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Growth of ZnO nanosheets by hydrothermal method on ZnO seed layer coated by spin-coating technique
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 6146–6152
www.materialstoday.com/proceedings
STEMa2016
Growth of ZnO nanosheets by hydrothermal method on ZnO seed layer coated by spin-coating technique Somyod Denchitcharoena,*, Nontakoch Siriphongsapaka, Pichet Limsuwana a
Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand
Abstract In this work, ZnO nanosheets that are dense and uniform can be synthesized by hydrothermal method on ZnO seed layer coated by spin-coating technique. The precursor concentrations of ZnO seed layer were varied from 2 to 22 mM. The seed layer at each concentration of 2, 10, 14, and 22 mM was used to synthesize ZnO nanosheets with the same hydrothermal condition. Then, ZnO seed layer and ZnO nanosheets were characterized by scanning electron microscope (SEM), X-ray diffraction technique (XRD), and UV-visible spectrophotometer (UV-vis) to study surface morphology, crystal structure, % transmittance, and optical band gap. The results showed that particle sizes on the surface of the seed layer were formed to be bigger and the XRD intensity of (100) peak tended to decrease with increasing precursor concentrations. The ZnO nanosheets on the seed layer at 14 mM have the sheet thicknesses from 10 to 25 nm and diameters from 0.2 to 0.5 μm. Moreover, ZnO nanosheets showed high crystallinity in (002) plane, high transparent in visible region, and optical band gap of about 3.33 eV. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Science and Technology of the Emerging Materials. Keywords: ZnO nanosheets; Hydrothermal; ZnO seed layer; Spin-coating
1. Introduction Zinc oxide (ZnO) is one of popular chemical compounds that has many impressive properties. For instance, ZnO is in the group of wide energy gap semiconductor (3.37 eV) and has higher excitron binding energy (60 meV). Therefore, ZnO presents thermal and chemical stabilities which are suitable for the many applications such as
* Corresponding author. Tel.: +66 51101729; fax: +66 4278785. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Science and Technology of the Emerging Materials.
N. Siriphongsapak et al. / Materials Today: Proceedings 4 (2017) 6146–6152
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photocatalyst [1]. Moreover, piezoelectric property of ZnO can be used in surface acoustic wave sensor and piezoelectric nanogenerator [2, 3]. There are many researches which study about one-dimensional ZnO such as nanorods because it is quite challenge to have better and different properties, comparing to those of bulk form [4]. However, ZnO nanorods can be broken when it receives too heavy force [3]. Therefore, two-dimensional ZnO structures or ZnO nanosheets become an alternative choice which is not only ZnO nanorods because nanosheets are more flexible than nanorods. As a results, nanosheet can be loaded by higher force while other properties are maintained [5]. Li et al. [6] revealed that ZnO nanosheet could be synthesized by hydrothermal method on bare aluminum substrate. Lv et al. [7] found that periods of time to synthesize nanostructures by hydrothermal method affected the formation of ZnO nanosheets (2 hours) and ZnO nanorods (6 hours) on ZnO seed layer. Bang et al. [8] reported that ZnO nanosheets could be grown on ZnO (1 nm) / Al2O3 (5 nm) layers and be formed to have ZnO nanorods due to higher thickness of ZnO layer. In this study, ZnO nanosheets were grown using hydrothermal method on ZnO seed layer. The ZnO seed layers were coated by spin-coating technique with various precursor concentrations. The ZnO seed layers and ZnO nanosheets were characterized by scanning electron microscope (FESEM), x-ray diffraction technique (XRD) and UV-visible spectrophotometer (UV-vis) to report surface morphology, crystal structure and optical property, respectively. 