單原子針離子電流的量測與分析

Abstract

本實驗藉著場離子顯微鏡，利用微通道板和法拉第杯量測單原子針所發射的離子電流，並研究提升其應用性。實驗主要分成覆銥鎢針和純銥針兩部分。 覆銥鎢針經加熱退火到870K~1070K，可在(111)皺化成頂端為單原子的金字塔。由於結構頂端為一顆原子，其產生的離子電流有較好的集中性。為了保持良好集中性同時增大電流，改變針尖半徑觀察其影響。實驗後發現，針尖半徑較大，因為表面積大，使得針尖上覆的成像氣體原子較多，容易補充離子電流所需的離子，故飽和離子電流也會提高，但是電流提升的幅度，會因為針柄傾斜角度變大而漸漸下降。 純銥針部分，可曝氧加熱到780K使(210)面皺化，形成金字塔，但皺化成單原子針尖的溫度範圍較小。若超過810K，隨溫度增高，會在(311)、(111)、(100)和(110)之間形成稜線，產生平衡晶形。除此之外，(110)在曝氧加熱下，容易出現(1×2)或(1×3)的重構，因為失蹤原子列的關係，會造成皺化金字塔結構改變，成長單原子針尖會變得比較困難。This study is about measuring ion current of single atom tip by using micro-channel plat and Faraday cap with field ion microscope and improving its application. The experiment has two parts : iridium covered tungsten tip and pure iridium tip.

For iridium covered tungsten tip, after annealing to 870K~1080K several times,(111) would facet to a pyramid structure with one-atom-top. Because there is only one atom on the top, the field ion current would befocus. In this study, we change the tip radius to investigate how to raise the field ion current per unit area.The investigationshowed that if the radius is larger, more image gas atom could adsorb the surface. It’s easier to supply with ions, so the field ion current could be larger. But the increasing range of ion current would go down because of the raise of shank angle.

For iridium tip, after covering oxygen and annealing to 780K , (210) would facet to a pyramid, but the range of annealing temperature is narrow. If the tip temperatureover 780K, the surface would become equilibrium structure which is caused crest line between (311),(111),(100) and (110).Otherwise, iridium (110) easily cause (1×2) or (1×3) restructure after annealing. Miss rowcould change the faceting pyramid structure, andlet the formation of single atom tip become more difficult.