Güney, Harun; İskenderoğlu, Demet; Akdağ, Adem; Karadeni̇z, Sibel Morkoç; Güldüren, Muhammed Emin

Undoped and Cu-doped nickel oxide (Cu:NiO) thin films were deposited on glass substrates by ultrasonic spray pyrolysis using Cu concentrations of 1, 2, 4, and 8 wt%. The influence of Cu incorporation on the structural, morphological, optical, Raman, photoluminescence, and temperature-dependent electrical properties of the films was systematically investigated. X-ray diffraction analysis confirmed the formation of polycrystalline cubic NiO with a preferred (111) orientation and no detectable secondary phases. The crystallite size increased at low Cu concentrations and decreased at higher doping levels because of defect-induced suppression of grain growth. SEM observations showed that Cu doping modified the surface morphology and grain distribution. The optical band gap decreased from 3.86 to 3.60 eV with increasing Cu content. Raman and photoluminescence analyses indicated that Cu incorporation altered the defect structure and increased non-radiative recombination. Temperature-dependent current–voltage measurements revealed typical negative temperature coefficient behavior, with conductivity increasing as both Cu concentration and temperature increased. These results demonstrated that controlled Cu doping effectively modified the structural, optical, and electrical properties of NiO thin films, making them promising materials for optoelectronic and sensing applications.

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

Fe-doped MgO thin films were successfully synthesized on glass substrates using the ultrasonic spray pyrolysis (USP) technique, and their structural, morphological, optical, and photocatalytic properties were systematically investigated. X-ray diffraction (XRD) confirmed that all films crystallized in the cubic MgO structure. The peak intensities and widths changed with Fe doping. These variations indicated that Fe incorporation affected both crystallinity and crystallite size. X-ray photoelectron spectroscopy (XPS) survey spectra confirmed the presence of Mg and O and revealed detectable Fe-related features at high doping levels, while detailed chemical-state analysis was beyond the scope of the present measurements. Scanning electron microscopy (SEM) showed that Fe doping modified the surface morphology from compact grains in pure MgO to increasingly agglomerated and clustered structures at higher dopant concentrations. The UV–Vis spectra showed a non-monotonic change in the optical band gap. The band gap widened up to 4% Fe and then decreased slightly at higher concentrations. This trend suggests competing effects from crystallite size and defect-related electronic states. Photoluminescence (PL) revealed a strong quenching effect due to dopant-induced non-radiative recombination pathways. Photocatalytic degradation of methylene blue (MB) dye under UVA illumination demonstrated that Fe doping significantly influenced catalytic activity, with the 0.5% Fe-doped film achieving the highest degradation efficiency (87.19%) and rate constant (0.0114 min−1). At higher doping levels, excess clustering reduced surface-active sites, leading to suppressed photocatalytic performance. These results demonstrated that controlled nominal Fe addition effectively tuned the structural and optical properties of MgO thin films, highlighting their potential for photocatalysis and environmental remediation applications.

Güney, Harun; İskenderoğlu, Demet; Karadeni̇z, Sibel Morkoç; Güldüren, Muhammed Emin; Saritaş, Sevda

In this study, zinc-doped copper oxide thin films were synthesized using the ultrasonic spray pyrolysis (USP) method and systematically characterized to evaluate their structural, morphological, optical, and gas-sensing properties. X-ray diffraction (XRD) confirmed the successful incorporation of Zn into the CuO lattice, revealing modifications in crystallinity and phase composition. Scanning electron microscopy (SEM) provided insights into surface morphology, and X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical states of Zn and Cu, confirming Zn substitution in the CuO matrix. Photoluminescence (PL) spectroscopy was utilized to analyze defect states and recombination dynamics, revealing changes in optical emission due to Zn doping. UV–Vis spectroscopy demonstrated a tunable optical absorbance and band gap characteristics with increasing Zn concentration. Gas sensor measurements were conducted to assess the films' sensitivity, and response time toward various hydrogen gas. The zinc-doped copper oxide thin films exhibited modified gas-sensing performance compared to the pure copper oxide samples attributed to improved carrier concentration, oxygen vacancy formation, and surface reactivity. These results suggest that Zn doping effectively tailors the properties of CuO thin films for potential applications in gas sensor technology.