2. Experimental 2.1. Preparation of ZnO seed layer Zinc acetate dihydrate (Zn(Ac)2) and monoethanolamine (MEA) were dissolved in isopropanol. The concentrations of Zn(Ac)2 are 2, 10, 14, and 22 mM mixing to MEA with the ratio of 1. The solutions were stirred at room temperature for 60 min. The clear solutions were used in spin-coating technique to coat seed layer on glass and silicon substrates with rotational speed of 2500 rpm for 30 sec. The coated layer were heated at 50˚C for 5 min before coating next layer. The spin-coating and heating were repeated about 4 times. Then, the seed layers were annealed in the furnace at 300˚C for 60 min. 2.2. Growth of ZnO nanosheets ZnO nanosheets were prepared on ZnO seed layer using hydrothermal method with aqueous solution of 10 mM zinc nitrate hexahydrate (Zn(NO3)2) and 10 mM hexamethylenetetramine (HMT). The Zn(NO3)2 solution and HMT solution were each stirred for 60 min before they were mixed together with ratio 1:1 and stirred again for 30 min. The mixed solution and substrate with ZnO seed layer would be put in Teflon® liner autoclave. The autoclave was placed in oven at 90˚C for 6 hours. 2.3. Characterization FESEM was used to investigate ZnO seed layer and ZnO nanosheets on seed layer. The FESEM images were analyzed to measure the size distribution and morphology of seed layer as well as the geometry of ZnO nanosheets. To confirm peak pattern of ZnO, XRD was used to present the crystal planes and crystalline quality of ZnO seed layer and nanosheets. Moreover, % transmittance spectra and optical band gap of samples were obtained by UV-vis. 3. Results and discussion 3.1. ZnO seed layer Fig. 1 shows the surface morphology of ZnO seed layers with various precursor concentrations. The particles on the surface are dense and the surfaces are not smooth. When the ZnO seed layer at 2 mM was compared with other
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conditions, it shows smaller particles on the surface as shown in Fig. 1(a). For precursor concentrations from 10 mM to 22 mM (Fig. 1(b – d)), particles tend to be bigger on the surface. Fig. 2(a) shows that average size and size distribution of particles on the seed layer at 2 mM is lower than those of the seed layers at other concentrations. This might be the seed layer at 2 mM having small amounts of colloid particles in the solution which are not easy to aggregate and agglomerate. The % transmittance spectra of ZnO seed layers with all precursor concentrations are shown in Fig. 2(b). The ZnO seed layers show high transmittance in visible region. The spectra of seed layers are more than 80% and decreased at wavelength below 380 nm that refers to energy absorption by energy gap. The intensity of absorption indicates quantity of ZnO on the substrate. Therefore, it can confirm that the amount of ZnO on seed layer is increased when precursor concentrations are increased. The x-ray diffraction patterns of ZnO seed layers at concentrations from 10 mM to 22 mM are shown in Fig. 3. The results of all seed layers show hexagonal wurtzite structure corresponding to JCPDS number 36-1451. The seed layer at concentration of 10 mM shows high intensity at (100) plane or a-plane due to interaction between ZnO particles and glass substrate [9]. When the precursor concentration of seed layer was increased, the intensity at (100) plane decreases because particles on surface have more chance to interact together.
b
a
150 nm
c
150 nm
d
150 nm
150 nm
Fig. 1. Surface morphology of ZnO seed layer spin-coated with precursor concentrations of (a) 2 mM, (b) 10 mM, (c) 14 mM, and (d) 22 mM.
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N. Siriphongsapak et al. / Materials Today: Proceedings 4 (2017) 6146–6152
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2 mM 10 mM 14 mM 22 mM
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(b)
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600
700
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Fig. 2. (a) Average particle sizes and size distributions of particles on the ZnO seed layer; (b) % transmittance of ZnO seed layer with various precursor concentrations.
seed layer 22 mM
intensity (a.u.)
seed layer 14 mM
(103)
JCPDS#36-1451
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50
60
(200) (112) (201)
(110)
(102)
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(101)
(100)
seed layer 10 mM
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Fig. 3. X-ray diffraction pattern of ZnO seed layer at concentrations of 10 mM, 14 mM, and 22 mM.
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a
c
b
600 nm
600 nm
600 nm
d
e
600 nm
150 nm
Fig. 4. Surface morphology of ZnO nanosheets on ZnO seed layers at concentrations of (a) 2 mM, (b) 10 mM, (c) 14 mM, (d) 22 mM, and (e) high magnification of ZnO nanosheets on ZnO seed layer at concentration of 14 mM.
