The Starting Material Concentration Dependence of Ag3PO4 Synthesis for Rhodamine B Photodegradation under Visible Light Irradiation

Synthesis of Ag3PO4 photocatalyst under the varied concentrations of AgNO3 and Na2HPO4·12H2O as starting material has been successfully synthesized using the co-precipitation method. The concentration of AgNO3 is 0.1; 0.5; 1.0; and 2.0 M, whereas Na2HPO4·12H2O is 0.03; 0.17; 0.33; and 0.67 M, respectively. The co-precipitations were carried out under aqueous solution. As-synthesized photocatalysts were examined to degrade Rhodamine B (RhB) under blue light irradiation. The results showed that varying concentrations of starting materials affect the photocatalytic activities, the intensity ratio of [110]/[200] facet plane, and their bandgap energies of Ag3PO4 photocatalyst. The highest photocatalytic activity of the sample was obtained by synthesized using the 1.0 M of AgNO3 and 0.33 M of Na2HPO4·12H2O (AP-1.0). This is due to the high [110] facet plane and increased absorption along the visible region of AP-1.0 photocatalyst. Therefore, this result could be a consideration for the improvement of Ag3PO4 photocatalyst.

TEM Analysis of Threading Dislocations in ELO-GaN Grown with Controlled Facet Planes

ABSTRACTCross sectional transmission electron microscope (TEM) observation has been performed for specimens of ELO-GaN (ELO: epitaxial-lateral-overgrowth) in order to analyze the behavior of dislocations, with special reference to the effect of facet plane orientation and the size of mask. An ELO-GaN layer was grown overlying on a thick GaN layer with a patterned mask by MOVPE with a carrier gas of hydrogen (H2) under a low-ambient pressure. The growth temperature and the reactor-pressure were controlled in a two-step way during the growth of ELO-GaN layer in order to change the dominant facet-planes and the aspect ratio in growth rate. The experimental results revealed that (a+c)-type threading dislocations (TDs) show a 90-degree-bending in the specimen with slanting facets (2 1 1 2), but not in those with vertical ones (2110). a-type TDs run upward without bending irrespective of the orientation of the facet planes. Dislocations lying on (0001) planes, or horizontal dislocations (HDs), have been generated in the specimens with wide mask-terraces. It is thought that the formation of HDs relieved stresses in the ELO-GaN and then suppressed the bending of a-type TDs. In the specimens with narrow terraces, the both type TDs penetrate upward without bending and few HDs are generated. The behavior of dislocations is attributable to the fact that the small size of terrace generates small stresses and promotes a fast meeting of wings of ELO-GaN.

Characterization of Voids in Rutile Nanoparticles by Transmission Electron Microscopy

ABSTRACTRutile nanoparticles containing voids or cavities have been characterized using transmission electron microscopy. The general morphology of the voids has been determined from images of nanoparticles in different orientations. In general, the longest dimension is along the c axis of rutile. Many of the voids show a prismatic morphology with dipyramid terminations. The prism consists of primarily four {110} faces with rounded or faceted comers between the primary faces. The pyramidal terminations can appear ovoid or faceted. A major facet plane of the pyramids is (101). A model consistent with the morphology of many voids in rutile nanoparticles is proposed.

Facet crystallography by electron diffraction in the SEM

The study of fracture in engineering materials often involves an analysis of the crystallography of the fracture surface. In particular, the question is often asked, "What, if any, low index plane corresponds to the plane of a particular fracture surface facet?" To determine the crystallographic plane of a surface facet, it is necessary to determine the orientation of the grain and the orientation of the facet plane relative to the grain. For example, if a euhedral crystal of known orientation is fractured, an optical reflection goniometer can be used to measure the angles between a facet and known crystal faces in order to deduce the direction of the facet normal. Laue x-ray diffraction patterns taken from well aligned facets can also be analyzed to determine the orientation of the crystal normal to the facet. In many engineering materials, the facets are small, usually as a result of a small grain size in the material, and it becomes impractical to use these techniques.