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Chemical vapour deposition growth and Raman characterization of graphene layers and carbon nanotubes
(2016-01-01)
Lai, Y-C
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Rafailov, P. M.
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Vlaikova, E.
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Marinova, V.
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Lin, S. H.
Single-layer graphene films were grown by chemical vapour deposition (CVD) on Cu foil. The CVD process was complemented by plasma enhancement to grow also vertically aligned multiwalled carbon nanotubes using Ni nanoparticles as catalyst. The obtained samples were characterized by Raman spectroscopy analysis. Nature of defects in the samples and optimal growth conditions leading to achieve high quality of graphene and carbon nanotubes are discussed.
Liquid crystal cell with graphene electrodes
(2017-01-01)
Marinova, V.
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Tong, Z. F.
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Petrov, S.
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Lin, S. H.
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Chen, M. S.
We demonstrate a graphene-based nematic liquid crystal cells fabricated by photo alignment technique. The modulation characteristics have been measured revealing that photo alignment method shows great potential for protecting the graphene layer on glass substrate during LC device fabrication.
Adiabatic treatment for vibrational predissociation of water dimers with channel interactions
(2015-01-01)
Mineo, H.
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Lin, S. H.
;
Fujimura, Y.
;
應用化學系
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應用化學系分子科學碩博班
The results of calculated vibrational predissociation (VPD) of water dimers are presented. The VPD processes considered here are the followings: initially closed channel of symmetric stretching mode is excited by one quantum, and dissociate to two open channels of the bending mode excitation by one quantum in the donor and acceptor units. The VPD rate constants are calculated in the quantum mechanical approach under the adiabatic approximation. The channel interactions were taken into account in and between the initial and final states. The results obtained by quantum-mechanical approach are compared with both experimental and semi-classical trajectory calculation results.
Influence of neighboring levels in three-pulse photon-echo processes
(2009-05-01)
Villaeys, A. A.
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Dappe, Y. J.
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Liang, K. K.
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Lin, S. H.
;
應用化學系
It is the purpose of the present paper to study the dynamics underlying a three-pulse photon-echo process performed on a vibronic system coupled to non-Markovian baths, when a neighboring level enters into the global dynamical evolution because of broadband excitation required in these experiments. Particular emphasis is on the energy gap between the vibronic levels, but also on the fluctuation amplitudes and correlation times of their corresponding thermal baths. The photon-echo signal appears to be very sensitive to the additional interfering contributions introduced by the neighboring vibronic level. It is shown that these contributions associated to the pathways involving different vibronic states are modulated by their corresponding energy gap. As a consequence, these contributions to the integrated photon-echo signal strongly decrease for large energy gaps. Also, an oscillating behavior is observed on the time dependence of the photon-echo signal resulting from the summation of the contributions provided by the individual vibronic levels. Moreover, the influence of the non-Markovian character of the baths, accountable for inhomogeneous broadening, affects the amplitude and the time dependence of the photon-echo signal, as well as its dependence with the delay time of the laser pulses. Of course, for longer times a Markovian dynamical evolution is recovered.
Adiabatically slow and adiabatically fast driven ratchets
(2012-04-12)
Rozenbaum, V. M.
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Makhnovskii, Yu. A.
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Shapochkina, I. V.
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Sheu, S. -Y.
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Yang, D. -Y.
We revisit two known models of deterministically driven ratchets, which exhibit high energetic efficiency, with the goal to uncover similarities and differences in the principles of their operation. Both the models rely on adiabaticity of the potential change process, however, the adiabaticity that we deal with in the two cases is of different types, slow and fast. It is shown that in the former (latter) case the drift velocity is an even (odd) functional of the potential, with the notable consequence that for the adiabatically slow driven ratchet the necessary symmetry breaking occurs only due to time-dependent parametric perturbations, while the spatial asymmetry of the potential is a mandatory condition for the adiabatically fast driven ratchet to operate. To treat energetic characteristics, the models are restated in terms of traveling potential ratchets. With such an approach, we find that in these cases (i) the conditions of high energetic efficiency to be reached are similar, and (ii) the symmetry properties of the kinetic coefficients are different. Based on our results, a strategy for designing efficient Brownian motors is suggested.
Two-state Brownian motor driven by synchronously fluctuating unbiased forces
(2011-08-04)
Rozenbaum, V. M.
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Makhnovskii, Yu A.
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Sheu, S. -Y.
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Yang, D. -Y.
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Lin, S. H.