3.2. ZnO nanosheets Fig. 4. shows the morphology of ZnO nanosheets on the ZnO seed layers with various precursor concentrations. The ZnO nanosheets slightly grow on seed layer at 2 mM due to small amounts of ZnO. For ZnO seed layer at higher concentrations of 10 mM and 22 mM, the ZnO nanosheets are very thin as shown in Fig. 4(b and d). Moreover, in case of 10 mM, there are big sheets of ZnO on top of nanosheets due to ZnO precipitation from the solution. Fig. 4(c and e) shows thick ZnO nanosheets on seed layer at 14 mM with the thicknesses from 10 to 25 nm and diameters from 0.2 to 0.5 μm. The x-ray diffraction patterns of ZnO nanosheets on ZnO seed layer are shown in Fig. 5. All of the XRD graphs show only one peak at (002) plane that is polar plane of hexagonal wurtzite structure [7]. The XRD peak of ZnO nanosheets on seed layer at 2 mM is much smaller than other conditions due to small amount of ZnO nanosheets as shown in Fig. 4(a). The ZnO nanosheets on seed layer at 10 mM show high intensity of XRD peak because of big sheets left on ZnO nanosheets. The % transmittance spectra of ZnO nanosheets on ZnO seed layer for all concentrations are shown in Fig. 6(a). The ZnO nanosheets on seed layers at 14 and 22 mM are more transparent than other conditions because ZnO nanosheets have higher uniformity and good crystalline quality. The optical band gap of ZnO nanosheets is studied using peak on dT/dλ (first derivative of % transmittance) graph [10] as shown in Fig. 6(b). The peaks of dT/dλ are at ~372 nm that means the optical band gap of ZnO nanosheets on seed layers are around 3.33 eV
.
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(002)
(002)
intensity (a.u.)
(002)
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N. Siriphongsapak et al. / Materials Today: Proceedings 4 (2017) 6146–6152
nanostructure on seed layer 22 mM nanostructure on seed layer 14 mM nanostructure on seed layer 10 mM nanostructure on seed layer 2 mM
20 0
30 1000
40 2000
50 3000
2-theta (degree)
60 4000
70 5000
Fig. 5. X-ray diffraction pattern of ZnO nanosheets on ZnO seed layer at concentrations of 2 mM, 10 mM, 14 mM, and 22 mM.
(a)
80 60 40
2 mM 10 mM 14 mM 22 mM
20 0 400
500
600
wavelength (nm)
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1.5 1.0 0.5 0.0 340
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420
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Fig. 6. (a) % Transmittance; (b) dT/dλ (first derivative of % transmittance) of ZnO nanosheets on ZnO seed layer at concentrations of 2 mM, 10 mM, 14 mM, and 22 mM.
4. Conclusion ZnO nanosheets were successfully grown using hydrothermal method on ZnO seed layers coated by spin-coating technique. The various precursor concentrations of seed layers affected crystalline quality, particle size on seed layer and morphology of nanosheets. The concentration of seed layer at 14 mM was an optimum condition to achieve ZnO nanosheets with high density, high uniformity, good crystalline quality and high transparent.
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Acknowledgements The authors would like to thank Mrs. Sumalee Ninlapruk in Office of Atoms for Peace (OAP) to allow us for using their facilities such as UV-visible spectrophotometer. Moreover, this research was financially supported by Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi (KMUTT) and by Science Achievement Scholarship of Thailand (SAST). References [1] A. Kołodziejczak-Radzimska, T. Jesionowski, Materials 7 (2014) 2833–2881. [2] H. Hong, G. Chung, Sensor Actuat. B-Chem. 195 (2014) 446–451. [3] X. Wang, Nano Energy 1 (2012) 13–24. [4] S. Xu, Z.L. Wang, Nano Res. 4 (2011) 1013–1098. [5] K. Kim, B. Kumar, K. Lee, H. Park, J. Lee, H. Lee, H. Jun, D. Lee, S. Kim, Sci. Rep. 3 (2013) 1–6. [6] X. Li, P. Liang, L. Wang, F. Yu., Front. Optoelectron. 7 (2014) 509–512. [7] J. Lv, C. Liu, W. Gong, Z. Zi, X. Chen, K. Huang, T. Wang, G. He, X. Song, Z. Sun, Sci. Adv. Mater. 4 (2012) 757–762. [8] S. Bang, S. Lee, Y. Ko, J. Park, S. Shin, H. Seo, H. Jeon, Nanoscale Res. Lett. 7 (2012) 1–11. [9] L. Znaidi, G.J.A.A. Soler Illia, S. Benyahia, C. Sanchez, A.V. Kanaev, Thin Solid Films 428 (2003) 257–262. [10] L. Xu, G. Zheng, J. Miao, F. Xian, Appl. Surf. Sci. 258 (2012) 7760–7765.
