Shock-Assisted Superficial Hexagonal-to-Cubic Phase Transition in GaN/Sapphire Interface Induced by Using Ultra-violet Laser Lift-Off Techniques

Ultra-violet （KrF excimer laser,λ =248 nm） laser lift-off （LLO） techniques have been operated to the GaN/sapphire structure to separate GaN from the sapphire substrate. Hexagonal to cubic phase transformation induced by the ultra-violet laser lift-off （UV-LLO） has been characterized by micro-Raman spectroscopy, miero-photoluminescence, along with high-resolution transmission electron microscopy （HRTEM）. HRTEM indicates that UV-LLO induced phase transition takes place above the LLO interface, without phase transition under the LLO interface. The formed cubic GaN often exists as nanocrystal grains attaching on the bulk hexagona/GaN. The half-loop-clusterlike UV-LLO interface indicates that the LLO-indueed shock waves has generated and played an assistant role in the decomposition of the hexagonal GaN and in the formation of cubic GaN grains at the LLO surface.     

蛇床子素酯类/磺酸酯类衍生物的合成与抗菌活性研究

为了寻找抗菌苗头化合物,以蛇床子素为原料,对其7位结构改造,经脱甲基化制得中间体Ⅰ,中间体Ⅰ再分别与酰氯、磺酰氯反应,合成了12个目标化合物,经_¹H NMR 、_¹³C NMR和MS确认结构。体外抗菌活性筛选结果表明：两类衍生物对金葡菌有较好的抗菌活性,磺酸酯衍生物的活性优于羧酸酯衍生物,尤以化合物Ⅲd和Ⅲe的抗金葡菌的活性最为显著,MIC值均为32mg/L,远优于蛇床子素的活性,接近对照药苯唑西林。该研究也表明蛇床子素7位的结构修饰能改善其抗菌活性,值得进一步研究。