Microstructure of metallorganic chemical vapor deposited aluminum coatings on Ti6242 titanium alloy

Article abstract of DOI:10.1149/1.2769265

Al-based alloys are used in aeronautics as a protective layer against the excessive oxidation of turbines blades. In this work, Al coatings were deposited by metallorganic chemical vapor deposition on Ti6242, a commercial titanium alloy, with Pt as a sublayer or codeposited to ensure this protection, eventually forming platinum aluminides. Continuous Al coatings were deposited on bare Ti6242, using both triisobutylaluminum and dimethylethylamine alane as precursors. The same operating conditions applied on a platinum sublayer lead to discontinuous layers mainly containing whiskers. The introduction of a surfactant, namely, ethyl iodide, in the input gas improves the coating morphology by providing nearly whisker-free continuous films, suitable for oxidation protection. Codeposition of Pt and Al results in reduced growth rate and yields layers with lower Pt content and with specific morphology. This behavior is attributed to the competition between Al and Pt compounds on the growing surface.

Full text of DOI:10.1149/1.2769265

D538
Journal of The Electrochemical Society, 154 ͑10͒ D538-D542 ͑2007͒
0013-4651/2007/154͑10͒/D538/5/$20.00 © The Electrochemical Society
Microstructure of Metallorganic Chemical Vapor Deposited
Aluminum Coatings on Ti6242 Titanium Alloy
,z
*
Mathieu Delmas and Constantin Vahlas
Centre Interuniversitaire de Recherche et d’Ingénierie des Matériaux (CIRIMAT–CNRS–INPT-UPS),
ENCIACET, 31077 Toulouse Cedex 4, France
Al-based alloys are used in aeronautics as a protective layer against the excessive oxidation of turbines blades. In this work, Al
coatings were deposited by metallorganic chemical vapor deposition on Ti6242, a commercial titanium alloy, with Pt as a sublayer
or codeposited to ensure this protection, eventually forming platinum aluminides. Continuous Al coatings were deposited on bare
Ti6242, using both triisobutylaluminum and dimethylethylamine alane as precursors. The same operating conditions applied on a
platinum sublayer lead to discontinuous layers mainly containing whiskers. The introduction of a surfactant, namely, ethyl iodide,
in the input gas improves the coating morphology by providing nearly whisker-free continuous films, suitable for oxidation
protection. Codeposition of Pt and Al results in reduced growth rate and yields layers with lower Pt content and with specific
morphology. This behavior is attributed to the competition between Al and Pt compounds on the growing surface.
© 2007 The Electrochemical Society. ͓DOI: 10.1149/1.2769265͔ All rights reserved.
Manuscript submitted April 18, 2007; revised manuscript received June 14, 2007. Available electronically August 15, 2007.
Ti6242 titanium alloy is a promising material for the manufac-
roughness. Also, protective coatings are often composed of two or
more elements and the microstructure of the main element can be
strongly influenced by the presence of the other͑s͒. This is the case
of the present study where Al is deposited on a Pt sublayer or code-
posited with Pt. The pure Pt deposition will be described in a forth-
coming paper. The microstructures of Al films regarding the nature
of the substrate will be discussed in this study. The improvement of
the rough microstructures obtained from deposition on Pt precoated
substrates via the use of surfactants will be discussed, regarding
surface chemistry phenomena. Finally, the simultaneous deposition
of Al and Pt will be described. The particularities of such a codepo-
sition will be illustrated and discussed.
turing of helicopter turbine components submitted to moderate
stresses. In addition to titanium, it contains aluminum, tin, zirco-
nium and molybdenum. The four digits in the Ti6242 code name
refer to the wt % of these elements, respectively. This alloy is
mainly composed of an ␣ phase and of a low amount of a ␤ phase,
the latter being stabilized in ambient temperature by the abovemen-
tioned elements. It can be used at operating temperatures up to
823 K, provided it is protected against cyclic oxidation. Such pro-
tection can be conferred by Al-containing coatings which are widely
used in the aeronautic industry, mainly as bond coats to prevent
parts such as turbine blades and vanes from excessive oxidation.
