Showing papers on "Crystal published in 2010"

Quartz crystal microbalance setup for frequency and G!?-factor rneasurements in gaseous and liquid environments

Abstract: An experimental setup has been constructed for simultaneous measurements of the frequency, the absolute Q factor, and the amplitude of oscillation of a quartz crystal microbalance (QCM). The technical solution allows operation in vacuum, air, or liquid. The crystal is driven at its resonant frequency by an oscillator that can be intermittently disconnected causing the crystal oscillation amplitude to decay exponentially. From the recorded decay curve the absolute Q factor (calculated from the decay time constant), the frequency of the freely oscillating crystal, and the amplitude of oscillation are obtained. AI1 measurements are fully automated. One electrode of the QCM in our setup was connected to true ground which makes possible simultaneous electrochemistry. The performance is illustrated by experiments in fluids of varying viscosity (gas and liquid) and by protein adsorption in situ. We found, in addition to the above results, that the amplitude of oscillation is not always directly proportional to the Q factor, as the commonly used theory states. This puts limitations on the customary use of the amplitude of oscillation as a measure of the Q factor. 8 1995 American Institute of Physics.

Observation of long-range exciton diffusion in highly ordered organic semiconductors

Abstract: Excitons in polycrystalline and disordered films of organic semiconductors have been shown to diffuse over distances of 10-50 nm. Here, using polarization- and wavelength-dependent photoconductivity in the highly ordered organic semiconductor rubrene, we show that the diffusion of triplet excitons in this material occurs over macroscopic distances (2-8 μm), comparable to the light absorption length. Dissociation of these excitons at the surface of the crystal is found to be the main source of photoconductivity in rubrene. In addition, we observe strong photoluminescence quenching and a simultaneous enhancement of photoconductivity when the crystal surface is functionalized with exciton splitters. In combination with time-resolved measurements, these observations strongly suggest that long-lived triplet excitons are indeed generated in molecular crystals by fission of singlets, and these triplets provide a significant contribution to the surface photocurrent generated in organic materials. Our findings indicate that the exciton diffusion bottleneck is not an intrinsic limitation of organic semiconductors.

Exfoliation and characterization of bismuth telluride atomic quintuples and quasi-two-dimensional crystals.

Abstract: Bismuth telluride (Bi2Te3) and its alloys are the best bulk thermoelectric materials known today. In addition, stacked quasi-two-dimensional (2D) layers of Bi2Te3 were recently identified as promising topological insulators. In this Letter we describe a method for “graphene-inspired” exfoliation of crystalline bismuth telluride films with a thickness of a few atoms. The atomically thin films were suspended across trenches in Si/SiO2 substrates, and subjected to detail material characterization, which included atomic force microscopy and micro-Raman spectroscopy. The presence of the van der Waals gaps allowed us to disassemble Bi2Te3 crystal into its quintuple building blocks—five monatomic sheets—consisting of Te(1)−Bi−Te(2)−Bi−Te(1). By altering the thickness and sequence of atomic planes, we were able to create “designer” nonstoichiometric quasi-2D crystalline films, change their composition and doping, the type of charge carriers as well as other properties. The exfoliated quintuples and ultrathin film...

A Diarylethene Cocrystal that Converts Light into Mechanical Work

Abstract: The photomechancial effect of a rectangular plate two-component cocrystal composed of a photochromic diarylethene derivative, 1,2-bis(2-methyl-5-(1-naphthyl)-3-thienyl)perfluorocyclopentene (1o), and perfluoronaphthalene (FN) has been examined. The crystal of 1o·FN with the size of 1-5 mm in length exhibits reversible bending motion upon alternate irradiation with ultraviolet (UV) and visible light. The reversible bending could be repeated over 250 times. In situ X-ray crystallographic analysis revealed that the deformation of the crystal is due to the elongation of the b-axis of the unit cell, which corresponds to the long axis of the plate crystal, induced by the shape change of component diarylethene molecules upon photocyclization. The bending motion was observed even at 4.7 K, and dynamic measurement of the bending proved that the anisotropic expansion of the crystal takes place in the microsecond time scale at the low temperature. Molecular crystal cantilevers made of 1o·FN can lift metal balls, the weight of which is 200-600 times heavier than the weight of the crystal, upon UV irradiation. The maximum stress generated by UV irradiation was estimated to be 44 MPa, which is 100 times larger than that of muscles (∼0.3 MPa) and comparable to that of piezoelectric crystals, such as lead zirconate titanate (PZT) (∼50 MPa).

