Decomposition of diborane on Pd(111): thermal and chemical behaviour of surface boron

Abstract

Recent Auger electron spectroscopy (AES)–low energy electron diffraction (LEED)–thermal desorption spectroscopy (TDS) results on interactions of diborane (B2H6) with Pd(111) surface and oxygen with a surface of Pd(111)–B solid solution are reported. The physicochemical behaviour of surfaces covered with the post-interaction layer is described. AES results following exposure of Pd(111) to B2H6 at 300 K indicate the formation of a B overlayer on the surface due to complete decomposition of the B2H6 molecules. The B surface concentration increases with rise of the B2H6 exposure, exhibiting a maximum constant value for exposures greater than 16 langmuirs (L). As found from TDS results, hydrogen is the only desorbing product (360 K<Tdes<750 K) detected for the B2H6 exposures studied. Exposure of a clean Pd(111)–B solid solution surface to O2 at T>600 K leads to a strong chemical interaction between dissolved boron and oxygen, evidenced by the formation of the BxOy overlayer on the surface. The kinetics of the B surface segregation process is analysed. The rate of this process, which is initially controlled by the bulk diffusion, diminishes at T>800 K due to the competitive dissolution of B into the Pd(111) bulk. The BxOy overlayer demonstrates a high level of thermal stability and a distinct chemical inertness in respect to hydrogen.