Degree Of Long-range Order Research Articles

Order and Orientation Control of Mesoporous Silica Films on Conducting Gold Substrates Formed by Dip-Coating and Self-Assembly: A Grazing Angle of Incidence Small-Angle X-ray Scattering and Field Emission Scanning Electron Microscopy Study

Grazing-angle of incidence small-angle X-ray scattering (GISAXS) and high-resolution field emission scanning electron microscopy have been used to characterize the mesophase symmetry, orientation, and long-range order in PEO20-PPO70-PEO20 (Pluronic P123) templated mesoporous silica thin films on conducting gold substrates as a function of silica-to-ethylene oxide (Si/EO) block ratio and relative humidity (RH). The films are formed by dip-coating followed by evaporation-induced self-assembly under tightly controlled RH. The general evolution of the mesophase follows the trends that are expected based on shape factors due to swelling of the PEO block. However, changes in orientation of the nanostructure relative to the substrate and the degree of long-range order are found to depend on Si/EO ratio. These effects are likely due to the dynamics of evaporation and self-assembly. Generally, at Si/EO ratios lower than 3.29, the films contained regions where the nanostructure was not oriented relative to the plane of the substrate. However, for Si/EO ratios greater than 3.62, conditions were found where the nanostructure of the film was highly oriented relative to the plane of the substrate. This is true over the range of RH studied, independent of the nanostructure symmetry. For low Si/EO ratios at the highest RH levels, the films were composed of a mixture of spherical and cylindrical pores. At high Si/EO ratios and high RH levels, the films had a highly oriented R-3m nanostructure but displayed streaking perpendicular to the substrate in the Bragg spots on GISAXS patterns. This streaking is interpreted as faulting along planes parallel to the substrate.

Atomic structure of a long-range ordered vicinal surface of SrTiO 3

We solved the structure of SrTiO 3(1 0 6) by grazing incidence X-ray diffraction and direct methods. The surface exhibits SrO and TiO 2 terminated half-steps, which are unstrained and the surface atoms are practically in their bulk-like positions. The resulting wavy surface exhibits an astonishing degree of long-range order, which is established by the alternating, weakly polar surface terminations. Since cation sites are partially occupied toward step edges, the surface is very smooth but lacks short-range order. This is very different from the behavior observed for metal and semiconductor surfaces, where stress resulting from short-range reconstruction is the driving force behind long-range order.

Effects of sediment iron mineral composition on microbially mediated changes in divalent metal speciation: Importance of ferrihydrite

Dissimilatory metal reducing bacteria (DMRB) can influence geochemical processes that affect the speciation and mobility of metallic contaminants within natural environments. Most investigations into the effect of DMRB on sediment geochemistry utilize various synthetic oxides as the Fe III source (e.g., ferrihydrite, goethite, hematite). These synthetic materials do not represent the mineralogical composition of natural systems, and do not account for the effect of sediment mineral composition on microbially mediated processes. Our experiments with a DMRB ( Shewanella putrefaciens 200) and a divalent metal (Zn II) indicate that, while complexity in sediment mineral composition may not strongly impact the degree of “microbial iron reducibility,” it does alter the geochemical consequences of such microbial activity. The ferrihydrite and clay mineral content are key factors. Microbial reduction of a synthetic blend of goethite and ferrihydrite (VHSA-G) carrying previously adsorbed Zn II increased both [Zn II-aq] and the proportion of adsorbed Zn II that is insoluble in 0.5 M HCl. Microbial reduction of Fe III in similarly treated iron-bearing clayey sediment (Fe-K-Q) and hematite sand, which contained minimal amounts of ferrihydrite, had no similar effect. Addition of ferrihydrite increased the effect of microbial Fe III reduction on Zn II association with a 0.5 M HCl insoluble phase in all sediment treatments, but the effect was inconsequential in the Fe-K-Q. Zinc k-edge X-ray absorption spectroscopy (XAS) data indicate that microbial Fe III reduction altered Zn II bonding in fundamentally different ways for VHSA-G and Fe-K-Q. In VHSA-G, ZnO 6 octahedra were present in both sterile and reduced samples; with a slightly increased average Zn-O coordination number and a slightly higher degree of long-range order in the reduced sample. This result may be consistent with enhanced Zn II substitution within goethite in the microbially reduced sample, though these data do not show the large increase in the degree of Zn-O-metal interactions expected to accompany this change. In Fe-K-Q, microbial Fe III reduction transforms Zn-O polyhedra from octahedral to tetrahedral coordination and leads to the formation of a ZnCl 2 moiety and an increased degree of multiple scattering. This study indicates that, while many sedimentary iron minerals are easily reduced by DMRB, the effects of microbial Fe III reduction on trace metal geochemistry are dependent on sediment mineral composition.