ScienceDirect Materials Today: Proceedings 4 (2017) 6146–6152
www.materialstoday.com/proceedings
STEMa2016
Growth of ZnO nanosheets by hydrothermal method on ZnO seed layer coated by spin-coating technique Somyod Denchitcharoena,*, Nontakoch Siriphongsapaka, Pichet Limsuwana a
Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand
Abstract In this work, ZnO nanosheets that are dense and uniform can be synthesized by hydrothermal method on ZnO seed layer coated by spin-coating technique. The precursor concentrations of ZnO seed layer were varied from 2 to 22 mM. The seed layer at each concentration of 2, 10, 14, and 22 mM was used to synthesize ZnO nanosheets with the same hydrothermal condition. Then, ZnO seed layer and ZnO nanosheets were characterized by scanning electron microscope (SEM), X-ray diffraction technique (XRD), and UV-visible spectrophotometer (UV-vis) to study surface morphology, crystal structure, % transmittance, and optical band gap. The results showed that particle sizes on the surface of the seed layer were formed to be bigger and the XRD intensity of (100) peak tended to decrease with increasing precursor concentrations. The ZnO nanosheets on the seed layer at 14 mM have the sheet thicknesses from 10 to 25 nm and diameters from 0.2 to 0.5 μm. Moreover, ZnO nanosheets showed high crystallinity in (002) plane, high transparent in visible region, and optical band gap of about 3.33 eV. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Science and Technology of the Emerging Materials. Keywords: ZnO nanosheets; Hydrothermal; ZnO seed layer; Spin-coating
1. Introduction Zinc oxide (ZnO) is one of popular chemical compounds that has many impressive properties. For instance, ZnO is in the group of wide energy gap semiconductor (3.37 eV) and has higher excitron binding energy (60 meV). Therefore, ZnO presents thermal and chemical stabilities which are suitable for the many applications such as
* Corresponding author. Tel.: +66 51101729; fax: +66 4278785. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Science and Technology of the Emerging Materials.
N. Siriphongsapak et al. / Materials Today: Proceedings 4 (2017) 6146–6152
6147
photocatalyst [1]. Moreover, piezoelectric property of ZnO can be used in surface acoustic wave sensor and piezoelectric nanogenerator [2, 3]. There are many researches which study about one-dimensional ZnO such as nanorods because it is quite challenge to have better and different properties, comparing to those of bulk form [4]. However, ZnO nanorods can be broken when it receives too heavy force [3]. Therefore, two-dimensional ZnO structures or ZnO nanosheets become an alternative choice which is not only ZnO nanorods because nanosheets are more flexible than nanorods. As a results, nanosheet can be loaded by higher force while other properties are maintained [5]. Li et al. [6] revealed that ZnO nanosheet could be synthesized by hydrothermal method on bare aluminum substrate. Lv et al. [7] found that periods of time to synthesize nanostructures by hydrothermal method affected the formation of ZnO nanosheets (2 hours) and ZnO nanorods (6 hours) on ZnO seed layer. Bang et al. [8] reported that ZnO nanosheets could be grown on ZnO (1 nm) / Al2O3 (5 nm) layers and be formed to have ZnO nanorods due to higher thickness of ZnO layer. In this study, ZnO nanosheets were grown using hydrothermal method on ZnO seed layer. The ZnO seed layers were coated by spin-coating technique with various precursor concentrations. The ZnO seed layers and ZnO nanosheets were characterized by scanning electron microscope (FESEM), x-ray diffraction technique (XRD) and UV-visible spectrophotometer (UV-vis) to report surface morphology, crystal structure and optical property, respectively. 