Photo-induced characteristics of TiO2 prepared by anodic
oxidation in sulfuric acid aqueous solution
Naoya Masahashi and Yoshiteru Mizukoshi
1. BackgroundTiO2 oxide has been used as photocatalyst due to degrading toxic organic
pollutants, bacteria, and viruses absorbed on its surface under ultraviolet (UV)light illumination [1-3]. The oxide is usually fabricated by wet (dip coating, spin
coating, spraying) or dry (sputtering, ion-plating, vapor deposition) methods.
Masahashi et al. studied an anodic oxidation to form photocatalyst TiO2 on Ti
and its alloys due to several advantages [4-8]. Firstly, it allows one to select thecomposition of electrolytes used for doping, which is beneficial for controlling theband gap structure of the oxide. Second, anodic oxidation occurs in equilibrium
based on the thermodynamic reaction and provides adhesion strength at theinterface. Third, it yields a porous microstructure due to the competitive reaction
between oxide formation and chemical dissolution of the oxide by controlling theelectrochemical parameters (conversion potential, current density andelectrolyte composition), which influences the photocatalytic activities andsuperhydrophilicity. In our study, the primary concept is to develop crystallinity ofanatase and/or rutile because it reduces a number of re-combination sites ofphoto-generated charges to promote photocatalytic reaction. The other is tocontrol the electronic structure of the oxide by doping an element provided fromthe electrolyte improving visible light response of the oxide.
2. Experimental procedures
Substrate is a pure titanium plate used as the anode. Anodic oxidation was
conducted in 0.002 M to 1.6 M sulfuric acid electrolyte using a Pt electrode for0.5 h and was controlled galvanostatically until the conversion voltage reached a
specified value. The anodic oxide was annealed at 723 K for 5 h in atmosphere.
The crystallographic structure of the oxide was determined by X-ray diffraction(XRD) with Cu-Kα radiation with a thin-film geometry arrangement, and a rotating
detector. Microstructure observations were conducted with field emission
scanning electron microscopy and transmission electron microscopy (TEM). A
TEM cross-sectional specimen was prepared by a focused ion beam. Surface
roughness and surface area were measured using a laser microscope with a1wavelength of 408 nm. X-ray photoelectron spectroscopy (XPS) measurements
were conducted with an electron spectrometer equipped with monochromated
Al-Kα radiation.
The photocatalytic activity under UV light illumination was evaluated using
methylene blue (MB) bleaching test and acetaldehyde decomposition test. The
contact angle of distilled water (0.1 mL) is the average of three measurements
taken for each sample by using a goniometer system. UV light of 0.1 mW/cm2
intensity was radiated and the contact angle was measured every half hour
during illumination.
3. Results
3.1. Microstructures
Figure1 shows micrographs of the anodic oxides in various concentrations ofsulfuric acid [6]. When the sulfuric acid concentration is 0.02M, glassy anodizedoxide with submicron sized pores is observed. The microstructure of theannealed oxide anodized in 0.1M sulfuric acid contains homogeneously
distributed nanosized pores, followed by growth of the pores with an increase of
the sulfuric acid concentration to 0.2M. Further increase of the sulfuric acidconcentration to 1.2 M promotes unevenness of surface morphology and acoalescence of each pore appears frequently. The average pore size increases
from approximately 170 to 950 nm with an increase in the concentration of
sulfuric acid.
0.02M

0.1M

2µm

2µm

0.2M

1.2M

2µm
FIG.1

2µm

Micrographs of the anodic oxides in various concentrations of sulfuric acid of 0.02 M (a),0.1 M (b), 0.2 M (c) and 1.2 M (d).

2

1200

1000

800

600

Ra
S

400

200

0
0.0

FIG.2

0.2

0.4

0.6

0.8

1.0

1.2

Plots of the surface area (S) and the average roughness (Ra) of the anodic oxideagainst the sulfuric acid concentration.

The surface area (S) and the average roughness (Ra) of the anodic oxide areplotted against the sulfuric acid concentration in the electrolyte (Fig. 2) [6]. It
shows that both S and Ra increase with an increase of the sulfuric acidconcentration in the electrolyte.
Figure 3 shows the cross-sectional TEM images of as-anodized (a) andannealed (b) oxides prepared in an electrolyte with a sulfuric acid concentrationof 1.2 M [6]. It reveals that the thicknesses of the oxides are approximately 7 µm,

rutile

(a)

(b)

B

Oxide layer

Oxide
layer
substrate
A 0.5 µm
Thin layer

1µm

substrate
Thin layer

anataseFIG. 3

Cross-sectional TEM micrographs of the as-anodized (a) and annealed (b) oxides
anodized in an electrolyte with a sulfuric acid concentration of 1.2 M.