Plasmon-waveguide Resonance Studies of Lateral Segregation of Lipids and Proteins into Microdomains (Rafts) in Solid-supported Bilayers

Plasmon-waveguide resonance (PWR) spectroscopy has been used to examine solid-supported lipid bilayers consisting of dioleoylphosphatidylcholine (DOPC), palmitoyloleoylphosphatidylcholine (POPC), sphingomyelin (SM), and phosphatidylcholine/SM binary mixtures. Spectral simulation of the resonance curves demonstrated an increase in bilayer thickness, long-range order, and molecular packing density in going from DOPC to POPC to SM single component bilayers, as expected based on the decreasing level of unsaturation in the fatty acyl chains. DOPC/SM and POPC/SM binary mixtures yielded PWR spectra that can be ascribed to a superposition of two resonances corresponding to microdomains (rafts) consisting of phosphatidylcholine- and SM-rich phases coexisting within a single bilayer. These were formed spontaneously over time as a consequence of lateral phase separation. Each microdomain contained a small proportion (<20%) of the other lipid component, which increased their kinetic and thermodynamic stability. Incorporation of a glycosylphosphatidylinositol-linked protein (placental alkaline phosphatase) occurred within each of the single component bilayers, although the insertion was less efficient into the DOPC bilayer. Incorporation of placental alkaline phosphatase into a DOPC/SM binary bilayer occurred with preferential insertion into the SM-rich phase, although the protein incorporated into both phases at higher concentrations. These results demonstrate the utility of PWR spectroscopy to provide insights into raft formation and protein sorting in model lipid membranes.

Structural investigations of DNA-polycation complexes

The internal structure of DNA-polycation complexes is investigated by synchrotron small-angle X-ray scattering (SAXS). Hexagonal packing of DNA is observed for DNA complexed with poly-L-lysine (PL), poly-L-arginine (PA), spermine (Sp), and linear and branched polyethyleneimine (lPEI and bPEI, respectively). Variations in the internal spacings and degree of long-range ordering are dependent on both polycation type and concentration of added salt. With increasing concentration of monovalent salt, a discontinuous phase transition is observed from compact to loose bundles and finally to an isotropic network phase. This salt-induced melting transition was found to be universal for all polyplexes studied and is in quantitative agreement with a simple free energy model based solely on electrostatic and entropic contributions. Using the osmotic stress method, bulk modulus (K) is measured for PL-DNA and PA-DNA polyplexes at various salt concentrations. With increasing osmotic force, we show that the salt-induced melting transition is shifted and compression in the loose bundle regime is in qualitative agreement with our model.

Ni 3Ga—an investigation of ordering kinetics by residual resistometry

Order–disorder transformations in the compound Ni 3Ga with L1 2 superstructure were investigated by residual electrical resistometry during isochronal and isothermal step-annealing treatments. Resistivity measurements after several isochronal annealing treatments at rising and falling temperatures in the range at 293–800 K showed a complex annealing behavior of Ni 3Ga. The first registration of a slight atomic mobility was identified already at 380 K, followed by the second step in atomic mobility observed between 500 and 650 K and attributed to a change in the degree of long range order (LRO) in the structure. Measurements at isothermal annealing have been performed after isothermal step treatments between 673 and 786 K also at rising and falling temperatures. The analysis of electrical resistivity curves allowed for conclusion that the order–disorder equilibrium in Ni 3Ga is reached not in a single exponential process, but as a result of two processes with distinctly different rates. The ordering activation energies of both fast and slow processes in Ni 3Ga were calculated. For the first, fast relaxation process an activation energy parameter was found equal to 1.47 eV; the second, slow process was characterized by an activation energy of 2.66 eV.

Influence of the buffer layers on magnetic properties of FePt (001) films sputter-deposited at reduced temperature

The magnetic properties of Fe38Pt62 and Fe52Pt48 films sputter deposited on MgO (001) substrates with and without a buffer layer at the substrate temperature Ts of 300 °C have been investigated. Pt, Au, and PtAu alloys with different compositions were used as the buffer layer to study the influence of the lattice mismatch between the FePt layer and the buffer layer. The L10 ordered structure with large perpendicular magnetic anisotropy has been obtained for the Fe38Pt62 films irrespective of the buffer layer. The degree of long-range order S and uniaxial magnetic anisotropy energy Ku increase with increasing the lattice mismatch, and S and Ku show maxima of 0.8±0.1 and 2.7×107 erg/cm3, respectively, for the film without a buffer layer. For Fe52Pt48 films, on the other hand, the L10 ordered structure with perpendicular magnetic anisotropy has been obtained only for the film with an Au buffer layer.

