Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h Vo lume 3, Issue 2 , Fe bruary -2012 1
ISSN 2229-5518
Spin-coated YSZ Thin Films on Silica Substrate Shirley Tiong Palisoc, Rose Ann Tegio, Michelle Natividad, Simon Gerard Mendiola, Kevin Kaw, Stephen Tadios, Benjamin Tu a- son
Abs tract— Diff erent concentrations of yttria stabilized zirconia (YSZ) grow n on silia (SiO2) substrate w as investiaged in this paper. Suspension containing 10w t%, 30w t%, and 50w t% YSZ w ere f abricated using the spin coating technique on silica keeping all othe r parameters constant such as the coating parameters and sintering temperature.The surf ace morphology and thickness of the f ilms w ere investigated using scanning electron microscopy (SEM). Results show ed porous YSZ f ilms w hich become less porous as the concen tration of YSZ increases. The thickness of the f ilms w as also aff ected by the YSZ concentration. As the concentration increases, the thickness of the f ilms also increases. The crystal structure of the f avricated f ilms w as also determined using X-Ray Diffraction (XRD) and Raman Spectroscopy. Both Techniques revealed a cubic f luorite structure independent of the concentration of YSZ.
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Ith a 1.2% annual growth rate of world population, the total consumption of marketed energy is expected to rise by 44% from 2006 – 2030 due to the increasing de-
mand for energy services making way for other power genera-
tion technologies to arise [1], [2]. However environmental con-
cers should also be considered. Technology, therefore, should be able to meet the dwemands of the growing population with lwess environmental impact and more efficient use of vital energy resources. One such energy source is solid oxide fuel cell (SOFC) [3]. A solix oxide fuel cell is an electrochemical device that convers chemical energy into electrical energy [4]. Much development is focused now on SOFCs because of its high efficiency in converting a wide variety of fuels. It is also environment friendly with low emissions of NOx and dust and since it has no moving parts and the cells are non -vibrating, noise is also eliminated [5].
Yttria stabilized zirconia (YSZ) is usually used as the electro- lyte of SOFCs because of its ion conductivity, mechanical stabili- ty and good chemical compatibility. However, at operating temperatures below 800°C, the conductivity of YSZ is not high enough to lessen the resistive losses. To solve the problem, it is desirable to fabricate either thinner (<5.0 µm) or more conduc- tive films generating a power density of 400mW/cm2 to 1500 mW/cm2 [6].
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Shirley Tiong Palisoc Ph.D. In Materials Science is a professor at the D e- partment of Physics, De La Salle University – Manila, Philippines.
E-mail: shirley.palisoc@dlsu.edu.ph
Rose Ann Tegio is a junior officer at PNB – Manila, Philippines.
E-mail: michelle.natividad@dlsu.edu.ph
Michelle Natividad Ph.D. in Physics is an assistant professor at the D e-
partment of Physics, De La Salle University – Manila, Philippines.
Simon Gerard Mendiola is a test engineer at Hitachi Philippines.
Kevin Kaw is a senior student at De La Salle University – Manila, Philip-
pines. E-mail: kevinkaw08@yahoo.com
Stephen Tadios is a senior student at De La Salle University – Manila,
Philippines. E-mail: stephentadios@yahoo.com
Benjamin Tuason is a senior student at De La Salle University – Manila,
Philippines. E-Mail: benjamintuason@yahoo.com
Previous Studies have reported several techniques in fabricat- ing YSZ thin films [7], [8], [9], [10]. In this study, spin coating technique is utilized because of the simplicity of its operational costs as compared to the other techniques mentioned. This study also seeks to determine the optimal condition in fabri cat- ing the films by varying the YSZ concentration and the type of substrate.
Different concentrations of YSZ namely 10wt%, 30wt%, and
50wt% are used to produce thin films on silica (SiO2). The YSZ concentration is varied to provide baseline information on how the sample behaves within such concentration range. The sa m- ple films are characterized in terms of their surface morphology and thickness through Scanning Electron Microscopy, crystal structure though X-Ray Diffraction, and Raman Spectra though Raman Spectroscopy.
Commercial yttria stabilized zirconia (YSZ8-U1, fuelcell- materials.com) and ethanol (95% ethyl alcohol, Aced Labora- tory) with wiegth rations of 10 YSZ:90ethanol, 30YSZ:70ethanol and
50YSZ:50ethanol were mixed to form a suspension. To ensure the consistency of the suspension, a Sonucator Ultrasonic Proces-
sor (Misonix) was used. The suspension was mixed for three hours with 60% output amplitude/instensity. It was then d e- posited on the substrate usin g the Spincoat G3P-8 spin coater. The substrate with YSZ layer was baked in a furnace (Thermo- lyne type 48000) at a temperature of 300 °C for three minutes until all of the solvent evaporates. In this paper, the substrate was only coated once with the YSZ suspension. The substrate with the YSZ layer was then sintered at 650 °C for four hours in the furnace.
