Optical properties of diamond-like carbon films subjected to ultraviolet irradiation
Influence of UV irradiation on optical properties of the nitrogen doped diamond-like carbon (DLC) films was studied. Transparency spectra of the initial, UV irradiated and concentrated UV irradiated films were measured. Dependences of the optical bandgap on the nitrogen content were obtained from...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2008
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| Цитувати: | Optical properties of diamond-like carbon films subjected to ultraviolet irradiation / N.I.Klyui, V.G.Litovchenko, A.N.Lukyanov, A.N.Klyui // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 4. — С. 396-399. — Бібліогр.: 12 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1190822025-06-03T16:25:27Z Optical properties of diamond-like carbon films subjected to ultraviolet irradiation Klyui, N.I. Litovchenko, V.G. Lukyanov, A.N. Klyui, A.N. Influence of UV irradiation on optical properties of the nitrogen doped diamond-like carbon (DLC) films was studied. Transparency spectra of the initial, UV irradiated and concentrated UV irradiated films were measured. Dependences of the optical bandgap on the nitrogen content were obtained from these spectra. Raman measurements revealed a decrease in the graphitic cluster size by two times after UV irradiation. It was shown that concentrated UV irradiation leads to smaller changes in comparison with nonconcentrated UV. Physical mechanism of air oxygen embedding into the DLC structure under UV irradiation is proposed to explain the changes in the properties of the films. Authors thank to Gule E.G. for UV irradiation experiments, L.A. Dolgov and I.B. Yanchuk for the transparency and Raman measurements, respectively. 2008 Article Optical properties of diamond-like carbon films subjected to ultraviolet irradiation / N.I.Klyui, V.G.Litovchenko, A.N.Lukyanov, A.N.Klyui // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 4. — С. 396-399. — Бібліогр.: 12 назв. — англ. 1560-8034 PACS 61.80.Ba, 68.55.–a, 81.05.Uw https://nasplib.isofts.kiev.ua/handle/123456789/119082 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
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Influence of UV irradiation on optical properties of the nitrogen doped
diamond-like carbon (DLC) films was studied. Transparency spectra of the initial, UV
irradiated and concentrated UV irradiated films were measured. Dependences of the
optical bandgap on the nitrogen content were obtained from these spectra. Raman
measurements revealed a decrease in the graphitic cluster size by two times after UV
irradiation. It was shown that concentrated UV irradiation leads to smaller changes in
comparison with nonconcentrated UV. Physical mechanism of air oxygen embedding
into the DLC structure under UV irradiation is proposed to explain the changes in the
properties of the films. |
| format |
Article |
| author |
Klyui, N.I. Litovchenko, V.G. Lukyanov, A.N. Klyui, A.N. |
| spellingShingle |
Klyui, N.I. Litovchenko, V.G. Lukyanov, A.N. Klyui, A.N. Optical properties of diamond-like carbon films subjected to ultraviolet irradiation Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Klyui, N.I. Litovchenko, V.G. Lukyanov, A.N. Klyui, A.N. |
| author_sort |
Klyui, N.I. |
| title |
Optical properties of diamond-like carbon films subjected to ultraviolet irradiation |
| title_short |
Optical properties of diamond-like carbon films subjected to ultraviolet irradiation |
| title_full |
Optical properties of diamond-like carbon films subjected to ultraviolet irradiation |
| title_fullStr |
Optical properties of diamond-like carbon films subjected to ultraviolet irradiation |
| title_full_unstemmed |
Optical properties of diamond-like carbon films subjected to ultraviolet irradiation |
| title_sort |
optical properties of diamond-like carbon films subjected to ultraviolet irradiation |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2008 |
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https://nasplib.isofts.kiev.ua/handle/123456789/119082 |
| citation_txt |
Optical properties of diamond-like carbon films subjected to ultraviolet irradiation / N.I.Klyui, V.G.Litovchenko, A.N.Lukyanov, A.N.Klyui // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 4. — С. 396-399. — Бібліогр.: 12 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT klyuini opticalpropertiesofdiamondlikecarbonfilmssubjectedtoultravioletirradiation AT litovchenkovg opticalpropertiesofdiamondlikecarbonfilmssubjectedtoultravioletirradiation AT lukyanovan opticalpropertiesofdiamondlikecarbonfilmssubjectedtoultravioletirradiation AT klyuian opticalpropertiesofdiamondlikecarbonfilmssubjectedtoultravioletirradiation |
| first_indexed |
2025-11-28T12:05:32Z |
| last_indexed |
2025-11-28T12:05:32Z |
| _version_ |
1850035706672447488 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 4. P. 396-399.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
396
PACS 61.80.Ba, 68.55.–a, 81.05.Uw
Optical properties of diamond-like carbon films
subjected to ultraviolet irradiation
N.I. Klyui, V.G. Litovchenko, A.N. Lukyanov, A.N. Klyui
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
41, prospect Nauky, 03028 Kyiv, Ukraine; phone/fax: +38(044)525-62-02
E-mail: klyui@isp.kiev.ua, lvg@isp.kiev.ua, lukyanov@isp.kiev.ua
Abstract. Influence of UV irradiation on optical properties of the nitrogen doped
diamond-like carbon (DLC) films was studied. Transparency spectra of the initial, UV
irradiated and concentrated UV irradiated films were measured. Dependences of the
optical bandgap on the nitrogen content were obtained from these spectra. Raman
measurements revealed a decrease in the graphitic cluster size by two times after UV
irradiation. It was shown that concentrated UV irradiation leads to smaller changes in
comparison with nonconcentrated UV. Physical mechanism of air oxygen embedding
into the DLC structure under UV irradiation is proposed to explain the changes in the
properties of the films.
