鈀/鎢(111)和鈀/鉬/鎢(111)表面的可逆皺/平相變之研究; Mass Transport of Adsorbate During Reversible faceted/planar phase transition for Pd/W(111) and Pd/Mo/W(111)

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/7353

Title:	鈀/鎢(111)和鈀/鉬/鎢(111)表面的可逆皺/平相變之研究;Mass Transport of Adsorbate During Reversible faceted/planar phase transition for Pd/W(111) and Pd/Mo/W(111)
Authors:	高光正;Kuang-Cheng Kao
Contributors:	物理研究所
Keywords:	相變;phase transition
Date:	2003-06-17
Issue Date:	2009-09-22 10:56:05 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	在超高真空(約1 x 10-10 torr)的環境下，我們利用了可程式控溫歐傑能譜(Temperature Programmed Auger, TPA)和可程式控溫低能量電子繞射(Temperature Progammed Low Energy Electron Diffraction, TPLEED)和可程式控溫熱脫附(Temperature Progammed Desorption ,TPD), 來研究鈀(Pd)覆蓋層及鉬(Mo)中間層對於鎢(W)基版的影響，亦即Pd/W(111)和Pd/Mo/W(111)表面系統中，溫度對表面結構變化的影響。在Pd/W(111)的系統中，我們用TPLEED得到表面在高溫下的即時資訊，進而觀測到可逆的皺/平相變 : (111)?? {112}。另外由TPA中Pd的訊號,更進一步發現在產生皺/平相變的溫度下，當形成(111)平面時，沾附於表面的Pd,其厚度是會稍微減少至約1.2個物理單層(physical monolayer, PML)，但在形成皺化{112}面時，Pd的厚度會稍微提升約0.1PML。至於在Pd/Mo/W(111)的系統中，當Mo增加到1PML時，發生相變的溫度會下降約300K，同時相變的緩滯區之寬度也會減少約45K，且相變的存在會越來越不明顯，所以Pd在Mo/W(111)的行為越來越像是Pd/Mo(111)的模式。若鉬的厚度繼續增加，則發生相變的溫度也會隨之下降。 We have used Temperature Programmed Auger (TPA) and Temperature Progammed Low Energy Electron Diffraction (TPLEED) and Temperature Progammed Desorption (TPD) to study the effect of temperature on the surface structure of Pd/W(111) and Pd/Mo/W(111) in an ultrahigh vacuum (UHV) chamber with a base pressure of 1 x 10-10 torr. In Pd/W(111) surfaces, we can get the real-time information of the surface at high temperature and then observe the reversible faceted/planar phase transition. Furthermore, TPA reveals that the apparent coverage of Pd changes across the transition. When the planar (111) surface appears, the wetting layer of Pd slightly reduces to about 1.2PML (physical monolayer). Besides, the coverage of Pd slightly raises about 0.1PML in the faceted surface below the temperature of the phase transition. In the case of Pd/Mo/W(111) surfaces, when the coverage of Mo is added to about 1PML, the temperature of phase transition reduces 300K and the width of the hysteresis also reduces by 45K. In addition, the phase transition becomes less apparent. Thus, the behavior of Pd on Mo/W(111) is closer and closer to that of Pd/Mo(111) as more and more Mo is added. For even thicker Mo layers, surprisingly, the temperature (as well as its width) of the phase transition is lowered with the increased coverage of Mo.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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