Showing papers on "Crystal published in 2000"
TL;DR: In this paper, a modification of the Saltikov correction method is proposed that is more accurate and can account for different crystal shapes and fabrics, and population densities determined by this method differ by factors of 0.02 to 100 from those determined by the Wager method.
Abstract: Studies of crystal size distributions (CSD) can reveal much about how rocks solidify and under what conditions. Data from two-dimensional sections can be readily acquired at many different scales, from electron microscope images, thin sections, slabs, outcrops, and so on, but the conversion to true, three-dimensional values is complex. The widely used Wager method does not have a good theoretical basis and does not give accurate results. A modification of the Saltikov correction method is proposed here that is more accurate and can account for different crystal shapes and fabrics. Population densities determined by this method differ by factors of 0.02 to 100 from those determined by the Wager method. Published CSDs determined using other methods can be recalculated if the crystal shape and fabric parameters can be estimated. The method has been incorporated into a new program, CSDCorrections.
573 citations
TL;DR: Scanning tunnelling microscopy is used to investigate the effects of individual zinc impurity atoms in the high-temperature superconductor Bi2Sr2CaCu 2O8+δ and reveals the long-sought four-fold symmetric quasiparticle ‘cloud’ aligned with the nodes of the d-wave superconducting gap which is believed to characterize superconductivity in these materials.
Abstract: Although the crystal structures of the copper oxide high-temperature superconductors are complex and diverse, they all contain some crystal planes consisting of only copper and oxygen atoms in a square lattice: superconductivity is believed to originate from strongly interacting electrons in these CuO2 planes. Substituting a single impurity atom for a copper atom strongly perturbs the surrounding electronic environment and can therefore be used to probe high-temperature superconductivity at the atomic scale. This has provided the motivation for several experimental and theoretical studies. Scanning tunnelling microscopy (STM) is an ideal technique for the study of such effects at the atomic scale, as it has been used very successfully to probe individual impurity atoms in several other systems. Here we use STM to investigate the effects of individual zinc impurity atoms in the high-temperature superconductor Bi2Sr2CaCu2O8+delta. We find intense quasiparticle scattering resonances at the Zn sites, coincident with strong suppression of superconductivity within approximately 15 A of the scattering sites. Imaging of the spatial dependence of the quasiparticle density of states in the vicinity of the impurity atoms reveals the long-sought four-fold symmetric quasiparticle 'cloud' aligned with the nodes of the d-wave superconducting gap which is believed to characterize superconductivity in these materials.
540 citations
TL;DR: The controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules is reported, which modifies the structures of these molecules without affecting their crystallinity.
Abstract: Considerable effort is being devoted to the fabrication of nanoscale devices1. Molecular machines, motors and switches have been made, generally operating in solution2,3,4,5,6,7, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required8. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure9. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion–reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage10. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches11,12.
474 citations
TL;DR: In this article, a liquid crystal was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 and a band gap wavelength range of 3.3-5.7 µm.
Abstract: The photonic band gap of a two-dimensional photonic crystal is continuously tuned using the temperature dependent refractive index of a liquid crystal. Liquid crystal $E7$ was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 $\ensuremath{\mu}$m and a band gap wavelength range of 3.3--5.7 \ensuremath{\mu}m. After infiltration, the band gap for the H polarized field shifted dramatically to 4.4--6.0 \ensuremath{\mu}m while that of the E-polarized field collapsed. As the sample was heated to the nematic-isotropic phase transition temperature of the liquid crystal $(59\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}),$ the short-wavelength band edge of the H gap shifted by as much as 70 nm while the long-wavelength edge was constant within experimental error. Band structure calculations incorporating the temperature dependence of the liquid crystal birefringence can account for our results and also point to an escaped-radial alignment of the liquid crystal in the nematic phase.
385 citations
TL;DR: In this paper, the structure of laser-crystallized thin films of Ge2Sb2+xTe5 (0.0
Abstract: The structure of laser-crystallized thin films of Ge2Sb2+xTe5 (0.0
384 citations
TL;DR: In this article, the crystal orientation (the c-axis of the polystyrene blocks) within nanoscale confined lamellae has been investigated using combined two-dimensional SAXS and wide-angle X-ray scattering experiments.
