Browsing by Author "Cheng, Xuan"

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Epitaxial NiO nanocrystals: a dimensional analysis
(2013-06-01)
Cheung, Jeffrey
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Okatan, Mahmut Baris
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Sullaphen, Jivika
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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.
Phase evolution of magnetite nanocrystals on oxide supports via template-free bismuth ferrite precursor approach
(2012-11-15)
Cheung, Jeffrey
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Bogle, Kashinath
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Cheng, Xuan
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Sullaphen, Jivika
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Kuo, Chang-Yang
This report investigates the phase evolution pathway of magnetite nanocrystal synthesis on oxide-supported substrates. A template-free phase separation approach, which exploits the thermodynamic instability of ternary perovskite BiFeO3 and inherent volatility of bismuth oxide in low oxygen pressure and high temperature is presented. The formation of an intermediate hematite nanocrystal phase is found as a key step that controls the eventual size and morphology of the magnetite nanocrystals. X-ray absorption spectra measurements and X-ray magnetic circular dichroism confirm that the spectral fingerprints of the magnetite nanocrystals match with that of bulk crystals. Magnetic measurements show that magnetic anisotropy is directly attributed to the nanocrystal morphology. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4766748]
Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy
(2015-09-02)
Liao, Sheng-Chieh
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Chen, Yong-Lun
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Kuo, Wei-Cheng
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Cheung, Jeffrey
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Wang, Wei-Cheng