Al-containing coatings are mainly processed by the classical pack
aluminization technique. Despite its simplicity, pack aluminization
presents several drawbacks among which are powders disposal or
high temperature operation. Considering that microstructural integ-
rity and hence appropriate performance of the Ti6242 alloy is main-
tained only up to 873 K, the latter drawback prevents pack alumi-
nization from being used for the application of protective coatings to
this material. Unlike pack aluminization, metallorganic chemical va-
por deposition ͑MOCVD͒ is not concerned by powders disposal; it
operates at low to moderate temperature and yields highly confor-
mal films. We recently presented a study on the MOCVD of pure
and Pt-alloyed Al coatings on Ti6242 coupons.1,2 Operating condi-
tions for the MOCVD, preliminary characterization of the micro-
structure of the coatings and oxidation kinetics were reported. Iso-
thermal oxidation of Ti6242 coupons covered by MOCVD
processed Al coatings revealed noticeable protection with more than
one order of magnitude lower oxidation kinetics than that of the bare
alloy.1 It was thus demonstrated that MOCVD is a promising alter-
native to the pack-aluminization technique.
However, the reported oxidation kinetics was characterized by an
initial strong transient regime which was partially attributed to the
rough microstructure of the coatings. It was concluded that more
accurate control of the coating microstructure would be necessary
for further decrease of both transient and steady state oxidation rate
of the coated parts. This is the aim of the present paper. The
MOCVD of Al films has been extensively studied for microelec-
tronic applications ͑see, for example, Ref. 3͒ with particular focus
on the improvement of their microstructure.4,5 However, the con-
straints on the process and film characteristics are depending upon
the aimed application. While microelectronics is concerned with re-
ducing the thickness of the films, protective coatings should be con-
tinuous and several micrometers thick, and be applied on various
commercial alloys or predeposited layers with industrial surface
Experimental
Depositions were performed on 2 mm thick, 15 mm diam
Ti6242 disks. Substrates were used as received, i.e., with 600 grit
surface polishing. Prior to deposition, they were etched in boiling
Turco, cleaned ultrasonically in deionized water and finally de-
greased in acetone. Some disks were coated with a Pt film before Al
deposition. A specially designed setup ͑the detailed description of
the setup can be found in Ref. 2͒ was used for the CVD experi-
ments. It allowed entire coating of coupons in a single run. It is
recalled here that it consists in a vertical cold wall reactor in which
the sample is maintained vertically by the two wires of an S-type
thermocouple. Temperature is monitored by using
a dual-
wavelength pyrometer ͑Williamson͒, with 1° accuracy. Triisobut-
ylaluminum ͑TIBA, 95% pure, Strem Chemicals͒, 99% pure di-
methylathylamine alane ͑DMEAA, EPICHEM͒, and 99% pure tri-
methylmethylcyclopentadienylplatinum͑IV͒ ͓͑MeCp͒Me3Pt͔ ͑Strem
Chemicals͒ were used as liquid aluminum and platinum precursors,
respectively, without further purification. TIBA and DMEAA are
aluminum precursors yet widely used in microelectronics.4,6 Decom-
position of ͓͑MeCp͒Me3Pt͔, in the presence of H2 was reported to
provide essentially pure platinum films.7
The precursors’ bubblers were loaded into a glove box. They
were immersed in thermoregulated water baths to ensure fixed vapor
pressure and, together with the flow rate of the bubbling gas, to
control the compounds’ molar fraction in the gas mixture entering
the reactor. Three 99.998% pure N2 lines were used: two for bub-
bling through the Al and Pt precursors and one for the dilution of the
input gas. Before entering the reactor, the dilution line was com-
bined with a 99.999% pure H2 line for Pt deposition. Gases through
all four lines were fed through computer driven mass flow control-
lers. The gas inlet circuit was made of stainless steel and wrapped
with heating elements both before and after the bubblers to ensure
efficient gas-liquid contact in the bubblers and to avoid premature
condensation of the precursors. The gas phase was evacuated at the
exit of the reactor by a vacuum pump via a cold trap. Operating
pressure was 9330 Pa for deposition from TIBA and 1330 Pa for
*
Electrochemical Society Active Member.
z E-mail: constantin.vahlas@ensiacet.fr
Downloaded on 2015-05-03 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 154 ͑10͒ D538-D542 ͑2007͒
D539
Table I. Operating conditions for the deposition of Al using TIBA and DMEAA.
Sample
Flow rate ͑sccm͒
Reactor
N2,dil.
N2,Pr
Prec.
C2H5I
T ͑K͒
P ͑Pa͒
t ͑min͒
AlT1
AlT2
AlT3
AlD1
AlD2
300
300
300
41
56.6
56.6
56.6
3.15
2.82
0.3654
0.3654
0.3654
0.1905
0.1704
No
No
Yes
Yes
Yes
623
623
623
473
473
9330
9330
9330
1330
1330
120
120
120
75
41
70
Table II. Operating conditions for the codeposition of Al and Pt.
