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收集所有交通大學研究人員與學生個人或團體所發表之各項學術著作，涵蓋期刊論文、教師專書、學位論文等項。;;Collections of Publications of NCTU Researchers and Students Like Journal Papers and Thesis.

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🏛️國立陽明交通大學機構典藏

Access type: Metadata onlyAuthor: search.filters.author.Nagarajan, Valanoor

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Now showing 1 - 7 of 7
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    Deterministic optical control of room temperature multiferroicity in BiFeO3 thin films
    (2019-06-01)
    Liou, Yi-De
    ;
    Chiu, Yu-You
    ;
    Hart, Ryan Thomas
    ;
    Kuo, Chang-Yang
    ;
    Huang, Yen-Lin
    Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO3 thin film at ambient temperature via laser illumination. Phase-field simulations indicate that a light-driven flexoelectric effect allows the targeted formation of ordered domains. We also achieved precise sequential laser writing and erasure of different domain patterns, which demonstrates a deterministic optical control of multiferroicity at room temperature. As ferroic orders directly influence susceptibility and conductivity in complex materials, our results not only shed light on the optical control of multiple functionalities, but also suggest possible developments for optoelectronics and related applications.
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    Exploring Topological Defects in Epitaxial BiFeO3 Thin Films
    (2011-02-01)
    Vasudevan, Rama K.
    ;
    Chen, Yi-Chun
    ;
    Tai, Hsiang-Hua
    ;
    Balke, Nina
    ;
    Wu, Pingping
    Using a combination of piezoresponse force microscopy (PFM) and phase-field modeling, we demonstrate ubiquitous formation of center-type and possible ferroelectric closure domain arrangements during polarization switching near the ferroelastic domain walls in (100) oriented rhombohedral BiFeO3. The formation of these topological defects is determined from the vertical and lateral PFM data and confirmed from the reversible changes in surface topography. These observations provide insight into the mechanisms of tip-induced ferroelastic domain control and suggest that formation of topological defect states under the action of local defect- and tip-induced fields is much more common than previously believed.
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    Item type:Item,
    Nanoscale Control of Phase Variants in Strain-Engineered BiFeO3
    (2011-08-01)
    Vasudevan, Rama K.
    ;
    Liu, Yunya
    ;
    Li, Jiangyu
    ;
    Liang, Wen-I
    ;
    Kumar, Amit
    Development of magnetoelectric, electromechanical, and photovoltaic devices based on mixed-phase rhombohedral-tetragonal (R-T) BiFeO3 (BFO) systems is possible only if the control of the engineered R phase variants is realized. Accordingly, we explore the mechanism of a bias induced phase transformation in this system. Single point spectroscopy demonstrates that the T -> R transition is activated at lower voltages compared to T -> - T polarization switching. With phase field modeling, the transition is shown to be electrically driven. We further demonstrate that symmetry of formed R-phase rosettes can be broken by a proximal probe motion, allowing controlled creation of R variants with defined orientation. This approach opens a pathway to designing next-generation magnetoelectronic and data storage devices in the nanoscale.
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    Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy
    (2015-09-02)
    Liao, Sheng-Chieh
    ;
    Chen, Yong-Lun
    ;
    Kuo, Wei-Cheng
    ;
    Cheung, Jeffrey
    ;
    Wang, Wei-Cheng
  • Thumbnail Image
    Item type:Item,
    Exploring Topological Defects in Epitaxial BiFeO(3) Thin Films
    (2011-02-01)
    Vasudevan, Rama K.
    ;
    Chen, Yi-Chun
    ;
    Tai, Hsiang-Hua
    ;
    Balke, Nina
    ;
    Wu, Pingping
    Using a combination of piezoresponse force microscopy (PFM) and phase-field modeling, we demonstrate ubiquitous formation of center-type and possible ferroelectric closure domain arrangements during polarization switching near the ferroelastic domain walls in (100) oriented rhombohedral BiFeO(3). The formation of these topological defects is determined from the vertical and lateral PFM data and confirmed from the reversible changes in surface topography. These observations provide insight into the mechanisms of tip-induced ferroelastic domain control and suggest that formation of topological defect states under the action of local defect- and tip-induced fields is much more common than previously believed.
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    Item type:Item,
    Epitaxial NiO nanocrystals: a dimensional analysis
    (2013-06-01)
    Cheung, Jeffrey
    ;
    Okatan, Mahmut Baris
    ;
    Sullaphen, Jivika
    ;
    Cheng, Xuan
    ;
    Nagarajan, Valanoor
    We present the study of the synthesis of (001) nickel oxide (NiO) epitaxial nanocrystals grown on (001) strontium titanate (SrTiO3) single crystal substrates. Pulsed laser deposition of the bismuth nickel oxide (BiNiO3, BNO) perovskite precursor followed by post-deposition processing is carried out to form the NiO nanocrystals. A detailed analysis of the dimensions of nanocrystals reveals that the morphology attained differs from the thermodynamically expected equilibrium shape. The deviations from the equilibrium shape are found to follow a systematic trend where the in-plane basal dimensions, that is, the length and width of the nanocrystals grown differ in discretized dimensions. This discretization suggests that for a given interfacial area of nanocrystals there are multiple stable basal rectangular geometries attainable.
  • Thumbnail Image
    Item type:Item,
    Nanoscale Control of Phase Variants in Strain-Engineered BiFeO(3)
    (2011-08-01)
    Vasudevan, Rama K.
    ;
    Liu, Yunya
    ;
    Li, Jiangyu
    ;
    Liang, Wen-I
    ;
    Kumar, Amit
    Development of magnetoelectric, electromechanical, and photovoltaic devices based on mixed-phase rhombohedral-tetragonal (R-T) BiFeO(3) (BFO) systems is possible only if the control of the engineered R phase variants is realized. Accordingly, we explore the mechanism of a bias induced phase transformation in this system. Single point spectroscopy demonstrates that the T -> R transition is activated at lower voltages compared to T -> - T polarization switching. With phase field modeling, the transition is shown to be electrically driven. We further demonstrate that symmetry of formed R-phase rosettes can be broken by a proximal probe motion, allowing controlled creation of R variants with defined orientation. This approach opens a pathway to designing next-generation magnetoelectronic and data storage devices in the nanoscale.