A novel urchinlike gold/platinum hybrid nanocatalyst with controlled size

In this paper, we have explored a simple and new strategy to obtain quasimonodisperse Au/Pt hybrid nanoparticles (NPS) with urchinlike morphology and controlled size and Pt shell thickness. Through changing the molar ratios of Au to Pt, the Pt shell thickness of urchinlike Au/Pt hybrid NPs could be easily controlled; through changing the size of Au NPs (the size was easily controlled from similar to 3 to similar to 70 nm via simple heating of HAuCl4-citrate aqueous solution), the size of urchinlike Au/Pt hybrid NPs could be facilely dominated. It should be noted that heating the solution (100 degrees C) was very necessary for obtaining three-dimensional (3D) urchinlike nanostructures while H2PtCl6 was added to gold NPs aqueous solution in the presence of reductant (ascorbic acid). The electrocatalytic oxygen reduction reaction (ORR, a reaction greatly pursued by scientists in view of its important application in fuel cells) and the electron-transfer reaction between hexacyanoferrate(III) ions and thiosulfate ions of urchinlike Au/Pt hybrid NPs were investigated. It is found that the as-prepared urchinlike Au/Pt hybrid NPs exhibited higher catalytic activities than that of similar to Pt NPs with similar size.

Glycyl glycine templating synthesis of single-crystal silver nanoplates

We describe the small-biomolecule ( glycyl glycine)-directed synthesis of single-crystalline silver nanoplates, and different experimental conditions have been explored for a more thorough understanding of the growth mechanism. The yield of silver nanoplates relative to the total number of nanoparticles formed was as high as similar to 80%. It was found that the ratio of glycyl glycine to AgNO3 was the key to forming Ag nanoplates.

A solvothermal route to size- and shape-controlled CdSe and CdTe nanocrystals

The size- and shape-controlled CdSe and CdTe nanocrystals, which exhibit obvious quantum confinement effect, have been synthesized by a solvothermal route. It is found that initial precursor concentrations are key factors in controlling the shape of the resulting nanocrystals. Moreover, the obtained nanocrystals are all of zinc blende structure, regardless of their sizes and shapes. A possible mechanism for the formation and growth of the nanocrystals is put forward. It is inferred that the adhesion and subsequent recrystallization of nanocrystals with an assistance of remaining monomers should be a major reason for formation and growth of the elongated nanocrystals.

Effects of reinforcement filler and temperature on the stability of beta-crystal in glass bead filled polypropylene

The effects of crystallization temperature (T,), glass bead content and its size on the, formation of beta-crystal and structural stability of originally formed beta-crystal in glass bead filled polypropylene (PP) were examined. The differential scanning calorimetry (DSC) measurements indicated that the amount of beta-phase in PP crystals was a function of the crystallization temperature and glass bead content. For a constant crystallization temperature, it was observed that the amount of beta-crystal initially increased with increase in glass bead content up to 30 wt.%, and then decreased slightly with further increase in the filler content. From the DSC data, a disorder parameter (S) was derived to define the structural stability of originally formed beta-crystals. The structural stability of originally formed beta-crystals was enhanced with increase in either the crystallization temperature or the glass bead content. Also, the influence of glass bead size (4-66 mu m) on the formation and stability of beta-crystals in PP/glass bead blends was studied. Large glass bead particles suppressed the formation and decreased the stability of beta-crystals.

Synthesis, crystal structure and properties of H-8[P4W14O58Na4 (H2O)(20)] center dot 16H(2)O

A novel heteropoly tungstophosphates, H-8[P4W14O58Na4(H2O)(20)] . 16H(2)O, was synthesized by hydrothermal method and characterized by elemental analysis, IR spectrum and single-crystal X-ray structure analysis. The thermal stability of the compound was investigated by using TG-DTA. The crystal is triclinic system with space group P (1) over bar, a = 1. 137 9(2) nm, b=1. 363 2(3) nm, c=1. 627 1(3) nm; alpha=78. 20(3)degrees, beta=71, 20(3)degrees, gamma= 71. 62(3)degrees; V = 2. 252 5(8) nm(3), Z=1, M-r= 4 374. 38, D-c = 3. 225 mg/cm(3), mu = 18. 007 mm(-1), F(000)=1 972, R=0. 074 2, R-w=0. 200 4. The result of structure analysis shows that the anion of the compound consists of two PW7O29Na2(H2O)(10) subunits and two linked phosphorous atoms. A kind of microporous with size of 0. 661 4 nm X 0. 318 9 nm was formed in the crystal structure.