Abstract: For a lamella-forming poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer (MnPEO = 87K and MnPS = 92K), the glass transition temperature of the PS blocks is 62 °C, and the melting temperature of the PEO crystals is around 51 °C when the sample is crystallized below 40 °C The PEO blocks thus crystallize in a one-dimensionally confined lamellar space of 88 nm, as studied recently by one-dimensional small-angle X-ray scattering (SAXS) and transmission electron microscopy In this report, the crystal orientation (the c-axis of the PEO crystals) within nanoscale confined lamellae has been investigated using combined two-dimensional SAXS and wide-angle X-ray scattering experiments The c-axis orientation in the PEO crystals is observed for the first time to change from random to perpendicular, then to inclined, and finally to parallel to the lamellar surface normal, depending only on the crystallization temperature (Tc) Detailed crystallographic analyses indicate that the c-axis orientati
377 citations
TL;DR: The complete crystallography of a one-dimensional crystal of potassium iodide encapsulated within a 1.6-nanometer-diameter single-walled carbon nanotube has been determined with high-resolution transmission electron microscopy.
Abstract: The complete crystallography of a one-dimensional crystal of potassium iodide encapsulated within a 1.6-nanometer-diameter single-walled carbon nanotube has been determined with high-resolution transmission electron microscopy. Individual atoms of potassium and iodine within the crystal were identified from a phase image that was reconstructed with a modified focal series restoration approach. The lattice spacings within the crystal are substantially different from those in bulk potassium iodide. This is attributed to the reduced coordination of the surface atoms of the crystal and the close proximity of the van der Waals surface of the confining nanotube.
358 citations
347 citations
TL;DR: In this article, the authors used hydrogel nanoparticles that undergo volume phase transitions in response to changes in temperature and pH to assemble colloidal crystal gels with environmentally tunable optical properties.
Abstract: Hydrogel nanoparticles that undergo volume phase transitions in response to changes in temperature and pH have been used to assemble colloidal crystal gels with environmentally tunable optical properties. When monodisperse, ∼210-nm-diameter hydrogel particles are close-packed via centrifugation, the resultant viscous polymer pellet displays a bright iridescence in the visible region of the spectrum. This iridescence can then be modulated via temperature changes, which induce the component nanoparticles to undergo thermo-initiated volume phase transitions. More importantly, these crystals undergo a completely reversible order−disorder transition in response to larger temperature fluctuations; the crystal can be processed in its disordered (solution) state and then reformed to the iridescent crystal spontaneously upon cooling. The preparation and initial characterization of these materials are presented.
323 citations
TL;DR: In this paper, a nanocrystalline ZSM-5 (crystal size in the range 10-100 nm) has been synthesized in only 24 h by hydrothermal crystallization of clear supersaturated homogeneous synthesis mixtures.
281 citations
TL;DR: In this article, the erased state of the recording layer in a four-layered phase change optical disk, which was produced by an optical disk drive, was identified as an fcc crystal structure.
TL;DR: In this article, the frequency band structure of an infinite photonic crystal and the transmission, reflection and absorption coefficients of light by a slab of this crystal are calculated using a new version of a program.
TL;DR: In this paper, the supramolecular chemistry and crystal structures of five bis(imidazolium 2,6-pyridinedicarboxylate)M(II) trihydrate complexes, where M = Mn2+, Co2+, Ni2+, Cu2+, or Zn2+ (1−5), are reported.
Abstract: The supramolecular chemistry and crystal structures of five bis(imidazolium 2,6-pyridinedicarboxylate)M(II) trihydrate complexes, where M = Mn2+, Co2+, Ni2+, Cu2+, or Zn2+ (1−5, respectively), are reported. These complexes serve as supramolecular building blocks that self-assemble when crystallized to generate a single, well-defined, predictable structure in the solid state. 2,6-Pyridinedicarboxylate anions and imidazolium cations form strong ionic hydrogen bonds that dominate crystal packing in compounds 1−5 by forming two-dimensional networks, or layers of molecules. This layer motif serves as a platform with which to control and predict molecular packing by design for engineering the structures of crystals. Moreover, compounds 1−5 create a robust organic host lattice that accommodates five different transition metals without significantly altering molecular packing. Growth of crystals from solutions that contain two or more different metal complexes produces mixed crystals in which mixtures of the diff...
