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Novel CdZnTe micro pillar films deposited by CSS method
Materials Letters 263 (2020) 127277
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Novel CdZnTe micro pillar films deposited by CSS method Jian Huang ⇑, Zhuorui Chen, Jiaying Bie, Yi Shang, Kefeng Yao, Zhe Chen, Ke Tang, Meng Cao ⇑, Linjun Wang School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
a r t i c l e
i n f o
Article history: Received 8 September 2019 Received in revised form 12 November 2019 Accepted 27 December 2019 Available online 28 December 2019 Keywords: Semiconductors CZT Optical materials and properties PL XPS Electrical properties
a b s t r a c t CdZnTe (CZT) micro pillar films with cubic zinc blend phase have been deposited on single layer graphene coated quartz substrate by close-spaced sublimation technique. Structural and phase purities of deposited micro pillar CZT films were investigated using X-ray diffraction and Raman spectroscopy. Scanning electron microscopy characterizations indicated that the diameters of CZT micro pillars were about 5 mm and their lengths were close to 57 mm. The band-gap of CZT micro pillar films was about 1.53 eV, which was confirmed by UV–Vis–NIR diffuse reflection spectra and PL spectra. The structure of Au/BGZO/CZT/graphene/quartz was fabricated to study its optoelectronic properties. Under the illumination of AM 1.5, CZT micro pillar films had good photo response, which indicated their great potential in the application of optoelectronic devices. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction As a ternary semiconductor, CdZnTe (CZT) has tunable bandgap of 1.44–2.26 eV, which can alter the properties of CZT. The little percent of Zn in CZT can increase its mechanical strength and avoid the polarization charges under bias, which would act as trapping centers to influence the space-charge distribution and the electric field profile. So, CZT has attracted considerable interest in optoelectronic devices applications, such as switching devices, radiation detector, high-resolution hard X-ray and c-ray detector, solar cells and so on [1–3]. High quality CZT thin film can be deposited with molecular beam epitaxy (MBE) and metal organic vapor phase epitaxy (MOVPE) by excellent control over the growth process at the nanometer scale [4,5]. But the prices of these two complicated devices are very high. Electrodeposition method can prepare CZT films with cheap devices and simple process [6]. However, the qualities of the obtained films are poor relatively. Comparing with the above methods, close-spaced sublimation (CSS) method can prepare high quality CZT films without complicated and high price devices. During the deposition of CZT films by CSS method, the structural and morphological characteristics of the deposited films are greatly influenced by the kinds of substrates. So, CTZ films with
⇑ Corresponding authors. E-mail addresses: [email protected] (J. Huang), [email protected] (M. Cao)[email protected] (J. Huang), [email protected] (M. Cao). https://doi.org/10.1016/j.matlet.2019.127277 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
various morphologies may be achieved by optimizing the surface properties of the substrates. In this paper, we prepared CZT films by CSS method on monolayer graphene covered quartz substrates. Novel pillar like CZT films were obtained. The possible morphological evolution of pillar like CZT films and optoelectronic properties of Au/BGZO/CZT/graphene/quartz have been studied, which are contributive to its application of optoelectronic devices.
2. Experimental procedures CZT films were grown on a 2 cm 2 cm graphene-coated quartz substrate (Fig. S1) by using CSS method. Polycrystalline CZT powders (>99.99999%) were used as the source materials. The temperature of the sublimation source and the substrate was controlled at 600 and 500 °C, respectively. The deposition times were 40–60 mins. The distance between the substrate and the source was 4 mm. Surface morphologies of the samples were analyzed by scanning electron microscopy (SEM, FEI Sirion 200). XRD (18KW D/ MAX-2500 V PC) and Raman spectra (JY-H800UV) were used to examine the phase purities of CZT films. The optical properties were studied by using UV–vis spectrophotometer (Jasco UV-570) and PL (JY-H800UV). After deposition, a 200 nm thick boron and gallium co-doped ZnO (BGZO) layer was deposited onto the surface of CZT micro pillar films, which used a BGZO ceramic target (97 wt % ZnO with 2.5 wt% Ga2O3 and 0.5 wt% B2O3, purity 99.99%). At last,
2
J. Huang et al. / Materials Letters 263 (2020) 127277
a 20 nm thick Au grid electrode was sputtered onto the surface of BGZO layer [7]. Then, the optoelectronic properties of Au/BGZO/ CZT/graphene/quartz were studied by using Keithley 4200A-SCS instrument. 3. Results and discussion
Fig. 1. XRD (a) and Raman spectra (b) of CZT micro pillar films.
