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Effect of annealing on electrical resistivity of rf-magnetron sputtered nanostructured SnO2 thin films
Applied Surface Science 255 (2009) 8562–8565
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Effect of annealing on electrical resistivity of rf-magnetron sputtered nanostructured SnO2 thin films Abdul Faheem Khan a,*, M. Mehmood a, A.M. Rana b, M.T. Bhatti b a b
National Centre for Nanotechnology & Department of Chemical and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad 45650, Pakistan Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 21 April 2009 Received in revised form 6 June 2009 Accepted 7 June 2009 Available online 13 June 2009
Tin oxide (SnO2) thin films were deposited by radio frequency (RF) magnetron sputtering on clean corning glass substrates. These films were then annealed for 15 min at various temperatures in the range of 100–5008C. The films were investigated by studying their structural and electrical properties. X-ray diffraction (XRD) results suggested that the deposited SnO2 films were formed by nanoparticles with average particle size in the range of 23–28 nm. XRD patterns of annealed films showed the formation of small amount of SnO phase in the matrix of SnO2. The initial surface RMS roughness measured with atomic force microscopy (AFM) was 25.76 nm which reduces to 17.72 nm with annealing. Electrical resistivity was measured as a function of annealing temperature and found to lie between 1.25 and 1.38 mV cm. RMS roughness and resistivity show almost opposite trend with annealing. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Nanostructured SnO2 SnO rf-magnetron sputtering Electrical resistivity Thin films Atomic force microscopy (AFM)
1. Introduction Transparent conductive oxides (TCOs) are very important in modern electronic industry and have been used as plastic liquidcrystal display devices, touch sensitive overlays, transparent electromagnetic shielding materials, front electrodes of solar cells, energy efficient windows, etc. Numerous works have been performed on SnO2 thin films for improvement of their electrical conductivity to utilize it as a TCO material in transparent electrode applications [1–6]. SnO2 films are low cost, chemically and environmentally more stable than other TCOs such as ZnO, and Sn-doped In2O3 (ITO) [7,8]. Tin oxide films have been widely fabricated by several workers using a variety of techniques such as chemical vapor deposition [9], metal-organic deposition [10], dc and rf-sputtering, etc. [11,12], among which sputtering is an extensively used technique in thin film processing to deposit compound thin films [12]. However, using a metallic target in sputtering has the advantage of higher yields with respect to compound targets, although more pronounced difficulties in the film stoichiometry are observed [13]. Effects of oxygen partial pressure, substrate type and temperature, deposition rate, deposition technique, annealing, doping, impedance, etc. on SnO2 films have been widely investigated. Being an
* Corresponding author. Tel.: +92 345 5914322; fax: +92 51 2207080. E-mail address: [email protected] (A.F. Khan). 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.06.020
n-type semiconductor the resistivity and dielectric properties of SnO2 films are too important factors for its characterization. The resistivity of these films is found to depend on oxygen vacancies [14] whose concentration cannot be easily controlled. Annealing processes are usually performed to reduce the intrinsic stress, to improve the lattice mismatch and to create longer mean paths for the free electrons to get better electrical conductivity [15]. Other factors that alter the properties of SnO2 thin films are dependent on their deviation from stoichiometry, on the nature and amount of impurities and on the microstructure [16]. Therefore, understanding the relationship between microstructure, chemical composition and other properties of thin films is essential in their applications [17]. In this study, the structural and electrical properties of SnO2 nanostructured thin films deposited on glass substrates by rfmagnetron sputtering have been investigated before and after annealing in the temperature range of 100–500 8C. This work tends to focus on the changes in the crystallinity, surface roughness, resistivity and electronic structure of SnO2 sputtered films as a result of annealing. RMS roughness and resistivity have been observed to show almost the opposite behavior with annealing. 2. Experimental SnO2 thin films were deposited by rf magnetron sputtering on clean Corning glass substrates. The deposition technique has been described elsewhere [18]. The films were annealed at various
A.F. Khan et al. / Applied Surface Science 255 (2009) 8562–8565
8563
Fig. 1. X-ray diffraction patterns of SnO2 thin films (a) as-deposited and annealed for 15 min at (b) 100 8C (c) 200 8C (d) 300 8C (e) 400 8C and (f) 500 8C.
