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

本研究旨在构建一种测量系统，使我们能够利用紫外光电子能谱(UPS)和逆光电子能谱(IPES)在测量精度相当的情况下，原位观察有机薄膜带隙以下和带隙以上的扩展电子结构。这项研究的动机是尽可能直接地掌握有机半导体薄膜中的扩展电子结构，因为这些薄膜作为分子电子器件的关键材料越来越引起人们的兴趣。本研究是在我们之前使用自制的UPS电子状态测量仪和IPES电子能谱测量低能空态的仪器对有机薄膜电子结构研究的基础上开始的。然后，我们构思了将两种性能更好的光电子能谱相结合的想法，并设计了一种新的装置，还配备了样品薄膜的制备和表征仪器。同时，我们收集了各种关于有机薄膜的实验数据，以便更好地利用它们来确定新装置的详细物理参数和规格；特别是对几种有机材料的薄膜进行了IPES测量，以了解该方法的关键情况，因为到目前为止关于有机薄膜的IPES研究还很少。因此，我们研究了我们的新装置所需的实际条件，以便尽可能准确地原位观察特定薄膜中的价态和未占据电子态。因此，我们几乎构建了这样一种装置，其中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.