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Two-dimensional networks made of metal nanowires are excellent paradigms for the experimental observation of electrical percolation caused by continuous jackstraw-like physical pathways. Such systems became very interesting as alternative material in transparent electrodes, which are fundamental components in display devices. This work presents the experimental characterization of low-haze and ultra-transparent electrodes based on silver nanowires. The films are created by dip-coating, a feasible and scalable liquid film coating technique. We have found dominant alignment of the silver nanowires in withdrawal direction. The impact of this structural anisotropy on electrical anisotropy becomes more pronounced for low area coverage. The rod alignment does not influence the technical usability of the films as significant electrical anisotropy occurs only at optical transmission higher than 99 %. For films with lower transmission, electrical anisotropy becomes negligible. In addition to the experimental work, we have carried out computational studies in order to explain our findings further and compare them to our experiments and previous literature. This paper presents the first experimental observation of electrical anisotropy in two-dimensional silver nanowire networks close at the percolation threshold.

This work addresses the impact of co-percolating carbon nanotubes within a silver nanowire network with regard to the optoelectrical performance as a transparent electrode. We carried out a comprehensive measurement series and focused on ultra-transparent electrodes with optical transmission above 95%. We found an immense improvement of the optoelectrical performance for networks near the percolation threshold of the silver nanowires after carbon nanotubes have been added. We were able to decrease the sheet resistance of the silver nanowire networks by a factor of up to 70 after adding carbon nanotubes. We produced transparent electrodes with industrially acceptable sheet resistance at optical transmission of higher than 97%. This work outlines the potential of co-percolating rod-like conductors as a network for ultratransparent electrodes. Our experimental work confirms theoretical approaches in percolation theory since we systematically evaluated films with high optical transmission. The most transparent films are beyond the descriptiveness with the percolation scaling law.

In this work we present a novel method for CNT/Sol-Gel film preparation, combining low resistivity and improved adhesion behaviour on glass substrates. Naturally occurring voids, with diameters of 50-100 nm, in sprayed CNT networks are used for Sol-Gel penetration via dip coating method. Thermal treatments, for composite film densification, in the range of 200-700°C are investigated and electrical properties were compared to identically treated reference samples with the same batch of nanotubes but without Sol-Gel. The resistivity of such composite films, with best value of 0.03 cm for MWNTs, is two orders of magnitudes lower than previously reported for CNT/Sol-Gel composites. Surprisingly the surface resistance of the composite film shows 25% improvement compared to thermally equal treated pure CNT films. In addition, crosscut adhesion behaviour is investigated, including tape test, showing good performance for composite films, where Sol-Gel acts as an adhesion promoter.

Motivated by numerous recent reports indicating attractive properties of composite materials of carbon nanotubes (CNTs) and liquid crystals (LCs) and a lack of research aimed at optimizing such composites, the process of dispersing CNTs in thermotropic LCs is systematically studied. LC hosts can perform comparably or even better than the best known organic solvents for CNTs such as N-methyl pyrrolidone (NMP), provided that the dispersion process and choice of LC material are optimized. The chemical structure of the molecules in the LC is very important; variations in core as well as in terminal alkyl chain influence the result. Several observations moreover indicate that the anisotropic nematic phase, aligning the nanotubes in the matrix, per se stabilizes the dispersion compared to a host that is isotropic and thus yields random tube orientation. The chemical and physical phenomena governing the preparation of the dispersion and its stability are identified, taking into account enthalpic, entropic, as well as kinetic factors. This allows a guideline on how to best design and prepare CNT–LC composites to be sketched, following which tailored development of new LCs may take the advanced functional material that CNT–LC composites comprise to the stage of commercial application.

Thermal expansion exhibits considerable challenges developing residual stresses at the interfaces of different materials treated at high temperature. Electrical devices containing materials with different thermal expansion behaviour very often suffer this problem. Thermal expansion co-efficient (TEC) of different metals can be tuned by using carbon nanotube (CNT). Metal matrix composites (MMCs) using CNT are fabricated by hot-press sintering method and TEC of the composites are investigated throughout a wide range of temperature (-155 to 275 °C). Reduction of TEC of the composite materials was observed up to 20% compared to that of pure metals. The effect of CNTs in the matrix materials and the mechanism behind the improvement are explained from the microscopic investigation of the composites.

