- Email: [email protected]
γ irradiation induced effects on the TCO thin films
Author’s Accepted Manuscript γ irradiation induced effects on the TCO thin films Ismail Kabacelik, Hakan Kutaruk, Serafettin Yaltkaya, Ramazan Sahin
www.elsevier.com/locate/radphyschem
PII: DOI: Reference:
S0969-806X(17)30125-1 http://dx.doi.org/10.1016/j.radphyschem.2017.01.042 RPC7398
To appear in: Radiation Physics and Chemistry Received date: 9 August 2016 Revised date: 2 December 2016 Accepted date: 31 January 2017 Cite this article as: Ismail Kabacelik, Hakan Kutaruk, Serafettin Yaltkaya and Ramazan Sahin, γ irradiation induced effects on the TCO thin films, Radiation Physics and Chemistry, http://dx.doi.org/10.1016/j.radphyschem.2017.01.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
γ irradiation induced effects on the TCO thin films Ismail Kabacelika,b , Hakan Kutaruka , Serafettin Yaltkayaa,b , Ramazan Sahina,b,c,∗ a b
Department of Physics Faculty of Science, Akdeniz University, 07058 Antalya, Turkey Nuclear Research and Application Center, Akdeniz University, 07058 Antalya, Turkey c Vocational School of Technical Sciences, Akdeniz University, 07058 Antalya, Turkey
Abstract We report on gamma irradiation induced changes both in the optical and electrical properties of the Transparent Conductive Oxide (TCO) thin films. We used Co-60 radioisotope as a natural source of γ in our experiments. Applied total irradiation doses to the prepared samples change from 1 to 4 kGy. The dose rate is kept finely constant at 200 Gy/min. Optical transmissions in VIS-NIR region of electromagnetic spectrum and electrical conductivity (I-V) measurements on irradiated samples are conducted with respect to the total dose. Results show that regardless of the irradiation dose, there is no change in the current flow through the contacts on the TCO thin films after the irradiation. On the other hand, based on the on-line measurements, the current increases with the gamma irradiation and a threshold irradiation is detected in the optical properties of irradiated samples. Also, thin films are seen to preserve their initial amorphous structures at such a low irradiation doses according to XRD measurements. We propose that these thin films can be used in gamma sensors for both optical and electrical applications. Keywords: Co-60, TCO, Gamma, irradiation 2016 MSC: 00-01, 99-00 1. Introduction
5
10
15
Due to their high transmittance in the visible region of electromagnetic spectrum and a good electrical conductivity, close to that of metals, 20 semiconductor TCO thin films have been gathering noticeable attention in a variety of applications [1, 2, 3]. The Indium Tin Oxide (ITO) and Aluminum zinc oxide (AZO) are widely used members of TCO thin films family [4, 5, 6, 7, 8]. 25 They also include a relatively higher density of free electrons in the conduction band when compared to other semiconductors. For example, ITO films coated on a glass substrate approximately posses an electrical conductivity of 10−4 Ω.cm and 30 an optical conductivity of ∼90% in the visible re∗
Corresponding author Email address: [email protected] (Ramazan Sahin) Preprint submitted to Radiation Physics and Chemistry
gion. These properties make TCO films a better candidate in the photovoltaic and electronic applications that are naturally exposed to irradiation in the outer space. There are there types of natural radioactivity in the universe; the α, the β, the γ. The alpha and the beta are in the form of particles whereas gamma irradiation is of a high energetic form of electromagnetic wave. Among them, highly energetic photons can carry strong potential to change or at least to modify properties of materials via transferring their energy to electrons of the target material. The effect of gamma irradiation on the bare glass [9, 10], doped glass [11, 12] samples, nanowires [13] and on other different types of thin films [14, 15, 16, 17, 18] has been extensively studied in the literature. Even though the semiconductors are quite sensitive to gamma irradiation, widely used TCO films have been ignored February 1, 2017
35
40
45
50
55
and only very few studies focus on the effect of 80 gamma irradiation on the TCO films [19] at such high level gamma irradiation doses. Co-60 is the most appropriate gamma radioisotope source to obtain or to trigger a maximum ionization at the samples. Therefore, in this work, 85 we investigate the effect of Co − 60(γ) irradiation on the optical and structural properties of TCO films as well as on electrical conductivity by measuring DC Current-Voltage (I-V) characteristics of TCO thin films at relatively lower doses. In 90 addition, we divide our experiment into two categories; on-line and off-line measurements. Then, we conduct a series of time-dependent measurements to discover the effects after gamma source is turned off. 95 The paper is organized as follows; first experimental setup and procedures are explained in Section 2, then the results of systematic dose experiments are presented. Finally, we conclude this paper in Section 4.
