WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
Browse
23 results
Search Results
Article Citation - WoS: 8Citation - Scopus: 8Writing Chemical Patterns Using Electrospun Fibers as Nanoscale Inkpots for Directed Assembly of Colloidal Nanocrystals(Royal Soc Chemistry, 2020) Kiremitler, N. Burak; Torun, Ilker; Altintas, Yemliha; Patarroyo, Javier; Demir, Hilmi Volkan; Puntes, Victor F.; Onses, M. SerdarApplications that range from electronics to biotechnology will greatly benefit from low-cost, scalable and multiplex fabrication of spatially defined arrays of colloidal inorganic nanocrystals. In this work, we present a novel additive patterning approach based on the use of electrospun nanofibers (NFs) as inkpots for end-functional polymers. The localized grafting of end-functional polymers from spatially defined nanofibers results in covalently bound chemical patterns. The main factors that determine the width of the nanopatterns are the diameter of the NF and the extent of spreading during the thermal annealing process. Lowering the surface energy of the substrates via silanization and a proper choice of the grafting conditions enable the fabrication of nanoscale patterns over centimeter length scales. The fabricated patterns of end-grafted polymers serve as the templates for spatially defined assembly of colloidal metal and metal oxide nanocrystals of varying sizes (15 to 100 nm), shapes (spherical, cube, rod), and compositions (Au, Ag, Pt, TiO2), as well as semiconductor quantum dots, including the assembly of semiconductor nanoplatelets.Article Citation - WoS: 12Citation - Scopus: 11Trans-Cis Isomerization Assisted Synthesis of Solution-Processable Yellow Fluorescent Maleic Anhydrides for White-Light Generation(Elsevier Science SA, 2015-12) Ozdemir, Mehmet; Genc, Sinan; Ozdemir, Resul; Altintas, Yemliha; Citir, Murat; Sen, Unal; Usta, HakanHeterocyclic maleic anhydride derivatives have been extensively studied in natural products chemistry over the past few decades. However, their incorporation into optoelectronic devices has lagged behind that of other pi-conjugated systems, and they have never been studied in white light emitting diodes (WLEDs). The development of emissive pi-conjugated materials for (WLEDs) has been an emerging scientific and technological research area to replace phosphors used in LED-based solid-state lighting. Here, we demonstrate the design, synthesis and characterization of two new highly emissive alkyl-substituted bis(thienyl)maleic anhydrides (C6-Th2MA and C12-Th2MA) with favorable photophysical properties. The new core is synthesized via a novel trans-to-cis isomerization-assisted one-pot reaction, which is demonstrated for the first time in the literature for the synthesis of a bis(heteroaryl)maleic anhydride. Due to its favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively, C12-Th2MA is studied as a potential wavelength-upconverting material. A WLED fabricated by drop-casting a polymeric solution of C12-Th2MA on a blue LED (InGaN, 455 nm) yields promising CIE coordinates and color-rendering index (CRI) values of (0.24, 0.20) and 65.0, respectively. Considering the simplicity of the current molecular structure and facile synthesis, alkyl-substituted bis(thienyl)maleic anhydrides stand as ideal phosphor alternatives. Therefore, the current findings may open new perspectives for the development of maleic anhydride-based small molecules for low-cost, energy-efficient, and solution-processed lighting technologies. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 53Citation - Scopus: 59Thickness-Tunable Self-Assembled Colloidal Nanoplatelet Films Enable Ultrathin Optical Gain Media(Amer Chemical Soc, 2020-07-31) Erdem, Onur; Foroutan, Sina; Gheshlaghi, Negar; Guzelturk, Burak; Altintas, Yemliha; Demir, Hilmi VolkanWe propose and demonstrate construction of highly uniform, multilayered superstructures of CdSe/CdZnS core/shell colloidal nanoplatelets (NPLs) using liquid interface self-assembly. These NPLs are sequentially deposited onto a solid substrate into slabs having monolayer-precise thickness across tens of cm(2) areas. Because of near-unity surface coverage and excellent uniformity, amplified spontaneous emission (ASE) is observed from an uncharacteristically thin film having 6 NPL layers, corresponding to a mere 42 nm thickness. Furthermore, systematic studies on optical gain of these NPL superstructures having thicknesses ranging from 6 to 15 layers revealed the gradual reduction in gain threshold with increasing number of layers, along with a continuous spectral shift of the ASE peak (similar to 18 nm). These observations can be explained by the change in the optical mode confinement factor with the NPL waveguide thickness and propagation wavelength. This bottom-up construction technique for thickness-tunable, three-dimensional NPL superstructures can be used for large-area device fabrication.Article Citation - WoS: 4Citation - Scopus: 4Thermal Conductivity and Interfacial Energy of Solid Bi in the Bi-Ag Eutectic System(Springer, 2015-05-15) Altintas, Yemliha; Ozturk, Esra; Aksoz, Sezen; Keslioglu, Kazim; Marasli, Necmettin; Maraşlı, Necmettin; Keşlioğlu, Kâzım; Altıntas, YemlihaThe equilibrated grain boundary groove shapes for solid Bi (Bi-2.87 at.%Ag) in equilibrium with Bi-Ag eutectic liquid have been observed from quenched sample with a radial heat flow apparatus. The Gibbs-Thomson coefficient, solid-liquid interfacial energy and grain boundary energy of solid Bi have been determined from the observed grain boundary groove shapes. The variation of thermal conductivity with temperature for eutectic solid phase (Bi-4.7 at.%Ag) has been measured. The ratio of thermal conductivity of equilibrated eutectic liquid phase to eutectic solid phase has also been measured with a Bridgman-type growth apparatus at the melting temperature. The Gibbs-Thomson coefficient, solid-liquid interfacial energy and grain boundary energy of solid Bi in equilibrium with Bi-Ag eutectic liquid were determined to be (9.2 +/- A 0.6) x 10(-8) K m, (52.7 +/- A 6.3) x 10(-3) J m(-2) and (102.4 +/- A 13.3) x 10(-3) J m(-2), respectively, from observed grain boundary groove shapes.Article Citation - WoS: 23Citation - Scopus: 21The Measurements of Electrical and Thermal Conductivity Variations With Temperature and Phonon Component of the Thermal Conductivity in Sn-Cd Sn-In Sn-Ag and Sn-Bi Alloys(Elsevier France-editions Scientifiques Medicales Elsevier, 2016-02) Altintas, Yemliha; Kaygisiz, Yusuf; Ozturk, Esra; Aksoz, Sezen; Keslioglu, Kazim; Marasli, Necmettin; Kayglslz, Yusuf; Altlntas, YemlihaThe electrical and thermal conductivity variations with temperature for lead-free ternary solders, namely Sn-41.39 at.% Cd-6.69 at.% Sb, Sn-49 at.% In-1 at.% Cu, Sn-50 at.% Ag-10 at.% Bi and Sn-32 at.% Bi-3 at.% Zn alloys, were measured by the d.c. four-point probe method and radial heat flow apparatus, respectively. The contributions of electrons and phonons to the thermal conductivity were separately determined by using the measured values of the thermal and electrical conductivities obtained by the Wiedemann-Franz law in the lead-free ternary solders. The percentages of the phonon component of thermal conductivity were found to be in the range of 46-55%, 46-50%, 38-47% and 69-73% for Sn-41.39 at.% Cd-6.69 at.% SU, Sn-49 at.% In-1 at.% Cu, Sn-50 at.% Ag-10 at.% Bi and Sn-32 at.% Bi-3 at.