Thin Nanotubes Research Articles

Tuning the self-assembled nanostructures of ultra-short bola peptides via side chain variations of the hydrophobic amino acids

The structure of amino acids in peptides significantly affect the supramolecular architecture. Even small changes in the peptide molecular structure can have dramatic impact on the morphology of the assemblies. Herein, we demonstrate that the replacement of the four hydrophobic amino acid residues I in Ac-KI4K-NH2 (KI4K) for nleucine (Nle), leucine (L), and tert-leucine (Tle) can greatly affect the aggregate morphology and their self-assembling abilities. As for KI4K, the β-branch carbon in the hydrophobic amino acid I greatly promotes the lateral association of β-sheets and facilitate the formation of wider nanotubes. When the four hydrophobic residues I was replaced by Nle or L, thin nanotubes with quite small inner diameter were dominant for Ac-K(Nle)4K-NH2 (K(Nle)4K) while only thin nanofibers can be obtained for Ac-KL4K-NH2 (KL4K), suggesting the important roles of the four β-branch carbon in promoting the lateral association of β-sheets. On the contrary, no obvious aggregate structure was observed for Ac-K(Tle)4K-NH2 (K(Tle)4K) due to the strong steric hindrance interactions. Small angle neutron scattering (SANS) results indicated the different inner structure information for the nanotubes and nanofibers even though they share the same basic lamellar structure. Circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and thioflavin-T (ThT) experiments indicated their different secondary structure and self-assembling abilities. These results can help us further understand the roles of β-branch carbon in controlling the aggregate morphology, which can benefit further research in establishing the relationship between the molecular structure and the final aggregate morphology.

Ultrafast Optoelectronic Processes in 1D Radial van der Waals Heterostructures: Carbon, Boron Nitride, and MoS2 Nanotubes with Coexisting Excitons and Highly Mobile Charges.

Heterostructures built from 2D, atomically thin crystals are bound by the van der Waals force and exhibit unique optoelectronic properties. Here, we report the structure, composition and optoelectronic properties of 1D van der Waals heterostructures comprising carbon nanotubes wrapped by atomically thin nanotubes of boron nitride and molybdenum disulfide (MoS2). The high quality of the composite was directly made evident on the atomic scale by transmission electron microscopy, and on the macroscopic scale by a study of the heterostructure's equilibrium and ultrafast optoelectronics. Ultrafast pump-probe spectroscopy across the visible and terahertz frequency ranges identified that, in the MoS2 nanotubes, excitons coexisted with a prominent population of free charges. The electron mobility was comparable to that found in high-quality atomically thin crystals. The high mobility of the MoS2 nanotubes highlights the potential of 1D van der Waals heterostructures for nanoscale optoelectronic devices.

Improving the fretting biocorrosion of Ti6Al4V alloy bone screw by decorating structure optimised TiO2 nanotubes layer

TiO2 nanotubes (NT) has been demonstrated its potential in orthopaedic applications due to its enhanced surface wettability and bio-osteointegration. However, the fretting biocorrosion is the main concern that limited its successfully application in orthopaedic application. In this study, a structure optimised thin TiO2 nanotube (SONT) layer was successfully created on Ti6Al4V bone screw, and its fretting corrosion performance was investigated and compared to the pristine Ti6Al4V bone screws and NT decorated screw in a bone-screw fretting simulation rig. The results have shown that the debonding TiO2 nanotube from the bone screw reduced significantly, as a result of structure optimisation. The SONT layer also exhibited enhanced bio-corrosion resistance compared pristine bone screw and conventionally NT modified bone screw. It is postulated that interfacial layer between TiO2 nanotube and Ti6Al4V substrate, generated during structure optimisation process, enhanced bonding of TiO2 nanotube layer to the Ti6Al4V bone screws that leading to the improvement in fretting corrosion resistance. The results highlighted the potential SONT in orthopaedic application as bone fracture fixation devices.

Ultrafast domain wall propagation due to the interfacial Dzyaloshinskii–Moriya interaction

It is shown that the interplay between curvature and interfacial Dzyalonshinsky–Moriya interaction (DMI) is a pathway to ultrafast domain wall (DW) dynamics in ferromagnetic nanotubes. In this work, we theoretically study the effect that interfacial DMI has on the average velocity of a vortex DW in thin ferromagnetic nanotubes grown around a core composed of heavy atoms. Our main result shows that by delaying the Walker breakdown instability, the DW average velocity is of the order of 103 m s−1, which is greater than usual values for these systems. The remarkable velocities achieved through this configuration could greatly benefit the development of spintronic devices.