Fig. 2. SEM charactrizations of CZT micro pillar films: surface (a) and cross section (b).
In Fig. 1a, the peaks at 23.75°, 39.42°, 46.60°, 71.48° and 76.45° correspond to (1 1 1), (2 2 0), (3 1 1), (4 2 2) and (5 1 1) planes of CZT with zinc blend cubic structure, respectively [8]. To exclude the phase segregations, such as ZnTe in the as-prepared CZT films, Raman characterizations were performed. In Fig. 1b, two peaks at 141 cm 1 and 164 cm 1 can be ascribed to LO phonon of CZT films [9]. Due to the low Zn content for the sample, no peak at 210 cm 1 is found, which corresponds to ZnTe [10]. Besides, the small peak at about 110 cm 1 indicates that some TeO2 exist in the films [11]. The atomic composition ratios of Cd:Zn:Te are determined to be about 52.13:3.29:44.58 by EDS measurement [Tab. S1]. The surface properties of CZT films are shown in Fig. 2a. As shown, CZT films consist of many micro pillars, whose diameters are about 5 lm. The diameters of the micro pillars are decreased with the decreasing of deposition times [Fig. S2]. The cross-section SEM characterizations indicate that the thickness of CZT micro pillar
Fig. 3. Diffuse reflections spectra of CZT micro pillar films (a), determined bandgap (b) and the PL spectra (c).
Fig. 4. Xps spectra of CZT micro pillar films:full spectra(a), Te3d(b), Zn2p(c), Cd3d(d).
J. Huang et al. / Materials Letters 263 (2020) 127277
3
Fig. 5. I-V (a) and I-T (b) curves of CZT micro pillar films.
films is about 57 lm. At the first deposition process, a thin layer of CZT nanoparticles are deposited on the surface of graphene/quartz substrates. According to the proposed ‘‘orientation attachment’’ theory, CZT micro pillars may be formed through oriented attachment of CZT nanoparticles at the hexagonal shape surface of graphene [12]. So, we think, the hexagonal shape of graphene at the surface of quartz substrates is the key factor to form the CZT micro pillars. Fig. 3a shows the diffuse reflection spectra of CZT micro pillar films. CZT micro pillar films have obvious absorption band edges at about 815 nm. Its bandgap is determined to be 1.53 eV (Fig. 3b), which is calculated by Kubelka-Munk equations [13]. Fig. 3c shows that the PL spectra of the CZT films. Only one broad peak at about 788 nm determines their band gap to be 1.57 eV. It is close to that determined by diffuse reflection spectra and agrees well with previous reported values [14]. Fig. 4 shows the XPS spectra of Te3d, Cd3d and Zn2p peaks of the CZT micro pillar films. As shown, the positions of the Te2 3d3/2 and Te2 3d5/2 peaks are found to be 582.3 eV and 572.0 eV [15]. The peak energy levels associated with Cd (3d5/2 and 3d3/2) appear at 404.5 and 411.2 eV, respectively [16]. The binding energy of Zn (2p1/2 and 2p3/2) was observed at 1025 eV and 1021.4 eV [17]. To study the optoelectronic properties, Au/BGZO/CZT/graphene/ quartz structure was fabricated and its J-V characteristics were measured under AM 1.5 illumination. As shown in Fig. 5a, the current density is obviously larger than that of the dark conditions at the same bias voltage. At the bias voltage of 5–10 V, the current density of Au/BGZO/CZT/graphene/quartz under illumination is about 1000 times that of dark current density. The typical transient response characteristics of Au/BGZO/CZT/graphene/quartz at the bias voltage of 5 V are investigated by a mechanical chopping method, in which light was switched on and off alternately. As shown in Fig. 5b, the photo/dark current exhibits a stable value and the photocurrent densities are about 2.25 10 2 A/cm2 during the light on/off cycle measurement. The optoelectronic performance of our structure is comparable with that of CZT single crystal photo detector [11]. 4. Conclusions CZT micro pillar films were deposited on graphene coated quartz substrates by using CSS method. The hexagonal shape of graphene was the key factor to form the CZT micro pillar. The optical band gap of deposited CZT micro pillar films was determined to be 1.53 eV. Optoelectronic measurements indicated that CZT micro pillar films had good visible light responses. Further work in this
