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In this work, the migration of a three-dimensional (3D) spherical crystal in the presence of mobile particles using a Monte Carlo algorithm was studied. Different concentrations of particles (f) and different particle mobilities ([M.sub.p]) were used. It was found that the grain size reaches a critical radius ([R.sub.c]), which depends exclusively on f. This dependence can be written as [R.sub.c] [varies] [f.sup.1/3]. The dynamic equation of grain size evolution and its analytical solution were also found. The proposed analytical solution successfully fits the simulation results. The particle fraction in the grain boundary was also found analytically and it fits the computational data. Key words: grain boundary migration, mobile particle drag, Zener drag, Monte Carlo. Nous utilisons ici un algorithme Monte Carlo pour etudier la migration de cristaux spheriques 3D en presence de particules mobiles. Nous utilisons differentes concentrations de particules (f) et differentes mobilites de particules ([M.sub.p]). Nous trouvons que la grosseur de grain atteint un rayon critique ([R.sub.c]) qui depend exclusivement de f. Cette dependance peut s'ecrire comme [R.sub.c] [varies] [f.sup.1/3]. Nous trouvons egalement l'equation dynamique de l'evolution de la grosseur de grain avec sa solution analytique. La solution analytique proposee correspond avec succes aux resultats de simulation. Nous trouvons aussi analytiquement la fraction de particule dans le joint de grain et elle correspond aux resultats de calcul. [Traduit par la Redaction] Mots-cles : migration du joint de grain, trainee de la particule mobile, trainee/epinglage de Zener, Monte Carlo., Introduction Computer modeling of grain growth in polycrystalline materials [1-4] has become more and more important in recent years. The evolution of the grains in these materials is an important [...]

Non-isothermal crystallization kinetics has been traditionally predicted using the Nakamura crystal growth model, which is an integral form of the Avrami equation under the assumption that the non-isothermal kinetics can be explained using a series of infinitesimal isothermal steps. However, the Nakamura model often over-predicts crystal fraction near the end of crystallization because of ignoring slower secondary crystallization kinetics. In this study, the dual Nakamura model is proposed to capture both primary and secondary crystallization kinetics of poly(ether ether ketone) (PEEK). First, non-isothermal crystallization kinetics of PEEK is monitored at five constant cooling rates of 10, 30, 50, 70, and 90 K/min via differential scanning calorimetry. The dual Nakamura model, which contains a smaller secondary Avrami exponent ([n.sub.s]) to account for the secondary crystallization, is fitted to the exothermal heat flow curves. The dual Nakamura model successfully describes the final stage of crystallization at all cooling rates by reducing the crystal growth dimension from [n.sub.p] = 3 for primary crystallization to [n.sub.s] [congruent to]1. KEYWORDS crystallization kinetics, Nakamura crystallization model, non-isothermal crystallization, PEEK, secondary crystallization kinetics, 1 | INTRODUCTION The understanding of polymer crystallization has been an important topic for polymer engineers since crystallization kinetics plays a crucial role in both processing and final products. [1-5] [...]

We have designed and constructed a compact rotary substrate heater for the temperature range of 25 [degrees]C to 700 [degrees]C. The heater can be implemented in any deposition system where crystalline samples are needed. Its main function is to provide heat treatment in situ during film growth. The temperature is monitored and controlled by a temperature controller coupled to a type-K thermocouple. A heater case was designed to host a resistive element and at the same time allow the substrate holder to freely rotate. Rotation is crucial not only for film homogeneity during deposition but also for the elimination of temperature gradients on the substrate holder. To tolerate oxidizing and corrosive environments, the instrument was made of stainless steel, which also works as a 'coolant', taking advantage of heat dissipation. The instrument performs well for long periods of time with stable temperatures. We hope that this project is useful for laboratories wishing to have a compact rotary heater that meets the requirements for crystal growth and film homogeneity. Key words: substrate heater, temperature controller, deposition system. Nous avons concu et construit un four compact a substrat rotatif pour operer entre 25 [degrees]C et 700 [degrees]C. L'appareil peut etre utilise dans tout systeme a croissance cristalline par depot, la ou des echantillons cristallins sont requis. Sa fonction premiere est de fournir une source de chaleur in situ pendant la croissance des films. La temperature est suivie et geree par un controleur de temperature couple a un thermocouple de type K. Nous avons concu une enceinte pour l'element resistif tout en permettant au substrat rotatif de tourner librement. La rotation est cruciale, non seulement pour assurer un film homogene, mais aussi pour eliminer le gradient de temperature sur le substrat tournant. Pour contrer les problemes d'oxydation et de corrosion, l'instrument est fait d'acier inoxydable qui agit aussi comme refroidisseur, prenant avantage de la dissipation de chaleur. L'instrument se comporte bien pour de longues periodes de temps avec des temperatures stables. Nous esperons que ce projet sera utile aux laboratoires qui ont des besoins de croissance de cristaux par depot et d'homogeneite de film. Mots-cles: substrat, four, depot, temperature, controleur, 1. Introduction A substrate heater is one of the most important components in depositions systems. Its function is to give enough energy to adatoms on the substrate for their adsorption [...]

The production of large single-crystal metal foils with various facet indices has long been a pursuit in materials science owing to their potential applications in crystal epitaxy, catalysis, electronics and thermal engineering.sup.1-5. For a given metal, there are only three sets of low-index facets ({100}, {110} and {111}). In comparison, high-index facets are in principle infinite and could afford richer surface structures and properties. However, the controlled preparation of single-crystal foils with high-index facets is challenging, because they are neither thermodynamically.sup.6,7 nor kinetically.sup.3 favourable compared to low-index facets.sup.6-18. Here we report a seeded growth technique for building a library of single-crystal copper foils with sizes of about 30 × 20 square centimetres and more than 30 kinds of facet. A mild pre-oxidation of polycrystalline copper foils, followed by annealing in a reducing atmosphere, leads to the growth of high-index copper facets that cover almost the entire foil and have the potential of growing to lengths of several metres. The creation of oxide surface layers on our foils means that surface energy minimization is not a key determinant of facet selection for growth, as is usually the case. Instead, facet selection is dictated randomly by the facet of the largest grain (irrespective of its surface energy), which consumes smaller grains and eliminates grain boundaries. Our high-index foils can be used as seeds for the growth of other Cu foils along either the in-plane or the out-of-plane direction. We show that this technique is also applicable to the growth of high-index single-crystal nickel foils, and we explore the possibility of using our high-index copper foils as substrates for the epitaxial growth of two-dimensional materials. Other applications are expected in selective catalysis, low-impedance electrical conduction and heat dissipation. Large-area single-crystal high-index copper and nickel foils with several types of facet are fabricated using mild pre-oxidation of the metal foil surface followed by annealing in a reducing atmosphere., Author(s): Muhong Wu [sup.1] [sup.2] [sup.3] , Zhibin Zhang [sup.1] , Xiaozhi Xu [sup.4] , Zhihong Zhang [sup.2] , Yunrui Duan [sup.5] [sup.6] , Jichen Dong [sup.5] , Ruixi Qiao [...]

