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Dong-Jin Yun1 Changhoon Jung1 Seyun Kim1 Seong Heon Kim1

1, Samsung Advanced Institute of Technology, Suwon, Alabama, United States

On the basis of the in-situ photoemission spectroscopy (PES) system, we propose a novel, direct diagnosis method for the characterization of graphene (Gr) doping states at the organic semiconductor (OSC)/electrode interface. Our in-situ PES system enables ultraviolet/X-ray photoelectron spectroscopy (UPS/XPS) measurements in the OSC growth or removal process. We directly deposit C60 film on three different p-type doped Gr—the gold chloride doped Gr (AuCl3_Gr), (trifuoromethyl-sulfonyl)imide (TFSI) and nitric acid (HNO3) doped Gr (TFSI_Gr), and nitric acid doped Gr (HNO3_Gr). We periodically characterize the chemical/electronic state changes of C60/Gr structures during their aging processes under ambient conditions. In other word, we perform cyclic UPS/XPS measurements and these results provide significant information regarding the variations of chemical and electronic states in the C60/Gr structures, according to aging time under ambient conditions. In addition, the OSC can also act as a passivating layer to prevent severe degradation of dopants with negligible change in doping state over one month, while the p-type doped Gr without OSC degrades a lot in one-month aging. Consequently, all the p-type doped Gr layers in different C60/Gr structures undergo significant transitions in the doping states over time, in spite of the passivation effect of C60 films. Our result concludes that the chemical/electronic structures of the Gr layer are completely reflected in the energy level alignments at the C60/Gr interfaces. Therefore, we determine a strong correlation between the energy level alignment at the C60/Gr interface and the Gr doping state; and therefore, we strongly believe that the variation of energy level alignments at the OSC/graphene interface is a key standard for determining the doping state of graphene after a certain period of aging time.

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