65
70
75
0.9
0.8 bare glass 1 kGy 2 kGy 3 kGy 4 kGy
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
(b)
1
Normalized Transmission
60
In our experiments, we used ITO as TCO samples deposited on 10 mm x 10 mm x 1 mm Schott glasses using RF magnetron sputtering process. Prior to irradiation with Co-60, the thicknesses of the prepared films were measured as 200 nm by a Profilometer (Dektak 150, Veeco). Then, the sheet resistances of the films were measured with four-point-probe (Jandel Model RM3-AR) as 13 Ohm/sq. Finally, 2-point contacts for I-V measurements were carried out on thin films with a conductive epoxy. The samples were always positioned perpendicular to the incoming direction of the gamma irradiation. Throughout the experiments, the dose rate was kept constant at 200 Gy/min in order to eliminate its effect. Also a homogenous dose distribution was obtained on the samples. All experiments were carried out at the room temperature and in ambient conditions. Potentiostat/Galvanostat (Ivium Technologies) device was used for I-V measurements and a fiber coupled spectrometer (CCS200-Thorlabs) was employed to acquire an optical transmission spectra
(a)
1
Normalized Transmission
2. Experiments
in 350-1000 nm wavelength range. The I-V measurements were taken in on-line and off-line modes. The on-line measurements were conducted under γ-irradiation while off-line measurements were conducted when the γ irradiation was turned off. During on-line measurements, the I-V device was shielded by lead bricks. Then, we checked the shielding via passing current through a resistance inside the lead brick with and without gamma radiation. In these measurements, we did not observe any change in the behavior of I-V characteristic of resistance. This indicates robustness of the shielding. The XRD measurements by a Rigaku MiniFlex X-ray diffractometer with monochromatic CuK incident beam (λ=0.154056 nm, high resolution) in the θ-2θ scan geometry were also performed in order to compare the structural properties between irradiated and deposited samples.
0.9
0.8 bare glass Just after After a day After 4 days After 7 days
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
Figure 1: (a) Transmission spectra of irradiated un-coated glass substrates with respect to total dose is presented and (b) its time dependent behavior is also presented
2
105
110
115
120
125
130
135
140
Since the ITO films were deposited on glass substrates, one would expect these substrates to be sensitive to gamma irradiation. In fact, they might be affected first at least. Therefore, we150 first analyzed the effect of gamma irradiation on the bare glass substrates. Those glass substrates were completely colorless before irradiation. However, they all begin to get brown in color with respect to irradiation dose and transparency of155 glass substrates gradually decreases. The spectra taken on irradiated samples showed decrease in transmission. In order to differentiate the wavelength dependent effect of gamma irradiation, we normalized the transmission spectra. All trans-160 mission measurements in this part of the experiments were taken 30 minutes after the γ irradiation for each sample. Fig. 1 (a) shows normalized transmission spectra of irradiated glass substrates found by dividing the spectra measured through irradiated glass sample by the spectra measured without glass sample taken just after the gammasource was turned off. As seen from Fig. 1 (a), the decrease in transmittance at visible region of electromagnetic spectrum is relatively higher and it is inversely proportional to the total irradiation dose. On the other hand, it indicates an opposite behavior in the near-infrared (NIR). Interestingly all transmission spectra exhibit a similar trend for different doses at this region. In order to discover its time dependence we also obtained transmission spectra of irradiated samples in time. Fig. 1 (b) shows recovery of transmission spectrum in the visible region while it preserves its behavior in the NIR. Hence, the effect of substrate should be considered when obtaining transmission spectra of ITO films. Therefore, all transmission spectra presented in this study are found by dividing the spectra measured through irradiated ITO film with glass substrate by spectra measured from glass substrate irradiated together at the same conditions. In order to observe the effect of total dose on the optical properties of the ITO films, we started with systematic dose experiments. We increased total dose up to 4 kGy with 1 kGy intervals. For 3
each dose, transmission spectra was measured and plotted as explained above. Fig. 2 shows our results for irradiated ITO samples. Recent studies show that high dose gamma irradiation changes optical properties of the TCO films [19, 20]. Although relatively small doses were employed in our experiments, the optical properties of ITO thin films were evidently changed. Up to 2 kGy, the optical property of ITO films deviated linearly to the gamma irradiation. On the other hand, a small increase in the total dose caused a change in the optical properties of the ITO films. At 3 kGy gamma irradiation, the optical transmission of the ITO film in the visible was much more sensitive than it was in the infrared region. Interestingly, at 4 kGy, the infrared region of the spectrum started to respond dominantly to gamma irradiation. Results were sketched in Fig. 2 (a). (a)
1
Normalized Transmission
100
145
0.9
0.8 as deposited 1 kGy 2 kGy 3 kGy 4 kGy
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
(b)
1
Normalized Transmission
3. Results and Discussions
0.9
0.8 as deposited Just after After a day After 4 days After 7 days
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
Figure 2: (a) Effect of total dose on transmission spectrum of radiated ITO samples is presented, (b) Time dependent transmission spectrum of irradiated ITO samples is also shown.
