Photo response of silver-TiO2 filma) M. A. J. Viernes, C. L. S. Mahinay, M. M. S. Villamayor, and H. J. Ramos Citation: Review of Scientific Instruments 85, 02C318 (2014); doi: 10.1063/1.4862206 View online: http://dx.doi.org/10.1063/1.4862206 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/85/2?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Optical properties of hierarchical-nanostructured TiO2 and its time-dependent photo-degradation of gaseous acetaldehyde Appl. Phys. Lett. 103, 261903 (2013); 10.1063/1.4857936 High quality transparent TiO2/Ag/TiO2 composite electrode films deposited on flexible substrate at room temperature by sputtering APL Mat. 1, 012102 (2013); 10.1063/1.4808438 Enhancement of optical absorption by modulation of the oxygen flow of TiO2 films deposited by reactive sputtering J. Appl. Phys. 111, 113513 (2012); 10.1063/1.4724334 Optical near-field induced visible response photoelectrochemical water splitting on nanorod TiO2 Appl. Phys. Lett. 99, 213105 (2011); 10.1063/1.3663632 Study of photocatalytic activity of TiO 2 thin films prepared in various Ar ∕ O 2 ratio and sputtering gas pressure J. Vac. Sci. Technol. A 25, 912 (2007); 10.1116/1.2717194
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REVIEW OF SCIENTIFIC INSTRUMENTS 85, 02C318 (2014)
Photo response of silver-TiO2 filma) M. A. J. Viernes, C. L. S. Mahinay,b) M. M. S. Villamayor, and H. J. Ramos National Institute of Physics, University of the Philippines, Diliman, Quezon City 1101, Philippines
(Presented 10 September 2013; received 9 September 2013; accepted 23 December 2013; published online 11 February 2014) Silver and TiO2 films were deposited on glass substrates via the plasma sputter type negative ion source and a compact planar magnetron, respectively. A silver target was biased and is sputtered by argon plasma for 30 min. TiO2 was deposited by sputtering a titanium disk and introducing oxygen in a 1:13 ratio with argon plasma for 2 h. The resulting composite films (silver on TiO2 and TiO2 on silver) were analyzed by its transmissivity in the UV-VIS region showing increased optical absorbance. The synthesized films were used in the photocatalytic degradation of methylene blue showing an increase in photocatalytic degradation when only TiO2 is used. The introduction of silver with TiO2 inhibited the effective photocatalytic degradation of methylene blue. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4862206] I. INTRODUCTION
Titanium dioxide is photo-catalytic under ultraviolet light.1, 2 Its photo-catalytic efficiency can be increased under visible and ultraviolet light when doped with metal oxides.3 Silver is currently one of the popularly studied metals since it occurs naturally in its pure form. Furthermore, it is the element with the highest electrical conductivity and the metal that has highest thermal conductivity, hence a good candidate as dopant to TiO2 . In this study, a plasma sputter-type negative ion source (PSTNIS) was used to deposit thin film of silver on glass and was doped with TiO2 using a compact planar magnetron. The photo-catalysis of titanium dioxide films doped with silver was analysed. II. EXPERIMENT DETAILS
Fig. 1 shows a schematic diagram of the PSTNIS. Silver atoms are sputtered from the metal target by bombardment of argon ions. A percentage of the sputtered silver atoms captures an electron from the plasma environment or from the target surface and are then repelled by the metal target bias. The negative silver ions then travel towards the sample substrate with energies approximately equal to the target potential. The details of the machine, plasma production, and negative ion production are described in Refs. 4–6. The chamber was evacuated to a base pressure of 3 × 10−5 Torr before plasma production and kept at 1 × 10−3 Torr during operation. The target potentials used were Vt = −200 V, −500 V, and −700 V. Increasing the target potentials will yield higher ion production and energies. The processing time is at 30 min with a plasma discharge current and voltage of 1.0 A and 6.0 V, respectively. The substrates are soda-lime glass slides that are cut into three. Before deposition, they a) Contributed paper, published as part of the Proceedings of the 15th Interna-