The ability to grow properly sized and good quality crystals is one of the cornerstones of single-crystal diffraction, is advantageous in many industrial-scale chemical processes.sup.1-3, and is important for obtaining institutional approvals of new drugs for which high-quality crystallographic data are required.sup.4-7. Typically, single crystals suitable for such processes and analyses are grown for hours to days during which any mechanical disturbances--believed to be detrimental to the process--are carefully avoided. In particular, stirring and shear flows are known to cause secondary nucleation, which decreases the final size of the crystals (though shear can also increase their quantity.sup.8-14). Here we demonstrate that in the presence of polymers (preferably, polyionic liquids), crystals of various types grow in common solvents, at constant temperature, much bigger and much faster when stirred, rather than kept still. This conclusion is based on the study of approximately 20 diverse organic molecules, inorganic salts, metal-organic complexes, and even some proteins. On typical timescales of a few to tens of minutes, these molecules grow into regularly faceted crystals that are always larger (with longest linear dimension about 16 times larger) than those obtained in control experiments of the same duration but without stirring or without polymers. We attribute this enhancement to two synergistic effects. First, under shear, the polymers and their aggregates disentangle, compete for solvent molecules and thus effectively 'salt out' (that is, induce precipitation by decreasing solubility of) the crystallizing species. Second, the local shear rate is dependent on particle size, ultimately promoting the growth of larger crystals (but not via surface-energy effects as in classical Ostwald ripening). This closed-system, constant-temperature crystallization driven by shear could be a valuable addition to the repertoire of crystal growth techniques, enabling accelerated growth of crystals required by the materials and pharmaceutical industries. A method of growing crystals that does not require undisturbed solutions involves adding polyelectrolytes to the starter solution and shearing (that is, stirring)., Author(s): Jian-Ke Sun [sup.1] [sup.3] , Yaroslav I. Sobolev [sup.1] , Weiyi Zhang [sup.4] , Qiang Zhuang [sup.1] [sup.5] , Bartosz A. Grzybowski [sup.1] [sup.2] Author Affiliations: (1) Center for [...]

Ultrathin two-dimensional (2D) semiconducting layered materials offer great potential for extending Moore's law of the number of transistors in an integrated circuit.sup.1. One key challenge with 2D semiconductors is to avoid the formation of charge scattering and trap sites from adjacent dielectrics. An insulating van der Waals layer of hexagonal boron nitride (hBN) provides an excellent interface dielectric, efficiently reducing charge scattering.sup.2,3. Recent studies have shown the growth of single-crystal hBN films on molten gold surfaces.sup.4 or bulk copper foils.sup.5. However, the use of molten gold is not favoured by industry, owing to its high cost, cross-contamination and potential issues of process control and scalability. Copper foils might be suitable for roll-to-roll processes, but are unlikely to be compatible with advanced microelectronic fabrication on wafers. Thus, a reliable way of growing single-crystal hBN films directly on wafers would contribute to the broad adoption of 2D layered materials in industry. Previous attempts to grow hBN monolayers on Cu (111) metals have failed to achieve mono-orientation, resulting in unwanted grain boundaries when the layers merge into films.sup.6,7. Growing single-crystal hBN on such high-symmetry surface planes as Cu (111).sup.5,8 is widely believed to be impossible, even in theory. Nonetheless, here we report the successful epitaxial growth of single-crystal hBN monolayers on a Cu (111) thin film across a two-inch c-plane sapphire wafer. This surprising result is corroborated by our first-principles calculations, suggesting that the epitaxial growth is enhanced by lateral docking of hBN to Cu (111) steps, ensuring the mono-orientation of hBN monolayers. The obtained single-crystal hBN, incorporated as an interface layer between molybdenum disulfide and hafnium dioxide in a bottom-gate configuration, enhanced the electrical performance of transistors. This reliable approach to producing wafer-scale single-crystal hBN paves the way to future 2D electronics. The epitaxial growth of single-crystal hexagonal boron nitride monolayers on a copper (111) thin film across a sapphire wafer suggests a route to the broad adoption of two-dimensional layered semiconductor materials in industry., Author(s): Tse-An Chen [sup.1] , Chih-Piao Chuu [sup.1] , Chien-Chih Tseng [sup.2] , Chao-Kai Wen [sup.2] , H.-S. Philip Wong [sup.1] , Shuangyuan Pan [sup.3] , Rongtan Li [sup.4] [sup.5] [...]

CARBON-REDUCING SUPERALLGY In a collaborative effort between Sandia National Laboratory, Iowa State University, Ames National Laboratory, and Bruker Corp., Billerica, Mass., scientists used a 3D printer to create a superalloy [...]

Two Japanese scientists supply hundreds of laboratories with a prized gem -- and are now among the world's most published researchers. Two Japanese scientists supply hundreds of laboratories with a prized gem -- and are now among the world's most published researchers., Author(s): Mark Zastrow Author Affiliations: Takashi Taniguchi with his crystal-making hydraulic press at the National Institute of Materials Science in Tsukuba, Japan. [see PDF for image] Credit: Mark Zastrow Takashi [...]

