Characterization and field-emission properties of vertically aligned ZnO nanonails and nanopencils fabricated by a modified thermal-evaporation process

Vertically aligned ZnO nanonails and nanopencils are synthesized on a silicon substrate using a modified thermal-evaporation process, without using a catalyst or predeposited buffer layers. An adiabatic layer is used to provide an abrupt temperature decrease and high gas concentration for the nanostructures growth. The structure and morphology of the as-synthesized ZnO nanonails and nanopencils are characterized using X-ray diffraction, and scanning and transmission electron microscopies. Raman and photoluminescence properties are also investigated at room temperature. Field-emission characterization shows that the turn-on fields for the vertically aligned ZnO nanonails and nanopencils are 7.9 and 7.2 V μm¹, respectively.