Diamond and Related Materials 8 (1999) 428–434

Diamond-like carbon: state of the art

Alfred Grill *
IBM Research Division, T.J. Watson Research Division, Yorktown Heights, New York 10598, USA

Received 18 July 1998; accepted 18 September 1998

Abstract

Diamond-like carbon films, amorphous hydrogenated or non-hydrogenated forms of carbon, are metastable amorphous
materials characterized by attractive mechanical, optical, electrical, chemical and tribological properties. The films can be prepared
at low temperatures by different techniques using a large variety of precursors and can be modified by incorporation of different
elements such as N, F, Si or metals. The diversity of methods used for the deposition of diamond-like carbon films provides the
flexibility to tailor their properties according to specific needs and potential applications. The hydrogenated form of DLC appears
to reach a maturity in understanding its properties and finding old and new practical applications for it. The non-hydrogenated
diamond-like carbon, or tetrahedral carbon, is at a much younger state of preparation and characterization and practical
applications have yet to be proven. The paper will review the state of the art of the preparation of the different types of diamond-
like carbon films, the characterization and understanding of their properties, and their practical applications. © 1999 Elsevier
Science S.A. All rights reserved.

Keywords: Applications; Deposition; Diamond-like carbon; Properties

1. Introduction illustrated by the recent announcement by the Gillete

corporation of their new razor blades incorporating
Diamond-like carbon is a name attributed to a variety DLC coatings. ‘‘MACH3’s patented DLC@ comfort
of amorphous carbon materials, some containing up to edges — the first major blade edge innovation in 30
about 50 at.% hydrogen (a-C:H ), other containing less years — are thinner than any other Gillette blade edges
then 1% hydrogen (a-C ). The diamond-like carbon films and glide through beard hairs more easily. With
contain significant fractions of sp3 type C bonds, giving MACH3, the consumer experiences less drag and pull
them attractive physical and mechanical properties that for an extraordinarily comfortable shave’’ [2]. taC is at
are, to a certain extent, similar to diamond. The a-C:H a much younger stage of its development and under-
films typically contain sp3 fractions smaller than 50%, standing and practical applications have yet to be devel-
while the a-C films can contain 85% or more sp3 bonds. oped for it.
The ‘‘DLC’’ term is commonly used to designate the A general review of DLC can be found in Ref. [3]
hydrogenated form of diamond-like carbon (a-C:H ), and a recent review of its tribological properties in
while the ‘‘taC’’ (tetrahedral carbon) term is used to Ref. [4]. The present paper will present the state of the
designate the non-hydrogenated carbon (a-C ), contain- art of hydrogenated DLC and some comparisons with
ing high fractions of sp3 hybridized carbon. the non-hydrogenated taC.
Both DLC and taC are metastable materials and have
to be prepared under ion bombardment of the growing
films. Studies of DLC have been performed extensively
since 1971, when Aisenberg and Chabot [1] first pre- 2. Deposition
pared such films, and the field has reached maturity in
understanding the growth mechanisms, material proper- 2.1. DLC and taC
ties and usage in industrial applications. This is best
In order to obtain the metastable structure of DLC,
* Tel: +1 914 945 1492; fax: +1 914 945 2141; such films are deposited by plasma assisted chemical
e-mail: grilla@us.ibm.com vapor deposition (PECVD) or physical vapor deposition

0925-9635/99/$ – see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0 9 2 5- 9 6 3 5 ( 9 8 ) 0 0 26 2 - 3
 A. Grill / Diamond and Related Materials 8 (1999) 428–434 429

