Prism Faces Research Articles

Molecular Dynamics Simulation Study of the Interfacial Structure and Differential Capacitance of Alkylimidazolium Bis(trifluoromethanesulfonyl)imide [Cnmim][TFSI] Ionic Liquids at Graphite Electrodes

The dependence on electrode potential of the interfacial structure and differential capacitance (DC) for 1-alkyl-3-methyimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][TFSI], n = 2, 4, 6, and 8) ionic liquids (IL) near basal (flat) and prismatic edge face (rough) graphite electrodes was investigated here with atomistic simulations. Overall camel-shaped DCs were observed for both surfaces. The prismatic graphite generated systematically larger capacitances than the atomically flat basal face. Although on the flat electrodes the DC is almost constant at electrode potential bellow saturation (i.e., roughly within ±2 V), on the prismatic edge face the DC showed large amplitude changes between minima and maxima. This trend in DC was explained from the dependence versus potential of the structure and composition of the interfacial electrolyte layer; specifically, faster counterions accumulation and ion segregation in the interfacial layer are observed for atomically corrugated electrode surfaces as compared to the flat ones. Surprisingly, the increase of the charge-neutral alkyl tail length of the cation resulted only in a small reduction in DC, indicating ions ability to rearrange/reorient charge-caring groups such that it maximizes the counterions charge near the surface. This finding shows a promising route for optimization of ions structure to achieve the desired/optimal properties of electrolyte (e.g., low melting point and viscosity) without significant reduction of energy density storage capabilities.

Crystal growth obsevation in prism face of zircon using cathodoluminescence

Crystal growth obsevation in prism face of zircon using cathodoluminescence

Interaction of gibbsite with oleic acid: Surface energetics and modelling

We examined the surface interaction energetics of gibbsite with oleic acid by employing both experimental techniques and quantum chemical calculations. The infrared frequencies computed for the pure oleic acid as well as for the sodium–oleate complex using the Amsterdam Density Functional program show a shift to lower wavenumbers associated with the formation of a metal-carboxylate fragment. Our MSINDO calculations indicate that the oleic acid-surface complex may form and influence the growth of gibbsite at a pH range of 5 to 9 as compared to more alkaline pH, however adsorption is most favoured at defect and dopant sites. Comparison of the theoretical results with experimental findings imply the possible role of intermediate species such as sodium–oleate at high pH. The morphological importance of the [110] prismatic face is shown by the more favourable adsorption energies for oleic acid (−201kJ/mol) and sodium–oleate (−173kJ/mol) evaluated for this face.

On the Influence of Surface Topography on the Electric Double Layer Structure and Differential Capacitance of Graphite/Ionic Liquid Interfaces

Molecular simulations reveal that the shape of differential capacitance (DC) versus the electrode potential can change qualitatively with the structure of the electrode surface. Whereas the atomically flat basal plane of graphite in contact with a room-temperature ionic liquid generates camel-shaped DC, the atomically corrugated prismatic face of graphite with the same electrolyte exhibits bell-shaped behavior and much larger DCs at low double-layer potentials. The observed bell-shaped and camel-shaped DC behavior was correlated with the structural changes occurring in the double layer as a function of applied potential. Therefore, the surface topography clearly influences DC behavior, suggesting that attention should be paid to the electrode surface topography characterization in the studies of DC to ensure reproducibility and unambiguous interpretation of experimental results. Furthermore, our results suggest that controlling the electrode roughness/structure could be a route to improving the energy den...

Synthesis and enhanced gas-sensing properties of ultralong NiO nanowires assembled with NiO nanocrystals

NiO crystallites based nanowires with different aspect ratios have been synthesized by a hydrothermal reaction of NiCl 2 with NaC 2O 4 and H 2O in the presence of ethylene glycol (EG) and subsequent annealing at 400 °C in air. Control over the aspect ratios of NiC 2O 4·2H 2O precursor nanowires in the range of 11–1050 was achieved by adjusting the hydrothermal reaction temperature and time. The formation of the NiC 2O 4·2H 2O nanowires results from the selective adsorption of EG molecules on ( 1 0 1 ¯ ) , ( 1 ¯ 0 1 ) , (0 1 0) and ( 0 1 ¯ 0 ) prismatic faces of NiC 2O 4·2H 2O with a monoclinic structure. The gas-sensing performance of the as-prepared NiO nanowires with different aspect ratios was investigated towards toluene, ethanol, acetone, triethylamine and methanol. It was found that the gas-sensing performance was improved with an increase on the aspect ratios of NiO nanowires.