temperatures ranging from 100 to 500 8C for 15 min. The electrical resistivity of these films was measured at room temperature by a well-known four-point probe method [19,20]. Structure was determined by recording X-ray diffraction (XRD) patterns at room temperature using Bruker D8 discover diffractometer equipped with Cu Ka radiation. Surface morphology of the films has been investigated by atomic force microscope (Quesant Universal SPM, Ambios Technology, USA). The contact mode operation was employed for AFM measurements on present films. An AFM tip of silicon nitride was used having an approximate radius of curvature of 10 nm. Data was taken in ambient air at a constant force of 107 N by scanning areas of 1 1, 2 2 and 5 5 mm2 with a resolution of 256 256 pixels. The mean RMS roughness values for four images taken at different sites of each film were obtained at atmospheric pressure and room temperature. Thickness and refractive index of these films were calculated from optical data and are presented elsewhere [18]. 3. Results and discussion The films deposited on Corning glass substrates are physically stable and have very good adhesion to the substrates. No break and peel-off are observed even after annealing at high temperature (500 8C). Fig. 1 shows the XRD patterns of the as-deposited and annealed SnO2 films. It can be seen that all the films are polycrystalline and contain the SnO2 tetragonal structure [21]. A weak (1 0 2) peak for SnO phase appears along with SnO2 after annealing at 200 8C. As the annealing temperature increase beyond 200 8C, the SnO phase also increases as shown in Fig. 1. The formation of SnO has also been confirmed by Raman spectroscopy [18]. The presence of SnO phase in SnO2 films has also been reported by Lee [22]. Crystallinity of the films improves with annealing as confirmed by the intensity and sharpness of the XRD peaks of SnO2 phase. Wideness of the peaks indicates that the present films are composed of small nanoparticles [23]. The average particle size as calculated by Scherrer formula [24]: t¼
0:9l bcos u
for the as-deposited and annealed films are in the range of 23– 28 nm in planes with Miller indices (1 1 0), (2 0 0) and (2 1 1). The high intensity of peaks suggests that these films consist of mostly crystalline phase. However, small amount of amorphous phase in the as-deposited film may not be ruled out. For instance, the grain size of the samples annealed up to 200 8C was smaller than that of
Fig. 2. Plots of resistivity (curve 1) and particle size (curve 2) vs. annealing temperature TA (8C) for SnO2 thin films.
as-deposited alloys, which may be possible due to crystallization of the amorphous phase. Fig. 2 shows the plot of resistivity and particle size vs. annealing temperature for the as-deposited and annealed films. The initial rise in resistivity from 1.25 mV cm to higher than 1.65 mV cm caused by annealing at 100 8C may be attributed to the smaller mean particle size as depicted by XRD analysis. The sudden fall of resistivity at temperature 200 8C could be related to a formation of conductive chains of excess metal particles which break up at tin melting point (231.9 8C) and are transformed to SnO at higher temperature [25]. This rise of resistivity might also be explained on the basis of Lee’s results [22] as follows: there might be a decrease in oxygen vacancies taken up by excess metal ions during annealing in air (oxidizing environment). As a consequence, the carrier concentration might decrease and hence the mobility [22], resulting in an increase in resistivity. The slow increase in resistivity for annealing above 200 8C could be associated with the appearance of SnO phase along with SnO2 tetragonal structure. Hall mobility measurements on SnO2 films [22] have already shown a decrease in mobility and consequently a rise in resistivity by the formation of SnO phase. Furthermore, an improvement in the crystallinity of annealed films can also be a source of increase in resistivity [26]. Microroughness of thin films plays a vital role for developing optical coatings especially in the UV region [27] for applications such as lithographic uses [28]. To characterize an optical surface (coatings) the root-mean-square (RMS) roughness is normally used. The RMS roughness not only describes the light scattering but also gives an idea about the quality of the surface under investigation. Surface morphology of the present SnO2 films annealed at different temperatures are shown in Fig. 3. It can be inferred from these AFM images that smoother films can be obtained by annealing. Thus annealing process is a good parameter that could affect the surface RMS roughness behavior. Fig. 3 is used to determine the average height and RMS roughness for all the films. The plot of RMS surface roughness values computed for the as-deposited and annealed films is shown in Fig. 4 as a function of annealing temperature, in comparison with resistivity and refractive index [18] data. It can be seen from Fig. 4 that RMS roughness and resistivity show almost opposite trend while the refractive index shows the opposite behavior with surface roughness up to 200 8C but beyond this annealing temperature, similar behavior is noted. Lindstro¨m et. al. [29] have shown by PSD (power spectral density) function calculations in sputtered SnO2 films that for thicker films (>300 nm), as the film surface smoothens it gives
8564
A.F. Khan et al. / Applied Surface Science 255 (2009) 8562–8565
Fig. 3. AFM images (2 2 mm2) showing the surface morphology of SnO2 thin films (a) as-deposited and annealed for 15 min at (b) 100 8C (c) 200 8C (d) 300 8C (e) 400 8C and (f) 500 8C.
