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Porous silicon based CO2 sensors with high sensitivity
Optik 164 (2018) 271–276
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Original research article
Porous silicon based CO2 sensors with high sensitivity Ersin Kayahan a,b,∗ a b
Kocaeli University, Electro-Optics and Systems Eng. Umuttepe, 41380, Kocaeli, Turkey Kocaeli University, Laser Technologies Research and Application Center (LATARUM), 41275, Yeniköy, Kocaeli, Turkey
a r t i c l e
i n f o
Article history: Received 23 July 2017 Accepted 8 March 2018 Keywords: Porous silicon Photoluminescence DC measurements Carbon dioxide sensor
a b s t r a c t Porous silicon (PS) has been an attractive material for bio-chemical sensors. Pore volume and surface area of the porous silicon are key parameters for the sensor applications. Its large surface area for the applications and compatibility with silicon-based technologies has been the driving force for this technology development. The carbon dioxide (CO2 ) gas is one of the most important greenhouse gases that cause global warming and air pollution. For this reason, detection of CO2 gas in living environment is essential. In this study, luminescence and electrical properties of the PS under different carbon dioxide levels and detection mechanisms were investigated. PS are fabricated by anodic etching in hydrofluoric acid based solution in a double anodization cell. The surface bond configurations and structural properties of PS were monitored by Fourier Transmission Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), respectively. The experimental results suggested that the PS surface very sensitive to CO2 gas and can be used for CO2 sensing. © 2018 Elsevier GmbH. All rights reserved.
1. Introduction Carbon dioxide (CO2 ) detecting is required and important in many fields such as clean energy technologies, agricultural production, food industry, health care and chemical industry [1,2]. CO2 gas is also one of the most important of greenhouses gases to produce global warming. Sensing and classification of harmful chemicals to protect human health and the environment is essential [3]. With concerns for air quality, CO2 monitoring is becoming more important. While CO2 is not an air pollutant, it can have an undesirable effect on us when levels exceed a determined level. When the level rise, we tend to get sleepy and have difficulty focusing, and some people even develop headaches. For this reason, it is important for our living areas to have CO2 monitored to stay at an under determined harmful level. Sensing studies of harmful chemicals in the air with PS are still an intensively studied subject [1–4]. Over the last two decades, porous silicon has been shown to be very effective for the production of integrated gas/vapor sensors with the low-cost process and room temperature operation [1–7]. Its high surface to volume ratio, up to 107 times larger than bulk materials, provides a strong interaction between material surface and gas molecules and allows high sensitivity of detection to be achieved for CO2 sensing [5]. Optical and electrical approaches have been established to be valuable for the detection of gas species and organic vapors using porous silicon based sensors [8]. The changes in optical and electrical properties of the porous silicon with the specific gas/vapor species have been showed through quantitative monitoring of the variation of different parameters (e.g., photoluminescence spectrum; reflected, transmitted, and diffracted optical power; capacitance; current; resistance; etc.) as a function of the gas/vapor concentration [7–13].
∗ Corresponding author at: Kocaeli University, Electro-Optics and Systems Eng. Umuttepe, 41380, Kocaeli, Turkey. E-mail address: [email protected] https://doi.org/10.1016/j.ijleo.2018.03.024 0030-4026/© 2018 Elsevier GmbH. All rights reserved.
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E. Kayahan / Optik 164 (2018) 271–276
Fig. 1. Schematic diagram for CO2 sensing.
