Density Functional Theory Study of the Adsorption and Dissociation of Copper(I) Acetamidinates on Ni(110): The Effect of the Substrate

Abstract

In order to assess the role of metal substrates on the thermal chemistry of adsorbed acetamidinate metalorganic compounds, we have studied the surface chemistry of copper-(I)−N,N′-dimethylacetamidinate on Ni(110) using density functional theory and contrasted it with similar calculations we previously carried out on Cu(110). At low coverages, it was found that, in its most stable configuration, the molecular adsorption of copper(I)−N,N′-dimethylacetamidinate dimers occurs with the Cu atoms occupying surface hollow sites. The ligands reorient away from those metal centers, and the N atoms develop new direct bonds with surface Ni atoms. However, this configuration is not stable and decomposes by losing both ligands to the surface. In the final state, the two ligands bind via their N atoms to Ni sites one lattice space away from the sites where the Cu atoms remain, with their molecular planes perpendicular to that of the surface. This is in contrast with what happens in the case of adsorption on Cu(110), where the Cu atoms from the metalorganic complex still occupy hollow sites but where only one of the ligands breaks away and binds directly to the surface; the other remains on top of the two Cu ions. In terms of the energetics of adsorption and decomposition, the reactions on Ni(110) are much more exothermic than on Cu(110). Further analysis of the distribution of charge within the adsorbates shows a minor reduction of the Cu atoms of the dimer upon interaction with the surface; full reduction to metallic copper is complete only when both ligands have fully migrated to their new Ni surface sites.

On the Mechanism of the Atomic Layer Deposition of Cu Films on Silicon Oxide Surfaces: Activation Using Atomic Hydrogen and Three-Dimensional Growth

“…This indicates that some of the adsorbed Cu-complex may remain in molecular form upon deposition at 450 K, or, perhaps more likely, that they undergo minimal conversion, reversible upon exposure to atomic hydrogen. The most likely explanation is that the dimeric (or tetrameric) form in which these Cu iminopyrrolidinate precursors exist in gas and solid phases is activated on the surface to form monomeric adsorbates. ,,,,− Upon exposure to atomic hydrogen, those can desorb as monomers, reversibly recombine to desorb back into the gas phase as dimers, or react to liberate the ligands in hydrogenated/protonated form and to reduce the Cu center.…”

Thermal Chemistry of Nickel Diketonate Atomic Layer Deposition (ALD) Precursors on Tantalum and Silicon Oxide Surfaces

“…Migration of the remaining ligands from the Ni atoms to the surface most likely occurs in tandem with ligand fractioning. It is interesting to note that ligand migration is in general one of the expected initial steps during the activation of metal organic ALD precursors adsorbed on solid surfaces. ,, What is not clear is if this transition occurs before or after any ligand decomposition. Previous reported quantum mechanics calculations with Cu­(acac) 2 on Cu and Ta surfaces led to the conclusion that stepwise migration of the acac ligands to the surface is facile but on Cu is not followed by any subsequent dissociation reactions. , On the other hand, our experimental studies of Cu­(acac) 2 activation on Cu and Ni surfaces indicated early ligand decomposition on the metal center (via the loss of a terminal methyl group), before migration to the surface.…”

“…It is interesting to note that ligand migration is in general one of the expected initial steps during the activation of metal organic ALD precursors adsorbed on solid surfaces. 79,124,125 What is not clear is if this transition occurs before or after any ligand decomposition. Previous reported quantum mechanics calculations with Cu(acac) 2 on Cu and Ta surfaces led to the conclusion that stepwise migration of the acac ligands to the surface is facile but on Cu is not followed by any subsequent dissociation reactions.…”

The Early Steps of Molecule-to-Material Conversion in Chemical Vapor Deposition (CVD): A Case Study

“…On the basis of these results, the present research work aims at providing a step forward in the investigation of these issues by combined calculations involving the density functional theory (DFT) coupled with ab initio molecular dynamics (AIMD) [ 25 ]. It is worth noticing that, despite the growing interest in understanding via quantum chemical approaches the microscopic details of molecule-to-material conversion in CVD or ALD processes [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ], most literature data refer to geometry optimization or transition state calculations performed at 0 K. Whereas these studies contribute to shedding light on the binding of the metal center with substrate atoms, the formation of metal-surface linkages for the target CVD precursors, where the metal center is completely surrounded by ligands, requires the dissociation of at least one metal-ligand bond, and remains a key issue to be further investigated.…”