Characterization of thin film electron emitters by scanning anode field emission microscopy

Scanning anode field emission microscopy is used to map the electron emission current I(x,y) under constant anode voltage and the electron extraction voltage V(x,y) under constant emission current as a function of tip position on carbon based thin film emitters. The spatially resolved field enhancement factor beta (x,y) is derived from V(x,y) maps. It is shown that large variations in the emission site density (ESD) and current density can be explained in terms of the spatial variation of the field enhancement beta (x,y). Comparison of beta (x,y) and I(x,y) shows that electron emission currents are correlated to the presence of high aspect ratio field enhancing structures. We introduce the concept of field enhancement distribution f(beta), which is derived from beta (x,y) maps to characterize the field emission properties of thin films. In this context f(beta )d beta gives the number of emitters on a unit surface with field enhancement factors in the interval (beta,beta +d beta). It is shown experimentally for the carbon thin film emitters investigated that f(beta) has an exponential dependence with regard to the field enhancement factor beta. The field enhancement distribution function f(beta) can be said to give a complete characterization of the thin film field emission properties. As a consequence, the emitted current density and ESD can be optimized by tuning f(beta) of the emitting thin film. (C) 2001 American Institute of Physics.