It is well-known that CO2 is generally non-reactive molecule; therefore, the sensing study of CO2 gas with new materials operating at room temperature is very important. In this study, the changes in luminescence and electrical properties of the porous silicon during different carbon dioxide levels were examined. The results show that porous silicon could be a suitable candidate as a new material for CO2 gas sensor applications. 2. Experimental details Details of electrochemical etching of crystalline silicon and PS production were given in details in our previous studies [12–15]. Schematic diagram of experimental setup for sensing CO2 gas can be seen in Fig. 1. The PL quenching measurements of PS were performed in optical module and DC electrical measurements were performed in the electrical module (modified of the optic module). Argon (Ar) gas was used as the carrier gas. Two flow meters from Sierra (smart track 100 and micro track 101), which have a maximum flow of 200 sccm and 4 sccm were used as argon and carbon dioxide gas controllers, respectively. Pre-determined argon and carbon dioxide gases were put together by T-type pipe to obtain homogenous CO2 and Ar gases mix, after this, out of the pipe was connected optical sensing module. 254 nm and 365 nm wave lengths of light from a UV lamp (Konrad Benda) were used for PL excitation. For electrical measurements, PS surface was coated with a metal inter-digital-electrode (IDE) (Aluminum, 0.2 g, 99.999%) combined with thermal evaporation system. Etching process and sensor measurements were carried out at room temperature. To perform sensor measurements, nitrogen gas was initially introduced into the optic module by a flow-meter (200 sccm) and continuous PL spectra were then taken to obtain stable PL. After this, the other flow-meter (4 sccm) which controls the CO2 gas was run to obtain a pre-determined Ar-CO2 gas mixture. The process was altered periodically (5 min) by varying CO2 concentrations. PS waited for each period in the optic module which was filled with pure Ar gas. The same procedure was repeated for electrical measurements. 3. Results and discussion Surface morphology of the porous silicon was studied by scanning electron microscope as shown in Fig. 2 where it was clear that there is a continuous distribution of pore sizes ranging between 2 and 3 m. In order to determine how the spatial changes take place during the sensing process at the PS surface, infrared absorption spectra of the PS sample was measured. The FTIR spectra of the PS sample as-prepared and just after sensing process are shown in Fig. 3. It can be seen that vibration bonds around 1105 cm−1 correspond to stretching mode of Si O Si. The band at 905 cm−1 is attributed to scissor mode of Si H2 and a large vibration absorption band saw at 610–660 cm−1 is a mixture of stretching mode of Si Si and wagging mode Si Hn (n = 1 and 2). The peak around 620 cm−1 corresponds to Si Si stretch mode and Si Hn wagging mode is seen at 665 cm−1 . In the high energy region of the spectra, the absorption peaks at 2105 and 2084 cm−1 are Si H2 and Si H stretching modes, respectively. The peak at 2196 is due to O2 SiH2 . Carbon related peaks are shown at 2900 cm−1 (as seen in inlet figure in Fig. 3). The peaks are attributed to C–H and C O at 2850 cm−1 and 2957 cm−1 and Si C at 2925 cm−1 . Moreover, it can be seen from Fig. 3 that marked changes take place in FTIR spectra when compared to just after the sensing process. These changes show especially at Si H related absorption peaks that the peaks decrease
E. Kayahan / Optik 164 (2018) 271–276
273
Fig. 2. The SEM pictures of the fresh PS with different magnifications.
Fig. 3. FTIR spectra of fresh and just after the sensing measurements were taken about 1 h of PS. Inlet figure shows carbon (C) related peaks.
after the sensing process. It is also seen in inlet figure in Fig. 3 that after the sensing process carbon related peaks slightly appears at around 2900 cm−1 . This could be due to the replacement of the hydrogen atoms by oxygen atoms of CO2 . The peaks are given in Fig. 3 are in good agreement with the data reported in the previous works [15–20]. From the FTIR spectra, it can be concluded that PS surface after the anodization is covered with hydrogen, oxygen atoms. After the sensing process taking about 1 h carbon related peaks slightly appear while Si H related peaks decrease. It can also be concluded that CO2 ad/absorbed onto PS surface over the hydrogen atoms comes from anodization process. Therefore, the weak hydrogen bonds on PS surface can play a critical role in sensing the CO2 gas. To get the PL spectra Ar gas was introduced into the sensing room (optical module) by a flow-meter (200 sccm) and waited about 30 min to obtain luminescence stability. After this, another flow-meter (4 sccm) which controls the CO2 gas was run for 5 min. The process was altered periodically (5 min) by varying CO2 concentrations. Fig. 4A shows that PL intensity decrease without any shifting with decreasing CO2 level. Fig. 4B which obtained from the PL spectra also shows the integrated area and normalized PL intensity versus CO2 quantity. As seen the Fig. 4A PL intensity decrease with CO2 gas, while the intensity increase with Ar gas for the periodic time of 5 min. It is also shown from Fig. 4B that the changes of PL intensity and the integrated area of PL spectra could be used as sensing parameters. The integrated area is more suitable than the intensity changes of PL spectra.
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E. Kayahan / Optik 164 (2018) 271–276
Fig. 4. (A) Shows the PL spectra of PS with respect to carbon dioxide concentration. Where PL spectra were taken by altering periodically (5 min) the CO2 concentrations. (B) shows the changes of PL intensity at 608 nm and the integrated area between 473 nm–721 nm of the PL spectra with CO2 concentrations. The solid lines show fitting functions.
