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Structural and Optical Properties of Vacuum Coated and Annealed Copper Phthalocyanine (CUPC) Thin Films
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 2 (2015) 1770 – 1775
4th International Conference on Materials Processing and Characterization
Structural and Optical Properties of Vacuum Coated and Annealed Copper Phthalocyanine (CUPC) Thin Films Vidya.Ca, Priya A Hoskeria, C.M. Josepha, Advanced Materials Research Laboratory, Department of Physics, Dayananda Sagar College of Engineering, Shavige Malleswara Hi lls, Kumaraswamy Layout, Bangalore 560078, Karnataka, India
Abstract Heat treatment is able to cause the structural transformation of phthalocyanine thin film during the post-deposition heat treatment. The annealing effects of the process on the film characteristics of vacuum deposited copper phthalocyanine thin fi lms were studied. However, the pre-annealing leads to a larger-grain and a more compact structure. Structure transformation was inhibited by post-deposition annealing at 300oC. Thin films of CuPc were deposited using vacuum evaporation technique method onto glass substrates. The films were annealed at 4 different temperatures (323, 333, 343 and 353 K) in air at different intervals of time. Optical studies were done and the results are discussed. The optical band gap for the film as obtained from the graph for all the thin films are tabulated and analyzed. X ray diffraction studies on the deposited film showed crystallinity with a major peak for CuPc. © 2014 The Authors. Elsevier Ltd. All rights reserved. © 2015 Elsevier Ltd. All rights reserved. ofInternational the 4th International Selection andpeer-review peer-review under responsibility ofconference the conference committee members Selection and under responsibility of the committee members of the 4th conferenceconference on Materialson Materials and Characterization. Processing Processing and Characterization. Keywords: Copper phthalocyanine; annealing; solar cells; optical study; structural study.
1.Introduction Phthalocyanines (Pcs) are small organic molecules characterized by their high symmetry, planarity and electron delocalization. Besides, Pcs can be easily sublimed in high vacuum systems resulting in high-purity thin films with excellent growth properties and chemical stability, taking into account that the use of the sublimation technique allows the deposition of thin films with controlled thickness and structural properties. Phthalocyanines are receiving * Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail address:[email protected]
2214-7853 © 2015 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Processing and Characterization. doi:10.1016/j.matpr.2015.07.019
C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
1771
considerable attention, as they are organic semiconductors having very interesting properties coupled with excellent stability to harsh chemical environments. Their optical and electronic properties were exploited for various applications such as pigments in paints and printing inks, infrared security devices, information storage and computer disk writing, conducting polymers and chemical sensors. Metal phthalocyanines (MPcs) discovered in the 1930s are represented by a broad family of metal-organic compounds with M = Be, Mn, Fe, Co, Ni, Cu, Pt, and Pb [1-4]. Due to their thermal stability, chemical inertness, high molecular symmetry, and favorable optical properties, MPcs are of great scientific and industrial interest [5]. Metal-based phthalocyanines have drawn increasing interest because of their potential applications in gas sensors, organic FETs, optical storage, optical switches and organic photovoltaic cells (OPVs) [6-14]. Most of these applications require the use of phthalocyanines in the form of thin films. Further, it is desirable to have ordered, well-packed and oriented molecular layers of phthalocyanines on various substrates for device applications. Besides, organic semiconductors have potential advantages for use as active layers in electroluminescent displays and sensor devices due to their low cost and large area device fabrication [15-17]. Among the MPcs, CuPc is the most popularly used due to its low cost and remarkable chemical and thermal stability. With a planar molecular structure, CuPc exhibits electron delocalization and high symmetry [18].Although copper phthalocyanine (CuPc) is one of the most studied p-type organic semiconductors, few studies have addressed its molecular orientation and structure as a function of the annealing temperature. Two typical crystalline polymorphous structures are usually observed in CuPc material: the well-known metastable α- and stable β-phases [19]. The main differences between them are the molecular overlapping area. Generally, the powder CuPc shows the so-called ‘β-phase’ (a = 19.4Å, b = 4.8Å, c = 14.6Å, β = 120◦ ). For α-phase CuPc thin films deposited at room temperature, the film grows in the α-phase (a = 25.92 Å, b = 3.79 Å, c = 23.92 Å, β = 90.4◦ ), whereas it can be converted to β-phase by depositing or annealing at higher temperature. It is possible that long-term operation at elevated temperature may lead to the annealing effect and thus causes the structure re-organization. Lee et al. have reported that the surface morphologies of CuPc films after heat treatment for various periods led to significant changes of the film structures. The fine-grain crystallites on the as-deposited films were transformed to a structure with grosser plate-like grains as a result of coalescence and reorganization of the grains during the heat treatment. It can also be inspected that the grains become larger when the annealing time is increased [20]. 2. Experimental The chemical structure of CuPc is shown in the Fig.1. The material used was commercially purchased from Sigma Aldrich and no further purification process was performed. Thin films of CuPc have been prepared by conventional thermal evaporation technique. Before deposition, the glass substrates were cleaned ultrasonically and then dried in vacuum.
