Browsing by Author "Vu Thanh Tra"

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Atomic Heterointerfaces and Electrical Transportation Properties in Self-Assembled LaNiO3-NiO Heteroepitaxy
(2018-04-09)
Zhu, Yuan Min
;
Thi Hien Do
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Vu Thanh Tra
;
Yu, Rong
;
Chu, Ying-Hao
Vertical nanostructure heteroepitaxy opens new opportunities for designing next-generation electronic devices due to the enthralling multifunction combinations and the abundant heterointerfaces manipulated effects. In this study, self-assembled heteroepitaxial thin films, vertically aligned metallic LaNiO3 (LNO) and semiconducting NiO with diverse heterointerfaces, are created and systematically investigated by advanced transmission electron microscopy. With the increase of LaNiO3 content, the LaNiO3 phases present as isolated islands encircled by the connected NiO nanoplates and eventually become the continuous matrix with embedded NiO nanopillars. The atomic heterointerface between NiO and LaNiO3 phases is determined to be [NiO2-LaO](LaNiO3)-LaO-[NiO](NiO), in which an extra La-O layer is enriched at the heterointerface. Besides, the formation mechanism of the heterointerface and antiphase boundaries observed in LaNiO3 phase is discussed. The electrical transport properties at room temperature can be tuned gradually by changing the volume ratio of constituents. The correlation among the insulator-to-metal transition, the carrier types associated with transport behaviors, and the heterostructure evolutions are explored. This study offers a desirable platform to design new multifunctional electronic devices based on the oxide heterojunctions.
Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light
(2016-01-27)
Lin, Jheng-Cyuan
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Vu Thanh Tra
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Tsai, Dung-Sheng
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Lin, Tai-Te
;
Huang, Po-Cheng
The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3/SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.
Controllable electrical conduction at complex oxide interfaces
(2014-06-01)
Vu Thanh Tra
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Yang, Jan-Chi
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Hsieh, Ying-Hui
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Lin, Jiunn-Yuan
;
Chen, Yi-Chun
Oxide interfaces have sparked considerable interest due to their fascinating physical properties and promising possibilities for next-generation nanoelectronics. Three intriguing oxide interfaces, hetero-, homo-, and tubular interfaces, will be discussed in detail in this review. First, the development and fundamental properties of classical heterointerfaces will be elaborated. Using LaAlO3/SrTiO3 as a case study, we present the most generic approach to control the two-dimensional electron conduction at the heterointerface. Secondly, several key issues based on interesting observations on ferroic homointerfaces will be addressed. Multiple controls of fascinating functionalities based on multiferroic BiFeO3 domain walls will be presented as a model system. Finally, as the most challenging task, we review a new type of complex oxide interfaces, the tubular interface. Further insights of recently emerged tubular interfaces in BiFeO3/CoFe2O4 system will be explored, which serve as one of the focal roles in developing new functional interfaces and potentially new type of nanostructures. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Depth-dependent atomic valence determination by synchrotron techniques
(2018-11-01)
Trappen, Robbyn
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Zhou, Jinling
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Vu Thanh Tra
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Huang, Chih-Yeh
;
Dong, Shuai
The properties of many materials can be strongly affected by the atomic valence of the contained individual elements, which may vary at surfaces and other interfaces. These variations can have a critical impact on material performance in applications. A non-destructive method for the determination of layer-by-layer atomic valence as a function of material thickness is presented for La0.7Sr0.3MnO3 (LSMO) thin films. The method utilizes a combination of bulk- and surface-sensitive X-ray absorption spectroscopy (XAS) detection modes; here, the modes are fluorescence yield and surface-sensitive total electron yield. The weighted-average Mn atomic valence as measured from the two modes are simultaneously fitted using a model for the layer-by-layer variation of valence based on theoretical model Hamiltonian calculations. Using this model, the Mn valence profile in LSMO thin film is extracted and the valence within each layer is determined to within an uncertainty of a few percent. The approach presented here could be used to study the layer-dependent valence in other systems or extended to different properties of materials such as magnetism.
Electrostatic potential and valence modulation in La0.7Sr0.3MnO3 thin films
(2018-09-25)
Trappen, Robbyn
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Garcia-Castro, A. C.
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Vu Thanh Tra
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Huang, Chih-Yeh
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Ibarra-Hernandez, Wilfredo
The Mn valence in thin film La0.7Sr0.3MnO3 was studied as a function of film thickness in the range of 1-16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn3.7+, whereas the interface valence reduces down to Mn2.5+. The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality.
