Crystallographic Faces Research Articles

Hydrothermal synthesis of highly symmetric 26‐facet Cu2O polyhedra

AbstractHighly symmetric 26‐facet polyhedral microcrystals of cuprous oxide (Cu2O) are successfully synthesized through a facile low temperature hydrothermal reaction. These polyhedra are constructed by well‐developed {100}, {110} and {111} crystallographic faces. The obtained microstructures were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Ultraviolet‐Visible (UV‐Vis) absorption spectrum. Cetyltrimethyl ammonium bromide (CTAB) and ethylenediaminetetraacetic acid disodium (EDTA‐2Na) have been confirmed to be necessary additives to the development of these perfect polyhedra. The growth process of the 26‐facet Cu2O polyhedra is depicted on the grounds of the time‐dependent experiments. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

TEM study of Mg distribution in micrite crystals from the Mishrif reservoir Formation (Middle East, Cenomanian to Early Turonian)

Microporous limestones composed of micrite crystals constitute sizeable hydrocarbon reservoirs throughout the world and especially in the Middle East. However, the crystallization history of micrites is poorly understood. Scanning electronic microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS) studies give morphological and bulk composition information about micrites, but no information exists on the distribution of minor elements inside micrite grains. This study proposes Mg maps obtained with X-ray EDS combined with scanning transmission electron microscopy (STEM) of micrite crystals from the Mishrif reservoir Formation (Middle East, Cenomanian to Early Turonian). Three types of Mg distribution were observed through micrite crystals from five different samples: (1) homogenous Mg concentration, (2) small Mg-enriched areas close to the center of the crystal, and (3) geometric Mg impoverishments near crystal edges and parallel to present crystallographic faces. The homogenous Mg distribution is the most frequent and is found both in microporous and in tight micrites. The second type of distribution showing small Mg-enriched areas inside micrite crystals relatively close to their center comes from a microporous sample located below an emersive surface. These enriched areas may correspond to crystal seeds. The third type of distribution was observed in micrite crystals from another microporous sample situated just below an emersive surface. The Mg-poor zones probably represent overgrowths that precipitated in contact with less Mg-rich meteoric fluids.

Crystal growth investigations of ice/water interfaces from molecular dynamics simulations: Profile functions and average properties

Attempts to simulate crystal growth of ice from liquid water and to provide a consistent microscopic description of this process have been challenging tasks. In this paper we have adapted our previously developed molecular dynamics simulation methodology to enable the investigation of steady-state directional crystal growth∕melting of ice. Specifically, we examine ice∕water systems of the (001), (110), and (111) faces of ice Ic and the (0001), (1010), and (1120) faces of ice Ih, where the TIP4P, TIP4P-Ew, and SPC∕E water models have been utilized. The influence of different growth∕melting conditions (temperature gradients and growth velocities) is investigated. Profile functions of properties of interest across the interface are obtained from nonequilibrium steady-state simulations and provide consistent descriptions of ice∕water interfaces. The widths of the various crystallographic faces are found to increase in the apparent order Ic111, Ih0001 < Ih1010 < Ih1120 < Ic001 < Ic110. The observed growth rates were in agreement with experimental values and the possible dependence on the various faces is explored. The melting temperatures obtained with the present methodology for the different models are in good agreement with estimates from other work.

Atomic scattering potentials for an aluminum surface: Test of ab initio calculations

Atom-surface potentials entering the calculations of fast atom scattering at surfaces are often taken to be purely repulsive and parameterized by variants of the ZBL potential. However, such surface potentials derived from pairwise superpositions of binary potentials fail to reproduce recent rainbow scattering measurements performed for various atomic projectiles above different faces of atomically flat single crystal Al surfaces. It was found that the dependence of the rainbow angle θ rb on the projectile’s kinetic energy component normal to the surface E ⊥ varies with the electronic structure of the projectile as well as with the crystallographic face of the aluminum surface. We determine static atom-surface potentials by ab initio methods which show fair agreement with the experiment.

