Enhanced Reflectivity Change and Phase Shift of Polarized Light: Double Parameter Multilayer Sensor

Herein, the concept of point of darkness based on polarized light phase difference and absorption of light is demonstrated by simulations using low refractive index and extinction coefficient semiconductor and dielectric, and high refractive index nonoxidizing metal multilayer thin film structures. Several multilayer sensor configurations show great sensitivity to thickness and refractive index variation of the detectable material by measuring the reflectivity ratio {\Psi} and phase shift {\Delta}. Focus is on such multilayers, which have sensitivity to both parameters ({\Psi}, {\Delta}) in the visible spectral range, thus opening the possibility for further research on a new biomedical sensor development with enhanced double parameter sensing

Fast-Response Single-Nanowire Photodetector Based on ZnO/WS₂ Core/Shell Heterostructures

The surface plays an exceptionally important role in nanoscale materials, exerting a strong influence on their properties. Consequently, even a very thin coating can greatly improve the optoelectronic properties of nanostructures by modifying the light absorption and spatial distribution of charge carriers. To use these advantages, 1D/1D heterostructures of ZnO/WS₂ core/shell nanowires with a-few-layers-thick WS₂ shell were fabricated. These heterostructures were thoroughly characterized by scanning and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Then, a single-nanowire photoresistive device was assembled by mechanically positioning ZnO/WS₂ core/shell nanowires onto gold electrodes inside a scanning electron microscope. The results show that a few layers of WS₂ significantly enhance the photosensitivity in the short wavelength range and drastically (almost 2 orders of magnitude) improve the photoresponse time of pure ZnO nanowires. The fast response time of ZnO/WS₂ core/shell nanowire was explained by electrons and holes sinking from ZnO nanowire into WS₂ shell, which serves as a charge carrier channel in the ZnO/WS₂ heterostructure. First-principles calculations suggest that the interface layer i-WS₂, bridging ZnO nanowire surface and WS₂ shell, might play a role of energy barrier, preventing the backward diffusion of charge carriers into ZnO nanowire

Unexpected Epitaxial Growth of a Few WS₂ Layers on {11̅00} Facets of ZnO Nanowires

Core–shell nanowires are an interesting and perspective class of radially heterostructured nanomaterials where epitaxial growth of the shell can be realized even at noticeable core–shell lattice mismatch. In this study epitaxial hexagonally shaped shell consisting of WS₂ nanolayers was grown on {11̅00} facets of prismatic wurtzite-structured [0001]-oriented ZnO nanowires for the first time. A synthesis was performed by annealing in a sulfur atmosphere of ZnO/WO₃ core–shell structures, produced by reactive dc magnetron sputtering of an amorphous a-WO₃ layer on top of ZnO nanowire array. The morphology and phase composition of synthesized ZnO/WS₂ core–shell nanowires were confirmed by scanning and transmission electron microscopy (SEM and TEM), micro-Raman, and photoluminescence spectroscopy. Epitaxial growth of WS₂(0001) layer(s) on {11̅00} facets of ZnO nanowire is unexpected due to incompatibility of their symmetry and structure parameters. To relax the interfacial incoherence, we propose a model of ZnO/WS₂ interface containing WS₂ bridging groups inside and use first-principles simulations to support its feasibility