Specific Crystal Planes Research Articles

Control over Growth of Hexagonal Sodium Tungstate Nanorods by Poly(styrenesulfonate)

Abstract Nanocrystals of sodium tungstates were synthesized using a hydrothermal route in the presence of poly(sodium 4-styrenesulfonate) to control the size of the crystals at the time of their growth. The lengths of the nanorods varied significantly, ranging from 400 nm to 6 µm, whereas the diameters varied only slightly, ranging from 200 to 270 nm. These results show that a polyelectrolyte with sulfonate effectively caps the specific crystal planes or provides steric hindrance upon crystal growth, providing control over the size of the nanocrystals by varying the polyelectrolyte concentration.

The growth mechanism of grain boundary carbide in Alloy 690

Abstract The growth mechanism of grain boundary M23C6 carbides in nickel base Alloy 690 after aging at 715 °C was investigated by high resolution transmission electron microscopy. The grain boundary carbides have coherent orientation relationship with only one side of the matrix. The incoherent phase interface between M23C6 and matrix was curved, and did not lie on any specific crystal plane. The M23C6 carbide transforms from the matrix phase directly at the incoherent interface. The flat coherent phase interface generally lies on low index crystal planes, such as {011} and {111} planes. The M23C6 carbide transforms from a transition phase found at curved coherent phase interface. The transition phase has a complex hexagonal crystal structure, and has coherent orientation relationship with matrix and M23C6: {111}matrix//{0001}transition//{111}carbide, 11 2 ¯ > matrix// 2 1 ¯ 10 > transition// 11 2 ¯ > carbide. The crystal lattice constants of transition phase are c transition = 3 × a matrix and a transition = 6 / 2 × a matrix . Based on the experimental results, the growth mechanism of M23C6 and the formation mechanism of transition phase are discussed.

Fabrication of different ZnO nanostructures and investigation of morphology dependence of their photocatalytic properties

In order to investigate the effect of morphology on the photocatalytic properties of different ZnO nanostructures, zinc oxide nanostructures were synthesized using thermal decomposition of zinc acetate dihydrate and sol–-gel methods. The samples were characterized by powder x-ray diffraction and scanning electron microscope measurements. The results revealed that the pure phase of different morphologies such as nanoparticles, nanowires and nanodisks have been synthesized successfully. Using such samples, the photodegradation of Methylene blue was performed by UV–vis absorption measurement. The results showed that the nanodisks have the best photocatalytic performance among the other morphologies. The reason was attributed to the presence of specific crystal planes such as (0001) facets in nanodisks which can improve their photocatalytic performance.

Melamine assisted one-pot synthesis of Au nanoflowers and their catalytic activity towards p-nitrophenol

This paper reports a simple, one-pot, template-free synthesis of uniform flower-like Au nanostructures with high yield at room temperature. The morphologies of Au are very sensitive to melamine and its concentrations. Since melamine, as a complexing agent, can selectively adsorb onto the specific crystal planes of Au and thereby expose the special facets for the anisotropic growth. Time-dependent measurements by UV-vis and TEM spectroscopy are used to monitor the reaction progress and evolution of the flower-like nanostructures. It was found that the Au nanoflowers, with tips preferentially grown along the (111) planes, exhibit excellent catalytic activity towards the reduction of p-nitrophenol.

Study of polymeric additive effect on calcium oxalate dihydrate crystal growth using real-time atomic force microscopy

Microscopic events associated with crystal growth and characterization of the growth hillocks on the (1 0 0) and (1 0 1) faces of COD were examined by atomic force microscopy. The (1 0 0) and (1 0 1) faces of COD developed elliptical and triangular hillocks and pits, respectively. Each face exhibited hillocks with step sites that can be assigned to specific crystal planes, enabling direct determination of the growth rates along specific crystallographic directions. The addition of macromolecules with anionic side chains, poly- l-aspartate, poly- l-glutamate, and polyacrylate resulted in inhibition of growth on the hillock step planes. The magnitude of their effect depended on the macromolecule structures and identity of the step site. The isotropic shape of the COD hillocks mimicked the shape of the resulting macroscopic COD crystals based on step-specific binding of the macromolecules to the COD crystal, with stronger step pinning along the [0 1 0] direction than in the [0 0 1] direction. Electrostatic matching between the crystal faces and additives according to the ionic array of calcium oxalate in the COD structure was found to be responsible for the preferential binding of the macromolecules to terraces.