area is on the way to improve the quality of CZT micro pillar films and its potential application in photodetectors. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was funded by the National Natural Science Foundation of China (No. 11875186 and No. 11905121). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.127277. References: [1] S. Tobeñas, E.M. Larramendi, E. Purón, O. De Melo, F. Cruz-Gandarilla, M. Hesiquio-Garduno, M. Tamura, J. Cryst. Growth 234 (2002) 311–317. [2] J. Huang, L.J. Wang, K. Tang, R. Xu, J.J. Zhang, Y.B. Xia, X.G. Lu, Phys. Procedia 32 (2012) 161–164. [3] O. de Melo, A. Domínguez, K. Gutiérrez Z-B, G. Contreras-Puente, S. GallardoHernández, A. Escobosa, J.C. González, R. Paniago, J. Ferraz Dias, M. Behar, Sol. Energ. Mat. Sol. C, 138 (2015) 17-21. [4] F.E. Arkun, D.D. Edwall, J. Ellsworth, S. Douglas, M. Zandian, M. Carmody, J. Electron. Mater. 46 (2017) 5374–5378. [5] M. Niraula, K. Yasuda, S. Namba, T. Kondo, S. Muramatsu, Y. Wajima, H. Yamashita, Y. Agata, I.E.E.E.T. Nucl, Sci. 60 (2013) 2859–2863. [6] A. Bansal, P. Rajaram, Mater. Lett. 59 (2005) 3666–3671. [7] K. Tang, J. Huang, Y.X. Lu, Y. Hu, Y.B. Shen, J.J. Zhang, Q.M. Gu, L.J. Wang, Y.C. Lu, Appl. Surf. Sci. 433 (2018) 177–180. [8] L.M. Cai, L.J. Wang, J. Huang, B.Y. Yao, K. Tang, J.J. Zhang, K.F. Qin, J.H. Min, Y.B. Xia, Vacuum 88 (2013) 28–31. [9] H.T. Xu, R. Xu, J. Huang, Jijun Zhang, Ke Tang, Linjun Wang, Appl. Surf. Sci. 305 (2014) 477–480. [10] V. Kosyak, Y. Znamenshchykov, A. Cˇerškus, Yu.P. Gnatenko, L. Grase, J. Vecstaudza, A. Medvids, A. Opanasyuk, G. Mezinskis, J. Alloy. Compd. 682 (2016) 543–551. [11] B. Ren, J.J. Zhang, M.Y. Liao, J. Huang, L.W. Sang, Y. Koide, L.J. Wang, Opt. Express 27 (2019) 8935–8942. [12] Y.W. Tang, L.J. Luo, Z.G. Chen, Y. Jiang, B.H. Li, Z.Y. Jia, L. Xu, Electrochem. Commun. 9 (2007) 289–292. [13] J.H. Nobbs, Rev. Prog. Color. Relat. Top 15 (1985) 66–75. [14] V. Kosyak, Y. Znamenshchykov, A. Cˇerškus, L. Grase, Yu.P. Gnatenko, A. Medvids, A. Opanasyuk, G. Mezinskis, J. Lumin. 171 (2016) 176–182. [15] A. Arbaoui, A. Outzourhit, N. Achargui, H. Bellakhder, E.L. Ameziane, J.C. Bernede, Sol. Energy Mater. Sol. Cells 90 (2006) 1364–1370. [16] K. Prabakar, S. Venkatachalam, Y.L. Jeyachandran, Sa.K. Narayandass, D. Mangalaraj, Mater. Sci. Eng. B 107 (2004) 99–105. [17] G. Gordilloa, C. Calderóna, P. Bartolo-Pérez, Appl. Surf. Sci. 305 (2014) 506– 514.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Novel CdZnTe micro pillar films deposited by CSS method Jian Huang ⇑, Zhuorui Chen, Jiaying Bie, Yi Shang, Kefeng Yao, Zhe Chen, Ke Tang, Meng Cao ⇑, Linjun Wang School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
a r t i c l e
i n f o
Article history: Received 8 September 2019 Received in revised form 12 November 2019 Accepted 27 December 2019 Available online 28 December 2019 Keywords: Semiconductors CZT Optical materials and properties PL XPS Electrical properties
