Browsing by Subject "Nanowire"
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Item Open Access High conducting nanowires obtained from uniform titanium covered carbon nanotubes(2005) Daǧ, Sefa; Durgun, Engin; Çıracı, SalimWe have shown that Ti atoms can form continuous coating of carbon nanotubes at different amount of coverage. The circular cross section changes to a square-like form, and the semiconducting tube becomes ferromagnetic metal with high quantum ballistic conductance. Metallicity is induced not only by the metal-metal coupling, but also by the band gap closing of SWNT at the corners of the square. The magnetic properties of Ti coated tubes depend strongly on the geometry, amount of Ti coverage and also on the elastic deformation of the tube. While the magnetic moment can be pronounced significantly by the positive axial strain, it can decrease dramatically upon the adsorption of additional Ti atoms to those already covering the nanotube. Besides, electronic structure and spin-polarization near the Fermi level can also be modified by radial strain. Our results have been obtained by the first-principles, spin-relaxed pseudopotential plane wave calculations within the density functional theory. © TÜBİTAK.Item Open Access Mechanical and electronic properties of metal chain nanowires(2003) Çakır, DenizThe fabrication of stable gold monoatomic chains suspended between two gold electrodes is one of the milestones in nanoscience and technology, since miniaturization of the electronic components is one of the great importance in development and improvement of new devices in nanoelectronic. Monoatomic chain nanowires show unusual mechanical and electronic properties such as quantized conductance and much stiff bonds compare to the ones in bulk. Ohnishi et al. [1], has visualized the monoatomic chains by using transmission electron microscopy (TEM). At the same time, Yanson et al [2], have produced the monoatomic chains and they measured its conductance. In the bond length measurement of monoatomic chains, unusually long interatomic lengths have been observed compare to interatomic distances in the bulk and dimer. In order to understand the nature of bonding and unusual structural properties, in this thesis, mechanical and electronic properties of metal chain nanowires are investigated from first principles by using pseudopotential plane wave calculations. Six different metals (Au, Ag, Al, Cu, Pt and Na) are studied in detail. All metals under study show two wire structure which are linear and zigzag structure. Au, Al and Pt show two different zigzag structure. All the wires are metallic. Relative stabilities are investigated by calculating the tension corresponding to apply force to keep the wire at a specific length. Au and Pt have bigger breaking force at breaking point relative to other metallic wires. In this thesis, effect of H, H2 and C impurities on mechanical and electronic properties of Au monoatomic chains are also studied. In wires with H and C impurities, wire under tension break from Au-Au bond away from the impurity. However, wire break from Au-H bond in H2 system. Except from Au-H system, wire become insulator when it contain C or H2 impurities. Before breaking, Au-impurity-Au bond length is in the range of long interatomic distance observed in experiment. So, the presence of an impurity can explain the observed long interatomic distances. However, changing of bond lengths and breaking bond during the stretching of wire depends on the type of impurity. If one stretch the Au-H system, all bond lengths increase in the same amount before breaking. However in Au-C system, Au-Au bond length away from the C impurity increase much more than other bonds. It is shown that absorption of impurity atoms modify the stiffness of the bonds in the wire. This related to the charge transfer from Au to impurity (for H and C). In H and C systems, wire break from Au-Au bond away from the impurity. However in H2 system, wire break from Au-H bond.Item Open Access Nanowire-shaped MoS2@MoO3 nanocomposites as a hole injection layer for quantum dot light-emitting diodes(American Chemical Society, 2022-08-23) Bastami, N.; Soheyli, E.; Arslan, A.; Sahrae, R.; Yazici, A. F.; Mutlugun, EvrenMolybdenum disulfides and molybdenum trioxides are structures that possess the potential to work as efficient charge transport layers in optoelectronic devices. In the present study, as opposed to the existing Mo-based nanostructures in flake, sheet, or spherical forms, an extremely simple and low-cost hydrothermal method is used to prepare nanowires (NWs) of MoS2@MoO3 (MSO) composites. The synthesis method includes several advantages including easy handling and processing of inexpensive precursors to reach stable MSO NWs without the need for an oxygen-free medium, which would facilitate the possibility of mass production of these nanostructures. The structural analysis confirmed the formation of MSO nanocomposites with different Mo valence states, as well as NWs of average length and diameter of 70 nm and 5 nm, respectively. In order to demonstrate their potential for optoelectronic applications, MSO NWs were blended into hole injection layers (HILs) in quantum dot-based light-emitting diodes (QLEDs). Electroluminescence measurements show a substantial enhancement in both luminance (from 44,330 to 68,630 cd.m–2) and external quantum efficiency (from 1.6 to 2.3%), based on the increase in the ratio of MSO NWs from 3 to 10%. Interestingly, the addition of 10% volume of MSO NWs resulted in a remarkably smoother HIL with improved current efficiency and stability in green-emitting QLEDs. The simplicity and cost-effective features of the synthesis method along with outstanding favorable morphology demonstrated their ability to enhance the QLED performance and mark them as promising agents for optoelectronics.Item Open Access Plasmonic metamaterials and nanocomposites with the narrow transparency