Formation of Pd-Cu structures in the process of MIS sensors fabrication ensures a high quality of devices if the corresponding electronic states in Pd-Cu system lead to large number of free active bonds on the electrode surface. In the present work the role of Pd surface doping with copper and related mechanisms of adsorption, desorption and bulk dissolution of hydrogen were considered. The theoretical modeling of Pd-Cu alloy was performed using density functional theory combined with coherent potential approximation. The total energy and the partial density of states (PDOS) for Pd_xCu_1-x alloy were analyzed for the Cu atomic fraction varied in the range of 0 - 100 at%.

The results show that the most radical changes in the electron structure of alloy take place when the Cu content is less than 50 at%. In this case p-states of Cu are mainly responsible for the reconstruction of intermetallic bonds in Pd-Cu system that leads to activation of catalytic processes in the system and formation of stable Pd-Cu compounds. The reorganization of a surface caused by formation of surface Cu_XPd composite may be applied for enhancement of Pd surface catalytic activity as to dissociative adsorption of H₂ with the following dissolution of atomic hydrogen in the bulk.

The obtained results allow us to explain the observed copper induced slowing down of Pd surface aging and degradation in MIS structures and predict behavior of sensor surfaces formed by this compound. The reconstruction of the surface layers that was observed experimentally [1] is explained on the basis of obtained results.

[1] V. Litovchenko, T. Gorbanyuk, A. Efremov and A. Evtukh, Sensors and Actuators (1999) 74, 233-236.

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