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Öğe Analysis of Current-Voltage-Temperature and Capacitance-Voltage-Temperature Characteristics of Re/n-Si Schottky Contacts(SPRINGER, 2018) Durmus, Haziret; Kilic, Hamdi Sukur; Gezgin, Serap Yigit; Karatas, SukruThe current-capacitance-voltage characteristics of Re/n-type Si Schottky contacts have been measured in the temperature range of 60-300 K by steps of 20 K. The ohmic and Schottky contacts are made by the Pulsed Laser Deposition (PLD) technique. The values of barrier heights, ideality factors and serial resistances have been found to be strongly temperature dependent. In short, the ideality factor decreased and the barrier height increased with increasing temperature, when the temperature-dependent (I-V) characteristics were analyzed on the basis of the thermionic emission (TE) theory. The experimental barrier height and ideality factor were plotted against (kT) (-1) which gives two slopes, one is over the 60-140 K region and the other is over the 160-300 K region presenting a double Gaussian distribution of barrier heights. Two Gaussian distribution analyses of the I-V characteristics of the Re/n-type Si Schottky barrier diodes gave the mean barrier heights of 0.812 and 0.473 eV and standard deviations (sigma (s) ) of 102 mV and 55 mV, respectively. Therefore, these values of the mean barrier height have been verified with the modified ln(I (0)/ T (2)) - /2 k (2) T (2) vs (k T)(-1) plot which belongs to two temperature sections.Öğe Comparison of transition probabilities calculated using different parameters on WBEPM theory for some p-d and d-p transitions in excited atomic nitrogen(JOHN WILEY & SONS INC, 2007) Celik, Gultekin; Akin, Erhan; Kilic, Hamdi SukurThe transition probabilities between individual and multiplet lines for some quartet terms of excited p-d and d-p transition arrays of nitrogen atom have been calculated using the weakest bound electron potential model (WBEPM) theory. For determination relevant parameters, we employed both numerical Coulomb approximation (NCA) method and numerical nonrelativistic Hartree-Fock (NRHF) wave functions for expectation values of radii. The necessary energy values have been taken from experimental energy data in the literature. The expectation values of radii obtained using the two different methods have been employed in the calculation of transition probabilities of all transition arrays. The results obtained have been compared with either each other or NIST data. Good agreement with accepted values taken from NIST has been observed for related excited transitions. (c) 2006 Wiley Periodicals, Inc.Öğe Effect of Different Surface Treatments on Porcelain-Resin Bond Strength(WILEY, 2017) Yavuz, Tevfik; Ozyilmaz, Ozgun Yusuf; Dilber, Erhan; Tobi, Elif Sumeyye; Kilic, Hamdi SukurPurpose:The aim of this study was to evaluate the effects of various surface treatments on the surface structure and shear bond strength (SBS) of different ceramics. Materials and Methods: total of 192 disk-shaped cores were prepared using two all-ceramic systems, of which 168 were submitted to SBS tests, and 24 were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The ceramics used were IPS Empress e.max (EX) lithium glass-ceramic and Vita In-Ceram Zirconia glass-infiltrated zirconia (ICZ). The specimens were randomly divided into seven groups (n = 12) on the basis of the surface treatment used: control; SB-sandblasting with 50 mu m Al2O3 particles; CJ-chairside silica coating with 30 mu m SiO2 particles and silanization (Clearfil Porcelain Bond Activator); HF-etching in 5% hydrofluoric acid and silanization; ER-etching with an Er:YAG laser (10 W); ND-Nd:YAG laser etching (0.8 W); and FS-etching with a femtosecond laser (860 mW). A luting cement (Clearfil Esthetic) was photopolymerized on each treated ceramic disk. After subjecting the specimens to thermocycling (1000 cycles, 5 degrees C to 55 degrees C), SBS tests were performed using a universal testing machine. The data were analyzed with two-way ANOVA and Tukey's tests using a significance limit of 5%. Results: ong the EX ceramics, the CJ (29.10 MPa) and HF (26.07 MPa) specimens had statistically higher SBS values. For the ICZ ceramics, the highest value (28.08 MPa) was obtained for the CJ specimens. Conclusions: lanization after coating with silica improves the bond strengths of both EX and ICZ specimens, while HF etching is favorable only for the EX specimens.