Using Scanning Electron Microscopy (SEM)(Jeol 5310), the surface morphology and the thickness of the films were inves- tigated. The crystal structure of the fabricated films was de- termined using X’Pert PRO Pananalytical X -Ray Diffractome- ter (XRD) with a CuK-α radiation. Raman Spectroscopy was also utilized in this study. R3000 Raman spectrometer with
785nm laser was used to acquire the Raman spectra of the
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Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h Vo lume 3, Issue 2, Fe bruary -2012 2
ISSN 2229-5518
films. Based on the Raman spectrum, the crystal structure of the sample was obtained and was compared to the XRD result.
Shown in Fig. 1 are the SEM images of the surface of the films fabricated on Silica substrate using three different con- centrations of YSZ namely 10wt%, 30wt%, and 50wt%. Poros i- ty of the films was evident based on the results. The film with
10wt% YSZ was highly porous that only a fre parts of the su b-
strate were covered with YSZ (lighter portions in the image correspond to YSZ while the darker portions correspond to the substrate). As the concentration of YSZ increases *30wt% and then 50wt%), more parts of the substrate were being coated which means that the pores were getting smaller. The porosity of the films is due to the fact that YSZ poweders do not dissolve in ethanol. The function of ethan ol as the suspen- sion medium is to suspend and disperse the particles, not to dissolve them.
s 
Fig. 1 SEM images of the surface of the films with different concentrations of YSZ on Silica Substrate
Fig. 2 shows the SEM images of the films fabricated on Sili- ca showing the film thickness. Thickness of 0.764 µm (average thickness), 0.983µm, and 2.47µm were achieved for films with
10wt%, 30wt%, and 50wt% YSZ respectively. It is seen that, as
the concentration of YSZ increases, the thickness of the film also increases which indicates that film thickness was directly proportional to the concentration of YSZ. The effecto f cutting was clearly shown especially in Fig. 2b wherein some parts were raised and others were adhered to the substrate.
Fig. 2 SEM images showing the thickness of the films with (a)
10wt% YSZ, (b) 30wt% YSZ, (c) 50wt% YSZ fabricated on Sili-
ca.
Listed in Table 1 are the film thicknesses of the different concentrations. Since the suspension with 10wt% YSZ was runny or less viscous, it was easily spun out of the substrate thus, making the film thinner. On the other hand, the suspen- sion with 50wt% YSZ id very viscous thus was not easily spun out of the substrate during spin coating process making the film thicker.
Table 1
Thickness of Films (in µm)
The crystal structure of fabricated YSZ thin films was de- termined by x-ray diffraction. Fig. 3 shows the x-ray diffrac- tion patter for 10wt% YSZ film fabricated on silica substrate. In X-Ray Diffraction technique, the position of the peaks indi- cates the crystal structure of the material while the intensity of the peaks depends on the material distribution in the s tructure [11]. Therefore, in determining the crystal structure of YSZ films, the focus is on the peak position. The peaks observed (30.17°, 34.97°, 50.17°, 59.71°, and 62.69°) are comparable to the XRD results obtained in the study conducted by Priyatham and Bauri [12] which signifies that the 10wt% YSZ film fabri- cated on Silica substrate aslo has a cubic fluorite structure. The XRD results of films with 30wt% and 50wt% YSZ were not anymore presented since the material used (YSZ) was the same for all concentrations and thus, will generate the same XRD pattern.
X-Ray Diffraction analysis revealed that the sample
films obtained in this study, exhibit a cubic fluorite structure.
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Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h Vo lume 3, Issue 2, Fe bruary -2012 3
ISSN 2229-5518
Fig.3 XRD patterns of films with 10wt% YSZ fa bricated on
Silica Substrate
To verify XRD results, another test was done which was the Raman spectroscopy. The attained Raman spectra were com- pared to the results obtained by Ghosh et.al. [15] and Cheng and Liu [16]. Shown in Fig. 4 are the Raman Spectra of the films containing 10wt%, 30wt%, and 50wt% YSZ fabricated on silica substrates respectively with the characteristic peaks (enricled peaks) for cubic fluorite YSZ.
