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Öğe Atomically resolved imaging of highly ordered alternating fluorinated graphene(Nature Publishing Group, 2014) Kashtiban, Reza J.; Dyson, M. Adam; Nair, Rahul R.; Zan, Recep; Wong, Swee L.; Ramasse, Quentin; Geim, Andre K.One of the most desirable goals of graphene research is to produce ordered two-dimensional (2D) chemical derivatives of suitable quality for monolayer device fabrication. Here we reveal, by focal series exit wave reconstruction (EWR), that C2F chair is a stable graphene derivative and demonstrates pristine long-range order limited only by the size of a functionalized domain. Focal series of images of graphene and C2F chair formed by reaction with XeF2 were obtained at 80 kV in an aberration-corrected transmission electron microscope. EWR images reveal that single carbon atoms and carbon-fluorine pairs in C2F chair alternate strictly over domain sizes of at least 150 nm(2) with electron diffraction indicating ordered domains >= 0.16 mu m(2). Our results also indicate that, within an ordered domain, functionalization occurs on one side only as theory predicts. In addition, we show that electron diffraction provides a quick and easy method for distinguishing between graphene, C2F chair and fully fluorinated stoichiometric CF 2D phases.Öğe Crystalline-silicon heterojunction solar cells with graphene incorporation(Elsevier, 2021) Zan, Recep; Altuntepe, Ali; Altan, Tolga; Seyhan, AyseAmongst the silicon (Si)-based photovoltaics, heterojunction solar cells are the most promising solar cells due to their low thermal coefficient, high efficiency, and compatibility with newly emerged materials, such as graphene and perovskite. Studies on Si-based solar cells with graphene have increased dramatically in recent years. Thus far, high power conversion efficiency has been achieved up to 15 % by integrating graphene into graphene/Si Schottky junction solar cells since graphene has excellent electrical and optical properties. © 2021 Elsevier Inc.Öğe Effect of reduced graphene oxide addition on cathode functional layer performance in solid oxide fuel cells(Pergamon-Elsevier Science Ltd, 2023) Timurkutluk, Cigdem; Zan, Recep; Timurkutluk, Bora; Toruntay, Furkan; Onbilgin, Sezer; Hasret, Onur; Altuntepe, AliSolid oxide fuel cells (SOFCs) operating at high temperatures are highly efficient electrochemical devices since they convert the chemical energy of a fuel directly into heat and electrical energy. The electrochemical performance of an SOFC is significantly influenced by the materials and microstructure of the electrodes since the electrochemical reactions in SOFCs take place at three/triple phase boundaries (TPBs) within the electrodes. In this study, graphene in the form of reduced graphene oxide (rGO) is added to cathode functional layer (CFL) to improve the cell performance by utilizing the high electrical properties of graphene. Various cells are prepared by varying the rGO content in CFL slurry (1-5 wt %), the number of screen printing (1-3) and the cathode sintering temperature (900-1100 degrees C). The electrochemical behavior of the cells is evaluated by electrochemical performance and impedance tests. It is observed that there is a similar to 26% increase in the peak performance of the cell coated with single layer CFL having 1 wt % graphene and 1050 degrees C sintering temperature, compared to that of the reference cell. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Electronic functionalisation of graphene via external doping and dosing(TAYLOR & FRANCIS LTD, 2015) Bangert, Ursel; Zan, RecepThere exist many reports on functionalisation of graphene on a non-spatially resolved scale; this report concentrates on reviewing atomic-scale interactions of functionalising agents, i.e. on the electronic behaviour of single atoms, which are introduced as adatoms or lattice site impurities for the purpose of external doping and dosing to achieve bandgap engineering and electrical contacting of graphene; it also reviews the associated defects. Emphasis is put on visualisation of such interactions by advanced imaging in conjunction with localised spectroscopy techniques. Whereas the existing literature describing the development of such techniques in the application to graphene warrants a review in its own right, here the authors focus on observations, with modelling support, of the interaction phenomena themselves and not on the evaluation of measurements by such techniques. Atomic resolution transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS) in imaging and scanning mode, as well as scanning tunnelling microscopy (STM) are the most