||We have used Temperature Programmed Auger (TPA) and Temperature Progammed Low Energy Electron Diffraction (TPLEED) and Temperature Progammed Desorption (TPD) to study the effect of temperature on the surface structure of Pd/W(111) and Pd/Mo/W(111) in an ultrahigh vacuum (UHV) chamber with a base pressure of 1 x 10-10 torr. In Pd/W(111) surfaces, we can get the real-time information of the surface at high temperature and then observe the reversible faceted/planar phase transition. Furthermore, TPA reveals that the apparent coverage of Pd changes across the transition. When the planar (111) surface appears, the wetting layer of Pd slightly reduces to about 1.2PML (physical monolayer). Besides, the coverage of Pd slightly raises about 0.1PML in the faceted surface below the temperature of the phase transition. In the case of Pd/Mo/W(111) surfaces, when the coverage of Mo is added to about 1PML, the temperature of phase transition reduces 300K and the width of the hysteresis also reduces by 45K. In addition, the phase transition becomes less apparent. Thus, the behavior of Pd on Mo/W(111) is closer and closer to that of Pd/Mo(111) as more and more Mo is added. For even thicker Mo layers, surprisingly, the temperature (as well as its width) of the phase transition is lowered with the increased coverage of Mo.|
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