溫度與吸附氣體對鈮針場發射特性的影響
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2014
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Abstract
鈮奈米針於先前的研究指出當鈮在9.2K時具有超導性，在此溫度下將其作為一電子源所發射出來的電子束會因為其超導的關係同時具有良好的空間同調性及時間同調性。因此鈮針在當成電子源的研究也具有其重要性。為了更深入了解鈮奈米針的特性及結構，我們將多晶鈮線蝕刻成針尖後置入超高真空環境的場離子顯微鏡，藉由通電流加熱使其形成熱穩定性的奈米針並同時觀察針間的皺化過程，在鈮針尖施加負高壓使針尖場發射出電子，並分析其電子電流的特性。
當鈮針被加熱到1319K時，可以在表面上觀察到4個{310}擴張擠壓{100}面形成皺化的平台，此時在針尖施加負高壓可以觀察到{100}平台由於功函數較低會場發射出電子。而當針尖加熱超1473K時，可以看到{100}面也有擴張的趨勢產生，此時並不會場發射出電子。
測量{100}面時通入不一樣的惰性氣體的場發射電流，經過量測一小時後的電流值會大於一開始所測量到的電流值。而通入氬氣時，一小時後的電流增加幅度比其於氣體小，通入越大分子量的惰性氣體其F-N plots斜率會上升。
Niobium(Nb) tips play an important role in scientific research of electron source. According to the precious study, electron beams field-emitted from Nb tips at 9.2K of good spatial and temporal coherence due to superconductivity of the tips. To investigate the structure and properties of Nb tips, we fabricated Nb tips by electrochemical process, followed by annealing the tips in ultra-high-vaccum(UHV) environment, to obtain thermally stable Nb nano-tips. The faceting process when annealing the tips were observed in field-ion microscope. Field-emission currents of Nb tips under different temperatures and various inert gases were recorded and discussed. We recorded the field-ion microscopy (FIM) images to observed the faceting process when annealing Nb tips. When the annealing temperature raised to 1319K, {100} plane formed at tip and due to the expansion of four surrounded {311} planes. If a negative bias was applied on the tip electron beam field-emitted from {100} plane, which has the lowest field emission work function can be observed. Field-emission currents under various inert gases environment were discussed. Small currents were obtained in the beginning of exposing tips under inert gas environment, but the currents gradually increased with time . Increasing values of the current and F-N plots under different gases environments were shown and discussed in this study.
Niobium(Nb) tips play an important role in scientific research of electron source. According to the precious study, electron beams field-emitted from Nb tips at 9.2K of good spatial and temporal coherence due to superconductivity of the tips. To investigate the structure and properties of Nb tips, we fabricated Nb tips by electrochemical process, followed by annealing the tips in ultra-high-vaccum(UHV) environment, to obtain thermally stable Nb nano-tips. The faceting process when annealing the tips were observed in field-ion microscope. Field-emission currents of Nb tips under different temperatures and various inert gases were recorded and discussed. We recorded the field-ion microscopy (FIM) images to observed the faceting process when annealing Nb tips. When the annealing temperature raised to 1319K, {100} plane formed at tip and due to the expansion of four surrounded {311} planes. If a negative bias was applied on the tip electron beam field-emitted from {100} plane, which has the lowest field emission work function can be observed. Field-emission currents under various inert gases environment were discussed. Small currents were obtained in the beginning of exposing tips under inert gas environment, but the currents gradually increased with time . Increasing values of the current and F-N plots under different gases environments were shown and discussed in this study.
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Keywords
鈮針, 場離子顯微鏡, 場發射, 功函數, Niobium tip, field-ion microscopy, Field-emission, work function