Çavuş, Murat; Dayı, Mustafa; Dağcı, Yunus; Ulusu, Hayati

The authors regret that this article was submitted and subsequently published as a Review article, which it should have been submitted and published as an Original Research Article. The authors would like to apologise for any inconvenience caused.

Acar, M.T.; Gelengeç, Z.

This study investigates the effects of varying sandblasting pressures on the adhesion, corrosion, and tribocorrosion resistance of Al2O3 films deposited on AISI 4140 steel via Physical Vapor Deposition (PVD). Sandblasting at pressures of 4, 6, and 8 bars was applied prior to Al2O3 coating to enhance the surface properties of the steel. Results indicated that increasing sandblasting pressure led to enhanced adhesion strength, with critical load (Lc) values rising from 18 N (untreated) to 25 N (8-bar sandblasted). However, corrosion resistance initially decreased due to increased surface roughness and microcrack formation from sandblasting, as shown by Ecorr values. Subsequent Al2O3 coating improved corrosion resistance, attributed to the protective oxide layer. Tribocorrosion tests revealed that Al2O3 coated samples exhibited lower wear rates and coefficients of friction, especially for the 8-bar sandblasted sample, due to enhanced surface hardness and reduced friction. This study demonstrates that the combination of sandblasting and Al2O3 PVD coating significantly improves adhesion, corrosion resistance, and tribocorrosion performance, with optimal results at an 8-bar sandblasting pressure. These findings underscore the effectiveness of this surface treatment for enhancing the durability of AISI 4140 steel in high-stress, corrosive environments.

Yıldırım, M. Ali; Tuna Yıldırım, Sümeyra; Karademir, Mert; Çağırtekin, Ali Orkun; Ateş, Aytunç; Acar, Selim

In this study, a nanowire network-based V2O5 nanostructure, designed as the active surface in H2S gas sensors, was produced using an environmentally friendly method known as hydrothermal synthesis. The morphological, structural, and electrical properties of the produced nanostructure were characterized using various measurement techniques. XRD, SEM, and EDX analyses confirmed that the nanostructure was in a pure monoclinic phase, had a two-dimensional (2-D) nanowire network morphology, and was deposited stoichiometrically. From UV–Vis analysis, the energy band gap value of the nanostructure was calculated to be 2.65 eV. In gas sensing measurements conducted between 27 °C and 102 °C, the optimal operating temperature of the fabricated sensor was determined to be 42 °C. At this temperature, which is close to room temperature, the sensor exhibited a high sensitivity of 21.16 % for 50 ppm H2S gas, along with good selectivity, stable repeatability, and baseline stability. Moreover, for 2 ppm H2S gas, the response and recovery times were 39 s and 58 s, respectively. A comprehensive electrical analysis of the sensor was carried out through impedance spectroscopy measurements over a wide temperature range. Our findings indicate that the 2-D V2O5 nanowire network structure (NNS) results in several notable effects, including low operating temperature, high selectivity, and stability for H2S gas, demonstrating considerable potential for industrial applications.

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

The technology of p-type transparent semiconductors is utilized in various fields, and enhancing their performance holds industrial significance. Thus, improving the versatility and efficiency of the p-type transparent conducting oxides (TCO) has become critical for the semiconductor industries and technologies. To be used as hole carrier layes in optoelectronic devices, this study aimed to modify the physical features of nickel oxide (NiO) through a doping approach which may broaden and strengthen the usage of NiO. A cost-effective ultrasonic pyrolysis spray technique was employed for pure and lead (Pb) doped nickel oxide thin film production. The influence of the lead concentration on optical, structural, and morphological traits of the NiO nanostructures was examined via various analyses, including energy-dispersive X-ray spectroscopy (EDAX), scanning electron microscopy (SEM), Photoluminescence, UV–visible spectroscopy, X-Ray Diffraction, and Raman spectroscopy, were utilized to investigate the optical and structural characteristics of these films. In correlation, the X-Ray Diffraction results indicated that the Pb doping induced strain and altered lattice parameters of the grown nanostructures while the cubic phase of NiO maintained. The crystallite size of NiO samples ranged from 31.49 nm to 18.75 nm based on Pb doping concentration which was notably influenced by species and doping content. The UV–vis measurements demonstrated that optical parameters, such as optical band gap, were sensitive to Pb doping ratios. The Raman spectrum analysis confirmed the successful incorporation of Pb ions into NiO. Additionally, the intensity of the PL spectra decreased with increasing Pb content, offering potential applications as window layers in solar cells, smart windows, and other optoelectronic devices.

