Browsing by Author "Usta, Hakan"

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Ambipolar small molecular semiconductor-based heterojunction diode
(ELSEVIER SCIENCE SAPO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2016) Ocaya, R. O.; Ozdemir, Mehmet; Ozdemir, Resul; Al-Ghamdi, Ahmed; Usta, Hakan; Farooq, W. A.; Yakuphanoglu, F.; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Ozdemir, Resul
A heterojunction diode based on an ambipolar organic semiconductor 2,8-bis(5-(2-octyldodecyl)thien-2-yl)indeno[1,2-b]fluorene-6,12-dione (20D-TIFDKT) was fabricated on p-Si using a drop-casting technique. The current-voltage and capacitance-voltage characteristics of Al/20D-TIFDKT/p-Si/Al devices with aluminized contacts were investigated under dark and 100 mW/cm(2) illumination intensity. The result is a novel interface-state controlled diode device that is shown to be rectifying. In the forward, bias it has a current that depends on the illumination intensity at constant bias, showing potential application in low-power solar cell application. In the reverse bias, it has a response that depends on the illumination intensity regardless of the applied reverse bias. This suggests a potential use as a sensor in photoconductive applications. Between 0 and 0.7 V forward bias, the ideality factor, series resistance and barrier height average at 2.35, 67.6 k Omega and 0.842 eV, respectively, regardless of illumination. (C) 2016 Elsevier B.V. All rights reserved.
Anhydrous proton conducting poly(vinyl alcohol) (PVA)/ poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS)/1,2,4-triazole composite membrane
(Elsevier Ltd, 2016) Erkartal, Mustafa; Aslan, Ayse; Erkilic, Ufuk; Dadi, Seyma; Yazaydin, Ozgur; Usta, Hakan; Sen, Unal; 0000-0002-9772-128X; 0000-0003-1849-9180; 0000-0001-8562-723X; 0000-0002-0618-1979; 0000-0003-3736-5049; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Erkartal, Mustafa; Erkılıç, Ufuk; Dadı, Şeyma; Usta, Hakan; Şen, Ünal
The design and fabrication of anhydrous proton exchange membranes are critically important for high temperature proton exchange membrane fuel cell (HT-PEMFC) operating between 100 and 200 °C. Herein, we demonstrate a novel proton conducting membrane consisting of poly(vinyl alcohol) (PVA), poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and 1,2,4-triazole, which was fabricated by physical blending, casting and solvent evaporation techniques. The in-situ chemical cross-linking was performed by glutaraldehyde (GA) to improve the water management of the membranes. The molecular structure of the membranes and intermolecular interactions between the constituents were confirmed by Fourier-transform infrared spectroscopy (FT-IR). The surface and cross-section morphologies of the membranes were observed by scanning electron microscopy (SEM). The thermal stability performance of the membranes was studied with thermogravimetric analysis (TGA). In order to determine the physico-chemical properties of the membranes, water uptake (WU), dimensional change and ion exchange capacity (IEC) tests were carried out. The proton conductivities of composite membranes increase with the temperature and the temperature dependencies exhibit an Arrhenius behavior. Proton conductivity measurements revealed an optimum ratio between PAMPS and 1,2,4-triazole content to achieve higher proton conductivity. In anhydrous state at 150 °C, the highest proton conductivity measured was 0.002 S/cm for PVA:PAMPS:1,2,4-triazole (1:1:1) composition. Overall, our investigation showed that 1,2,4-triazole is a promising proton carrier reagent above 100 °C when it is embedded into appropriate host polymers.
