Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 14Citation - Scopus: 14Dispersion Stability of Amine Modified Graphene Oxides and Their Utilization in Solution Processed Blue Oled(Elsevier Ltd., 2020) Diker, Halide; Bozkurt, Hakan; Varlıklı, CananGraphene oxide (GO) was modified with amine derivatives which contain short (SACA) and long (LACA) alkyl chains. SACAs were n-propylamine, dipropylamine, propanolamine and LACAs were 2-ethylhexylamine, di-hexylamine, dioctylamine, and 1,12-diaminododecane and modified GOs (mGOs) were named as nPRYLA-GO, DPRYLA-GO, PRPOHA-GO, 2EHA-GO, DHA-GO, DOA-GO, and DADOD-GO, respectively. Amine modification resulted in approximately 2-folds of decrement in d-spacing of GO (8.36 angstrom). The C:O ratio, N% and d-spacing values were increased as the alkyl chain length of amine source increased. Except for PRPOHA-GO, all of the mGOs were thermally stable until 100 degrees C. All mGOs were dispersed in dimethylformamide (DMF), ethylene glycol (EG) and isopropyl alcohol (iPA). Regardless of their structural differences, all of the mGOs formed stable dispersions in DMF, whereas SACA-mGOs and LACA-mGOs were compatible with EG and iPA, respectively. DMF, EG and iPA dispersions of DOA-GO, 2EHA-GO, nPRYLA-GO and PRPOHA-GO were doped in Al4083 and prepared composites were utilized as hole transport layer in solution processed blue OLEDs. Ground state energy levels of Al4083:DOA-GO, Al4083:EG, Al4083:PRPOHA-GO, Al4083:2EHA-GO and Al4083:nPRYLA-GO extracted from their X-ray photoelectron spectra were 0.49 eV, 0.67 eV, 0.91 eV, 0.98 eV and 1.00 eV below the work function of ITO, respectively. Among all Al4083:mGOs, the best device performance was obtained with the device that contains Al4083:DOA-GO (in EG), which presented 1.6, 1.7 and 1.5 fold enhancements in current, power and external quantum efficiencies, respectively, compared to those of Al4083:EG based device.Article Citation - WoS: 19Citation - Scopus: 19Navigating Cie Space for Efficient Tadf Downconversion Woleds(Elsevier Ltd., 2020) Aksoy, Erkan; Danos, Andrew; Varlıklı, Canan; Monkman, Andrew P.High efficiency orange and green emitting perylene dyes have been synthesized and dispersed in an inert polymer host to form an optical downconversion layer. To avoid dye aggregation and allow controlled colour tuning, this layer was deposited in multiple low-concentration spin-coating steps, directly on top of a high performance blue thermally activated delayed fluorescence (TADF) organic light emitting diode (OLED). The orange downconversion layer partially absorbs the blue OLED emission, while emitting a complementary orange to give white light. However, as energy transfer between the TADF and perylene downconverter is based on emission and reabsorption, absorptive filtering of the blue OLED emission band necessitates the inclusion of an additional green-emitting perylene top-layer to achieve optimal white balance. The optimised white OLED fabricated in this way displayed excellent white colour balance (CIE x, y; 0.33, 0.33) with perfect stability, good colour rendering (CRI 80), and a high maximum efficiency (maximum EQE 17.2%) with minimal losses compared to the base blue OLED. This approach is widely applicable for generating white emission from any kind of blue OLED, and is compatible with a wide range of downconverting dyes and host materials.Article Citation - WoS: 5Citation - Scopus: 6Boosting Up Printability of Biomacromolecule Based Bio-Ink by Modulation of Hydrogen Bonding Pairs(Elsevier Ltd., 2020) Köksal, Büşra; Önbaş, Rabia; Başkurt, Mehmet; Şahin, Hasan; Arslan Yıldız, Ahu; Yıldız, Ümit HakanThis study describes low dose UV curable and bioprintable new bioink made of hydrogen bond donor-acceptor adaptor molecule 2-isocyanatoethyl methacrylate (NCO)modified gelatin (NCO-Gel). Our theoretical calculations demonstrate that insertion of 2-isocyanatoethyl methacrylate doubles the interaction energy (500 meV) between gelatin chains providing significant contribution in interchain condensation and self-organization as compared to methacrylic anhydride modified gelatin (GelMA). The NCO-Gel exhibits peak around 1720 cm?1 referring to bidentate hydrogen bonding between H-NCO and its counterpart O[dbnd]CN[sbnd]H. These strong interchain interactions drive chains to be packed and thereby facilitating UV crosslinking. The NCO-Gel is exhibiting a rapid, 10 s gelation