Ceren başköse | Gazi University (original) (raw)

Papers by Ceren başköse

Chemical Papers, Mar 13, 2019

The all conformers of 5-methyl-4-(2-thizolylazo)resorcinol have been identified by Spartan 13 sof... more The all conformers of 5-methyl-4-(2-thizolylazo)resorcinol have been identified by Spartan 13 software. All conformers have been optimized B3LYP/6-311G (d, p) level of theory in Gaussian 09 software. According to potential energy surface search, 5-methyl-4-(2-thizolylazo)resorcinol has eight conformers. All the structural parameters of the most stable conformer of 5-methyl-4-(2-thizolylazo)resorcinol are predicted using DFT (B3LYP) method with the same basis set given above. The vibrational frequencies are recorded by the Fourier transform infrared (FT-IR 4000-550 cm −1) and Fourier transform Raman (FT-Raman; 4000-100 cm −1) spectra in the powder form. The vibrational frequencies are predicted and compared with experimental FT-IR and FT-Raman ones. The experimental 1 H and 13 C NMR spectra have been recorded and compared with the theoretical chemical shifts determined by the GIAO method. The results of UV-Vis spectra of molecule are also presented. Theoretical results compared with the experimental results for the identification and characterization of 5-methyl-4-(2-thizolylazo)resorcinol molecule. Keywords 5-Methyl-4-(2-thizolylazo)resorcinol • DFT • FT-IR and FT-Raman spectra • NMR and UV-Vis spectra * Y. Erdogdu

Applied Physics A, Dec 19, 2018

In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with st... more In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with steps of 50 °C. InGaN/ GaN multi-quantum well structure is deposited on c-orientated sapphire wafer by metal organic chemical vapour deposition method. All the parameters except for temperature kept constant during growth period. InGaN/GaN structures with different In content are investigated by XRD technique. Their structural, optical and morphological characteristics are determined by high resolution X-ray diffraction, Fourier transform spectroscopy (FTIR), photo luminescence (PL), transmission and atomic force microscopy (AFM). According to FTIR and PL spectra's, it is noticed that band gap values coincide with blue region in the electromagnetic spectrum. As a result of transmission measurements it is seen that light is completely absorbed by the sample at approximately 390 nm. Using XRD technique, dislocation densities and strain are calculated. Full width at half maximum of the XRD peak values gained from X-ray diffraction are used in an alternative method called Williamson-Hall (W-H). Using W-H method, lateral and vertical crystal lengths and tilt angles are determined. Surface roughness parameters are investigated by AFM. Different properties of GaN and InGaN layers are compared as dependent on increasing temperature. According to AFM images it is seen that these structures have high surface roughness and large crystal size. All the results yielded from the mentioned methods are in good agreement with the previous works done by different authors.

gazi university journal of science, 2014

In this work, ZnO thin films with different thickness (100 nm and 50 nm) were deposited onto flex... more In this work, ZnO thin films with different thickness (100 nm and 50 nm) were deposited onto flexible-transparent substrates by high vacuum (HV) reactive direct current (DC) magnetron sputtering technique, using oxygen as a reactive gas. The structural and optical properties of the films were investigated by X-ray diffractometer (XRD), room temperature photoluminescence (PL) and UV–Vis spectrometer. The both obtained films had a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. The e lectronic transitions from the conduction band to the valence band (called as band gap) of the films was about 3.2 eV. It was observed that the exitonic transition energy of the films shifted blue emission with increasing the film thickness. In addition, the optical transmittances of the films were about 80 % in the visible region .

Journal of Materials Science: Materials in Electronics, 2020

In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriente... more In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriented sapphire substrate using metal organic chemical vapor deposition method. Optical properties of the structure are investigated by photoluminescence (PL) and ultraviolet (UV-Vis.) spectras. According to PL results, direct bandgap of AlN is determined around 2.80 eV. In UV-Vis. spectra it is seen that conduction of AlInN layer starts at 360 nm. Swanepoel envelope method is applied on transmission spectra and some optical properties such as refractive index (n), film thickness (t), absorption coefficient (α), and extinction coefficient (k) are determined. Forbidden energy bandgap is determined again from Tau method and it is compared with the value gained from PL spectra. This study is a rare one that presents optical properties of HEMTs using Swanepoel and Tau methods. In addition to this, it helps estimating how optical properties of HEMTs effect electrical properties.

