Browsing by Author "Wu, Shang-Ying"

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Ab Initio Chemical Kinetics for Reactions of H Atoms with SiHx (x=1-3) Radicals and Related Unimolecular Decomposition Processes
(2013-06-15)
Raghunath, Putikam
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Lee, Yun-Min
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Wu, Shang-Ying
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Wu, Jong-Shinn
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Lin, Ming-Chang
Hydrogen atoms and SiHx (x = 1-3) radicals coexist during the chemical vapor deposition (CVD) of hydrogenated amorphous silicon (a-Si: H) thin films for Si-solar cell fabrication, a technology necessitated recently by the need for energy and material conservation. The kinetics and mechanisms for H-atom reactions with SiHx radicals and the thermal decomposition of their intermediates have been investigated by using a high high-level ab initio molecular-orbital CCSD (Coupled Cluster with Single and Double)(T)/CBS (complete basis set extrapolation) method. These reactions occurring primarily by association producing excited intermediates, (SiH2)-Si-1, (SiH2)-Si-3, SiH3, and SiH4, with no intrinsic barriers were computed to have 75.6, 55.0, 68.5, and 90.2 kcal/mol association energies for x = 1-3, respectively, based on the computed heats of formation of these radicals. The excited intermediates can further fragment by H-2 elimination with 62.5, 44.3, 47.5, and 56.7 kcal/mol barriers giving Si-1, Si-3, SiH, and (SiH2)-Si-1 from the above respective intermediates. The predicted heats of reaction and enthalpies of formation of the radicals at 0 K, including the latter evaluated by the isodesmic reactions, SiHx + CH4 SiH4 + CHx, are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and unimolecular reactions have been predicted with tunneling corrections using transition state theory (for direct abstraction) and variational Rice-Ramsperger-Kassel-Marcus theory (for association/decomposition) by solving the master equation covering the P, T-conditions commonly employed used in industrial CVD processes. The predicted results compare well experimental and/or computational data available in the literature. (C) 2013 Wiley Periodicals, Inc.
Ab Initio Chemical Kinetics for the Unimolecular Decomposition of Si2H5 Radical and Related Reverse Bimolecular Reactions
(2014-02-15)
Wu, Shang-Ying
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Lee, Yun-Min
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Wu, Jong-Shinn
;
Lin, Ming-Chang
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機械工程學系
For plasma enhanced and catalytic chemical vapor deposition (PECVD and Cat-CVD) processes using small silanes as precursors, disilanyl radical (Si2H5) is a potential reactive intermediate involved in various chemical reactions. For modeling and optimization of homogeneous a-Si:H film growth on large-area substrates, we have investigated the kinetics and mechanisms for the thermal decomposition of Si2H5 producing smaller silicon hydrides including SiH, SiH2, SiH3, and Si2H4, and the related reverse reactions involving these species by using ab initio molecular-orbital calculations. The results show that the lowest energy path is the production of SiH+SiH4 that proceeds via a transition state with a barrier of 33.4 kcal/mol relative to Si2H5. Additionally, the dissociation energies for breaking the SiSi and HSiH2 bonds were predicted to be 53.4 and 61.4 kcal/mol, respectively. To validate the predicted enthalpies of reaction, we have evaluated the enthalpies of formation for SiH, SiH2, HSiSiH2, and Si2H4(C-2h) at 0 K by using the isodesmic reactions, such as (HSiSiH2)-H-2+(C2H6Si2H6)-C-1-Si-1+(HCCH2)-H-2 and (Si2H4)-Si-1(C-2h)+(C2H6)-C-1 (Si2H6)-Si-1+(C2H4)-C-1. The results of SiH (87.2 kcal/mol), SiH2 (64.9 kcal/mol), HSiSiH2 (98.0 kcal/mol), and Si2H4 (68.9 kcal/mol) agree reasonably well previous published data. Furthermore, the rate constants for the decomposition of Si2H5 and the related bimolecular reverse reactions have been predicted and tabulated for different T, P-conditions with variational Rice-Ramsperger-Kassel-Marcus (RRKM) theory by solving the master equation. The result indicates that the formation of SiH+SiH4 product pair is most favored in the decomposition as well as in the bimolecular reactions of SiH2+SiH3, HSiSiH2+H-2, and Si2H4(C-2h)+H under T, P-conditions typically used in PECVD and Cat-CVD. (c) 2013 Wiley Periodicals, Inc.
