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3D-graphene-laser patterned p-type silicon Schottky diode
(Elsevier Sci Ltd, 2021) Orhan, Elif Oz; Efil, Esra; Bayram, Ozkan; Kaymak, Nuriye; Berberoglu, Halil; Candemir, Ozun; Pavlov, Ihor
The influence of the laser patterning (LP) process on the quality of graphene (Gr) film and Schottky diode characteristics was researched in this study. First of all, p-type silicon (Si) was patterned by homemade femto-second laser source. To compare the resulting effect, non-patterned n-Si and p-Si were used as substrates. To achieve vertically oriented three-dimensional (3D) Gr nanosheets (VGNs) onto the laser patterned p-type Si, non patterned n-Si, and p-Si substrates, we used Radio-Frequency Plasma Enhanced Chemical Vapor Deposition (RFPECVD) technique. Then, Raman analyses for VGNs obtained on patterned and non-patterned p-Si and n-Si substrates were conducted. All results indicate that the Gr obtained on all substrates is vertically oriented. Scanning electron microscopy (SEM) analyses were also performed to obtain information about the morphological properties of the 3D Gr structure. In addition, the influence of the laser patterning at the Gr-Si interface was evaluated by comparing two sets of devices which are junctions of Gr-Laser Patterned Si (Gr-LPSi) and GrInsulator-Silicon (Gr-I-Si) at 300 K in the dark medium. D1 device consists of a Gr-LPSi junction that involves RFPECVD grown Gr on the silicon, whose surface exposed the laser beam for patterning. D2 device consists of a GrI-Si junction that involves RF-PECVD grown Gr onto the silicon, whose surface involves a thin native oxide layer (similar to 2 nm). The results show that the laser treatment causes an increment in Schottky barrier height (SBH) and decreases leakage currents under a reverse bias voltage of the diode. Notably, we have seen the influence of the laser patterning process on 3D Gr nano-sheets which is that the entire surface of the substrate has now reformed new structures in the nano-sphere and nano-rose morphology, so we believe that this is the first work that shows these structures in this form.
Current voltage analyses of Graphene-based structure onto Al2O3/p-Si using various methods
(Pergamon-Elsevier Science Ltd, 2020) Efil, Esra; Kaymak, Nuriye; Seven, Elanur; Orhan, Elif Oz; Bayram, Ozkan; Ocak, Sema Bilge; Tataroglu, Adem
The present study's main purpose is to determine the current-voltage (I-V) performance of Graphene (Gr) based hetero nanostructure produced on Al2O3/p-Si. Graphene synthesis was carried out using the chemical vapor deposition (CVD) technique on Copper (Cu) foils used as a metal catalyst and transferred onto Al2O3/p-Si using the conventional transfer method. The I-V characteristics of this structure were measured in the dark environment, and the electrical properties of the Gr/Si structure were characterized at room temperature. The rectifying ratio (RR) of the structure was found to be about 103 at +/- 3 V. The electrical properties of ideality factor (n), series resistance (R-S), and barrier height (Phi(b)) were examined by using the theory of Thermionic Emission (TE), Norde's method, and Cheung's method. The values of Phi(b), which were calculated using Norde's method, Cheung's method, and the theory of thermionic emission (TE), were found to be 0.69 eV, 0.71 eV, and 0.68 eV, respectively. The ideality factor was found to be approximately 3.89 according to the theory of TE. The values of series resistance were also determined using the Norde's method and Cheung's two different parameters (dV/dln (I) and H(I)) found to be 9.60 k Omega, 9.12 k Omega, and 5.94 k Omega, respectively.
