1292_1.pdf

INVESTIGATION OF THERMAL DIFFUSIVITY OF
NANO-STRUCTURED TiO2 FILMS
X. R. Zhang, S. Lin, J, He
Laboratory of Modern Acoustics and Institute of Acoustics, Nanjing University
Nanjing 210093, China
G. H. Li, L. D. Zhang
Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031
China
ABSTRACT. We investigate the thermal diffusivity of nano-structured TiO2 and TiO2 with 3%
ZnFe2O4 ceramic films (nm films) sputtered on a <111> cut Si substrates by using the Mirage effect
method. Two series of films are prepared by the magneto-rf-spurt method. The investigation results
show that: The thermal diffusivity of nano-structured film depends on the thickness of film and the
annealing temperature. The thicker the film, the lower thermal diffusivity of the sample is. The
value of thermal diffusivity increases with the increasing of the annealing temperature. It means that
the thermal diffusivity depends on the phase structure of the film. The detail results, analyses and
discussions will be presented in this paper.
INTRODUCTION
In recent years, researchers and engineers paid special attention to TiO2 thin films,
which have many applications in catalysis, photocatalysis and solar cells [1-4]. TiC>2 is a
wide bandgap semiconductor and can only absorb about 5% of sunlight in the ultraviolet
light region, which largely limits its practical applications. Many studies have been
devoted to the extension of the photoresponse and improvement of the photoactivity. In
the peculiar case of iron-doped nanosized TiCh powder, when Fe content reach 2.5% the
photoactivity increased by four order for the photocatalytic destruction of dichloroacetic
acid as compared with that without doping [5]. It also has been found that spinel ZnFe2O4
is another semiconductor (band gap 1.9 eV) that has potential application in the
conversion of sunlight, but the property of photoelectric conversion of ZnFe2O4 is poor.
Nanosized TiO2 has high photoactivity and superior property in photoelectric conversion,
while nanosized ZnFeiC^ is sensitive to visible light. So the compound of these two
semiconductors in nanoscale, which utilizes the special properties of nanoparticles and
the coupling between them, will be a new type of composite that will have high utility of
sun light, high photoactivity and high efficiency of photoelectric conversion. The
elaboration of TiO2 thin film and TiO2 + 2 wt.% ZnFe2O4 composite film prepared by r.f.
CP657, Review of Quantitative Nondestructive Evaluation Vol. 22, ed. by D. O. Thompson and D. E. Chimenti
© 2003 American Institute of Physics 0-7354-0117-9/03/S20.00
1292
sputtering and on the effect of post-deposition annealing upon the structural and optical
properties of the films have been reported by G.H. Li et al..[6]
However, until now, no researches related to their thermal properties have been
reported. Usually, the thermal property is an important parameter for the devices. In this
paper, we report on the measured thermal diffusivity of the TiO2 thin film and TiO2 + 3
wt.% ZnFe2O4 composite film prepared by r.f. sputtering and the effect of
post-deposition annealing upon the thermal diffusivity of the films.
EXPERIMENTS
Samples Preparation and Structures
The TiO2 thin film and TiO2 + 3 wt.% ZnFe2C>4 composite film are prepared by r.f.
sputtering method. The deposition is carried out in a sputtering unit equipped with a r.f.
generator. Pure TiO2 and TiO2 + 3 wt.% ZnFe2O4 (purity 99.99%) composite targets of
60 mm diameter fixed on a magnetron-effect cathode is used. The composite target is a
mixture of TiO2 and ZnFe2C>4 powder prepared by chemical coordination method; both
targets are sintered 1350°C in air for 2 h. The base vacuum of sputtering chamber is 10~4
Pa, and a high purity argon gas with pressure of 2 Pa is used. The r.f. power is 150 W.
The coatings are deposited on <111> cut Si crystal plates. For all the depositions, the
target-to-substrate distance is 50 mm. During the deposition, the substrates were not
intentionally heated and the maximum temperature of the substrates was lower than 65°
C. Post-deposition annealing was performed in air at temperature ranges from 200 to
1000°C.
