Molybdenum disulfide (MoS2) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of $ E_{2{\rm g}}^1 $ and $ A_{{\rm 1g}}^{} $ peaks vary monotonously with the layer number of ultrathin MoS2 flakes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS2. The asymmetric Raman peak at 454 cm−1, which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS2, is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ($ A_{{\rm 2u}}^{} $). Our findings suggest a clear evolution of the coupling between electronic transition and phonon when MoS2 is scaled down from three‐ to two‐dimensional geometry.

The main challenge for all electrical, mechanical and optical sensors is to detect low molecular weight (less than 400 Da) chemical and biological analytes under extremely dilute conditions. Surface plasmon resonance sensors are the most commonly used optical sensors due to their unique ability for real-time monitoring the molecular binding events. However, their sensitivities are insufficient to detect trace amounts of small molecular weight molecules such as cancer biomarkers, hormones, antibiotics, insecticides, and explosive materials which are respectively important for early-stage disease diagnosis, food quality control, environmental monitoring, and homeland security protection. With the rapid development of nanotechnology in the past few years, nanomaterials-enhanced surface plasmon resonance sensors have been developed and used as effective tools to sense hard-to-detect molecules within the concentration range between pmol and amol. In this review article, we reviewed and discussed the latest trend and challenges in engineering and applications of nanomaterials-enhanced surface plasmon resonance sensors (e.g., metallic nanoparticles, magnetic nanoparticles, carbon-based nanomaterials, latex nanoparticles and liposome nanoparticles) for detecting "hard-to-identify" biological and chemical analytes. Such information will be viable in terms of providing a useful platform for designing future ultrasensitive plasmonic nanosensors.

Graphene-gold metasurface architectures that can provide significant gains in plasmonic detection sensitivity for trace-amount target analytes are reported. Benefiting from extreme phase singularities of reflected light induced by strong plasmon-mediated energy confinements, the metasurface demonstrates a much-improved sensitivity to molecular bindings nearby and achieves an ultralow detection limit of 1 × 10(-18) m for 7.3 kDa 24-mer single-stranded DNA.

International audienceComplex ceramic parts, designed by 3D electromagnetic simulations for microwave devices of high performances, are difficult, even impossible, to elaborate by classical ceramic processing routes. This paper demonstrates the direct fabrication of useful complex microwave devices in millimeter and submillimeter wavelength domains, with a high dimensional resolution, by the numerical techniques of stereolithography and microstereolithography. Alumina and zirconia formulations have been developed with a powder loading 450 vol%, a suitable rheology to spread thin (25-50 lm) and homogeneous layers, and with a sufficient reactivity to UV for polymerization. Devices built with a satisfying manufacturing accuracy have presented excellent experimental electrical behaviors in good agreement with the theoretical ones