Time variation of the work function of field emitter tip surface and the development of adsorption of residual gas molecules studied by sawtoothlike emission current method

Abstract

The sawtoothlike emission current (STEC) method and its theory are described, and this method is shown to make possible the simultaneous measurement of the time variation of the work function φ(t) and its derivative dφ/dt. Application of the STEC method to the field emission (FE) current from a tungsten emitter tip in an ultra-high vacuum of 2×10−8 Pa shows that the time variation of φ(t) and dφ/dt can be divided into four stages. In addition, it gives the effective tip radius αr0=1.1 μm, resulting in α=6.9 for the observed tip radius r0=0.16 μm. The observed time variation of φ(t) and dφ/dt is analyzed from the viewpoint of the development of the adsorption of residual gas molecules on the emitter tip surface, and each stage is successfully identified as follows: The first stage is the formation stage of adsorption nuclei and clusters, the second stage is the free growth stage of adsorption islands, the third stage is their coalescence growth stage, and the fourth stage is their Langmuir growth stage. The mode of adsorption development is similar to the mode of crystal growth taking place in three-dimensional space and on surface.