Tunable Size and Shape Control of Platinum Nanocrystals from a Single Peptide Sequence

Nanoscale platinum architectures have been extensively studied as potential materials for applications in catalysis and fuel cells. Due to the high cost of platinum, much of the research has been geared toward developing methods to obtain monodisperse, monomorphic nanocrystals smaller than 10 nm. Peptide-mediated synthesis of inorganic materials is an attractive alternative to colloidal synthesis because it can be performed under ambient conditions and the peptides can be removed from the metal surfaces at mild pH or in the presence of enzymes. As a first step to achieve size and shape-controlled nanocrystals using peptides, we demonstrate here (a) the isolation of peptides that bind to specific crystal planes of platinum and (b) that a single peptide can produce structures ranging from sub-2 nm seed crystals to monodisperse 4 nm platinum polyhedra to 7 to 8 nm platinum cubes simply by changing the rates of metal reduction. This work demonstrates the first steps toward achieving biochemical control of platinum nanocrystal synthesis.

Flame Synthesis of Tin Oxide Nanorods: A Continuous and Scalable Approach

Well-crystalline SnO2 nanorods were first synthesized via a continuous and scalable iron-assisted flame approach with production rate up to 50 g/h in laboratory-scale. The as-prepared SnO2 nanorods with uniform length up to 200 nm and diameter around 20 nm are smooth and single crystal rutile structures, growing along the [001] direction. Iron dopant is incorporated into the SnO2 lattice and selectively effects a specific SnO2 crystal plane, promoting the further crystal oriented growth into nanorods. Meanwhile, the photoluminescence (PL) spectrum of such SnO2 nanorods exhibits a broad, stronger orange-emission peak around 620 nm, suggesting potential applications in optoelectronics. It is noteworthy that this dopant-assisted flame approach provides a new strategy for sequentially engineering one-dimensional nanomaterials.

Diverse-shaped iron sulfide nanostructures synthesized from a single source precursor approach

Iron sulfide nanostructures with diverse shapes (nanoparticles, nanoribbons and nanoplates) have been synthesized via a single-source precursor of Fe(Ddtc)3 or Fe(Ddtc)2(Phen) (Phen = 1,10-phenanthroline; Ddtc = diethyldithiocarbamate) in the mixture solvents of oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE). The chemical compositions of the as-formed iron sulfide nanostructures are found to be determined by the valencies of iron in the precursors. For phase-pure Fe3S4 and Fe7S8 nanostructures, their shape-selective syntheses could be realized mainly by modifying the ratio of reaction solvent compositions and the chemical composition of precursors. The growth of nanoparticles and nanoplates of iron sulfide is likely due to the selective adsorption of the capping ligands on specific crystal planes of the nanocrystals. Meanwhile, for FeSx nanoribbons, the growth of nanoribbons may come from the template-direction of micellar structures formed by self-assembly of capping ligands. Furthermore, the Fe3S4 and Fe7S8 nanostructures display strong ferromagnetic properties at room temperature.

Biomineralization of BSA-Chalcogenide Bioconjugate Nano- and Microcrystals

Lead selenide (PbSe), cadmium selenide (CdSe), and selenium (Se) nano- and microcrystals were synthesized by using respective metal acetate salts along with sodium selenite as the Se source in the presence of bovine serum albumen (BSA) as the capping/stabilizing agent. Aqueous phase hydrazine reduction at 85 °C produced fine crystalline morphologies within 48 h. Both PbSe and CdSe reactions produced Se microrods (MRs) as reaction byproduct. The concentrations of metal acetate and sodium selenite used were always 1:1 (i.e., 1.25 mM in each case) and that of hydrazine was fixed at 0.78 M. The amount of BSA was changed systematically from 1−10 × 10−4 g/mL to determine its influence on the crystal growth of these chalcogenides. Their morphologies and chemical compositions were determined with FESEM, TEM, and EDX analysis. A selective and precise EDX analysis of a single particle helped us to elucidate its shape and chemical composition. Such analyses lead to the finding that both reactions produced Se rods, their sizes varied from the nano to micro scale with an increase of the amount of BSA. PbSe polyhedral nanocrystals were obtained at a low BSA amount, which ultimately attained the shape of thick MRs. However, no rod formation was observed for CdSe particles, which were always present in the form of groups of small nanoparticles along with Se MRs. Protein estimation indicated the presence of adsorbed BSA on the surface of chalcogenide particles. A potential reaction mechanism was proposed to explain the Se MRs formation as byproduct. Finally, the results were discussed on the basis of selective adsorption of denatured BSA on specific crystal planes of the rock salt (PbSe) geometry in order to produce rod like morphologies.

