D.L. Sun

Distinct Growth Phenomena Observed on Zinc Cadmium Thiocyanate Crystals by Atomic Force Microscopy

Atomic force microscopy is used to investigate the surface morphology of the prismatic (100) face of ZCTC crystal grown at 30°C at a supersaturation of 0.16. This surface is distinctly formed by periodic macrosteps that advance along different directions and join with each other leading to the interlaced growth layers with an inclination of about 137°. These two macrostep trains well correspond to the pyramidal faces of (011) and (011) in orientation, therefore they probably propagate from the edges of these faces. The macrosteps are practically formed by highly dense steps at the front with regular elementary steps in between. The alternation of macrosteps and elementary steps vividly reflects Chernovs kinematic waves of steps theory (CHERNOV, (1984)) on a nanometer scale. Wide indentations and long clefts are generated at the macrosteps. The former is generated by two-dimensional nucleation growth at a relatively faster growth rate than that of the underlying layer. The latter is probably caused by step trains generated by individual growth sources that have not merged.

Effect of excessive amount of Cd(II) cations on surface morphology of prismatic {1 1 0} faces of cadmium mercury thiocyanate crystals

Surface morphologies of cadmium mercury thiocyanate crystals grown from synthesized mother solutions with excessive amount of Cd(II) cations (5%, 20% and 50% in molar ratio) are investigated by atomic force microscopy. Unlike our previous observations, strong anisotropic growths occur at the large two-dimensional nuclei as well as at steps generated by 2D nuclei. These steps are highly bunched macrosteps varying from 1.6 up to 35 nm in height with distinctly well-oriented protuberance trains at the step fronts while regular elementary steps are hardly observed. These protuberances, however, become fewer and less distinct with the increase of excessive Cd(II) cations in the solution and even disappear at a much higher concentration of 50%. Steps also vary from macrosteps to dominant substeps with the height of 1 and 2 elementary steps of 0.81 nm at this high concentration. These distinct surface morphological variations are assumed to result from the effect of Cd–SCN complex anions as either growth units or impurities under different growth conditions. r 2002 Elsevier Science B.V. All rights reserved.

Direct Growth of Aggregates on {110} Faces of Cadmium Mercury Thiocyanate Crystals

New growth phenomena - direct incorporation of aggregates have been observed on the {110} faces of cadmium mercury thiocyanate CdHg(SCN) 4 crystals by atomic force microscopy. These aggregates grow in two forms: some directly cover up the steps and forms new growth layers; while others are just incorporated at the step edges. These aggregates, which are mostly oriented along [111] direction, are formed by small columnar structural units. The aggregates have the similar structure of CdHg(SCN) 4 crystals and greatly vary in nature with the variation of solution supersaturation σ and growth time t. With the increase of σ the aggregates become larger, consistent with the variation of growth units dimension with the supersaturation; and with the increase of growth time the aggregates become more structurally substantial. These observations have led to a new understanding about the crystal growth.

Mass Transport and Growth Kinetics Related to the Interface Supersaturations of Lithium Formate Monohydrate

The mass transport during LFM crystal growth at 312.25K was studied. The concentration distribution in the boundary layers and the interface supersaturations of the (021) and (010) faces were calculated. The growth kinetic data as a function of interface supersaturations were discussed, and it proved that the crystal growth was mainly controlled by continuous growth. The edge energy and kinetic coefficient were calculated.

Atomic Force Microscopy Studies on Growth Mechanisms and Defect Formations on {110} Faces of Cadmium Mercury Thiocyanate Crystals

Growth mechanisms and defect formations on {110} faces of cadmium mercury thiocyanate crystals grown at 30°C (σ = 0.24)were investigated by using atomic force microscopy (AFM). It was found that, under this condition, spiral dislocation controlled mechanism and 2D nucleation mechanism operates simultaneously and equally during growth, which is completely different from the traditional 2D nucleation and dislocation source controlled mechanisms. A number of 2D nucleus are formed at the large step terraces generated by dislocation sources, leading to the unequal growth rates of the elementary steps and thereby step bunches are caused. Various defects are formed under this growth condition, which is assumed to result from the incongruence between the steps generated by different sources. A new kind of 2D defect, corresponding to one growth layer in height, was observed for the first time.

Photorefractive Properties of Co-Doped Potassium Sodium Strontium Barium Niobate Crystals

The transmissivity and the results of two-beam coupling and self-pumped phase conjugation (SPPC) experiments on Co-doped potassium sodium strontium barium niobate (KNSBN) single crystals are reported. The Co ions doped into KNSBN can form a deep energy level near 2.25 eV. The two-beam coupling gain coefficients of the Co-doped KNSBN are nearly 20 cm-1 at 2 teta = 370 for the transmission photorefractive index grating and larger than 29.2 cm-1 for the reflecting photorefractive index grating. A striking single-beam asymmetric transmission was observed. The maximum SPPC reflectivity is larger than 70% at teta = 49.70 for an intensity W = 77 mW, which is the largest value measured in the family of KNSBN crystals.