This page lists some things that can be added to the basic scanning tunneling microscope. Since they add cost and increase build time, they may not be appropriate for all student builds.
During sample positioning and approach, it is nice to have an optical image from the tip/sample region. Recently, a borescope with a short focal length has become available on Ebay. It is called the “3 in 1 USB Ear Cleaning Endoscope Earpick Waterproof Borescope Inspection Camera” and costs $11.90. While it only has 640x480 resolution (0.3 MP), the 1.5 cm focus distance is a required feature. Windows 10 recognizes this camera without any additional drivers and includes software to view the live image.
Integration to the STM is very easy. A 7/32” bit can be used to drill a hole or holes in the PVC housing at a point where both the tip and the sample can be seen. One good position for the hole is as close to the flange as possible, angled slightly down to point at the end of the tip, and rotated about 90º from the sample access hole. Another good position for the hole is right at the tip level without any tilt on the hole. The picture below on the left shows the housing just after the hole has been drilled. The picture on the right is from the borescope showing the tip approaching the DVD sample. The borescope is mounted in the angled hole. On the far side of the tip, the untilted hole is visible.