Benzotiyeno[3,2-B][1]Benzotiyofen (BTBT) Tabanlı, Yüksek Performanslı N-Tipi/Ambipolar Yarı-İletkenlerin Geliştirilmesi Ve Yüksek Hızda Alan-Etkili Transistör (OFET) Uygulamaları
(TUBİTAK, 2019) Usta, Hakan; Demirel, Gökhan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Bu projede, daha önce literatürde bulunmayan, özgün kimyasal yapılara sahip 6 farklı düşük LUMO’lu BTBT-tabanlı yarı-iletken moleküler malzeme quantum mekaniksel hesaplamalarla teorik olarak tasarlanmış ve sentezlenmiştir. Bu yeni yarı-iletkenlerin saflaştırma sonrası detaylı bir şekilde yapısal, fizikokimyasal ve optoelektronik karakterizasyonları yapılıp organik alan-etkili transistör uygulamaları çalışılmıştır. Bunun sonucunda, dünyada ilk defa n-tipi olarak çalışabilen ve oldukça yüksek yarı-iletkenlik performansı gösteren (μe = 0.6 cm2 /V·s; Ion/Ioff = 107 -108 ) BTBT yarı-iletken molekülü, D(PhFCO)-BTBT, perflorofenilkarbonil grupları ile geliştirilmiştir. Geliştirilen D(PhFCO)-BTBT molekülü, son yılların en önemli π-sistemlerinden birisi olan BTBT yapısının elektron iletimi yapabileceğini literatürde ilk defa göstermesinin yanında, sahip olduğu yüksek elektron akışkanlığı ile literatürdeki sayılı n-tipi yarı-iletken moleküllerden birisi olarak kayda geçmiştir. Alkildisiyanovinilen ile fonksiyonelleştirilmiş D(C7CC(CN)2)-BTBT ise literatürde geliştirilmiş ilk solüsyondan proses edilebilir n-tipi BTBT (μe = 0.001 cm2 /V·s, Ion/Ioff = 104 ) yarı-iletken molekülü olmuştur. Karbonil ve disiyanovinilen fonksiyonelleştirmelerinin BTBT yapısındaki LUMO ve molekül-içi düzlemsellik etkisinin daha önceki π-sistemlerinden oldukça farklı olduğu bulgusuna ulaşılmıştır. Geliştirilen moleküler yarı-iletkenlerin moleküler dizilim/morfolojik/mikro-nanoyapı özellikleri dikkatlice incelendiğinde fonksiyonel grupların ve sübstitüyenlerin yarı-iletkenlik üzerindeki etkisi ortaya çıkarılmıştır. Ayrıca, bu projede geliştirilen farklı π-sistemlere sahip yarı-iletken kütüphanesinin detaylı incelemesi sonucunda “kimyasal yapı-optoelektronik özellikler-aygıt performansı” ilişkileri detaylı olarak çalışılmış, elektron-iletim özelliği olan yeni BTBT malzemelerinin geliştirilmeye devam edilmesi için ileriki çalışmalara ışık tutacak önemli bulgulara erişilmiştir.
BODIPY-Based Semiconducting Materials for Organic Bulk Heterojunction Photovoltaics and Thin-Film Transistors
(WILEY-V C H VERLAG GMBH, POSTFACH 101161, 69451 WEINHEIM, GERMANY, 2019) Ho, Dongil; Ozdemir, Resul; Kim, Hyungsug; Earmme, Taeshik; Usta, Hakan; Kim, Choongik; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
The rapid emergence of organic (opto)electronics as a promising alternative to conventional (opto)electronics has been achieved through the design and development of novel pi-conjugated systems. Among various semiconducting structural platforms, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) pi-systems have recently attracted attention for use in organic thin-films transistors (OTFTs) and organic photovoltaics (OPVs). This Review article provides an overview of the developments in the past 10 years on the structural design and synthesis of BODIPY-based organic semiconductors and their application in OTFT/OPV devices. The findings summarized and discussed here include the most recent breakthroughs in BODIPYs with record-high charge carrier mobilities and power conversion efficiencies (PCEs). The most up-to-date design rationales and discussions providing a strong understanding of structure-property-function relationships in BODIPY-based semiconductors are presented. Thus, this review is expected to inspire new research for future materials developments/applications in this family of molecules.
Design and development of functional organic small molecules and polymers for optoelectronics
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2016) Usta, Hakan; Demirel, Gokhan; Facchetti, Antonio; Muccini, Michele; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Design and development of functional organic small molecules and polymers for optoelectronics
The design and fabrication of supramolecular semiconductor nanowires formed by benzothienobenzothiophene (BTBT)-conjugated peptides
(Royal Society of Chemistry, 2018) Khalily, Mohammad Aref; Usta, Hakan; Ozdemir, Mehmet; Bakan, Gokhan; Dikecoglu, F.Begum; Gayle, Charlotte Edwards; Hutchinson, Jessica A.; Hamley, Ian W.; Dana, Aykutlu; Guler, Mustafa O.; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
?-Conjugated small molecules based on a [1]benzothieno[3,2-b]benzothiophene (BTBT) unit are of great research interest in the development of solution-processable semiconducting materials owing to their excellent charge-transport characteristics. However, the BTBT ?-core has yet to be demonstrated in the form of electro-active one-dimensional (1D) nanowires that are self-assembled in aqueous media for potential use in bioelectronics and tissue engineering. Here we report the design, synthesis, and self-assembly of benzothienobenzothiophene (BTBT)–peptide conjugates, the BTBT–peptide (BTBT-C3–COHN-Ahx-VVAGKK-Am) and the C8-BTBT–peptide (C8-BTBT-C3–COHN-Ahx-VVAGKK-Am), as ß-sheet forming amphiphilic molecules, which self-assemble into highly uniform nanofibers in water with diameters of 11–13(±1) nm and micron-size lengths. Spectroscopic characterization studies demonstrate the J-type ?–? interactions among the BTBT molecules within the hydrophobic core of the self-assembled nanofibers yielding an electrical conductivity as high as 6.0 × 10-6 S cm-1. The BTBT ?-core is demonstrated, for the first time, in the formation of self-assembled peptide 1D nanostructures in aqueous media for potential use in tissue engineering, bioelectronics and (opto)electronics. The conductivity achieved here is one of the highest reported to date in a non-doped state.