This could understandable that CO2 gas ad/absorption on PS surface causes quenching of the PL spectra. The quenching could also be explained by electron transfer mechanisms, where, photo-excited PS endorses electron-hole pairs localized at Si O SiR moieties on the surface of crystallites and these moieties also act as electron donors and gas molecules act as acceptors. When the gas molecules achieve the PS surface, their molecular orbitals mix to a donor excited states localized at the Si O SiR moieties promoting the electron transfer reaction and consequently the PL quenches as was mentioned in Ref. [21] in detail. Fig. 5 shows the electrical response of PS surface during exposure to various concentrations of CO2 gas. It is shown in the figure that the electrical signal increases during exposure to a mixture of Ar + CO2 gas and then decreases during exposure to carrier gas (Ar). This could also be explained by the electron transfer mechanisms [21].
E. Kayahan / Optik 164 (2018) 271–276
275
Fig. 5. The electrical response of PS with respect to carbon dioxide concentration.
4. Conclusions We propose a novel and simple way to use PS as an active material for sensing CO2 gas. The possibility of a CO2 gas sensing using PS layer was demonstrated. Changes of PL spectra (intensity and area) and resistivity with the CO2 gas levels were also investigated in this study. We observed that PL intensity decreases, whereas, electrical signal (current) increases during exposure to increasing CO2 gas concentrations, because of the electron transfer mechanisms. The decrease in PL intensity during increasing CO2 level obeys to a linear function. However, the linear fitting obtained by PL spectrum area is more suitable than the intensity changes. The optical and electrical measurement results indicated that PS surface showed creditable gas sensing performances with respect to CO2 gas. Therefore, it can be concluded that PS is an ideal candidate material for fabrication of high performance, selective electrical/optical gas sensor in the near future. However, it is clear that many types of research are needed before application of porous silicon as a CO2 sensor. Acknowledgments The author is grateful to Prof. Dr. A.Y. Oral (Gebze Technical University at Turkey) for helpful discussions. This research was also financially supported by the Scientific and Technological Research Council of Turkey-TUBITAK (Project no. 111T357) and project unit of Kocaeli University (Project no. 2013/64 HDP). References [1] N. Zouadi, S. Messaci, S. Sam, D. Bradai, N. Gabouz, CO2 detection with CNx thin films deposited on porous silicon, Mater. Sci. Semicond. Process. 29 (2015) 367–371. [2] H.G. Shiraz, Efficient room temperature hydrogen gas sensing based on graphene oxide and decorated porous silicon, Int. J. Hydrogen Energy 42 (2017) 15966–15972. [3] W. Wang, Y. Goa, Q. Tao, Y.-Z. Liu, J.-J. Juo, X.-C. Ju, J.-K. Zhang, A novel porous silicon composite sensor for formaldehyde detection, Chin. J. Anal. Chem. 43 (6) (2015) 849–855. [4] P. Dwivedi, S. Dhanekar, S. Das, S. Chandra, Effect of TiO2 functionalization on nano-porous silicon for selective alcohol sensing at room temperature, J. Mater. Sci. Technol. 33 (6) (2017) 516–522. [5] Giuseppe Barillaro, Porous silicon gas sensing, in: Leigh Canham (Ed.), Handbook of Porous Silicon, Springer, 2014, p. 845. [6] U.M. Nayef, I.M. Khudhair, Study of porous silicon humidity sensor vapors by photoluminescence quenching for organic solvents, Optik 135 (2017) 169–173. [7] F. Tebizi-Tighilt, F. Zane, N. Belhaneche-Bensemra, S. Belhousse, S. Sam, N. Gabouze, Electrochemical gas sensors based on polypyrrole-porous silicon, Appl. Surf. Sci. 269 (2013) 180–183. [8] S. Ozdemir, J.L. Gole, The potential of porous silicon gas sensor, Curr. Opin. Solid State Mater. Sci. 11 (2007) 92–100. [9] G. Barillaro, A. Nannini, F. Pieri, Temperature behavior of the APSFET—a porous silicon-based FET gas sensor, Sens. Actuators B: Chem. 100 (2004) 185–189.
