Nonlinear optical absorption and reflection of single wall carbon nanotube thin films by ZZ-scan technique

"Both the nonlinear optical transmission and reflection characteristics of HiPco-based single wall carbon nanotube (SWNT) thin films are studied by using the ZZ-scan method with femtosecond laser pulses at a wavelength of 1.46μm1.46μm. The nonlinear absorption coefficient and nonlinear refractive index are obtained as (5.4±2.0)×10−7cm/W(5.4±2.0)×10−7cm∕W and (1.1±0.5)×10−11cm2/W(1.1±0.5)×10−11cm2∕W, respectively, which are considerably greater than those of other optical materials. This large optical nonlinearity is ascribed to (a) homogeneously deposited thin nanotube film on optically transparent barium fluoride, (b) just-resonant excitation condition, and (c) intrinsic saturable absorption feature of SWNTs.

Novel hetero-layered materials with tunable direct band gaps by sandwiching different metal disulfides and diselenides

"Although bulk hexagonal phases of layered semiconducting transition metal dichalcogenides (STMD) such as MoS2, WS2, WSe2 and MoSe2 exhibit indirect band gaps, a mono-layer of STMD possesses a direct band gap which could be used in the construction of novel optoelectronic devices, catalysts, sensors and valleytronic components. Unfortunately, the direct band gap only occurs for mono-layered STMD. We have found, using first principles calculations, that by alternating individual layers of different STMD (MoS2, WS2, WSe2 and MoSe2) with particular stackings, it is possible to generate direct band gap bi-layers ranging from 0.79 eV to 1.157 eV. Interestingly, in this direct band gap, electrons and holes are physically separated and localized in different layers. We foresee that the alternation of different STMD would result in the fabrication of materials with unprecedented optical and physico-chemical properties that would need further experimental and theoretical investigations.

Enhanced thermal conductivity of carbon fiber/phenolic resin composites by the introduction of carbon nanotubes

"The authors report a significant enhancement in the thermal conductivity of a conventional carbon fiber/phenolic resin composite system when adding highly crystalline multiwalled carbon nanotubes. They demonstrate that 7wt%7wt% of carbon nanotubes dispersed homogeneously in a phenolic resin acted as an effective thermal bridge between adjacent carbon fibers and resulted in an enhancement of the thermal conductivity (e.g., from 250to393W∕mK250to393W∕mK). These results indicate that highly crystalline carbon nanotubes can be used as a multifunctional filler to enhance simultaneously the mechanical and thermal properties of the carbon fiber/phenolic resin composites.

An anticorrosive magnesium/carbon nanotube composite

"Here, we report a drastically improved anticorrosive characteristic of magnesium alloy composites with the introduction of multiwalled carbon nanotubes. Highly depressed corrosion of nanotube-filled magnesium composite in salt water is due to the formation of stable oxide films along the grain boundaries of magnesium. Our results indicate that carbon nanotube acted as effective multifunctional filler to improve both mechanical and anticorrosive performances of magnesium alloy.

Atomically sharp non-classical ripples in graphene

A fundamental property of a material is the measure of its deformation under applied stress. After studying the mechanical properties of bulk materials for the past several centuries, with the discovery of graphene and other two-dimensional materials, we are now poised to study the mechanical properties of single atom thick materials at the nanoscale. Despite a large number of theoretical investigations of the mechanical properties and rippling of single layer graphene, direct controlled experimental measurements of the same have been limited, due in part to the difficulty of engineering reproducible ripples such that relevant physical parameters like wavelength, amplitude, sheet length and curvature can be systematically varied. Here we report extreme (>10%) strain engineering of monolayer graphene by a novel technique of draping it over large Cu step edges. Nanoscale periodic ripples are formed as graphene is pinned and pulled by substrate contact forces. We use a scanning tunneling microscope to study these ripples to find that classical scaling laws fail to explain their shape. Unlike a classical fabric that forms sinusoidal ripples in the transverse direction when stressed in the longitudinal direction, graphene forms triangular ripples, where bending is limited to a narrow region on the order of unit cell dimensions at the apex of each ripple. This non-classical bending profile results in graphene behaving like a bizarre fabric, which regardless of how it is pulled, always buckles at the same angle. Using a phenomenological model, we argue that our observations can be accounted for by assuming that unlike a thin classical fabric, graphene undergoes significant stretching when bent. Our results provide insights into the atomic-scale bending mechanisms of 2D materials under traditionally inaccessible strain magnitudes and demonstrate a path forward for their strain engineering.Comment: 22 pages, 4 figure

Design of graphene electronic devices using nanoribbons of different widths

"We present a simple design of a field effect transistor based on graphene nanoribbons, taking advantage of the metallic and semiconductor nature of nanoribbons with different widths. Such device could be constructed by using lithography techniques. The conductance of the proposed device is obtained by using the Kubo formula, assuming a strong damping due to the substrate and imperfections of the lattice. By removing the control electrodes, the design could also be used as an electrical resistance.

Controlled growth of one-dimensional clusters of molybdenum atoms using double-walled carbon nanotube templating

"We report the controlled growth of one-dimensional clusters of molybdenum atoms inside the inner cores of double-walled carbon nanotubes. A combined characterization including high resolution transmission electron microscopy, nitrogen adsorption measurement at 77 K, x-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis reveals that the growth of one-dimensional Mo clusters can be controlled by varying the reaction conditions. The products have specific surface areas of 360–480 m2 g−1360–480 m2 g−1, and their characteristic properties are attributed to the presence of Mo cluster, which affect the electronic structure and can be exploited for the development of nanotube electronic devices.

Defects and impurities in graphene-like materials

Graphene-like materials could be used in the fabrication of electronic and optoelectronic devices, gas sensors, biosensors, and batteries for energy storage. Since it is almost impossible to work with defect-free or impurity-free materials, it is essential to understand how defects and impurities alter the electronic and vibrational properties of these systems. Technologically speaking it is more important to distinguish between different types of defects (impurities) and determine if their presence is desirable or not. This review discusses these issues and provides an updated overview of the current characterization tools able to identify and detect defects in different forms of graphene.United States. Office of Naval Research. Multidisciplinary University Research Initiative (ONR-MURI-N00014-09-1-1063