TL;DR: In this paper, the authors present a review of existing models for predicting crystal shape, as well as their utility for process and product design, and present new approaches for predicting the effects of solvents.
Abstract: The shape of a crystalline organic solid has a major impact on its downstream processing and on its end-product quality, issues that are becoming increasingly important in the specialty and fine chemical, as well as the pharmaceutical and life science, industries. Though it is widely known that improved crystal shapes can be achieved by varying the conditions of crystallization (such as solvent type and impurity levels), there is far less understanding of how to effect such a change. Until recently, most methods for predicting crystal shapes were based exclusively on the internal crystal structure, and hence could not account for solvent or impurity effects. New approaches, however, offer the possibility of accurately predicting the effects of solvents. Models for predicting crystal shape are reviewed, as well as their utility for process and product design.
TL;DR: A direct calculation by molecular-dynamics computer simulation of the crystal/melt interfacial free energy gamma for a system of hard spheres of diameter sigma finds the interfacialfree energy to be slightly anisotropic with gamma = 0.62+/-0.01k(B)T/sigma(2) for the (100), (110), and (111) fcc crystal/fluid interfaces.
Abstract: We present a direct calculation by molecular-dynamics computer simulation of the crystal/melt interfacial free energy gamma for a system of hard spheres of diameter sigma. The calculation is performed by thermodynamic integration along a reversible path defined by cleaving, using specially constructed movable hard-sphere walls, separate bulk crystal, and fluid systems, which are then merged to form an interface. We find the interfacial free energy to be slightly anisotropic with gamma = 0.62+/-0.01, 0.64+/-0.01, and 0. 58+/-0.01k(B)T/sigma(2) for the (100), (110), and (111) fcc crystal/fluid interfaces, respectively. These values are consistent with earlier density functional calculations and recent experiments.
TL;DR: The high brilliance of third-generation synchrotron radiation sources allows new applications in x-ray microdiffraction and micro-small-angle scattering as discussed by the authors, and beam sizes down to about one µm are routinely used and sub-µm beam sizes are becoming available.
Abstract: The high brilliance of third-generation synchrotron radiation sources allows new applications in x-ray microdiffraction and microsmall-angle scattering. Beam sizes down to about one µm are routinely used and sub-µm beam sizes are becoming available. Scanning diffractometry can be used to examine samples like single fibres without the necessity for sectioning, as is required for transmission electron scattering experiments. Examples are taken principally from weakly scattering polymers and biopolymers. In single-crystal diffraction, sub-µm3 crystal volumes have been reached for inorganic crystals. Protein crystallography has been demonstrated for a few tenths of µm linear crystal size, which reduces the crystallization time for many proteins.
TL;DR: In this paper, the authors investigated the relationship between different types and amounts of bulk defects and the surface morphology of TiO{sub 2}(110) single crystals prepared by annealing in ultrahigh vacuum and in oxygen.
Abstract: The authors have investigated the relationship between different types and amounts of bulk defects and the surface morphology of TiO{sub 2}(110) single crystals prepared by annealing in ultrahigh vacuum and in oxygen. Rutile TiO{sub 2}(110) specimens were cut from the same crystal and were heated in a furnace to different temperatures which resulted in different states of reduction (colors of the crystals). After characterization of the bulk defects with electron paramagnetic resonance (EPR), the specimens were studied with scanning tunneling microscopy (STM), low-energy He{sup +} ion scattering (LEIS), and work function measurements. EPR reveals that darker rutile crystals exhibit higher concentrations of extended Ti{sup 3+} related bulk defects such as crystallographic shear planes (CSP), with a decrease in substitutional and interstitial defects as compared to lighter crystals. Surface structures with (1 x 2) features are preferably formed upon UHV annealing on these darker crystals. LEIS measurements show that all of the crystals' (110) surfaces are reoxidized upon annealing in {sup 18}O{sub 2} (573 K, 1 x 10{sup {minus}6} mbar, 10 min) and that the {sup 18}O surface content is proportional to the bulk reduction state. UV-visible adsorption spectra and resistivity measurements also scale with the reduction states of crystals. Onlymore » the (1 x 1) structure is observed on the surface of slightly reduced crystals. Annealing in oxygen induces additional metastable structures, i.e., TiO{sub 2} clusters on blue crystals and rosette networks on dark blue crystals.« less
TL;DR: The charge density distribution of a protein has been refined experimentally and the resulting electron density maps of redistributed valence electrons compare quantitatively well with a high-level quantum mechanical calculation performed on a monopeptide.