A new crystal modification of gutta percha

Single chain and pauci chain single crystals of gutta percha in nanometer size were prepared by a dilute solution spraying method. A new crystal modification of gutta percha was found. The unit cell of the new modification of gutta percha was determined by electron diffraction crystal structure analysis to be a hexagonal form with cell dimensions: a = b = 0.695 nm, c = 0.661 nm, alpha = beta = 90 degrees, gamma =120 degrees; the space group is P6. The molecular packing in the unit cell was determined by computer modelling with Cerius(2) 2.0 software. (C) 1998 Elsevier Science Ltd. All rights reserved.

In situ scanning tunneling microscopy studies of nanometer size palladium particles on highly oriented pyrolytic graphite

A special electrodeposition process of palladium was studied by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and in situ scanning tunneling microscopy (STM). A kind of palladium(IV) complex was attached to the highly oriented pyrolytic graphite (HOPG) electrode surface by electro-oxidation of palladium(II) complex first, and was then reduced to palladium particles. The surface complexes and particles of palladium were both characterized by in situ STM and XPS. The Pd particles are in the nanometer range of size and exhibit electrocatalytic activity towards the oxidation of hydrazine and hydroxylamine.

Crystal structure and crystallinity of poly(aryl ether biphenyl ether ketone ketone)

The crystal structure of poly(aryl ether biphenyl ether ketone ketone) (PEDEKK) was determined to comprise a two-chain orthorhombic unit cell with dimensions a 0.778 nm, b = 0.606 nm and c = 2.375 nm by using wide-angle X-ray diffraction (WAXD). According to the orthorhombic system, the 12 reflections of this polymer were indexed. The crystallite size increases with increasing the crystallization temperature. The results of the degree of crystallinity (W-c,W-x) calculated from WAXD were compatible with those from density (W-c,W-d) and calorimetry (W-c,W-h) measurements.

Effect of heat treatment on the parameters of crystal structure and degree of crystallinity of poly(aryl-ether-ether-ketone)

The variations of unit cell parameters and crystallite size of nine PEEK samples treated at various temperatures have been studied by using Wide-Angle X-ray Diffraction (WAXD), The results indicate a decrease in unit cell parameter a,b and c but an increase in crystallite size L(hkl) With the increase beat treatment temperature. Based on X-ray scattering intensity theory and using the graphic multipeak resolution method, the formula of degree of crystallinity (W-c,W-X) for PEEK is derived. The results calculated are compatible with the density measurement and calorimetry.

Crystal structure of polypropylene filled with rare earth oxides

The effect of a fine powder of Y2O3, Nd2O3, and Ho2O3 on the crystal structure of isotactic polypropylene (iPP) was studied with WAXD and DSC techniques. The results showed that the addition of the three rare earth oxides (REOs) can increase the crystallite size of the alpha-form crystal and the degree of crystallinity of iPP at an annealing temperature of 120 degrees C and that both Y2O3 and Nd2O3 are the beta-nucleator of iPP. REOs enhance the overall growth rate of the spherulites of iPP. All the iPP samples filled with REOs which were crystallized isothermally at 132 degrees C from the melt exhibited their melting peaks of the beta-form on the DSC heating traces, indicating that the REOs are the nucleating agents for both the alpha- and beta-forms of iPP under isothermal conditions. (C) 1996 John Wiley & Sons, Inc.

Crystal structure of the blend of polyamide 1010 with a bismaleimide by WAXD and SAXS

The blend polyamide 1010/N,N'-(diphenylmethane-4,4'-diyl)bismaleimide (PA1010/ BMI) has been investigated by means of WAXD and SAXS. The results obtained with the help of the Ruland, variance and 1D EDCF analysis showed that the degree of crystallinity (W-c,W-x), crystallite size (L(hikl)), long period (L) and thickness of average crystal lamellae (d) decrease with BMI content. Experimental and calculated density values (rho(c)) are in good agreement. Addition of BMT to PA1010 causes an increase in structural distortion. The results from SAXS analysis also supported that a crystalline amorphous interphase exists in the lamellae of semicrystalline polymers, so that a three-phase model instead of the traditional two-phase model should be used.