Keywords: diamond-like carbon film, ultraviolet irradiation, optical properties.
Manuscript received 22.07.08; accepted for publication 20.10.08; published online 11.11.08.
1. Introduction
The unique properties of diamond-like carbon (DLC)
films make them an attractive material to improve
various properties of devices. In particular, the films
may be used to develop a variety of electronic devices.
They allow decreasing the work function, threshold
emission voltage and increasing stability of field
emission cathodes [1]. When the DLC films are used as
antireflection and protective coatings for solar cells
(SC), the efficiency is improved by the factor 1.3-1.45
[2]. One of the ways to change parameters of DLC films
is introduction of nitrogen into these films [3, 4].
Because of nitrogen has different bond configurations
inside the film, it can change structure and properties of
the DLC films substantially [4-6].
Although DLC structure and properties are formed
during deposition, they also can be modified through
post-growth ultraviolet (UV) irradiation [7-9]. Optical
transparency of a-C:H films increases and adsorption
edge shifts to the short-wave area after UV irradiation
[7, 8]. Authors of [8] point out the possible participation
of oxygen in changing the characteristics. UV irradiation
results in decreasing the number of C-H bonds with
simultaneous increasing in the quantity of double bonds
of carbon atoms including bonds with nitrogen [7]. UV
irradiation may also result in oxidation of the film
surface, while the N to C concentration ratio increases
after irradiation.
That structure modifications cause changes in the
electronic structure of the films. The DLC films deposited
from a gas source with larger amount of nitrogen have a
smaller optical bandgap Eopt before UV irradiation. After
irradiation Eopt approaches to Eopt of the films deposited
from the gas source with smaller amount of nitrogen [7].
However, in our previous works we observed just an
opposite behavior of the optical bandgap in dependence
on the nitrogen content in DLC films [10, 11].
It is an additional evidence of necessity to study
more detailed effect of nitrogen and post-growth UV
irradiation on the DLC films properties.
Nitrogen in the structure of DLC films causes the
photoluminescence band of about 2.75 eV (450 nm). The
intensity of this band only very weakly depends on the
nitrogen concentration [10]. The same band appears after
UV irradiation of a-C:H:N films [7], and the intensity of
the band linearly depends on the nitrogen concentration
in these films.
Taking into account that amount of works devoted
to investigation of the influence of UV irradiation on
properties of DLC films is very small and the physical
mechanism of this influence is not clear enough, the aim
of this work was to study changes in optical charac-
teristics of DLC a-C:H:N after UV irradiation.
2. Experimental
a-C:H:N DLC films were obtained by plasma-enhanced
chemical vapor deposition [11]. The deposition
conditions are listed in Table 1. The samples were
deposited onto Si (100) and glass substrates at room
temperature.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 4. P. 396-399.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
397
Table 1. Parameters of deposition of studied samples.
# Number
of
sample
Gas mixture
content
N2:H2:Ar:CH4
Deposition
time, min
Pressure,
Pa
Power,
Wt
1 272 20:35:5:25 30 100 250
2 281 30:25:5:25 30 100 250
3 278 45:10:5:25 45 100 250
4 248 0:55:5:25 30 100 150
UV irradiation of DLC films was carried out by a
high-pressure mercury lamp ДРШ-250, the samples
were irradiated by concentrated and non-concentrated
UV light. In the latter case, the samples were placed
instead of the concentrator lens on the distance of 14 cm
from the lamp. All irradiations were carried out
throughout 2 hours in air.
The spectra of photoluminescence and transparency
were measured after UV irradiation. Also, for the sample
deposited from precursor gas that contains 20 % of
nitrogen the Raman spectra were measured. Intensive
photoluminescence was hindered to measure Raman
spectra for other samples with higher nitrogen content.
The data of optical density of the studied samples are
shown in Fig. 1.
Tauc’ dependences were calculated from the
obtained spectra by using the equation [5]:
)( optEEBE −=α ,
where α is the absorption coefficient, E – energy, Eopt
means the value of optical bandgap, B is the coefficient
that takes into account the graphitic cluster size.
Optical bandgaps of the studied DLC films before
and after irradiations were calculated from these curves
and are shown in Fig. 2.
Raman spectra were measured only for the sample
#272 prepared from precursor gas with 20 % of nitrogen,
because of other samples show intensive photolumi-
nescence. Measured Raman spectra are shown in Fig. 3,
and the main parameters of the spectra obtained after
fitting the experimental spectra by two Gaussians are
summarized in Table 2.
