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1Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida-201307,. India. 2Physics ...
M4A.10.pdf

Photonics 2014: 12th International Conference on Fiber Optics and Photonics © OSA 2014

Surface Plasmon Resonance Based Fiber Optic Hydrogen Sulphide Gas Sensor Utilizing Titanium Dioxide Thin Film Sarika Shukla1, Satyendra K. Mishra2, Anisha Pathak2, Banshi D. Gupta2 and Navneet K. Sharma1 1

Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida-201307, India 2 Physics Department, Indian Institute of Technology Delhi, New Delhi-110016, India [email protected]

Abstract: Fabrication and characterization of a surface plasmon resonance based fiber optic hydrogen sulphide gas sensor is presented. SPR spectra for different concentrations of gas are obtained. Resonance wavelength increases with increase in concentration of gas. OCIS codes: (060.2310) Fiber optics; (060.2370) Fiber optics sensors; (240.6680) Surface plasmons

1. Introduction  Enormous research studies have been conducted on various sensing techniques, which may be employed for a quick and accurate measurement of several physical, chemical and biochemical parameters in past three decades. Liedberg et al. [1] were the first to demonstrate the exploitation of surface plasmon resonance (SPR) for chemical sensing. Since then, the surface plasmon resonance sensing principle has been studied rigorously [2]. Collective resonating oscillations of free electrons exist on the metal surface, giving rise to a charge density wave propagating along the metal surface. This transverse electromagnetic wave, propagating parallel to the metal-dielectric interface is known as the surface plasmon wave. Being transverse in nature, surface plasmon wave can be excited by exponentially decaying evanescent field of incident p-polarized light. For observing SPR, Kretschmann’s configuration is most widely used over other SPR sensing structures [3]. However, optical fiber based SPR sensing has large number of advantages over Kretschmann’s configuration based SPR sensing [4-6]. Optical fiber based SPR sensing have been carried out in both experimental and theoretical research studies [7-12]. Lot of research investigations have been done on the detection and control of various harmful and toxic gases including hydrogen sulphide (H2S). Hydrogen sulphide gas is found in water, crude petroleum, natural gas, volcanic gas, hot springs and ground water [7]. Hydrogen sulphide is colorless and flammable gas having characteristic odor of rotten-eggs [10]. This gas is produced naturally by the decay of organic matter and by certain industrial processes. Metal oxide based semiconductors are generally used as gas sensing materials for the detection of these toxic gases. Recently, titanium dioxide (TiO2) has attracted huge attention of scientific communities because of its extraordinary physical and chemical properties. TiO2 is a wide band gap semiconductor (band gap around 3.0-3.2 eV) and is mainly important for use in solar energy and environment purification. Besides, due to its high efficiency and high stability, this material has also been used in many applications such as photocatalysts, pigments, gas sensors and dye sensitized solar cells [13,14]. In this work, we have fabricated and characterized a surface plasmon resonance based fiber optic hydrogen sulphide gas sensor utilizing silver (Ag)-titanium dioxide (TiO2) thin films. For the fabrication of probe, we first unclad the fiber and then deposit a 40 nm thick Ag film, which is again coated by 10 nm thick TiO2 film by using thermal evaporation coating machine. For characterization of the sensor, wavelength interrogation scheme is utilized. 2. Experimental 2.1 Fabrication of probe For the fabrication of hydrogen sulphide gas probe, 24 cm long plastic clad silica (PCS) fiber is taken. Nearly, 1 cm of plastic cladding is removed from the middle portion of PCS fiber (Numerical aperture = 0.4 and core diameter = 600 µm) and then the fiber probe is cleaned with acetone and methanol followed by ultrasonic bath with de-ionized (DI) water. Afterwards, we have done ion bombardment on unclad portion of fiber core for the removal of unwanted contaminated impurities by using thermal evaporation coating machine. Then, we have deposited a 40 nm thick Ag film followed by 10 nm thick TiO2 film over the unclad portion of the fiber core using a thermal evaporation coating unit. The coating pressure of the machine is taken as 5 x 10-6 mbar. The boat used for the coating is made of molebedeum.

M4A.10.pdf

Photonics 2014: 12th International Conference on Fiber Optics and Photonics © OSA 2014

2.2 Experimental setup

Ag layer + TiO2 layer Unclad fiber core

Source

Spectrometer

MO

Computer

Gas chamber Fig. 1 The schematic diagram of the experimental setup for fiber optic hydrogen sulphide gas sensor is shown in fig. 1. To study the response of the SPR sensor, the fabricated fiber optic probe is fixed inside the gas chamber. The gas chamber has inbuilt feature for the gas inlet and outlet. The hydrogen sulphide gas cylinder is also connected to the nitrogen gas cylinder for puzzling. Both cylinders are connected to the gas chamber by steel wall tube. For recording the SPR spectra, the unpolarized light from a polychromatic source is launched into one end of the fiber, while the other end is connected to the spectrometer. The spectrometer is interfaced with a computer. Before passing the gas inside the chamber, the chamber is evacuated with the help of a rotary pump. Different concentrations of hydrogen sulphide gas in the range 10-100 ppm are passed inside the chamber. 3. Results and discussions

