微粒電漿液體的淬火行為; Quenching dusty plasma liquids

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题名:	微粒電漿液體的淬火行為;Quenching dusty plasma liquids
作者:	蘇彥碩;Yen-Shuo Su
贡献者:	物理研究所
关键词:	液體;淬火;微粒電漿;玻璃態;dusty plasma liquid;quench;glass
日期:	2010-07-28
上传时间:	2010-12-08 14:24:00 (UTC+8)
出版者:	國立中央大學
摘要:	快速冷卻可使液體在低於熔點溫度下維持其不規則結構，此為一典型將液體轉換至玻璃態之方法。玻璃為一在典型觀察尺度下具備固體性質(彈性反應)，卻在極端長的觀察時間下顯現出液體行為(塑性流動)的型態。為何快速冷卻可防止物質結晶化和為何玻璃在不同觀測時間尺度下能顯露出如此不同的性質為一尚未完全解決的議題。研究在微觀液體淬火下之暫態過程為一深入理解玻璃態形成之物理起源的方法。然而由於原子的特徵時空間尺度過小且過快，直接觀察物質微觀淬火過程仍然是實驗上的一大挑戰。微粒電漿液體是藉由帶負電之微米尺度粉塵微粒懸浮在低壓弱游離氣體下所構成，其時空間特徵尺度使其可類比真實液體並藉此在動態尺度下研究其微運動。空間上，藉由背景熱擾動，微粒可顯現出不同的動態行為，侷限運動及跳躍運動。近來研究指出侷限運動及跳躍運動的異質性為一接近玻璃態時之普遍性法則。在微粒電漿系統中，藉由調動射頻游離能量能瞬間降低背景熱擾動，稱作淬火。在這篇論文中，我們研究微粒電漿液體在淬火後的暫態反應。淬火後，雖然熱擾動瞬間降低，不規則結構仍能保有形變位能，藉由釋放形變位能所引發的跳躍運動可形成小尺度之規則結構。小尺度規則結構可逐漸合併成大尺度的規則結構並保有較長的空間相關性和結構重整時間，亦增加動態異質性。藉由相鄰規則結構之間的錯位可防止系統結晶化並造成規則結構邊界上的不穩定現象亦被探討。 Fast cooling can make liquids maintain its disordered structure even below the melting temperature. It is a way to turn liquids into the glassy state. In general, the glass is the system which has solid-like behaviors (elastic response) for our typical observation time scale and liquid-like behaviors (plastic flow) for extremely long observation time. Why the fast cooling rate can prevent material crystallizing, and why the glass can exhibit so distinct properties at different observation time scales are old puzzles and an open issue. In order to answer these questions, studying the transient process of the quenched liquid microscopically may be a way to deeply understand the origin of glassy systems. However to directly observe this quenching process microscopically is still a challenge due to the spatiotemporal scale (too small and too fast). The dusty plasma liquid is formed by the negatively charged micro-meter size dust particles suspended in low pressure gaseous discharge. The spatiotemporal characteristic scale makes it possible to mimic the real liquid and investigate the micro-motion of the liquid at kinetic level. Spatially, the particles could exhibit distinct dynamics, caged and hopping motion, due to the background excitation. Recently, the increase of the degree of heterogeneity between caged and hopping motion is considered as a universal law near the glass transition. In the dusty plasma system, the rf discharge power can be tuned to decrease background temperature instantaneously, namely quenching. In this work the transient process after quenching is presented. Although the thermal agitation decreases suddenly, the local strain cannot be released at the same time. It can induce the hopping motion associated with structural arrangement which in term to release local strain energy and forming more ordered structure. The small size ordered domains gradually merge into larger ordered domain with longer spatial correlation and slower structural reorganization. The forming of larger ordered domain also increase the dynamic heterogeneity. However the dislocations between different ordered domains prevent the crystallization and make boundary of ordered domain unstable. The character of order parameter fluctuation due to instability of local domain boundary is presented and discussed.
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