Measurement of the Sticking Coefficients of Silver and Gold in an Ultrahigh Vacuum

The sticking coefficients of silver and gold evaporated on a SiO substrate under ultrahigh-vacuum conditions have been measured as a function of the thickness of the metal deposit. The mass of the deposit was determined by a quartz crystal oscillator. The incident rate of the metal was measured by observing the metal vapor flux through an ionization gauge. Observations were made at an incident flux between 3 and 4×1013 atoms/cm2/sec and substrate temperatures of 300° and 450°K. A sticking coefficient of unity was found for silver when the mean thickness of the deposit was greater than 10 Å and for gold when the deposit was thicker than 20 Å. The mean sticking coefficient measured for silver is 0.81±0.05 in the thickness range of 0–10 Å. Gold was found to have a mean coefficient of 0.89±0.05 in the thickness range 0–20 Å. These values are higher than those previously reported in the literature. The experiments indicate that the discrepancies are due to a higher substrate contamination in previous studies.