Studies of molybdenum surface modification for growth of adherent CVD diamond film
ABSTRACT Surfaces with very poor mechanical and frictional properties can be improved, or even, acquire new properties similar to diamond if good adherent CVD diamond film is obtained on it. In this work, nitrogen ions were sub-implanted on pure molybdenum as a means to enhance CVD diamond film adherence. Deposition time from 2 up to 60 h were used for deposition of 10 to 400 mm thick CVD diamond films with very good adherence on sub-implanted molybdenum substrate. Characterizations were carried out by XPS, X-ray diffraction and nano indentation on prepared surfaces prior to diamond growth and after the onset nucleation. The ionic sub-implantation with nitrogen possibly assists in adhesion, with the creation of a thin layer of nitrates and complexes.
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ABSTRACT: The substrate preparation for CVD diamond growth is of basic importance due to several reasons. A new molybdenum substrate preparation method, the aluminum oxide abrasion jetting, is introduced and compared with the traditional ones. Raman Scattering Spectroscopy (RSS) and Scanning Electron Microscopy (SEM) characterize CVD diamond films. CVD diamond films of good quality and uniformity were obtained. The substrate preparation by aluminum oxide blasting allowed for a higher nucleation rate.
Vol. 6, No. 2, 2003
Materials Research, Vol. 6, No. 2, 305-309, 2003.
Studies of Molybdenum Surface Modification for Growth of Adherent CVD Diamond Film305
Studies of Molybdenum Surface Modification for
Growth of Adherent CVD Diamond Film
Vladimir Jesus Trava-Airoldia*, Evaldo José Corata, Lúcia Vieira Santosa,b,
João Roberto Moroc, Nélia Ferreira Leitea
aInstituto Nacional de Pesquisas Espaciais, INPE, São José dos Campos - SP, Brazil
bInstituto Tecnológico de Aeronáutica, ITA/CTA, São José dos Campos - SP, Brazil
cUniversidade São Francisco, USF, Itatiba - SP, Brazil
Received: January 02, 2002; Revised: September 30, 2002
Surfaces with very poor mechanical and frictional properties can be improved, or even, ac-
quire new properties similar to diamond if good adherent CVD diamond film is obtained on it. In
this work, nitrogen ions were sub-implanted on pure molybdenum as a means to enhance CVD
diamond film adherence. Deposition time from 2 up to 60 h were used for deposition of 10 to
400 µm thick CVD diamond films with very good adherence on sub-implanted molybdenum
substrate. Characterizations were carried out by XPS, X-ray diffraction and nano indentation on
prepared surfaces prior to diamond growth and after the onset nucleation. The ionic sub-implanta-
tion with nitrogen possibly assists in adhesion, with the creation of a thin layer of nitrates and
Keywords: CVD Diamond, surface modification, ion sub-implantation, thin film
fect of intrinsic and extrinsic stresses involving diamond
and DLC films on different kinds of substrate materials6,7.
