Browsing by Author "Lin, Cheng-Te"

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Cone-stacked carbon nanofibers with cone angle increasing along the longitudinal axis
(2007-02-01)
Lin, Cheng-Te
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Chen, Wen-Chao
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Yen, Ming-Yu
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Wang, Lung-Shen
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Lee, Chi-Young
Using porous anodic aluminum oxide as template and petroleum pitch as precursor, a massive amount of uniform carbon nanofibers was obtained after thermal treatment. The diameter and length were 300 nm and 60 pm, respectively. The difference between these and the classic herringbone structure is that the angle between the graphenes and the fiber axis increases regularly along the axis instead of being fixed. TEM observations show that the nanofiber consists of stacked conical graphenes with cone angles that steadily increase from 60 degrees to 180 degrees along the fiber axis. This structure is the first to be produced without using catalytic CVD, and has not been reported using template procedures. The large deformation of the graphene planes at the tip of the nanofiber may produce interesting electronic applications. (c) 2006 Elsevier Ltd. All rights reserved.
Efficient Heat Dissipation of Photonic Crystal Microcavity by Mono layer Graphene
(2013-12-01)
Shih, Min-Hsiung
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Li, Lain-Jong
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Yang, Yi-Chun
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Chou, Hsiang-Yu
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Lin, Cheng-Te
Graphene, which exhibits excellent thermal conductivity, is a potential heat dissipation medium for compact optoelectronic devices. Photonic devices normally produce large-quantity of unwanted heat, and thus, a heat dissipation strategy is urgently needed. In this study, single-layer graphene (SLG) grown by chemical vapor deposition (CVD) is used to cover the surface of a photonic crystal (PhC) cavity, where the heat flux produced by the PhC cavity can be efficiently dissipated along the in-plane direction of the SLG. The thermal properties of the graphene-capped PhC cavity were characterized by experiments and theoretical calculations. The thermal resistance of the SLG-capped PhC cavity obtained from experiments is lower than half of that of a bare PhC cavity. The temperature of a SLG-capped PhC cavity is 45 K lower than that without SLG capping under an optical power of 100 mu W. Our simulation results indicate that SLG receives the majority of the heat fluxes from the device, leading to the efficient heat dissipation. Both the experimental and simulation results suggest that the SLG is a promising material to enhance the heat dissipation efficiency for optoelectronic applications.
Electrical Probing of Submicroliter Liquid Using Graphene Strip Transistors Built on a Nanopipette
(2012-01-09)
Chen, Chang-Hsiao
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Lin, Cheng-Te
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Lee, Yi-Hsien
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Liu, Keng-Ku
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Su, Ching-Yuan
Enhanced Electrocatalytic Activity of MoSx on TCNQ-Treated Electrode for Hydrogen Evolution Reaction
(2014-10-22)
Chang, Yung-Huang
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Nikam, Revannath D.
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Lin, Cheng-Te
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Huang, Jing-Kai
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Tseng, Chien-Chih
Molybdenum sulfide has recently attracted much attention because of its low cost and excellent catalytical effects in the application of hydrogen evolution reaction (HER). To improve the HER efficiency, many researchers have extensively explored various avenues such as material modification, forming hybrid structures or modifying geometric morphology. In this work, we reported a significant enhancement in the electrocatalytic activity of the MoSx via growing on Tetracyanoquinodimethane (TCNQ) treated carbon cloth, where the MoSx was synthesized by thermolysis from the ammonium tetrathiomolybdate ((NH4)(2)MoS4) precursor at 170 degrees C. The pyridinic N- and graphitic N-like species on the surface of carbon cloth arising from the TCNQ treatment facilitate the formation of Mo5+ and S-2(2-) species in the MoSx, especially with S-2(2-) serving as an active site for HER. In addition, the smaller particle size of the MoSx grown on TCNQ-treated carbon cloth reveals a high ratio of edge sites relative to basal plane sites, indicating the richer effective reaction sites and superior electrocatalytic characteristics. Hence, we reported a high hydrogen evolution rate for MoSx on TCNQ-treated carbon cloth of 6408 mL g(-1) cm(-2) h(-1) (286 mmol g(-1) cm(-2) h(-1)) at an overpotential of V = 0.2 V. This study provides the fundamental concepts useful in the design and preparation of transition metal dichalcogenide catalysts, beneficial in the development in clean energy
Graphene structure in carbon nanocones and nanodiscs
(2007-12-18)
Lin, Cheng-Te
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Lee, Chi-Young
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Chiu, Hsin-Tien
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Chin, Tsung-Shune
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應用化學系
Carbon nanoparticles, like nanocones and nanodiscs, can be obtained by mechanical treatment of carbon nanofilaments. Microstructural studies suggest that in nanocones the conical graphene stacking with progressively increasing apex (cone) angles does not fully agree with current theoretical geometry models, such as a closed cones model and a cone-helix model. The unusual stacking form of nanocones was taken into account in a modified cone-helix model. The formation mechanism of the distinctive microstructure is attributed to the inclined anchoring effect, and the relaxation of internal stresses, which were induced by the confined pyrolysis process, resulting in easier disintegration by sonication the nanofilaments. This is disclosed for the first time in literature regarding the attainment of uniform carbon nanoparticles.