Abstract: The charge density distribution of a protein has been refined experimentally. Diffraction data for a crambin crystal were measured to ultra-high resolution (0.54 A) at low temperature by using short-wavelength synchrotron radiation. The crystal structure was refined with a model for charged, nonspherical, multipolar atoms to accurately describe the molecular electron density distribution. The refined parameters agree within 25% with our transferable electron density library derived from accurate single crystal diffraction analyses of several amino acids and small peptides. The resulting electron density maps of redistributed valence electrons (deformation maps) compare quantitatively well with a high-level quantum mechanical calculation performed on a monopeptide. This study provides validation for experimentally derived parameters and a window into charge density analysis of biological macromolecules.
TL;DR: In this article, the free energy of a defect-free hard-sphere crystal of particles interacting through an r-12 potential is estimated. But this is not the case for an equilibrium hardsphere with a fixed center of mass.
Abstract: We analyze the finite-size corrections to the free energy of crystals with a fixed center of mass. When we explicitly correct for the leading (ln N/N) corrections, the remaining free energy is found to depend linearly on 1/N. Extrapolating to the thermodynamic limit (N → ∞), we estimate the free energy of a defect-free crystal of particles interacting through an r–12 potential. We also estimate the free energy of perfect hard-sphere crystal near coexistence: at ρσ3 = 1.0409, the excess free energy of a defect-free hard-sphere crystal is 5.918 89(4)kT per particle. This, however, is not the free energy of an equilibrium hard-sphere crystal. The presence of a finite concentration of vacancies results in a reduction of the free energy that is some two orders of magnitude larger than the present error estimate.
TL;DR: In this article, the authors measured zinc self-diffusion in single crystal zinc oxide using nonradioactive 70Zn as the tracer isotope and secondary ion mass spectrometry for data collection.
Abstract: Zinc self-diffusion was measured in single crystal zinc oxide using nonradioactive 70Zn as the tracer isotope and secondary ion mass spectrometry for data collection. Crystal mass was closely monitored to measure ZnO evaporation. Diffusion coefficients were isotropic with an activation energy of 372 kJ/mol. Zinc self-diffusion is most likely controlled by a vacancy mechanism. Electrical property measurements exhibit a plateau in conductivity at intermediate pO2 with an increase in reducing atmospheres. An analysis of the defect structure is presented that indicates that oxygen vacancies are probably the intrinsic ionic defects responsible for n-type conductivity in reducing atmospheres.
TL;DR: In this paper, the role of C−X−π interactions in conformational and crystal engineering control in organic crystal structures was investigated. But the results showed that organic fluorine has a greater propensity for the formation of such interactions rather than accepting hydrogen bonds.
TL;DR: In this article, a planar blackbody structure of a 3D photonic crystal was used to suppress silicon thermal radiation in the photonic band gap spectral regime, which was found to be highly effective in suppressing photonic thermal radiation.
Abstract: The emission and detection of electromagnetic radiation are essential optical processes that govern performance of lasers, detectors and solar cells. Through light-photonic crystal interaction, a three-dimensional (3D) photonic crystal offers a way to alter such optical processes. Experimental realization is done by building a thin slab of 3D photonic crystal onto a silicon material. The 3D crystal structure is found to be highly effective in suppressing silicon thermal radiation in the photonic band gap spectral regime. Emission is also enhanced in the photonic passbands. At passband resonant frequencies, a thin slab of 3D photonic crystal actually acts like a planar blackbody.
TL;DR: In this article, a room temperature free shear strain of 5.7% is reported in a single crystal of Ni-Mn-Ga having a composition close to the Heusler alloy Ni2MnGa.
