Dresden 2026 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 82: Focus Session: Unoccupied States by Inverse Photoemission III
O 82.2: Hauptvortrag
Donnerstag, 12. März 2026, 11:00–11:30, WILL/A317
Enhanced Sensitivity in Low-Energy Inverse Photoemission Spectroscopy with an Off-Axis Parabolic Mirror for Efficient Light Collection — •Yongsup Park1,2, Jong-Am Hong1, Kyu-Myung Lee1, and Min-Jae Maeng1 — 1Dept. of Physics, Kyung Hee University, Seoul, Republic of Korea — 2Dept. of Information Display, Kyung Hee University, Seoul, Republic of Korea
Inverse photoemission spectroscopy (IPES) is a powerful tool for studying unoccupied electronic states but suffers from low sensitivity due to the low photon emission probability during free electron transitions. To improve sensitivity via better photon collection, an off-axis parabolic (OAP) mirror was designed and built for low-energy IPES (LEIPS). Optical simulations showed the OAP mirror raised photon collection efficiency from 3.06% to 63.3%, confirmed experimentally through LUMO spectra of C60 thin films. The OAP mirror-LEIPS system was applied to study energy level alignment (ELA) of pentacene films on substrates with different work functions (WF). By measuring HOMO and LUMO levels, the changes in transport gaps and the ELA with respect to the Fermi level were analyzed. Pentacene showed n-type behavior on low WF substrate (Cs2CO3) and p-type on high WF substrate (ITO). This OAP mirror-enhanced LEIPS system significantly shortened experiment times, enabling efficient and reliable measurements.
Keywords: Inverse photoemission; unoccupied state density of states; organic semiconductors; interface energy level alignments