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    A study of the electronic and physical properties of SnO2 thin films as a function of substrate temperature
    (Elsevier Sci Ltd, 2019) Erken, O.; Ozkendir, O. M.; Gunes, M.; Harputlu, E.; Ulutas, C.; Gumus, C.
    In this work, tin dioxide (SnO2) thin films were prepared at various substrate temperatures (380-440 degrees C, in steps of 20 degrees C) on glass substrates by the Spray Pyrolysis Method. X-ray Diffraction (XRD) measurements revealed that the SnO2 thin films were formed in a tetragonal crystallized structure. The electronic structure of the tin dioxide thin films that were prepared at several substrate temperatures were investigated with the collected X-ray Absorption Spectroscopy (XAS) data. The crystal structure analysis was also supported by the Extended X-ray Absorption Fine Structure (EXAFS) data analysis extracted from the X-ray Absorption Fine Structure (XAFS) data. Unstable crystal behaviors were detected in the samples due to metastable SnO structure formations as a result of phase transitions from the SnO to SnO2 structure during the annealing processes. Clear information on the atomic displacements in the samples as a picture of the crystal mechanism was obtained from the analysis of EXAFS data. The SnO2 thin films were found to exhibit high transmittance (average 90%) in the 400-1100 nm interval. The thickness of the SnO2 thin film (t) and refractive index (n) were calculated from transmittance spectra in the visible region using envelope method. The direct energy band gaps of the films obtained were 4.01-4.09 eV. Atomic force microscope (AFM) measurements were performed in order to investigate the surface roughness of the SnO2 thin films.
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    Öğe
    Investigation on the electronic and physical properties of gamma-MnS films as a function of thickness
    (Elsevier Sci Ltd, 2022) Ulutas, C.; Erken, O.; Gunes, M.; Ozkendir, O. M.; Gumus, C.
    In this study, gamma-manganese sulphide (gamma-MnS) films were prepared at various thickness and deposition time at a temperature of 50 degrees C by Chemical Bath Deposition Method (CBD). The characterization of the gamma-MnS films were determined by using the following methods; X-ray Absorption Fine Structure Spectroscopy (XAFS), Xray diffraction (XRD), optical absorption, Field Emission-Scanning Electron Microscope (FE-SEM), Energy Dispersive X-ray analysis (EDX). The electronic interplay via the coupling between Mn 3d levels and S 2p levels was determined to build up strong molecular bonds containing broad band with hybrid pd levels at low energy levels. The results of the electronic structure analysis were also tested with the absorption spectroscopy calculations and high agreement is reported. XRD analysis revealed that the film deposited for 5 h had amorphous structure and turned to be crystal structure in hexagonal phase with deposition time 10, 15, 20 h due to increasing film thickness value. The optical band gap values were reduced from 3.86 eV to 3.10 eV with increasing film thickness. The average refractive index value of films at visible region were calculated between 1.55 and 2.81 as a function of increment in film thickness. The mobility and resistivity of the films were measured as 8.65-55.76 cm2/Vs and 3.10 x 105-2.39 x 106 omega cm, respectively, by Hall measurement.