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Abstract: Single-phase β-FeSi2 thin films have been grown on quartz substrates using femtosecond laser deposition (800nm, 50fs, 1KHz) under gas pressure of 3.0×10−4 Pa. X-ray diffraction (XRD) and field-emission scanning electron microscopy (SEM) were used to determine the structural properties and surface images of the films. Typical XRD patterns of the film showed that no other diffraction peak except β-FeSi2 was found. The SEM results indicated that the films were composed of well-distributed grains, in the range 50–150nm in diameter. In addition, normal incidence spectral transmittance and reflectance data suggested that the β-FeSi2 film has a direct energy gap of about 0.85eV. The thickness of the layer and the refractive index of the film were determined by performed calculation in the wavelength range 1.9–2.7μm. Furthermore, the Raman spectra of the films were also discussed. [Copyright &y& Elsevier]

The elastic properties and thermal expansion behavior of lead-free halide double perovskite, Cs 2 AgBiBr 6 , were studied first with the aid of first principles calculations, which were followed by experimental characterization. The calculated full elastic constants enable the complete mapping of Young’s and shear moduli, and Poisson’s ratios of Cs 2 AgBiBr 6 along all crystallographic orientations. Results show that significant anisotropy in them despite the fact that Cs 2 AgBiBr 6 possesses cubic symmetry. Detailed structural analysis and a spring model were utilized to rationalize the observed anisotropy. Further, the theoretical results were validated by recourse to nanoindentation and high-pressure synchrotron powder X-ray diffraction experiments. The superior mechanical behavior of Cs 2 AgBiBr 6 over the hybrid bromide analogues, MAPbBr 3 (MA = CH 3 NH 3 + ), were attributed to the higher framework stiffness of the former, which is a result of the presence of relatively stronger Ag-Br and Bi-Br bonds in it. Variable temperature single crystal X-ray diffraction reveal linear and volumetric thermal expansion coefficients to be about 20% lower than those of MAPbBr 3 , again suggesting its higher framework rigidity. The superior stiffness, thermal expansion behavior, moisture stability, and nontoxicity of Cs 2 AgBiBr 6 make it a strong candidate for potential applications in optoelectronics and photovoltaics. [ABSTRACT FROM AUTHOR]

The high pressure behaviour of a cubic dense inorganic–organic framework [DABCOH22+][K(ClO4)3] (DABCOH22+ = diazabicyclo[2.2.2]octane-1,4-diium) has been systematically studied via synchrotron X-ray powder diffraction, over the range of 0–3.12 GPa. The framework [DABCOH22+][K(ClO4)3] shows a more rigid response, with a bulk modulus of 30(1) GPa and an axial compressibility of 7.6(4) × 10−3 GPa−1, compared with ZIF-8 and the dense hybrid solar cell perovskite CH3NH3PbI3. Density functional theory calculations reveal that the structural change in [DABCOH22+][K(ClO4)3] is attributed to the contraction of the KO12 polyhedra, which consequently results in the rotation of the perchlorate linkers and synergistic movement of the DABCOH22+ guest. Further extensive theoretical calculations of full elastic tensors give full mapping of the Young's moduli, shear moduli and Poisson's ratios of [DABCOH22+][K(ClO4)3], which are in the range of 31.6–36.6, 12.3–14.6 GPa and 0.2–0.32, respectively. The Young's and shear moduli of [DABCOH22+][K(ClO4)3] are larger than those of cubic MOF-5, ZIF-8 and CH3NH3PbI3. In addition, the narrow range of Poisson's ratios in [DABCOH22+][K(ClO4)3] indicates its very isotropic nature in response to biaxial stress. [ABSTRACT FROM AUTHOR]

Abstract: CuO nanocrystalline thin films are deposited on quartz substrates by pulsed laser deposition. The grown single-phase CuO films are characterized by X-ray diffraction, X-ray photoelectron spectrometer and transmission electron microscopy. The optical nonlinearity of CuO films is investigated by the Z-scan method under a high-repetition-rate (HRR) femtosecond laser (800nm, 50fs, 80MHz). The CuO nanocrystalline films are found to be good optical limiters with a limiting threshold of 0.3GW/cm2 and a damage threshold of 1.65GW/cm2. The possible mechanisms of the optical limiting are also proposed. [Copyright &y& Elsevier]