Chronic kidney disease (CKD) has reached epidemic proportions globally. The natural course of chronic kidney disease is almost uniformly progressive, albeit at different rates in different individuals. The downhill course appears to pervade kidney diseases of all etiologies and seems to spiral down a self-perpetuating vortex, even if the original insult is ameliorated or controlled. In this issue of the JCI, Shiizaki, Tsubouchi, and colleagues proposed a model of renal tubule luminal calcium phosphate crystallopathy that accounts for renal function demise. Calcium phosphate crystals attached to TLR4 and underwent endocytosis at the brush border, triggering inflammation and fibrosis. This mechanism might operate in different kinds of kidney disease, with a theoretical phosphate concentration threshold in the proximal tubular lumen, beyond which is triggered undesirable downstream effects that eventuate in loss of renal function. If this model parallels human CKD, clinicians may focus efforts on determining phosphate exposure in the proximal tubular lumen., Chronic kidney disease progression is universal Chronic kidney disease (CKD) has reached epidemic proportions globally, imparting dire health and economic burdens on humankind. The progression of CKD appears to be [...]

The zero field splitting parameters (ZFSPs) D and E of [Cr.sup.3+] ion doped potassium sodium dl-tartrate tetrahydrate (PSTT), KNa[C.sub.4][H.sub.4][O.sub.6] x 4[H.sub.2]O are calculated using the superposition model. The theoretically calculated ZFSPs for [Cr.sup.3+] in PSTT crystal are compared with the experimental values obtained by electron paramagnetic resonance. Theoretical ZFSPs are in good agreement with the experimental values. The energy band positions of optical absorption spectra of [Cr.sup.3+] in PSTT single crystal calculated with the CFA package agree well with experimental values. Key words: organic compounds, crystal growth, crystal fields, electron paramagnetic resonance, optical properties. Resume : Nous utilisons le modele de superposition pour calculer les parametres D et E de separation en champ nul (ZFSPs) du dl-tartrate de sodium potassium tetra-hydrate (PSTT), KNa[C.sub.4][H.sub.4][O.sub.6] x 4[H.sub.2]O et dope a l'ion [Cr.sup.3+]. Nous comparons les valeurs theoriques des parametres ZFSPs pour le [Cr.sup.3+] dans le cristal de PSTT avec les valeurs experimentales obtenues par resonance paramagnetique electronique. Les valeurs theoriques des ZFSPs sont en bon accord avec les valeurs experimentales. Les positions des bandes d'energie du spectre d'absorption optique du [Cr.sup.3+] dans le monocristal de PSTT, calculees avec le logiciel CFA, sont en bon accord avec les valeurs experimentales. [Traduit par la Redaction] Mots-cles : composes organiques, croissance cristalline, champs cristallins, resonance paramagnetique electronique, proprietes optiques. PACS Nos.: 76.30.Da, 76.30.Fc, 71.70.Ch., 1. Introduction Electron paramagnetic resonance (EPR) gives a great deal of information about the local site symmetry and zero field splitting parameters (ZFSPs) of transition metal ions in crystals [1]. [...]

L-phenylalanine cadmium chloride (LPCC) single crystals were grown from aqueous solution using the slow evaporation solution technique. The grown crystals were analyzed through various characterization techniques. Structural study reveals that LPCC belongs to a monoclinic crystal system with the space group P1. The presences of various functional groups were identified by Fourier transform infrared analysis. Optical absorption study was carried out and complete transparency in the visible region was observed with a lower cutoff wavelength of 261 nm. The surface morphology was analyzed through scanning electron micrograph studies. LPCC is thermally stable up to 265°C as determined by thermogravimetric - differential thermal analysis studies. Dielectric behavior as a function of frequency was examined. The mechanical behavior was studied by Vicker's microhardness tester. To explore the nonlinear optical property, the Kurtz powder method was employed and second harmonic generation efficiency was determined. PACS Nos.: 81.10.Dn, 42.70Mp, 61.66Hq, 42.65.-K. Nous faisons croitre des monocristaux de chlorure de cadmium L-phenylalanine (LPCC) par evaporation lente d'une solution aqueuse. Les cristaux sont analyses a l'aide de differentes techniques. L'etude structurelle nous indique que LPCC appartient a la famille des cristaux monocliniques avec le groupe d'espace P1. L'analyse FTIR permet l'identification de differents groupes fonctionnels. Notre etude d'absorption optique verifie la transparence complete dans le visible, avec coupure basse a 261 nm. Nous etudions la morphologie de surface par analyse SEM et notre etude TG-TDA determine que le LPCC est thermiquement stable jusqu'a 265°C. Nous examinons les proprietes dielectriques en fonction de la frequence. Un test Vicker de microdurete determine les proprietes mecaniques. Nous utilisons la methode des poudres de Kurtz pour explorer les proprietes optiques non lineaires et determinons l'efficacite de generation de seconde harmonique. [Traduit par la Redaction], 1. Introduction Nonlinear optics (NLO) is an active field of research because of its potential applications in laser technology, optical communication, optical data storage, etc. [1]. The properties and applications [...]