a b s t r a c t CdZnTe (CZT) micro pillar films with cubic zinc blend phase have been deposited on single layer graphene coated quartz substrate by close-spaced sublimation technique. Structural and phase purities of deposited micro pillar CZT films were investigated using X-ray diffraction and Raman spectroscopy. Scanning electron microscopy characterizations indicated that the diameters of CZT micro pillars were about 5 mm and their lengths were close to 57 mm. The band-gap of CZT micro pillar films was about 1.53 eV, which was confirmed by UV–Vis–NIR diffuse reflection spectra and PL spectra. The structure of Au/BGZO/CZT/graphene/quartz was fabricated to study its optoelectronic properties. Under the illumination of AM 1.5, CZT micro pillar films had good photo response, which indicated their great potential in the application of optoelectronic devices. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction As a ternary semiconductor, CdZnTe (CZT) has tunable bandgap of 1.44–2.26 eV, which can alter the properties of CZT. The little percent of Zn in CZT can increase its mechanical strength and avoid the polarization charges under bias, which would act as trapping centers to influence the space-charge distribution and the electric field profile. So, CZT has attracted considerable interest in optoelectronic devices applications, such as switching devices, radiation detector, high-resolution hard X-ray and c-ray detector, solar cells and so on [1–3]. High quality CZT thin film can be deposited with molecular beam epitaxy (MBE) and metal organic vapor phase epitaxy (MOVPE) by excellent control over the growth process at the nanometer scale [4,5]. But the prices of these two complicated devices are very high. Electrodeposition method can prepare CZT films with cheap devices and simple process [6]. However, the qualities of the obtained films are poor relatively. Comparing with the above methods, close-spaced sublimation (CSS) method can prepare high quality CZT films without complicated and high price devices. During the deposition of CZT films by CSS method, the structural and morphological characteristics of the deposited films are greatly influenced by the kinds of substrates. So, CTZ films with
⇑ Corresponding authors. E-mail addresses: [email protected] (J. Huang), [email protected] (M. Cao)[email protected] (J. Huang), [email protected] (M. Cao). https://doi.org/10.1016/j.matlet.2019.127277 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
various morphologies may be achieved by optimizing the surface properties of the substrates. In this paper, we prepared CZT films by CSS method on monolayer graphene covered quartz substrates. Novel pillar like CZT films were obtained. The possible morphological evolution of pillar like CZT films and optoelectronic properties of Au/BGZO/CZT/graphene/quartz have been studied, which are contributive to its application of optoelectronic devices.
2. Experimental procedures CZT films were grown on a 2 cm 2 cm graphene-coated quartz substrate (Fig. S1) by using CSS method. Polycrystalline CZT powders (>99.99999%) were used as the source materials. The temperature of the sublimation source and the substrate was controlled at 600 and 500 °C, respectively. The deposition times were 40–60 mins. The distance between the substrate and the source was 4 mm. Surface morphologies of the samples were analyzed by scanning electron microscopy (SEM, FEI Sirion 200). XRD (18KW D/ MAX-2500 V PC) and Raman spectra (JY-H800UV) were used to examine the phase purities of CZT films. The optical properties were studied by using UV–vis spectrophotometer (Jasco UV-570) and PL (JY-H800UV). After deposition, a 200 nm thick boron and gallium co-doped ZnO (BGZO) layer was deposited onto the surface of CZT micro pillar films, which used a BGZO ceramic target (97 wt % ZnO with 2.5 wt% Ga2O3 and 0.5 wt% B2O3, purity 99.99%). At last,
2
J. Huang et al. / Materials Letters 263 (2020) 127277
a 20 nm thick Au grid electrode was sputtered onto the surface of BGZO layer [7]. Then, the optoelectronic properties of Au/BGZO/ CZT/graphene/quartz were studied by using Keithley 4200A-SCS instrument. 3. Results and discussion
Fig. 1. XRD (a) and Raman spectra (b) of CZT micro pillar films.