3irrespective of annealing. A thin layer on the titanium substrate with a thicknessof approximately 200 nm is observed in both the as-anodized and annealedoxides. The inserted bottom-left and top-middle diffraction patterns are obtained
from the areas indicated by circles (A) and (B), respectively; the area circled (A)and circled (B) show the anatase and rutile form, respectively.
3.2 Crystal structure
Figure 4 is XRD profiles of as-anodized (left) and annealed (right) oxides
prepared in an electrolyte with a sulfuric acid concentration of 0.02 M, 0.1 M, 0.2
M, 0.4 M, 1.2 M, and 1.6 M [6]. The peak intensity of the substrate hcp-Ti 101(2θ = 40.18) decreases with an increase in the sulfuric acid concentration,
indicating that the thickness of the oxide layer increases with the sulfuric acidconcentration. The predominant oxide phase converted from anatase to rutile at
0.4 M of sulfuric acid. This implies that the rutile-structured phase is stabilized as
the sulfuric acid concentration in the electrolyte is increased.
anatase 101 rutile 110 rutile 101

anatase 101 rutile 110 rutile 101

50k

50k

0.02 M H2SO4
40k

30k

40k

0.1 M H2SO4
0.2 M H2SO4

30k

0.4 M H2SO4

0.2 M H2SO4

20k

1.2 M H2SO4

1.2 M H2SO4
10k

1.6 M H2SO40

1.6 M H2SO4

0
10

20

30

40

50

60

70

80

10

rutileanataseFIG.4

0.1 M H2SO4

0.4 M H2SO4

20k

10k

0.02 M H2SO4

20

30

40

50

60

70

80

titan

XRD profiles of the as-anodized (a) and annealed (b) oxides anodized in an electrolytewith a sulfuric acid concentration of 0.02 M, 0.1 M, 0.2 M, 0.4 M, 1.2 M and 1.6 M.

The crystallite size (ε) and inhomogeneous lattice strain (η) in the oxide were
calculated from the full width at half maximum (FWHM) of the oxide peak byusing Hall’s methods. The parameters ε and η are plotted against the sulfuric
acid concentration in the left and right of Figure 5, respectively [6]. In this figures,the parameters of the monolithic rutile TiO2 powders with particle sizes of 1–2µm was plotted to compare with those of the anodic oxide. The left figure shows4that the crystallite size varied between 10 nm and 30 nm and decreased slightly
with annealing. The crystallite size of anatase increases with the sulfuric acidconcentration in the electrolyte, irrespective of annealing, and the as-anodizedoxide exhibits a larger crystallite size than that of the annealed oxide. However,the crystallite size of rutile is approximately 30 nm, irrespective of the sulfuric
acid concentration, and no explicit difference is found between the as-anodized
and annealed oxide. The right figure shows that the inhomogeneous latticestrain of the oxide is quite low or free (calculated as negative value) andannealing treatment further reduces the inhomogeneous strain. This implies thatthe amounts of lattice defects detectable by X-ray are so small, which isfavorable to suppress recombination of the exited charges and improve
photocatalytic activities.
6.0x10-3

as-anodized (anatase)annealed (anatase)as-anodized (rutile)
annealed (rutile)

50
40

reference
30
20
10
0

0.0

0.5

1.0

Inhomogeneous lattice strain / εCrystallite size η / nm

60

2.0x10-3
0.0-2.0x10-3-4.0x10-3

1.5

Concentration of H2SO4 / M

FIG.5

4.0x10-3

reference

0.0

0.5

1.0

1.5

Concentration of H2SO4 / M

Crystallite size (a) and inhomogeneous lattice strain (b) of the as-anodized andannealed oxides versus the sulfuric acid concentration in the electrolyte.

