Chemical and structural components of work function changes in the process of palladium hydride formation within thin Pd film

Surface phenomena which occur in the process of palladium hydride PdHx formation during H-2 interaction "in situ" with thin palladium films were studied by means of two methods: (i) measurements of work function changes Delta Phi, and (ii) determination of topographical images using atomic force microscopy (AFM). A very strong decrease of the work function up to similar to 2 V was registered in the course of the reaction at 78 K when thin Pd films deposited on Pyrex glass were applied. However a small Delta Phi was noticed when using Pd films deposited on glass precovered with a thick platinum film. AFM topography exhibited a net of distinct protrusions in the first case, but the topography was almost unchanged in the second. We suggest that the above unusually high decrease of the work function in the process of PdHx formation within a Pd/glass system is caused by the change of thin Pd film topography, and not by very strong polarization of hydrogen adspecies on PdH, surface. (c) 2005 Elsevier B.V. All rights reserved.