Browsing by Subject "Nanowires"
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Item Open Access 97 percent light absorption in an ultrabroadband frequency range utilizing an ultrathin metal layer: randomly oriented, densely packed dielectric nanowires as an excellent light trapping scaffold(Royal Society of Chemistry, 2017) Ghobadi, A.; Dereshgi, S. A.; Hajian, H.; Birant, G.; Butun, B.; Bek, A.; Özbay, EkmelIn this paper, we propose a facile and large scale compatible design to obtain perfect ultrabroadband light absorption using metal-dielectric core-shell nanowires. The design consists of atomic layer deposited (ALD) Pt metal uniformly wrapped around hydrothermally grown titanium dioxide (TiO2) nanowires. It is found that the randomly oriented dense TiO2 nanowires can impose excellent light trapping properties where the existence of an ultrathin Pt layer (with a thickness of 10 nm) can absorb the light in an ultrabroadband frequency range with an amount near unity. Throughout this study, we first investigate the formation of resonant modes in the metallic nanowires. Our findings prove that a nanowire structure can support multiple longitudinal localized surface plasmons (LSPs) along its axis together with transverse resonance modes. Our investigations showed that the spectral position of these resonance peaks can be tuned with the length, radius, and orientation of the nanowire. Therefore, TiO2 random nanowires can contain all of these features simultaneously in which the superposition of responses for these different geometries leads to a flat perfect light absorption. The obtained results demonstrate that taking unique advantages of the ALD method, together with excellent light trapping of chemically synthesized nanowires, a perfect, bifacial, wide angle, and large scale compatible absorber can be made where an excellent performance is achieved while using less materials.Item Open Access Ab initio study of hydrogenic effective mass impurities in Si nanowires(Institute of Physics Publishing, 2017-01) Peelaers, H.; Durgun, Engin; Partoens, B.; Bilc, D. I.; Ghosez, P.; Van De Walle C. G.; Peeters, F. M.The effect of B and P dopants on the band structure of Si nanowires is studied using electronic structure calculations based on density functional theory. At low concentrations a dispersionless band is formed, clearly distinguishable from the valence and conduction bands. Although this band is evidently induced by the dopant impurity, it turns out to have purely Si character. These results can be rigorously analyzed in the framework of effective mass theory. In the process we resolve some common misconceptions about the physics of hydrogenic shallow impurities, which can be more clearly elucidated in the case of nanowires than would be possible for bulk Si. We also show the importance of correctly describing the effect of dielectric confinement, which is not included in traditional electronic structure calculations, by comparing the obtained results with those of G0W0 calculations.Item Open Access Anatase TiO2 nanowires functionalized by organic sensitizers for solar cells: a screened Coulomb hybrid density functional study(American Institute of Physics Inc., 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtıoğlu, S.; Mete, E.The adsorption of two different organic molecules cyanidin glucoside (C21O11H20) and TA-St-CA on anatase (101) and (001) nanowires has been investigated using the standard and the range separated hybrid density functional theory calculations. The electronic structures and optical spectra of resulting dye-nanowire combined systems show distinct features for these types of photochromophores. The lowest unoccupied molecular orbital of the natural dye cyanidin glucoside is located below the conduction band of the semiconductor while, in the case of TA-St-CA, it resonates with the states inside the conduction band. The wide-bandgap anatase nanowires can be functionalized for solar cells through electron-hole generation and subsequent charge injection by these dye sensitizers. The intermolecular charge transfer character of Donor-π-Acceptor type dye TA-St-CA is substantially modified by its adsorption on TiO2 surfaces. Cyanidin glucoside exhibits relatively stronger anchoring on the nanowires through its hydroxyl groups. The atomic structures of dye-nanowire systems re-optimized with the inclusion of nonlinear solvation effects showed that the binding strengths of both dyes remain moderate even in ionic solutions.Item Open Access Biomimicry of multifunctional nanostructures in the neck feathers of mallard (Anas platyrhynchos L.) drakes(Nature Publishing Group, 2014-04-22) Khudiyev, T.; Dogan, T.; Bayındır, MehmetBiological systems serve as fundamental sources of inspiration for the development of artificially colored devices, and their investigation provides a great number of photonic design opportunities. While several successful biomimetic designs have been detailed in the literature, conventional fabrication techniques nonetheless remain inferior to their natural counterparts in complexity, ease of production and material economy. Here, we investigate the iridescent neck feathers of Anas platyrhynchos drakes, show that they feature an unusual arrangement of two-dimensional (2D) photonic crystals and further exhibit a superhydrophobic surface, and mimic this multifunctional structure using a nanostructure composite fabricated by a recently developed top-down iterative size reduction method, which avoids the above-mentioned fabrication challenges, provides macroscale control and enhances hydrophobicity through the surface structure. Our 2D solid core photonic crystal fibres strongly resemble drake neck plumage in structure and fully polymeric material composition, and can be produced in wide array of colors by minor alterations during the size reduction process.Item Open Access Characteristic equations for the lasing Modes of infinite periodic chain of quantum wires(IEEE, 2008-06) Byelobrov, V. O.; Benson, T. M.; Altıntaş, Ayhan; Nosich, A.I.In this paper, we study the lasing modes of a periodic open optical resonator. The resonator is an infinite chain of active circular cylindrical quantum wires standing in tree space. Characteristic equations for the frequencies and associated linear thresholds of lasing are derived. These quantities are considered as eigenvalues of specific electromagnetic-field problem with "active" imaginary part of the cylinder material's refractive index - Lasing Eigenvalue Problem (LEP). ©2008 IEEE.Item Open Access Comment on "modeling the electrical conduction in DNA nanowires: Charge transfer and lattice fluctuation theories"(American Physical Society, 2016) Panahi, M.; Chitsazanmoghaddam, M.In a recent paper [S. Behnia and S. Fathizadeh, Phys. Rev. E 91, 022719 (2015)10.1103/PhysRevE.91.022719] an analytical approach is proposed for the investigation of the conductivity properties of DNA. The authors use mean Lyapunov exponent methods as the backbone of their approach and try to interpret properties of the system based on its behavior. Their interpretation regarding the change in nature of the mean Lyapunov exponent at the denaturation temperatures and discussions of stability and instability based on the mean Lyapunov exponent method are questioned. Moreover there is misunderstanding between mean Lyapunov exponent and Lyapunov exponent. © 2016 American Physical Society.Item Open Access Disorder-free localization around the conduction band edge of crossing and kinked silicon nanowires(A I P Publishing LLC, 2015) Keleş, Ü.; Çakan, A.; Bulutay, C.We explore ballistic regime quantum transport characteristics of oxide-embedded crossing and kinked silicon nanowires (NWs) within a large-scale empirical pseudopotential electronic structure framework, coupled to the Kubo-Greenwood transport analysis. A real-space wave function study is undertaken and the outcomes are interpreted together with the findings of ballistic transport calculations. This reveals that ballistic transport edge lies tens to hundreds of millielectron volts above the lowest unoccupied molecular orbital, with a substantial number of localized states appearing in between, as well as above the former. We show that these localized states are not due to the oxide interface, but rather core silicon-derived. They manifest the wave nature of electrons brought to foreground by the reflections originating from NW junctions and bends. Hence, we show that the crossings and kinks of even ultraclean Si NWs possess a conduction band tail without a recourse to atomistic disorder.Item Open Access Electroless synthesis of 3nm wide alloy nanowires inside Tobacco mosaic virus(2012) Balci, S.; Hahn, K.; Kopold P.; Kadri, A.; Wege, C.; Kern, K.; Bittner, A.M.We show that 3nm wide cobaltiron alloy nanowires can be synthesized by simple wet chemical electroless deposition inside tubular Tobacco mosaic virus particles. The method is based on adsorption of Pd(II) ions, formation of a Pd catalyst, and autocatalytic deposition of the alloy from dissolved metal salts, reduced by a borane compound. Extensive energy-filtering TEM investigations at the nanoscale revealed