Structure factor of thin films near continuous phase transitions

The two-point correlation function in thin films is studied near the critical point of the corresponding bulk system. Based on field-theoretic renormalization-group theory, the dependences of this correlation function on the lateral momentum, the two distances normal to the free surfaces, the temperature, and the film thickness are determined. The corresponding scattering cross section of x rays and neutrons under grazing incidence is calculated. This reveals the various singularities of the two-point correlation function. [S0163-1829(99)03732-7].