Search results for "NANOTUBES"
showing 10 items of 383 documents
Synthesis and characterization of highly ordered cobalt-magnetite nanocable arrays.
2006
Magnetically tunable, high-density arrays of coaxial nanocables within anodic aluminum oxide (AAO) membranes have been synthesized. The nanocables consist of magnetite nanowires surrounded by cobalt nanotube sheaths and cobalt nanowires surrounded by magnetite nanotube sheaths. These materials are a combination of separate hard (Co) and soft (Fe3O4) magnetic materials in a single nanocable structure. The combination of two or more magnetic materials in such a radial structure is seen as a very powerful tool for the future fabrication of magnetoresistive, spin-valve and ultrafast spin-injection devices with nonplanar geometries. The nanocable arrays were prepared using a supercritical-fluid …
High-Yield of Memory Elements from Carbon Nanotube Field-Effect Transistors with Atomic Layer Deposited Gate Dielectric
2008
Carbon nanotube field-effect transistors (CNT FETs) have been proposed as possible building blocks for future nano-electronics. But a challenge with CNT FETs is that they appear to randomly display varying amounts of hysteresis in their transfer characteristics. The hysteresis is often attributed to charge trapping in the dielectric layer between the nanotube and the gate. This study includes 94 CNT FET samples, providing an unprecedented basis for statistics on the hysteresis seen in five different CNT-gate configurations. We find that the memory effect can be controlled by carefully designing the gate dielectric in nm-thin layers. By using atomic layer depositions (ALD) of HfO$_{2}$ and T…
A study on the stability of carbon nanoforms–polyimidazolium network hybrids in the conversion of co2 into cyclic carbonates
2021
Three different carbon nanoforms (CNFs), single-walled and multi-walled carbon nanotubes (SWCNTs, MWCNTs) and carbon nanohorns (CNHs), have been used as supports for the direct polymerization of variable amounts of a bis-vinylimidazolium salt. Transmission electron microscopy confirmed that all CNFs act as templates on the growth of the polymeric network, which perfectly covers the nanocarbons forming a cylindrical (SWCNTs, MWCNTs) or spherical (CNHs) coating. The stability of these hybrid materials was investigated in the conversion of CO2 into cyclic carbonate under high temperature and CO2 pressure. Compared with the homopolymerized monomer, nanotube-based materials display an improved c…
Ab initio simulations on N and S co-doped titania nanotubes for photocatalytic applications
2015
In this paper we present the results of quantum chemical modeling for energetically stable anatase (001) TiO2 nanotubes, undoped, doped, and codoped with N and S atoms. We calculate the electronic structure of one-dimensional (1D) nanotubes and zero-dimensional (0D) atomic fragments cut out from these nanotubes, employing hybrid density functional theory with a partial incorporation of an exact, nonlocal Hartree–Fock exchange within the formalism of the linear combination of atomic orbitals, as implemented in both CRYSTAL and NWChem total energy codes. Structural optimization of 1D nanotubes has been performed using CRYSTAL09 code, while the cut-out 0D fragments have been modelled using the…
Electronic properties of single-walled carbon nanotubes inside cyclic supermolecules
2006
Possible ways for manipulating carbon nanotubes (CNTs) with cyclic supermolecules are studied using density functional theory. Electronic structure calculations with structure optimizations have been performed for the (4,4) and (8,0) single-walled carbon nanotubes (SWNTs) complexed with crown ethers as well as for the (4,0) SWNT with beta-cyclodextrin. A slight polarization of charge in both the nanotube and the supermolecule is observed upon rotaxane complexation, but the interaction is mainly repulsive, and the systems stay 2.8-3.5 A apart. The supermolecule does not affect the electronic band structure of the nanotube significantly within such a configuration. The situation differs notic…
Anomalous Slowdown of Polymer Detachment Dynamics on Carbon Nanotubes
2019
The "wrapping" of polymer chains on the surface of carbon nanotubes allows one to obtain multifunctional hybrid materials with unique properties for a wide range of applications in biomedicine, electronics, nanocomposites, biosensors, and solar cell technologies. We study by means of molecular dynamics simulations the force-assisted desorption kinetics of a polymer from the surface of a carbon nanotube. We find that, due to the geometric coupling between the adsorbing surface and the conformation of the macromolecule, the process of desorption slows down dramatically upon increasing the windings around the nanotube. This behavior can be rationalized in terms of an overdamped dynamics with a…
Lateral force microscopy of multiwalled carbon nanotubes
2009
Carbon nanotubes are usually imaged with the atomic force microscope (AFM) in non-contact mode. However, in many applications, such as mechanical manipulation or elasticity measurements, contact mode is used. The forces affecting the nanotube are then considerable and not fully understood. In this work lateral forces were measured during contact mode imaging with an AFM across a carbon nanotube. We found that, qualitatively, both magnitude and sign of the lateral forces to the AFM tip were independent of scan direction and can be concluded to arise from the tip slipping on the round edges of the nanotube. The dependence on the normal force applied to the tip and on the ratio between nanotub…
First principles modeling of 3d-metal doped three-layer fluorite-structured TiO2 (4,4) nanotube to be used for photocatalytic hydrogen production
2017
This study has been supported by the EC ERA.Net RUS Plus project No. 237 WATERSPLIT, Russian Basic Research Foundation No. 16-53-76019, and additionally by the IMIS2 Program (Latvia). The authors are also indebted to R. A. Evarestov and O. Lisovski for stimulating discussions as well as to A. Chesnokov for technical assistance.
Effect of Polymer Length on the Adsorption onto Aluminogermanate Imogolite Nanotubes
2021
This study evidences the adsorption of model nonionic polymers onto aluminogermanate imogolite nanotubes, attractive porous nanofillers with potential molecular loading and release applications. We resolve the underlying mechanisms between nanotubes and polyethylene glycols with different molecular weights by means of nanoisothermal titration calorimetry. The analysis of the results provides a direct thermodynamic characterization, allowing us to propose a detailed description of the energetics involved in the formation of polymer/imogolite complexes. The affinity toward the nanotube surface is enthalpy-driven and strongly depends on the polymer chain length, which significantly affects the…
Controlling electrical percolation in multicomponent carbon nanotube dispersions
2011
Carbon nanotube reinforced polymeric composites can have favourable electrical properties, which make them useful for applications such as flat-panel displays and photovoltaic devices. However, using aqueous dispersions to fabricate composites with specific physical properties requires that the processing of the nanotube dispersion be understood and controlled while in the liquid phase. Here, using a combination of experiment and theory, we study the electrical percolation of carbon nanotubes introduced into a polymer matrix, and show that the percolation threshold can be substantially lowered by adding small quantities of a conductive polymer latex. Mixing colloidal particles of different …