INAE Lett DOI 10.1007/s41403-017-0019-7
ORIGINAL ARTICLE
Optical and Structural Characteristics of NiO Thin Films Doped with AgNPs by Sputtering Method Mustafa Mohammed Ali Hussein1
Received: 28 December 2016 / Accepted: 20 March 2017 Ó Indian National Academy of Engineering 2017
Abstract NiO thin films doped with three different concentrations of Ag nanoparticles (AgNPs) are deposited on glass slide substrates at 450 °C by sputtering method. The effect of AgNPs on the optical and structural characteristics of NiO thin film is studied by X-ray diffraction, scanning electron microscopy and ultraviolet–visible spectra. It is found that all the samples have a cubic structure. When Ag doping is made, the intensity of the diffraction peaks and the transmittance are decreased. On the other hand, the optical band gaps of NiO films doped with AgNPs are increased. Keywords NiO thin film Ag nanoparticles X-ray diffraction Scanning electron microscopy Ultraviolet– visible spectra
Introduction Nickel oxide is a straightforward conductive oxide and p-sort semiconducting material (Ai et al. 2008) and it has a wide bandgap more noteworthy than 3 eV (Patil and Kadam 2002). Since numerous utilizations of NiO, for example, concoction sensors (Stamataki et al. 2008), impetuses (Bakar et al. 2009), hostile to ferromagnetic material (Mallick and Mishra 2012), dye sensitized solar cells (DSSCs) (Bandara and Weerasinghe 2005), electrochromic gadgets (Kamal et al. 2005), it draws in the specialists consideration towards it. A few strategies to get & Mustafa Mohammed Ali Hussein
[email protected] 1
Department of Physics, College of Science, University of Baghdad, Baghdad, Iraq
ready NiO thin films relied on upon the applications, synthetic and physical, for example, chemical bath deposition (Vidales-Hurtado and Mendoza-Galva´n 2008), sol–gel (Zayim et al. 2008), sputtering (Mendoza-Galva´n et al. 2009) and beat laser testimony (Valyukh et al. 2010). This paper reports the impact of AgNPs as a vital parameter on the arrangement of NiO thin films by sputtering procedure. The significant enthusiasm for sputtering is because of its ease, while it is progressively being utilized for some business procedures, for example, the testimony of a straightforward layer on glass (Major et al. 1983).
The Experimental Part The NiO thin films were prepared using sputtering method. The NiO (1:1) powder from Sigma Aldrich Company is used to deposit 100 nm thin film on the glass substrates at 450 °C. On the other hand Silver powder (nanopowder, \150 nm particle size, 99% trace metals basis Aldrich) was mixed with NiO powder to make different doping concentrations (2, 4, 6%), and then the result powders were deposited on glass substrates at 450 °C by the same procedure. The strongest peak of thin films was used to determine the average grain size using Scherrer’s equation (Arai et al. 1996): s¼
0:9k b cos h
where s is the mean size of the ordered (crystalline) domains, which may be smaller or equal to the grain size ˚ ), b is the full(nm), k is the X-ray wavelength (1.5408 A width at half-maximum (FWHM) intensity (in radians), and (h) is the half of the diffraction peak angle.
