Single-dot tunneling spectroscopy of CdSe colloidal nano-dot by atomic force microscopy

近年来，高度单分散的胶体半导体纳米点因其独特的光学性质而受到广泛关注。我们一直感兴趣的胶体纳米点的电子特性，因为他们似乎是重要的，以解释光学。特别是，界面能态可能与非线性光学性质，如点的光学记忆效应相关。因此，研究胶体纳米点的电流-电压（I-V）特性对于利用隧穿光谱揭示胶体纳米点的能级结构具有重要意义。(AFM)我们已经表明，电流-电压特性的单个CdSe胶体纳米点，即使在室温下测量导电针尖原子力显微镜。然而，我们发现用接触式原子力显微镜测得的点高度远小于平均直径。 关于我们 根据光学吸收测量估计的点的亮度。我们推测，当金属涂层的硅尖端接触接触模式AFM测量时，点稍微改变了它们的位置。这种位置波动可能是由于针尖与样品之间存在较大的毛细作用力，使我们无法准确测量点的高度和通过点的电流。因此，我们采用导电碳纳米管（CNT）针尖用于CdSe胶体纳米点的导电针尖AFM，并发现CNT针尖和样品之间的毛细力减小到金属涂覆的Si针尖的大约三十分之一，并且点高度测量的精度大大提高。结果表明，在室温下获得了单个胶体纳米点的I-V特性，而不需要额外的点锚定过程，这是所需的金属涂层硅尖。在I-V曲线中，观察到明显的电导变化，这表明电子在纳米点中发生了共振隧穿。此外，为了在导电针尖AFM测量过程中稳定纳米点的位置，研究了由胶体纳米点组成的二维岛的形成。在云母衬底上蒸镀的Au（111）薄膜上，采用水平剥离法制备了单点高度的胶体纳米点薄膜，并通过接触式原子力显微镜证实了100 nm尺度的二维纳米点岛的存在。将对这些岛进行I-V测量。少

Recently, highly monodisperse colloidal semiconductor nano-dots have been attracting much attention since they exhibit unique optical properties. We have been interested in the electronic properties of colloidal nano-dots since they seem to be important to explain optical ones. In particular, the interface energy states are likely correlated with non-linear optical properties such as optical memory effect of the dots. It is therefore important to investigate the current-voltage (I-V) characteristics of the colloidal nano-dots in order to reveal the energy levels of the dots by tunneling spectroscopy.For the study of the electron transport through single CdSe colloidal nanodots, we have employed conductive-tip atomic force microscopy. (AFM) We have shown that current-voltage characteristics of single CdSe colloidal nanodot were measured even at room temperature by conductive-tip AFM. However, we found that the measured dot heights by contact-mode AFM were much smaller than the average d … More iameter of the dots estimated from optical absorption measurement. We speculated that the dots slightly changed their positions when the metal-coated Si tips came in contact for contact-mode AFM measurements. This position fluctuation seemed to be caused by the large capillary force between the tip and sample, and prevents us from accurate measurement of the dot height and the current through the dot.We therefore adopted conductive carbon nano-tube(CNT) tips for conductive-tip AFM of CdSe colloidal nano-dots, and found that the capillary force between the CNT tip and sample is reduced to be about one thirtieth of that for the metal-coated Si tips, and that the dot height measurement is much improved in accuracy. As a result, I-V characteristics of single colloidal nano-dots have been obtained at room temperature without extra dot anchoring process which was required for metal-coated Si tips. In the I-V curves, clear conductance changes were observed which suggested resonant electron tunneling through the nano-dot.Also, the formation of two-dimensional islands consist of colloidal nano-dots was investigated in order to stabilize the dot position during conductive-tip AFM measurements. We fabricated single-dot height films of the colloidal nano-dots by horizontal lift-off process on Au (111) films evaporated on mica substrates, and confirmed the existence of 100-nm-scale two-dimensional islands of the dots by contact-mode AFM. I-V measurements of these islands will be performed. Less