Simultaneous formation of diamond-like carbon and carbon nitride films in the electrodeposition of an organic liquid

Article abstract of DOI:10.1016/S0009-2614(98)01426-2

Diamond-like carbon (DLC) and carbon nitride (CN_x) films have been simultaneously prepared on the cathode and the anode in the electrodeposition of an acetonitrile liquid at atmospheric pressure and temperatures below 80°C. The deposits were an

Full text of DOI:10.1016/S0009-2614(98)01426-2

1
9 February 1999
Chemical Physics Letters 301 Ž1999. 87–90
Simultaneous formation of diamond-like carbon and carbon
nitride films in the electrodeposition of an organic liquid
Qiang Fu, Jin-Ting Jiu, Hao Wang, Chuan-Bao Cao, He-Sun Zhu )
Research Center of Materials Science, Beijing Institute of Technology, PO Box 327, Beijing, 100081, China
Received 27 October 1998
Abstract
Diamond-like carbon ŽDLC. and carbon nitride ŽCN . films have been simultaneously prepared on the cathode and the
x
anode in the electrodeposition of an acetonitrile liquid at atmospheric pressure and temperatures below 808C. The deposits
were analyzed by X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. The deposits on the cathode
2
3
were amorphous DLC films consisting of sp and sp carbon, while the deposits on the anode were CN films in which the
x
NrC ratio was about 0.25. The mixed phases of a-C N and b-C N may exist in the CNx films. The related reaction
3
4
3
4
mechanism is also discussed in this Letter. q 1999 Elsevier Science B.V. All rights reserved.
1
. Introduction
deposition makes the equipment rather complicated
and the control of the experiments difficult. At the
same time, the comparatively high substrate tempera-
ture also limits the application of these materials.
Compared to the vapor deposition techniques, the
electrodeposition in the liquid phase can be per-
formed in an atmospheric environment and at room
temperature, bringing many advantages. Increasing
attention has been attracted to by liquid phase elec-
trodeposition research.
In recent years following the pioneering work of
Namba w7x, several attempts have been made in the
field of electrodepositing diamond and the related
materials in the liquid phase w8–10x. However, the
depositing liquid was mainly limited to alcohol or
alcohol–water systems, and carbon materials were
the only deposits. Therefore, the synthesis of dia-
mond and the related materials besides carbon mate-
rials from a new liquid system may have great
scientific and technological significance.
Because of the extraordinary physical and chemi-
cal properties of diamond and the realization of
depositing the material at low pressures, research
into diamond and diamond-like films has become an
area of intense interest in the field of condensed
matter physics since the 1980s. Recently, the first-
principle pseudopotential approach was used by Liu
and Cohen w1,2x to predict a hypothetical covalent
3
sp bonded compound b-C N , with characteristics
3
4
comparable to or better than those of diamond. Here-
after, an intense new interest in the synthesis of
b-C N has been stimulated. Many research groups
have tried to synthesize these materials using various
techniques and great progress has been made w3–6x.
3
4
However, these methods are all vapor deposition
techniques. The high vacuum required in the vapor
)
Corresponding author. Fax: q86 10 6891 5023
0
009-2614r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
PII: S0009-2614Ž98.01426-2

