Transport Properties And Induced Voltage In The Structure Of Water-Filled Single-Walled Boron-Nitrogen Nanotubes

Density functional theory/molecular dynamics simulations were employed to give insights into the mechanism of voltage generation based on a water-filled single-walled boron-nitrogen nanotube (SWBNNT). Our calculations showed that (1) the transport properties of confined water in a SWBNNT are different from those of bulk water in view of configuration, the diffusion coefficient, the dipole orientation, and the density distribution, and (2) a voltage difference of several millivolts would generate between the two ends of a SWBNNT due to interactions between the water dipole chains and charge carriers in the tube. Therefore, this structure of a water-filled SWBNNT can be a promising candidate for a synthetic nanoscale power cell as well as a practical nanopower harvesting device.

Transport properties and induced voltage in the structure of water-filled single-walled boron-nitrogen nanotubes

Density functional theory/molecular dynamics simulations were employed to give insights into the mechanism of voltage generation based on a water-filled single-walled boron-nitrogen nanotube (SWBNNT). Our calculations showed that (1) the transport properties of confined water in a SWBNNT are different from those of bulk water in view of configuration the diffusion coefficient the dipole orientation and the density distribution and (2) a voltage difference of several millivolts would generate between the two ends of a SWBNNT due to interactions between the water dipole chains and charge carriers in the tube. Therefore this structure of a water-filled SWBNNT can be a promising candidate for a synthetic nanoscale power cell as well as a practical nanopower harvesting device.

Hydrothermal synthesis and luminescent properties of Y2O3:Tb3+ and Gd2O3:Tb3+ microrods

One-dimensional (1D) Y2O3:Tb3+ and Gd2O3:Tb3+ microrods have been successfully prepared through a large-scale and facile hydrothermal method followed by a subsequent calcination process in N-2/H-2 mixed atmosphere. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), thermogravimetric analysis (TGA), energy-dispersive X-ray spectra (EDX). scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The as-formed products via the hydrothermal process could transform to cubic Y2O3:Tb3+ and Gd2O3:Tb3+ with the same morphology and slight shrinking in size after a postannealing process.

The dynamics of polymerized carbon nanotubes in semiconductor polymer electronics and electro-mechanical sensing

Polymerized carbon nanotubes (CNTs) are promising materials for polymer-based electronics and electro-mechanical sensors. The advantage of having a polymer nanolayer on CNTs widens the scope for functionalizing it in various ways for polymer electronic devices. However, in this paper, we show for the first time experimentally that, due to a resistive polymer layer having carbon nanoparticle inclusions and polymerized carbon nanotubes, an interesting dynamics can be exploited. We first show analytically that the relative change in the resistance of a single isolated semiconductive nanotube is directly proportional to the axial and torsional dynamic strains, when the strains are small, whereas, in polymerized CNTs, the viscoelasticity of the polymer and its effective electrical polarization give rise to nonlinear effects as a function of frequency and bias voltage. A simplified formula is derived to account for these effects and validated in the light of experimental results. CNT–polymer-based channels have been fabricated on a PZT substrate. Strain sensing performance of such a one-dimensional channel structure is reported. For a single frequency modulated sine pulse as input, which is common in elastic and acoustic wave-based diagnostics, imaging, microwave devices, energy harvesting, etc, the performance of the fabricated channel has been found to be promising.

C-BN Single-Walled Nanotubes from Hybrid Connection of BN/C Nanoribbons: Prediction by ab initio Density Functional Calculations

We demonstrated for the first time by ab initio density functional calculation and molecular dynamics simulation that C0.5(BN)0.5 armchair single-walled nanotubes (NT) are gapless semiconductors and can be spontaneously formed via the hybrid connection of graphene/BN Nanoribbons (GNR/BNNR) at room temperature. The direct synthesis of armchair C0.5(BN)0.5 via the hybrid connection of GNR/BNNR is predicted to be both thermodynamically and dynamically stable. Such novel armchair C0.5(BN)0.5 NTs possess enhanced conductance as that observed in GNRs. Additionally, the zigzag C0.5(BN)0.5 SWNTs are narrow band gap semiconductors, which may have potential application for light emission. In light of recent experimental progress and the enhanced degree of control in the synthesis of GNRs and BNNR, our results highlight an interesting avenue for synthesizing a novel specific type of C0.5(BN)0.5 nanotube (gapless or narrow direct gap semiconductor), with potentially important applications in BNC-based nanodevices.