Order and Magnetic Properties of Fe89‐xMn11Alx Alloys: Magnetization Measurements and X‐Ray Diffraction.

Abstract We report experiments performed on a series of fourteen Fe 89− x Mn 11 Al x alloys in the concentration range 2 at .% at.% examining structure, degree of long range order and the magnetic properties. We found the type of long range order is concentration dependent, changing from A2, crossing a DO 3 region up to B2. The structural order found in this system is of great influence on the magnetic moments of the Fe atoms. Therefore the wide concentration range of the alloys investigated allowed us to observe the change from ferromagnetism via a region of re-entrance from ferromagnetism to spin glass till antiferromagnetism. In the re-entrant concentration range, we derive the magnetic field dependence on characteristic temperatures for the alloys Fe 62 Mn 11 Al 27 and Fe 59 Mn 11 Al 30 and demonstrate that the latter is very near the critical concentration where the Curie temperature and the freezing temperature of the re-entrant spin glass become equal.

The First Example of Ordered Two-Dimensional Self-Assembly of Au Nanoparticles from Stable Hydrosol

A novel hydrosol of alkanethiol-modified Au nanoparticles was reported for constructing large-scale ordered two-dimensional (2D) self-assembly for the first time. The degree of long-range order is displayed by both the low-angle transmission electron diffraction and fast Fourier transform pattern of the electron microscope image. We discuss the preparation of stable hydrosol ofAu nanoparticles coated with octanethiol and the role of ethanol and octanethiol in the preparation as well as the 2D self-assembly ofAu nanoparticles from the hydrosol in reference to the nanoparticle without stabilizers.

High-resolution molecular structure of a peptide in an amyloid fibril determined by magic angle spinning NMR spectroscopy.

Amyloid fibrils are self-assembled filamentous structures associated with protein deposition conditions including Alzheimer's disease and the transmissible spongiform encephalopathies. Despite the immense medical importance of amyloid fibrils, no atomic-resolution structures are available for these materials, because the intact fibrils are insoluble and do not form diffraction-quality 3D crystals. Here we report the high-resolution structure of a peptide fragment of the amyloidogenic protein transthyretin, TTR(105-115), in its fibrillar form, determined by magic angle spinning NMR spectroscopy. The structure resolves not only the backbone fold but also the precise conformation of the side chains. Nearly complete (13)C and (15)N resonance assignments for TTR(105-115) formed the basis for the extraction of a set of distance and dihedral angle restraints. A total of 76 self-consistent experimental measurements, including 41 restraints on 19 backbone dihedral angles and 35 (13)C-(15)N distances between 3 and 6 A were obtained from 2D and 3D NMR spectra recorded on three fibril samples uniformly (13)C, (15)N-labeled in consecutive stretches of four amino acids and used to calculate an ensemble of peptide structures. Our results indicate that TTR(105-115) adopts an extended beta-strand conformation in the amyloid fibrils such that both the main- and side-chain torsion angles are close to their optimal values. Moreover, the structure of this peptide in the fibrillar form has a degree of long-range order that is generally associated only with crystalline materials. These findings provide an explanation of the unusual stability and characteristic properties of this form of polypeptide assembly.

Phase Transformation in Orthorhombic Ti2AlNb Alloys Under Severe Deformation

ABSTRACTIt was found that severe plastic deformation of orthorhombic alloys caused phase transformations of the displacement type and those associated with a change in the degree of long-range order, namely B2→ω(B82 ), B2→B19 and B2→β (BCC) (in the case of alloy with initial B2-phase structure) and O→B19→A20 (initial O-phase structure, Ti2AlNb). Unlike to ordinary metals, severe plastic deformation of the titanium aluminum intermetallics leads to decreasing of the strength of the material. The B19 and A20 phases are metastable. They are absent in the equilibrium phase diagrams of the compounds under investigation. The formation of the disordered phase states with extensive sliding and having great plasticity under severe deformation makes possible to consider severe deformation as the way for increasing of plasticity of the titanium aluminides.