window effect in broad extinction spectra(American Chemical Society, 2014) Zhang, H.; Demir, Hilmi Volkan; Govorov, A. O.We propose and describe plasmonic nanomaterials with unique optical properties. These nanostructured materials strongly attenuate light across a broad wavelength interval ranged from 400 nm to S pm but exhibit a narrow transparency window centered at a given wavelength. The main elements used in our systems are nanorods and nanocrosses of variable sizes. The nanomaterial can be designed as a solution, nanocomposite film or metastructure. The principle of the formation of the transparency window in the broad extinction spectrum is based on the narrow lines of longitudinal plasmons of single nanorods and nanorod complexes. To realize the spectrum with a transmission window, we design a nanocomposite material as a mixture of nanorods of different sizes. Simultaneously, we exclude nanorods of certain lengths from the nanorod ensemble. The width of the plasmonic transparency window is determined by the intrinsic and radiative broadenings of the nanocrystal plasmons. Nanocrystals can be randomly dispersed in a solution or arranged in metastructures. We show that interactions between nanocrystals in a dense ensemble can destroy the window effect and, simultaneously, we design the metastructure geometries with weak destructive interactions. We also describe the effect of narrowing of the transparency window with increasing the concentration of nanocrystals. Two well-established technologies can be used to fabricate such nano- and metamaterials, the colloidal synthesis, and lithography. Nanocomposites proposed here can be used as optical materials and smart coatings for shielding of electromagnetic radiation in a wide spectral interval with a simultaneous possibility of communication using a narrow transparency window.Item Open Access Synthetic biogenesis of bacterial amyloid nanomaterials with tunable inorganic-organic interfaces and electrical conductivity(American Chemical Society, 2017) Seker U.O.S.; Chen, A. Y.; Citorik, R. J.; Lu, T. K.Amyloids are highly ordered, hierarchal protein nanoassemblies. Functional amyloids in bacterial biofilms, such as Escherichia coli curli fibers, are formed by the polymerization of monomeric proteins secreted into the extracellular space. Curli is synthesized by living cells, is primarily composed of the major curlin subunit CsgA, and forms biological nanofibers with high aspect ratios. Here, we explore the application of curli fibers for nanotechnology by engineering curli to mediate tunable biological interfaces with inorganic materials and to controllably form gold nanoparticles and gold nanowires. Specifically, we used cell-synthesized curli fibers as templates for nucleating and growing gold nanoparticles and showed that nanoparticle size could be modulated as a function of curli fiber gold-binding affinity. Furthermore, we demonstrated that gold nanoparticles can be preseeded onto curli fibers and followed by gold enhancement to form nanowires. Using these two approaches, we created artificial cellular systems that integrate inorganic-organic materials to achieve tunable electrical conductivity. We envision that cell-synthesized amyloid nanofibers will be useful for interfacing abiotic and biotic systems to create living functional materials.Item Open Access Theoretical study of Ga-based nanowires and the interaction of Ga with single-wall carbon nanotubes(American Physical Society, 2004) Durgun, Engin; Dag, S.; Çıracı, SalimGallium displays physical properties which can make it a potential element to produce metallic nanowires and high-conducting interconnects in nanoelectronics. Using first-principles pseudopotential plane method we showed that Ga can form stable metallic linear and zigzag monatomic chain structures. The interaction between individual Ga atom and single-wall carbon nanotube (SWNT) leads to a chemisorption bond involving charge transfer. Doping of SWNT with Ga atom gives rise to donor states. Owing to a significant interaction between individual Ga atom and SWNT, continuous Ga coverage of the tube can be achieved. Ga nanowires produced by the coating of carbon nanotube templates are found to be stable and high conducting.Item Open Access Thermal conductivity measurements in nanosheets via bolometric effect(IOP Publishing Ltd, 2020) Çakıroğlu, Onur; Mehmood, Naveed; Çiçek, Mert Miraç; Rasouli, Hamid Reza; Durgun, Engin; Kasırga, T. Serkan; Aikebaier, AizimaitiThermal conductivity measurement techniques for materials with nanoscale dimensions require fabrication of very complicated devices or their applicability is limited to a class of materials. Discovery of new methods with high thermal sensitivity are required for the widespread use of thermal conductivity measurements in characterizing materials' properties. We propose and demonstrate a simple non-destructive method with superior thermal sensitivity to measure the in-plane thermal conductivity of nanosheets and nanowires using the bolometric effect. The method utilizes laser beam heating to create a temperature gradient, as small as a fraction of a Kelvin, over the suspended section of the nanomaterial with electrical contacts. Local temperature rise due to the laser irradiation alters the electrical resistance of the device, which can be measured precisely. This resistance change is then used to extract the temperature profile along the nanomaterial using thermal conductivity as a fitting parameter. We measured the thermal conductivity of V2O3 nanosheets to validate the applicability of the method and found an excellent agreement with the literature. Further, we measured the thermal conductivity of metallic 2H-TaS2 for the first time and performed ab initio calculations to support our measurements. Finally, we discussed the applicability of the method on semiconducting nanosheets and performed measurements on WS2 and MoS2 thin flakes.