Sağlam, Hilal Kübra; İskenderoğlu, Demet; Güldüren, Muhammed Emin; Güney, Harun; Şahin, Burak; Ertuğrul, Mehmet

Unspoiled and copper (Cu) doped magnesium oxide (MgO) thin films were successfully grown via ultrasonic spray pyrolysis method on soda lime glass substrates. Aftermath of the varied impurity presence in the host material were examined by conducting scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), photoluminescence (PL) spectroscopy, ultraviolet–visible (UV) spectroscopy, and photocatalytic measurements. The structural observations unveiled that the grown films showed (101) plane orientations with no secondary phases such as Cu or copper oxide present. Also, the XRD data discovered that the grain size of pure MgO sample decreased owing to the fact that Cu impurities introduced into the host material lattice system. In addition to that, the SEM images revealed that the impurity addition into the MgO nanocrystallites switched molecular shapes from regular to spherical structures. Besides, the aimed elemental compositions in the synthesized thin films were verified by the XPS. Furthermore, the photocatalytic measurements uncovered that the right amount of the magnesium content in the host material can enhance and tune the photocatalytic performance of the MgO films as desired. In the optical measurements, it was observed that optical absorbance values increased in the presence of varied percentages although these increments followed a random trend in respect to the doping levels (0.5%, 1%, 2%, 4% and 8 wt.%). The PL spectra revealed that the intensity of luminescent emissions gradually decreased which can be ascribed to the imperfections as a result of the introduced Cu into MgO.

Güney, Harun; İskenderoğlu, Demet; Güldüren, Muhammed Emin; Karadeniz, Sibel Morkoç

Herein, we report on synthesizing pure and aluminum (Al) doped cadmium oxide (CdO) thin films onto glass slides by successive ionic layer adsorption and reaction (SILAR) method. The optical, electrical, structural, and morphological evaluations were conducted for the produced samples after the grown thin films heat treated in a convection ashing furnace at 200 °C. X-ray diffraction (XRD) results disclosed that the prepared samples posses the polycrystalline cubic phase of CdO material and the (1 1 1) plane was the preferred growth orientation. Besides, the XRD analysis strongly suggested that the integration of aluminum into the CdO lattices completed as no other phases, such as Cd, Al, or related oxides, were present in the diffraction patterns. From the field emission scanning electron microscope (FE-SEM) images, it was noticed that Al doping concentration changed the surface morphologies. Energy dispersive X-ray analysis (EDAX) confidently proves the presence of Al as a result of the SILAR process. The optical properties were assessed by performing Ultraviolet–visible spectroscopy (Uv–vis), and it was observed that the optical bandgap increased from 2.5 eV to 3 eV due to the increased percentages of Al content in the Al:CdO nanostructures. The Photoluminescence (PL) spectrum evidently showed that the PL emission intensity of prepared samples was directly influenced over varying Al content in the CdO nanostructures. The electrical features of the SILAR derived CdO thin films uncovered that the resistivity of samples showed increment with the Al doping, thus the electrical conductivity of the grown samples decreased in return.

Güney, Harun; İskenderoğlu, Demet; Güldüren, Muhammed Emin; Demi̇r, Kübra Çınar; Karadeniz, Sibel Morkoç

Copper oxide (CuO) thin films were grown on glass substrates by performing ultrasonic spray pyrolysis (USP) method at different substrate temperatures (300 °C, 400 °C, 450 °C, and 500 °C). The prepared CuO thin films were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX), UV–visible spectroscopy, and photoluminescence (PL) spectroscopy measurements in order to assess the effects changed substrate temperature on structural, morphological, and optical properties of the grown materials. Also, the suitability of the grown films as electrodes in supercapacitor applications was investigated with respect to variable substrate temperatures. The XRD patterns revealed that the samples were polycrystalline in nature exhibiting tenorite phase of CuO structure preferential orientation along (11 1‾) plane and the corresponding crystallite size ranged from 28.14 nm to 67.98 nm. The SEM images displayed morphological modifications in the prepared CuO thin films as the substrate temperatures incresed. The XPS and EDX analyses confirmed the successful deposition of aimed materials on the fabricated thin films. It was also obtained that optical absorbance decreased due to the increased substrate temperatures and optical energy bandgaps changed between 1.53 eV and 1.71 eV as the substrate temperatures varied. The electrochemical supercapacitive features of the CuO nanostructures thin films were studied with the help of cyclic voltammetry (CV), galvostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS).

Pepe, Yasemin; Yildirim, Mehmet Ali; Karatay, Ahmet; Ates, Aytunc; Unver, Huseyin; Elmali, Ayhan

The effects of annealing and Al dopant on the nonlinear absorption characteristics of amorphous ZnO thin films were studied experimentally and theoretically. The structural patterns of AZO thin films grown at various growth temperatures (80ᵒC, 90ᵒC, 100ᵒC) and Al doping ratios (%5, %10, %20) were determined by using x-ray diffraction. The results revealed that the crystallinity increased with increasing growth temperature and Al doping ratio. The optical band gap decreased from 3.91 to 3.78 eV and the transmittance of AZO thin films decreased from 90% to 55% with increasing Al molar ratio. The open aperture Gaussian beam Z-scan measurements indicated that all studied films exhibited nonlinear absorption behavior due to the defect states inside energy bandgap. The nonlinear absorption coefficients increased from 1.34 × 10−4 to 6.12 × 10−4 cm/W for 4 ns pulse duration with increasing of doping concentration. The experimental curves were fitted to the theory of open aperture Gaussian beam Z-scan based on the Adomian decomposition method to obtain nonlinear absorption coefficients along with saturation intensity thresholds. In order to investigate the effect of free carrier absorption, the OA Z-scan experiments were also performed for 65 ps pulse duration. The nonlinear absorption coefficients were found to be 0.58 × 10−4, 1.81 × 10−4 and 3.29 × 10−4 cm/W for 65 ps pulse duration. For nanosecond pulse durations, the obtained nonlinear absorption coefficient values of thin films are bigger than the values of picosecond pulse durations due to the greater contribution of free carrier absorption. Increasing annealing temperature from 100ᵒC to 400ᵒC leads to decreasing nonlinear absorption coefficients owing to decreasing localized defect states.