Comparison of temperature driven ordering in bulk foil and thin film of L10ordered FePd

ABSTRACTChanges in the degree of long-range order of 10 μm thick FePd foil are presented and compared with results on 50 nm thick FePd films. The films were produced by dc and rf magnetron co-sputtering on Si as well as by molecular beam epitaxy co-deposition on MgO substrates. Long-range order was studied by electrical resistivity measurement, X-ray diffraction and Möβbauer spectroscopy.

Synthesis and characterization of amino acid-functionalized hydroxyapatite nanorods

Synthesis of aqueous colloids of amino acid-functionalized hydroxyapatite (HAP; Ca10(PO4)6(OH)2) nanoparticles with rod-like morphology and uniform size was achieved by hydrothermal crystallization at 80 °C and pH 9 in highly supersaturated solutions with a Ca2+∶amino acid molar ratio of 1∶2. Stable suspensions of positively charged nanorods, less than 80 nm in length and ca. 5 nm in width, were obtained in the presence of glycine, alanine, serine, lysine and arginine, and together with FTIR spectroscopy data this was consistent with a general model in which the α-carboxylate of the amino acid was preferentially bound to the crystal surfaces. Variations in the size and shape of the nanoparticles with amino acid used were consistent with differences in the strength of binding at the HAP surfaces. In comparison, stable colloids could not be prepared with aspartic acid due to a relatively low surface charge; instead, the precipitate consisted of highly elongated nanorods, ca. 150 × 3.5 nm in dimension. XRD textural analysis suggested a model for nanorod formation based on the oriented aggregation and fusion of primary crystallite domains specifically along the c axis direction. Colloids consisting of HAP/alanine or HAP/arginine nanoparticles were cross-linked in situ by thermal, hydrothermal or chemical polymerisation of surface-attached and unbound amino acids to produce aggregated nanostructures with variable degrees of long-range order.

The effect of boron on the reordering of Ni 3Al powders produced by filing

Changes in the degree of long-range order (LRO) and the evolution of the microstructure of pure and boron-doped (0.1 and 0.2wt%) Ni 3Al powders have been investigated using XRD and DSC. The powders obtained by filing were completely disordered, with a crystallite size of 100 to 120 Å and an equivalent strain of 0.5 to 1.1%. From the comparison between the experimental heat-flows recorded in DSC and the estimated ordering energy, it was deduced that reordering process is the result of nucleation and growth of ordered domains. The influence of boron on the thermal evolution was investigated. During isochronal anneals, the recovery of the microstructure and of the long-range order takes place at higher temperatures in boron-doped alloys. A comparison of the present results with those of previous irradiation experiments revealed that the effect of boron in slowing-down the reordering processes is the same with and without irradiation, indicating a possible similarity between the operating mechanism of reordering.

Order and magnetic properties of Fe 89− xMn 11Al x alloys: magnetization measurements and X-ray diffraction

We report experiments performed on a series of fourteen Fe 89− x Mn 11Al x alloys in the concentration range 2 at.%<x<40 at.% examining structure, degree of long range order and the magnetic properties. We found the type of long range order is concentration dependent, changing from A2, crossing a DO 3 region up to B2. The structural order found in this system is of great influence on the magnetic moments of the Fe atoms. Therefore the wide concentration range of the alloys investigated allowed us to observe the change from ferromagnetism via a region of re-entrance from ferromagnetism to spin glass till antiferromagnetism. In the re-entrant concentration range, we derive the magnetic field dependence on characteristic temperatures for the alloys Fe 62Mn 11Al 27 and Fe 59Mn 11Al 30 and demonstrate that the latter is very near the critical concentration where the Curie temperature and the freezing temperature of the re-entrant spin glass become equal.

Structure determination of ordered and disordered organic molecules on a surface from the substrate diffraction spots in low energy electron diffraction: ( [formula omitted])R30°-C 2H 2 and disordered CH 3OH on Pd(1 1 1)

We examine the effects of chemisorbed organic molecules on the intensity versus beam energy ( I/ E) variation of the substrate (1 × 1) Bragg spots in low energy electron diffraction (LEED). We find that these integer-order spots alone can provide important information about the local geometries of the molecules on the surface, largely independent of the degree of long-range order of an adsorbate overlayer. This is demonstrated by comparing LEED studies of two different adsorbates on Pd(1 1 1), namely: C 2H 2 which forms an ordered ( 3 × 3 )R30° overlayer, and thus gives rise to superstructure (or fractional-order) Bragg spots, and disordered CH 3OH, which scatters diffusely into directions between the integer-order spots. This allows LEED to be used conveniently for the determination of the structures of adsorbates on surfaces as a continuous function of coverage, independent of the degree of long-range order of the adlayer.

