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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.
Broadband Omnidirectional Light Trapping in Gold-Decorated ZnO Nanopillar Arrays
(2017-04-05)
Chang, Yuan-Ming
;
Lin, Man-Ling
;
Lai, Tung-Yen
;
Chen, Chang-Hung
;
Lee, Hsin-Yi
The photoluminescence (PL) and reflectivity characteristics of zinc oxide nanopillars- (ZnO-NPs) grown on indium tin oxide (ITO)-coated glasses were investigated. The room temperature PL showed bright -white -light emission for the undoped ZnO-NPs grown at 600 degrees C, suggesting the close relation between the optical characteristic and "the growth conditions being, carried out for,obtaining the present ZnO-NPs. The reflectivity of the as -grown ZnO-NPs array was about, similar to 29% with the wavelength of the incident light ranging from 200 to 1800 nm. Nevertheless, the reflectance reduced significantly to less than 9.9% when a layer of gold (Au) was deposited on ZnO=NPg by sputtering for 5 min, corresponding to more than 65% reduction in Au -coated ZnQ-NPs (Au/ZnO-NPs). Moreover, the angle -resolved reflectance measurement's on the present Au/ZnO-NPs array show an omnidirectional light -trapping characteristic. These remarkable characteristics, broadband and omnidirectional light -trapping -of Ati/ZnO-NPs, are attributed to the extended effective optical path of the incident light due to subwavelength scattering resulting,from the presence of Au nanoparticics.
High mobility transparent conductive Al-doped ZnO thin films by atomic layer deposition
(2017-12-15)
Lin, Man-Ling
;
Huang, Jheng-Ming
;
Ku, Ching-Shun
;
Lin, Chih-Ming
;
Lee, Hsin-Yi
The effects of growth temperature on the microstructure, transport and optoelectronic properties of a series of Al-doped ZnO (AZO) films with thickness of similar to 30 nm deposited on polished silicon-(100) and glass substrates by the atomic layer deposition (ALD) were investigated. By adopting an in-situ doping growth scheme the critical length effect associated with adjacent Al2O3 layers commonly encountered in previous ALD growth schemes was avoided and effective Al-doping was achieved with the growth temperature ranging from 100 degrees C to 300 degrees C. Experimental results showed that, in general, increasing the growth temperature would result in much improved film crystallinity and carrier mobility, with the average transmittance in the visible wavelength range being exceeding 95% in all cases. In particular, for AZO films grown at 300 degrees C, an unprecedented mobility of 136 cm(2)V(-1)s(-1) was obtained, comparing to the typical values of 50-60 cm(2)V(-1)s(-1) reported previously. The resistivity of these 300 degrees C films (rho approximate to 6 x 10(-4) Omega-cm), nevertheless, is slightly higher than that of some highly-doped ZnO (rho approximate to 2 -4 x 10(-4) Omega-cm) prepared by sputtering methods. The secondary ion mass spectroscopy (SIMS) analyses revealed that hydrogen incorporation is the key in reducing the charge trap density and, hence, resulting in much enhanced carrier mobility. The present results promise a keen competitiveness of AZO with the indium tin oxide (ITO) film for thin-film-transistor (TFT) as well as in photovoltaic device applications. (C) 2017 Elsevier B.V. All rights reserved.
Enhanced electrical properties and field emission characteristics of AZO/ZnO-nanowire core-shell structures
(2016-06-14)
Huang, Jheng-Ming
;
Tsai, Shang-You
;
Ku, Ching-Shun
;
Lin, Chih-Ming
;
Chen, San-Yuan
The electrical properties and field-emission characteristics of ZnO nanowires (ZnO-NWs) fabricated using a vapor-liquid-solid method were systematically investigated. In particular, we explored the effects of Al-doped ZnO (AZO) films (thickness 4-100 nm) deposited on ZnO-NWs using an atomic layer deposition (ALD) method on the optoelectronic properties. The results show that the sheet resistance of net-like ZnO-NW structures can be significantly improved, specifically to become similar to 1/1000 of the sheet resistance of the as-grown ZnO-NWs, attaining less than 10 Omega Sq(-1). The emission current density measured at the maximum field was roughly quadrupled relative to that of the as-grown ZnO-NWs. The data of the enhanced field-emission characteristics show that, with the ALD system, the AZO films of small resistance are readily coated on a structure with a high aspect ratio and the coating radius is controlled relative to the turn-on voltage and current density. The ultrathin AZO film from a one-monolayer coating process also significantly improved emission properties through modification of the effective work function at the AZO/ZnO-NW surface.
