Browsing by Author "Kuo, Jer-Lai"

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A High-Pressure Study of the Effects of TiO(2) Nanoparticles on the Structural Organization of Ionic Liquids
(2011-12-08)
Chang, Hai-Chou
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Chang, Shu-Chieh
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Hung, Tzu-Chieh
;
Jiang, Jyh-Chiang
;
Kuo, Jer-Lai
The local structures between nano-TiO(2) and 1-ethyl-3-methylimidazolium trifluorornethanesulfonate (EMI(+)TFS(-) ) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMI(+)TES(-)) were investigated using high-pressure infrared spectroscopy. No significant changes in C-H spectral features of EMI(+)TFS(-) were observed in the presence of nano-TiO(2) under ambient pressure. As the EMI(+)TES(-)/nano-TiO(2) mixture was compressed to 0.3 GPa, the imidazolium C-H absorptions became two sharp bands at 3108 and 3168 cm(-1), respectively, and the alkyl C-H stretching absorption exhibits a new band at 3010 cm(-1) associated with a weaker band at 3028 cm(-1). It appears that pressure stabilizes the isolated conformations due to pressure-enhanced imidazolium C-H-nano-TiO(2) interactions. Our results also reveal that alkyl C-H groups play non-negligible roles at the conditions of high pressures. The results of BMI(+)TFS(-)/nano-TiO(2) are remarkably different from what is revealed for EMI(+)TFS(-)/nano-TiO(2). The spectral features and band frequencies of BMI(+)TFS(-)/nano-TiO(2) are almost identical to those of pure BMI(+)TES(-) under various pressures. This study demonstrates that changes to the alkyl chain length of the cation could be made to control the order and strength of ionic liquid/nano-TiO(2) interactions.
A High-Pressure Study of the Effects of TiO2 Nanoparticles on the Structural Organization of Ionic Liquids
(2011-12-08)
Chang, Hai-Chou
;
Chang, Shu-Chieh
;
Hung, Tzu-Chieh
;
Jiang, Jyh-Chiang
;
Kuo, Jer-Lai
The local structures between nano-TiO2 and 1-ethyl-3-methylimidazolium trifluorornethanesulfonate (EMI+TFS- ) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMI+TES-) were investigated using high-pressure infrared spectroscopy. No significant changes in C-H spectral features of EMI+TFS- were observed in the presence of nano-TiO2 under ambient pressure. As the EMI+TES-/nano-TiO2 mixture was compressed to 0.3 GPa, the imidazolium C-H absorptions became two sharp bands at 3108 and 3168 cm(-1), respectively, and the alkyl C-H stretching absorption exhibits a new band at 3010 cm(-1) associated with a weaker band at 3028 cm(-1). It appears that pressure stabilizes the isolated conformations due to pressure-enhanced imidazolium C-H-nano-TiO2 interactions. Our results also reveal that alkyl C-H groups play non-negligible roles at the conditions of high pressures. The results of BMI+TFS-/nano-TiO2 are remarkably different from what is revealed for EMI+TFS-/nano-TiO2. The spectral features and band frequencies of BMI+TFS-/nano-TiO2 are almost identical to those of pure BMI+TES- under various pressures. This study demonstrates that changes to the alkyl chain length of the cation could be made to control the order and strength of ionic liquid/nano-TiO2 interactions.