Philosophical Magazine, 2015

This study demonstrates the power conversion efficiency enhancement on In0.19Ga0.81As/GaAs quantu... more This study demonstrates the power conversion efficiency enhancement on In0.19Ga0.81As/GaAs quantum well solar cells (QWSC). The solar cell structure was grown on n-type (100)-oriented GaAs substrate by using solid-source molecular beam epitaxy technique and divided into square pieces. In order to understand whether the eight quantum wells were grown or not, scanning electron microscopy (SEM), and secondary ion mass spectrometry characterizations were done at room temperature. After that, the Si3N4 antireflection layers were coated onto both two square pieces of In0.19Ga0.81As/GaAs QWSC structure and p-GaAs substrate at different temperatures by the radio frequency magnetron sputtering system. The optical properties of the Si3N4 coated and uncoated p-GaAs samples have been evaluated by means of ultraviolet-visible spectrometry measurements at room temperature. According to ultraviolet-visible spectrometry results, the best Si3N4 antireflection coated one was obtained at 100 °C substrate temperature. Thus, the In0.19Ga0.81As/GaAs QWSC structure with and without Si3N4 layer, which was coated at 100 °C substrate temperature, was selected for other measurements and processes. Moreover, the In0.19Ga0.81As/GaAs QWSC samples with and without Si3N4 antireflection coating were separately fabricated with different metallization materials for obtaining the solar cell electrical output parameters. AuGe and AuGeNi metallization materials were used for the fabrication processes. After fabrication, the electrical output parameters were extracted from the current-voltage measurements at room temperature both in dark and under AM1.5 – 1 Sun illumination. The proposed design which includes the AuGeNi metallization and Si3N4 antireflection layer enhanced the power conversion efficiency by 44.40%.

Semiconductors, 2015

The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering m... more The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering method. The properties of ZnMnO thin films were investigated by high-resolution x-ray diffractometer (HRXRD),atomic force microscopy (AFM), UV-Vis spectrometer and room temperature photoluminescence (PL), under the influence of substrate temperature. The substrate temperature was varied from 300, 400 and 500°C. With increasing the substrate temperature, the structure of the films changed from cubic to hexagonal. The cubic ZnMnO thin films grown along [210] direction, while the hexagonal ones grown along [002] direction. The changes in surface morphology provided a proof on the structural transition. Also, decrease and increase of optical band gap is associated with cubic or hexagonal structure of the films.

Journal of Materials Science: Materials in Electronics, 2014

In this paper, we study structural and morphological properties of metal-organic chemical vapour ... more In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another.

Journal of Molecular Structure

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Journal of Materials Science and Engineering B, 2013

Porous silicon layers manufactured by using (100), 1-5 ohm•cm p-type (boron doped) wafer by elect... more Porous silicon layers manufactured by using (100), 1-5 ohm•cm p-type (boron doped) wafer by electrochemical etching in HF etanol solution. Photoluminescence (PL) spectra of anodically etched silicon obtained for different conditions studied and surface characteristics are investigated by AFM. This study gives a simple way to determine specific surface are of porous silicon which plays a major role with porosity for explaining the blue shift in photoluminescence peak. Properties such as specific surface area, pore size, and pore size distribution, the main surface properties of layer are investigated from AFM data which are important material characteristics in many processing applications. The "specific surface area" (S specific) generally defined as the area of solid surface per unit mass of material, solid volume or cross section area. From 3-D reconstructions of AFM data, the surface area and the volume of the porous layer can be estimated directly and volume-surface specific area is calculated. For porous silicon this feature can be defined as the total surface area per volume and given by the unit m 2 /cm 3. The method is simple not need to construct a special set up for measurement and non destructive.

