Carbon nanotube-polycarbonate composites for ultrafast lasers

Carbon nanotube polycarbonate composites with controlled nanotube-bundle size are prepared by dispersion with conjugated polymers followed by blending with polycarbonate. The composite has uniform sub-micrometer nanotube bundles in high concentration, shows strong nonlinear optical absorption, and generates 193 fs pulses when used as passive mode-locker in a fiber laser.

Viscoelasticity and high buckling stress of dense carbon nanotube brushes

We report on the mechanical behavior of a dense brush of small-diameter (1–3 nm) non-catalytic multiwall (2–4 walls) carbon nanotubes (CNTs), with ~10 times higher density than CNT brushes produced by other methods. Under compression with spherical indenters of different radii, these highly dense CNT brushes exhibit a higher modulus (~17–20 GPa) and orders of magnitude higher resistance to buckling than vapor phase deposited CNT brushes or carbon walls. We also demonstrate the viscoelastic behavior, caused by the increased influence of the van der Waals’ forces in these highly dense CNT brushes, showing their promise for energy-absorbing coatings.

Passive mode-locked lasing by injecting a carbon nanotube-solution in the core of an optical fiber

In this paper, we propose a saturable absorber (SA) device consisting on an in-fiber micro-slot inscribed by femtosecond laser micro fabrication, filled by a dispersion of Carbon Nanotubes (CNT). Due to the flexibility of the fabrication method, efficient and simple integration of the mode-locking device directly into the optical fiber is achieved. Furthermore, the fabrication process offers a high level of control over the dimensions and location of the micro-slots. We apply this fabrication flexibility to extend the interaction length between the CNT and the propagating optical field along the optical fiber, hence enhancing the nonlinearity of the device. Furthermore, the method allows the fabrication of devices that operate by either a direct field interaction (when the central peak of the propagating optical mode passes through the nonlinear media) or an evanescent field interaction (only a fraction of the optical mode interacts with the CNT). In this paper, several devices with different interaction lengths and interaction regimes are investigated. Self-starting passively modelocked laser operation with an enhanced nonlinear interaction is observed using CNT-based SAs in both interaction regimes. This method constitutes a simple and suitable approach to integrate the CNT into the optical system as well as enhancing the optical nonlinearity of CNT-based photonic devices.

In-fiber microchannel device filled with a carbon nanotube dispersion for passive mode-lock lasing

Fueled by their high third-order nonlinearity and nonlinear saturable absorption, carbon nanotubes (CNT) are expected to become an integral part of next-generation photonic devices such as all-optical switches and passive mode-locked lasers. However, in order to fulfill this expectation it is necessary to identify a suitable platform that allows the efficient use of the optical properties of CNT. In this paper, we propose and implement a novel device consisting of an optofluidic device filled with a dispersion of CNT. By fabricating a microchannel through the core of a conventional fiber and filling it with a homogeneous solution of CNTs on Dimethylformamide (DMF), a compact, all-fiber saturable absorber is realized. The fabrication of the micro-fluidic channel is a two-step process that involves femtosecond laser micro-fabrication and chemical etching of the laser-modified regions. All-fiber high-energy, passive mode-locked lasing is demonstrated with an output power of 13.5 dBm. The key characteristics of the device are compactness and robustness against optical, mechanical and thermal damage.

Nanotube-polymer composites for ultrafast photonics

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Ion interactions with the carbon nanotube surface in aqueous solutions:understanding the molecular mechanisms

We study the molecular mechanisms of alkali halide ion interactions with the single-wall carbon nanotube surface in water by means of fully atomistic molecular dynamics simulations. We focus on the basic physical-chemical principles of ion–nanotube interactions in aqueous solutions and discuss them in light of recent experimental findings on selective ion effects on carbon nanotubes.

