Selamet, Yusuf
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Selamet, Y
Selamet, Y.
Selamet, Y.
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04.05. Department of Pyhsics
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1NO POVERTY
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2ZERO HUNGER
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4QUALITY EDUCATION
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9INDUSTRY, INNOVATION AND INFRASTRUCTURE
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37
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847
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This researcher does not have a WoS ID.
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41
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24
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14
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WoS Citation Count
601
Scopus Citation Count
650
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5
WoS Citations per Publication
14.66
Scopus Citations per Publication
15.85
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40
Supervised Theses
14
| Journal | Count |
|---|---|
| Journal of Electronic Materials | 4 |
| Journal of Physics D: Applied Physics | 2 |
| Tekstil ve Mühendis | 2 |
| Applied Surface Science | 1 |
| Diamond and Related Materials | 1 |
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Master Thesis Applications of Transparent Conductive Indium Tin Oxide Films in Automotive and Vitrifications Industries(Izmir Institute of Technology, 2009) Tuna, Öcal; Selamet, Yusuf; Selamet, YusufDue to its unique electrical and optical properties, highly doped n-type Indium tin oxide used for various applications such as smart glass, LCDs, OLEDs, solar cells and car windows. In this study Indium Tin Oxide (ITO) thin films were grown by both DC and RF magnetron sputtering techniques. To know deposition rate of ITO, system was calibrated for both DCMS and RFMS and then ITO were grown on glass substrate with the thickness of 70 nm and 40 nm by changing substrate temperature. The effect of substrate temperature, film thickness and sputtering method on structural, electrical and optical properties were investigated. Wan der Pauw method was used for electrical characterization and to use this method properly, we patterned ITO thin films by photolithography and Ion beam etching techniques. The results show that substrate temperature and film thickness substantially affects the film properties, especially crystallization and resistivity. The thin films grown at the lower than 150 oC showed amorphous structure. However, crystallization was detected with the further increase of substrate temperature. Substrate temperature and film thickness increment were lead to increase band gap of ITO which can be explained by BMS. Band gap of ITO was calculated to be about 3.64 eV at the substrate temperature of 150 oC, and it widened with substrate temperature increment. From electrical measurements the resistivity at room temperature was obtained 1.28*10 and 1.29*10 cm, for DC and RF sputtered films, respectively. We also measured temperature dependence resistivity and the Hall coefficient of the films, and we calculated carrier concentration and Hall mobility.Article Citation - WoS: 4Citation - Scopus: 4Effect of Aromatic Sams Molecules on Graphene/Silicon Schottky Diode Performance(Electrochemical Society, Inc., 2016) Yağmurcukardeş, Nesli; Aydın, Hasan; Can, Mustafa; Yanılmaz, Alper; Mermer, Ömer; Okur, Salih; Selamet, YusufAu/n-Si/Graphene/Au Schottky diodes were fabricated by transferring atmospheric pressure chemical vapor deposited (APCVD) graphene on silicon substrates. Graphene/n-Si interface properties were improved by using 5-[(3-methylphenyl)(phenyl) amino]isophthalic acid (MePIFA) and 5-(diphenyl)amino]isophthalic acid (DPIFA) aromatic self-assembled monolayer (SAM) molecules. The surface morphologies of modified and non-modified films were investigated by atomic force microscopy and scanning electron microscopy. The surface potential characteristics were obtained by Kelvin-probe force microscopy and found as 0.158 V, 0.188 V and 0,383 V as a result of SAMs modification. The ideality factors of n-Si/Graphene, n-Si/MePIFA/Graphene and n-Si/DPIFA/Graphene diodes were found as 1.07, 1.13 and 1.15, respectively. Due to the chain length of aromatic