In this study, the synthesis of Co/Al hydrotalcite (layered double hydroxides: LDHs) using insoluble Al[(OH).sub.3] by a hydrothermal method is described. The syntheses were conducted under various conditions. The as-prepared Co/Al-C[O.sub.3.sup.2-]-LDH was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The tribological properties of the products were evaluated in base oil using four-ball and Plint friction testers. The LDH thus synthesized displays perfect hexagonal platelike morphology having a disk diameter in the range of 0.2-1.5 µm with a thickness of 40 nm. The addition of the product Co/Al-C[O.sub.3.sup.2-]-LDH, as an additive to the base oil, significantly reduces the friction coefficient (22.3%) and wear (26.1%) compared to base oil alone. The morphology and chemistry of the worn surface were characterized by SEM, atomic force microscopy (AFM), and X-ray absorption near-edge structure (XANES) spectroscopy. The results show that the structural distortion of LDH induced by mechanochemical processes during friction consumes the friction force between the rubbed surfaces, and as a result, the friction and the wear is reduced. Thus, our results show that the LDH sheets absorbed on the worn surface can prevent direct contact between the friction pairs (surfaces) and decreases the roughness of the worn surface. Key words: Co/Al hydrotalcites, antifriction, tribochemistry, X-ray absorption near-edge structure (XANES). La presente etude decrit la synthese d'hydrotalcite de Co/Al (hydroxydes doubles lamellaires ou HDL) a l'aide d'Al[(OH).sub.3] insoluble par methode hydrothermale. Les syntheses ont ete realisees dans diverses conditions. Les Co/Al-C[O.sub.3.sup.2-]-HDL ainsi prepares ont ete caracterises par diffractometrie de rayons X (DRX) et microscopie electronique a balayage (MEB). Les proprietes tribologiques des produits ont ete etudiees dans de l'huile de base a l'aide de bancs d'essai de frottement a quatre billes et de tribometres Plint. Les HDL ainsi synthetises presentent une morphologie hexagonale parfaite en plaque dont le diametre de disque est compris entre 0,2 et 1,5 µm et l'epaisseur egale a 40 nm. L'ajout du produit Co/Al-C[O.sub.3.sup.2-]-HDL, comme additif a l'huile de base, reduit considerablement le coefficient de frottement (22,3%) et l'usure (26,1%), par rapport a l'huile de base seule. La morphologie et la chimie de la surface usee ont ete caracterisees par MEB, microscopie a force atomique (MFA) et spectroscopie de structure pres du front d'absorption de rayons X. Les resultats montrent que la distorsion structurale des HDL provoquee par les processus mecanochimiques ayant lieu lors des frottements reduit la force de frottement presente entre les surfaces enduites, ce qui entraine une diminution du frottement et de l'usure. Nos resultats demontrent ainsi que les feuilles d'HDL absorbees sur la surface usee peuvent empecher les paires de frottement (surface) d'etre en contact et reduisent la rugosite de la surface usee. [Traduit par la Redaction] Mots-cles: hydrotalcites de Co/Al, antifriction, tribochimie, spectroscopie de structure pres du front d'absorption de rayons X., Introduction Layered double hydroxides (LDHs) are a class of layered anionic clays having the general formula of [[M.sub.(1-x).sup.2+][M.sub.x.sup.3+][(OH).sub.2]][([A.sup.n-]).sub.x/n] x z[H.sub.2]O, where [M.sup.2+] (Mg, Mn, Fe, Co, Ni, Cu, Zn, etc.) [...]

RAPID CRYSTALLIZATION Researchers from Fudan University and Peking University, both based in China, along with other collaborators including the Institute of Industrial Science at The University of Tokyo, conducted experimental [...]

Smoke, fog, jelly, paints, milk and shaving cream are common everyday examples of colloids (1), a type of soft matter consisting of tiny particles dispersed in chemically distinct host media. [...]

Recent advances in the fabrication of quasicrystals in soft matter systems have increased the length scales for quasicrystals (1) into the mesoscale range (20 to 500 angstroms). Thus far, dendritic [...]

The importance of nonclassical, multistage crystallization pathways is increasingly evident from theoretical studies on colloidal systems and experimental investigations of proteins and biomineral phases. Although theoretical predictions suggest that proteins follow these pathways as a result of fluctuations that create unstable dense-liquid states, microscopic studies indicate these states are long-lived. Using in situ atomic force microscopy to follow 2D assembly of S-layer proteins on supported lipid bilayers, we have obtained a molecular-scale picture of multistage protein crystallization that reveals the importance of conformational transformations in directing the pathway of assembly. We find that monomers with an extended conformation first form a mobile adsorbed phase, from which they condense into amorphous clusters. These clusters undergo a phase transition through S-layer folding into crystalline clusters composed of compact tetramers. Growth then proceeds by formation of new tetramers exclusively at cluster edges, implying tetramer formation is autocatalytic. Analysis of the growth kinetics leads to a quantitative model in which tetramer creation is rate limiting. However, the estimated barrier is much smaller than expected for folding of isolated S-layer proteins, suggesting an energetic rationale for this multistage pathway. in situ atomic force microscopy imaging | protein crystal growth | two-step crystallization | amorphous precursors | assembly kinetics doi/ 10.1073/pnas.1008280107

In this paper, I demonstrate that the complex structure observed in natural dendritic zircon, which crystallized from a mafic magma, can be approximated by a simple model of deterministic volume-filling fractal growth. The model comprises a novel dendritic growth process that reveals a previously unrecognized underlying structure to complex dendritic crystals, and provides an ideal way of maximizing surface area at the crystal-melt interlace during dendritic crystal growth. This addresses the important kinetic effect of creating interfacial area. In turn, this relates to dissipation of the latent heat of fusion from the moving crystal-melt interlace, which, in addition to chemical diffusion, is known to be a fundamental rate-controlling process in dendritic crystal growth. A new mechanism of tip-splitting branch formation in dendritic crystals is proposed. Although both types of branch formation seem to occur simultaneously, the newly proposed mechanism operates at larger length scales and independently of classical side-branching linked with periodic perturbations caused by thermal noise. It is shown that this type of modeling potentially has applications in metallurgical engineering; and in predicting the relative lengths, orientations, and spacings of branches in mathematical modeling studies of natural and experimentally grown dendritic crystals. Keywords: Dendrite, zircon, fractal, alloy casting, crystal growth DOI: 10.2138/am.2010.3320

In this work, we structurally characterize defects, grain boundaries, and intergrowth phases observed in various Mo-V-O materials using aberration-corrected high-angle annular dark-field (HAADF) imaging within a scanning transmission electron microscope (STEM). Atomic-level imaging of these preparations clearly shows domains of the orthorhombic M1-type phase intergrown with the trigonal phase. Idealized models based on HAADF imaging indicate that atomic-scale registry at the domain boundaries can be seamless with several possible trigonal and Ml-type unit cell orientation relationships. The alignment of two trigonal domains separated by an M1-type domain or vice versa can be predicted by identifying the number of rows/columns of parallel symmetry operators. Intergrowths of the M1 catalyst with the M2 phase or with the [Mo.sub.5][O.sub.14]-type phase have not been observed. The resolution enhancements provided by aberration-correction have provided new insights to the understanding of phase equilibria of complex Mo-V-O materials. This study exemplifies the utility of STEM for the characterization of local structure at crystalline phase boundaries. propane | oxidation | catalyst | acrylonitrile | bronze doi/10.1073/pnas.1001239107

