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J. Choi, W. Mayr-Schmölzer, I. Valenti, P. Luches, F. Mittendorfer, J. Redinger, U. Diebold, M. Schmid:
"Metal Adatoms and Clusters on Ultrathin Zirconia Films";
Journal of Physical Chemistry C, 120 (2016), 9920 - 9932.

Nucleation and growth of transition metals on
zirconia has been studied by scanning tunneling microscopy
(STM) and density functional theory (DFT) calculations.
Since STM requires electrical conductivity, ultrathin ZrO
2
fi
lms grown by oxidation of Pt
3
Zr(0001) and Pd
3
Zr(0001)
were used as model systems. DFT studies were performed for
single metal adatoms on supported ZrO
2
fi
lms as well as the
(1
11) surface of monoclinic ZrO
2
. STM shows decreasing
cluster size, indicative of increasing metal
−
oxide interaction, in
the sequence Ag < Pd
≈
Au < Ni
≈
Fe. Ag and Pd nucleate
mostly at steps and domain boundaries of ZrO
2
/Pt
3
Zr(0001)
and form three-dimensional clusters. Deposition of low
coverages of Ni and Fe at room temperature leads to a high density of few-atom clusters on the oxide terraces. Weak
bonding of Ag to the oxide is demonstrated by removing Ag clusters with the STM tip. DFT calculations for single adatoms show
that the metal
−
oxide interaction strength increases in the sequence Ag < Au < Pd < Ni on monoclinic ZrO
2
, and Ag
≈
Au < Pd <
Ni on the supported ultrathin ZrO
2
fi
lm. With the exception of Au, metal nucleation and growth on ultrathin zirconia
fi
lms follow
the usual rules: More reactive (more electropositive) metals result in a higher cluster density and wet the surface more strongly
than more noble metals. These bind mainly to the oxygen anions of the oxide. Au is an exception because it can bind strongly to
the Zr cations. Au di
ff
usion may be impeded by changing its charge state between
−
1 and +1. We discuss di
ff
erences between the
supported ultrathin zirconia
fi
lms and the surfaces of bulk ZrO
2
, such as the possibility of charge transfer to the substrate of the
fi
lms. Due to their large in-plane lattice constant and the variety of adsorption sites, ZrO
2
{111} surfaces are more reactive than
many other oxygen-terminated oxide surfaces.