CVD VE PECVD TEKNİĞİ KULLANILARAK BAKIR FOLYOLAR ÜZERİNDE GRAFEN NANOYAPILARIN ELDE EDİLMESİ VE KARAKTERİZASYONU
(2019) Bayram, Ozkan; İğman, Erdal; Şimşek, Önder
Bu çalışmada, CH4 gazı kullanılarak bakır folyolar üzerinde grafen ince filmlerin sentezlenmesi amaçlanmıştır.İnce filmlerin elde edilebilmesi için plazma destekli kimyasal buhar biriktirme (PECVD) ve kimyasal buharbiriktirme (CVD) yöntemi kullanılmıştır. Bakır alt-taşlar, standart ön temizlik yapıldıktan sonra kuvars camdanyapılmış reaktöre yerleştirilmiştir. Vakum odasının taban basıncı 5-10 mTorr’a düşürüldükten ve hidrojen gazıile tavlama işlemi yapıldıktan sonra, CH4 gazı ortama gaz akış kontrol ünitesi yardımıyla gönderilmiştir. PECVDsisteminde; RF güç kaynağı (13,56 MHz), kontrol ünitesi vasıtasıyla aktif hale getirilerek, üretilen enerji ortamagönderilmiştir. İşlem basıncı 100 mTorr, sıcaklık 600 ?C, RF gücü 50 W ve kaplama süresi ise 20 dakika olarakayarlanmıştır. CVD tekniğinde ise, RF gücü ortadan kaldırılmış ve büyütme sıcaklığı 1000 ?C olarakbelirlenmiştir. Elde edilen Grafen nanoyapıların karakterizasyonu için Raman, SEM ve TEM analizlerigerçekleştirilmiştir. Raman sonuçlarına göre, CVD yöntemiyle elde edilen yapılar, tek tabaka grafen yapısınıdoğrulamıştır. Bununla beraber PECVD tekniği ile tek tabaka grafen nanoyapılardan ziyade çok tabakalı yapıelde edildi.
Determination of the Optical Properties of ppTh Nanostructured Films Obtained by RF Plasma Polymerisation Technique
(2019) Bayram, Ozkan
In this study, it is aimed to obtain plasma polymerized Thiophene (ppTh) thin films by Radio Frequency (RF) plasma polymerization technique and to determine optical, chemical and morphological properties of these films. ppTh thin films were fabricated at 25, 50, 75 and 100 W RF power, 15 minutes coating duration and 500 mTorr base pressure. ppTh thin films were analyzed by Scanning Electron Microscopy (SEM), FTIR and Uv-Vis spectroscopy. Functional groups of thin films were determined by FTIR spectroscopy, and it was investigated how coating parameters affect the chemical structure of these films. Optical properties such as absorbance, transmittance and optical band gap were determined by Uv-Vis spectroscopy. The optical band gaps of the ppTh thin films were determined to be 2.97 eV, 3.13 eV, 3.17 eV and 3.68 eV with increasing RF power, respectively. In addition, all thin films were highly transparent in the visible region (500 nm), and this transparency tended to increase with increasing RF power. SEM analysis showed that the thin films had nanosphere structure and the radius of these spheres was about 90 nm.
Dielectric characteristics and electrical conductivity behavior of graphene/Al2O3/p-type silicon structure
(Elsevier Science Sa, 2021) Kaymak, Nuriye; Orhan, Elif Oz; Bayram, Ozkan; Ocak, Sema Bilge
Graphene nanosheets (Gns) obtained by the chemical vapor deposition (CVD) method have been employed for the fabrication of Graphene/Al2O3/p-type silicon (Si) structure. The Raman, scanning-electron-microscopy (SEM) and transmission-electron-microscopy (TEM) have been used to analyze the morphology and structural features of the graphene nanosheet. The dielectric features and electrical-conductivity of Graphene/Al2O3/p-type Si have been studied in the frequency range 10 kHz-400 kHz and in the voltage range,-4 V to +4 V at 300 K. The obtained experimental outcomes imply that electrical conductivity and dielectric features of Graphene/ Al2O3/p-type Si were found out to be powerful functions of frequency and applied bias voltage. It can be seen that almost all of the interface states between metal and silicon contribute to modify of dielectric features of Graphene/Al2O3/p-type Si structure.
Double-exponential current-voltage (I-V) behavior of bilayer graphene-based Schottky diode
(Iop Publishing Ltd, 2021) Kutluoglu, Esra Efil; Orhan, Elif Oz; Tataroglu, Adem; Bayram, Ozkan
Researches on layered materials such as graphene have attracted lots of attention recently. It has been shown that these materials have make a junction with many semiconductor materials that behave like Schottky diodes and have rectifying characteristics. The comprehension of its fabrication process and properties are a critical need toward graphene-based integrated electronics. The purpose of this study is to find out the current-voltage (I-V) performance of Bilayer Graphene (BLGr) based heterostructure fabricated on Al2O3/p-Si, and the effect of BLGr on diode parameters. Graphene has been grown on copper (Cu) foil by Chemical Vapor Deposition (CVD) method and transferred onto Al2O3/p-Si by using the polymethyl methacrylate (PMMA) wet transfer method. Raman analysis has been performed to obtain supportive information about CVD synthesized graphene film. The I-V plot of the diode exhibited two linear regions named Region 1 (0.08-0.19 V) and Region 2 (0.21-0.40 V). The double-exponential I-V behavior of the diode has been analyzed. The diode characteristics such as barrier height (phi(B0)), series resistance (R-s), and ideality factor (n) have been calculated by using thermionic emission (TE), Norde, and Cheung methods. Especially, the values of the barrier height were compared with one another. It was found that they are in good agreement. Additionally, current conduction mechanisms of the diode were investigated using the forward bias ln(I) versus ln (V) plot. At lower and higher forward bias regions, the conduction mechanisms were determined as ohmic behavior and trap charge limiting current mechanism (TCLC), respectively.