Using clumped isotopes to help understand isotopic sector zoning in calcite

Debated among scientists for decades, observations of compositional differences between different crystallographic faces within a same growth zone, called ‘sector zoning’, represents a major challenge for geochemistry and in particular for isotope geochemistry. Nowadays, convincing evidence for the existence of sector zoning has been reported in the literature. However, no consensus on the mechanisms triggering sector zoning has been reached. Understanding how and why sector zoning occurs is essential because the presence of sector zoning could skew the isotopic characterization of a carbonate mineral depending on the area being sampled. This would result in an ambiguous interpretation of the data. The emphasis of this study, which is part of the Qatar Carbonates and Carbon Storage Research Center (QCCSRC), is therefore placed on deciphering the different processes leading to isotopic sector zoning in calcite, with the help of a new tool: the clumped isotopes (i.e. isotopologues). Large calcite crystals with clearly visible growth zones have been collected from fracture infills in Oman. The minerals growth zones and sectors are recognized via cathodoluminescence microscopy and the trace element content of the different zones in several sectors is estimated via electron microprobe. These different sectors are then sampled by a micro-drill following single growth zones and analyzed for their oxygen and carbon isotopic compositions. The approach highlighted above allows for recognition of the presence of sector zoning, but does not constrain the type of mechanism(s) leading to the observed isotopic fractionation. To gain further insight, we turn to clumped isotopes (multiply substituted isotopologues) which are molecules with distinct chemical and physical properties. This should theoretically lead to distinctive fractionations. Clumped isotopes have been used recently to measure the temperature of precipitation of carbonate minerals. If each of the crystalline phases of a given crystal were precipitated under thermodynamic equilibrium, one would expect a constant clumped isotope value between sectors. However, we intend to use clumped isotopes as a discriminative geochemical tool to check if differences in the Δ47 values between sectors exist. If this was the case, isotopologues could provide new insights on sector zoning and would give an extra dimension to the quest for the different factors resulting in these types of isotopic zonations. Combining compositional, stable isotopes and clumped isotopes information could ultimately help to reveal the secrets of sector zoning.

Additive-Assisted Aqueous Synthesis of BaTiO3 Nanopowders

The effect of poly(acrylic acid) (PAA), poly(vinylpyrrolidone) (PVP), sodium dodecylsulfate (SDS), hydroxypropylmethylcellulose (HPMC), and D-fructose additives on the growth of BaTiO3 particles by aqueous synthesis is studied. Through different mechanisms, all the tested additives influenced the growth of BaTiO3. For high concentrations, PAA adsorbed on specific crystallographic faces changing the growth kinetics and inducing the oriented attachment of the particles acting as a crystal growth modifier. PVP, SDS, and HPMC behave as growth inhibitors rather than crystal habit modifiers, and barium titanate crystals as small as 26 nm were obtained. D-Fructose appeared to increase the activation energy for barium titanate nucleation when the additive concentration increases. The present study gives new insights into how additives control barium titanate particle growth in aqueous media.

Mechanical Properties of Potassium Dihydrogen Phosphate Single Crystal by the Nanoindentation Technique

Mechanical properties of potassium dihydrogen phosphate single crystal (KH2PO4, KDP) at room temperature were investigated using nanoindentation approaches. This study was carried out for two crystallographic planes of KDP single crystal, (001) crystallographic plane and the tripler crystallographic plane. The hardness and the reduced modulus values were calculated by the most commonly used Oliver–Pharr method. It was found that hardness and reduced modulus exhibited significant peak load dependence. Furthermore, the strong anisotropy of the hardness and reduced modulus were observed on two tested surfaces. At the same time, the indentation anisotropy of hardness and reduced modulus on each crystallographic face along different directions were estimated in detail. The results showed that these two faces behave quite differently from each other. The variations of hardness and reduced modulus values for (001) face and the tripler face both were periodic due to the rotational symmetry of crystallographic face microstructure and the indenter shape, and the periods were 90 and 120 degrees, respectively.