Graphene/MoS2 Heterostructures for Ultrasensitive Detection of DNA Hybridisation
(2014-07-23)
Phan Thi Kim Loan
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Zhang, Wenjing
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Lin, Cheng-Te
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Wei, Kung-Hwa
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Li, Lain-Jong
The photoluminescence signals of a graphene/MoS2 heterostructural stacking film are sensitive to environmental charges, which allows the single-base sequence-selective detection of DNA hybridization with sensitivity to the level of aM. [GRAPHICS] .
Growth selectivity of hexagonal-boron nitride layers on Ni with various crystal orientations
(2012)
Lee, Yi-Hsien
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Liu, Keng-Ku
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Lu, Ang-Yu
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Wu, Chih-Yu
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Lin, Cheng-Te
Layered hexagonal-boron nitride (h-BN) films were synthesized by chemical vapor deposition (CVD) on Ni foils using ammonia borane as a precursor. Confocal Raman spectroscopy and electron backscatter diffraction (EBSD) were used to probe the effect of underlying Ni crystals with various orientations on growth behaviors of h-BN layers. The growth of the h-BN layers strongly depends on the Ni crystal orientations, where the growth rate of h-BN is larger on Ni(100)-like crystal surfaces but the growth on Ni(111)-like surfaces is not detectable, suggesting that Ni (100)-like facets are likely to promote the growth of h-BN compared with Ni (111)-like surfaces. The observation is in clear contrast to the reported growth of h-BN on Ni(111) in an ultrahigh vacuum environment. The as-grown CVD h-BN films on Ni exhibit a layered structure as revealed by atomic force microscopy (AFM). Thin h-BN layers are found on the Ni domain with a low growth rate. The observation of h-BN growth on various Ni grains may provide insights for the control of thickness, size and morphology of CVD h-BN films.
Highly Efficient Electrocatalytic Hydrogen Production by MoSx Grown on Graphene-Protected 3D Ni Foams
(2013-02-06)
Chang, Yung-Huang
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Lin, Cheng-Te
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Chen, Tzu-Yin
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Hsu, Chang-Lung
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Lee, Yi-Hsien
Label-free detection of DNA hybridization using transistors based on CVD grown graphene
(2013-03-15)
Chen, Tzu-Yin
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Phan Thi Kim Loan
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Hsu, Chang-Lung
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Lee, Yi-Hsien
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Wang, Jacob Tse-Wei
The high transconductance and low noise of graphene-based field-effect transistors based on large-area monolayer graphene produced by chemical vapor deposition are used for label-free electrical detection of DNA hybridization. The gate materials, buffer concentration and surface condition of graphene have been optimized to achieve the DNA detection sensitivity as low as 1 pM (10(-12) M), which is more sensitive than the existing report based on few-layer graphene. The graphene films obtained using conventional PMMA-assisted transfer technique exhibits PMMA residues, which degrade the sensing performance of graphene. We have demonstrated that the sensing performance of the graphene samples prepared by gold-transfer is largely enhanced (by 125%). (C) 2012 Elsevier B.V. All rights reserved.
Label-Free Electrical Detection of DNA Hybridization on Graphene using Hall Effect Measurements: Revisiting the Sensing Mechanism
(2013-05-13)
Lin, Cheng-Te
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Phan Thi Kim Loan
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Chen, Tzu-Yin
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Liu, Keng-Ku
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Chen, Chang-Hsiao
There is broad interest in using graphene or graphene oxide sheets as a transducer for label-free and selective electrical detection of biomolecules such as DNA. However, it is still not well explored how the DNA molecules interact with and influence the properties of graphene during the detection. Here, Hall effect measurements based on the Van der Pauw method are used to perform single-base sequence selective detection of DNA on graphene sheets, which are prepared by chemical vapor deposition. The sheet resistance increases and the mobility decreases with the addition of either complementary or one-base mismatched DNA to the graphene device. The hole carrier concentration of the graphene devices increases significantly with the addition of complementary DNA but it is less affected by the one-base mismatched DNA. It is concluded that the increase in hole carrier density, indicating p-doping to graphene, is better correlated with the DNA hybridization compared to the commonly used parameters such as conductivity change. The different electrical observations of p-doping from Hall effect measurements and n-doping from electrolyte-gated transistors can be explained by the characteristic morphology of partially hybridized DNA on graphene and the mismatch between DNA chain length and Debye length in electrolytes.