Laser dynamics and relative timing jitter analysis of passively synchronized Er- and Yb-doped mode-locked fiber lasers
(2014-07-01)
Wu, Shang-Ying
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Hsiang, Wei-Wei
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Lai, Yinchieh
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光電工程學系
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Department of Photonics
Passively synchronized Er-doped and Yb-doped mode-locked fiber lasers with a master-slave configuration are theoretically investigated based on the pulse propagation model for simulating pulse collision in the common fiber section and on the master equation model for simulating laser dynamics. Computational results indicate that the central optical frequency of the slave Er laser will be shifted by the significant cross phase modulation (XPM) effect for the laser to become synchronized with the injected master Yb laser pulse train. Pulse duration change caused by fiber dispersion in the common fiber section will distort the ideal anti-symmetric characteristics of the XPM-induced frequency shift versus the relative timing position of the two color pulses. The relative timing jitter noises of the two synchronized lasers can be minimized by adjusting the relative pulse timing position, and the predicted dependence agrees well with the experimental observation. (C) 2014 Optical Society of America
Laser dynamics and relative timing jitter analysis of passively synchronized Er- and Yb-doped mode-locked fiber lasers
(2014-07-01)
Wu, Shang-Ying
;
Hsiang, Wei-Wei
;
Lai, Yinchieh
;
光電工程學系
;
光電工程研究所
Passively synchronized Er-doped and Yb-doped mode-locked fiber lasers with a master-slave configuration are theoretically investigated based on the pulse propagation model for simulating pulse collision in the common fiber section and on the master equation model for simulating laser dynamics. Computational results indicate that the central optical frequency of the slave Er laser will be shifted by the significant cross phase modulation (XPM) effect for the laser to become synchronized with the injected master Yb laser pulse train. Pulse duration change caused by fiber dispersion in the common fiber section will distort the ideal anti-symmetric characteristics of the XPM-induced frequency shift versus the relative timing position of the two color pulses. The relative timing jitter noises of the two synchronized lasers can be minimized by adjusting the relative pulse timing position, and the predicted dependence agrees well with the experimental observation. (C) 2014 Optical Society of America
Relative carrier-envelope phase stabilization of hybridly synchronized ultrafast Yb and Er fiber-laser systems with the feed-forward scheme
(2015-03-15)
Fong, Bo-Jyun
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Lin, Wei-Ting
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Wu, Shang-Ying
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Peng, Jin-Long
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Hsiang, Wei-Wei
Stabilization of the relative carrier-envelope (CE) phase for hybridly synchronized two-color fs Yb and Er fiber-laser systems is demonstrated for the first time by utilizing the feed-forward scheme based on an acousto-optic frequency shifter. The slow drift issues arising from the feed-forward scheme are solved by adding the in-loop relative CE frequency coarse stabilization via modulating the laser pump current. Sub-fs timing locking between the two-color pulses is still maintained due to the fast response and large locking range of hybrid synchronization. The approach provides an alternative way to obtain phase-stable synchronized two-color pulses with higher pulse energies. (C) 2015 Optical Society of America
Relative Timing Jitter of Passively Synchronized Er-doped and Yb-doped Mode-Locked Fiber Lasers
(2013)
Wu, Shang-Ying
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Hsiang, Wei-Wei
;
Lai, Yinchieh
;
光電工程學系
;
Department of Photonics
The relative timing jitter of passively synchronized Er-doped and Yb-doped mode-locked fiber lasers is investigated. The predicted dependence on the relative timing position of the two-color pulses agrees nicely with the experimental observation.
Stabilizing the relative carrier-envelop phase of hybridly synchronized ultrafast Yb and Er fiber laser systems by the feed-forward scheme
(2015)
Hsiang, Wei-Wei
;
Fong, Bo-Jyun
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Lin, Wei-Ting
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Wu, Shang-Ying
;
Peng, Jin-Long
Stabilization of the relative carrier-envelope (CE) phase for hybridly synchronized two-color fs Yb and Er fiber laser systems is demonstrated for the first time by utilizing the feed-forward scheme based on an acousto-optic frequency shifter.
Subfemtosecond hybrid synchronization between ultrafast Yb and Er fiber laser systems by controlling the relative injection timing
(2013-09-01)
Tsai, Bo-Wei
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Wu, Shang-Ying
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Hu, Chieh
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Hsiang, Wei-Wei
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Lai, Yinchieh
We report experimental as well as theoretical investigation of the key factors that influence the relative timing jitter between hybrid synchronized ultrafast Yb and Er fiber laser systems. Experimental results show that, within the achievable synchronization range, the synchronization performance varies significantly with the relative injection timing between the 1 mu m master and 1.5 mu m slave pulses. This observation is in agreement with the insights obtained from the theoretical analysis, which identifies the retiming effect as a function of the initial condition of the master-slave pulse collision. By controlling the relative injection timing with a low-bandwidth intracavity feedback, relative timing jitter as low as 0.87 fs (within 1.9 MHz bandwidth) is successfully obtained. (C) 2013 Optical Society of America
Subfemtosecond Synchronization between Yb-fiber and Er-fiber Lasers by Controlling the Relative Injection Timing
(2013-01-01)
Hsiang, Wei-Wei
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Tsai, Bo-Wei
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Hu, Chieh
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Wu, Shang-Ying
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Lai, Yinchieh
The relative timing between the injection and slave pulses is found to be the key factor to achieve sub-fs timing jitter (0.87 fs, 1.9 MHz bandwidth) between Yb-fiber and Er-fiber fs lasers with hybrid synchronization.
Synchronous-asynchronous laser mode-locking transition
(2015-07-27)
Wu, Shang-Ying
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Hsiang, Wei-Wei
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Lai, Yinchieh
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光電工程學系
;
光電工程研究所
Synchronous-asynchronous mode-locking transition in a hybrid active and passive mode-locked laser is investigated theoretically. Three distinct mode-locking states are found and their transition diagram under varying detuning frequency and modulation strength is determined. By examining the steady-state lasing gain as a function of the detuning modulation frequency, we also clarify why the laser will become unstable near the transition points and why the nonlinear saturable absorption effect is crucial for the stable asynchronous mode-locking operation.