2.2
50
unirradiated 2 kGy 4 kGy Current (mA)
n
1.8
40
Current (mA)
2
34 33 32 31 0.85
0.9 Voltage (V)
0.95
30
as deposited 1 kGy 2 kGy 3 kGy 4 kGy
1.6
1.4
400
500
600 700 800 Wavelength (nm)
900
20 0.5
1000
170
175
180
185
190
0.7
0.8 0.9 Voltage (V)
1
1.1
1.2
Figure 4: Current-Voltage characteristics of as deposited and irradiated samples. Inset shows the current values at 0.9 V for different doses.
Figure 3: Spectroscopic Ellipsometry measurements of refractive index (n) of ITO thin films for un-irradiated, 2 kGy and 4 kGy total doses.
165
0.6
In order to show characteristic behavior of induced optical changes, we performed time-dependent 195 transmission spectra analysis after irradiation. Fig. 2 (b) shows obtained results for 4 kGy irradiated ITO thin films. The spectrum taken after a week is similar to the spectrum taken fron un-irradiated samples. These results clearly support that opti200 cal changes due to very low dose γ irradiation are temporary which allows several uses of these thin films without any disposal for space, electronic and sensor applications. Refractive index of prepared ITO thin films 205 were analyzed through Spectroscopic Ellipsometry (SE) measurements using SEMILAB SOPRA GES5E equipped with Sopra Winelli II software. Ellipsometric angles (ψ and Δ) were measured in the spectral range of 350-1000 nm at at 70◦ an210 gle of incidence at room temperature with a xenon lamp as source. SE measurements were conducted even after γ-ray source was turned off. Results in Fig. 3 are in well agreement with obtained transmission spectra. The optical properties of 215 ITO thin films did not change much until 2 kGy mentioned as a threshold for nonlinear optical response above dose was applied. After optical observation of gamma irradiation induced effects on the ITO films, we conducted IV measurements in the following way. First, the ITO films were exposed to the gamma rays. Then,220 4
the gamma source was turned off and irradiated samples were taken off for the I-V measurement from the source. Although optically induced effects were observed after gamma irradiation, no change was present in I-V character of deposited and irradiated samples. On the other hand, we observed a little increase in the DC conductivity of irradiated samples during on-line measurements as shown in Fig.4. This change was seen to be more significant in higher doses in our experiments. The physics behind this observation can be explained as follows. When the photon interact with a charged particle, in our case it is electron , it either transfers a momentum or increases number of free charge carriers. This kind of effect was also observed at relatively higher doses in the gamma irradiated CdSe nanowires [13]. We also conducted on XRD measurements on irradiated ITO samples. Fig. 5 shows XRD measurements for two different cases. These two measurements obtained from as deposited and irradiated at 4 kGy demonstrate that multi-crystalline structure of ITO film keeps entirely preserved at these conditions. 4. Conclusion γ-irradiation induced effects on the ITO thin films were studied through I-V, optical transmission in VIS-NIR region and XRD measurements.
250
(222) (400)
Intensity (a.u.)
(440)
(622)
255
as deposited irradiated 10
30
50 2θ (degree)
70
260
90
Figure 5: XRD measurements on as deposited and irradiated samples. The spectra obtained from 4 kGy irradiated265 sample is shifted a small amount for clarity.