Sample
Flow rate ͑sccm͒
Reactor
N2,dil.
N2,Al.
DMEAA
N2,Pt.
Me3͑MeCp͒Pt
C2H5I
T ͑K͒
P ͑Pa͒
t ͑min͒
AlPt1
AlPt2
40.5
40.5
1.8
1.8
0.0433
0.0433
9
9
0.0242
0.0242
Yes
Yes
473
523
1330
1330
120
120
deposition from DMEAA and codeposition. These values are higher
than those reported in previous studies for the CVD of Al. They are
compatible with the aimed industrial application. Cu and Al CVD
deposited films present similar morphological characteristics, due to
a Volmer-Weber growth mode.8 It was reported that the use of ethyl
iodide as a surfactant improves copper deposition. Ethyl iodide ad-
sorbs dissociatively upon Al surfaces in the same way as on Cu
surfaces.9,10 Subsequently, we used iodine as a surfactant during Al
deposition upon Pt. This was achieved by introducing a small
amount of ethyl iodide in the gas phase during deposition. Tables I
and II sum up the conditions used for the films deposition.
Surface and cross section scanning electron microscopy ͑SEM͒,
transmission electronic microscopy ͑TEM͒, X-ray energy dispersive
spectroscopy ͑EDS͒, grazing incident X-ray diffraction ͑GIXRD͒,
interferometry, and atomic force microscopy ͑AFM͒ were used to
investigate the morphology, microstructure, composition, surface to-
pography, and roughness of the coatings.
Figure 4 presents the SEM micrograph of the surface morphol-
ogy ͑a͒ and the TEM cross section focusing on the area by the Pt
sublayer, of sample AlD2; i.e., processed from DMEAA on Pt, by
using C2H5I. Film AlD2 presents small sharp crystals whose shape
is different from those observed on AlD1 and has no whiskers. The
film is continuous and was processed at a growth rate of 1 ␮m/h.
The 300 nm thick Pt sublayer appears as a black, compact strip.
AFM measurements prior to Al deposition reveal that it is smooth
and covers conformally the surface of the substrate. In addition, this
Pt film did not show any scaling or peeling after deposition, even on
a mirror-like, 1 ␮m polished substrate. A crystalline continuous Al
film can be observed on the platinum film. The inset on this figure
Results
Figure 1 presents the AlT1 ͑a͒ and the AlD1 ͑b͒ samples surface.
All SEM micrographs were realized at similar magnifications. Films
obtained upon bare Ti6242 using TIBA ͑sample AlT1͒ present a
continuous base and surface characteristics of Al crystals.3 The av-
erage roughness of AlT1 is 1.7 ␮m. No preferential orientation
could be observed with GIXRD analysis, and the carbon contami-
nation is lower than 1 wt %. Observation of micrograph 1b reveals
that the DMEAA based process ͑involving lower deposition tem-
perature͒ leads to similar but finer microstructure than the TIBA
based one.
Figure 2 presents the Arrhenius plot of DMEAA deposition on
bare Ti6242 at 1330 Pa. From this diagram, activation energy of
0.3 eV was measured. The DMEAA processed coating, AlD1, ex-
hibits an average roughness of 0.5 ␮m and a continuous base similar
with results found by Vahlas et al.11 Neither preferential orientation
nor carbon contamination could be observed in AlD1.
Sample AlT2 corresponds to Al growth on Pt sublayer in the
same conditions as for sample AlT1; it results in the formation of
whiskers instead of continuous film. This microstructure does not
present any significant continuous zone. Deposition from DMEAA
results in a similar morphology. It is clear that such a discontinuous,
rough morphology cannot meet the expected property from these
coatings, namely the protection of the substrate against oxygen in-
gress.
Figure 3 presents surface ͑a͒ and cross section ͑b͒ SEM micro-
graphs of sample AlT3. The microstructure of this coating consists
of small crystals and only few surface whiskers. This morphology
surmounts a continuous Al layer, illustrated in the cross section mi-
crograph.
Figure 1. Surface SEM micrographs of samples AlT1 ͑a͒ and AlD1 ͑b͒: Al
deposited on bare Ti6242 using TIBA and DMEAA, respectively.