frequently applied techniques in aid of revealing topography and defect assisted interactions of graphene with foreign atoms and molecules. Electron-probe based investigations additionally lead to electron beam assisted interactions of foreign species with graphene. The graphene metal interaction observed in a transmission electron microscope is a prevalent example of how reactions occurring between metals and graphene can be emphasised and thereby assessed: metal-mediated etching of graphene has proven to be a common phenomenon after metal dosing, e.g. to fabricate electrical contacts. The review reports furthermore on investigations revealing atomic position, bonding and dynamics of non-metal p- and n-dopants as well as on revealing the functionalisation of graphene via molecular self-assembly, intercalation and nano-sculpting. Literature till the end of 2013/begin of 2014 is reviewed.Öğe Electronic Structure Modification of Ion Implanted Graphene: The Spectroscopic Signatures of p- and n-Type Doping(AMER CHEMICAL SOC, 2015) Kepaptsoglou, Demie; Hardcastle, Trevor P.; Seabourne, Che R.; Bangert, Ursel; Zan, Recep; Amani, Julian Alexander; Ramasse, Quentin M.A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations is used to describe the electronic structure modifications incurred by free-standing graphene through two types of single-atom doping. The N K and C K electron energy loss transitions show the presence of pi* bonding states, which are highly localized around the N dopant. In contrast, the B K transition of a single B dopant atom shows an unusual broad asymmetric peak which is the result of delocalized pi* states away from the B dopant. The asymmetry of the B K toward higher energies is attributed to highly localized sigma* antibonding states. These experimental observations are then interpreted as direct fingerprints of the expected p- and n-type behavior of graphene doped in this fashion, through careful comparison with density functional theory calculations.Öğe Enhanced photovoltaic performance of silicon-based solar cell through optimization of Ga-doped ZnO layer(Iop Publishing Ltd, 2023) Erkan, Serkan; Altuntepe, Ali; Yazici, Duygu; Olgar, Mehmet Ali; Zan, RecepIn the present study, the impact of deposition pressure and substrate temperature of Ga-doped Zinc Oxide (GZO) thin film and the photovoltaic performance of this structure as a transparent conductive oxide (TCE) layer in silicon-based solar cell were investigated. Implementing a single target of GZO, the structural, optical, and electrical properties of 350 nm thick GZO thin films with various deposition pressure (5 mTorr, 10 mTorr, 15 mTorr and 20 mTorr) at room temperature (RT) and substrate temperature (RT, 150 degrees C, 200 degrees C, 250 degrees C) at 15 mTorr deposition pressure were fabricated using RF magnetron sputtering technique. The aim here was to find out the GZO films with the optimum pressure and substrate temperature to incorporate them into solar cell as a TCE layer. The X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques were used to determine the structural properties of all samples. The optical transmission measurements were performed using spectroscopic Ellipsometer and the band gap values were calculated by Tauc plot using optical transmission data. In addition, the electrical characterization of the GZO samples were analyzed by the Van der Pauw method and Hall measurements. Finally, the most promising GZO thin film was determined based on the structural and optoelectrical characterization. The findings indicated that the XRD pattern of all the prepared films was dominated by (002) preferential orientation irrespective of the deposition pressure and substrate temperature. The AFM measurements showed that all the samples had a dense surface morphology regardless of the deposition pressures, but the surface morphology of the samples was clearly changed upon increasing substrate temperatures. The transmission values of the film did not significantly alter (similar to 82%) when the deposition pressures except for the substrate temperature of 200 degrees C (86%) were changed. The band gap values were calculated between 3.30 eV and 3.36 eV, which can be associated with enhancement of crystalline quality of the films. The lowest resistivity and the highest carrier concentration values belonged to the film fabricated at 15 mTorr@200 degrees C by 2.0 x 10-3 omega.cm and 1.6 x 1020 cm-3, respectively. Both increasing the deposition pressure (up to 15 mTorr) and substrate temperature (up to 200 degrees C) contributes to improving the crystallite size, widening the optical band gap, lowering the resistivity, and