% Zn alloys at the ranges of 318-443 K temperature, respectively. The temperature coefficients (alpha) of electrical conductivity for the lead-free ternary solders were found to be 2.47 x 10(-3), 4.97 x 10(-3), 1.14 x 10(-3) and 1.00 x 10(-3) K-1, respectively. The thermal conductivities of the solid phases at their melting temperature and the thermal temperature coefficients for the lead-free ternary solders were also found to be 47.72 +/- 2.38, 68.57 +/- 3.42, 73.52 +/- 3.67, 37.53 +/- 1.87 W/Km and 1.47 x 10(-3), 1.48 x 10(-3), 1.85 x 10(-3) and 2.21 x 10(-3) K-1, respectively. (C) 2015 Elsevier Masson SAS. All rights reserved.Article Citation - WoS: 15Citation - Scopus: 14The Effect of Ligand Chain Length on the Optical Properties of Alloyed Core-Shell InPZnS/ZnS Quantum Dots(Elsevier Science SA, 2017-07) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, EvrenIn this work, we demonstrate the effect of organic ligands on the optical properties of alloyed core-shell InPZnS/ZnS quantum dots (QDs). We have systematically studied the synthesis and characterization of InPZnS/ZnS QDs using short and long chain length ligands i.e., butyric (C4), hexanoic (C6), octanoic (C8), dodecanoic (C12), myristic (C14), palmitic (C16) and stearic acids (C18), respectively. This study achieved more than 85% quantum yield with 43 nm full-width-half maximum value, using dodecanoic acid as the capping ligand. The properties of the QDs with short and long chain length ligands have been analyzed using UV Vis absorption spectrophotometer, steady state and time resolved photoluminescence spectrometer, X-ray diffraction, Zeta sizer, transmission electron microscopy and energy dispersive X-ray spectroscopy. (C) 2017 Published by Elsevier B.V.Article Citation - WoS: 37Citation - Scopus: 39Spectrally Wide-Range Efficient, and Bright Colloidal Light-Emitting Diodes of Quasi-2D Nanoplatelets Enabled by Engineered Alloyed Heterostructures(Amer Chemical Soc, 2020-08-25) Altintas, Yemliha; Liu, Baiquan; Hernandez-Martinez, Pedro Ludwig; Gheshlaghi, Negar; Shabani, Farzan; Sharma, Manoj; Demir, Hilmi VolkanRecently, there has been tremendous interest in the synthesis and optoelectronic applications of quasi-two-dimensional colloidal nanoplatelets (NPLs). Thanks to the ultranarrow emission linewidth, high-extinction coefficient, and high photostability, NPLs offer an exciting opportunity for high-performance optoelectronics. However, until now, the applications of these NPLs are limited to available discrete emission ranges, limiting the full potential of these exotic materials as efficient light emitters. Here, we introduce a detailed systematic study on the synthesis of NPLs based on the alloying mechanisms in core/shell, core/alloyed shell, alloyed core/shell, and alloyed core/alloyed shell heterostructures. Through the engineering of the band gap supported by the theoretical calculations, we carefully designed and successfully synthesized the NPL emitters with continuously tunable emission. Unlike conventional NPLs showing discrete emission, here, we present highly efficient core/shell NPLs with fine spectral tunability from green to deep-red spectra. As an important demonstration of these efficient emitters, the first-time implementation of yellow NPL light-emitting diodes (LEDs) has been reported with record device performance, including the current efficiency surpassing 18.2 cd A(-1), power efficiency reaching 14.8 lm W-1, and record luminance exceeding 46 900 cd m(-2). This fine and wide-range color tunability in the visible range from stable and efficient core/shell NPLs is expected to be extremely important for the optoelectronic applications of the family of colloidal NPL emitters.Article Citation - WoS: 16Citation - Scopus: 17Solid-State Encapsulation and Color Tuning in Films of Cesium Lead Halide Perovskite Nanocrystals for White Light Generation(Amer Chemical Soc, 2019-01-30) Torun, Ilker; Altintas, Yemliha; Yazici, Ahmet Faruk; Mutlugun, Evren; Onses, M. SerdarPerovskite nanocrystals (PNCs) are highly demanding nanomaterials for solid-state lighting applications. A challenge for their exploitation in practical applications is the insufficient ambient and water stability associated with their ionic nature. Here we report a novel route for solid-state encapsulation of films