Determination of the coverage dependent work function for Li adsorbed on Ru(0 0 1)

The coverage dependent work function change ΔΦ was measured for Lithium adsorbed on Ru(0 0 1) at T=100 K. A highly flux stable source of atomic Lithium was employed to ensure linear dependence of coverage with time. An absolute coverage calibration with an uncertainty of about 3% was achieved through observation of the (3×3)R30° overlayer structure by LEED. The temperature programmed desorption monolayer was thus found to be n/nRu=0.76±0.02. Continuous work function measurements were performed using the diode method, while ultraviolet photoelectron spectroscopy has been used to check the work function change at selected points. Our new data are intended as a benchmark for theoretical calculations of work function changes in these systems. Considerable deviations between experiment and theory were the reason to remeasure ΔΦ versus coverage in a precise way. The discrepancy towards theory remained. This instigated a new effort in the calculation of work function changes with coverage. The agreement between the ab initio theory and experiment is now close to perfect.