Öğe Effect of Different Surface Treatments on the Bond Strength of Lithium Disilicate Ceramic to the Zirconia Core(MARY ANN LIEBERT, INC, 2016) Yilmaz-Savas, Tuba; Demir, Necla; Ozturk, A. Nilgun; Kilic, Hamdi SukurObjective:The aim of this study was to evaluate the effect of different surface treatments [sandblasting, Erbium:Yttrium-Aluminium-Garnet (Er:YAG), and femtosecond lasers] on the shear bond strength (SBS) of the CAD-on technique. Background data:Although demand for all-ceramic restorations has increased, chipping remains one of the major problems for zirconia-based restorations. Materials and methods:Forty yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) zirconia plates (IPS e.max ZirCAD, Ivoclar Vivadent) were cut, sintered (12.4 x 11.4 x 3 mm) and divided into four groups according to the surface treatments (n = 10): a control group with no surface treatment (Group C), sandblasting with 50 mu m Al2O3 (Group S), Er:YAG laser irradiation (Group E), and femtosecond laser irradiation (Group F). Also, 40 cylindrical (5mm diameter, 2mm height) lithium disilicate (IPS e.max CAD) veneer ceramics were cut and fused to all zirconia cores by a glassfusion ceramic and crystallized according to the CAD-on technique. Specimens were subjected to shear force using a universal testing machine. The load was applied at a crosshead speed of 0.5 mm/min until failure. Mean SBS (MPa) were analyzed with one way ANOVA (p < 0.05). The failed specimens were examined under a stereomicroscope at x 20 to classify the mode of failure. Results:The highest SBS was observed in Group F (36 +/- 3.31 MPa), followed by Group S (33.03 +/- 5.05 MPa), and Group C (32.52 +/- 10.15 MPa). The lowest SBS was observed in Group E (31.02 +/- 4.96 MPa), but no significant differences were found between the control and surface treated groups (p = 0.377). All the specimens showed a mixed type of failure. Conclusions: Femtosecond laser application increased the bond strength between zirconia-veneer specimens. However, the novel CAD-on technique with no surface treatment also showed high bonding strength. Thus, this technique could prevent ceramic chipping without additional surface treatments.Öğe Effect of different surface treatments on the shear bond strength of resin cement to zirconia ceramic and metal alloy(TAYLOR & FRANCIS LTD, 2018) Yucel, Munir Tolga; Kilic, Ismail; Okutan, Yener; Tobi, Elif Sumeyye; Kilic, Hamdi Sukur; Kepceoglu, Abdullah; Donmez, Mustafa BorgaThe bonding of resin cement to ceramic materials plays an important role in dentistry. The purpose of this study is to evaluate the effects of various surface treatments on the shear bond strength (SBS) of zirconia ceramic and metal alloy. A total of 60 specimens were prepared from Y-TZP ceramic and metal alloy. The specimens were divided into three subgroups (n=10) that received different surface treatments for each material. An Er:YAG laser (ER), a femtosecond laser (FS), and air-borne particle abrasion (A) were employed as surface treatments. One specimen from each group was analyzed using a scanning electron microscope (SEM) at 500 x magnification after surface treatments. The self-adhesive resin cement was then bonded to the treated surfaces using a Teflon mold. The specimens were thermocycled for 5,000 cycles at 5-55 degrees C, and then the SBS test was performed. Kruskal-Wallis and Mann-Whitney U tests were used to determine the differences between the groups (p=0.05), and failure modes were evaluated for each specimen. Statistical analyses revealed significant differences between the surface treatment methods. The mean SBS values of the air-borne particle-abraded groups were higher than those of the other groups. The femtosecond-irradiated groups of each material showed significantly higher SBS values than the Er:YAG-irradiated groups (p<0.05). Within the limitations of this study, air-borne particle abrasion and the femtosecond laser were more effective than Er:YAG laser treatment.