In the present study, the properties of copper oxide thin films prepared by spray pyrolysis were investigated at different substrate temperatures (573 – 723 К) and at constant spraying volume of precursor. The compositions, structural and morphological properties of the films were investigated by field emission scanning electron microscopy, atomic force microscopy and Raman spectroscopy

Cheong, H.

Diachenko, Oleksii Viktorovych

Hnatenko, Yurii Pavlovych

Nam, D.

Opanasiuk, Anatolii Serhiiovych

Salohub, A.O.

Гнатенко, Юрий Павлович

Гнатенко, Юрій Павлович

Д`яченко, Олексій Вікторович

Дьяченко, Алексей Викторович

Опанасюк, Анатолий Сергеевич

Опанасюк, Анатолій Сергійович

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 4 No 1, 01NTF15(4pp) (2015)   2304-1862/2015/4(1)01NTF15(4) 01NTF15-1  2015 Sumy State University Structural Features of Nanostructured Copper Oxide Thin Films,  Synthesized by Spray Pyrolysis Technique  O.V. Diachenko1,*, A.S. Opanasuyk1, A.O. Salohub1, D. Nam2, H. Cheong2, Yu.P. Gnatenko3  1 Sumy State University, 2, Rymsky Korsakov Str., 40007 Sumy, Ukraine 2 Department of Physics, Sogang University, Seoul 121-742, South Korea 3 Institute of Physics of National Academy of Sciences of Ukraine, Nauky Ave. 46, UA-03028 Kyiv, Ukraine  (Received 01 August 2015; published online 22 August 2015)  In the present study, the properties of copper oxide thin films prepared by spray pyrolysis were investigated at different substrate temperatures (573 – 723 К) and at constant spraying volume of precursor. The compositions, structural and morphological properties of the films were investigated by field emission scanning electron microscopy, atomic force microscopy and Raman spectroscopy.   Keywords: Copper oxide, Raman, atomic force microscope, Thin films, Structure, Spray pyrolysis,  Optoelectronic devices, Solar cells.   PACS numbers: 81.05.Dz, 81.15.Rs                                                             * alexey.dyachenko@ukr.net 1. INTRODUCTION  The rapid development of semiconductor technolo-gies require application an ever various materials with different physical, electrical and optical properties. Therefore, increasing attention is being paid to studies on less known chemical compounds able to act as semi-conductors. Among them, compounds of metals with oxygen may be considered as most promising [1].  There are many technics have been used to grown oxide thin films molecular beam epitaxy [2], vapor phase epitaxy [3] electrochemically deposition [4], plasma evaporation method [5], sol–gel synthesis [6], reactive sputtering [7], pulsed laser deposition[8], chemical vapor deposition [9], metal – organic chemical vapor deposition [10], spray pyrolysis [11], etc. Spray pyrolysis has been shown as effective method for ob-taining high quality thin films of oxides. This is a very simple and relatively cost-effective processing method (especially with regard to equipment costs) in compari-sons to many other film deposited technique which allows to prepare both thin and thick films. It offers an extremely easy technique for preparing films of any composition.  