Yuxia Wang

Investigation on the origin of the blue emission in titanium doped sapphire: Is F+ color center the blue emission center?

Titanium doped sapphire (Ti:Al2O3) shows a 420 nm blue emission band whose corresponding excitation band lies at 244 nm. With the aim of ascertaining the origin of this blue emission, using synchrotron radiation we measured the vacuum ultraviolet to ultraviolet absorption spectrum of titanium doped sapphire. It is suggested that the blue emission is due to a center other than a trivalent Ti3+ ion or a tetravalent Ti4+ ion, most probably an F+‐type color center formed in the crystal.

Ionic conductivity of nano-scale γ-AgI

Abstract Nano-scale γ-AgI with grain sizes of 7–9xa0nm was synthesized by quenching molten AgI in liquid nitrogen (LN). The temperature dependence of ionic conductivity of nano-scale γ-AgI was studied by complex impedance measurement. Linear fit for the log σT vs. 1/T curve revealed that the curve was composed of three segments with different slopes, with two kinks at about 147°C and 223°C. The activation energies for the three segments were calculated to be 0.40, 1.61, and 0.12xa0eV, respectively. The curve reveals a continuous transition between 147°C and 223°C instead of a break at 147°C that occurring in normal AgI, indicating a change from first-order phase transition to a second-order one after AgI was quenched in LN. The room temperature (RT) conductivity of nano-AgI is about two orders of magnitude larger than that of normal AgI. We suggest that the ionic conduction of nano-AgI within temperature ranges of RT to 147°C, 147–223°C, and above 223°C are controlled by grain boundaries and dislocations induced by quenching, formation and diffusion of Frenkel defects inside the grains, and transport of quasi-liquid silver ion, respectively. The second-order phase transition is attributed to lattice deformation and formation of Frenkel defects.

The preparation of single-crystal 4H-SiC film by pulsed XeCl laser deposition

By ablating ceramic SiC target with pulsed XeCl laser, SiC films were prepared on Si(100) substrate at temperature 850°C, and post-deposition annealing at high temperature above 1100°C (1100°C<T<1400°C) in high vacuum (10−9 Torr). We studied the morphology of the surface, crystal structure, composition and chemical state of the element of the films before and after annealing by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Auger electron spectrum (AES), X-ray photoelectron spectrum (XPS) and photoluminescence (PL) methods. It was obtained from the analysis that the films consisted of polycrystal 4H-SiC structure before annealing and of oriented single-crystal epitaxial 4H-SiC after annealing. The surfaces of the films were smooth and stuck well to the substrate. The films were transparent. Excited by the 290 nm laser at room temperature, the films gave out two emission peaks at 377 and 560 nm. The emission at 377 nm was assigned to the combination of the transmission between the valence band and conductor band, and the other at 560 nm was assigned to the exciton emission.

Origin of the blue photoluminescence from SiO2(SiC)/SiC on Si substrate

SiC film is prepared by heating the polystyrene/Si in 1atm ambient Ar at 1270°C. The as-grown SiC film is characterized by scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Based on the results, it is suggested that a SiO2(SiC) layer is located on the top of the as-grown SiC film. A blue photoluminescence band is observed from the as-grown sample. The photoluminescence band has the same origin as those from silica nanowires and SiC nanostructures and is associated with the near interface traps at the interface of SiO2∕SiC or SiO2∕Si.

Growth of crystalline SiC film free of cavities by heating PS/silica sol-gel coatings on Si (111) substrate

Abstract Single crystalline 6H-SiC films were prepared by spin-coating silica and polystyrene (PS) sol-gel layers subsequently on Si (111) substrate, and then the sample heated in vacuum (10 −3 Pa) to temperature above 1000 °C. The films were investigated by Fourier transform infrared absorption (FTIR), transmission electron diffraction (TED), X-ray diffraction (XRD), and scanning electron microscopy (SEM) measurements. Plan-view SEM observations indicated that the silica layer sandwiched by PS and Si substrate can suppress the interface cavity formation. It was proposed that the silica layer acted as a barrier of out-diffused Si atoms, and took the place of the substrate as the reservoir of Si supply to form SiC during the heat treatment.

Influence of high Sn concentrations on the structure and properties of YBaCuO compounds

Abstract Mossbauer measurements of YBa2Cu3−xSnxO7−y compounds with high Sn concentrations have revealed that the Sn dopants all exist as Sn4+, with their majority occupying Ba,Y,Cu(2) sites, and only a small part in Cu(1) sites. The amount of Sn in each site varies with Sn content (x). As for superconductivity, the sample systems are all with Tc above 77k. this indicates that the substitutions for the metal ions in Cu(2) and Y sites have little effect on Tc, which strongly supports the concept that Cuue5f8O chain doesnt predominate the superconductivity.