increasing the carrier concentration. In order to evaluate and compare the effect of both deposition pressure and substrate temperature, Silicon-based solar cells were fabricated using the most promising layers (15 mTorr@RT, 15 mTorr@200 degrees C). The cell performance with the GZO thin film as a TCE layer showed that varying both the pressure and substrate temperature of the GZO film contributed to enhancing the solar cell parameters. Thus, the conversion efficiency increased from 9.24% to 12.6% with the sequential optimization of pressure and temperature. It can be concluded that the pressure applied during the deposition and substrate temperature had a significant impact on the properties of GZO thin films and its photovoltaic performance of solar cell used as TCE layer.Öğe Fabrication of CZTS thin film on flexible Cu-foil substrate by two-stage process(2024) Olğar, Mehmet Ali; Zan, RecepIn this research, CZTS thin films were grown on flexible Cu-foil substrates with varying sulfurization times. Distinct characterization methods were employed, including X-ray diffraction (XRD), Raman spectroscopy, Energy-Dispersive X-ray Spectroscopy (EDX), Scanning Electron Microscopy (SEM), optical transmission, and Photoluminescence (PL) measurements. Distinctive diffraction peaks characteristic of the kesterite CZTS phase were observed in the XRD analysis, occurring around at 2?= 28.45° (112), 47° (220/204), and 56° (312/116). Additionally, some secondary phases such as Cu2S and SnS were identified. Raman spectroscopy confirmed the presence of the kesterite CZTS phase, with a prominent peak detected at approximately ~336 cm-1, attributed to sulfur atom vibrations within the kesterite structure. Apart from CZTS structure, minor peaks suggesting the presence of the Cu2SnS3 (CTS) phase was detected. EDX analysis revealed compositions with Cu-poor content and Zn-rich content across all samples, with slight variations in sulfurization dwell times affecting the chemical composition. SEM imaging at different magnifications showed alterations in surface morphology and grain structures. Films sulfurized for 30 s and 60 s displayed a granular structure morphology, while extending the dwell time to 120 s resulted in a more compact surface morphology. Optical band gap values ranged between 1.57 and 1.60 eV. PL measurements consistently exhibited strong PL emission around 1.25 eV for all samples, attributed to various transitions within the band structure of CZTS film. The absence of observable band-to-band transitions in the PL measurements indicated the presence of intrinsic defect levels and recombination centers within CZTS. Overall, it was demonstrated in this study that CZTS thin films can be produced on flexible Cu-foils with short sulfurization times, thereby expanding the application areas of CZTS thin-film solar cells.Öğe GRAFEN SENTEZİ İÇİN ALT-TAŞ TEMİZLEME YAKLAŞIMLARI(2019) Altuntepe, Ali; Öztürk, M.; Kartal, Emre; Seyhan, Ayşe; Zan, RecepSon yılların nanoteknoloji alanında en ilgi çekici ve en yoğun araştırılan malzemelerinden bir tanesi olangrafen; yüksek elektrik ve ısı iletkenliği, saydamlık ve yüksek dayanım gibi birçok üstün özellikleri ile optoelektronikten medikal uygulamalara kadar geniş bir yelpazede kullanım alanına sahiptir. Grafen sentezinde ensık tercih edilen yöntemlerden biri kimyasal buhar biriktirme tekniği olup, bu teknikte kullanılan gazlar, alt-taş,alt-taş temizliği, sıcaklık, büyütme süresi, tavlama süresi, soğutma hızı ve basınç gibi birçok parametre grafensentezinde etkilidir. Bu parametreler arasında sentez sürecini direkt olarak etkileyen en önemli faktörlerden birtanesi alt-taş seçimi ve bunun temizlenme sürecidir. Bu çalışmada alt-taş olarak bakır tercih edilmiş olup, yüzeytemizliğinin grafen sentezine olan etkisi detaylı olarak araştırılmıştır. Bu anlamda literatürde bilinen dört farklıyüzey temizleme işlemi, grafen sentezinde kullanılan bakır folyolar için uygulanmış ve elde edilen sonuçlarortaya konmuştur. Sonuç olarak alt-taş temizliğinde grafen sentezini kolaylaştıran ve iyileştiren en etkiliyöntemlerin HF ile standart temizleme yöntemi olduğu belirlenmiş ve bu yöntemlerle tek katlı homojen grafensentezi gerçekleştirilmiştir. Diğer temizleme yöntemleri sonrası yapılan sentezde genellikle çok katmanlı vehomojen olmayan grafen filmler elde edilmiştir.