Trimethylamine Probes Isolated Silicon Dangling Bonds and Surface Hydroxyls of (H,OH)-Si(001)

Ramírez, L.P. and Fornefeld, N. and Bournel, F. and Kubsky, S. and Magnano, E. and Bondino, F. and Köhler, U. and Carniato, S. and Gallet, J.-J. and Rochet, F.

Volume: 126 Pages: 2548-2560
DOI: 10.1021/acs.jpcc.1c09776
Published: 2022

To better understand why amines catalyze the reactivity of SiOH with silanes, we examined the adsorption of trimethylamine under a low pressure (10-9-10-8 mbar) and a low temperature (105-160 K) on water-terminated (H,OH)-Si(001), which is both a model surface for adsorption studies and a promising starting substrate for atomic layer deposition. Trimethylamine bonding configurations were determined by combining real-time synchrotron radiation X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS) with density functional theory (DFT) calculations of core-level ionization energies and vibrational spectra. Both spectroscopies showed that the majority of species are trimethylamine molecules making acceptor H bonds with surface hydroxyls. Moreover, HREELS indicated that the hydrogen-bonding modes (single and double hydrogen acceptor bonds) depend on temperature and/or coverage, which may in turn affect the weakening of the O-H bond, and hence the catalytic effects of trimethylamine. XPS also clearly detected a minority species, trimethylamine, datively bonded to the isolated silicon dangling bonds (a few 1/100th of a monolayer). This species is prone to breaking, and a detailed analysis of the reaction products was made. The reactivity of the electrically active isolated silicon dangling bonds with the amine may impact the Fermi-level position in the gap. © 2022 American Chemical Society

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