Öğe Effect of femtosecond laser beam angle and formed shape on surface roughness and shear bond strength between zirconia and resin cement(TAYLOR & FRANCIS LTD, 2018) Yucel, Munir Tolga; Kilic, Ismail; Kilic, Hamdi Sukur; Gundogdu, Yasemin; Okutan, YenerAchieving adhesion between resin cement and zirconia requires pretreatment of the surface. This in vitro study aimed to evaluate the effect of femtosecond laser beam angle and the shape of the formed surfaces, on the roughness and shear bond strength (SBS) of resin cement to zirconia ceramic. Seventy Y-TZP ceramic specimens were divided into seven groups (n=10). A femtosecond laser irradiation was performed on the ceramic surface of three shapes (spiral (SP), square (SQ) and circular (CI) and at two angles (30 and 90 degrees) to give SP-30, SQ-30 and CI-30 and SP-90, SQ-90 and CI-90, respectively. After treatment, the surface roughness of all specimens was evaluated using a profilometer. One specimen from each group was analysed using a scanning electron microscope. The bonded specimens were thermocycled 5000 times and then an SBS test was performed. Kruskal-Wallis and Mann-Whitney U tests were used to analyse surface roughness and SBS values. The control group had statistically lower surface roughness (R-a) values than the treated groups (p<0.05). SP-30 and SQ-30 laser treated specimens showed higher R-a values than the other specimens. Statistically significant SBS values (p=0.000) were observed between the groups. All laser treated samples showed greater SBS compared to the control group. SP-30, SQ-30 and SQ-90 groups showed the highest SBS values. Within the limitations of this experimental study, the highest mean values for R-a and SBS were achieved with SP and SQ surfaces using a 30 degrees angle laser beam.Öğe Effect of Various Lasers on the Bond Strength of Two Zirconia Ceramics(MARY ANN LIEBERT, INC, 2015) Kara, Ozlem; Kara, Haluk Baris; Tobi, Elif Sumeyye; Ozturk, Atiye Nilgun; Kilic, Hamdi SukurObjective: The purpose of this study was to compare and evaluate the effects of various laser systems on surface roughness and shear bond strengths of zirconia ceramics. Material and methods: Seventy-two ceramic discs (10 mmx2 mm) obtained from two sintered zirconia ceramics (Zirkonzahn, Zirkonzahn Prettau((R))) were divided into two groups (n=36) according to the computer-aided design (CAD)-computer-aided manufacturing (CAM) technique and then further divided into three groups (n=12). Each group was treated with one of the following: (1) femtosecond (FS), (2) Nd:YAG (NY), and (3) Er:YAG (EY) lasers. After laser irradiation, a scanning electron micrograph (SEM) was taken at 500x magnification for qualitative examination. Following surface roughness measurement by profilometry, resin cement (Rely X U200) was bonded to the ceramic specimens using Teflon tubes (3 mm height, 4 mm diameter). Specimens were stored in distilled water at 37 degrees C for 24 h and then thermal cycled for 5000 cycles. A shear bond strength (MPa) test was performed using a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed by two way analysis of variance (ANOVA) and Tukey honest significant difference (HSD) tests for pairwise comparisons among groups (p=0.05). Results: MPa and roughness were significantly affected by laser type (p<0.001), and there was no significant interaction between the two zircon ceramics. The group irradiated with FS laser had significantly higher (p<0.05) roughness and MPa mean values than those of the other groups. No significant difference was found between the groups irradiated with NY and EY laser (p>0.05). In the SEM, the surfaces of the FS group were rougher than those of the NY and EY groups. NY and EY surfaces were nearly smooth. Conclusions: FS laser is an effective surface treatment for roughening surfaces of zirconia ceramics. Furthermore, it reveals the highest MPa.Öğe ESR analysis of kumyer location archeological ceramics and determination of suitability for ESR dating(GAZI UNIV, 2017) Bakkal, Gamze; Sayin, Ulku; Isik, Ilker; Ozmen, Ayhan; Kilic, Hamdi SukurIn this study paramagnetic centers in quartz minerals of Kumyer Location archeological samples were identified using Electron Spin Resonance (ESR) technique. ESR spectra were recorded at different microwave powers and various spectrometer temperatures with JEOL JESFa-300 X-band ESR spectrometer located in Selcuk University Advanced Technology Research and Application Center (ILTEK). It was determined that there is Al, Ti-Li, Ti-H and Ge paramagnetic centers which were produced by natural radiation in quartz minerals of ceramic samples and ESR parameters of these centers were measured. In order to determine whereas Kumyer Location archeological ceramics are suitable samples for ESR dating, ESR spectra of artificial irradiated samples recorded at 300K and 81K temperature were analyzed. Thermal stability of Al and Ti centers were determined by isochronal annealing experiment of artificial irradiated samples. As a result of experimental studies, it was determined that quartz minerals of Kumyer location archeological ceramic samples have stable and radiation dependent paramagnetic centers thus, these samples can be used for ESR dating.