US Penny

Preparation: A cheap option for the third sample is a new US penny. A new penny is usually still shiny so it only needs to be cleaned with methanol to get the finger oil off it. It can be mounted to a washer but the simplest method is to just placed it on the STM sample holder and let gravity hold it down. 

Imaging: Two images of the penny are shown below. In all cases, the flat area just above the date is where the images were taken. On the top is the penny as it appears when imaged using a light microscope. This microscope has a magnification of 800 times so the field of view (top to bottom) is about 210 μm. Ridges from the manufacturing process are all in the same direction, but the ridge separation is not consistent. At this size, the penny is quite similar to the aluminum foil sample. On the bottom is an image taken by an atomic force microscope with a field of view (top to bottom) of 15 μm. At this scan size, ridges and bumps are both visible. The ridges are spaced at about 4000 nm and the bumps are 700 nm and smaller.

Two pictures taken from the STM are shown below. Both pictures are taken at approximately the same location, with the same bias of +1 V, and with the same the same scan speed (300 mS per line). The image on the top has a scan size of 4200 nm and the image on the bottom has a scan size of 600 nm. Both images have their share of randomly-sized ridges but the smaller scan size shows a number of smaller bumps – some as small as 20 nm in diameter.