Studies on Electronic Structures of Molecularly Doped
Polymer: Measurement of Charge Transfer Force

Taishi Shigematsu	Corporate Research Center, Advanced Research Lab.
Chikara Manabe	Corporate Research Center, Advanced Research Lab.
Hiroyuki Watanabe	Corporate Research Center, Advanced Research Lab.
Masaaki Shimizu	Corporate Research Center, Advanced Research Lab.

Abstract

We have proposed a new method of electron spectroscopy which is measuring charge transfer force between a sample and a metal by atomic force microscopy. Our method can investigate the occupied and unoccupied states simultaneously even in dry nitrogen atmosphere. Accordingly, the method allows us to measure the electronic structure of molecularly doped polymer which can not be measured by previous methods. We have applied this new method to a typical molecularly doped polymer system (Polycarbonate and N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (TPD)) to elucidate the electronic structure of the system. The measurement results obtained show that the energy gap continuously decreases with increasing the TPD concentration. The continuous change in the gap can be explained by polaronic transfer integral. Furthermore, we have applied this new method to typical polymers (Polycarbonate and Poly(methyl Methacrylate)) to elucidate the electronic structure of the charge injected polymers. The energy gap of Polycarbonate is estimated to be ~5eV. This value is in agreement with the optical gap of Polycarbonate (~4.4eV). On the other hand, in the Poly(methyl Methacrylate) case, the energy gap is ~2eV which is smaller than the optical gap (~4.3eV). Finally, we have discussed the behavior of the energy gaps in connection with the stabilization energy of injected charge. The stabilization would be caused by the polymer conformation change.

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