Design, synthesis, and characterization of alpha,omega-disubstituted indeno[1,2-b]fluorene-6,12-dione-thiophene molecular semiconductors. Enhancement of ambipolar charge transport through synthetic tailoring of alkyl substituents
(ROYAL SOC CHEMISTRYTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2016) Ozdemir, Mehmet; Choi, Donghee; Kwon, Guhyun; Zorlu, Yunus; Kim, Hyekyoung; Kim, Myung-Gil; Seo, SungYong; Sen, Unal; Citir, Murat; Kim, Choongik; Usta, Hakan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan; Ozdemir, Mehmet; Sen, Unal
A series of indeno[1,2-b]fluorene-6,12-dione-thiophene derivatives with hydrocarbon substituents at alpha,omega-positions as side groups have been designed and synthesized. The new compounds were fully characterized by H-1/C-13 NMR, mass spectrometry, cyclic voltammetry, UV-vis absorption spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and melting point measurements. The solid state structure of the indeno[1,2-b]fluorene-6,12-dione acceptor core has been identified based on single-crystal X-ray diffraction (XRD). The structural and electronic properties were also studied using density functional theory calculations, which were found to be in excellent agreement with the experimental findings and provided further insight. The detailed effects of alkyl chain size and orientation on the optoelectronic properties, intermolecular cohesive forces, thin-film microstructures, and charge transport performance of the new semiconductors were investigated. Two of the new solution-processable semiconductors, 2EH-TIFDKT and 2OD-TIFDKT, were deposited as thin-films via solution-shearing, drop-casting, and droplet-pinned crystallization methods, and their morphologies and microstructures were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The solution-processed thin-film transistors based on 2EH-TIFDKT and 2OD-TIFDKT showed ambipolar device operations with electron and hole mobilities as high as 0.12 cm(2) V-1 s(-1) and 0.02 cm(2) V-1 s(-1), respectively, with Ion/Ioff ratios of 105 to 106. Here, we demonstrate that rational repositioning of the b-substituents to molecular termini greatly benefits the p-core planarity while maintaining a good solubility, and results in favorable structural and optoelectronic characteristics for more efficient charge-transport in the solid-state. The ambipolar charge carrier mobilities were increased by two-three orders of magnitude in the new indeno[1,2-b]fluorene-6,12-dione-thiophene core on account of the rational side-chain engineering.
Development of highly transparent Pd-coated Ag nanowire electrode for display and catalysis applications
(ELSEVIER, 2015) Canlier, Ali; Ucak, Umit Volkan; Usta, Hakan; Cho, Changsoon; Lee, Jung-Yong; Sen, Unal; Citir, Murat; 0000-0002-0618-1979; 0000-0003-3736-5049; 0000-0002-6666-4980; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Canlier, Ali; Ucak, Umit Volkan; Usta, Hakan; Sen, Unal; Citir, Murat
Ag nanowire transparent electrode has excellent transmittance (90%) and sheet resistance (20 Omega/sq), yet there are slight drawbacks such as optical haze and chemical instability against aerial oxidation. Chemical stability of Ag nanowires needs to be improved in order for it to be suitable for electrode applications. In our recent article, we demonstrated that coating Ag nanowires with a thin layer of Au through galvanic exchange reactions enhances the chemical stability of Ag nanowire films highly and also helps to obtain lower haze. In this study, coating of a thin Pd layer has been applied successfully onto the surface of Ag nanowires. A mild Pd complex oxidant [Pd(en)(2)](NO3)(2) was prepared in order to oxidize Ag atoms partially on the surface via galvanic displacement. The mild galvanic exchange allowed for a thin layer (1-2 nm) of Pd coating on the Ag nanowires with minimal truncation of the nanowire, where the average length and the diameter were 12.5 mu m and 59 nm, respectively. The Pd-coated Ag nanowires were suspended in methanol and then electrostatically sprayed on flexible polycarbonate substrates. It has been revealed that average total transmittance remain around 95% within visible spectrum region (400-800 nm) whereas sheet resistance rises up to 175 Omega/sq. To the best of our knowledge, for the first time in the literature, Pd coating was employed on Ag nanowires in order to design transparent electrodes for high transparency and strong chemical resistivity against nanowire oxidation. The current Pd-coated Ag nanowires may render an excellent catalyst system for fuel cell applications, as well as in organic synthesis with relatively low costs since our approach enables the fabrication of these nanowires with a very thin layer of Pd. We believe that mesh form of Pd-coated Ag nanowires will coin a new catalyst concept to the related areas since their sheet conductivity is high enough, and also little amount of Pd displays a large surface area as thin layers. (C) 2015 Elsevier B.V. All rights reserved.
A dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT)-based hole transporting layer for highly stable perovskite solar cells with efficiency over 22%
(ROYAL SOC CHEMISTRY, 2022) Kaya, Ismail Cihan; Ozdemir, Resul; Usta, Hakan; Sonmezoglu, Savas; 0000-0002-7957-110X; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Özdemir, Resul; Usta, Hakan
In this study, for the first time, n-i-p PSCs were fabricated using dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as the solution-processed hole transporting layer (HTL). The power conversion efficiency (PCE) of the optimized device with the C8-BTBT film that favored edge-on molecular alignment was 22.45% with negligible hysteresis. A thinner dopant-free C8-BTBT HTL effectively protected the perovskite layer from moisture resulting in better shelf-life stability for un-encapsulated PSCs, which maintained >80% of its initial PCE (after a period of 120 days) at a relative humidity level of 40-45%. In addition, the C8-BTBT-based PSCs kept their high performance with no obvious PCE loss at 60 degrees C for 20 days in the ambient atmosphere and retained 82% of their initial PCE at 85 degrees C for 10 days. Overall, our findings revealed that a thin solution-processed C8-BTBT HTL plays a critical role not only in hole extraction and transport but also in greatly improving the ambient and thermal stability of n-i-p PSCs.
Dynamic Tuning of Plasmonic Hot-Spot Generation through Cilia-Inspired Magnetic Actuators
(WILEY, 2023) Liman, Gorkem; Ergene, Emre; Yildiz, Emrecan; Hukum, Kubra Ozkan; Huri, Pinar Yilgor; Cetin, Arif E.; Usta, Hakan; Demirel, Gokhan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
Soft actuators that draw inspiration from nature are powerful and versatile tools for both technological applications and fundamental research, yet their use in hot-spot engineering is very limited. Conventional hot-spot engineering methods still suffer from complexity, high process cost, and static generation of hot-spots, thus, underperforming particularly in the application side. Herein, we demonstrate a strategy based on plasmonic nanoparticles decorated cilia-inspired magnetic actuators that enable highly accessible millimeter-sized hot-spot generation via bending motion under a magnetic field. The hot-spot formation is shown to be reversible and tunable, and leads to excellent Raman signal enhancements of up to approximate to 120 folds compared to the unactuated platforms. Accessible electromagnetic field magnification in the platforms can be manipulated by controlling magnetic field strength, which is further supported by finite difference time domain (FDTD) simulations. As a proof-of-concept demonstration, a centipede-inspired robot is fabricated and used for sample collection/analysis in a target environment. Our results demonstrate an effective strategy in soft actuator platforms for reversible and tunable large-area hot-spot formation, which provides a promising guidance toward studying the fundamentals of hot-spot generation and advancing real-life plasmonic applications.
Electrochemical polymerization of ambipolar carbonyl-functionalized indenofluorene with memristive properties
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2019) Figa, Viviana; Usta, Hakan; Macaluso, Roberto; Salzner, Ulrike; Ozdemir, Mehmet; Kulyk, Bohdan; Krupka, Oksana; Bruno, Maurizio; 0000-0002-0618-1979; 0000-0001-5581-2557; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Carbonyl-functionalized indenofluorene was electropolymerized with a high faradaic efficiency of 85% and the solid state properties of the resulting polymeric thin films were investigated. They displayed modular optical properties depending on their oxidation state. The approach used for inorganic semiconductors was applied to polyindeonofluorene derivative. Mott-Schottky analysis evidenced a switching from p-type to n-type electrical conduction, suggesting an ambipolar behaviour of the polymer. As an application, flexible organic memristors were fabricated and resistive switching properties were observed.