Neutron structure of type‐III antifreeze protein allows the reconstruction of AFP–ice interface

Antifreeze proteins (AFPs) inhibit ice growth at sub-zero temperatures. The prototypical type-III AFPs have been extensively studied, notably by X-ray crystallography, solid-state and solution NMR, and mutagenesis, leading to the identification of a compound ice-binding surface (IBS) composed of two adjacent ice-binding sections, each which binds to particular lattice planes of ice crystals, poisoning their growth. This surface, including many hydrophobic and some hydrophilic residues, has been extensively used to model the interaction of AFP with ice. Experimentally observed water molecules facing the IBS have been used in an attempt to validate these models. However, these trials have been hindered by the limited capability of X-ray crystallography to reliably identify all water molecules of the hydration layer. Due to the strong diffraction signal from both the oxygen and deuterium atoms, neutron diffraction provides a more effective way to determine the water molecule positions (as D(2) O). Here we report the successful structure determination at 293 K of fully perdeuterated type-III AFP by joint X-ray and neutron diffraction providing a very detailed description of the protein and its solvent structure. X-ray data were collected to a resolution of 1.05 Å, and neutron Laue data to a resolution of 1.85 Å with a "radically small" crystal volume of 0.13 mm(3). The identification of a tetrahedral water cluster in nuclear scattering density maps has allowed the reconstruction of the IBS-bound ice crystal primary prismatic face. Analysis of the interactions between the IBS and the bound ice crystal primary prismatic face indicates the role of the hydrophobic residues, which are found to bind inside the holes of the ice surface, thus explaining the specificity of AFPs for ice versus water.

Stabilities of crystal faces of aragonite-type strontianite (SrCO 3) and cerussite (PbCO 3) compared by AFM observation of facet formation in acid

Micro-facet formation processes were observed, with atomic force microscopy (AFM), at various crystal faces of two aragonite-type minerals, cerussite (PbCO 3) and strontianite (SrCO 3), in dilute aqueous acetic acid. Among the prismatic faces, parallel to the c-axis, electrically neutral (1 0 0) and (1 3 0) faces were stabilized in the acidic environment, as in the case of aragonite (CaCO 3). On the other hand, polar (1 1 0) and (0 1 0) faces of PbCO 3 remained to be stable, in contrast with the case of aragonite. Even atom-resolved AFM images were observed with the (1 1 0) face, corresponding to the arrangement of carbonate ions, most probably protonated. Since Pb 2+ is a more polarizable soft acid, Pb–O bonds bear covalent nature in addition to Coulombic nature. Due to diminished polarity with the bonds, the (1 1 0) face remained stable even in the acidic condition. Among the crystal faces intersecting with the c-axis, stabilization, in the acidic condition, of (1 1 1) faces of SrCO 3 and (0 2 1) faces of PbCO 3 was observed in contrast to the stabilization of (1 1 2) faces of aragonite, suggesting flexible nature of the mineral faces having larger cations. Relationship between natural crystal forms and growth environment was discussed.

Theoretical ELNES spectra of Si-K, Si-L, N-K, and O-K edges of an intergranular glassy film model in β-Si3N4

A realistic atomic model of an intergranular glassy film (IGF) between the prismatic faces of crystalline β-Si3N4 has been used for ab initio exploration of variations in electron energy loss near edge structure (ELNES) spectral response from each of the component elements and available edges. The computed ELNES spectra within the IGF region show substantial variability that sometimes defy expectation. Upon careful analysis, we have devised guidelines for comparison and interpretation of the spectra in terms of the local coordination and bonding environment. The bond lengths, bond angles, coordination number, and elemental types of the bonded atoms cannot be relied upon to systematically explain the computed variations. It is anticipated that the rise of ELNES spectral measurements with enhanced spatial and energy resolution that are performed in conjunction with atomic scale imaging techniques will require new methods to interpret observed results. The intent of this work is to make progress and stimulate others in that direction.

