NON-GAUSSIAN ROUGHNESS OF INTERFACES - CUMULANT EXPANSION IN X-RAY AND NEUTRON REFLECTIVITY

Within the Born approximation, a cumulant expansion is used for the fo rmulation of X-ray or neutron reflectivity. Odd- (third-) order cumula nts indicate asymmetric profiles; they may only be detected in layer s ystems via a Q(z). dependence of the oscillation period of Kiessig fri nges. Fourth-order cumulants are also visible in the larger Q(z) regim e for single interface systems. As an example of an asymmetric surface , a triangular height distribution function is discussed.