Low-field emission of electrons by thin metal films: effect of composition, deposition conditions and morphology on emission capability of a film

Abstract

The paper presents experimental study of the phenomenon of low-threshold field electron emission from thin films of several metals: Mo, W, Zr, Ni and Ti. We used magnetron sputtering with variable process parameters to deposit films of various thicknesses on silicon substrates of different types. A number of species of these films having effective (mean) thickness 6–10 nm produced electron emission at room temperature in dc electric field with macroscopic strength as low as a few Volts per micrometer. Optimized thermal/field treatment procedure further improved their emission properties reducing the threshold field by several times. Atomic force microscopy study revealed a correlation between emission properties of the films and their surface topography, namely, the presence of grains with lateral dimensions 20–50 nm and height ~2 nm. At the same time, no equally pronounced correlation of the emissivity with other characteristics of coatings (including the sort of the metal and the silicon substrate conductivity type) was detected. Results of the study witness in favor of two-temperature (or hot-electron) emission mechanism for the investigated coatings.

Keywords

• field emission
• thin films
• atomic force microscopy
• hot-electron emission