Öğe Grafen Tabanlı Hibrit Saydam Elektrot Dizaynı Ve Günes Hücresi Uygulamaları(2020) Zan, Recep; Olgar, Mehmet Ali; Sürmegözlüer, Ayşe SeyhanIsıgı geçiren ve elektriksel olarak iletken olan saydam iletken elektrotlar (TCE), dokunmatik ve esnek ekran teknolojilerinde (LCD, OLED) ve fotovoltaik hücreler gibi birçok optoelektronik aygıtlarda kullanılan temel bilesenlerden bir tanesidir. Dogada bilinen rezervleri sınırlı olan indiyumun yogun olarak kullanıldıgı saydam iletken elektrotlar yüksek maliyet ve mekanik olarak düsük dayanım gibi dezavantajlara sahiptir. Bu özellikler tüm dünyada indiyum içermeyen saydam iletken elektrotların gelistirilmesi arayısını tüm dünyada hızlandırmıstır. Bu amaç dogrultusunda, projede çinko oksit (ZnO), alüminyum katkılı çinko oksit (AZO), molibden katkılı çinko oksit (MZO), galyum katkılı çinko oksit (GZO) ve indiyum kalay oksit (ITO) saçtırma teknigi kullanılarak farklı kalınlıklarda üretilmis ve yapısal, elektriksel ve optik özellikleri incelenmistir. Daha sonra bu yapılara tek tabakalı grafen transfer edilerek hibrit elektrot yapısı olusturulmus ve en iyi performans (yapısal, elektriksel ve optik) gösteren hibrit elektrot yapısı belirlenmistir. Projenin devamında silisyum tabanlı PN yapısı olusturulmus ve TCE olarak optimize edilen hibrit yapılar kullanılarak hetero-eklem günes hücrelerinin üretimi tamamlanmıstır. Bu kapsamda grafenli ve grafensiz bütün TCE yapılar kullanılarak hücreler üretilmis ve son asamada ise hücre verimlilikleri belirlenmistir. Tek tabakalı formdaki grafen kullanımı ile üretilen hibrit TCE yapıların kullanıldıgı hücrelerin verimliliginin grafen kullanılmadan üretilen hücrelerden daha yüksek oldugu tespit edilmistir. Bununla birlikte verimlilik artısının oransal olarak en yüksek oldugu hücrenin GZO+grafen yapısının kullanıldıgı hücre olmustur. Proje ile alternatif elektrotların gelistirilmesi, günes hücresi üretiminde daha az malzeme kullanımı ve/veya aynı miktarda malzeme kullanımı ile daha verimli hücre üretiminin mümkün olabilecegi gösterilmistir.Öğe Graphene for Si-based solar cells(Elsevier, 2020) Altuntepe, Ali; Seyhan, Ayse; Zan, RecepIn this paper, we report on the single layer graphene synthesis to establish the growth conditions and improve the opto-electronic properties that can be employed in silicon based heterojunction solar cells. To do this, the effect of hydrogen and methane flow on the graphene growth on copper foil in a CVD system was investigated. The analyses were conducted by changing either the hydrogen or the methane flow by keeping all the other growth parameters constant. Single layer graphene growth recipe was established in order to have the optimum optical transmission and sheet resistance values via amending the graphene growth conditions. It was found that the sheet resistance values of the single layer graphene should be lowered further to be used as transparent conductive electrode. However, the combination of graphene with indium tin oxide film functioned well as transparent conductive electrode in the silicon based the solar cells. Additionally, the cell efficiency increased by about 10% as a result of incorporating it with the single layer graphene. (C) 2019 Elsevier B.V. All rights reserved.Öğe Hydrogen storage capacity of two-dimensional MoS2(Pergamon-Elsevier Science Ltd, 2024) Altuntepe, Ali; Erkan, Serkan; Olgar, Mehmet Ali; Celik, Selahattin; Zan, RecepHydrogen storage holds a crucial place for the future of the world in terms of green energy. Two-dimensional materials, in particular, are important in this regard. The aim of this study is to evaluate the performance of MoS2 which is one of the most popular member of two-dimensional materials family. To do this, bulk and exfoliated MoS2 were used. Firstly, the liquid phase exfoliation method was employed to obtain exfoliated MoS2 layers. Then, the hydrogen storage potential of the bulk and exfoliated MoS2 was addressed under 1, 3, 5, 7, and 9 bar hydrogen pressure. After the absorption process, all the samples were characterized using XRD, Raman Spectrometer, and BET ahead of evaluating their hydrogen storage potential. The XRD pattern showed that the peak positions of bulk and exfoliated MoS2 were not affected critically by hydrogen storage. In the Raman spectra, the A1g and E2g 1 peaks of all hydrogenated materials shifted to low wavelengths. Moreover, the BET measurements revealed that the specific surface area and the pore size of the bulk MoS2 were 12.31 m2/g and <= 67.46 nm respectively. Additionally, the specific surface area and the pore size of the exfoliated MoS2 were 23.16 m2/g and <= 69.28 nm, respectively. The hydrogen storage potential of the bulk and the exfoliated MoS2 was evaluated through an MFC in sccm unit. The bulk and exfoliated MoS2 stored 220 and 450 sccm hydrogen, respectively. Besides, the weight percent hydrogen storage for H-MoS2 and H -exfoliated MoS2 was determined to be 1.2 and 2.4 wt%, respectively. In summary, this study has shown that exfoliated MoS2, one of the twodimensional materials, can play a critical role for hydrogen storage due to their high specific surface area.