Diameter-Selective Dispersion of Carbon Nanotubes via Polymers: A Competition between Adsorption and Bundling

The mechanism of the selective dispersion of single-walled carbon nanotubes (CNTs) by polyfluorene polymers is studied in this paper. Using extensive molecular dynamics simulations, it is demonstrated that diameter selectivity is the result of a competition between bundling of CNTs and adsorption of polymers on CNT surfaces. The preference for certain diameters corresponds to local minima of the binding energy difference between these two processes. Such minima in the diameter dependence occur due to abrupt changes in the CNT's coverage with polymers and their calculated positions are in quantitative agreement with preferred diameters, reported experimentally. The presented approach defines a theoretical framework for the further understanding and improvement of dispersion/extraction processes.Comment: 22 pages, 5 figures, ACS Nano (2015

Recent Advances in Molecular Electronics Based on Carbon Nanotubes

Carbon nanotubes (CNTs) have exceptional physical properties that make them one of the most promising building blocks for future nanotechnologies. They may in particular play an important role in the development of innovative electronic devices in the fields of flexible electronics, ultra-high sensitivity sensors, high frequency electronics, opto-electronics, energy sources and nano-electromechanical systems (NEMS). Proofs of concept of several high performance devices already exist, usually at the single device level, but there remain many serious scientific issues to be solved before the viability of such routes can be evaluated. In particular, the main concern regards the controlled synthesis and positioning of nanotubes. In our opinion, truly innovative use of these nano-objects will come from: i) the combination of some of their complementary physical properties, such as combining their electrical and mechanical properties, ii) the combination of their properties with additional benefits coming from other molecules grafted on the nanotubes, and iii) the use of chemically- or bio-directed self-assembly processes to allow the efficient combination of several devices into functional arrays or circuits. In this article, we outline the main issues concerning the development of carbon nanotubes based electronics applications and review our recent results in the field

In Operando Study of Charge Modulation in MoS 2 Transistors by Excitonic Reflection Microscopy

International audienceMonolayers of transition metal dichalcogenides (2D TMDs) experience strong modulation of their optical properties when the charge density is varied. Indeed, the transition from carriers composed mostly of excitons at low electron density to a situation in which trions dominate at high density is accompanied by a significant evolution of both the refractive index and the extinction coefficient. Using optical interference reflection microscopy at the excitonic wavelength, this (n, κ)–q relationship can be exploited to directly image the electron density in operating TMD devices. In this work, we show how this technique, which we call XRM (excitonic reflection microscopy), can be used to study charge distribution in MoS2 field-effect transistors with subsecond throughput, in wide-field mode. Complete maps of the charge distribution in the transistor channel at any drain and gate bias polarization point (VDS, VGS) are obtained, at ∼3 orders of magnitude faster than with scanning probe techniques such as KPFM. We notably show how the advantages of XRM enable real-time mapping of bias-dependent charge inhomogeneities, the study of resistive delays in 2D polycrystalline networks, and the evaluation of the VDS vs VGS competition to control the charge distribution in active devices

Inverted optical reflection microscopy to study visibility and local charge modulation in electrolyte-gated monolayer MoS2_2 Nathan Ullberg

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Highly selective sorting of semiconducting single wall carbon nanotubes exhibiting light emission at telecom wavelengths

International audienceSingle wall carbon nanotubes (SWNTs) are known for their exceptional electronic properties. However, most of the synthesis methods lead to the production of a mixture of carbon nanotubes having different chiralities associated with metallic (m-SWNTs) and semiconducting (s-SWNTs) characteristics. For application purposes, effective methods for separating these species are highly desired. Here, we report a protocol for achieving a highly selective separation of s-SWNTs that exhibit a fundamental optical transition centered at 1,550 nm. We employ a polymer assisted sorting approach, and the influence of preparation methods on the optical and transport performances of the separated nanotubes is analyzed. As even traces of m-SWNTs can critically affect performances, we aim to produce samples that do not contain any detectable fraction of residual m-SWNTs

Catalytic activity of cobalt and iron phthalocyanines or porphyrins supported on carbon nanotubes towards oxygen reduction reaction

International audienceNon-noble metal catalysts for O2 reduction were prepared by dispersing iron(II) phthalocyanine, cobalt(II) tetra-tert-butylphthalocyanine, cobalt(II) 2,3,7,8,12,13,17,18-octaethyl-porphine, and cobalt(II) 5,10,15,20-tetrakis(4-tert-butylphenyl)-porphyrine on carbon nanotubes (CNTs) used as high surface area support. Different types of CNTs (SWCNTs, DWCNTs and MWCNTs) were investigated as an effective substitute for commonly used carbon black in carbon-supported phthalocyanines and porphyrins. The oxygen reduction reaction (ORR) activity of those CNT-supported catalysts in alkaline and acidic solutions was studied. The results show that: (i) all catalytic systems including MWCNTs are more efficient for O2 reduction than those with SWCNTs and DWCNTs, (ii) the oxidative chemical treatment of the CNTs increases the electrocatalytic performance of the corresponding CNT-supported catalysts, (iii) similarly to Vulcan-supported catalysts, iron(II) phthalocyanine gives the best electroactivity among the investigated CNT-supported materials and (iv) finally, the MWCNT-supported iron(II) phthalocyanine catalyst chemically treated in oxidative conditions shows an ORR catalytic activity comparable to a commonly used Pt/C catalyst with similar current densities and a very low overpotential (60 mV)

Labile Diazo Chemistry for Efficient Silencing of Metallic Carbon Nanotubes

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Coupling carbon nanotubes through DNA linker using a biological recognition complex

International audienceWe present a simple and versatile method for linking single wall carbon nanotubes (SWNT) together through DNA by non-covalent chemistry using streptavidin-biotin recognition complex. Streptavidin coated SWNTs are reacted with biotin or bis-biotin ended DNA double strands leading to SWNT-DNA and SWNT-DNA-SWNT adducts in high yield. This method avoids strong acidic treatment of SWNTs prior to functionalization as usually required in covalent routes. Complementary characterizations by gel electrophoresis and AFM demonstrated the efficiency of the present binding method. In addition, SWNTs bound to DNA can be aligned on a substrate using the combing properties of DNA strands, bringing a new tool into the toolkit for self-assembling SWNTs onto surfaces