Hydrogen Bonding in the Hexagonal Ice Surface

A recently developed technique in sum frequency generation spectroscopy, polarization angle null (or PAN-SFG), is applied to two orientations of the prism face of hexagonal ice. It is found that the vibrational modes of the surface are similar in different faces. As in the basal face, the prism face of ice contains five dominant resonances: 3096, 3146, 3205, 3253, and 3386 cm(-1). On the basal face, the reddest resonance occurs at 3098 cm(-1); within the bandwidth, the same as the prism face. On both the prism and basal faces, this mode contains a significant quadrupole component and is assigned to the bilayer stitching hydrogen bonds. The bluest of the resonances, 3386 cm(-1), occurs slightly blue-shifted at 3393 cm(-1) in the basal face. The prism face has two orientations: one with the optic or c axis in the input plane (the plane formed by the surface normal and the interrogating beam propagation) and one with the c axis perpendicular to the input plane. The 3386 cm(-1) mode has significant intensity only with the c axis in the input plane. On the basis of these orientation characteristics, the 3386 cm(-1) mode is assigned to double-donor molecules in either the top half bilayer or in the lower half bilayer. On the basis of frequency considerations, it is assigned to double-donor molecules in the top half bilayer. These are water molecules containing a nonbonded lone pair. In addition to identification of the components of the broad hydrogen-bonded region, PAN-SFG measures the tangential vs longitudinal content of the vibrational modes. In accord with previous suggestions, the lower frequency modes are predominantly tangential, whereas the higher frequency modes are mainly longitudinal. On the prism face, the 3386 cm(-1) mode is entirely longitudinal.

The rapid growth of large-scale KDP single crystal in brief procedure

Potassium dihydrogen phosphate (KDP) is the necessary nonlinear optical material used to convert laser light to shorter wavelengths for laser fusion experiment. Large bulk KDP crystals, usually with sizes up to 55×55cm2 so as to make the frequency doubler designed at cross section 43×43cm2 for the facility requirement loading highly flux of power laser, were grown rapidly in a Holden-type crystallizer by the temperature reduction method. Pure water and KDP raw material with few ion impurities, such as Fe, Cr and Al less than 0.5ppm, were used. The growth procedure provided briefly here started from inserting the point seed on crystallizer in overheated solution and programmed at temperature 60–35°C, growth rate 5–15mm/day, proper rotation of about 10–15rpm, 80–100 days required for rapid growth that would produce large, transparent and above 300kg weight single crystals. Growth parameters for stable growth are summarized; the most significant one for growing large KDP crystals is the assurance of solute transportation at prism face. The disturbance of irregular solution flow could easily cause inclusions near the edge area of pyramid or prism face. The optical transmission, light scattering and laser damage threshold of crystals were determined.

Monodisperse rutile TiO2 nanorod-based microspheres with various diameters: hydrothermal synthesis, formation mechanism and diameter- and crystallinity-dependent photocatalytic properties

Monodisperse microspheres constructed with rutile TiO2 nanorods were synthesized by a hydrothermal reaction of TiCl3 with Na2C2O4, ethylene glycol (EG) and H2O at 140–220°C for 4–12 h. The diameter of the microspheres can be changed in the range of 190–1200 nm by tuning the reaction temperature and time. The constituent nanorods grow along the c-axis of rutile, the side facets of which are (110), ( $\overline{1}10),(1\overline{1}0)$ , and ( $\overline{1}\overline{1}0)$ . The formation of the rod-like structure results from the selective adsorption of $\mathrm{C}_{2}\mathrm{O}_{4}^{2-}$ ions on {110} prismatic faces of rutile TiO2 nanorods. The hydrogen bonding formed between rutile TiO2 nanorods adsorbing EG drives the formation of the nanorod-based spherical nanoarchitectures. The photocatalytic ability of the as-prapared the anatase-rutile composite TiO2 nanorod-based nanospheres with a diameter of about 190 nm is stronger than that of rutile TiO2 nanorod-based nanospheres with diameters of 500 and 1000 nm.

