Süleyman Özçelik’s research while affiliated with Gazi University and other places

Bu çalışma, dönel kaplama tekniği kullanılarak, yakın kızılötesi (NIR) bölgede 1064 nm dalga boyunu soğuracak şekilde verimli alan emisyon özelliklerine sahip nanoyapılı La(OH)3 ve LaB6 malzemelerinin sentezlenmesi daha sonra da LaB6 malzemesinin nadir toprak elementlerinde olan Ce ve Sm ile katkılanmasının üzerine odaklanmıştır. La(OH)3 ve LaB6 malzemeleri laboratuvar ortamında sentezlenmiş, ardından optik ve yapısal karakterizasyonları tamamlanarak nadir toprak elementlerinden olan Ce ve Sm ile katkılandıktan sonra katkılı ince filmler oluşturulmuştur. Difüzyon fırınında katkılama işlemi yapılmış ve süreçteki reçeteler, ekonomik ve tekrarlanabilir sonuçlar için optimize edilmiştir. Dönel kaplama sistemi ile cam alttaşlar üzerine kaplanan filmlerin yapısal ve optik özellikleri incelenmiştir. Katkılı LaB6 filmlerinin 900-1000 nm aralığındaki soğurma vadisinde %60 oranında NIR soğurma ve %70 oranında görünür ışık geçirgenliği sağladığı gözlemlenmiştir. XRD, FTIR, SEM, AFM ve SIMS analizleri ile malzemelerin homojen bir dağılıma sahip olduğu ve başarıyla sentezlendiği doğrulanmıştır. Bu sonuçlar, LaB6 ince filmlerinin optik performansını artırarak kızılötesi cihazlarda kullanım potansiyelini ortaya koymaktadır.

In this work, the optoelectronic response of Al/p‐Si photodiodes (PDs) with and without (PVP:Gr‐ZnTiO3) composite interlayer is investigated in dark and under various light intensities (P). The manufacturing/surface preparation is thoroughly explained. The electric/optic parameters including leakage/saturation current (I0), series/shunt resistances (Rs/Rsh), barrier height (BH), ideality factor (n), energy‐dependent density distribution of surface/interface levels (Nss), photoinduced current (Iph), photosensitivity (S), optical responsivity (R), and specific detectivity (D*) are calculated from the I–V data in dark and under illumination intensities. Raising the light intensity results in a drop in ΦB0 and Rs quantities while increasing the I0 and n values due to photogenerated electron–hole pairs under illumination. The ΦB0‐P and ΦB0‐n graphs are used to calculate the illumination factor and the ΦB0 in the ideal form. An acceptable linear behavior appears in the Iph–P profiles for the negative‐bias region, where the illumination dependence of photocurrent is explored. It is found that the (PVP:Gr‐ZnTiO3) interlayer leads to an increase in the S, R, and D* values of the PD to ≈1200, 400 mA W⁻¹, and 1.14 × 10¹⁴ Jones, respectively. These results show that the used (PVP:ZnTiO3) interlayer displays an excellent photoresponse and may effectively replace conventional PDs for applications in optoelectronic and photovoltaic devices.

In this work, flexible transparent conductive silver nanowire (AgNW) electrodes were fabricated on polyethylene naphthalate (PEN) substrates using the aerosol jet printing (AJP) technique, providing a versatile and cost-effective alternative to conventional transparent conductive oxide (TCO) material production. Additionally, the impact of printing cycles on the transparency and surface resistivity of the electrodes was investigated. Ultraviolet–visible (UV–Vis) spectrometry, optical microscopy, and four-point probe techniques were used to characterize the obtained AgNW electrodes. When the three-cycle printing process was applied, AgNW electrodes with sheet resistance of 30.96 Ω/sq and average transparency of 78% in the visible region were obtained. This means that the electrodes produced with both good properties and flexibility can be used in several optoelectronic and electrochemical applications.