techniques (sputtering or ion beams) using a variety of films appears to reach a maximum at impinging particle
precursors, as described in detail elsewhere [3]. In the energy of about 100 eV [9].
PECVD methods, the substrates have to be at a negative
bias relative to the plasma to achieve ion bombardment 2.2. Modified DLC and taC
of the growing film. The deposition is performed in
hydrogen-containing environments to obtain DLC films Various materials derived from the diamond-like
containing 10–50 at.% hydrogen. The hydrogen is carbon films have been developed to change and improve
required for obtaining ‘‘diamond-like’’ properties in their properties. Such materials are similar in structure
these materials. It determines the film structure, passi- to DLC or taC but, in addition to carbon and/or
vates the dangling bonds in the amorphous structures, hydrogen, include nitrogen (NDLC or CN films), sili-
x
thus controlling the optical and electrical properties, con (SiDLC ), silicon and oxygen, fluorine ( FDLC ),
and affects the internal stresses of the films. In most and metal atoms (MeDLC ). Most modifications have
cases the deposition is a line-of-sight technique and the been made to DLC to reduce its, typically high, internal
film is deposited on only one surface of the substrate. compressive stresses (N, Si, metal incorporation), to
Industrial tools based on this technique have been reduce its surface energy [14] for further lowering, its
developed and are used in manufacturing. Deposition already low, friction coefficients (F, Si–O incorporation)
of DLC films by a high density plasma in a helical [3,4,15], or to modify its electrical properties [16,17].
resonator PECVD process has also been reported [5]. Nitrogen incorporation has been used to improve field
The growth and properties of DLC films are controlled emission properties of both DLC and taC [18,19]. Si
by the substrate temperature and bias, the latter having incorporation in DLC has been found useful in reducing
the dominant control [3]. The hardness, density and the etching rate of DLC in oxygen plasma and makes
refractive index of the films increase with increasing it useful as an etch stop for undoped DLC [16 ]. The
substrate bias. The deposition rates also usually increase modified diamond-like carbon films are deposited by
with increasing bias. Even for films deposited in a helical the same techniques as the regular films by adding
resonator, the substrates had to be biased negatively to species containing the modifying elements to the depos-
obtain diamond-like properties. Films deposited in this ition environment and details can be found in the
reactor on grounded substrates had polymeric character- references cited above.
istics [5].
A more recent technique for deposition of DLC films
is the plasma source ion implantation (PSII ) [6 ]. In this 3. Properties
technique, the substrates are placed directly in a plasma
source and then pulse-biased. This is a non-line-of-sight 3.1. Structure
technique and enables the coating of complex structures.
Another non-line-of-sight technique for deposition of Diamond-like carbon films are amorphous materials
DLC has been demonstrated in an ionitriding tool in with carbon atoms bonded in mainly sp3 and sp2 hybrid-
which DLC has been deposited by bipolar-pulsed DC izations. Diamond-like carbon is a low-mobility semi-
PECVD [7]. The films have been found to have proper- conductor, with a bandgap of 1–4 eV, room temperature
ties similar to RF PECVD-deposited films, with the photoluminiscence and low electron affinity [20]. The
advantage of being deposited in an existing industrial properties of the films are determined by the relative
reactor. ratio of the two hybridizations. DLC films can have
The superhard properties of taC films are achieved sp3 fractions up to about 40% [21], while taC can reach
by the high energies of the impinging particles that form sp2 fractions of up to 87% when deposited at ion energies
the films. It is assumed that in this case the films grow of about 100 eV [9,22]. Angus and Jahnsen [23] have
by subplantation, instead of by the conventional conden- described the structure of hydrogenated DLC by a
sation, as in the case of DLC films [8]. The required random covalent, fully constrained, network model.
high energies of the depositing species are achieved by According to this model, the DLC structure can be
different variations of vacuum or cathodic arc dis- described as a three-dimensional array of mostly six-
charges, such as filtered arc [9], pulsed arc [10], laser membered rings, which is able to contain 17–61 at.%
controlled arc [8,10], pulsed laser depositions [8,11] or bound hydrogen. The role of hydrogen in controlling
mass selected ion beams [12]. Vacuum arc discharges the properties of DLC has been discussed in detail
can cause local overheating of the cathode and micro- elsewhere [3,24].
spaling, resulting in deposition of rough films. Such Robertson [25] modeled the structure of diamond-
problems can be overcome by the mentioned modifica- like carbon in 1986 as a random network of covalently
tions of the techniques to deposit smooth and very hard bonded carbon atoms in the different hybridizations,
taC films. The PSII technique can also be used for the with a substantial degree of medium range order on the
deposition of taC films [13]. The sp3 fraction in the taC 1 nm scale. In a recent refinement of his model,
430 A. Grill / Diamond and Related Materials 8 (1999) 428–434