225
230
235
240
Off-line I-V measurements showed that the electrical properties of the ITO thin films are not de-270 pendent on the total dose. On the other hand, the current passing through terminals of the samples increases with the total dose during on-line measurements. Optical transmission experiments275 conducted in off-line mode showed a dose threshold effect. Transmission spectra of irradiated samples were seen to have change after a certain irradiation dose value. The shape of transmission280 spectra was preserved until this certain value. We also acquired time dependent optical transmission spectra to discover temporary and permanent effects of gamma irradiation. We found that the 285 transmission spectra taken from irradiated sample nearly returns back to optical transmission spectra of unirradiated ITO films after a couple of days when it is kept in ambient conditions. All systematical experiments show that ITO thin290 films can be candidate as a radiation sensor provided that systematic dose experiments with other gamma radiation sources and radiation types are 295 carried out. Acknowledgments
245
The authors thank GUNAM (Center for So-300 lar Energy Research and Applications) for sample preparation, Dr. Edip Bayram for I-V measurements, NUBA (Akdeniz University Nuclear Research and Application Center) and Department 5
of Physics (Akdeniz University) for irradiation facility. We also would like to thank Dr. Timur Sahin and Dr. Ismail Boztosun for useful discussions. [1] K. Chopra, S. Major, D. Pandya, Transparent Conductors - A Status Review, Thin Solid Films 102 (1) (1983) 1–46. [2] A. Shah, H. Schade, M. Vanecek, J. Meier, E. VallatSauvain, N. Wyrsch, U. Kroll, C. Droz, J. Bailat, Thin-film silicon solar cell technology, Progress in Photovoltaics 12 (2-3) (2004) 113–142. [3] H. Hosono, Recent progress in transparent oxide semiconductors: Materials and device application, Thin Solid Films 515 (15) (2007) 6000–6014, Symposium on Thin Film Chalcogenide Photovoltaic Materials Held at the EMRS 2006 Spring Conference, Nice, France, May 29-Jun 02, 2006. [4] S.-H. Chuang, C.-S. Tsung, C.-H. Chen, S.-L. Ou, R.-H. Horng, C.-Y. Lin, D.-S. Wuu, Transparent Conductive Oxide Films Embedded with Plasmonic Nanostructure for Light-Emitting Diode Applications, ACS Applied Materials & Interfaces 7 (4) (2015) 2546–2553. [5] M. R. Haraty, M. Naser-Moghadasi, A. A. LotfiNeyestanak, A. Nikfarjam, Circular Ring Optically Transparent Antenna for Ultra-Wideband Applications, Applied Computational Electromagnetics Society Journal 30 (2) (2015) 208–212. [6] S.-H. Chan, M.-C. Li, H.-S. Wei, S.-H. Chen, C.-C. Kuo, The Effect of Annealing on Nanothick Indium Tin Oxide Transparent Conductive Films for Touch Sensors, Journal Of Nanomaterials vol. 2015 (Article ID 179804). doi:{10.1155/2015/179804}. [7] M. Dosmailov, L. N. Leonat, J. Patek, D. Roth, P. Bauer, M. C. Scharber, N. S. Sariciftci, J. D. Pedarnig, Transparent conductive ZnO layers on polymer substrates: Thin film deposition and application in organic solar cells, Thin Solid Films 591 (A) (2015) 97–104. [8] S. Boscarino, I. Crupi, S. Mirabella, F. Simone, A. Terrasi, TCO/Ag/TCO transparent electrodes for solar cells application, Applied Physics A-Materials Science & Processing 116 (3) (2014) 1287–1291. [9] J. Du, J. Wu, L. Song, L. Zhao, Reflectivity and absorption coefficient of a borosilicate glass during 60co- irradiation calculated from data measured by an integrating sphere, Radiation Effects and Defects in Solids 167 (1) (2012) 37–48. [10] J. Du, J. Wu, L. Zhao, L. Song, Color centers of a borosilicate glass induced by 10 mev proton, 1.85 mev electron and 60co- ray, Radiation Physics and Chemistry 86 (2013) 59–63. [11] F. ElBatal, M. Ouis, A. Abdelghany, N. A. Ghoneim, Structural and optical correlation of gammairradiated 3d transition metals-doped lithium disili-
305
310
315
320
325
330
335
340
345
cate glasses, Silicon 7 (4) (2015) 409–417. [12] A. Abdelghany, H. ElBatal, F. EzzElDin, Influence of cuo content on the structure of lithium fluoroborate glasses: Spectral and gamma irradiation studies, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 788–792. [13] M. Kumari, P. Rana, R. Chauhan, Modifications in structural and electrical properties of gamma irradiated CdSe nanowires, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 753 (2014) 116–120. [14] T. Maity, S. Sharma, Effect of gamma radiation on optical and electrical properties of tellurium dioxide thin films, Bulletin of Materials Science 31 (6) (2008) 841–846. [15] M. El-Nahass, B. Khalifa, I. Soliman, Gamma radiation-induced changes on the structural and optical properties of aluminum phthalocyanine chloride thin films, Optical Materials 46 (2015) 115–121. [16] S. Raghu, K. Archana, C. Sharanappa, S. Ganesh, H. Devendrappa, The physical and chemical properties of gamma ray irradiated polymer electrolyte films, Journal of Non-Crystalline Solids 426 (2015) 55–62. [17] N. V. Duy, T. H. Toan, N. D. Hoa, N. V. Hieu, Effects of gamma irradiation on hydrogen gas-sensing characteristics of pdsno2 thin filmsensors, International Journal of Hydrogen Energy 40 (36) (2015) 12572– 12580. [18] L. Gui-ang, L. Da, Z. Chang-wei, X. Wei, C. Lianquan, Effects of rays irradiation on structure and property of tio2 thin films, Radiation Effects and Defects in Solids 169 (4) (2014) 293–299. [19] S. M. Al-Sofiany, H. E. Hassan, A. H. Ashour, M. M. Abd El-Raheem, Study of gamma-rays Enhanced Changes of the ZnO:Al Thin Film Structure and Optical Properties, International Journal of Electrochemical Science 9 (6) (2014) 3209–3221. [20] A. Alyamani, N. Mustapha, Effects of high dose gamma irradiation on ITO thin film properties, Thin Solid Films 611 (2016) 27–32.
