披覆不同貴金屬對單原子針發射電子束的研究

Abstract

單原子針可應用在同調繞射電子顯微鏡。本研究針對鋪覆金、銥、鉑、銠、鈀五種貴金屬單原子針的場發射電子電流的大小及電流穩定性進行比較研究發現，以覆銥鎢針的場發射電流最大。在外加負高壓下可測量到超過1nA的電子電流，在1nA的電子電流下做電流對時間的穩定測量，其不穩定性大約10%；在1nA以下的電流不穩定性皆低於1%。 以覆銥鎢針場發電流大且穩定的優點，最適合進一步應用使用。 從Fowler-Nordheim分析中討論場發射特性，雖然覆鉑鎢針Fowler-Nordheim plot的斜率較小，但其場發射電流小且不穩定，在目前狀況下不適合往後的實驗研究中使用。本實驗也針對鋪覆貴金屬鎢針做照射綠光雷射的探討，初步結果顯示照射雷射並不會使場發射電流更大或更穩定。The single-atom tip is a good candidate for coherence diffraction electron microscope. This research compared the field emission electron current, and current stability of noble metals deposition on single-atom tips, specifically those of gold (Au), iridium (Ir), platinum (Pt), rhodium (Rh), and palladium (Pd). At negative high voltage, the field emission current of Ir deposited W tip was the largest. The current instability is about 10% with emission current of over 1nA; below 1nA the instability was less than 1%. In the presence of Ir deposits, the slope of Fowler-Nordheim plot was noticeably reduced. Furthermore, its emission current was large and stable, which promotes its suitability for further application. Based on the Fowler-Nordheim analysis, the Pt-deposited W tip had the gentler slope. Due to its small and unstable field emission current, it is not suitable for use in future experimental studies. This research also investigated the effect of laser on single-atom tips with different noble metal deposits. Initial result showed that irradiation did not make the field emission current larger or more stable.