In situ atomic force microscopy investigation of the [100] face of KH2PO4 in the presence of Fe(III), Al(III), and Cr(III)

Crystal Growth of Defect-Free Single-Crystalline Fibers in Super-High Supersaturation Solution

By controlling the supersaturation and choosing high-quality seeds, we successfully suppress the prismatic growth of the tetragonal potassium dihydrogen phosphate (KDP) SCFs, realize the rapid growth along the [001] direction, and obtain SCFs less than 10 μm in width with lengths of centimeters. The experimental results show that there exist critical supersaturation points, 22.40% and 41.41% at 25 °C, for initiating the growth of KDP SCF on its pyramidal and prismatic faces, respectively, which are quite different from those of the bulk crystals. We use the mechanism of 2D nucleation on smooth faces to explain the peculiar phenomena, assuming that there is no 2D or 3D defect on the surfaces of the seed fiber crystal. The assumption is supported by AFM observation of the surface micromorphology of the SCFs. Our solution growth technique developed can be used to grow ultrafine SCFs unable to be achieved by existing melt growth techniques.

Inhibition of Spiral Growth and Dissolution at the Brushite (010) Interface by Chondroitin 4-Sulfate

Modulation of mineralization and demineralization of calcium phosphates (Ca-Ps) with organic macromolecules is a critical process which prevents human kidney stone disease. As a long unbranched polysaccharide of urinary glycosaminoglycans, chondroitin 4-sulfate (Ch4S) has been shown to play an essential role in inhibiting the formation of kidney stones. However, the mechanism of the role of Ch4S remains poorly understood. Here, we used in situ atomic force microscopy to observe the growth and dissolution of spirals on brushite (CaHPO₄·2H₂O) (010) surfaces. The results show that Ch4S preferentially inhibits the [101]_Cc step growth/dissolution by step pinning. This step-specific effect appears to be related to specific binding of Ch4S to Ca sites, as the observed inhibition is not seen in other crystallographic directions where there are fewer Ca terminations. Moreover, Ch4S promotes an increase in the terrace width of [101̅]_Cc by the modification of the interfacial energies of the step edge. These in vitro direct observations of Ch4S modulating brushite mineralization and demineralization reveal a dual control of both step kinetics and interfacial energy.

Chelating ligand-mediated hydrothermal synthesis of samarium orthovanadate with decavanadate as vanadium source

A new ethylenediaminetetraacetic acid- (EDTA-) mediated hydrothermal route to prepare chrysanthemum-shaped samarium orthovanadate (SmVO₄) nanocrystals with decavanadate (K₆V₁₀O₂₈·9H₂O) as vanadium source has been developed. The present hydrothermal approach is simple and reproducible and employs a relatively mild reaction temperature. The EDTA, pH value, and temperature of the reaction systems play important roles in determining the morphologies and growth process of the SmVO₄ products. The products have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectra (PL), and UV-Vis spectroscopy.

Theory of impurity induced step pinning and recovery in crystal growth from solutions

We extend the terrace-step-kink model of crystal growth to impure solutions where the impurities act as barriers to step motion. The effects of supersaturation, step curvature, step repulsions, and impurities on step motion are treated in a unified free energy framework. The model reproduces several features seen in experiments on growth of potassium dihydrogen phosphate crystals, wherein a dead zone at low supersaturations and a recovery of crystal growth by motion of large coherent step bunches at larger supersaturations are observed. We identify a key feature of solution growth that leads to these effects.

Dynamics of Biomineralization and Biodemineralization

In order to understand the fundamental processes leading to biomineralization, this chapter focuses on the earliest events of homo/heterogeneous nucleation from an initial supersaturated solution phase and subsequent growth involving various possible precursor phases (amorphous or crystalline) to the final mineral phase by specific template and other influences. We also discuss how the combination of macroscopic constant composition and microscopic atomic force microscopy provides insights into the physical mechanisms of crystal growth and phase stability and the influences of proteins, peptides or other small molecules.Biodemineralization reactions of tooth enamel and bone may be inhibited or even suppressed when particle sizes fall into certain critical nanoscale levels. This phenomenon actually involves particle-size-dependent critical conditions of energetic control at the molecular level. Clearly, this dissolution termination is a kinetic phenomenon and cannot be attributed to reaction retardation as a result of surface modification by additives. Almost all biomineralized structures are highly hierarchical at many different length scales. At the lowest level they often consist of tiny crystals, typically tens to hundreds of nanometers. This size is not arbitrary; rather, it seems to give biominerals such as bone and tooth remarkable physical characteristics.