Enabling three-dimensional porous architectures via carbonyl functionalization and molecular-specific organic-SERS platforms
(NATURE RESEARCHHEIDELBERGER PLATZ 3, BERLIN 14197, GERMANY, 2021) Deneme, Ibrahim; Liman, Gorkem; Can, Ayse; Demirel, Gokhan; Usta, Hakan; 0000-0002-9778-917X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Can, Ayse; Demirel, Gokhan; Usta, Hakan
Nanostructured films of organic semiconductors with low lying LUMO orbitals can enhance Raman signals via a chemical enhancement mechanism but currently the material choice is limited to fluorinated oligothiophenes. Here, the authors investigate the growth of a porous thienoacene film enabled by carbonyls and demonstrate molecular specific organic-SERS platforms. Molecular engineering via functionalization has been a great tool to tune noncovalent intermolecular interactions. Herein, we demonstrate three-dimensional highly crystalline nanostructured D(C7CO)-BTBT films via carbonyl-functionalization of a fused thienoacene pi-system, and strong Raman signal enhancements in Surface-Enhanced Raman Spectroscopy (SERS) are realized. The small molecule could be prepared on the gram scale with a facile synthesis-purification. In the engineered films, polar functionalization induces favorable out-of-plane crystal growth via zigzag motif of dipolar C = O center dot center dot center dot C = O interactions and hydrogen bonds, and strengthens pi-interactions. A unique two-stage film growth behavior is identified with an edge-on-to-face-on molecular orientation transition driven by hydrophobicity. The analysis of the electronic structures and the ratio of the anti-Stokes/Stokes SERS signals suggests that the pi-extended/stabilized LUMOs with varied crystalline face-on orientations provide the key properties in the chemical enhancement mechanism. A molecule-specific Raman signal enhancement is also demonstrated on a high-LUMO organic platform. Our results demonstrate a promising guidance towards realizing low-cost SERS-active semiconducting materials, increasing structural versatility of organic-SERS platforms, and advancing molecule-specific sensing via molecular engineering.
Engineering functionalized low LUMO [1]benzothieno[3,2-b][1]benzothiophenes (BTBTs): unusual molecular and charge transport properties
(ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2020) Ozdemir, Resul; Ahn, Kyunghan; Deneme, Ibrahim; Zorlu, Yunus; Kim, Dojun; Kim, Myung-Gil; Usta, Hakan; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Diacene-fused thienothiophenes (DAcTTs) have provided an excellent pi-framework for the development of high mobility p-type molecular semiconductors in the past decade. However, n-type DAcTTs are rare and their electron transport characteristics remain largely unexplored. Herein, a series of functionalized low LUMO (lowest unoccupied molecular orbital) [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based small molecules, D(C7CO)-BTBT, C7CO-BTBT-CC(CN)(2)C-7, and D(C7CC(CN)(2))-BTBT, have been developed. Detailed structural, physicochemical, optoelectronic, and single-crystal characterization were performed. The new molecules exhibit large optical band gaps (similar to 2.8-3.1 eV) and highly stabilized (-Delta E-LUMO = 1.2-1.4 eV)/pi-delocalized LUMOs as compared to p-type DAcTTs. Symmetric functionalization is found to be important to enable strong intermolecular interactions in the solid-state. All molecules exhibit alternately stacked layers of "F-BTBT-F" and "S" (F: functional group/S: substituent) with strong herringbone-like interactions (2.8-3.6 angstrom distances) between pi-cores. While carbonyls, regardless of the substituent, adopt nearly coplanar pi-backbones with BTBT, dicyanovinylenes are found to be twisted (47.5 degrees). The conformational difference at the molecular level has unusual effects on the pi-electron deficiencies, frontier molecular orbital energetics, thermal/photophysical properties, and pi-electronic structures. Dicyanovinylenes at the 2,7 positions, despite twisted conformations, are shown for the first time to yield good electron transport in DAcTTs. The D(C7CC(CN)(2))-BTBT thin film exhibits large 2D plate-like crystalline grains (similar to 1-2 mu m sizes) of terraced islands and becomes a rare example of an n-type DAcTT in organic field-effect transistors (OFETs). Although a stabilized/pi-delocalized LUMO, largely governed by functional groups and intramolecular twists, is essential for electron transport, our findings suggest that it should be combined with proper substituents to yield a favorable three-dimensional BTBT/functional group pi-electronic structure and a low intramolecular reorganization energy. Combined with our first n-type DAcTT semiconductor D(PhFCO)-BTBT, a molecular library with systematically varied chemical structures has been studied herein for the first time for low LUMO DAcTTs. The molecular engineering perspectives presented in this study may give unique insights into the design of novel electron transporting thienoacenes for unconventional optoelectronics.