We had measured the structure change with annealing temperature of the sample by
using X-ray diffraction (XRD) (Philips PW 1710 diffractometer by using Cu Kal
radiation) and atomic force microscopy (AFM). The entire tests were performed in air at
room temperature, and found: the polycrystalline anatase formed in 250 °C< Tan< 800°C,
the polycrystalline rutile formed in Tan > 950 °C, for the TiO2 film. The polycrystalline
anatase formed in 400 °C< Tan< 650°C, the polycrystalline rutile formed in Tan 650 °C 800 °C, for the composite film. The AFM images of TiO2 Films are show in Figure 1
(a-d). The labels 2 x 2 and 5 x 5 mean the image showing a 2x 2 and 5x5 mm field,
respectively. The AFM images of TiO2/ZnFe2O4 composite films (hereafter composite
films) are shown in Figure 2(a-d). From Figure 1, we learn that the average particle size
of TiO2 particle in the composite films is small than that in TiO2 films, in spite of it is in
anatase or in rutile phase. The particle size of anatase TiO2 almost linearly increases with
annealing temperature below 600°C, In Figure 1 (a) and (c), the particle size is 25 and 32
nm, respectively, and quickly increases to about 120 nm at 800°C in TiO2 thin films.
From Figure 2, we can see that for annealing temperature Tan =400 °C, the particle size of
TiO2 in the composite film is small than in TiO2 film.
Four series of samples with TiO2 and TiO2 with 3% ZnFe2O4 ceramic films (nm
films) are prepared by the magneto-rf-spurt method. The nano-structured films are
1293
FIGURE 1 The AFM images of TiO2 Films, (a) for the annealing temperature Tan =400 °C, the film in
anatase phase and with particle size of TiO2 d= 25 run, (b) for Tan =600 °C, the film in polycrystalline
anatase phase and with d=32 nm, (c) for Tan =800 °C, in anatase and rutile mixture phase, d=120 nm, (d)
for Tan =900 °C, in anatase and rutile mixture phase, d=200 nm, respectively.
FIGURE 2 The AFM images of TiO2/ZnFe2O4 composite films (a) for annealing temperature Tan -400 °C,
the particle size of TiO2 in the composite film is small than in TiO2 film, (b) for Tan =600 °C, in anatase
phase formed in 400 °C Tan <650 °C, (c) for Tan =700 °C, in anatase and rutile mixture phase, (d) for Tan
=800 °C, in rutile phase, respevtively.
sputtered on a <111> cut Si substrates. The first series of samples are 3-l# and 3-2# (c.f.
Table 1). The second series of samples are 33-l#, 33-2#, 33-3# and 33-4#; the fabrication
conditions of the samples are shown in Table 1 respectively. The third series of sample
are 1#, 3# and 4# and the fourth series of samples are 5#, 6#, 7#, and 8#. The fabrication
conditions for those samples are listed in Table 2 respectively.
Experiment and Results
We measure the thermal diffusivity of TiO2/Si and TiO2 + 3% ZnFe2O4 /Si
(composite filme/Si) samples by means of the well-known transverse mirage method, in
which the probe beam works in skimming way and is measured at the front surface of the
films. It is called zero crossing method [7]. The experimental system used by us is the
same as that described in reference [8]. First, We measure the profiles of in-phase cpt
signals of transverse mirage signals by using different frequency. Then we obtained the
zero crossing distance for each frequency. Second, we obtained the thermal diffusivity
1294
TABLE 1 The fabrication condition and the experimental results for the first and second series samples.