Roberston describes the structure of both DLC and taC internal stresses. These properties are directly correlated
as being controlled by the energy of the p bonding of to the fraction of sp3 C in the films. The hardness of
the sp2 sites [20]. According to Robertson, the p bonding DLC films is in the range 10–30 GPa [28], with a
of the sp2 carbon favors clustering of sp2 sites to corresponding Young’s modulus 6–10 times larger. The
maximize the p-bonding energy. The sp2 sites can gain films are characterized by internal compressive stresses
further energy by forming sixfold planar ‘‘aromatic’’ in the range 0.5–7 GPa. The stresses can be reduced by
rings and fusing the rings into larger graphitic clusters. incorporating N, Si, O or metals in the films [13,24],
However, the energy gain resulting from increasing although the reduction in stresses is often associated
cluster size beyond pairing is small, therefore, the cluster with a reduction in hardness and elastic modulus of
size remains small. For planar graphitic clusters of sp2 the films.
carbon, the band gap was found to be given by The hardness of taC films can reach higher values (in
E =6/M1/2 eV, where M is the number of sixfold rings the range of 40–80 GPa) [8,22], and their Young’s
g
in the cluster [25]. According to Robertson, the small modulus can reach values up to 900 GPa [10], but the
sp2 clusters cannot explain the small bandgap of DLC stress can also reach high values up to 13 GPa [22]. The
and the small bandgap is caused by the fact that the high internal stresses limit the thickness of films that
distorted clusters have much smaller bandgaps [20]. The
can be used for any application, often to less than 1 mm
bandgap is therefore controlled by the distortion of the
thick. The stresses in taC have been reduced by incorpo-
clusters and not their size. Robertson also found that
ration of metals [13] or by building multilayered struc-
the optical gap of all types of diamond-like carbon,
tures comprising soft and hard films using a filtered
hydrogenated or non-hydrogenated, depends mainly on
the sp2 fraction in the films and decreases with increas- vacuum arc and varying the ion energy during composi-
ing sp2 fraction. Non-hydrogenated taC, which has tion [29,30]. The bias of the substrate was changed
small sp2 fractions, has a very rigid network, while between −100 eV (to obtain the hardest layers with an
hydrogenated DLC has a softer polymeric network, yet sp3 fraction of 85% and hardness of 60 GPa) and −2 kV
both types of films have similar bandgaps. (to deposit soft films with an sp3 fraction of 39%) [30].
The multilayered structures had hardness (40–23 GPa)
3.2. Characterization and modulus (350–245 GPa), corresponding to the frac-
tion of the hard and soft layers, and the stresses in the
The structural characterization of diamond-like films were reduced in the multilayered films from
carbon films is complicated by their amorphous nature. 10.5 GPa, for the hard film, to 3.8 GPa, for the film
High resolution nuclear magnetic resolution (NMR) containing a 90% soft fraction.
spectroscopy with its recent refinements [21] appears to
be the best technique for characterization of the carbon 3.4. Material stability
hybridization of hydrogenated DLC. Fourier transform
infrared spectroscopy ( FTIR) is still being used by some Both the hydrogenated and non-hydrogenated DLC
authors to quantify the carbon hybridization ratios and are metastable materials and their structures will change
hydrogen content in DLC films, in spite of the fact that towards graphite-like carbon by either thermal activa-
it has been shown that the technique can give erroneous tion or irradiation with energetic photons or particles.
information [26 ]. Electron energy loss spectroscopy Heating of hydrogenated DLC films results in the loss
( EELS ) has become the established method to measure of hydrogen and CH species, starting at about 400 °C,
the sp2 bonding fraction in non-hydrogenated taC [20]. x
or even lower, depending on the deposition conditions
The technique is, however, not suitable for DLC, which and the dopant contained in the films [3,16,17]. This
is sensitive to irradiation with an electron beam [27]. causes changes in the dimensions and properties of the
FTIR can be used for qualitative characterization of
material and limits the use of DLC in applications
different bonds in hydrogenated diamond-like carbon
involving temperatures above 400 °C. The temperature
films or their modifications. Film compositions can be
at which changes take place in the DLC films appears
determined by Rutherford backscattering ( RBS) analy-
to be correlated to the power used for the preparation
sis of C and heavier elements and forward recoil elastic
scattering ( FRES) for H concentrations. Mechanical of the films [16 ]. The thermal instability of DLC films
properties are usually determined by nanoindentation is generally associated with the loss of hydrogen, result-
measurements for hardness and Young’s modulus deter- ing in a collapse of the structure into a mostly
mination and measurements of radius of curvature of sp2-bonded network.
coated substrates for stress determination [3,22]. It has been reported that thermal activation can also
induce changes in taC films and cause the conversion of
3.3. Mechanical properties some sp3 carbon bonds to sp2 bonds [31]. The onset of
relaxation started at temperatures as low as 100 °C and
Diamond-like carbon films are characterized by high near full relaxation has been observed at 600 °C. An
hardness and a high elastic modulus, but also by high activation energy in the range of 1–3 eV has been
 A. Grill / Diamond and Related Materials 8 (1999) 428–434 431