Copper oxide is one of the most promising oxide ma-terials because of its favorable properties in wide range of applications. This compound can be used in diodes [12], field emitters, gas sensors [13], optical switches, magneto resistance materials, catalysts, high tempera-ture superconductors [14] and soil lignin study [15]. The narrow band gap of this material (1.2 eV) favors its use in photoconductive and photothermal applications, optoelectronic devices and solar cells [16-19]. Moreover, this oxide also is an important material for the fabrica-tion of lithium ion battery [20]. For these applications CuO are technologically interesting due to the chemical and physical properties of this material depend on its composition, structure, phase, shape, size, and size distribution [21]. A low production cost and excellent stability at room temperature, non-toxic nature of the copper oxide material makes it an attractive option for these appli-cations, good hole mobility, large minority carrier diffu-sion length, and a direct energy gap ideal for efficient absorption.  Synthesizing copper oxides of preferred phase still poses a challenge. The two possible phases of this oxide are copper oxide (CuO) and cuprous oxide (Cu2O) of monoclinic and cubic structures with band gap values of 1.3 – 2.1 eV and 2.0 – 2.6 eV respectively [22].  2. EXPERIMENTAL DETAILS  Copper oxide thin films were obtained by spray py-rolysis method used laboratory system described in details in [11]. For sample preparation, the 1x1 cm2 glass substrates of thickness 1 mm were ultrasonically cleaned with pure water and ethanol for 6 minutes. 0.05 molar of copper chloride (CuCl22H2O) were dis-solved in 100 mL of deionized water under constant stirring. Note, that most authors of previous works have studied copper oxide thin films obtained from solution based on copper acetate [14, 23-27] or copper nitrate [28, 29]. The precursor solution was sprayed using a jet nozzle using air as the carrier gas on to heated substrate. The diameter of the nozzle is 0.2 mm. The distance between the nozzle and the heated sub-strate surface was equal to 15 cm. Spraying rate was 2 ml/min and the volume of sprayed solution of 3 ml per sample. The substrate temperature range for synthesis of the films was changed from Ts = 573 K to 723 K with step 50 K. The substrates temperature during the obtaining of films was measured using а chromel-alumel thermocouple. Field emission scanning electron microscope JEOL JSM-7600F was used to investigate morphological properties of the obtained layers. The thickness of the samples was determined using by a probe Profilers Dektak XT. Measurements were carried out relative to the area of the substrate without a copper oxide layer. During the measurements were used next experimental conditions: scan length – 2000  O.V. DIACHENKO, A.S. OPANASUYK ET.AL. PROC. NAP 4, 01NTF15 (2015)   01NTF15-2 µm, resolution – 0.666 µm, stylus force – 3 mg, stylus scan range – 65.5 µm The surface morphology was probed using atomic force microscopy (AFM). The scanning area was 50  50 μm. Non-contact mode was used during the measure-ments. RMS were calculated using AFM data analysis software. Macro-Raman spectroscopy enables fast, large area Raman mapping needed for statistical studies of mate-rials properties. Raman spectroscopy measurements were carried out in ambient conditions with the 441.6 nm-line of a He-Cd laser as excitation source. A laser beam with a power of ~20 mW was focused to a line of ~5 mm × 50 μm in a quasi-backscattering configura-tion. Jobin-Yvon TRIAX 550 spectrometer (2400 grooves/mm) was used to disperse the signals. The measurement range was up to 700 cm-1. The slit width was fixed at 0.1 mm. An long-wave-pass (LWP) edge filter lens was used to eliminate the laser signals. A spike lens was also used. The signals were detected with a liquid-nitrogen-cooled back-illuminated charge-coupled-device detector array. 