Electrical properties of Graphene/Silicon structure with Al2O3 interlayer
(Springer, 2020) Kaymak, Nuriye; Bayram, Ozkan; Tataroglu, Adem; Ocak, Sema Bilge; Orhan, Elif Oz
The electrical properties of the fabricated Al/Gr/Al2O3/p-Si structure have been analyzed using frequency-dependent capacitance/conductance-voltage (C/G-V) measurements. Graphene (Gr) nanosheets were grown on to copper (Cu) catalyst substrate, which has 99.99% purity, by Chemical Vapor Deposition (CVD) technique, and then the Graphene was transferred on -Al2O3/p-Si by the standard transfer process. The Graphene structures have been characterized by Raman Spectroscopy and Transmission Electron Microscopy (TEM) analyses, and the results of both analyses confirmed the monolayer/bilayer Graphene nanostructure. The forward and reverse bias G- V and C-V measurements of this structure have been performed in 10 kHz-400 kHz and at 300 K. The frequency dispersion in C and G can be evaluated for interface state density ( D it) and series resistance ( R s) values. The values of D it and R s are dependent on frequency and increase with decreasing frequency. The R s - V graph shows a peak form at all frequencies in the depletion region and vanishes with increasing frequency. The obtained results suggest that the prepared structure can be used in electronic device applications.
Gamma-ray irradiation effects on capacitance and conductance of graphene-based Schottky diode
(Elsevier, 2021) Kutluoglu, Esra Efil; Orhan, Elif Oz; Bayram, Ozkan; Ocak, Sema Bilge
The purpose of this study is to determine the effects of gamma (gamma)-ray irradiation on capacitance and conductance features of Al/Graphene/Al2O3/p-Si structure. Graphene has been grown on copper foil by the Chemical Vapor Deposition (CVD) method and transferred onto Al2O3/p-Si by the wet transfer method. After Al/Graphene/Al2O3/p-Si structure has been exposed to 30 kGy and 60 kGy gamma-ray irradiation, capacitance, and conductance measurements have been accomplished at 300 K. Electrical parameters have been compared before and after gamma-ray irradiation for 50 kHz and 500 kHz. These results have been confirmed that capacitance and conductance values have increased after gamma-ray irradiation and, have decreased when the radiation dose was increased from 30 kGy to 60 kGy. It has been observed that series resistance has decreased after 30 kGy radiation dose and has increased with increasing radiation dose.
Graphene/polyaniline nanocomposite as platinum-free counter electrode material for dye-sensitized solar cell: its fabrication and photovoltaic performance
(Springer, 2020) Bayram, Ozkan; Igman, Erdal; Guney, Harun; Demir, Zeynep; Yurtcan, Mustafa Tolga; Cirak, Cagri; Hasar, Ugur Cem
In this study, it was aimed to produce graphene/polyaniline nanocomposite thin films as counter electrode materials by PECVD system and to determine the photovoltaic performances of these counter electrodes in dye-sensitized solar cells (DSSCs). Graphene/polyaniline counter electrode (GPCE) material was produced in two different steps. Firstly, a single-layer and multilayer graphene thin films were produced on the fluorine-doped tinoxide (FTO) substrates. Then, polyaniline (PANI) thin films were grown on each graphene thin films using plasma polymerization technique, and eventually the production of the graphene/PANI nanocomposite was completed. The fabricated graphene/PANI nanocomposites were used in place of platinum (Pt)-counter electrode which is widely used in DSSCs and the photovoltaic performance of these counter electrodes was investigated. The DSSCs consisted of titanium dioxide (TiO2) nanotube photoanode, N719 dye, iodolyte liquid electrolyte, and graphene/PANI nanocomposite counter electrode. I-V measurements were carried out in order to calculated photoconversion efficiency (PCE) and it was found that the these efficiency of GPCEs changed between 0.56 and 1.36% according to the number of graphene layers. The photovoltaic performance of DSSC, consisting of TiO2 nanotube photoanode and Pt-counter electrode was 1.1%.