Field-Effect and Frequency Dependent Transport in Semiconductor-Enriched Single-Wall Carbon Nanotube Network Device

The electrical and optical response of a field-effect device comprising a network of semiconductor-enriched single-wall carbon nanotubes, gated with sodium chloride solution is investigated. Field-effect is demonstrated in a device that uses facile fabrication techniques along with a small-ion as the gate electrolyte-and this is accomplished as a result of the semiconductor enhancement of the tubes. The optical transparency and electrical resistance of the device are modulated with gate voltage. A time-response study of the modulation of optical transparency and electrical resistance upon application of gate voltage suggests the percolative charge transport in the network. Also the ac response in the network is investigated as a function of frequency and temperature down to 5 K. An empirical relation between onset frequency and temperature is determined.

Irradiation-mediated tailoring of carbon nanotubes

The ever-increasing demand for faster computers in various areas, ranging from entertaining electronics to computational science, is pushing the semiconductor industry towards its limits on decreasing the sizes of electronic devices based on conventional materials. According to the famous law by Gordon E. Moore, a co-founder of the world s largest semiconductor company Intel, the transistor sizes should decrease to the atomic level during the next few decades to maintain the present rate of increase in the computational power. As leakage currents become a problem for traditional silicon-based devices already at sizes in the nanometer scale, an approach other than further miniaturization is needed to accomplish the needs of the future electronics. A relatively recently proposed possibility for further progress in electronics is to replace silicon with carbon, another element from the same group in the periodic table. Carbon is an especially interesting material for nanometer-sized devices because it forms naturally different nanostructures. Furthermore, some of these structures have unique properties. The most widely suggested allotrope of carbon to be used for electronics is a tubular molecule having an atomic structure resembling that of graphite. These carbon nanotubes are popular both among scientists and in industry because of a wide list of exciting properties. For example, carbon nanotubes are electronically unique and have uncommonly high strength versus mass ratio, which have resulted in a multitude of proposed applications in several fields. In fact, due to some remaining difficulties regarding large-scale production of nanotube-based electronic devices, fields other than electronics have been faster to develop profitable nanotube applications. In this thesis, the possibility of using low-energy ion irradiation to ease the route towards nanotube applications is studied through atomistic simulations on different levels of theory. Specifically, molecular dynamic simulations with analytical interaction models are used to follow the irradiation process of nanotubes to introduce different impurity atoms into these structures, in order to gain control on their electronic character. Ion irradiation is shown to be a very efficient method to replace carbon atoms with boron or nitrogen impurities in single-walled nanotubes. Furthermore, potassium irradiation of multi-walled and fullerene-filled nanotubes is demonstrated to result in small potassium clusters in the hollow parts of these structures. Molecular dynamic simulations are further used to give an example on using irradiation to improve contacts between a nanotube and a silicon substrate. Methods based on the density-functional theory are used to gain insight on the defect structures inevitably created during the irradiation. Finally, a new simulation code utilizing the kinetic Monte Carlo method is introduced to follow the time evolution of irradiation-induced defects on carbon nanotubes on macroscopic time scales. Overall, the molecular dynamic simulations presented in this thesis show that ion irradiation is a promisingmethod for tailoring the nanotube properties in a controlled manner. The calculations made with density-functional-theory based methods indicate that it is energetically favorable for even relatively large defects to transform to keep the atomic configuration as close to the pristine nanotube as possible. The kinetic Monte Carlo studies reveal that elevated temperatures during the processing enhance the self-healing of nanotubes significantly, ensuring low defect concentrations after the treatment with energetic ions. Thereby, nanotubes can retain their desired properties also after the irradiation. Throughout the thesis, atomistic simulations combining different levels of theory are demonstrated to be an important tool for determining the optimal conditions for irradiation experiments, because the atomic-scale processes at short time scales are extremely difficult to study by any other means.

Carbon dioxide detection by boron nitride nanotubes

The effect of gas molecule adsorption is investigated on the density of states of (9,0) zigzag boron nitride nanotube within a random tight-binding Hamiltonian model. The Green function approach and coherent potential approximation have been implemented. The results show that the adsorption of carbon dioxide gas molecules by boron atoms only leads to a donor type semiconductor while the adsorption by nitrogen atoms only leads to an acceptor. Since the gas molecules are adsorbed by both boron and nitrogen atoms, a reduction of the band gap is found. In all cases, increasing the gas concentration causes an increase in the height of the peaks in the band gap. This is due to an increasing charge carrier concentration induced by adsorbed gas molecules.

Growth of branched carbon nanotubes with doped/un-doped intratubular junctions by one-step co-pyrolysis

Branched CNTs with nitrogen doped/un-doped intratubular junctions have been synthesized by a simple one-step co-pyrolysis of hexamethylenetetramine and benzene. The difference in the vapor pressure and the insolubility of the precursors are the keys for the formation of the branched intratubular junctions. The junctions behave like Schottky diodes with nitrogen-doped portion as metal and un-doped portion as p-type semiconductor. The junctions also behave like p-type field effect transistors with a very large on/off ratio.