Solar Energy, 2021

Abstract In this work, we report the incorporation of sodium (Na) alkaline element into copper-zi... more Abstract In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-sulphide (Cu-Zn-Sn-S) precursor films by adding radio frequency (RF)-sputtered sodium fluoride (NaF) intermediate layers bringing a new approach to the bifacial sodium-incorporated treatment (BIST) and its effect on the properties of Cu2ZnSnS4 (CZTS) absorber films. Due to the absence of alkaline diffusion barrier layers on soda lime glass (SLG) substrates, Na additions from both NaF intermediate layers and SLG substrate were evaluated together. With additional NaF intermediate layers among the elemental metal stacks, the films exhibited better crystalline properties and a more compact structure. However, the amount of the Cu2-xS secondary phases formed on the surfaces increased by the additional NaF layers. Raman spectra confirmed the formation of the kesterite phase and showed the peaks corresponding to Cu3SnS4 and Cu2-xS secondary phases. Na diffusion originating from NaF layers deposited on molybdenum (Mo) films occurred in both directions of the CZTS film and the SLG substrate. The photoluminescence (PL) bands located at around 1.40 eV were attributed to the band to band (BB) transitions. The film with additional NaF intermediate layers exhibited higher carrier concentrations and lower resistivity than the other film due to the presence of the higher amount of Cu2-xS secondary phases on its surface.

Applied Physics A, 2015

Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephtha... more Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method under various RF powers in the range of 25-100 W. Structural, morphological, optical and electrical properties of the films were investigated by X-ray diffractometer, atomic force microscope, UV-Vis spectrometer and Hall effect measurement system. All the obtained films had a highly preferred orientation along [002] direction of the c-axis perpendicular to the flexible PET substrate and had a high-quality surface. The energy band gap (E g) values of the films varied in the range of 3.30-3.43 eV. The minimum resistivity of 1.84 9 10-4 X cm was obtained at a 50 W RF power. The small changes in the RF power had a critical important role on the structural, optical and electrical properties of the sputtered AZO thin films on flexible PET substrate. In addition, UV sensing of the fabricated AZO thin film-based sensors was explored by using current-voltage (I-V) characteristics. The sensors were sensitive in the UV region of the electromagnetic spectrum.

Bu tez çalışması kapsamında ince film optik kaplamalar üzerine araştırma ve geliştirme faaliyetle... more Bu tez çalışması kapsamında ince film optik kaplamalar üzerine araştırma ve geliştirme faaliyetleri gerçekleştirildi. Yansıtıcı ve yansıtıcı olmayan optik ince filmler fiziksel buhar biriktirme yöntemlerinden püskürtme ve eş odaklı püskürtme sistemleri kullanılarak üretildi. Yansıma önleyici kaplamalar için ince film malzeme olarak silikon nitrat (Si3N4), yansıtıcı kaplamalar için ise altın/krom (Au/Cr) kullanıldı. Farklı altlıklar üzerinde oluşturulan bu ince filmlerin doğasına ve işlevselliğine ışık tutabilmek için, X-ışını kırınım yöntemi ile yapısal analizler; foto lüminesans, kızılötesi ve mor ötesi-görünür bölge spektroskopileri ile optik analizler; atomik kuvvet mikroskobu ile morfolojik analizler yapıldı. Üretilen Au/Cr ince filmleri, alternatif kullanıma uygunluğunun değerlendirilebilmesi için termal dayanım testine tabii tutuldu. Farklı üretim süreçleri, üretim sonrası ısıl işlemler ve bu süreçlerin malzeme üzerindeki etkileri, analiz ve test sonuçları üzerinden detaylı ol...

Solar Energy, 2021

In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-su... more In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-sulphide (Cu-Zn-Sn-S) precursor films by adding radio frequency (RF)-sputtered sodium fluoride (NaF) intermediate layers bringing a new approach to the bifacial sodium-incorporated treatment (BIST) and its effect on the properties of Cu2ZnSnS4 (CZTS) absorber films. Due to the absence of alkaline diffusion barrier layers on soda lime glass (SLG) substrates, Na additions from both NaF intermediate layers and SLG substrate were evaluated together. With additional NaF intermediate layers among the elemental metal stacks, the films exhibited better crystalline properties and a more compact structure. However, the amount of the Cu2-xS secondary phases formed on the surfaces increased by the additional NaF layers. Raman spectra confirmed the formation of the kesterite phase and showed the peaks corresponding to Cu3SnS4 and Cu2-xS secondary phases. Na diffusion originating from NaF layers deposited on molybdenum (Mo) films occurred in both directions of the CZTS film and the SLG substrate. The photoluminescence (PL) bands located at around 1.40 eV were attributed to the band to band (BB) transitions. The film with additional NaF intermediate layers exhibited higher carrier concentrations and lower resistivity than the other film due to the presence of the higher amount of Cu2-xS secondary phases on its surface.

