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

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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.