18 research outputs found
Ein neues Konzept fĂŒr die Anwendung von einwandigen Kohlenstoffnanoröhren fĂŒr die pH-Sensorik
Einwandige Kohlenstoffnanoröhren (SWCNTs) gelten aufgrund ihrer hohen LadungstrĂ€germobilitĂ€t, des hohen OberflĂ€che-Volumen-VerhĂ€ltnisses und der Tatsache, dass all ihre Atome mit der Umgebung wechselwirken, als hoch interessant fĂŒr die Sensorik. Hier wird ein neues Konzept fĂŒr die Messung des pH-Wertes, der als wichtigster Parameter der FlĂŒssiganalytik gilt, auf Basis von SWCNTs vorgestellt und anhand der Charakterisierung der hergestellten Sensoren die FunktionsfĂ€higkeit nachgewiesen
Quantifying alignment in carbon nanotube yarns and similar twoâdimensional anisotropic systems
The uniaxial orientational order in a macromolecular system is usually specified using the Hermans factor which is equivalent to the second moment of the system\u27s orientation distribution function (ODF) expanded in terms of Legendre polynomials. In this work, we show that for aligned materials that are twoâdimensional (2D) or have a measurable 2D intensity distribution, such as carbon nanotube (CNT) textiles, the Hermans factor is not appropriate. The ODF must be expanded in terms of Chebyshev polynomials and therefore, its second moment is a better measure of orientation in 2D. We also demonstrate that both orientation parameters (Hermans in three dimensional (3D) and Chebyshev in 2D) depend not only on the respective fullâwidthâatâhalfâmaximum of the peaks in the ODF but also on the shape of the fitted functions. Most importantly, we demonstrate a method to rapidly estimate the Chebyshev orientation parameter from a sample\u27s 2D Fourier power spectrum, using an analysis program written in Python which is available for open access. As validation examples, we use digital photographs of dry spaghetti as well as scanning electron microscopy images of directâspun carbon nanotube fibers, proving the technique\u27s applicability to a wide variety of fibers and images
The mechanical and electrical properties of direct-spun carbon nanotube mats
The mechanical and electrical properties of a direct-spun carbon nanotube mat are measured. The mat comprises an interlinked random network of nanotube bundles, with approximately 40 nanotubes in a bundle. A small degree of in-plane anisotropy is observed. The bundles occasionally branch, and the mesh topology resembles a 2D lattice of nodal connectivity slightly below 4. The macroscopic in-plane tensile response is elasto-plastic in nature, with significant orientation hardening. In-situ microscopy reveals that the nanotube bundles do not slide past each other at their junctions under macroscopic strain. A micromechanical model is developed to relate the macroscopic modulus and flow strength to the longitudinal shear response of the nanotube bundles. The mechanical and electrical properties of the mat are compared with those of other nanotube arrangements over a wide range of density
Artificial Neurons on Flexible Substrates: A Fully Printed Approach for Neuromorphic Sensing
Printed electronic devices have demonstrated their applicability in complex electronic circuits. There is recent progress in the realization of neuromorphic computing systems (NCSs) to implement basic synaptic functions using solution-processed materials. However, a fully printed neuron is yet to be realised. We demonstrate a fully printed artificial neuromorphic circuit on flexible polyimide (PI) substrate. Characteristic features of individual components of the printed system were guided by the software training of the NCS. The printing process employs graphene ink for passive structures and In2O3 as active material to print a two-input artificial neuron on PI. To ensure a small area footprint, the thickness of graphene film is tuned to target a resistance and to obtain conductors or resistors. The sheet resistance of the graphene film annealed at 300 °C can be adjusted between 200 Ω and 500 kΩ depending on the number of printed layers. The fully printed devices withstand a minimum of 2% tensile strain for at least 200 cycles of applied stress without any crack formation. The area usage of the printed two-input neuron is 16.25 mm2, with a power consumption of 37.7 mW, a propagation delay of 1 s, and a voltage supply of 2 V, which renders the device a promising candidate for future applications in smart wearable sensors
Photonic Sorting of Aligned, Crystalline Carbon Nanotube Textiles
Floating catalyst chemical vapor deposition uniquely generates aligned carbon nanotube (CNT) textiles with individual CNT lengths magnitudes longer than competing processes, though hindered by impurities and intrinsic/extrinsic defects. We present a photonic-based post-process, particularly suited for these textiles, that selectively removes defective CNTs and other carbons not forming a threshold thermal pathway. In this method, a large diameter laser beam rasters across the surface of a partly aligned CNT textile in air, suspended from its ends. This results in brilliant, localized oxidation, where remaining material is an optically transparent film comprised of few-walled CNTs with profound and unique improvement in microstructure alignment and crystallinity. Raman spectroscopy shows substantial D peak suppression while preserving radial breathing modes. This increases the undoped, specific electrical conductivity at least an order of magnitude to beyond that of single-crystal graphite. Cryogenic conductivity measurements indicate intrinsic transport enhancement, opposed to simply removing nonconductive carbons/residual catalyst
Catalystâmediated enhancement of carbon nanotube textiles by laser irradiation: Nanoparticle sweating and bundle alignment
The photonic post-processing of suspended carbon nanotube (CNT) ribbons made by floating catalyst chemical vapor deposition (FC-CVD) results in selective sorting of the carbon nanotubes present. Defective, thermally non-conductive or unconnected CNTs are burned away, in some cases leaving behind a highly crystalline (as indicated by the Raman G:D ratio), highly conductive network. However, the improvement in crystallinity does not always occur but is dependent on sample composition. Here, we report on fundamental features, which are observed for all samples. Pulse irradiation (not only by laser but also white light camera flashes, as well as thermal processes such as Joule heating) lead to (1) the sweating-out of catalyst nanoparticles resulting in molten catalyst beads of up to several hundreds of nanometres in diameter on the textile surface and (2) a significant improvement in CNT bundle alignment. The behavior of the catalyst beads is material dependent. Here, we show the underlying mechanisms of the photonic post-treatment by modelling the macro- and microstructural changes of the CNT network and show that it is mainly the amount of residual catalyst which determines how much energy these materials can withstand before their complete decomposition
Aligned carbon nanotubeâepoxy composites: the effect of nanotube organization on strength, stiffness, and toughness
Ein neues Konzept fĂŒr die Anwendung von einwandigen Kohlenstoffnanoröhren fĂŒr die pH-Sensorik
Einwandige Kohlenstoffnanoröhren (SWCNTs) gelten aufgrund ihrer hohen LadungstrĂ€germobilitĂ€t, des hohen OberflĂ€che-Volumen-VerhĂ€ltnisses und der Tatsache, dass all ihre Atome mit der Umgebung wechselwirken, als hoch interessant fĂŒr die Sensorik. Hier wird ein neues Konzept fĂŒr die Messung des pH-Wertes, der als wichtigster Parameter der FlĂŒssiganalytik gilt, auf Basis von SWCNTs vorgestellt und anhand der Charakterisierung der hergestellten Sensoren die FunktionsfĂ€higkeit nachgewiesen