Central European Journal of Chemistry, 2012

The conformational analysis of rasagiline [N-propargyl-1(R)-aminoindan] was performed by the dens... more The conformational analysis of rasagiline [N-propargyl-1(R)-aminoindan] was performed by the density functional theory (DFT) B3LYP method using the 6–31++G (d,p) basis set. A single point energy calculations based on the B3LYP optimized geometries were also performed at MP2/6-31++G (d, p) level. The vibrational frequencies of the most stable conformer of rasagiline was calculated at the B3LYP level and vibrational assignments were made for normal modes on the basis of scaled quantum mechanical force field (SQM) method. The influence of mesylate and ethanedisulfonate salts on the geometry of rasagiline free base and its normal modes are also discussed.

Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephtha... more Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method under various RF powers in the range of 25–100 W. Structural, morphological, optical and electrical properties of the films were investigated by X-ray diffractometer, atomic force microscope, UV–Vis spectrometer and Hall effect measurement system. All the obtained films had a highly preferred orientation along [002] direction of the c-axis perpendicular to the flexible PET substrate and had a high-quality surface. The energy band gap (Eg) values of the films varied in the range of
3.30–3.43 eV. The minimum resistivity of 1.84 9 10-4 X cm was obtained at a 50 W RF power. The small changes in the RF power had a critical important role on the structural, optical and electrical properties of the sputtered AZO thin films on flexible PET substrate. In addition, UV sensing of the fabricated AZO thin film-based sensors was explored by using current–voltage (I–V) characteristics. The sensors were sensitive in the UV region of the electromagnetic spectrum.

In this paper, we study structural and morphological properties of metal-organic chemical vapour ... more In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another.

Chemical Papers, Mar 13, 2019

The all conformers of 5-methyl-4-(2-thizolylazo)resorcinol have been identified by Spartan 13 sof... more The all conformers of 5-methyl-4-(2-thizolylazo)resorcinol have been identified by Spartan 13 software. All conformers have been optimized B3LYP/6-311G (d, p) level of theory in Gaussian 09 software. According to potential energy surface search, 5-methyl-4-(2-thizolylazo)resorcinol has eight conformers. All the structural parameters of the most stable conformer of 5-methyl-4-(2-thizolylazo)resorcinol are predicted using DFT (B3LYP) method with the same basis set given above. The vibrational frequencies are recorded by the Fourier transform infrared (FT-IR 4000-550 cm −1) and Fourier transform Raman (FT-Raman; 4000-100 cm −1) spectra in the powder form. The vibrational frequencies are predicted and compared with experimental FT-IR and FT-Raman ones. The experimental 1 H and 13 C NMR spectra have been recorded and compared with the theoretical chemical shifts determined by the GIAO method. The results of UV-Vis spectra of molecule are also presented. Theoretical results compared with the experimental results for the identification and characterization of 5-methyl-4-(2-thizolylazo)resorcinol molecule. Keywords 5-Methyl-4-(2-thizolylazo)resorcinol • DFT • FT-IR and FT-Raman spectra • NMR and UV-Vis spectra * Y. Erdogdu

Applied Physics A, Dec 19, 2018

In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with st... more In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with steps of 50 °C. InGaN/ GaN multi-quantum well structure is deposited on c-orientated sapphire wafer by metal organic chemical vapour deposition method. All the parameters except for temperature kept constant during growth period. InGaN/GaN structures with different In content are investigated by XRD technique. Their structural, optical and morphological characteristics are determined by high resolution X-ray diffraction, Fourier transform spectroscopy (FTIR), photo luminescence (PL), transmission and atomic force microscopy (AFM). According to FTIR and PL spectra's, it is noticed that band gap values coincide with blue region in the electromagnetic spectrum. As a result of transmission measurements it is seen that light is completely absorbed by the sample at approximately 390 nm. Using XRD technique, dislocation densities and strain are calculated. Full width at half maximum of the XRD peak values gained from X-ray diffraction are used in an alternative method called Williamson-Hall (W-H). Using W-H method, lateral and vertical crystal lengths and tilt angles are determined. Surface roughness parameters are investigated by AFM. Different properties of GaN and InGaN layers are compared as dependent on increasing temperature. According to AFM images it is seen that these structures have high surface roughness and large crystal size. All the results yielded from the mentioned methods are in good agreement with the previous works done by different authors.

