Nanometer-Sized Microstructures

ABSTRACTMaterials with nanometer-sized microstructures are solids that contain such a high density of defects (point defects, dislocations, grain boundaries, interphase boundaries etc.) that the volume fraction of the defect cores becomes comparable to the residual, defect free volume. Since 1970, the interest of materials scientists focused on solids with nanometer-sized microstructures when it was recognized that specifically tailored nanometer-sized microstructures permit the generation of materials with new atomic and/or electronics structures. In the area of semiconductors, quantum well structures and superlattices consisting of thin coherent layers with different dopings or compositions have been studied extensively. In these structures quantum size effects prevail because the coherent boundaries structures between the layers act as electron confinements. Research activities aiming towards the synthesis of new atomic (and electronic) structures in metals, ceramics and semiconductors by means of three-dimensional nanometer-sized micro-structure were initiated by the proposal, to generate solids a large volume fraction of which consists of the cores of defects such as incoherent grain and/or interphase boundaries, such solids differ structurally and property-wise from crystals and glasses with the same chemical composition because the atomic arrangements formed in the cores of incoherent grain or interphase boundaries deviate from crystalline or glassy structures. Recent studies of nanometer-sized materials by x-ray/neutron diffraction, EXAFS, different spectroscopies as well as property measurements support this idea. The properties of materials with nanometer-sized microstructures are discussed on the basis of the knowledge available from the numerous studies that have been carried out in the last two decades about the structure and properties of grain and/or interphase boundaries.