Browsing by Author "Chou, Li-Jen"

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In Situ Observation of Dehydration-Induced Phase Transformation from Na2Nb2O6-H2O to NaNbO3
(2012-10-25)
Jung, Jong Hoon
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Chen, Chih-Yen
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Wu, Wen-Wei
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Hong, Jung-Il
;
Yun, Byung Kil
We have monitored the phase transformation from a Sandia octahedral molecular sieve Na2Nb2O6-H2O to a piezoelectric NaNbO3 nanowire through in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements at high temperatures. After dehydration at 288 degrees C, the Na2Nb2O6-H2O becomes significantly destabilized and transforms into NaNbO3 with the increase of time. The phase transformation time is exponentially proportional to the inverse of temperature, for example, similar to 10(5) is at 300 degrees C and similar to 10(1) at 500 degrees C, and follows an Arrhenius equation with the activation energy of 2.0 eV. Real time TEM investigation directly reveals that the phase transformation occurs through a thermally excited atomic rearrangement due to the small difference of Gibbs free energy between two phases. This work may provide a clue of kinetic control for the development of high piezoelectric lead-free alkaline niobates and a deep insight for the crystallization of oxide nanostructures during a hydrothermal process.
Localized CO2 laser annealing induced dehydrogenation/ablation and optical refinement of silicon-rich silicon dioxide film with embedded Si nanocrystals
(2006-12-01)
Lin, Gong-Ru
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Lin, Chun-Jung
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Chou, Li-Jen
;
Chueh, Yu-Lun
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光電工程學系
CO2 laser annealing induced effects of dehydrogenation, Si nanocrystal precipitation, ablation, and optical refinement in PECVD grown SiO1.25 film are investigated. Dehydrogenation shrinks SiO1.25 thickness by 40 nm after annealing at laser intensity (P-laser) of 4 kW/cm(2) for 1.4 ms. As P-laser increases to 6 kW/cm(2), the photoluminescence (PL) red-shifts to 806 nm due to the size enlargement of Si nanocrystals, while a reduced optical bandgap energy from 3.3 to 2.43 eV and an enlarged refractive index from 1.57 to 1.87 are also observed. Transmission electron microscopy analysis reveals that the randomly oriented Si nanocrystals exhibit an average diameter of 5.3 nm and a volume density of 1.9 X 10(18) cm(-3). CO2 Laser ablation initiates at intensity higher than 7 kW/cm(2), which introduces numerous structural defects with a strong PL at 410 nm. Such an ablation inevitably leads to a blue-shifted optical bandgap energy from 2.43 to 2.76 eV as P-laser enlarges from 6 to 12 kW/cm(2) are concluded.
Microphotoluminescence and microphotoreflectance analyses of CO2 laser rapid-thermal-annealed SiOx surface with buried Si nanocrystals
(2006-09-01)
Lin, Gong-Ru
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Lin, Chun-Jung
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Chou, Li-Jen
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Chueh, Yu-Lun
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材料科學與工程學系
The optical properties of a SiOx film rapid-thermal-annealed (RTA) by CO2 laser are primarily investigated. The microphotoluminescence (mu-PL) and high-resolution transmission electron microscopy (HRTEM) analyses indicate that the precipitation of random-oriented Si nanocrystals can be initiated when laser intensity (P-laser) is larger than 4.5 kW/cm(2). At P-laser of 6 kW/cm(2), the Si nanocrystal exhibits a largest diameter of 8 run and a highest density of 4.5 x 10(16) cm(-3), which emits strong PL at 790-825 nm. The microphotoreflectance of the CO2 laser RTA SiOx film reveals a volume density product dependent refractive index increasing from 1.57 to 1.87 as P-laser increases from 1.5 to 7.5 kW/cm(2). Nonetheless, the laser ablation of the SiOx film occurs with a linear ablation slope of 35 nm/kW/cm(2) at beyond 7.5 kW/cm(2), which terminates the enlargement of Si nanocrystals, degrades the near-infrared PL, and slightly reduces the refractive index of the CO2 laser RTA SiOx film.
Self-assembly of an antireflective moth-like structure using antibody-functionalized nanowires and nanopore arrays
(2011-11-25)
Chen, Yu-Shiun
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Hung, Ning
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Chou, Li-Jen
;
Chiou, Jin-Chern
;
Hong, Meng-Yen
A novel framework to fabricate moth-like nanopillar arrays was proposed. In this scheme, nanowires were first cross-linked with anti-gold nanoparticle (GNP) antibodies and mixed with the nanopore array pre-deposited by GNP, which was then followed by centrifugation. An optimal success rate of 95% was finally obtained by choosing nanorods with an aspect ratio of 5:1 by modifying with 10 ng mL(-1) antibodies, and by inserting them into a pore array pre-deposited with 54.4 mu M GNP. The nanopillar arrays thus fabricated showed high levels of antireflective efficiency across a broad wavelength. Here we demonstrate the assembly of nanowires and nanopores into nanopillar arrays by the assistance of antibody-antigen binding. The application of bio-nano-interaction provides an economic, time-saving, and throughput approach to manipulating objects on the nanoscale.