gazi university journal of science, 2014

In this work, ZnO thin films with different thickness (100 nm and 50 nm) were deposited onto flex... more In this work, ZnO thin films with different thickness (100 nm and 50 nm) were deposited onto flexible-transparent substrates by high vacuum (HV) reactive direct current (DC) magnetron sputtering technique, using oxygen as a reactive gas. The structural and optical properties of the films were investigated by X-ray diffractometer (XRD), room temperature photoluminescence (PL) and UV–Vis spectrometer. The both obtained films had a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. The e lectronic transitions from the conduction band to the valence band (called as band gap) of the films was about 3.2 eV. It was observed that the exitonic transition energy of the films shifted blue emission with increasing the film thickness. In addition, the optical transmittances of the films were about 80 % in the visible region .

Journal of Materials Science: Materials in Electronics, 2020

In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriente... more In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriented sapphire substrate using metal organic chemical vapor deposition method. Optical properties of the structure are investigated by photoluminescence (PL) and ultraviolet (UV-Vis.) spectras. According to PL results, direct bandgap of AlN is determined around 2.80 eV. In UV-Vis. spectra it is seen that conduction of AlInN layer starts at 360 nm. Swanepoel envelope method is applied on transmission spectra and some optical properties such as refractive index (n), film thickness (t), absorption coefficient (α), and extinction coefficient (k) are determined. Forbidden energy bandgap is determined again from Tau method and it is compared with the value gained from PL spectra. This study is a rare one that presents optical properties of HEMTs using Swanepoel and Tau methods. In addition to this, it helps estimating how optical properties of HEMTs effect electrical properties.

Philosophical Magazine, 2015

This study demonstrates the power conversion efficiency enhancement on In0.19Ga0.81As/GaAs quantu... more This study demonstrates the power conversion efficiency enhancement on In0.19Ga0.81As/GaAs quantum well solar cells (QWSC). The solar cell structure was grown on n-type (100)-oriented GaAs substrate by using solid-source molecular beam epitaxy technique and divided into square pieces. In order to understand whether the eight quantum wells were grown or not, scanning electron microscopy (SEM), and secondary ion mass spectrometry characterizations were done at room temperature. After that, the Si3N4 antireflection layers were coated onto both two square pieces of In0.19Ga0.81As/GaAs QWSC structure and p-GaAs substrate at different temperatures by the radio frequency magnetron sputtering system. The optical properties of the Si3N4 coated and uncoated p-GaAs samples have been evaluated by means of ultraviolet-visible spectrometry measurements at room temperature. According to ultraviolet-visible spectrometry results, the best Si3N4 antireflection coated one was obtained at 100 °C substrate temperature. Thus, the In0.19Ga0.81As/GaAs QWSC structure with and without Si3N4 layer, which was coated at 100 °C substrate temperature, was selected for other measurements and processes. Moreover, the In0.19Ga0.81As/GaAs QWSC samples with and without Si3N4 antireflection coating were separately fabricated with different metallization materials for obtaining the solar cell electrical output parameters. AuGe and AuGeNi metallization materials were used for the fabrication processes. After fabrication, the electrical output parameters were extracted from the current-voltage measurements at room temperature both in dark and under AM1.5 – 1 Sun illumination. The proposed design which includes the AuGeNi metallization and Si3N4 antireflection layer enhanced the power conversion efficiency by 44.40%.