Samples
Components of
Sputtering
Annealing
Annealing
Phase of
Thermal
the sample
time
temperature
time
the films
diffusivity
TiO2+3%wt
(°C)
450
(h)
3_1#
(h)
6
2
Anatase
0.471
3_2#
TiO2+3%wt
6
900
2
Rutile
0.657
12
450
2
Anatase
0.388
12
650
2
Anatase
0.530
12
750
2
Anatase +
0.554
(cm2/s)
ZnFe2O4/Si
ZnFe2O4/Si
33_1#
TiO2+3%wt
ZnFe2O4/Si
33_2#
TiO2+3%wt
ZnFe2O4/Si
33_3#
TiO2+3%wt
Rutile
ZnFe2O4/Si
33_4#
TiO2+3%wt
12
900
Rutile
2
0.598
ZnFe2O4/SI
TABLE 2 The fabrication condition and the experimental results for the third and fourth series samples.
Samples
Components of
Sputter-
Annealing
Annealing
Phase
Thermal
the
samples
ing Time
temperature
time
of the films
diffusivity
(°C)
400
(h)
2
Anatase
0.508
(cm2/s)
1#
TiO2/Si
(h)
5
3#
Ti02/Si
15
400
2
Anatase
0.449
4#
TiO2/Si
20
400
2
Anatase
0.365
5#
TiO2+3%wt
2
300
2
Anatase
0.84
ZnFe2O4/Si
6#
Ti02/Si
2
300
2
Anatase
0.739
7#
TiO2+3%wt
2
600
2
Anatase
0.862
2
600
2
Anatase
0.800
ZnFe2O4/Si
8#
Ti02/Si
from crossing distance for each frequency. Second, we obtained the thermal diffusivity
from the slope of the zero crossing distance versus inverse square root frequency for the
sample. Figure 3 (a) and (b) show a comparison of the zero crossing distances versus
inverse root square frequency between TiCVSi and composite films/Si, when the
sputtered time tsput =2 h, the annealing time tan=2 h, and the annealing temperature Tan=
300 °C and 600 °C respectively. The annealing time (i.e. the structure of film), and the
sputtering time (i.e. the thickness of the film) influence on the thermal diffusivity are
show in Figure 4 and Figure 5 respectively. Figure 4 (a) and (b) show the comparison of
1295
the
zero
root
square
frequency
between
thezero
zerocrossing
crossingdistances
distancesversus
versusinverse
inverseroot
root square
square frequency
frequency between
between the
the samples
samples
composite/Si
prepared
under
different
annealing
temperatures
(300
°C
and
600
°C),
and
composite/Siprepared
preparedunder
underdifferent
differentannealing
annealingtemperatures
temperatures (300
(300 °C
°C and
and 600
600 °C),
°C), and
and
composite/Si
between
prepared
under
T
=
600
°C
and
300
°C
when
the
other
an
/Si
prepared
under
T
=
600
°C
and
300
°C
when
the
other
betweenthe
thesamples
samplesTiCVSi
TiO2/Si
prepared
under
T
=
600
°C
and
300
°C
when
the
other
between
the
samples
TiO
2
anan
conditions
conditionsare
arethe
the same,
same, respectively.
respectively. Figure
Figure 555 The
The comparison
comparison of
of the
the zero
zero crossing
crossing
conditions
are
the
same,
respectively.
Figure
The
comparison
of
the
zero
crossing
distances
versus
inverse
root
square
frequency
of
the
samples
composites/Si
prepared
distances versus inverse root square frequency
frequency of the
the samples
samples composites/Si
composites/Si prepared
under
underdifferent
differentsputtering
sputteringtime
time(i.e.
(i.e.the
thethickness),
thickness),(a)
(a)between
betweenthe
thesample
sampleprepared
prepared under
under
different
=
=
tsput
6=6hhhand
t
12
h,
and
when
the
t
=2
h,
T^
450
°C
are
the
same,
(b)
between
for
an
andttspu
tsput
=12
h,
and
when
the
t
=2
h,
T
=
450
°C
are
the
same,
(b)
between
for
tsput=6
and
=12
h,
and
when
the
t
=2
h,
T
=
450
°C
are
the
same,
(b)
between
for
tsput
sput
an
anan
an
samples
prepared
under
tsput
=6
h
and
t
=12
h,
when
the
t
=2
h,
T
=
900
°C
are
the
sput
an
an
=12
h,
when
the
t
=2
h,
T
=
900
°C
samples
prepared
under
tsput
=6
h
and
t
samples prepared under tsput =6 h and tsput
sput=12 h, when the tan
an=2 h, Tan
an= 900 °C are the
same,
same,respectively.
respectively.
same,
respectively.
