Nanoscale crystal imperfection-induced characterization changes of manganite nanolayers with various crystallographic textures
© Liang et al.; licensee Springer. 2013
Received: 9 May 2013
Accepted: 6 July 2013
Published: 6 August 2013
(La,Sr)MnO3 (LSMO) nanolayers with various crystallographic textures were grown on the sapphire substrate with and without In2O3 epitaxial buffering. The LSMO nanolayer with In2O3 epitaxial buffering has a (110) preferred orientation. However, the nanolayer without buffering shows a highly (100)-oriented texture. Detailed microstructure analyses show that the LSMO nanolayer with In2O3 epitaxial buffering has a high degree of nanoscale disordered regions (such as subgrain boundaries and incoherent heterointerfaces) in the film. These structural inhomogeneities caused a low degree of ferromagnetic ordering in LSMO with In2O3 epitaxial buffering, which leads to a lower saturation magnetization value and Curie temperature, and higher coercivity and resistivity.
Because of their versatile physical properties, various transition metal oxides, specifically perovskite-based manganites, have attracted considerable scientific and technological attention [1–3]. There is potential for the application of La1 - xSr x MnO3 (LSMO) in the magnetic storage device and spin-sensitive device field, or it can be used as an important hole-doping material to construct microelectronic devices [2, 4, 5]. To realize nanodevice applications with high efficiency, it is imperative that LSMO thin films be fabricated on a nanometric scale.
High-quality epitaxial manganite films with specific orientations are essential for the next-generation of microelectronic and magnetic devices. However, single-crystalline perovskite oxide substrates are expensive, and a large diameter substrate is currently technologically unavailable. These factors hinder the practical application of epitaxial LSMO films in the electronic industry [4, 6]. Two factors might cause lattice stress in nanoscale manganite thin films. An ultra-thin LSMO epilayer grown on the lattice-mismatched perovskite oxide substrate usually induces built-in stresses in the film, which greatly affect its physical properties [4, 7–9]. Moreover, a large thermal expansion coefficient (TEC) difference between the film and substrate also significantly affects the lattice stress in nanoscale manganite thin films. In comparison to randomly oriented thin films, the highly crystallographic textured film usually exhibits superior crystal quality. If the TEC value of a substrate and film is similar, then highly textured ultra-thin polycrystalline LSMO films would not suffer from the lattice distortion that was caused by a lattice mismatch on the single crystalline substrates. This might be promising for practical applications in devices. The sapphire substrate and LSMO have similar TEC sizes . Sapphire substrates can be fabricated with a large diameter and relatively low cost in comparison to perovskite oxide substrates. Such fabrication could attain the practical mass production of a device. Moreover, to form functional heterostructure microelectronic devices, sapphire substrates can be used to integrate LSMO nanofilms with other high-quality optoelectronic thin films [11, 12]. During this project, two different crystallographic textured LSMO thin films with a nanoscale thickness were grown using In2O3 epitaxial underlayering. These films did not suffer lattice stress. These results enable an analysis of the correlation between nanoscale crystal imperfections and manganite nanofilm physical properties.
LSMO nanolayers (the Sr content is approximately 39%) with thickness of approximately 60 nm were grown on the c-axis-oriented sapphire substrates with and without 40-nm-thick In2O3 (222) epitaxial buffering. The deposition of the In2O3 epitaxy layers and LSMO nanolayers was performed using a radiofrequency magnetron-sputtering system. During the deposition, the substrate temperature for the thin-film growth of the In2O3 epitaxy and LSMO nanolayer was kept at 600°C and 750°C, respectively. Moreover, the gas pressure of deposition was fixed at 10 mTorr with an Ar/O2 ratio of 3:1. The as-synthesized samples are further annealed in air ambient at 950°C for 30 min.
The crystal structure of the samples was investigated by X-ray diffraction (XRD) with Cu Kα radiation. The detailed microstructure of the as-synthesized samples was characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The composition analysis was performed using energy dispersive X-ray spectrometer (EDS) attached to the TEM. The surface morphology of the LSMO nanolayers was investigated by atomic force microscopy (AFM) with an area size of 2 μm × 2 μm. The surface current images of the LSMO nanolayers were also observed using conductive atomic force microscopy (CAFM) with PtIr tips. A superconducting quantum interference device magnetometer was used to measure the magnetic properties of the samples.