that the synthesized wires are alloys of Co, Fe, and Ni. We confirmed by high-resolution TEM that our alloy nanowires are at least partially crystalline, which is compatible with typical Co-rich alloys. Ni traces bestow higher stability, presumably against corrosion, as also known from bulk CoFe. Alloy nanowires, as small as the ones presented here, might be used for a variety of applications including high density data storage, imaging, sensing, and even drug delivery. © 2012 IOP Publishing Ltd.Item Open Access Enhanced Performance of Nanowire-Based All-TiO2 Solar Cells using Subnanometer-Thick Atomic Layer Deposited ZnO Embedded Layer(Pergamon Press, 2015) Ghobadi, A.; Yavuz, H. I.; Ulusoy, T. G.; Icli, K. C.; Ozenbas, M.; Okyay, Ali KemalIn this paper, the effect of angstrom-thick atomic layer deposited (ALD) ZnO embedded layer on photovoltaic (PV) performance of Nanowire-Based All-TiO2 solar cells has been systematically investigated. Our results indicate that by varying the thickness of ZnO layer the efficiency of the solar cell can be significantly changed. It is shown that the efficiency has its maximum for optimal thickness of 1 ALD cycle in which this ultrathin ZnO layer improves device performance through passivation of surface traps without hampering injection efficiency of photogenerated electrons. The mechanisms contributing to this unprecedented change in PV performance of the cell have been scrutinized and discussed.Item Open Access Fabrication of supramolecular n/p-nanowires via coassembly of oppositely charged peptide-chromophore systems in aqueous media(American Chemical Society, 2017-07) Khalily, M. A.; Bakan, G.; Kucukoz, B.; Topal, A. E.; Karatay, A.; Yaglioglu, H. G.; Dana, A.; Güler, Mustafa O.Fabrication of supramolecular electroactive materials at the nanoscale with well-defined size, shape, composition, and organization in aqueous medium is a current challenge. Herein we report construction of supramolecular charge-transfer complex one-dimensional (1D) nanowires consisting of highly ordered mixed-stack π-electron donor-acceptor (D-A) domains. We synthesized n-type and p-type β-sheet forming short peptide-chromophore conjugates, which assemble separately into well-ordered nanofibers in aqueous media. These complementary p-type and n-type nanofibers coassemble via hydrogen bonding, charge-transfer complex, and electrostatic interactions to generate highly uniform supramolecular n/p-coassembled 1D nanowires. This molecular design ensures highly ordered arrangement of D-A stacks within n/p-coassembled supramolecular nanowires. The supramolecular n/p-coassembled nanowires were found to be formed by A-D-A unit cells having an association constant (KA) of 5.18 × 105 M-1. In addition, electrical measurements revealed that supramolecular n/p-coassembled nanowires are approximately 2400 and 10 times more conductive than individual n-type and p-type nanofibers, respectively. This facile strategy allows fabrication of well-defined supramolecular electroactive nanomaterials in aqueous media, which can find a variety of applications in optoelectronics, photovoltaics, organic chromophore arrays, and bioelectronics.Item Open Access Fourier transform plasmon resonance spectrometer using nanoslit-nanowire pair(American Institute of Physics, 2019) Uulu, Doolos Aibek; Ashirov, Timur; Polat, N.; Yakar, O.; Balcı, S.; Kocabaş, C.In this paper, we present a nanoscale Fourier transform spectrometer using a plasmonic interferometer consisting of a tilt subwavelength slit-nanowire pair on a metallic surface fabricated by the focused ion beam microfabrication technique. The incident broadband light strongly couples with the surface plasmons on the gold surface, and thus, surface plasmon polaritons (SPPs) are generated. The launched SPPs interfere with the incident light and generate high contrast interference fringes in the nanoslit. The transmitted SPPs through the metal nanoslit can decouple into free space and are collected by an objective in the far field. The spectroscopic information of the incidence light is obtained by fast Fourier transform of the fringe pattern of the SPPs. In our design, there is no need for a bulky dispersive spectrometer or dispersive optical elements. The dimension of the spectrometer is around 200 μm length. Our design is based on inherent coherence of the SPP waves propagating through the subwavelength metal nanoslit structures etched into an opaque gold film.Item Open Access Half-metallic silicon nanowires: First-principles calculations(American Physical Society, 2007) Durgun, Engin; Çakır, D.; Akman, N.; Çıracı, SalimFrom