Synthesis of diamondlike films by an electrochemical method at atmospheric pressure and low temperature

Article abstract of DOI:10.1063/1.118355

A technique of carbon film synthesis based on an electrochemical process was developed. A solution of acetylene in liquid ammonia was employed as the electrolyte. Films were deposited at the metallic anode. Two types of films were produced. Films of type I are transparent and fragile, whereas those of type II are black and plastic. The films were investigated by the electron diffraction method and Raman spectroscopy. The electron diffraction data for type I films demonstrate the films' high degree of crystallinity. Values of lattice plane spacings agree with data on cubic diamond modifications. The Raman spectrum of type I films shows a line at 1334 cm^-1 (full width at half-maximum equal to 15 cm^-1), inherent in that of diamond and an essentially amorphous carbon component. Spectra of the type II films do not feature the Raman peak of diamond.

Full text of DOI:10.1063/1.118355

Synthesis of diamondlike films by an electrochemical method at atmospheric pressure
and low temperature
V. P. Novikov and V. P. Dymont
Citation: Applied Physics Letters 70, 200 (1997); doi: 10.1063/1.118355
View online: http://dx.doi.org/10.1063/1.118355
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/70/2?ver=pdfcov
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Synthesis of diamondlike films by an electrochemical method
at atmospheric pressure and low temperature
V. P. Novikova) and V. P. Dymont
Academy of Sciences of Belarus, Institute of Solid State Physics and Semiconductors, Minsk 220072,
Belarus
͑Received 17 July 1996; accepted for publication 8 November 1996͒
A technique of carbon film synthesis based on an electrochemical process was developed. A
solution of acetylene in liquid ammonia was employed as the electrolyte. Films were deposited at
the metallic anode. Two types of films were produced. Films of type I are transparent and fragile,
whereas those of type II are black and plastic. The films were investigated by the electron diffraction
method and Raman spectroscopy. The electron diffraction data for type I films demonstrate the
films’ high degree of crystallinity. Values of lattice plane spacings agree with data on cubic diamond
modifications. The Raman spectrum of type I films shows a line at 1334 cmϪ1 ͑full width at
half-maximum equal to 15 cmϪ1), inherent in that of diamond and an essentially amorphous carbon
component. Spectra of the type II films do not feature the Raman peak of diamond. © 1997
American Institute of Physics. ͓S0003-6951͑97͒02602-8͔
108 –1010 ⍀ cm.The type II films were black and plastic.
The diamondlike carbon ͑DLC͒ films have unique prop-
erties that make them candidates for a number of applica-
tions. Among these are corrosion protective coatings of met-
als, wear-resistant coatings and use as optical and electronic
components. As a rule, diamondlike carbon films are depos-
ited using a variety of chemical vapor deposition techniques,
as well as the ion-beam techniques, and laser processing.1,2
We have succeeded in demonstrating a new method in which
the metastable growth of DLC films occurs at atmospheric
pressure and low substrate temperature. Our method is based
on an electrochemical ͑galvanic͒ process.
They had a platelike morphology of grains. Their resistivity
was 102 –104 ⍀ cm.
Both types of films were inert to heavy acids and alkalies
and did not dissolve in organic solvents. The type of film
produced depended on various factors, such as electrode ma-
terial, its preliminary treatment, and the electrolysis voltage.
Type II films were grown when the electrochemical etching
of the electrode took place. Figure 2 presents typical trans-
mission electron microscopy ͑TEM͒ diffraction micrographs
of the annealed films. The electron diffraction pattern of type
I films shows up as a system of narrow rings. This means
there is a high degree of film crystallinity. Lattice plane spac-
ings measured from diffraction patterns are given in Table I
in comparison with the ASTM values for diamond. It is
A solution of acetylene in liquid ammonia was used as a
starting electrolyte. The choice of such a system is based on
the assumption that the acetylene dissociates in NH3 by the
scheme:
C H —— C HϪϩHϩ,
→
2
2
2
and the ions are discharged:
Ϫ
Ϫ2e
C2HϪ —— C •ϩHϩ.
͑1͒
→
2n
The acetylene was synthesized by calcium acetylide hydroly-
sis. The ammonia was obtained via distillation of NH4OH. A
Dewar vessel with a volume of 50 cm3 was used as an elec-
trochemical cell. This cell was filled up by the electrolyte.
Plates of different metal foils ͑Ni, Co, Fe͒ 1–2 cm2 in area
were used as electrodes. The electrolysis voltage and current
density were varied in the 2.0–5.0 V and 10Ϫ3 –10Ϫ5
A/cm2 ranges, respectively. The deposition time ranged from
5 to 10 h. The thickness of films lay between 0.5 and 3 ␮m.
Assuming that reaction ͑1͒ takes place, the estimated current
efficiency of carbon was 40%ϩ20%. The films were inves-
tigated by scanning electron microscopy, the electron dif-
fraction method, and Raman spectroscopy.
Depending on the electrolysis conditions, two types of
films were produced on the anode. Films of type I were
transparent and fragile. They were smooth and homogeneous
in thickness, as shown in Fig. 1. Their resistivity was
FIG. 1. Scanning electron micrographs of carbon films: ͑a͒ type I films and
͑b͒ type II films.
a͒
Electronic mail: ifttpanb%iftt.basnet.minsk.by@demos
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200 Appl. Phys. Lett. 70 (2), 13 January 1997 0003-6951/97/70(2)/200/3/$10.00 © 1997 American Institute of Physics
68.37.176.114 On: Mon, 07 Apr 2014 00:14:48

