Browsing by Author "Lee, Chih-Wei"

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Curved polymer nanodiscs by wetting nanopores of anodic aluminum oxide templates with polymer nanospheres
(2014)
Chi, Mu-Huan
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Kao, Yi-Huei
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Wei, Tzu-Hui
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Lee, Chih-Wei
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Chen, Jiun-Tai
Although nanostructures with diverse morphologies have been fabricated, it is still a great challenge to prepare anisotropic two-dimensional (2-D) nanostructures, especially non-planar disc-like nanostructures. In this work, we develop a simple method to prepare curved polymer nanodiscs with regular sizes by wetting polymer nanospheres in the nanopores of anodic aluminum oxide (AAO) templates. Polystyrene (PS) nanospheres are first fabricated by using a non-solvent-assisted template wetting method. By annealing the PS nanospheres in the nanopores of AAO templates, curved PS nanodiscs can be produced. The length and morphology of the curved PS nanodiscs can be controlled by the wetting conditions such as the annealing temperatures and times. For some stacked nanospheres, the annealing process can result in the formation of helix-like nanostructures. To demonstrate the universality of this work, this approach is also applied to poly(methyl methacrylate) (PMMA), another common polymer, and similar results are obtained.
Effect of Nonsolvent on the Formation of Polymer Nanomaterials in the Nanopores of Anodic Aluminum Oxide Templates
(1970-01-01)
Lee, Chih-Wei
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Wei, Tzu-Hui
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Chang, Chun-Wei
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Chen, Jiun-Tai
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應用化學系
"We study the effect of nonsolvent on the formation of polymer nanomaterials in the nanopores of porous templates. Water (nonsolvent) is added into a poly (methyl methacrylate) (PMMA) solution in dimethylformamide (DMF) confined in the nanopores of an anodic aluminum oxide (AAO) template. Water forms a wetting layer on the pore wall and causes the PMMA solution to be isolated in the center of the nanopore, resulting in the formation of PMMA nanospheres or nanorods after the solvent is evaporated. The formation of the polymer nanomaterials induced by nonsolvent is found to be driven by the Rayleigh-instability-type transformation. Without adding the nonsolvent, PMMA chains precipitate on the walls of the nanopores after the solvent is evaporated, and PMMA nanotubes are obtained."
Solvent-Annealing-Induced Nanowetting in Templates: Towards Tailored Polymer Nanostructures
(2013-02-25)
Chen, Jiun-Tai
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Lee, Chih-Wei
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Chi, Mu-Huan
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Yao, I-Chun
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應用化學系
We study the solvent-annealing-induced nanowetting in templates using porous anodic aluminum oxide membranes. The morphology of polystyrene and poly(methyl methacrylate) nanostructures can be controlled, depending on whether the swollen polymers are in the partial or complete wetting regimes, which are characterized by the spreading coefficient. When the swollen polymers are in the partial wetting regime, polymers wet the nanopores by capillary action, resulting in the formation of polymer nanorods. When the swollen polymers are in the complete wetting regime, polymers form wetting layers in the nanopores, resulting in the formation of polymer nanotubes. The solubility parameters of polymers and solvents are also used to predict the wetting behavior of swollen polymers in cylindrical geometry.
Solvent-Induced Dewetting on Curved Substrates: Fabrication of Porous Polymer Nanotubes by Anodic Aluminum Oxide Templates
(2015-09-08)
Chi, Mu-Huan
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Chang, Chun-Wei
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Ko, Hao-Wen
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Su, Chun-Hsien
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Lee, Chih-Wei
Dewetting of polymer thin films triggered by thermal or solvent annealing on flat substrates have been widely studied. Research on dewetting of polymer thin films on curved substrate, however, has been rarely investigated and remains a great challenge, especially for dewetting induced by solvent annealing. In this work, we study the dewetting of polymer thin films on curved substrates by annealing poly(methyl methacrylate) (PMMA) nanotubes in cylindrical nanopores of anodic aluminum oxide (AAO) templates via dimethylformamide (DMF) vapor treatment. After solvent annealing, dewetting of the curved PMMA thin films is induced, resulting in the formation of porous PMMA nanotubes. By changing the experimental conditions such as annealing time, solvent quality, and molecular weight of polymer, the hole sizes of the PMMA nanotubes can be controlled or even prevented. To demonstrate the universality of this method, porous nanotubes of polystyrene (PS) and fluorescent pyrene-ended PMMA (Py-PMMA) are also fabricated. This work not only provides a better understanding of dewetting of polymer thin films on curved substrates but also offers a promising new way to prepare porous polymer nanotubes with controllable hole sizes.
Temperature-Oriented Mobility Measurement and Simulation to Assess Surface Roughness in Ultrathin-Gate-Oxide (similar to 1 nm) nMOSFETs and Its TEM Evidence
(2012-04-01)
Chen, Ming-Jer
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Chang, Li-Ming
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Kuang, Shin-Jiun
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Lee, Chih-Wei
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Hsieh, Shang-Hsun
On a 1.27-nm gate-oxide nMOSFET, we make a comprehensive study of SiO2/Si interface roughness by combining temperature-dependent electron mobility measurement, sophisticated mobility simulation, and high-resolution transmission electron microscopy (TEM) measurement. Mobility measurement and simulation adequately extract the correlation length lambda and roughness rms height Delta of the sample, taking into account the Coulomb-drag-limited mobilities in the literature. The TEM measurement yields the apparent correlation length lambda(m) and roughness rms height Delta(m). It is found that the following hold: 1) lambda approximate to lambda(m) for both the Gaussian and exponential models, validating the temperature-oriented extraction process; 2) the extracted Delta (similar to 1.3 angstrom for the Gaussian model and 1.0 angstrom for the exponential one) is close to that (similar to 1.2 angstrom) of Delta(m), all far less than the conventional values (similar to 3 angstrom) in thick-gate-oxide case; and 3) the TEM 2-D projection correction coefficient Delta(m)/Delta is approximately 1.0, which cannot be elucidated with the current thick-gate-oxide-based knowledge.
Transformation of Polymer Nanofibers to Nanospheres Driven by the Rayleigh Instability
(2013-04-24)
Huang, Yu-Chieh
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Fan, Ping-Wen
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Lee, Chih-Wei
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Chu, Chien-Wei
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Tsai, Chia-Chan
We study the thermal annealing effect of poly(methyl methacrylate) (PMMA) nanofibers made from anodic aluminum oxide (AAO) templates and their transformation to PMMA nanospheres. The PMMA nanofibers are prepared by wetting an AAO template with a 30 wt % PMMA solution, followed by the evaporation of the solvent, After the AAO template is removed by a weak base, the PMMA nanofibers are thermally annealed in ethylene glycol, a nonsolvent for PMMA. The surfaces of the nanofibers undulate and transform into nanospheres, driven by the Rayleigh instability. The driving force for the transformation process is the minimization of the interfacial energy between PMMA nanofibers and ethylene glycol. The transformation times at higher annealing temperatures are shorter than those at lower annealing temperatures. This study provides a facile route to prepare polymer nanospheres which are not accessible by other traditional methods.