Photonics / Fotonik
Permanent URI for this collectionhttps://hdl.handle.net/11147/2590
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Article Citation - WoS: 7Citation - Scopus: 7Breaking the Boundaries of the Goldschmidt Tolerance Factor With Ethylammonium Lead Iodide Perovskite Nanocrystals(American Chemical Society, 2024) Güvenç, Çetin Meriç; Toso, Stefano; Ivanov, Yurii P.; Saleh, Gabriele; Balcı, Sinan; Divitini, Giorgio; Manna, LiberatoWe report the synthesis of ethylammonium lead iodide (EAPbI3) colloidal nanocrystals as another member of the lead halide perovskites family. The insertion of an unusually large A-cation (274 pm in diameter) in the perovskite structure, hitherto considered unlikely due to the unfavorable Goldschmidt tolerance factor, results in a significantly larger lattice parameter compared to the Cs-, methylammonium- and formamidinium-based lead halide perovskite homologues. As a consequence, EAPbI3 nanocrystals are highly unstable, evolving to a nonperovskite delta-EAPbI3 polymorph within 1 day. Also, EAPbI3 nanocrystals are very sensitive to electron irradiation and quickly degrade to PbI2 upon exposure to the electron beam, following a mechanism similar to that of other hybrid lead iodide perovskites (although degradation can be reduced by partially replacing the EA+ ions with Cs+ ions). Interestingly, in some cases during this degradation the formation of an epitaxial interface between (EA x Cs1-x )PbI3 and PbI2 is observed. The photoluminescence emission of the EAPbI3 perovskite nanocrystals, albeit being characterized by a low quantum yield (similar to 1%), can be tuned in the 664-690 nm range by regulating their size during the synthesis. The emission efficiency can be improved upon partial alloying at the A site with Cs+ or formamidinium cations. Furthermore, the morphology of the EAPbI3 nanocrystals can be chosen to be either nanocube or nanoplatelet, depending on the synthesis conditions.Article Anisotropic Tunability of Vibrational Modes in Black Phosphorus Under Uniaxial Compressive/Tensile Strain(Wiley, 2023) Li, Hao; Kutlu, Tayfun; Carrascoso, Felix; Şahin, Hasan; Munuera, Carmen; Castellanos Gomez, AndresStrain engineering is a powerful strategy for tuning the optical, electrical, vibrational properties of 2D nanomaterials. In this work, a four-point bending apparatus is constructed to apply both compressive and tensile strain on 2D anisotropic black phosphorus flake. Further polarized Raman spectroscopy is used to study the vibrational modes of black phosphorus flakes under uniaxial strain applied along various crystalline orientations. Here, a strong anisotropic blue/redshift of A1g, B2g, and A2g modes is found under compressive/tensile strain, respectively. Interestingly, mode A1g exhibits the maximum/minimum shift while mode B2g and mode A2g present the minimum/maximum shift when the strain is applied along armchair/zigzag direction. Density functional theory calculations are carried out to investigate the anisotropic strain response mechanism, finding that the strain-induced regulation of the PP bond angle, bond length, and especially interlayer interaction has a giant influence on the Raman shift. A four-point bending apparatus is constructed to study the effect of uniaxial strain on the vibrational property of anisotropic black phosphorus. Particularly, strong anisotropy on the Raman blueshift/redshift rate upon compressive/tensile strain can be observed, which results from the strain-induced regulation of the bond angle, bond length, and interlayer interactions according to density functional theory calculation analysis.imageArticle Citation - WoS: 40Citation - Scopus: 38Gas Permeation Through Graphdiyne-Based Nanoporous Membranes(Nature Research, 2022) Zhou, Zhihua; Tan, Yongtao; Yang, Qian; Bera, Achintya; Xiong, Zecheng; Yağmurcukardeş, Mehmet; Kim, MinsooNanoporous membranes based on two dimensional materials are predicted to provide highly selective gas transport in combination with extreme permeance. Here we investigate membranes made from multilayer graphdiyne, a graphene-like crystal with a larger unit cell. Despite being nearly a hundred of nanometers thick, the membranes allow fast, Knudsen-type permeation of light gases such as helium and hydrogen whereas heavy noble gases like xenon exhibit strongly suppressed flows. Using isotope and cryogenic temperature measurements, the seemingly conflicting characteristics are explained by a high density of straight-through holes (direct porosity of ∼0.1%), in which heavy atoms are adsorbed on the walls, partially blocking Knudsen flows. Our work offers important insights into intricate transport mechanisms playing a role at nanoscale.Article Citation - WoS: 17Citation - Scopus: 19Strong Coupling of Carbon Quantum Dots in Liquid Crystals(American Chemical Society, 2022) Sarısözen, Sema; Polat, Nahit; Mert Balcı, Fadime; Güvenç, Çetin Meriç; Kocabaş, Çoşkun; Yağlıoğlu, Halime Gül; Balcı, SinanCarbon quantum dots (CDs) have