Chemistry Reference
In-Depth Information
deposited on Si(001) by magnetron sputtering
47
and subsequently be oxi-
dized at various temperatures,
48
exposing the substrate to molecular oxygen,
ozone, NO
2
or plasma-activated O
2
.
Sputtering
49,50
is the most commonly used technique to deposit thin RuO
2
films on dissimilar substrates. O
2
-containing plasmas are frequently utilized
for Ru etching.
51
The Ru etching rate can be increased by Cl
2
addition to an
O
2
plasma.
52
Magnetron plasma sputtering
53-55
or even better reactive
sputtering in O
2
atmosphere produces RuO
2
films with a Ru:O film stoi-
chiometry of 1 : 2.
56,57
These oxide films are in general poly-crystalline and
therefore less suited as model catalysts.
Metal organic chemical vapor deposition (MOCVD) provides another
technology to form thin RuO
2
films.
58-61
However, these films suffer some-
times from carbon contamination. With this method conductive RuO
2
films
could be prepared either with (110)- or with (101)-textured orientations on
SiO
2
/Si(001).
62
The structural texture of the RuO
2
films can be controlled by
both temperature and growth rate. The roughness of MOCVD-grown RuO
2
films can be reduced by co-deposition of iodine containing molecules.
63
Very
clean and thermally stable RuO
2
films can be produced by chemical vapor
deposition (CVD) using RuO
4
64-67
d
n
9
r
4
n
g
|
8
or hydrous-RuO
2
68
as the metallic
precursor.
Pulsed laser deposition (PLD) is a powerful method to deposit RuO
2
films
on dissimilar substrates such as LaAlO
3
69
with an epitaxial RuO
2
film in
(100) orientation normal to the surface. RuO
2
films were also grown on a
MgO(100) substrate using PLD.
70
High quality films on MgO(100) could be
produced at sample temperatures above 870 K resulting in RuO
2
films that
are expitaxial and (110) oriented.
71
Under oxygen deficient conditions the
RuO
2
film grows in (101) orientation on Si.
72
Epitaxial single crystalline films
of Ru(0001) and other platinum group metals can be produced on YSZ-
buffered Si(111) wafers by PLD.
73
Subsequent oxidation leads to the growth
of ultra thin RuO
2
(110) films which serve as perfect single crystalline model
catalysts.
Thin films of metallic Ru have been grown on thin Al
2
O
3
and TiO
2
films by
atomic layer deposition (ALD), employing bis(cyclopentadienyl)ruthenium
(RuCp
2
) and oxygen as precursors.
74
ALD film growth is self-limited and
based on surface reactions, which offers the possibility to control the de-
position process on the atomic scale. By keeping the precursors separate
throughout the coating process, the grown film layer can be controlled as
precise as
.
0.1 angstroms per monolayer. Oxygen has been used in Ru-ALD
as a reactant gas for several Ru precursors. The supplied Ru precursor is
adsorbed on the surface in a first pulse and reacts with the oxygen in the
second pulse. The ligands of the Ru precursor are completely or partly
oxidized to volatile by-products, mainly H
2
O and CO
2
. In the next pulse the
Ru precursor is adsorbed onto the surface and again oxidized. The cycliza-
tion of this two-step process leads in a conformal layer-by-layer growth of the
Ru or RuO
2
75,76
on a substrate with arbitrary topography.
B
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