Characterization of AlInN/AlN/GaN Heterostructures with Different AlN Buffer Thickness

Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (101 ¯ 2) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (101 ¯ 2) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 × 108 cm−2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results. © 2016, The Minerals, Metals & Materials Society

Antioxidant activity of some Turkish medicinal plants

<div><p>DPPH, superoxide and nitric oxide radical scavenging activities and total phenolic content (TPC) of some less known plants, distributed in Burdur-Antalya provinces and consumed both as food and for the medicine, <i>Asplenium ceterach</i> L. (golden herb), <i>Valeriana dioscoridis</i> Sm. (valerian), <i>Doronicum orientale</i> Hoffm. (tiger herb), <i>Cota pestalozzae</i> (Boiss.) Boiss. (camomile), <i>Eremurus spectabilis</i> M. Bieb. (foxtail lily), <i>Asphodeline lutea</i> (L.) Rchb. (asphodel) and <i>Smyrnium connatum</i> Boiss. and Kotschy (hemlock) were investigated. As a result, the highest 2,2-diphenyl-1-picril hydrazyl (DPPH) radical scavenging activity was determined in <i>C. pestalozzae</i> extract (IC₅₀ = 18.66 μg mL^− 1), the highest superoxide and nitric oxide radical scavenging activity was determined in <i>A. ceterach</i> extract (IC₅₀ = 145.17 and 372.03 μg mL^− 1). The highest TPC was determined in <i>A. ceterach</i> extract (59,26 μg mL^− 1) as gallic acid equivalent. Further bioactivity and phytochemistry studies on these plants may enlighten new drug discovery researches.</p></div