DISCUSSION
DISCUSSION
DISCUSSION
g 0.14n
0.14
0.14
0.120.12
0.12
(a)
(a)
for5#5#TiO
TiOfilm
film
for
2 2
2 2/s
α=0.84cm
cm
α=0.84
/s
12
0.12IT °-0.12
^ o.n0.11
0.11
Zero
Zerocrossing
crossingdistance
distance(cm)
(cm)
Zero crossing distance (cm)
Zero crossing distance (cm)
Thevalues
valuesofofof
the
thermal
diffusivity
samples
can
be calculated
from
the
values
the
thermal
diffusivity
forfor
thethe
samples
canbe
becalculated
calculated
from the
the slope
slope
The
the
thermal
diffusivity
for
the
samples
can
from
slope
ofcurves
the curves
shown
in Figure
3 to
Figure
respectively.The
Thevalues
values of
the
the
curves
shown
Figure
Figure
respectively.
The
values
of the
the thermal
thermal
ofofthe
shown
inin Figure
33 toto
Figure
55 5respectively.
thermal
diffusivity
obtained
are
listed
in
Table
1
and
Table
2.
We
can
see
that
the
thermal
diffusivity
obtained
are
listed
in
Table
1
and
Table
2.
We
can
see
that
the
thermal
diffusivity obtained are listed in Table 1 and Table 2. We can see that the thermal
diffusivity
is
related
to
the
component
of
the
nano-films
(c.
f.
Fig.
3),
the
fabrication
diffusivity
is
related
to
the
component
of
the
nano-films
(c.
f.
Fig.
3),
the
fabrication
diffusivity is related to the component of the nano-films (c. f. Fig. 3), the fabrication
conditions
conditions
conditions
2
for
for8#,
8#,TiO/SI
TiO/SI
/SIa=0.80
=0.80cm7s
cm2/s/s
for
8#,
TiO
αα=0.80
cm
2
2
(b)
(b)
(b)
|0.10
0.100.10
0.100.10
0.10
^ 0.090.09
0.09
00
for
for6#ZnFe
ZnFe
Ofilm
film
2O
for
6#6#ZnFe
O
2 4 4film
0.080.08
0.08
0.06
0.06
0.06
0.03
0.03
0.03
2
4
22 2
a=0.7387
=0.7387cm
cm/s
αα
=0.7387
cm
/s/s
0.04
0.04
0.04
0.05
0.05
0.05
0.06
0.06
0.06
|
0.080.080.08
22
for
for7#,
7#,a=0.862
=0.862cm
cm2/s
for
7#,
αα=0.862
cm
/s/s
2 0.070.07
0.07
0.07
0.07
0.07
0.060.06
0.06
0.03
0.04
0.05
0.06
0.07
0.03
0.04
0.05
0.06
0.07
0.03
0.04
0.05
0.06
0.07
-1/2
1/2
-1/2
Invers
) ))
Inverssqure
squreroot
rootfrequency
frequency(Hz"
(Hz
Invers
squre
root
frequency
(Hz
N
-1/2
1/2
-1/2
Invers
Inverssqure
squreroot
rootfrequency
frequency(Hz"
(Hz )) )
Invers
squre
root
frequency
(Hz
0.14-,
0.14
0.14
0.12
0.12
2 2
2/s/s
for^,a=0.84cm
for5#,
5#,α=0.84
α=0.84cm
cm
for
/s
o
TTan=300°C
= 300o C
Tan = 300 C
(a)
(a)
o
0.12
V 0.120.12
0.10
0.10
2
2
2/s/s
for8#,oF0.80cm
for8#,
8#,αα=0.80
=0.80cm
cm
for
/s
o
o
=,600 CC
TTan=,600
(b)
(b)
an
0.10
|
0.100.10
2
0.08
0.080.08
0.06
§ 0.06
0.060.03
N
0.03
0.03
0.14
0.14
x-s °-141
Zero
Zerocrossing
crossingdistance
distance(cm)
(cm)
Zero crossing distance (cm)
Zero crossing distance (cm)