X-ray propagation in carbon nanotubes

The maintenance of the growth of the multibillion-dollar semiconductor industry requires the development of techniques for the fabrication and characterisation of nanoscale devices. Consequently, there is great interest in photolithography techniques such as extreme UV and x-ray. Both of these techniques are extremely expensive and technologically very demanding. In this paper we describe research on the feasibility of exploiting x-ray propagation within carbon nanotubes (CNT's) for the fabrication and characterisation of nanoscale devices. This work discusses the parameters determining the design space available. To demonstrate experimentally the feasibility of x-ray propagation, arrays of carbon nanotubes have been grown on silicon membranes. The latter are required to provide structural support for the CNT's while minimising energy loss. To form a waveguide metal is deposited between the nanotubes to block x-ray transmission in this region at the same time as cladding the CNT's. The major challenge has been to fill the spaces between the CNT's with material of sufficient thickness to block x-ray transmission while maintaining the structural integrity of the CNT's. Various techniques have been employed to fill the gaps between the nanotubes including electroplating, sputtering and evaporation. This work highlights challenges encountered in optimising the process.

Electric conduction improvement of well-structured multi-walled carbon nanotubes

We characterized the electrical conductance of well-structured multi-walled carbon nanotubes (MWCNTs) which had post-treated by a rapid vacuum arc thermal annealing process and structure defects in these nanotubes are removed. We found that the after rapid vacuum arc annealing, the conductivity of well-structured MWCNTs can be improved by an order of magnitude. We also investigated the conductivity of MWCNTs bundle by the variation of temperatures. These results show that the conductance of annealed defect-free MWCNTs is sensitive to temperature imply the phonon scatting dominated the electron conductions. Compare to the well-structured MWCNTs, the defect scattering dominated the electron conduction in the as-grown control sample which has large amount of structure defects. A detail measurement of electron conduction from an individual well-structured MWCNT shows that the conductivity increases with temperatures which imply such MWCNTs exhibited semiconductor properties. We also produced back-gated field-effect transistors using these MWCNTs. It shows that the well-structured MWCNT can act as p-type semiconductor. © 2010 IEEE.

Broadband ultrafast pulse generation with double wall carbon nanotubes

Materials with nonlinear optical properties are much sought after for ultrafast photonic applications. Mode-locked lasers can generate ultrafast pulses using saturable absorbers[1]. Currently, the dominant technology is based on semiconductor saturable absorber mirrors (SESAMs). However, narrow tuning range (tens of nm), complex fabrication and packaging limit their applications[2]. Single wall nanotubes (SWNTs) and graphene offer simpler and cost-effective solutions[1]. Broadband operation can be achieved in SWNTs using a distribution of tube diameters[1,3], or by using graphene[4-8], due to the gapless linear dispersion of Dirac electrons[8,9]. © 2011 IEEE.

Complementary metal-oxide-semiconductor-compatible and self-aligned catalyst formation for carbon nanotube synthesis and interconnect fabrication

We have for the first time developed a self-aligned metal catalyst formation process using fully CMOS (complementary metal-oxide-semiconductor) compatible materials and techniques, for the synthesis of aligned carbon nanotubes (CNTs). By employing an electrically conductive cobalt disilicide (CoSi 2) layer as the starting material, a reactive ion etch (RIE) treatment and a hydrogen reduction step are used to transform the CoSi 2 surface into cobalt (Co) nanoparticles that are active to catalyze aligned CNT growth. Ohmic contacts between the conductive substrate and the CNTs are obtained. The process developed in this study can be applied to form metal nanoparticles in regions that cannot be patterned using conventional catalyst deposition methods, for example at the bottom of deep holes or on vertical surfaces. This catalyst formation method is crucially important for the fabrication of vertical and horizontal interconnect devices based on CNTs. © 2012 American Institute of Physics.

Rectangular AgIn(WO4)(2) nanotubes: A promising photoelectric material

Rectangular AgIn(WO4)(2) nanotubes with a diameter range of 80 to 120 nm and length up to 2 mu m have been synthesized by a hydrothermal method. These nanotubes exhibit interesting white light emissions when using 320 nm as the excitation wavelength. A photocatalytic reaction for water decomposition to evolve K, was performed under UV irradiation, and the rate of H, evolution is nearly seven times that of the sample prepared by a solid-state reaction, which shows much higher photocatalytic activities compared with their bulk counterparts.