Elementary steps at the surface of ice crystals visualized by advanced optical microscopy

Due to the abundance of ice on earth, the phase transition of ice plays crucially important roles in various phenomena in nature. Hence, the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. In this study we demonstrate, by laser confocal microscopy combined with differential interference contrast microscopy, that elementary steps (the growing ends of ubiquitous molecular layers with the minimum height) of ice crystals and their dynamic behavior can be visualized directly at air-ice interfaces. We observed the appearance and lateral growth of two-dimensional islands on ice crystal surfaces. When the steps of neighboring two-dimensional islands coalesced, the contrast of the steps always disappeared completely. We were able to discount the occurrence of steps too small to detect directly because we never observed the associated phenomena that would indicate their presence. In addition, classical two-dimensional nucleation theory does not support the appearance of multilayered two-dimensional islands. Hence, we concluded that two-dimensional islands with elementary height (0.37 and 0.39 nm on basal and prism faces, respectively) were visualized by our optical microscopy. On basal and prism faces, we also observed the spiral growth steps generated by screw dislocations. The distance between adjacent spiral steps on a prism face was about 1/20 of that on a basal face. Hence, the step ledge energy of a prism face was 1/20 of that on a basal face, in accord with the known lower-temperature roughening transition of the prism face.

Crystallization of beryllian indialite from its own melt under oxidizing conditions

It is established that beryllian indialite (ideal formula Mg2BeAl2Si6O18) is formed spontaneously under oxidizing conditions in a wide range of relatively high cooling rates at small overheatings of its own melt and short overheating times. The significant difference in the growth rates of the prism and pinacoid faces of beryllian indialite from its own melt (0.08 and 0.40 mm/h, respectively) obtained by the Steber method is explained by the fact that the prism grows according to the tangential mechanism, while the pinacoid grows in the normal way. The face effect in these crystals manifests itself in the enrichment of the prism with beryllium and silicon as opposed to pinacoid.

Microwave Absorption and Magnetic Studies of Strontium Hexaferrites Nanoparticles Synthesized by Modified Flux Method

M-type strontium hexaferrite nanocrystals of radar absorbing material (NRAM) i.e. SrFe12O19 were synthesized by modified flux method that combine the controlled chemical co-precipitation process for nucleation and complete uniform growth during annealing with NaCl flux. Uniform structural morphological transformation of nanocrystals from needle to hexagonal prism faces were noticed after annealing with increasing of heat treatment (HT) temperature from 800 to 1200°C for 4h. X-ray diffraction (XRD) results show the formation of various phases with increase in annealing temperature. The crystallinity and crystallite size are found to increase with increase in heat treatment temperature (15-40nm). The superparamagnetic behavior of strontium hexaferrite is confirmed by vibrating sample magnetometer (VSM) wherein it was noticed that magnetic field (10000 gauss max) did not have any effect on these materials. The transformation of magnetic properties i.e. from superparamagnetic to ferromagnetic behaviour after heating at various HT temperatures have been revealed by hysteresis loops under VSM study. The increase in saturation magnetization from 2.44 to 75.03 emu/gm is observed. Formation of ultrafine particles has been confirmed through field emission scanning electron microscope (FESEM). About 5 to10% of the needle like crystals in the ‘as synthesized’ condition were transformed to hexagonal pyramidal structure and most of the crystals are found to have plate like hexagonal structures with increase in heat treatment temperatures. The effect of such systematic morphological transformation of nanocrystals was observed in reflection loss properties in X band (8-12 GHz). The maximum reflection loss of -20.05, -24.31, -24.16, -25.22, -25.12, -24.01 dB at 8.1, 8.6, 9.2, 9.6, 10.7, and 12 GHz respectively are observed for the material heat treated at 1200°C. A significant increment from - 6.5 to -25.22 dB at 9.6 GHz in reflection loss (RL) is noticed due to symmetric morphological growth of RAM nanocrystal during annealing.