Table 2. Parameters of the measured Raman spectra of the
sample #272 (N2 = 20 %).
Parameter Initial Irradiated by
concentrated UV
ωD, cm–1 1338.4 1370.8
∆ωD, cm–1 157.06 257.2
ID, arb. u. 0.180 0.322
ωG, cm–1 1542.8 1542.0
∆ωG, cm–1 139.39 128.21
IG, arb.u. 0.736 0.762
ID/IG 0.245 0.423
300 400 500 600 700
0
1
2
3
1
O
pt
ic
al
D
en
si
ty
, a
.u
.
λ, nm
2
3
4
a)
300 400 500 600 700
0
1
2
3
4
5
O
pt
ic
al
D
en
si
ty
, a
rb
. u
.
λ, nm
b)
2
3
4
300 400 500 600 700
0
1
2
3
4
O
pt
ic
al
D
en
si
ty
, a
rb
.u
.
λ, nm
c)
1
2
3
4
5
Fig. 1. Optical density of DLC films: a – initial; b – UV
irradiated; c – irradiated by concentrated UV. Nitrogen
content: 1 – 0; 2 – 20; 3 – 30; 4 – 45; 5 – 45 % (irradiated
through glass substrate from the rear).
3. Results and discussion
Obtained dependences show that UV irradiation of the
DLC films leads to significant growth of the optical
bandgap (Fig. 2). At the same time, resulting values of
the optical bandgap practically do not depend on the
nitrogen content in the films and are close to about
3.6 eV for the films irradiated by non-concentrated UV
light. Irradiation of the DLC films by concentrated UV
results in optical bandgaps close to 3.4 eV.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 4. P. 396-399.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
398
0 20 30 40
2,0
2,5
3,0
3,5
E g, e
V
N2, %
1
2
3
Fig. 2. Dependences of the optical bandgap versus
concentration of nitrogen in precursor gas: 1 – initial samples
of DLC films; 2 – UV DLC films irradiated during two hours;
3 – DLC films irradiated by concentrated UV light during two
hours. Optical bandgaps of the DLC film without nitrogen
(initial and UV irradiated) are shown separately because this
sample was prepared in other conditions.
1100 1200 1300 1400 1500 1600 1700 1800
0,0
0,2
0,4
0,6
0,8
1,0
G
In
te
ns
ity
, a
rb
. u
.
Raman Shift, cm-1
D
a)
1100 1200 1300 1400 1500 1600 1700 1800
0,0
0,2
0,4
0,6
0,8
1,0 G
In
te
ns
ity
, a
rb
. u
.
Raman Shift, cm-1
D
b)
Fig. 3. Raman spectra for the DLC film prepared from the
precursor gas with 20 % of nitrogen: а – initial; b – after
irradiation by concentrated UV light.
Thus, increase of the optical bandgap of the DLC
films after concentrated UV irradiation is lower than that
for the DLC films after nonconcentrated UV irradiation.
This behavior is caused by additional thermal influence
of concentrated UV light (sample heating). As a result,
hydrogen can partially leave out the samples and
corresponding decrease in the optical bandgap can be
observed [12].
It should be noted that UV irradiation of a-C:H
films (without nitrogen) have no influence on the optical
bandgap. It indicates nitrogen influence on degradation
stability of the DLC films.
The mechanism of UV influence on the properties
of the DLC films is probably concerned with air oxygen
embedding into the DLC structure. UV irradiation
activates oxygen that diffuses into the film and creates
bonds with carbon, hydrogen and/or nitrogen atoms
presented in the film. Presence of oxygen in the DLC
film structure causes decrease of a dangling bond
amount, defect states in the bandgap, appearance of
additional oxygen states near π and σ diamond bands.
On the whole, it leads to the increasing optical bandgap
[8].
Taking into account the dependence of ID/IG ratio,
the size of graphitic clusters in DLC film from [5] and
ID/IG values obtained for our samples (Table 2), we
conclude that after UV irradiation the size of graphitic
clusters in UV irradiated DLC films is decreased.
4. Conclusions
UV irradiation of the nitrogen doped diamond-like
carbon films for two hours leads to a substantial increase
in the optical bandgap from 1.8-2.8 up to 3.4-3.6 eV.
ID/IG ratio of the Raman peaks increases by two
times, that is the consequence of the decreasing number
of graphitic clusters in the structure of the DLC films by
two times after UV irradiation because of air oxygen
embedding into the DLC structure.
It has been shown that the optical bandgap of the
DLC films increases up to a certain value that weakly
depends from the nitrogen content in them.
Concentrated UV irradiation causes smaller
changes of the film optical properties in comparison with
nonconcentrated UV irradiation. It can be related to
additional sample heating during concentrated UV
irradiation.
Authors thank to Gule E.G. for UV irradiation
experiments, L.A. Dolgov and I.B. Yanchuk for the
transparency and Raman measurements, respectively.
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 4. P. 396-399.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
399
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