Role of oligomer structures in the surface chemistry of amidinate metal complexes used for atomic layer deposition of th
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FOCUS ISSUE
ATOMIC LAYER DEPOSITION FOR EMERGING THIN-FILM MATERIALS AND APPLICATIONS
Role of oligomer structures in the surface chemistry of amidinate metal complexes used for atomic layer deposition of thin films Jonathan Guerrero-Sánchez1, Bo Chen2, Noboru Takeuchi3, Francisco Zaera2,a) 1
Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Ensenada, Baja California 22800, México Department of Chemistry, University of California, Riverside, California 92521, USA 3 Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Ensenada, Baja California 22800, México; and Department of Chemistry, University of California, Riverside, California 92521, USA a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 11 July 2019; accepted: 3 September 2019
The initial steps of the thermal chemistry of Cu(I)-2-(tert-butylimino)-5,5-dimethyl-pyrrolidinate on metal surfaces were characterized using temperature-programmed desorption experiments and density functional theory (DFT). The relative stability of the initial dimer relative to its dissociation on metal surfaces was evaluated. Several molecular desorption temperatures were identified on Ni(110), but all correspond to dimers, either containing the initial Cu ions or after their removal; no monomer was ever detected. DFT calculations also indicated preferential bonding on Cu(110) as a dimer, albeit with a distorted configuration, via the Cu atoms and in registry with the lattice of the substrate. A potential dissociation pathway of the adsorbed dimer was identified involving the partial detachment of the ligands via the scission of one Cu–N bond at the time and migration to adjacent surface sites. This process is accompanied by the reduction of the Cu centers of the metal–organic complex, indicating that it may be the rate-limiting reaction that leads to further fragmentation of the ligands.
Introduction The chemistry of metal-organic complexes on solid surfaces is quite relevant to several practical applications, in the making of heterogeneous catalysts [1, 2] and the growth of thin solid films [3, 4, 5], for instance. In general, adsorption of those compounds is assumed to take place via the formation of new bonds involving the metal center of the discrete metal-organic complex, a step that may require either rearrangement of the original ligands or displacement of one or more of those by a surface site [6]. However, in some instances, this chemistry may be complicated by the fact that the gas-phase precursor may exist in an oligomeric form, typically as a dimer but sometimes as a trimer or a tetramer. An early example where this issue was recognized was in the study of the deposition of aluminum-containing films (i.e., nitrides and oxides) using a trimethylaluminum [TMA, Al(CH3)3] precursor [7], which is well known to dimerize in the gas phase [8]. Many bidentate ligands may also favor the formation of dimers, trimers, or even tetramers, upon complexation with metal centers [9, 10,
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