Abdou Hassanien

A novel hybrid carbon material

Both fullerenes and single-walled carbon nanotubes (SWNTs) exhibit many advantageous properties. Despite the similarities between these two forms of carbon, there have been very few attempts to physically merge them. We have discovered a novel hybrid material that combines fullerenes and SWNTs into a single structure in which the fullerenes are covalently bonded to the outer surface of the SWNTs. These fullerene-functionalized SWNTs, which we have termed NanoBuds, were selectively synthesized in two different one-step continuous methods, during which fullerenes were formed on iron-catalyst particles together with SWNTs during CO disproportionation. The field-emission characteristics of NanoBuds suggest that they may possess advantageous properties compared with single-walled nanotubes or fullerenes alone, or in their non-bonded configurations.

Effect of Carbon Nanotube Network Morphology on Thin Film Transistor Performance

AbstractThe properties of electronic devices based on carbon nanotube networks (CNTNs) depend on the carbon nanotube (CNT) deposition method used, which can yield a range of network morphologies. Here, we synthesize single-walled CNTs using an aerosol (floating catalyst) chemical vapor deposition process and deposit CNTs at room temperature onto substrates as random networks with various morphologies. We use four CNT deposition techniques: electrostatic or thermal precipitation, and filtration through a filter followed by press transfer or dissolving the filter. We study the mobility using pulsed measurements to avoid hysteresis, the on/off ratio, and the electrical noise properties of the CNTNs, and correlate them to the network morphology through careful imaging. Among the four deposition methods thermal precipitation is found to be a novel approach to prepare high-performance, partially aligned CNTNs that are dry-deposited directly after their synthesis. Our results provide new insight into the role of the network morphologies and offer paths towards tunable transport properties in CNT thin film transistors.

Carbon-Nanotube Metrology

Scientific and industrial metrology provided tools for technological growth andinnovation, by fostering competitiveness and creating a favorable environment forscientific and industrial development. Every major country has its own metrologyinstitute to support companies in increasing their productivity and the quality oftheir goods and services. The fast development of carbon-nanotube science andapplications urged studies on metrology, standardization and industrial qualitycontrol. Development of protocols for the definition of sample parameters likestructural metrics, physical properties and stability are important for both researchand applications of single-, double- and multiwall carbon nanotubes. This workdiscusses some of the experimental techniques that are broadly used forcarbon-nanotube characterization, including scanning probe microscopy andspectroscopy, electron microscopy and diffraction, and optical spectroscopies, fromthe molecular level to bulk properties, addressing achievements, limitations anddirections where further research is needed for the development of standards andprotocols for metrology, standardization and industrial quality control of carbonnanotubes.

Fermi electron wave packet interference images on carbon nanotubes at room temperature

We report on the structure and electronic properties of single wall carbon nanotubes tips with atomically spatial resolution. Scanning tunneling microscopy shows topographic images of closed tips with a variety of geometrical structure; these include round, conical, as well as tips with a messy shape. Standing wave pattern of the charge density is observed at the tube cap which is formed due to constructive interference between the electronic states and its reflection on the nanotube tips. Atomically resolved images show asymmetry in the charge density that decay out within 6 nm away from the cap. These distinctive tip states do not exist elsewhere on the tube and are related to the presence of topological defects at tube ends.

Atomic force microscope study of photo-polymerized and photo-dimerized epitaxial C60 films

We have used an atomic force microscope to analyze the surface of C60 thin films, which have been grown epitaxially on a mica surface and illuminated with a 514.5 nm laser light at different temperatures. Two regimes of light-induced polymerization are observed. If the illumination temperature Tp is lower than 320 K, the illuminated surface shows polymer chains typically six molecules long with an intermolecular distance of 9.2±0.1 A . Because of the strain associated with the shorter inter-C60 distance in the polymer compared to the bulk, the surface is buckled with a period of ∼100 A and amplitude of ∼5 A resulting in a characteristic herringbone three-dimensional structure. For films, illuminated above 350 K, the surface shows primarily dimers and trimers with an unusually short inter-C60 distance of 8.8±0.1 A, this being the shortest interbuckyball distance reported so far. We also find large changes in the adhesive forces on the polymerized films compared to unpolymerized ones, suggesting that the po...