Öğe Improved CZTSe solar cell efficiency via silver and germanium alloying(Pergamon-Elsevier Science Ltd, 2024) Atasoy, Yavuz; Bacaksiz, Emin; Ciris, Ali; Olgar, Mehmet Ali; Zan, Recep; Ali, Ahmed M. J. Al-dala; Kucukomeroglu, TayfurIn this study, we report systematic investigation of the effects of Ag and Ge alloying on properties of CZTSe layers, as well as, on the performance of solar cells fabricated using these films. In this context, Ag-Ge doped CZTSe layers were produced by selenization of Cu/Sn/Zn/Cu/(Ag,Ge)/Se precursor stack structures using rapid thermal processing. All precursor stacks and the Ag-Ge doped CZTSe films obtained after selenization exhibited (Cu + Ag)-poor and Zn-rich chemical composition. XRD studies demonstrated pure kesterite phase for all reacted films. Raman spectra confirmed this finding. Cross-sectional SEMs showed large grain structure, which resulted from Ag-Se and Ge-Se liquid phase formation that assisted crystal growth during high temperature annealing. While a slight Ag-front-gradient was achieved in Ag-doped CZTSe film, the Ag gradient disappeared with incorporation of Ge into the lattice. Addition of Ge formed a gradient within the material such that near-contact region was more Ge-rich. Solar cells fabricated using films with various compositions demonstrated that double doping CZTSe with both Ag and Ge improved the device efficiency from about 5 % to over 8 %.Öğe Integration of graphene with GZO as TCO layer and its impact on solar cell performance(Pergamon-Elsevier Science Ltd, 2022) Zan, Recep; Olgar, Mehmet Ali; Altuntepe, Ali; Seyhan, Ayse; Turan, RasitIn this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (GZO) when employing them as a TCO layer on Si-based solar cell. GZO thin films with various thicknesses (50-450 nm) were fabricated by the sputtering method using a single target. The aim here was to determine the GZO film with the optimum thickness to incorporate it with single layer graphene as TCO. This thickness was found to be 350 nm as that was the best crystalline quality found in the Opattern. Further, this sample had the lowest sheet resistance and highest transmission values as confirmed by electrical (sheet resistance), and optical characterizations (transmission). Topographic (SEM and AFM), electrical (resistivity and carrier concentration) measurements were also conducted on the same sample. The graphene film grown on copper in a CVD system was then transferred on top of this sample to fabricate the hybrid TCO structure. We found that graphene integrated GZO hybrid TCO film showed higher sheet resistance due to high sheet resistance of graphene and similar optical properties thanks to high optical transmission of graphene. Employing graphene-based TCO layer in the solar cell resulted in higher open-circuit voltage, consequently improving the conversion efficiency from 10.0% to 11.2%. (c) 2021 Elsevier Ltd. All rights reserved.Öğe Investigating surface area and hydrogen pressure effects on LiH and NaH(Academic Press Inc Elsevier Science, 2024) Altuntepe, Ali; Erkan, Serkan; Olgar, Mehmet Ali; Celik, Selahattin; Zan, RecepNaH and LiH are theoretically capable of storing hydrogen, but several challenges remain to be overcome before they can be widely used for hydrogen storage. In this study, LiH and NaH were ball-milled and the effect of surface area and hydrogen pressure on hydrogen storage capacity was investigated using the solid-state hydrogen storage method. XRD patterns and Raman spectra show significant shifts in main peak positions of LiH and NaH after hydrogen adsorption. BET analysis shows a significant increase in the specific surface area of LiH and NaH from 6.25 m(2)/g to 12.35 m(2)/g and from 1.34 m(2)/g to 2.33 m(2)/g respectively due to ball milling. The FTIR spectra showed more bonds in the 400-1200 cm(-1) fingerprint region after storing hydrogen in LiH and NaH. This suggests structural changes with enhanced bond bending due to hydrogen. At 9 bar pressure, LiH and NaH exhibited excellent hydrogen storage, with ball-milled LiH reaching about 3.55 wt% and 652 sccm, and NaH achieving approximately 1.58 wt% and 291 sccm. These results highlight the significant influence of surface area and hydrogen pressure on hydrogen storage potential. Incorporating the storage potential within the evaluation of PEM fuel cell performance, we suggest that an increased storage capacity directly corresponds to an augmented power density. The analysis of power density over time revealed that the hydrogen adsorbed ball-milled LiH exhibited the highest power density, peaking at 0.075 Wcm(-2) over the long term. In contrast, LiH displayed a lower power density (0.025 Wcm(-2)) while maintaining its long-term performance. The hydrogen adsorbed NaH and hydrogen adsorbed ball-milled NaH displayed power densities 0.050 Wcm(-2) and 0.073 Wcm(-2), respectively, but they showed short-term performance.