Downloaded on 2015-05-03 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

D540
Journal of The Electrochemical Society, 154 ͑10͒ D538-D542 ͑2007͒
Figure 2. Arrhenius plot for the deposition of Al from DMEAA at 1330 Pa.
points out the Pt–Al interface. A 50 nm thick interdiffusion zone is
shown to be developed during the deposition of Al; i.e., after 70 min
at 473 K. The Pt/Al interface is very reactive,12 the diffusion rate of
Pt into Al being several orders of magnitude higher than that of Al
into Pt.13 The result of this phenomenon is the formation of platinum
aluminides and especially Al2Pt. It thus appears that, as for TIBA
processed samples, ethyl iodide assisted Al deposition from
DMEAA on Pt provides continuous films. Both TIBA and DMEAA
processed films show very low C contamination ͑less than 1 wt %͒
and no preferential orientation. Iodine contamination of the surfac-
tant assisted films remains under 1 wt %.
Figure 4. Surface SEM micrograph ͑a͒ and cross section TEM micrograph
with detail of the Al–Pt interface ͑b͒ of sample AlD2: Al deposited on Pt
using DMEAA with surfactant.
Al–Pt codeposition in conditions AlPt1 corresponds to a growth
rate of ϳ1 ␮m/h. This value is low compared with the calculated
growth rates of Al ͑6 ␮m/h͒ and Pt ͑1 ␮m/h͒ in the same condi-
tions. Figure 5 presents a surface SEM micrograph of such a film,
processed for 2 h. The Ti6242 surface roughness can be observed
thus confirming the conformality and the reduced thickness of the
film.
Figure 6 presents a SEM micrograph of the AlPt2 surface. This
coating consists of a codeposition performed at 523 K, with a re-
sulting growth rate of 6 ␮m/h. It can be noticed that the microstruc-
ture is close to that of the 473 K processed codeposited sample.
AlPt2 presents a higher average roughness of 240 nm and does not
show any carbon contamination. The Pt content is about 16 wt %,
still lower than the Pt molar fraction in the gas phase, but signifi-
cantly higher than that of the 473 K deposited coatings.
Despite the low processing temperature, GIXRD patterns of
samples AlPt1 and AlPt2 indicate that both films are composed of
Figure 3. Surface ͑a͒ and cross section ͑b͒ SEM micrographs of sample
AlT3: I-assisted Al deposition on Pt using TIBA.
Figure 5. Secondary ͑left͒ and backscattered ͑right͒ electrons surface SEM
micrographs of sample AlPt1: Al and Pt codeposited on Ti6242 at 473 K.
Downloaded on 2015-05-03 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 154 ͑10͒ D538-D542 ͑2007͒
D541
atomic steps. Diffusion of the adatoms through atomic steps is then
improved again, allowing the growth of a smoother surface. Based
on these mechanisms, addition of a C2H5I stream in the dilution gas
during deposition leads to coatings presenting a continuous base. Al
films grown on Pt using DMEAA and surfactant assistance also
yield continuous and whisker-free morphology ͑Fig. 4͒. As I pre-
sents an atomic radius far larger than that of Al, and is a low surface-
energy element, it segregates at the surface during the growth and
results in no significant contamination, as was attested by EDS.
The mechanisms of Al and Pt codeposition are different from
those prevailing for single elements. However, due to the lack of in
situ observations, we can only make several assumptions. Pt depo-
sition using Me3͑MeCp͒Pt presents an induction period followed by
an autocatalytic growth.7 The autocatalytic growth appears when the
Pt clusters’ size allows the catalytic properties to appear. During
codeposition, Al growth prevents Pt atoms from forming clusters.
The deposition rate of platinum drops dramatically. The reduced
concentration of Pt in the films is attributed to this phenomenon. The
shift of growth rate to higher temperature indicates further interac-
tions between the two precursors. According to Nakajima et al.,17
DMEAA decomposes in dimethylethylamine and alane while ap-
proaching the surface. Two possibilities can be foreseen for the in-
teraction between the alane and the Pt precursor: First, alane would
react rapidly with the Pt precursor in the gas phase thus reducing the
availability of the latter in the deposition process. Second, the alane
would adsorb on the substrate, with the Al atom first. As the Pt
precursor coordinates to the surface through the cyclopentadienyl
ligand,7,19 this ligand may remain at the aluminum surface. The
work of Zhuk et al. enlightens the influence of such an adsorption on
Al film growth.18 This phenomenon results in the decrease of the
growth rate of Al and ultimately of the film, since Al is the major
component of the latter. Moreover, it is worth noting that the area of
an adsorbed cyclopentadienyl on a Pt ͑111͒ surface is about ten
times larger than that of Al.6,19 This difference can also explain to a
certain extent the morphological perturbation of Al films in the pres-
ence of Me3͑MeCp͒Pt.