reported for this thermal relaxation [31]. The thermal DLC may have a lower stability then taC because of
relaxation reduced the internal stresses of the taC films the hydrogen content [18].
and increased their electrical conductivity. However, it DLC coatings have also been found to increase the
has been claimed at the present conference that taC emission current from metallic FED tips [36 ]. Nitrogen
films can be stable at least up to temperatures of 600 °C. incorporation in DLC coatings can enhance this effect.
The diamond-like carbon films can also be changed Thus, a 20 nm PECVD-deposited NDLC coating was
by UV [32] or ion beam irradiation [33]. Irradiation of found to enhance the emission current from Spindt type
DLC in air with UV irradiation from a high pressure Mo tips of a FED from 160 to 1520 mA [19]. The
mercury lamp was found to break C–C and C–H bonds surface roughness of the films can strongly affect the
and cause oxidation of the film with formation of C–O field emission effects of DLC, as was observed for DLC
bonds [32]. CO , CH and H evolved from the film films deposited by laser ablation [11].
2 4 2
during the irradiation, resulting in a reduction of film In spite of said above, it now appears that the field
thickness. UV irradiation of NDLC films containing emission from diamond-like carbon, or other forms of
about 11 at.% nitrogen resulted in a decrease in C–H carbon films, is not related to electron affinity of the
bonding and an increase in C–C, CNN and CON materials, but is controlled instead by the nano-level
bonds. The sp2 cluster size in the films became smaller, roughness of the films.
therefore, the optical gap increased. NDLC films with
high N content (~37 at.%) did not show any FTIR
changes after UV irradiation [32]. However, their optical 3.6. Tribology
gap increased, indicating a reduction of the cluster size
in the absence of material loss. The widest use of diamond-like carbon films is mainly
Room temperature irradiation of taC films with an of the hydrogenated DLC in applications exploiting the
ion beam of 200 keV Xe+ transformed the material into low friction coefficients and high wear-resistance of these
a conducting amorphous carbon with an sp2 fraction of materials. It is therefore natural that a lot of efforts
0.6. At higher temperatures, the same irradiation have been invested in the characterization of the tribo-
increased the sp2 fraction to about 0.8 and increases the logical properties of DLC. A recent review of the
degree of ordering towards a graphitic material [33]. tribological properties of DLC films and their modified
forms [4] shows that, in all environments, the tribologi-
cal behavior of DLC is controlled by an interfacial
3.5. Field emission transfer layer formed during friction. The transfer layer
is formed by a friction-induced transformation of the
In the quest for finding new applications for diamond- top layer of the DLC film into a material of low shear
like carbon, a significant effort has been directed in the strength. This transformation may be caused by friction-
last few years to the investigation of the field emission induced annealing, caused by thermal and strain effects
properties of DLC or taC. Flat panel field emission generated during sliding [37]. The shear strength of the
displays (FED) use sharp Mo or Si tips for emission of transfer layer and its adhesion to sliding surfaces can
electrons for the excitation of phosphor screen pixels. be affected by the environment and by contact load and
The sharp tips are needed to obtain the high electric sliding speed. The composition of the transfer layer can
field required to extract the electrons from these materi- also be affected by the material of the sliding counter-
als which are characterized by a high work function of part. The low friction and ultra low wear of DLC and
about 5 eV. The hydrogenated surface of diamond has counterparts can be explained by the low shear strength
a negative electron affinity, therefore diamond or dia- of the transfer layer [4], which can also be affected by
mond-like carbon films have the potential to serve as the testing environment [38].
electron emitters for FEDs, without needing the 1 mm A compilation of friction coefficients of DLC films
lithography for the preparation of sharp tips [34]. It [39] shows that the friction coefficients of DLC span a
was found that the threshold field for electron emission range of m=0.007–0.4, in vacuum below 10−4 Pa, while
in the taC films reaches a minimum of about in ambient air at relative humidities of 20%<RH<60%,
10 V mm−1 when the films contain a high fraction of they span a range of m=0.05–1.00. The large spread in
about 80% of sp3 bonds [18]. The addition of N to taC the values of the friction coefficient are caused by
further reduced the threshold field, with the maximum variations in the structure and composition of the films.
reduction of ~5 V mm−1 being obtained in taC contain- The transfer layer described above has a lubricating
ing 1 at.% nitrogen. A further increase in the nitrogen effect and its formation can be enhanced by hydrogen,
content reduced the sp3 fraction in the films, reduced but may be restricted in the presence of water or oxygen.
the bandgap and increased the threshold voltage [18]. Water and oxygen were found to have different effects
Similar behavior has been observed in N-modified on the friction of DLC at low concentrations [40]. It
hydrogenated DLC [35], however, it is assumed that was also found that the hydrogen content of DLC has
432 A. Grill / Diamond and Related Materials 8 (1999) 428–434

