Search

We have constructed a new nanomanipulator (NM) in a field emission scanning electron microscope (FE-SEM) to fabricate carbon nanotube (CNT) tip to precisely adjust the length and attachment angle of CNT onto the mother atomic force microscope (AFM) tip. The new NM is composed of 2 modules, each of which has the degree of freedom of three-dimensional rectilinear motion x, y and z and one-dimensional rotational motion θ. The NM is mounted on the stage of a FE-SEM. With the system of 14 axes in total which includes 5 axes of FE-SEM and 9 axes of nano-actuators, it was possible to see CNT tip from both rear and side view about the mother tip. With the help of new NM, the attachment angle error could be reduced down to 0° as seen from both the side and the rear view, as well as, the length of the CNT could be adjusted with the precision using electron beam induced etching. For the proper attachment of CNT on the mother tip surface, the side of the mother tip was milled with focused ion beam. In addition, electron beam induced deposition was used to strengthen the adhesion between CNT and the mother tip. In order to check the structural integrity of fabricated CNT, transmission electron microscope image was taken which showed the fine cutting of CNT and the clean surface as well. Finally, the performance of the fabricated CNT tip was demonstrated by imaging 1-D grating and DNA samples with atomic force microscope in tapping mode. [ABSTRACT FROM AUTHOR]

Molten salt electrochemistry is cited as one of the most efficient ways to convert stable but unwanted CO2 into value-added chemical fuels and functional materials, in particular carbon nanotubes (CNTs). In this work, we report the high yield and scalable CO2-deriving CNTs by adding ZnO to molten carbonate electrolyte. The physicochemical properties such as crystal structure, morphology and element composition of the carbon products were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD) and Raman spectrometer (Raman). It is demonstrated that an appropriate amount of ZnO additives can greatly increase the content of CNTs in carbon products. However, the micromorphology and microstructure of the carbon products are found to be significantly changed when the ZnO content is insufficient or excessive. Compared with molten salt electrolyte without ZnO, ZnO-included electrolyte endows CNTs with a higher degree of graphitization and crystallinity. This work demonstrates the feasibility of improving CNTs content in carbon products and lowering required energy for CNTs production by adding ZnO as a promoter. [ABSTRACT FROM AUTHOR]

The electrical properties of individual multiwall carbon nanotubes (CNTs) filled with Fe3C nanowires (Fe-CNTs) grown by chemical vapor deposition were investigated. The individual Fe-CNTs were measured by two-probe configuration in a scanning electron microscope, in which one probe was used to contact one end of the nanotubes and the other varied its contact position to measure the resistance along the Fe-CNTs. The data suggest that the ferromagnetic nanowires and the CNTs were well connected into a conduction network, and the resistance of the individual Fe-CNTs decreased as the filling rate increased. Analysis shows that the encapsulated ferromagnetic nanowires played a profound part in determining the electrical behavior of individual Fe-CNTs. The results may be useful for understanding of electronic transport of individual Fe-CNTs and applications based on individual Fe-CNTs. [ABSTRACT FROM AUTHOR]

A sensitive and selective electrochemical sensor for catechol (CC) using a multi-walled carbon nanotubes-poly(1,5-diaminonaphthalene) composite modified glassy carbon electrode (MWCNTs/p-DAN/GCE) is reported. The surface features of the modified electrodes were characterized by a scanning electron microscope (SEM), and an energy-dispersive X-ray spectrometer (EDX). The electrochemical behavior was investigated using cyclic voltammetry (CV). The cyclic voltammogram of the modified electrode is characterized by a remarkable increase in the redox peak currents for CC, which indicates that MWCNTs/p-DAN film enhances significantly the electrocatalytic response toward CC. The effects of different parameters, such as pH, accumulation time, amount of MWCNTs, and scan rate on the response of the developed sensor were investigated. The analytical performances were also investigated using differential pulse voltammetry (DPV). The optimized MWCNTs/p-DAN/GCE based CC sensor exhibited a linear response over a range of 2.0 × 10−8 to 1.3 × 10−4 M with a lower limit of detection (LOD) of 1.0 × 10−8 M (S/N = 3). Moreover, the developed CC sensor is characterized by high sensitivity, excellent repeatability, and excellent selectivity. The proposed sensor showed high selectivity for catechol relative to most potential interferents particularly hydroquinone (HQ) and resorcinol (RC), typical interfering agents. The developed sensor was successfully applied for the determination of CC in real water samples with satisfactory recovery results. [ABSTRACT FROM AUTHOR]