Enhanced mass transfer rate and solubility of methane via addition of alcohols for Methylosinus trichosporium OB3b fermentation
(ELSEVIER SCIENCE INCSTE 800, 230 PARK AVE, NEW YORK, NY 10169, 2017) Kim, Kwangmin; Kim, Yujin; Yang, Jeongmo; Ha, Kyoung-Su; Usta, Hakan; Lee, Jinwon; Kim, Choongik; 0000-0002-0618-1979; 0000-0003-3926-6626; 0000-0001-7494-0677; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The effect of alcohol on methane-water volumetric mass transfer coefficient (1(0) and solubility of methane was investigated in this study. Various alcohols including methanol, ethanol, 1-propanol, butanol, and pentanol were added to aqueous solution and enhancement of both methane-water k(L)a (from 72h(-1) to 471 h(-1)) and solubility (from 21.72 mg/L to 30.41 mg/L) was observed, depending on alcohol type and concentration. Among all alcohols, 1-propanol exhibited largest enhancement via bubble coalescence inhibition effect. Enhanced methane-water kLa and methane solubility in aqueous solution were employed for the fermentation of Methylosinus trichosporium OB3b, and cell growth rate and maximum optical density were increased by 700% and 730%, respectively, by addition of 1-propanol. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Enhancement of Anhydrous Proton Conductivity of Poly(vinylphosphonic acid)-Poly(2,5-benzimidazole) Membranes via In Situ Polymerization
(WILEY-V C H VERLAG GMBH, 2015) Sen, Unal; Usta, Hakan; Acar, Oktay; Citir, Murat; Canlier, Ali; Bozkurt, Ayhan; Ata, Ali; 0000-0002-6666-4980; 0000-0003-3736-5049; 0000-0002-0618-1979; 0000-0001-6055-2817; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sen, Unal; Usta, Hakan; Canlier, Ali; Citir, Murat
Polymer electrolyte membranes (PEMs) are synthesized via in situ polymerization of vinylphosphonic acid (VPA) within a poly(2,5-benzimidazole) (ABPBI) matrix. The characterization of the membranes is carried out by using Fourier transform infrared (FTIR) spectroscopy for the interpolymer interactions, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for the thermal properties, and scanning electron microscopy (SEM) for the morphological properties. The physicochemical characterizations suggest the complexation between ABPBI and PVPA and the formation of homogeneous polymer blends. Proton conductivities in the anhydrous state (150 degrees C) measured by using impedance spectroscopy are considerable, at up to 0.001 and 0.002 S cm(-1) for (1: 1) and (1: 2) molar ratios, respectively. These conductivities indicate signifi cant improvements (> 1000x) over the physically blended samples. The results shown here demonstrate the great potential of in situ preparation for the realization of new PEM materials in future high-temperature and non-humidified polymer electrolyte membrane fuel cell (PEMFC) applications.
Frequency and electric field controllable photodevice: FYTRONIX device
(ELSEVIERRADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2017) Tataroglu, A.; Al-Sehemi, Abdullah G.; Ozdemir, Mehmet; Ozdemir, Resul; Usta, Hakan; Al-Ghamdi, Ahmed A.; Farooq, W. A.; Yakuphanoglu, F.; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Ozdemir, Resul; Usta, Hakan
Al/p-Si/BODIPY/Al diode was fabricated by forming BODIPY organic layer on p-Si having ohmic contact. The electrical and photoresponse properties of the prepared diode were investigated in detail. The current-voltage ( I-V) measurements were performed under dark and various illumination intensities. It is observed that the photocurrent under illumination is higher than the dark current. The transient measurements indicate that the device exhibits both photodiode and photocapacitor behavior. We called this device as FYTRONIX device. The photoresponse behavior of the FYTRONIX device is controlled simultaneously by frequency and electric field. The FYRONIX device can be used as a photoresponse sensor in optoelectronic applications.
From 2-methylimidazole to 1,2,3-triazole: a topological transformation of ZIF-8 and ZIF-67 by post-synthetic modification
(ROYAL SOC CHEMISTRYTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2017) Erkartal, Mustafa; Erkilic, Ufuk; Tam, Benjamin; Yazaydin, Ozgur; Hupp, Joseph T.; Farha, Omar K.; Sen, Unal; 0000-0002-0618-1979; 0000-0003-1849-9180; 0000-0002-9772-128X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Erkartal, Mustafa; Erkilic, Ufuk; Usta, Hakan
Bridging ligand replacement in zeolitic imidazolate frameworks, ZIF-8 and ZIF-67, by 1,2,3-triazole was investigated. A complete substitution of 2-methylimidazole by 1,2,3-triazole resulted in a topological transformation of the parent framework from a sodalite (SOD) network to a diamond (DIA) network.
