Advanced Materials Research Vols. 306-307

Abstract: The effect of AlN buffer layer on the quality of GaN epilayer grown on Si substrate by metalorganic chemical vapor deposition (MOCVD) has been investigated. It was found that the quality of GaN epilayer strongly related with the crystal quality of AlN buffer layer. As the full width at half maximum (FWHM) of AlN (0 0 2) plane increased from 1.23 degree to 3.41 degree, the FWHM of GaN (0 0 2) plane varied from 432 arcsec to 936 arcsec and the FWHM of GaN (1 0 2) plane varied from 677 arcsec to 1226 arcsec. Besides, more cracks formed and threading dislocation (TD) density increased. The deteriorated AlN buffer layer also led to a rougher morphology of the GaN layer, as can be seen from the root mean square (RMS) roughness of GaN layer which varied from 0.178 nm to 0.476 nm. And the morphology of AlN and the quality of GaN epilayer are not appear to be relevant due to the ruleless values of RMS roughness of AlN.

Abstract: Two novel silicon-centered benzimidazole derivatives, Bis(4-(benzimidazol-1-yl)phenyl) dimethylsilane (1) and Bis(3-(benzimidazol-1-yl)phenyl)dimethylsilane (2) have been synthesized and determined by IR, ¹H NMR, ¹³C NMR and mass spectroscopy. These compounds have high thermal stability and are fluorescent with emission in the region of violet to blue, which could be potentially applied as blue emitters in organic light-emitting diodes (OLEDs) display.

Abstract: LaPO₄:Eu³⁺ nanoparticles were prepared by the hydrothermal synthesis method at different temperatures. The phase composition and microstructure of nanoparticles were characterized by XRD (X-ray diffraction) and SEM (Scanning electron microscopy), respectively. The results reveal that the phase composition of the powders is dependent on the water bath temperature but the microstructure has little effect. The doped powders can be well crystallized at 120°C with the hexagonal monazite-type structure of the LaPO₄ phase. The monoclinic structure of LaPO₄ phase generated as the temperature increases. The sample has pure monoclinic structure of LaPO₄ phase when the temperature increased to 200°C. It has been shown that all the nanocrystals obtained at different temperatures present a long rod-like shape. The analysis of the fluorescence spectra shows that the luminous intensity of the monoclinic structure of LaPO₄:Eu³⁺ is stronger than the hexagonal structure.

Abstract: A series of main-chain polyimides containing azo aryl with different substituted groups have been synthesized by a condensation of corresponding N,N-dichloroethylaminoaryl azo compounds with 4,4’-(hexafluoroisopropylidene) diphthalic bis-imide in an alkaline DMF solution, which have high thermal stability and good solubility in organic solvents. The third-order NLO measurements made with Z-scan technique at 532 nm indicate that the polyimides containing p-nitrophenylazo and nitrobenzothiazole azo group (P2 and P3) have larger third-order nonlinear absorption coefficient (ß) and the nonlinear refractive coefficient (n₂).

Abstract: Semi-interpenetrating polymer network of coal/polyaniline (PANI) composite material were prepared by in situ polymerization. Raw coal was oxidized in different conditions by H₂O₂ and HNO₃, respectively. The total acidic groups analysis, Fourier transform infrared (FTIR) spectrum, and conductivity test of the raw coal and the oxidized coal/PANI composite material were conducted. The results showed that the increases of the carboxyl groups and the hydroxyl groups were mainly attributed to the hydrolysis of the weak ether link and the transform from the carboxylate to carboxylic acid. These increases were benefit to the reaction of coal and PANI, and consequently enhanced the conductivity of the composite material. The maximum conductivity of oxidized coal/PANI reached 4.72×10^‑1 S/cm.

Abstract: A new Eu(III) complex Eu(phen)(DMF)₂(NO₃)₃ (1) containing phenanthroline (phen) and DMF (N,N-dimethylformamide) as ligands has been synthesized and characterized by IR and single-crystal X-ray diffraction. The photoluminescence property of 1 is investigated to show the characteristic emission of the Eu(III) ion.

Abstract: A new ligand, 1,1'-(pyridin-2,6-diyl)bis-3-p-tolylpropane-1,3-dione(H₂L), was prepared and its crystal structure displays its enol isomer. The binary complex, Ln₂L₃·4H₂O [Ln = Eu(III) and Tb(III)], were synthesized by the reaction of synthesized ligand (H₂L) and Ln(III). With 1,10-phenanthroline (Phen) as the synergistic ligand, the ternary complex, Ln₂L₃(Phen)₂ [Ln = Eu(III) and Tb(III)], were synthesized. The compounds were characterized by ¹H-NMR spectroscopy, MS, IR, UV, DTA-TG and fluorescence spectrum. The luminescent properties of the ligand and its complexes were investigated and the results showed that the prepared ligand was a good luminescent compound, all complexes emitted characteristic luminescence of corresponding lanthanide ions and 1,10-phenanthroline as the synergistic ligand can obviously enhance the luminescence of Eu(III) in the ternary complex.

Abstract: The facile processes were developed for synthesizing vanadium dioxide (VO₂) by pyrolyzing ammonium metavanadate (NH₄VO₃) in nitrogen (N₂) flow and by thermal reduction of vanadium pentoxide (V₂O₅) in ammonia gas. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were applied to analyzing the product VO₂. The experimental results indicated that VO₂ microcrystal particles were successfully synthesized from both NH₄VO₃ and V₂O₅. From NH₄VO₃ the product VO₂ presents two kinds of micro morphologies, torispherical and pentagonal prism. The phase transition mainly takes place at 337.8K and 341.8K. The average enthalpy of phase transition is 28.82 J/g. From V₂O₅ the product VO₂ presents rhombohedral. The phase transition temperature is approximately 342.6K and the enthalpy of phase transition is 44.90 J/g.

Abstract: Borates, phosphates, aluminates, silicates or sulphides are usually used as host lattices for display phosphors. These phosphors reacted similarly under electron bombardment. Nano and micron phosphors normally lose brightness upon bombardment with electron, ion or photon beams. A combination of techniques such as XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) and CL (cathodoluminescence) spectroscopy were used to show that the main reason for the degradation in luminescent intensity, of the different phosphors, under electron bombardment is the formation of a non-luminescent layer on the surface due to an electron stimulated surface chemical reaction (ESSCR). The decrease in luminance was found to be the result of the growing of a “dead layer” on the surface. In some cases, however, a thermodynamically stable layer formed on the surface as a result of the electron stimulated surface chemical reactions lead to CL stability of the phosphor. The formation of an altered layer (oxide layer) on the surface of the different phosphors leads to a decrease in the luminescent intensity at that specific wavelength and in some cases to an increase of the intensity at another wavelength.

Abstract: A new organometallic palladium coordinated liquid crystal that was written by PdS6 had been synthesized by chelating reaction of the tetrachloropalladate (PdCl₄^2-) and the star-like liquid crystal (S6) containing four hexyloxyazobenzene mesogens in its periphery. The structure and liquid crystallinity (LC) of PdS6 were characterized by infrared absorption spectroscopy (IR), ultraviolet absorption spectra (UV), nuclear magnetic resonance spectroscopy (NMR), elemental analysis (EA), polarizing optical microscope (POM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The phase behavior of PdS6 was Cr155N230I205N160Cr, its melting point and clearing temperature were higher than those of the free azo ligand S6, its mesophase range wass broader than S6’s. It will be used as a new type photoelectric functional material in the future.