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02월 28일 17시 이후 : 초록수정 불가능, 일정확인 및 검색만 가능
제123회 대한화학회 학술발표회, 총회 및 기기전시회 안내
Effects of Dielectric Environment on Optical Spectra of Monolayer Tetracene Crystals
2019년 2월 1일 15시 50분 03초
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4월 19일 (금요일) 11:00~12:30
, Sunmin Ryu
Department of Chemistry, Pohang University of Science and Technology, Korea
Wavefunction and binding energy of an exciton are largely affected by not only its dielectric but also geometric environments. Excitons may be further confined in two-dimensional (2D) molecular crystals because of reduced dielectric screening. However, it has been a challenge to realize such molecular systems in a reproducible and spectroscopy-compatible manner. In this study, we created 2D Tetracene (Tc) films sandwiched between two graphene or hexagonal boron nitride (hBN) layers with high chemical stability and mechanical strength. To form such a vertical heterostructure, a top graphene (or hBN) layer was dry-transferred onto Tc film thermally evaporated on a bottom graphene (or hBN) layer. Besides being a confining wall, graphene and hBN also served as an ideal ‘spectroscopic window’ because of their high optical transparency. Tetracene formed flat films with multiples of its minimum thickness, ~1.2 nm, corresponding to a monolayer and were found stable in the ambient conditions and even under intense laser irradiation. Polarization-resolved photoluminescence (PL) spectra and atomic force microscope (AFM) image showed that Tc films have a long-range order suggesting their crystalline nature. Absorption and PL spectra revealed that there are slight but noticeable energy shifts in major optical transitions between 2D and 3D Tc crystals. PL intensity substantially decreased when supported on graphene compared to on hBN, which indicated efficient energy transfer between Tc and metallic materials. The efficiency of energy transfer was systematically investigated by varying the number of bottom graphene layers. We will also discuss structural details and excitonic dynamics that will be probed by time-resolved spectroscopy. The demonstrated method will be highly useful in investigating the behavior of confined molecules and interactions between molecules and 2D materials.
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