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

preprint
revised on 31.03.2021, 10:54 and posted on 31.03.2021, 12:12 by Davide Barreca, Ettore Fois, Alberto Gasparotto, Chiara Maccato, Mario Oriani, gloria tabacchi
Transition metal complexes with β-diketonate and diamine ligands are valuable precursors for the chemical vapor deposition (CVD) of metal oxide nanomaterials, but the metal-ligand bond dissociation mechanism on the growth surface is not clarified yet. We address this question by Density Functional Theory (DFT) and ab initio molecular dynamics (AIMD) in combination with the Bluemoon (BM) statistical sampling approach. AIMD simulations of the Zn β-diketonate-diamine complex Zn(hfa)2TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N’,N’-tetramethylethylenediamine) show that rolling diffusion of this precursor at 500 K on a hydroxylated silica slab leads to an octahedral-to-square pyramidal rearrangement of its molecular geometry. The free energy profile of the octahedral-to-square pyramidal conversion indicates that the process barrier (5.8 kcal/mol) is of the order of magnitude of the thermal energy at the operating temperature. The formation of hydrogen bonds with surface hydroxyls plays a key role in aiding the dissociation of a Zn-O bond. In the square-pyramidal complex, the Zn center has a free coordination position, which might promote the interaction with incoming reagents on the deposition surface. These results provide a valuable atomistic insight on the molecule-to-material conversion process which, in perspective, might help to tailor by design the first nucleation stages of the target ZnO-based nanostructures.

Funding

We gratefully acknowledge University of Insubria FAR2020, Padova University (DOR 2018–2020, P-DiSC#04BIRD2020-UNIPD EUREKA) and the INSTM Consortium (INSTM21PDBARMAC – ATENA; NSTM21PDGASPAROTTO - NANOMAT) for financial support.

History

Email Address of Submitting Author

gloria.tabacchi@uninsubria.it

Institution

University of Insubria

Country

Italia

ORCID For Submitting Author

0000-0002-1988-6775

Declaration of Conflict of Interest

NO conflict of interest

Version Notes

Second version

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