The geometry of the GISAXS experiment. (a) The orientation of the primary and scattered X-ray beams with the wavevectors and , respectively. The plane of incidence is xz, the detector plane is parallel to the yz plane. (b) The orientation of the basis vectors of the dot lattice. The vectors lie in the xy plane parallel to the sample surface. The circular arrow indicates possible averaging over the azimuthal orientations of the vector set , keeping constant the angles between the vectors. (c) and (d) show the parallel and perpendicular configurations, in which the vector lies in the xz and yz planes, respectively.