Öğe An Experimental Investigation of Localised Surface Plasmon Resonance (LSPR) for Cu Nanoparticles Depending as a Function of Laser Pulse Number in Pulsed Laser Deposition(AMER INST PHYSICS, 2017) Gezgini, Serap Yigit; Kepceoglu, Abdullah; Kilic, Hamdi SukurCopper is a low cost metal and its nanoparticles have a unique optical properties such as LSPR. The location of LSPR wavelength can be tuned by controlling nanoparticles sizes and size distributions of nanoparticles, shapes and interparticle distances. This morphological changes are provided by controlling system parameters in PLD. For this work, 48000 and 36000 laser pulses from Nd:YAG laser were applied to produce Cu nanoparticle thin tilms. These thin films were characterised by performing-UV-VIS absorption spectroscopy, Atomic Force Microscopy (AFM) analysis. When the number of laser pulse decreases, the size of Cu nanoparticles and the number of nanoparticles arriving on the substrate are reduced, and LSPR peak of thin films are red shifted depending on the geometrical shapes of the Cu nanoparticles. We have driven a conclusion in this work that LSPR properties of Cu nanoparticles can be tuned by proposed method.Öğe Femtosecond laser induced photodynamic therapy on 5-ALA treated SKMEL-30 cells: An efficient theranostic strategy to combat melanoma(ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER, 2014) Kars, Meltem Demirel; Kara, Reyhan; Gundogdu, Yasemin; Kepceoglu, Abdullah; Kilic, Hamdi SukurPurpose: Photodynamic therapy (PDT) is a type of photo-chemotherapy that is based on the application of photosensitizer and irradiation of the region by laser sources. Photosensitizer and light interaction will develop reactive oxygen radicals ( O-1(2)) in the cells and elimination of cells by apoptosis or necrosis. Methods: Metastatic skin cancer cells SKMEL-30 were treated by 5-ALA in dark and then they were irradiated by 90-femtosecond (fs) laser with different pulse powers for different durations. The effects of 5-ALA mediated photodynamic therapy on the cells were determined by XTT proliferation kit and by flow cytometry measurements of Annexin V, 7-AAD and mitochondrial membrane potential alterations. Fluorescent accumulation of protoporphyrin IX was investigated by fluorometry and confocal laser microscope. Results: The viability tests for SKMEL-30 cells treated with different 5-ALA doses and femtosecond laser power and durations demonstrated that 635 nm, 45 mW pulse energy at 90 fs laser pulse applications for 60 sec to 1 mM 5-ALA exposed cells decreased the cell proliferation by 30%. Flow cytometric measurements exhibit that PDT caused 63% of mitochondria membrane potential alteration, 30% of cell death in the population by apoptosis and 39% of cells by necrosis. There was 1 mM 5-ALA exposure that also exhibited about 32% accumulation of fluorescence in the cells. Conclusion: The pretreatment of the cells with the precursor 5-ALA lets the imaging due to increased protoporphyrin IX fluorescence. This treatment method may be proposed as an effective theranostic strategy for melanoma because of its rapid and effective anticancer consequences. (C) 2014 Elsevier Masson SAS. All rights reserved.Öğe Identification of the Isomers Using Principal Component Analysis (PCA) Method(AMER INST PHYSICS, 2016) Kepceoglu, Abdullah; Gundogdu, Yasemin; Ledingham, Kenneth William David; Kilic, Hamdi SukurIn this work, we have carried out a detailed statistical analysis for experimental data of mass spectra from xylene isomers. Principle Component Analysis (PCA) was used to identify the isomers which cannot be distinguished using conventional statistical methods for interpretation of their mass spectra. Experiments have been carried out using a linear TOF-MS coupled to a femtosecond laser system as an energy source for the ionisation processes. We have performed experiments and collected data which has been analysed and interpreted using PCA as a multivariate analysis of these spectra. This demonstrates the strength of the method to get an insight for distinguishing the isomers which cannot be identified using conventional mass analysis obtained through dissociative ionisation processes on these molecules. The PCA results dependending on the laser pulse energy and the background pressure in the spectrometers have been presented in this work.