Figure 1.Molecular structure of CuPc. Thin films were deposited onto pre-cleaned glass substrates kept at ambient conditions using a coating unit (Hind Hivac Vacuum coating unit model-12A4D) maintained at a vacuum of 2x10-6 Torr during deposition. Required quantity of CuPc powder was taken in the molybdenum boat and deposited at a rate of 10Ås-1 with 2000Å thickness. Then the thin films of CuPc were annealed in at temperatures (323, 333, 343 and 353 K) for 30 min and at 343K for different intervals of time (60min, 90min and 120min). Optical properties of CuPc films were studied from optical transmission spectra. For optical characterization, uv-vis-nir spectra were taken for the deposited films in the range 400 to 1200 nm. Structure and purity of the CuPc films were verified using x-ray diffraction (XRD) technique and optical
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C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
band gap of CuPc film was determined by optical transmission. X ray diffraction studies on the deposited films showed crystallinity and a major peak with preferred orientation for CuPc. XRD pattern in Fig. 5 for CuPc thin film was used to get the hkl values and showed the main peak with preferred orientation for 2θ of 7 o (100) with interplanar distance d of 1.26 nm. 3. Results and discussion Optical spectrum was taken for the films and different absorption peaks were observed in the UV-VIS-NIR region. Two absorption bands were observed in the 400-500 nm and in 900-1000 nm regions as shown in Fig.2 and 3. Optical properties of CuPc thin films were studied by the optical transmission of %T versus wavelength λ.
Figure 2 .%T against wavelength λ for CuPc thin film annealed at different temperature for 30 min and at 343K different intervals of time.
forFigure 3. %T against wavelength λ for CuPc thin film annealed at 343K.
A slight effect of annealing is registered on the transmission for the films. Observations suggest that film annealed at 323K exhibited the lowest transmittance while the film annealed at 343K showed the highest transmittance. Absorption coefficient α is related to the photon energy hν by, α = αo (hν - Eg)n, where Eg is the optical band gap. For allowed transitions, (αhν) 2is plotted against hν as shown in Fig. 4 from which the extrapolation of linear portion to α = 0 near the edge gave the band gap energy. It was observed that all films showed identical patterns and there were no systematic changes with respect to the annealing temperature.
Figure. 4. (αhν) 2against Energy gap hν in eV for CuPc thin film annealed at 343K .
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C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
Table-1. Table for the optical band gap for the film annealed at different temperature. Sample no.
Temp (K)
Time of annealing (min)
%T
λ max (nm)
Eg (eV)
1
298
-
89
898
2.22
2
343
60
91
948
2.27
3
343
90
93
913
2.27
4
343
120
90
1086
2.22
5
323
30
81
1099
2.27
6
333
30
93
917
1.87
7
343
30
97
959
1.73
8
353
30
89
1099
2.17
Hoshi et al. reported that the unstable morphology layer may exist on the CuPc film and only can be rid off by heat treatment [21]. Optical band gaps obtained from the graphs are tabulated in Table 1.Results show that the optical band gaps were dependent on annealing temperature. From the table it is very evident that Eg is found to have a minimum value at 343K. The change in optical band gap in the case of nanostructured Zinc Aluminum Oxide thin films can be explained in terms of Burstein-Moss band gap widening and band gap narrowing due to the A slight decrease in average transmission is observed electron-electron and electron-impurity scattering [22]. in the case of Nd:ZnO thin films annealed in air, oxygen and is attributed to increase of surface roughness, which is evident from the AFM result of that sample[23]. XRD pattern of the film (Fig 5) was used to get the hkl values and the grain size is found using Scherrer’s formula.The XRD of CuPc film deposited onto a glass substrate at room temperatures showed two main peaks with preferred orientations with 2θ around 7o (100) for CuPc. The mean crystallite size (L) was estimated using the Scherrer’s expression: L = kSλ/ β cos(θ) where λ isthe X-ray wavelength of Cu kα(0.15418 nm), β is the width of the strong peak at half maximum intensity for the thin film, θ is the corresponding Bragg’s angle and kS is the Scherrer’s constant. The mean grain size L for the CuPc films deposited at room temperatures was found to be in the range 60-100nm.