to be above a threshold of about 40 at.% to obtain very 10−7 mm3 N−1 m−1, however the wear rate had a mini-
low friction coefficients in ultra high vacuums [41,42]. mum of about 3×10−8 mm3 N−1 m−1 for a multilayer
Metal-containing DLC films have been found to modulated film containing 50% soft phase [29].
reduce friction and wear, not only in sliding, but also
in vibrating contacts for a broad range of testing condi- 3.7. DLC materials as low-k dielectrics
tions [43]. Fluorinated DLC with high F and low H
content having wear resistance similar to pure DLC has Special interest has recently been addressed to the
been demonstrated [15]. Because of the thermal instabil- dielectric constant (k) of DLC and FDLC films
ity of DLC films, their wear behavior is temperature [17,46,47]. Low-k materials are needed for the back
sensitive and that sensitivity will be affected by the end of the line (BEOL) interconnect structures of ULSI
deposition conditions of the studied films. For some ( Ultra Large Scale Integrated) circuits to improve their
films, the wear behavior in ambient air has been found performance. It was found that, by adjusting the depos-
to change with temperature in the range 100–300 °C, ition conditions, it is possible to obtain DLC films with
with both the friction coefficient and wear resistance the dielectric constant in the range 2.7–3.8 and FDLC
decreasing with increasing temperature [44]. films with dielectric constants k<2.8 (as compared with
Tribo-emission of electrons, negative and positive ions k=4.0 for the presently used SiO dielectric). Integration
2
and photons were observed during tribological tests in of such films in the BEOL structures, however, imposes
ambient air, with diamond sliding over DLC, deposited further requirements on the low-k material, such as low
by DC magnetron sputtering and containing 0–43 at.% stresses and thermal stability at 400 °C. It was found
hydrogen [45]. Photon emissions were observed only in that, for the as-deposited DLC films, the intrinsic stresses
films containing >15% hydrogen, while particle emis- decrease, but so also does the thermal stability, with
sions were detected also in films containing lower con- decreasing k values [16 ].
centrations of hydrogen. The tribo-emission was FDLC films with dielectric constants k<2.8 have
explained by the formation of micro-plasma by dark been prepared having intrinsic stresses below 200 MPa.
discharge, at low hydrogen content, and spark dis- Both DLC and FDLC films could be stabilized by
charges, at higher hydrogen concentrations. Tribo- annealing in an inert ambiance [17,48] and a first
charging to local potentials up to several hundred volts metallization level in a Cu-based damascene process
were observed. The friction coefficients of these films with DLC as the dielectric has been demonstrated [48].
had very high values (0.6–0.8) in air [45]. Such films become attractive candidates as low-k dielec-
In contrast to DLC, very few results were published trics for the BEOL interconnect structure, however
for the tribological properties of the non-hydrogenated further integration issues have yet to be addressed
taC. Friction coefficients at RH=50% of taC films and solved.
deposited by a filtered cathodic vacuum arc have been
reported to correlate to the sp3 fraction in the films,
reaching values down to 0.08 [22]. The wear rates of
multilayered taC films described earlier were measured
at RH=30% [29]. The authors found that both soft
and hard monolithic films had wear rates of about

Fig. 1. Phase diagram of diamond-like carbon materials (from Fig. 2. Delimitation of properties of diamond-like carbon (after
Ref. [20]). Ref. [60]).
 A. Grill / Diamond and Related Materials 8 (1999) 428–434 433

