Growth and crystallographic feature-dependent characterization of spinel zinc ferrite thin films by RF sputtering
© Liang and Hsia; licensee Springer. 2013
Received: 18 October 2013
Accepted: 9 December 2013
Published: 19 December 2013
The Erratum to this article has been published in Nanoscale Research Letters 2014 9:313
ZnFe2O4 (ZFO) thin films exhibiting varying crystallographic features ((222)-epitaxially, (400)-epitaxially, and randomly oriented films) were grown on various substrates by radio-frequency magnetron sputtering. The type of substrate used profoundly affected the surface topography of the resulting ZFO films. The surface of the ZFO (222) epilayer was dense and exhibited small rectangular surface grains; however, the ZFO (400) epilayer exhibited small grooves. The surface of the randomly oriented ZFO thin film exhibited distinct three-dimensional island-like grains that demonstrated considerable surface roughness. Magnetization-temperature curves revealed that the ZFO thin films exhibited a spin-glass transition temperature of approximately 40 K. The crystallographic orientation of the ZFO thin films strongly affected magnetic anisotropy. The ZFO (222) epitaxy exhibited the strongest magnetic anisotropy, whereas the randomly oriented ZFO thin film exhibited no clear magnetic anisotropy.
Recently, spinel-structured ferrite oxides have been intensively investigated because of their versatile physical and chemical properties as well as technological applications in magnetic sensors, biosensors, and photocatalysts [1, 2]. ZnFe2O4 (ZFO) is one of the major ferrite oxides with a spinel structure, and it has remarkable magnetic and electromagnetic properties regarding its state of chemical order and cation site occupancy in lattices . Moreover, it is also a semiconductor, processes light response, has photochemical characteristics, and can be used as a material for supercapacitors [4, 5].
ZFO in various forms, such as powders, films, and various nanostructures, prepared using different methodologies have been reported [6–8]. Many ZFO nanostructures can be used as versatile building blocks for fabricating functional nanodevices; however, integrating the reported methodologies for preparing nanostructured ZFO into Si-based semiconductor device processes remains a challenge. ZFO in thin-film form is promising and is compatible in the fabrication of devices with Si semiconductors. Yamamoto et al. prepared ZFO thin films on a single-crystal sapphire substrate by using pulsed laser deposition and examined the effect of the deposition rate on its magnetic properties . ZFO thin films with a microlevel scale were grown on glass substrates by radio-frequency (RF) sputtering at room temperature, and the magnetic properties of the films were investigated . Ogale et al. used a pulsed laser evaporation method to synthesize ZnO and Zn x Fe3−xO4 mixed-phase thin films on sapphire substrates using ZnFe2O4 pellets; however, this is not an efficient method for obtaining single-phase spinel ZFO thin films . Polycrystalline ZFO films were also prepared by spin-spray deposition; however, controlling the film thickness to be less than several hundred nanometers is challenging . Although several groups have proposed the fabrication of ZFO films using versatile methodologies, the sputtering technique is promising for preparing oxide thin films with excellent crystalline quality and controllable film thickness for device applications because it is a technique that enables large-area deposition and easy process control [13, 14]. It is well known that crystallographic features affect the properties of versatile oxide films [13, 15]. However, the crystallographic feature-dependent properties of sputtering-deposited spinel ZFO thin films are still inadequate. This might obstruct applications of such films in devices. In this study, ZFO thin films were grown on various single-crystal substrates by RF sputtering to fabricate ZFO thin films with varying crystallographic features. The correlation between the crystallographic features and the characterization of the ZFO thin films was investigated.
ZnFe2O4 (ZFO) thin films were grown on yttria-stabilized zirconia (YSZ) (111), SrTiO3 (STO) (100), and Si(100) substrates, using RF magnetron sputtering. The yttria content in YSZ substrates was 15%. The sputtering ceramic target adopted in the experiment was prepared by mixing the precursor oxide powders of ZnO and Fe2O3 to obtain a proportion of Fe/Zn = 2, pressing the powders into a pellet, and sintering the pellet at a high temperature to achieve a high density. The thickness of the ZFO thin films was fixed at approximately 125 nm, and the growth temperature was maintained at 650°C. The gas pressure of deposition was fixed at 30 mTorr, using an Ar/O2 ratio of 2:1 for the films. The atomic percentages of the as-deposited films were calculated based on the X-ray photoelectron spectroscopy (XPS) spectra of the Zn2p, Fe2p, and O1s regions. The chemical binding states of the constituent elements of the ZFO thin films were also investigated.
The crystal structures of the samples were investigated using X-ray diffraction (XRD), applying Cu Kα radiation. The surface morphology of the ZFO films was determined using scanning electron microscopy (SEM) and atomic force microscopy (AFM) at an area of 1 μm2. The detailed microstructures of the as-synthesized samples were characterized using high-resolution transmittance electron microscopy (HRTEM). The composition analysis was performed using an energy-dispersive X-ray spectrometer (EDS) attached to the TEM. Thin slices for cross-sectional TEM analysis were prepared using a dual-beam focused-ion-beam (FIB) instrument. The areas selected for cutting with an ion beam were protected by an amorphous carbon overlayer. Adjust the beam currents to mill initial trenches, thin the central membrane, and polish for electron transparency of membrane. Finally, FIB milling was used to capture a free membrane from trenches for a TEM analysis. The room temperature-dependent photoluminescence (PL) spectra were captured using the 325-nm line of a He-Cd laser. A superconducting quantum-interference device magnetometer was used to measure the magnetic properties of the samples.