rise to defects and strain variations. Therefore, if the RMS roughness of the film decreases, surface smoothness increases and defects and strain variations are produced which can hinder the flow of electrons and so the resistivity rises. With regard to refractive index variations in comparison with RMS roughness values; it is noted that where roughness is high, refractive index is
low (up to 200 8C). A similar type of behavior has been observed in Gd2O3 films [28]. 4. Conclusions SnO2 films sputtered at room temperature are mostly crystalline in nature possibly with small amount of amorphous phase and crystallinity improves with annealing temperature. The post annealing shows greater tendency to affect the structural and electrical properties of SnO2 thin films fabricated by rf-magnetron sputtering, which composed of nano-particles. A small amount of SnO phase has been detected along with SnO2 at higher annealing temperatures. Electrical resistivity of present films shows an oscillatory behavior with annealing temperature. RMS roughness and resistivity are found to show almost the opposite behavior with annealing. Annealing decreases the RMS roughness values. Acknowledgement The authors are thankful to the Higher Education Commission (HEC), Government of Pakistan, for financial support. References
Fig. 4. Plots of RMS roughness (curve 1), resistivity (curve 2) and refractive index (curve 3) as a function of annealing temperature TA (8C) for SnO2 thin films.
[1] H.J. Kim, J.W. Bae, J.S. Kim, Y.C. Jang, G.Y. Yeom, N.E. Lee, Surf. Coat. Technol. 131 (2000) 201.
A.F. Khan et al. / Applied Surface Science 255 (2009) 8562–8565 [2] Y.K. Fang, J.J. Lee, Thin Solid Films 169 (1989) 52. [3] W.A. Badway, H.H. Afifi, E.M. Elgair, J. Electrochem. Soc. 137 (1990) 1592. [4] J.C. Mannifacier, L. Szepessy, J.F. Bresse, M. Perotin, R. Stuck, Mater. Res. Bull. 14 (1979) 163. [5] E. Shanthi, V. Dutta, A. Banerkee, K.L. Chopra, J. Appl. Phys. 51 (1980) 6243. [6] I.H. Kim, J.H. Ko, D. Kim, K.S. Lee, T.S. Lee, J.-h. Jeong, B. Cheong, Y.-J. Baik, W.M. Kim, Thin Solid Films 515 (2006) 2475. [7] T. Minami, S. Takata, H. Sato, J. Vac. Sci. Technol. 13 (1995) 1095. [8] B. Thangaraju, Thin Solid Films 402 (2002) 71. [9] J. Kane, H.P. Schwiezer, J. Electrochem. Soc. 123 (1976) 270. [10] T.N. Blanton, M. Lelental, Mater. Res. Bull. 29 (1994) 537. [11] R.S. Dale, C.S. Rastomjee, F.H. Potter, R.G. Egdell, Appl. Surf. Sci. 70/71 (1993) 359. [12] A. Martel, F. C-Briones, J. Fandino, R. C-Rodriguez, P. B-Perez, A. Z-Navarro, M. ZTorres, J.L. Pena, Surf. Coat. Technol. 122 (1999) 136. [13] A. Martel, F. C-Briones, P. Quintana, P. B-Perez, J.L. Pena, Surf. Coat. Technol. 201 (2007) 4659. [14] X. Feng, J. Ma, F. Yang, F. Ji, F. Zong, C. Luan, H. Ma, Mater. Lett. 62 (2008) 1779. [15] A.O. -Flores, P.B. -Perez, R.C. -Rodriguez, A.I. Oliva, Rev. Mex. Fis. 52 (2006) 15. [16] B.N. Mukashev, S.Zh. Tokmoldin, N.B. Beisenkhanov, S.M. Kikkarin, I.V. Valitova, V.B. Glazman, A.B. Aimagambetov, E.A. Dmitrieva, B.M. Veremenithev, Mater. Sci. Eng. B 118 (2005) 164.