Results and discussion
In summary, 60-nm-thick LSMO nanolayers were grown on sapphire substrates with and without In2O3 (222) epitaxial buffering. The LSMO experienced improved (110) preferred crystal growth via In2O3 (222) epitaxial buffering. Comparatively, the surface grain size is more homogeneous for the LSMO nanolayer grown on the sapphire substrate. The rugged surface of the In2O3 epitaxial underlayer further incurred rougher surface morphology of the LSMO nanofilm. The columnar crystallite feature of the In2O3 epitaxial underlayer caused a relatively smaller lateral domain size of the manganite ultra-thin layer on it. Moreover, In2O3 epitaxial buffering resulted in rugged heterointerfaces between the LSMO nanolayer and In2O3 epitaxy. These factors contributed to a higher content of subgrain boundaries and incoherent interfaces on a nanometric scale in the LSMO nanofilm via In2O3 epitaxial buffering. These disordered regions caused disordered spins to exist in the LSMO nanolayer. Therefore, lower saturation magnetization value and Curie temperature, and higher coercivity and resistivity are found in the highly (110)-textured LSMO nanolayer.
YCL is a professor of the Institute of Materials Engineering at National Taiwan Ocean University (Taiwan). HZ received his Masters degree in Materials Engineering at National Taiwan Ocean University (Taiwan) in 2013. WKL is a graduate student of the Institute of Materials Engineering at National Taiwan Ocean University (Taiwan).
This work is supported by the National Science Council of Taiwan (grant nos.: NSC102-2221-E-019-006-MY3 and NSC100-2628-E-019-003-MY2) and National Taiwan Ocean University (grant no.: NTOU-RD-AA-2012-104012).
- Liang YC, Liang YC: Correlation between lattice modulation and physical properties of La0.72Ca0.28MnO3 films grown on LaAlO3 substrates. J Crystal Growth 2007, 303: 638–644. 10.1016/j.jcrysgro.2007.01.027View ArticleGoogle Scholar
- Sahu DR: Lateral parameter variations on the properties of La0.7Sr0.3MnO3 films prepared on Si (1 0 0) substrates by dc magnetron sputtering. J Alloys Compounds 2010, 503: 163–169. 10.1016/j.jallcom.2010.04.225View ArticleGoogle Scholar
- Tsuchiya T, Daoudi K, Manabe T, Yamaguchi I, Kumagai T: Preparation of the La0.8Sr0.2MnO3 films on STO and LAO substrates by excimer laser-assisted metal organic deposition using the KrF laser. Appl Surf Sci 2007, 253: 6504–6507. 10.1016/j.apsusc.2007.01.035View ArticleGoogle Scholar
- Liang YC, Liang YC: Strain-dependent surface evolution and magneto-transport properties of La0.7Sr0.3MnO3 epilayers on SrTiO3 substrates. J Crystal Growth 2007, 304: 275–280. 10.1016/j.jcrysgro.2007.02.034View ArticleGoogle Scholar
- Liang YC, Hu CY, Zhong H, Wang JL: Crystal synthesis and effects of epitaxial perovskite manganite underlayer conditions on characteristics of ZnO nanostructured heterostructures. Nanoscale 2013, 5: 2346–2351. 10.1039/c3nr33159hView ArticleGoogle Scholar
- Yang Z, Sun L, Ke C, Chen X, Zhu W, Tan O: Growth and structure properties of La1-xSr x MnO3-σ ( x = 0.2, 0.3, 0.45) thin film grown on SrTiO3 (0 0 1) single-crystal substrate by laser molecular beam epitaxy. J Crystal Growth 2009, 311: 3289–3294. 10.1016/j.jcrysgro.2009.03.039View ArticleGoogle Scholar
