Investigation of the properties of nanostructured Li-doped NiO films using the modified spray pyrolysis method
© Chia-Ching and Cheng-Fu; licensee Springer. 2013
Received: 14 November 2012
Accepted: 22 December 2012
Published: 18 January 2013
The lithium-doped nickel oxide (L-NiO) films were synthetized using the modified spray pyrolysis method with a two-step grown process. By observing the spectra of X-ray photoemission spectroscopy of L-NiO films, the intensity of Ni 2p3/2 peak of Ni3+ bonding state increases with increasing Li concentration that causes the decrease of transparency and resistivity. The L-NiO films with optimum characteristics were obtained at Li = 8 at%, where a p-type resistivity of 4.1 × 10−1 Ω cm and optical transparency above 76% in the visible region are achieved.
KeywordsModified spray pyrolysis method Nickel oxide Lithium Conductivity Transparency
N-type transparent conductive oxide (TCO) films, such as indium tin oxide, aluminum zinc oxide, indium gallium zinc oxide, etc., are widely used as transparent electrodes, solar cells, and touch panels. However, not many TCO films have the p-type properties, and they are also required in other applications. Nickel oxide (NiO) films are a promising candidate for p-type semi-TCO in the visible light with the band gap (Eg) values from 3.6 to 4.0 eV. NiO films have a wide range of applications, such as (1) transparent conductive films , (2) electrochromic display devices , (3) anode material in organic light emitting diodes , and (4) functional layer material for chemical sensors .
In the past, NiO films were prepared by various methods, including electron beam evaporation, chemical deposition, atomic layer deposition, sol–gel, and spray pyrolysis method (SPM) . Sputtering is one of the most popular methods to deposit NiO films with low resistivity of 1.4 × 10−1 Ω cm . The SPM is a very important non-vacuum deposition method to fabricate TCO films because it is a relatively simple and inexpensive non-vacuum deposition method for large-area coating. However, the resistivity of SPM deposited doped NiO films is about 1 Ω cm , which is almost 1 order of magnitude higher than that of sputter-deposited NiO thin films.
Undoped NiO has a wide Eg value and exhibits low p-type conductivity. The conduction mechanism of NiO films is primarily determined by holes generated from nickel vacancies, oxygen interstitial atoms, and used dopant. The resistivity of NiO-based films can be decreased by doping with lithium (Li) . In 2003, Ohta et al. fabricated an ultraviolet detector based on lithium-doped NiO (L-NiO) and ZnO films . However, only few efforts have been made to systematically investigate the effects of deposition parameters and Li concentration on the electrical and physical properties of SPM deposited NiO films. In this research, a modified SPM method was used to develop the L-NiO films with higher electrical conductivity. We would investigate the effects of Li concentration on the physical, optical, and electrical properties of NiO thin films.
where α is the absorption coefficient, hv is the photon energy, A is a constant, Eg is the energy band gap (eV), and n is the type of energy band gap. The NiO films are an indirect transition material, and n is set to 2 .
Results and discussion
Non-vacuum SPM method was used to deposit high quality p-type L-NiO films. The (200) preferred orientation of L-NiO films increases over (111) as the Li concentration increases, which would cause the better conductive properties and resist electrical aging in the L-NiO films. In this study, the characteristics of modified SPM deposited L-NiO films were comparable to the sputter-deposited ones, and the optimum Li doping amount is set at 8 at %.
C-CW was born in Taiwan, in 1979. He received the Ph.D. degree in electrical engineering from the National Sun Yat-sen University, Kaohsiung, Taiwan, in 2009. In 2009, he joined department of electronic engineering, Kao Yuan University, where he investigated on organic/inorganic nanocomposites materials, integrated passive devices (IPDs), transparent conductive oxide (TCO) films, electron ceramics and carbon nanotubes and graphene.
C-FY was born in Taiwan, in 1964. He received the BS, MS, and Ph.D degree in electrical engineering from the National Cheng Kung University, Tainan, Taiwan, in 1986, 1988, and 1993. In 2014, he joined department of Chemical and Materials Engineering, National University of Kaohsiung, where he investigated on ferroelectric ceramics and thin films, application ferroelectric materials in memory devices, organic/nanotubes nanocomposites, organic/inorganic nanocomposites, YZO thin films, transparent conduction oxide thin films and their applications in solar cells, microwave antennas, and microwave filters.