Molten carbonate electrolysis demonstrates a feasible approach for the direct transformation of CO2 into reusable carbonaceous substance. In this work, in addition to previously commonly used expensive Li2CO3, alkaline earth carbonates of CaCO3, SrCO3 and BaCO3 which are abundant in nature and of much lower price are employed to combine with Li2CO3 and contribute to the production of valuable carbon nanotubes. Structural features of the synthetic carbon nanotubes are characterized by scanning electron microscope, transmission electron microscope, high resolution transmission electron microscope andX-ray diffractometer. The results demonstrate that galvanostatic electrolysis in pure or alkaline-earth-carbonate-included Li2CO3 provides a high yield of valuable carbon nanotubes production. Alkaline earth carbonate additives produce thicker carbon nanotubes than pure Li2CO3 case, but the lattice distances of the carbon nanotubes electro-deposited in different electrolytes exhibit a good consistency with the standard data of multi-walled carbon nanotubes. Thermodynamic calculations are conducted in order to figure out why alkaline earth carbonate additives prefer thicker carbon nanotubes production. Summarily, this work discloses a rich understanding of how alkaline earth carbonates impact the size of carbon nanotubes and should be helpful to the future size control study. [ABSTRACT FROM AUTHOR]

Carbon nanotubes are considered to be an ideal imaging tip for atomic force microscopy (AFM) applications, and a number of methods for fabricating these types of probe have been developed in recent years. This work reports the attachment of carbon nanotubes to AFM probes using a micromanipulator within a scanning electron microscope. Electron beam induced deposition and etching are used to enhance the quality and attachment of the carbon nanotube tip and improve the fabrication rate of the CNT AFM probes compared to existing techniques. The attachment process is also improved by using a mat of SWCNTs (buckypaper) as a CNT source, which simultaneously improves the ease of fabrication and rate of nanotube probe production. The aim of these improvements is to simplify and improve the attachment process such that these probes can be better and more widely used in applications that benefit from their unique properties. This improved process is then used to attach CNTs to the new generation of low-mass, high-frequency probes, which are designed for rapid AFM imaging. The ability of these probes to operate with CNT tips is demonstrated, and their wear-resistance properties were found to be significantly enhanced compared to unmodified probes. These wear-resistant probes imaging at high scan rates are proposed to be effective tools for increasing throughput in metrological analysis, particularly for imaging high-modulus surfaces with high roughness and high-aspect-ratio features. [ABSTRACT FROM AUTHOR]

This paper examines the effect of iron catalyst thickness on the straightness of growth of carbon nanotubes (CNTs) for microelectromechanical systems fabricated using the CNT-templated-microfabrication (CNT-M) process. SEM images of samples grown using various iron catalyst thicknesses show that both straight sidewalls and good edge definition are achieved using an iron thickness between 7 and 8 nm. Below this thickness, individual CNTs are well aligned, but the sidewalls of CNT forests formed into posts and long walls are not always straight. Above this thickness, the CNT forest sidewalls are relatively straight, but edge definition is poor, with significantly increased sidewall roughness. The proximity of a device or feature to other regions of iron catalyst also affects CNT growth. By using an iron catalyst thickness appropriate for straight growth, and by adding borders of iron around features or devices, a designer can greatly improve straightness of growth for CNT-MEMS. [ABSTRACT FROM AUTHOR]

Li-air cells based on Li foil as an anode electrode, freestanding carbon nanotube/nanofiber mixed buckypaper as an air (cathode) electrode, and organic electrolyte were assembled. The air electrode was made with single-wall carbon nanotube (SWNT) and carbon nanofiber (CNF) without any binder. The discharge capacity was strongly dependent on both the discharge current density and the thickness of the air electrode. A discharge capacity as high as 2500 mAh/g was obtained for an air electrode at a thickness of 20 μm with a discharge current density of 0.1 mA/cm2 however, it was reduced to 400 mAh/g when the thickness of the air electrode was increased to 220 μm. For a 66 μm thick air electrode, the discharge capacity decreased from 1600 to 340 mAh/g when the discharge current density increased from 0.1 to 0.5 mA/cm2. The scanning electron microscope images on surfaces of the air electrode from a fully discharged cell showed that the voids at the air side were almost fully filled by the solid deposition; however, the voids at the membrane side were still wide open. [ABSTRACT FROM AUTHOR]

We employed an electroless deposition technique to prepare Ni seeds uniformly on a carbon cloth, followed by carbon nanotube (CNT) formation at an elevated temperature. Subsequently, a pulse electrodeposition was used to impregnate PtRu nanoparticles on the CNT structure. Similar procedures were performed on carbon supports including Vulcan XC72R, BP2000, and carbon nanocapsules (CNCs) for comparison purposes. Diffraction patterns from an X-ray confirmed a PtRu alloyed phase. An analysis from inductively coupled plasma-mass spectrometry indicated that the PtRu composition was relatively unchanged. Images from scanning and transmission electron microscopes revealed dense CNTs throughout the carbon cloth with nanoparticulate PtRu evenly impregnated. Considerable PtRu aggregations were found on the CNCs and BP2000. We observed a significantly improved coulomb efficiency and an electrochemically active surface area for the CNT-grown carbon cloth. In both apparent current density and mass activity for methanol electro-oxidation, the CNT-grown carbon cloth revealed the largest values. We attribute the performance enhancement to the large-area CNT structure that allowed facile access of electrolytes. [ABSTRACT FROM AUTHOR]

