Taşdemirci, Tuba Çayir

Bi₂O₃ thin films were deposited on glass substrates using RF magnetron sputtering at 80, 100, and 120 W, and the effects of post-annealing at 200 °C and 300 °C were investigated. XRD results show that all films crystallize in the monoclinic α-Bi2O3 phase, with the (–112) plane becoming increasingly dominant as annealing temperature increases. Grain size increases while dislocation density and microstrain decrease with both higher sputtering power and annealing, indicating improved crystallinity. SEM analyses reveal homogeneous spherical grains in unannealed films, which transform into smoother surfaces or rod-like structures after annealing, depending on the sputtering power. EDAX confirms increased oxygen incorporation with rising annealing temperature. UV–Vis spectroscopy shows a systematic reduction in optical band gap with annealing, from 3.57 to 3.38 eV (80 W), 3.29 to 3.08 eV (100 W), and 2.88 to 2.79 eV (120 W). Overall, thermal treatment significantly enhances structural quality and tunes the optical properties of Bi2O3 thin films, making them suitable for optoelectronic and sensing applications.

Horoz, Banu; Tuna Yıldırım, Sümeyra; Soltabayev, Baktiyar; Ateş, Aytunç; Acar, Selim; Yıldırım, M. Ali

In2O3 thin films were deposited via Successive Ionic Layer Adsorption and Reaction (SILAR) method on glass substrates at 20, 30, 40, and 50 SILAR cycles. The effect of SILAR cycle on the general and CO gas sensing properties of the films was investigated. The GIXRD and FE-SEM results indicated that the films had cubic phase and porous morphology. As a function of temperature and gas concentration, CO gas sensing measurements of In2O3 thin film-based sensors were made, and the detection limit and operating temperature values were determined. The optimal operating temperature was found to be 222 °C for all sensors. The CO sensing results demonstrated that the sensor with 30 SILAR cycle had higher sensitivity for 1–100-ppm gas concentration values at 222 °C operating temperature than the others. The sensing responses of the sensors increased from 12 to 29% for 1-ppm CO gas and from 52 to 91% for 100-ppm CO gas at 222 °C, depending on the SILAR cycle. The detection limit of the sensors toward CO gas at 222 °C reached 1 ppm, and the response and recovery times of the sensor with 30 SILAR cycle were found to be 54.2 s and 49 s for 1-ppm CO, and 47.4 and 62.5 s for 100-ppm CO gas at 222 °C, respectively. The activation energy (E a) values of the sensors were found to change between 0.08 and 0.15 eV in the temperature range of 300–340 K and between 0.700 and 0.749 eV in the temperature range of 350–520 K, with SILAR cycle number. Finally, in this study, it was revealed that SILAR cycle number changed the structural, morphological, and CO gas sensing properties of the In2O3 thin films, and SILAR cycle optimization was performed for the highly sensitive In2O3 thin film-based CO gas sensor.

Karadeniz, Sibel Morkoç; Iskenderoğlu, Demet; Güldüren, Muhammed Emin; Güney, Harun; Sarıtaş, Sevda

The pure and Fe-doped CuO thin films were successfully grown by using ultrasonic spray pyrolysis method (USP) onto glass substrates. The changes in structural, morphological, H2 gas sensor, and optical properties of the synthesized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy, photoluminescence (PL) spectroscopy, and gas detection analyses were carried out. XRD data showed that the synthesized nanostructures belonged to the monoclinic phase of CuO with predominant (002) and (111) plane orientations and the grain sizes vary between 54.19 and 41.73 nm. In the morphological inquiry, structures possessed mostly rod-like polyhedral shapes and semi-spherical formations especially after Fe doping. EDAX and XPS verified that all the aimed materials were present on the deposited thin films. Gas sensor measurements clearly hinted that the Fe doping could lead to notable differences in H2 gas sensing abilities of samples. In the PL spectroscopy, weakened emission peak intensities recorded owing to the fact that the added impurities into the CuO lattice structures, which had major luminescence peaks at about 555 nm. Lastly, the ultraviolet–visible spectroscopy study discovered that the Fe doping affected the optical characteristics and the optical energy band gap increased.

