Quasi One-dimensional Nanostructures Research Articles

Differential multi-probe thermal transport measurements of multi-walled carbon nanotubes grown by chemical vapor deposition

Carbon nanotubes (CNTs) are quasi-one dimensional nanostructures that display both high thermal conductivity for potential thermal management applications and intriguing low-dimensional phonon transport phenomena. In comparison to the advances made in the theoretical calculation of the lattice thermal conductivity of CNTs, thermal transport measurements of CNTs have been limited by either the poor temperature sensitivity of Raman thermometry technique or the presence of contact thermal resistance errors in sensitive two-probe resistance thermometry measurements. Here we report advances in a multi-probe measurement of the intrinsic thermal conductivity of individual multi-walled CNT samples that are transferred from the growth substrate onto the measurement device. The sample-thermometer thermal interface resistance is directly measured by this multi-probe method and used to model the temperature distribution along the contacted sample segment. The detailed temperature profile helps to eliminate the contact thermal resistance error in the obtained thermal conductivity of the suspended sample segment. A differential electro-thermal bridge measurement method is established to enhance the signal-to-noise ratio and reduce the measurement uncertainty by over 40%. The obtained thermal resistances of multiple suspended segments of the same MWCNT samples increase nearly linearly with increasing length, revealing diffusive phonon transport as a result of phonon-defect scattering in these MWCNT samples. The measured thermal conductivity increases with temperature and reaches up to 390 ± 20 W m−1 K−1 at room temperature for a 9-walled MWCNT. Theoretical analysis of the measurement results suggests submicron phonon mean free paths due to extrinsic phonon scattering by extended defects such as grain boundaries. The obtained thermal conductivity is decreased by a factor of 3 upon electron beam damage and surface contamination of the CNT sample.

Simulation-aided studies on the superior thermoelectric performance of printable PBDTT-FTTE/SWCNT composites

Quasi one-dimensional (1D) carbon nanostructures hybridized with π-conjugated polymeric systems are vastly explored for their unique heat/carrier transport beneficial for thermoelectric (TE) applications. We present the TE response of all-organic composites fabricated with poly[4,8-bis(5-(2-ethylyhexyl)thiophene-2-yl)benzo[1,2-b; 4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)3-fluorothieno[3,4-b']thiophene-)-2-carboxylate-2-6-diyl)] (PBDTT-FTTE) and single-walled carbon nanotube (SWCNT). SWCNTs form strong π-π interfacial interactions with the polymer, and their TE performance is improved through p-doping with ferric chloride (FeCl3). Investigation of the electrical conductivity (σ) and Seebeck coefficient (α) reveals a characteristic mechanism arising from low-energy carrier filtering and Fermi-level pinning. DIGIMAT-MF© material modeling platform simulates σ and thermal conductivity (κ) and indicates a CNT aspect ratio distribution in the system. The doped composite with 55 wt% SWCNT exhibits the maximum ZT value of 0.044 at 303 K using the simulated κ value. A flexible TE generator (TEG) consisting of 21 legs is dispenser printed that produces ∼32.7 nW power output with a 65 K temperature gradient across 15 kΩ load resistance. COMSOL Multiphysics® simulation is used to optimize TEG design for maximum extractable output power.

Early Stages of Aluminum-Doped Zinc Oxide Growth on Silicon Nanowires.

Aluminum-doped zinc oxide (AZO) is an electrically conductive and optically transparent material with many applications in optoelectronics and photovoltaics as well as in the new field of plasmonic metamaterials. Most of its applications contemplate the use of complex and nanosized materials as substrates onto which the AZO forms the coating layer. Its morphological characteristics, especially the conformality and crystallographic structure, are crucial because they affect its opto-electrical response. Nevertheless, it was difficult to find literature data on AZO layers deposited on non-planar structures. We studied the AZO growth on silicon-nanowires (SiNWs) to understand its morphological evolution when it is formed on quasi one-dimensional nanostructures. We deposited by sputtering different AZO thicknesses, leading from nanoclusters until complete incorporation of the SiNWs array was achieved. At the early stages, AZO formed crystalline nano-islands. These small clusters unexpectedly contained detectable Al, even in these preliminary phases, and showed a wurtzite crystallographic structure. At higher thickness, they coalesced by forming a conformal polycrystalline shell over the nanostructured substrate. As the deposition time increased, the AZO conformal deposition led to a polycrystalline matrix growing between the SiNWs, until the complete array incorporation and planarization. After the early stages, an interesting phenomenon took place leading to the formation of hook-curved SiNWs covered by AZO. These nanostructures are potentially very promising for optical, electro-optical and plasmonic applications.