first-principles calculations, we predict that specific transition metal (TM) atom-adsorbed silicon nanowires have a half-metallic ground state. They are insulators for one spin direction, but show metallic properties for the opposite spin direction. At high coverage of TM atoms, ferromagnetic silicon nanowires become metallic for both spin directions with high magnetic moment and may have also significant spin polarization at the Fermi level. The spin-dependent electronic properties can be engineered by changing the type of adsorbed TM atoms, as well as the diameter of the nanowire. Present results are not only of scientific interest, but also can initiate new research on spintronic applications of silicon nanowires. © 2007 The American Physical Society.Item Open Access Hartree-Fock approximation of bipolaron state in quantum dots and wires(Springer, 2010) Senger, R. T.; Kozal, B.; Chatterjee, A.; Erçelebi, A.The bipolaronic ground state of two electrons in a spherical quantum dot or a quantum wire with parabolic boundaries is studied in the strong electron-phonon coupling regime. We introduce a variational wave function that can conveniently conform to represent alternative ground state configurations of the two electrons, namely, the bipolaronic bound state, the state of two individual polarons, and two nearby interacting polarons confined by the external potential. In the bipolaron state the electrons are found to be separated by a finite distance about a polaron size. We present the formation and stability criteria of bipolaronic phase in confined media. It is shown that the quantum dot confinement extends the domain of stability of the bipolaronic bound state of two electrons as compared to the bulk geometry, whereas the quantum wire geometry aggravates the formation of stable bipolarons.Item Open Access Hybrid functional calculated optical and electronic structures of thin anatase TiO2 nanowires with organic dye adsorbates(Elsevier, 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtioğlu, Ş.; Mete, E.The electronic and optical properties of thin anatase TiO2 (1 0 1) and (0 0 1) nanowires have been investigated using the screened Coulomb hybrid density functional calculations. For the bare nanowires with sub-nanometer diameters, the calculated band gaps are larger relative to the bulk values due to size effects. The role of organic light harvesting sensitizers on the absorption characteristics of the anatase nanowires has been examined using the hybrid density functional method incorporating partial exact exchange with range separation. For the lowest lying excitations, directional charge redistribution of tetrahydroquinoline (C2-1) dye shows a remarkably different profile in comparison to a simple molecule which is chosen as the coumarin skeleton. The binding modes and the adsorption energies of C2-1 dye and coumarin core on the anatase nanowires have been studied including non-linear solvation effetcs. The calculated optical and electronic properties of the nanowires with these two different types of sensitizers have been interpreted in terms of their electron-hole generation, charge carrier injection and recombination characteristics.Item Open Access Laser induced sponge-like Si in Si-rich oxides for photovoltaics(Optical Society of American (OSA), 2013) Gundogdu, S.; Sungur Ozen, E.; Hübner, R.; Heinig, K.H.; Aydınlı, AtillaWe show that a sponge-like structure of interconnected Si nanowires embedded in a dielectric matrix can be obtained by laser annealing of silicon rich oxides (SRO). Due to quantum confinement, the large bandgap displayed by these percolated nanostructures can be utilized as a tandem stage in 3rd generation thin-film solar cells. Well passivated by the SiO2 dielectric matrix, they are expected to overcome the difficulty of carrier separation encountered in the case of isolated crystalline quantum dots. In this study PECVD grown SRO were irradiated by a cw Ar+ laser. Raman spectroscopy has been used to assess the crystallinity of the Si nanostructures and thus to optimize the annealing conditions as dwell times and power densities. In addition, Si plasmon imaging in the transmission electron microscope was applied to identify the sponge-like structure of phase-separated silicon. © 2013 Optical Society of America.Item Open Access Lasing modes of infinite periodic chain of quantum wires(IEEE, 2009-06-07) Byelobrov, V. O.; Benson, T. M.; Sewell, P.; Altıntaş, Ayhan; Nosich, A. I.In this paper, we study the scattering and eigenvalue problems for a periodic open optical resonator