Structure and fluctuations of liquid surfaces and interfaces

X-ray scattering techniques are increasingly used for the study of liquid surfaces and interfaces. We give here scattering cross-sections for diffraction or diffuse scattering from liquid interfaces and we discuss the examples of the liquid–vapour interface and of films at a liquid–liquid interface. We show that the interfacial structure can be understood as resulting of the interplay between thermal fluctuations, van der Waals forces, and elastic properties.