Lattice dynamics of twisted ZnO nanowires under generalized Born–von Karman boundary conditions

Due to their excellent structural flexibility, low dimensional materials allow to modulate their properties by strain engineering. In this work, we illustrate the phonon calculation of deformed quasi-one dimensional nanostructures involving inhomogeneous strain patterns. The key is to employ the generalized Born–von Karman boundary conditions, where the phonon states are characterized with screw and rotational symmetries. We use wurtzite ZnO nanowire (NW) as a representative to demonstrate the validity and efficiency of the present approach. First, we show the equivalence between the phonon dispersions obtained with this approach and that obtained with standard phonon approach. Next, as an application of the present approach, we study the phonon responses of ZnO NWs to twisting deformation. We find that twisting has more influence on the phonon modes resided in the NW shell than those resided around the NW core. For phonon at the NW shell, the modes polarized along the NW axis is more sensitive to twisting than those polarized in the NW radial dimension. Twisting also induces significant reduction in group velocities for a large portion of optical modes, hinting a non-negligible impact on the lattice thermal conductivity. The present approach may be useful to study the strain-tunable thermal properties of quasi-one dimensional materials.

Studies of quasi one-dimensional nanostructures at high pressures

The ultimate goals of researches of one-dimensional (1D) nanomaterials, quasi-one-dimensional atomic/molecular chains are expected to exhibit their strong quantum effects and novel optical, electrical, magnetic properties due to their unique 1D structures. At present, synthesis and manipulation of 1D atomic/molecular chains on an atomic/molecular level in a controllable way have been the frontier subject of scientific research. The 1D atomic/molecular chains, which can be stable in ambient conditions, have been prepared successfully by using a confinement template, such as carbon nanotubes (CNTs), zeolite, etc. High pressure can effectively tune the interatomic and intermolecular interactions over a broad range of conditions and thus to change the structures of materials. High pressure techniques have been recently adopted to investigate the 1D nanomaterials. In this paper, we briefly review some recent progress in the high pressure studies of 1D nanostructures, including iodine chains (I2)n confined in the 1D nanochannels of zeolite, multiwalled carbon nanotube (MWNT) arrays, and 1D carbon chains confined in CNTs. Particularly, polarized Raman spectroscopy combined with theoretical simulations has been used in the high pressure studies of 1D nanostructures. These studies reveal many interesting phenomena, including pressure-induced population increase and growth of 1D atomic/molecular chains. The underlying driven mechanisms have also been uncovered. Induced by pressure, the I2 molecules in zeolite 1D nanochannels rotates to the channel axial direction and the compression of the channel length in turn leads to a concomitant decrease of the intermolecular distance such that the iodine molecules come sufficiently close to the formation of longer (I2)n polymers. The novel polarized photoluminescence (PL) from the iodine chains and the pressure-induced PL enhancement due to the growth of 1D iodine chains under pressure. The depolarization effect vanishing in the polarized Raman spectra of compressed MWNT arrays. These are related to the pressure-induced enhancement of intertube interactions and inter/intratube sp3 bonding. The results obtained by polarized Raman spectroscopy overcome the difficulty:MWNTs have no obvious fingerprints for identifying the structural transformation under pressure. Above all, the 1D nanostructures exhibit interesting and fantastic behaviors under pressure, which deserve further investigations in this research field. In addition, polarized Raman spectroscopy is an effective tool to study the structural transformations of 1D nanomaterials at high pressures, which can be extended to the studies of other analogous 1D nanostructures under pressure.