Figure 6. Surface SEM micrograph of sample AlPt2: Al and Pt codeposited
on Ti6242 at 523 K.
Al, with several Al–Pt compounds, such as PtAl2, Al21Pt8, Al21Pt6,
Pt2Al. No preferential orientation could be observed in Al.
Discussion
Vahlas et al.11 reported that MOCVD processed Al coatings from
TIBA on silicon carbide strongly depend on surface pretreatments.
Deposition on Ti6242 is more straightforward as nucleation is easier
on metallic surfaces. DMEAA allows deposition on Ti6242 of con-
tinuous films without pretreatments, as well. The activation energy
of DMEAA processed Al coatings on Ti6242 ͑0.3 eV͒ is consistent
with those reported in the literature ͑between 0.1 and 0.7 eV, de-
pending on the substrate͒.14-17 However, DMEAA seems to be very
sensitive to the nature of the substrate. Jang et al. demonstrated that
a better conductivity of the substrate decreases the activation
energy.14 The value determined by Jang for conductive substrates
͑TiN͒ is three times lower than the one estimated in the present
work. However, other studies using Si as a substrate indicate higher
values than Jang’s ones,15,16 and modeling of DMEAA decomposi-
tion on Al surface resulted in Ea = 0.3 eV;17 it can thus be con-
cluded that this is an accurate value for activation energy on metallic
surfaces.
The loose microstructure of the AlT2 sample can be linked to the
catalytic properties of Pt. Deposition of Al from TIBA can lead
spontaneously to the formation of whiskers, as described by Zhuk et
al.18 The obtained whiskers are rather thick ͑—a few hundreds na-
nometers in diameter—͒ and present many bends but no branching.
This behavior has been observed on Ti6242, as well. This growth
mode is due to adsorption on the Al surface of precursor ligands
leading to volatile compounds with Al adatoms. Surface mobility of
those compounds allows their concentration on preferential sites
where they are decomposed, forming the growing whiskers. This
whiskers growth mechanism seems to be enhanced by the Pt sub-
layer. Whiskers appearing then are thinner and branched ͑sample
AlT2͒. It has been reported that co-adsorption of ferrocene on the
surface prevents such a behavior through the blocking action of the
adsorbed cyclopentadienyl groups.18 These adsorbed cyclopentadi-
enyl groups seem to prevent such behavior, avoiding then the whis-
kers growth. However, this solution could not be applied here, be-
cause of the resulting undesirable Fe contamination. On the other
hand, copper deposition encounters rough and discontinuous micro-
structures. As has already been mentioned, the use of surfactant,
namely C2H5I, allows to achieve continuous and smoother films.8 It
has been reported that alkyliodides are dissociatively adsorbed on Al
surfaces, with the C–I bond breaking since 200 K.9 According to
Tölkes et al.,17 the iodine atoms may act in two ways. First, by
lowering the surface energy of the system, the balance between the
activation energies for nucleation and for growth of Al is shifted
towards the nucleation, this resulting in surface smoothening. Sec-
ond, the presence of I lowers the Ehrlich-Schwoebel barrier, i.e., the
energy barrier responsible for the diffusion of adatoms across the
The above observed microstructures can be correlated to the per-
formance of the as processed oxidation barriers. Thermogravimetric
tests were performed in dry air on such processed samples, with the
test conditions and the obtained results reported in Ref. 1. The link
between samples’ morphology and oxidation behavior was estab-
lished and quantified through the parabolic rate constant of oxida-
tion kinetics, kp ͑mg2 cm−4 s−1͒, determined by plotting the mass
gain vs square root of time.20 It is recalled that sample AlT1 yields
no reduction of the kp compared with the bare alloy. Also, in the
same test conditions samples AlD2 and AlPt2 showed an improve-
ment of the oxidation protection, resulting in a kp ten times lower
than that of the bare alloy. This improvement can be attributed to the
compactness of these films and their smoother surface morphology
with regard to films processed in conditions AlT1.
Conclusion
The deposition of several micrometers thick Al by MOCVD us-
ing TIBA and DMEAA on titanium alloy Ti6242 leads to films with
a continuous base, no C contamination and no preferred orientation.