FIGURE
comparison
ofofthe
the
zero
crossing
distances
frequency
between
FIGURE333The
Thecomparison
comparisonof
thezero
zerocrossing
crossingdistances
distancesversus
versusinverse
inverseroot
root square
square frequency
frequency between
between
FIGURE
The
versus
inverse
root
square
the
samples
TiO
/Si
and
composite
films/Si,
(a)
for
the
samples
prepared
under
t
=2
h,
T
=
300
°C,
°C, and
the
samples
TiO
/Si
and
composite
films/Si,
(a)
for
the
samples
prepared
under
t
=2
h,
T
=
300
and
anan
2 and composite films/Si, (a) for the samples prepared under tsput
sput
the samples TiO22/Si
sput =2 h, Tan = 300 °C, and
ttantan
=2
h,
(b)
for
the
samples
prepared
under
t
=2
h,
T
=
600
°C,
and
t
=2
h,
respectively.
=2 h, (b) for the samples prepared under sput
tsput =2 h, Tanan= 600 °C, and tanan=2 h, respectively.
an=2 h, (b) for the samples prepared under tsput =2 h, Tan= 600 °C, and tan=2 h, respectively.
2 /s
for 7#,ce=0.86
α=0.86cm/s
cm
far
for 7#,
7#, α=0.86
cm /s
o
T =600o C
T
T an=600°C
=600 C
an
0.04
0.04
0.04
0.05
0.05
0.05
0.06
0.06
0.06
2
0.08
'% 0.080.08
0.06
0.06
0.06
0.03
0.03
0.03
0.07
0.07
0.07
-1/2
1/2
-1/2
Invers
squre
root
frequency(Hz"
(Hz )) )
Invers
squre
root
frequency
Invers
squre
root
frequency
(Hz
for 6#, α=0.74 cm2 /s
for^,a=0.74cm7s
for 6#, α=0.74
cm /s
o
T = 300o C
T an= 300 C
an
0.04
0.04
0.04
0.05
0.05
0.05
0.06
0.06
0.06
0.07
0.07
0.07
-1/2
-1/2 1/2
Inverssqure
squreroot
rootfrequency
frequency
(Hz
Invers
squre
root
frequency(Hz
(Hz"
Invers
)) )
FIGURE444The
Thecomparison
comparison of
the zero
zero crossing
crossing distances
distances versus
versus inverse
inverse root
root square
square frequency
frequency (a)
FIGURE
comparison
ofof the
the
zero
crossing
distances
versus
inverse
root
square
frequency
(a)
FIGURE
The
between
the
samples
composite/Si
prepared
under
different
annealing
temperatures,
and
the
t
=2
h,
and
between
the
samples
composite/Si
prepared
under
different
annealing
temperatures,
and
the
t
=2
h,
and
sput
sput
between the samples composite/Si prepared under different annealing temperatures, and the tsput
=2 h, and
arethe
thesame,
same,(b)
(b)between
betweenthe
thesamples
samplesTiO
TiO2/Si
preparedunder
underTTanan==600
600°C
°Cand
and300
300°C
°Cwhen
whenthe
the
ttant=2
an=2h,h,are
2 /Siprepared
an=2 h, are the same, (b) between the samples TiO2 /Si prepared under Tan= 600 °C and 300 °C when the
otherconditions
conditionsare
arethe
thesame,
same,respectively.
respectively.
other
other conditions are the same, respectively.
