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O: Fachverband Oberflächenphysik

O 70: Invited talk (Nobuo Ueno)

O 70.1: Hauptvortrag

Donnerstag, 29. März 2012, 15:00–15:45, HE 101

First-principles experiment on electrical conductivity of organic devices with UPS: Charge delocalization, vibration coupling and band-gap states — •Nobuo Ueno — Graduate School of Advanced Integration Science, Chiba University, Chiba, Japan

We will discuss following two topics, which are related to quantum mechanical/chemical studies of electrical conductivity in organic devices, by using UV photoelectron spectroscopy (UPS):

(i) Energy band dispersion, electron-phonon coupling and polaron.

(ii) Direct detection of very low density of electronic states in organic HOMO-LUMO gap.

As the electrical conductivity (σ) is given by σ=neµ, where n is the carrier concentration and e the charge and µ the charge mobility, the topic (i) is a direct experimental study of µ in molecular aggregates and in a molecule based on energy and momentum conservation rules, and the topic (ii) is related to study n, since n is related to the energy level alignment/the Fermi level position that must be controlled by unknown and undetectable electronic states in organic HOMO-LUMO gaps. The topic (ii) is thus related to elucidation of a well-known mystery; why do the transport types appear depending on molecules without impurity doping? In other words why does the Fermi level move in HOMO-LUMO gap? The mystery might be originated from a primary deference between organic semiconductors and their inorganic counter parts.