organic MePIFA and DPIFA molecules, also the barrier height φB values of the devices were decreased. While the barrier height of n-Si/Graphene diode was obtained as 0.931 eV, n-Si/MePIFA/Graphene and n-Si/DPIFA/Graphene diodes have barrier height of 0.820 and 0.720 eV, respectively.Conference Object Growth and Characterization of Carbon Nanostructures(American Institute of Physics, 2007) Selamet, Yusuf; Yüce, GörkemCarbon nanostructures were grown by arc-discharge method and characterized by SEM, AFM, STM, and XRD techniques. We observe broadening in the radial distribution of nanofibers grown with Co and Ni application. The nanofibers grown with Co/Ni application were straighter and shorter in length than nanofibers without Co/Ni application. This might be due to catalyst particle poisoning resulting in termination of the growth process earlier than expected.Article Citation - WoS: 6Citation - Scopus: 6Influence of Buffer Layers on Ni Thin Film Structure and Graphene Growth by Cvd(IOP Publishing Ltd., 2015) Özçeri, Elif; Selamet, YusufBuffer and/or adhesive layers were used to decrease the dewetting of Ni thin film at graphene growth temperatures of around 900 °C. Depositing a thin buffer (Al2O3) layer onto SiO2/Si substrate significantly reduced the dewetting effect and surface roughness of Ni catalyst film. Thin adhesive (Cr) layers with or without Al2O3 buffer layers increased the texturing in (1 1 1) orientation, which was promoted by growing at an elevated temperature (450 °C). The effects of pretreatment and growth temperature on crystal orientation, grain size and surface roughness of Ni film were analyzed. Our results indicated a large positive correlation coefficient between the film thickness and surface roughness for thinner and non-buffered films, and a negative correlation coefficient between the thickness and 900 °C -annealed film roughness for thicker and buffered films. The graphene coverage was greatly improved over the films grown with Al2O3 and/or Cr layers. In summary, we suggest that growing high quality, large area, 1- or 2-layer graphene on polycrystalline Ni transition metal thin film is optimized by using Al2O3 and/or Cr layers to reduce Ni dewetting, surface roughness, and groove depth while controlling grain size and texturing in (1 1 1) orientation by annealing at 900 °C.Article Citation - WoS: 8Citation - Scopus: 10Experimental and Computational Investigation of Graphene/Sams Schottky Diodes(Elsevier Ltd., 2018) Aydın, Hasan; Bacaksız, Cihan; Yağmurcukardeş, Nesli; Karakaya, Caner; Mermer, Ömer; Can, Mustafa; Senger, Ramazan Tuğrul; Şahin, Hasan; Selamet, YusufWe have investigated the effect of two different self-assembled monolayers (SAMs) on electrical characteristics of bilayer graphene (BLG)/n-Si Schottky diodes. Novel 4″bis(diphenylamino)-1, 1′:3″-terphenyl-5′ carboxylic acids (TPA) and 4,4-di-9H-carbazol-9-yl-1,1′:3′1′-terphenyl-5′ carboxylic acid (CAR) aromatic SAMs have been used to modify n-Si surfaces. Cyclic voltammetry (CV) and Kelvin probe force microscopy (KPFM) results have been evaluated to verify the modification of n-Si surface. The current–voltage (I–V) characteristics of bare and SAMs modified devices show rectification behaviour verifying a Schottky junction at the interface. The ideality factors (n) from ln(I)–V dependences were determined as 2.13, 1.96 and 2.07 for BLG/n-Si, BLG/TPA/n-Si and BLG/CAR/n-Si Schottky diodes, respectively. In addition, Schottky barrier height (SBH) and series resistance (R s ) of SAMs modified diodes were decreased compared to bare diode due to the formation of a compatible interface between graphene and Si as well as π–π interaction between aromatic SAMs and graphene. The CAR-based device exhibits better diode characteristic compared to the TPA-based device. Computational simulations show that the BLG/CAR system exhibits smaller energy-level-differences than the BLG/TPA, which supports the experimental findings of a lower Schottky barrier and series resistance in BLG/CAR diode.Article Citation - WoS: 4Citation - Scopus: 5Identifying Threading Dislocations in Cdte Films by Reciprocal Space Mapping and Defect Decoration Etching(American Institute of Physics, 2018) Polat, Mustafa; Bilgilisoy, Elif; Arı, Ozan; Öztürk, Orhan; Selamet, YusufWe study threading dislocation (TD) density of high-quality cadmium telluride (CdTe) layers grown on a (211) oriented GaAs substrate