By controlling the oxygen pressure, single-phase CuO and CuO thin films have been obtained on quartz substrates using a pulsed laser deposition technique. The structure properties and linear optical absorption of the films were characterized by X-ray diffraction and UV-VIS spectroscopy. By performing z-scan measurements using a femtosecond laser (800 nm, 50 fs), the real and imaginary parts of the third-order nonlinear susceptibility, Re χ and Im χ, of the films were determined. Both CuO and CuO films exhibited large optical nonlinearities, which is comparable to those in some representative semiconductor films such as ZnO and GaN films using femtosecond laser excitation. Compared with CuO films, the CuO films showed larger third-order nonlinear optical effects under off-resonance excitation. Furthermore, the mechanisms of the optical nonlinearities in CuO and CuO films are explained in the main text. It was suggested that the reasons of the difference in their nonlinear refractive effects may be related to the different electronic structure in CuO and CuO materials. [ABSTRACT FROM AUTHOR]

Abstract: In this work we investigate the third-order optical nonlinearities in CuO films by Z-scan method using a femtosecond laser (800 nm, 50 fs, 200 Hz). Single-phase CuO thin films have been obtained using pulsed laser deposition technique. The structure properties, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV–vis spectroscopy. The Z-scan results show that laser-deposited CuO films exhibit large nonlinear refractive coefficient, n 2 =−3.96×10−17 m2/W, and nonlinear absorption coefficient, β =−1.69×10−10 m/W, respectively. [Copyright &y& Elsevier]

Abstract: Copper oxide, Cu2O and CuO, thin films have been synthesized on Si (100) substrates using pulsed laser deposition method. The influences of substrate temperature and oxygen pressure on the structural properties of copper oxide films were discussed. The X-ray diffraction results show that the structure of the films changes from Cu2O to CuO phase with the increasing of the oxygen pressure. It is also found that the (200) and (111) preferred Cu2O films can be modified by changing substrate temperature. The formation of Cu2O and CuO films are further identified by Fourier transform infrared spectroscopy. For the Cu2O films, X-ray photoelectron spectroscopic studies indicate the presence of CuO on the surface. In addition, the optical gaps of Cu2O and CuO films have been determined by measuring the transmittance and reflectance spectra. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) thin films have been grown on Si (100) substrates using a femto-second pulsed laser deposition (fsPLD) technique. The effects of substrate temperature and laser energy on the structural, surface morphological and optical properties of the films are discussed. The X-ray diffraction results show that the films are highly c-axis oriented when grown at 80°C and (103)-oriented at 500°C. In the laser energy range of 1.0mJ–2.0mJ, the c-axis orientation increases and the mean grain size decreases for the films deposited at 80°C. The field emission scanning electron microscopy indicates that the films have a typical hexagonal structure. The optical transmissivity results show that the transmittance increases with the increasing substrate temperature. In addition, the photoluminescence spectra excited with 325nm light at room temperature are studied. The structural properties of ZnO films grown using nanosecond (KrF) laser are also discussed. [Copyright &y& Elsevier]

Abstract: Titanium dioxide thin films have been synthesized on Si (100) substrates using pulsed laser deposition method (KrF: 248 nm, 20 ns, 5 Hz). The emission spectra of the plasma induced by ablating TiO2 target in the oxygen or argon ambient gas were analyzed. The influences of substrate temperature and ambient gas pressure on the structural properties of TiO2 films were discussed. The X-ray diffraction results show that the films deposited at 750 °C are (004)-oriented anatase phase and (110)-oriented rutile phase under the oxygen and argon pressure of 5 Pa, respectively. The scanning electron microscopy images indicate that the TiO2 films have a uniform and smooth surface and are composed of nanocrystal grains. The pure anatase and rutile phase TiO2 films are further proved by Raman spectromicroscopy. In addition, the optical transmission spectra and Fourier Transform infrared spectroscopy of the films were also studied. [Copyright &y& Elsevier]