Astam, Aykut; İnanç, Cemal Turgay

Transition metal carbonates are of great interest, not only as alternative electrode materials in Li/Zn/Na/K-ion batteries or supercapacitors, but also as solid precursors for the synthesis of transition metal oxides via thermal decomposition. In this work, thin films of MnCO3 were deposited on quartz substrates via a mild one-pot hydrothermal process without using any catalysts or templates and the conversion of these films to manganese oxides through post-deposition thermal annealing for 1 h in air and nitrogen atmospheres was investigated. The films were analyzed by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and optical absorption measurements before and after annealing. The obtained results showed that as deposited films composed of MnCO3 with an impurity phase of Mn3O4 and annealing in air atmosphere caused the conversion of the films to Mn2O3, whereas nitrogen atmosphere led to the conversion to MnO with a secondary phase of Mn3O4. After annealing in both atmospheres, the size and shape of the microcubic structure were mainly retained, except for porosity caused by the release of CO2 and O2 gases. From the analysis of the room temperature optical absorption measurements, direct optical band gaps of the as deposited and air annealed films were determined as 3.27 eV and 2.30 eV, respectively, whereas the nitrogen annealed film was found to have two band gaps of 2.50 eV and 2.71 eV.

Aydogan, Sakir; Kocyigit, Adem; Cirak, Burcu Bozkurt; Erdogan, Erman; Yilmaz, Mehmet

Zinc oxide (ZnO) rods film was fabricated by homemade and simple spray pyrolysis technique on a p-type silicon (Si) substrate, and the film layer was employed as an interfacial material between the Co and p-type Si for obtaining Co/ZnO-Rods/p-Si heterostructure. The scanning electron microscopy (SEM) was used to discover the rods-like structures and uniform morphology of the ZnO film. The impedance spectroscopy technique was performed on the Co/ZnO-Rods/p-Si heterostructure to determine electrical and dielectric properties depending on the frequency. The C–V and G–V characteristics revealed that the electrical properties related to the frequency and voltage changes. The dielectric properties were studied depending on frequency by extracting dielectric constant (ε′), dielectric loss (ε′′), loss tangent (tan δ), ac electrical conductivity (σ), and real and imaginary parts of the electric modulus (M′ and M′′). The results highlighted that the Co/ZnO-Rods/p-Si heterostructures can be employed for intermediate frequency applications.

Gülnahar, Murat; Nasser, Hisham; Salimi, Arghavan; Turan, Raşit

In this work, the electrical and charge conduction characteristics of a contact structure featuring thermally evaporated MoOx, deposited on n- and p-type crystalline silicon (c-Si), are extensively investigated by room temperature current–voltage (I–V), transmission line measurements (TLM), and temperature-dependent current–voltage measurements (I–V–T). XRD diffraction spectrum shows that the deposited MoOx film exhibits amorphous nature. From TLM measurements, the values of contact resistivity are calculated to be ρc: 55.9 mΩ-cm2 for Ag/MoOx/n-Si and ρc: 48.7 mΩ-cm2 for Ag/MoOx/p-Si. The barrier parameters such as barrier height (ϕe) and ideality factor (n) are investigated by the thermionic emission theory for I–V and I–V–T measurements. The ϕe, n, and conventional Richardson plot demonstrate resolute temperature dependency, obeying the barrier height of Gaussian distribution model. The uniform barrier height values are calculated to be ϕb:1.24 eV for Ag/MoOx/n-Si and ϕb:0.66 eV for Ag/MoOx/p-Si from the extrapolation of ϕe at n= 1 of the linear fitting of the variation with the experimental barrier height ϕe with ideality factor. The activation energy (Ea) and Richardson constant (A*), obtained from Richardson plot, are much smaller than ϕb and the theoretical values of n- and p-type c-Si. The modified Richardson plot yields more reliable Richardson constant and homogeneous barrier height values of 106.2 Acm−2 K−2 and 1.21 eV, 23.4 Acm−2 K−2 and 0.63 eV for Ag/MoOx/n-Si and Ag/MoOx/p-Si heterostructures, respectively. The results demonstrate that thermally evaporated MoOx has particular advantages due to its good rectifying characteristics such as the extra enhancement to barrier height and low contact resistivity for interfacial layer applications.

Yesilbag, Yasar Ozkan; Tuzluca Yesilbag, Fatma Nur; Huseyin, Ahmad; Tuzluca, Metin; Ismail, Ismayadi; Ertugrul, Mehmet

We reported a combination of the unique properties of (2D) graphene and (1D) carbon nanotubes (CNTs) by synthesizing a novel graphene/CNTs hybrid structure. Graphene and CNTs were synthesized by a two-step chemical vapor deposition (CVD) system. In the first step, multilayer graphene (MLG) was grown on nickel substrates by changing the methane gas flow rate and growth time. In the second step, the CNTs were then grown on the synthesized MLG surface previously. Both the Ni catalyst film thickness and H2 gas flow rate were changed to investigate their effects on the growth densities and average diameters of the hybrid structures. Structural and morphological analysis of both MLG and MLG/CNT hybrid structures were determined using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Raman analysis. As the Ni catalyst film thickness was increased, CNTs grew more densely on the MLG. It was observed that CNTs with smaller diameters and longer lengths formed with increasing H2 gas flow rate. This hybrid structure is useful in electronic, optoelectronic, and energy storage applications.

