Browsing by Author "Yan, F."

Now showing 1 - 8 of 8
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    Effect of bottom electrodes on nanoscale switching characteristics and piezoelectric response in polycrystalline BiFeO3 thin films
    (American Institute of Physics, 2011-10-17) Yan, F.; Zhu, T. J.; Lai, M. O.; Lu, L.; National University of Singapore; Zhejiang University; University of Alabama Tuscaloosa
    We have investigated the nanoscale switching characteristics and piezoelectric response based on polycrystalline BiFeO3 (BFO) thin films with different orientations deposited on different oxide bottom electrodes. The BFO film deposited on the LaNiO3 (LNO)-coated Si substrate shows a (001) preferred orientation and higher ferroelectric properties, while the BFO film grown on the SrRuO3 (SRO) buffered Si substrate shows a random orientation. The domain structures have been determined via piezoresponse force microscopy (PFM) for both films, predicting that the BFO film with the LNO bottom electrode has a larger piezoelectricity property corresponding to the ferroelastic domain. Through local switching spectroscopy measurements, the evidence of ferroelectric switching and the origin of the enhanced piezoresponse properties have been provided. A greatly improved piezoelectric response has been demonstrated using PFM that is 66.8 pm V-1 for the BFO with a SRO bottom electrode, while we obtain a value of 348.2 pm V-1 for the BFO with a LNO bottom electrode due to the increased density of the polarization vectors along the external electrical field. (C) 2011 American Institute of Physics. [doi:10.1063/1.3651383]
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    Ferromagnetic (Mn, N)-codoped ZnO nanopillars array: Experimental and computational insights
    (American Institute of Physics, 2014-01-16) Wang, D. D.; Xing, G. Z.; Yan, F.; Yan, Y. S.; Li, S.; Jiangsu University; University of New South Wales Sydney; Harvard University; University of Alabama Tuscaloosa
    To reveal the mechanism responsible for ferromagnetism in transition metal and hole codoped oxide semiconductors, we carry out a comparative study on Mn-doped and (Mn, N)-codoped ZnO nanopillars. Compared with Mn-doped ZnO samples, (Mn, N)-codoped ZnO nanopillars exhibit an enhanced room temperature ferromagnetism. The modulation of bound magnetic polarons via Mn and N codoping corroborates the correlation between the ferromagnetism and hole carriers, which is also verified by first-principles density functional theory calculations. Our study suggests that the electronic band alteration as a result of codoping engineering plays a critical role in stabilizing the long-range magnetic orderings. (C) 2014 AIP Publishing LLC.
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    Low temperature dependent ferroelectric resistive switching in epitaxial BiFeO3 films
    (American Institute of Physics, 2014-04-02) Yan, F.; Xing, G. Z.; Li, L.; Harvard University; University of New South Wales Sydney; University of Alabama Tuscaloosa
    The ferroelectric switchable diode induced resistive switching behavior at low temperature has been investigated in the epitaxial BiFeO3 (BFO) thin films. The switchable diode can be tuned using a higher voltage at low temperatures. The diode barrier is determined to be similar to 0.55 eV at the interface between BFO and electrode. The resistive switchable barrier with respect to the ferroelectric domain switching has been systematically characterized at various low temperatures. The temperature dependent conduction and leakage mechanisms have also been identified. These results can advance our understanding of resistive switching based on ferroelectric switchable diode at low working temperatures and potentially extend the applications of memristor to a larger temperature scale. (C) 2014 AIP Publishing LLC.