Few-Layer Nanoplates of Bi2Se3 and Bi2Te3 with Highly Tunable Chemical Potential

Abstract: A topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk band gap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that group V−VI materials Bi2Se3, Bi2Te3, and Sb2Te3 are TIs with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi2Te3 and Bi2Se3 nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor−solid (VS) growth mechanism. Optical images reveal thickness-dependent color and contrast for nanoplates grown on oxidized silicon (300 nm SiO2/Si). As a new mem...

A Strong Second-Harmonic Generation Material Cd4BiO(BO3)3 Originating from 3-Chromophore Asymmetric Structures

Abstract: In this communication, the novel nonlinear optical crystal material Cd4BiO(BO3)3 with 3-chromophore asymmetric structures of CdOn, BiO6, and BO3 groups has been prepared by a flux method, and the s

Crystal Phase Engineering in Single InAs Nanowires

Abstract: Achieving phase purity and control in III-V nanowires is a necessity for future nanowire-based device applications. Many works have focused on cleaning specific crystal phases of defects such as twin planes and stacking faults, using parameters such as diameter, temperature, and impurity incorporation. Here we demonstrate an improved method for crystal phase control, where crystal structure variations in single InAs nanowires are designed with alternating wurtzite (WZ) and zinc blende (ZB) segments of precisely controlled length and perfect interfaces. We also demonstrate the inclusion of single twin planes and stacking faults with atomic precision in their placement, designed ZB quantum dots separated by thin segments of WZ, acting as tunnel barriers for electrons, and structural superlattices (polytypic and twin plane). Finally, we present electrical data to demonstrate the applicability of these designed structures to investigation of fundamental properties. From electrical measurements we observe clear signatures of controlled structural quantum dots in nanowires. This method will be directly applicable to a wide range of nanowire systems.

Modelling organic crystal structures using distributed multipole and polarizability-based model intermolecular potentials

Abstract: Crystal structure prediction for organic molecules requires both the fast assessment of thousands to millions of crystal structures and the greatest possible accuracy in their relative energies. We describe a crystal lattice simulation program, DMACRYS, emphasizing the features that make it suitable for use in crystal structure prediction for pharmaceutical molecules using accurate anisotropic atom–atom model intermolecular potentials based on the theory of intermolecular forces. DMACRYS can optimize the lattice energy of a crystal, calculate the second derivative properties, and reduce the symmetry of the spacegroup to move away from a transition state. The calculated terahertz frequency k = 0 rigid-body lattice modes and elastic tensor can be used to estimate free energies. The program uses a distributed multipole electrostatic model (Qat, t = 00,…,44s) for the electrostatic fields, and can use anisotropic atom–atom repulsion models, damped isotropic dispersion up to R−10, as well as a range of empirically fitted isotropic exp-6 atom–atom models with different definitions of atomic types. A new feature is that an accurate model for the induction energy contribution to the lattice energy has been implemented that uses atomic anisotropic dipole polarizability models (αat, t = (10,10)…(11c,11s)) to evaluate the changes in the molecular charge density induced by the electrostatic field within the crystal. It is demonstrated, using the four polymorphs of the pharmaceutical carbamazepine C15H12N2O, that whilst reproducing crystal structures is relatively easy, calculating the polymorphic energy differences to the accuracy of a few kJ mol−1 required for applications is very demanding of assumptions made in the modelling. Thus DMACRYS enables the comparison of both known and hypothetical crystal structures as an aid to the development of pharmaceuticals and other speciality organic materials, and provides a tool to develop the modelling of the intermolecular forces involved in molecular recognition processes.

Crystal Phase Quantum Dots

Abstract: In semiconducting nanowires, both zinc blende and wurtzite 1 crystal structures can coexist. 2-4 The band structure difference between the two structures can lead to charge confinement. 5 Here we fabricate and study single quantum dot devices 6 defined solely by crystal phase in a chemically homogeneous nanowire and observe single photon generation. More generally, our results show that this type of carrier confinement represents a novel degree of freedom in device design at the nanoscale.

Bonding origin of optical contrast in phase-change memory materials

Abstract: The large optical contrast between crystalline and amorphous phases of phase change memory materials is shown to arise from a large difference in the optical matrix elements. These are enhanced in the crystal by aligned rows of resonantly bonded $p$ orbitals. Amorphous phases have normal-sized matrix elements due to an absence of this order, irrespective of coordination number. This is a more general description of local order differences between the crystalline and amorphous phases, which applies even when coordinations in the amorphous phases exceed the $8\ensuremath{-}\text{N}$ value.