The Hansen solubility approach towards green solvent processing: n-channel organic field-effect transistors under ambient conditions
(Royal Society of Chemistry, 2024) Deneme, Ibrahim; Yıldız, Tevhide Ayça; Kayaci, Nilgun; Usta, Hakan; 0000-0001-9415-0242; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Deneme, Ibrahim; Yıldız, Tevhide Ayça; Kayaci, Nilgun; Usta, Hakan
The adoption of green solvents is of utmost importance for the solution-based fabrication of semiconductor thin films and for the commercialization of (opto)electronic devices, especially in response to evolving regulatory mandates for handling organic materials. Despite the increasing interest in this area, the scarcity of green solvent-processed n-channel OFETs, especially functioning under ambient conditions, highlights the need for further research. In this study, we demonstrated the Hansen solubility approach to study the solubility behavior of an ambient-stable n-type semiconductor, 2,20 - (2,8-bis(3-dodecylthiophen-2-yl)indeno[1,2-b]fluorene-6,12-diylidene)dimalononitrile (b,b0 -C12-TIFDMT), and to analyze potential green solvents for thin-film processing. The Hansen solubility parameters were determined to be dD = 20.8 MPa1/2, dP = 5.8 MPa1/2, and dH = 5.5 MPa1/2 with a radius (R0) of 8.3 MPa1/2. A green solvent screening analysis based on the minimal distance constraint and quantitative sustainability score identified ethoxybenzene, anisole, 2-methylanisole, and 2-methyltetrahydrofuran as suitable green solvents (Ra0s = 5.17–7.93 MPa1/2 o R0). A strong thermodynamic correlation was identified between the solubility and the semiconductor–solvent distance in the 3D Hansen solubility space, in which the maximum solubility limit could be estimated with the enthalpy of fusion (DHfus) and melting temperature (Tmp) of the semiconductor. To the best of our knowledge, this relationship between the maximum solubility limit and thermal properties has been established for the first time for organic semiconductors. Bottom-gate/top-contact OFETs fabricated by spin-coating the semiconductor green solutions exhibited mes reaching B0.2 cm2 V1 s 1 (Ion/Ioff B106 –107 and Von B0–5 V) under ambient conditions. This device performance, to our knowledge, is the highest reported for an ambient-stable green solvent-processed n-channel OFET. Our HSP-based rational approach and unique findings presented in this study can shed critical light on how green solvents can be efficiently incorporated in solution processing in organic (opto)electronics, and whether ambient-stable n-type semiconductors can continue to play an important role in green OFETs.
Hibrit Kuantum Noktacık-Nanofiber Esnek Elektrolüminesant Aygıtlar
(TUBİTAK, 2019) Mutlugün, Evren; Usta, Hakan; Önses, Serdar; 0000-0003-3715-5594; 0000-0002-0618-1979; 0000-0001-6898-7700; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Mutlugun, Evren; Usta, Hakan; ÖNSES, Mustafa Serdar
Yarı iletken kuantum noktacıklar üstün renk dönüşüm özellikleri, yüksek soğurma katsayıları ve kararlılıkları sebebiyle son yıllarda aydınlatma ve ekran teknolojileri için oldukça önemli malzemeler durumundadır. Genel itibariyle II-VI ve III-V malzemeler temelli kuantum noktacıklar, optik ya da elektriksel olarak uyarılma sayesinde yüksek verimlilikle ışık üretimi sağlamaktadırlar. Sahip oldukları spektral dar ışımaları sayesinde özellikle ekran teknolojileri için saf renk özelliklerini ön plana çıkaran kuantum noktacıklar, geleneksel olarak kullanılan fosfor katkılı ışıyıcıların yerini almaktadır. Renk saflığının oldukça ön planda olduğu ekran teknolojileri için de kuantum noktalar LCD arka plan aydınlatmada üstün nitelikli beyaz ışık üretimini sağlamak için kullanılmakta ve ticari açıdan da önem kazanmaktadır. Nanofiberler ise organik yarıiletken malzemelerin optoelektronik uygulamalarda 3 boyutlu alanlar için önerdiği yüksek verimlilik, hafiflik, geniş alanlara uygulanabilme özelliklerini fiziksel