Optical homogeneity of ADP crystals from rapid growth

ADP (NH4H2PO4) crystals were grown through the traditional method and rapid growth technology. The optical homogeneity of rapid grown ADP crystals was analyzed by laser interferometry and X-ray topography. Laser interferometry revealed sector boundaries at which optical homogeneity decreased dramatically. The main defects that seriously reduced the optical homogeneity of the rapid grown ADP crystal were sector boundaries, growth bands and inclusions. The concentration of Fe and Cr impurities was tested by a plasma emission spectrometer. It was found that the preferential incorporation of metallic impurities into the prismatic faces resulted in high density of growth bands and inclusions, thus reducing optical homogeneity of the prismatic sector.

Biological influences on modern sulfates: Textures and composition of gypsum deposits from Guerrero Negro, Baja California Sur, Mexico

Abstract Gypsum (CaSO 4 ·2H 2 O) deposits from a range of sedimentary environments at Guerrero Negro, Baja California Sur, Mexico were investigated for microscale texture and composition in order to differentiate features formed under substantial microbial influence from those for which microbial effects were relatively minor or absent. Gypsum deposits were classified according to their sedimentary environment, textures, crystal habit, brine composition and other geochemical factors. The environments studied included subaqueous sediments in anchialine pools and in solar salterns, as well as subsurface sediments of mudflats and saltpans. Gypsum that developed in the apparent absence of biofilms included crystals precipitated in the water column and subsedimentary discs that precipitated from phreatic brines. Subsedimentary gypsum developed in sabkha environments exhibited a sinuous microtexture and poikilitically enclosed detrital particles. Water column precipitates had euhedral prismatic habits and extensive penetrative twinning. Gypsum deposits influenced by biofilms included bottom nucleated crusts and gypsolites developing in anchialine pools and saltern ponds. Gypsum precipitating within benthic biofilms, and in biofilms within subaerial sediment surfaces provided compelling evidence of biological influences on crystal textures and habits. This evidence included irregular, high relief surface textures, accessory minerals (S°, Ca-carbonate, Sr/Ca-sulfate and Mg-hydroxide) and distinctive crystal habits such as equant forms and crystals having distorted prism faces.

Modulation of Calcium Oxalate Dihydrate Growth by Selective Crystal-face Binding of Phosphorylated Osteopontin and Polyaspartate Peptide Showing Occlusion by Sectoral (Compositional) Zoning

Calcium oxalate dihydrate (COD) mineral and the urinary protein osteopontin/uropontin (OPN) are commonly found in kidney stones. To investigate the effects of OPN on COD growth, COD crystals were grown with phosphorylated OPN or a polyaspartic acid-rich peptide of OPN (DDLDDDDD, poly-Asp(86-93)). Crystals grown with OPN showed increased dimensions of the {110} prismatic faces attributable to selective inhibition at this crystallographic face. At high concentrations of OPN, elongated crystals with dominant {110} faces were produced, often with intergrown, interpenetrating twin crystals. Poly-Asp(86-93) dose-dependently elongated crystal morphology along the {110} faces in a manner similar to OPN. In crystal growth studies using fluorescently tagged poly-Asp(86-93) followed by imaging of crystal interiors using confocal microscopy, sectoral (compositional) zoning in COD was observed resulting from selective binding and incorporation (occlusion) of peptide exclusively into {110} crystal sectors. Computational modeling of poly-Asp(86-93) adsorption to COD {110} and {101} surfaces also suggests increased stabilization of the COD {110} surface and negligible change to the natively stable {101} surface. Ultrastructural, colloidal-gold immunolocalization of OPN by transmission electron microscopy in human stones confirmed an intracrystalline distribution of OPN. In summary, OPN and its poly-Asp(86-93) sequence similarly affect COD mineral growth; the {110} crystallographic faces become enhanced and dominant attributable to {110} face inhibition by the protein/peptide, and peptides can incorporate into the mineral phase. We, thus, conclude that the poly-Asp(86-93) domain is central to the OPN ability to interact with the {110} faces of COD, where it binds to inhibit crystal growth with subsequent intracrystalline incorporation (occlusion).