The evolution of electronic structure in few-layer graphene revealed by optical spectroscopy

Abstract: The massless Dirac spectrum of electrons in single-layer graphene has been thoroughly studied both theoretically and experimentally. Although a subject of considerable theoretical interest, experimental investigations of the richer electronic structure of few-layer graphene (FLG) have been limited. Here we examine FLG graphene crystals with Bernal stacking of layer thicknesses N = 1,2,3,...8 prepared using the mechanical exfoliation technique. For each layer thickness N, infrared conductivity measurements over the spectral range of 0.2-1.0 eV have been performed and reveal a distinctive band structure, with different conductivity peaks present below 0.5 eV and a relatively flat spectrum at higher photon energies. The principal transitions exhibit a systematic energy-scaling behavior with N. These observations are explained within a unified zone-folding scheme that generates the electronic states for all FLG materials from that of the bulk 3D graphite crystal through imposition of appropriate boundary conditions. Using the Kubo formula, we find that the complete infrared conductivity spectra for the different FLG crystals can be reproduced reasonably well within the framework a tight-binding model.

Crystal Growth Inhibitors for the Prevention of l-Cystine Kidney Stones Through Molecular Design

Abstract: Crystallization of L-cystine is a critical step in the pathogenesis of cystine kidney stones. Treatments for this disease are somewhat effective but often lead to adverse side effects. Real-time in situ atomic force microscopy (AFM) reveals that L-cystine dimethylester (L-CDME) and L-cystine methylester (L-CME) dramatically reduce the growth velocity of the six symmetry-equivalent {100} steps because of specific binding at the crystal surface, which frustrates the attachment of L-cystine molecules. L-CDME and L-CME produce l-cystine crystals with different habits that reveal distinct binding modes at the crystal surfaces. The AFM observations are mirrored by reduced crystal yield and crystal size in the presence of L-CDME and L-CME, collectively suggesting a new pathway to the prevention of L-cystine stones by rational design of crystal growth inhibitors.

Gold-free growth of GaAs nanowires on silicon: arrays and polytypism

Abstract: We report growth by molecular beam epitaxy and structural characterization of gallium-nucleated GaAs nanowires on silicon. The influences of growth temperature and V/III ratio are investigated and compared in the case of oxide-covered and oxide-free substrates. We demonstrate a precise positioning process for Ga-nucleated GaAs nanowires using a hole array in a dielectric layer thermally grown on silicon. Crystal quality is analyzed by high resolution transmission electron microscopy. Crystal structure evolves from pure zinc blende to pure wurtzite along a single nanowire, with a transition region.

Two and three-body interatomic dispersion energy contributions to binding in molecules and solids

Abstract: We present numerical estimates of the leading two- and three-body dispersion energy terms in van der Waals interactions for a broad variety of molecules and solids. The calculations are based on London and Axilrod-Teller-Muto expressions where the required interatomic dispersion energy coefficients, C(6) and C(9), are computed "on the fly" from the electron density. Inter- and intramolecular energy contributions are obtained using the Tang-Toennies (TT) damping function for short interatomic distances. The TT range parameters are equally extracted on the fly from the electron density using their linear relationship to van der Waals radii. This relationship is empiricially determined for all the combinations of He-Xe rare gas dimers, as well as for the He and Ar trimers. The investigated systems include the S22 database of noncovalent interactions, Ar, benzene and ice crystals, bilayer graphene, C(60) dimer, a peptide (Ala(10)), an intercalated drug-DNA model [ellipticine-d(CG)(2)], 42 DNA base pairs, a protein (DHFR, 2616 atoms), double stranded DNA (1905 atoms), and 12 molecular crystal polymorphs from crystal structure prediction blind test studies. The two- and three-body interatomic dispersion energies are found to contribute significantly to binding and cohesive energies, for bilayer graphene the latter reaches 50% of experimentally derived binding energy. These results suggest that interatomic three-body dispersion potentials should be accounted for in atomistic simulations when modeling bulky molecules or condensed phase systems.

Synthesis and crystal growth of Cs0.8(FeSe0.98)2: a new iron-based superconductor with Tc=27K

Abstract: We report on the synthesis of large single crystals of a new FeSe-layer superconductor Cs0.8(FeSe0.98)2. X-ray powder diffraction, neutron powder-diffraction and magnetization measurements have been used to compare the crystal structure and the magnetic properties of Cs0.8(FeSe0.98)2 with those of the recently discovered potassium intercalated system KxFe2Se2. The new compound Cs0.8(FeSe0.98)2 shows a slightly lower superconducting transition temperature (Tc=27.4 K) in comparison to 29.5 in K0.8(FeSe0.98)2). The volume of the crystal unit cell increases by replacing K by Cs - the c-parameter grows from 14.1353(13) A to 15.2846(11) A. For the so far known alkali metal intercalated layered compounds (K0.8Fe2Se2 and Cs0.8(FeSe0.98)2) the Tc dependence on the anion height (distance between Fe-layers and Se-layers) was found to be analogous to those reported for As-containing Fe-superconductors and Fe(Se1-xChx), where Ch=Te, S.

