posted on 2022-01-27, 19:07authored byLucía
Pérez Ramírez, Niklas Fornefeld, Fabrice Bournel, Stefan Kubsky, Elena Magnano, Federica Bondino, Ulrich Köhler, Stéphane Carniato, Jean-Jacques Gallet, François Rochet
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.