Rapid synthesis of hexagon-shaped gold nanoplates by microwave assistant method

The microwave (MW)-based thermal process was applied to the preparation of hexagon-shaped gold nanoplates. The fort-nation of gold nanoplates occurs rapidly in a single step, carried out by directly heating a reaction mixture of HAuCl4 with sodium citrate in an MW reactor. And the gold nanoplates were characterized by UV-visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experimental results indicated that the sizes and morphologies of the gold nanomaterials strongly depend both on the heating methods and molar ratio of HAuCl4 to sodium citrate in the initial reaction mixture. At the molar ratio 5 : 4 (HAuCl4 to sodium citrate), hexagonal nanoplates with large Au (111) crystallographic facet were preferentially synthesized by the MW assistant method.

A method to collect an infrared spectrum in solution

Herein we report a new method to collect a qualified infrared spectrum of a solute in solution by two solvent cells with different thickness during background single-beam spectrum scanning. By collecting the background spectrum with two cells (two stages), we successfully achieved accurate solvent compensation between a sample and a reference, namely, the solvent amounts in the sample and background measurements could become congruent. Therefore, the solvent bands were thoroughly suppressed in the infrared spectrum and a qualified spectrum of the solute was obtained.

Morphology of head-to-tail poly(3-hexylthiophene) single crystals from solution crystallization

Single crystals of head-to-tail poly(3-hexylthiophene)s have been grown through the method of isothermal solution crystallization. Electron diffraction in combination with powder X-ray diffraction revealed the crystal structure, a = 1.52 nm, b = 3.36 nm, c = 1.56 nm and alpha = beta = gamma = 90 degrees.

Single molecule dynamics and statistical fluctuations of gene regulatory networks: A repressilator

The authors developed a time dependent method to study the single molecule dynamics of a simple gene regulatory network: a repressilator with three genes mutually repressing each other. They quantitatively characterize the time evolution dynamics of the repressilator. Furthermore, they study purely dynamical issues such as statistical fluctuations and noise evolution. They illustrated some important features of the biological network such as monostability, spirals, and limit cycle oscillation. Explicit time dependent Fano factors which describe noise evolution and show statistical fluctuations out of equilibrium can be significant and far from the Poisson distribution. They explore the phase space and the interrelationships among fluctuations, order, amplitude, and period of oscillations of the repressilators. The authors found that repressilators follow ordered limit cycle orbits and are more likely to appear in the lower fluctuating regions. The amplitude of the repressilators increases as the suppressing of the genes decreases and production of proteins increases. The oscillation period of the repressilators decreases as the suppressing of the genes decreases and production of proteins increases.

The magnetic and structural properties of hydrothermal-synthesized single-crystal Sn1-xFexO2 nanograins

The crystal structure and magnetic properties of Sn1-xFexO2 nanograins synthesized by simple hydrothermal method using SnCl4 center dot 5H(2)O and FeCl3 center dot 6H(2)O as raw materials are studied. No secondary phase was found in the XRD spectrum. The linear change of lattice volume for different Fe content strongly supports that the Fe3+ substitutes Sn4+ in SnO2 lattice. A Raman and IR spectra study indicated that the Fe incorporates into the SnO2 lattice. Both ferromagnetic and paramagnetic signals are detected in the Mossbauer spectra. The Sn1-xFexO2 (x <= 0.10) samples show room-temperature ferromagnetism (RTFM) and the saturation magnetization increased with increasing Fe percent. Fe ions present three kinds of magnetic behaviors including paramagnetic, ferromagnetic, and antiferromagnetic in the samples observed by investigation of the M-H and M-T curves. The weak RTFM was due to only a fraction of Fe ions contributing to magnetic-order coupling mediated by oxygen vacancy.

Facile sonochemical synthesis of single-crystalline europium fluorine with novel nanostructure

A single-crystalline EuF3 nanoflower with a novel three-dimensional (3D) nanostructure has been successfully synthesized via a facile, fast, efficient, and mild ultrasonic irradiation solution route employing the reaction of Eu(NO3)(3) and KBF4 under ambient conditions without any template or surfactant. The ultrasonic irradiation plays an important role and is necessary for the synthesis of EuF3 with the complex structure. The formation mechanism of this complex nanostructure is proposed in this paper. No template or surfactant is used in this method, which avoids the subsequent complicated workup for the removal of the template or surfactant. Furthermore, a substantial reduction in the reaction time as well as the reaction temperature is observed compared with the hydrothermal process.

Preparation of Ni0.65Zn0.35Cu0.1Fe1.9O4/SiO2 nanocomposites by sol-gel method

(Ni0.65Zn035Cu0.1Fe1.904)-Cu-./SiO2 natiocomposites were fabricated by the sol-gel method using tetraethylorthosilicate as a precursor of silica, and metal nitrates as precursors of NiZnCu ferrite. With infrared spectra, X-ray diffraction, transmission electron microscope, Raman spectra, Mossbauer spectroscopy and vibrating sample magnetometer measurements, the formation of single phase nanocrystalline NiZnCu ferrites dispersed in silica matrix is confirmed when the sample is annealed at 550degreesC. The transition from the paramagnetic to the ferromagnetic state is observed as the annealing temperature increases from 750degreesC to 1150degreesC. The magnetic properties of these nanocomposites are clearly size dependent. The saturation magnetization increases with the annealing temperature.