Table 1
Summary of properties and applications of diamond-like carbon films. Text in parentheses indicates potential applications

Property Type of use Applications

Transparency in Vis and IR; Optical coatings Antireflective and wear-resistant coatings for IR optics
optical bandgap=1.0–4.0 eV
Chemical inertness to acids, Chemically passivating coatings Corrosion protection of magnetic media, biomedical
alkalis and organic solvents
High hardness; H=5–80 Gpa: Tribological, wear-resistant coatings Magnetic hard drives, magnetic tapes,
low friction coefficient=<0.01–0.7 razor blades (bearings, gears)
Nanosmooth Very thin coatings <5 nm Magnetic media
Wide range of electrical resistivities Insulating coatings Insulating films
=102−1016 V cm−1
Low dielectric constants <4 Low-k dielectrics (Interconnect dielectrics)
Field emission (Field emission flat panel displays)

4. Applications biological environments. Due to their chemical inertness

and being impermeable to liquids, DLC coatings could
The unique properties of diamond-like carbon films protect biological implants against corrosion and serve
and their modifications, together with the possibility to as diffusion barriers. DLC films are considered for use
adjust the properties by choosing the right deposition as coatings of metallic as well as polymeric, such as
parameters, make them suitable for a variety of applica- polyurethane, polycarbonate and polyethylene, biocom-
tions. The exploited properties include the high wear ponents, to improve their compatibility with body tissues
resistance and low friction coefficients, chemical inert- [55,56 ]. Diamond-like carbon, deposited on stainless
ness, infrared transparency, high electrical resistivity steel and titanium alloys used for components of artifi-
and, potentially, the field emission properties and the cial heart valves, has been found to satisfy both mechan-
low dielectric constants. While taC has properties that ical and biological requirements and be capable of
are similar, some of them even superior, to DLC, only improving the performance of these components [57].
DLC appears to have found practical applications so The same properties may make DLC useful as a protec-
far. Due to its IR transparency, DLC can be used as a tive coating for joint implants. Improvement of
antireflective and scratch-resistant wear-protective coat- carbon/carbon composite prostheties by DLC coatings
ing for IR optics (at a wavelength of 8–13 mm) made of has also been demonstrated [58]. Presently, DLC and
Ge, ZnS, ZnSe [49,50]. The low deposition temperatures its modifications are being considered as low dielectric
of DLC allows its use as a wear-protective layer on materials for the interconnecting structures of ULSI. A
products made of plastic and is therefore used for better understanding of the means to control their
protection against abrasion of sunglass lenses made of thermal stability and other integration problems will
polycarbonate [51]. potentially expand their use in the ULSI chips.
The most widespread use of DLC films is in wear and The non-hydrogenated taC films have yet to find
corrosion protection of magnetic storage media. widespread applications. The most promising appears
Nanosmooth and very thin (<50 nm, even <10 nm) to be its use as cathodes in field emission-based flat
DLC films are used as corrosion and wear-protective panel displays or as pixel elements in large outdoor
coatings for both the magnetic disks and the magnetic displays [59].
heads. Tapes for video recording or magnetic data
storage, using ferromagnetic metal as a recording media,
as well as the metallic capstans in contact with the tapes, 5. Summary
are also being protected with DLC coatings to reduce
wear and friction, thus extending the life of the tapes The state of the art of diamond-like carbon may be
and their reliability [52]. The announcements of the best summarized by the next two figures and one table.
latest MACH3 razor blades by Gillete underscore the Fig. 1 (from Robertson [20]), describes the structure-
use of DLC as a coating, improving the quality and composition of diamond-like carbon in a ternary phase
performance of the blades [2]. DLC seems to find its diagram of sp2, sp3 and H concentrations. The specific
uses in tribological coatings for metal bearings, gears position of a diamond-like material on this diagram is
and seals [53]. Its potential use for phase shift masks determined by the deposition system, i.e. precursor,
for deep ultraviolet DUV lithography has been demon- method and parameters of the method. The energy of
strated [54]. the particles bombarding the growing film appears to
Diamond-like carbon appears to be biocompatible be the most important parameter determining the posi-
and applications are being developed for its use in tion of the film on the ternary diagram.
434 A. Grill / Diamond and Related Materials 8 (1999) 428–434

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