반데르발스 반도체의 단일 보우타이 안테나 기반 테라헤르츠 분광 특성: 화학적 처리 및 한계
Single Bowtie Antenna-based Terahertz Time-domain Spectroscopy of Semiconducting van der Waals Materials: Chemical Treatment and Limitations
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초록
본 연구에서는 테라헤르츠(THz) 주파수 대역에서 공진하는 금속 보우타이 안테나 갭에 μm 크기의 MoS 2 를 배치하여 화학적 도핑에 따른 전류-전압 특성과 THz파 투과를 동시에 측정함으로써, 반데르발스 물질의 전기 전도도 변조가 THz파의 투과 특성에 미치는 영향을 확인하였다. 이는 THz파의 변조 및 나노 물질 감지에 필요한 전기 전도도 하한값을 예상하고, 반데르발스 물질의 도핑 효과가 THz 특성에 미치는 영향을 이해하는 데 기여할 것이다.
Abstract
We investigate changes in terahertz (THz) transmission characteristics by placing micrometer-sized van der Waals materials at the gap of metal bowtie antennas resonant in the THz frequency range. Specifically, the electrical conductivity of MoS 2 with a thickness of tens of nanometers is tuned by chemical doping using N-methyl-2-pyrrolidone (NMP), and DC current–voltage characteristics are measured using the bowtie antenna electrodes. Corresponding changes in THz transmission are measured to analyze the impact of conductivity modulation on the THz responses. First, MoS 2flakes with electrical conductivities of 8.8 × 10 −3 S/cm and 5.7 × 10 −3 S/cm showed no change in antenna transmission, indicating semiconducting offstate behavior. After NMP treatment, the electrical conductivities increased by up to an order of magnitude, reaching 8.7 × 10 −2 S/cm and 3.7 × 10 −2S/cm, respectively, yet no significant change in THz transmittance was observed. This result is consistent with previous theoretical predictions thattransmission changes become observable when the conductivity of the material at the bowtie gap reaches approximately 10 2 S/cm or higher. Thesefindings enable estimation of the lower conductivity threshold required for effective THz modulation and nanomaterial detection, and advance the understanding of doping effects in van der Waals materials for THz applications.