tional Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
[email protected] 0034-6748/2014/85(2)/02C318/3/$30.00
were cleansed using ethanol and discharge cleaning using argon plasma. A schematic diagram of Compact Planar Magnetron (CPM) is shown in Fig. 2. The CPM is used to deposit the TiO2 . In the CPM, a doughnut shaped plasma is produced by a combination of an annular (OD 50 mm and ID 30 mm) and cylindrical (10 mm) magnets which are both 10 mm thick and it has about 11–12 kG on the surface that enhances the sputtering of the titanium disk placed at the anode which is biased between −340 V to −390 V. The plasma current is maintained at 15 mA. The base pressure is at 7 × 10−5 Torr and the filling pressure is at 1.2 × 10−2 Torr. Reactive oxygen gas is mixed with argon at a 1:13 mass flow ratio which is then fed into the system for the 2 h deposition. The synthesized silver and silver-TiO2 films on the glass substrates were characterized by X-ray diffraction (XRD). The transmittance of each sample versus its wavelength was analyzed using UV-VIS spectroscopy. To show the photocatalytic effect of silver-TiO2 films, the synthesized films were used for the photocatalytic degradation of methylene blue. Each synthesized film was immersed in a 5 ml concentrated methylene blue solution. The solution with the sample is then subjected to a fluorescent lamp (Omni, 5 W) for 39 h each. The absorbance at UV-VIS region of methylene blue was measured using UV-VIS spectroscopy.
III. RESULTS AND DISCUSSION
Confirming the presence of silver deposits was done by using XRD spectroscopy, which is shown in Figs. 3–5. The characteristic peaks are then compared to the XRD pattern of the silver target from Malapit et al.6 The peaks, shown in Fig. 3, indicate the presence of crystalline silver deposited on the glass substrate. The broad peak is a characteristic of an amorphous structure, which is exhibited by the TiO2 , while sharp peaks are a characteristic of a crystalline structure, which is exhibited by the silver peaks. Introducing TiO2 with silver will affect the lattice parameters causing residual stress
85, 02C318-1
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FIG. 1. A schematic diagram of the plasma sputter-type negative ion source.
FIG. 5. Intensity versus 2θ of silver and TiO2 doped films (silver on the outer surface) on glass substrate using x-ray diffraction spectroscopy. The broad peak represents the amorphous TiO2 (a-TiO2 ).
FIG. 2. A schematic diagram of the compact planar magnetron.
FIG. 3. Intensity versus 2θ using x-ray diffraction spectroscopy of silver films on glass substrate.
FIG. 4. Intensity versus 2θ using x-ray diffraction spectroscopy of silver and TiO2 doped films (TiO2 on the outer surface) on glass substrate.
FIG. 6. Images of the samples for (a) −200 V Ag, (b) −500 V Ag, (c) −700 V Ag, (d) −200 V Ag + TiO2 , (e) −500 V Ag + TiO2 , and (f) −700 V Ag + TiO2 . The opacity of the silver on glass is reduced after TiO2 deposition.
FIG. 7. (a) SEM image at 90× magnification of the silver film deposited at −500 V target voltage and with microparticles, and (b) at 230× magnification with silver deposited using −700 V target bias and TiO2 .
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degradation. Introducing silver though, lowers the photocatalytic degradation. However, when comparing the absorbance of −200Vt Ag + TiO2 and −700Vt Ag + TiO2 , an increase in the amount of silver decreases the absorbance of the methylene blue solution, as seen in Fig. 9. Increasing the amount of silver might exhibit an increase in degradation of the methylene blue solution. IV. CONCLUSION
FIG. 8. Percent transmittance versus wavelength of six samples using UVVIS spectroscope where TiO2 has TiO2 deposit; −200, −500, −700 Ag has Ag deposit biased at −200 Vt, −500 Vt, and −700 Vt, respectively; TiO2 +Ag has TiO2 and Ag deposit (Ag on the outer surface); and Ag + TiO2 has TiO2 and Ag deposit (TiO2 on the outer surface).