Evidences for the relationship between surface structure and reactivity of goethite nanoparticles based on advanced molecular-probe methods

Surface properties of two goethites have been studied in order to compare the amount of acid surface sites and their distribution over the various surface domains. For this purpose, ammonia, pyridine and nitrogen were used as basic molecular probes. Calorimetry measurements of ammonia adsorption provided the image of the average surface acidity being moderate. This conclusion was supported by the moderate resistance of the adsorbed pyridine molecules to degassing conditions. Adsorption and desorption of pyridine prior to gaseous nitrogen adsorption resulting in masking/unmasking of acid surface sites on the goethite surface allowed confirmation of the acid character of the specific adsorption sites characterized by the high-energy adsorption of electron-donating molecular nitrogen. The amount of acid sites probed by nitrogen and ammonia were of the same order of magnitude but systematically higher for ammonia. The subsequent analysis of the argon and nitrogen derivatives of first-layer adsorption isotherm led to determine the distribution of {101} and {121} crystallographic faces and discuss the location of acid sites on these surface domains.

Growth of AlN single crystalline boules

We have obtained high-quality, crack-free AlN wafers using a convex thermal field inside the growth chamber. Free-standing AlN boules of 15 mm in height and 15 mm in diameter were grown. The carbon concentration was found to be similar in all parts of the boule (∼8×10 18 cm −3) while the initial O concentration was higher (∼1×10 19 cm −3) and slightly decreased during growth. It was found that O incorporated differently on different crystallographic faces. High resolution XRD showed a continuous improvement in crystal quality as a function of boule length. The full width at half maximum (FWHM) of the double crystal rocking curves decreased from 78 in at the beginning of growth to 13 in at the growth end. To the best of our knowledge, this is the first report on impurity incorporation on different crystallographic facets obtained from the same boule.

Crystallographically engineered, hydrothermally crystallized hydroxyapatite films: an in vitro study of bioactivity

The aim of this study was to evaluate the bioactivity of hydroxyapatite films composed of hexagonal single crystals that display {1010} and {0001} crystallographic faces. The effect of engineered [0001] crystallographic orientation was investigated in parallel. Films were deposited by triethyl phosphate/ethylenediamine-tetraacetic acid doubly regulated hydrothermal crystallization on Ti6Al4V substrates (10, 14, 24 h). Bioactivity was investigated by analysis of MC3T3-E1 pre-osteoblast spreading using scanning electron microscopy and quantitative analysis of cell metabolic activity (Alamar Blue) (0-28 days). Scanning electron microscopy and X-ray diffraction were used to evaluate the ability of films to support the differentiation of MC3T3-E1 pre-osteoblasts into matrix-secreting, mineralizing osteoblasts. Results demonstrated that all films enabled MC3T3-E1 cells to spread, grow, and differentiate into matrix-secreting osteoblasts, which deposited biomineral that could not be removed after extraction of organic material. Differences in [0001] HA crystallographic orientation were not, however, found to significantly affect bioactivity. Based on these results, it is concluded that these hydrothermal hydroxyapatite films are non-toxic, bioactive, osteoconductive, and biomineral bonding. The lack of a relationship between reported hydroxyapatite crystallographic face specific protein adsorption and bulk HA bioactivity are discussed in terms of crystallographic texture, surface roughness, assay robustness, and competitive protein adsorption.

Anisotropic Transformation of 4H-SiC Etching Shapes by High Temperature Annealing

We investigated transformation of 4H-SiC etching shapes by high temperature annealing. Although the etching mask was circular, the etched shape resulted in a hexagon, dodecagon, or octadecagon, depending on the etching area size. A hexagon was transformed into a dodecagon along with the high temperature annealing, and a dodecagon was transformed into an octadecagon.Hexagon as well as dodecagon designed with different edge directions undergo different transformation by the annealing, owing to common preference of crystallographic faces. An edge corresponding to one of the {1-10x} faces appears as a straight line and seems most preferred. Edges corresponding to the {11-2x} faces also appear in a curvy feature, suggesting to be second most preferred. Faceted structures (bunching) were observed clearly on the {1-10x} faces but faintly on the {11-2x} faces. Therefore, it is necessary to design the shapes and their directions in an actual device in consideration of the transformation by annealing.

