介觀狹縫中二維庫倫系統結構及微動力行為：數值模擬; Commensurability Induced Packing and Micro-dynamics in Mesoscopically Confined 2D Coulomb Systems: Numerical Simulation

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题名:	介觀狹縫中二維庫倫系統結構及微動力行為：數值模擬;Commensurability Induced Packing and Micro-dynamics in Mesoscopically Confined 2D Coulomb Systems: Numerical Simulation
作者:	劉國安;Kuo-An Liu
贡献者:	物理研究所
关键词:	軟凝體;結構;相稱性;動力學;晶體;液體;微流道;剪力;缺陷;庫倫系統;介觀;本質缺陷;侷限;晶格;奈米;soft condensed matter;structure;dynamics;liquid;crystal;micro-channel;shear;defect;Coulomb system;nano;mesoscopy;commensurability;confinement;intrinsic defect;lattice
日期:	2009-07-03
上传时间:	2009-09-22 11:00:32 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	利用分子動力學模擬，我們研究二維庫倫晶體及液體在寬度為數個粒子間距的介觀微流道中的微觀結構及運動。過去的研究指出緊密的侷限可引起層狀結構及緩慢的動力行為，然而微小的狹縫並不總是保證較整齊的結構。當系統被侷限在平直的微流道中，我們還必須考慮系統的相稱性，調整系統的粒子數可以影響微觀結構及粒子的堆疊。如果粒子數目使得系統寬度可與正常晶體相稱，系統則表現出 l 層等向三角晶格結構，其擁有固定長度的鍵結。加入額外的粒子可以破壞相稱性及產生本質缺陷。若外加的粒子無法使系統轉變成 l+1 層結構，單層中的平均粒子數則會層加，這會使得水平(平行於侷限邊界)的鍵結長度變短，及層與層的間距增加，因此不相稱的系統展現非等向結構。我們亦觀察到 l+1 層的不相稱結構，其擁有較長的水平鍵結以及較短的層間距。如果粒子總數不是層數的整數倍，粒子則無法均勻地分佈於各層，此時本質缺陷即產生。本質缺陷以斷層的形式出現，用以連結含有不同粒子數的相鄰兩層。　　除了微觀結構外，我們也探討不同型態結構中的熱效應及外加應力對微動力行為的影響。粒子在本質缺陷附近或不相稱的結構中有較差的相互連結，這使得他們較容易有結構重組及產生熱缺陷。外在剪力產生的「停滯－滑動」型態的運動及紊亂的缺陷動力學也將會被討論。 We use molecular dynamics (MD) simulation to investigate the micro-structure and motion of the 2D Coulomb crystals and liquids confined in straight mesoscopic channels about a few inter-particle distances in width. It has been reported that the tight confinement can induce layered structure associated with slow dynamics. However, the small gap does not always guarantee better ordering. The commensurability, a characteristic of system in straight confinement, has to be considered. Tuning the particle number can affect the micro-structure and packing. If the particle number makes the system width commensurate with the natural crystal, the system exhibits -layer isotropic triangular lattice in which the bond length is a constant. Adding extra particles can destroy the commensurability and generate intrinsic defects (IDs). If the extra particles cannot induce the transition to layer structure, the horizontal layers parallel to the confinement get extra particles, leading to shorter horizontal bond length and larger inter-layer spacings. Thus the incommensurate system exhibits anisotropic structure. Another incommensurate structure with layers is observed when the particle number in a layer is fewer than that in the commensurate one. IDs can be generated if the particle number is not an integer multiples of the layer number. IDs form an edge dislocation to connect two adjacent layers consisting different particle numbers. In addition to the micro-structure, we also investigate heat and stress induced micro-motions in different types of packing. The worse interlocking between particles around ID region or in incommensurate structure makes easier structural rearrangements and generates thermal defects. The stress induced stick-slip motions of IDs and particles, and the defect turbulence are also presented and discussed.
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