Double-crystal X-ray diffractometry in the role of X-ray standing-wave method

It is shown that the atomic displacements (induced by foreign layers) comparable with or smaller than the interatomic distances can be detected in perfect multilayer systems by double-crystal X-ray diffractometry alone. It was earlier thought that the detection of displacements as small as those was accessible only to the specific methods such as the X-ray standing-wave method. The measurements were carried out on a GaAs/InAs/GaAs system, where InAs was a foreign layer. Its thickness did not exceed three monolayers, while the structure was of the insular type and represented a set of separate quantum dots. The displacement of the capping GaAs layer relative to the GaAs buffer was measured with an accuracy of less than $0.1$ of the thickness of the atomic layer.