Solution based approaches for the morphology control of BaTiO3 particulates

Within the action COST 539 - ELENA our contribution was aimed at studying solution based approaches for the morphology control of BaTiO3 particulates. Initially, our kinetic analysis and systematic structural and morphological studies, demonstrated that during hydrothermal synthesis from layered titanate nanotubes (TiNTS), BaTiO3 forms via two mechanisms depending on the temperature and time. At low temperatures (90?C), 'wild' type BaTiO3 dendritic particles with cubic structure were formed through a phase boundary topotactic reaction. At higher temperatures and/or for longer times time, the reaction is controlled by a dissolution precipitation mechanism and 'seaweed' type BaTiO3 dendrites are formed. Our results unambiguously elucidated why TiNTs do not routinely act as templates for the formation of 1D BaTiO3. In our subsequent investigations, the effect of additives on the aqueous and hydrothermal synthesis of BaTiO3 was assessed. We reported that although the tested additives influenced the growth of BaTiO3, their behaviour varied; poly(acrylic acid) (PAA) adsorbed on specific crystallographic faces changing the growth kinetics and inducing the oriented attachment of the particles; poly(vinyl pyrrolidone) (PVP), sodium dodecylsulfate (SDS) and hydroxypropylmethylcellulose (HPMC) act as growth inhibitors rather than crystal habit modifiers; and DFructose appeared to increase the activation energy for nucleation, resulting in small crystals (26 nm). Our work clearly indicates that the synthesis of 1D nanostructures of complex oxides by chemical methods is non trivial.

Control of morphology and nanostructure of copper and cobalt oxalates: Effect of complexing ions, polymeric additives and molecular weight

Precipitated oxalates are often nanostructured and can be used as precursors for nanostructured oxides for different applications. The modification of the particle shape and nanostructures of both copper and cobalt oxalates has been demonstrated using polymeric additives or complexing counter-ions. In the case of cobalt oxalate the characteristic elongated rod particle shape (axial ratio of 10) can be modified by using polymethymethacrylate (PMMA) to produce particles with lower axial ratios of 2, through cubes all the way to platelets (axial ratio 0.2). The PMMA inhibits the growth of the particles along the [101] direction more and more strongly as the concentration of the polymer increases. The crystallite size from XRD line broadening is not modified by the PMMA indicating that the PMMA does not influence the nucleation and growth but modifies the aggregation kinetics. Copper oxalates precipitated in the presence of different cellulose derived polymers with different molecular weights and functional groups (methyl and propyl) showed sensitivity to both molecular weight and functional group. Higher molecular weights did not influence the copper oxalate particle shape, whereas methyl cellulose gave elongated particles and propyl celluloses gave platelet like particles. Copper oxalate precipitated in the presence of acetate counter ions gave platelets with an axial ratio of 0.15 compared to the cushion-like morphology (axial ratio 0.5). The primary crystallites were more elongated along the [001] direction in the presence of acetate, modifying the proportion of the hydrophobic and hydrophilic surfaces and hence influencing the aggregation kinetics and particle shape. The copper and cobalt oxalate particle formation seems to be dominated by the primary particle aggregation with the different additives interacting specifically with different crystallographic faces of the primary particles. By tuning this interaction particles with different shapes and substructures can be formed.

Role of Intrasurface Hydrogen Bonding on Silica Dissolution

A recently formulated reactive Monte Carlo (RxMC) algorithm has been applied to determine the differential dissolution probability in topographically distinct crystallographic faces of β-cristobalite. Although the contribution of edge, kink, and step sites to the overall dissolution from a crystal is well-established, the effect of hydrogen bonding on flat terrace sites is less understood. In an earlier study (J. Phys. Chem. 111, 5169, 2007), 40 β-cristobalite surfaces were shown to have distinct intrasurface hydrogen bonding patterns between the hydroxylated surface groups. This study is an extension of the previous work with the aim to identify the role intrasurface hydrogen bonding has toward overall dissolution from these surfaces. Five surfaces have been chosen with varying ratios of Q2 (two surface OH groups per Si site) and Q3 (one surface OH group per Si site) groups. The results successfully show that pure Q2 {100} terrace sites with intrasurface hydrogen are less reactive than non-hydrogen bonde...