1296
for 3-1#, tsput.=6h
=6 h
for3-l#,t
' sput
o
5
0.14
IT 0.14-
2
0.10
2 /s)
α=0.4710 (cm
cc=0.4710(cm
/s)
for 33_4#,
33_4#, t^U
tsput=12 hh,,
for
2
0.08
•I
0.08</>
2
α=0.38816 (cm2/s)
/s)
a=0.38816(cm
0.04
0.04
0.05
0.05
0.06
0.06
^%^
A-"""^ „--<
GO
for 33-1#, tsput.=12
=12hh
for33-l#,t
ag
0.07
0.07
-1/2
N
Inversesquar
squarroot
rootfrequency
frequency(Hz"
(Hz-1/2))
Inverse
X
0.06
0.06-
(b)
(b)
cm2/s
α=0.5982 cm
a=0.5982
/s
0.12
t 0.12-
' sput.
0.06
0.06
0.03
0.03
A
|0.10
0.10-
0.08
.a o.os-i
o
(a)
Zero crossing distance (cm)
Zero crossing distance (cm)
0.12
0.12-1
•^v^^ °
""^""" jy-"""°
""^
0.03
0.03
for
3_2#, tsput=66hh,
for3_2#,t
s] ur >
P2
α=0.6572 cm 2/s
a=0.6572 cm /s
0.04
0.04
0.05
0.05
0.06
0.06
0.07
0.07
-1/2
Inverse squar
squar root
root fequency
Inverse
fequency (Hz
(Hz" ))
FIGURE5 5The
Thecomparison
comparison of
of the
the zero
zero crossing
crossing distances
distances versus
versus inverse
FIGURE
inverse root
root square
square frequency
frequency ofofthe
the
samples composites/Si prepared under different sputtering time (i.e. the thickness), (a) between the sample
samples composites/Si prepared under different sputtering time (i.e. the thickness), (a) between the sample
prepared under tsput =6 h and tsput =12 h, and when the tan=2 h, Tan= 450 °C are the same, (b) between for
prepared under tsput
=6 h and tsput =12 h, and when the tan=2 h, Tan= 450 °C are the same, (b) between for
samples prepared under tsput =6 h and tsput =12 h, when the tan=2 h, Tan= 900 °C are the same, respectively.
samples prepared under tsput =6 h and tsput
=12 h, when the tan=2 h, Tan= 900 °C are the same, respectively.
including the structure phase of the film depending on the annealing temperature (c. f.
including the structure phase of the film depending on the annealing temperature (c. f.
Figure 4), and the thickness of film depending on the sputtering time (c. f. Figure 5).
Figure 4), and the thickness of film depending on the sputtering time (c. f. Figure 5).
For the first series samples, the annealing temperatures of sample 3_2# is higher that
For the first series samples, the annealing temperatures of sample 3_2# is higher that
that of sample 3_1#. We can see that the thermal diffusivity of the sample 3_2# is larger
that of sample 3_1#. We can see that the thermal diffusivity of the sample 3_2# is larger
than that of the sample 3_1#. Since the substrates and the other fabrications of the
than that of the sample 3_1#. Since the substrates and the other fabrications of the
samples are the same, we can say, the thermal diffusivity of the composite film increase
samples are the same, we can say, the thermal diffusivity of the composite film increase
with the annealing temperature.
with the annealing temperature.
For the second series sample, the influence of the annealing temperature on the
For
the second series sample, the influence of the annealing temperature on the
thermal diffusivity is shown in Figure 6. It is obvious the thermal diffusivity linearly
thermal
diffusivity
shown intemperature.
Figure 6. ItByiscomparing
obvious the
increases
with the isannealing
thethermal
thermaldiffusivity
diffusivity linearly
of the
increases
with
the
annealing
temperature.
By
comparing
the
thermal
of the
the
first series samples with that of the second series samples, we found thatdiffusivity
the value of
first
series
samples
with
that
of
the
second
series
samples,
we
found
that
the
value
of
the
thermal diffusivity for 33_1# or 33_4# is small than that for 3_1# or 3_2# when the other
thermal
diffusivity
for
33_1#
or
33_4#
is
small
than
that
for
3_1#
or
3_2#
when
the
other
parameters are the same. We can say that the thermal diffusivity depends on the thickness
parameters
the the
same.