Effects of ball milling and annealing of an alloy in the Al-Fe-Cu system: Implications for phase equilibria

An icosahedral quasicrystalline alloy in the Al-Fe-Cu system has been mechanically milled in a high-energy ball mill (Szegvari attritor) for 1, 3, 6 and 10 h. Samples were characterized by X-ray diffraction and transmission electron microscopy. The evolution of nanosize crystallites of the disordered B2 phase (bcc; a = 0.29 nm), coexisting with either the parent icosahedral phase or an amorphous phase, occurs during milling. Isothermal heat treatment of milled powder at various temperatures (200, 500, 600, 700, 800 and 850°C) leads in all cases, except at 200°C, to the transformation from disordered B2 and amorphous phases to an ordered B2 phase with a high degree of long-range ordering. The maximum degree of superlattice ordering was found after isothermal treatment at 800oC. The implications of these results are discussed with reference to phase equilibria existing between crystalline and quasicrystalline phases in the Al-Fe-Cu system.

Growth of NiO ultrathin films on Pd(1 0 0) by post-oxidation of Ni films: the effect of pre-adsorbed oxygen

This paper reports on the optimisation of the growth parameters of NiO ultrathin films on Pd(1 0 0). Growth is performed by means of UHV metal deposition and post-oxidation cycles. Chemical and structural characterisation of the deposits is achieved by means of electron spectroscopy (X-ray photoelectron spectroscopy, XPS; angle resolved XPS) and electron diffraction techniques (low energy electron diffraction, LEED; X-ray photoelectron diffraction, XPD). Three growth procedures have been investigated, which differ for the particular growth parameters adopted in each case. We demonstrate that post-oxidation is effective in order to obtain epitaxial NiO only if the initial dose of Ni evaporated on the clean Pd(1 0 0) substrate exceeds a critical value, corresponding approximately to two equivalent monolayers. However, the overlayer thus obtained is strongly understoichiometric in oxygen close to the metal/oxide interface and poorly ordered on the long range. When a Ni dose below this limiting first value is used, the layer evolves toward polycrystalline NiO, due to substantial oxidation of the Pd substrate promoted by the presence of Ni, very likely through a work function decrease upon direct metal/metal interface formation. On the contrary, epitaxial NiO(1 0 0) layers of good structural quality, with limited oxygen deficiency at the interface, with negligible substrate oxidation and with a good degree of long-range order are obtained if deposition and post-oxidation cycles are initiated on an oxygen pre-saturated Pd surface, characterised by the (√5×√5)- R27° O/Pd(1 0 0) LEED pattern. We therefore demonstrate that oxygen can act either as an inhibitor or as a promoter of NiO epitaxial growth on Pd(1 0 0), depending on the way it is used.

Synthesis of Periodic Large Mesoporous Organosilicas and Functionalization by Incorporation of Ligands into the Framework Wall

Highly ordered large mesopore organosilicas have been obtained by direct liquid crystal templating in acid media using bridged silsesquioxane (EtO)3Si−CH2−CH2−Si(OEt)3 [bis(triethoxysilyl)ethane, BTSE] precursor and triblock copolymers as structure-directing species. The degree of long-range ordering of the structure as determined from X-ray diffraction and transmission electron microscopy, and the most probable pore diameter, in the range 4−8 nm, were observed to depend on the concentration of triblock copolymer used in the synthesis. Further pore-wall functionalization was achieved by co-condensation with Cu(II)-complexed N,N‘-bis[3-(trimethoxysilyl)propyl]ethylenediamine (BTSPED). Surfactant extraction produces periodic mesoporous organosilicas functionalized with this complex in the framework, from which the Cu(II) can then be removed by acid leaching. Such hybrid bridged bifunctional organosilicas are homogeneously mesoporous, and the pore diameter increases in the range 11−21 nm as the mole ratio of...

Chemical ordering at low temperatures in FePd films

We demonstrate that, if a high degree of short range order is present in FePd disordered films, a high value of the long range order parameter S can be obtained by using postgrowth ion irradiation at very low processing temperatures. FePd films deposited monolayer by monolayer at room temperature on MgO(001) substrates exhibit a very low degree of long range order (S∼0.1) but a high degree of short range order as demonstrated by extended x-ray absorption fine structure measurements. Irradiation with 130 keV He+ ions at low fluences (2.0×1016 ions/cm2) leads to a large increase in the long range order parameter and to a large increase in perpendicular anisotropy for irradiation at substrate temperatures lower than 200 °C. This could have a great impact on the current race toward high magnetic recording density media.