What would be the “recommended purity” for SEM applications?
This would probably be one of those kinds of questions for which there is no universally accepted answer. We believe that for most if not all SEM applications, 0.9999 purity is quite fine and using 0.99999 could very well be overkill. In any case, there is a noticeable difference in the cost when comparing 0.9999 vs. 0.99999 purity. But there is a cost associated with purification. For example, taking gold from 0.98 to 0.99 involves a higher cost, and there is even more of a cost when going to 0.999 purity. And as one goes from 0.9999 to 0.99995 and then to 0.99999 is still more cost. In other words, while one really does want the highest purity gold in their cathodes, there is a cost consideration. But on the down side of purity, there clearly is a point where the impurity elements that don’t sputter begin to build up on the surface, resulting in a mostly non-gold layer. When when this happens the sputtering rate essentially “stops”. Now we know this would never ever happen with a cat
