DECOMPOSITION OF DIBORANE ON PD(111) - THERMAL AND CHEMICAL BEHAVIOR OF SURFACE BORON

Recent Auger electron spectroscopy (AES)-low energy electron diffracti on (LEED)-thermal desorption spectroscopy (TDS) results on interaction s of diborane (B2H6) with Pd(111) surface and oxygen with a surface of Pd(lll)-B solid solution are reported. The physicochemical behaviour of surfaces covered with the post-interaction layer is described. AES results following exposure of Pd(lll) to B2H6 at 300 K indicate the fo rmation 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 exposur es greater than 16 langmuirs (L). As found from TDS results, hydrogen is the only desorbing product (360 K < T-des < 750 K) detected for the B2H6 exposures studied. Exposure of a clean Pd(lll)-B solid solution surface to O-2 at T > 600 K leads to a strong chemical interaction bet ween dissolved boron and oxygen, evidenced by the formation of the BxO y overlayer on the surface. The kinetics of the B surface segregation process is analysed. The rate of this process, which is initially cont rolled by the bulk diffusion, diminishes at T > 800 K due to the compe titive dissolution of B into the Pd(lll) bulk. The BxOy overlayer demo nstrates a high level of thermal stability and a distinct chemical ine rtness in respect to hydrogen. (C) 1998 Elsevier Science B.V. All righ ts reserved.