Ultrahigh Ion-Selective and Durable Nafion-NdZr Composite Layer Membranes for All-Vanadium Redox Flow Batteries

A thin Nafion-neodymium zirconium oxide nanotube (NdZr) composite (Nafion-NdZr) membrane has been fabricated and further modified by the polycation, poly(diallyldimethylammonium chloride) (PDDA), a...

Giant Axial Dielectric Response in Water-Filled Nanotubes and Effective Electrostatic Ion-Ion Interactions from a Tensorial Dielectric Model.

Molecular dynamics simulations in conjunction with effective medium theory are used to investigate dielectric effects in water-filled nanotubes. The resulting effective axial dielectric constant shows a divergent increase for small nanotube radii that depends on the nanotube length, while the effective radial dielectric constant decreases significantly for thin nanotubes. By solving Poisson's equation for an anisotropic dielectric medium in cylindrical geometry, we show that the axial ion-ion interaction depends for small separations primarily on the radial dielectric constant, not on the axial one. This means that electrostatic ion-ion interactions in thin water-filled nanotubes are on the linear dielectric level significantly enhanced due to water confinement effects at small separations, while at large separations the outside medium dominates. If the outside medium is metallic, then the ion-ion interaction decays exponentially for large ion separation.

Speed of domain walls in thin nanotubes: The transition from the linear to the magnonic regime

Numerical simulations of domain wall propagation in thin nanotubes when an external magnetic field is applied along the nanotube axis have shown an unexpected behavior described as a transition from a linear to a magnonic regime. As the applied magnetic field increases, the initial regime of linear growth of the speed with the field is followed by a sudden change in slope accompanied by the emission of spin waves. In this work an analytical formula for the speed of the domain wall that explains this behavior is derived by means of an asymptotic study of the Landau Lifshitz Gilbert equation for thin nanotubes. We show that the dynamics can be reduced to a one dimensional hyperbolic reaction diffusion equation, namely, the damped double Sine Gordon equation, which shows the transition to the magnonic regime as the domain wall speed approaches the speed of spin waves. This equation has been previously found to describe domain wall propagation in weak ferromagnets with the mobility proportional to the Dzyaloshinskii-Moriya interaction constant, for Permalloy nanotubes the mobility is proportional to the nanotube radius.

Experimental Evidence of Large Bandgap Energy in Atomically Thin AlN

AbstractUltrathin III‐nitrides beyond BN, such as GaN and AlN, have attracted much research interest due to their potential applications in 2D optoelectronic devices. Taking advantage of the atomic thickness, the bandgap is expected to be widened in these thin films due to quantum confinement. As a promising intrinsic dielectric and tunneling layer for optoelectronic devices, ultrathin freestanding AlN structures have not been systematically studied, and the band structure still remains in the theoretical description. In this work, atomically thin hexagonal AlN nanotubes with controllable wall thickness have been fabricated via selective thermal evaporating the GaN/AlN core/shell nanowires, where the GaN cores entirely decomposed and are removed from the bottom open end while the robust AlN shells remain and form tubular structures. The bandgap energy of 9.2±0.1 eV is confirmed through spectrally resolved X‐ray photoelectron spectroscopy and spatially resolved electron energy loss spectroscopy measurements on AlN nanotubes with the wall thickness of two monolayers.

Mechanical performance of lightweight polycrystalline Ni nanotubes

The mechanical properties of metallic nanowires and nanotubes were investigated using atomistic molecular dynamics simulations on Ni polycrystalline structures, similar to those experimentally obtained by Atomic Layer Deposition. We studied the response of nanostructures under uniaxial deformations with different thickness, geometry, and crystalline degree. Plastic deformation is due to stacking fault and coherent twin boundary formation, and to grain boundary activity. Different fracture processes are obtained from these systems, being the thin nanotubes failing thanks to a mix of brittle failure by grain boundary decohesion and ductile fracture due to significantly more twins than with a thicker nanotube and nanowire during the ductile fracture. The stress-strain curves, atomic displacements, and defects formation were analyzed, finding that nanotubes with a fraction of the volumetric mass have practically the same Young modulus and ultimate tensile stress, while fracture strain is slightly larger for nanowire. From all these studied cases, it is remarkable the result where ultra-thin nanotubes can withstand a 21% of tensile stress-strain with a similar yield strength than nanowires, but with a volumetric mass reduction of 60%, offering a lightweight alternative to design mechanical nanodevices with minimal loss of mechanical performance.