3.3 XPS analysis
Figure 6 shows Ti 2p (left) and O 1s (right) XPS of the annealed oxides
anodized in the electrolytes of a sulfuric acid concentration of 0.1 M and 1.2 M,
respectively [6]. Two single peaks at approximately 465 eV and 459 eVcorrespond to the Ti4+ 2p1/2 and 2p3/2 contributions of TiO2. The Ti 2p XPS
reveals that the surface is completely composed of TiO2. They have asymmetrical shape, indicating that reduced Ti3+ ions are not present in theoxides. It is beneficial for the photocatalysis to lower the recombination
frequencies, because the reduced Ti3+ ions act as recombination sites. The O 1
s XPS profiles have an asymmetrical shape accompanied with a shoulder bandat approximately 532.4 eV on the higher binding energy side of the main peak.
This shoulder peak has been observed in the previous study and is ascribed to5hydroxyl groups [9]. It should be noted that the intensity of the shoulder peak in
the oxide anodized in the electrolyte with a sulfuric acid concentration of 1.2 M ishigher than that in the electrolyte of a sulfuric acid concentration of 0.1 M. Thissuggests that the former anodic oxide could adsorb a large amount of watermolecule as compared to the latter oxide.
0.1 M H2SO4
1.2 M H2SO4

0.1 M H2SO4
1.2 M H2SO4hydroxyl groups

0.0

0.0

470

FIG. 6

465

460

455

450

540

535

530

525

Ti 2p (left) and O 1s (right) XPS spectrum of the oxides anodized in an electrolyte of asulfuric acid concentration of 0.1 M and 1.2M.

3.4 Adhesion strength
Adhesion strength between the anodic oxide and the Ti substrate wascharacterized by the load-bearing capacity of the oxide layer using scratch test.
Figure 7 shows the friction signal of the oxide anodized in an electrolyte of asulfuric acid concentration of 0.1 M (a) and 1.2 M (b) with anatase TiO2 preparedby sol-gel method (c) [10]. Distinct signal change (blue line) is found in (a) and(c), while continuous change is found in (b). The adhesion strength of the oxide
anodized in an electrolyte of a sulfuric acid concentration of 0.02 M, 0.1 M, 0.2 M
(a)

(b)

Sensor output
Sensor force

50

2500

50

2000

40

20

500

10

0

0

0

0

100

150

Time / s

FIG.7

200

250

300

0

50

100

150

Time / s

200

250

300

Sensor output

1000

10

20
500

30

1500

Sensor force / mN

30

1000

Sensor output

40

50

60

Critical exfoliation strength=25.10 mN

600

Critical exfoliation strength=29.60 mN

0Sensor output
Sensor force

3000

2000

1500

30
700

60

Sensor force / mN

Sensor output

2500

(c)
70

3500

500

25

20

Sensor output
Sensor force

400

15

300
10
200
5

100
0

0
0

20

40

60

80

100

120

140

Time / sFriction signal (blue) in the scratch test of the oxide anodized in an electrolyte of asulfuric acid of 0.1 M (a) and 1.2 M (b) with TiO2 prepared by sol-gel method (c).

6

Sensor force / mN

70

3000

and 1.2 M are calculated as 26.60 mN, 28.63 mN, 32.10 mN and over thedetection limit, respectively. On the other hand, those of the oxide prepared bysol-gel methods and CVD are 24.53 mN and 14.87 mN. This result suggests thatthe anodic oxide has high adhesion strength with an increase of sulfuric acidconcentration in the electrolyte.
3.5 Photocatalytic activities
Figure 8 plots MB degradation calculated reaction rate constant under UVlight illumination against concentration of sulfuric acid in the electrolyte [6]. The
predominant oxide phase is replaced from anatase to rutile at 0.4 M of sulfuric
acid concentration with an increase of sulfuric acid concentration, and the rutile
form exhibits high MB degradation rate as compared to anatase form. In addition,an annealed oxide (red mark) is higher in the MB degradation rate thanas-anodized oxide (blue mark) irrespective of the predominant phase.

Reaction rate constant / min-1

0.00350.0030as-anodized
annealed

0.00250.00200.00150.00100.00050.0000
0.0

0.5

1.0

1.5

Sulfuric acid concentration / M

FIG. 8Plots of MB degradation calculated reaction rate constant against the sulfuric acidconcentration in the electrolyte.

Figure 9 shows the wavelength dependence of the photocatalytic activity of
the anodic oxides and commercially available anatase oxide prepared by sol-gel
method [7]. At longer wavelengths of visible light, the MB degradation rate of theanatase-structured anodic oxide prepared in 0.02 M and 0.1 M sulfuric acidaqueous solution was quite low, which is similar to the commercially available
anatase-structured TiO2. In contrast, the rutile-structured anodic oxides preparedin 1.2 M sulfuric acid aqueous solution exhibited photocatalytic activity whenilluminated with visible light.