2. Experimental 2.1. Preparation of ZnO seed layer Zinc acetate dihydrate (Zn(Ac)2) and monoethanolamine (MEA) were dissolved in isopropanol. The concentrations of Zn(Ac)2 are 2, 10, 14, and 22 mM mixing to MEA with the ratio of 1. The solutions were stirred at room temperature for 60 min. The clear solutions were used in spin-coating technique to coat seed layer on glass and silicon substrates with rotational speed of 2500 rpm for 30 sec. The coated layer were heated at 50˚C for 5 min before coating next layer. The spin-coating and heating were repeated about 4 times. Then, the seed layers were annealed in the furnace at 300˚C for 60 min. 2.2. Growth of ZnO nanosheets ZnO nanosheets were prepared on ZnO seed layer using hydrothermal method with aqueous solution of 10 mM zinc nitrate hexahydrate (Zn(NO3)2) and 10 mM hexamethylenetetramine (HMT). The Zn(NO3)2 solution and HMT solution were each stirred for 60 min before they were mixed together with ratio 1:1 and stirred again for 30 min. The mixed solution and substrate with ZnO seed layer would be put in Teflon® liner autoclave. The autoclave was placed in oven at 90˚C for 6 hours. 2.3. Characterization FESEM was used to investigate ZnO seed layer and ZnO nanosheets on seed layer. The FESEM images were analyzed to measure the size distribution and morphology of seed layer as well as the geometry of ZnO nanosheets. To confirm peak pattern of ZnO, XRD was used to present the crystal planes and crystalline quality of ZnO seed layer and nanosheets. Moreover, % transmittance spectra and optical band gap of samples were obtained by UV-vis. 3. Results and discussion 3.1. ZnO seed layer Fig. 1 shows the surface morphology of ZnO seed layers with various precursor concentrations. The particles on the surface are dense and the surfaces are not smooth. When the ZnO seed layer at 2 mM was compared with other
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conditions, it shows smaller particles on the surface as shown in Fig. 1(a). For precursor concentrations from 10 mM to 22 mM (Fig. 1(b – d)), particles tend to be bigger on the surface. Fig. 2(a) shows that average size and size distribution of particles on the seed layer at 2 mM is lower than those of the seed layers at other concentrations. This might be the seed layer at 2 mM having small amounts of colloid particles in the solution which are not easy to aggregate and agglomerate. The % transmittance spectra of ZnO seed layers with all precursor concentrations are shown in Fig. 2(b). The ZnO seed layers show high transmittance in visible region. The spectra of seed layers are more than 80% and decreased at wavelength below 380 nm that refers to energy absorption by energy gap. The intensity of absorption indicates quantity of ZnO on the substrate. Therefore, it can confirm that the amount of ZnO on seed layer is increased when precursor concentrations are increased. The x-ray diffraction patterns of ZnO seed layers at concentrations from 10 mM to 22 mM are shown in Fig. 3. The results of all seed layers show hexagonal wurtzite structure corresponding to JCPDS number 36-1451. The seed layer at concentration of 10 mM shows high intensity at (100) plane or a-plane due to interaction between ZnO particles and glass substrate [9]. When the precursor concentration of seed layer was increased, the intensity at (100) plane decreases because particles on surface have more chance to interact together.
b
a
150 nm
c
150 nm
d
150 nm
150 nm
Fig. 1. Surface morphology of ZnO seed layer spin-coated with precursor concentrations of (a) 2 mM, (b) 10 mM, (c) 14 mM, and (d) 22 mM.
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% Transmittance
average particle size (nm)
N. Siriphongsapak et al. / Materials Today: Proceedings 4 (2017) 6146–6152
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20
80 60 40
2 mM 10 mM 14 mM 22 mM
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(b)
0
400
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500
600
700
wavelength (nm)
precursor concentrations of seed layer (mM)
Fig. 2. (a) Average particle sizes and size distributions of particles on the ZnO seed layer; (b) % transmittance of ZnO seed layer with various precursor concentrations.
seed layer 22 mM
intensity (a.u.)
seed layer 14 mM
(103)
JCPDS#36-1451
20
30
40
50
60
(200) (112) (201)
(110)
(102)
(002)
(101)
(100)
seed layer 10 mM
70
2-theta (degree)
Fig. 3. X-ray diffraction pattern of ZnO seed layer at concentrations of 10 mM, 14 mM, and 22 mM.
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a
c
b
600 nm
600 nm
600 nm
d
e
600 nm
150 nm
Fig. 4. Surface morphology of ZnO nanosheets on ZnO seed layers at concentrations of (a) 2 mM, (b) 10 mM, (c) 14 mM, (d) 22 mM, and (e) high magnification of ZnO nanosheets on ZnO seed layer at concentration of 14 mM.
