Tsukasa Washio

Field emission property of Al:ZnO whiskers modified by amorphous carbon and related films

A new type of ceramic field emitter was designed using the chemical vapor deposition process. There are two major features of the materials used to construct the emitter: an electrically conductive Al:ZnO whisker with an extremely sharp tip and amorphous carbon and related coating materials with a relatively low electron affinity at the tip region. Some aggregations of whiskers were synthesized as a function of the radius of curvature at the whisker tip. In addition, four types of amorphous coatings were provided for this experiment: C:H, CNx:H with C–H and N–H terminations, CNx:H with N–H termination and CNx films. The field emission property was influenced not only by the radius of curvature at the tip but also by the termination structure of the amorphous carbon and related films.

Work Function of Amorphous Carbon Nitride with Various Functional Groups

The work function of the amorphous phase of hydrogenated carbon nitride (a-CNx:H) was calculated using Fowler–Nordheim field emission. First, metal films were deposited on conductive ZnO:Al whiskers to determine the geometric field enhancement factor at the tip of the field emitter. The radius of curvature at the whisker tip after the deposition of metal films was measured. Next, the geometric field enhancement factor of ceramic whiskers was calculated using the work function of the metals and the radius of curvature of the emitter tip. Finally, the work function of a-CNx:H was introduced using the Fowler–Nordheim equation with the geometric field enhancement factor. The work function of a-CNx:H is dependent upon the functional group.

Cu2ZnSnS4 thin film deposited by sputtering with Cu2ZnSnS4 compound target

Cu2ZnSnS4 (CZTS) thin films were prepared by a single sputtering process with a CZTS compound target or a co-sputtering process with Cu, ZnS, and SnS targets followed by annealing in a H2S-containing atmosphere at several temperatures. Between the CZTS thin films prepared by both single and co-sputtering processes annealed at 500 °C, there are no major differences in the X-ray diffraction patterns, optical properties, and chemical composition. However, there is a difference in the scanning electron microscopy images. Although the CZTS thin films prepared by the co-sputtering process have some voids, the CZTS thin films prepared by the single sputtering process have no voids. The solar cells prepared with the CZTS thin films deposited by the single sputtering process followed by annealing at 500 °C show a higher efficiency of 4.40% than those prepared with the CZTS thin films prepared by the co-sputtering process (2.06%).

Surface Damage of Whisker-Type Cold Emitter after Overload Test

An overload test of a new type of ceramic field emitter, ZnO:Al whisker covered with amorphous hydrogenated carbon nitride film, was performed. The aim of this study is to investigate surface damage of the whisker-type cold emitter under overload conditions. The morphologies of the emitter surface before and after operation were compared using scanning electron microscopy. The emission was terminated after the generation of surge current that severely damaged the emission surface.