Fuqiang Guo

A novel plasmonic waveguide structure consisting of a rectangular resonator side coupled with a split ring resonator (SRR) and a metal–insulator–metal (MIM) waveguide with metal baffle was proposed. The transmission characteristics of the present structure were simulated by a finite-difference time-domain (FDTD) method. The results show that the structure can realize three typical plasmonically-induced reflection (PIR) windows. Meantime, the PIR window can be tuned vertically and horizontally, respectively, and multiple PIR windows with different wavelength intervals can also be obtained by changing the split position. In addition, the sensitivity of the proposed structure can reach up to 1,075[ ]nm/RIU. Furthermore, a rectangular resonator was added to the other side of the plasmonic waveguide structure for realizing the dual-channel PIR window. Another SRR was added to form a symmetrical structure, which further improved the sensitivity and transmittance. Undoubtedly, the proposed structure will have potential applications in sensor and optical switches.

For the first time, Pd nanoparticle-functionalized, rGO nanosheet-modified 3D rod-like CuO (Pd–CuO/rGO) with a nanowire hierarchical structure was successfully synthesized using a facile hydrothermal strategy. Interestingly, the developed Pd–CuO/rGO sensor exhibited more prominent features compared with the CuO, Pd–CuO and CuO/rGO sensors towards trace NO₂ gas at room temperature (RT, 23 °C). In particular, the Pd–CuO/rGO sensor demonstrated an ultra-high response of 64.2 towards 100 ppm NO₂ gas at RT, which was approximately 3.4 times that of the pristine CuO sensor, 2.7 times that of the Pd–CuO sensor and 2 times that of the CuO/rGO sensor, respectively. Simultaneously, a response/recovery time of 10.7/9.2 s towards 10 ppm NO₂ gas at RT was indicated for the Pd–CuO/rGO sensor, and the extremely low limit of detection was down to 50 ppb, ensuringreal-time detection at a ppb-level NO₂ gas concentration. Furthermore, the fabricated sensors had reliable consistency, excellent repeatability and long-term stability. In addition to the contribution from the porous rGO-modified CuO providing abundant active places for gas adsorption and diffusion, Pd and partially oxidized Pd NPs that chemically and electronically sensitized the CuO supporter greatly improved the sensitivity and selectivity of the fabricated Pd–CuO/rGO sensor. Moreover, abundant surface oxygen vacancies were also to some extent beneficial for the sensing performance. Our scientific and systematic work has great potential for practical applications in extremely harsh environments.