RESUMEN
This work demonstrates a dual-functional tunable terahertz metamaterial absorber based on thermally controllable vanadium dioxide (VO2) and electrically tunable graphene. The switchable absorption functions could be obtained in the same metamaterial, which consists of alternating stacked cross-cut graphene disks (CGDs) and VO2 square rings (VSRs) separated by an ultra-thin dielectric film placed on a continuous gold mirror. The metallic state of VSRs is the dominant factor for the broadband absorption function, resulting in a broadband absorption of 4.746 THz. Based on this, the Fermi energy level of CGDs increases to 0.7 eV, which could broaden the absorption bandwidth to 5.398 THz. When the VSRs are in the insulating state, CGDs dominate the absorption, and the suggested device switches to the dual-band absorption function. These two absorption peaks appear to be larger than 97% and their frequencies could be dynamically controlled by the Fermi energy level of CGDs. In addition to the excellent absorption characteristics of dynamic switching of two different functions, polarization insensitivity and large-angle tolerance are also advantages of this work, which could provide new insights and guidance for the study of dynamically tunable metamaterial absorbers.
RESUMEN
Multi-band electromagnetically induced transparency (EIT) effects have attracted widespread attention due to their great application prospects. However, their realization is mainly based on the coupling of multiple sub-resonators that typically exceed the number of transparency peaks, resulting in complex structural designs and cumbersome preparation procedures. This paper reports a simple design of a terahertz metamaterial that can produce the triple-band EIT effect using two "big-bright" mode coupling of two sub-resonators. The design adopts the classical two-layer structure. A U-shaped split-ring resonator and a fork-shaped resonator form a periodic array on the surface of the flexible organic polymer material. Three transparency peaks around 0.59 THz, 1.07 THz, and 1.34 THz are experimentally realized, and their formation mechanisms are explored. Furthermore, the triple-band EIT metamaterial was prepared by the photolithography technology and characterized by terahertz time-domain spectroscopy. Theoretical simulation results agree well with experimental results. Sensing characteristics and slow light effects of the terahertz metamaterial are further discussed experimentally. The proposed triple-band EIT metamaterial having excellent properties, including thin size, good flexibility, simple and compact structure, and high sensing sensitivity, could provide guidance for the subsequent design and implementation of multifunctional multi-band EIT metamaterials.
RESUMEN
We design a four-band narrow-band near-perfect absorber based on bulk Dirac semimetal (BDS) metamaterial in the terahertz region. The absorber has a top-to-bottom three-layer structure of a BDS layer, an insulating dielectric slab, and a gold layer. The BDS is flexible and tunable, allowing the Fermi energy level to be adjusted by changing the applied bias voltage, thus changing the absorption characteristics of the absorber. We use the time-domain finite-difference method to simulate the absorption characteristics of the absorber, which could achieve four discrete near-perfect absorption peaks at 0.98 THz, 1.70 THz, 2.02 THz, and 2.36 THz. The absorber is polarization sensitive, and the conversion between four-band absorption and three-band absorption is achieved by changing the incident polarization angle. We also change the structure of the absorber to study the absorption characteristics and break the structural symmetry to achieve a larger number of absorption peaks. Besides, the sensing performance of four-band narrow-band absorption is analyzed, and the maximum sensitivity of the absorber is 112.78 GHz/RIU. The device should have vast application prospects for bio-detection and high-sensitivity biosensing detection.
RESUMEN
Surface-enhanced Raman scattering (SERS) is widely used as a powerful analytical technology in cutting-edge areas such as food safety, biology, chemistry, and medical diagnosis, providing ultra-fast, ultra-sensitive, nondestructive characterization and achieving ultra-high detection sensitivity even down to the single-molecule level. Development of Raman spectroscopy is strongly dependent on high-performance SERS substrates, which have long evolved from the early days of rough metal electrodes to periodic nanopatterned arrays building on solid supporting substrates. For rigid SERS substrates, however, their applications are restricted by sophisticated pretreatments for detecting solid samples with non-planar surfaces. It is therefore essential to reassert the principles in constructing flexible SERS substrates. Herein, we comprehensively review the state-of-the-art in understanding, preparing and using flexible SERS. The basic mechanisms behind the flexible SERS are briefly outlined, typical design strategies are highlighted and diversified selection of materials in preparing flexible SERS substrates are reviewed. Then the recent achievements of various interdisciplinary applications based on flexible SERS substrates are summarized. Finally, the challenges and perspectives for future evolution of flexible SERS and their applications are demonstrated. We propose new research directions focused on stimulating the real potential of SERS as an advanced analytical technique for commercialization.
RESUMEN
Triple-band terahertz metamaterial absorber with design of miniaturization and compactness is presented in this work. The unit cell of the terahertz absorber is formed by an analogy I-typed resonator (a rectangular patch with two small notches) deposited on top of dielectric sheet and metallic mirror. The miniaturized structure design exhibits three discrete frequency points with near-perfect absorption at terahertz regime. The three absorption peaks could be ascribed to localized resonances of analogy I-typed resonator, while the response positions of these absorption peaks at the analogy I-typed resonator are different by analyzing the near-field patterns of these resonance peaks. Changes in structure parameters of the analogy I-typed resonator are also investigated. Simulation results revealed that the notch sizes of the rectangular patch are the key factor to form the triple-band near-perfect absorption. Further structure optimization is given to demonstrate triple-band polarization insensitive performance. Moreover, actively tunable absorption properties are realized by inserting or introducing vanadium dioxide with adjustable conductivity into the metamaterial structure. It is revealed that the insulator-metal phase transition of vanadium dioxide is the main reason for the modulation of absorption performance. Compared with previous multiple-band absorbers, the device given here has excellent features of high degrees of simplification, miniaturization, and active modulation, these are important in practical applications.