Results and discussion
ZFO spinel thin films exhibiting epitaxially and randomly oriented crystallographic features were grown on various substrates by RF magnetron sputtering at 650°C. The XRD and TEM results indicated that growing the ZFO thin films on the YSZ (111) and STO (100) substrates promoted the formation of (222) and (400) epitaxial films, respectively. The film grown on the Si substrate exhibited a polycrystalline structure. The surface morphology of the ZFO thin film substantially depended on its crystallographic features. The SEM and AFM images demonstrated that the surface of the ZFO (222) epitaxial film was flat and smooth; however, the surface of the randomly oriented film was rough and exhibited 3D grains. The visible emission bands of the ZFO thin films were attributed to growth-induced oxygen vacancies. The ZFO thin films demonstrated a spin-glass transition temperature of approximately 40 K. The ZFO (222) epitaxial film exhibited the most marked magnetic anisotropy among the samples.
This work is supported by the National Science Council of Taiwan (grant no.NSC 102-2221-E-019-006-MY3) and National Taiwan Ocean University (grant no. NTOU-RD-AA-2012-104012). The authors thank assistance in SEM examination given by the sophisticated instrument user center of National Taiwan Ocean University.
- Liu GG, Zhang XZ, Xu YJ, Niu XS, Zheng LQ, Ding XJ: Effect of ZnFe2O4doping on the photocatalytic activity of TiO2. Chemosphere 2004, 55: 1287–1291. 10.1016/j.chemosphere.2004.01.035View ArticleGoogle Scholar
- Gudiksen MS, Lauhon LJ, Wang JF, Smith DC, Lieber CM: Growth of nanowire superlattice structures for nanoscale photonics and electronics. Nature 2002, 415: 617–620. 10.1038/415617aView ArticleGoogle Scholar
- Oliver SA, Hamdeh HH: Localized spin canting in partially inverted ZnFe2O4fine powders. Phys Rev B 1999, 60: 3400–3405. 10.1103/PhysRevB.60.3400View ArticleGoogle Scholar
- Sun L, Shao R, Tang L, Chen Z: Synthesis of ZnFe2O4/ZnO nanocomposites immobilized on graphene with enhanced photocatalytic activity under solar light irradiation. J Alloys Compounds 2013, 564: 55–62.View ArticleGoogle Scholar
- Liu H, Guo Y, Zhang Y, Wu F, Liu Y, Zhang D: Synthesis and properties of ZnFe2O4replica with biological hierarchical structure. Mater Sci Eng B 2013, 178: 1057–1061. 10.1016/j.mseb.2013.06.012View ArticleGoogle Scholar
- Chen CH, Liang YH, Zhang WD: ZnFe2O4/MWCNTs composite with enhanced photocatalytic activity under visible-light irradiation. J Alloys Compounds 2010, 501: 168–172. 10.1016/j.jallcom.2010.04.072View ArticleGoogle Scholar
- Chen ZP, Fang WQ, Zhang B, Yang HG: High-yield synthesis and magnetic properties of ZnFe2O4single crystal nanocubes in aqueous solution. J Alloys Compounds 2013, 550: 348–352.View ArticleGoogle Scholar
- Tanaka K, Nakashima S, Fujita K, Hirao K: High magnetization and the Faraday effect for ferrimagnetic zinc ferrite thin film. J Phys Condens Matter 2003, 15: L469-L474. 10.1088/0953-8984/15/30/101View ArticleGoogle Scholar
- Yamamoto Y, Tanaka H, Kawai T: The control of cluster-glass transition temperature in Spinel-type ZnFe2O4-δthin film. Jpn J Appl Phys 2001, 40: L545-L547. 10.1143/JJAP.40.L545View ArticleGoogle Scholar
- Nakashima S, Fujita K, Tanaka K, Hirao K: High magnetization and the high-temperature superparamagnetic transition with intercluster interaction in disordered zinc ferrite thin film. J Phys Condens Matter 2005, 17: 137. 10.1088/0953-8984/17/1/013View ArticleGoogle Scholar
- Ogale SB, Nawathey R: Deposition of zinc ferrite (ZnxFe3−xO4) films by pulsed laser evaporation process. J Appl Phys 1989, 65: 1367–1369. 10.1063/1.343008View ArticleGoogle Scholar
- Taheri M, Carpenter EE, Cestone V, Miller MM, Raphael MP, McHenry ME, Harris VG: Magnetism and structure of ZnxFe3−xO4films processed via spin-spray deposition. J Appl Phys 2002, 91: 7595–7597. 10.1063/1.1456428View ArticleGoogle Scholar