Öğe Investigating the Impact of Growth Time and Methane Flow on Graphene Synthesis using Nickel Foil(Gazi Univ, 2021) Bozkaya, Meryem; Altuntepe, Ali; Ate, Hakan; Zan, RecepGraphene has been one of the most investigated nanomaterials in recent years due to its one atom thickness nature and its extraordinary properties such as high conductivity and excellent transmittance in visible range, bendability and high carrier mobility. Although there are many techniques to grow graphene, chemical vapor deposition technique is one of the best approach to synthesize homogeneous and commercial scale graphene in thin film form. Many parameters can affect the quality and homogeneity of the graphene film that is grown with this technique. In this study, two growth parameters which are methane flow rate and growth time were investigated to find out their effect on the quality of the graphene film, which is grown on nickel foil. Graphene film grown with different flow rates of methane (from 20 to 50 sccm) and growth time (50 to 20 mins.) were examined. We found that single layer graphene film could only be grown under 20 sccm methane flow in 20 mins. growth time as evidenced via Raman spectroscopy measurements. Furthermore, the single layer graphene film was found to be in high homogeneity as confirmed by Raman mapping. On the other hand, multi-layer graphene film was obtained by increasing both methane flow and growth time.Öğe Katkılı Ve Katkısız Grafen Sentezi Ve Günes Hücresi Uygulamaları(2020) Zan, Recep; Sürmegözlüer, Ayşe SeyhanKarbonun bir formu olan grafen yüksek elektrik ve ısı iletkenligi, yüksek ısık geçirgenligi, yüksek yüzey alanı, esneklik ve dayanıklılık gibi özellikler ile öne çıkarken, yüksek tabaka direnci ve sıfır band aralıgı gibi özelliklerle dezavantajlı hale gelmektedir. Grafendeki bu handikapların giderilmesi ve kullanım alanlarının yaygınlastırılması amacıyla katkılama (doping) gerçeklestirilerek grafenin elektronik ve optik özellikleri kontrol edilebilmektedir. Bu anlamda yürütülen bu projenin temel amacı katkısız ve katkılı grafen filmlerin sentezlenerek silisyum tabanlı günes hücrelerine uygulanabilirligini ve performanslarını belirlemektir. Proje kapsamında katkısız ve katkılı grafen filmlerin sentezi bakır folyo üzerinde kimyasal buhar depolama (CVD) teknigi kullanılarak gerçeklestirilmistir. Kalıcı katkılama elde etmek için katkılama grafen sentezi sırasında gerçeklestirilmistir. Katkıcılar belirlenirken katkı atomlarının atomik yarıçapları karbona yakın olan ve karbonla bag yapabilen nitrojen ve bor tercih edilmistir. Bu kapsamda katkılama amacıyla nitrojen kaynagı olarak gaz formda amonyak ve nitrojen ve sıvı formda piridin; bor kaynagı olarak gaz formda diboran, sıvı formda fenilboronik asit ve katı formda trietilbor kullanılmıstır. Katkıcı miktarı ve sentez süresinin optimizasyonu ile homojen ve genis alanda katkılı grafen filmler sentezlenmistir. Bu sekilde üretilen katkısız ve katkılı grafen filmler hetero-eklem günes hücrelerine uygulanmıstır. Es zamanlı olarak günes hücrelerinde saydam iletken elektrot olarak kullanılan indiyum kalay oksitin (ITO) film kalınlıgı optimize edilmistir. Hücre üretimi kapsamında öncelikli olarak silisyum tabanlı p-n yapısı olusturulmus ve daha sonra ITO üzerine kaplanan grafen filmlerle olusturulan hibrit saydam iletken elektrot yapısı p-n yapısında kullanılarak günes hücresinin üretimi tamamlanmıstır. Bu kapsamda grafensiz, katkısız grafen, nitrojen katkılı grafen ve bor katkılı grafen filmlerin kullanıldıgı günes hücreleri üretilerek performansları ve verimlilikleri belirlenmistir. Grafen kullanılan günes hücrelerinin kullanılmayan hücrelere göre daha yüksek verime sahip oldukları belirlenmistir. Ayrıca, katkılı grafen kullanılan hücrelerin de katkısız grafen kullanılan hücrelerden daha verimli oldugu tespit edilmistir. Bununla birlikte verimlilik artısının oransal olarak en yüksek oldugu hücrenin nitrojen katkılı grafenin kullanıldıgı hücre oldugu bulunmustur. Proje kapsamında gerçeklestirilen çalısmalarla grafen handikaplarının minimize edilmesi sonucunda opto-elektronik uygulamalarda kullanımının yaygınlastırılmasına, hibrit saydam elektrotların gelistirilmesine ve böylelikle günes hücresi üretiminde daha az malzeme kullanımı ve/veya aynı miktarda malzeme kullanımı ile daha verimli hücre üretiminin saglanmasına katkıda bulunulmustur.