Submonolayer h-BN was grown on Ni foil in ultra-high vacuum by the diffusion and precipitation method and the growth process was studied by X-ray photoelectron spectroscopy. Formation of h-BN started to be observed at 600 degrees C. All through the process, the surface was always slightly B-rich, which is consistent with the fact that B which is soluble in Ni at a high temperature can diffuse in Ni by the conventional bulk diffusion and insoluble N cannot. Moreover, both formation and decomposition of h-BN were found to occur at elevated temperatures possibly depending on provision of N atoms to the surface. On the Ni surface, decomposition of h-BN was observed at a relatively low temperature of 800 degrees C. (C) 2019 The Japan Society of Applied Physics