ZnO THIN FILMS: RECENT DEVELOPMENT, FUTURE PERSPECTIVES AND APPLICATIONS FOR DYE SENSITIZED SOLAR CELL

Dye sensitized solar cells (DSSCs) provide promisingly, organic–inorganic, clean hybrid, cost effective and efficient molecular solar cell devices. Due to their distinct and multifunctional qualities, zinc oxide (ZnO) nanostructures are promising materials used to create photoanodes for DSSCs due to the availability of larger surface area than bulk sheet substance, effectual light-dispersing centers, and when mixed with titanium dioxide they produce a core–shell formation that diminishes the coalition rate and provide direct charge. Moreover, ZnO thin sheets have been broadly observed due of its potential application in various fields i.e. piezoelectric, photovoltaic, pyroelectric and optoelectronic utilization. This review studies the recent advances in the fabrication of zinc oxide-based photovoltaics; synthesis of ZnO nanostructures with variable morphologies including thin sheets, nanotubes, nanorods, nanoflowers, nanofibers and factors that control the growth and morphologies of these nanospecies and part of crystallographic planes for the fabrication of various zinc oxide nanoshapes. In the next part of this paper, numerous fabrication routes — doped and undoped ZnO thin films — are discussed and different parameters of photovoltaics are investigated, e.g. efficiency pre and post annealing temperatures, fill factors spinning speed and coating time, additives, nature of precursor which impacts on morphological and optical parameters of these sheets. In short, this review is dedicated to the ZnO photoanode, its properties, issues related to ZnO photoanode, various improvement approaches, fabrication methods successfully trialled so far followed by market potential of the DSSC technology, conclusion and recommendations

Comparison of vibrational and thermodynamic properties of MoS2 and WS2 nanotubes: first principles study

Hybrid density functional theory investigations are conducted to compare the structural properties, stability, vibrational frequencies, and thermodynamic functions of MoS2 and WS2-based monolayers and single-wall nanotubes using the same calculation scheme. The thermal contributions to thermodynamic functions for the layers and nanotubes are computed using phonon frequencies in the harmonic approximation. The thin MoS2 and WS2 nanotubes’ thermodynamic properties in regard to the same properties of the corresponding monolayers are obtained. It is found a noticeable deviation in these relative thermodynamic properties of the MoS2 and WS2 nanotubes. It is also shown that the thermal contribution to the stability of nanotubes is appreciable, especially for the nanotubes with small diameters. The deviation of nanotube free energy, entropy, and heat capacity from the layer values is larger in the case of MoS2 than in the case of WS2.

Temperature dependence of thermodynamic properties of MoS2 monolayer and single-wall nanotubes: Application of the developed three-body force field

MoS2 nanostructures, especially mono-, multilayer nanothin films as well as single- and multiwall nanotubes are rather interesting popular objects in nanomaterials chemistry. The thermodynamic properties of inorganic nanotubes, and the temperature dependence of their properties can be efficiently investigated by first-principles and molecular mechanics methods in the framework of harmonic approximation. At the same time, only thin single-wall nanotubes are available for the first-principles calculations. The classical mechanics is suitable to simulate very large atomic systems and their phonon frequencies, but developing sufficiently accurate force field is rather tedious work. Herein, we report the force field fitted to the experimental and first-principles data on the structure of 2H- and 3RMoS2 polytypes of bulk crystal, structure of monolayer and several bilayers, vibrational frequencies of 2HMoS2 bulk and monolayer, relative energetic stability of polytypes experimental and first-principles data, elastic constants, strain energy of a (12, 12) MoS2 nanotube. The thermodynamic functions and their temperature dependence for the armchair and zigzag nanotubes are calculated within the formalism of molecular mechanics using elaborated interatomic potential. The results of molecular mechanics and first-principles method application to the thinnest nanotubes are compared.