3.2. ZnO nanosheets Fig. 4. shows the morphology of ZnO nanosheets on the ZnO seed layers with various precursor concentrations. The ZnO nanosheets slightly grow on seed layer at 2 mM due to small amounts of ZnO. For ZnO seed layer at higher concentrations of 10 mM and 22 mM, the ZnO nanosheets are very thin as shown in Fig. 4(b and d). Moreover, in case of 10 mM, there are big sheets of ZnO on top of nanosheets due to ZnO precipitation from the solution. Fig. 4(c and e) shows thick ZnO nanosheets on seed layer at 14 mM with the thicknesses from 10 to 25 nm and diameters from 0.2 to 0.5 μm. The x-ray diffraction patterns of ZnO nanosheets on ZnO seed layer are shown in Fig. 5. All of the XRD graphs show only one peak at (002) plane that is polar plane of hexagonal wurtzite structure [7]. The XRD peak of ZnO nanosheets on seed layer at 2 mM is much smaller than other conditions due to small amount of ZnO nanosheets as shown in Fig. 4(a). The ZnO nanosheets on seed layer at 10 mM show high intensity of XRD peak because of big sheets left on ZnO nanosheets. The % transmittance spectra of ZnO nanosheets on ZnO seed layer for all concentrations are shown in Fig. 6(a). The ZnO nanosheets on seed layers at 14 and 22 mM are more transparent than other conditions because ZnO nanosheets have higher uniformity and good crystalline quality. The optical band gap of ZnO nanosheets is studied using peak on dT/dλ (first derivative of % transmittance) graph [10] as shown in Fig. 6(b). The peaks of dT/dλ are at ~372 nm that means the optical band gap of ZnO nanosheets on seed layers are around 3.33 eV
.
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(002)
(002)
intensity (a.u.)
(002)
(002)
N. Siriphongsapak et al. / Materials Today: Proceedings 4 (2017) 6146–6152
nanostructure on seed layer 22 mM nanostructure on seed layer 14 mM nanostructure on seed layer 10 mM nanostructure on seed layer 2 mM
20 0
30 1000
40 2000
50 3000
2-theta (degree)
60 4000
70 5000
Fig. 5. X-ray diffraction pattern of ZnO nanosheets on ZnO seed layer at concentrations of 2 mM, 10 mM, 14 mM, and 22 mM.
(a)
80 60 40
2 mM 10 mM 14 mM 22 mM
20 0 400
500
600
wavelength (nm)
700
1st derivative of % T
% Transmittance
100
2.0
(b)
2 mM 10 mM 14 mM 22 mM
1.5 1.0 0.5 0.0 340
360
380
400
420
440
460
wavelength (nm)
Fig. 6. (a) % Transmittance; (b) dT/dλ (first derivative of % transmittance) of ZnO nanosheets on ZnO seed layer at concentrations of 2 mM, 10 mM, 14 mM, and 22 mM.
4. Conclusion ZnO nanosheets were successfully grown using hydrothermal method on ZnO seed layers coated by spin-coating technique. The various precursor concentrations of seed layers affected crystalline quality, particle size on seed layer and morphology of nanosheets. The concentration of seed layer at 14 mM was an optimum condition to achieve ZnO nanosheets with high density, high uniformity, good crystalline quality and high transparent.
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Acknowledgements The authors would like to thank Mrs. Sumalee Ninlapruk in Office of Atoms for Peace (OAP) to allow us for using their facilities such as UV-visible spectrophotometer. Moreover, this research was financially supported by Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi (KMUTT) and by Science Achievement Scholarship of Thailand (SAST). References [1] A. Kołodziejczak-Radzimska, T. Jesionowski, Materials 7 (2014) 2833–2881. [2] H. Hong, G. Chung, Sensor Actuat. B-Chem. 195 (2014) 446–451. [3] X. Wang, Nano Energy 1 (2012) 13–24. [4] S. Xu, Z.L. Wang, Nano Res. 4 (2011) 1013–1098. [5] K. Kim, B. Kumar, K. Lee, H. Park, J. Lee, H. Lee, H. Jun, D. Lee, S. Kim, Sci. Rep. 3 (2013) 1–6. [6] X. Li, P. Liang, L. Wang, F. Yu., Front. Optoelectron. 7 (2014) 509–512. [7] J. Lv, C. Liu, W. Gong, Z. Zi, X. Chen, K. Huang, T. Wang, G. He, X. Song, Z. Sun, Sci. Adv. Mater. 4 (2012) 757–762. [8] S. Bang, S. Lee, Y. Ko, J. Park, S. Shin, H. Seo, H. Jeon, Nanoscale Res. Lett. 7 (2012) 1–11. [9] L. Znaidi, G.J.A.A. Soler Illia, S. Benyahia, C. Sanchez, A.V. Kanaev, Thin Solid Films 428 (2003) 257–262. [10] L. Xu, G. Zheng, J. Miao, F. Xian, Appl. Surf. Sci. 258 (2012) 7760–7765.