7

40
30
20
10

360

0

400

Wa
440
vel
eng
480
th
520
/n
m
FIG.9

0.1
M
0.0
2M

MB degradatio
n50

rate / %

60

com
me
1.2
rcia
M
l

The wavelength dependence of MB degradation rate of the anodized TiO2 in 0.02 M,
0.1 M, 1.2 M sulfuric acid and commercially available TiO2.

Figure 10 summarizes the yield of CO2 by acetaldehyde decomposition
under visible light illumination with a wavelength longer than 400 nm and 422 nm
for 1 h [10]. It is explicit that the oxide anodized in an electrolyte of a sulfuric acidconcentration of 1.2 M records the highest yield irrespective of the wavelength of
the illuminated light among the investigated samples.

CO2 evolved / micro mol

10> 400 nm
> 420 nm

8
6
4
2
0
0.02M

FIG.10

0.1 M

1.2M

commercial

blank

Yield of CO2 in the photocatalytic decomposition of acetaldehyde under visible lightillumination with a wavelength longer than 400 nm and 422 nm for 1 h.

3.6 Hydrophilicity
Figure 11 shows the plots of the contact angle against the duration of UV
illumination for the anodic oxide; as-anodized (a) and annealed (b). The contact
angle of the oxide prepared in an electrolyte with a high sulfuric acidconcentration is lower than that in an electrolyte with a low sulfuric acid8

concentration, regardless of the duration of UV light illumination before
annealing. In the annealed anodic oxides, it should be noted that in the absenceof UV light illumination, the contact angle of the oxide prepared in an electrolytewith a high sulfuric acid concentration is quite low.
(b)

(a)
60

60

0.02 M
0.1 M
0.2 M
0.4 M
1.2 M
1.6 M

50
40
30

FIG.11

40
30

20

20

10

10

0

0.0

0.5

1.0

1.5

2.0

2.5

0.02 M
0.1 M
0.2 M
0.4 M
1.2 M
1.6 M

50

0

3.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Plots of the contact angle against the duration of UV illumination for the oxide;
as-anodized (a) and annealed (b).

Figure 12 shows the images of a water droplet with a drop size of 400-pL
before (a) and 5 ms after (b) being dropped on the surface of the oxide preparedin 1.2M sulfuric acid [5]. The change in the volume of the water droplet is plottedagainst the elapsed time (c). The change in the volume of a 180-pL water droplet
dropped on the surface of the oxide prepared in 0.1M sulfuric acid is used as the

(b)

(a)

400

0.1M H2SO4
1.2M H2SO4

(c)

300
200
100
0

FIG.121

10100

Images of the 400-pL water droplet before (a) and 5 ms after (b) being dropped on thesurface of the oxide prepared in 1.2M sulfuric acid, and the change in the volume of the droplet
against the elapsed time (c).

9reference. The 400-pL water droplet is perfectly spread across the surface within
1 ms, and the water contact angle becomes zero. This is an extremelyinteresting phenomenon because the water droplet is spread across the surface
at a rather high speed and it occurs in the absence of UV light illumination.
4. Consideration
4.1 Visible light response
The visible light response of TiO2 photocatalyst is attributed to the electronic
structure, and band gap narrowing is required to improve the property. The firstprinciple calculation predicted a priority of anion ion doping such as nitrogen andsulfur [11], and the validity of nitrogen doping was reported [12-16]. Figure 13
illustrates the band gap structure of TiO2 with doping [17]. The visible light
response arises from occupied N 2p localized states located above the valenceband edge with interstitial N 2p states lying further up from the valence band.
The presence of localized states near the valence band edge has been said to
be at the origin of the visible-light activity of anion-doped TiO2. On the other hand,cation or defect-derived states at 2.0-2.5 eV above the valence band results innarrowing the band gap. However, this lower the oxidizing power and cation
could be a recombination site. Therefore, the left side design in Figure 13 isrecommended to achieve visible light response.

Metal ion dopingor oxygen-deficit TiO2

TiO2-xNx

Conduction band
H2/H2O

Decrease ofoxidizing power !
Impurity or defectstate

3.2 eVO2/H2O
Mixed orbital by
Oxygen and nitrogen

Valence band

Recombination site !