thus there is a shift in the XRD pattern7 as can be seen from the Ag (220) peak. The transmittance versus wavelength of each sample is shown in Fig. 8. As the target voltage increases for the samples with the silver deposit, the transmittance decreases also. This is maybe due to the increasing amount of silver film that increases the opacity of the sample, as seen in Figs. 6 and 7. From the measurement of optical absorbance of the methylene blue solution, as seen in Fig. 8, the sample with TiO2 only exhibits the lowest absorbance; meaning the methylene blue had a higher degradation when TiO2 is introduced thus it also shows the highest photocatalytic
Silver was successfully doped on TiO2 using plasma sputter-type negative ion source and compact planar magnetron as confirmed by XRD analysis. The optical absorbance property of the metal doped film was analyzed by UVVIS spectroscopy. Introducing a layer of silver significantly decreases the transmittance. Photocatalytic degradation of methylene blue was also used to exhibit the photocatalytic effect of the introduced dopants. It showed that with TiO2 only, there is an increase in the photocatalytic degradation. When silver is introduced, photocatalytic degradation decreases, however an increase in amount of silver with TiO2 increases its photocatalytic activity. ACKNOWLEDGMENTS
We would like to acknowledge the support of the bilateral research agreement of Japan Society for the Promotion of Science (JSPS) and the Philippines’ Department of Science and Technology (DOST). We would also like to thank the help of the following: Mae S. Villamayor Venice Mascariñas, Giovanni Malapit, and the Department of Chemical Engineering in the University of the Philippines, Diliman. We would also like to thank Mae S. Villamayor for the tremendous amount of time and effort she contributed to fulfill this research paper. 1 A.
FIG. 9. Absorbance against wavelength of −200 Vt Ag + TiO2 , −700 Vt Ag + TiO2 , and TiO2 degraded methylene blue.
Fujishima, “Discovery and applications of photocatalysis—Creating a comfortable future by making use of light energy,” Japan Nanonet Bulletin Issue 44, 12 May 2005. 2 A. Fujishima and K. Honda, Nature (London) 238(5358), 37 (1972). 3 M. E. Kurtoglu, T. Longenbach, and Y. Gogotski, Int. J. Appl. Glass Sci. 2(2), 108 (2011). 4 G. D. Alton, Y. Mori, A. Takagi, A. Ueno, and S. Fukumoto, Rev. Sci. Instrum. 61, 372 (1990). 5 G. M. Malapit, C. L. S. Mahinay, M. D. Poral, and H. J. Ramos, Rev. Sci. Instrum. 83, 02B704 (2012). 6 G. M. Malapit, J. I. L. Bugante, C. L. S. Mahinay, M. Wada, and H. J. Ramos, in Proceedings of the 12th APPC, Makuhari, Japan, 14–19 July 2013 (JPS Conf. Proc., 2013), p. 157, see http://www.jps.or.jp/APPC12/ index.html. 7 Progress in Inorganic Chemistry, edited by K. D. Karlin (Wiley, 2005), Vol. 54, pp. 47–126.
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REVIEW OF SCIENTIFIC INSTRUMENTS 85, 02C318 (2014)
Photo response of silver-TiO2 filma) M. A. J. Viernes, C. L. S. Mahinay,b) M. M. S. Villamayor, and H. J. Ramos National Institute of Physics, University of the Philippines, Diliman, Quezon City 1101, Philippines
(Presented 10 September 2013; received 9 September 2013; accepted 23 December 2013; published online 11 February 2014) Silver and TiO2 films were deposited on glass substrates via the plasma sputter type negative ion source and a compact planar magnetron, respectively. A silver target was biased and is sputtered by argon plasma for 30 min. TiO2 was deposited by sputtering a titanium disk and introducing oxygen in a 1:13 ratio with argon plasma for 2 h. The resulting composite films (silver on TiO2 and TiO2 on silver) were analyzed by its transmissivity in the UV-VIS region showing increased optical absorbance. The synthesized films were used in the photocatalytic degradation of methylene blue showing an increase in photocatalytic degradation when only TiO2 is used. The introduction of silver with TiO2 inhibited the effective photocatalytic degradation of methylene blue. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4862206] I. INTRODUCTION
Titanium dioxide is photo-catalytic under ultraviolet light.1, 2 Its photo-catalytic efficiency can be increased under visible and ultraviolet light when doped with metal oxides.3 Silver is currently one of the popularly studied metals since it occurs naturally in its pure form. Furthermore, it is the element with the highest electrical conductivity and the metal that has highest thermal conductivity, hence a good candidate as dopant to TiO2 . In this study, a plasma sputter-type negative ion source (PSTNIS) was used to deposit thin film of silver on glass and was doped with TiO2 using a compact planar magnetron. The photo-catalysis of titanium dioxide films doped with silver was analysed. II. EXPERIMENT DETAILS