process by the exposure of laser (3 W, 365 nm). The dynamic light scattering characterization also reveals that NCO-Gel has faster sol to gel transition as compared to GelMA depending on the UV curing time. The NCO-Gel was found to be more firm and mechanically strong that provides advantages in molding as well as bioprinting processes. Bioprinted NCO-Gel has shown sharp borders and stable 3D geometry as compared to GelMA ink under 10 s UV curing time. The cell viability tests confirm that NCO-Gel facilitates cell proliferation and supports cell viability. We foresee that NCO-Gel bioink formulation provides a promising opportunity when low dose UV curing and rapid printing are required. © 2020 Elsevier LtdArticle Citation - WoS: 7Citation - Scopus: 8Stable janus TaSe2 single-layers via surface functionalization(Elsevier Ltd., 2021) Kahraman, Zeynep; Başkurt, Mehmet; Yağmurcukardeş, Nesli; Chaves, A.; Şahin, HasanFirst-principles calculations are performed in order to investigate the formation of Janus structures of single-layer TaSe2. The structural optimizations and phonon band dispersions reveal that the formation and stability of hydrogenated (HTaSe2), fluorinated (FTaSe2), and the one-side hydrogenated and one-side fluorinated (Janus-HTaSe2F) single-layers are feasible in terms of their phonon band dispersions. It is shown that bare metallic single-layer TaSe2 can be turned into a semiconductor as only one of its surface is functionalized while it remains as a metal via its two surfaces functionalization. In addition, the semiconducting nature of single-layers HTaSe2 and FTaSe2 and the metallic behavior of Janus TaSe2 are found to be robust under applied uniaxal strains. Further analysis on piezoelectric properties of the predicted single-layers reveal the enhanced in-plane and out-of-plane piezoelectricity via formed Janus-HTaSe2F. Our study indicates that single-layer TaSe2 is a suitable host material for surface functionalization via fluorination and hydrogenation which exhibit distinctive electronic and vibrational properties. © 2020 Elsevier B.V.Article Citation - WoS: 3Citation - Scopus: 4Lipid Bilayer on Wrinkled-Interfaced Graphene Field Effect Transistor(Elsevier Ltd., 2021) Özkendir İnanç, Dilce; Çelebi, Cem; Yıldız, Ümit HakanThis study describes lipid bilayer-based sensor interface on SiO2 encapsulated graphene field effect transistors (GFET). The SiO2 layer was utilized as a lipid compatible surface that drives bilayer formation. The two types of surface morphologies i) wrinkled morphology by thermal evaporation (TE) and ii) flat morphology by pulsed electron deposition (PED) were obtained. The sensing performance of wrinkled and flat interfaced-GFETs were investigated, pH sensitivity of wrinkled interfaced-GFETs were found to be ten fold larger than the flat ones. The enhanced sensitivity is attributed to thinning of the oxide layer by formation of wrinkles thereby facilitating electrostatic gating on graphene. We foresee that described wrinkled SiO2 interfaced-GFET holds promise as a cell membrane mimicking sensing platform for novel bioelectronic applications. © 2020Article Citation - WoS: 30Citation - Scopus: 32Perylene-Embedded Electrospun Ps Fibers for White Light Generation(Elsevier Ltd., 2019) Güner, Tuğrul; Aksoy, Erkan; Demir, Mustafa Muammer; Varlıklı, CananPerylene dyes have been employed in the fabrication of white light due to their superior photophysical properties and relatively easy synthetic methods. However, their molecular aggregation in solid state is one of the main handicaps since it causes deviation in their optical properties and quenches photoluminescence quantum yields (Phi(f)). Investigation of the photophysical properties of a green (PTE), a yellow (PDI) and a new red (DiPhAPDI) emitting perylene derivative in solution, drop-casted films, polystyrene (PS) fibers and PS fibers embedded in poly (dimethyl siloxane) (PDMS) showed that PS:dye fibers prevent aggregation to some extend and allows high Of of dyes. The Of values of PTE, PDI and DiPhAPDI were all higher than 93.0% in solution and 84.8%, 94.3% and 73.6%, respectively in PS:dye fibers. Embedding the fibers in PDMS improved the photostabilities of the dyes two folds compared to their solution phases. The prepared dye containing fibers were combined together into a single PDMS film and utilized as a frequency conversion layer on a blue LED. Fabricated samples were found to show high color rendering index (>= 90), adjustable CCT (7500 K-5000 K), and power efficiency values exceeding 2001m/W depending on the used fiber amount in mass.