利用介電泳法組裝硒化鉛量子點陣列及其電性研究

Abstract

本實驗是利用介電泳的技術，外加交流電壓於電極兩端，在溶液中的硒化鉛奈米顆粒會往電極兩端電場強度高的地方移動。介電泳實驗中去調整頻率、電壓、時間、濃度和電極間隙這些參數，使硒化鉛量子點組裝在電極間隙中，形成不同的量子點陣列，從實驗結果可得到組裝硒化鉛量子點所需要的電壓與電極間隙是一正相關的趨勢。將製作完成的硒化鉛量子點陣列元件，在不同的溫度下，量測其電流—電壓特性，低溫下觀察到有庫倫阻斷的現象產生，當電壓大於截止電壓藉時，電流呈現指數上升，由Middleton和Wigreen提出的理論， I~(V/Vth-1)^ζ，ζ＝1、5/3或2(數值模擬得到)對於在1維、2維系統，其意義是代表著電流路徑數目的多寡，可解釋集體電荷傳輸的行為。對於四組樣品所得到的ζ其範圍2.19–3.67。從實驗電流—電壓圖形也能得到，截止電壓與溫度的關係圖是呈現線性關係，根據Klara Elteto等人提出截止電壓對溫度的關係式，隨著溫度的下降，截止電壓會增加，將式子與實驗的圖形做比較，可求出量子點電容的平均值為2.45 aF。

Suspensions of PbSe nanocrystals (NCs) in liquid is assembled by dielectrophoresis (DEP) which is an action of an alternating voltage to drive dielectric fine particles into nanogaps. Under DEP reaction, the PbSe NCs move towards stronger electric field region. In this experiment, we try to control the assembly of nanocrystals through the voltage, frequency, time, NC concentration, and the nanogap width. By tuning the DEP parameters, PbSe QDs are assembled to form different QD arrays. We found that the optimum voltage for PbSe QD assembly is proportional to the gap distance. In addition, we obtained the current-voltage (I-V) characteristics as a function of temperature for our PbSe QD-array nanodevices. The Coulomb blockade phenomena were discovered at low temperature. Furthermore, as the voltage is larger than threshold voltage (Vth), the current follows the power law of (V/Vth-1)^ζ, which agrees with the model of collective charge transport proposed by Middleton and Wingreen (MW), where ζ is a scaling exponent depending on dimensionality of arrays. We estimated the values of ζ from our I-V curves and the scaling exponents ζ range from 2.19 to 3.67. On the other hand, Klara Elteto et al. proposed a model to explain the temperature dependences of threshold voltage. In our experiments, the estimated threshold voltage is inversely proportional to temperature which is in good agreement with the theoretical arguments.Self-capatance has been evaluated to be about 2.45 aF.