FIG. 2. Electron diffraction pattern of type I films.
shown that values of d for type I film coincide with those for
diamond. It is particularly remarkable that reflexes, forbid-
den for diamond, were observed as well. The films of type II
have no crystalline structure.
Raman spectra of the type I films had a diamond peak at
1334 cmϪ1 ͑full width at half-maximum is equal to 15
cmϪ1) and an essentially amorphous carbon component. The
spectra also showed the presence of a Raman peak at 1309
cmϪ1 ͓Fig. 3͑a͔͒. As yet, the origin of this peak has not been
determined. Spectra of the type II films do not feature a
Raman peak of diamond. The broad spectra band with maxi-
mum in the neighborhood of 1580 cmϪ1may be attributed to
amorphous carbon ͓Fig. 3͑b͔͒.
Electrochemical oxidation of the acetylene ion on the
anode,
Ϫ
Ϫne
n CwCHϪ͒ → C H ,
͑
2n
n
creates hydrogenated carbon with a hydrogen content of the
order of 33.3 at %. It is well known that carbon hydroge-
nated to an equally high degree can exist only in the amor-
phous state. The formation of a highly crystalline diamond-
like deposit is the indirect evidence of low hydrogen content.
It is suggested that the following schemes of the carbon de-
hydrogenation take place:
FIG. 3. Raman spectra of carbon films: ͑a͒ type I films and ͑b͒ type II films.
cal anode process:
Ϫ
Ϫe
uCwC—H —— u CwC• ϩHϩ͑solv.͒.
→
͑1͒ dehydrogenation of the growing film by an electrochemi-
chem. sorb.
chem. sorb.
͑2͒ Dehydrogenation of the film by another ion, for ex-
TABLE .I.The lattice plane spacing values for electrolytical carbon film and
cubic diamond.
ample,
Ϫ
Ϫe
NHϪ2 —— NH •;
→
2
Film
Diamond ͑aϭ0.3566 nm͒
uCwCHϩNH —— — CwC• ϩNH .
→
2
3
h2ϩk2ϩl2
Intensity
d ͑nm͒
d ͑nm͒
chem. sorb.
chem. sorb
s
0.240
0.201
0.174
0.141
0.121
0.117
0.104
0.092
0.089
0.082
0.251
0.206
0.178
0.143
0.126
0.118
0.107
0.095
0.089
0.081
2
3
4
6
8
͑3͒ Catalytic dehydrogenation by metal cations:
v
s
Ϫ
Ϫ2e
w
s
Me0 → Meϩ2
;
s
v
2Ϫn
Meϩ2ϩn CwCHϪ͒ —— Me͑CwC͒
͑
→
w
9
n
w
w
w
w
12
14
16
19
ϩnHϩ ͑solv.͒;
Ϫ
Ϫ͑2Ϫn͒e
2Ϫn
n
Me͑CwC͒
—— Meϩ2ϩC2n
.
→
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Appl. Phys. Lett., Vol. 70, No. 2, 13 January 1997 V. P. Novikov and V. P. Dymont 201
68.37.176.114 On: Mon, 07 Apr 2014 00:14:48

It is clear that scheme ͑3͒ refers to formation of type II films.
Of great importance is the problem of primary growth of
diamondlike films under metastable conditions that are more
thermodynamically advantageous for growth of the graphite
phase. In our case the nonequilibrium nature of electrolysis
has to be taken into account. According to Ostwald’s step
rules, the formation of phases in nonequilibrium conditions
begins with the least stable phase. There are, however, some
favorable conditions for the growth of the diamondlike phase
in this experiment:
We have thus shown that diamondlike films can be created
by an electrochemical method at atmospheric pressure and
low substrate temperature. This method has a number of po-
tential advantages over other methods, as for instance, plas-
mochemical ones. Among these are ͑1͒ simplicity of appara-
tus, energy saving, and material saving; ͑2͒ simplicity of film
doping and film modification; ͑3͒ favorable conditions for
growing new metastable forms of carbon because of the low
temperature and the fact that the process is not in equilib-
rium.
͑1͒ the possibility of hydrogen and nitrogen capture by the
growing film that stabilizes the sp3 configuration of
carbon;4
1 P. K. Bachmann, D. Leers, and H. Lidtin, Diam. Relat. Mater. 1, 1 ͑1991͒
2 D. R. McKenzie et al., Diam. Relat. Mater. 1, 51 ͑1991͒
͑2͒ the low temperature of the synthesis that closely ap-
proaches the thermodynamic potential of the diamond
and graphite phases.
3 J. Angus and F. Jansen, J. Vac. Sci. Technol. A 6, 1778 ͑1988͒
4 J. Seth, A. J. I. Ward, and S. V. Babu, Appl. Phys. Lett. 60, 1957 ͑1992͒
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202 Appl. Phys. Lett., Vol. 70, No. 2, 13 January 1997 V. P. Novikov and V. P. Dymont
68.37.176.114 On: Mon, 07 Apr 2014 00:14:48