recently received a tremendous amount of interest owing to their attractive optical properties. However, CDs have broad absorption and emission spectra limiting their application ranges. We herein, for the first time, show synthesis of water-soluble red emissive CDs with a very narrow line width (∼75 meV) spectral absorbance and hence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystalline mesophases. The excited state dynamics of CDs has been studied by ultrafast transient absorption spectroscopy, and CDs display very stable and strong photoluminescence emission with a quantum yield of 35.4% and a lifetime of ∼2 ns. More importantly, we compare J-aggregate dyes with CDs in terms of their absorption line width, photostability, and ability to do strong coupling, and we conclude that highly fluorescent CDs have a bright future in the mixed light-matter states for emerging applications in future quantum technologies.Article Citation - WoS: 62Citation - Scopus: 59Exponentially Selective Molecular Sieving Through Angstrom Pores(Nature Publishing Group, 2021) Sun, Pengzhan; Yağmurcukardeş, Mehmet; Zhang, R.; Kuang, Wenjun; Lozada-Hidalgo, Marcelo; Liu, B. L.; Geim, Andre K.Two-dimensional crystals with angstrom-scale pores are widely considered as candidates for a next generation of molecular separation technologies aiming to provide extreme, exponentially large selectivity combined with high flow rates. No such pores have been demonstrated experimentally. Here we study gas transport through individual graphene pores created by low intensity exposure to low kV electrons. Helium and hydrogen permeate easily through these pores whereas larger species such as xenon and methane are practically blocked. Permeating gases experience activation barriers that increase quadratically with molecules’ kinetic diameter, and the effective diameter of the created pores is estimated as ∼2 angstroms, about one missing carbon ring. Our work reveals stringent conditions for achieving the long sought-after exponential selectivity using porous two-dimensional membranes and suggests limits on their possible performance.Article Citation - WoS: 35Citation - Scopus: 36Understanding Radiative Transitions and Relaxation Pathways in Plexcitons(Cell Press, 2021) Finkelstein-Shapiro, Daniel; Mante, Pierre-Adrien; Sarısözen, Sema; Wittenbecher, Lukas; Minda, Iulia; Balcı, Sinan; Pullerits, TonuMolecular aggregates on plasmonic nanoparticles have emerged as attractive systems for the studies of polaritonic light-matter states, called plexcitons. Such systems are tunable, scalable, easy to synthesize, and offer sub-wavelength confinement, all while giving access to the ultrastrong light-matter coupling regime, promising a plethora of applications. However, the complexity of these materials prevented the understanding of their excitation and relaxation phenomena. Here, we follow the relaxation pathways in plexcitons and conclude that while the metal destroys the optical coherence, the molecular aggregate coupled to surface processes significantly contributes to the energy dissipation. We use two-dimensional electronic spectroscopy with theoretical modeling to assign the different relaxation processes to either molecules or metal nanoparticle. We show that the dynamics beyond a few femtoseconds has to be considered in the language of hot electron distributions instead of the accepted lower and upper polariton branches and establish the framework for further understanding.Article Citation - WoS: 192Citation - Scopus: 194Multispectral Graphene-Based Electro-Optical Surfaces With Reversible Tunability From Visible To Microwave Wavelengths(Nature Research, 2021) Ergoktas, M. Said; Bakan, Gökhan; Kovalska, Evgeniya; Le Fevre, Lewis W.; Fields, Richard P.; Steiner, Pietro; Yu, Xiaoxiao; Balcı, SinanOptical materials with colour changing abilities have been explored for use in display devices(1), smart windows(2,3) or in the modulation of visual appearance(4-6). The efficiency of these materials, however, has strong wavelength dependence, which limits their functionality to a specific spectral range. Here, we report graphene-based electro-optical devices with unprecedented optical tunability covering the entire electromagnetic spectrum from the visible to microwave. We achieve this non-volatile and reversible tunability by electro-intercalation of lithium into graphene layers in an optically accessible device structure. The unique colour changing capability, together with area-selective intercalation, inspires the fabrication of new multispectral devices, including display devices and electro-optical camouflage coating. We anticipate that these results provide realistic approaches for programmable smart optical surfaces with a potential utility in many scientific and engineering fields such as active plasmonics and adaptive thermal management.Article Citation - WoS: 43Citation - Scopus: 46Glucuronoxylan-Based Quince Seed Hydrogel: a Promising Scaffold for Tissue Engineering