Dye Sensitization of Single Crystal Semiconductor Electrodes

Even though investigations of dye-sensitized nanocrystalline semiconductors in solar cells has dominated research on dye-sensitized semiconductors over the past two decades, single crystal electrodes represent far simpler model systems for studying the sensitization process with a continuing train of studies dating back more than 40 years. Even today single crystal surfaces prove to be more controlled experimental models for the study of dye-sensitized semiconductors than the nanocrystalline substrates. This Account analyzes the scientific advances in the model sensitized single crystal systems that preceded the introduction of nanocrystalline semiconductor electrodes. It then follows the single crystal research to the present, illustrating both their striking simplicity of use and clarity of interpretation relative to nanocrystalline electrodes. Researchers have employed many electrochemical, photochemical, and scanning probe techniques for studying monolayer quantities of sensitizing dyes at specific crystallographic faces of different semiconductors. These methods include photochronocoulometry, electronic spectroscopy, and flash photolysis of dyes at potential-controlled semiconductor electrodes and the use of total internal reflection methods. In addition, we describe the preparation of surfaces of single crystal SnS(2) and TiO(2) electrodes to serve as reproducible model systems for charge separation at dye-sensitized solar cells. This process involves cleaving the SnS(2) electrodes and a photoelectrochemical surface treatment for TiO(2) that produces clean surfaces for sensitization (as verified by AFM) resulting in near unity yields for electron transfer from the molecular excited dyes into the conduction band. In recent experiments with ruthenium complexes at TiO(2) and with carboxylated cyanine dyes, we demonstrate the promise of this simple model for understanding dye-sensitized solar cells. In each of these systems, we can observe and analyze the complex photochemistry in a quantitative manner. Molecules of the well-known N3 ruthenium complex attach to four different crystallographic faces of anatase and rutile TiO(2) at different rates and to a different extent. With carboxylated cyanine dye sensitizers on these surfaces, molecular aggregation on the surface is a function of molecular structure and crystallographic face. In contrast with the N3 sensitizer these organic dyes undergo a photoinduced dimerization and desorption reaction when hydroquinone regenerators are present. With both classes of sensitizers, we demonstrate a new photochronocoulometric technique that quantifies the amount of attached dye on the electrode surface. We have completed initial experiments examining quantum dot sensitization of TiO(2) crystals, which could eventually lead to sensitizers with higher stability and absorption coefficients. Although these single crystal electrode models show promise for providing insights and predictive value in understanding the sensitization process, more sophisticated models will be needed to fully understand the charge transfer from the localized electronic states of the sensitizer to the extended states of the semiconductor.

Orientation Controllable Growth of MoO3 Nanoflakes: Micro-Raman, Field Emission, and Birefringence Properties

A simple but effective way to control the orientational arrangement of MoO3 nanoflakes is presented, which offers an opportunity to investigate the anisotropic properties of different crystallographic faces. Their electrical and optical properties are investigated. According to the polarized micro-Raman spectra, oxygen vacancies preferred to be located at the sharp side edges of the lamella, which might play an important role in the catalytic properties of samples. Ascribing to the unique structural geometry and the oxygen-defects-induced reduction of the work function, the electron field emission properties of the samples show that the erect MoO3 nanoflakes are potential candidates for the cold-cathode-based electronics. Furthermore, strong optical birefringence properties of samples are also first observed.