Imaging the interlayer interactions of multiwall carbon nanotubes using scanning tunneling microscopy and spectroscopy

Using atomically-resolved scanning tunneling microscopy and spectroscopy, we probe the nature of interwall interactions within multiwall carbon nanotubes at room temperature. We find that, at low bias voltages, the tunnel current depends strongly on the atomic position, introducing visibility differences between adjacent lattice sites. Since all atoms are equally visible in analogous measurements on single-wall nanotubes, we conclude that these modulations are introduced by the interwall interactions and provide unique information about the stacking nature.

Hydrogen-Driven Cage Unzipping of C60 into Nano-Graphenes

Annealing of C60 in hydrogen at temperatures above the stability limit of C–H bonds in C60Hx (500–550 °C) is found to result in direct collapse of the cage structure, evaporation of light hydrocarbons, and formation of solid mixture composed of larger hydrocarbons and few-layered graphene sheets. Only a minor part of this mixture is soluble; this was analyzed using matrix-assisted laser desorption/ionization MS, Fourier transform infrared (FTIR), and nuclear magnetic resonance spectroscopy and found to be a rather complex mixture of hydrocarbon molecules composed of at least tens of different compounds. The sequence of most abundant peaks observed in MS, which corresponds to C2H2 mass difference, suggests a stepwise breakup of the fullerene cage into progressively smaller molecular fragments edge-terminated by hydrogen. A simple model of hydrogen-driven C60 unzipping is proposed to explain the observed sequence of fragmentation products. The insoluble part of the product mixture consists of large planar polycyclic aromatic hydrocarbons, as evidenced by FTIR and Raman spectroscopy, and some larger sheets composed of few-layered graphene, as observed by transmission electron microscopy. Hydrogen annealing of C60 thin films showed a thickness-dependent results with reaction products significantly different for the thinnest films compared to bulk powders. Hydrogen annealing of C60 films with the thickness below 10 nm was found to result in formation of nanosized islands with Raman spectra very similar to the spectra of coronene oligomers and conductivity typical for graphene.

A novel facile synthesis and characterization of molybdenum nanowires

We describe a straightforward technique to synthesize pure Mo nanowires (NWs) from Mo6SyIz (8,2 < y + z ≤ 10) NWs as precursor templates. The structural transformations occur when Mo6SyIz NWs are annealed in Ar/H2 mixture leading to the formation of pure Mo NWs with similar structures as initial morphologies. Detailed microscopic characterizations show that large diameters (>15 nm) Mo NWs are highly porous, while small diameters (<7 nm) are made of solid nanocrystalline grains. We find NW of diameter 4 nm can carry up to 30 μA current without suffering structural degradation. Moreover, NWs can be elastically deformed over several cycles without signs of plastic deformation.

Broadband laser polarization control with aligned carbon nanotubes.

We introduce a simple approach to fabricate an aligned carbon nanotube (ACNT) device for broadband polarization control in fiber laser systems. The ACNT device was fabricated by pulling from as-fabricated vertically-aligned carbon nanotube arrays. Their anisotropic properties are confirmed with various microscopy techniques. The device was then integrated into fiber laser systems (at two technologically important wavelengths of 1 and 1.5 μm) for polarization control. We obtained a linearly-polarized light output with the maximum extinction ratio of ∼12 dB. The output polarization direction could be fully controlled by the ACNT alignment direction in both lasers. To the best of our knowledge, this is the first time that the ACNT device is applied to polarization control in laser systems. Our results exhibit that the ACNT device is a simple, low-cost, and broadband polarizer to control laser polarization dynamics, for various photonic applications (such as material processing, polarization diversity detection in communications etc.), where linear polarization control is necessary.

Scanning Tunneling Microscopy and Spectroscopy of Short Multiwall Carbon Nanotubes

We report on the structural analysis of multiwall carbon nanotubes (MWNTs), produced by DC arc discharge in hydrogen gas, using a scanning tunneling microscope operated at ambient conditions. On a microscopic scale the images show tubes condensed in ropes as well as individual tubes which are separated from each other. Individual nanotubes exhibit various diameters (2.5-6 nm) and chiralities (0-30A). For MWNTs rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter (4-5 nm) and chirality. Strong correlation is found between the structural parameters and the electronic properties in which the MWNTs span the metallic-semiconductor regime. True atomic-resolution topographic STM images of the outer shell show hexagonal arrangements of carbon atoms that are unequally visible by STM tip. This suggests that the stacking nature of MWNTs, may effect the electronic band structure of the tube shells. Unlike other MWNTs produced by arc discharge in helium gas, the length of the tubes are rather short (80-500 nm), which make it feasible to use them as a components for molecular electronic devices.