Wideband-tuneable, nanotube mode-locked, fibre laser

Ultrashort-pulse lasers with spectral tuning capability have widespread applications in fields such as spectroscopy, biomedical research and telecommunications1–3. Mode-locked fibre lasers are convenient and powerful sources of ultrashort pulses4, and the inclusion of a broadband saturable absorber as a passive optical switch inside the laser cavity may offer tuneability over a range of wavelengths5. Semiconductor saturable absorber mirrors are widely used in fibre lasers4–6, but their operating range is typically limited to a few tens of nanometres7,8, and their fabrication can be challenging in the 1.3–1.5 mm wavelength region used for optical communications9,10. Single-walled carbon nanotubes are excellent saturable absorbers because of their subpicosecond recovery time, low saturation intensity, polarization insensitivity, and mechanical and environmental robustness11–16. Here, we engineer a nanotube–polycarbonate film with a wide bandwidth (>300 nm) around 1.55 mm, and then use it to demonstrate a 2.4 ps Er31-doped fibre laser that is tuneable from 1,518 to 1,558 nm. In principle, different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tuneable over a much broader range of wavelengths than other systems.

In situ studies of titania-supported Au shell-Pd core nanoparticles for the selective aerobic oxidation of crotyl alcohol

The thermal evolution of titania-supported Au shell–Pd core bimetallic nanoparticles, prepared via colloidal routes, has been investigated by in situ XPS, DRIFTS, EXAFS and XRD and ex situ HRTEM. As-prepared nanoparticles are terminated by a thin (∼5 layer) Au shell, encapsulating approximately 20 nm diameter cuboctahedral palladium cores, with the ensemble stabilised by citrate ligands. The net gold composition was 40 atom%. Annealing in vacuo or under inert atmosphere rapidly pyrolyses the citrate ligands, but induces only limited Au/Pd intermixing and particle growth <300 °C. Higher temperatures promote more dramatic alloying, accompanied by significant sintering and surface roughening. These changes are mirrored by the nanoparticle catalysed liquid phase selective aerobic oxidation of crotyl alcohol to crotonaldehyde; palladium surface segregation enhances both activity and selectivity, with the most active surface alloy attainable containing ∼40 atom% Au.

Carbon nanotube-supported metal catalysts for NOx reduction using hydrocarbon reductants. Part 1:catalyst preparation, characterization and NOx reduction characteristics

A dual catalyst system for the Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NOx emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NOx reduction activity in comparison with Pt/Al2O3, while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H2SO4 and HNO3 prior to the metal deposition step proved to be beneficial for the metal dispersion and the NOx reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt–Rh alloy as the supported phase.

Highly selective Pd/titanate nanotube catalysts for the double-bond migration reaction

Pd(II) and Pd(0) catalysts supported onto titanate nanotubes (H2Ti3O7) were prepared by an ion-exchange technique. The catalysts are characterised by narrow size distribution of metal nanoparticles on the external surface of the nanotubes. Pd(II) catalysts show high selectivity toward double-bond migration reaction versus hydrogenation in linear olefins. The catalytic activity exhibits a volcano-type dependence on the metal loading, with the maximum activity observed at ca. 8 wt%. The Pd(II) was shown to be rapidly reduced to Pd(0) by appropriate choice of solvent. Prereduced Pd(0) catalysts were found to be less active toward double-bond migration and more selective toward hydrogenation. The DBM reaction was faster in protic solvents, such as methanol or ethanol. © 2006 Elsevier Inc. All rights reserved.