Fig. 2. SEM charactrizations of CZT micro pillar films: surface (a) and cross section (b).
In Fig. 1a, the peaks at 23.75°, 39.42°, 46.60°, 71.48° and 76.45° correspond to (1 1 1), (2 2 0), (3 1 1), (4 2 2) and (5 1 1) planes of CZT with zinc blend cubic structure, respectively [8]. To exclude the phase segregations, such as ZnTe in the as-prepared CZT films, Raman characterizations were performed. In Fig. 1b, two peaks at 141 cm 1 and 164 cm 1 can be ascribed to LO phonon of CZT films [9]. Due to the low Zn content for the sample, no peak at 210 cm 1 is found, which corresponds to ZnTe [10]. Besides, the small peak at about 110 cm 1 indicates that some TeO2 exist in the films [11]. The atomic composition ratios of Cd:Zn:Te are determined to be about 52.13:3.29:44.58 by EDS measurement [Tab. S1]. The surface properties of CZT films are shown in Fig. 2a. As shown, CZT films consist of many micro pillars, whose diameters are about 5 lm. The diameters of the micro pillars are decreased with the decreasing of deposition times [Fig. S2]. The cross-section SEM characterizations indicate that the thickness of CZT micro pillar
Fig. 3. Diffuse reflections spectra of CZT micro pillar films (a), determined bandgap (b) and the PL spectra (c).
Fig. 4. Xps spectra of CZT micro pillar films:full spectra(a), Te3d(b), Zn2p(c), Cd3d(d).
J. Huang et al. / Materials Letters 263 (2020) 127277
3
Fig. 5. I-V (a) and I-T (b) curves of CZT micro pillar films.
films is about 57 lm. At the first deposition process, a thin layer of CZT nanoparticles are deposited on the surface of graphene/quartz substrates. According to the proposed ‘‘orientation attachment’’ theory, CZT micro pillars may be formed through oriented attachment of CZT nanoparticles at the hexagonal shape surface of graphene [12]. So, we think, the hexagonal shape of graphene at the surface of quartz substrates is the key factor to form the CZT micro pillars. Fig. 3a shows the diffuse reflection spectra of CZT micro pillar films. CZT micro pillar films have obvious absorption band edges at about 815 nm. Its bandgap is determined to be 1.53 eV (Fig. 3b), which is calculated by Kubelka-Munk equations [13]. Fig. 3c shows that the PL spectra of the CZT films. Only one broad peak at about 788 nm determines their band gap to be 1.57 eV. It is close to that determined by diffuse reflection spectra and agrees well with previous reported values [14]. Fig. 4 shows the XPS spectra of Te3d, Cd3d and Zn2p peaks of the CZT micro pillar films. As shown, the positions of the Te2 3d3/2 and Te2 3d5/2 peaks are found to be 582.3 eV and 572.0 eV [15]. The peak energy levels associated with Cd (3d5/2 and 3d3/2) appear at 404.5 and 411.2 eV, respectively [16]. The binding energy of Zn (2p1/2 and 2p3/2) was observed at 1025 eV and 1021.4 eV [17]. To study the optoelectronic properties, Au/BGZO/CZT/graphene/ quartz structure was fabricated and its J-V characteristics were measured under AM 1.5 illumination. As shown in Fig. 5a, the current density is obviously larger than that of the dark conditions at the same bias voltage. At the bias voltage of 5–10 V, the current density of Au/BGZO/CZT/graphene/quartz under illumination is about 1000 times that of dark current density. The typical transient response characteristics of Au/BGZO/CZT/graphene/quartz at the bias voltage of 5 V are investigated by a mechanical chopping method, in which light was switched on and off alternately. As shown in Fig. 5b, the photo/dark current exhibits a stable value and the photocurrent densities are about 2.25 10 2 A/cm2 during the light on/off cycle measurement. The optoelectronic performance of our structure is comparable with that of CZT single crystal photo detector [11]. 