Plasmon-free surface enhanced Raman scattering (SERS) based on the chemical mechanism (CM) is drawing great attention due to its capability for controllable molecular detection. However, in comparison to the conventional noble-metal-based SERS technique driven by plasmonic electromagnetic mechanism (EM), the low sensitivity in the CM-based SERS is the dominant barrier toward its practical applications. Herein, we demonstrate the 1T' transition metal telluride atomic layers (WTe and MoTe) as ultrasensitive platforms for CM-based SERS. The SERS sensitivities of analyte dyes on 1T'-W(Mo)Te reach EM-comparable ones and become even greater when it is integrated with a Bragg reflector. In addition, the dye fluorescence signals are efficiently quenched, making the SERS spectra more distinguishable. As a proof of concept, the SERS signals of analyte Rhodamine 6G (R6G) are detectable even with an ultralow concentration of 40 (400) fM on pristine 1T'-W(Mo)Te, and the corresponding Raman enhancement factor (EF) reaches 1.8 × 10 (1.6 × 10). The limit concentration of detection and the EF of R6G can be further enhanced into 4 (40) fM and 4.4 × 10 (6.2 × 10), respectively, when 1T'-W(Mo)Te is integrated on the Bragg reflector. The strong interaction between the analyte and 1T'-W(Mo)Te and the abundant density of states near the Fermi level of the semimetal 1T'-W(Mo)Te in combination gives rise to the promising SERS effects by promoting the charge transfer resonance in the analyte-telluride complex.
The potential barrier at the apex of a single-wall carbon nanotube emitter is found to be strongly and nonlinearly dependent on the external applied field, due to a quantum mechanical mechanism instead of the correction of image potential in Fowler-Nordheim theory. The field enhancement factor depends on the applied field and is much smaller than that predicted by the classical theory. The field induced apex-vacuum barrier lowering is confirmed to be the essential mechanism for efficient field electron emission from capped carbon nanotubes.
A series of new aggregation-induced emission compounds with strong blue light-emitting properties derived from triphenylethylene were facilely synthesized by a Wittig-Horner reaction of bis(4-bromophenyl)methanone with diethyl 4-bromobenzylphosphonate, followed by a Suzuki reaction with arylboronic acids. Their maximum fluorescence emission wavelengths were 452-462 nm. The glass transition temperatures ranged from 70-145 C, and the decomposition temperatures were 360-508 C. The unoptimized device fabricated with benzofuranyl substituted compound as emitter turned on at $6 V, and the maximum luminance was $1500 cd m À2 .
Optical complex materials offer unprecedented opportunity to engineer fundamental band dispersion which enables novel optoelectronic functionality and devices. Exploration of photonic Dirac cone at the center of momentum space has inspired an exceptional characteristic of zero-index, which is similar to zero effective mass in fermionic Dirac systems. Such all-dielectric zero-index photonic crystals provide an in-plane mechanism such that the energy of the propagating waves can be well confined along the chip direction. A straightforward example is to achieve the anomalous focusing effect without longitudinal spherical aberration, when the size of zero-index lens is large enough. Here, we designed and fabricated a prototype of zero-refractive-index lens by comprising large-area silicon nanopillar array with plane-concave profile. Near-zero refractive index was quantitatively measured near 1.55 m through anomalous focusing effect, predictable by effective medium 2 theory. The zero-index lens was also demonstrated to perform ultralow longitudinal spherical aberration. Such IC compatible device provides a new route to integrate all-silicon zero-index materials into optical communication, sensing, and modulation, and to study fundamental physics on the emergent fields of topological photonics and valley photonics.Dirac cones in fermionic systems have attracted tremendous attention in the fields of topological insulator and graphene [1][2][3] . Following the pace of condensed matter, these conical dispersion bands have been extended to bosonic systems particularly for electromagnetic waves 4-12 . Bosonic Dirac cones at the zone boundary reveal many similar phenomena with fermionic particles. For example, bianisotropic metamaterials can access to modulate the spin flow of light with backscattering immune at the boundary of topological photonic crystals, after opening a nontrivial gap from Dirac cone 13,8,11 . An alternative method is proposed to implement photonic analogue of the integer quantum Hall effect by using periodic coupling resonators on a silicon-on-insulator platform in near-infared (NIR) wavelength scale 7,14,15 .Beyond those predominant behaviors, bosonic Dirac cones also present extra features other than femionic systems. Recently, another type of photonic Dirac cones induced by accidental degeneracy at the zone center has been found in a class of all-dielectric photonic crystals 16,17 , in which the optical response shows very different to the case at the zone boundary. One of the remarkable properties is zero-index behavior such that the effective permittivity and permeability are simultaneously to be zero at Dirac frequency. To date, nanorod-array structure is the exclusive way to realize all-dielectric zero-index photonic crystal in optical frequency regime. How to sufficiently confine the propagation wave in the plane of periodicity is a practical challenge for 3 rod-slab structures. The first implementation at near-infrared (NIR) wavelength has been fabricated by alternating silicon/silica layers ...
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