Facet enhanced photocatalytic effect with uniform single-crystalline zinc oxide nanodisks

Uniform single-crystalline ZnO nanodisks and nanowires (thick and thin nanowires) with well-developed facets have been synthesized hydrothermally. It is demonstrated that the unique ZnO nanodisks with a high (0 0 0 1) facet population and small surface area show the best photocatalytic activity among the samples. All the samples are in the same comparable dimension and surface area regime and the design of nanodisk and nanowire reduce the effect of unwanted facet effect to a degree as minimum as possible when catalytic activity of (0 0 0 1) and { 1 0 1 ¯ 0 } facets are compared. The results indicate that photocatalytic activity strongly depend on specific crystal planes.

Manipulating Crystal Orientation in Nanoscale Cylindrical Pores by Stereochemical Inhibition

Glycine nanocrystals, grown in aligned nanometer-scale cylindrical pores of nanoporous polystyrene-poly(dimethyl acrylamide) monoliths by evaporation of imbibed aqueous solutions, adopt preferred orientations with their fast-growth axes aligned parallel with the pore direction. X-ray diffraction analysis revealed the exclusive formation of the metastable beta-polymorph, with crystal size comparable with the 22 nm pore diameter, in contrast to the formation of alpha-glycine in the absence of nanoscale confinement. When grown from aqueous solutions alone, the nanocrystals were oriented with their [010] and [010] axes, the native fast growth directions of the (+) and (-) enantiomorphs of beta-glycine, respectively, aligned parallel with the pore direction. In contrast, crystallization in the presence of racemic mixtures of chiral auxiliaries known to inhibit growth along the [010] and [010] directions of the enantiomorphs produced beta-glycine nanocrystals with their [001] axes nearly parallel to the pore direction. Enantiopure auxiliaries that inhibit crystallization along the native fast growth direction of only one of the enantiomorphs allow the other enantiomorph to grow with the [010] axis parallel to the cylinder. Collectively, these results demonstrate that crystal growth occurs such that the fast-growing direction, which can be altered by adding chiral auxiliaries, is parallel to the pore direction. This behavior can be attributed to a competition between differently aligned crystals due to critical size effects, the minimization of the surface energy of specific crystal planes, and a more effective reduction of the excess free energy associated with supersaturated conditions when the crystal grows with its fast-growth axis unimpeded by pore walls. These observations suggest that the beta-glycine nanocrystals form by homogeneous nucleation, with minimal influence of the pore walls on orientation.

Sensitivity of catalysis to surface structure: The example of CO oxidation on Rh under realistic conditions

Using a combination of surface x-ray diffraction and mass spectrometry at realistic pressures, the CO oxidation reactivity of Rh(111) and Rh(100) model catalysts has been studied in conjunction with the surface structure. The measurements show that the presence of a specific thin surface oxide is crucial for the high activity of the Rh based CO oxidation. As this oxide is readily formed on all Rh facets, we conclude that the specific Rh crystal planes exposed during catalysis will not directly influence the reactivity. This is fortified by the very close similarity between the Rh(111) and the Rh(100) results.

Two Domains of RD3 Antifreeze Protein Diffuse Independently

Antifreeze proteins (AFPs) make up a class of structurally diverse proteins that help to protect many organisms from freezing temperatures by inhibiting ice crystal growth at temperatures below the colligative freezing point. AFPs are typically small proteins with a relatively flat, slightly hydrophobic binding region that matches the lattice structure of a specific ice crystal plane. The only known two-domain AFP is RD3 from the Antarctic eel pout. It consists of two nearly identical type III domains connected by a nine-residue linker. This protein exhibits higher activity than the single-domain protein at low concentrations. The initial solution structure of RD3 revealed that the domains were aligned so that the binding regions were nearly coplanar, effectively doubling the surface area for binding. A more recent report suggests that the domains may not be aligned in solution but rather diffuse independently. To resolve the issue, we have measured the NMR residual dipolar couplings using alignment media of stretched gels and filamentous phage to determine the relative orientation of the domains. We find that the two domains of RD3 are free to move relative to each other, within the constraint of the flexible nine-residue linker. Our data show that there is no strongly preferred alignment in solution. Furthermore, the flexibility and length of the linker are sufficient to allow the two domains to have their binding faces in the same orientation and coplanar for simultaneous binding to an ice crystal surface.