Ferroelectric Control of the Conduction at the LaAlO3/SrTiO3 Heterointerface
(2013-06-25)
Vu Thanh Tra
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Chen, Jhih-Wei
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Huang, Po-Cheng
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Huang, Bo-Chao
;
Cao, Ye
Mapping Band Alignment across Complex Oxide Heterointerfaces
(2012-12-12)
Huang, Bo-Chao
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Chiu, Ya-Ping
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Huang, Po-Cheng
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Wang, Wen-Ching
;
Vu Thanh Tra
In this study, direct observation of the evolution of electronic structures across complex oxide interfaces has been revealed in the LaAlO3/SrTiO3 model system using cross-sectional scanning tunneling microscopy and spectroscopy. The conduction and valence band structures across the LaAlO3/SrTiO3 interface are spatially resolved at the atomic level by measuring the local density of states. This study directly maps out the electronic reconstructions and a built-in electric field in the polar LaAlO3 layer. Results also clearly reveal the band bending and the notched band structure in the SrTiO3 adjacent to the interface. DOI: 10.1103/PhysRevLett.109.246807
Observation of a three-dimensional quasi-long-range electronic supermodulation in YBa2Cu3O7 (-) (x)/La0.7Ca0.3MnO3 heterostructures
(2016-03-01)
He, Junfeng
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Shafer, Padraic
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Mion, Thomas R.
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Vu Thanh Tra
;
He, Qing
Recent developments in high-temperature superconductivity highlight a generic tendency of the cuprates to develop competing electronic (charge) supermodulations. While coupled with the lattice and showing different characteristics in different materials, these supermodulations themselves are generally conceived to be quasi-two-dimensional, residing mainly in individual CuO2 planes, and poorly correlated along the c axis. Here we observed with resonant elastic X-ray scattering a distinct type of electronic supermodulation in YBa2Cu3O7 (- x) (YBCO) thin films grown epitaxially on La0.7Ca0.3MnO3 (LCMO). This supermodulation has a periodicity nearly commensurate with four lattice constants in-plane, eight out of plane, with long correlation lengths in three dimensions. It sets in far above the superconducting transition temperature and competes with superconductivity below this temperature for electronic states predominantly in the CuO2 plane. Our finding sheds light on the nature of charge ordering in cuprates as well as a reported long-range proximity effect between superconductivity and ferromagnetism in YBCO/LCMO heterostructures.
Thickness dependence of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 magnetoelectric interfaces
(2015-10-05)
Zhou, Jinling
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Vu Thanh Tra
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Dong, Shuai
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Trappen, Robbyn
;
Marcus, Matthew A.
Magnetoelectric materials have great potential to revolutionize electronic devices due to the coupling of their electric and magnetic properties. Thickness varying La0.7Sr0.3MnO3 (LSMO)/PbZro(0.2)Ti(0.8)O(3) (PZT) heterostructures were built and measured in this article by valence sensitive x-ray absorption spectroscopy. The sizing effects of the heterostructures on the LSMO/PZT magnetoelectric interfaces were investigated through the behavior of Mn valence, a property associated with the LSMO magnetization. We found that Mn valence increases with both LSMO and PZT thickness. Piezoresponse force microscopy revealed a transition from monodomain to polydotnain structure along the PZT thickness gradient. The ferroelectric surface charge may change with domain structure and its effects on Mn valence were simulated using a two-orbital double-exchange model. The screening of ferroelectric surface charge increases the electron charges in the interface region, and greatly changes the interfacial Mn valence, which likely plays a leading role in the intetfacial magnetoelectric coupling. The LSMO thickness dependence was examined through the combination of two detection modes with drastically different attenuation depths. The different length scales of these techniques\' sensitivity to the atomic valence were used to estimate the depth dependence Mn valence. A smaller interfacial Mn valence than the bulk was found by globally fitting the experimental results. (C) 2015 AIP Publishing LLC.
Tuning Electronic Transport in a Self-Assembled Nanocomposite
(2014-06-01)
Chang, Wei Sea
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Liu, Heng-Jui
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Vu Thanh Tra
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Chen, Jhih-Wei
;
Wei, Tzu-Chiao
Self-assembled nanocomposites with a high interface-to-volume ratio offer an opportunity to overcome limitations in current technology, where intriguing transport behaviors can be tailored by the choice of proper interactions of constituents. Here we integrated metallic perovskite oxide SrRuO3 - wurzite semiconductor ZnO nanocomposites to investigate the room-temperature metal - insulator transition and its effect on photoresponse. We demonstrate that the band structure at the interface can be tuned by controlling the interface-to-volume ratio of the nanocomposites. Photoinduced carrier injection driven by visible light was detected across the nanocomposites. This work shows the charge interaction of the vertically integrated multiheterostructures by incorporating a controllable interface-to-volume ratio, which is essential for optimization of the design and functionality of electronic devices.