Profile URL: https://hdl.handle.net/20.500.12573/2710
Job Title:Prof. Dr.
Email Address:hakan.usta@agu.edu.tr
Main Affiliation:02.07. Malzeme Bilimi ve Nanoteknoloji Mühendisliği
Status: Current Staff
ORCID:
0000-0002-0618-1979
0000-0002-0618-1979Scopus ID:
14042943100
14042943100YÖK Akademik: 3469683DEC5253DE
Google Scholar:
1f-qx-oAAAAJ
1f-qx-oAAAAJWeb of Science ID:
L-6636-2013
L-6636-2013Name Variants:
HAKAN USTA Usta, H.
77 results
Scholarly Output Search Results
Now showing 1 - 10 of 77
Article Citation - WoS: 109Citation - Scopus: 115Proton Conducting Poly(Vinyl Alcohol) (PVA)/Poly (2-Acrylamido Sulfonic Acid) (PAMPS)/Zeolitic Imidazolate Framework (ZIF) Ternary Composite Membrane(Elsevier, 2016-02) Erkartal, Mustafa; Usta, Hakan; Citir, Murat; Sen, UnalThe design, synthesis and characterization of novel proton exchange membranes (PEMs) are of significant scientific and technological importance for the realization of fuel cells, actuators, and sensors. Here, we demonstrate a novel ternary composite membrane consisting of poly(vinyl alcohol) (PVA), poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), zeolitic imidazolate framework-8 (ZIF-8), which is prepared by physical blending and casting methods. To enhance the water management of the membranes, in situ chemical cross-linking is carried out by glutaraldehyde (GA). During the characterization of the new membranes, FT-IR is used for intermolecular and inter-polymer interactions between different components of the membrane, SEM is used to identify morphology, XRD is used to prove the presence of ZIF-8 nanoparticles, and finally TGA is used for thermal stability. The proton conductivity of the membranes is found to increase with temperature and also with the increasing content of PAMPS. The highest proton conductivity under fully hydrated state at 80 degrees C is measured as 0.134 S cm(-1) for PVA: PAMPS: ZIF-8 (55:40:5) composition. In this study, it is clearly shown that ZIF-8 nanoparticles contribute to the proton conductivity by forming hydrogen bonds with the polymer network in the membrane. The water uptake (WU) and ion exchange capacity (IEC) values are 3.28 (gig) and 1.52 meq g(-1), respectively for the same membrane. To the best our knowledge, this study shows one of the first example of a MOFcontaining membrane with truly high proton conductivities, and both values of proton conductivity and electrochemical properties are comparable to those of well-studied membrane, Nation. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 30Citation - Scopus: 32A Solution-Processable Liquid-Crystalline Semiconductor for Low-Temperature Air-Stable N-Channel Field-Effect Transistors(Wiley-VCH Verlag GmbH, 2017-02-22) Ozdemir, Resul; Choi, Donghee; Ozdemir, Mehmet; Kim, Hyekyoung; Kostakoglu, Sinem Tuncel; Erkartal, Mustafa; Usta, HakanA new solution-processable and air-stable liquid-crystalline nchannel organic semiconductor (2,2'-(2,8-bis(5-(2-octyldodecyl) thiophen-2-yl) indeno[1,2-b] fluorene-6,12-diylidene) dimalononitrile, alpha,omega-2OD-TIFDMT) with donor-acceptor-donor (D-AD) pi conjugation has been designed, synthesized, and fully characterized. The new semiconductor exhibits a low LUMO energy (-4.19 eV) and a narrow optical bandgap (1.35 eV). The typical pseudo-focal-conic fan-shaped texture of a hexagonal columnar liquid-crystalline (LC) phase was observed over a wide temperature range. The spin-coated semiconductor thin films show the formation of large (approximate to 0.5-1 mu m) and highly crystalline platelike grains with edge-on molecular orientations. Low-temperature-annealed (50 degrees C) top-contact/bottom-gate OFETs have provided good electron obility values as high as 0.11 cm(2) (Vs)(-1) and high I-on/I-off ratios of 10(7) to 10(8) with excellent ambient stability. This indicates an enhancement of two orders of magnitude (100 V) when compared with the b-substituted parent semiconductor, beta-DD-TIFDMT (2,2'-(2,8-bis(3-dodecylthiophen- 2-yl) indeno[1,2-b] fluorene-6,12-diylidene) dimalononitrile). The current rational alkyl-chain engineering route offers great advantages for D-A-D pi-core coplanarity in addition to maintaining good solubility in organic solvents, and leads to favorable optoelectronic/physicochemical characteristics. These remarkable findings demonstrate