Studies on SiC film deposited by pulsed XeCl excimer laser sputtering method

Abstract Thin films of SiC were grown by pulsed excimer laser deposition (PLD). The quality and structure of the films were examined by AES, XPS, TEM, SEM, XRD and IR. The deposited films were dense and uniform and stuck tightly to the substrates. The compositions of the films were quite uniform and the ratio of silicon to carbon atomic in the films was nearly 1:1, with slight excess carbon. The films contained less than 10% oxide contamination. The basic stage of the chemical valence in the films was the Siue5f8C covalent bond. The valence electrons density in the films was 94.4% of that in single crystal SiC. The structure of the films was the polycrystalline nHue5f8SiC ( n = 4, 6 or both) hexagonal system.

The effects of annealing disposition on α-SiC thin films prepared by pulsed laser deposition

Abstract SiC thin films have been grown in situ on Si[100] substrates using a XeCl excimer laser (λ = 308 nm). The films were deposited at different temperatures, from room temperature to 900 °C. The structure of the films was studied using modern analysis techniques, such as AES, XPS, TEM, STM, and IR. Polycrystalline α-SiC thin films grown on Si[100] substrates were obtained at 800 °C. The thin films were annealed at 1000 °C in a vacuum system. The effect of annealing disposition on the structure of the film was studied. TEM analysis shows that the annealed film has a hexagonal structure which includes 4H, 8H Or 4H + 8H.

Mesoporous hollow Zn{sub 2}SiO{sub 4}:Mn{sup 2+} nanospheres: The study of photoluminescence and adsorption properties

Graphical abstract: Mesoporous hollow structure of Zn{sub 2}SiO{sub 4}:Mn{sup 2+} phosphors. - Highlights: • Mesoporous hollow Zn{sub 2}SiO{sub 4}:Mn{sup 2+} nanospheres are prepared via the layer-by-layer technique. • The Zn{sub 2}SiO{sub 4}:Mn{sup 2+} nanospheres exhibit better adsorption capabilities of Pb{sup 2+}, Fe{sup 3+} than Cd{sup 2+}. • The Zn{sub 2}SiO{sub 4}:Mn{sup 2+} nanospheres exhibit strong green emission around 524 nm. • With the increase of doped Mn{sup 2+} concentration, the emission peak shows a red-shift. - Abstract: Mesoporous hollow Zn{sub 2}SiO{sub 4}:Mn{sup 2+} nanospheres were prepared via the layer-by-layer technique using CTAB as surfactant. The structures/microstructures and morphologies of the as-synthesized phosphors were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and N{sub 2} adsorption–desorption porosimetry. The adsorption capacity to remove toxic metal ions in water was tested and the results showed that the Zn{sub 2}SiO{sub 4}:Mn{sup 2+} nanospheres exhibited better adsorption capabilities of Pb{sup 2+}, Fe{sup 3+} than Cd{sup 2+}. Moreover, the as-obtained hollow Zn{sub 2}SiO{sub 4}:Mn{sup 2+} phosphors exhibited strong green emission around 524 nm at room temperature. When the atomic ratio of Zn to Mn was 97:3, the emission intensity of Zn{sub 2}SiO{sub 4}:Mn{sup 2+} phosphor was about 1.2 times that of commercial phosphors. Furthermore,morexa0» with the increase of doped Mn{sup 2+} concentration, the emission peak showed a red-shift.«xa0less

Growth Kinetics of Silicon Carbide Film Prepared by Heating Polystyrene/Si(111)

SiC films were prepared by heating polystyrene/Si(111) in normal pressure argon atmosphere at different temperatures. The films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared absorption measurements. The thicknesses of SiC films were calculated from FTIR spectra. The growth kinetics of the growth process of SiC films were investigated as well. The thicknesses of the SiC films grown for 1 h with increasing growth temperatures have different trends in the three temperature ranges: increasing slowly (1200–1250 °C), increasing quickly (1250–1270 °C), and decreasing (1270–1300 °C). The apparent activation energies of the growth process of SiC films in the three ranges were calculated to be 122.5, 522.5, and −127.5 J/mol respectively. Mechanisms of the different growth processes were discussed. The relation between film thicknesses and growth temperatures indicated that the growth process was a 2D mechanism in the first range and 3D mechanism in the second range. In the third range, the thicknesses of SiC films were decreased by the volatility of Si and C atoms.