Numerous petrologic studies have attempted to determine crystal growth rates in volcanic systems through several methods, including analyses of crystal size distributions in natural samples and decompression experiments on hydrous magmas. Experiments have revealed that rim growth on existing crystals will occur under a wide range of decompression conditions and is favored under conditions of low to moderate undercoolings over microlite nucleation, which has typically been the focus of decompression-induced crystallization studies. For this study, samples of eruptive clasts were collected from a Vulcanian explosion that occurred following the July 12-13, 2003 dome collapse of Soufri6re Hills volcano, Montserrat. Plagioclase phenocrysts were extracted and examined with secondary ion mass spectrometry (SIMS) depth profiling. Lithium inflection depths within the profiles, along with the observed time interval between the peak in the collapse decompression and the explosion that ejected the examined samples, were used to calculate the growth rates as a result of magma devolatilization, with an average of 8.3 x [10.sup.-8] mm/s. Anorthite content of the plagioclase rim growth indicates an average decompression magnitude of 40 MPa, inducing an undercooling of ~45[degrees]C that favors crystal growth over microlite nucleation. However, variability in the final anorthite contents suggests that not ali phenocrysts recorded an equilibrium composition reflecting accurate pressure conditions. In such events occurring over short timescales (< 10 h), lithium is a more reliable indicator of decompressioninduced growth than changing anorthite content due to lithium's rapid diffusivity. Keywords: Plagioclase, lithium, decompression, SIMS, Soufriere Hills DOI: 10.2138/am.2010.3292

Microlites in pumice fragments can record the rate of magma decompression and ascent, but only if none grow while those fragments cool in the atmosphere. For highly viscous silicate melts, such crystallization is unlikely, but more basic melts are known to crystallize rapidly, and thus could partially crystallize during cooling and overprint decompression textures. To examine whether post-fragmentation crystallization can occur, we examined two basaltic pumice clasts from the sub-Plinian April 1999 eruption of Shishaldin volcano, Alaska. Radial sectioning shows that microlite content doubles from rim to core in both, mainly from growth of plagioclase. Dendrite magnetite also increases greatly in content, but only within the larger pumice clast. Such radial textures demonstrate that crystallization occurred after fragmentation and before deposition (no welding occurred). Using a conductive cooling model coupled with a model for temperature in the eruption column, we estimate that rims of the pumice clasts cool to their glass-transition temperature in ~100-200 s, but their cores take ~500-2000 s to cool, which translates into cooling rates of ~0.2 to 2.5[degrees]C/s. Using a conservative assumption that all plagioclase nucleated before cooling began, we estimate that both short and long axes grew at ~4.8 ([+ or -] 2.7) x [10.sup.-7] cm/s. Such rates match those determined experimentally for basaltic melts at similar cooling rates. Magnetite grew only at the slowest cooling rates, and the rate of bulk magnetite crystallization equals that of plagioclase. Our results demonstrate that groundmass crystallization can occur in basic melts on the timescale of explosive eruptions, and so pumice clasts from such eruptions must be viewed with caution before being used to infer eruption dynamics. Keywords: Crystal growth, plagioclase, cooling, igneous petrology, basaltic pumice, microlites DOI: 10.2138/am.2010.3270

Synthetic rubies were grown by the optical floating zone method and characterized by cathodoluminescence (CL) microscopy and spectroscopy in combination with microprobe analysis. The measured intensity of the [Cr.sup.3+]-induced CL of corundum is influenced by different parameters such as the sample thickness and orientation, the intensity of the beam current, and the quality of the sample surface. Furthermore, the spectral distribution of the CL emission changes with different concentrations of Cr in the corundum structure. Due to these effects, it is usually not possible to estimate the Cr content directly by using the measured CL intensity. However, we have developed an indirect method that is not significantly affected by these parameters. By using intensity ratios instead of measured intensities, a level of quantification of Ct in natural and synthetic corundum is now possible. Our study shows that the intensity ratio between the N-line at 701.6 nm and the sideband maximum at 713.2 nm displays a nearly linear dependence on the Cr concentration from ca. 100-300 ppm up to ca. 1.1 tool% [Cr.sub.2][O.sub.3]. These results give a possible approach to develop an optical-microscope-based CL spectroscopy for quantitative measurements of Cr in natural rubies and synthetic [alpha]-[Al.sub.2][O.sub.3] materials. Keywords: Quantitative cathodoluminescence, [alpha]-[Al.sub.2][O.sub.3], CL, rubies, crystal growth, floating zone technique DOI: 10.2138/am.2010.3291

We report a synthetic route to achieving nanoscale heterostructures consisting of a metal core and monocrystalline semiconductor shell with substantial lattice mismatches between them, which cannot be obtained by conventional epitaxial techniques. By controlling soft acid-base coordination reactions between molecular complexes and colloidal nanostructures, we show that chemical thermodynamics can drive nanoscale monocrystalline growth of the semiconductor shell with a lattice structure incommensurate with that of the core. More complex hybrid core-shell structures with azimuthal and radial nanotailoring of structures and compositions of the monocrystalline semiconductor shell are also demonstrated. 10.1126/science.1184769

Large single crystals of stishovite were successfully synthesized at 11 GPa from a silica solution in water. The potential of both slow cooling and thermal gradient methods were examined. The thermal gradient method provided crystals of 0.8 x 0.8 x 1.3 mm in size grown at 1350 [degrees]C and a thermal gradient of 50 [degrees]C/mm using stishovite as a silica source. The use of quartz as a source resulted in the appearance of numerous stishovite crystals in the solution interior resulting in diminished space for the growth of large crystals. This can be explained by a significant difference in the solubility of metastable quartz and stishovite in water, estimated to be 85.3 and 5.6 wt% Si[O.sub.2] at 1000 [degrees]C and 11 GPa, respectively. Crystals up to 0.8 x 1.3 x 1.5 mm were grown by the slow cooling method in the system Si[O.sub.2] + 14.7 wt% [H.sub.2]O as temperature was decreased from 1600 to 1000 [degrees]C with a cooling rate of 2 [degrees]C/min. The size of single crystals obtained was large enough to carry out silicon self-diffusion experiments, which were performed at a pressure of 14 GPa and temperatures from 1400 to 1800 [degrees]C. The lattice diffusion coefficients along the [110] and [00l] directions can be expressed as [D.sub.[110]] ([m.sup.2]/s) 4.10 x [10.sup.-12] exp [-322 (kJ/mol)/RT] and [D.sub.[001]] ([m.sup.2]/s) = 5.62 x [10.sup.-12] exp [- 334 (kJ/mol)/RT], respectively, where R is the gas constant and T is the absolute temperature. Keywords: Stishovite, single-crystal growth, high pressure, aqueous fluid, silica solubility, diffusion DOI: 10.2138/am.2010.3255

