Figure 3.

(a) Measured 3D surface profile of the water–oil interface at f=15.2 nm. (b) Scatter plot of surface height h(x,y) vs ρ(x,y) at f=15.2 mm. ρ(x,y) is the distance between point (x,y) and the vertex, as defined in Fig. 1b. When ρ(x,y) is relatively small, i.e., within the area near the center, the surface is approximately spherical in shape; near the boundary, the shape of the surface becomes much more linear.