6
www.elsevier.com/locate/radphyschem
PII: DOI: Reference:
S0969-806X(17)30125-1 http://dx.doi.org/10.1016/j.radphyschem.2017.01.042 RPC7398
To appear in: Radiation Physics and Chemistry Received date: 9 August 2016 Revised date: 2 December 2016 Accepted date: 31 January 2017 Cite this article as: Ismail Kabacelik, Hakan Kutaruk, Serafettin Yaltkaya and Ramazan Sahin, γ irradiation induced effects on the TCO thin films, Radiation Physics and Chemistry, http://dx.doi.org/10.1016/j.radphyschem.2017.01.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
γ irradiation induced effects on the TCO thin films Ismail Kabacelika,b , Hakan Kutaruka , Serafettin Yaltkayaa,b , Ramazan Sahina,b,c,∗ a b
Department of Physics Faculty of Science, Akdeniz University, 07058 Antalya, Turkey Nuclear Research and Application Center, Akdeniz University, 07058 Antalya, Turkey c Vocational School of Technical Sciences, Akdeniz University, 07058 Antalya, Turkey
Abstract We report on gamma irradiation induced changes both in the optical and electrical properties of the Transparent Conductive Oxide (TCO) thin films. We used Co-60 radioisotope as a natural source of γ in our experiments. Applied total irradiation doses to the prepared samples change from 1 to 4 kGy. The dose rate is kept finely constant at 200 Gy/min. Optical transmissions in VIS-NIR region of electromagnetic spectrum and electrical conductivity (I-V) measurements on irradiated samples are conducted with respect to the total dose. Results show that regardless of the irradiation dose, there is no change in the current flow through the contacts on the TCO thin films after the irradiation. On the other hand, based on the on-line measurements, the current increases with the gamma irradiation and a threshold irradiation is detected in the optical properties of irradiated samples. Also, thin films are seen to preserve their initial amorphous structures at such a low irradiation doses according to XRD measurements. We propose that these thin films can be used in gamma sensors for both optical and electrical applications. Keywords: Co-60, TCO, Gamma, irradiation 2016 MSC: 00-01, 99-00 1. Introduction
5
10
15
Due to their high transmittance in the visible region of electromagnetic spectrum and a good electrical conductivity, close to that of metals, 20 semiconductor TCO thin films have been gathering noticeable attention in a variety of applications [1, 2, 3]. The Indium Tin Oxide (ITO) and Aluminum zinc oxide (AZO) are widely used members of TCO thin films family [4, 5, 6, 7, 8]. 25 They also include a relatively higher density of free electrons in the conduction band when compared to other semiconductors. For example, ITO films coated on a glass substrate approximately posses an electrical conductivity of 10−4 Ω.cm and 30 an optical conductivity of ∼90% in the visible re∗
Corresponding author Email address: [email protected] (Ramazan Sahin) Preprint submitted to Radiation Physics and Chemistry
gion. These properties make TCO films a better candidate in the photovoltaic and electronic applications that are naturally exposed to irradiation in the outer space. There are there types of natural radioactivity in the universe; the α, the β, the γ. The alpha and the beta are in the form of particles whereas gamma irradiation is of a high energetic form of electromagnetic wave. Among them, highly energetic photons can carry strong potential to change or at least to modify properties of materials via transferring their energy to electrons of the target material. The effect of gamma irradiation on the bare glass [9, 10], doped glass [11, 12] samples, nanowires [13] and on other different types of thin films [14, 15, 16, 17, 18] has been extensively studied in the literature. Even though the semiconductors are quite sensitive to gamma irradiation, widely used TCO films have been ignored February 1, 2017
35
40
45
50
55
and only very few studies focus on the effect of 80 gamma irradiation on the TCO films [19] at such high level gamma irradiation doses. Co-60 is the most appropriate gamma radioisotope source to obtain or to trigger a maximum ionization at the samples. Therefore, in this work, 85 we investigate the effect of Co − 60(γ) irradiation on the optical and structural properties of TCO films as well as on electrical conductivity by measuring DC Current-Voltage (I-V) characteristics of TCO thin films at relatively lower doses. In 90 addition, we divide our experiment into two categories; on-line and off-line measurements. Then, we conduct a series of time-dependent measurements to discover the effects after gamma source is turned off. 95 The paper is organized as follows; first experimental setup and procedures are explained in Section 2, then the results of systematic dose experiments are presented. Finally, we conclude this paper in Section 4.