Growth Strategy and Physical Properties of the High Mobility P-Type CuI Crystal

Abstract: Acquiring stable binary wide band-gap semiconductor (WBS) materials with high p-type mobility is essential for the development of WBS optoelectronic devices. CuI is a p-type WBS material with a large band gap (3.1 eV) and high exciton binding energy (62 meV). However, the semiconductor characteristics of the CuI single crystal are unknown due to the lack of a large sized and high quality crystal. Our approach focuses on the design of the mineralizer for the hydrothermal method to effectively control the growth habit and the impurity concentration in the crystal. A large size (15 mm × 10 mm × 1 mm) and high quality CuI single crystal is obtained by using a new mineralizer (NH4I + KI). The crystal shows high p-type mobility (43.9 cm2·V−1·S1−). The strong and sharp band-edge emission at 410 nm indicates that the interband excitonic transition dominates the optical response in the spectrum. Such a binary crystalline material may open the way to new applications in optoelectronic devices.

The minimum crystal size needed for a complete diffraction data set.

Abstract: In this work, classic intensity formulae were united with an empirical spot-fading model in order to calculate the diameter of a spherical crystal that will scatter the required number of photons per spot at a desired resolution over the radiation-damage-limited lifetime. The influences of molecular weight, solvent content, Wilson B factor, X-ray wavelength and attenuation on scattering power and dose were all included. Taking the net photon count in a spot as the only source of noise, a complete data set with a signal-to-noise ratio of 2 at 2 A resolution was predicted to be attainable from a perfect lysozyme crystal sphere 1.2 µm in diameter and two different models of photoelectron escape reduced this to 0.5 or 0.34 µm. These represent 15-fold to 700-fold less scattering power than the smallest experimentally determined crystal size to date, but the gap was shown to be consistent with the background scattering level of the relevant experiment. These results suggest that reduction of background photons and diffraction spot size on the detector are the principal paths to improving crystallographic data quality beyond current limits.

Characterization of the Nanoscale in Triacylglycerol Crystal Networks

Abstract: Here we report on the characterization of the nanoscale in triacylglycerol crystal networks of edible fats. Blends of tristearin and triolein were prepared in proportions between 20 and 100% w/w to achieve a wide range of supersaturations. Crystal networks were subjected to mechanical disruption using isobutanol at 10 °C and visualized using cryogenic transmission electron microscopy (cryo-TEM). This method allowed the breakdown of spherulitic structures into their primary crystals: nanoplatelets of approximate sizes 150 × 60 × 30 nm to 370 × 160 × 40 nm depending on supersaturation conditions, and a length to width aspect ratio of 2.3. The method also allowed the visualization of bimolecular triacylglycerol lamellae within a cross-section of a nanoplatelet. The tristearin d-spacing (∼4.5 nm) and domain size (30−50 nm) of the (001) plane, by cryo-TEM and small-angle X-ray diffraction, agreed quantitatively. Scherrer analysis provided an accurate estimate of the cross-sectional thickness of the nanoplatele...

High quality factor metallodielectric hybrid plasmonic-photonic crystals

Abstract: A 2D polystyrene colloidal crystal self-assembled on a flat gold surface supports multiple photonic and plasmonic propagating resonance modes. For both classes of modes, the quality factors can exceed 100, higher than the quality factor of surface plasmons (SP) at a polymer–gold interface. The spatial energy distribution of those resonance modes are carefully studied by measuring the optical response of the hybrid plasmonic–photonic crystal after coating with dielectric materials under different coating profiles. Computer simulations with results closely matching those of experiments provide a clear picture of the field distribution of each resonance mode. For the SP modes, there is strong confinement of electromagnetic energy near the metal surface, while for optical modes, the field is confined inside the spherical particles, far away from the metal. Coating of dielectric material on the crystal results in a large shift in optical features. A surface sensor based on the hybrid plasmonic–photonic crystal is proposed, and it is shown to have atomic layer sensitivity. An example of ethanol vapor sensing based on physisorption of ethanol onto the sensor surface is demonstrated.