Tuning the magnetic properties of self-assembled BiFeO3-CoFe2O4 heteroepitaxy by magneto-structural coupling
(2016)
Amrillah, Tahta
;
Vandrangi, Suresh K.
;
Bitla, Yugandhar
;
Do, Thi Hien
;
Liao, Sheng-Chieh
Magnetic and multiferroic nanocomposites with two distinct phases have been a topic of intense research for their profound potential applications in the field of spintronics. In addition to growing high-quality phase separated heteroepitaxial nanocomposites, the strain engineering that is conducive to enhance the tunability of material properties, in general, and the magnetic properties, in particular, is of utmost importance in exploring new possibilities. Here, we investigated the magneto-structural coupling between anti-ferromagnetic BiFeO3 (BFO) and ferrimagnetic CoFe2O4 (CFO) in self-assembled vertically aligned nanocomposites grown on LaAlO3 (LAO) and SrTiO3 (STO) substrates. We found that BFO exhibits tetragonal (T) and rhombohedral (R) structures as the stable phases and CFO has high magnetocrystalline anisotropy even in the form of nanocomposites. The temperature and magnetic field dependent magnetizations of T_ BFO-CFO/LAO and R_ BFO-CFO/STO nanocomposites primarily demonstrate the magnetoelastic coupling between these variants.
Optoelectronic properties in vertically aligned ZnO/Si-nanopillars
(2012)
Lee, Hsin-Yi
;
Chang, Yuan-Ming
;
Tseng, Wen-Shou
;
Kao, Pin-Hsu
;
Wang, Hau-Wei
An effective method of fabricating vertically aligned silicon nanopillars (Si-NPs) was realized by using the self-assembled silver nanodots as natural metal-nanomask for subsequent etching process. Ultrathin (similar to 9 nm) ZnO films were deposited on the Si-NPs by atomic layer deposition to enhance the field emission property. The turn-on field defined by the 10 mu A/cm(2) current density criterion is similar to 0.74 V/mu m with an estimated beta similar to 1.33X10(4). The low turn-on field and marked enhancement in beta were attributed to the small radius of curvature, high aspect ratio, and perhaps more importantly, proper density distribution of the ZnO/Si-NPs. On the other hand, room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on Si nanowires fabricated by self-masking dry etching in hydrogen-containing plasma. For films deposited at 200 degrees C, an intensive UV emission corresponding to free-exciton recombination was observed with a nearly complete suppression of the defect-associated broad visible range emission peak.
In situ Al-doped ZnO films by atomic layer deposition with an interrupted flow
(2015-09-01)
Huang, Jheng-Ming
;
Ku, Ching-Shun
;
Lin, Chih-Ming
;
Chen, San-Yuan
;
Lee, Hsin-Yi
In situ aluminum-doped ZnO (AZO) films were grown on glass substrates by atomic layer deposition (AID) with an interrupted flow at temperatures in range 200-280 degrees C; the optimal temperature, 260 degrees C, depended on the electrical properties. To assess the effect of the ratio of pulses of diethylzinc (DEZn) and trimethylaluminium (TMA) on the structural, optical and electrical properties, we grew AZO films with various pulse ratios of DEZn:TMA in a range from 3:1 to 10:1 at 260 degrees C. These properties and the content of Al were investigated with X-ray diffraction, X-ray reflectivity (XRR), a high-resolution transmission electron microscope (HRTEM), a secondary-ion mass spectrometer (SIMS), transmission spectra, Hall measurements and X-ray photoelectron spectra (XPS). The electrical resistivity was least, 5.7 x 10(-4) Omega cm, for ALD-AZO films with pulse ratio 6:1; the carrier mobility was 8.80 cm(2) V-1 s(-1) and optical transmittance up to 94%. The epitaxial AZO films grown in situ also on m-plane sapphire exhibited the two-fold symmetry of ZnO (110) in the orthorhombic crystal system. All results show that a novel in situ doping method with an interrupted flow controls the Al content of AZO films more easily, and is more usefully applicable for a structure with a large aspect ratio for an advanced photoelectric device. (C) 2015 Elsevier B.V. All rights reserved.
Characteristics of highly orientated BiFeO(3) thin films on a LaNiO(3)-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
BiFeO(3) (BFO) films were grown on LaNiO(3)-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.

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