Local investigation of the emissive properties of LaB6–ZrB2 eutectics

LaB 6 –ZrB 2 composites obtained by directional solidification at eutectic composition have been investigated by low-energy electron microscopy (LEEM) and thermal emission electron microscopy (ThEEM). The transitions from the mirror electron microscopy mode to the LEEM mode for the hexa- and diborides indicate lower work functions of the two phases when embedded in the composite compared to the corresponding single phases. In the composite, the work function of the ZrB 2 fibers is similar to that of the matrix and ThEEM images display a brighter contrast for the fibers. This is explained by the thermally activated diffusion of La on the fiber surface.