- Liang YC, Zhong H, Liao WK: Nanoscale crystal imperfection-induced characterization changes of manganite nanolayers with various crystallographic textures. Nanoscale Res Lett 2013, 8: 345–352. 10.1186/1556-276X-8-345View ArticleGoogle Scholar
- Liang YC, Deng XS: Structure dependent luminescence evolution of c-axis-oriented ZnO nanofilms embedded with silver nanoparticles and clusters prepared by sputtering. J Alloys Compounds 2013, 569: 144–149.View ArticleGoogle Scholar
- Liang YC: Surface morphology and conductivity of zirconium-doped nanostructured indium oxide films with various crystallographic features. Ceram Int 2010, 36: 1743–1747. 10.1016/j.ceramint.2010.03.004View ArticleGoogle Scholar
- Ayyappan S, Philip Raja S, Venkateswaran C, Philip J, Raj B: Room temperature ferromagnetism in vacuum annealed ZnFe2O4nanoparticles. Appl Phys Lett 2010, 96: 143106–143109. 10.1063/1.3374332View ArticleGoogle Scholar
- Liang YC, Lee HY: Growth of epitaxial zirconium-doped indium oxide (222) at low temperature by RF sputtering. CrystEngComm 2010, 12: 3172–3176. 10.1039/c004452kView ArticleGoogle Scholar
- Liang YC, Liang YC: Fabrication and electrical properties of strain-modulated epitaxial Ba0.5Sr0.5TiO3 thin-film capacitors. J Electrochemical Soc 2007, 154: G193-G197. 10.1149/1.2755636View ArticleGoogle Scholar
- Liang YC, Huang CL, Hu CY, Deng XS, Zhong H: Morphology and optical properties of ternary Zn–Sn–O semiconductor nanowires with catalyst-free growth. J Alloys Compounds 2012, 537: 111–116.View ArticleGoogle Scholar
- Graat P, Somers MAJ: Quantitative analysis of overlapping XPS peaks by spectrum reconstruction: determination of the thickness and composition of thin iron oxide films. Surf Interface Anal 1998, 26: 773–782. 10.1002/(SICI)1096-9918(199810)26:11<773::AID-SIA419>3.0.CO;2-#View ArticleGoogle Scholar
- Brundle CR, Chuang TJ, Wandelt K: Core and valence level photoemission studies of iron oxide surfaces and the oxidation of iron. Surf Sci 1977, 68: 459–468.View ArticleGoogle Scholar
- Liang YC, Deng XS, Zhong H: Structural and optoelectronic properties of transparent conductive c-axis-oriented ZnO based multilayer thin films with Ru interlayer. Ceram Int 2012, 38: 2261–2267. 10.1016/j.ceramint.2011.10.076View ArticleGoogle Scholar
- Srivastava AK, Deepa M, Bahadur N, Goyat MS: Influence of Fe doping on nanostructures and photoluminescence of sol–gel derived ZnO. Mater Chem Phys 2009, 114: 194–198. 10.1016/j.matchemphys.2008.09.005View ArticleGoogle Scholar
- Liang YC: Microstructure and optical properties of electrodeposited Al-doped ZnO nanosheets. Ceramics Inter 2012, 38: 119–124. 10.1016/j.ceramint.2011.05.154View ArticleGoogle Scholar
- Kamiyama T, Haneda K, Sato T, Ikeda S, Asano H: Cation distribution in ZnFe2O4fine particles studied by neutron powder diffraction. Solid State Commun 1992, 81: 563–566. 10.1016/0038-1098(92)90412-3View ArticleGoogle Scholar
- Liang YC, Zhong H: Materials synthesis and annealing-induced changes of microstructure and physical properties of one-dimensional perovskite–wurtzite oxide heterostructures. Appl Surf Sci 2013, 283: 490–497.View ArticleGoogle Scholar
- Marcu A, Yanagida T, Nagashima K, Tanaka H, Kawai T: Transport properties of ZnFe2O4−δthin films. J Appl Phys 2007, 102: 023713–023717. 10.1063/1.2751492View ArticleGoogle Scholar
- Nakashimaa S, Fujita K, Tanaka K, Hirao K, Yamamoto T, Tanaka I: Thermal annealing effect on magnetism and cation distribution in disordered ZnFe2O4thin films deposited on glass substrates. J Magnetism Magn Mater 2007, 310: 2543–2545. 10.1016/j.jmmm.2006.11.144View ArticleGoogle Scholar
- Gao D, Shi Z, Xu Y, Zhang J, Yang G, Zhang J, Wang X, Xue D: Synthesis, magnetic anisotropy and optical properties of preferred oriented zinc ferrite nanowire arrays. Nanoscale Res Lett 2010, 5: 1289–1294. 10.1007/s11671-010-9640-zView ArticleGoogle Scholar
- Luo CP, Liou SH, Gao L, Liu Y, Sellmyer DJ: Nanostructured FePt:B2O3thin films with perpendicular magnetic anisotropy. Appl Phys Lett 2000, 77: 2225–2227. 10.1063/1.1314289View ArticleGoogle Scholar
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