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[10] T. Holec, T. Chvojka, I. Jelinek, J. Jindiric, I. Nemec, I. Pelant, J. Valenta, J. Dian, Determination of sensoric parameters of porous silicon in sensing of organic vapors, Mater. Sci. Eng. C 19 (2002) 251–254. [11] H.K. Min, H.S. Yang, S.M. Cho, Extremely sensitive optical sensing of ethanol using porous silicon, Sens. Actuators B: Chem. 67 (2000) 199–202. [12] E. Kayahan, Z.B. Bahsi, A.Y. Oral, M. Sezer, Porous silicon based sensor for organic vapors, Acta Phys. Pol. A 127 (2015) 1400–1402. [13] E. Kayahan, Porous silicon based humidity sensor, Acta Phys. Pol. A 127 (2015) 1397–1399. [14] O. Yılmaz, E. Kayahan, F. Gören, F. Dumludag, Methanol vapor sensing by porous silicon, Acta Phys. Pol. A 125 (2014) 288–289. [15] E. Kayahan, The role of surface oxidation on luminescence degradation of porous silicon, Appl. Surf. Sci. 257 (2011) 4311–4316. [16] Michael J. Sailor, Chemical reactivity and surface chemistry of porous silicon, in: Leigh Canham (Ed.), Handbook of Porous Silicon, Springer, 2014, p. 355. [17] P. Gupta, A.C. Dillon, A.S. Bracker, S.M. George, FTIR studies of H2O and D2O decomposition on porous silicon, Surf. Sci. 245 (1991) 360–372. [18] Y. Ogata, H. Niki, T. Sakka, M. Iwasaki, Oxidation of porous silicon under water-vapor environment, J. Electrochem. Soc. 142 (1995) 1595–1601. [19] J.M. Buriak, Organometallic chemistry on silicon surfaces: formation of functional monolayers bound through Si C bonds, Chem. Commun. 12 (1999) 1051–1060. [20] T.K. Mischki, R.L. Donkers, B.J. Eves, G.P. Lopinski, D.D.M. Wayner, Reaction of alkenes with hydrogen-terminated and photo-oxidized silicon surfaces: a comparison of thermal and photochemical processes, Langmuir 22 (2006) 8359–8365. [21] W.J. Salcedo, F.J.R. Fernandez, J.C. Rubim, Photoluminescence quenching effect on porous silicon films for gas sensors application, Spectrochim. Acta Part A 60 (2004) 1065–1070.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Original research article
Porous silicon based CO2 sensors with high sensitivity Ersin Kayahan a,b,∗ a b
Kocaeli University, Electro-Optics and Systems Eng. Umuttepe, 41380, Kocaeli, Turkey Kocaeli University, Laser Technologies Research and Application Center (LATARUM), 41275, Yeniköy, Kocaeli, Turkey
a r t i c l e
i n f o
Article history: Received 23 July 2017 Accepted 8 March 2018 Keywords: Porous silicon Photoluminescence DC measurements Carbon dioxide sensor
a b s t r a c t Porous silicon (PS) has been an attractive material for bio-chemical sensors. Pore volume and surface area of the porous silicon are key parameters for the sensor applications. Its large surface area for the applications and compatibility with silicon-based technologies has been the driving force for this technology development. The carbon dioxide (CO2 ) gas is one of the most important greenhouse gases that cause global warming and air pollution. For this reason, detection of CO2 gas in living environment is essential. In this study, luminescence and electrical properties of the PS under different carbon dioxide levels and detection mechanisms were investigated. PS are fabricated by anodic etching in hydrofluoric acid based solution in a double anodization cell. The surface bond configurations and structural properties of PS were monitored by Fourier Transmission Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), respectively. The experimental results suggested that the PS surface very sensitive to CO2 gas and can be used for CO2 sensing. © 2018 Elsevier GmbH. All rights reserved.
1. Introduction Carbon dioxide (CO2 ) detecting is required and important in many fields such as clean energy technologies, agricultural production, food industry, health care and chemical industry [1,2]. CO2 gas is also one of the most important of greenhouses gases to produce global warming. Sensing and classification of harmful chemicals to protect human health and the environment is essential [3]. With concerns for air quality, CO2 monitoring is becoming more important. While CO2 is not an air pollutant, it can have an undesirable effect on us when levels exceed a determined level. When the level rise, we tend to get sleepy and have difficulty focusing, and some people even develop headaches. For this reason, it is important for our living areas to have CO2 monitored to stay at an under determined harmful level. Sensing studies of harmful chemicals in the air with PS are still an intensively studied subject [1–4]. Over the last two decades, porous silicon has been shown to be very effective for the production of integrated gas/vapor sensors with the low-cost process and room temperature operation [1–7]. Its high surface to volume ratio, up to 107 times larger than bulk materials, provides a strong interaction between material surface and gas molecules and allows high sensitivity of detection to be achieved for CO2 sensing [5]. Optical and electrical approaches have been established to be valuable for the detection of gas species and organic vapors using porous silicon based sensors [8]. The changes in optical and electrical properties of the porous silicon with the specific gas/vapor species have been showed through quantitative monitoring of the variation of different parameters (e.g., photoluminescence spectrum; reflected, transmitted, and diffracted optical power; capacitance; current; resistance; etc.) as a function of the gas/vapor concentration [7–13].
