Papers by Author: Chun Jiang Zhou

Abstract: Cadmium Selenide/Cadmium Sulfide (CdSe/CdS) core/shell quantum dots (QDs) in aqueous solution were prepared by solve-separate method using CdSe as core and mercapto-acetate acid as stabilizer and surfactants. The results of experiments indicate that the size of the CdSe/CdS QDs was about 5nm estimated by FE-TEM, which is accordant with that calculated from the XRD data by the Scherer equation after emendation. The QDs belong to the cubic structure (zinc blende) by XRD analysis. The intensity of luminescence of the quantum dots was greatly improved after the surface was coated with CdS shell. With increasing the time of refluence, the intensity of photoluminescence was promoted correspondingly. The excitation wavelength was 350nm, two emission peaks were clearly observed, the first high-energy peak was at 600nm and the second one located in 700nm. The first high-energy band was attributed to electron–hole recombination after relaxation and the second energy band was to deep traps in quantum-confined systems.

Abstract: A new preparation method was developed to produce Si₃N₄-SiO₂-Si₂N₂O composites for broad band radome applications. The three-dimensional cross-linked polyphenylsiloxane (PPS) was used as an organic precursor. The composites obtained through react bonding between Si and the precursor powders in the stream of N₂ were examined. The conversion of the PPS polymer to the ceramic was examined by TG analysis and conventional X-ray diffraction (XRD) techniques. It was found that the ceramics contained a primary Si₂N₂O phase, some β-Si₃N₄ phase and a minor α-SiO₂ phase. Despite low density (1.7-2.0g•cm^-3), the flexural strengths of the composites reaches 195Mpa at room temperature. The ceramic has excellent dielectric properties with dielectric constants as low as 3.2-5.5.