Hem obtingut capes primes de Nanotubs de Carboni d'una sola paret (CNT) sobre un substrat amb un mètode molt simple, que poden ser emprades com elèctrodes flexibles i transparents en dispositius electrònics. Per tal d'obtenir dispositius reproduïbles amb propietats similars, en particular amb similar impedància Z(ω), és important relacionar les propietats elèctriques amb la quantitat de CNTs presents en la capa. Per això, hem realitzat capes primes de CNTs sobre substrats flexibles i transparents (PPC, policarbonat de propilè) amb diferents densitats de CNT. A partir d'un mètode iteratiu matemàtic i de l'Anàlisi Tèrmogravimètric (TGA) de cada mostra, hem pogut determinar la quantitat de CNTs presents en cada mostra. També n'hem fet una estimació a partir de l'espectroscòpia d'absorció òptica. Hem vist que els dos mètodes donen resultats coherents. Hem analitzat les diferents mostres mesurant la impedància elèctrica a diferents frequències, fins 110 MHz. Les capes primes amb poca densitat de CNTs són semiconductores, en canvi les denses són metàl·liques, i prou conductores per ser utilitzades com elèctrode de treball en un procés electroquímic. Podem obtenir així composites CNT-polímer conductor o CNT-metall, electroquímicament. Amb l'objectiu de les aplicacions per a sensors, utilitzant les capes primes de CNT com elèctrode de treball hem obtingut composites CNT-polímer conductor, depositant-hi electroquímicament un polímer conductor, polipirrol o polianilina. Hem analitzat les propietats del dispositiu com a sensor electroquímic, observant la seva resposta en funció del pH, mesurant el potencial en circuit obert en funció del pH de la solució, entre 1 i 13. Els resultats mostren una bona sensibilitat, linearitat i estabilitat. Per això, els dispositius CNT/polipirrol i CNT/polianilina poden tenir aplicacions com a sensors o biosensors en estat sòlid, depositats sobre qualsevol superfície de forma arbitrària, que pot ser transparent i flexible., We obtained thin films of single-walled carbon nanotubes (CNTs), which may be used as transparent, flexible electrodes in electronic devices, on a substrate using a very simple method. In order to construct reproducible devices with similar properties, in particular with similar impedance Z(ω), it is important to associate the electrical properties with the number of CNTs in a network. We prepared thin CNT networks on transparent, flexible substrates (PPC, polypropylene carbonate) with different CNT densities. The number of CNTs was estimated using a mathematical method based on the data obtained from thermo-gravimetric analysis (TGA). We were able to estimate the relative number of CNTs using optical absorption spectroscopy. These two methods are in good agreement. We also analysed the various samples using electrical impedance measurements at frequencies of up to 110 MHz. Low-density networks are semiconductors, whilst high-density networks behave like metals and are sufficiently good conductors to be used as working electrodes in electrochemical processes. It is thus possible to obtain CNT polymer and metal composite conductors electrochemically. With sensor applications in mind, we used CNT thin films as a working electrode to obtain a composite CNT-conducting polymer. This was performed by electrochemically depositing a conducting polymer ? polypyrrole or polyaniline ? on the electrode. The pH dependence of the device was measured by recording its open circuit potential in various buffer solutions. This enabled us to analyse the properties of the device as an electrochemical sensor. The results showed a good sensitivity, linearity and stability in both cases. Thus, the CNT/polypyrrole and CNT/polyaniline devices could have applications as solidstate gas sensors or biosensors when they are deposited on transparent and flexible surfaces of any shape.

Carbon nanotube research, whilst still in its infancy, has come a long way since their discovery in 1991. Considerable characterisation work is still to be done on nanotubes, however this requires a reliable production method of the raw material in sufficient volumes to enable thorough experimental analysis. As part of his fullerene research, fullerenes being of the same carbon family as carbon nanotubes, Wolfgang Kraetschmer made a major breakthrough in synthesis technology in 1990, with the resultant device now bearing his name and being used in nanotechnology research groups around the world. Fullerene, C60, is a nearly spherical molecule composed of 60 carbon atoms arranged in pentagons and hexagons, like a soccer ball. Fullerenes are molecules with a well determined finite size (0.71nm for C60). Nanotubes, on the other hand, are tiny needle-like structures. A nanotube can be considered as a seamless roll of a graphene sheet, with a typical diameter of 1nm and lengths up to microns. Nanotubes are molecules in their cross section, but along the axis they are infinite solids. Nanotube physics is an interesting superposition of molecular physics in the cross section and solid state physics along the axis.