  We investigate the shape and mechanical properties of liquid interfaces down
to nanometer scale by atomic force microscopy (AFM) and scanning electron
microscopy (SEM) combined with in situ micromanipulation techniques. In both
cases, the interface is probed with a cylindrical nanofiber with radius R of
the order of 25-100 nm. The effective spring constant of the nanomeniscus
oscillated around its equilibrium position is determined by static and
frequency-modulation (FM) AFM modes. In the case of an unbounded meniscus, we
find that the effective spring constant k is proportional to the surface
tension {\gamma} of the liquid through k = (0.51 +- 0.06) {\gamma}, regardless
of the excitation frequency from quasistatic up to 450 kHz. A model based on
the equilibrium shape of the meniscus reproduces well the experimental data.
Electron microscopy allowed to visualize the meniscus profile around the fiber
with a lateral resolution of the order of 10 nm and confirmed its catenary
shape. The influence of a lateral confinement of the interface is also
investigated. We showed that the lateral extension L of the meniscus influences
the effective spring constant following a logarithmic evolution k ~
2{\pi}{\gamma}/ln(L/R) deduced from the model. This comprehensive study of
liquid interface properties over more than four orders of magnitude in meniscus
size, shows that advanced FM-AFM and SEM techniques are promising tools for the
investigation of mechanical properties of liquids down to nanometer scale.