65
70
75
0.9
0.8 bare glass 1 kGy 2 kGy 3 kGy 4 kGy
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
(b)
1
Normalized Transmission
60
In our experiments, we used ITO as TCO samples deposited on 10 mm x 10 mm x 1 mm Schott glasses using RF magnetron sputtering process. Prior to irradiation with Co-60, the thicknesses of the prepared films were measured as 200 nm by a Profilometer (Dektak 150, Veeco). Then, the sheet resistances of the films were measured with four-point-probe (Jandel Model RM3-AR) as 13 Ohm/sq. Finally, 2-point contacts for I-V measurements were carried out on thin films with a conductive epoxy. The samples were always positioned perpendicular to the incoming direction of the gamma irradiation. Throughout the experiments, the dose rate was kept constant at 200 Gy/min in order to eliminate its effect. Also a homogenous dose distribution was obtained on the samples. All experiments were carried out at the room temperature and in ambient conditions. Potentiostat/Galvanostat (Ivium Technologies) device was used for I-V measurements and a fiber coupled spectrometer (CCS200-Thorlabs) was employed to acquire an optical transmission spectra
(a)
1
Normalized Transmission
2. Experiments
in 350-1000 nm wavelength range. The I-V measurements were taken in on-line and off-line modes. The on-line measurements were conducted under γ-irradiation while off-line measurements were conducted when the γ irradiation was turned off. During on-line measurements, the I-V device was shielded by lead bricks. Then, we checked the shielding via passing current through a resistance inside the lead brick with and without gamma radiation. In these measurements, we did not observe any change in the behavior of I-V characteristic of resistance. This indicates robustness of the shielding. The XRD measurements by a Rigaku MiniFlex X-ray diffractometer with monochromatic CuK incident beam (λ=0.154056 nm, high resolution) in the θ-2θ scan geometry were also performed in order to compare the structural properties between irradiated and deposited samples.
0.9
0.8 bare glass Just after After a day After 4 days After 7 days
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
Figure 1: (a) Transmission spectra of irradiated un-coated glass substrates with respect to total dose is presented and (b) its time dependent behavior is also presented
2
105
110
115
120
125
130
135
140
Since the ITO films were deposited on glass substrates, one would expect these substrates to be sensitive to gamma irradiation. In fact, they might be affected first at least. Therefore, we150 first analyzed the effect of gamma irradiation on the bare glass substrates. Those glass substrates were completely colorless before irradiation. However, they all begin to get brown in color with respect to irradiation dose and transparency of155 glass substrates gradually decreases. The spectra taken on irradiated samples showed decrease in transmission. In order to differentiate the wavelength dependent effect of gamma irradiation, we normalized the transmission spectra. All trans-160 mission measurements in this part of the experiments were taken 30 minutes after the γ irradiation for each sample. Fig. 1 (a) shows normalized transmission spectra of irradiated glass substrates found by dividing the spectra measured through irradiated glass sample by the spectra measured without glass sample taken just after the gammasource was turned off. As seen from Fig. 1 (a), the decrease in transmittance at visible region of electromagnetic spectrum is relatively higher and it is inversely proportional to the total irradiation dose. On the other hand, it indicates an opposite behavior in the near-infrared (NIR). Interestingly all transmission spectra exhibit a similar trend for different doses at this region. In order to discover its time dependence we also obtained transmission spectra of irradiated samples in time. Fig. 1 (b) shows recovery of transmission spectrum in the visible region while it preserves its behavior in the NIR. Hence, the effect of substrate should be considered when obtaining transmission spectra of ITO films. Therefore, all transmission spectra presented in this study are found by dividing the spectra measured through irradiated ITO film with glass substrate by spectra measured from glass substrate irradiated together at the same conditions. In order to observe the effect of total dose on the optical properties of the ITO films, we started with systematic dose experiments. We increased total dose up to 4 kGy with 1 kGy intervals. For 3
each dose, transmission spectra was measured and plotted as explained above. Fig. 2 shows our results for irradiated ITO samples. Recent studies show that high dose gamma irradiation changes optical properties of the TCO films [19, 20]. Although relatively small doses were employed in our experiments, the optical properties of ITO thin films were evidently changed. Up to 2 kGy, the optical property of ITO films deviated linearly to the gamma irradiation. On the other hand, a small increase in the total dose caused a change in the optical properties of the ITO films. At 3 kGy gamma irradiation, the optical transmission of the ITO film in the visible was much more sensitive than it was in the infrared region. Interestingly, at 4 kGy, the infrared region of the spectrum started to respond dominantly to gamma irradiation. Results were sketched in Fig. 2 (a). (a)
1
Normalized Transmission
100
145
0.9
0.8 as deposited 1 kGy 2 kGy 3 kGy 4 kGy
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
(b)
1
Normalized Transmission
3. Results and Discussions
0.9
0.8 as deposited Just after After a day After 4 days After 7 days
0.7
0.6
500
600 700 800 Wavelength (nm)
900
1000
Figure 2: (a) Effect of total dose on transmission spectrum of radiated ITO samples is presented, (b) Time dependent transmission spectrum of irradiated ITO samples is also shown.
