Precise analysis of extended electronic structure in organic thin films by in situ normal and inverse photoemission spectroscopies

本研究的目的是建立一个测量系统，使我们能够在同一个样品的有机薄膜的紫外光电子能谱（UPS）和逆光电子能谱（IPES）的测量精度相当，以观察在现场扩展的电子结构的能级以下和以上的状态。有机半导体薄膜作为分子电子器件的关键材料，越来越受到人们的关注，因此，尽可能直接地掌握有机半导体薄膜中的扩展电子结构是非常重要的。本研究是在利用自制装置对有机薄膜中的电子结构进行研究的基础上开始的，如用于测量价电子态的UPS和用于测量低能未占据态的BIS模式下的IPES。然后，我们设想了将两种光电子能谱结合起来的想法，并设计了一种新的装置，该装置还配备了用于制备和表征样品样品膜的仪器。同时，我们收集了有关有机薄膜的各种实验数据，以便充分利用这些数据来确定新装置的详细物理参数和技术指标;特别是对几种有机材料薄膜进行了IPES测量，以了解该方法的关键情况，因为迄今为止对有机薄膜的IPES研究报道很少。因此，我们已经研究了我们的新装置所需的实际条件，这种装置可以在一个特定的薄膜中尽可能精确地原位观察价态和未占电子态。2结果，我们几乎已经建造了这样一个装置，但有几个问题有待进一步讨论。

This research is aiming at constructing a measurement system which enables us to observe in situ extended electronic structure of the states below and above the energy gap in the same specimen of an organic thin film by means of ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) with comparable measurement precisions. Such a research was motivated by the importance of grasping the extended electronic structure in thin films of organic semiconductors in particular as directly as possible, since those films attract increasing interests as key materials toward molecular electronic devices.This research has been started on the basis of our previous studies on the electronic structures in organic thin films using our home-built apparatuses, such as a UPS one for the measurement of valence electronic states and an IPES one in the BIS mode for the measurement of low-energy unoccupied states. Then, we have conceived an idea of combination of the two kinds of photoemission spectroscopies with even better performance and have designed a new apparatus also furnished with instruments for preparation and characterization of a sample specimen films. Simultaneously, we have collected various experimental data concerning organic thin films to make good use of them for determining detailed physical parameters and specifications for the new apparatus ; especially, IPES measurements of thin films of several organic materials were carried out to know the critical situation of this method, as only a few IPES studies on organic thin films have been reported so far.Thus, we have investigated the practical conditions needed for our new apparatus which permits in situ observation of both valence and unoccupied electronic states in a particular thin film as precisely as possible.As a result, we have almost constructed such an apparatus with a few points in question open to further discussion.