High aspect ratio nanotubes assembled from macrocyclic iminium salts

One-dimensional nanostructures such as carbon nanotubes and actin filaments rely on strong and directional interactions to stabilize their high aspect ratio shapes. This requirement has precluded making isolated, long, thin organic nanotubes by stacking molecular macrocycles, as their noncovalent stacking interactions are generally too weak. Here we report high aspect ratio (>103), lyotropic nanotubes of stacked, macrocyclic, iminium salts, which are formed by protonation of the corresponding imine-linked macrocycles. Iminium ion formation establishes cohesive interactions that, in organic solvent (tetrahydrofuran), are two orders of magnitude stronger than the neutral macrocycles, as explained by physical arguments and demonstrated by molecular dynamics simulations. Nanotube formation stabilizes the iminium ions, which otherwise rapidly hydrolyze, and is reversed and restored upon addition of bases and acids. Acids generated by irradiating a photoacid generator or sonicating chlorinated solvents also induced nanotube assembly, allowing these nanostructures to be coupled to diverse stimuli, and, once assembled, they can be fixed permanently by cross-linking their pendant alkenes. As large macrocyclic chromonic liquid crystals, these iminium salts are easily accessible through a modular design and provide a means to rationally synthesize structures that mimic the morphology and rheology of carbon nanotubes and biological tubules.

Sorting Transition-Metal Dichalcogenide Nanotubes by Centrifugation

Tungsten disulfide (WS2) nanotubes are cylindrical, multiwall nanotubes with various diameters and wall numbers. They can exhibit various unique properties depending on their structures and thus preparing samples with uniform structures is important for understanding their basic properties and applications. However, most synthesis methods have difficulty to prepare uniform samples, and thus, a purification method to extract nanotubes with a selected diameter and wall number must be developed. Here, we demonstrate a solution-based purification of WS2 nanotubes using a surfactant solution. Stable dispersions of nanotubes were prepared using nonionic surfactants, which enabled us to sort the diameters and wall numbers of the nanotubes through a centrifugation process. By optimizing the conditions, we successfully obtained thin nanotubes with a mean diameter of 32 nm and mean wall number of 13 with relatively small distributions. Finally, we clarified the relationships between the structure and optical properties of the nanotubes.

A power model to predict the electrical conductivity of CNT reinforced nanocomposites by considering interphase, networks and tunneling condition

This study develops a power-law model for characterizing the conductivity of polymer carbon nanotube (CNT) nanocomposite by defining the “b” exponent as a function of main parameters such as filler dimensions, filler waviness, interphase thickness, network fraction, tunneling distance, and polymer-filler interfacial energy. Both “b” and conductivity are calculated, and the effects of these parameters on the conductivity are determined. The model accurately predicts the experimentally measured conductivity of the samples. The highest filler conductivity and the lowest “b” exponent cause the maximum conductivity. Some parameters, such as tunneling distance, filler concentration, filler radius, interphase thickness, and waviness, directly affects the “b” exponent, while other parameters, such as the fraction of percolated CNT, interfacial energy, and filler length, demonstrate an inverse relationship with “b.” In addition, short tunneling distance, high filler fraction, thin and large nanotubes, thick interphase, poor waviness, high network fraction, and high interfacial energy produce a high conductivity.

Axial buckling behavior of single-walled carbon nanotubes: Atomistic structural instability analysis

To reveal the atomistic scale mechanism of buckling of single-walled carbon nanotubes (SWCNTs) under axial compression, we carried out molecular dynamics (MD) simulation and atomistic structural instability (ASI) analysis. The ASI analysis enables us to reveal the development of ‘latent’ instability modes until buckling of structure, which cannot be clarified with MD alone. Euler-type buckling was found in relatively thin and long nanotube models, while buckling triggered by change of cross-sectional shape (i.e., radial buckling) was found in thick and short models. With growing radius, a crossover between the Euler-type and radial buckling modes was clearly found in the ASI analysis. Even when the deformation behavior was apparently the same, the buckling can be triggered by different instability modes. We also analyzed the structural instability using the Flügge theory based on linear continuum mechanics (LCM) to compare the results with the ASI analysis. Initial eigenvalues and development of instability modes were different between the ASI and LCM results, leading to a significant deviation of buckling strain and instability crossover points. We investigated the effect of chirality of CNT which is difficult to explain by LCM.

