ON THE TEMPERATURE-INDUCED TRANSFORMATION BETWEEN THE 2 AL(111)-(ROOT-3X-ROOT-3) R30-DEGREES-RB STRUCTURES

The dynamics of the temperature induced transformation between low and high temperature adsorption phases of Rb on Al(111) has been followed by high resolution core level spectroscopy. Particular emphasis has b een paid to the order-preserving transformation between the low and hi gh temperature Al(111)-Rb-(root 3 X root 3)R30 degrees structures in w hich Rb atoms occupy on-top and substitutional sites, respectively. Fo r a Rb coverage of 0.33 monolayer the rate of conversion from on-top t o substitutional sites is found to increase strongly at 250 K. For Rb coverages below 0.33 but above approximately 0.14 monolayers the conve rsion occurs at lower temperatures. Increasing the coverage above 0.33 monolayers increases the conversion temperature. The possibility to d etect the Al atoms which are expelled from the first Al layer during t he conversion is demonstrated.