Abstract: A room temperature free shear strain of 5.7% is reported in a single crystal of Ni–Mn–Ga having a composition close to the Heusler alloy Ni2MnGa. A twin boundary was created in a 2 mm×2 mm×25 mm single crystal using a permanent magnet with surface field strength of about 320 000 A/m. A sharp 6.5° bend occurs in the sample at the twin boundary. The surface magnetization changes abruptly across this boundary. By moving the sample relative to the edge of the magnet, we were able to sweep the boundary back and forth along the crystal length. Surface magnetization was measured using a Hall probe and the results confirm that the easy axis is the tetragonal c axis. Powder x-ray diffraction shows that the fcc to body-centered-tetragonal bct martensitic transition of this material involved a 6% reduction of the bct cell c/a ratio, from √ to about 1.33. The maximum achievable strain is thus estimated to be 6.2%. The twin planes in the system are the {112}bct and were observed to lie almost normal to the long axis of the sample tested.
TL;DR: Using atomic force microscopy, it is shown that the I(alpha) phase of native cellulose first proposed in 1984 and subsequently characterized by a triclinic unit cell exists over large areas of the surface of microcrystals from Valonia, one of the most highly crystalline celluloses.
TL;DR: Komanduri et al. as discussed by the authors investigated the anisotropy in hardness and friction coefficient of single crystal aluminum in various crystal orientations and directions of scratching, and found that the hardness is increased significantly as the indentation depth is reduced to atomic dimensions.
TL;DR: In this paper, the authors used atomic force microscopy to investigate the patterns obtained by isothermal crystallization of quasi-2D monolayers of poly(ethylene oxide) adsorbed onto bare silicon wafers.
Abstract: We have used atomic force microscopy to investigate the patterns obtained by isothermal crystallization of quasi-2-D monolayers of poly(ethylene oxide) adsorbed onto bare silicon wafers. These monolayers were prepared by a pseudo-dewetting process. Fingerlike branched structures were observed with a characteristic width which increased rapidly with crystallization temperature. The patterns are explained by a simple model considering the interplay of transport on the surface and the probability of attachment to the crystal. The influence of molecular weight was also studied. The average stem length increases with increasing temperature for the longer polymer. The shorter one crystallized in the (almost) fully extended form for all temperatures investigated. Temperature jumps during crystallization resulted in patterns with two different length scales.
TL;DR: The results demonstrate that functional crystals can be formed three dimensionally in glasses by use of a nonresonant ultrashort pulsed laser.
Abstract: We report on space-selective growth of a second-harmonic-generation β‐BaB2O4 (BBO) crystal inside a BaO–Al2O3–B2O3 glass sample at the focal point of an 800-nm femtosecond laser beam. A spherical heated region was formed during the focused laser irradiation through observation with an optical microscope. We moved the heated region by changing the position of the focal point of the laser beam relative to the glass sample. We grew BBO crystal continuously in the glass sample by adjusting the moving speed of the heated zone. Our results demonstrate that functional crystals can be formed three dimensionally in glasses by use of a nonresonant ultrashort pulsed laser.
TL;DR: In this paper, the authors make hard-sphere colloidal crystals from polymethyl methacrylate spheres suspended in organic solvents at high volume fractions, where the samples are crystallized between two glass plates separated by 10-ensuremath{mu}m spacer beads.
Abstract: We make hard-sphere colloidal crystals from polymethyl methacrylate spheres suspended in organic solvents at high volume fractions. The samples are crystallized between two glass plates separated by 10-\ensuremath{\mu}m spacer beads. We study the optical scattering from these systems and describe methods for discriminating between the various crystal packings. Crystals formed simply by increasing the volume fraction beyond the liquid-solid phase transition tend to be small and predominantly random close packed. However, we find that by forming these crystals while applying controlled shear to the glass plates, large-area single crystals can be made. These crystals are much more regular and appear to be predominantly twinned face-centred cubic. The creation of single-orientation face-centred cubic crystals appears possible when shear is applied in one direction.
TL;DR: Light waves are shown to be guided along a triple-line defect formed within a 2D crystal and vertically by a strong index-guiding mechanism, suggesting lossless guiding along this photonic one-dimensional conduction channel.
Abstract: Highly efficient transmission of 1.5 {micro}m light in a two-dimensional (2D) photonic crystal slab waveguide is experimentally demonstrated. The light wave is shown to be guided along a triple-line defect formed within a 2D crystal and vertically by a strong index-guiding mechanism. At certain wavelength ranges, a complete transmission is observed, suggesting a lossless guiding along this photonic 1D conduction channel.