Plasma assisted TiN stacked TiO2 thin film fabrication in the
context of anti-fog and anti freeze effect
Shankar Parajulee, Anil Pandey, Subash Sharma, Shunjiro Ikezawa
Department of Electrical and Electronic Engineering, Graduate School of Engineering,
Chubu University ,Kasugai, Aichi 487-850
Japan
Introduction
The industrial application of TiO2 film
with the super- hydrophilic property to anti-fog
& anti-freeze mirror is an important subject.
The important and left problems for the
industrial applications are 1) large diameter
coating 2) life time and 3) visible light photo
catalysis, which was developed in N2 gas by
Taga [1,2]We have developed a large mirror of
35 cm diameter coated by TiO2 film using
plasma gun and magnetron sputtering gun.
Titanium nitride (TiN) thin films were deposited
on unheated quartz (SiO2) substrate by an
evaporating process as a buffer zone to enhance
the mechanical durability and optical sensitivity.
Thereafter, the TiN film obtained by plasma
evaporating process was superposed by titanium
dioxide thin film by plasma sputtering process.
In this paper we have observed anti-fog, antifreeze effect and self cleaning property of the
film. It is found that TiN stacked TiO2 film has
good photo-catalytic effect and can be used as
anti fog & anti freeze mirror in the snowy
region.
In order to observe photo
catalytic behavior, samples were exposed to the
sun light soon after the sun rise and 20 min after
the sun rise. It is found that treated surface are
photo sensitive during the sun light irradiation
and showed good anti-fog and anti-freeze effect
in 20 min irradiation. In all conditions TiN/TiO2
surface showed an excellent anti-fog and antifrozen effect as compared to TiO2 surface. The
suitable conditions of the deposition of TiO2
film on glass by the plasma process were that
TiN film was coated first by 10nm thin operated
by plasma gun, and TiO2 film was superposed
on it by 10nm by magnetron sputtering gun. The
coating times of making Glass/TiN/TiO2 were
30sec and 10min, respectively. The anti-fog &
anti-freeeze mirror will be produced as an
attractive industrial application.
Experimental apparatus
Two apparatuses, plasma gun and magnetron
sputtering gun have been employed to develop
TiN/TiO2 films comprising with special layer of
TiON as an interface. We have highlighted
Fig. 1 Magnetron sputtering
apparatus (Ti target area: 37cm×37cm)
magnetron sputtering apparatus for the TiO2
coating on the glass surface as shown by Fig.1.
First, the deposition of TiN thin layer by
plasma gun process is mentioned. In this
process Ti was evaporated from the Ti melting
anode pot in N2 plasma. The gun was used for
TiN strong sticking film coating on a glass. For
an example of operational parameters; N2 gas 5
sccm, Ar gas 15 sccm, gas pressure 1 mTorr
gun voltage 90V and current 60A were used.
And the strong sticking thin film; for example,
by the scratch method, a critical load of over
20(N) were obtained [3]. The coating of TiN
was carried out for 30 sec ~ a few minutes.
The result thus obtained was transparent gray
thin film with the thickness of 10 nm  100nm.
Similarly, we have developed a large area
magnetron sputtering with a 35cm35cm Ti
target plate source. The target was placed at the
bottom of a large diameter reactor 1.2 m. From
the Ti target source, Ti was evaporated in O2
plasma. The coating was
carried out for 10 minutes; TiO2 transparent
film of a few 10 nm thickness was formed. For
the measurement of light transmittance, as
shown in Fig.3, we have employed the He-Ne
laser
Laser on
Laser on
Laser on
Laser on
Rotation motor
Laser off
(Lamp 10 m.)
Laser on
Substrate
position
Glass only + Lamp
Window
Plasma
reaction
chamber
C
B
A
Laser on
Glass + Lamp +Fog
D
(Lamp 20 m.)
Laser on
Glass/TiN/TiO2 + Lamp +Fog
Transmitted Light (%) B,C,D/A
Vaccum out let
Plasma gun
constant Voltage
and current in
carrier gass (Ar)
Electron beam plasma
accelerated towards the target
Ti - Target
Fig. 2 Experimental set up of plasma gun
apparatus
measurement. In this system, we set a coating
glass between the He-Ne laser and the
photomul., which have the different parameters
operated by both the
plasma gun and
magnetron sputtering gun. The sputtering
process was normally used for TiO2 film coating
here. The parameters of the process were that
O2 gas flow was 15 sccm, Ar gas 15 sccm, the
gas pressure 34 mTorr, the sputtering electric
power source 1 KW, 100 KHz, pulse duty rate
50 %. The experimental outline of the laser
measurement [4] is shown in Fig.3(a). Just
Glass/TiN/TiO2
He-Ne Laser
Photomul.
Elec.
Source
Tungsten
Lamp(40 W)
Fluorescent
Lamp(20W）
X-Y
Recorder
Fig. 3(a) Experimental system of He-Ne laser
measurement
below the glass plate, a pot of fog source was
set and the glass was covered by the fog. At the
same time, the glass was irradiated by a light
from 40 W tungsten lamp or a fluorescent lamp
with 45 degrees angle and 35 cm distance.
Fig. 3 (b) Transmitted light (%) observed
by X-Y recorder
Results and discussions
As we have already mentioned in the above
experiment of TiO2 and TiN coating, the
significant achievement of our experiment is the
interface layer. The laser light transmittance
through each glass sample was observed as
shown in Fig.3(b).