Fig. 1 shows a schematic diagram of the PSTNIS. Silver atoms are sputtered from the metal target by bombardment of argon ions. A percentage of the sputtered silver atoms captures an electron from the plasma environment or from the target surface and are then repelled by the metal target bias. The negative silver ions then travel towards the sample substrate with energies approximately equal to the target potential. The details of the machine, plasma production, and negative ion production are described in Refs. 4–6. The chamber was evacuated to a base pressure of 3 × 10−5 Torr before plasma production and kept at 1 × 10−3 Torr during operation. The target potentials used were Vt = −200 V, −500 V, and −700 V. Increasing the target potentials will yield higher ion production and energies. The processing time is at 30 min with a plasma discharge current and voltage of 1.0 A and 6.0 V, respectively. The substrates are soda-lime glass slides that are cut into three. Before deposition, they a) Contributed paper, published as part of the Proceedings of the 15th Interna-
tional Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
[email protected] 0034-6748/2014/85(2)/02C318/3/$30.00
were cleansed using ethanol and discharge cleaning using argon plasma. A schematic diagram of Compact Planar Magnetron (CPM) is shown in Fig. 2. The CPM is used to deposit the TiO2 . In the CPM, a doughnut shaped plasma is produced by a combination of an annular (OD 50 mm and ID 30 mm) and cylindrical (10 mm) magnets which are both 10 mm thick and it has about 11–12 kG on the surface that enhances the sputtering of the titanium disk placed at the anode which is biased between −340 V to −390 V. The plasma current is maintained at 15 mA. The base pressure is at 7 × 10−5 Torr and the filling pressure is at 1.2 × 10−2 Torr. Reactive oxygen gas is mixed with argon at a 1:13 mass flow ratio which is then fed into the system for the 2 h deposition. The synthesized silver and silver-TiO2 films on the glass substrates were characterized by X-ray diffraction (XRD). The transmittance of each sample versus its wavelength was analyzed using UV-VIS spectroscopy. To show the photocatalytic effect of silver-TiO2 films, the synthesized films were used for the photocatalytic degradation of methylene blue. Each synthesized film was immersed in a 5 ml concentrated methylene blue solution. The solution with the sample is then subjected to a fluorescent lamp (Omni, 5 W) for 39 h each. The absorbance at UV-VIS region of methylene blue was measured using UV-VIS spectroscopy.
III. RESULTS AND DISCUSSION
Confirming the presence of silver deposits was done by using XRD spectroscopy, which is shown in Figs. 3–5. The characteristic peaks are then compared to the XRD pattern of the silver target from Malapit et al.6 The peaks, shown in Fig. 3, indicate the presence of crystalline silver deposited on the glass substrate. The broad peak is a characteristic of an amorphous structure, which is exhibited by the TiO2 , while sharp peaks are a characteristic of a crystalline structure, which is exhibited by the silver peaks. Introducing TiO2 with silver will affect the lattice parameters causing residual stress
85, 02C318-1
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02C318-2
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Rev. Sci. Instrum. 85, 02C318 (2014)
FIG. 1. A schematic diagram of the plasma sputter-type negative ion source.
FIG. 5. Intensity versus 2θ of silver and TiO2 doped films (silver on the outer surface) on glass substrate using x-ray diffraction spectroscopy. The broad peak represents the amorphous TiO2 (a-TiO2 ).
FIG. 2. A schematic diagram of the compact planar magnetron.
FIG. 3. Intensity versus 2θ using x-ray diffraction spectroscopy of silver films on glass substrate.
FIG. 4. Intensity versus 2θ using x-ray diffraction spectroscopy of silver and TiO2 doped films (TiO2 on the outer surface) on glass substrate.
FIG. 6. Images of the samples for (a) −200 V Ag, (b) −500 V Ag, (c) −700 V Ag, (d) −200 V Ag + TiO2 , (e) −500 V Ag + TiO2 , and (f) −700 V Ag + TiO2 . The opacity of the silver on glass is reduced after TiO2 deposition.
