协同”机制）对叔丁基胺的形成和脱附具有深远的影响，这是在 SiO2 上初始二维 MoS2 的 ALD 沉积过程中的关键步骤。循环 ALD 反应导致缓冲层的形成，这可能对随后的同质沉积中形成的二维层的电学和光学性质产生重要影响。
