Sf. Alvarado et al., STM-excited electroluminescence and spectroscopy on organic materials for display applications, IBM J RES, 45(1), 2001, pp. 89-100
We present an overview of the current status of our work on scanning-tunnel
ing-microscope-based (SIM) spectroscopy and electroluminescence (EL) excita
tion to study the physical and electronic structure of organic materials us
ed in organic light-emitting devices (OLEDs). By these means we probe the c
ritical device parameters in charge-carrier injection and transport, i,e,,
the height of the barrier for charge-carrier injection at interfaces betwee
n different materials and the energy gap between positive and negative pola
ronic states. In combination with optical absorption measurements, we gauge
the exciton binding energy, a parameter that determines energy transport a
nd EL efficiency, In STM experiments involving organic EL excitation, the t
ip functions as an OLED electrode in a highly localized fashion, allowing o
ne to map the spatial distribution of the EL intensity across thin-film sam
ples with nanometer lateral resolution as well as to measure the local EL e
mission spectra and the influence of thin-film morphology.