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Characteristics of highly orientated BiFeO3 thin films on a LaNiO3-coated Si substrate by RF sputtering
(2010-10-01)
Liu, Yen-Ting
;
Chen, San-Yuan
;
Lee, Hsin-Yi
;
材料科學與工程學系
;
加速器光源科技與應用學位學程
BiFeO3 (BFO) films were grown on LaNiO3-coated Si substrate by a RF magnetron sputtering system at temperatures in the range of 300-700 degrees C. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. For a substrate temperature below 300 degrees C and at 700 degrees C only partially crystalline films and completely randomly polycrystalline films were grown, whereas highly (001)-orientated BFO film was obtained for a substrate temperature in the range of 400-600 degrees C. The crystalline quality of BFO thin films increase as the deposition temperature increase except for the film deposited at 700 degrees C. The fitted result from X-ray reflectivity curves show that the densities of the BFO films are slightly less than their bulk values. For the BFO films deposited at 300-600 degrees C, the higher the deposition temperature, the larger the remnant polarization and surface roughness of the films present. (C) 2010 Elsevier B.V. All rights reserved.
Growth of BiFeO3/SrTiO3 artificial superlattice structure by RF sputtering
(2011-11-01)
Chiu, Shang-Jui
;
Liu, Yen-Ting
;
Lee, Hsin-Yi
;
Yu, Ge-Ping
;
Huang, Jia-Hong
Asymmetric superlattice structures consisting of multiferroic BiFeO3 (BFO) and paraelectric SrTiO3 (STO) sublayers were grown on a Nb-doped STO substrate by RF magnetron sputtering at temperatures in the range 500-800 degrees C. For substrate temperatures less than 500 degrees C and at 800 degrees C, only poorly crystalline films resulted, whereas a BFO/STO superlattice structure film of great crystalline quality was obtained for a substrate temperature in the range 550-750 degrees C. The formation of a superlattice structure was confirmed through both the appearance of Bragg lines separated by Kiessig fringes in X-ray reflectivity curves and the satellite features of a (002) diffraction pattern. The clearly discernible main and satellite features on both sides of the substrate about the (002) STO Bragg peak of superlattice films indicate the high quality of the BFO/STO artificial superlattice structure. For BFO/STO superlattice films deposited at 600-700 degrees C, the increased crystalline quality with smaller interface roughness correlates with larger lattice strain and remanent polarization of the film. The lattice strain and interface quality might be important factors that influence the leakage and ferroelectric properties in BFO/STO artificial superlattices. (C) 2011 Elsevier B.V. All rights reserved.
Preparation of a BiFeO3/LaNiO3 multiferroic oxide superlattice structure by RF magnetron sputtering
(2011-12-25)
Liu, Yen-Ting
;
Chiu, Shang-Jui
;
Lee, Hsin-Yi
;
Chen, San-Yuan
;
材料科學與工程學系
Artificial superlattices consisting of multiferroic BiFeO3 (BFO) and conductive LaNiO3 (LNO) were grown epitaxially on a Nb-doped SrTiO3 (STO) (001) single-crystal substrate at temperatures in a range 560-810 degrees C with a RF magnetron sputtering system. The superlattice contained 30 periods of symmetric BFO/LNO bilayers with a thickness of 2 nm of each individual layer. Ferroelectric and conductive superlattice materials of this type can serve for an investigation of the strain dependence of ferroelectric properties of BFO layers in superlattice structures. Measurements of X-ray reflectivity and X-ray diffraction at high resolution were employed to characterize the microstructure of these films. The formation of a superlattice structure was confirmed by the appearance of Bragg peaks separated by Kiessig fringes in the X-ray reflectivity curve and a diffraction pattern. The clearly discernible main feature and satellite features on both sides of the substrate feature about the (002) STO Bragg peak indicate the high quality of the BFO/LNO artificial superlattice structure formed on a STO substrate at all deposition temperatures. X-ray measurements show that these superlattice films become subject to greater compressive strain in the in-plane direction, and possess increased crystalline quality when increasing the deposition temperature to 660 degrees C. The measurement of hysteresis loops shows that the largest remanent polarization (P-r) occurs at 660 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Fabrication of epitaxial ZnO films by atomic-layer deposition with interrupted flow
