Initial stage of atomic layer deposition of 2D-MoS₂ on a SiO₂ surface: a DFT study

Abstract

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.

Edge-Site Nanoengineering of WS2 by Low-Temperature Plasma-Enhanced Atomic Layer Deposition for Electrocatalytic Hydrogen Evolution

“…A complete list of ALD reactions of the amide precursor can be found in previous studies. 60−62 In this study, we only looked at the adsorption energy of the W precursor and the consequence of ligand protonation on the adsorption of the W precursor.…”

“…More computational details can be found in a previous work. 60 In principle, the following ALD reactions are included: adsorption, protonation of ligands, desorption of the protonated ligands, densification, cooperative effects, and ligand exchange. A complete list of ALD reactions of the amide precursor can be found in previous studies.…”

Atomic Layer Deposition of 2D Metal Dichalcogenides for Electronics, Catalysis, Energy Storage, and Beyond

“…However, with typical substrates that contain dangling bonds, such as SiO 2 , formation of covalent bonds and therefore an interlayer between the substrate and TMDC seems likely and is also supported by theoretical studies. [132,133] All of the abovementioned factors affect the resulting morphology of ALD TMDC films. Furthermore, it is often observed that in the beginning of the film growth, very thin ALD TMDC films are smooth.…”

“…However, with typical substrates that contain dangling bonds, such as SiO 2 , formation of covalent bonds and therefore an interlayer between the substrate and TMDC seems likely and is also supported by theoretical studies. [ 132,133 ]…”

Applications of Density Functional Theory on Heavy Metal Sensor and Hydrogen Evolution Reaction (HER)

“…This kind of databases will be the standard reference for the future research. In computational chemistry, the various DFT methods have been implemented and studied in several systems including chemosensor [22,23], hydrogen evolution reaction (HER) [24][25][26], oxygen reduction reaction (ORR) [27,28], oxygen evolution reaction (OER) [29], molecular machines [30,31], DNA mutation [32][33][34], selective etching [35,36], atomic layer deposition (ALD) [37,38] etc. Although a number of applications of DFT were reported, this book chapter precisely focused on heavy metal sensor and hydrogen evolution reaction.…”