Solid-State Reaction Synthesis of MgAl2O4 Spinel from MgO-Al2O3 Composite Particles Prepared via Electrostatic Adsorption.

This paper presents the formation of magnesium aluminate spinel using composite particles prepared via electrostatic adsorption (ESA). Scanning electron microscopy (SEM) images confirmed the presence of Al2O3-MgO composite particles. A mixture of Al2O3 and MgO raw materials was also prepared by using the conventional bead-milling method for comparison. The samples sintered at elevated temperatures were characterized through X-ray diffraction, SEM, and relative density measurements. Additionally, the lattice parameter and strain of the samples were determined using the Nelson-Riley function and the Williamson-Hall equation. A pure spinel phase formed in the ESA-derived sample sintered at 1400 °C, while the MgO structure remained in the conventionally prepared sample sintered at 1600 °C. The densities of samples sintered at 1450 °C or higher exceeded 90%. The lattice strain of the prepared samples was inversely proportional to the sintering temperature, attributed to the formation of large grains at higher temperatures. However, the sample sintered at 1600 °C for 8 h exhibited the highest strain of 0.0074 because the crystals grew in a certain direction.

Simulation and Verification of the Direct Current Electric Field on Fabricating High Porosity f-MWCNTs Thin Films by Electrophoretic Deposition Technique.

Electrophoretic deposition (EPD) is the potential process in high porosity thin films' fabrication or complex surface coating for perovskite photovoltaics. Here, the electrostatic simulation is introduced to optimize the EPD cell design for the cathodic EPD process based on functionalized multiwalled carbon nanotubes (f-MWCNTs). The similarity between the thin film structure and the electric field simulation is evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) results. The thin-film surface at the edge has a higher roughness (Ra) compared to the center position (16.48 > 10.26 nm). The f-MWCNTs at the edge position tend to be twisted and bent due to the torque of the electric field. The Raman results show that f-MWCNTs with low defect density are more easily to be positively charged and deposited on the ITO surface. The distribution of oxygen and aluminum atoms in the thin film reveals that the aluminum atoms tend to have adsorption/electrostatic attraction to the interlayer defect positions of f-MWCNTs without individually depositing onto the cathode. Finally, this study can reduce the cost and time for the scale-up process by optimizing the input parameters for the complete cathodic electrophoretic deposition process through electric field inspection.

Enhancing the light extraction efficiency of AlInN nanowire ultraviolet light-emitting diodes with photonic crystal structures.

In this paper, AlInN nanowire ultraviolet light-emitting diodes (LEDs) with emission at ∼299 nm have been successfully demonstrated. We have further studied the light extraction properties of these nanowire LEDs using photonic crystal structures with square and hexagonal lattices of nanowires. The light extraction efficiency (LEE) of the periodic nanowire LED arrays was found to be significantly increased as compared to random nanowire LEDs. The LEEs reach ∼ 56%, and ∼ 63% for the square and hexagonal photonic crystal-based nanowire structures, respectively. Moreover, highly transverse-magnetic polarized emission was observed with dominant vertical light emission for the AlInN nanowire ultraviolet LEDs.