by molecular beam epitaxy. High-resolution X-ray diffraction was performed to calculate the density of screw-type TDs by measuring the broadening of the asymmetrical (511) Bragg reflections of CdTe epilayers. In addition, total TD densities were determined by the Everson-etching method and were compared with screw TDs. Our results show that the total TD densities in CdTe films were dominated by those with screw character. The screw component TDs are estimated to account for more than 90% of the total TD density. CdTe layers grown at a thickness of less than 3.0 μm typically exhibit the screw TD densities in the 106 cm-2 and 107 cm-2 range. It can be noted that as the nucleation temperature increases, i.e., ≥222 °C, both the area density of TDs with the screw component of the CdTe films and the total TD density are roughly four times larger than those of the epilayer grown at the nucleation temperature of 215 °C. Furthermore, we discuss the influence of the II/VI flux ratio on the density of threading dislocations. The contribution of screw TDs to the total TD density showed a significant decrease in roughly 30% in the case of a high II/VI flux ratio. We further examine the reciprocal space maps in the vicinity of the (422) reflections.Master Thesis Growth and Characterization of Carbon Nanotubes Over Co-mo/Mgo Catalysts(Izmir Institute of Technology, 2010) İnce Yardımcı, Atike; Selamet, YusufThis thesis work is focused on synthesis of high quality and high yield Carbon nanotubes by methane decomposition catalytic chemical vapor deposition method on Co-Mo/MgO catalyst prepared by gel-combustion method. Catalyst contained weight %1.06 Co and weight %0.86 Mo having a molar ratio of Co:Mo:MgO;0.5:0.25:10. CNTs were grown in a quartz tube. In this study, three different growth conditions were examined. Argon, hydrogen or mixture of two gases were added to methane during growth. And for all of the three growth conditions, four different pretreatment processes were investigated. Pretreatment lasted for one hour at 850 oC. Firstly hydrogen effect was examined with 200 sccm flow rate, then argon effect was examined with again 200 sccm flow rate. And the third pretreatment included both argon and hydrogen gases flow together. For these three pretreatment conditions cooling and heating processes also took place with the same gas rates. However, the last pretreatment condition was carried out with hydrogen gas at 850 oC for just one hour, and for heating and cooling processes argon was used. The highest quality CNTs were sythesized under pure hydrogen atmosphere for both pretreatment and growth processes. Then, three different H2 flow rates were investigated; 100, 150 and 200 sccm. High hydrogen flow rate during growth was better for CNT growth in terms of quality. Growth temperature was performed as another important parameter. Four different temperatures were investigeted; 850 oC, 900 oC, 950 oC and 1000 oC. With increasing growth temperatures, structural quality increased and tangled CNTs formation decreased. It was found that 950 oC was the optimum growth tempertaure to obtain high yield of CNT. Finally, the growth time effect on CNT growth was examined for four different growth times; 10, 20, 30 and 40 minutes and the results showed that amount of CNTs increased with increasing time and CNTs became longer and graphitization was higher at longer growth times. Disorder also decreases with increasing time.Master Thesis Characterization of Molecular Beam Epitaxially Crown Cdte Layers Over Gaas by Spectroscopic Ellipsometry(Izmir Institute of Technology, 2014) Günnar, Merve; Selamet, YusufThe infrared detectors consist of two main parts that are optical elements and sensing elements. The sensor component is generally formed by semiconductor materials that can detect Infrared (IR) light which cannot be seen by human eye. Mercury Cadmium Telluride (MCT, HgCdTe) is widely used as a sensor material for this purpose. The adjustable bandgap (0-1.5 eV) which corresponds to energies of IR light can be obtained by changing the composition x of cadmium (Cd) in the ternary alloy Hg1-xCdxTe. HgCdTe has very high quantum efficiency for the detectible IR wavelengths in the atmospheric windows. HgCdTe which has a great importance in defense industry as an IR detecting material should be grown with high crystallinity in order to obtain high resolution images even under