ZnO Quasi-1D Nanostructures: Synthesis, Modeling, and Properties for Applications in Conductometric Chemical Sensors

One-dimensional metal oxide nanostructures such as nanowires, nanorods, nanotubes, and nanobelts gained great attention for applications in sensing devices. ZnO is one of the most studied oxides for sensing applications due to its unique physical and chemical properties. In this paper, we provide a review of the recent research activities focused on the synthesis and sensing properties of pure, doped, and functionalized ZnO quasi-one dimensional nanostructures. We describe the development prospects in the preparation methods and modifications of the surface structure of ZnO, and discuss its sensing mechanism. Next, we analyze the sensing properties of ZnO quasi-one dimensional nanostructures, and summarize perspectives concerning future research on their synthesis and applications in conductometric sensing devices.

Impurity-limited resistance and phase interference of localized impurities under quasi-one dimensional nano-structures

The impurity-limited resistance and the effect of the phase interference among localized multiple impurities in the quasi-one dimensional (quasi-1D) nanowire structures are systematically investigated under the framework of the scattering theory. We derive theoretical expressions of the impurity-limited resistance in the nanowire under the linear response regime from the Landauer formula and from the Boltzmann transport equation (BTE) with the relaxation time approximation. We show that the formula from the BTE exactly coincides with that from the Landauer approach with the weak-scattering limit when the energy spectrum of the in-coming electrons from the reservoirs is narrow and, thus, point out a possibility that the distinction of the impurity-limited resistances derived from the Landauer formula and that of the BTE could be made clear. The derived formulas are applied to the quasi-1D nanowires doped with multiple localized impurities with short-range scattering potential and the validity of various approximations on the resistance are discussed. It is shown that impurity scattering becomes so strong under the nanowire structures that the weak-scattering limit breaks down in most cases. Thus, both phase interference and phase randomization simultaneously play a crucial role in determining the impurity-limited resistance even under the fully coherent framework. When the impurity separation along the wire axis direction is small, the constructive phase interference dominates and the resistance is much greater than the average resistance. As the separation becomes larger, however, it approaches the series resistance of the single-impurity resistance due to the phase randomization. Furthermore, under the uniform configuration of impurities, the space-average resistance of multiple impurities at room temperature is very close to the series resistance of the single-impurity resistance, and thus, each impurity could be regarded as an independent scattering center. The physical origin of this “self-averaging” under the fully coherent environments is attributed to the broadness of the energy spectrum of the in-coming electrons from the reservoirs.

A Simple Low Temperature and Pressure Method for the Synthesis of Quasi-One Dimensional Nano Structures of TiO<sub>2</sub> for Dye Synthesized Solar Cells

In this work we have synthesized TiO2 nanostructures using a modified autoclave-free hydrothermal method from bulk powders. In the absence of pressure, Toluene was used as the dispersing agent to prohibit particle aggregation during the thermal treatment. Toluene to Ti mole ratio (X) was varied from 0 up to 30 to obtain different morphologies of TiO2. X-ray diffraction (XRD) analysis demonstrated the Anatase phase for all the samples. FTIR analysis indicated that samples are free of carbon rich compounds and carbon contaminants. SEM images showed that with the increase of Toluene to Ti ratio, the morphology of the powders change from spherical particles with an average size of about 45 nm for X=0 to broccoli-shape structure for X=10, nanotubes for X=20 and nanosticks/wires for X=30. The synthesized TiO2 nanotubes have been used as photoanode in a dye synthesized solar cell (DSSCs). The efficiency of the fabricated solar cell without any further modification was obtained about 2.3%.