that alpha,omega-2OD-TIFDMT is a promising semiconductor material for the development of n-channel OFETs on flexible plastic substrates and LC-state annealing of the columnar liquid crystals can lower the electron mobility for transistor-type charge transport.Book Part Citation - Scopus: 2Paper-Based Substrates for Sustainable (OPTO)Electronic Devices(Elsevier, 2022) Usta, Hakan; Facchetti, A. F.Cellulose-based paper has been a convenient eco-friendly platform for storing and exchanging information for thousands of years. Amazingly, the studies and advancements in the past decade have demonstrated that paper and nanocellulose-based substrates are also attractive for fabricating flexible electronic circuits as well as optoelectronic components and devices. Paper and nanocellulose-based substrates have been considered for use in new generation green devices and optoelectronic applications based on their sustainable and inexpensive source, lightweight, and superior mechanical/optical properties, all factors that could also reduce manufacturing costs for producing these devices. In this chapter, we review functional materials and optoelectronic devices fabricated on paper or nanocellulose-based substrates including transistors and circuits, solar cells, light-emitting diodes, and other devices, such as sensors/actuators, batteries, supercapacitors/energy-harvesters, and breathalyzer/diagnosis devices. We also thoroughly discuss remaining challenges and promising research directions with paper-based substrates for future advancements in green optoelectronics. © 2022 Elsevier B.V., All rights reserved.Book Part Citation - Scopus: 19Polymeric and Small-Molecule Semiconductors for Organic Field-Effect Transistors(wiley, 2015-01-16) Usta, Hakan; Facchetti, A. F.This chapter reviews the achievements in the development of molecular and polymeric semiconductors for charge transport in thin-film transistors (TFTs). In particular, it introduces the basic concepts of organic semiconductor structure and organic thin-film transistor (OTFT) operation and then focuses on initial studies and works. Organic semiconductors for OTFTs must possess two essential structural features for their successful implementation in printed electronics. The first feature is a π-conjugated core/chain composed of linked unsaturated units. The second feature is core functionalization with solubilizing substituents, which is essential for inexpensive manufacture by solution methods as well as for enhancing solid-state core interactions. There are several advantages in using polymeric versus molecular p-conjugated semiconductors. Isoindigo has become a popular conjugated moiety in polymer semiconductor design because of its strong electron-withdrawing character. Polymeric p-channel TFTs have reached new heights, with hole mobilities unthinkable only few years back and surpassing 10 cm2V-1 s-1. © 2018 Elsevier B.V., All rights reserved.Article Citation - WoS: 11Citation - Scopus: 11Logarithmic Organic Photodetectors(Elsevier Science SA, 2015-12) Elgazzar, Elsayed; Ozdemir, Mehmet; Usta, Hakan; Al-Ghamdi, Ahmed A.; Dere, A.; El-Tantawy, Farid; Yakuphanoglu, F.A novel photodetector of Al/GO:C8-BTBT/n-Si/Au with various graphene oxide (GO) contents has been investigated. The electrical properties of the diodes were characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The values of barrier height, ideality factor, and series resistance of the diodes were determined from I-V characteristic curves by using Norde's equations. The photocurrent properties of the diode were studied under various illumination intensities. The photoconducting mechanism of the diodes is controlled by the traps. The photoresponse properties of the diodes are increased with GO contents. The obtained results indicate that graphene oxide doped 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene/n-Si heterojunctions can be used as a photodetector for optoelectronic applications. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 40Citation - Scopus: 38A Dopant-Free 2,7-Dioctyl[1]Benzothieno[3,2 (C8-BTBT) 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, SavasIn 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.Article Citation - WoS: 13Citation - Scopus: 14Enhanced Mass Transfer Rate and Solubility of Methane via Addition of Alcohols for Methylosinus Trichosporium OB3b Fermentation(Elsevier Science inc, 2017-02) Kim, Kwangmin; Kim, Yujin; Yang, Jeongmo; Ha, Kyoung-Su; Usta, Hakan; Lee, Jinwon; Kim, ChoongikThe 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.Article Citation - WoS: 2Citation - Scopus: 2Stochastic Orientational Encoding via Hydrogen Bonding Driven Assembly of Woven-Like Molecular Physically Unclonable Functions(Wiley-VCH Verlag GmbH, 2025) Kayaci, Nilgun; Kiremitler, Nuri Burak; Deneme, Ibrahim; Kalay, Mustafa; Ozbasaran, Aleyna; Zorlu, Yunus; Usta, HakanThe prevention of counterfeiting and the assurance of object authenticity require stochastic encoding schemes based on physically unclonable functions (PUFs). There is an urgent need for exceptionally large encoding capacities and multi-level responses within a molecularly defined, single-material system. Herein, a novel stochastic orientational encoding approach is demonstrated using a facile ambient-atmosphere solution processing of a molecular thin film based on the rod-shaped oligo(p-phenyleneethynylene) (OPE) pi-architecture. The nanoscopic film, derived from the small molecule 2EHO-CF3PyPE with donor, acceptor, and pi-spacer building units, is designed for energetically favorable uniaxial molecular assembly and crystal growth via directional multiple hydrogen-bonding motifs at the molecular termini and short C & horbar;H<middle dot><middle dot><middle dot>pi contacts at the center. A facile solvent vapor annealing induces concurrent dewetting and microscopic 1D random crystallization, yielding a woven-textured random features. Using convolutional neural networks, the rich variations in microcrystal domain properties and stochastic encoding of 1D crystal orientations generate artificial coloration, achieving an encoding capacity reaching (6.5 x 10(4))(2752 x 2208). The results demonstrate an effective strategy for achieving ultrahigh encoding capacities in a thin film composed of a single-material. This approach enables low-cost, solution-processed fabrication for mass production and broad adoption, while opening new opportunities to explore molecular-PUFs through structural design and engineering noncovalent interactions.Conference Object Design and Development of Functional Organic Small Molecules and Polymers for Optoelectronics(Amer Chemical Soc, 2016) Usta, Hakan; Demirel, Gokhan; Facchetti, Antonio; Muccini, MicheleConference Object Thin Films of Inert Metal Nanowires for Display Applications(Tanger Ltd, 2015) Citir, Murat; Sen, Unal; Usta, Hakan; Canlier, Ali; Hakan, Usta; Ali, Canlier; Murat, Citir; Unal, SenAg nanowire transparent electrode has excellent transmittance (90%) and sheet resistance (20 Ohm/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. Coating Ag nanowires with a thin layer of inert metals such as Au and Pd through galvanic exchange reactions may enhance the chemical stability of Ag nanowire films highly and also helps to obtain lower haze. In this study, coating of thin Au and Pd layers has been applied successfully onto the surface of Ag nanowires. Usually coatings are carried out by salts such as HAuCl4 and K2PdCl4 in order to make nanotubes. In this study, novel ethylenediamine(en) complexes of inert metal cations with mild oxidation power were prepared in order to oxidize Ag atoms partially on the surface through galvanic displacement. The mild galvanic exchange allowed for a thin layer (1-4 nm) of inert metal coating on the Ag nanowires with minimal truncation of the nanowire, where the average lengths and the diameters were between 10 similar to 14 mu m and 55 similar to 65 nm, respectively. The crystalline structure of the shell was formed epitaxially on the surface. The new Ag nanowires were suspended in methanol and then electrostatically sprayed on glass and flexible substrates. It was revealed that average total transmittance remain around 90% within visible spectrum region (400-800 nm) whereas sheet resistance rises up to 175 Ohm/sq. Very thin layer of inert metal costs low, though this may render an excellent catalyst for applications such as fuel cell and organic synthesis, whereas transparent films of inert metal-coated Ag nanowire can be utilized as working electrodes for spectro-electrochemical cells as well.