2.2
50
unirradiated 2 kGy 4 kGy Current (mA)
n
1.8
40
Current (mA)
2
34 33 32 31 0.85
0.9 Voltage (V)
0.95
30
as deposited 1 kGy 2 kGy 3 kGy 4 kGy
1.6
1.4
400
500
600 700 800 Wavelength (nm)
900
20 0.5
1000
170
175
180
185
190
0.7
0.8 0.9 Voltage (V)
1
1.1
1.2
Figure 4: Current-Voltage characteristics of as deposited and irradiated samples. Inset shows the current values at 0.9 V for different doses.
Figure 3: Spectroscopic Ellipsometry measurements of refractive index (n) of ITO thin films for un-irradiated, 2 kGy and 4 kGy total doses.
165
0.6
In order to show characteristic behavior of induced optical changes, we performed time-dependent 195 transmission spectra analysis after irradiation. Fig. 2 (b) shows obtained results for 4 kGy irradiated ITO thin films. The spectrum taken after a week is similar to the spectrum taken fron un-irradiated samples. These results clearly support that opti200 cal changes due to very low dose γ irradiation are temporary which allows several uses of these thin films without any disposal for space, electronic and sensor applications. Refractive index of prepared ITO thin films 205 were analyzed through Spectroscopic Ellipsometry (SE) measurements using SEMILAB SOPRA GES5E equipped with Sopra Winelli II software. Ellipsometric angles (ψ and Δ) were measured in the spectral range of 350-1000 nm at at 70◦ an210 gle of incidence at room temperature with a xenon lamp as source. SE measurements were conducted even after γ-ray source was turned off. Results in Fig. 3 are in well agreement with obtained transmission spectra. The optical properties of 215 ITO thin films did not change much until 2 kGy mentioned as a threshold for nonlinear optical response above dose was applied. After optical observation of gamma irradiation induced effects on the ITO films, we conducted IV measurements in the following way. First, the ITO films were exposed to the gamma rays. Then,220 4
the gamma source was turned off and irradiated samples were taken off for the I-V measurement from the source. Although optically induced effects were observed after gamma irradiation, no change was present in I-V character of deposited and irradiated samples. On the other hand, we observed a little increase in the DC conductivity of irradiated samples during on-line measurements as shown in Fig.4. This change was seen to be more significant in higher doses in our experiments. The physics behind this observation can be explained as follows. When the photon interact with a charged particle, in our case it is electron , it either transfers a momentum or increases number of free charge carriers. This kind of effect was also observed at relatively higher doses in the gamma irradiated CdSe nanowires [13]. We also conducted on XRD measurements on irradiated ITO samples. Fig. 5 shows XRD measurements for two different cases. These two measurements obtained from as deposited and irradiated at 4 kGy demonstrate that multi-crystalline structure of ITO film keeps entirely preserved at these conditions. 4. Conclusion γ-irradiation induced effects on the ITO thin films were studied through I-V, optical transmission in VIS-NIR region and XRD measurements.
250
(222) (400)
Intensity (a.u.)
(440)
(622)
255
as deposited irradiated 10
30
50 2θ (degree)
70
260
90
Figure 5: XRD measurements on as deposited and irradiated samples. The spectra obtained from 4 kGy irradiated265 sample is shifted a small amount for clarity.
225
230
235
240
Off-line I-V measurements showed that the electrical properties of the ITO thin films are not de-270 pendent on the total dose. On the other hand, the current passing through terminals of the samples increases with the total dose during on-line measurements. Optical transmission experiments275 conducted in off-line mode showed a dose threshold effect. Transmission spectra of irradiated samples were seen to have change after a certain irradiation dose value. The shape of transmission280 spectra was preserved until this certain value. We also acquired time dependent optical transmission spectra to discover temporary and permanent effects of gamma irradiation. We found that the 285 transmission spectra taken from irradiated sample nearly returns back to optical transmission spectra of unirradiated ITO films after a couple of days when it is kept in ambient conditions. All systematical experiments show that ITO thin290 films can be candidate as a radiation sensor provided that systematic dose experiments with other gamma radiation sources and radiation types are 295 carried out. Acknowledgments
245