4. Conclusions CZT micro pillar films were deposited on graphene coated quartz substrates by using CSS method. The hexagonal shape of graphene was the key factor to form the CZT micro pillar. The optical band gap of deposited CZT micro pillar films was determined to be 1.53 eV. Optoelectronic measurements indicated that CZT micro pillar films had good visible light responses. Further work in this
area is on the way to improve the quality of CZT micro pillar films and its potential application in photodetectors. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was funded by the National Natural Science Foundation of China (No. 11875186 and No. 11905121). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.127277. References: [1] S. Tobeñas, E.M. Larramendi, E. Purón, O. De Melo, F. Cruz-Gandarilla, M. Hesiquio-Garduno, M. Tamura, J. Cryst. Growth 234 (2002) 311–317. [2] J. Huang, L.J. Wang, K. Tang, R. Xu, J.J. Zhang, Y.B. Xia, X.G. Lu, Phys. Procedia 32 (2012) 161–164. [3] O. de Melo, A. Domínguez, K. Gutiérrez Z-B, G. Contreras-Puente, S. GallardoHernández, A. Escobosa, J.C. González, R. Paniago, J. Ferraz Dias, M. Behar, Sol. Energ. Mat. Sol. C, 138 (2015) 17-21. [4] F.E. Arkun, D.D. Edwall, J. Ellsworth, S. Douglas, M. Zandian, M. Carmody, J. Electron. Mater. 46 (2017) 5374–5378. [5] M. Niraula, K. Yasuda, S. Namba, T. Kondo, S. Muramatsu, Y. Wajima, H. Yamashita, Y. Agata, I.E.E.E.T. Nucl, Sci. 60 (2013) 2859–2863. [6] A. Bansal, P. Rajaram, Mater. Lett. 59 (2005) 3666–3671. [7] K. Tang, J. Huang, Y.X. Lu, Y. Hu, Y.B. Shen, J.J. Zhang, Q.M. Gu, L.J. Wang, Y.C. Lu, Appl. Surf. Sci. 433 (2018) 177–180. [8] L.M. Cai, L.J. Wang, J. Huang, B.Y. Yao, K. Tang, J.J. Zhang, K.F. Qin, J.H. Min, Y.B. Xia, Vacuum 88 (2013) 28–31. [9] H.T. Xu, R. Xu, J. Huang, Jijun Zhang, Ke Tang, Linjun Wang, Appl. Surf. Sci. 305 (2014) 477–480. [10] V. Kosyak, Y. Znamenshchykov, A. Cˇerškus, Yu.P. Gnatenko, L. Grase, J. Vecstaudza, A. Medvids, A. Opanasyuk, G. Mezinskis, J. Alloy. Compd. 682 (2016) 543–551. [11] B. Ren, J.J. Zhang, M.Y. Liao, J. Huang, L.W. Sang, Y. Koide, L.J. Wang, Opt. Express 27 (2019) 8935–8942. [12] Y.W. Tang, L.J. Luo, Z.G. Chen, Y. Jiang, B.H. Li, Z.Y. Jia, L. Xu, Electrochem. Commun. 9 (2007) 289–292. [13] J.H. Nobbs, Rev. Prog. Color. Relat. Top 15 (1985) 66–75. [14] V. Kosyak, Y. Znamenshchykov, A. Cˇerškus, L. Grase, Yu.P. Gnatenko, A. Medvids, A. Opanasyuk, G. Mezinskis, J. Lumin. 171 (2016) 176–182. [15] A. Arbaoui, A. Outzourhit, N. Achargui, H. Bellakhder, E.L. Ameziane, J.C. Bernede, Sol. Energy Mater. Sol. Cells 90 (2006) 1364–1370. [16] K. Prabakar, S. Venkatachalam, Y.L. Jeyachandran, Sa.K. Narayandass, D. Mangalaraj, Mater. Sci. Eng. B 107 (2004) 99–105. [17] G. Gordilloa, C. Calderóna, P. Bartolo-Pérez, Appl. Surf. Sci. 305 (2014) 506– 514.