We report the insertion of a new intermediate layer, a multi-layered graphitic carbon (MLGC), at Mo/CZTS interface and its impact on the structural and morphological characteristics of the back interface and absorber. MLGC was synthesized directly on Mo-coated SLG under a gas mixture flow of H2/CH4 at 550 °C via PECVD for 3 and 5 h. CZTS precursors were prepared on SLG/Mo and MLGC-coated SLG/Mo in a hybrid physical vapor deposition system, including evaporation and sputtering techniques, then subjected to sulfurization at 550 °C. The sheet resistance of back contact, microstructural parameters of the absorbers, the distributions of C and constituent elements were investigated. The diffraction peaks of the hexagonal Mo2C indicated the reaction between the C and Mo before the MLGC’s growth. Raman analysis confirmed the formation of the MLGC during the long deposition time after the Mo2C formation. With the addition of MLGC, the sheet resistance of the back contact decreased from 2 to 0.5 Ω/sq, and the crystallite size of the absorbers improved. Raman spectra from the interface exhibited that MoS2 peaks’ intensities significantly reduced with increasing the growth time. This implied that the 5 h-deposited MLGC was more effective in blocking the reaction between Mo and S. The absorbers with the MLGC had more uniform surface morphologies, densely packed grains, and fewer secondary phases. FIB analysis revealed the separation of the absorber with the 5 h-deposited MLGC into two parts due to C impurity. More C diffusion into the absorber for this sample was confirmed by SIMS.

In the present study, both metal/semiconductor (MS) and metal/polymer/semiconductor (MPS) Schottky Diodes (SDs) were grown onto the same n-Si wafer to compare their electrical and optical characteristics. Firstly, ZnO and CeO2 nanostructures were synthesized by ultrasonic-assisted method (UAM), and structurally characterized by utilizing x-ray diffraction (XRD), Ultraviolet-visible spectroscopy (UV–vis), and Fourier-Transform-IR (FTIR) methods. The mean submicron crystallite sizes were estimated to be below 11.39 nm for CeO2 and 54.37 nm for ZnO nanostructures through the Debye–Scherrer method. The optical bandgap was calculated as 3.84 eV for CeO2 and 3.88 eV for ZnO nanostructures via Tauc plot. Electrical parameters such as reverse-saturation current (Io), ideality-factor (n), zero-bias barrier height (ΦBo), and rectification-ratio (RR) were found as 0.596 μA, 5.45, 0.64 eV, 2.74 × 10⁵ in dark and 5.54 μA, 5.88, 0.59 eV, 8.60 × 10³ under illumination for the MS SD and 0.027 μA, 4.36, 0.72 eV, 1.85 × 10⁷ in dark and 0.714 μA, 5.18, 0.64 eV, 7.61 × 10⁴ under illumination for the MPS SD, respectively. The energy-dependent profile of surface-states was obtained via the Card-Rhoderick method, by considering ΦB(V) and n. RR of the MPS SD is almost sixty-seven times the RR of the MS SD in the dark. The sensitivity of the MPS SD (=710) is nineteen and five-tenths the sensitivity of the MS SD (=36.4), so the MPS SD is considerably more sensitive to illumination. These results indicate that the (ZnO:CeO2:PVP) organic interlayer significantly improves the performance of the MS SD.

In this research, the optical properties of the PVP: ZnTiO3 nanocomposite are studied using the spectroscopic ellipsometry technique. The preparation procedure of the ZnTiO3 nanocomposite is explained in detail. The absorbance/transmittance, surface morphology, structural information, chemical identification, and surface topography of the ZnTiO3 nanocomposite is studied using UV-Vis spectroscopy, field-emission scanning electron microscopy, Raman spectroscopy, Fourier transform infra-red, and atomic force microscopy, respectively. The ellipsometry method is used to obtain the spectra of the real and imaginary parts of the dielectric function and refractive index in the photon energy range of 0.59-4.59 eV. Moreover, using two machine learning algorithms, namely artificial neural network and support vector regression methods, the ellipsometric parameters ψ and Δ are analyzed and compared with non-linear regression. The error and accuracy of each three methods, as well as the time required for their execution, are calculated to compare their suitability in the ellipsometric data analysis. Also, the absorption coefficient was used to determine the band gap energy of the ZnTiO3 nanocomposite, which is found to be 3.83 eV. The second-energy derivative of the dielectric function is utilized to identify six critical point energies of the prepared sample. Finally, the spectral-dependent optical loss function and optical conductivity of the ZnTiO3 nanocomposite are investigated.

