ISSN 1063-7745, Crystallography Reports, 2012, Vol. 57, No. 2, pp. 185–192. © Pleiades Publishing, Inc., 2012. Original Russian Text © A.A. Lomov, V.I. Punegov, V.A. Karavanskii, A.L. Vasil’ev, 2012, published in Kristallografiya, 2012, Vol. 57, No. 2, pp. 232–240. 185 INTRODUCTION In the last few years, much interest has been shown in the application of micro- and nanostructures (nanowires, nanodots, nanotubes, synthetic opals, etc.) in photonic optics. Porous silicon (PS), which is composed of linked coherent crystallites, is a promis- ing material for these applications. By forming crystal- lites of certain shapes and arrangements, one can not only locally or periodically change permittivity but also induce, for example, optical anisotropy in a medium where birefringence is observed [1]. Currently, the most widespread way for forming PS layers is electrochemical anodization. The structural parameters of layers (porosity, thickness, strain, pore morphology, crystallite size, etc.) are easily varied in this process. Thus, one can form not only layers with pores of different types [2], but also multilayered and surface periodic structures. Electrochemical etching was used in [3] to prepare superlattices with nanopo- rous layers on p-Si(001) substrates. Bragg structures for optical range were formed by modulating current density [4–6]. Lerondel et al. [7] demonstrated the possibility of lateral pore ordering in Si and InP layers [8]. High-resolution X-ray diffraction is a high-power tool for studying the real structure of surface layers of single crystals and multilayered heterostructures, including such nanoobjects as quantum wells, wires, dots, tori, etc. [9]. Note that the main mechanisms of interaction between X rays and homogeneous materials have been studied fairly well for continuum layers [10]. In the case of multilayered structures, a quantitative analysis of the diffraction reflection intensity far from the exact Bragg angle makes it possible to extract extensive information about the internal structure of a sample with a high spatial resolution [11]. For crystals that are locally inhomogeneous in density, the problem of for- mation of a coherent X-ray wave remains open because the phase shift of the waves reflected by the crystallites involved in scattering must be correctly taken into account. In addition, the “porosity” effect weakens the interference and, as a consequence, leads to a partial loss of structural information. PS is a model object with crystallites containing coherent crystalline layers; these crystallites are sto- chastically distributed and differ in shape. It was experimentally proven [3, 12] that in some cases the parameters of thin single-layer and multilayered peri- odic structures of PS can be determined in a wide range of porosities based on continuum models. A successful attempt at simulating rocking curves from several-micrometer-thick uniform PS layers was made in [13]. However, the occurrence of new 3D locally inhomogeneous materials and PS structures [14] requires developing the existing techniques. An addi- tional complexity in analyzing the scattering from PS layers is related to their strain and sensitivity to envi- ronment. In this paper we report the results of an experimen- tal and theoretical study of the specific features of dif- † Deceased. DIFFRACTION AND SCATTERING OF IONIZING RADIATIONS X-ray Scattering by Porous Silicon Modulated Structures A. A. Lomov a , V. I. Punegov b , V. A. Karavanskii † c , and A. L. Vasil’ev d a Institute of Physics and Technology, Russian Academy of Sciences, Nakhimovskii pr. 36/1, Moscow, 117218 Russia e-mail: lomov@ftian.ru b Komi Research Center, Ural Branch, Russian Academy of Sciences, ul. Pervomaiskaya 54, Syktyvkar, 167610 Russia c Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia d Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia Received January 18, 2011 Abstract—A multilayered porous structure formed as a result of the anodization of a Si(111)(Sb) substrate in an HF:C 2 H 5 OH (1 : 2) solution with a periodically alternating current has been investigated by high-resolu- tion X-ray diffraction. It is established that, despite 50% porosity, a thickness of 30 μm, and significant strain (4 × 10 –3 ), the porous silicon structure consists mainly of coherent crystallites. A model of coherent scatter- ing from a multilayered periodic porous structure is proposed within the dynamic theory of diffraction. It is shown that the presence of gradient strains of 5 × 10 –4 or higher leads to phase loss upon scattering from porous superlattices and the suppression of characteristic satellites in rocking curves. DOI: 10.1134/S1063774511060162