The Thermosalient Phenomenon. “Jumping Crystals” and Crystal Chemistry of the Anticholinergic Agent Oxitropium Bromide

Abstract: The anticholinergic agent oxitropium bromide possesses rich crystal chemistry, most remarkably exhibiting a strong thermosalient effect ("jumping crystal" effect), a mechanical property with potential applications in organic-based actuators. The thermosalient effect, manifested in forceful jumps of up to several centimeters, was investigated by a combination of structural, microscopic, spectroscopic, and thermoanalytical techniques, providing data on which to base a proposed mechanism for the phenomenon. Direct observation of the effect in a single crystal and structure determination of both phases revealed that the jumping of the crystals is a macroscopic manifestation of a highly anisotropic change in the cell volume. The cell distortion is accompanied by a conformational change of the oxitropium cation, which triggers increased separation between the ion pairs in the lattice at nearly identical separation between the cation and the anion within each ion pair. At the molecular level, the cation acts as a molecular shuttle composed of two rigid parts (epoxy-aza-tricyclic-nonyl portion and phenyl ring) that are bridged by a flexible ester linkage. The structure of the rigid, inert aza-tricyclic portion remains practically unaffected by the temperature, suggesting a mechanism in which the large, thermally accumulated strain is transferred over the ester bridge to the phenyl ring, which rotates to trigger the phase transition. Mechanistic details of the higher temperature solid-state phenomena are also presented. The high-temperature phase can also be obtained by grinding or UV irradiation of the room-temperature phase. In addition, if it is irradiated with UV light in the presence of KBr, the high-temperature phase undergoes intramolecular photochemical rearrangement. Heating the high-temperature phase to slightly below the melting temperature results in an additional solid-state reaction that results in the conversion of the salt to a mixture of neutral compounds.

Ligand exchanges and selective catalytic hydrogenation in molecular single crystals

Abstract: Chemical reactions inside single crystals are likely to be highly selective, but examples of single crystal to single crystal (SC-SC) transformations are uncommon, because crystallinity is difficult to retain following the rearrangement of atoms in the solid state. The most widely studied SC-SC transformations involve solvent exchange reactions in porous coordination polymers or metal-organic frameworks, which take advantage of the robust polymeric networks of the hosts. Examples of reactions occurring within molecular organic crystals generally involve photo-induced reactions, such as the coupling of alkenes or alkynes within the crystal. For nonporous molecular inorganic or organometallic crystals, single-crystal transformations involving the formation or cleavage of metal-ligand bonds are rare; known examples usually involve ligand loss from the single crystal and reversible religation, a process sometimes accompanied by decay of the single crystal to a microcrystalline powder. Here we report a series of SC-SC transformations that involve the interchange of multiple small gaseous ligands (N(2), CO, NH(3), C(2)H(4), H(2) and O(2)) at an iridium centre in molecular single crystals of a pincer Ir(I) complex. The single crystal remains intact during these ligand-exchange reactions, which occur within the crystal and do not require prior ligand extrusion. We reveal a selective catalytic transformation within a nonporous molecular crystal: pincer iridium single crystals ligated with nitrogen, ethylene or hydrogen show selective hydrogenation of ethylene relative to propylene (25:1) when surface sites are passified by CO.

Confinement-induced one-dimensional ferroelectric polymer arrays.

Abstract: This work demonstrates the use of wetting nanoporous alumina template with polymer solution to produce arrays of isolated poly(vinylidene fluoride) (PVDF) ferroelectric γ-type nanorods supported within a nonpolar α-structure film. The method is based upon a crystal phase transition which occurs due to PVDF confinement within alumina nanoporous. The system was studied using scanning X-ray microdiffraction (μ-XRD) that allows the solid−solid phase transition from the α-nonpolar crystal form (bulk) to the γ polar ferroelectric form (nanorod array) to be spatially resolved, as well as providing crystallinity and orientation information. The results reveal that the interaction between polymer chains and the porous membrane’s walls imposes a flat-on lamella growth along the nanorrods long axis, while improving crystal orientation.

Phase diagram of a tetrahedral patchy particle model for different interaction ranges

Abstract: We evaluate the phase diagram of the Kern–Frenkel patchy model with four interaction sites for four different values of the radial interaction range (all in the single-bond-per-patch regime) keeping the area of the interaction patches fixed. Four stable crystal phases are investigated, namely diamond cubic (DC), bcc, fcc, and plastic fcc. The DC is favored at low temperatures and pressures, while the bcc is favored at low temperatures and intermediate to high pressures. At low temperatures and very high pressures an ordered fcc phase is found, while—as expected—at high temperatures, the only stable crystal is a plastic fcc phase. We find a rich phase diagram with several re-entrant coexistence lines, which can be brought in the equilibrium phase diagram by a proper choice of the range. We also show that the gas-liquid phase separation becomes metastable as the range narrows, and it takes place in a region of the phase diagram where the low density diamond crystal is the thermodynamically stable phase.

