Seminar & Colloquium
[세미나: 11월 15일(화), 오후 1시 30분] University of Minnesota, 서동제 박사
Title
A PATH TOWARD ACHIEVING PERFECT ABSORPTION IN A 2D HETEROSTRUCTURE
Speaker
서동제 박사, Postdoctoral Researcher, Electrical & Computer Engineering, University of Minnesota-Twin Cities
Education
- 2012-2020 Joint M.S and Ph.D., Materials Science and Engineering, Yonsei University, Seoul, Republic of Korea
Relevant Coursework: Semiconductor Process, Advanced Nanomaterials, Diffusion and its Application in Materials, Materials chemistry
- 2005-2012 B.S., Physics, Yonsei University, Seoul, Republic of Korea
Relevant Coursework: Modern Physics, Quantum Mechanics, Solid state Physics, and Math Mathematical Physics
Professional Experience
- 2022-Present Postdoctoral Researcher, Electrical & Computer Engineering, University of Minnesota-Twin Cities
| Date | Tuesday, November 15th, 2022
| Time | 13:30 ~
| Venue | 33동 223호 (동부 세미나실)
[Abstract]
MoS2 is a promising material for atomically thin perfect absorbers due to the high oscillator strength of its excitonic transitions and excellent band nesting. As MoS2 is thinned from multilayer to monolayer, the magnitude and energy of its optical conductivity were exponential attenuation in magnitude and manifested by a gradual blueshift in energy with decreasing layer number due to interlayer orbital hybridization. The intrinsically poor light absorption of monolayer MoS2, which varies by about 12 % in visible spectral range, induces the weak light-matter interaction. Although this absorption is surprising for the atomic thickness of MoS2, these values must be increased to design MoS2-based absorbers. Most approaches to improving the light-matter interaction of MoS2 have been devoted to plasmonic nanostructure and photonic crystal. The photonic crystal slab with a perfect conductor mirror achieves near-unity absorption at 450 nm and average absorption of 51 % over the spectrum from 400 to 700 nm in the MoS2 [1].
Here, we demonstrate a new approach to achieving perfect light absorption in MoS2/graphene/MoS2 (MGM) heterostructure. By putting graphene in the intermediate layer to reduce the interlayer interaction of MoS2 with each other, the doubling effect of light absorption can be obtained. As a demonstration of the concept, we experimentally show the optical contrast of MGM heterostructure can be improved by ~28 % compared to the bilayer MoS2 at λ = 442 nm near the band nesting region. This result is in excellent agreement with the density functional theory of absorbance of a freestanding MGM heterostructure. Based on this structure, we also demonstrate a method based on the insertion of a silver (Ag) mirror layer between the dielectric layer and the substrate to enhance the optical absorption, resulting from Fabry-Perot cavity reflection. The interband absorption of MGM heterostructure is maximized by the cavity resonance and can reach the near-perfect absorption for frequencies satisfying the cavity resonance condition. With various 2D materials and optimization strategies, we can realize ideal absorption over the wide frequency range from UV to IR. Our study points to a new opportunity to combine 2D heterostructure with cavity optics to enable novel device applications such as high-efficiency solar cells with nanometer-scale thickness.
REFERENCES
[1] J. Piper and S. Fan, ACS Photonics 3(4),(2016) 571–577
| Host | 이관형 교수 (880-8366)