that scientists in New South Wales, Australia, have created a single atom transistor. The actual transistor is composed of a single atom of the phosphorous-31 isotope.
This single atom was precisely placed on a base of silicon using a Scanning Tunneling Microscope in an ultra-high vacuum chamber. The unique part of the technique that was employed was that they were able to position and confirm the individual phosphorous atoms precisely on the silicon.
There is still a long way to go for researchers as they will need to build off of this technology to develop chips comprised of many P-31 transistors that are able to be used for calculations. The current cost of the technology is also incredibly expensive.
The experiment details have been published here
and you can also view a YouTube video here.