Optical and structural properties of the GaAs heterostructures grown using AlGaAs superlattice buffer layer on compliant Si(100) substrates with the preformed porous-Si (por-Si) layer.

360 nm and 700 nm thick GaAs layers were grown by MO MOCVD growth technique directly on compliant Si (100) substrate and on supper-lattice (SL) AlGaAs buffer layer. The XRD study revealed better structural quality for the sample grown on SL / por-Si buffer. AFM study revealed a smoother sample surface with blocks of more regular rectangular shape and larger size as well. Photoluminescence spectra of the samples revealed an energy shift of PL maximum intensity for both samples. Sample grown on SL buffer also showed higher PL intensity corresponding to better crystalline perfection.

Enhancement of Temperature Fluorescence Brightness of Zn@Si Core-Shell Quantum Dots Produced via a Unified Strategy

Despite many dedicated efforts, the fabrication of high-quality ZnO-incorporated Zinc@Silicon (Zn@Si) core–shell quantum dots (ZnSiQDs) with customized properties remains challenging. In this study, we report a new record for the brightness enhancement of ZnSiQDs prepared via a unified top-down and bottom-up strategy. The top-down approach was used to produce ZnSiQDs with uniform sizes and shapes, followed by the bottom-up method for their re-growth. The influence of various NH4OH contents (15 to 25 µL) on the morphology and optical characteristics of ZnSiQDs was investigated. The ZnSiQDs were obtained from the electrochemically etched porous Si (PSi) with Zn inclusion (ZnPSi), followed by the electropolishing and sonication in acetone. EFTEM micrographs of the samples prepared without and with NH4OH revealed the existence of spherical ZnSiQDs with a mean diameter of 1.22 to 7.4 nm, respectively. The emission spectra of the ZnSiQDs (excited by 365 nm) exhibited bright blue, green, orange-yellow, and red luminescence, indicating the uniform morphology related to the strong quantum confinement ZnSiQDs. In addition, the absorption and emission of the ZnSiQDs prepared with NH4OH were enhanced by 198.8% and 132.6%, respectively. The bandgap of the ZnSiQDs conditioned without and with NH4OH was approximately 3.6 and 2.3 eV, respectively.

Microstructure and properties of porous Si3N4 ceramics by gelcasting-self-propagating high-temperature synthesis (SHS)

Porous silicon nitride ceramics have attracted a considerable attention due to their excellent overall performance, but poor porosity homogeneity and structural shrinkage induced by prolonged high temperature sintering limit its further application. Herein, as a three-in-one solution for the above issues, for the first time we develop a novel approach that integrates the merits of gelcasting-SHS (self-propagating high-temperature synthesis) to prepare porous Si3N4 ceramics to simultaneously achieve high porosity, high strength, high toughness, and low thermal conductivity across a wide temperature range. By regulating the solid content, porous Si3N4 ceramics with homogeneous pore structure are obtained, where the pore size falls inbetween 1.61 and 4.41 µm, and the elongated grains are interlaced and interlocked to form micron-sized coherent interconnected pores. At the same time, porous Si3N4 ceramics with porosity of 67.83% to 78.03% are obtained, where the compressive strength reaches 11.79 to 47.75 MPa and fracture toughness reaches 1.20 to 6.71 MPa·m1/2.

Porous Materials Based on Poly(methylvinylsiloxane) Cross-Linked with 1,3,5,7-Tetramethylcyclotetrasiloxane in High Internal Phase Emulsion as Precursors to Si-C-O and Si-C-O/Pd Ceramics

Polysiloxane networks were prepared by hydrosilylation of poly(methylvinylsiloxane) (V3 polymer) with 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) at various Si-Vinyl: Si-H groups molar ratios in water-in-oil high internal phase emulsion (HIPE). Curing the emulsions followed by removal of water led to foamed cross-linked polysiloxane systems differing in the cross-linking degrees, as well as residual Si-H and Si-Vinyl group concentrations. Treatment of thus obtained materials in Pd(OAc)2 solution in tetrahydrofuran resulted in the formation of porous palladium/polymer nanocomposites with different Pd contents (1.09–1.70 wt %). Conducted investigations showed that pyrolysis of the studied materials at 1000 °C in argon atmosphere leads to porous Si-C-O and Si-C-O/Pd ceramics containing amorphous carbon and graphitic phases. Thermogravimetric (TG) analysis of the starting cross-linked polymer materials and those containing Pd nanoparticles revealed that the presence of palladium deteriorates thermal stability and decreases ceramic yields of preceramic networks. The extent of this effect depends on polymer cross-linking density in the system.