∗ Corresponding author at: Kocaeli University, Electro-Optics and Systems Eng. Umuttepe, 41380, Kocaeli, Turkey. E-mail address: [email protected] https://doi.org/10.1016/j.ijleo.2018.03.024 0030-4026/© 2018 Elsevier GmbH. All rights reserved.
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E. Kayahan / Optik 164 (2018) 271–276
Fig. 1. Schematic diagram for CO2 sensing.
It is well-known that CO2 is generally non-reactive molecule; therefore, the sensing study of CO2 gas with new materials operating at room temperature is very important. In this study, the changes in luminescence and electrical properties of the porous silicon during different carbon dioxide levels were examined. The results show that porous silicon could be a suitable candidate as a new material for CO2 gas sensor applications. 2. Experimental details Details of electrochemical etching of crystalline silicon and PS production were given in details in our previous studies [12–15]. Schematic diagram of experimental setup for sensing CO2 gas can be seen in Fig. 1. The PL quenching measurements of PS were performed in optical module and DC electrical measurements were performed in the electrical module (modified of the optic module). Argon (Ar) gas was used as the carrier gas. Two flow meters from Sierra (smart track 100 and micro track 101), which have a maximum flow of 200 sccm and 4 sccm were used as argon and carbon dioxide gas controllers, respectively. Pre-determined argon and carbon dioxide gases were put together by T-type pipe to obtain homogenous CO2 and Ar gases mix, after this, out of the pipe was connected optical sensing module. 254 nm and 365 nm wave lengths of light from a UV lamp (Konrad Benda) were used for PL excitation. For electrical measurements, PS surface was coated with a metal inter-digital-electrode (IDE) (Aluminum, 0.2 g, 99.999%) combined with thermal evaporation system. Etching process and sensor measurements were carried out at room temperature. To perform sensor measurements, nitrogen gas was initially introduced into the optic module by a flow-meter (200 sccm) and continuous PL spectra were then taken to obtain stable PL. After this, the other flow-meter (4 sccm) which controls the CO2 gas was run to obtain a pre-determined Ar-CO2 gas mixture. The process was altered periodically (5 min) by varying CO2 concentrations. PS waited for each period in the optic module which was filled with pure Ar gas. The same procedure was repeated for electrical measurements. 3. Results and discussion Surface morphology of the porous silicon was studied by scanning electron microscope as shown in Fig. 2 where it was clear that there is a continuous distribution of pore sizes ranging between 2 and 3 m. In order to determine how the spatial changes take place during the sensing process at the PS surface, infrared absorption spectra of the PS sample was measured. The FTIR spectra of the PS sample as-prepared and just after sensing process are shown in Fig. 3. It can be seen that vibration bonds around 1105 cm−1 correspond to stretching mode of Si O Si. The band at 905 cm−1 is attributed to scissor mode of Si H2 and a large vibration absorption band saw at 610–660 cm−1 is a mixture of stretching mode of Si Si and wagging mode Si Hn (n = 1 and 2). The peak around 620 cm−1 corresponds to Si Si stretch mode and Si Hn wagging mode is seen at 665 cm−1 . In the high energy region of the spectra, the absorption peaks at 2105 and 2084 cm−1 are Si H2 and Si H stretching modes, respectively. The peak at 2196 is due to O2 SiH2 . Carbon related peaks are shown at 2900 cm−1 (as seen in inlet figure in Fig. 3). The peaks are attributed to C–H and C O at 2850 cm−1 and 2957 cm−1 and Si C at 2925 cm−1 . Moreover, it can be seen from Fig. 3 that marked changes take place in FTIR spectra when compared to just after the sensing process. These changes show especially at Si H related absorption peaks that the peaks decrease
E. Kayahan / Optik 164 (2018) 271–276
273
Fig. 2. The SEM pictures of the fresh PS with different magnifications.