Investigation of SR method grown 〈0 0 1〉 directed KDP single crystal and its characterization by high-resolution X-ray diffractometry (HRXRD), laser damage threshold, dielectric, thermal analysis, optical and hardness studies

〈0 0 1〉 directed potassium dihydrogen orthophosphate (KDP) single crystal was grown by Sankaranarayanan–Ramasamy (SR) method. The 〈0 0 1〉 oriented seed crystals were mounted at the bottom of the platform and the size of the crystals were 10 mm diameter, 110 mm height. Two different growths were tried, in one the crystal diameter was the ampoule's inner diameter and in the other the crystal thickness was less than the ampoule diameter. In the first case only the top four pyramidal faces were existing whereas in the second case the top four pyramidal faces and four prismatic faces were existing through out the growth. The crystals were grown using same stoichiometric solution. The results of the two growths are discussed in this paper. The grown crystals were characterized by high-resolution X-ray diffractometry (HRXRD), laser damage threshold, dielectric, thermal analysis, UV–vis spectroscopy and microhardness studies. The HRXRD analysis indicates that the crystalline perfection is excellent without having any very low angle internal structural grain boundaries. Laser damage threshold value has been determined using Nd:glass laser operating at 1054 nm. The damage threshold for the KDP crystal is greater than 4.55 GW cm −2. The dielectric constant was higher and the dielectric loss was less in SR method grown crystal as against conventional method grown crystal. In thermal analysis, the starting of decomposition nature is similar in SR method grown KDP crystal and conventional method grown crystal. The SR method grown KDP has higher transmittance and higher hardness value compared to conventional method grown crystals.

Facile synthesis of elongated calcite superstructure by triblock copolymers with precisely designed block length

Calcite crystals elongated along the c-axis and capped by (1 0 4) rhombohedral faces were grown in the solutions of two kinds of triblock copolymers poly (ethylene glycol)- block-poly (acrylic acid)- block-poly ( n-butyl acrylate) (PEG- b-PAA- b-P nBA) with different PAA block length. The copolymer with 3:1 PEG:PAA block ratio facilitates the formation of spindle-shaped calcite elongated along the c-axis and with curved (1 0 0) or (1 1 0) prismatic faces. CaCO 3 obtained from the copolymer with 6:1 PEG:PAA block ratio exhibits stack-like calcite elongated along the c-axis and with no newly developed faces. The formation of elongated calcite could be due to the aggregation of nanoparticles via an oriented attachment mechanism. The calcite crystals recovered their rhombohedral {1 0 4} faces gradually with decreasing PAA block length from 3:1 to 6:1 PEG:PAA block ratio, which could be attributed to the weakening of the inhibition efficiency of the PAA block on the non-rhombohedral planes.

Evidence of growth and sector zoning in hydrothermal quartz from Alpine veins

Several quartz crystals from three different Alpine vein localities and of known petrologic setting and evolution have been examined for possible elemental sector zoning in order to help to constrain the mechanisms of such trace element incorporation. Using different in situ techniques (EMPA, LA-ICPMS, SIMS, FTIR-spectroscopy), it was established that Al and Li concentrations can exceed several hundreds of ppma for distinct growth zones within crystals formed at temperatures of about 300 °C or less and that also display patterns of cyclic growth when examined with cathodoluminescence. In contrast, crystals formed at temperatures closer to 400 °C and without visible cyclic growth have low concentrations of Al and Li as well as other trace elements. Al and Li contents are correlated along profiles measured within the crystals and in general their proportion does not change along the profiles. No relationships were found between Al, Na, and K, and germanium has a qualitative relationship with Al. FTIR spectra also show OH − absorption bands within the quartz, with higher amplitudes in zones rich in Al and Li. Sector zoning is present. It is most pronounced between prismatic and rhombohedral faces of the same growth zone, but also between the rhombohedral faces of r and z , which contain different amounts of trace elements. The sector zoning is also expressed by changes in the Li/Al ratio, with higher ratios in z compared to r faces. It is concluded that the incorporation of trace elements into hydrothermal quartz from Alpine veins is influenced by growth mechanisms and surface-structures of the growing quartz crystals, the influence of which may change as a function of temperature, pH, as well as the chemical composition of the fluid.