Photoluminescence and structural properties of zirconium dioxide thin films produced by RF sputtering technique
(Springer, 2021) Bakacak, Pinar K.; Gur, Emre; Bayram, Ozkan; Tuzemen, Sebahattin; Simsek, Onder
In this study, Zirconium Oxide (ZrO2) thin films were produced by using radio frequency magnetron sputtering method on glass substrate at various pressures. The effects of growth pressure on the characteristics of grown Zirconia nanostructures were investigated by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Uv-Visible Spectroscopy and Photoluminescence Spectrometry (PL). XRD analysis showed that peaks of the monoclinic and tetragonal phases were more effective at low growth pressure, but different monoclinic phase peaks were present at increasing growth pressures. The surface morphological properties of the films such as average and maximum roughness, changed significantly with increasing growth pressure, and the maximum peak height first increased to 40 nm and then decreased to 20 nm. The optical transmittance of these thin films was examined in the 450-1100 nm wavelength range, covering both the visible and near-infrared spectral range, and it was found to be approximately 95% at 550 nm wavelength, and the optical band gaps were calculated to be approximately 3.26 eV by PL analyses. Uv-Visible spectroscopy analysis showed that the refractive index of the Zirconia films decreases from 2.09 to 1.79 with increasing wavelength of the incident photon. ZrO2 thin films are considered potential materials for transparent electronic devices because of their high transmittance value.
Photovoltaic performance of non-covalent functionalized single-layer graphene in dye-sensitized solar cells (DSSCs)
(Springer, 2021) Igman, Erdal; Bayram, Ozkan; Mavi, Ahmet; Hasar, Ugur Cem; Simsek, Onder
In this study, it was aimed to fabricate new effective alternative counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). For this purpose, firstly, single-layer graphene (SLG) thin films were grown by chemical vapor deposition (CVD) method. Then, these films were separately functionalized with 1,8-cineole (ppCin/SLG), D-Limonene (ppLim/SLG) and Thiophene (ppTh/SLG) by plasma polymerization. Number of layers in CVD-grown graphene determined by Raman, transmission electron microscope (TEM) and ultraviolet-visible (UV-Vis) spectroscopy. Chemical structures of plasma polymerised (pp) thin films were investigated by Fourier transform infrared (FTIR) spectroscopy. Photovoltaic parameters of DSSCs were calculated, and electrocatalytic properties of CEs were investigated by electrochemical impedance spectroscopy (EIS). Polymer functionalization greatly enhanced the electrical conductivity and electrocatalytic activity properties of graphene compared to that of SLG. The efficiencies of DSSCs with ppCin/SLG and ppLim/SLG CEs were 1.10% and 1.02%, respectively. As a result, the cell efficiencies of ppCin/SLG and ppLim/SLG could be as alternative materials to platinum (Pt) counter electrode.
Plasma polymerized linalool (ppLin): an antimicrobial and biocompatible coating
(Tubitak Scientific & Technological Research Council Turkey, 2019) Cakmak, Kenan; Bayram, Ozkan; Solak, Kubra; Kaban, Guzin; Simsek, Onder; Mavi, Ahmet
Bacterial infections in medical devices and drug resistance of bacteria can cause chaos in the world due to loss of lives in addition to the cost of device revisions, quarantine, disinfection of infected areas, and patient treatment. Antibacterial coatings of essential oils on medical devices can prevent bacterial attachment and reduce costs. Linalool is an antibacterial constituent of essential oils. Herein, we examine for the first time the fabrication and characterization of radio frequency (RF) plasma polymerized hydrophilic thin films from linalool (ppLin) by varying deposition parameters (RF power and deposition time) and the behavior of ppLin with two bacteria (Escherichia coli and Staphylococcus aureus) commonly related to microbial contamination of medical devices. While a dramatic reduction in E. coli and S. aureus attachment was observed on ppLin films, their hydrophilic surface was also bactericidal to S. aureus. Additionally, ppLin films were shown to be adherent and noncytotoxic to human fibroblast cells. ppLin can be potentially integrated into medical and other clinical devices as a promising low-cost biocompatible antimicrobial coating.