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[17] Q.-H. Wu, J. Song, J. Kang, Q.-F. Dong, S.-T. Wu, S.-G. Sun, Mater. Lett. 61 (2007) 3679. [18] A.F. Khan, M. Mehmood, A.M. Rana, M.T. Bhatti, A. Mahmood, Chin. Phys. Lett. 7 (2009) 077803. [19] A.M. Rana, A. Qadeer, T. Abbas, in: M.A. Khan, K. Hussain, A.Q. Khan (Eds.),Proceedings of the Sixth International Symposium, A.Q. Khan Research Labs, Islamabad, Pakistan, Adv. Mater. (1999) 151. [20] M.T. Bhatti, A.M. Rana, A.F. Khan, M.I. Ansari, Pak. J. Appl. Sci. 2 (2002) 570. [21] The Joint Committee on Powder Diffraction Standards (JCPDS), Card No. 77-0452, by International Centre for Diffraction Data (ICDD), Swarthmore, PA, USA. [22] J. Lee, Thin Solid Films 516 (2008) 1386. [23] H.R. Fallah, M. Ghaesmi, A. Hassanzadeh, Physica E 39 (2007) 69. [24] B.D. Cullity, Elements of X-ray Diffraction, first ed., Addison-Wesley, 1977, p. 81. [25] D.M. Mukhamedshina, N.B. Beisenkhanov, K.A. Mit’, I.V. Valitova, V.A. Botvin, J. High Temp. Mater. Process 10 (4) (2006) 603. [26] D.Y. Ku, I.H. Kim, I. Lee, K.S. Lee, T.S. Lee, J.-H. Jeong, B. Cheong, Y.-J. Baik, W.M. Kim, Thin Solid Films 515 (2006) 1364. [27] A. Duparre, Light scattering of thin dielectric films, Handbook of Optical Properties, vol. 1, CRC Press, 1995, pp. 273–304. [28] M. Senthilkumar, N.K. Sahoo, S. Thakur, R.B. Tokas, Appl. Surf. Sci. 245 (2005) 114. [29] T. Lindstrom, J. Isidorsson, G.A. Niklasson, Thin Solid Films 401 (2001) 165.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Effect of annealing on electrical resistivity of rf-magnetron sputtered nanostructured SnO2 thin films Abdul Faheem Khan a,*, M. Mehmood a, A.M. Rana b, M.T. Bhatti b a b
National Centre for Nanotechnology & Department of Chemical and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad 45650, Pakistan Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 21 April 2009 Received in revised form 6 June 2009 Accepted 7 June 2009 Available online 13 June 2009
Tin oxide (SnO2) thin films were deposited by radio frequency (RF) magnetron sputtering on clean corning glass substrates. These films were then annealed for 15 min at various temperatures in the range of 100–5008C. The films were investigated by studying their structural and electrical properties. X-ray diffraction (XRD) results suggested that the deposited SnO2 films were formed by nanoparticles with average particle size in the range of 23–28 nm. XRD patterns of annealed films showed the formation of small amount of SnO phase in the matrix of SnO2. The initial surface RMS roughness measured with atomic force microscopy (AFM) was 25.76 nm which reduces to 17.72 nm with annealing. Electrical resistivity was measured as a function of annealing temperature and found to lie between 1.25 and 1.38 mV cm. RMS roughness and resistivity show almost opposite trend with annealing. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Nanostructured SnO2 SnO rf-magnetron sputtering Electrical resistivity Thin films Atomic force microscopy (AFM)
