A new metallization scheme has been developed for obtaining very low Ohmic contact to n-GaN. The metallization technique involves the deposition of a composite metal layer Ti/Al/Ni/Au (150 Å/2200 Å/400 Å/500 Å) on n-GaN preceded by a reactive ion etching (RIE) process which most likely renders the surface highly n type. Of the several attempts and with annealing at 900 °C for 30 s, contacts with specific resistivity values of ρs=8.9×10−8 Ω cm2 or lower for a doping level of 4×1017 cm−3 were obtained. The physical mechanism underlying the realization of such a low resistivity is elucidated.

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The chemical composition of the essential oil (EO) obtained by solvent-free microwave extraction (SFME) and hydrodistillation (HD) from the peel of grapefruit (Citrus Paradisi. L) was analysed by gas chromatography ⁄ mass spectrometry (GC ⁄ MS). Totally, twenty-five components were identified in the EO. Limonene was observed as dominant (91.5-88.6%) for two extraction methods, SFME and HD, respectively. b-Pinene (0.8-1.2%), linalool (1.1-0.7%), a-terpinene (0.7-1.0%) and the other minor components were also detected. Disc diffusion method was applied to determine the antibacterial properties of the EO. The results showed that the EO of grapefruit peel had a wide spectrum of antimicrobial activities against Staphylococcus aureus, Enterococcus faecalis, Staphylococcus epidermidis, Escherichia coli, Salmonella typhimurium, Serratia marcescens and Proteus vulgaris, with their inhibition zones ranging from 11 to 53 mm.

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