FIG. 7. (a) SEM image at 90× magnification of the silver film deposited at −500 V target voltage and with microparticles, and (b) at 230× magnification with silver deposited using −700 V target bias and TiO2 .
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Rev. Sci. Instrum. 85, 02C318 (2014)
degradation. Introducing silver though, lowers the photocatalytic degradation. However, when comparing the absorbance of −200Vt Ag + TiO2 and −700Vt Ag + TiO2 , an increase in the amount of silver decreases the absorbance of the methylene blue solution, as seen in Fig. 9. Increasing the amount of silver might exhibit an increase in degradation of the methylene blue solution. IV. CONCLUSION
FIG. 8. Percent transmittance versus wavelength of six samples using UVVIS spectroscope where TiO2 has TiO2 deposit; −200, −500, −700 Ag has Ag deposit biased at −200 Vt, −500 Vt, and −700 Vt, respectively; TiO2 +Ag has TiO2 and Ag deposit (Ag on the outer surface); and Ag + TiO2 has TiO2 and Ag deposit (TiO2 on the outer surface).
thus there is a shift in the XRD pattern7 as can be seen from the Ag (220) peak. The transmittance versus wavelength of each sample is shown in Fig. 8. As the target voltage increases for the samples with the silver deposit, the transmittance decreases also. This is maybe due to the increasing amount of silver film that increases the opacity of the sample, as seen in Figs. 6 and 7. From the measurement of optical absorbance of the methylene blue solution, as seen in Fig. 8, the sample with TiO2 only exhibits the lowest absorbance; meaning the methylene blue had a higher degradation when TiO2 is introduced thus it also shows the highest photocatalytic
Silver was successfully doped on TiO2 using plasma sputter-type negative ion source and compact planar magnetron as confirmed by XRD analysis. The optical absorbance property of the metal doped film was analyzed by UVVIS spectroscopy. Introducing a layer of silver significantly decreases the transmittance. Photocatalytic degradation of methylene blue was also used to exhibit the photocatalytic effect of the introduced dopants. It showed that with TiO2 only, there is an increase in the photocatalytic degradation. When silver is introduced, photocatalytic degradation decreases, however an increase in amount of silver with TiO2 increases its photocatalytic activity. ACKNOWLEDGMENTS
We would like to acknowledge the support of the bilateral research agreement of Japan Society for the Promotion of Science (JSPS) and the Philippines’ Department of Science and Technology (DOST). We would also like to thank the help of the following: Mae S. Villamayor Venice Mascariñas, Giovanni Malapit, and the Department of Chemical Engineering in the University of the Philippines, Diliman. We would also like to thank Mae S. Villamayor for the tremendous amount of time and effort she contributed to fulfill this research paper. 1 A.
FIG. 9. Absorbance against wavelength of −200 Vt Ag + TiO2 , −700 Vt Ag + TiO2 , and TiO2 degraded methylene blue.
Fujishima, “Discovery and applications of photocatalysis—Creating a comfortable future by making use of light energy,” Japan Nanonet Bulletin Issue 44, 12 May 2005. 2 A. Fujishima and K. Honda, Nature (London) 238(5358), 37 (1972). 3 M. E. Kurtoglu, T. Longenbach, and Y. Gogotski, Int. J. Appl. Glass Sci. 2(2), 108 (2011). 4 G. D. Alton, Y. Mori, A. Takagi, A. Ueno, and S. Fukumoto, Rev. Sci. Instrum. 61, 372 (1990). 5 G. M. Malapit, C. L. S. Mahinay, M. D. Poral, and H. J. Ramos, Rev. Sci. Instrum. 83, 02B704 (2012). 6 G. M. Malapit, J. I. L. Bugante, C. L. S. Mahinay, M. Wada, and H. J. Ramos, in Proceedings of the 12th APPC, Makuhari, Japan, 14–19 July 2013 (JPS Conf. Proc., 2013), p. 157, see http://www.jps.or.jp/APPC12/ index.html. 7 Progress in Inorganic Chemistry, edited by K. D. Karlin (Wiley, 2005), Vol. 54, pp. 47–126.
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