We present a simulation study on the peeling of carbon nanotubes bundles interacting with a flat substrate, represented by the back surface of an atomic force microscopy cantilever. A defected sample, acquired in situ using a scanning electron microscope, was investigated under different peeling configurations by finite element method simulations. The coupled computational-experimental analysis let to identify the position and the entity of a structural defect by means of reverse image correlation problem. By exploiting this defective fiber it was also possible to quantify, as indirect measure, the friction and adhesion forces between the bundle and the substrate of few pN magnitude, otherwise difficult to measure with the resolution of currently available instruments. The proposed approach can be useful to study the tribology-induced mechanical behavior of one-dimensional nanostructures as well as for real-time identification and monitoring of nanodefects for industrial applications, such as nanoelectronics. [ABSTRACT FROM AUTHOR]

Three-dimensional carbon nanotube field-effect transistors (3D CNTFETs) possess predictable characteristics that rival those of planar CNTFETs and Si-based MOSFETs. However, due to the lack of a reliable assembly technology, they are rarely reported on, despite the amount of attention they receive. To address this problem, we propose the novel concept of a 3D CNTFET and develop its assembly strategy based on nanomanipulation and the electron-beam-induced deposition (EBID) technique inside a scanning electron microscope (SEM). In particular, the electrodes in our transistor design are three metallic cuboids of the same size, and their front, top and back surfaces are all wrapped up in CNTs. The assembly strategy is employed to build the structure through a repeated basic process of pick-up, placement, fixing and cutting of CNTs. The pick-up and placement is performed through one nanomanipulator with four degrees of freedom. Fixing is carried out through the EBID technique so as to improve the mechanical and electrical characteristics of the CNT/electrodes connection. CNT cutting is undertaken using the typical method of electrical breakdown. Experimental results showed that two CNTs were successfully assembled on the front sides of the cubic electrodes. This validates our assembly method for the 3D CNTFET. Also, when contact resistance was measured, tens of kilohms of resistance was observed at the CNT-EBID deposition-FET electrodes junction.. This manifests the electrical reliability of our assembly strategy. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon nanotubes (NCNTs) were prepared using a simple ultrasonic spray pyrolysis method. The precursor concentration effect was examined to effectively control alignment, open tip and diameter of the NCNTs by changing xylene/cyclohexylamine ratio. The structure and morphology of the resultant NCNTs were characterized by scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy. The degree of alignment and the diameter of the NCNTs increased as the xylene/cyclohexylamine precursor mixture was changed from 0 to 35% cyclohexylamine. This precursor composition also caused a large number of open-ended nanotubes to form with graphite layers inside the cavities of the NCNTs. However, further increase cyclohexylamine content in the precursor reduced the degree of alignment and diameter of the NCNTs. We demonstrate control over the NCNT alignment and diameter, along with the formation of open-ended nanotube tips, and propose a growth mechanism to understand how these properties are interlinked. [ABSTRACT FROM AUTHOR]

Dry spun carbon nanotube yarns made from vertically aligned multiwalled carbon nanotube forests possess high mechanical strength and behave like semiconductors with electrical conductivity of the order of 4 × 104 S m−1. Coating a submicron-thick film of silver particle-filled polymer on the surface increased the electrical conductivity of the carbon nanotube yarn by 60-fold without significantly sacrificing its mechanical strength. The transitional characteristics of the silver-coated carbon nanotube yarn were investigated by varying the take-up ratio of the silver coating. A step change in conductivity was observed when the silver content in the coated yarn was between 7 and 10 wt% as a result of the formation of connected silver particle networks on the carbon nanotube yarn surface. [ABSTRACT FROM AUTHOR]

A facile and rapid assembly of powdered carbon nanotubes (CNTs) into compressible, porous, macroscale monoliths is reported. Despite a Poisson's ratio just above zero, we found that the sample under compression inside a scanning electron microscope (SEM) revealed CNT regions behaving in auxetic and vortex-like rotational modes as well as standard collapse responses. This method is crucial in understanding the macroscale behaviour based on the accumulation of nanoscale responses to an applied force. [ABSTRACT FROM AUTHOR]

The patterning of carbon nanostructures by electron beam stimulated oxidation is described. Sputter deposited carbon thin films and carbon nanotubes are locally oxidized in a scanning electron microscope using injected water vapor. The resulting structures are examined with scanning electron microscopy and transmission electron microscopy. The electrical resistance obtained postprocessing is comparable to the as-deposited values. Linewidths are demonstrated down to 20 nm along with sub-2 nm nanowire fabrication in sputtered carbon films. A carbon nanowire is fabricated using this process and electrically characterized. [ABSTRACT FROM AUTHOR]

Functional devices can be directly assembled using microgrippers with an in situelectron microscope. Two simple and compact silicon microgripper designs are investigated here. These are operated by electrothermal actuation, and are used to transfer a catalytically grown multi-walled carbon nanofibre from a fixed position on a substrate to the tip of an atomic force microscope cantilever, inside a scanning electron microscope. Scanning of high aspect ratio trenches using the nanofibre supertip shows a significantly better performance than that with standard pyramidal silicon tips. Based on manipulation experiments as well as a simple analysis, we show that shear pulling (lateral movement of the gripper) is far more effective than tensile pulling (vertical movement of gripper) for the mechanical removal of carbon nanotubes from a substrate. [ABSTRACT FROM AUTHOR]