Öğe KİMYASAL BUHAR BİRİKTİRME YÖNTEMİ İLE GRAFEN SENTEZİNE TAVLAMA VE BÜYÜTME SÜRELERİNİN ETKİSİ(2019) Zan, Recep; Utku, Gülcan; Altuntepe, AliSon yılların en ilgi çekici malzemelerinden biri olan grafen yüksek iletkenlik, yüksek dayanım vesaydamlık gibi birçok üstün özelliğe sahiptir. Grafenin kimyasal buhar biriktirme tekniği kullanılaraksentezlenmesinde, büyütme sıcaklığı, büyütme süresi, tavlama süresi, basınç, kullanılan alt-taş,kullanılan gazların saflıkları ve akış miktarları gibi birçok parametre etkilidir. Bu parametrelerdenbüyütme ve tavlama süreleri grafen sentezinde en önemli parametrelerdendir, bu nedenle bu çalışmadabüyütme ve tavlama sürelerinin tek katmanlı homojen grafen sentezine olan etkisi araştırılmıştır. Farklıbüyütme ve tavlama süreleri kullanılarak üretilen grafen filmler Raman Spektroskopisi tekniğikullanılarak karakterize edilmiş olup tek tabakalı homojen grafen sentezi için üretim süreci optimizeedilmiştir. Genel anlamda tavlama sürelerinin 20 dakikadan 40 dakikaya kadar arttırıldığı deneygruplarında grafen kalitesinde ciddi bir değişim gözlenmemiştir. Büyütme sürelerinin arttırıldığı deneygruplarında ise 40 dakikaya kadar olan süre artışlarıyla doğru orantılı olarak grafen kalitesinin iyileştiğitespit edilmiştir.Öğe Niğde Üniversitesi Ar-Ge Strateji Belgesi (Nanoteknoloji Araştırmaları)(2017) Konuklu, Yeliz; Zan, Recep; Soylu, Asım; Ersoy, OrkunNanoteknoloji birçok alandaki uygulamalarından dolayı yüksek bir potansiyele sahip bir alandır. Uluslararası platformda Nanoteknolojik araştırma ve uygulamalar için yapılan yatırımlar günden güne artmaktadır. Dünyadaki bilimsel ve teknolojik gelişmeleri her alanda takip edebilmek ve uluslararası standartlara ulaşmak için Nanobilim ve Nanoteknoloji konusundaki çalışmaların ülkemizde de yoğunlaşması gerekmektedir. Hazırlanan strateji belgesinin temel amacı Ömer Halisdemir Üniversitesi'nin Nanoteknoloji Araştırmaları alanında mevcut araştırma - geliştirme potansiyelinin belirlenerek arttırılması, ayrıca üniversite-sanayi arasında işbirliğinin geliştirilmesi ve bu alanda ?Ar-Ge Strateji Belgesinin? hazırlanmasıdır. Hazırlanan Nanoteknoloji Araştırmaları Ar-Ge Strateji belgesi ile üniversite-sanayi işbirliği yapılarak katma değeri yüksek teknolojik ürünlerin ortaya çıkarılması ve geliştirilmesi hedeflenmektedir. Ömer Halisdemir Üniversitesi Nanoteknoloji Uygulama ve Araştırma Merkezimiz Nanoteknoloji alanında üç ana konu üzerinde yog?unlas?mıs?tır. Bunlar 1)fonksiyonel özellikli nanokompozit ve nanoenkapsülasyon çalışmaları 2) nanoyapıların üretimi ve optimizasyonu çalışmaları 3)karbon temelli nanomalzemelerin sentezi, karakterizasyonu ve farklı endüstrilerde kullanılabilirlikleri üzerine yapılan çalışmalardır. Ayrıca bazı araştırmacılarımız nano ölçekte manyetik özellik gösteren örneklerin üretimi ile ilgili çalışmalara başlamıştır. Ömer Halisdemir Üniversitesi, sahip olduğu insan kaynağı ve altyapı olanakları açısından Nanoteknoloji alanında ülkemizin ihtiyaç duyduğu Ar-Ge çalışmalarını yapacak ve bu alanda ilk beş üniversite arasına girebilecek potansiyele sahiptir. TÜBİTAK 1000 kodlu ?Üniversitelerde Ar-Ge Strateji Belgesi Hazırlatılması ve Uygulatılması? çağrısı kapsamında hazırlanan beş yıllık Ar-Ge Strateji Belgesi ile Ömer Halisdemir Üniversitesi?nin Nanoteknoloji Araştırmaları alanındaki mevcut potansiyelinin en iyi şekilde değerlendirilmesi ve ülkemizde ilk beş üniversite içerisine girmesi için gerekli yol haritası çizilmiştir. Ömer Halisdemir Üniversitesi Nanoteknoloji Araştırmaları alanında yapacağı çalışmalarla gelecek on yıl içerisinde sadece Türkiye?deki ilk beş üniversite arasına girmeyi değil aynı zamanda bu alanda dünyada da önemli bir eğitim ve Ar-Ge merkezi olmayı hedeflemektedir. Ömer Halisdemir Üniversitesi Nanoteknoloji Araştırmaları alanında Ar-Ge strateji Belgesi?nin hazırlanması esnasında üniversite-sanayi işbirliğinin desteklenmesi ve teşvik edilmesi konusunda üniversitenin Nanoteknoloji Araştırmaları Ar-Ge altyapısındaki eksiklikler tespit edilmiş ve bu eksikliklerin giderilmesine yönelik beş yıl içerisinde atılacak olan adımlar Üniversite üst yönetimi desteğiyle bes? adet is? paketi ile gerçekleştirilmiştir. Bunlar; 1.Nanoteknoloji Araştırmaları Mevcut Durum ve Sektörel ihtiyaç çalışmaları çalıs?tayının düzenlenmesi 2.Web Sayfası, Bros?ür, Posterlerin hazırlanması 3.I?s?birlig?i ve Tanıtım Toplantıları 4.Proje Hazırlama Eg?itimi: Nig?de Üniversitesinde Nanoteknoloji alanında çalıs?ma yapan ve bu alanda projeler yapmak isteyen üniversite personeline projeler hakkında bilgi verilecektir. 