As a model of the Brownian motor, we consider a particle moving unidirectionally under the action of two synchronously fluctuating unbiased forces, transverse and longitudinal with respect to the particle track. The former force induces track-normal transitions of the particle between the attached and detached states (with and without a periodic potential, respectively), whereas the latter drives track-parallel motion in either state. Analytical expressions of the current and efficiency are derived for different regimes, with due account of the delayed response of the system to force fluctuations. For a sawtooth potential in the attached state, we reveal several motion regimes affording the maximum current or the maximum efficiency. A special emphasis is placed on the possibility of current reversal. As shown, the interplay between two phase-shifted harmonically varied forces as well as inherent and externally induced asymmetry can lead to the emergence of multiple current reversals, thus enabling the flexible controllability of the motion direction.
Chemical vapour deposition growth of graphene layers on metal substrates
(2014-01-01)
Lai, Y-C
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Yu, S-C
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Rafailov, P. M.
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Vlaikova, E.
;
Valkov, S.
Graphene layers were grown by chemical vapour deposition (CVD) on Si wafers covered by a SiO2 substrate layer and a Ni interlayer, and on copper and nickel foil. The obtained graphene layers were characterized by Raman spectroscopy. The films grown on SiO2/Ni substrate and Ni foil comprise mainly multilayer defect-rich graphene, while those on Cu foil exhibit the spectroscopic fingerprint of relatively defect-free single-layer graphene due to the low carbon solubility in copper and the suitably chosen substrate position in a quasi-closed volume. Optimal growth conditions and the nature of defects in the layers are discussed.
Anharmonic effect of the unimolecular dissociation of CH3COOH
(2014-11-02)
Zhang, Liwei
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Yao, Li
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Li, Qian
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Wang, Guiqiu
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Lin, S. H.
Anharmonic and harmonic rate constants of the reactions have been calculated with the Rice-Ramsperger-Kassel-Marcus theory, and the anharmonic results are higher than the harmonic ones. The anharmonic effect and isotopic effect on the decomposition reactions have also been examined. The anharmonic effect in all the four reactions is obvious, especially at the high temperatures or energies. Relatively, the anharmonic effect on the reaction trans-acetic acid -> TS2 radical is the least obvious among the four reactions. In the microcanonical system, the difference of the rate constants between the deuterated results and the non-deuterated results is not negligible; in other words, the isotopic effect is obvious in all the four reactions. Among these reactions, three of the deuterated results (d, d3 and d4) have a big difference.
Ultrafast electronic motion in hydrogen molecular ions induced by a high power intense laser
(2010-10-20)
Mineo, H.
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Teranishi, Y.
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Chao, S. D.
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Lin, S. H.
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應用化學系分子科學碩博班
In this Letter we report a method for controlling electronic localization in a molecular ion, on an attosecond time scale, using a high-intensity laser, based on two different excitation mechanisms. One takes place during ionization, and the other takes place sequentially, following ionization. The electronic excited states of the hydrogen molecular ion are created during ionization by taking the configuration interaction mixing of neutral molecules into account. We detect the ultrafast oscillatory electronic motion between two atoms in a hydrogen molecular ion occurring due to the creation of excited states during the course of ionization. (c) 2010 Elsevier B.V. All rights reserved.
Effect of the Medium on Intramolecular H-Atom Tunneling: Cis-Trans Conversion of Formic Acid in Solid Matrixes of Noble Gases
(2010-12-30)
Trakhtenberg, Leonid I.
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Fokeyev, Anatoly A.
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Zyubin, Alexander S.
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Mebel, Alexander M.
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Lin, S. H.
Intramolecular tunneling of a hydrogen atom in formic acid at low temperatures has been studied theoretically on the basis of quantum-chemical modeling of HCOOH@Nb(12) clusters. Three noble matrixes (Ar, Kr, and Xe) are considered. Energetic and geometric parameters as well as vibrational frequencies for the formic acid in cis and trans configurations surrounded by 12 Nb atoms are calculated within the frame of the MP2 approach with extended basis sets. The rate constant of HCOOH cis-trans conversion is analyzed by taking into account matrix reorganization and the change of HCOOH position in the cluster. The matrix reorganization is considered within the Debye model of lattice vibrations, whereas the external motion of HCOOH in the cluster is treated using the Einstein model of solids. It has been shown that the literature experimental data on the cis to trans tunneling reaction in the formic acid can be accounted for within the proposed mechanism, which describes the matrix reorganization and the change of the HCOOH position in the noble gas matrix, with fitting parameters of the suggested theoretical model attaining reasonable values.

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