Er, Irmak Karaduman; Çağırtekin, Ali Orkun; Ajjaq, Ahmad; Yıldırım, Memet Ali; Ateş, Aytunç; Acar, Selim

In this study, pure zinc oxide (ZnO) and tin-doped zinc oxide (Zn1−xSnxO) thin films were synthesized using successive ionic layer adsorption and reaction (SILAR) method in 40 cycles with doping ratios x = 0.05, 0.10, 0.15, and 0.20. Subsequently, structural, optical, and electrical characteristics of all synthesized thin films were properly investigated by the appropriate techniques. For structural characterizations, X-ray diffraction (XRD) technique was employed, and the data demonstrated the appropriate hexagonal wurtzite structure of the synthesized thin films and predicted the decrease of crystallite size with Sn doping. Likewise, optical characterizations were carried out through ultraviolet–visible (UV–Vis) technique, and the data showed good transparency of ZnO thin film and confirmed the increase in transparency and bandgap upon Sn doping. Additionally, to probe the electrical aspects of the synthesized thin films, impedance, modulus, and conductivity analyses were carried out as a function of frequency in a wide temperature range (450–750 K). The results demonstrated the critical effect of temperature and Sn doping ratio in ZnO thin films. At high enough temperatures, inductive effects became evident in the low-frequency region of all the thin films. And at all temperatures, 5 wt%- and 10 wt%-doped films exhibited extreme responses in the investigated doping range, where the former and the latter showed, respectively, highest and lowest conductivity as well as lowest and highest possibility of grain effects in the film structure. This behavior was confirmed using two different analysis techniques with two separate data sets, (Z, θ) and (C, G).

Cimilli Çatir, Fulya Esra

In this study, the reduced graphene oxide (rGO) was synthesized from graphene oxide (GO) by using chemical reduction method. The spray pyrolysis technique was used to deposit rGO film on n-InP substrate. The structural, morphological, and optical properties of rGO film were investigated by XRD, SEM, and UV–Vis spectroscopies. Au/rGO/n-InP device was fabricated and the current–voltage characteristics were examined in the temperature range of 60–300 K. The device parameters of barrier height (BH) and ideality factor are found to be strong functions of temperature due to the barrier inhomogeneities at metal–semiconductor interface. The temperature dependency of the electrical characteristics of the Au/rGO/n-InP SBD was explained by the thermionic field emission (TFE) theory with Gaussian distribution (GD) of the BH values. The BH has a GD with a mean barrier height of Φ ¯ bo = 0.93 eV between 120 and 300 K temperatures and Φ ¯ bo = 0.62 eV between 60 and 120 K temperatures. It was seen that the existing current mechanism is predominantly controlled by space-charge-limited current (SCLC) at large forward bias according to the sample temperature. The rGO interface plays also an important role in the conduction mechanism and electronic properties of the device.

Bayram, Ozkan; Igman, Erdal; Guney, Harun; Demir, Zeynep; Yurtcan, Mustafa Tolga; Cirak, Cagri; Hasar, Ugur Cem; Simsek, Onder

In this study, it was aimed to produce graphene/polyaniline nanocomposite thin films as counter electrode materials by PECVD system and to determine the photovoltaic performances of these counter electrodes in dye-sensitized solar cells (DSSCs). Graphene/polyaniline counter electrode (GPCE) material was produced in two different steps. Firstly, a single-layer and multilayer graphene thin films were produced on the fluorine-doped tinoxide (FTO) substrates. Then, polyaniline (PANI) thin films were grown on each graphene thin films using plasma polymerization technique, and eventually the production of the graphene/PANI nanocomposite was completed. The fabricated graphene/PANI nanocomposites were used in place of platinum (Pt)-counter electrode which is widely used in DSSCs and the photovoltaic performance of these counter electrodes was investigated. The DSSCs consisted of titanium dioxide (TiO2) nanotube photoanode, N719 dye, iodolyte liquid electrolyte, and graphene/PANI nanocomposite counter electrode. I–V measurements were carried out in order to calculated photoconversion efficiency (PCE) and it was found that the these efficiency of GPCEs changed between 0.56 and 1.36% according to the number of graphene layers. The photovoltaic performance of DSSC, consisting of TiO2 nanotube photoanode and Pt-counter electrode was 1.1%.