5.Nanoteknoloji Aras?tırmaları Ar-Ge Strateji Belgesinin Hazırlanması olarak özetlenebilir. Ömer Halisdemir Üniversitesi ?Nanoteknoloji Aras?tırmaları? alanındaki stratejik amaçları; 1. Nanoteknoloji alanında Ar-Ge faaliyetlerini artırmak, 2. Araştırma sonucunda ortaya çıkan bilginin geniş kitlelere ulaşmasını sağlamak, 3. Nanoteknoloji alanında işbirliğinin sağlanmasına yönelik akademik ve bilgilendirme toplantıları yapmak, 4. Nanoteknoloji alanında Ar-Ge altyapısının iyileştirilmesi ve geliştirilmesini sağlamak olarak belirlenmiştir.Öğe Nitrogen Doped Graphene Film Synthesis and Characterization(Gazi Univ, 2022) Zan, Recep; Altuntepe, Ali; Erkan, Serkan; Seyhan, AyseHaving a single atom thickness formed by the combination of carbon atoms in a hexagonal mesh, graphene has been one of the most intensely researched areas in recent years. This is especially due to its wide range of uses thanks to its numerous superior properties such as high electrical and thermal conductivity, high light transmittance, high strength and large surface area. Despite these superior properties, graphene's high sheet resistance and lack of energy band gap limit its use in optoelectronic applications. Yet, these disadvantages can be overcome by implementing doping to the graphene structure. However, although the doping selection and synthesis method are very important in the doped graphene synthesis process, the permanence and homogeneity of the doping is even more critical. In this study, the synthesis and characterization of pure and nitrogen-doped graphene were carried out on copper foil using CVD system. Pyridine was used for the synthesis of the doped graphene, as a carbon and nitrogen source. We found out that the use of the CVD technique allows both homogeneous and permanent doping. In addition to pyridine, in the present study, the film thickness was also optimized by providing a low amount of methane gas flow to the CVD system during the synthesis. To enable the characterization of doped films, Raman spectroscopy, Energy Dispersive X-ray spectroscopy and Xray photo electron spectroscopy techniques were used, and the film quality, thickness, homogeneity, doping rate and type were determined.Öğe Nitrogen doped single layer graphene for CZTS-based thin film solar cells(Elsevier, 2024) Olgar, Mehmet Ali; Erkan, Serkan; Altuntepe, Ali; Zan, RecepCdS thin films are commonly utilized as a buffer layer in chalcopyrite thin-film solar cells. However, due to the toxic nature of Cadmium (Cd), ongoing efforts are being directed towards exploring alternative options. In this contribution, doped graphene film with remarkable optical and electrical properties has been introduced for the first time as an alternative buffer layer, replacing CdS in CZTS thin-film solar cell application. In this study, nitrogen-doped graphene (N-doped graphene) film was utilized as a substitute buffer layer in the CZTS thin-film solar cell structure, replacing the conventional CdS thin film. For comparative analysis, CZTS/N-doped graphene and CZTS/CdS traditional solar cell structures were fabricated and separately characterized. The CZTS thin films produced were examined through EDX, XRD, SEM, Raman, optical transmission and PL spectroscopy measurements. According to performed analyses, the Cu-poor and Zn-rich kesterite CZTS thin films exhibited a uniform and dense polycrystalline microstructure as observed in surface and cross-sectional SEM images. XRD spectra of the kesterite CZTS thin film displayed predominant peaks corresponding to the (112), (220/204), and (312/116) diffraction planes of the kesterite CZTS phase. Raman spectra showed a dominant peak at similar to 336 cm (-1) associated with the kesterite CZTS phase. PL emission spectra indicated transitions from the conduction band to defect levels. The CVD-grown doped graphene film exhibited a 3.43 I-2D/I-G ratio and a 25 cm (-1) FWHM of the 2D peak, indicating a single -layer graphene according to Raman analysis. Permanent nitrogen doping with a 2% atomic concentration was confirmed by XPS measurement. The optical transmission measurement of the single layer doped graphene film showed a 95% transmittance value. Nitrogen doping was contributed to decrease the sheet resistance of the graphene film. The Glass/Mo/CZTS/N-doped graphene/i-ZnO/ITO/Al solar cell displayed a V-OC of 0.267 V, J(SC) of 24.6 mA/cm(2), FF of 36.46, and eta of 2.37%, showing higher FF and Jsc values but lower conversion efficiency compared to the Glass/Mo/CZTS/CdS/i-ZnO/ITO/Al traditional solar cell structure. Hence, the superior working function and transparency properties position the N-doped graphene film as a competitive buffer layer for use in CZTS-based thin-film solar cells.
