Browsing by Author "Qiu, Cheng-Wei"

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Giant photoluminescence enhancement in tungsten-diselenide-gold plasmonic hybrid structures
(2016-05-01)
Wang, Zhuo
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Dong, Zhaogang
;
Gu, Yinghong
;
Chang, Yung-Huang
;
Zhang, Lei
Impressive properties arise from the atomically thin nature of transition metal dichalcogenide two-dimensional materials. However, being atomically thin limits their optical absorption or emission. Hence, enhancing their photoluminescence by plasmonic nanostructures is critical for integrating these materials in optoelectronic and photonic devices. Typical photoluminescence enhancement from transition metal dichalcogenides is 100-fold, with recent enhancement of 1,000-fold achieved by simultaneously enhancing absorption, emission and directionality of the system. By suspending WSe2 flakes onto sub-20-nm-wide trenches in gold substrate, we report a giant photoluminescence enhancement of similar to 20,000-fold. It is attributed to an enhanced absorption of the pump laser due to the lateral gap plasmons confined in the trenches and the enhanced Purcell factor by the plasmonic nanostructure. This work demonstrates the feasibility of giant photoluminescence enhancement in WSe2 with judiciously designed plasmonic nanostructures and paves a way towards the implementation of plasmon-enhanced transition metal dichalcogenide photodetectors, sensors and emitters.
Nearly lattice-matched molybdenum disulfide/gallium nitride heterostructure enabling high-performance phototransistors
(2019-03-01)
Liu, Xinke
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Chen, Yuxuan
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Li, Dabing
;
Wang, Sheng-Wen
;
Ting, Chao-Cheng
Molybdenum disulfide (MoS2)-based phototransistors are attractive for optical electronics in a large-scale size, such as transparent touch screens. However, most of the work done over the past decade has been on an opaque SiO2/Si wafer with a small size (micrometer to millimeter). In this work, a large-scale multilayer MoS2-based phototransistor has been fabricated on a transparent freestanding gallium nitride (GaN) wafer using a scalable chemical vapor deposition method. Due to the near lattice match and small thermal expansion mismatch between GaN and MoS2, the as-grown multilayer MoS2-on-GaN film shows high material quality in terms of low full width at half-maximum (similar to 5.16 cm(-1)) for the E-2g(1) Raman mode and a high absorption coefficient (similar to 10(6) cm(-1)) in the wavelength range of 405-638 nm. Under a wavelength of 405 nm at an incident power of 2 mWand applied voltage of 9 V, the fabricated MoS2-on-GaN phototransistor achieved a maximum responsivity of 17.2 A/W, a photocurrent gain of 53.6, and an external quantum efficiency of 5289%, with specific detectivity (similar to 10(10)-10(12) Jones) and low noise equivalent power (10(-12)-10(-14) W/Hz(1/2)) in the visible range of 405-638 nm. A typical response time of 0.1-4 s in the ambient air has also been recorded for the demonstrated MoS2-on-GaN phototransistor. Our work paves a technologic stepping stone for MoS2-based phototransistors for multifunctional transparent and touch-based optoelectronics in the future. (C) 2019 Chinese Laser Press
Twisted Surface Plasmons with Spin-Controlled Gold Surfaces
(2019-04-01)
Tsai, Wei-Yi
;
Sun, Quan
;
Hu, Guangwei
;
Wu, Pin Chieh
;
Lin, Ren Jie
Twisted photon, associated with orbital angular momentum (OAM), is a physical notion that has long captivated the intriguing imagination and wide applications. Owing to the native orthogonality between different topological charges of the vortices, it will be of significant value to generate, access, and discriminate the vortex on integrated chips. Archimedean spirals or multiple split gratings are commonly employed to generate OAMs on plasmonic films. However, the single-crystalline plasmonic surface sets a very stringent condition of probing the on-chip OAM dynamics at sub-femtosecond scale. In previous reports, spins of the incident light and actual topological charge of the on-chip OAM generator are also hybridized due to the intrinsic spin-to-orbital angular momentum conversion, making the direct discrimination of plasmonic vortex impossible. Here, a paradigm of generating twisted surface plasmons is presented in a fully spin-controlled fashion. With the two-photon photoemission electron microscopy, the dynamics of OAM formation is demonstrated at subwavelength spatial resolution and sub-femtosecond temporal resolution simultaneously, revealing its OAM-dependent angular velocity. In addition, this scheme of twisting on-chip plasmons shows that the challenging crystalline requirement of the thin film can be significantly alleviated. The results open up a distinct way to multiplex, record, and read the information with plasmons.