Semiconductors, 2015

The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering m... more The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering method. The properties of ZnMnO thin films were investigated by high-resolution x-ray diffractometer (HRXRD),atomic force microscopy (AFM), UV-Vis spectrometer and room temperature photoluminescence (PL), under the influence of substrate temperature. The substrate temperature was varied from 300, 400 and 500°C. With increasing the substrate temperature, the structure of the films changed from cubic to hexagonal. The cubic ZnMnO thin films grown along [210] direction, while the hexagonal ones grown along [002] direction. The changes in surface morphology provided a proof on the structural transition. Also, decrease and increase of optical band gap is associated with cubic or hexagonal structure of the films.

Journal of Materials Science: Materials in Electronics, 2014

In this paper, we study structural and morphological properties of metal-organic chemical vapour ... more In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another.

Journal of Molecular Structure

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Journal of Materials Science and Engineering B, 2013

Porous silicon layers manufactured by using (100), 1-5 ohm•cm p-type (boron doped) wafer by elect... more Porous silicon layers manufactured by using (100), 1-5 ohm•cm p-type (boron doped) wafer by electrochemical etching in HF etanol solution. Photoluminescence (PL) spectra of anodically etched silicon obtained for different conditions studied and surface characteristics are investigated by AFM. This study gives a simple way to determine specific surface are of porous silicon which plays a major role with porosity for explaining the blue shift in photoluminescence peak. Properties such as specific surface area, pore size, and pore size distribution, the main surface properties of layer are investigated from AFM data which are important material characteristics in many processing applications. The "specific surface area" (S specific) generally defined as the area of solid surface per unit mass of material, solid volume or cross section area. From 3-D reconstructions of AFM data, the surface area and the volume of the porous layer can be estimated directly and volume-surface specific area is calculated. For porous silicon this feature can be defined as the total surface area per volume and given by the unit m 2 /cm 3. The method is simple not need to construct a special set up for measurement and non destructive.

Solar Energy, 2021

Abstract In this work, we report the incorporation of sodium (Na) alkaline element into copper-zi... more Abstract In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-sulphide (Cu-Zn-Sn-S) precursor films by adding radio frequency (RF)-sputtered sodium fluoride (NaF) intermediate layers bringing a new approach to the bifacial sodium-incorporated treatment (BIST) and its effect on the properties of Cu2ZnSnS4 (CZTS) absorber films. Due to the absence of alkaline diffusion barrier layers on soda lime glass (SLG) substrates, Na additions from both NaF intermediate layers and SLG substrate were evaluated together. With additional NaF intermediate layers among the elemental metal stacks, the films exhibited better crystalline properties and a more compact structure. However, the amount of the Cu2-xS secondary phases formed on the surfaces increased by the additional NaF layers. Raman spectra confirmed the formation of the kesterite phase and showed the peaks corresponding to Cu3SnS4 and Cu2-xS secondary phases. Na diffusion originating from NaF layers deposited on molybdenum (Mo) films occurred in both directions of the CZTS film and the SLG substrate. The photoluminescence (PL) bands located at around 1.40 eV were attributed to the band to band (BB) transitions. The film with additional NaF intermediate layers exhibited higher carrier concentrations and lower resistivity than the other film due to the presence of the higher amount of Cu2-xS secondary phases on its surface.

Applied Physics A, 2015

Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephtha... more Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method under various RF powers in the range of 25-100 W. Structural, morphological, optical and electrical properties of the films were investigated by X-ray diffractometer, atomic force microscope, UV-Vis spectrometer and Hall effect measurement system. All the obtained films had a highly preferred orientation along [002] direction of the c-axis perpendicular to the flexible PET substrate and had a high-quality surface. The energy band gap (E g) values of the films varied in the range of 3.30-3.43 eV. The minimum resistivity of 1.84 9 10-4 X cm was obtained at a 50 W RF power. The small changes in the RF power had a critical important role on the structural, optical and electrical properties of the sputtered AZO thin films on flexible PET substrate. In addition, UV sensing of the fabricated AZO thin film-based sensors was explored by using current-voltage (I-V) characteristics. The sensors were sensitive in the UV region of the electromagnetic spectrum.