Theory study on glycine linear oligopeptide vibrational spectrum frequency shift

By using the density functional theory, glycine linear oligopeptide of different lengths was geometrically optimized on the 6-31G (d) basis set level, their growth processes were simulated, and the average binding energy and vibration frequency were calculated with geometry. The results showed that the average binding energies tend to change in a regular pattern and stabilize with the number of residues increasing; With the oligopeptide chain bond length analysis it was found that the chain to the radial direction there is a opposite trend for chain and radial direction, which is anisotropic. It was found by the IR spectrum analysis that red shifts and blue shifts occur respectively when the same group of peptide bond vibrate, which is anisotropic; These phenomena originate from that quasi one-dimensional nanostructures lead to the anisotropy of the bond length; the induced effects, coupling effects and hydrogen bonding etc. between the same groups lead to the vibration frequency red shifts and blue shifts. The authors conclude that the growth of glycine linear oligopeptide is conducive to stability of the structure, and the authors infer that the oligopeptide has the tendency of self-assembled growth; Through the conformation and spectrum, the authors infer that there is a size effect in physical and chemical properties. The physical and chemical properties of peptide chain end group are extremely stable and unaffected by the impact of the oligopeptide chain length The results are significant to measuring the length and the number of residue of peptide, and to manufacturing the special features oligopeptide chain.

Thermo-physical behaviors of carbon nanofiber reinforced polylactic acid

ABSTRACT:Studies have demonstrated that the reinforcement of polymeric matrices using nanofiller can results with better thermo-physical properties of polymer. Carbon nanofiber (CNF) is a unique quasi-one dimensional nanostructure with large numbers of edges and defects compared to carbon nanotube (CNT). Further the availability in large quantity along with lower cost makes them an important nanomaterial for future technology. We have previously used CNF in different thermoplastic polymers. In this study CNFs were used with water soluble thermoplastic aliphatic polyster polylactic acid (PLA) and studied their thermal and mechanical properties. Thermal analysis using Thermogravimetric Analysis showed enhanced thermal stability of the polymer at higher nanotube loading (>1 wt%) and decrease of thermal stability at higher loading (>10 wt%). Crystallization thermogram of PLA was modified heavily with the addition of nanofibers changing clearly from one stage to two stage crystallization. In addition, CNF facilitates the crystallization of PLA resulting in an increase of its crystallization. The mechanical testing showed the steady increase of modulus of the composites with the nanofiber content within the range of study which can be regarded as due to the change in interface property of the composites.

Thermal Growth and Nanomagnetism of the Quasi-one Dimensional Iron Oxide

Quasi-one dimensional iron oxide nanowires with flat needle shape were synthesized on the iron powders by a rather simple catalyst-free thermal oxidation process in ambient atmosphere. The characterization by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman and high-resolution transmission electron microscopy (HRTEM) revealed that these nanos-tructures are single crystalline α-Fe 2 O 3 . The various dimensions with 40–170 nm in width and 1–8 μm in length were obtained by tuning the growth temperature from 280 to 480°C. A surface diffusion mechanism was proposed to account for the growth of quasi-one dimensional nanostructure. The typical α-Fe 2 O 3 nanowires synthesized at 430°C had a reduced Morin temperature T M of 131 K in comparison with their bulk counterpart. The coercivitis H c of these nanowires are 321 and 65 Oe at 5 and 300 K, respectively. The temperature of synthesis also has important effects on the magnetic properties of these nanowires.

The Growth Mechanism of Quasi One-Dimensional ZnO Nanostructures Synthesized by Carbon Reduction without Catalyst

In order to obtain quasi one-dimensional nanostructures, various methods have been developed for the preparation and many mechanisms have been put forward such as VS (vapor-solid), VLS (vapor-liquid-solid), SLS (solid-liquid-solid), and so on. In present study, the zinc oxide one-dimensional nanostructures synthesized by carbon reduction route without catalyst isn’t controlled by the conventional VLS mechanism because that there is no droplet at the growth end of the nanostructures. By using a variety of growth times and the ratios of the zinc oxide and the activated carbon, it can be deduced that the liquid zinc island formed firstly and then the ZnO nanostructures growth on them. The morphologies and microstructures of samples were characterized by scanning electron microscope (SEM) observations, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The structure characterization confirms that all the grown one-dimensional materials are hexagonal wurtzite ZnO.