123
INAE Lett
Fig. 1 XRD patterns of pure NiO and NiO doped with AgNPs films with different Ag concentrations. a Pure NiO, b NiO:Ag 2%, c NiO:Ag 4%, d NiO:Ag 6%
Table 1 The structure and optical information of NiO films doped with AgNPs Ag concentration
2h (°)
(hkl)
Intensity
Energy gap (eV)
Grain size (nm) by Scherrer’s equation
Grain size (nm) by AFM
Roughness (nm)
Pure NiO
37.35
(111)
1285
3.419
103
90
0.91
0%
43.38
(200)
176
62.98
(220)
104
79.6
(222)
110
NiO:Ag
37.29
(111)
1276
3.435
79
82
1.09
2%
40.37
(101)
231
43.24 62.88
(200) (220)
246 142 3.467
68
71
1.11
3.543
63
54
2.24
79.6
(222)
112
NiO:Ag
37.27
(111)
1255
4%
43.31
(200)
223
45.74
(103)
157
53.69
(102)
110
62.81
(220)
145
74.47
(311)
46
79.54
(222)
122
NiO:Ag
37.26
(111)
1196
6%
43.26
(200)
221
44.73
(200)
144
52.84
(102)
105
79.49
(222)
90
123
INAE Lett Fig. 2 SEM images of pure NiO and NiO doped with AgNPs films with different Ag concentrations. a pure NiO, b NiO:Ag 2%, c NiO:Ag 4%, d NiO:Ag 6%
Results and Discussion A. Structure Different coatings were prepared by changing the ratio of AgNPs in NiO thin films. Figure 1 shows the XRD patterns for the examples arranged under the test conditions. For pure NiO Fig. 1a the peaks at scattering angles (2h) of 37.35°, 43.37°, 62.08° and 79.6° comparing with the reflection from (111), (200), (220) and (222) crystal planes, separately. The peaks appointed to diffractions from different planes compared to octahedral structure of NiO. At the point when Ag doped NiO with concentration of 2, 4 and 6% by weight as appeared in Fig. 1b–d, one peak (101) of Ag development in structure at (2h = 40.1°) when the concentration 2% and there are two peaks for (103) and (102) at angles (45.7°) and (53.6°) respectively when concentration shifted from 2 to 4%. Other peaks of Ag grown (200) and (102) at angles (44.7°) and (52.8°) separately in concentration 6%, which could be credited to metallic Ag fcc phase, and demonstrate the arrangement of Ag as the second phase clusters. By increasing Ag
concentration, peak position is moved toward lower values, as appeared in Table 1. This move recommends the incomplete substitution of Ag? particles at the ZnO lattice. The X-ray of NiO diminishes with increasing nano Ag concentration. It might be expected the expanding volume of unit cell and also diminishing sub-atomic weight of the specimens. To start with approach to figure the normal grain estimate by Scherrer’s condition, it discovered decrease from 103 to 63 nm as the concentration of Ag increases from 0–6%. It might be because of the little grain development of nano Ag doped NiO as compared with pure NiO. The grain size and shape can be gotten by SEM investigation. Surface morphology of the pure NiO and AgNPs doped NiO is appeared in Fig. 2. The molecule sizes were obviously of the request of nanometers and state of particles was quasi-spherical. The normal grain size in scope of 54–90 nm is appeared in Table 1. Using silver doping, the grain size diminish with expanding concentration and the roughness of surface of thin films increase as concentration increases because of the increase of the concentrations of nucleation on the surface.
123
INAE Lett Fig. 3 Transmittance as a function of wavelength for pure NiO and NiO:Ag films with different Ag concentrations. a Pure NiO, b NiO:Ag 2%, c NiO:Ag 4%, d NiO:Ag 6%
concentrations is shown in Fig. 4. The energy gap, Eg, is evaluated by extrapolating the linear part of curve (ahm)2 as a function of intercept energy. It is found that the Eg value shifts from 3.41 to 3.54 eV with expanding nano Ag doping concentrations. Diminishing grain size prompts to expanding grain boundaries and expanding the barrier height between the grains and finally the energy gap will be increased.