More specifically, adherence between CVD diamond film
and metallic substrate represent, for many research groups,
the challenge to overcome. The main problems are related
to difference in thermal expansion coefficient and adher-
ence between the substrate and the diamond film. Using
different kind of surface preparation and intermediate in-
terface, good adherence between CVD diamond and
WC-Co, Si3N4, SiC, and others1,8,9 have been obtained with
relatively success in order to improve the lifetime of differ-
ent kind of tools. Stainless steel and tool steel have been
tried as a permanent substrate for CVD diamond growth,
where, at the first time, the sub-implantation was mentioned9
as a surface preparation technique. Nitride films are known
as a diffusion barriers in microelectronics devices and as
well as superconductors10. Synthesis and analysis of mo-
lybdenum nitrites formed during ion implantation were in-
vestigated by some authors in order to improve molybde-
num tribologycal properties and to understand the complexes
The interest in diamond coating technology specifically
on pre-shaped parts and synthesis of freestanding shapes of
diamond has increased worldwide especially because of vast
and exotic applications1-5. CVD diamond is far beyond the
traditional technology, and it has been deposited on a vari-
ety of substrates, including metals, refractory metals, semi-
conductors and ceramics. Applications are widespread on
several areas, and new applications are continuously pro-
posed, even for the applications categorized as advantageous
substitution of traditional products. The novelty products
are the ones only possible due to the advent of CVD dia-
mond technology. CVD diamond coated cutting tools, heat
sinks, abrading devices, special optical coatings, substrates
for multichip modules technology (MCM), electron field
emitters and electrodes for electrochemical uses, is only a
small list of interesting area of exploration. In the develop-
ment of these application areas, there is much interest in
understanding the mechanism and the role of the interface
between the film and substrate concerning the adhesion proc-
ess and, a lot of effort has been spent to understand the ef-
306Vladimir et al.Materials Research
In this work, concerning carbon diffusion during growth,
the improvement of the adherence of the diamond film on
molybdenum has been studied as a function of the surface
modification by nitrogen ion implantation and deposition
time in order to get thick diamond films. The adherence
between them depends on how properly the interface is pre-
pared. In this case very thin interface between diamond and
metal was studied in order to avoid carbon diffusion onto
the bulk of the substrate at diamond growth conditions, and
also, for improving the chemical bond between the film and
Molybdenum rods of 1.6 mm diameter and 20 mm long
were polished using diamond powder of 0.25 µm grit and
slurred in n-hexane ultrasonic bath (1 g/20 ml) during 60 min
and annealed in H2 prior to DC discharge nitrogen ion sub-
The experimental apparatus for nitrogen sub-implanta-
tion consists of a conventional DC discharge with special
geometry of the electrodes. A conventional hot filament re-
actor with convenient substrate holder, as it is shown in
Fig. 1, was used for diamond film growth.
Nitrogen and hydrogen mixtures were used in the DC
discharge to produce a thin-nitrated layer by ion sub-im-
plantation. The best set of parameters was found according
to the best adherence after diamond deposition. Diamond
deposition was carried out with conventional mixtures of
2% vol.% of CH4 in H2. The total gas flow rate was fixed at
100 sccm and the pressure inside the reactor was maintained
at 50 torr. The 850 °C substrate temperature was measured
by a thermocouple, and from 2 up to 60 h deposition time
was used for deposition of 10 to 400 µm thick CVD dia-
mond films, without delaminating.
Small angle X-ray Diffraction was performed in the
nitrated molybdenum and nitrated molybdenum after 10 min
of diamond nucleation. The XPS analysis was made on the
molybdenum surface for all sets of samples.
In order to get good nano-indentation tests, only the
10 µm thick films grown in pure and nitrated molybdenum
3. Results and Discussions
Experiments have shown that higher temperature helped
to improve the film adhesion, but it was not sufficient to
avoid the film peeling off from the substrate after growing.
An optimization of the sub-implantation parameters have
been made in order to keep the integrity of the molybde-
num structure during all sub-implantation process at tem-
peratures ranging from 500 to 600 °C and, to increase the
film adhesion. We found that good film quality and high
nucleation density are reached at temperatures as high as
850 °C, for films grown up to 400 µm thick during 60 h
nitrated molybdenum substrate. In this work the best con-
dition for nitrogen ion implantation was reached using ni-
trogen 20% vol. in hydrogen and at 600 V DC discharge.
Small angle X-ray Diffraction was performed in order
to understand surface modification and how the most
probable mechanism interferes on diamond adherence to
the molybdenum surface when nitrogen ion-sub-implanta-
tion occurs. The results of pure molybdenum, nitrated mo-
lybdenum and nitrated molybdenum after 10 min of dia-
mond nucleation are shown in Fig. 2. The apparent molyb-
denum nitride peaks give us the evidence of the surface
modification for the nitrated molybdenum. The spectrum
of a substrate after submitted to 10 min diamond nucleation
shows the evident mixture of the molybdenum nitrides and
carbides. However, the X-ray analysis is not sensitive to
other complexes formed during the sub-implantation.