olarak 1 boyutta gerçekleştirebilen, desenlenebilir ve elektroeğirme yöntemi ile farklı yüzeylere uygulanabilir çözümler sunmaktadır. Gerçekleştirdiğimiz proje nano boyutlu fiber yapıları içerisinde kuantum noktaların üstün renk dönüştürücü özelliklerini ön plana çıkarmış, farklı mimarilerde enerji transferinin de çalışıldığı fotolüminesans ve elektrolüminesans temelli aygıtlar gerçekleştirilmiştir. Bu projede %16’ya ulaşan dış kuantum verimliliğine (external quantum efficiency) sahip aygıt gösterimleri ve yüksek kaliteli beyaz ışık eldesi gerçekleştirilmiştir. Aynı zamanda esnek, ayarlanabilir renk özelliklerinde aygıt üretimi için gösterilen kuantum nokta aygıtlar saf ve spektral olarak simetrik ışımayı sağlama yetisinde, üstün renk özellikleri ile yüksek kaliteli esnek elektrolüminesant aygıt üretimini mümkün kılmaktadır. Önümüzdeki 10 yıl içerisinde küresel ekran teknolojileri pazarının 100 milyar dolarlar mertebesine ulaşacağı bilgisi doğrultusunda (Global Industry Analysts, Inc., raporu) en önemli aşamalardan biri de özellikle esnek mimarilerde üstün renk özelliklerine sahip malzemeleri gerçekleştirmek olacaktır. Yeni nesil esnek elektrolüminesant aygıtların aydınlatma ve ekran teknolojilerinde önemli bir paya sahip olacağı beklenmektedir. Bu tür yeni nesil yapıların gerçekleştirilmesi, fiziksel mekanizmaların araştırılması ve teknolojik problemlerine çözüm üretilme süreci büyük resimde çok kritik önemdedir. Teknolojiye yön verme doğrultusunda önerilen proje ekseninde yapılacak olan yatırımın ülkemiz için yüksek teknoloji üretme hamlesine büyük bir katkıda bulunacağı, yeni bilgi, ürün ve patent süreçlerini geliştireceği, ülkemizde bu alanda yetişmiş insan gücüne katkıda bulunup ülkemiz rekabet gücünü arttıracağı öngörülmektedir.
High Electron Mobility in [1]Benzothieno[3,2-b][1]benzothiophene-Based Field-Effect Transistors: Toward n-Type BTBTs
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2019) Usta, Hakan; Kim, Dojeon; Ozdemir, Resul; Zorlu, Yunus; Kim, Sanghyo; Ruiz Delgado, M. Carmen; Harbuzaru, Alexandra; Kim, Seonhyoung; Demirel, Gokhan; Hong, Jongin; Ha, Young-Geun; Cho, Kilwon; Facchetti, Antonio; Kim, Myung-Gil; 0000-0002-2891-5785; 0000-0003-2811-1872; 0000-0002-7957-110X; 0000-0002-8211-732X; 0000-0002-0618-1979; 0000-0002-9778-917X; 0000-0003-2434-3182; 0000-0001-8180-7153; 0000-0001-9632-3557; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The first example of an n-type [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based semiconductor, D-(PhFCO)-BTBT, has been realized via a two-step transition metal-free process without using chromatographic purification. Physicochemical and optoelectronic characterizations of the new semiconductor were performed in detail, and the crystal structure was accessed. The new molecule exhibits a large optical band gap (similar to 2.9 eV) and highly stabilized (Delta E-LUMO = 1.54 eV)/pi-delocalized lowest unoccupied molecular orbital (LUMO) mainly comprising the BTBT pi-core and in-plane carbonyl units. The effect of out-of-plane twisted (64 degrees) pentafluorophenyl groups on LUMO stabilization is found to be minimal. Polycrystalline D(PhFCO)-BTBT thin films prepared by physical vapor deposition exhibited large grains (similar to 2-5 mu m sizes) and "layer-by-layer" stacked edge-on oriented molecules with an in-plane herringbone packing (intermolecular distances similar to 3.25-3.46 angstrom) to favor two-dimensional (2D) source-to-drain (S -> D) charge transport. The corresponding TC/BG-OFET devices demonstrated high electron mobilities of up to similar to 0.6 cm(2)/V.s and I-on/I-off ratios over 10(7)-10(8). These results demonstrate that the large band gap BTBT pi-core is a promising candidate for high-mobility n-type organic semiconductors and, combination of very large intrinsic charge transport capabilities and optical transparency, may open a new perspective for next-generation unconventional (opto)electronics.