Katsuo Tsukamoto, Graduate School of Sciencie, Universitat de Tohoku, Sendai, Japó
Sala d'Actes de l'Institut de Ciencies de la Terra "Jaume Almera"

"Single layer etching" has been developed to reveal microdefects contained in elementary growth at various conditions.

The surface was observed in-situ by transmission prase-contrast microscopy (Olympus, IMT-2) with a CCD camera which is capable of resolving growth steps with mono-molecular step height. Growth rate of the crystals have been measured by newly developed white-beam phase-shift interferometry which also possesses the molecular step height resolution. Two types of defects were observed depending on the degree of undersaturation, -σ. One is a dislocation etch pit appearing at lower -σ ~ 0.05% and the other is the etch pit with a flat-bottomed rounded shape appearing at higher -σ~ 0.4%.
Hen egg-white lysozyme (98.5% purity, six times recrystallized, Seikagaku Co., and 99.99% purity, Maruwa food industries, Inc.) was dissolved in 50 mM sodium acetate buffer (pH 4.5). NaCl was used as a precipitant.
Under the microscope, the growth layers with a few monomolecular heights grew larger at given temperatures for several hours. After the growth, these thin single layers were dissolved slightly for several min. at -σ=0.3-0.6, which resulted in the development of etch pits. It was found that steps grown soon after dissolution contains numbers of defects as revealed by deep etch pits, whereas steps formed continuously contains much less defects.
2D islands and spiral growth hillocks were often observed on the same crystal surface. The tip of the elongated spiral steps (<110> direction) was sharper than that of the 2D islands at σ=0.3-1.4, meaning that spiral steps have less impurity poisoning, the poisoning of which was also supported by the fact that the velocity of spiral steps was faster by 10-20% than that of 2D islands under the same supersaturation. It is surprising to observe that spiral steps contain much less microdefects than the steps generated by 2D nucleation, if the surface is etched soon after the growth