Our first attempt to observe the existence of such com-
plexes was by using XPS analysis. Fig. 3a shows the analy-
sis from nitrated molybdenum surface prepared for diamond
growth. The binding energy around 227 and 232 eV are the
evidence of nitrides and oxides formation. In Fig. 3b the
peaks around 396 and 412 eV correspond to surface com-
pounds with nitrogen and oxygen, respectively. Again, one
Figure 1. Experimental diagrams: a) DC discharge; b) diamond
Vol. 6, No. 2, 2003Studies of Molybdenum Surface Modification for Growth of Adherent CVD Diamond Film 307
Figure 3. XPS analysis characterization for nitrated molybdenum: a) molybdenum nitrides and oxides; b) complexes with nitrogen and
Figure 2. Small angle X-ray Diffraction for: a) pure molybdenum (continuous line) and nitrated molybdenum (dashed line);
b) nitrated molybdenum surface after 10 min diamond onset nucleation.
Figure 4. XPS analysis characterization for nitrated molybdenum after 10 min diamond growth: a) shifted and asymmetric binding energy
peak for the carbon; b) shifted and asymmetric binding energy peaks for molybdenum complexes.
308Vladimir et al.Materials Research
can speculate that even complexes can be formed on mo-
lybdenum surface from ion bombardment and contrib-
ute to form a barrier against carbon diffusion during dia-
mond growth process. In order to see the influence of this
barrier, XPS analysis were carried out on substrate-cleaned
surface after 10 min diamond nucleation. It is observed again
the evidence of complex compounds now involving carbon
atoms, characterized by the shifted and asymmetric bind-
ing energy peaks centered at 393 and 411 eV, as shown in
Fig. 4a. In Fig. 4b the C1s peak, binding energy centered at
282 eV, depicts a strong asymmetry that corroborates the
idea of a complex compound formation.
Figure 5 shows the change of C and N% content on
nitrated molybdenum surface and C% content on nitrite
molybdenum bulk as a function of the growth time. We can
see that the N% content is almost independent of the growth
time, the C content increase on nitrite molybdenum surface
with the growth time but in the molybdenum bulk, the C%
content remains constant as long as for 20 h of growth, in-
dicating that the complex barrier help to avoid the diffu-
sion of the carbon to the bulk of the substrate.
It is observed from Fig. 6a, that the bulk hardness is
higher for samples with nitrated surface prior to diamond
growth conditions, and it decrease when submitted to 10 min
diamond growth conditions, but it is still high and keep the
same behavior. The hardness is higher in the surface and
decrease up to a depth of 150 nm. Substrates without nitro-
gen sub-implantation and submitted to 10 min diamond
growth condition has lower hardness and it doesn’t exhibit
hardness variation as function of the depth. Also, the stiff-
ness (Fig. 6b) has been analyzed for the same samples. Sam-
ples with nitrogen sub-implantation exhibit dependence with
the depth, while only a small variation of the stiffness was
observed for samples without nitrogen sub-implantation.
These results confirm that a barrier for carbon diffusion
could be formed when nitrogen sub-implantation is used,
indicating a surface modification.
Using this results, diamond thin and thick film have been
obtained on molybdenum submitted to nitrogen sub-implan-
tation with very good adherence even at growth tempera-
ture as low as 700 °C, and different kind of devices have
been developed. Examples of these devices are the diamond
burr used in very high rotation, as higher as 400.000 rpm,
and in high-energy ultrasound application. The lifetime of
these devices is over than 30 times larger than conventional
one. Figure 7 shows some examples of mentioned devices.
Figure 6. Nano Indentation showing a) surface hardness; b) stiffness of (?) 10 min diamond growth on molybdenum, (?) nitrated
molybdenum and (?) 10 min diamond growth on nitrite molybdenum as function of penetration depth.
