Energy Procedia 34 ( 2013 ) 734 – 739
1876-6102 © 2013 The Authors. Published by Elsevier B.V.
Selection and peer-review under responsibility of COE of Sustainalble Energy System, Rajamangala University of Technology Thanyaburi (RMUTT)
doi: 10.1016/j.egypro.2013.06.807
10th Eco-Energy and Materials Science and Engineering
(EMSES2012)
Optical Absorptivity Enhancement of SiO
2Thin Film by
Ti and Ag Additive
Prasopporn Junlabhut
a*, Sakoolkarn Boonruang
band Wisanu Pecharapa
a,ca b
Photonics Technology Laboratories, National Electronics and Computer Technology Centre, NSTDA, Khlong Luang, Pathumthani, Thailand
c
Thailand and Center of Excellence in Physics (ThEP Center), CHE, 328 Si Ayutthaya RD, Bangkok, Thailand
Abstract
This paper presents the visible optical absorptivity enhancement of SiO2thin films by Ti and Ag additive. SiO2thin
films were prepared on glass substrate by sol-gel technique. Methacryloxy propyl trimethoxysilane (MAPTMS), Titanium isopropoxide (TiP) and Silver nitrate were used as precursors. MAPTMS was dissolved in absolute ethanol with various Ti and Ag content. The physical properties of as-prepared films were characterized by X-ray diffraction (XRD) and Transmission electron micrograph (TEM). The effects of Ti and Ag addition on optical properties were investigated from its optical absorption measured by UV-VIS Spectrophotometer (UV-VIS). XRD patterns shows the formation of TiO2and Ag in thin film. The effect of Ti and Ag additive on SiO2thin films were scrutinized by meanff
of the optical absorption in visible region. XRD and TEM results disclose the existence of TiO2and Ag nanoparticles
in the as-prepared films. It can be observed that the improvement in optical absorption in both UV and visible region can be efficiently accomplished by the incorporation of Ti and Ag into SiO2films.
© 2013 The Authors. Published by Elsevier B.V.
Selection and/or peer-review under responsibility of COE of Sustainable Energy System, Rajamangala University of Technology Thanyaburi(RMUTT)
Keywords: Ti and Ag additive on SiOO thin film, sol-gel technique, Surface plasmon resonance.2
* Corresponding author. Tel.: +66-2-329-8000; fax: +66-2-329-8265. E-mail address: kpewisan@gmail.com.
© 2013 The Authors. Published by Elsevier B.V.
Selection and peer-review under responsibility of COE of Sustainalble Energy System, Rajamangala University of Technology Thanyaburi (RMUTT)
Open access under CC BY-NC-ND license.
1. Introduction
Over past decades, Silicon dioxide (SiO2) has been extensively utilized in wide range of applications due to its unique chemical and mechanical properties such as high porosity, low thermal conductivity and low index of refraction [1]. Moreover, SiO2 has distinguished mechanical properties which can increase the adhesion with substrate [5]. Sol-gel technique has been employed to prepare the various types of thin films because of considerable advantages such as cost-effectiveness, low temperature process, mass production capability for uniform large coating areas and ease of doping [5]-[6].
Because of their advantageous profit of sol-gel preparation, the additive material can be readily incorporated to improve crucial optical properties of SiO2 thin film. Titania has been chosen as potential additive due to its outstanding optical and mechanical properties such as high refractive index, chemical stability, structure stability, high oxidation rate and cheapness. Titania is a non toxic material that has been used in various applications such as environmental treatments (air, water and purification) and photocatalytic activity [3]. Furthermore, it is proven that metal nanoparticles of Pt, Au and Ag with strong optical absorption associated to surface plasmon resonance (SPR) phenomena at nano scale is one of potential candidate as a promising additive. It has been widely reported the achievement in an enhancement of optical absorption properties in visible region via the incorporation of metal nanostructures [3], [7], [8].
This present paper reports the preparation of SiO2 thin film using sol-gel spin coating technique on glass substrate and the effect of Ti and Ag additive materials on optical absorption properties. The physical properties of thin film were characterized by X-ray diffraction (XRD) and Transmission electron micrograph (TEM). The effects of Ti and Ag addition on optical properties were investigated from its optical absorption measured by UV-VIS Spectrophotometer (UV-VIS).
2. Experimental
2.1. Sample preparation
Silica solution was prepared by dissolving the network silica polymer (C10H20O5Si
absolute ethanol and hydrolyzing with De-ionization water (DI water) and 0.2 M HCl. The solution was homogeneously mixed with magnetic stirrer for 30 min at room temperature. Then photoinitiator (bis (.eta. - , -cyclopentadien- -yl) bis [ , -difluoro- - H-pyrrol- -yl) phenyl] titanium) or irgacure 784 was added into the stocked solution under continuous stirring for another 20 min. After vigorous homogenization via magnetic stirrer, silica solution was transformed into yellow color due to photo initiator additive. The silica solution was kept in the darkness using aluminums foil sealing at room temperature and aging for 24 h. Ti and Ag addition also been able to improve the optical properties of silica solution. Titanium isopropoxide (C12H28O4Ti 3) were used as precursor sources of Ti and Ag, respectively. AgNO3 was added in silica solution with vary Ag concentration at 0%, 2%, 5% and 10%. TiP with different of Ti content at 0, 0.3, 0.5, 0.7 and 1 mol was prepared by mixing the precursor in acetyl acetone (C5H8O2) and stirried for 30 min. Both precursors were mixed together before the addition of Irgacure 784 photo initiator. Finally, Addition Ti and Ag in silica sol were obtained after aging in the dark room for 24 hr. The Ti and Ag-added silica solution was coated on cleaned glass substrates by spin coating at 2500 rpm for 45 s. As-prepared samples were baked at 80oC for 5 min to evaporate all solvents. After that, transparent Ti and Ag-doped SiO2 thin films were obtained after thermal treated at various temperatures of 150, 350, and 550 C for 2 h.