1. Introduction Transparent conductive oxides (TCOs) are very important in modern electronic industry and have been used as plastic liquidcrystal display devices, touch sensitive overlays, transparent electromagnetic shielding materials, front electrodes of solar cells, energy efficient windows, etc. Numerous works have been performed on SnO2 thin films for improvement of their electrical conductivity to utilize it as a TCO material in transparent electrode applications [1–6]. SnO2 films are low cost, chemically and environmentally more stable than other TCOs such as ZnO, and Sn-doped In2O3 (ITO) [7,8]. Tin oxide films have been widely fabricated by several workers using a variety of techniques such as chemical vapor deposition [9], metal-organic deposition [10], dc and rf-sputtering, etc. [11,12], among which sputtering is an extensively used technique in thin film processing to deposit compound thin films [12]. However, using a metallic target in sputtering has the advantage of higher yields with respect to compound targets, although more pronounced difficulties in the film stoichiometry are observed [13]. Effects of oxygen partial pressure, substrate type and temperature, deposition rate, deposition technique, annealing, doping, impedance, etc. on SnO2 films have been widely investigated. Being an
* Corresponding author. Tel.: +92 345 5914322; fax: +92 51 2207080. E-mail address: [email protected] (A.F. Khan). 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.06.020
n-type semiconductor the resistivity and dielectric properties of SnO2 films are too important factors for its characterization. The resistivity of these films is found to depend on oxygen vacancies [14] whose concentration cannot be easily controlled. Annealing processes are usually performed to reduce the intrinsic stress, to improve the lattice mismatch and to create longer mean paths for the free electrons to get better electrical conductivity [15]. Other factors that alter the properties of SnO2 thin films are dependent on their deviation from stoichiometry, on the nature and amount of impurities and on the microstructure [16]. Therefore, understanding the relationship between microstructure, chemical composition and other properties of thin films is essential in their applications [17]. In this study, the structural and electrical properties of SnO2 nanostructured thin films deposited on glass substrates by rfmagnetron sputtering have been investigated before and after annealing in the temperature range of 100–500 8C. This work tends to focus on the changes in the crystallinity, surface roughness, resistivity and electronic structure of SnO2 sputtered films as a result of annealing. RMS roughness and resistivity have been observed to show almost the opposite behavior with annealing. 2. Experimental SnO2 thin films were deposited by rf magnetron sputtering on clean Corning glass substrates. The deposition technique has been described elsewhere [18]. The films were annealed at various
A.F. Khan et al. / Applied Surface Science 255 (2009) 8562–8565
8563
Fig. 1. X-ray diffraction patterns of SnO2 thin films (a) as-deposited and annealed for 15 min at (b) 100 8C (c) 200 8C (d) 300 8C (e) 400 8C and (f) 500 8C.