FIG. 13 Band gap structure of TiO2 on doping it with nonmetals.

The present anodic oxide shows visible light response, and it is considered tobe due to the modification of band gap structure by sulfur doping provided fromthe sulfuric acid in the electrolyte. Sulfur was detected from the anodic oxide by
XPS analysis as shown in Figure 14(a), and sulfur existed over the oxide with
10

(b)

(a)
0.5

0.6

0.4

0.3

0

0.2

100

120

0.1

0.2

0.0
-180

0s
20 s (16.4 nm)
40 s (32.8 nm)
60 s (49.2 nm)
80 s (65.6 nm)

0.4

d{E･N(E)}/dE

0.8

S 2p

0.04 M H2SO4
0.1 M H2SO4
1.2 M H2SO4

Peak hight ratio S/Ti

Intensity (Normalized)

1.0

-175

-170

-165

-160

140

160

180

200

Kinetic energy / eV

0.0
0

100

200

300

400

500

600

Sputtering time / s

Binding energy (eV)FIG.14 S 2p XPS of the anodized TiO2 (a) and a plot of the peak height ratio of sulfur (152 eV) totitanium (418 eV) during sputtering for the oxide anodized in an electrolyte of 1.2 M sulfuric acid(b). (AES spectra of before and after sputtering for 20, 40, 60, and 80 s are inserted in (b))

segregation near the surface as shown in Figure 14(b). The amount of sulfur
was analyzed by measuring SO2 [7] extracted from the oxide during combustionin high frequency furnace, and the result is shown in Figure 15 [7]. Assumingthat density of TiO2 is 4.23 g/cm3 and the thickness of the layer is fixed as thevalue determined by cross-section TEM observation, the sulfur concentration in
the oxide could be calculated; 1.83 at.%, 1.50 at. %, 0.73 at. %, 0.38 at. %, 0.36
at. %, and 0.17 at. % for the oxides anodized in an electrolyte of a sulfuric acidconcentration of 0.002 M, 0.02 M, 0.1 M, 0.2 M, 0.4 M and 1.2 M, respectively.
Thus, the sulfur concentration in the oxide decreases with sulfuric acidconcentration in the electrolyte.
3.5

Analyzed sulfur / µg

3.0
2.5
2.0
1.5
1.0

averageraw data

0.5
0.0

0.0

0.5

1.0

1.5

Sulfuric acid concentration / M

FIG. 15 Plots of the analyzed sulfur content against the sulfuric acid concentration in theelectrolyte.

11According to theoretical calculation[11], sulfur doping is difficult as comparedwith nitrogen doping, because large formation energies is required for sulfur
doping to substitute sulfur for oxygen in TiO2. Several studies to fabricate
sulfur-doped photocatalytic oxide have been reported; oxidation of TiS2 powder[18], sol–gel techniques using thiourea [19] and ion-implantation [20]. Distinct
difference between the present oxide and references is a form of TiO2; thepresent oxide is rutile, whereas the reference oxide is anatase. Calculation of theelectronic band structure focusing on crystal structure and site occupation of
sulfur is in progress by using first-principle method.
4.2 Superhydrophilicity
The present results show that the contact angle of the oxide prepared in anelectrolyte with a high sulfuric acid concentration is lower than that with a low
sulfuric acid concentration and is quite low in the absence of UV light illumination.
As revealed in Figure 6, the former anodic oxide could adsorb a large amount ofwater molecules as compared to the latter oxide. Figure 16 shows O 1s XPS
spectra of the as-anodized (left) and annealed (right) oxides prepared in anelectrolyte of 1.2 M sulfuric acid concentration for the following conditions:
before illumination (a), exposure to oxygen (0.5 kPa) for 5 min under UV
illumination (b), UV illumination for 30 min in the analysis chamber (c), andexposure to air (1.05 kPa) for 1 h followed by UV illumination in the analysis
chamber (d) [4]. All the oxides show an asymmetric O 1s XPS due to theadsorption of water molecules, and the intensity of the shoulder peak in the
O 1s

20000

Intensity / arbitary units

Intensity / arbitary units

12000

hydroxyl groupor molecular water
9000

(d)
6000

(c)
(b)

3000

hydroxyl groupor molecular water
O 1s

15000

(d)
10000

(c)
(b)

5000

(a)

(a)

0

0
540

535

530

525

520

540

535

530

525

520

Binding energy / eV

Binding energy / eV

FIG. 16 O 1s XPS spectra of the as-anodized (left) and annealed (right) oxides: before
illumination (a), exposure to oxygen (0.5 kPa) for 5 min under UV illumination (b), UV illuminationfor 30 min in the analysis chamber (c), and exposure to air (1.05 kPa) for 1 h followed by UV
illumination in the analysis chamber (d).