Morphological population balance for modeling crystal growth in face directions

AbstractA morphological (or polyhedral) population balance (PB) model is presented for modeling the dynamic size evolution of crystals grown from solution in all crystal growth directions. The morphological PB approach uses the crystal shape information for a single crystal obtained from morphology prediction, or experiment as the initial face locations, as well as face growth rates to predict the shape evolution of the crystal population. For each time instant during the crystallization process, the prediction uses its shape at the previous time moment, and the growth rate for the specific crystal habit plane. The methodology is demonstrated through a study of potash alum (KAl (SO4)2·12H2O), for which literature data is available for comparison and validation. The discretization method, method of classes, was used to convert the equations to ordinary differential form with the computational domain being discretized into small meshes. The ordinary differential equations (>1.5 million) were then solved simultaneously using the Runge‐Kutta‐Fehlbergh 4th/5th‐order solver with automatic time‐step control. The results obtained clearly demonstrate that the morphological PB model developed can predict crystal growth and surface area of individual habit faces in detail, together with crystal shape and size evolution. © 2007 American Institute of Chemical Engineers AIChE J, 2008

Electrochemical preparation of copper–dendrimer nanocomposites: picomolar detection of Cu2+ ions

The present work describes, for the first time, in situ electrochemical preparation of dendrimer-encapsulated Cu nanoparticles using a self-assembled monolayer of fourth-generation amine-terminated polyamidoamine (PAMAM) dendrimer as the template. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) studies of the modified surface confirmed the presence of Cu nanoparticles entrapped in dendrimer film. Au electrode modified with a monolayer of the dendrimer enables preconcentration and subsequent voltammetric detection of Cu(2+) at picomolar concentrations. Further, Cu nanoparticles in the dendrimer monolayer could be electrochemically derivatised to Cu hexacyanoferrate, which exhibits specific crystal planes, unlike the random distribution of crystal planes in bulk-formed Cu hexacyanoferrate, which is another catalytically active material for sensor applications.

Structure of calcium titanate/titania bioceramic composite coatings on titanium alloy and apatite deposition on their surfaces in a simulated body fluid

In this study, TiO 2-based coatings containing Ca and P ions were prepared on titanium alloy surfaces by microarc oxidation (MAO). After soaking in aqueous NaOH solution and subsequent heat treatment at 700 and 800 °C, calcium titanate/titania bioceramic composite (CTBC) coatings were obtained. The results show that the outer layers (0–1.5 μm) of the CTBC coatings are mainly composed of Ca, Ti, O and Na constituents with a uniform distributions with increasing the depth near the surfaces. The surface phase compositions of the CTBC coating formed at 700 °C are anatase, rutile and CaTi 21O 38 phases, as well as a few CaTiO 3, while those of the CTBC coating formed at 800 °C are anatase, rutile and CaTiO 3. When incubated in a simulated body fluid (SBF), apatite was deposited on the CTBC coatings probably via formation of hydroxyl functionalized surface complexes on the CTBC coating surfaces by ionic exchanges between (Ca 2+, Na +) ions of the CTBC coatings and H 3O + ions in the SBF. The CTBC coating formed at 800 °C seems to facilitate the deposition of Ca and P probably due to the good crystallographic match between perovskite CaTiO 3 and HA on specific crystal planes.

Dwell Fatigue Microstructure in a Near-α Titanium Alloy

The dwell fatigue microstructure of a near-α titanium alloy was studied by optical microscopy and transmission electron microscopy. Optical microscopy revealed primary α grains as being crack initiation sites. The majority of the cracks nucleated on and propagated along specific crystal planes in the primary α grains perpendicular to the α platelets in their neighboring transformed β grains. The propagation of the cracks is effectively blocked by α platelets with axes parallel to the directions of crack in the transformed β grains. Transmission electron microscopy revealed the formation of different types of slip bands across α platelet boundaries in transformed β grains and dislocation networks and subgrain boundaries in primary α grains. The most active slip system was identified as the type dislocation, which slips on the basal planes of α phase. Slip bands in transformed β grains were found to be on the basal planes of the α colonies, perpendicular to the α platelets. The retained β phase at the α platelet boundaries have limited effect on blocking the propagation of the slip bands. The dwell effects are explained in terms of the dislocation movement in relation to the crystallography of the primary α grains and α platelets in the transformed β grains.