A study on 3D graphene synthesized directly on Glass/FTO substrates: Its Raman mapping and optical properties
(Elsevier Sci Ltd, 2019) Bayram, Ozkan
In this study, vertically oriented (3D) graphene nanostructures (VGN) were obtained on Glass and Fluorine doped tin oxide (FTO) substrates at relatively low temperatures (approaximatelly at 400 degrees C) by using plasma enhanced chemical vapor deposition (PECVD) technique. VGNs were characterized using Raman, Uv-Vis and SEM spectroscopies, respectively. Raman spectroscopy showed that growth temperature significantly affected VGN formation and film quality. The layer structures of these VGNs were also confirmed by Raman mapping. The most important data obtained from this study is that although the applied radio frequency (RF) power is the same, the growth temperature significantly affects the graphene formation and morphologies. This was attributed to the fact that CH4 decomposition was very difficult at low temperatures. The optical transmittance of VGNs ranged from 50% to 95% (at 550 nm wavelength) and their electrical conductivity was also determined to be between 5.94 kohm/sqr and 11.2 kohm/sqr. The electrical and optical properties of VGNs, which have a large surface area, indicated that they may be an alternative material for sensor, solar cell and supercapacitor applications.
Thin films derived from Zn(Al)O mixed metal oxides nanoparticles dispersed in polyethylene glycol: Structural, morphological and optical properties
(Elsevier Sci Ltd, 2020) El Hassani, Kaoutar; Bayram, Ozkan; Anouar, Abdellah; Mavi, Ahmet
In this study, Zn(Al)O thin films were produced using colloidal solution of Zn(Al)O nanoparticles dispersed in polyethylene glycol (PEG). Zn(Al)O mixed metal oxides were obtained by a simple pyrolysis of Zn-Al containing layered double hydroxide materials with different Al content. Survey of textural analysis of Zn(Al)O mixed oxides displayed characteristic peaks of ZnO structure. The calculated ratios of lattice parameters c/a were found to be 1.61 and 1.60 for 3-ZAO and 5-ZAO, respectively. The optical transmittance of the prepared thin films was not significantly affected by the increase in Al content; however, this increase changed the optical band gap from 3.27 eV to 3.33 eV. ZAO thin films, which are both cost-effective with good optical properties, have the potential to be an alternative to those used in many optical devices lately.
Vertically oriented graphene nano-sheets grown by plasma enhanced chemical vapor deposition technique at low temperature
(Elsevier Sci Ltd, 2019) Bayram, Ozkan; Simsek, Onder
In this study, it was aimed to obtain vertically-oriented graphene nano-sheets (VGNs) on copper foils using CH4 gas as the precursor material by means of plasma enhanced chemical vapor deposition (PECVD) technique. VGNs were obtained at 50 W, 75 W and 100 W Radio Frequency (RF) powers by this technique and the effect of RF power on the morphological structure of graphene layers was investigated. VGNs were also analyzed by Raman spectroscopy, scanning electron microscopy (SEM) and water contact angle (WCA) measurements. The SEM images showed that the VGNs became more tightly packed with the increase of RF power and thus these coating parameters had a significant effect on the morphological structure. WCA analyzes for VGNs were also performed and it was found that VGNs obtained at 100 W RF power had higher contact angle value than the other RF powers. These VGNs, which have both large surface area and optically transparent, are thought to be materials that have the potential to be used in supercapacitors and solar cells.
WETTABILITY, OPTICAL AND CHEMICAL CHARACTERISTICS OF PLASMA-POLYMERIZED D-LIMONENE THIN FILMS
(2019) Bayram, Ozkan
In this study, organic based polymer thin films were obtained on various substrates using D-Limoneneessential oil, which is an organic compound by radio frequency (RF) plasma polymerization technique. Theoptical band gap and absorption spectra of thin films were investigated by Uv-VIS spectra and depending on theincreased RF power, the optical band gap of the thin films was found to be 3.19, 3.25 and 3.31 eV, respectively.WCA analyzes were also performed to determine the wettability properties of thin films and all thin films hadhydrophilic properties and these properties were significantly affected by increased RF power. Considering boththe morphological and optical properties of plasma polymerized (pp) D-Limonene thin films, it is thought thatthese films may be an alternative to those already used in current electronic applications due to their organiccompound-based nature.

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