3. RESULT AND DISCUSSION   Micrographs of obtained thin films are shown on fig-ure 1. As see from the figure the films have polycrystal-line structure. With increasing substrate temperature crystal size are generally decreasing from 1 µm (Ts = 573 К) to 20 nm (Ts = 673 К). However, at higher synthesis temperatures  grain size films grew reaching 1.5-2.0 µm n the layers obtained at Ts = 723 К. The crystallites of the samples synthesized at low temperatures had cubic shape. The surface profiles were investigated using by a probe Profilers Dektak XT. There are three measure-ments of each sample were held. Initially, the average profile graph was found by using OriginPro software packet followed by a shift of the graphs with respect to minimum point to zero in y-axis direction. Minimum point is a glass substrate without film layer. Thus it is possible to measure the thickness of the sample. Estab-lished that the average thickness of the samples ranged from 0.8 μm at Ts = 723 K to 2.2 μm at Ts =573 K.     Fig. 1 – FESEM images of samples obtained at Ts = 573 K (a), 623 K (b), 673 K (c), 723 K (d).  AFM images of copper oxide thin films are shown in Fig. 2. Obtained films show uniform surface with closely packed microstructure all over the substrate. The simi-lar surface texture has been observed by Yasui et al.  [22].  Copper Oxide (CuO) is a compound which crystallizes in a monoclinic crystal structure where Cu2+ ions are fourfold coordinated by oxygen and described by the space group C2h (C 2/c) [30-31]. There are four molecular units in the crystallographic unit cell and only two in the primitive cell. Since two molecular units in the primitive cell there are 12 vibrational modes at the zone center. The two Cu atoms in the primitive cell are on sites with symmetry described by C1(2) and the oxygen atoms on C2 (2) [30].  There are 12 zone-center optical-phonon modes ГRA = 4Au + 5Bu + Ag + 2Bg, where Г is the degree of vibration-al freedom, Au and Bu represent Infrared modes; Ag and Bg represents Raman modes. There are six infrared active modes (3Au + 3Bu), three acoustic modes (Au +  NANOSTRUCTURED COPPER OXIDE THIN FILMS … PROC. NAP 4, 01NTF15 (2015)   01NTF15-3 2Bu), and three Raman active modes (Ag + 2Bg) [32-34]. Figure 3 shows the Raman spectra of copper oxide films. In comparison with the vibrational spectra of CuO powder [35], single crystals [36], nanoparticles [33, 37] and nanostructures [32, 34] we can assign the peak at 274 cm−1 to the Ag mode and the peak at 327 cm-1 to the Bg modes. The peak at 616 cm−1 that correspond to the B2g mode didn’t detect since it has weak natural. Also the peak at 486 cm-1 assigned to the 2Eu mode of Cu2O. These wavenumbers are close to those reported in the literature [32-38]. They reported that the intensity is related to the grain size. Stronger and sharper Raman peaks are observed which also shift to longer wave-numbers with increasing or decreasing grain size. Our results are in agreement with the previously reported data. There are several peaks at wavenumbers range from 100 cm-1 to 250 cm-1 can be assigned to the bending vibrations of CuO2 and CuO4 clusters [37].      a) b)  Fig. 2 – AFM images of copper oxide thin films obtained at Ts = 643 K (a), 653 K (b)     Fig. 3 – Raman spectra of copper oxide thin films obtained at Ts = 573 K (1), 623 K (2), 723 K (3), 673 K (4).  4. CONCLUSIONS  Homogeneous and single phase nanostructured MgO films have been obtained by a simple and cost effective spray pyrolysis method. Copper chloride (CuCl22H2O) used as a precursor. Optical and morpho-logical properties of MgO thin films have been investi-gated by field emission scanning electron microscopy, atomic force microscopy and Raman spectroscopy.  