bad weather conditions. In addition, HgCdTe must be grown uniformly over a large area in order to have large format and high operability focal plane arrays. The defect density of HgCdTe strongly depends on the lattice mismatch between substrate and HgCdTe. In order to reduce the lattice mismatch which causes dislocations in HgCdTe the best suitable option is to grow Cadmium Telluride (CdTe) buffer layer on a substrate before growing HgCdTe. Studies have been focusing on semiconductors which are Gallium Arsenide (GaAs), Silicon (Si) and Germanium (Ge) as alternative substrates for CdTe growth. In this study, the CdTe films grown on (211) oriented GaAs wafers by molecular beam epitaxy (MBE) were characterized by ex-situ spectroscopic ellipsometry (SE). The properties of CdTe films such as thickness, surface roughness and optical constants were characterized by comparison with the growth conditions. It was also investigated that how these properties vary over the film surface. Characterization results were compared to those obtained by atomic force microscopy (AFM), Nomarski microscopy, Fourier transformation infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The temperature dependencies of the optical properties of the material obtained by SE were also investigated.Article Citation - WoS: 54Citation - Scopus: 53Nitrogen Doping for Facile and Effective Modification of Graphene Surfaces(Royal Society of Chemistry, 2017) Yanılmaz, Alper; Tomak, Aysel; Akbalı, Barış; Bacaksız, Cihan; Özçeri, Elif; Arı, Ozan; Senger, Ramazan Tuğrul; Selamet, Yusuf; Zareie, Hadi M.We report experimental and theoretical investigations of nitrogen doped graphene. A low-pressure Chemical Vapor Deposition (CVD) system was used to grow large-area graphene on copper foil, using ethylene as the carbon source. Nitrogen-doped graphene (N-graphene) was prepared by exposing the graphene transferred to different substrates to atomic nitrogen plasma. The effect of varying nitrogen flow rates on doping of graphene was investigated while keeping the power and time constant during the process. The N-graphene was characterized via Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Tunneling Microscopy and Spectroscopy (STM and STS), and Fourier Transform Infrared spectroscopy (FTIR). Raman mapping of N-graphene was also performed to show homogeneity of nitrogen on the graphitic lattice. XPS results have revealed the presence of different nitrogen configurations in the graphitic lattice with similar doping concentrations. Density functional theory (DFT) based calculations showed that the periodic adsorption of N atoms predominantly occurs on top of the C atoms rather than through substitution of C in our N-graphene samples. Our results indicate a feasible procedure for producing N-graphene with homogenous and effective doping which would be valuable in electronic and optical applications.Article Citation - WoS: 2Citation - Scopus: 2Surface Roughness Estimation of Mbe Grown Cdte/Gaas(211)b by Ex-Situ Spectroscopic Ellipsometry(American Institute of Physics, 2016) Karakaya, Merve; Bilgilisoy, Elif; Arı, Ozan; Selamet, YusufSpectroscopic ellipsometry (SE) ranging from 1.24 eV to 5.05 eV is used to obtain the film thickness and optical properties of high index (211) CdTe films. A three-layer optical model (oxide/CdTe/GaAs) was chosen for the ex-situ ellipsometric data analysis. Surface roughness cannot be determined by the optical model if oxide is included. We show that roughness can be accurately estimated, without any optical model, by utilizing the correlation between SE data (namely the imaginary part of the dielectric function, <ϵ2 > or phase angle, ψ) and atomic force microscopy (AFM) roughness. <ϵ2 > and ψ values at 3.31 eV, which corresponds to E1 critical transition energy of CdTe band structure, are chosen for the correlation since E1 gives higher resolution than the other critical transition energies. On the other hand, due to the anisotropic characteristic of (211) oriented CdTe surfaces, SE data (<ϵ2 > and ψ) shows varieties for different azimuthal angle measurements. For this reason, in order to estimate the surface roughness by considering these correlations, it is shown that SE measurements need to be taken at the same surface azimuthal angle. Estimating surface roughness in this manner is an accurate way to eliminate cumbersome surface roughness measurement by AFM.