Browsing by Author "Liu, Pingping"

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Enhanced Structural and Magnetic Coupling in a Mesocrystal-Assisted Nanocomposite
(2016-01-20)
Zhu, Yuanmin
;
Zhan, Qian
;
Yang, Jan-Chi
;
Bitla, Yugandhar
;
Liu, Pingping
Benefiting from the advances made in well-controlled materials synthesis techniques, nanocomposites have drawn considerable attention due to their enthralling physics and functionalities. In this work, we report a new heteroepitaxial mesocrystalperovskite nanocomposite, (NiFe2O4)(0.33):(La0.67Ca0.33MnO3)(0.67). Elaborate structural studies revealed that tiny NiFe2O4 nanocrystals aggregate into ordered octahedral mesocrystal arrays with {111} facets together with a concomitant structural phase transition of the La0.67Ca0.33MnO3 matrix upon postannealing process. Combined magnetic and X-ray absorption spectroscopic measurements show significant enhancement in the magnetic properties at room temperature due to the structural evolution of magnetic NiFe2O4 and the consequent magnetic coupling at the heterointerfaces mediating via well connected octahedrons of Mn-O-6 in La0.67Ca0.33MnO3 and (Ni,Fe)-O-6 in NiFe2O4. This work demonstrates an approach to manipulate the exciting physical properties of material systems by integrating desired functionalities of the constituents via synthesis of a self-assembled mesocrystal embedded nanocomposite system.
Orientation-tuning in self-assembled heterostructures induced by a buffer layer
(2014)
Zhu, Yuanmin
;
Liu, Pingping
;
Yu, Rong
;
Hsieh, Ying-Hui
;
Ke, Dan
Anisotropic nano-plate structures in self-assembled perovskite-spinel thin films, BiFeO3-NiFe2O4 and BiFeO3-CoFe2O4, which were deposited on (001)(c) SrRuO3/SrTiO3 and DyScO3 substrates, respectively, have been demonstrated using transmission electron microscopy combined with strain analysis. Unlike the unitary cube-on-cube orientation relationship reported widely, the growth direction of the CoFe2O4 and NiFe2O4 plates was tuned to [011](c) while the BiFeO3 matrix kept [001](c) in both systems. In particular, a thin stress-sensitive BiFeO3 buffer layer between the spinel nanostructure and the substrate was introduced for providing a complex strain state in both film systems. The novel orientation tuning and the pattern configuration of the heterostructures are mainly attributed to the strain imposed on the films and the anisotropic ledge growth mechanism of spinels.
Self-assembled gold nanostructures in complex oxide thin films
(2020-01-01)
Wang, Hongliang
;
Yen, Min
;
Er, Xiaokuo
;
Liu, Pingping
;
Wan, Farong
Recently, noble metal-complex oxide nanocomposites with a high interface-to-volume ratio have attracted considerable interest for their potential applications in advanced devices. In this work, Nb:SrTiO3 epitaxial thin films embedded with different ratios of Au nanophase were fabricated using pulsed laser deposition. Detailed heterostructures at an atomic scale have been investigated based on advanced transmission electron microscopy. The results reveal that the pattern tunability of Au nanostructures can be realized by controlling the volume ratios between Au and Nb:SrTiO3, resulting in the manipulation of absorption characteristics in the visible light region. It is suggested that elastic energy and surface energy anisotropy are important factors to control the growth of the present Au/Nb:SrTiO3 heterostructures. This work offers a desirable platform to design nano composites with novel optical properties.