From Trifluoroacetate Complex Precursors to Monodisperse Rare‐Earth Fluoride and Oxyfluoride Nanocrystals with Diverse Shapes through Controlled Fluorination in Solution Phase

We report the first systematic synthesis of monodisperse rare-earth (RE=La to Lu, Y) fluoride and oxyfluoride nanocrystals with diverse shapes (trigonal REF3 triangular, truncated-triangular, hexagonal, and polygonal nanoplates; orthorhombic REF3 quadrilateral and zigzag-shaped nanoplates; cubic REOF nanopolyhedra and nanorods) from single-source precursors (SSP) of [RE(CF(3)COO)(3)] through controlled fluorination in oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE). To selectively obtain REF3 or REOF nanocrystals, the fluorination of the RE-O bond to the RE-F bond at the nucleation stage was controlled by finely tuning the ratio of OA/ODE or OA/OM, and the reaction temperature. For phase-pure REF3 or REOF naocrystals, their shape-selective syntheses could be realized by further modifying the reaction conditions. The two-dimensional growth of the REF3 nanoplates and the one-dimensional growth of the REOF nanorods were likely due to the selective adsorption of the capping ligands on specific crystal planes of the nanocrystals. Those well-shaped nanocrystals with diverse geometric symmetries (such as D(3h), D(6h), C(2h), O(h), and D(nh)) displayed a remarkable capability to form self-assembled superlattices. By manipulating the solvent-substrate combination, the plate-shaped REF3 nanocrystals could form highly ordered nanoarrays by means of either the face-to-face formation or the edge-to-edge formation. By using this SSP strategy, we also obtained high-quality LaF3:Eu and LaF3:Eu/LaF3 triangular nanoplates that showed photoluminescent red emissions of Eu3+ ions sensitive to the surface effect.

Characterization of Surface Biocompatibility of Crystallographically Aligned Hydroxyapatite Fabricated Using Magnetic Field

Hydroxyapatite (HAp) is the main mineral component of bone and is used as a raw material for artificial bones and teeth, and as an adsorbent in liquid chromatography, among its other uses. As a result of its anisotropic crystal structure, HAp shows adsorption behavior that depends on the crystal plane. However, the differences between the a-plane and the c-plane of the HAp crystal in terms of their bioactivity, cellpropagation behavior, etc., have not yet been fully clarified. In this study, we fabricated highly crystallographically aligned samples of HAp by using a 10-T magnetic field, and we studied the effects of the specific crystal plane of HAp on its bioactivity by immersing the samples in a simulated body fluid. HAp is precipitated on both a-plane- and c-plane-aligned HAp sample surfaces. The rate of precipitation on a HAp sample immersed in the simulated body fluid depended on the crystal plane, especially during the first 24 h of immersion. Because the rate of precipitation on the c-plane is faster than on the a-plane, HAp is precipitated preferentially on the c-plane during the early stages of precipitation. [doi:10.2320/matertrans.MI200712]

Controlled-Synthesis, Self-Assembly Behavior, and Surface-Dependent Optical Properties of High-Quality Rare-Earth Oxide Nanocrystals

Single-crystalline and monodisperse cubic rare-earth (RE = La to Lu, Y) oxide nanocrystals (ultrathin nanoplates and nanodisks) have been synthesized via a nonhydrolytic approach in oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE) using various rare-earth complexes, including acetylacetonate, benzoylacetonate, and acetate, as the precursors. The transformation from the complex precursors to RE2O3 was proposed to occur in two stages: first, the formation of rare-earth oleates by ligand exchange in solution, and second, the subsequent decomposition of the oleates into RE2O3 catalyzed by the base of OM. The selective adsorption of coordinating OA ligands onto specific crystal planes of cubic RE2O3 nanocrystals made them adopt a plate shape with the confined growth of {100} facets and/or a disk shape with the confined growth of {111} facets. Along with delicately tuning the polarity of the dispersant, the RE2O3 nanocrystals could be aligned to form “side-to-side” or “face-to-face” self-assembly nanoarrays ...