Enhanced Field Emission and Optical Properties of Controlled Tapered ZnS Nanostructures

High-quality ZnS tapered ID nanostructures were successfully synthesized by a simple thermal evaporation technique after having careful control on the size of the catalyst and growth temperature. The dynamics of varied gas flow on the extent of tapering was monitored with specific experimental settings. Systematic optical investigations revealed that the PL emission was due to the surface states. Surface optical phonons in tapered nanostructutes were also observed, which showed variation in the surface potential. The dielectric continuum model was used to calculate the wavelength of the surface potential perturbation. The field emission (FE) measurements Were carried out to determine the correlation between the FE and the shape of nanostructures. It was observed that tapered nanowires with an average diameter of 60 nm were excellent field emitters with low turn-on fields ranging from 5.5 to 11.67 V/mu m and the field enhancement factors from 1940 to 890, respectively, at various cathode distances. By the two-region field emission model, the absolute amplification factor was calculated and found to be comparable to that of carbon nanotubes. The fitting of the experimental points with the Fowler-Nordheim equation concluded that the emission is from the tips of nanowires. The present study on FE showed that the tapered nanowires can be potential materials for the novel optoelectronic devices.