The surface of such films is composed of Al crystals, smaller for
DMEAA-processed films. When deposited on Pt sublayer in similar
conditions, the deposits are mainly composed of very thin whiskers.
By adding a C2H5I stream in the dilution gas, the obtained micro-
structure is whisker-free, continuous, with no texture. No C con-
tamination could be detected, and I concentration remains at the
EDS detection threshold. Simultaneous deposition of Pt and Al leads
to Al coatings containing Pt–Al phases. A lower growth rate than
those of single elements and an Al/Pt ratio in the films higher than
the input gas phase are characteristics of the specific growth mecha-
nism taking place during codeposition. Those interferences between
decomposition mechanisms and coatings characteristics can be ex-
plained by competitive adsorption at the growing surface and the
difference between the Al and Pt catalytic behaviors. The direct
Downloaded on 2015-05-03 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

D542
Journal of The Electrochemical Society, 154 ͑10͒ D538-D542 ͑2007͒
4. R. Jonnalagadda, D. Yang, B. R. Rogers, J. T. Hillman, R. F. Foster, and T. S. Cale,
J. Mater. Res., 14, 1982 ͑1999͒.
5. K. Sugai, H. Okabayashi, S. Kishida, and T. Shinzawa, Thin Solid Films, 280, 142
͑1996͒.
relations between the microstructure of the deposited coatings and
the properties of use, namely protection against oxidation, have been
illustrated.
6. W. L. Gladfelter and E. C. Phillips, U.S. Pat. ͑1991͒.
7. Z. Xue, H. Tridandam, H. D. Kaesz, and R. F. Hicks, Chem. Mater., 4, 162 ͑1992͒.
8. E. S. Hwang and J. Lee, Electrochem. Solid-State Lett., 3, 138 ͑2000͒.
9. B. E. Bent, R. G. Nuzzo, and L. H. Dubois, J. Am. Chem. Soc., 111, 1634 ͑1989͒.
10. B. E. Bent, R. G. Nuzzo, B. R. Zegarski, and L. H. Dubois, J. Am. Chem. Soc.,
113, 1137 ͑1991͒.
11. C. Vahlas, P. Ortiz, D. Oquab, and I. W. Hall, J. Electrochem. Soc., 148, C583
͑2001͒.
12. E. G. Colgan, J. Appl. Phys., 62, 1224 ͑1987͒.
13. P. Gas, J. Labar, G. Clugnet, A. Kovacs, C. Bergman, and P. Barma, J. Appl. Phys.,
90, 3899 ͑2001͒.
14. T. W. Jang, H. S. Rhee, and B. T. Ahn, Mater. Res. Soc. Symp. Proc., 514, 351
͑1998͒.
15. H. Matsuhashi, C.-H. Lee, T. Nishimura, K. Masu, and K. Tsubouchi, Mater. Sci.
Semicond. Process., 2, 303 ͑1999͒.
16. Y. Neo, M. Niwano, H. Mimura, and K. Yokoo, Appl. Surf. Sci., 142, 443 ͑1999͒.
17. T. Nakajima, M. Nakatomi, and K. Yamashita, Mol. Phys., 101, 267 ͑2003͒.
18. B. V. Zhuk and V. K. Khamylov, Dokl. Akad. Nauk, 233, 862 ͑1977͒.
19. N. R. Avery, Surf. Sci., 146, 363 ͑1984͒.
Acknowledgments
The authors are indebted to Yolande Kihn, CEMES, for TEM
observations. This work is part of the APROSUTIS project sup-
ported by the Réseau National Matériaux et Procédés ͑RNMP͒ net-
work ͑Ministère de la Recherche, opération 02 K0298͒. It was per-
formed through a grant to M.D. from the French Ministry of
Education.
Centre National de la Recherche Scientifique assisted in meeting the
publication costs of this article.
References
1. M. Delmas, D. Poquillon, C. Vahlas, and Y. Kihn, Surf. Coat. Technol., 200, 1413
͑2005͒.
2. M. Delmas, M. Ucar, L. Ressier, M. Pons, and C. Vahlas, Surf. Coat. Technol.,
188–189, 49 ͑2004͒.
3. T. Kodas, M. G. Simmonds, and W. L. Gladfelter, in The Chemistry of Metal CVD,
T. T. Kodas, M. Hampden-Smith, Editors, p. 45 VCH, ͑1994͒.
20. D. Monceau and B. Pieraggi, Oxid. Met., 50, 477 ͑1998͒.
Downloaded on 2015-05-03 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).