The authors thank GUNAM (Center for So-300 lar Energy Research and Applications) for sample preparation, Dr. Edip Bayram for I-V measurements, NUBA (Akdeniz University Nuclear Research and Application Center) and Department 5
of Physics (Akdeniz University) for irradiation facility. We also would like to thank Dr. Timur Sahin and Dr. Ismail Boztosun for useful discussions. [1] K. Chopra, S. Major, D. Pandya, Transparent Conductors - A Status Review, Thin Solid Films 102 (1) (1983) 1–46. [2] A. Shah, H. Schade, M. Vanecek, J. Meier, E. VallatSauvain, N. Wyrsch, U. Kroll, C. Droz, J. Bailat, Thin-film silicon solar cell technology, Progress in Photovoltaics 12 (2-3) (2004) 113–142. [3] H. Hosono, Recent progress in transparent oxide semiconductors: Materials and device application, Thin Solid Films 515 (15) (2007) 6000–6014, Symposium on Thin Film Chalcogenide Photovoltaic Materials Held at the EMRS 2006 Spring Conference, Nice, France, May 29-Jun 02, 2006. [4] S.-H. Chuang, C.-S. Tsung, C.-H. Chen, S.-L. Ou, R.-H. Horng, C.-Y. Lin, D.-S. Wuu, Transparent Conductive Oxide Films Embedded with Plasmonic Nanostructure for Light-Emitting Diode Applications, ACS Applied Materials & Interfaces 7 (4) (2015) 2546–2553. [5] M. R. Haraty, M. Naser-Moghadasi, A. A. LotfiNeyestanak, A. Nikfarjam, Circular Ring Optically Transparent Antenna for Ultra-Wideband Applications, Applied Computational Electromagnetics Society Journal 30 (2) (2015) 208–212. [6] S.-H. Chan, M.-C. Li, H.-S. Wei, S.-H. Chen, C.-C. Kuo, The Effect of Annealing on Nanothick Indium Tin Oxide Transparent Conductive Films for Touch Sensors, Journal Of Nanomaterials vol. 2015 (Article ID 179804). doi:{10.1155/2015/179804}. [7] M. Dosmailov, L. N. Leonat, J. Patek, D. Roth, P. Bauer, M. C. Scharber, N. S. Sariciftci, J. D. Pedarnig, Transparent conductive ZnO layers on polymer substrates: Thin film deposition and application in organic solar cells, Thin Solid Films 591 (A) (2015) 97–104. [8] S. Boscarino, I. Crupi, S. Mirabella, F. Simone, A. Terrasi, TCO/Ag/TCO transparent electrodes for solar cells application, Applied Physics A-Materials Science & Processing 116 (3) (2014) 1287–1291. [9] J. Du, J. Wu, L. Song, L. Zhao, Reflectivity and absorption coefficient of a borosilicate glass during 60co- irradiation calculated from data measured by an integrating sphere, Radiation Effects and Defects in Solids 167 (1) (2012) 37–48. [10] J. Du, J. Wu, L. Zhao, L. Song, Color centers of a borosilicate glass induced by 10 mev proton, 1.85 mev electron and 60co- ray, Radiation Physics and Chemistry 86 (2013) 59–63. [11] F. ElBatal, M. Ouis, A. Abdelghany, N. A. Ghoneim, Structural and optical correlation of gammairradiated 3d transition metals-doped lithium disili-
305
310
315
320
325
330
335
340
345
cate glasses, Silicon 7 (4) (2015) 409–417. [12] A. Abdelghany, H. ElBatal, F. EzzElDin, Influence of cuo content on the structure of lithium fluoroborate glasses: Spectral and gamma irradiation studies, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 788–792. [13] M. Kumari, P. Rana, R. Chauhan, Modifications in structural and electrical properties of gamma irradiated CdSe nanowires, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 753 (2014) 116–120. [14] T. Maity, S. Sharma, Effect of gamma radiation on optical and electrical properties of tellurium dioxide thin films, Bulletin of Materials Science 31 (6) (2008) 841–846. [15] M. El-Nahass, B. Khalifa, I. Soliman, Gamma radiation-induced changes on the structural and optical properties of aluminum phthalocyanine chloride thin films, Optical Materials 46 (2015) 115–121. [16] S. Raghu, K. Archana, C. Sharanappa, S. Ganesh, H. Devendrappa, The physical and chemical properties of gamma ray irradiated polymer electrolyte films, Journal of Non-Crystalline Solids 426 (2015) 55–62. [17] N. V. Duy, T. H. Toan, N. D. Hoa, N. V. Hieu, Effects of gamma irradiation on hydrogen gas-sensing characteristics of pdsno2 thin filmsensors, International Journal of Hydrogen Energy 40 (36) (2015) 12572– 12580. [18] L. Gui-ang, L. Da, Z. Chang-wei, X. Wei, C. Lianquan, Effects of rays irradiation on structure and property of tio2 thin films, Radiation Effects and Defects in Solids 169 (4) (2014) 293–299. [19] S. M. Al-Sofiany, H. E. Hassan, A. H. Ashour, M. M. Abd El-Raheem, Study of gamma-rays Enhanced Changes of the ZnO:Al Thin Film Structure and Optical Properties, International Journal of Electrochemical Science 9 (6) (2014) 3209–3221. [20] A. Alyamani, N. Mustapha, Effects of high dose gamma irradiation on ITO thin film properties, Thin Solid Films 611 (2016) 27–32.
6