A proposal for a mechanism of nucleation in zeolite synthesis

Assembly of 2D patterns on crystal surfaces has been widely investigated to reveal the structural and energetic relationships between substrate and overlying architecture. Progress has been achieved in understanding and controlling their assembly, yet little is known about the mechanism by which they nucleate. Understanding the dominant pathways and formation kinetics would enable precise control over phase and morphology during synthesis of 2D materials. In our study, short peptides were selected for their ability to bind on MoS2 (0001). We studied nucleation and growth of 2D films of these peptides with AFM and compared our results to MD simulations. We find the peptide arrays exhibit an epitaxial relationship to the underlying lattice, but assemble row-by-row from dimeric growth. The nuclei are ordered from the earliest stages. Although the final crystals are 2D, due to the 1D nature of the constituent rows, there is no critical size and the nucleation rate varies linearly with concentration and is finite for all concentrations above the solubility limit. Our results verify long-standing but unproven predictions of CNT while revealing the key interactions responsible for ordered assembly.

Mechanisms of Nucleation and Growth of …

The consumption of the precursor could lead to a two‐step nucleation and growth process.

19/12/2017 · Mechanisms of Nucleation and Growth of ..

Furthermore, chemical perturbations made during thenucleation stage of zeolite Y hydrogel synthesis is shown to acceleratecrystal growth by a factor of 3-4, depending on the specific sol gelchemistry.

Nucleation, Growth, and Robust Synthesis of SPP …

The synthesis of multicomponent mesocrystals represents an emerging strategy for obtaining nanomaterials with unique functionalities as a result of combining porosity and crystallographic order. This study presents the first synthesis of multicomponent Sb–Nb:TiO2 mesocrystals (Sb-mesoNb/TO) by using a microwave-assisted nonaqueous sol–gel method. Structural and chemical analyses, carried out using various transmission electron microscopy techniques, show that Sb-mesoNb/TO are 25–35 nm in size and composed of crystallographically aligned Nb:TiO2 subunits, embedded in a porous amorphous Sb-rich scaffold (Sb-scaffold). On the basis of the characterization of the intermediate products, the formation mechanism is proposed, involving a kinetically controlled particle-based assembly process. The latter is triggered by the occurrence of the Sb-scaffold in the early reaction stages, acting as a support for heterogeneous nucleation of Nb:TiO2 subunits. Subsequently, Nb:TiO2 subunits grow and assemble in a mutual crystallographic direction, while the Sb-scaffold prevents their complete fusion, hence leading to porosity in the final Sb-mesoNb/TO. Photocatalytic tests were performed by measuring the degradation of organic dyes under solar and visible light.

These findings are applied to the nanocrystal seeding andrapid hydrothermal growth of zeolite Y membranes on inexpensivepolymeric supports.
Chen, “Identification of the First Nucleated Phase in the Interfacial Reactions of Ultrahigh Vacuum Deposited Titanium Thin Films on Silicon,”

Nanostructures synthesis and crystal growth

We investigate quasicrystal-forming soft matter such as dendrimers and star block copolymers, using a two-scale phase field crystal model. At state points near thermodynamic coexistence between bulk quasicrystals and the liquid phase, we find multiple metastable spatially localized quasicrystals embedded in a background of liquid. We use the terminology of spatially localized quasicrystals to refer to structures that turn into an extended quasicrystal in a continuous manner when a system parameter is varied. In two dimensions, we compute several families of spatially localized quasicrystals with dodecagonal structure and investigate their properties as a function of the system parameters. In three dimensions we obtain spatially localized icosahedral quasicrystals. In both 2D and 3D the localized quasicrystals are metastable, and so correspond to energetically locally favored structures. The presence of such structures is expected to crucially affect the dynamics of the crystallization process.

JO - Crystal Growth and Design

Crystal Growth and Nucleation : Royal Society Of …

AB - Tl6SeI4 is a promising wide-bandgap semiconductor for room-temperature high-energy photon detection. Because of the air-sensitive Tl precursor or Tl-based binary precursors used in the synthesis, this material can contain deleterious Tl oxide impurities. These impurities lead to problems during syntheses and crystal growth including glass attack, tube rupture, and parasitic nucleation, which subsequently deteriorate detector performance. In this work, we present a facile way to chemically reduce Tl oxides and eliminate oxygen impurities in Tl6SeI4 by adding high-purity graphite powder during synthesis. The addition of carbon leads to reduction of the residual Tl oxides and formation of CO2 and CO. The resistivity and hard radiation detection performance for 122 keV γ-rays of Tl6SeI4 single crystals were significantly improved. The improvement in the crystallinity was also confirmed by a narrower near-band-edge emission band in the photoluminescence spectra. We confirmed that the reaction between Tl oxide and graphite occurs, and propose a mechanism which is highly effective in substantially reducing oxide impurities from Tl-containing precursors. First-principles density functional theory calculations reveal that the presence of interstitial oxygen atoms (Oint) leads to the formation of a deep level located near the middle of the gap, which can act as carrier traps detrimental to detector performance. The calculations also indicate that graphite addition is safe for detector performance because all carbon-induced defects have high formation energy and are not likely to appear in lattice.

A silicide is expected to grow epitaxially on silicon if the crystal structures are similar and the lattice mismatch between them is small.

Synthesis mechanism of Zeolite Molecular ..

We study the nucleation of crystalline cluster phases in the generalized exponential model with exponent n=4. Due to the finite value of this pair potential for zero separation, at high densities the system forms cluster crystals with multiply occupied lattice sites. Here, we investigate the microscopic mechanisms that lead to the formation of cluster crystals from a supercooled liquid in the low-temperature region of the phase diagram. Using molecular dynamics and umbrella sampling, we calculate the free energy as a function of the size of the largest crystalline nucleus in the system, and compare our results with predictions from classical nucleation theory. Employing bond-order parameters based on a Voronoi tessellation to distinguish different crystal structures, we analyze the average composition of crystalline nuclei. We find that even for conditions where a multiply-occupied fcc crystal is the thermodynamically stable phase, the nucleation into bcc cluster crystals is strongly preferred. Furthermore, we study the particle mobility in the supercooled liquid and in the cluster crystal. In the cluster crystal, the motion of individual particles is captured by a simple reaction-diffusion model introduced previously to model the kinetics of hydrogen bonds.