Çavuş, Murat; Dayı, Mustafa; Dağcı, Yunus; Ulusu, Hayati

In this study, air lime was substituted by three different pozzolanic materials, namely BFS and brick powder and zeolite in different proportions as individual or double. The produced pozzolanic lime mortars were cured in air and high relative humidity environments. Special attention was given to the mechanical and physical properties of mortars under different curing conditions. In addition to the curing effect, the effect of using different pozzolans was also investigated. As a result, it has been observed that high relative humidity cure improves the mechanical properties of pozzolan mortars but is not effective on their physical properties. It shows that there are significant differences in the mechanical properties of mortars with pozzolan, which are exposed to different curing conditions, especially at an early age. It shows that the mechanical properties of mortars with pozzolan, which are exposed to different curing conditions, especially at an early age, increase twice on average. The high relative humidity cure shows that the non-pozzolan air-lime mortars slow down the performance properties. Overall, conditions of high relative humidity can more quickly improve the performance characteristics of puzolan mortars.

Mobtakeri, Soheil; Akaltun, Yunus; Özer, Ali; Kılıç, Merhan; Tüzemen, Ebru Şenadım; Gür, Emre

In this study, gallium oxide (Ga2O3) thin films were deposited on sapphire and n-Si substrates using Ga2O3 target by radio frequency magnetron sputtering (RFMS) at substrate temperature of 300 °C at variable RF power and deposition pressure. The effects of deposition pressure and growth power on crystalline structure, morphology, transmittance, refractive index and band gap energy were investigated in detail. X-ray diffraction results showed that amorphous phase was observed in all the as-deposited thin films except for the thin films grown at low growth pressure. All the films showed conversion to poly-crystal β-Ga2O3 phase after annealing process. When the deposition pressure increased from 7.5 mTorr to 12.20 mTorr, change in the 2D growth mode to 3D columnar growth mode was observed from the SEM images. Annealing clearly showed formation of larger grains for all the thin films. Lower transmission values were observed as the growth pressure increases. Annealing caused to obtain similar transmittance values for the thin films grown at different pressures. It was found that a red shift observed in the absorption edges and the energy band gap values decrease with increasing growth pressure. For as-deposited and annealing films, increasing sputtering power resulted in the increase refractive index.

Kovacı, Halim; Yetim, Ali Fatih; Baran, Özlem; Çelik, Ayhan

Diamond-like carbon (DLC) films are effectively utilized to improve the tribological properties of materials due to their low friction coefficient, good wear resistance and high hardness. In recent years, different pre-treatments such as plasma assisted diffusional processes have been used to increase long-term durability of these coatings. In the present work, DLC films were deposited on untreated and plasma nitrided AISI 4140 low-alloy steel samples using physical vapor deposition method (PVD). The effect of nitride layers on the structural and mechanical properties of DLC films was examined by XRD, SEM, microhardness tester and reciprocating tribotester. The wear tests were performed under dry, saltwater and lubricant environments. The microhardness results indicated that surface hardness considerably increased after duplex treatment and this caused to increase plastic deformation resistance of the material. The reciprocating test results showed that DLC films deposited on untreated and plasma nitrided samples reduced the coefficient of friction because of the formation of transfer film between sliding/mating surfaces. Also, wear rates improved significantly after duplex treatment in consequence of high plastic deformation resistance of duplex treated samples. The highest wear resistance was obtained in lubricated condition while the lowest wear resistance was for the samples tested in dry conditions.