Alloy semiconductors exhibit properties of a single crystalline semiconductor, although they are condidered as mixtures of elemental and/or compound semiconductors in a uniform phase, i. e., the solid solution. Crystalline microstructure of III- V alloy semiconductors is investigated with thermodynamical analysis and described in terms of (i) relative numbers of tetrahedron constituting composite compound semiconductors, (ii) bond lengths between the nearest neighbour atoms, and (iii) averaged bond lengths. The strain energy calculated from the valence- force field is taken as the enthalpy for a ternary alloy, and the sum of the strain energy and the cohesive energy for a quaternary alloy. The analysis is applied to 18 ternary alloy semiconductors consisting of the group III elements such as Al, Ga, In and the group V elements such as P, As, Sb. Further it is applied to 6 quaternary alloy semiconductors of AB1-x-y Cx Dy type and 9 of A1-x Bx C1-y Dy type. Theoretical results show that atomic arrangemen in alloy semiconductors grown through a quasi-equilibrium process is not random. It is different from an arrangement commomly believed. The bond length in alloy is not single valued and different from the value derived from the Vegard law. However, the averaged bond length follows a linear dependence on composition, i. e., the Vegard law. The analysis derives uniquely the rate of composite compounds in quaternary alloy of A1-x Bx C1-y Dy type.
Intercrystalline interfaces are classified systematically by the parameters that change across the interface; the crystal lattice sites, orientation, structure, chemical species, the nature of the bonding etc. Examples of recent high resolution transmission electron microscopic observations of each kind of interfaces are described to show problems and the present level of understanding that was found to differ considerably by the kind of the interfaces. In each cases, however, the high resolution observation is proving to be a key tool in analysing and designing the interface.
X-ray fiber diffraction method was used to deduce the molecular structure of tobacco mosaic virus. Multi- dimensional multiple isomorphous replacement method was applied to overcome the information loss by the cylindrical average in the fiber diffraction pattern, and some other developments in the analysis made it possible to build the molecular model of the whole virus particle. Protein- protein interaction and protein- RNA interaction found in the molecular structure gave us a clear understanding on the mechanism of self assembly.