(2009-12-31)
Ku, Ching-Shun
;
Huang, Jheng-Ming
;
Lin, Chih-Ming
;
Lee, Hsin-Yi
;
材料科學與工程學系
We formed epitaxial ZnO thin films on a (0001) c-plane sapphire substrate through deposition of atomic layers (ALD) at 25-160 degrees C using diethylzinc (DEZn) and deionized water as precursors in combination with interrupted flow. High-resolution X-ray diffraction measurements were employed to characterize the microstructure of these films. With interrupted flow, we obtained ZnO thin films with an optimal growth window in a range of 40-160 degrees C, effectively decreasing the growth temperature by about 120 degrees C relative to a conventional method involving continuous flow. X-ray reflectivity measurements showed that the rate of growth increased also between 20 degrees C and 120 degrees C. The XRD results indicate that the stock time might extend the reaction of DEZn and water through an increased duration. All results show that a low temperature for growth improves the crystalline quality and is consistent with thermodynamically blocked self-compensation. (C) 2009 Elsevier B.V. All rights reserved.
Growth of high-quality epitaxial ZnO films on (10-10) sapphire by atomic layer deposition with flow-rate interruption method
(2013-09-01)
Huang, Jheng-Ming
;
Ku, Ching-Shun
;
Lee, Hsin-Yi
;
Lin, Chih-Ming
;
Chen, San-Yuan
A novel process in an atomic layer deposition system with "flow-rate interruption" (FRI) was developed to obtain epitaxial ZnO films of high quality. The m-plane ZnO thin films were grown on m-plane sapphire substrates by atomic layer deposition with FRI or a conventional continuous-flow method at the temperature in the range of 25-260 degrees C; 200 degrees C appeared optimal. Measurements of X-ray reflectivity indicated that the thickness of ZnO films with FRI is almost twice than that grown with the continuous-flow method. The structural, optical and electrical properties were investigated with X-ray diffraction (XRD), photoluminescence and Hall measurements. The diffraction results indicated that the interrupted flow might extend the reaction of diethylzinc and water through an increased duration to improve the crystallographic quality of the films. According to the results from XRD at high resolution, to substantiate the epitaxial relation between the thin film and the substrate, an off-normal azimuthal scan along ZnO (201) demonstrated two-fold symmetry that indicated the ZnO films to be in epitaxial growth on sapphire. The photoluminescence results showed a strongly enhanced near-band-edge emission of an FRI sample, and the donor-bond exciton appearing in films also indicated superior crystalline qualities. The Hall mobility of the FRI method was up to 64.7 cm(2) V-1 s(-1). The FRI method evidently improved the structural, optical and electrical properties of the ZnO films with small consumption of precursors. (C) 2012 Elsevier B.V. All rights reserved.
Epitaxial growth of ZnO films at extremely low temperature by atomic layer deposition with interrupted flow
(2010-04-15)
Ku, Ching-Shun
;
Lee, Hsin-Yi
;
Huang, Jheng-Ming
;
Lin, Chih-Ming
;
材料科學與工程學系
Thin crystalline films of zinc oxide (ZnO) of high quality have been grown epitaxially on a (0 0 0 1) c-plane of a sapphire substrate with atomic layer deposition (ALD) at extra-low temperature. With diethylzinc (DEZn) and deionized water as precursors in combination with interrupted flow, we obtained ZnO thin films with an optimal growth window in a range 25-160 degrees C, so effectively lowering the growth temperature by about 120 degrees C relative to the conventional method involving a continuous-flow. We characterized the microstructure of these films with X-ray reflectivity and high-resolution X-ray diffraction (XRD) measurements. The XRD results indicate that the stock time might extend the reaction of DEZn and water through an increased duration. This low temperature for growth results in increased crystalline quality and reduced the non-radiative recombination process to enhance the optical properties of ZnO films. (c) 2009 Elsevier B.V. All rights reserved.

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