Browsing by Subject "Yarn"

Now showing 1 - 7 of 7

Open Access
All-fiber nonlinearity-and dispersion-managed dissipative soliton nanotube mode-locked laser
(American Institute of Physics, 2015) Zhang Z.; Popa, D.; Wittwer, V. J.; Milana, S.; Hasan, T.; Jiang, Z.; Ferrari, A. C.; Ilday F. Ö.
We report dissipative soliton generation from an Yb-doped all-fiber nonlinearity- and dispersion-managed nanotube mode-locked laser. A simple all-fiber ring cavity exploits a photonic crystal fiber for both nonlinearity enhancement and dispersion compensation. The laser generates stable dissipative solitons with large linear chirp in the net normal dispersion regime. Pulses that are 8.7 ps long are externally compressed to 118 fs, outperforming current nanotube-based Yb-doped fiber laser designs.
Open Access
Atomic layer deposition: an enabling technology for the growth of functional nanoscale semiconductors
(Institute of Physics Publishing, 2017) Bıyıklı, Necmi; Haider A.
In this paper, we present the progress in the growth of nanoscale semiconductors grown via atomic layer deposition (ALD). After the adoption by semiconductor chip industry, ALD became a widespread tool to grow functional films and conformal ultra-thin coatings for various applications. Based on self-limiting and ligand-exchange-based surface reactions, ALD enabled the low-temperature growth of nanoscale dielectric, metal, and semiconductor materials. Being able to deposit wafer-scale uniform semiconductor films at relatively low-temperatures, with sub-monolayer thickness control and ultimate conformality, makes ALD attractive for semiconductor device applications. Towards this end, precursors and low-temperature growth recipes are developed to deposit crystalline thin films for compound and elemental semiconductors. Conventional thermal ALD as well as plasma-assisted and radical-enhanced techniques have been exploited to achieve device-compatible film quality. Metal-oxides, III-nitrides, sulfides, and selenides are among the most popular semiconductor material families studied via ALD technology. Besides thin films, ALD can grow nanostructured semiconductors as well using either template-assisted growth methods or bottom-up controlled nucleation mechanisms. Among the demonstrated semiconductor nanostructures are nanoparticles, nano/quantum-dots, nanowires, nanotubes, nanofibers, nanopillars, hollow and core-shell versions of the afore-mentioned nanostructures, and 2D materials including transition metal dichalcogenides and graphene. ALD-grown nanoscale semiconductor materials find applications in a vast amount of applications including functional coatings, catalysis and photocatalysis, renewable energy conversion and storage, chemical sensing, opto-electronics, and flexible electronics. In this review, we give an overview of the current state-of-the-art in ALD-based nanoscale semiconductor research including the already demonstrated and future applications.
Open Access
Confined linear carbon chains as a route to bulk carbyne
(Nature Publishing Group, 2016-04) Shi, L.; Rohringer, P.; Suenaga, K.; Niimi, Y.; Kotakoski, J.; Meyer, J. C.; Peterlik, H.; Wanko, M.; Cahangirov, S.; Rubio, A.; Lapin, Z. J.; Novotny, L.; Ayala, P.; Pichler, T.
Strong chemical activity and extreme instability in ambient conditions characterize carbyne, an infinite sp1 hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for production, and even more so for application. We report a method for the bulk production of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk production of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbyne's bulk production.
Open Access
DFT studies of CNT-functionalized uracil-acetate hybrids
(Elsevier, 2015) Mirzaei, M.; Gulseren, O.
Calculations based on density functional theory (DFT) have been performed to investigate the stabilities and properties of hybrid structures consisting of a molecular carbon nanotube (CNT) and uracil acetate (UA) counterparts. The investigated models have been relaxed to minimum energy structures and then various physical properties and nuclear magnetic resonance (NMR) properties have been evaluated. The results indicated the effects of functionalized CNT on the properties of hybrids through comparing the results of hybrids and individual structures. The oxygen atoms of uracil counterparts have been seen as the detection points of properties for the CNT-UA hybrids.
Open Access
Hierarchical self-assembly of histidine-functionalized peptide amphiphiles into supramolecular chiral nanostructures
(American Chemical Society, 2017) Koc, M. H.; Ciftci, G. C.; Baday, S.; Castelletto, V.; Hamley, I. W.; Güler, Mustafa O.
Controlling the hierarchical organization of self-assembling peptide amphiphiles into supramolecular nanostructures opens up the possibility of developing biocompatible functional supramolecular materials for various applications. In this study, we show that the hierarchical self-assembly of histidine- (His-) functionalized PAs containing d- or l-amino acids can be controlled by both solution pH and molecular chirality of the building blocks. An increase in solution pH resulted in the structural transition of the His-functionalized chiral PA assemblies from nanosheets to completely closed nanotubes through an enhanced hydrogen-bonding capacity and π-π stacking of imidazole ring. The effects of the stereochemistry and amino acid sequence of the PA backbone on the supramolecular organization were also analyzed by CD, TEM, SAXS, and molecular dynamics simulations. In addition, an investigation of chiral mixtures revealed the differences between the hydrogen-bonding capacities and noncovalent interactions of PAs with d- and l-amino acids.
Open Access
Modulation of electronic properties in laterally and commensurately repeating graphene and boron nitride composite nanostructures
(American Chemical Society, 2015) Özçelik, V. O.; Durgun, Engin; Çıracı, Salim
Graphene and hexagonal boron nitride (h-BN) nanoribbons of diverse widths and edge geometries are laterally repeated to form commensurate, single-layer, hybrid honeycomb structures. The resulting composite materials appear as continuous, one atom thick stripes of graphene and BN having the average mechanical properties of constituent structures. However, depending on the widths of constituent stripes they can be metal or semiconductor with band gaps in the energy range of the visible light. These two-dimensional (2D) composite materials allow strong dimensionality in electrical conductivity and undergo transition from 2D to one-dimensional (1D) metal in a 2D medium, resulting in multichannel narrow conductors. As for the composite ribbons, such as one dielectric BN stripe placed between two graphene stripes with bare zigzag edges, charge separation of opposite polarity is possible under applied electric field and they exhibit resonant tunneling effects at nanoscale. Graphene/BN composite materials also form stable single-wall nanotubes with zigzag or armchair geometries.
Open Access
Surface ionic states and structure of titanate nanotubes
(Royal Society of Chemistry, 2015) Vempati S.; Kayaci-Senirmak, F.; Ozgit Akgun, C.; Bıyıklı, Necmi; Uyar, Tamer
Here we present an investigation on Zn-Ti-O ternary (zinc titanate) nanostructures which were prepared by a combination of electrospinning and atomic layer deposition. Depending on the ZnO and TiO2 molar ratio, two titanates and one mix phased compound were synthesized by varying the post-annealing temperatures. Specifically Zn2TiO4, ZnTiO3 and ZnO/TiO2 nanostructures were fabricated via thermal treatments (900, 700, 800 °C, respectively). Structural studies unveiled the titanate phase of the nanostructures. Furthermore, the ionic states of the titanate nanostructures on the surface are revealed to be Ti3+ and Zn2+. Spin-orbit splitting of Zn2p and Ti2p doublets were, however, not identical for all titanates which vary from 23.09-23.10 eV and 5.67-5.69 eV respectively. Oxygen vacancies were found on the surface of all titanates. The valance band region was analyzed for Zn3d, Ti3p, O2s and O2p and their hybridization, while the edge (below Fermi level) was determined to be at 2.14 eV, 2.00 eV and 1.99 eV for Zn2TiO4, ZnTiO3 and ZnO/TiO2 respectively.