Preparation of 3-D ordered macroporous tungsten oxides and nano-crystalline particulate tungsten oxides using a colloidal crystal template method, and their structural characterization and application as photocatalysts under visible light irradiation

Abstract: Three-dimensionally ordered macroporous (3DOM) tungsten(VI) oxide (WO3) was prepared using a colloidal crystal template method. Well-ordered 3DOM WO3 was prepared with a high pore fraction using ammonium metatungstate ((NH4)6H2W12O40), a Keggin-type dodecatungstate, as a tungsten precursor; WO3 materials prepared by other commercially available W precursors, tungsten chloride (WCl6), tungsten(V) ethoxide (W(OEt)5), and phosphotungstic acid (H3PW12O40), have a low 3DOM pore fraction. These WO3 materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) analysis of nitrogen adsorption isotherm, and Raman spectroscopy. Non-porous WO3 prepared from ammonium metatungstate without a poly(methyl metacrylate) (PMMA) template grew to crystal sizes of up to several micrometres with a low specific surface area (ca. 1–2 m2 g−1). In the presence of a colloidal crystal template of PMMA spheres, WO3 crystal grew in the nanometre-sized voids between the PMMA spheres, and the specific surface area thus increased up to ca. 30 times compared to non-porous WO3. The surface area is tunable by changing the PMMA sphere diameter. Calcination of the 3DOM WO3 produced WO3 nano-crystalline particles by sintering-induced disassembly. After Pt-loading, these WO3 materials showed higher photocatalytic activity compared to non-porous WO3 for decomposition of acetic acid in air under visible light irradiation.

Crystal growth processes based on capillarity : czochralski, floating zone, shaping and crucible techniques