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: 21Citation - Scopus: 27Increasing Solubility of Metal Silicates by Mixed Polymeric Antiscalants(Elsevier Ltd., 2019) Topçu, Gökhan; Çelik, Aslı; Kandemir, Ali; Baba, Alper; Şahin, Hasan; Demir, Mustafa MuammerThe increase of silicate solubility is a big challenge for both hot and cold water because it reduces the deposition of metal silicates frequently observed in such systems and causes operational obstacles. The deposition of silicate coats the inner surface of the pipelines in an uncontrolled manner and reduces the harvesting of energy from brines. In this work, the solubility performance of two commercial water-soluble polymeric agents (poly(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA)) of various molecular weights employing dosage from 25 to 100 mg/L was examined. Along with dispersant-type antiscalant, poly(acrylamide) (PAM), poly(vinylsulfonic acid, sodium salt) (PVSA), and poly(vinylphosphonic acid) (PVPA) having chelating acidic groups were employed. Metal silicate deposits were obtained artificially in the lab-scale pressurized reactor. The experimental conditions employed were quite similar to a model power plant located in Çanakkale, Turkey. The concentration of dissolved silica was increased from 130 to 420 mg/L when 100 mg/L PEG 1500 and 25 mg/L PVSA were employed as a mixture. For the atomic-level understanding of the interaction of chelating groups with metal cations, DFT calculations were performed too.Article Citation - WoS: 12Citation - Scopus: 12Ultra-Thin Znse: Anisotropic and Flexible Crystal Structure(Elsevier Ltd., 2017) Bacaksız, Cihan; Şenger, Ramazan Tuğrul; Şahin, HasanBy performing density functional theory-based calculations, we investigate the structural, electronic, and mechanical properties of the thinnest ever ZnSe crystal [11]. The vibrational spectrum analysis reveals that the monolayer ZnSe is dynamically stable and has flexible nature with its soft phonon modes. In addition, a direct electronic band gap is found at the gamma point for the monolayer structure of ZnSe. We also elucidate that the monolayer ZnSe has angle dependent in-plane elastic parameters. In particular, the in-plane stiffness values are found to be 2.07 and 6.89 N/m for the arm-chair and zig-zag directions, respectively. The angle dependency is also valid for the Poisson ratio of the monolayer ZnSe. More significantly, the in-plane stiffness of the monolayer ZnSe is the one-tenth of Young modulus of bulk zb-ZnSe which indicates that the monolayer ZnSe is a quite flexible single layer crystal. With its flexible nature and in-plane anisotropic mechanical properties, the monolayer ZnSe is a good candidate for nanoscale mechanical applications.Article Citation - WoS: 2Citation - Scopus: 2Atomic-scale understanding of dichlorobenzene-assisted poly 3-hexylthiophene-2,5-diyl nanowire formation mechanism(Elsevier Ltd., 2017) Yağmurcukardeş, Mehmet; Kıymaz, D.; Zafer, C.; Senger, Ramazan Tuğrul; Şahin, HasanLow-dimensional Poly 3-hexylthiophene-2,5-diyl (P3HT) structures that serve efficient exciton dissociation in organic solar cells, play a major role in increasing the charge collection, and hence, the efficiency of organic devices. In this study, we theoretically and experimentally investigate the Dichlorobenzene (DCB)-assisted formation of P3HT nanowires. Our experiments show that the solution of DCB molecules drive randomly oriented P3HT polymers to form well-stacked nanowires by stabilizing tail-tail and π−π interactions. Here the question is how DCB molecules migrate into the P3HT layers while forming the nanowire structure. Our density functional theory-based calculations reveal that the vertical migration of the DCB molecules between P3HT layers is forbidden due to a high energy barrier that stems from strong alkyl chain-DCB interaction. In contrast to vertical diffusion, lateral diffusion of DCB molecules in between P3HT layers is much more likely. Our results show that migration of a DCB molecule occurs through the alkyl groups with a low energy barrier. Therefore, laterally diffused DCB molecules assist nucleation of top-to-top stacking of P3HT polymers and formation of well-ordered nanowires.