Distinguishing nanobubbles from nanodroplets with AFM: the influence of   vertical and lateral imaging forces
  The widespread application of surface-attached nanobubbles and nanodroplets in biomedical engineering and nanotechnology is limited by numerous experimental challenges, in particular, the possibility of contamination in nucleation experiments. These challenges are complicated by recent reports that it can be difficult to distinguish between nanoscale drops and bubbles. Here we identify clear differences in the mechanical responses of nanobubbles and nanodroplets under various modes of AFM imaging which subject the objects to predominantly vertical or lateral forces. This allows to distinguish between nanodroplets, nanobubbles, and oil covered nanobubbles in water. 
Hongjie An, Beng Hau Tan, and Claus-Dieter Ohl
cond-mat.soft