It found that the copper oxide thin films have uni-form surface with closely packed microstructure with a grain size of 20 nm - 2 μm and have low rough-ness.  The surface roughness was also calculated. It was established that the average thickness of the sam-ples ranged from 0.8 μm at Ts = 723 K to 2.2 μm at Ts =573 K. According to Raman spectroscopy the samples have CuO phase with impurities of Cu2O phase. Thus, the layers of copper oxide can be used in op-toelectronic devices and solar cell as optical window material with p-type conductivity.  AKNOWLEDGEMENTS  This research was supported by the Ministry of Ed-ucation and Science of Ukraine (Grant No. 0113U000131 and 0112U000772) and the International Research & Development Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) of Korea.   REFERENCES  1. Z.M. Jarzebski, Oxide Semiconductors (Pergamon Press: Oxford: 1973). 2. M.S. Kim, et al., J. Korean Phys. Soc. 59, 2354 (2011). 3. S.S. Lee, et al., Proc. of the Fifteenth International Sympo-sium on Chemical Vapor Deposition 200, 277 (2000). 4. A. Kathalingam, et al., J. Korean Phys. Soc. 55, 2476 (2009). 5. K. Santra, et al., Thin Solid Films 213, 226 (1992). 6. J.G. Yoon, H.K. Kim., J. Korean Phys. Soc. 31, 613 (1997). 7. Y.S. Yoon, J.S. Kim, S.H. Choi, Thin Solid Films 460, 41 (2004). 8. I. Bouessay, A. Rougier, J.M. Tarascon, Electrochrom. Mater. Appl.: Proc. Int. Symp, 91 (2003). 9. T. Maruyama, S. Arai, J. Electrochem. Soc. 143, 1383 (1996). 10. J.H. Boo, et al., Thin Solid Films 341, 63 (1999). 11. A.V. Dyachenko, et al., NAP Proc. 3, 01PCSI05 (2014).  O.V. DIACHENKO, A.S. OPANASUYK ET.AL. PROC. NAP 4, 01NTF15 (2015)   01NTF15-4 12. İ.Y. Erdoğan, Ö. Güllü, J. Alloys Compnds 492, 378 (2010). 13. A. Chowdhuri et al., Appl. Phys. Lett. 84, 1180 (2004). 14. V. Saravanan, et al., J. Anal. Appl. Pyrolysis 62, 327 (2014). 15. M.F. Dignac et al., J. Anal. Appl. Pyrolysis 85, 426 (2009). 16. H. Kidowaki, et al., J. Mater. Sci. Res. 1, 138 (2012). 17. V. Kumar, et al., Nanoelectronics Conference (INEC), 2013 IEEE 5th International, 443 (2013). 18. S. Gubbala, J. Thangala, M.K. Sunkara, Sol. Energ. Mat. Sol. Cells 9, 813 (2007). 19. H.D. Banerjee, et al., Opt. Eng. 27, 271133 (1988). 20. P. Poizot, et al., Nature 407, 496 (2000). 21. A.P. Moura, et al., Adv. Powder Tech. 21, 197 (2010). 22. T. Maruyama, Sol. Energ. Mat. Sol. Cells 56, 85 (1998). 23. W. DeSisto, et al., Mater. Res. Bull. 6, 753 (1989). 24. J. Morales, et al., Electrochim, Acta 29, 4589 (2004). 25. T. Kosugi, S. Kaneko, J. Am. Ceram. Soc. 12, 3117 (1998). 26. K. Rajaram, E. Savarimuthu, S. Arumugam, Res. J. Ma-ter. Sci. 2320, 6055 (2013). 27. J. Morales, et al., Thin Solid Films 474, 133 (2005). 28. D. Majumdar, et al., J. Mater. Res. 11, 2861 (1996). 29. C.Y. Chiang, et al., Int. J. Hydr. Energ. 24, 15519 (2011). 30. S. Asbrink., L.J. Norrby, Acta Cryst. B 26, 8 (1970). 31. M. Heinemann, B. Eifert, C. Heiliger, Phys. Rev. B 11, 115111 (2013). 32. K. Mageshwari, R. Sathyamoorthy, J. Mater Sci. Tech. 29, 909 (2013). 33. S.K. Maji, et al., J. Solid State Chem. 8, 1900 (2010). 34. X. Wang, et al., Crystal Growth 5, 930 (2007). 35. W. Reichardt, et al., Zeit. Phys. B 81, 19 (1990). 36. J. Chrzanowski, J.C. Irwin, Solid State Comm. 70, 11 (1989). 37. T. Baruah, R.R. Zope, M.R. Pederson, Phys. Rev. A 69, 023201 (2004). 38. M. Rashad, et al., J. Nanomater. 13, 82 (2013).  

Structural Features of Nanostructured Copper Oxide Thin Films, Synthesized by Spray Pyrolysis Technique

Structural Features of Nanostructured Copper Oxide Thin Films, Synthesized by Spray Pyrolysis Technique

Abstract

Similar works

Full text

Available Versions

Electronic Sumy State University Institutional Repository