8
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Q. Fu et al.rChemical Physics Letters 301 (1999) 87–90
In our present work acetonitrile was chosen as the
the N content being less than 3%, and N may come
from the adsorption of acetonitrile; in contrast, the
anodic deposits B consisted of both C and N and the
NrC ratio was about 0.25. This indicates that the
carbon film was deposited on the cathode, while the
depositing liquid and DLC and CNx films were
prepared simultaneously on the cathode and the an-
ode using electrodeposition. X-ray photoelectron
spectroscopy ŽXPS., X-ray diffraction ŽXRD. and
Raman spectroscopy were applied to study the de-
posited films. The reaction mechanism is discussed
in detail.
CN film was deposited on the anode.
x
The deconvoluted C1s and N1s XPS spectra of
deposits A and deposits B are given in Fig. 1. The
C1s spectrum has a main peak at 284.5 eV, which
corresponds to the C–C bond w10x. Three additional
smaller peaks are also observed in this spectrum,
which are due to the C bonded to the oxygen and to
Si in the substrate ŽFig. 1A.. The N1s spectrum
consists of only one peak at 399.6 eV ŽFig. 1B.. This
value is identical to that of nitrile w11x, which sug-
2
. Experimental
The experimental setup comprised an electrolytic
cell system, which is similar to that reported in Ref.
w8x. The difference is that in this research the cathode
and anode are both used as substrates. Silicon Ž100.
gests that the N element in the film A come from the
absorbed acetonitrile. Due to the incorporation of
nitrogen, the C1s spectrum ŽFig. 1C. shows an in-
wafers with a resistivity of 20 V cm and a size of
3
1
0=20=0.3 mm were selected as substrates, as
well as the both electrodes. They were both mounted
on graphite plates and the distance between the two
electrodes was 7 mm. Before deposition, the sub-
strates were cleaned by ultrasonic treatment and
were then treated by a dilute HF solution. After
several random trials with acetonitrile, propionitrile
and acrylonitrile, analytically pure acetonitrile was
used as the depositing liquid.
crease in intensity of the high binding energy com-
ponents. The spectrum can be deconvoluted into
three lines peaked at 284.57, 286.50 and 288.11 eV.
We have assigned the peak at 284.57 eV to C–C
2
bonds, the peak at 286.50 eV to sp trigonal CN
3
bonding and the peak at 288.11 eV to sp tetrahedral
CN bonding w12x. The N1s spectrum ŽFig. 1D. has
two peaks located at 398.6 and 399.85 eV, which
A DC power source was used to supply the high
voltage applied to the substrates, which can be regu-
lated from 0 to 4000 V. The reaction current recorded
3
correspond to the N surrounded by sp -coordinated
2
C atoms and sp -coordinated C, respectively w12,13x.
Fig. 2A,B shows the Raman spectra for the car-
y2
was in the range of 0–50 mA cm and the reacting
bon film and the CN film. Spectrum A is composed
x
temperature was between 208C and 808C. In this
work, the samples were deposited at 508C and 1500
V.
y1
of an asymmetric broad band at 1575 cm ŽG band.
y1
with a shoulder peak at 1350 cm ŽD band., which
is a typical DLC characteristic spectrum and indi-
2
3
cates the existence of the sp C as well as the sp C
in the film w14,15x. Spectrum B also consists of two
3
. Results and discussion
y1
similar bands at 1595 and 1355 cm . The presence
2
After deposition for a certain length of time pale
of nitrogen makes the bond angles of the sp carbon
gray films Ždeposits A. and pale yellow or deep gray
films Ždeposits B. were obtained on the cathode and
anode, respectively. The resistance of the films was
measured by the standard four-point probe method.
We found that the body resistivities of the films were
all above 10 V cm. The scratch tests suggested that
the both deposits on the Si substrates were qualita-
tively hard w4x.
The composition of the deposits was investigated
by XPS analysis. The results revealed that the ca-
thodic deposits A consisted mainly of carbon with
atoms in the CN films more disordered, and conse-
x
quently the CN films have an more intense D peak
x
than that of the DLC film w16x. In all the Raman
spectra of the CN films the peaks at about 2200
x
y1
cm , corresponding to the characteristic peak of the
6
C[N bonds w15x, have not been detected, which is
similar to the IR results. The IR spectra also show no
characteristic peaks of the C–H groups in the carbon
and CN films.
x
The two films were studied by XRD ŽFig. 3.. The
pattern of the carbon film ŽFig. 3A. indicates that the

Q. Fu et al.rChemical Physics Letters 301 (1999) 87–90
89
Fig. 2. Raman spectra of carbon film ŽA. and CNx film ŽB..
Raman measurements were carried out by using a Renishaw-1000
type confocal Raman spectrometer. The 514.5 nm radiation of an
argon ion laser was focused to spots of about 1–2 mm in
diameter.
a-C N Ž201. Žd s0.2377 nm, d s0.2375 nm.
3
4
exp
cal
and b-C N Ž210. Žd s0.2054 nm, d s0.2043
3
4
exp
cal
nm., respectively. The results indicate that the de-
posited CNx films may contain mixed phases of
a-C N and b-C N in the amorphous carbon ma-
3
4
3
4
trix.
According to the above results, DLC and CNx
films have formed on the cathode and the anode
simultaneously in the electrodeposition of liquid
acetonitrile. The deposit on the cathode was amor-
2
3
phous DLC films consisting of sp and sp carbon.
The deposit on the anode was CN film, in which
x
the NrC ratio was about 0.25; mixed phases of
Fig. 1. The deconvoluted binding energy spectra of the deposits:
ŽA. Cls spectrum of the carbon film; ŽB. Nls spectrum of the
carbon film; ŽC. Cls spectrum of the CNx film; ŽD. Nls spectrum
of the CNx film. The spectra were recorded using MgKa with a
Perkin–Elmer PHI 5300 ESCA.
film was amorphous. The CN film has a polycrys-
x
talline structure ŽFig. 3B.. In the pattern of the CNx
film there are two new peaks besides the Si substrate
peak. The d values of the two peaks are identical to
the calculated data w17x, which are attributed to
Fig. 3. The XRD patterns of the carbon film ŽA. and CNx film ŽB.
Žusing X’Pert MRD, Philips..

9
0
Q. Fu et al.rChemical Physics Letters 301 (1999) 87–90
a-C N and b-C N may exist in the CN films.
multaneously using a high voltage electrodeposition
technique in a suitable liquid phase system. Our
present results demonstrate exciting prospects for
this further research into simple but effective tech-
nique.
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4
3
4
x
Accordingly, the deposition mechanism may be in-
ferred as follows: in the beginning, the acetonitrile
molecules are absorbed on the substrates randomly.
When high voltages are applied to the substrates the
absorbed molecules become polarized because of the
large dielectric constant ´ Ž37.5. and dipole moment
Acknowledgements
D Ž3.92. of acetonitrile, i.e. CH CN becomes polar-
3
dq
dy
ized CH3 PPP CN . The potential direction deter-
mines the polarization direction of molecules. When
the substrate is selected as the anode, the potential
applied to the substrates is positive and then the
negative end of the polarized molecule ŽCH3
PPP CN . turns towards the surface of the sub-
This work was supported by National Science
Foundation of China.
dq
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