Synthesis and characterization of semiconducting nanowires for gas sensing

Quasi one-dimensional nanostructures of semiconducting metal oxides are promising for the development of nano-devices. Tin, indium, and zinc oxides were produced in form of single-crystalline nanowires through condensation from vapor phase. Such a growth occurs in controlled thermodynamical condition and size reduction effects on the electrical and optical response to gases have been exploited. Preparation, microstructural, and electrical characterization of nanowires are presented and the peculiarities of these innovative structures are highlighted.

Quasi One-dimensional ZnO Nanostructures Fabricated without Catalyst at Lower Temperature

One- or quasi one-dimensional zinc oxide nanostructures possess plenty of morphologies. Only by controlling the gas flow rates, and partial pressures of argon, oxygen and zinc vapor, can various types of high-quality ZnO nanomaterials (such as wires, belts, arrays, saws or combs, tetraleg rods, nails, and pins) be synthesized through pure zinc powder evaporation without a catalyst at the temperature range of 600–700°C. In this study, deposited nanostructures were characterized by means of scanning electron microscopy, X-ray diffraction and high-resolution transmission electron microscopy. The authors propose and discuss the growth mechanisms of various ZnO. In addition, properties of room temperature photoluminescence and field emission of several typical ZnO nanostructures are measured and investigated.

Coating carbon nanotubes with polymer in supercritical carbon dioxide

A facile and efficient method has been developed for coating MWNTs with solvent resistant polymer in scCO2, which permits the selective deposition of high molecular weight fluorinated graft poly(methyl vinyl ether-alt-maleic anhydride) polymer onto MWNTs in scCO2 under 100-170 bar at 40 degrees C and forms quasi one-dimensional nanostructures with conducting cores and insulating surfaces.

Defects in Carbon Nanotubes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Defects in carbon nanotubes.

Carbon nanotubes are quasi one-dimensional nanostructures with unique eletrical prroperties that make them prime candidates for molecular electronics, which is certainly a most promising direction in nanotechnology. Early theoretical works predicted that the electronic properties of "ideal" carbon nanotubes depend on their diameter and chirality. However, carbon nanotubes are probably not as perfect as they were once thought to be. Defects such as pentagons, heptagons, vacancies, or dopant are found to modify drastically the electronic properties of these nanosystems. Irradiation processes can lead to interesting, highly defective nanostructures and also to the coalescence of nanotubes within a rope. The introduction of defects in the carbon network is thus an interesting way to tailor its intrinsic properties, to create new potential nanodevices. The aim of the present Acount is to investigate theoretically the effects of different types of defects on the electronic properties of carbon nanotubes, and to propose new potential applications in nanoelectronics.

Ion tracks — quasi one-dimensional nano-structures

Our current understanding of the short-time interaction of fast heavy ions with matter is reviewed. Fast ions move along straight line trajectories and loose their energy mainly via collisions with electrons in the close surrounding of the ion path. Thus, the initial stages of corresponding ion tracks are highly excited cylindrical regions with diameters of the order of nanometers that extend over some micrometers in length. The energy dissipation inside these cylinders and the different possible pathways from dense electronic excitations to atomic motions and phase transitions are discussed in the light of recent experimental results.

Ga 2O 3 nanowires prepared by physical evaporation

Gallium oxide nanowires (GaONWs) were obtained by evaporation from a bulk gallium target. The GaONWs, with mean diameter around 60 nm, are of monocrystalline nature with length up to 100 μm, and identified to be monoclinic Ga 2O 3 with space group of C2/m. The growth of the GaONWs is not controlled by the well-known vapor–liquid–solid (VLS) mechanism, instead they are seemingly grown via a vapor–solid (VS) process, in which the structural defects play an important role both during the nucleation and the preferable axial growth of the wires. Understanding such a growth process would be helpful in the synthesis of other quasi one-dimensional nanostructures.