Growth and surface properties of lanthanum hexaboride crystals

Single crystal lanthanum hexaboride (LaB6) has been grown in a tammann furnace. In the furnace and at 1500 K, lanthanum (La) and boron (B) are melted in proportion to the stoichiometry mass ratio in 30–45 kg/cm2 argon atmosphere. When the diffusion time at 1500 K took less, the cubical crystal grew and when it took longer, the needlelike crystal grew. The crystal growing direction was 〈100〉 for both cases. From the etch-pit observation, this crystal growth has been shown to be stratified along the direction 〈100〉 and therefore the periodic crystal growth has been certified. The height of remolded microprotrusion, which was formed on LaB6 emitter apex, was about 30 Å and the curvature radius was between 10 and 20 Å. The brightness (B) of the electron beam emitted from this remolded tip was about 1×1011 A ⋅ cm−2 ⋅ sr. This was unstable, however, because of the random walk of La atoms on the tip. Variation of the work function of platelike LaB6 tip takes a constant value beyond monolayer formation of O2 and H2 on the surface, respectively. Therefore, the LaB6 emitter is stable even in low quality of vacuum (10−7–10−8 Torr). Pyramidlike etch pit has about 30° dip angle. The etching degree defined to be the ratio of x/h was between three and four.