Morphology and structure of poly(di-n-butylsilane) single crystals prepared by controlling kinetic process of solvent evaporation

The silicon backbone conformation in poly(di-n-butylsilane) (PDBS) has been shown to be a 7/3 helix at ambient conditions, which is in marked contrast to the near-planar conformation of its homologous polymers with side chain lengths of one to three or six to eight carbon atoms. In this work, both the 7/3 helical and near-planar chain conformations are achieved by controlling the solvent evaporation rate around room temperature. The chain conformation and crystal structure obtained in this method have been correlated to the crystal morphology by wide-angle X-ray diffraction, transmission electron microscopy, electron diffraction, optical microscopy, atomic force microscopy, and UV absorption spectrum. The lath-shaped single crystals obtained at 12 degreesC correspond to an orthorhombic form with near-planar chain conformation whereas the lozenge-shaped single crystals obtained at 30 degreesC (in coexistence with the lath-shaped crystals) are orthohexagonal with a 7/3 helix.

Morphology-controllable synthesis and characterization of single-crystal molybdenum trioxide

Molybdenum trioxide nanobelts and prism-like particles with good crystallinity and high surface areas have been prepared by a facile hydrothermal method, and the morphology could be controlled by using different inorganic salts, such as KNO3, Ca(NO3)(2), La(NO3)(3), etc. The possible growth mechanism of molybdenum trioxide prism-like particles is discussed on the basis of the presence of HI and the modification of metal cations. The as-prepared nanomaterials are characterized by means of powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and ultraviolet and visible spectroscopy (UV-vis). TEM and HRTEM micrographs show that the molybdenum trioxide nanobelts and prism-like particles have a relatively high degree of crystallinity and uniformity. BET specific surface areas of the as-prepared molybdenum trioxide nanocrystals are 67-79 m(2)g(-1). XPS analysis indicates that the hexavalent molybdenum is predominant in the nanocrystals. UV-vis spectra reveal that the direct band gap energy of the annealed molybdenum trioxide prism-like particles shows a pronounced blue shift compared to that of bulk MoO3 powder.

An one-pot epitaxial growth method to synthesize cactus-like ZnO

In this work, we have developed a one-pot, morphology controlled epitaxial growth method to synthesize novel cactus-like ZnO in solution. Utilizing zinc acetate and hexamethylenetetramine as the precursors, ZnO nanorods synthesized in the first step remained in the solution, without any separation, served directly as the matrix for the epitaxial growth in the second step. Control experiments revealed that a proper mass of precursors added in the second step was crucial to form cactus-like ZnO. The as-synthesized ZnO was single crystalline and possessed three photoluminescence emissions centered at 390, 425 and 490 run. Finally, a possible mechanism for the epitaxial growth ZnO was proposed and discussed.

Growth and vibrational spectra of doped KMgF3 single crystal

The different ions doped KMgF3 single crystals are prepared by the vertical Bridgman method. The near-infrared absorption spectra for different parts of all as-growth crystals indicate that there is the best transparency in middle part. The correlation between the vibronic frequencies of Eu2+ and the site displacement of Cu+ co-doped ions is firstly studied, which indicates that Cu+ ions replace the site of the Mg2+ ions. The co-doped Eu2+ counteracts the charge misfit causing by the replacement of Mg2+ with Cu+. The overlapping of the emission spectra of the Eu2+ and the excitation spectra of the Cu+ results in the energy transfer from Eu2+ to Cu+.

Study of color centers and trace oxygen in KMgF3 : Eu single crystal

Using the Bridgeman-Stockbarger method, the KMgF3:EU2+ single crystal was grown. The color centers in unirradiated KMgF3:Eu crystal were studied. By thermal annealing, we confirmed the 422-nm emission resulted from color centers and oxygen centers, and we proved the energy transfer from EU2+ to color centers. From spectra, the relative oxygen content in crystal was calculated, and the relationships of oxygen displacing fluorine were studied.

Investigating mechanical response of single chain polystyrene particles by scanning probe techniques

Single chain polystyrene particles were obtained by dilute solution casting method. The sample with both single chain polystyrene particles and multi-chain (more than 1000 molecular chains) polystyrene particles was obtained by a little more concentrate solution. Force modulation technique showed that single chain polystyrene particles were softer than multichain polystyrene particles. On the other hand, nanoindentation experiments on multi-chain particles and bulk polystyrene manifested that the elastic modulus of multi-chain polystyrene particles was very close to that of bulk polystyrene. Therefore, it was concluded that single chain polystyrene particles were softer than bulk polystyrene,which indicated that the density of intrachain entanglement points in the single chain polystyrene particles was not as large as that of the interchain entanglement points in the bulk state.

Estimation of individual phases from the four-phase structure invariants in the single isomorphous replacement case

The probability distribution of the four-phase invariants in the case of single isomorphous replacement has been developed to estimate some individual phases. An example of its application to obtain the phases having special values of 0, pi or +/-pi /2 is given for a known protein structure in space group P2(1)2(1)2(1). The phasing procedure includes the determination of starting phases and an iterative calculation. The initial values of starting phases, which are required by the formula, can be obtained from the estimate of one-phase seminvariants and by specifying the origin and enantiomorph. In addition, the calculations lead to two sets of possible phases for each type of reflection by assigning arbitrarily an initial phase value. The present method provides a possibility for the multisolution technique to increase greatly the number of known phases while keeping the number of the trials quite small.

High resolution electron microscopy study of single chain single crystals of gutta percha

Single chain single crystals (SCSC) of gutta percha (GP) were prepared by a dilute-solution spraying method. Electron diffraction (ED) patterns revealed that the single chain single crystal was of a new crystalline modification, the delta form. The images of SCSC of GP obtained with a high resolution electron microscope (HREM) showed a two dimensional periodic structure. Most of the images consisted of lattice fringes derived from the (001) zone. This is the first time that the single chain single crystal images of GP have been observed at a molecular level. Micrographs were image processed using optical filtering methods to improve the signal-to-noise ratio, and were compared with computer-generated simulations of the images. From the viewpoint of the defects seen in high resolution images, the crystal formation and melting processes are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.