Fig. 3. FTIR spectra of fresh and just after the sensing measurements were taken about 1 h of PS. Inlet figure shows carbon (C) related peaks.
after the sensing process. It is also seen in inlet figure in Fig. 3 that after the sensing process carbon related peaks slightly appears at around 2900 cm−1 . This could be due to the replacement of the hydrogen atoms by oxygen atoms of CO2 . The peaks are given in Fig. 3 are in good agreement with the data reported in the previous works [15–20]. From the FTIR spectra, it can be concluded that PS surface after the anodization is covered with hydrogen, oxygen atoms. After the sensing process taking about 1 h carbon related peaks slightly appear while Si H related peaks decrease. It can also be concluded that CO2 ad/absorbed onto PS surface over the hydrogen atoms comes from anodization process. Therefore, the weak hydrogen bonds on PS surface can play a critical role in sensing the CO2 gas. To get the PL spectra Ar gas was introduced into the sensing room (optical module) by a flow-meter (200 sccm) and waited about 30 min to obtain luminescence stability. After this, another flow-meter (4 sccm) which controls the CO2 gas was run for 5 min. The process was altered periodically (5 min) by varying CO2 concentrations. Fig. 4A shows that PL intensity decrease without any shifting with decreasing CO2 level. Fig. 4B which obtained from the PL spectra also shows the integrated area and normalized PL intensity versus CO2 quantity. As seen the Fig. 4A PL intensity decrease with CO2 gas, while the intensity increase with Ar gas for the periodic time of 5 min. It is also shown from Fig. 4B that the changes of PL intensity and the integrated area of PL spectra could be used as sensing parameters. The integrated area is more suitable than the intensity changes of PL spectra.
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E. Kayahan / Optik 164 (2018) 271–276
Fig. 4. (A) Shows the PL spectra of PS with respect to carbon dioxide concentration. Where PL spectra were taken by altering periodically (5 min) the CO2 concentrations. (B) shows the changes of PL intensity at 608 nm and the integrated area between 473 nm–721 nm of the PL spectra with CO2 concentrations. The solid lines show fitting functions.
This could understandable that CO2 gas ad/absorption on PS surface causes quenching of the PL spectra. The quenching could also be explained by electron transfer mechanisms, where, photo-excited PS endorses electron-hole pairs localized at Si O SiR moieties on the surface of crystallites and these moieties also act as electron donors and gas molecules act as acceptors. When the gas molecules achieve the PS surface, their molecular orbitals mix to a donor excited states localized at the Si O SiR moieties promoting the electron transfer reaction and consequently the PL quenches as was mentioned in Ref. [21] in detail. Fig. 5 shows the electrical response of PS surface during exposure to various concentrations of CO2 gas. It is shown in the figure that the electrical signal increases during exposure to a mixture of Ar + CO2 gas and then decreases during exposure to carrier gas (Ar). This could also be explained by the electron transfer mechanisms [21].
E. Kayahan / Optik 164 (2018) 271–276
275
Fig. 5. The electrical response of PS with respect to carbon dioxide concentration.
