This paper reviews the recent progress of experimental and theoretical works on the understanding of the pattern selection in dendritic crystal growth. The dendritic tip is usually an paraboloidal revolution, whose radius of curvature and the growth speed are experimentally determined by the undercooling or the supersaturation. An intuitive argument is presented that geometric mean of macroscopic diffusion length and microscopic capillary length is the length scale of this physical system. Also the mechanism and the nature of sidebranching instability are discussed.
Many organic compounds have been reported to exhibit photochromism in various media such as solid state, rigid matrices, fluid solutions and polymer films. Some of the compounds show distinct photochromic behavior in crystals and in solutions based on the different media. In this brief review crystal packings, polymorphisms and intermolecular hydrogen bonds which affect on the reaction mechanism in crystals are discussed.
Structural analysis of the defect on {113} in Si has been carried out by transmission electron diffraction and microscopy. A proposed atomic model shows that interstitial Si atoms aggregate on {113} and form a reconstructed structure in the interior of a Si crystal. The model is characterized by 5-, 6-, 7- and 8-membered atomic rings and has no dangling bond. The 6-membered rings constitute the tiny rods of the hexagonal structure, and the 8-membered rings are related to the {113} surface structure.
Effects of sample current on Si (001) 2×1 domain conversions and on Si-MBE growth, are investigated. It is found that diffusion anisotropy of Si adatoms on 2×1 surfaces exists and that the domain conversion velocity is proportional to the sample current. This indicates that the conversion process is induced by the diffusion anisotropy and the force acting on positively charged Si adatoms. Preferential detachment of atoms from steps to lower sides than upper ones is also found. This causes biatomic step growth during Si-MBE growth process.
We have recently constructed a new H-1500 type ultra-high-resolution high-voltage electron microscope. Using this microscope we have succeeded in imaging directly not only Zr atoms but also oxygen atoms in a zirconia (ZrO2) crystal. Imaging conditions for getting so-called crystal structure images are discussed in terms of the amount of defocus and the thickness of crystal.