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C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
Figure 5 . XRD for CuPc thin film annealed at 343K.
4.
Conclusion
Thin films of CuPc were prepared by vacuum evaporation technique. The optical properties of the films were affected by the annealing process. The optical band gap for the films as obtained from the graphs was tabulated. It was found that the energy gap for the film annealed at 343K showed the minimum value. X ray diffraction studies on the deposited film showed crystallinity with a major peak for CuPc. 5. Acknowledgements This work was funded by Visveswaraya Technological University (VTU, Belgaum) through a research grant and the support by the Vision Group on Science and Technology (VGST), Department of Information Technology, Biotechnology & Science and Technology, Government of Karnataka, India through a CISE grant is also acknowledged. References J.M. Robertson, J. Chem. Soc. Part 1 (1935) 615. R.P. Linstead, J.M. Robertson, J. Chem. Soc. Part 2 (1936) 1736. N. Uyeda, M. Ashida, E. Suito, J. Appl. Phys. 36 (1965) 1453. K. Ukei, Acta. Cryst. B. 29 (1973) 2290. L.T. Ueno, A.E.H. Machado, F.B.C. Machado, J. Mol. Struct. THEOCHEM 899 (2009)71. I. Zhivkov, J. Optoelectron. Adv. Mater. 11 (2009) 1396. I. Kim, H.M. Haverinen, Z.X. Wang, S. Madakuni, Y. Kim, J. Li, G.E. Jabbour, Chem. Mater. 21 (2009) 4256. [8] J. Meiss, K. Leo, M.K. Riede, C. Uhrich, W.M. Gnehr, S. Sonntag, M. Pfeiffer, Appl. Phys. Lett. 95 (2009) 213306. [9] T.W. Ng, M.F. Lo, Z.T. Liu, F.L. Wong, S.L. Lai, M.K. Fung, C.S. Lee, S.T. Lee, J. Appl. Phys. 106 (2009) 114501. [10] G. Chintakula, S. Rajaputra, V.P. Singh, Sol. Energy Mater. Sol. Cells 94 (2010) 34. [11] T. Yasuda, T. Tsutsui, Chem. Phys. Lett. 402 (2005) 395. [12] J. Wang, H.B. Wang, X.J. Yan, H.C. Huang, D.H. Yan, Appl. Phys. Lett. 87 (2005) 093507. [13] J. Wang, H.B. Wang, X.J. Yan, H.C. Huang, D. Jin, J.W. Shi, Y.H. Tang, D.H. Yan, Adv. Funct. Mater. 16 (2006) 824. [14] L. Chen, Y.W. Tang YW, X. Fan, C. Zhang, Z.Z. Chu, D. Wang, D.C. Zou, Org. Electron. 10 (2009) 724. [15] Joseph C. M and Menon C.S, Mater Lett 52 (2002)220. [16] Jungyoon E, Sunmi Kim, Eunju Lim, Kiejin Lee, Deokjoon Cha and Barry Friedman, , Appl Surf [1] [2] [3] [4] [5] [6] [7]
C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
Sci, 205(2003)274. [17] Soliman H S, El-Barry A M A, Khosifan N M and El Nahass M M, Eur Phys J Appl Phys 37(2007)1. [18] C.C.Leznof, A.B.P.Lever, VCH, New York, 1993. [19] Berger O, Fischer W J, Adolphi B, Tierbach S, Melev V and Schreiber J J. Mater. Sci. Mater . Electron. 11 (2000)331. [20] Yuh-Lang Lee, Chuan-Yi Hsiaoand Rung-Hwa Hsiao, thin solid films 468 (2004) 280. [21] Hoshi H, Dann A and Maruyama Y, Journal of Applied Physics 67 (1990) 1845. [22] Rajesh Kumar B and Subba Rao T, Journal of Nanomaterials and Biostructures 7 (2012) 1051. [23] Prasad Rao T, Gokul Raj S, Santhosh Kumar M C, Procedia material Science 6 (2014) 1631.
