AuPd coating is done according to recipe. The target thickness is 10-25 nm depending upon the topography of the samples. Thicker coatings are desirable for samples with more topographic contrast to guarantee a continuous film across topographical features. Since the sputter coater does not have a deposition rate monitor-- many of coaters for SEM sample preparation do not-- deposition under fixed conditions is used to guarantee target film thickness.
The following parameters are considered fixed in the recipes that follow:
- Sample-Target Distance = 25 mm.
- Ar Partial Pressure = 5x10-2 mbar.
The calibrated AuPd thickness is 0.015 nm/mA/s.
For practical applications, for a very smooth insulating sample with very little topgraphic relief, a thin AuPd layer of ~ 15 nm would be desirable. Assuming a 30 mA emission current this would require a 33 s deposition time. For a sample with larger topographic relief a ~ 25 nm AuPd film thickness would be desirable. Again assuming a 30 mA emission current this would require a 55 s deposition time.