Porous layers were produced on a p-type (100) Si wafer by electrochemical anodic etching. The morphological, nanostructural and optical features of the porous Si were investigated as functions of the etching conditions. As the wafer resistivity was increased from 0.005 to 15 Ω·cm, the etched region exhibited ‘sponge’, ‘mountain’ and ‘column’-type morphologies. Among them, the sponge-type structured sample showed the largest surface area per unit volume. Silicon nanocrystallites, 2.0 to 5.3 nm in size, were confirmed in the porous layers. The photoluminescence peaks varied in the wavelength range of 615 to 722 nm. These changes in the maximum peak position were related to the size distribution of the Si crystallites in the porous silicon. The doping levels of the wafers significantly affect the size distribution of the Si crystallites as well as the light-emitting behavior of the etched Si, which contains nanoscale Si crystallites.

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The effects of initial powder size on microwave-assisted sintering (MWS) were investigated. BaTiO 3 powders with an average particle size of 50, 100, and 500 nm were prepared and sintered with MWS and conventional heating-based sintering (CS). Samples of the 50 -and 100-nm-sized BaTiO 3 powders were mechanically milled to study the effects of powder crystallinity on microwave absorption during the MWS process. The MWS of the 50-nm-sized BaTiO 3 powder resulted in a relative mass density of more than 90% when sintered at 1050°C, whereas the same density was achieved at 1200°C with CS. This difference between the optimal sintering temperatures, which is caused by the absorption of microwaves, was not observed when the 500-nm-sized BaTiO 3 powder was used. The sinterability of the BaTiO 3 ceramics prepared through the MWS of mechanically milled, 50-nm-sized powders decreased with increasing milling time. However, the sinterability was much higher than that of the BaTiO 3 ceramics prepared through the MWS of the 100-and 500-nm-sized unmilled powders. In conclusion, microwave absorption has significant effects on the sintering behavior of~50-nm-sized powders, but is negligible for 500-nm-sized powders.The BaTiO 3 ceramics were produced at temperatures ranging from 900°C to 1350°C with CS or MWS for 10 min. Three different soaking time zones (0-10, 10-20, and 20-30 min) were applied to calculate the variation in the activation energy of densification as a function of the soaking time. When raising the temperature, the MWS and CS heating rates were 50°C/min and 5°C/min, respectively, and after soaking, the samples were cooled naturally. CS was performed in an electric furnace operating at 220 V H. Chan-contributing editor Manuscript No. 35499.

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