The authors acknowledge the financial support of the National Science Council of the Republic of China (NSC 101-2221-E-244-006 and 101-3113-S-244-001).
- Chen SC, Kuo TY, Lin YC, Chang CL: Preparation and properties of p-type transparent conductive NiO films. Adv Mater Res 2010, 123: 181–184.
- Korosec RC, Bukovec P: Sol–gel prepared NiO thin films for electrochromic applications. Acta Chim Slov 2006, 53: 136–147.
- Chan IM, Hong FC: Improved performance of the single-layer and double-layer organic light emitting diodes by nickel oxide coated indium tin oxide anode. Thin Solid Films 2004, 450: 304–311. 10.1016/j.tsf.2003.10.022View Article
- Hotovy I, Huran J, Siciliano P, Capone S, Spiess L, Rehacek V: Enhancement of H2 sensing properties of NiO-based thin films with a Pt surface modification. Sens Actuator B-Chem 2004, 103: 300–311. 10.1016/j.snb.2004.04.109View Article
- Reguig BA, Khelil A, Cattin L, Morsli M, Bernède JC: Properties of NiO thin films deposited by intermittent spray pyrolysis process. Appl Surf Sci 2007, 253: 4330–4334. 10.1016/j.apsusc.2006.09.046View Article
- Sato H, Minami T, Takata S, Yamada T: Transparent conducting p-type NiO thin films prepared by magnetron sputtering. Thin Solid Films 1993, 236: 27–31. 10.1016/0040-6090(93)90636-4View Article
- Hasan AJ, Mohammad-Mehdi BM, Mehrdad SS: Nickel–lithium oxide alloy transparent conducting films deposited by spray pyrolysis technique. J Alloy Comp 2011, 509: 2770–2773. 10.1016/j.jallcom.2010.11.075View Article
- Joseph DP, Saravanan M, Muthuraaman B, Renugambal P, Sambasivam S, Raja SP, Maruthamuthu P, Venkateswaran C: Spray deposition and characterization of nanostructured Li doped NiO thin films for application in dye-sensitized solar cells. Nanotechnology 2008, 19: 485707. 10.1088/0957-4484/19/48/485707View Article
- Ohta H, Kamiya M, Kamiya T, Hirano M, Hosono H: UV-detector based on pn-heterojunction diode composed of transparent oxide semiconductors, p-NiO/n-ZnO. Thin Solid Films 2003, 445: 317–321. 10.1016/S0040-6090(03)01178-7View Article
- Mattheiss LF: Electronic structure of the 3D transition-metal monoxides. I. Energy-band results. Phys Rev 1972, B5: 209.
- Chen X, Zhao L, Niu Q: Electrical and optical properties of p-type Li, Cu-codoped NiO thin films. J Electro Mater 2012, 41: 3382–3386. 10.1007/s11664-012-2213-4View Article
- Jang WL, Lu YM, Hwang WS, Chen WC: Electrical properties of Li-doped NiO films. J Eur Ceram Soc 2010, 30: 503–508. 10.1016/j.jeurceramsoc.2009.05.041View Article
- Yu GH, Zhu FW, Chai CL: X-ray photoelectron spectroscopy study of magnetic films. Appl Phys A 2003, 76: 45–47. 10.1007/s003390201292View Article
- Oswald S, Bruckner W: XPS depth profile analysis of non-stoichiometric NiO films. Surf Interface Anal 2004, 36: 17–22. 10.1002/sia.1640View Article
- Tanaka S, Taniguchi M, Tanigawa H: XPS and UPS studies on electronic structure of Li2O. Nucl J Mater 2000, 283–287: 1405–1408.View Article
- Dedryvère R, Laruelle S, Grugeon S, Poizot P, Gonbeau D, Tarascon JM: Contribution of X-ray photoelectron spectroscopy to the study of the electrochemical reactivity of CoO toward lithium. Chem Mater 2004, 16: 1056–1061. 10.1021/cm0311269View Article
- Wu QH, Thissen A, Jaegermann W: Photoelectron spectroscopic study of Li oxides on Li over-deposited V2O5 thin film surfaces. Appl Surf Sci 2005, 250: 57–62. 10.1016/j.apsusc.2004.12.023View Article
- Lu YM, Hwang WS, Yang JS: Effect of substrate temperature on the resistivity of non-stoichiometric sputtered NiO x films. Surf Coat Technol 2002, 155: 231–235. 10.1016/S0257-8972(02)00037-3View Article
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