These are un-etched 4" silicon wafers, part of a lot of 25 I purchased for the series of museum displays I am helping coordinate. These 5 are my element tax on that shipment. As un-etched wafers they have a beautiful mirror-like finish on the front, and an interesting iridescent surface on the back. I'm not sure why they were being sold on eBay, but I can only assume there was some defect that caused them to be rejected, or maybe they were a custom-made batch that turned out not to be needed. Assuming the front surfaces are not the cause of their rejection, they are probably the smoothest, most perfectly polished objects in my collection: Silicon wafers are superlative in all respects, purity, mechanical perfection, fineness of detail (in etched wafers), you name it.
According to the label they are doped with antimony, but I suspect the amount added is very small compared to the bulk amount of silicon, being only in a very thin layer on the surface, so I am assigning a very high purity to this sample.
Source: eBay seller surenet
Contributor: Theodore Gray
Acquired: 11 July, 2003