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ScienceDirect Materials Today: Proceedings 2 (2015) 1770 – 1775
4th International Conference on Materials Processing and Characterization
Structural and Optical Properties of Vacuum Coated and Annealed Copper Phthalocyanine (CUPC) Thin Films Vidya.Ca, Priya A Hoskeria, C.M. Josepha, Advanced Materials Research Laboratory, Department of Physics, Dayananda Sagar College of Engineering, Shavige Malleswara Hi lls, Kumaraswamy Layout, Bangalore 560078, Karnataka, India
Abstract Heat treatment is able to cause the structural transformation of phthalocyanine thin film during the post-deposition heat treatment. The annealing effects of the process on the film characteristics of vacuum deposited copper phthalocyanine thin fi lms were studied. However, the pre-annealing leads to a larger-grain and a more compact structure. Structure transformation was inhibited by post-deposition annealing at 300oC. Thin films of CuPc were deposited using vacuum evaporation technique method onto glass substrates. The films were annealed at 4 different temperatures (323, 333, 343 and 353 K) in air at different intervals of time. Optical studies were done and the results are discussed. The optical band gap for the film as obtained from the graph for all the thin films are tabulated and analyzed. X ray diffraction studies on the deposited film showed crystallinity with a major peak for CuPc. © 2014 The Authors. Elsevier Ltd. All rights reserved. © 2015 Elsevier Ltd. All rights reserved. ofInternational the 4th International Selection andpeer-review peer-review under responsibility ofconference the conference committee members Selection and under responsibility of the committee members of the 4th conferenceconference on Materialson Materials and Characterization. Processing Processing and Characterization. Keywords: Copper phthalocyanine; annealing; solar cells; optical study; structural study.
1.Introduction Phthalocyanines (Pcs) are small organic molecules characterized by their high symmetry, planarity and electron delocalization. Besides, Pcs can be easily sublimed in high vacuum systems resulting in high-purity thin films with excellent growth properties and chemical stability, taking into account that the use of the sublimation technique allows the deposition of thin films with controlled thickness and structural properties. Phthalocyanines are receiving * Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail address:[email protected]
2214-7853 © 2015 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Processing and Characterization. doi:10.1016/j.matpr.2015.07.019
C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
1771
considerable attention, as they are organic semiconductors having very interesting properties coupled with excellent stability to harsh chemical environments. Their optical and electronic properties were exploited for various applications such as pigments in paints and printing inks, infrared security devices, information storage and computer disk writing, conducting polymers and chemical sensors. Metal phthalocyanines (MPcs) discovered in the 1930s are represented by a broad family of metal-organic compounds with M = Be, Mn, Fe, Co, Ni, Cu, Pt, and Pb [1-4]. Due to their thermal stability, chemical inertness, high molecular symmetry, and favorable optical properties, MPcs are of great scientific and industrial interest [5]. Metal-based phthalocyanines have drawn increasing interest because of their potential applications in gas sensors, organic FETs, optical storage, optical switches and organic photovoltaic cells (OPVs) [6-14]. Most of these applications require the use of phthalocyanines in the form of thin films. Further, it is desirable to have ordered, well-packed and oriented molecular layers of phthalocyanines on various substrates for device applications. Besides, organic semiconductors have potential advantages for use as active layers in electroluminescent displays and sensor devices due to their low cost and large area device fabrication [15-17]. Among the MPcs, CuPc is the most popularly used due to its low cost and remarkable chemical and thermal stability. With a planar molecular structure, CuPc exhibits electron delocalization and high symmetry [18].Although copper phthalocyanine (CuPc) is one of the most studied p-type organic semiconductors, few studies have addressed its molecular orientation and structure as a function of the annealing temperature. Two typical crystalline polymorphous structures are usually observed in CuPc material: the well-known metastable α- and stable β-phases [19]. The main differences between them are the molecular overlapping area. Generally, the powder CuPc shows the so-called ‘β-phase’ (a = 19.4Å, b = 4.8Å, c = 14.6Å, β = 120◦ ). For α-phase CuPc thin films deposited at room temperature, the film grows in the α-phase (a = 25.92 Å, b = 3.79 Å, c = 23.92 Å, β = 90.4◦ ), whereas it can be converted to β-phase by depositing or annealing at higher temperature. It is possible that long-term operation at elevated temperature may lead to the annealing effect and thus causes the structure re-organization. Lee et al. have reported that the surface morphologies of CuPc films after heat treatment for various periods led to significant changes of the film structures. The fine-grain crystallites on the as-deposited films were transformed to a structure with grosser plate-like grains as a result of coalescence and reorganization of the grains during the heat treatment. It can also be inspected that the grains become larger when the annealing time is increased [20]. 2. Experimental The chemical structure of CuPc is shown in the Fig.1. The material used was commercially purchased from Sigma Aldrich and no further purification process was performed. Thin films of CuPc have been prepared by conventional thermal evaporation technique. Before deposition, the glass substrates were cleaned ultrasonically and then dried in vacuum.