of perovskite nanocrystals (PNCs) through vapor-phase deposition of a thin and hydrophobic layer of fluoroalkyltrichlorosilanes (FAS). High quality nanoscale crystals of CsPbBr3 were synthesized with well established colloidal methods and coated on solid substrates. The films of PNCs were then subjected to vapor of FAS for short durations of time (<60 s) in ambient atmosphere, resulting in deposition of a thin (<20 nm) hydrophobic layer. Besides providing a barrier for water and humidity, the vapor-phase deposition of FAS was accompanied by the blue shift of the emission wavelength of the PNCs. The color shift results from the partial exchange of Br with Cl anions, which emerge during the self-hydrolysis of the silane molecules. Throughout this process, we demonstrate the enhanced water stability of the films of PNCs and fine tunability of the wavelength in films from 516 nm to 488 nm. The fabrication of a white-light-emitting diode and tunability of the color coordinates with the duration of the FAS deposition were demonstrated. The rapid, scalable, and inexpensive solid-state encapsulation approach shows great promise for films of halide perovskites.Article Citation - WoS: 11Citation - Scopus: 9Single-Mode Lasing From a Single 7 nm Thick Monolayer of Colloidal Quantum Wells in a Monolithic Microcavity(Wiley-VCH Verlag GmbH, 2021-03-03) Foroutan-Barenji, Sina; Erdem, Onur; Delikanli, Savas; Yagci, Huseyin Bilge; Gheshlaghi, Negar; Altintas, Yemliha; Demir, Hilmi VolkanIn this work, the first account of monolithically-fabricated vertical cavity surface emitting lasers (VCSELs) of densely-packed, orientation-controlled, atomically flat colloidal quantum wells (CQWs) using a self-assembly method and demonstrate single-mode lasing from a record thin colloidal gain medium with a film thickness of 7 nm under femtosecond optical excitation is reported. Specially engineered CQWs are used to demonstrate these hybrid CQW-VCSELs consisting of only a few layers to a single monolayer of CQWs and are achieved the lasing from these thin gain media by thoroughly modeling and implementing a vertical cavity consisting of distributed Bragg reflectors with an additional dielectric layer for mode tuning. Accurate spectral and spatial alignment of the cavity mode with the CQW films is secured with the help of full electromagnetic computations. While overcoming the long-pending problem of limited electrical conductivity in thicker colloidal films, such ultrathin colloidal gain media can be helpful to enable fully electrically-driven colloidal lasers.Article Citation - WoS: 25Citation - Scopus: 25Self-Resonant Microlasers of Colloidal Quantum Wells Constructed by Direct Deep Patterning(Amer Chemical Soc, 2021-05-24) Gheshlaghi, Negar; Foroutan-Barenji, Sina; Erdem, Onur; Altintas, Yemliha; Shabani, Farzan; Humayun, Muhammad Hamza; Demir, Hilmi VolkanHere, the first account of self-resonant fully colloidal mu-lasers made from colloidal quantum well (CQW) solution is reported. A deep patterning technique is developed to fabricate well-defined high aspect-ratio on-chip CQW resonators made of grating waveguides and in-plane reflectors. The fabricated waveguide-coupled laser, enabling tight optical confinement, assures in-plane lasing. CQWs of the patterned layers are closed-packed with sharp edges and residual-free lifted-off surfaces. Additionally, the method is successfully applied to various nanoparticles including colloidal quantum dots and metal nanoparticles. It is observed that the patterning process does not affect the nanocrystals (NCs) immobilized in the attained patterns and the different physical and chemical properties of the NCs remain pristine. Thanks to the deep patterning capability of the proposed method, patterns of NCs with subwavelength lateral feature sizes and micron-scale heights can possibly be fabricated in high aspect ratios.
- «
- 1 (current)
- 2
- 3
- »