temperatures ranging from 100 to 500 8C for 15 min. The electrical resistivity of these films was measured at room temperature by a well-known four-point probe method [19,20]. Structure was determined by recording X-ray diffraction (XRD) patterns at room temperature using Bruker D8 discover diffractometer equipped with Cu Ka radiation. Surface morphology of the films has been investigated by atomic force microscope (Quesant Universal SPM, Ambios Technology, USA). The contact mode operation was employed for AFM measurements on present films. An AFM tip of silicon nitride was used having an approximate radius of curvature of 10 nm. Data was taken in ambient air at a constant force of 107 N by scanning areas of 1 1, 2 2 and 5 5 mm2 with a resolution of 256 256 pixels. The mean RMS roughness values for four images taken at different sites of each film were obtained at atmospheric pressure and room temperature. Thickness and refractive index of these films were calculated from optical data and are presented elsewhere [18]. 3. Results and discussion The films deposited on Corning glass substrates are physically stable and have very good adhesion to the substrates. No break and peel-off are observed even after annealing at high temperature (500 8C). Fig. 1 shows the XRD patterns of the as-deposited and annealed SnO2 films. It can be seen that all the films are polycrystalline and contain the SnO2 tetragonal structure [21]. A weak (1 0 2) peak for SnO phase appears along with SnO2 after annealing at 200 8C. As the annealing temperature increase beyond 200 8C, the SnO phase also increases as shown in Fig. 1. The formation of SnO has also been confirmed by Raman spectroscopy [18]. The presence of SnO phase in SnO2 films has also been reported by Lee [22]. Crystallinity of the films improves with annealing as confirmed by the intensity and sharpness of the XRD peaks of SnO2 phase. Wideness of the peaks indicates that the present films are composed of small nanoparticles [23]. The average particle size as calculated by Scherrer formula [24]: t¼
0:9l bcos u
for the as-deposited and annealed films are in the range of 23– 28 nm in planes with Miller indices (1 1 0), (2 0 0) and (2 1 1). The high intensity of peaks suggests that these films consist of mostly crystalline phase. However, small amount of amorphous phase in the as-deposited film may not be ruled out. For instance, the grain size of the samples annealed up to 200 8C was smaller than that of
Fig. 2. Plots of resistivity (curve 1) and particle size (curve 2) vs. annealing temperature TA (8C) for SnO2 thin films.
as-deposited alloys, which may be possible due to crystallization of the amorphous phase. Fig. 2 shows the plot of resistivity and particle size vs. annealing temperature for the as-deposited and annealed films. The initial rise in resistivity from 1.25 mV cm to higher than 1.65 mV cm caused by annealing at 100 8C may be attributed to the smaller mean particle size as depicted by XRD analysis. The sudden fall of resistivity at temperature 200 8C could be related to a formation of conductive chains of excess metal particles which break up at tin melting point (231.9 8C) and are transformed to SnO at higher temperature [25]. This rise of resistivity might also be explained on the basis of Lee’s results [22] as follows: there might be a decrease in oxygen vacancies taken up by excess metal ions during annealing in air (oxidizing environment). As a consequence, the carrier concentration might decrease and hence the mobility [22], resulting in an increase in resistivity. The slow increase in resistivity for annealing above 200 8C could be associated with the appearance of SnO phase along with SnO2 tetragonal structure. Hall mobility measurements on SnO2 films [22] have already shown a decrease in mobility and consequently a rise in resistivity by the formation of SnO phase. Furthermore, an improvement in the crystallinity of annealed films can also be a source of increase in resistivity [26]. Microroughness of thin films plays a vital role for developing optical coatings especially in the UV region [27] for applications such as lithographic uses [28]. To characterize an optical surface (coatings) the root-mean-square (RMS) roughness is normally used. The RMS roughness not only describes the light scattering but also gives an idea about the quality of the surface under investigation. Surface morphology of the present SnO2 films annealed at different temperatures are shown in Fig. 3. It can be inferred from these AFM images that smoother films can be obtained by annealing. Thus annealing process is a good parameter that could affect the surface RMS roughness behavior. Fig. 3 is used to determine the average height and RMS roughness for all the films. The plot of RMS surface roughness values computed for the as-deposited and annealed films is shown in Fig. 4 as a function of annealing temperature, in comparison with resistivity and refractive index [18] data. It can be seen from Fig. 4 that RMS roughness and resistivity show almost opposite trend while the refractive index shows the opposite behavior with surface roughness up to 200 8C but beyond this annealing temperature, similar behavior is noted. Lindstro¨m et. al. [29] have shown by PSD (power spectral density) function calculations in sputtered SnO2 films that for thicker films (>300 nm), as the film surface smoothens it gives
8564
A.F. Khan et al. / Applied Surface Science 255 (2009) 8562–8565
Fig. 3. AFM images (2 2 mm2) showing the surface morphology of SnO2 thin films (a) as-deposited and annealed for 15 min at (b) 100 8C (c) 200 8C (d) 300 8C (e) 400 8C and (f) 500 8C.