Figure 1.Molecular structure of CuPc. Thin films were deposited onto pre-cleaned glass substrates kept at ambient conditions using a coating unit (Hind Hivac Vacuum coating unit model-12A4D) maintained at a vacuum of 2x10-6 Torr during deposition. Required quantity of CuPc powder was taken in the molybdenum boat and deposited at a rate of 10Ås-1 with 2000Å thickness. Then the thin films of CuPc were annealed in at temperatures (323, 333, 343 and 353 K) for 30 min and at 343K for different intervals of time (60min, 90min and 120min). Optical properties of CuPc films were studied from optical transmission spectra. For optical characterization, uv-vis-nir spectra were taken for the deposited films in the range 400 to 1200 nm. Structure and purity of the CuPc films were verified using x-ray diffraction (XRD) technique and optical
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C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
band gap of CuPc film was determined by optical transmission. X ray diffraction studies on the deposited films showed crystallinity and a major peak with preferred orientation for CuPc. XRD pattern in Fig. 5 for CuPc thin film was used to get the hkl values and showed the main peak with preferred orientation for 2θ of 7 o (100) with interplanar distance d of 1.26 nm. 3. Results and discussion Optical spectrum was taken for the films and different absorption peaks were observed in the UV-VIS-NIR region. Two absorption bands were observed in the 400-500 nm and in 900-1000 nm regions as shown in Fig.2 and 3. Optical properties of CuPc thin films were studied by the optical transmission of %T versus wavelength λ.
Figure 2 .%T against wavelength λ for CuPc thin film annealed at different temperature for 30 min and at 343K different intervals of time.
forFigure 3. %T against wavelength λ for CuPc thin film annealed at 343K.
A slight effect of annealing is registered on the transmission for the films. Observations suggest that film annealed at 323K exhibited the lowest transmittance while the film annealed at 343K showed the highest transmittance. Absorption coefficient α is related to the photon energy hν by, α = αo (hν - Eg)n, where Eg is the optical band gap. For allowed transitions, (αhν) 2is plotted against hν as shown in Fig. 4 from which the extrapolation of linear portion to α = 0 near the edge gave the band gap energy. It was observed that all films showed identical patterns and there were no systematic changes with respect to the annealing temperature.
Figure. 4. (αhν) 2against Energy gap hν in eV for CuPc thin film annealed at 343K .
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C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
Table-1. Table for the optical band gap for the film annealed at different temperature. Sample no.
Temp (K)
Time of annealing (min)
%T
λ max (nm)
Eg (eV)
1
298
-
89
898
2.22
2
343
60
91
948
2.27
3
343
90
93
913
2.27
4
343
120
90
1086
2.22
5
323
30
81
1099
2.27
6
333
30
93
917
1.87
7
343
30
97
959
1.73
8
353
30
89
1099
2.17
Hoshi et al. reported that the unstable morphology layer may exist on the CuPc film and only can be rid off by heat treatment [21]. Optical band gaps obtained from the graphs are tabulated in Table 1.Results show that the optical band gaps were dependent on annealing temperature. From the table it is very evident that Eg is found to have a minimum value at 343K. The change in optical band gap in the case of nanostructured Zinc Aluminum Oxide thin films can be explained in terms of Burstein-Moss band gap widening and band gap narrowing due to the A slight decrease in average transmission is observed electron-electron and electron-impurity scattering [22]. in the case of Nd:ZnO thin films annealed in air, oxygen and is attributed to increase of surface roughness, which is evident from the AFM result of that sample[23]. XRD pattern of the film (Fig 5) was used to get the hkl values and the grain size is found using Scherrer’s formula.The XRD of CuPc film deposited onto a glass substrate at room temperatures showed two main peaks with preferred orientations with 2θ around 7o (100) for CuPc. The mean crystallite size (L) was estimated using the Scherrer’s expression: L = kSλ/ β cos(θ) where λ isthe X-ray wavelength of Cu kα(0.15418 nm), β is the width of the strong peak at half maximum intensity for the thin film, θ is the corresponding Bragg’s angle and kS is the Scherrer’s constant. The mean grain size L for the CuPc films deposited at room temperatures was found to be in the range 60-100nm.
