The effect of size on transitions between defect-induced magnetic phases in ZnO nanowires is investigated in a temperature range from 1.8 K to 300 K using calorimetric measurements of specific heat. The obtained results demonstrated interesting magnetic phenomena in unusual magnetic nanomaterials. At low temperatures, we observed isolated magnetic ions in nanowires of diameters 45-50 nm, and ferromagnetic phases in nanowires of diameters 85-100 nm. However, at higher temperatures, we observed multiple transitions between superparamagnetic phases in the thinner nanowires and multiple transitions between spin-glass phases in the thicker nanowires.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Near field, Atomic force microscopy, Integrated optics, Wafer-level optics, Transformers, Temporal resolution, Spectroscopy, Spatial resolution
Near-field scanning optical microscopy (NSOM) is a powerful technique to characterize the chemical and physical properties of materials with nanometer-scale resolution. Adaptation of NSOM has remained mainly in research labs partly due to a lack of commercial availability of high-quality probes. We present a wafer-scale realization of Campanile near-field probes. Campanile probes offer a strong local electromagnetic field enhancement, efficient far-field to near-field coupling, nanoscale spatial resolution, background-free operation, and broadband photon-plasmon coupling to enable high spatial and temporal resolution. The near-field optical mapping of dark-excitonic states of WSe2 monolayers is presented as a use-case example.
In scanning near-field optical microscope, the optical resolution is determined by the actual size of the optical nano-antenna at the apex of the tip. In this talk, I will introduce our recent improvements in fabricating the ‘Campanile’ near-field Probe with the gap in a sub-20nm scale size. The near-field optical performance of the probe will be demonstrated through the polarization-resolved transmission measurement and the nano-photoluminescence mapping of the WSe2 monolayer.
We present an all ZnO-based core-shell microrod, composed of a green light-emitting shell and a hexagonal microcavity core, obtained through the desulfurization treatment. The whispering gallery mode emission of the highly defective shell induced by the ZnO microcavity is realized. The resonant properties of the single core-shell microrod at different positions are investigated by the Cathodoluminescence measurement.
ZnO is a multifunctional nanomaterial having various applications. The real challenge is to produce large scale, well-aligned, reproducible ZnO nanowires (NWs) using low-cost techniques. The aim of this work is to show a simple approach for the uniform growth of NWs, on entire silicon wafers, using a low-temperature chemical method. A study of the substrate size dependent growth of NWs was conducted to understand the limitations in the growth. A time dependent growth study was performed on ZnO NWs grown on 3-inch wafers to track their morphological evolution. Simultaneous growth of ZnO NWs on two 4-inch wafers will be demonstrated.
Among alternative nanomaterials for energy related photonic applications, one-dimensional semiconductor nanowires are of a great interest due to their physical properties coming from electronic or quantum confinement. In particular, ZnO nanowires (or nanorods) has been widely investigated since ZnO has many unique properties such as wide direct band gap, large exciton binding energy and relatively high refractive index. Large optical gain also makes ZnO a well suited material for energy transfer in hybrid systems and especially optical energy transfer. There are however two issues remaining to be addressed, one is related to the control in size and dispersion in nanowires array and the other is related to the modeling of nanowires arrays. In this study, we report on a theoretical study on ZnO nanowires, in order to reach a better understanding of the mechanisms that govern the light propagation in nanowires arrays.
A phenomenological model has been developed and discussed. The model is able to describe the experimentally measured light transmission nanowires arrays. A slab of nanospheres and rough layers with thickness waviness were combined to simplify the nanowires structure description. This phenomenological description was proved to be feasible by fitting the experimental data. As a conclusion, light transmitted by randomly distributed nanowires can be explained by the combination of Mie theory and a rough Fresnel reflection at the interfaces.
The optical properties of ZnO has been widely investigated in detail. Typical photoluminescence (PL) of ZnO contains two parts of emission: near bandgap transition induced ultraviolet emission, and a relatively wide visible emission ranging from green to red, which is closely related to concentration of the structural defects. While the green luminescent has been reported to be associated with oxygen vacancies Vo. In this work, we report on an efficient technique namely desulfurization to increase the amount of oxygen vacancy in a ZnO nanowires array. In the case of the desulfurized sample the PL is increased by more than 1 order of magnitude as to compare with the sulfurized one and more than 2 orders of magnitude as to compare with the as grown sample. Structural analysis as well as morphological analysis confirm the origin of the green band emission enhancement in PL emission. Samples preparation as well an in-depth analysis including quantum efficiency will be presented and discussed within the frame of new rare-earth free phosphor material.
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