We cantime
say that
depends
thickness
of the film,are
since
sputtering
usedthe
forthermal
the firstdiffusivity
series sample
is halfonofthe
that
for the
ofsecond
the film,
since
the
sputtering
time
used
for
the
first
series
sample
is
half
of
that
for the
series sample,
second
series
sample,
For the third series samples, the thicknesses of the TiO2 films corresponding to the
For thetime
third5 series
thicknesses
of 1.5
the µm
TiOiand
films
corresponding
the
sputtering
h, 15 samples,
h and 20 the
h are
of 0.5 µm,
2 µm
respectively.toThe
sputtering
h, 15 h and
20TiO
h are
of
0.5
jiim,
1.5
jum
and
2
(im
respectively.
The
film
on
the
thermal
diffusivity
is
shown
in
Figure
5.
influence time
of the5thickness
of the
2
influence
of
the
thickness
of
the
TiO
film
on
the
thermal
diffusivity
is
shown
in
Figure
2
It is clearly see that the thermal diffusivity linearly decrease with the thickness of the5.
Itsample.
is clearly
seebethat
the thermal
linearly
decrease
with the the
thickness
of the
It can
known
that, by diffusivity
using different
annealing
temperature,
structures
of
sample.
It and
can the
be known
by using
temperature,
the Figure
structures
of
the films are
different (c.f.
1 and
the films
averagethat,
particle
size ofdifferent
TiO2 in annealing
the
and the
sizedepends
of TiC>2on
in the particle
films aresize
different
(c.f. Figure
and
2).films
Therefore,
theaverage
thermalparticle
diffusivity
and structure
of the 1film
2).too.
Therefore,
the thermal
dependsdiffusivity
on the particle
sizeAFM
and images
structure
the
By comparison
of the diffusivity
values of thermal
with the
of of
TiO
2
film
too.
By
comparison
of
the
values
of
thermal
diffusivity
with
the
AFM
images
films and TiO2/ZnFe2O4 films for the samples, we can say that the lager the particle size,of
TiC>2
films and
TiCVZnFeiCU
films diffusivity
for the samples,
we can say that the lager the particle
the higher
the value
of the thermal
is.
size, the higher the value of the thermal diffusivity is.
1297
0.9-,
£»
J?
| 0.6-
IS 0.4-
i 0.50-3 H
"3 0.4-
0.3
400
500
600
700
800
900 1000
Thermal Processing temperature (°C)
0.20.4
0.8
1.2
1.6
2.0
Thickness of film (urn)
FIGURE 6 (a) The thermal diffusivity versus the annealing temperature for the TiO2/ZnFe2O4 composite
films, (b) The thermal diffusivity versus thickness of the TiO2 film, respectively.
CONCLUSIONS
The thermal diffusivity of nano-structured TiCh and nano-structured TiC>2 with 3%
ZnFe2O4 ceramic films (nm films) sputtered on a <1 1 1> cut Si substrates were measured
by using the mirage effect method. The investigation results show that: The thermal
diffusivity of nano-structured film depends on the thickness of film and the annealing
temperature. The thicker the film, the lower thermal diffusivity of the sample is. The
value of thermal diffusivity increases with the increasing of the annealing temperature. It
means that the thermal diffusivity depends on the phase structure of the film.
ACKNOWLEDGMENTS
This work is supported by The State Key Lab. of Modern Acoustics, Nanjing
University, Nanjing, China.
REFERENCES
1. B. O'Regan, M. Gra»tzel, Nature 353, 737 (1991).
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4. P. Babelon, A.S. Dequiedt, H. Moste-sa-Sba, S. Bourgeois, P. Sibillot, M. Sacilotti,
Thin Solid Films 322, 63 (1998).
5. D.W. Bahneman, J. Phys. Chem. 98, 1025 (1994).
6. G.H. Li*, L. Yang, Y.X. Jin, L.D. Zhang, Thin Solid Films 368, 163 (2000).
7. P. K. Kuo, L. D. Favro, and R. L. Thomas, in Photothermal Investigations of
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