Bu tez çalışması kapsamında ince film optik kaplamalar üzerine araştırma ve geliştirme faaliyetle... more Bu tez çalışması kapsamında ince film optik kaplamalar üzerine araştırma ve geliştirme faaliyetleri gerçekleştirildi. Yansıtıcı ve yansıtıcı olmayan optik ince filmler fiziksel buhar biriktirme yöntemlerinden püskürtme ve eş odaklı püskürtme sistemleri kullanılarak üretildi. Yansıma önleyici kaplamalar için ince film malzeme olarak silikon nitrat (Si3N4), yansıtıcı kaplamalar için ise altın/krom (Au/Cr) kullanıldı. Farklı altlıklar üzerinde oluşturulan bu ince filmlerin doğasına ve işlevselliğine ışık tutabilmek için, X-ışını kırınım yöntemi ile yapısal analizler; foto lüminesans, kızılötesi ve mor ötesi-görünür bölge spektroskopileri ile optik analizler; atomik kuvvet mikroskobu ile morfolojik analizler yapıldı. Üretilen Au/Cr ince filmleri, alternatif kullanıma uygunluğunun değerlendirilebilmesi için termal dayanım testine tabii tutuldu. Farklı üretim süreçleri, üretim sonrası ısıl işlemler ve bu süreçlerin malzeme üzerindeki etkileri, analiz ve test sonuçları üzerinden detaylı ol...

Solar Energy, 2021

In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-su... more In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-sulphide (Cu-Zn-Sn-S) precursor films by adding radio frequency (RF)-sputtered sodium fluoride (NaF) intermediate layers bringing a new approach to the bifacial sodium-incorporated treatment (BIST) and its effect on the properties of Cu2ZnSnS4 (CZTS) absorber films. Due to the absence of alkaline diffusion barrier layers on soda lime glass (SLG) substrates, Na additions from both NaF intermediate layers and SLG substrate were evaluated together. With additional NaF intermediate layers among the elemental metal stacks, the films exhibited better crystalline properties and a more compact structure. However, the amount of the Cu2-xS secondary phases formed on the surfaces increased by the additional NaF layers. Raman spectra confirmed the formation of the kesterite phase and showed the peaks corresponding to Cu3SnS4 and Cu2-xS secondary phases. Na diffusion originating from NaF layers deposited on molybdenum (Mo) films occurred in both directions of the CZTS film and the SLG substrate. The photoluminescence (PL) bands located at around 1.40 eV were attributed to the band to band (BB) transitions. The film with additional NaF intermediate layers exhibited higher carrier concentrations and lower resistivity than the other film due to the presence of the higher amount of Cu2-xS secondary phases on its surface.

Central European Journal of Chemistry, 2012

The conformational analysis of rasagiline [N-propargyl-1(R)-aminoindan] was performed by the dens... more The conformational analysis of rasagiline [N-propargyl-1(R)-aminoindan] was performed by the density functional theory (DFT) B3LYP method using the 6–31++G (d,p) basis set. A single point energy calculations based on the B3LYP optimized geometries were also performed at MP2/6-31++G (d, p) level. The vibrational frequencies of the most stable conformer of rasagiline was calculated at the B3LYP level and vibrational assignments were made for normal modes on the basis of scaled quantum mechanical force field (SQM) method. The influence of mesylate and ethanedisulfonate salts on the geometry of rasagiline free base and its normal modes are also discussed.

Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephtha... more Al-doped zinc oxide (AZO) thin films of thickness 150 nm were deposited on polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method under various RF powers in the range of 25–100 W. Structural, morphological, optical and electrical properties of the films were investigated by X-ray diffractometer, atomic force microscope, UV–Vis spectrometer and Hall effect measurement system. All the obtained films had a highly preferred orientation along [002] direction of the c-axis perpendicular to the flexible PET substrate and had a high-quality surface. The energy band gap (Eg) values of the films varied in the range of
3.30–3.43 eV. The minimum resistivity of 1.84 9 10-4 X cm was obtained at a 50 W RF power. The small changes in the RF power had a critical important role on the structural, optical and electrical properties of the sputtered AZO thin films on flexible PET substrate. In addition, UV sensing of the fabricated AZO thin film-based sensors was explored by using current–voltage (I–V) characteristics. The sensors were sensitive in the UV region of the electromagnetic spectrum.

In this paper, we study structural and morphological properties of metal-organic chemical vapour ... more In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another.