Formation of urchin-like CuO structure through thermal oxidation and its field-emission lighting application

Urchin-like CuO microstructures were formed using simple, template-free, one-step thermal oxidation of Cu solid microspheres in an air atmosphere at temperatures ranging from 350 to 500 °C. The urchin-like CuO microstructure consists of crystalline CuO nanowires grown radially on the surface of the sphere, a shell layer of CuO a few micrometers in thickness, and a hollow core. Study of the formation mechanism revealed that during oxidation, the nanowires grow from the surface, and the diameter, length, and population density of the nanowires increase with the oxidation time. For a sample formed at 450 °C for a dwell time of 24 h, the average diameter, length, and population density of the nanowires were 44.0 nm, 11.5 μm, and 25 nanowires/μm2, respectively. The novel urchin-like structure and high aspect ratio of the nanowires elicit unique properties. Study of the magnetic properties revealed that the urchin-like CuO is a semihard magnetic material with a coercive force of 135 Oe. Studies on the field-emission characteristics of the material demonstrated that an urchin-like emitter had a low turn-on field of 2.94 V/μm, a high field enhancement factor of 3715, a high luminance of 11,080 cd/m2, an excellent emission uniformity of over 3.5 × 3.5 cm2, and high emission stability during a 50-h test at a current density of 100 μA/cm2.