2.2. XRD, TEM analysis
The structural properties of Ti and Ag-doped SiO2 powders were characterized by XRD (Rigaku Mini Flex) using Cu-K radiation operated at 40 kV and 15 mA over 2 range of 20-80º. The diffraction patterns were recorded with a scanning rate 2º/min. The morphologies of as-prepared thin films were examined by TEM (FEI, TECNAI G2 20). Preparation of the samples for TEM measurement was conducted by diffusing a detached piece of the thin film in NaOH and droped onto copper grids and dried in air.
2.3. Optical measurement
The optical properties of as-prepared thin films were investigated by UV-Vis spectrophotometer measured at 280-800 nm regions.
3. Results and Discussion
3.1. Physical properties
The XRD patterns of as-synthesized Ti/Ag-doped SiO2 powder and the samples annealed at 350 C and 550 C are illustrated in Fig 1. Characteristic peaks of TiO2 and Ag crystallite phase can be observed in the XRD patterns. Typically, silica have been structured in amorphous phase. Four distinct peaks at 2 value of 38.11 , 44.27 , 64.25 and 77.54 correspond to cubic Ag orientation (111), (200), (220) and (311), respectively. These peaks become more intense and narrower with further increasing annealing temperature. The additional XRD patterns of the as-synthesized sample can be indexed to the silicon titanium oxide phase. The peak observed for silicon titanium oxide phase have been compared with data standards JCPDS (ICSD 89-8099). As temperature elevates to 350 oC the corresponded peak of silicon titanium oxide disappears, implying the decomposition or phase transformation of intermediate Si-Ti-O structure. Further increasing annealing temperature to 550 C results to the formation of titania in anatase phase accompanying the board XRD peakat 2 value of 25.3o [9-10].
Fig.2. TEM image of Ti /Ag-dopedSiO2 thin film.
TEM image of Ti/ Ag-dopedSiO2 thin film is shown in Fig. 2. This result exhibits that Ag nanoparticles are well dispersed on SiO2 film. The Ag nanoparticles are spherical in shape with smooth surface morphology and size of Ag nanoparticle varies in the range of 5-20 nm. This result is agreeable to the XRD pattern [11]. The morphology of Ag nanoparticles can be further monitored using the optical absorption band in SPR effect of Ag nanoparticles.
3.2. Optical properties
Fig 3. shows the optical absorption spectra of SiO2 thin films annealed at 150ºC, 350ºC and 550ºC. The result indicates the formation of SiO2 films as temperature increases. SiO2 thin films are typically observed in colorless with a prominent absorption in UV region and no absorption in visible. Typically, SiO2 film exhibits lower absorption. As seen in Fig. 4. with Ti additive, the optical absorption range in 280-320 nm region becomes stronger and more intense and additionally exhibits observable red shift to longer wavelength in visible region with increasing Ti adding content [12-13]. To further enhance the optical absorption in visible region of the film, Ag nanoparticles with different %Ag content were utilized by adding into the films. It could be seen that the optical absorption of Ti-doped SiO2 is obviously different from Ti/Ag doped SiO2 thin films.
Fig.3. Optical absorption of SiO2 thin film annealed at various Fig.4. Optical absorption of Ti-addedSiO2 thin film with
Fig.5. Optical absorption of Ag/ Ti-doped SiO2 thin films with Fig.6. Optical absorption of 2% Ag/ Ti-doped SiO2 thin
various Ag content at 0%, 2%, 5% and 10%. films annealed at with various temperatures ; 150 C, 350 C and 550 C
Fig. 5 shows the result of optical absorption of the film with various Ag adding contents. The additional absorption regime in visible range of 400-500 nm is clearly observed in Ag-doped films. This feature is due to the effect of surface plasmon resonance (SPR) of electron in Ag nanoparticles incorporated in the film. The SPR effect were occured due to the oscillation of electrons of silver nanoparticles in resonance with the light wave radiation. The broad absorption in 2% and 5% Ag might be ralated to the variation in size of Ag nanoparticles on the surface of the films. In addition, greater amount of silver at 10% Ag content may cause the agglomeration of silver particles cluster, affecting the deterioration of SPR effect and consequently resulting to the decrease in optical absorption. Fig 6 demonstrates the optical spectra of Ti/Ag -doped SiO2 thin films annealed at different temperatures. The result implies the better formation of Ag nanoparticles with increasing temperature accompanying the stronger SPR-induced absorption band in visible region [14-16].
4. Conclusion
The addition of Ti and Ag on SiO2 thin films were successfully deposited on glass substrates by sol-gel spin coating technique. The effects of Ti and Ag additives on physical and optical properties of the films were investigated. An optimized recipe of Ti and Ag additive and annealing temperature was obtained. The physical properties of thin films are confirmed by XRD analysis and TEM image. The optical absorption of the SiO2 films was enhanced by Ti and Ag additive due to optical properties of Ti and the effect of surface plasmon resonance of Ag nanoparticles. This occurrence implies that the optical absorptivity of SiO2 in visible region can be improved by Ti and Ag additive.
Acknowledgements
This work has partially been supported by National Nanotechnology Center (NANOTEC), NSTDA, Ministry of Science and Technology, Thailand, through its program of Center of Excellence Network. Authors would like to thank Thailand Graduate Institute of Science and Technology (TGIST), NSTDA, for student fund supported no. TG-44-22-53-069M.
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