Islam Mohammad A
Department of Physics, American University of Sharjah, Sharjah, UAE. Columbia Center for Nanostructured Materials, Columbia University, New York, NY, USA.
Nanotechnology. 2008 Jun 25;19(25):255708. doi: 10.1088/0957-4484/19/25/255708. Epub 2008 May 15.
The nanocrystal quantum dot (NQD) charge states strongly influence their electrical transport properties in photovoltaic and electroluminescent devices, optical gains in NQD lasers, and the stability of the dots in thin films. We report a unique electrostatic nature of CdSe NQDs, studied by electrophoretic methods. When we submerged a pair of metal electrodes, in a parallel plate capacitor configuration, into a dilute solution of CdSe NQDs in hexane, and applied a DC voltage across the pair, thin films of CdSe NQDs were deposited on both the positive and the negative electrodes. Extensive characterizations including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman studies revealed that the films on both the positive and the negative electrodes were identical in every respect, clearly indicating that: (1) a fraction (<1%) of the CdSe NQDs in free form in hexane solution are charged and, more importantly, (2) there are equal numbers of positive and negative CdSe NQDs in the hexane solution. Experiments also show that the number of deposited dots is at least an order of magnitude higher than the number of initially charged dots, indicating regeneration. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of the CdSe NQDs.
纳米晶体量子点（NQD）的电荷状态强烈影响其在光伏和电致发光器件中的电输运特性、NQD激光器中的光学增益以及薄膜中量子点的稳定性。我们报道了通过电泳方法研究的CdSe量子点独特的静电性质。当我们将一对呈平行板电容器配置的金属电极浸没在己烷中CdSe量子点的稀溶液中，并在这对电极上施加直流电压时，CdSe量子点薄膜沉积在正负极上。包括扫描电子显微镜（SEM）、原子力显微镜（AFM）、傅里叶变换红外（FTIR）和拉曼研究在内的广泛表征表明，正负极上的薄膜在各方面都是相同的，这清楚地表明：（1）己烷溶液中呈自由形式的CdSe量子点中有一小部分（<1%）带电，更重要的是，（2）己烷溶液中带正电和带负电的CdSe量子点数量相等。实验还表明，沉积的量子点数量比初始带电量子点的数量至少高一个数量级，这表明存在再生现象。我们用简单的热力学来解释CdSe量子点的这种两性性质以及充电/再生过程。