Exploration of hydrogen bond networks and potential energy surfaces of methanol clusters using a two-stage clustering algorithm
(2017)
Hsu, Po-Jen
;
Ho, Kun-Lin
;
Lin, Sheng-Hsien
;
Kuo, Jer-Lai
;
應用化學系
The potential energy surface (PES), structures and thermal properties of methanol clusters (MeOH)(n) with n = 8-15 were explored by replica-exchange molecular dynamics (REMD) simulations with an empirical model and refined using density functional theory (DFT) methods. For a given size, local minima structures were sampled from REMD trajectories and archived by a newly developed molecular database via a two-stage clustering algorithm (TSCA). Our TSCA utilizes both the topology of O-H center dot center dot center dot O hydrogen bonding networks and the similarity of the shapes to filter out duplicates. The screened molecular database contains only distinct conformers sampled from REMD and their structures are further optimized by the two DFT methods with and without dispersion correction to examine the influence of dispersion on their structures and binding energies. Inspecting different O-H center dot center dot center dot O networks, the binding energies of methanol clusters are highly degenerated. The degeneracy is more significant with the dispersion effect that introduces weaker but more complex C-H center dot center dot center dot O bonds. Based on the structures we have searched, we were able to extract general trends and these datasets can serve as a starting point for further high-level ab initio calculations to reveal the true energy landscape of methanol clusters.
Infrared spectra and anharmonic coupling of proton-bound nitrogen dimers N-2-H+-N-2, N-2-D+-N-2, and N-15(2)-H+-N-15(2) in solid para-hydrogen
(2017-08-21)
Liao, Hsin-Yi
;
Tsuge, Masashi
;
Tan, Jake A.
;
Kuo, Jer-Lai
;
Lee, Yuan-Pern
The proton-bound nitrogen dimer, N-2-H+-N-2, and its isotopologues were investigated by means of vibrational spectroscopy. These species were produced upon electron bombardment of mixtures of N-2 (or N-15(2)) and para-hydrogen (p-H-2) or normal-D-2 (n-D-2) during deposition at 3.2 K. Reduced-dimension anharmonic vibrational Schrodinger equations were constructed to account for the strong anharmonic effects in these protonated species. The fundamental lines of proton motions in N-2-H+-N-2 were observed at 715.0 (NH+N antisymmetric stretch, nu(4)), 1129.6 (NH+N bend, nu(6)), and 2352.7 (antisymmetric NN/NN stretch, nu(3)) cm(-1), in agreement with values of 763, 1144, and 2423 cm(-1) predicted with anharmonic calculations using the discrete-variable representation (DVR) method at the CCSD/aug-cc-pVDZ level. The lines at 1030.2 and 1395.5 cm(-1) were assigned to combination bands involving n nu(2) + n4 (n = 1 and 2) according to theoretical calculations; nu(2) is the N-2 ... N-2 stretching mode. For N-15(2)-H+-N-15(2) in solid p-H-2, the corresponding major lines were observed at 710.0 (nu(4)), 1016.7 (nu(2) + nu(4)), 1124.3 (nu(6)), 1384.8 (2 nu(2) + nu(4)), and 2274.9 (nu(3)) cm(-1). For N-2-D+-N-2 in solid n-D-2, the corresponding major lines were observed at 494.0 (nu(4)), 840.7 (nu(2) + nu(4)), 825.5 (nu(6)), and 2356.2 (nu(3)) cm(-1). In addition, two lines at 762.0 (weak) and 808.3 cm(-1) were tentatively assigned to be some modes of N-2-H+-N-2 perturbed or activated by a third N-2 near the proton.
Microscopic evidence for the dissociation of water molecules on cleaved GaN(1(1)over bar00)
(2018-01-14)
Wu, Shih-Yu
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Lang, Liang-Wei
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Cai, Pei-Yang
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Chen, Yun-Wen
;
Lai, Yu-Ling
The dissociation of water molecules absorbed on a cleaved non-polar GaN(1(1)over bar00) surface was studied primarily with synchrotron-based photoemission spectra and density-functional-theory calculations. The adsorbed water molecules are spontaneously dissociated into hydrogen atoms and hydroxyl groups at either 300 or 130 K, which implies a negligible activation energy (<11 meV) for the dissociation. The produced H and OH were bound to the surface nitrogen and gallium on GaN(1(1)over bar00) respectively. These results highlight the promising applications of the non-polar GaN(1(1)over bar00) surface in water dissociation and hydrogen generation.
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
;
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.