硒化鉛量子點陣列的穿隧能譜對尺寸之相關性

Abstract

由於硒化鉛的激子波耳半徑，比其他二六族或三五族的材料還大(aB = 46 nm)，造成溶膠法所製備之硒化鉛量子點的量子局限效應更為顯著，且表現出其他材料量子點所沒有的特殊量子效應。不僅如此，硒化鉛較大的介電常數(εm = 23)，彰顯電荷的屏蔽效果，並增強電容耦合效應。在過去的許多研究報告中，已指出量子陣列系統的電性是複雜，且不容易由簡單理論來解釋。直到目前為止，文獻上對於由單顆量子點所組裝而成的二維量子陣列之尺寸效應，及量子點間的電容耦合也尚未有完整的報導。 在本實驗中，我們控制量子陣列的成長條件，使膠體硒化鉛量子點在Au(111)表面上，自組裝成不同尺寸大小的量子點陣列，並且分別在室溫及液態氮溫度，利用掃描穿隧電流顯微鏡來觀測此量子點陣列的掃描穿隧能譜。在數據分析上，我們先用雙穿隧接面模型，分析不同尺寸陣列的I-V曲線，進而得到樣品與基板的等效電容與陣列尺寸關係。從電容的緩慢遞增和飽和現象中，發現量子陣列是不能被視為單一導電島嶼，亦不能完全忽略量子點與量子點間耦合的效應。為了解是此量子點陣列的電容偶合與尺寸關係，我們將使用集體傳輸理論，試圖了解電荷經過此陣列的傳輸行為。

Interdot Coulomb interactions and collective Coulomb blockade were theoretically argued to be a newly important topic and experimentally identified in semiconductor quantum dots, formed in the gate confined two-dimensional electron gas system. The developments of the cluster science and colloidal synthesis accelerated the studies of electron transport in colloidal nanocrystal or quantum-dot solids. To study the interdot coupling, various sizes of two-dimensional arrays of colloidal PbSe quantum dots are self-assembled on flat gold surfaces for scanning tunneling microscopy and scanning tunneling spectroscopy measurements at both room and liquid-nitrogen temperatures. The tip-to-array, array-to-substrate, and interdot capacitances are evaluated and the tunneling spectra of quantum-dot arrays are analyzed by the theory of collective Coulomb blockade. The current-voltage of PbSe quantum-dot arrays conforms properly to a scaling power law function. In this study, a dependence of tunneling spectra on sizes (numbers of quantum dots) of arrays is reported and the capacitive coupling between quantum dots in the arrays is explored.