Influence of Size and Aggregation on the Reactivity of an Environmentally and Industrially Relevant Nanomaterial (PbS)

Rarely observed nanoparticle dissolution rate data have been collected and explained for an environmentally and industrially relevant nanomaterial (PbS, the mineral galena) as a function of its particle size and aggregation state using high-resolution transmission electron microscopy (HRTEM) and solution analysis. Under identical anoxic acidic conditions (pH 3 HCl), it has been determined that the dissolution rate of PbS galena varies by at least 1 order of magnitude simply as a function of particle size, and also due to the aggregation state of the particles (dissolution rates measured are 4.4 x 10(-9) mol m(-2) s(-1) for dispersed 14 nm nanocrystals; 7.7 x 10(-10) mol m(-2) s(-1) for dispersed 3.1 microm microcrystals; and 4.7 x 10(-10) mol m(-2) s(-1) for aggregated 14 nm nanocrystals). The dissolution rate difference between galena microparticles and nanoparticles is due to differences in nanotopography and the crystallographic faces present. Aggregate vs. dispersed dissolution rates are related to transport inhibition in the observed highly confined spaces between densely packed, aggregated nanocrystals, where self-diffusion coefficients of water and ions decrease dramatically. This study shows that factors at the nanometer scale significantly influence the release rate of aqueous, highly toxic and bioavailable Pb in natural or industrial environments during galena dissolution.

Modelling protein crystallisation using morphological population balance models

Protein crystallisation is known to be affected by many factors and inherently difficult to control. Being able to model the crystal growth behaviour, especially at process scale for the population of particles in a crystalliser will no doubt greatly help the formulation and controlled manufacture of protein crystals. In this paper, a morphological population balance model for crystallisation of tetragonal Hen-Egg-White (HEW) lysozyme is presented. Since the population balance model has incorporated crystal shape information, it is able to simulate the dynamic evolution of the shape distribution as well as size distribution. The morphological population balance model requires faceted growth kinetics data, which was obtained from published data in literature for the two identified independent crystallographic faces, {1 0 1} and {1 1 0}, of HEW lysozyme crystals.

Fabrication of well ordered Zn nanorod arrays by ion irradiation method at room temperature and effect on crystal orientations

Highly oriented and densely packed one-dimensional (1D) polycrystalline Zn nanorods were fabricated on zinc plate without any catalyst at room temperature by bombardment with obliquely incident Ar + ion via ion irradiation method. The sputtered surfaces were fully covered with Zn nanostructures with diameter and the length around 60 nm and 1.3 μm, respectively, confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal orientation of the Zn plate was investigated by electron back scattering pattern method (EBSP). The numerical density and morphology of Zn nanostructures (nanoneedle or nanorods) were found to be 2.1 × 10 6 to 9 × 10 6/mm 2 depending upon the crystal orientation and the atomic density on different crystallographic faces. ( 2 1 ¯ 1 ¯ 0 ) faces of Zn polycrystal tended to form more dense nanostructures compared to ( 0 0 0 1 ¯ ) faces. This is because of lower atomic density on ( 2 1 ¯ 1 ¯ 0 ) faces in comparison with ( 0 0 0 1 ¯ ) faces. This indicates that lower atomic density on any crystallographic faces is favorable to form nanostructure of higher density. The outstanding feature of this growth technique is that it provides a new direction for the controllable growth of desired nanostructures of variable density at room temperature without any catalyst. These well-aligned arrays of Zn nanorods/nanoneedle might be a promising material for the future application in nanodevices.

Identification of etch‐pit crystallographic faces induced on diamond surface by H2/O2 etching plasma treatment

AbstractEven for samples exhibiting excellent electronic properties in terms of carrier mobility, sample‐to‐sample variability remains considerable and dislocation density is still very high, the latter characteristic being often related to damages induced either by the substrate polishing step or by substrate bulk dislocations. In order to limit the polishing effect, a pre‐treatment based on H2/O2 plasma etching under relatively high pressure (a few 100 mbar) has been routinely used for several years. Nevertheless, those bulk dislocations present in the substrate that reach its surface lead to square etch‐pit formation which depth can grow to several 100 nm, preventing the growth of smooth and flat thin films (&lt;few µm). In order to overcome this limitation, we have focused our work on the identification of the crystallographic faces constitutive of the etch‐pits. Starting from a geometrical model describing the diamond crystal morphology evolution, and by carefully choosing the initial growth conditions, we show that it is possible to fill the etch‐pits rapidly and thus to recover the H2/O2 plasma pre‐treatment advantages, even for thin film deposition with smooth surface.