Fig. 2a

Fig. 2b

Fig. 2a depicts the variations in normalized transmitted power with wavelength for various concentrations of the hydrogen sulphide gas around the probe. It is clear that with increase in concentration of hydrogen sulphide gas, the resonance wavelength increases. Fig. 2b shows the variation of resonance wavelength with the concentration of hydrogen sulphide gas. The resonance wavelength increases with increase in concentration of hydrogen sulphide gas. The reason for the shift in resonance wavelength is attributed to the hydrogen sulphide gas induced changes in the dielectric function of TiO2 film. When the molecules of hydrogen sulphide gas come in contact with TiO2 thin film, it gets reacted with the film and as a consequence titanium sulphide is formed. Due to the formation of titanium

M4A.10.pdf

Photonics 2014: 12th International Conference on Fiber Optics and Photonics © OSA 2014

sulphide, dielectric constant of TiO2 film changes. This results in change in resonance wavelength of the SPR spectrum. 4. Conclusions The fabrication and characterization of a surface plasmon resonance based fiber optic hydrogen sulphide gas sensor has been carried out. The fiber optic probe is prepared by coating a 40 nm thick Ag film followed by 10 nm thick TiO2 film over the unclad portion of the fiber core by using thermal evaporation coating machine. The sensor works on the wavelength interrogation scheme and the reactivity of hydrogen sulphide gas towards the TiO2 film results in change in dielectric constant of TiO2 film. The resonance wavelength is shown to increase with increase in concentration of hydrogen sulphide gas. 5. References [1] B. Liedberg, C. Nylander and I. Sundstrom, “Surface plasmon resonance for gas detection and biosensing,” Sensors and Actuators B 4, 299304 (1983). [2] R. D. Harris and J. S. Wilkinson, “Waveguide surface plasmon resonance sensors,” Sensors and Actuators B 29, 261-267 (1995).

[3] E. Kretschmann and H. Reather, “Radiative decay of non-radiative surface plasmons excited by light,” Zeitschrift für Naturforschung 23, 2135-2136 (1968). [4] J. Homola, “Optical fiber sensor based on surface plasmon excitation,” Sensors and Actuators B 29, 401-405 (1995). [5] W.B. Lin, N. Jaffrezic-Renault, A. Gagnaire and H. Gagnaire, “The effects of polarization of the incident light-modeling and analysis of a SPR multimode optical fiber sensor,” Sensors and Actuators A 84, 198-204 (2000). [6] A.K. Sharma and B.D. Gupta, “Absorption based fiber optic surface plasmon resonance sensor: a theoretical evaluation,” Sensors and Actuators B 100, 423-431 (2004). [7] S.K. Mishra, S. Rani, and B.D. Gupta, “Fabrication and characterization of a surface plasmon resonance based fiber optic hydrogen sulphide gas sensor utilizing nickel oxide doped ITO thin film,” Sensors and Actuators B 195, 215-222 (2014). [8] S. Singh, S.K. Mishra and B.D. Gupta, “Sensitivity enhancement of a surface plasmon resonance based fiber optic refractive index sensor utilizing as additional layer of oxides,” Sensors and Actuators A 193, 136-140 (2013). [9] S.K. Mishra, D. Kumari and B.D. Gupta, “Surface plasmon resonance based fiber optic ammonia gas sensor using ITO and polyaniline,” Sensors and Actuators B 171-172, 976-983 (2012). [10] R. Tabassum , S.K. Mishra and B.D. Gupta, “Surface plasmon resonance based fiber optic hydrogrn sulphide gas sensor utilizing Cu-ZnO thin films ,” Phys. Chem. Chem. Phys. 15, 11868-11874 (2013). [11] N.K. Sharma, M. Rani, and V. Sajal, “Surface plasmon resonance based fiber optic sensor with double resonance dips,” Sensors and Actuators B 188, 326-333 (2013). [12] M. Rani, S. Shukla, N.K. Sharma and V. Sajal, “Theoretical study of nanocomposites based fiber optic SPR sensor,” Optics Communications 313, 303-314 (2014). [13] Y.J. Choi, Z. Seeley, A. Bandyopadhyay, S. Bose and S.A. Akbar, “Aluminium doped TiO2 nano powers for gas sensors,” Sensors and Actuators B 124, 111-117 (2007). [14] T.A. Kandiel, A. Feldhoff, L. Robben, R. Dillert, and D.W. Bahnemann, “Tailored titanium dioxide nanomaterials: anatase nanoparticles and brookite nanorods as highly active photocatalysts,” Chmistry of materials 22, 2050-2060 (2010).