Abstract: Preface. Introduction. Acknowledgements. Nomenclature. Contributors. 1. Basic Principles of Capillarity in Relation to Crystal Growth (Nicolas Eustathopoulos, Beatrice Drevet, Simon Brandon and Alexander Virozub). 1.1 Definitions. 1.1.1 Characteristic Energies of Surfaces and Interfaces. 1.1.2 Capillary Pressure. 1.1.3 Surface Energy versus Surface Tension. 1.2 Contact Angles. 1.2.1 Thermodynamics. 1.2.2 Dynamics of Wetting. 1.2.3 Measurements of Contact Angle and Surface Tension by the Sessile Drop Technique. 1.2.4 Selected Data for the Contact Angle for Systems of Interest for Crystal Growth. 1.3 Growth Angles. 1.3.1 Theory. 1.3.2 Measurements of Growth Angles: Methods and Values. 1.3.3 Application of the Growth Angle Condition in Simulations of Crystal Growth. 1.3.4 Summary. Acknowledgements. References. 2. The Possibility of Shape Stability in Capillary Crystal Growth and Practical Realization of Shaped Crystals (Vitali A. Tatartchenko). 2.1 Crucible-Free Crystal Growth Capillary Shaping Techniques. 2.2 Dynamic Stability of Crystallization the Basis of Shaped Crystal Growth by CST. 2.2.1 Lyapunov Equations. 2.2.2 Capillary Problem Common Approach. 2.2.3 Equation of Crystal Dimension Change Rate. 2.2.4 Equation of Crystallization Front Displacement Rate. 2.2.5 Stability Analysis in a System with Two Degrees of Freedom. 2.3 Stability Analysis and Growth of Shaped Crystals by the Cz Technique. 2.3.1 Capillary Problem. 2.3.2 Temperature Distribution in the Crystal Melt System. 2.3.3 Stability Analysis and Shaped Crystal Growth. 2.3.4 Dynamic Stability Problem for the Kyropoulos Technique. 2.4 Stability Analysis and Growth of Shaped Crystals by the Verneuil Technique. 2.4.1 Principal Schemes of Growth. 2.4.2 Theoretical Investigation. 2.4.3 Practical Results of the Theoretical Analysis. 2.4.4 Stability Analysis-Based Automation. 2.5 Stability Analysis and Growth of Shaped Crystals by the FZ Technique. 2.6 TPS Techniques: Capillary Shaping and Impurity Distribution. 2.6.1 Capillary Boundary Problem for TPS. 2.6.2 Stability Analysis. 2.6.3 Experimental Tests of the Capillary Shaping Theory Statements. 2.6.4 Impurity Distribution. 2.6.5 Definition of TPS. 2.6.6 Brief History of TPS. 2.7 Shaped Growth of Ge, Sapphire, Si, and Metals: a Brief Presentation. 2.7.1 Ge. 2.7.2 Sapphire. 2.7.3 Si. 2.7.4 Metals and Alloys. 2.8 TPS Peculiarities. References. 3 Czochralski Process Dynamics and Control Design (Jan Winkler, Michael Neubert, Joachim Rudolph, Ning Duanmu and Michael Gevelber). 3.1 Introduction and Motivation. 3.1.1 Overview of Cz Control Issues. 3.1.2 Diameter Control. 3.1.3 Growth Rate Control. 3.1.4 Reconstruction of Quantities not Directly Measured. 3.1.5 Specifi c Problems for Control in Cz Crystal Growth. 3.1.6 PID Control vs. Model-Based Control. 3.1.7 Components of a Control System. 3.1.8 Modelling in Crystal Growth Analysis and Control. 3.2 Cz Control Approaches. 3.2.1 Proper Choice of Manipulated Variables. 3.2.2 Feedforward Control. 3.2.3 Model-Based Analysis of the Process. 3.2.4 Stability. 3.2.5 Model-Based Control. 3.2.6 Identification. 3.2.7 Measurement Issues and State Estimation. 3.3 Mathematical Model. 3.3.1 Hydromechanical Geometrical Model. 3.3.2 Model of Thermal Behaviour. 3.3.3 Linear System Model Analysis. 3.4 Process Dynamics Analysis for Control. 3.4.1 Operating Regime and Batch Implications. 3.4.2 Actuator Performance Analysis. 3.4.3 Curved Interface. 3.4.4 Nonlinear Dynamics. 3.5 Conventional Control Design. 3.5.1 Control Based on Optical Diameter Estimation. 3.5.2 Weight-Based Control. 3.6 Geometry-Based Nonlinear Control Design. 3.6.1 Basic Idea. 3.6.2 Parametrization of the Hydromechanical Geometrical Model in Crystal Length. 3.6.3 Flatness and Model-Based Feedback Control of the Length-Parametrized Model. 3.6.4 Control of Radius and Growth Rate. 3.7 Advanced Techniques. 3.7.1 Linear Observer Design. 3.7.2 Nonlinear Observer Design. 3.7.3 Control Structure Design for Batch Disturbance Rejection. References. 4 Floating Zone Crystal Growth (Anke Ludge, Helge Riemann, Michael Wunscher, Gunter Behr, Wolfgang Loser, Andris Muiznieks and Arne Croll). 4.1 FZ Processes with RF Heating. 4.1.1 FZ Method for Si by RF Heating. 4.1.2 FZ Growth for Metallic Melts. 4.2 FZ Growth with Optical Heating. 4.2.1 Introduction. 4.2.2 Image Furnaces. 4.2.3 Laser Heating. 4.2.4 FZ Growth for Oxide Melts. 4.3 Numerical Analysis of the Needle-Eye FZ Process. 4.3.1 Literature Overview. 4.3.2 Quasi-Stationary Axisymmetric Mathematical Model of the Shape of the Molten Zone. 4.3.3 Numerical Investigation of the Influence of Growth Parameters on the Shape of the Molten Zone. 4.3.4 Nonstationary Axisymmetric Mathematical Model for Transient Crystal Growth Processes. Appendix: Code for Calculating the Free Surface During a FZ Process in Python. References. 5 Shaped Crystal Growth (Vladimir N. Kurlov, Sergei N. Rossolenko, Nikolai V. Abrosimov and Kheirreddine Lebbou). 5.1 Introduction. 5.2 Shaped Si. 5.2.1 EFG Method. 5.2.2 Dendritic Web Growth. 5.2.3 String Ribbon. 5.2.4 Ribbon Growth on Substrate (RGS). 5.3 Sapphire Shaped Crystal Growth. 5.3.1 EFG. 5.3.2 Variable Shaping Technique (VST). 5.3.3 Noncapillary Shaping (NCS). 5.3.4 Growth from an Element of Shape (GES). 5.3.5 Modulation-Doped Shaped Crystal Growth Techniques. 5.3.6 Automated Control of Shaped Crystal Growth. 5.4 Shaped Crystals Grown by the Micro-Pulling Down Technique ( -PD). 5.4.1 Crucible Melt Relation During Crystal Growth by the -PD Technique. 5.4.2 Examples of Crystals Grown by the -PD Technique. 5.5 Conclusions. References. 6 Vertical Bridgman Technique and Dewetting (Thierry Duffar and Lamine Sylla). 6.1 Peculiarities and Drawbacks of the Bridgman Processes. 6.1.1 Thermal Interface Curvature. 6.1.2 Melt Crystal Crucible Contact Angle. 6.1.3 Crystal Crucible Adhesion and Thermomechanical Detachment. 6.1.4 Spurious Nucleation on Crucible Walls. 6.2 Full Encapsulation. 6.2.1 Introduction. 6.2.2 LiCl KCl Encapsulant for Antimonides. 6.2.3 B2O3 Encapsulant. 6.2.4 Conclusion. 6.3 The Dewetting Process: a Modified VB Technique. 6.3.1 Introduction. 6.3.2 Dewetting in Microgravity. 6.3.3 Dewetting in Normal Gravity. 6.3.4 Theoretical Models of Dewetting. 6.3.5 Stability Analysis. 6.4 Conclusion and Outlook. References. 7 Marangoni Convection in Crystal Growth (Arne Croll, Taketoshi Hibiya, Suguru Shiratori, Koichi Kakimoto and Lijun Liu). 7.1 Thermocapillary Convection in Float Zones. 7.1.1 Model Materials. 7.1.2 Semiconductors and Metals. 7.1.3 Effect of Oxygen Partial Pressure on Thermocapillary Flow in Si. 7.1.4 Fluid Dynamics of Thermocapillary Flow in Half-Zones. 7.1.5 Full Float Zones. 7.1.6 The Critical Marangoni Number Mac2. 7.1.7 Controlling Thermocapillary Convection in Float Zones. 7.2 Thermocapillary Convection in Cz Crystal Growth of Si. 7.2.1 Introduction. 7.2.2 Surface Tension-Driven Flow in Cz Growth. 7.2.3 Numerical Model. 7.2.4 Calculation Results. 7.2.5 Summary of Cz Results. 7.3 Thermocapillary Convection in EFG Set-Ups. 7.4 Thermocapillary Convection in Bridgman and Related Set-Ups. 7.5 Solutocapillary Convection. References. 8 Mathematical and Numerical Analysis of Capillarity Problems and Processes (Liliana Braescu, Simona Epure and Thierry Duffar). 8.1 Mathematical Formulation of the Capillary Problem. 8.1.1 Boundary Value Problems for the Young Laplace Equation. 8.1.2 Initial and Boundary Conditions of the Meniscus Problem. 8.1.3 Approximate Solutions of the Axisymmetric Meniscus Problem. 8.2 Analytical and Numerical Solutions for the Meniscus Equation in the Cz Method. 8.3 Analytical and Numerical Solutions for the Meniscus Equation in the EFG Method. 8.3.1 Sheets. 8.3.2 Cylindrical Crystals. 8.4 Analytical and Numerical Solutions for the Meniscus Equation in the Dewetted Bridgman Method. 8.4.1 Zero Gravity. 8.4.2 Normal Gravity. 8.5 Conclusions. Appendix: Runge Kutta Methods. A.1 Fourth-Order Runge Kutta Method (RK4). A.2 Rkfixed and Rkadapt Routines for Solving IVP. References. Index.