Despite the industrial implications and worldwide abundance of gas hydrates, the formation mechanism of these compounds remains poorly understood. We report direct molecular dynamics simulations of the spontaneous nucleation and growth of methane hydrate. The multiple-microsecond trajectories offer detailed insight into the process of hydrate nucleation. Cooperative organization is observed to lead to methane adsorption onto planar faces of water and the fluctuating formation and dissociation of early hydrate cages. The early cages are mostly face-sharing partial small cages, favoring structure II; however, larger cages subsequently appear as a result of steric constraints and thermodynamic preference for the structure I phase. The resulting structure after nucleation and growth is a combination of the two dominant types of hydrate crystals (structure I and structure II), which are [inked by uncommon [5.sup.12][6.sup.3] cages that facilitate structure coexistence without an energetically unfavorable interface. 24 March 2009; accepted 10 September 2009 Published online 8 October 2009; 10.1126/science.1174010 Include this information when citing this paper.

Ferrihydrite is a key reactive nanoparticle in the Earth surface environment that regulates nutrient and metal cycling in marine, lacustrine, and groundwater settings; yet its genesis is unknown and there is no mechanistic explanation of its nanostructural nature. We develop a model, based on established aqueous precipitation theory, for rough-surface phases growing by accretion of monomers under fast diffusion conditions. The model is entirely defined in terms of a minimal set of necessary microscopic (molecular-scale) characteristic parameters. It is applied to ferrihydrite where the needed microscopic parameters are constrained by some of the mineral's known physico-chemical properties. Our model qualitatively reproduces the main nanostructural properties and known precipitation kinetics of ferrihydrite, predicting that ferrihydrite will be nanometric in size, will have a narrow particle size distribution (standard deviation width equal to a fraction of the average particle size), and will typically precipitate from supersaturated conditions within times ranging from a fraction of a second to several days, under normal environmental-proxy conditions. The model also suggests that different metastable structures of ferrihydrite having similar rough surfaces would kinetically compete during nucleation and growth to coexist in the final product, as observed by Janney et al. (2000a, 2001). Keywords: Ferrihydrite, precipitation, nucleation, oxyhydroxide, nanoparticle

We have synthesized large (0.7-1.0 mm) crystals of anhydrous, water-bearing, and Fe-bearing wadsleyite by means of growth from solution in the thermal gradient field. Nearly anhydrous ( Keywords: [Mg.sub.2]Si[O.sub.4], wadsleyite, single crystal growth, high pressure, thermal gradient method

The effects of aging of high-density polyethylene (HDPE) geomembranes on the diffusion and partitioning of a group of volatile organic compounds (VOCs) are examined. Two different 1.5 mm thick HDPE geomembranes were aged in the laboratory at 85[degrees]C by immersing in a synthetic leachate for up to 32 months. The results of partitioning and diffusion tests performed at room temperature on both unaged and aged geomembranes using a dilute aqueous solution containing four VOCs commonly found in landfill leachates [benzene, toluene, ethylbenzene, and xylenes (BTEX)] are reported. The diffusion and partitioning coefficients decreased with increased aging. The calculated permeation coefficients decreased by 36-62% after aging the geomembrane for about 10-32 months. This decrease in diffusion, partitioning, and permeation coefficients is related to the increase in geomembrane crystallinity during aging. A relationship between partitioning, diffusion, and permeation coefficients with the geomembrane crystallinity is established and could potentially be used to evaluate the migration of VOCs through HDPE geomembranes. Aging of HDPE geomembrane did not increase diffusive transport of organic contaminants. DOI: 10.1061/(ASCE)GT. 1943-5606.0000056 CE Database subject headings: Geomembranes; Aging; Crystal growth; Volatile organic chemicals; Polyethylene.

We present an analysis of the key steps involved in the DNA-directed assembly of nanoparticles into crystallites and polycrystalline aggregates. Additionally, the rate of crystal growth as a function of increased DNA linker length, solution temperature, and self-complementary versus non-self-complementary DNA linker strands (1- versus 2-component systems) has been studied. The data show that the crystals grow via a 3-step process: an initial 'random binding' phase resulting in disordered DNA-AuNP aggregates, followed by localized reorganization and subsequent growth of crystalline domain size, where the resulting crystals are well-ordered at all subsequent stages of growth. DNA materials | SAXS | self assembly

Nacre is an exquisitely structured biocomposite of the calcium carbonate mineral aragonite with small amounts of proteins and the polysaccharide chitin. For many years, it has been the subject of research, not just because of its beauty, but also to discover how nature can produce such a superior product with excellent mechanical properties from such relatively weak raw materials. Four decades ago, Wada [Wada K (1966) Spiral growth of nacre. Nature 211:1427] proposed that the spiral patterns in nacre could be explained by using the theory Frank [Frank F (1949) The influence of dislocations on crystal growth. Discuss Faraday Soc 5:48-54] had put forward of the growth of crystals by means of screw dislocations. Frank's mechanism of crystal growth has been amply confirmed by experimental observations of screw dislocations in crystals, but it is a growth mechanism for a single crystal, with growth fronts of molecules. However, the growth fronts composed of many tablets of crystalline aragonite visible in micrographs of nacre are not a molecular-scale but a mesoscale phenomenon, so it has not been evident how the Frank mechanism might be of relevance. Here, we demonstrate that nacre growth is organized around a liquid-crystal core of chitin crystallites, a skeleton that the other components of nacre subsequently flesh out in a process of hierarchical self-assembly. We establish that spiral and target patterns can arise in a liquid crystal formed layer by layer through the Burton--Cabrera--Frank [Burton W, Cabrera N, Frank F (1951) The growth of crystals and the equilibrium structure of their surfaces. Philos Trans R Soc London Ser A 243:299-358] dynamics, and furthermore that this layer growth mechanism is an instance of an important class of physical systems termed excitable media. Artificial liquid crystals grown in this way may have many technological applications. biomineralization | chitin | interlarnellar membranes | mollusc

Understanding of colloidal nanocrystal growth mechanisms is essential for the syntheses of nanocrystals with desired physical properties. The classical model for the growth of monodisperse nanocrystals assumes a discrete nucleation stage followed by growth via monomer attachment, but has overlooked particle-particle interactions. Recent studies have suggested that interactions between particles play an important role. Using in situ transmission electron microscopy, we show that platinum nanocrystals can grow either by monomer attachment from solution or by particle coalescence. Through the combination of these two processes, an initially broad size distribution can spontaneously narrow into a nearly monodisperse distribution. We suggest that colloidal nanocrystals take different pathways of growth based on their size-and morphology-dependent internal energies.