Figure 5. Change of C and N content on nitrated molybdenum
surface and C content on nitrated molybdenum bulk as a function
of the growth time. (?) % atom on N on nitrated molybdenum
surface; (?) % atom C on nitrated molybdenum surface;
(?) % atom on C on nitrated molybdenum bulk.
Vol. 6, No. 2, 2003Studies of Molybdenum Surface Modification for Growth of Adherent CVD Diamond Film309
Ions sub-implantation on molybdenum has been pre-
sented as a good way to obtain good adherence with CVD
diamond. Nano indentation, small angle X-ray diffraction
and XPS analysis show an evidence of surface modifica-
tion by the formation of nitrogen and carbon complexes.
This surface modification was efficient in inhibiting carbon
diffusion during the diamond growth process keeping the
mechanical properties of the substrate. Also, these com-
plexes contribute to improve the adherence of diamond to
the modified molybdenum surface. Examples, as diamond
burr, of very adherent diamond thick film on modified mo-
lybdenum surface confirm the success of these studies.
The authors are very grateful to FAPESP and CNPq for
financial support, Nilson Cristino da Cruz and Elidiane
Cipriano Rangel for nano indentation analysis, and Eduardo
Abramof for X-ray analysis.
1. Busch, J.V.; Dismukes, J.P. “A comparative Assessment
of CVD Diamond Manufacturing Technology and Eco-
nomics” in Synthetic Diamond: Emerging CVD Science
and Technology, Edited by Spear, K.E.; Dismuskes, J.P.
John Wiley & Sons, Inc., N.Y., p. 581 1994.
2. Trava-Airoldi, V.J.; Corat, E.J.; Baranauskas, V. “Dia-
mond Chemical Vapor Deposition: Emerging Technol-
Figure 7. Examples of devices developed with molybdenum surface modification, a) Diamond burr used in very high rotation; b) used in
high-energy ultrasound equipment.
ogy for Tooling Applications, on Advanced Ceramics for
Cutting Toll Applications, Editor: Dr. Jim Low, Trans
Tech Publications-Switzerland, p. 195. 1997.
3. Trava-Airoldi, V.J.; Corat, E.J.; Ferreira, N.G.; Leite, N.F.
“CVD-Diamond: An Overview of Research and Devel-
opment at INPE”, Brazilian Journal of Phisics, v. 27A,
p. 88, 1997.
4. Trava-Airoldi, V.J.; Moro, J.R.; Corat, E.J.; Goulart,
E.C.; Silva, A.P.; Leite, N.F. “Cylindrical CVD Diamond
as a High Performance Small Abrading Device”, Sur-
face Coating and Technology, v. 108-109, p. 437-441,
5. Trava-Airoldi, V.J.; Corat, E.J.; Moro, J.R. “CVD-Dia-
mond Tools and its Uses, Deposited at INPI at the provi-
sory number, INPI0000/01.
6. Zhang, S.; Xie, H.; Zeng, X.; Hing, P. Surface and Coat-
ings Technology, v. 122, p. 219, 1999.
7. Nesladek, M.; Spinnewyn, J.; Asinari, C.; Lebout, R.;
Lorent, R. Diamond Relat. Mater., v. 3, p. 98, 1993.
8. Saijo, K.; Yagi, M.; Shibuki, K.; Takatsu, S. Surf. Coat.
Technol., v. 43/44, p. 30, 1990.
9. Borges, C.F.M.; Moisan, M.; Roy, F. Method for Produc-
ing a High Adhesion Thin Film of Diamond on a Fe-
Based Substrate, US Patent n. 5, v. 759, p. 623, 1998.
10. Saito, K.; Asada, Y.; J. Phys. F, v. 17, p. 2273, 1987.
11. Bredell, L.J.; Van Der Berg, N.G.; Surf. Coat. Technol.,
v. 104, p. 118, 1998.
12. Braun, M. Nuclear Instruments & Methods in Physics
Research B, v. 59, Part 2, p. 914, 1991.