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C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
Figure 5 . XRD for CuPc thin film annealed at 343K.
4.
Conclusion
Thin films of CuPc were prepared by vacuum evaporation technique. The optical properties of the films were affected by the annealing process. The optical band gap for the films as obtained from the graphs was tabulated. It was found that the energy gap for the film annealed at 343K showed the minimum value. X ray diffraction studies on the deposited film showed crystallinity with a major peak for CuPc. 5. Acknowledgements This work was funded by Visveswaraya Technological University (VTU, Belgaum) through a research grant and the support by the Vision Group on Science and Technology (VGST), Department of Information Technology, Biotechnology & Science and Technology, Government of Karnataka, India through a CISE grant is also acknowledged. References J.M. Robertson, J. Chem. Soc. Part 1 (1935) 615. R.P. Linstead, J.M. Robertson, J. Chem. Soc. Part 2 (1936) 1736. N. Uyeda, M. Ashida, E. Suito, J. Appl. Phys. 36 (1965) 1453. K. Ukei, Acta. Cryst. B. 29 (1973) 2290. L.T. Ueno, A.E.H. Machado, F.B.C. Machado, J. Mol. Struct. THEOCHEM 899 (2009)71. I. Zhivkov, J. Optoelectron. Adv. Mater. 11 (2009) 1396. I. Kim, H.M. Haverinen, Z.X. Wang, S. Madakuni, Y. Kim, J. Li, G.E. Jabbour, Chem. Mater. 21 (2009) 4256. [8] J. Meiss, K. Leo, M.K. Riede, C. Uhrich, W.M. Gnehr, S. Sonntag, M. Pfeiffer, Appl. Phys. Lett. 95 (2009) 213306. [9] T.W. Ng, M.F. Lo, Z.T. Liu, F.L. Wong, S.L. Lai, M.K. Fung, C.S. Lee, S.T. Lee, J. Appl. Phys. 106 (2009) 114501. [10] G. Chintakula, S. Rajaputra, V.P. Singh, Sol. Energy Mater. Sol. Cells 94 (2010) 34. [11] T. Yasuda, T. Tsutsui, Chem. Phys. Lett. 402 (2005) 395. [12] J. Wang, H.B. Wang, X.J. Yan, H.C. Huang, D.H. Yan, Appl. Phys. Lett. 87 (2005) 093507. [13] J. Wang, H.B. Wang, X.J. Yan, H.C. Huang, D. Jin, J.W. Shi, Y.H. Tang, D.H. Yan, Adv. Funct. Mater. 16 (2006) 824. [14] L. Chen, Y.W. Tang YW, X. Fan, C. Zhang, Z.Z. Chu, D. Wang, D.C. Zou, Org. Electron. 10 (2009) 724. [15] Joseph C. M and Menon C.S, Mater Lett 52 (2002)220. [16] Jungyoon E, Sunmi Kim, Eunju Lim, Kiejin Lee, Deokjoon Cha and Barry Friedman, , Appl Surf [1] [2] [3] [4] [5] [6] [7]
C. Vidya et al. / Materials Today: Proceedings 2 (2015) 1770 – 1775
Sci, 205(2003)274. [17] Soliman H S, El-Barry A M A, Khosifan N M and El Nahass M M, Eur Phys J Appl Phys 37(2007)1. [18] C.C.Leznof, A.B.P.Lever, VCH, New York, 1993. [19] Berger O, Fischer W J, Adolphi B, Tierbach S, Melev V and Schreiber J J. Mater. Sci. Mater . Electron. 11 (2000)331. [20] Yuh-Lang Lee, Chuan-Yi Hsiaoand Rung-Hwa Hsiao, thin solid films 468 (2004) 280. [21] Hoshi H, Dann A and Maruyama Y, Journal of Applied Physics 67 (1990) 1845. [22] Rajesh Kumar B and Subba Rao T, Journal of Nanomaterials and Biostructures 7 (2012) 1051. [23] Prasad Rao T, Gokul Raj S, Santhosh Kumar M C, Procedia material Science 6 (2014) 1631.
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