As for Fig 3 (b), the transmitted light (%) is
obtained as follows. When the laser was on and
off with the glass plate only and the lamp (Glass
only +Lamp), the A was obtained by X-Y
recorder. When the fog was added (Glass
+Lamp + Fog), the laser transmittance was
decreased and the B was obtained. When the
Glass /TiN/TiO2 plate was set as shown in
Fig.3(a) (Glass/TiN/TiO2 + Lamp + Fog), the C
increasing compared to B, was observed. The
increased C was come from the superhydrophilic effect of photocatalytics. When the
irradiation time was increased, the increased
intensity D was obtained.
The graph of transmittance of light shows
that the glass superposed by TiO2/TiN for 20
minutes has high label of transmittance (97%)
as compared to other parameters. For the sample
1 of only glass, the transmittance is about 54%
however for the sample 2~5 of coated glass, it is
over 54%. So the super hydrophilic effect is
operational for the sample 2~5. The result for
the comparative study of the laser light
transmittance, carried out by plasma gun and
magnetron sputtering gun in different time span
is shown in Fig.5.
55
21
Contact angle(degree)
18
Sample1~4
It is supposed that on extremely hydrophilic
1. Plasma gun 10 min.
surface,
a water droplet will completely spread
2. Magnetron gun 10 min.
(an
effective
3. Plasma gun 2 min. contact angle of 0 degree). This
for1 min.
surfaces that have a large affinity for
4.occurs
Plasma gun
1
2
15
12
3
9
4
6
3
0
0
5
10
15
20
Irradiation time(minute)
Fig. 4 Results of Laser Transmittance
(The coating parameters are in the right hand
side, Tungsten lamp: 20 min)
T ransm itted L ight (% )
100
80
60
40
30 m in
water (including materials that absorb water).
On many hydrophilic surfaces, water droplets
will exhibit contact angles of 10° to 30°. On
highly hydrophobic surfaces, which are
incompatible with water , one observes a large
contact angle (70° to 90°). Some surfaces have
water contact angles as high as 150° or even
nearly 180°. On these
surfaces, water droplets simply rest on the
surface, without actually wetting to any
significant extent. Thus information on the
interaction energy between the surface of
Glass/TiN/TiO2 plate and the liquid is measured
by the contact angle meter FACE ,CA-D.The
result is shown in Fig.6. It is found that the
contact angle decreases in two steps[5].
At the first step the contact angle of only glass,
55° suddenly decreases to 18-8 degrees when
the glass were coated. At the second step the
contact angle decreases as the irradiation time
increases.
Samples
1~5 Also, the irradiation to the glass (with
coating
1: laser cut and without coating) was carried out by
the gun
sources
2:both
Magnetron
10min tungsten lamp (40W) and
3:fluorescent
Plasma gun 1 min
lamp (20W). In the Fig .6, for the
4:samples
plasma gun1,2 min
2 the irradiation was carried out by
5:tungsten
Plasma gun lamp
10 min and for the samples 3,4 by
fluorescent lamp.Thus, hydrophilicity is found
to be increasing as the surface is coated by TiO2
and also further enhanced by irradiating the
surface.
20
0
.
1
20 m in
10 m in
2
3
4
5
Sample Number
Fig. 5 Comparison of plasma process between
the magnetron-sputtering gun with the plasma
gun (Tungsten lamp irradiation times up solid
squares: 30min., center solid squares: 20min.,
bottom solid squares: 10min.)
For the plasma gun samples 3~5, when the
coating time increases from 1 min to 10 min the
film thickness increases and the transmittance
decreases because of the gray coating color.
And corresponding to the film thickness as the
irradiation time increases from 10 min to 30 min
the transmittance increases.
Fig. 6 Curve mirror (35cmφ, left-hand side:
coated, right-hand side: non-coated)
In fig.6, two curve mirrors are observed and the
left hand side curve mirror which was coated by
TiN / TiO2 is found to be transparent and
hydrophilic as compared to the right hand side
(non- coated) curve mirror, The surface
character of the film was measured by ESCA
and confirmed that the nitrogen atomic peak
from the coating parameters, N2: 12 sccm and
10 min (sample-2 in Fig.4), the binding energy
at about 400/ev and intensity count 1400 –1500,
however Taga has observed nitrogen peak N1S
at 396/ev [2].
Conclusions
A curve mirror of TiO2 films with interface
layer of TiN/TiO2 , which currently are the
interest for their application in anti-fog mirror,
were developed by plasma gun and magnetron
sputtering gun. The suitable conditions of the
deposition TiO2 film on glass by the plasma
process are that TiN film was coated first by
10nm thin operated by plasma gun, and TiO2
film was superposed on it by 10nm by
magnetron sputtering gun. The coating times of
making Glass/TiN/TiO2 were 30sec and 10min,
respectively. The anti-fog mirror will be
produced as an attractive industrial application.
Acknowledgment
One of the authors, S. Ikezawa would like to
thank Professor T. Hara and Professor Y.Taga
for their discussions and supports. This work
was supported in part by grants from the Conbru
scholarship of Nagoya University, the special
fund of Chubu University, the project fund of
the Industrial Consortium of NEDO.
References
[1] A.Fujishima and K.Honda, Nature 238,
(1972) p36
[2] R.Asahi, T.Morikawa, T.Owaki, K.Aoki and
Y.Taga, Science 293, (2001) p 263
[3] H.Freller and H.Haessler, Thin Solid Films
153, (1987) pp.67-72
[4] Shankar Parajulee, Shunjiro Ikezawa, Tamio
Hara,
Yasunori
Taga;
International
Symposium on Plasma chemistry ISPC-18,
2007,Kyoto University, Full- paper CD (27p179)
[5] JIN KUM, IN-HWAN KIM, Applied Polymer
Science 79, (2001) pp.2251-2257