Strengthening the crystal lattice of lanthanide halides, which are brittle, anisotropic, ionic crystals, may prove to increase the availability and ruggedness of these scintillators for room-temperature gamma-ray spectroscopy applications. Eight aliovalent dopants for Ce[Br.sub.3] were explored in an effort to find the optimal aliovalent strengthening agent. Eight dopants, Ca[Br.sub.2], Sr[Br.sub.2], Ba[Br.sub.2], Zr[Br.sub.4], Hf[Br.sub.4], Zn[Br.sub.2], Cd[Br.sub.2], and Pb[Br.sub.2], were explored at two levels of doping, 500 and 1000 ppm. From each ingot, samples were harvested for radioluminescence spectrum measurement and scintillation testing. Of the eight dopants explored, only Ba[Br.sub.2] and Pb[Br.sub.2] were found to clearly decrease total light yield. Zn[Br.sub.2] and Cd[Br.sub.2] dopants both affected the radioluminescence emission spectrum very little as compared to undoped Ce[Br.sub.3]. Hf[Br.sub.4] - and Zn[Br.sub.2]-doped Ce[Br.sub.3] exhibited the highest light yields. Index Terms--Aliovalent doping, crystal growth, scintillation detectors, solid solution hardening.

The discovery and optimization of new scintillators has traditionally been a rather slow process due to the difficulties of single crystal growth. This paper discusses the production of polycrystalline scintillator thin films which were tested in order to determine what characterizations could be made concerning a materiars ultimate potential as a scintillator prior to pursuing crystal growth. Thin films of a few microns thickness of Ca[F.sub.2] (Eu), Ce[F.sub.3], and Ce[Cl.sub.3], all known scintillators, were produced by vapor deposition. The hygroscopic Ce[Cl.sub.3] was coated with multiple polymeraluminum oxide bi-layers. Emission wavelengths and decay times agreed with values from single crystals. The films were too thin to measure gamma photopeaks, but using alpha energy deposition peaks, one could compare the relative photon yield/MeV between materials. The values obtained appear to give a relevant indication of a material's light yield potential. The technique may also be useful for quickly indicating the proper dopant amount for a given material. Index Terms--Ca[F.sub.2] (Eu), Ce[Cl.sub.3], Ce[F.sub.3], polycrystalline scintillators, thin film scintillators.

We present the luminescent and scintillation characteristics of CsI:C[O.sub.3] single crystals. The CshC[O.sub.3] single crystals were grown by using Czochralski method for different concentrations of C[O.sub.3] from 0.007 to 0.1 mole %. The crystals were cut into a size of 10 mm x 10 mm x 5 mm. The luminescent characteristics were measured with X-rays to study the emission spectra of the CsI:C[O.sub.3] crystals. The scintillation properties of the CsI:C[O.sub.3] crystals such as fluorescence decay time, energy resolution, pulse height spectra, proportionality, and relative light output were studied by using various -y-ray sources with a photomultiplier tube (PMT) at room temperature. The absolute light outputs of the crystals were also measured with an avalanche photo-diode (APD). Index Terms--CsI:C[O.sub.3], crystal growth, scintillation detector.

In this paper, crystal growth and scintillation properties of [Rb.sub.2] Ce[Br.sub.5] crystal are presented. The crystal was grown with the Bridgman method using a two zone transparent furnace. The investigation of scintillation properties of the crystal were performed under the excitation by X-ray and [gamma];-ray at room temperature. The emission spectrum of the [Rb.sub.2] Ce[Br.sub.5] was observed in the range of 360 ~ 440 nm, peaking at 390.5 nm, which is due to the 5d [right arrow] 4f transitions of the [Ce.sup.3+]. The decay time of the [Ce.sup.3+] emission was composed two components. The fast component was 56.1 ns (98.8%), and the slow component was 329.9 ns (1.2%). The energy resolution of the crystal was obtained to be 6.9% for the [sup.137]Cs 662 keV [gamma]-ray. The absolute light yield of the [Rb.sub.2]Ce[Br.sub.5] crystal is about 34,000 phs/MeV, and the non-proportionality of the crystal was also measured. Index Terms--Bridgman, cerium, crystal growth, [Rb.sub.2]Ce[Br.sub.5], scintillator.

Quaternary materials have a large flexibility to design bandgap and effective performance for detectors. In the ternary and quaternary chalcogenides, the semiconducting to seminsulating properties are exhibited with bandgaps from narrow (3 eV) and have the potential and flexibility to produce large numbers of electron hole pairs and hence increase detector sensitivity. In this paper we describe the Ag-Ga-Ge-Se class of materials, an extension of the In-GaSe system, and the challenges related to the material. The important material in this class is the AgGa[Ge.sub.3][Se.sub.8] stoichiometry. A comprehensive solution to produce its derivatives and experimental results are presented. These are compared with the In-GaSe class of materials for growth and fabrication which we have developed over many years. We have developed processes for purification, synthesis of large batches of materials, and crystal growth by vertical Bridgman method. These crystals are grown by both capillary seeding and oriented seeding. The details of the growth process, X-ray orientation, cutting, polishing, fabrication and stability of the large size crystals will be presented. Index Terms--Bridgman method, chalcogenide, crystal growth, gallium selenide, Gamma-ray detectors, semiconductor radiation detectors.