From the Raman spectra of films, it is observed in Fig. 5 and
Table 2 that the intensity of the peaks increases with ncreaseing concentration of YSZ, in agreement with Umback
and Hines [17].
Fig. 5 Width to height ratio of Raman peaks of 10wt%,
30wt%, and 50wt% YSZ films fabricated on Silica substrate
Table 2
With to height ratios of Raman peaks of 10wt%, 30wt%, and
50wt% YSZ films on silica substrate
Fig. 4 Raman spectras of films with (a) 10wt% (b) 30wt% (c)
50wt% YSZ fabricated on Silica substrate
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Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h Vo lume 3, Issue 2, Fe bruary -2012 4
ISSN 2229-5518
SEM images of the surface of the fabricated films showed that the films are porous. The porosity depends on the concen- tration of YSZ used in fabricating the films. Greater concentra- tion means more amount of YSZ that can cover up the pores and thereby lessening the porosity of the films.
Viscosity of the suspension used was the main factor in de-
termining the thickness of the films. Films with 10wt% YSZ are relatively thinner compared to the films with 30wt% YSZ and much thinner as compared to films with 50wt% YSZ.
X-Ray Diffraction patterns show that crystal structure of the fabricated thin film is cubic fluorute which coincides with the result obtained by Priyatham and Bauri [12]. A cubic flu o- rite structure indicates that the films are stable. The intensity of the peaks gets higher as the concentration of YSZ gets larg- er.
study‖, Materials Letters, 60, pp. 1170-1173, 2006
[16] Z. Cheng and M. Liu, ―Characterization of sulphur poisoning of Ni- YSZ anodes for solid oxide fuel cells using in situ Raman microspec- troscopy‖, Solid State Ionics, 178, pp. 925 -935, 2007
[17] C.C. Umback and M.A. Hines, ―Applications of Raman Spectrosco-
py‖,http://www.ccmr.cornell.edu/igert/modular/docs/Appl_of_R
aman_Spectroscopy, 2009
Similar results were observed from the Raman patters of the fabricated films. The intensity of the peaks get higher as the concentration of YSZ increases. Raman spectra of the films obtained in this study contain the characteristic peaks of cubic fluorite structure YSZ which agree with the results obtained by Ghosh et.al. and Cheng and Liu [16]. Raman spectra of the films above 1000cm-1 were also observed in this study.
[1] Statistics Division of the Department of Economic and Social Affairs of the United Nations Secretariat, Population and Vital Statistics Report,
2009, Series A61 (2)
[2] Energy Information Administration, International Energy Outlook
2009, pp. 17, 2009
[3] A. Boudghene Stambouli and E. Traversa, ―Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy‖, Renewable and Sustainable Energy Reviews, 6(5), pp. 433-455,
2002
[4] S. C. Singhal, ―Zirconia Electrolyte-based Solid Oxude Fuel Cells‖,
Encyclopedia of Materials: Science and Tehcnology , pp. 9898-9902, 2001
[5] X. Xu, S. Huang, and D. Peng, ―YSZ thin films deposited by spin- coating for IT-SOFCs‖, Ceramics International, 31, pp. 1061-1064, 2005
[6] K. Chen et al., ―Fabrication and performance of anode-supported
YSZ films by slurry spin coating‖, Solid State Ionics, 177, pp.3455-
3460, 2007
[7] Z. Ogumi et al., ―Preparation of thin yttria -stablized zirconia films by
vapor phase electrolytic deposition‖, Solid State Ionics, 58(3-4), pp.
345-350, 1992
[8] G. Laukaitis et al., ―YSZ thin films deposited by e-beam technique‖,
Thin Solid Film, 515(2), pp. 678-682, 2006
[9] M.F. Garcia-Sanchez et al., ―Nanostructured YSZ thin films for solid oxide fuel cells deposited by ultrasonic spray pyrolysis‖, Solid State Ionic, 179 (7-8), pp. 243-249, 2008
[10] B. Hobein et al., ―DC Sputtering of yttria-stabilized zirconia films for
solid oxide fuel cell applications‖, Journal of the European Ceramic So- ciety, 21 (10-11), pp. 1843-1846, 2001
[11] J.R. Connolly, ―Introduction Quantitative X-Ray Diffraction Me-
thods‖, 2010
[12] T. Priyatham and R. Bauri, ―Synthesis and characterization of nano- crystalline Ni-YSZ cermet anode for SOFC‖, 61, pp. 54-58, 2010
[15] A. Ghosh et al., ―Nanocrystalline zirconia -yttria system-a Raman
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