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    Magnetic, ferroelectric, and dielectric properties of Bi(Sc0.5Fe0.5)O-3-PbTiO3 thin films
    (American Institute of Physics, 2009-04-01) Yan, F.; Sterianou, I.; Miao, S.; Reaney, I. M.; Lai, M. O.; Lu, L.; National University of Singapore; University of Sheffield; University of Alabama Tuscaloosa
    Bi(Sc0.5Fe0.5)O-3-PbTiO3 (BSF-PT) thin films with a composition in the vicinity of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases have been grown on LaNiO3/SiO2/Si substrates at 550 degrees C and 150 mTorr by pulsed laser deposition. The dielectric properties of the film were enhanced due to high crystallinity, low porosity, and the vicinity of the MPB. A saturated ferroelectric hysteresis loop was obtained with 2P(r)=76 mu C/cm, and the leakage current was minimized by cooling the samples, postdeposition in O-2. Magnetic measurements revealed that BSF-PT thin films were antiferromagnetic confirming their anticipated multiferroic nature. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3093691]
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    Orientation-dependent surface potential behavior in Nb-doped BiFeO3
    (American Institute of Physics, 2012-04-23) Yan, F.; Xing, G. Z.; Islam, M.; Li, S.; Lu, L.; Drexel University; University of New South Wales Sydney; National University of Singapore; University of Alabama Tuscaloosa
    Single-phase epitaxial Nb doped BiFeO3 (BFNO) films have been grown on diverse oriented-SrTiO3 substrates by pulsed laser deposition. The orientation dependent surface potential distributions arising from combination of the screen and polarization charges on the BFNO surfaces were characterized by Kelvin probe force microscopy combining with corresponding domain structures investigation using piezoresponse force microscopy. The relationship between surface potential and potential barrier was quantitatively analyzed through tuning the substrate orientation. The present study indicates that data stability and storage density can be controlled via engineering the substrate orientations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4705405]
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    Positive magnetoresistance in ferromagnetic Nd-doped In2O3 thin films grown by pulse laser deposition
    (American Institute of Physics, 2014-05-23) Xing, G. Z.; Yi, J. B.; Yan, F.; Wu, T.; Li, S.; University of New South Wales Sydney; Harvard University; King Abdullah University of Science & Technology; University of Alabama Tuscaloosa
    We report the magnetic and magnetotransport properties of (In0.985Nd0.015)(2)O-2.89 thin films grown by pulse laser deposition. The clear magnetization hysteresis loops with the complementary magnetic domain structure reveal the intrinsic room temperature ferromagnetism in the as-prepared films. The strong sp-f exchange interaction as a result of the rare earth doping is discussed as the origin of the magnetotransport behaviours. A positive magnetoresistance (similar to 29.2%) was observed at 5K and ascribed to the strong ferromagnetic sp-f exchange interaction in (In0.985Nd0.015)(2)O-2.89 thin films due to a large Zeeman splitting in an external magnetic field of 50 KOe. (C) 2014 AIP Publishing LLC.
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    Role of Pb(Zr0.52Ti0.48)O-3 substitution in multiferroic properties of polycrystalline BiFeO3 thin films
    (American Institute of Physics, 2011-12-09) Yan, F.; Zhu, T. J.; Lai, M. O.; Lu, L.; National University of Singapore; Zhejiang University; University of Alabama Tuscaloosa
    Multiferroic materials are of considerable interest due to the intriguing science and application potential. Effects of Pb(Zr0.52Ti0.48)O-3 (PZT) modification on the structural, electrical, ferroelectric domain structure and ferromagnetic properties of BiFeO3 (BFO) polycrystalline films were investigated in detail. A morphotropic phase boundaries between rhombohedral perovskite (R3c) and tetragonal (P4 mm) were found in the PZT modified BFO thin films. 2% and 5% PZT modified BFO films exhibit uniform surface, larger domain size, fewer domain walls density, and lower electrical conductivity comparing with the pure BFO film. The 2% and 5% PZT modified BFO thin films show well saturated P-E hysteresis loops with improved remnant polarization close to 76.8 and 96.7 mu C/cm(2). The improved ferroelectric and dielectric properties of the PZT modified BFO films are attributed to the modified phase structure and bond lengths of Bi-O, decreased concentration of defects and defect dipole complexes, and different domain structures. The saturated magnetizations under a magnetic field of 5 000 Oe at room temperature are 8.5, 11.4, and 14.3 emu/cm(3) for the pure, 2% and 5% PZT modified BFO films, respectively. The elevated magnetic properties of PZT modified BFO may be due to the distorted spin cycloid, varied canting angle of Fe-O-Fe bond via the Zr/Ti substitution, and suppressed spiral spin structure via Pb ions substitution of Bi ions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3668123]
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    Strain effect on the surface potential and nanoscale switching characteristics of multiferroic BiFeO3 thin films
    (American Institute of Physics, 2012-03-28) Yan, F.; Miao, S.; Zhu, T. J.; Lai, M. O.; Lu, L.; Drexel University; Chinese Academy of Sciences; Dalian Institute of Chemical Physics, CAS; Zhejiang University; National University of Singapore; University of Alabama Tuscaloosa
    The BiFeO3 films were deposited on the SrTiO3 (001) substrates via tuning the thickness of the SrRuO3 (SRO) bottom electrode by pulsed laser deposition. The macroscopic ferroelectric and dielectric properties were dramatically impacted by the various nanoscale domain structures for both films due to the tunable SRO thickness. The nanoscale domain switching behaviors for both films were investigated via piezoresponse force microscopy, and results suggest that the domain structure could be changed by tuning the strain state. The surface potential investigation indicates that strain helps increase data storage density and stability. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3698155]