INTRODUCTION Cupric oxide (CuO) is an important p-type transitionmetal-oxide semiconductor. Owing to its photoconductive and photochemical properties, CuO has many potential applications, such as solar cell 1 , gas sensors 2 , lithium ion electrode materials 3 , catalysts 4 and superconductor 5 . The morphology and sizes of nanomaterials have been proved to have a significant influence on their properties and applications. Over the past years, various methods have been applied to prepare CuO

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... h special morphologies, such as nanofibers 6 , hollow nanospheres 7 , rose-like nanoarchitectures 8 , urchin-nanostructures 9 , sheaf-like nanostructures 10 , hollow submicrospheres 11 and nanowires 12 . In this work, a convenient microwaveassisted chemical route was applied to prepare leaf-like CuO nanocrystals using CuCl 2 •2H 2 O and triethylamine as starting reactants. According to the optical absorption spectrum, the band-gap energy of as-prepared CuO nanoleaves was estimated to be 2.56 eV, showing a good quantum size effect. EXPERIMENTAL All chemicals (analytical grade reagents) were purchased from Shanghai Chemical Reagents Co. and used without further purification. Microwave-heating was carried out by a domestic microwave oven (Galanz WG800SL23-K6, 2.45 GHz, maximum power 800 W).