Thin (similar to 10 nm) BaO films on tungsten substrates, prepared at
specific coverages from multilayer Langmuir-Blodgett precursor films,
were heated to different temperatures between 200 and 1200 degrees C i
n a vacuum environment. The chemical changes occurring at the BaO/W in
terface were characterized by X-ray photoelectron spectroscopy, infrar
ed reflection spectroscopy, spectroscopic ellipsometry, and X-ray diff
raction analyses. The results show that a BaWO4 phase forms above an a
pproximate threshold temperature of 800 degrees C and, contrary to pre
vious observations reported for heterogeneous reactions in powders, no
evidence for a Ba3WO6 phase is seen. These data form a fundamental ba
sis for understanding the regulation of the emission work function in
the operation of an alkaline-earth-coated tungsten cathode fluorescent
lamp.