Conclusions Fig. 4 (aht)2 versus energy curves of pure NiO and NiO:Ag films with different Ag concentrations. a Pure NiO, b NiO:Ag 2%, c NiO:Ag 4%, d NiO:Ag 6%
B. Optical Properties Figure 3 demonstrates the transmittance spectra of NiO thin films doped with various AgNPs. The transmittance decreases with expanding doping concentration. This continuous decrease in transmittance is because of lattice defects. The nano Ag? may involve interstitial site on the NiO lattice and decrease transmittance of light, so, the absorbance will increase. The energy gap (Eg) can be evaluated by expecting an immediate move between the valence band and conduction band utilizing the relation (Katayama-Yoshida and Sato 2003): 1=2 ahm ¼ A hm Eg where a is the absorption coefficient, hm is photon energy and A is the absorbance. The reliance of (ahm)2 versus photon energy (hm) for NiO films with various dopant
123
The expansion of AgNPs concentration on NiO thin film prompted to expanding volume of unit cell and in addition diminishing atomic weight of the thin film. It might be because of the little grain development of AgNPs doped NiO as compared with pure NiO, this is clear from SEM test. The grain size diminish with expanding the concentration of AgNPs and the roughness of surface of thin films increase as expanding the concentration because of the increase of the concentrations of nucleation on the surface. The transmittance diminishes with expanding doping concentrations. This continuous decrease in transmittance is because of lattice defects. It is found that the energy gap value, Eg, changes from 3.41 to 3.54 eV with expanding AgNPs doping concentrations. Diminishing grain size prompts to expanding grain boundaries and expanding the barrier height between the grains and finally energy gap expanded.
References Ai L, Fang G, Yuan L, Liu N, Wang M, Li C, Zhang Q, Li J, Zhao X (2008) Influence of substrate temperature on electrical and
INAE Lett optical properties of p-type semitransparent conductive nickel oxide thin films deposited by radio frequency sputtering. Appl Surf Sci 254(8):2401–2405 Arai Y, Akers RJ, Treasure CRG (1996) Chemistry of powder production, 1st edn. Chapman & Hall, London, p 281 Bakar WAWA, Othman MY, Ali R, Yong CK, Toemen S (2009) The investigation of active sites on nickel oxide based catalysts towards the insitu reactions of methanation and desulfurization. Modern Appl Sci 3(2):35–43 Bandara J, Weerasinghe H (2005) Solid-state dye-sensitized solar cell with p-type NiO as a hole collector. Sol Energy Mater Sol Cell 85(3):385–390 Kamal H, Elmaghraby EK, Ali SA, Abdel-Hady K (2005) The electrochromic behavior of nickel oxide films sprayed at different preparative conditions. Thin Solid Films 483:330–339 Katayama-Yoshida H, Sato K (2003) Materials design for semiconductor spintronics by ab initio electronic-structure calculation. Phys B 327(2):337–343 Major S, Banerjee A, Chopra KL (1983) Highly transparent and conducting indium-doped zinc oxide films by spray pyrolysis. Thin Solid Films 108(3):333–340 Mallick P, Mishra NC (2012) Evolution of structure, microstructure, electrical and magnetic properties of nickel oxide (NiO) with transition metal ion doping. Am J Mater Sci 2(3):66–71
Mendoza-Galva´n A, Vidales-Hurtado MA, Lo´pez-Beltra´n AM (2009) Comparison of the optical and structural properties of nickel oxide-based thin films obtained by chemical bath and sputtering. Thin Solid Films 517(10):3115–3120 Patil PS, Kadam LD (2002) Preparation and characterization of spray pyrolyzed nickel oxide (NiO) thin films. Appl Surf Sci 199:211–221 Stamataki M, Tsamakis D, Brilis N, Fasaki I, Giannoudakos A, Kompitsas M (2008) Hydrogen gas sensors based on PLD grown NiO thin film structures. Phys Stat Sol (A) 205(8):2064–2068 Valyukh I, Green S, Arwin H, Niklasson GA, Wa¨ckelga˚rd E, Granqvist CG (2010) Spectroscopic ellipsometry characterization of electrochromic tungsten oxide and nickel oxide thin films made by sputter deposition. Sol Energy Mater Sol Cells 94:724–733 Vidales-Hurtado MA, Mendoza-Galva´n A (2008) Optical and structural characterization of nickel oxide-based thin films obtained by chemical bath deposition. Mater Chem Phys 107(1):33–38 Zayim EO, Turhan I, Tepehan FZ, Ozer N (2008) Sol–gel deposited nickel oxide films for electrochromic applications. Sol Energy Mater Sol Cells 92:164–196
123
