https://scholars.lib.ntu.edu.tw/handle/123456789/32588
標題: | 氧在鈮(111)上可逆的熔析及相關之皺化 Reversible segregation of oxygen onto Nb(111) and associated faceting |
作者: | 黃仲祥 Huang, Chung-Hsiang |
關鍵字: | 擴散;熔析;皺化;歐傑能譜;diffusion;segregation;faceting;Auger spectra | 公開日期: | 2006 | 摘要: | 吸附誘發皺化的現象是平面經由吸附物的沉積,再經過適當的退火(annealing)後,使得表面露出能量較低的面而形成遍佈不同大小的金字塔的表面。而這樣的吸附誘發皺化可以在針尖上形成單原子針尖(single atom tip)。單原子針尖可以在高解析顯微術及場發射電子源或離子源上有很好的應用潛力。而鈀(palladium)在鎢(111)表面會誘發皺化而露出能量較低的{112}面,這是被研究過並已經可以產生單原子針尖的系統。美中不足的是由於鎢的表面功函數(work function)大,造成它的場發射電流(emission current)較小。而鈮(niobium)的表面功函數較鎢來的低,同時又有超導的特性[18]。特別的是,在超導的狀態下,鈮的場發射電子能量分佈會在費米能量附近有特別大的電流密度。因此若能在鈮(111)的表面上產生皺化的現象,在各方面應用的表現上會比鎢來的理想。在我們的實驗中,我們發現氧(oxygen)在鈮(111)表面上會產生複雜的皺化現象。而且藉由可程式控溫歐傑能譜(TPA),我們及時地觀察到氧在鈮的表面隨溫度變化可逆的擴散(diffusion)進塊材內及熔析(segregation)回表面。我們也在氧化的表面鍍上鉑(Pt),發現鉑的聚散可以被氧化層隨溫度的消長所影響。而鈀在氧化的表面上較為穩定,且鈀的覆蓋對於氧擴散進塊材內的行為有顯著的影響。同時我們也嘗試了用金、鉑及鈀對鈮(111)表面引發皺化,然而到目前為止並沒有發現任何皺化的結構。 When the planar surface is covered by certain adsorbate and annealed, facets with lower surface energy will be exposed and pyramids with different size will be formed on the surface. This phenomenon is called adsorbate induced faceting. The adsorbate induced faceting can be used to fabricate single atom tip, which has applied potential for high resolution microscopy, field emission electron source, and ion source. Pd on W(111) can induce surface transition from planar(111) to faceting{112}, which has been researched a lot in our laboratory. However, since the work function of W is large, the emission current of W tip is small. On one hand the work function of Nb (4.87eV) is lower than that of W (5.25eV) [11], and on the other Nb is one of superconductive materials [18]. In superconducting state, the electron intensity of field emission energy distribution has an extra peak near the Fermi level. Thus, if the faceting of Nb(111) can be induced. The performance of single atom Nb tip will be better than W tip in many applications. In our experiments, we found that oxygen can induce complex faceting on Nb(111). Moreover, by Temperature Programmed Auger (TPA), we can trace real-time reversible diffusion and segregation of oxygen with temperature variation. We also deposited Pt on oxidized surface and found that aggregation or wetting of Pt would depend on the variation of oxide. Pd is more stable than Pt on oxidized surface, and the coverage of Pd has significant effect on diffusion of oxygen. We also tried Au, Pt, and Pd to induced Nb faceting, but we haven’t observed any faceting structure in these systems so far. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/54641 | 其他識別: | en-US |
顯示於: | 物理學系 |
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ntu-95-R93222047-1.pdf | 23.53 kB | Adobe PDF | 檢視/開啟 |
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