12annealed oxide is higher than that in the as-anodized oxide regardless of the
exposure and UV illumination. No difference was observed with regard to theintensity of the shoulder peak among the O 1s XPS of the as-anodized oxide,
while the spectrum of the annealed oxide varies upon exposure and UV
illumination treatment. These results imply that the annealed oxide interacts
strongly with the hydroxyl groups.
The mechanism of superhydrophilicity is proposed based on a newly formed
oxygen defect by Sakai et al [21]. In this model, the oxygen defect is formed after
the surface oxygen traps two holes generated by the photocatalysis reaction.
Water molecule adsorbs on this oxygen defect, and the water droplet spreads on
the surface of the oxide. In this model, oxygen defects are required forsuperhydrophilicity under UV illumination. According to this proposed model,
holes should be generated under visible light illumination in the present oxide.
However, a generation of oxygen vacancy was not verified in the anodic oxidefrom Ti 2p XPS as shown in Fig. 5, the symmetrical shape of the Ti 2p XPS
spectrum suggests that reduced Ti3+ ions are not present in the oxides. Further
studies to explain the results in the current study have been in progress.
5. Conclusions
The photo-induced characteristics and adhesion strength of TiO2 prepared byanodic oxidation are investigated. With an increase of sulfuric acid concentrationin the electrolyte, the predominant phase converts from anatase to rutile. The
crystallite size of rutile is constant at approximately 30 nm, and theinhomogeneous lattice strain is quite small or close to zero. The surface area
increases due to the appearance of nano-sized pores in the oxide with anincrease in the concentration of sulfuric acid in the electrolyte. Adhesion strengthof the anodic oxide from the substrate increased with an increase of sulfuric acidin the electrolyte, which is benefit for durability in application. The contact angles
of rutile-structured TiO2 anodized in an electrolyte with a high concentration of
sulfuric acid is almost zero in the absence of UV light illumination. XPS analysis
revealed that the oxide interacts strongly with the hydroxyl groups. The
photocatalytic activity is improved with an increase in the concentration of
sulfuric acid and rutile exhibits better characteristics as compared to anatase.
Moreover, rutile-structured TiO2 degraded MB aqueous solution and yielded CO2
by decomposing acetaldehyde under visible light illumination, in which thewavelengths of the illuminated light is longer than those corresponding to the13band gap of monolithic rutile TiO2. This is attributable to a modification of the
band-gap structure of the oxide by sulfur doping.
Acknowledgements
The authors wish to thank Prof. Hanada, Prof. Oku, Prof. Suzuki, Dr. Semboshi
from Tohoku Univ., Dr. Ohtsu from Kitami Institute of Technology, Prof. Saito fromWaseda Univ. and Prof. Maeda, Prof. Nishimura and Dr. Okitsu from Osaka
Prefecture Univ. for their valuable discussions and encouragement for the
pursuance of this study. The authors wish to acknowledge Ms. Matsuda and Mr.
Sugiyama from IMR, Tohoku Univ. for sample preparations, Dr. Ashino and Mr.
Sakamoto from IMR, Tohoku Univ. for chemical analysis, Mr. Murakami from IMR,
Tohoku Univ. for AES experiments, Mr. Yamane from Kitami Institute ofTechnology for XPS experiments, and Mr. Ozawa and Dr. Moroishi from Tig. Co.
Ltd. This study was partly supported by a Grant-in-Aid for Scientific Research (A)(No.17206070) from the Ministry of Education, Culture, Sports, Science, andTechnology, Japan.

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Remarks
Part of this study was achieved by collaboration research project with plural
private companies, and several patents concerning the current results havebeen applied.
Contact toNaoya Masahashi
Institute for Materials Research, Tohoku University
e-mail: masahasi@imr.tohoku.ac.jp
Yoshiteru Mizukoshi
Institute for Materials Research, Tohoku University
e-mail: mizukosi@imr.tohoku.ac.jp15