Hierarchical WO3/TiO2 nanotube nanocomposites for efficient photocathodic protection of 304 stainless steel under visible light

A new photoanode of hierarchical WO3 and TiO2 nanotube arrays with a layered composite structure is prepared through in situ deposition of WO3 into TiO2 nanotubes by one-pot hydrothermal method. Photo-induced open circuit potential, photocurrent density, electrochemical impedance spectroscopy, and Tafel curves are measured under visible light to evaluate the photoelectrochemistry properties and the photocathodic protection effect of the composite photoelectrode. The result showed that compared with the hierarchical WO3 deposited on bare Ti substrate, the photocurrent density of WO3/TiO2/Ti with the thin TiO2 nanotube arrays as the transition layer increased from 0.072 mA/cm2 to 2.5 mA/cm2. Moreover, as for the photocathodic protection application, the photo-induced open circuit potential drop of the nanocomposite photoanode was about 260 mV and the charge transfer resistance was reduced by 106 times, indicating the efficient photogenerated cathode protection of the coupled metals under visible light illumination.

Improved gas sensing performance of p-copper oxide thin film/n-TiO2 nanotubes heterostructure

CuO thin film/TiO2 nanotubes heterostructures were fabricated to investigate the effect of p-n heterojunction on sensing properties. TiO2 nanotubes were synthesized via anodization of Ti foil. Then, CuO thin film was covered on the nanotubes by oxidation of thermally evaporated Cu layer. For comparison, sensor devices those are composed of only CuO thin film and composed of TiO2 nanotubes have been also fabricated. The heterostructure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to H2, ethanol, acetone, chloroform and NO2 gases at different operation temperatures. Experimental results showed that the heterostructure sensor has better performance toward H2 in sensing with low operation temperature, low detection limit and high sensor response compared to TiO2 nanotubes and CuO thin film. Moreover, the formation of heterostructure not only increased response toward H2 but also dramatically decreased response toward VOCs and NO2. These improved sensing properties are attributed to the heterojunction between CuO thin film and TiO2 nanotubes.

Validation of a constrained 2D slab model for water adsorption simulation on 1D periodic TiO2 nanotubes

Solar light driven hydrogen evolution is one focus of modern materials research. Among the different emerging technologies, particular interest is devoted towards metal oxide photocatalysts in the form of various 1D nanostructures. Presently, the mismatch between regular structures that can be synthesized and the largest structures that are feasible for computer simulation is still very large. For example, an in-depth study of water adsorption on nanotube (NT) surfaces requires, in addition to DFT calculations, molecular dynamics simulations to take into account the disordered nature of the aqueous phase. To completely immerse even a very thin nanotube into an aqueous system requires very large system sizes, the modeling of which is computationally extremely expensive. On the other hand, the typical surface science approach when modeling planar interfaces is computationally much less demanding, but can be adequate only for NTs of very large diameters possessing low strain energies. Here, we present three simplified slab models derived from local NT geometries as approximations for inner and outer interfaces of thin TiO2 NTs. In order to describe the role of NT strain on the electronic structure of the water/NT interface, these models contain additional constraints on some of the atoms to alleviate some of the shortcomings of the slab approach. We use the energy of water adsorption, equilibrium interatomic distances, calculated densities of states (DOS) and Mulliken charge distribution as criteria for estimating the model quality. Specifically we analyze the suitability of this approach for the very thin TiO2 (001) slab and the thicker TiO2 (001) NT.

High-performance bipolar plate of thin IrOx-coated TiO2 nanotubes in vanadium redox flow batteries

Thin DSA (dimensionally stable anode) bipolar plates designed to replace thick graphite were employed for the first time to obtain improved dimensions, and electrochemical catalytic properties in all-vanadium redox flow batteries (VRFBs). We found that a 0.127mm-thick DSA consisting of nanotubular TiO2 on Ti substrate coated with a layer of IrOx worked extremely well as a bipolar plate. Using this material, overpotential and charge transfer resistance for charging and discharging were reduced due to the catalytic properties of IrOx, which improved the transfer of electrons or the electrical current. Furthermore, the stability of the IrOx layer on the TiO2 nanotubular structure grown from the Ti substrate was confirmed after 100 cycles. The efficiency of the VRFB based on the DSA bipolar plate increased by 3–4% compared to that of the graphite bipolar plate, suggesting that this thin DSA bipolar plate offers not only dimensional advantages, but also electrochemical advantages for VRFB applications.