Applications(Elsevier, 2021) Güzelgülgen, Meltem; Özkendir İnanç, Dilce; Yıldız, Ümit Hakan; Arslan Yıldız, AhuNatural gums and mucilages from plant-derived polysaccharides are potential candidates for a tissue-engineering scaffold by their ability of gelation and biocompatibility. Herein, we utilized Glucuron-oxylanbased quince seed hydrogel (QSH) as a scaffold for tissue engineering applications. Optimization of QSH gelation was conducted by varying QSH and crosslinker glutaraldehyde (GTA) concentrations. Structural characterization of QSH was done by Fourier Transform Infrared Spectroscopy (MR). Furthermore, morphological and mechanical investigation of QSH was performed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The protein adsorption test revealed the suitability of QSH for cell attachment. Biocompatibility of QSH was confirmed by culturing NIH-3T3 mouse fibroblast cells on it. Cell viability and proliferation results revealed that optimum parameters for cell viability were 2 mg mi(-1)of QSH and 0.03 M GTA. SEM and DAPI staining results indicated the formation of spheroids with a diameter of approximately 300 pm. Furthermore, formation of extracellular matrix (ECM) microenvironment was confirmed with the Collagen Type-I staining. Here, it was demonstrated that the fabricated QSH is a promising scaffold for 3D cell culture and tissue engineering applications provided by its highly porous structure, remarkable swelling capacity and high biocompatibility. (C) 2021 Published by Elsevier B.V.Article Citation - WoS: 13Citation - Scopus: 15Hybrid J-aggregate-graphene phototransistor(American Chemical Society, 2020) Yakar, Ozan; Balcı, Osman; Uzlu, Burkay; Polat, Nahit; Arı, Ozan; Tunç, İlknur; Balcı, SinanJ-aggregates are fantastic self-assembled chromophores with a very narrow and extremely sharp absorbance band in the visible and near-infrared spectrum, and hence they have found many exciting applications in nonlinear optics, sensing, optical devices, photography, and lasing. In silver halide photography, for example, they have enormously improved the spectral sensitivity of photographic process due to their fast and coherent energy migration ability. On the other hand, graphene, consisting of single layer of carbon atoms forming a hexagonal lattice, has a very low absorption coefficient. Inspired by the fact that J-aggregates have carried the role to sense the incident light in silver halide photography, we would like to use Jaggregates to increase spectral sensitivity of graphene in the visible spectrum. Nevertheless, it has been an outstanding challenge to place isolated J-aggregate films on graphene to extensively study interaction between them. We herein noncovalently fabricate isolated J-aggregate thin films on graphene by using a thin film fabrication technique we termed here membrane casting (MC). MC significantly simplifies thin film formation of water-soluble substances on any surface via porous polymer membrane. Therefore, we reversibly modulate the Dirac point of graphene in the J-aggregate/graphene van der Waals (vdW) heterostructure and demonstrate an all-carbon phototransistor gated by visible light. Owing to the hole transfer from excited excitonic thin film to graphene layer, graphene is hole-doped. In addition, spectral and power responses of the all-carbon phototransistor have been measured by using a tunable laser in the visible spectrum. The first integration of J-aggregates with graphene in a transistor structure enables one to reversibly write and erase charge doping in graphene with visible light that paves the way for using J-aggregate/graphene vdW heterostructures in optoelectronic applications.Article Citation - WoS: 8Citation - Scopus: 8Strain Tunable Band Structure of a New 2d Carbon Allotrope C-568(IOS Press, 2020) Gao, Qiang; Kang, Jun; Şahin, HasanRecently, C(568)has emerged as a new carbon allotrope, which shows semiconducting properties with a band gap around 1 eV and has attracted much attention. In this work, the external strain effects on the electronic properties of C(568)have been studied theoretically through first-principle calculations. The numerical results show that while in-plane uniaxial and biaxial strains both reduces the band gap of C(568)in case of tensile strain, their effects are quite different in the case of compressive strain. With increasing compressive uniaxial strain, the band gap of C(568)first increases, and then dramatically decreases. In contrast, the application of compressive biaxial strain up to -10% only leads to a slight increase of band gap. Moreover, an indirect-to-direct gap transition can be realized under both types of compressive strain. The results also show that the optical anisotropy of C(568)can be induced under uniaxial strain, while biaxial strain does not cause such an effect. These results indicate good strain tunability of the band structure of C-568, which could be helpful for the design and optimization of C-568-based nanodevices.