覆鈀、銥於鉬針形成金字塔單原子針尖之研究

Abstract

本實驗利用場離子顯微鏡觀察純鉬針與鈀、銥蒸鍍於鉬針上加熱退火後的皺化行為，利用不同的加熱退火溫度觀察鉬{111}面的皺化。在純鉬實驗中發現，加熱退火溫度在800℃以上時，三個{211}往{111}擴張形成金字塔結構，其每層原子數分別為3、10、21顆，並未形成單原子針尖。而在覆鈀於鉬針的實驗中，在低溫即可觀察到{211}面劇烈擴張，並在加熱退火至700~900℃時，觀察到{211}面取代{111}形成兩種類型的結構，分別為1、3、10及1、6、15堆疊之金字塔單原子針尖。此外，在覆銥於鉬針的實驗中，由於銥和鉬容易形成合金，無法形成單原子針尖。 最後，本實驗亦研究純鉬系統其它切面的皺化行為，發現{110}、{211}、{210}切面在{741}面形成奈米針尖；{211}、{210}、{311}切面在{732}面組成奈米針尖；{310}、{210}、{311}切面在{831}面組成奈米針尖；兩個{211}和{110}切面在{221}面組成奈米針尖。

The effect of annealing temperature on the faceting phenomena has been studied for pure Mo、Pd-covered and Ir-covered Mo tips by field ion microscopy. For pure Mo samples, three {211} faces were found to expand to {111} facet and form pyramidal structure after annealing at the temperature of 800℃. The number of atoms forming three top layers of the pyramid amounts to 3, 10 and 21, respectively. This indicates that there is no possibility to obtain Mo single atom tips. In contrast, for the Pd/Mo systems, the expansion of the {211} facets was observed at the annealing temperature of 700~900℃, as a result, the {111} surface were replaced by {211} facets and form two types of pyramidal structure with the number of atoms constituting their three top layers of 1, 3 and 10 or 1, 6 and 15, respectively. Additionally, for the Ir/Mo systems, because Ir is easy to alloy with Mo, we did not obtain single atom tips. Finally, we also studied the faceting phenomena for the other faces of pure Mo. In this system, we observed that it could form four nano tips, one grown upon {741} consisted of {110},{211} and {210} facets, one grown upon {732} consisted of {211},{210} and {311} facets, another grown upon {831} consisted of {310},{210} and {311} facets, the other grown upon {221} consisted of {211} and {110} facets.