that is an infinite chain of active circular cylindrical quantum wires standing in free space. The scattering problem is solved by the method of partial separation of variables. The eigenvalue problem differs from the first one by the absence of the incident field and presence of "active properties" of cylinders and yields the frequencies and thresholds of lasing. ©2009 IEEE.Item Open Access Macroscopic photoconductive nanowire arrays(IEEE, 2011) Bayındır, Mehmet; Yaman, Mecit; Özgür, Erol; Aktaş, Ozan; Khudiyev, Tural; Kanık, Mehmet; Deniz, HakanA novel high-throughput fabrication technique to produce polymer embedded functional chalcogenide nanowire arrays is demonstrated. Indefinitely-long selenium nanowire arrays are obtained and their size dependent photoconductivity is investigated. Logarithmic increase in photo-conductance is observed. © 2011 IEEE.Item Embargo Nanoimprinted halide perovskite nanowires with directly-written gratings(Elsevier BV, 2022-12-01) Pushkarev, A.P.; Sinev, I.S.; Ladutenko, K.S.; Song, M.; Demir, Hilmi Volkan; Makarov, S.V.Perovskite nanowires demonstrate low-threshold lasing owing to the huge optical gain of their material and their self-resonance behavior. However, their lasing properties still can be optimized and improved because light outcoupling through their subwavelength facets is not optimal for many applications. Here we demonstrate a versatile method for improvement of the lasing properties of a single perovskite CsPbBr3 nanowire by defining an additional grating on its surface. Such direct patterning is carried out by high-throughput nanoimprinting method, which does not damage the material or worsen its material properties as it might happen after applying conventional lithographical approaches. Such direct imprinting of gratings on the CsPbBr3 nanowires provides us with the ability to modify their eigen- modes, improve directivity of their outcoupled stimulated emission and narrow their lasing spectral lines, while keeping their lasing threshold almost unchanged. Concurrently, the number of their modes are reduced (by half) and the quality factor of their remaining lasing modes is increased (by about 2-folds). These findings indicate that direct writing of nanopatterns on halide perovskite nanowires via nanoimprint lithography holds great promise for imparting additional structural functions to these nanowires while leaving their material unharmed. © 2022 Elsevier B.V.Item Open Access Nanosprings harvest light more efficiently(OSA - The Optical Society, 2015) Khudiyev, T.; Bayındır, MehmetNanotechnology presents versatile architectural designs for the purpose of utilization as a building block of 1D optoelectronic nanodevices because current nanowire-based schemes require more effective solutions for low absorption capacity of nanoscale volumes. We report on the potential of nanospring absorbers as an alternative light-harvesting platform with significant advantages over conventional nanowires. Absorption capacity of nanospring geometry is found to be superior to cylindrical nanowire shape. Unlike nanowires, they are able to trap a larger amount of light thanks to characteristic periodic behavior that boosts light collection for the points matched with Mie resonances. Moreover, nanospring shape supplies compactness to a resulting device with area preservation as high as twofold. By considering that a nanospring array with optimal periods yields higher absorption than individual arrangements and core-shell designs, which further promote light collection due to unique antireflection features of shell layer, these nanostructures will pave the way for the development of highly efficient self-powered nanosystems.Item Open Access Networks of silicon nanowires: A large-sclae atomistic electronic structure analysis(AIP Publishing LLC, 2013) Keleş, Ü.; Liedke, B.; Heinig, Karl-Heinz.; Bulutay, C.Networks of silicon nanowires possess intriguing electronic properties surpassing the predictions based on quantum confinement of individual nanowires. Employing large-scale atomistic pseudopotential computations, as yet unexplored branched nanostructures are investigated in the subsystem level as well as in full assembly. The end product is a simple but versatile expression for the bandgap and band edge alignments of multiply-crossing Si nanowires for various diameters, number of crossings, and wire orientations. Further progress along this line can potentially topple the bottom-up approach for Si nanowire networks to a top-down design by starting with functionality and leading to an enabling structure.