In this research, the optical properties of the PVP: ZnTiO3 nanocomposite are studied using the spectroscopic ellipsometry technique. The preparation procedure of the ZnTiO3 nanocomposite is explained in detail. The absorbance/transmittance, surface morphology, structural information, chemical identification, and surface topography of the ZnTiO3 nanocomposite is studied using UV–Vis spectroscopy, field-emission scanning electron microscopy, Raman spectroscopy, Fourier transform infra-red, and atomic force microscopy, respectively. The ellipsometry method is used to obtain the spectra of the real and imaginary parts of the dielectric function and refractive index in the photon energy range of 0.59–4.59 eV. Moreover, using two machine learning algorithms, namely artificial neural network and support vector regression methods, the ellipsometric parameters ψ and Δ are analyzed and compared with non-linear regression. The error and accuracy of each three methods, as well as the time required for their execution, are calculated to compare their suitability in the ellipsometric data analysis. Also, the absorption coefficient was used to determine the band gap energy of the ZnTiO3 nanocomposite, which is found to be 3.83 eV. The second-energy derivative of the dielectric function is utilized to identify six critical point energies of the prepared sample. Finally, the spectral-dependent optical loss function and optical conductivity of the ZnTiO3 nanocomposite are investigated.

The effects of Ar sputtering deposition pressure on the optical, structural, morphological, and electrical properties of amorphous InGaZnO thin films were investigated. The InGaZnO thin films, which have amorphous structures determined by grazing incidence X-Ray diffraction, contained In, Ga, Zn, and O confirmed by secondary ion mass spectrometry method. Additionally, when the thicknesses of the deposited thin films are examined, it was seen that the profilometer measurement results of the crater formed by secondary ion mass spectrometer and scanning electron microscope measurement results are nearly similar, and it is approximately 100 nm. The surface roughness, obtained from Atomic Force Microscopy results, show that decreased up to a particular value with the increase of the working pressure, and then the surface roughness increased. The optical band gaps of the films were obtained in the range of 3.50 eV-3.58 eV via Tauc relation by using the Ultraviolet-Visible measurements carried out in the wavelength range of 200 nm-1100 nm. It was seen that the optical band gap was decreased with the increase in Ar pressure. The electrical properties of InGaZnO thin film-based Schottky diodes, such as the barrier height, ideality factor, saturation current, series resistance, and shunt resistance, have also been studied comprehensively. The electrical results showed that diode properties change with increasing deposition pressure.

In this paper, we introduce the synthesis of undoped ZnO and 5 wt % Gd/K co‐doped ZnO compounds to improve photocatalytic activity. Undoped ZnO particles and Gd/K co‐doped ZnO particles were synthesized by the sol‐gel method. The samples were studied by X‐ Ray Diffraction (XRD), Scanning Electron Microscopy (SEM)/energy dispersive X‐ray (EDX), Ultraviolet Visible Spectroscopy (UV‐Vis), Brunauer–Emmett–Teller (BET), and particle size analysis. Then tehir photocatalytic activities were tested. SEM micrographs showed that the particle size was in the sub‐micrometer or nanometer range. Particle size analysis revealed that the mean size was closer to the micrometer range. The specific surface area of the powder was obtained quite low in accordance with the larger particle size. The photocatalytic activity of 5% Gd/K co‐doped ZnO was compared with undoped ZnO in the degradation methyl blue. When their photocatalytic activities were examined, Gd/K co‐doped ZnO showed ∼66% degradation at 60 min, while undoped ZnO showed ∼52% degradation at the same time.