Molecular mechanisms of salt effects on carbon nanotube dispersions in an organic solvent (N-methyl-2-pyrrolidone)

We consider the effects of salt (sodium iodide) on pristine carbon nanotube (CNT) dispersions in an organic solvent, N-methyl-2-pyrrolidone (NMP). We investigate the molecular-scale mechanisms of ion interactions with the nanotube surface and we show how the microscopic ion-surface interactions affect the stability of CNT dispersions in NMP. In our study we use a combination of fully atomistic Molecular Dynamics simulations of sodium and iodide ions at the CNT-NMP interface with direct experiments on the CNT dispersions. In the experiments we analyze the effects of salt on the stability of the dispersions by photoluminescence (PL) and optical absorption spectroscopy of the samples as well as by visual inspection. By fully atomistic Molecular Dynamics simulations we investigate the molecular-scale mechanisms of sodium and iodide ion interactions with the nanotube surface. Our simulations reveal that both ions are depleted from the CNT surface in the CNT-NMP dispersions mainly due to the two reasons: (1) there is a high energy penalty for the ion partial desolvation at the CNT surface; (2) NMP molecules form a dense solvation layer at the CNT surface that prevents ions to come close to the CNT surface. As a result, an increase of the salt concentration increases the "osmotic" stress in the CNT-NMP system and, thus, decreases the stability of the CNT dispersions in NMP. Direct experiments confirm the simulation results: addition of NaI salt into the NMP dispersions of pristine CNTs leads to precipitation of CNTs (bundle formation) even at very small salt concentration (∼10 -3 mol L -1). In line with the simulation predictions, the effect increases with the increase of the salt concentration. Overall, our results show that dissolved salt ions have strong effects on the stability of CNT dispersions. Therefore, it is possible to stimulate the bundle formation in the CNT-NMP dispersions and regulate the overall concentration of nanotubes in the dispersions by changing the NaI concentration in the solvent. © 2012 The Royal Society of Chemistry.

Polarization insensitive in-fiber mode-locker based on carbon nanotube with N-methyl-2-pryrrolidone solvent filled fiber microchamber

We report an in-fiber laser mode locker based on carbon nanotube with n-methyl-2-pryrrolidone solvent filled in-fiber microchamber. Symmetrically femtosecond laser fabricated in-fiber microchamber with randomly oriented nanotubes assures polarization insensitive oscillation of laser mode locking. The proposed and demonstrated passively mode locked fiber laser shows higher energy soliton output. The laser has an output power of ∼29 mW (corresponding to 11 nJ energy). It shows stable soliton output with a repetition rate of ∼2.3 MHz and pulse width of ∼3.37 ps. © 2012 American Institute of Physics.

Polarization dynamics of dissipative solitons in a erbium doped fiber laser passively mode locked by carbon nanotube polymer composite

Here we present first investigation of polarization dynamics from a carbon nanotube mode locked erbium doped fiber laser. Both vector and polarization switching dissipative soliton have been observed. © 2014 Optical Society of America.

Photonic gas sensors exploiting directly the optical properties of hybrid carbon nanotube localized surface plasmon structures

We investigate the modification of the optical properties of carbon nanotubes (CNTs) resulting from a chemical reaction triggered by the presence of a specific compound (gaseous carbon dioxide (CO2)) and show this mechanism has important consequences for chemical sensing. CNTs have attracted significant research interest because they can be functionalized for a particular chemical, yielding a specific physical response which suggests many potential applications in the fields of nanotechnology and sensing. So far, however, utilizing their optical properties for this purpose has proven to be challenging. We demonstrate the use of localized surface plasmons generated on a nanostructured thin film, resembling a large array of nano-wires, to detect changes in the optical properties of the CNTs. Chemical selectivity is demonstrated using CO2 in gaseous form at room temperature. The demonstrated methodology results additionally in a new, electrically passive, optical sensing configuration that opens up the possibilities of using CNTs as sensors in hazardous/explosive environments.

Salting out in organic solvents:a new route to carbon nanotube bundle engineering

In this study we investigate salt effects on bundle formation of carbon nanotubes (CNTs) dispersed in an organic solvent, N-methyl-2-pyrrolidone (NMP). Addition of NaI salt leads to self-assembly of CNTs into well-recognizable bundles. It is possible to control the size of the CNT bundles by varying the salt concentration. © the Owner Societies 2011.