rise to defects and strain variations. Therefore, if the RMS roughness of the film decreases, surface smoothness increases and defects and strain variations are produced which can hinder the flow of electrons and so the resistivity rises. With regard to refractive index variations in comparison with RMS roughness values; it is noted that where roughness is high, refractive index is
low (up to 200 8C). A similar type of behavior has been observed in Gd2O3 films [28]. 4. Conclusions SnO2 films sputtered at room temperature are mostly crystalline in nature possibly with small amount of amorphous phase and crystallinity improves with annealing temperature. The post annealing shows greater tendency to affect the structural and electrical properties of SnO2 thin films fabricated by rf-magnetron sputtering, which composed of nano-particles. A small amount of SnO phase has been detected along with SnO2 at higher annealing temperatures. Electrical resistivity of present films shows an oscillatory behavior with annealing temperature. RMS roughness and resistivity are found to show almost the opposite behavior with annealing. Annealing decreases the RMS roughness values. Acknowledgement The authors are thankful to the Higher Education Commission (HEC), Government of Pakistan, for financial support. References
Fig. 4. Plots of RMS roughness (curve 1), resistivity (curve 2) and refractive index (curve 3) as a function of annealing temperature TA (8C) for SnO2 thin films.
[1] H.J. Kim, J.W. Bae, J.S. Kim, Y.C. Jang, G.Y. Yeom, N.E. Lee, Surf. Coat. Technol. 131 (2000) 201.
A.F. Khan et al. / Applied Surface Science 255 (2009) 8562–8565 [2] Y.K. Fang, J.J. Lee, Thin Solid Films 169 (1989) 52. [3] W.A. Badway, H.H. Afifi, E.M. Elgair, J. Electrochem. Soc. 137 (1990) 1592. [4] J.C. Mannifacier, L. Szepessy, J.F. Bresse, M. Perotin, R. Stuck, Mater. Res. Bull. 14 (1979) 163. [5] E. Shanthi, V. Dutta, A. Banerkee, K.L. Chopra, J. Appl. Phys. 51 (1980) 6243. [6] I.H. Kim, J.H. Ko, D. Kim, K.S. Lee, T.S. Lee, J.-h. Jeong, B. Cheong, Y.-J. Baik, W.M. Kim, Thin Solid Films 515 (2006) 2475. [7] T. Minami, S. Takata, H. Sato, J. Vac. Sci. Technol. 13 (1995) 1095. [8] B. Thangaraju, Thin Solid Films 402 (2002) 71. [9] J. Kane, H.P. Schwiezer, J. Electrochem. Soc. 123 (1976) 270. [10] T.N. Blanton, M. Lelental, Mater. Res. Bull. 29 (1994) 537. [11] R.S. Dale, C.S. Rastomjee, F.H. Potter, R.G. Egdell, Appl. Surf. Sci. 70/71 (1993) 359. [12] A. Martel, F. C-Briones, J. Fandino, R. C-Rodriguez, P. B-Perez, A. Z-Navarro, M. ZTorres, J.L. Pena, Surf. Coat. Technol. 122 (1999) 136. [13] A. Martel, F. C-Briones, P. Quintana, P. B-Perez, J.L. Pena, Surf. Coat. Technol. 201 (2007) 4659. [14] X. Feng, J. Ma, F. Yang, F. Ji, F. Zong, C. Luan, H. Ma, Mater. Lett. 62 (2008) 1779. [15] A.O. -Flores, P.B. -Perez, R.C. -Rodriguez, A.I. Oliva, Rev. Mex. Fis. 52 (2006) 15. [16] B.N. Mukashev, S.Zh. Tokmoldin, N.B. Beisenkhanov, S.M. Kikkarin, I.V. Valitova, V.B. Glazman, A.B. Aimagambetov, E.A. Dmitrieva, B.M. Veremenithev, Mater. Sci. Eng. B 118 (2005) 164.
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