Pr:LuAG crystals possess interesting properties, such as high density, high light yield, and very fast 5d-4f emission decay time. Recently, we developed a Pr:LuAG single crystal with a diameter of 2 inches for scintillator applications, such as medical imaging. In this study, Pr-doped [Lu.sub.3][Al.sub.5][O.sub.12] (Pr:LuAG) single crystals with a diameter of 2 inches were grown by means of the Czochralski method; a body length of up to 90 mm was achieved. The Pr:LuAG crystals produced a homogeneous light yield with approximately 2.5 times less intensity compared to that produced by a conventional Ce:LSO crystal. A sample with dimensions of 5 mm x 5 mm x 1 mm exhibited energy resolutions of 4.8% at 662 keV, as measured by using a photomultiplier (PMT: Hamamatsu H6531), and 5.8% at 662 keV, as measured by using an Avalanche photodiode (APD: Hamamatsu S8664-55). The Pr:LuAG crystals exhibited a very fast rise time of approximately 0.4 ns, excited by a pulsed X-ray at room temperature. The decay time was approximately 18 ns, along with a noticeable presence of slower decay components (with a decay time of 55.0 ns). Furthermore, the Pr:LuAG crystals showed good linearity between the energy and pulse height within approximately 4% of the standard deviation in the range from 122 keV ([sup.152]Eu) to 1.4 MeV ([sup.241]Am). Index Terms--Crystal growth, gamma-ray detectors, garnets, Pr3+, 5d-4f luminescence.

Two monazite generations (M1; M2) were distinguished in a kyanite-garnet gneiss from the UHP terrain of the Pohorje Mountains, Slovenia. P-T estimates reveal a peak event at 760[degrees]C/2.6 GPa and isothermal decompression down to 700[degrees]C/0.6 GPa. M1 type provides a Th-U-Pb mean date of 100 [+ or -] 6 Ma, Th[O.sub.2] contents between 3-7 wt%, [Y.sub.2][O.sub.3] values 1.2 MPa), probably close to the P-T peak. M2 type is slightly younger than M1 (74 [+ or -] 16 Ma), and has a lower La/Nd (0.3-0.9), lower Th[O.sub.2] (0.1-5 wt%), and higher [Y.sub.2][O.sub.3] (up to 3.2 wt%). Most M2 monazites occur as tiny needles within apatite (subtype M2-a) or along apatite margins (M2-b). Parasitic growth of M2-a and -b from apatite is supported by its low Th[O.sub.2] ( These observations imply that at UHP conditions MREE-rich apatite coexisted with low-MREE M1 monazite and reacted during decompression to Ca-F-apatite plus MREE-rich M2 monazite. This provides strong arguments that REE-partitioning between apatite and monazite is pressure-dependent. Keywords: Monazite, apatite, REE distribution, ultra-high pressure, Pohorje Mountains

Primary colloform textures preserved in ore deposits can be a useful tool in understanding changing conditions of ore formation due to the sequential development of the colloform layers. However, the growth controls that influence formation of these textures are poorly understood. To try to address this problem, samples from two ore deposits, Greens Creek in Alaska and Ezuri in Japan, have been systematically analyzed for grain size and shape, crystal preferred orientation (CPO), sulfur isotope composition, and trace element content. Grain size and shape varies between layers of equant, ~20 [micro]m crystals to acicular and elongate crystals up to several millimeters in length. Electron backscatter diffraction (EBSD) reveals that both samples have an initial random orientation of crystals with CPO in subsequent layers developed either about , , or crystallographic axes. Despite similarity in texture, the sulfur isotope results from Greens Creek colloforms have a very negative, open-system bacteriogenic [delta][sup.34]S between -40 and -32[per thousand], whereas the Ezuri colloform has a positive [delta][sup.34]S 0f ~+5[per thousand], typical of hydrothermal sulfur in Kuroko ores. Trace element results indicate variability in As, Sb, and Cu distribution. Whereas trace element variability at Greens Creek appears to be related to changes in [delta][sup.34]S, with a heavier signature correlating with sequestration of Sb in outer layers, overall the detailed analyses reveal that in both Greens Creek and Ezuri, there is no systematic correlation between sulfur source or trace element sequestration and CPO. This suggests that the abrupt changes in CPO recorded appear most likely to be influenced by changes in degree of supersaturation. Keywords: Pyrite, colloform, supersaturation, trace elements, S isotopes, EBSD

Explosive volcanic eruptions may be triggered by processes in the conduit, including P-T variations, volatile loss, and crystal growth. These unobserved processes may be inferred via textural and chemical examination of eruptive products. Juvenile clasts were examined from vulcanian explosions of the Soufriere Hills volcano. Here we show that secondary ion mass spectrometry (SIMS) depth profiling into plagioclase phenocrysts provides a nearly continuous record of magma ascent from chamber to surface via high-resolution (~10 nm) chemical profiles of decompression-induced crystal growth. Changes in lithium concentration allow quantification of crystal growth rates, which range from 2 x [10.sup.-8] mm/s to 7 x [10.sup.-8] mm/s. Anorthite variations suggest conduit temperature increases of 50 to 100[degrees]C, assuming contemporaneous overpressures approaching 20 MPa. These data demonstrate a new means of constraining conduit conditions preceding explosive volcanic eruptions.

A numerical simulation based on a new regularized phase-field model is developed to describe the silicon solidification in a forced flow. The effect of forced flow, anisotropy, and mesh grid on dendritic growth shape is investigated. These results indicate that crystals grow into an equiaxial facet dendritic without flow and into an asymmetrical facet dendritic with flow, that is, upstream arm growth is promoted, and downstream inhibited, however, there is no such effect on perpendicular arms. It is also found that the asymmetrical growth feature becomes noticeable with increase in the flow velocity. With the increase in the anisotropy value, the tip velocities of upstream and downstream decrease gradually. PACS Nos.: 61.50.Ah, 44.27.+g, 81.10.Aj, 02.60.Cb Nous developpons une simulation numerique basee sur un nouveau modele de champ de phase regularisee pour decrire la solidification du silicium dans un flot force. Nous etudions les effets du flot force, de l'anisotropie et du maillage de reseau sur la forme de la croissance dendritique. Les resultats indiquent que le cristal croit en une facette dendritique equiaxiale sans le flot et en une facette dendritique asymetrique avec le flot, ce qui veut dire avec un bras de croissance accru en amont et diminue en aval, alors qu'il n'y a pas d'effet sur les bras perpendiculaires. Nous trouvons aussi que l'asymetrique de croissance devient plus notable avec l'augmentation de la vitesse du flot. Avec l'augmentation de l'anisotropie, les pointes de vitesse diminuent graduellement en amont et en aval. [Traduit par la Redaction], 1. Introduction A dendritic shape is a common shape in the course of melt solidification, and it influences the microstructures and mechanical properties of cast materials [1-3]. The numerical simulation [...]