Quantum dots (Q-dots) are particles whose size is limited to a few nanometers.
What makes Q-dots interesting is that their physical properties are controlled by their small size.
The white particles are 30nm large Q-dots. The mono atomic terraces in the underlying surface are clearly visible and prove the quality of the measurement.
The lower image on the left hand side is a zoom into the previous image. It shows the perfectly round shape of the Q-dots.