Measurement and interpretation of the mid-infrared properties of single crystal and polycrystalline gold

The contribution of electron-phonon scattering and grain boundary scattering to the mid-IR (lambda = 3.392 mum) properties of An has been assessed by examining both bulk, single crystal samples-Au(1 1 1) and Au(1 1 0)-and thin film, polycrystalline An samples at 300 K and 100 K by means of surface plasmon polariton excitation. The investigation constitutes a stringent test for the in-vacuo Otto-configuration prism coupler used to perform the measurements, illustrating its strengths and limitations. Analysis of the optical response is guided by a physically based interpretation of the Drude model. Relative to the reference case of single crystal Au at 100 K (epsilon = - 568 + i17.5), raising the temperature to 300 K causes increased electron-phonon scattering that accounts for a reduction of similar to40 nm in the electron mean free path. Comparison of a polycrystalline sample to the reference case determines a mean free path due to grain boundary scattering of similar to 17 nm, corresponding to about half the mean grain size as determined from atomic force microscopy and indicating a high reflectance coefficient for the An grain boundaries. An analysis combining consideration of grain boundary scattering and the inclusion of a small percentage of voids in the polycrystalline film by means of an effective medium model indicates a value for the grain boundary reflection coefficient in the range 0.55-0.71. (C) 2005 Elsevier B.V. All rights reserved.

Origin of Ferroelastic domains in Free-Standing Single Crystal Ferroelectric Films

The origin of the unusual 90 degrees ferroelectric/ferroelastic domains, consistently observed in recent studies on mesoscale and nanoscale free-standing single crystals of BaTiO3 [Schilling , Phys. Rev. B 74, 024115 (2006); Schilling , Nano Lett. 7, 3787 (2007)], has been considered. A model has been developed which postulates that the domains form as a response to elastic stress induced by a surface layer which does not undergo the paraelectric-ferroelectric cubic-tetragonal phase transition. This model was found to accurately account for the changes in domain periodicity as a function of size that had been observed experimentally. The physical origin of the surface layer might readily be associated with patterning damage, seen in experiment; however, when all evidence of physical damage is removed from the BaTiO3 surfaces by thermal annealing, the domain configuration remains practically unchanged. This suggests a more intrinsic origin, such as the increased importance of surface tension at small dimensions. The effect of surface tension is also shown to be proportional to the difference in hardness between the surface and the interior of the ferroelectric. The present model for surface-tension induced twinning should also be relevant for finely grained or core-shell structured ceramics.

Effect of wall thickness on the ferroelastic domain size of BaTiO3

Extremely regular self-organized patterns of 90^o ferroelastic domains have been reported in freestanding single crystal thin films of ferroelectric BaTiO₃. Lukyanchuk et al. [Phys Rev B 79, 144111 (2009)] have recently shown that the domain size as a function of thickness for such free standing films can be well described assuming that the domains are due to stress caused by a surface tension layer that does not undergo the paraelectric–ferroelectric transition. From the starting point of Lukyanchuk’s model, it is shown here that the ‘‘universal’’relationship between domain size and domain wall thickness previously observed in ferroelectrics, ferromagnets and multiferroics is also valid for ferroelastic domains.Further analysis of experimental data also shows that the domain wall thickness can vary considerably (an order of magnitude) from sample to sample even for the same material (BaTiO₃), in spite of which the domain size scaling model is still valid, provided that the correct,sample dependent, domain wall thickness is used.

Design and measurement of reconfigurable millileter wave reflectarray cells with nematic liquid crystal

Numerical simulations are used to study the electromagnetic scattering from phase agile microstrip reflectarray cells which exploit the voltage controlled dielectric anisotropy property of nematic state liquid crystals (LC). In the computer model two arrays of equal size elements constructed on a 15?m thick tuneable LC layer were designed to operate at centre frequencies of 102 GHz and 130 GHz. Micromachining processes based on the metallization of quartz/silicon wafers and an industry compatible LCD packaging technique were employed to fabricate the grounded periodic structures. The loss and phase of the reflected signals were measured using a quasi-optical test bench with the reflectarray cells inserted at the beam waist of the imaged Gaussian beam, thus eliminating some of the major problems associated with traditional free-space characterisation at these frequencies. By applying a low frequency AC bias voltage of 10 V, a 165o phase shift with a loss 4.5 dB-6.4 dB at 102 GHz and 130o phase shift with a loss variation between 4.3 dB – 7 dB at 130 GHz was obtained. The experimental results are shown to be in close agreement with the computer model.