- Du YS, Wang B, Li T, Yu CB, Yan H: Effects of annealing procedures on the structural and magnetic properties of epitaxial La0.7Sr0.3MnO3 films. J Mag Mag Mater 2006, 297: 88–92. 10.1016/j.jmmm.2005.02.062View ArticleGoogle Scholar
- Vailionis A, Boschker H, Siemons W, Houwman EP, Blank DHA, Rijnders G, Koster G: Misfit strain accommodation in epitaxial ABO3 perovskites: lattice rotations and lattice modulations. Phys Rev B 2011, 83: 064101–064111.View ArticleGoogle Scholar
- Lee YH, Lee CC, Liu ZX, Liang CS, Wu JM: Epitaxial growth of the La-substituted BiFeO3 thin films. Electrochem Solid State Lett 2006, 9: F38-F40. 10.1149/1.2185837View ArticleGoogle Scholar
- Choi KK, Taniyama T, Yamazaki Y: Strain-induced anisotropic low-field magnetoresistance of La–Sr–Mn–O thin films. J Appl Phys 2001, 90: 6145–6151. 10.1063/1.1416860View ArticleGoogle Scholar
- Liang YC, Lee HY: Growth of epitaxial zirconium-doped indium oxide (222) at low temperature by rf sputtering. Cryst Eng Comm 2010, 12: 3172–3176. 10.1039/c004452kView ArticleGoogle Scholar
- Dai J, Liu H, Fang W, Wang L, Pu Y, Jiang F: Comparisons of structural and optical properties of ZnO films grown on (0 0 0 1) sapphire and GaN/(0 0 0 1) sapphire template by atmospheric-pressure MOCVD. Mat Sci Eng 2006, B127: 280–284.View ArticleGoogle Scholar
- Mei ZX, Wang Y, Du XL, Zeng ZQ, Ying MJ, Zheng H, Jia JF, Xue QK, Zhang Z: Growth of In2O3 single-crystalline film on sapphire (0 0 0 1) substrate by molecular beam epitaxy. J Crystal Growth 2006, 289: 686–689. 10.1016/j.jcrysgro.2005.12.086View ArticleGoogle Scholar
- Narayan J, Larson BC: Domain epitaxy: a unified paradigm for thin film growth. J Appl Phys 2003, 93: 278–285. 10.1063/1.1528301View ArticleGoogle Scholar
- Pradhan AK, Hunter D, Williams T, Lasley-Hunter B, Bah R, Mustafa H, Rakhimov R, Zhang J, Sellmyer DJ, Carpenter EE, Sahu DR, Huang JL: Magnetic properties of La0.6Sr0.4MnO3 thin films on SrTiO3 and buffered Si substrates with varying thickness. J Appl Phys 2008, 103: 023914–023922. 10.1063/1.2833388View ArticleGoogle Scholar
- Ju HL, Gopalakrishnan J, Peng JL, Li Q, Xiong GC, Venkatesan T, Greene RL: Dependence of giant magnetoresistance on oxygen stoichiometry and magnetization in polycrystalline La0.67Ba0.33MnOz. Phys Rev B 1995, 51: 6143–6146. 10.1103/PhysRevB.51.6143View ArticleGoogle Scholar
- Moreno C, Abellan P, Sandiumenge F, Casanove MJ, Obradors X: Nanocomposite lanthanum strontium manganite thin films formed by using a chemical solution deposition. Appl Phys Lett 2012, 100: 023103–023106. 10.1063/1.3675461View ArticleGoogle Scholar
- Sahu DR, Mishra DK, Huang JL, Roul BK: Annealing effect on the properties of La0.7Sr0.3MnO3 thin film grown on Si substrates by DC sputtering. Physica B 2007, 396: 75–80. 10.1016/j.physb.2007.03.016View ArticleGoogle Scholar
- Zhang N, Ding W, Zhong W, Xing D, Du Y: Tunnel-type giant magnetoresistance in the granular perovskite La0.85Sr0.15MnO3. Phys Rev B 1997, 56: 8138–8142. 10.1103/PhysRevB.56.8138View ArticleGoogle Scholar
- Li M, Wang GC: Effect of surface roughness on magnetic properties of Co films on plasma-etched Si (100) substrates. J Appl Phys 1998, 83: 5313–5321. 10.1063/1.367357View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.