4. Conclusions We propose a novel and simple way to use PS as an active material for sensing CO2 gas. The possibility of a CO2 gas sensing using PS layer was demonstrated. Changes of PL spectra (intensity and area) and resistivity with the CO2 gas levels were also investigated in this study. We observed that PL intensity decreases, whereas, electrical signal (current) increases during exposure to increasing CO2 gas concentrations, because of the electron transfer mechanisms. The decrease in PL intensity during increasing CO2 level obeys to a linear function. However, the linear fitting obtained by PL spectrum area is more suitable than the intensity changes. The optical and electrical measurement results indicated that PS surface showed creditable gas sensing performances with respect to CO2 gas. Therefore, it can be concluded that PS is an ideal candidate material for fabrication of high performance, selective electrical/optical gas sensor in the near future. However, it is clear that many types of research are needed before application of porous silicon as a CO2 sensor. Acknowledgments The author is grateful to Prof. Dr. A.Y. Oral (Gebze Technical University at Turkey) for helpful discussions. This research was also financially supported by the Scientific and Technological Research Council of Turkey-TUBITAK (Project no. 111T357) and project unit of Kocaeli University (Project no. 2013/64 HDP). References [1] N. Zouadi, S. Messaci, S. Sam, D. Bradai, N. Gabouz, CO2 detection with CNx thin films deposited on porous silicon, Mater. Sci. Semicond. Process. 29 (2015) 367–371. [2] H.G. Shiraz, Efficient room temperature hydrogen gas sensing based on graphene oxide and decorated porous silicon, Int. J. Hydrogen Energy 42 (2017) 15966–15972. [3] W. Wang, Y. Goa, Q. Tao, Y.-Z. Liu, J.-J. Juo, X.-C. Ju, J.-K. Zhang, A novel porous silicon composite sensor for formaldehyde detection, Chin. J. Anal. Chem. 43 (6) (2015) 849–855. [4] P. Dwivedi, S. Dhanekar, S. Das, S. Chandra, Effect of TiO2 functionalization on nano-porous silicon for selective alcohol sensing at room temperature, J. Mater. Sci. Technol. 33 (6) (2017) 516–522. [5] Giuseppe Barillaro, Porous silicon gas sensing, in: Leigh Canham (Ed.), Handbook of Porous Silicon, Springer, 2014, p. 845. [6] U.M. Nayef, I.M. Khudhair, Study of porous silicon humidity sensor vapors by photoluminescence quenching for organic solvents, Optik 135 (2017) 169–173. [7] F. Tebizi-Tighilt, F. Zane, N. Belhaneche-Bensemra, S. Belhousse, S. Sam, N. Gabouze, Electrochemical gas sensors based on polypyrrole-porous silicon, Appl. Surf. Sci. 269 (2013) 180–183. [8] S. Ozdemir, J.L. Gole, The potential of porous silicon gas sensor, Curr. Opin. Solid State Mater. Sci. 11 (2007) 92–100. [9] G. Barillaro, A. Nannini, F. Pieri, Temperature behavior of the APSFET—a porous silicon-based FET gas sensor, Sens. Actuators B: Chem. 100 (2004) 185–189.
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E. Kayahan / Optik 164 (2018) 271–276
[10] T. Holec, T. Chvojka, I. Jelinek, J. Jindiric, I. Nemec, I. Pelant, J. Valenta, J. Dian, Determination of sensoric parameters of porous silicon in sensing of organic vapors, Mater. Sci. Eng. C 19 (2002) 251–254. [11] H.K. Min, H.S. Yang, S.M. Cho, Extremely sensitive optical sensing of ethanol using porous silicon, Sens. Actuators B: Chem. 67 (2000) 199–202. [12] E. Kayahan, Z.B. Bahsi, A.Y. Oral, M. Sezer, Porous silicon based sensor for organic vapors, Acta Phys. Pol. A 127 (2015) 1400–1402. [13] E. Kayahan, Porous silicon based humidity sensor, Acta Phys. Pol. A 127 (2015) 1397–1399. [14] O. Yılmaz, E. Kayahan, F. Gören, F. Dumludag, Methanol vapor sensing by porous silicon, Acta Phys. Pol. A 125 (2014) 288–289. [15] E. Kayahan, The role of surface oxidation on luminescence degradation of porous silicon, Appl. Surf. Sci. 257 (2011) 4311–4316. [16] Michael J. Sailor, Chemical reactivity and surface chemistry of porous silicon, in: Leigh Canham (Ed.), Handbook of Porous Silicon, Springer, 2014, p. 355. [17] P. Gupta, A.C. Dillon, A.S. Bracker, S.M. George, FTIR studies of H2O and D2O decomposition on porous silicon, Surf. Sci. 245 (1991) 360–372. [18] Y. Ogata, H. Niki, T. Sakka, M. Iwasaki, Oxidation of porous silicon under water-vapor environment, J. Electrochem. Soc. 142 (1995) 1595–1601. [19] J.M. Buriak, Organometallic chemistry on silicon surfaces: formation of functional monolayers bound through Si C bonds, Chem. Commun. 12 (1999) 1051–1060. [20] T.K. Mischki, R.L. Donkers, B.J. Eves, G.P. Lopinski, D.D.M. Wayner, Reaction of alkenes with hydrogen-terminated and photo-oxidized silicon surfaces: a comparison of thermal and photochemical processes, Langmuir 22 (2006) 8359–8365. [21] W.J. Salcedo, F.J.R. Fernandez, J.C. Rubim, Photoluminescence quenching effect on porous silicon films for gas sensors application, Spectrochim. Acta Part A 60 (2004) 1065–1070.