Mechanical anisotropy in crystalline saccharin: nanoindentation studies

Abstract: The nanoindentation technique has been employed to relate the mechanical properties of saccharin single crystals with their internal structure Indentations were performed on (100) and (011) faces to assess the mechanical anisotropy The load-displacement (P-h) curves indicate significant differences in the nature of the plastic deformation on the two faces The P-h curves obtained on the (011) plane are smooth, reflecting homogeneous plasticity However, displacement bursts (pop-ins) are observed in the P-h curves obtained on the (100) plane suggesting a discrete deformation mechanism Marginal differences exist in the hardness and modulus on the two faces that may, in part, be rationalized, although one notes that saccharin has a largely three-dimensional close-packed structure The structural origins of the fundamentally different deformation mechanisms on (100) and (011) are discussed in terms of the dimensionality of the hydrogen bonding networks Down the (100) planes, the saccharin dimers are stacked and are stabilized by nonspecific van der Wants interactions mostly between aromatic rings However, down the (011) planes, the molecules are stabilized by more directional and cross-linked C-H O hydrogen bonds This anisotropy in crystal packing and interactions is reflected in the mechanical behavior on these faces The displacements associated with the pop-ins were found to he integral multiples oldie molecule separation distances Nanoindentation offers an opportunity to compare experimentally, and in a quantitative way, the various intermolecular interactions that fire present in a molecular crystal