Layer-by-Layer Graphene/TCNQ Stacked Films as Conducting Anodes for Organic Solar Cells
(2012-06-01)
Hsu, Chang-Lung
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Lin, Cheng-Te
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Huang, Jen-Hsien
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Chu, Chih-Wei
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Wei, Kung-Hwa
Large-area graphene grown by chemical vapor deposition (CVD) is a promising candidate for transparent conducting electrode applications in flexible optoelectronic devices such as light-emitting diodes or organic solar cells. However, the power conversion efficiency (PCE) of the polymer photovoltaic devices using a pristine CVD graphene anode is still not appealing due to its much lower conductivity than that of conventional indium tin oxide. We report a layer-by-layer molecular doping process on graphene for forming sandwiched graphene/tetracyanoquinodimethane (TCNQ)/graphene stacked films for polymer solar cell anodes, where the TCNQ molecules (as p-dopants) were securely embedded between two graphene layers. Poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM) bulk heterojunction polymer solar cells based on these multilayered graphene/TCNQ anodes are fabricated and characterized. The P3HT/PCBM device with an anode structure composed of two TCNQ layers sandwiched by three CVD graphene layers shows optimum PCE (similar to 2.58%), which makes the proposed anode film quite attractive for next-generation flexible devices demanding high conductivity and transparency.
Opening an Electrical Band Gap of Bilayer Graphene with Molecular Doping
(2011-09-01)
Zhang, Wenjing
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Lin, Cheng-Te
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Liu, Keng-Ku
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Tite, Teddy
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Su, Ching-Yuan
The opening of an electrical band l gap in graphene Is crucial for its application for logic circuits. Recent studies have shown that an energy gap in Bernal-stacked bilayer graphene can be generated by applying an electric displacement field. Molecular doping has also been proposed to open the electrical gap of bilayer graphene by breaking either in-plane symmetry or inversion symmetry; however, no direct observation of an electrical gap has been reported. Here we discover that the organic molecule triazine is able to form a uniform thin coating on the top surface of a bilayer graphene, which efficiently blocks the accessible doping sites and prevents ambient p-doping on the top layer. The charge distribution asymmetry between the top and bottom layers can then be enhanced simply by increasing the p-doping from oxygen/moisture to the bottom layer. The on/off current ratio for a bottom-gated bilayer transistor operated in ambient condition Is improved by at least 1 order of magnitude. The estimated electrical band gap is up to similar to 111 meV at room temperature. The observed electrical band gap dependence on the hole-carrier density increase agrees well with the recent density-functional theory calculations. This research provides a simple method to obtain a graphene bilayer transistor with a moderate on/off current ratio, which can be stably operated in air without the need to use an additional top gate.
Quantitative appraisal of the interfacial anchoring state of polyaromatic hydrocarbons during the formation of C/C composites
(2010-04-01)
Lin, Cheng-Te
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Tsai, Min-Chiao
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Lee, Chi-Young
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Chiu, Hsin-Tien
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Chin, Tsung-Shune
The preferred anchoring state for polycyclic aromatic hydrocarbons (PAHs) pyrolyzed onto carbon substrates has been studied by semi-quantitative methods, examining their interfacial lattice arrangements. The samples were prepared by decomposing petroleum pitch inside carbon nanotubes resulting in a variety of crystallinities forming one-dimensional C/C composites. Studies indicate that the preferred anchoring state of PAH molecules depends on the nature of the substrate. Accordingly the PAHs in mesophase pitch should exhibit a face-on orientation on the carbonaceous substrates, including a graphite sheet, glassy carbon, and pyrolytic carbon. However, it showed that the anchoring state (face-on or edge-on) of PAH units can be altered even on carbonaceous substrates. The results demonstrated that in C/C composites the anchoring state is predominantly determined by the relative degree of crystallinity of the pitch/carbon substrate, and can be semi-quantitatively estimated using the I(D)/I(G) ratio from Raman spectra. Face-on anchoring is preferred when the I(D)/I(G); ratio of substrate is smaller (higher crystallinity) than that of the pyrolyzed precursor, whereas edge-on anchoring is favored when it is larger. Such an estimation method is useful in tailoring microstructures in the fabrication of C/C composites using PAH precursors. (C) 2009 Elsevier Ltd. All rights reserved.
Quasi two-dimensional carbon nanobelts synthesized using a template method
(2008-04-01)
Lin, Cheng-Te
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Chen, Tsung-Han
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Chin, Tsung-Shune
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Lee, Chi-Young
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Chiu, Hsin-Tien
Carbon nanobelts have been synthesized using nanoporous anodic alumina as template and ethanol as precursor. The length and width are tens of micrometers and 470 nm, respectively The thickness was measured to be 5 nm, exhibiting a high-aspect-ratio morphology. After annealing, the crystallinity of the nanobelts can be improved. The formation mechanism of such morphology is demonstrated as a radial deformation of large thin nanotubes. This is disclosed for the first time in the literature regarding the attainment of a quasi two-dimensional nanocarbon via a template route. Field emission measurements on the sample annealed at 800 degrees C show a turn-on voltage 3.25V/mu m and stable long-term emission efficiency The lower threshold voltage is attributed to the strong edge emitter effect. (C) 2008 Elsevier Ltd. All rights reserved.