Öğe An Investigation of Localised Surface Plasmon Resonance (LSPR) of Ag Nanoparticles Produced by Pulsed Laser Deposition (PLD) Technique(AMER INST PHYSICS, 2017) Gezgin, Serap Yigit; Kepceoglu, Abdullah; Kilic, Hamdi SukurNoble metal nano-structures such as Ag, Cu, Au are used commonly to increase power conversion efficiency of the solar cell by using their surface plasmons. The plasmonic metal nanoparticles of Ag among others that have strong LSPR in near-UV range. They increase photon absorbance via embedding in the active semiconductor of the solar cell. Thin films of Ag are grown in the desired particle size and interparticle distance easily and at low cost by PLD technique. Ag nanoparticle thin films were grown on micro slide glass at 25-36 mJ laser pulse energies under by PLD using nsNd:YAG laser. The result of this work have been presented by carrying out UV-VIS and AFM analysis. It was concluded that a laser energy increases, the density and size of Ag-NPs arriving on the substrate increases, and the interparticle distance was decreases. Therefore, LSPR wavelength shifts towards to longer wavelength region.Öğe Molecular Structure and TD-DFT Study of the Xylene Isomers(GAZI UNIV, 2019) Kepceoglu, Abdullah; Gundogdu, Yasemin; Dereli, Omer; Kilic, Hamdi SukurIn this work, we have investigated the xylene isomers in concepts of vertical and adiabatic ionization energy parameters and molecular orbital (HOMO-1, HOMO/SOMO, LUMO, LUMO+1) energies of the neutrals and singly charged cation radicals. As a first step of the calculations, conformational analysis has been performed for all isomers using the semi-empirical method with PM3 core type Hamiltonian. Geometry optimization and frequency calculations were performed by using Density Functional Theory (DFT) with Becke, three-parameter, Lee-Yang-Parr (B3LYP) exchange-correlation functional and 6-311++G(d,p) basis sets. UV-Vis electronic spectra of the neutral xylene isomers were calculated by using the TD-DFT method with cam-B3LYP functional and 6-311++G(2d,2p) basis set.Öğe Plasmonic Tuning of Gold Doped Thin Films for Layers of Photovoltaic Devices(AMER INST PHYSICS, 2016) Gezgin, Serap Yigit; Kilic, Hamdi Sukur; Kepceoglu, Abdullah; Bayir, Sercan; Nalbantoglu, Izzet Ercan; Toprak, AhmetIn order to increase the absorption rates in solar cells, increasing research activities on the plasmonic nanostructures are followed carefully. The plasmonic nanoparticles provides an important enhancement in the trapping of photons in the active layer of the solar cells by means of interaction between incident light and plasmonic nanoparticles. In order to obtain this approach, under of 5x10(-4) mbar and 1x10(-2) mbar ambient argon gas pressure, gold thin film was deposited on the silicon substrate by applying PLD system. The morphology of thin films obtained was investigated by AFM and SEM considering the effect of Ar gas pressure on the plasma plume. SPR peaks for Au nanoparticles deposited under 5x10(-4) mbar and 1x10(-2) mbar Ar gas pressure were observed at 756 nm and 658 nm wavelengths respectively. It has been stated that the SPR peak in the infrared is depend on the near field interaction between Au nanoparticles. Furthermore, when the pressure is increased to 1x10(-2) mbar Ar, it has been observed that the SPR peak for thin film is shifted towards to shorter wavelengths, and it has also been observed that the intensity of absorption peak is decreased.Öğe Production and Characterization of Titanium (Ti), Platinum (Pt) and Tantalum (Ta) Thin Films for Native DNA Biosensors(AMER INST PHYSICS, 2017) Genc, Eminegul; Kepceoglu, Abdullah; Gezgin, Serap Yigit; Kars, Meltem Demirel; Kilic, Hamdi SukurThe use of the femtosecond (fs) laser pulses for ablation applications have several advantageous and Laser Induced Forward Transfer (LIFT) is an ablation-driven transfer process. The use of fs laser pulses for LIFT is gaining a great attraction nowadays. The most of the Direct Writing (DW) methods are laser based techniques and the LIFT technique is the one of them. This spectacular technique allows high resolution without lithographic processes. In this study, we have grown Ti, Pt and Ta thin films on the microscope slides by Pulse Laser Deposition (PLD) teclmique using Nd:YAG laser in the high vacuum condition. As a result, thin films produced in this work is a good candidate to produce native DNA biosensors based on LIFT teclmique.
