  We report X-ray Photon Correlation Spectroscopy (XPCS) results on a
bidimensional (2D) gel formed by a Langmuir monolayer of gold nanoparticles.
The system allows an experimental determination of the fourth order time
correlation function which is compared to the usual second order correlation
functions and to the mechanical response measured on macroscopic scale. The
observed dynamics is anisotropic, heterogeneous and super-diffusive on the
nanoscale. Different time scales, associated with fast heterogeneous dynamics
inside 2D cages and slower motion of larger parts of the film, can be
identified from the correlation functions.
