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Carbonassisted catalyst pretreatment enables straightforward synthesis of high-density carbon nanotube forests. Carbon

Dark-field microscopy is a standard imaging technique widely employed in biology that provides high image contrast for a broad range of unstained specimens 1. Unlike bright-field microscopy, it accentuates high spatial frequencies and can therefore be used to emphasize and resolve small features. However, the use of dark-field microscopy for reliable analysis of blood cells, bacteria, algae, and other marine organisms often requires specialized, bulky microscope systems, and expensive additional components, such as dark-field-compatible objectives or condensers 2,3. Here, we propose to simplify and downsize dark-field microscopy equipment by generating the high-angle illumination cone required for dark field microscopy directly within the sample substrate. We introduce a luminescent photonic substrate with a controlled angular emission profile and demonstrate its ability to generate high-contrast dark-field images of micrometre-sized living organisms using standard optical microscopy equipment. This new type of substrate forms the basis for miniaturized lab-on-chip dark-field imaging devices, compatible with simple and compact light microscopes.

Composites of polymers and organized carbon nanotube (CNT) networks have been proposed as next-generation lightweight structural materials, yet polymer infiltration of CNT networks often results in stress-concentrating heterogeneities, due to local CNT aggregation or incomplete infiltration. Herein, it is demonstrated that dense CNT-polymer composites with tailored polymer distribution can be obtained by interfacial polymerization (IP), performed in situ within CNT networks. Three regimes of the in situ interfacial polymerization (ISIP) process are identified: a reaction-limited regime where the polymer forms beads on the CNTs; a uniformly-filled regime with polymer throughout the CNT network; and a transport-limited regime with polymer only near the outer surface of the network. Uniform polyamide-CNT composite sheets obtained by this method have a Young's modulus of 31 GPa and a tensile strength of 776 MPa, which is a twofold increase compared to the pristine CNT sheets. Premature failure of the composites is attributed to large voids in the pristine CNT sheets, suggesting that further improved mechanical properties can be achieved with a more homogeneous CNT network. Nevertheless, the rapid rate and overall controllability of ISIP suggest its viability for formation of polymers within CNT networks via roll-to-roll methods.

Vertically aligned carbon nanotubes (CNTs)also called CNT forestsare attractive for use in battery electrodes, capacitive sensors, thermal interface materials, and many other applications. However, for practical use in most cases, the CNT forest must be dense and have mechanically robust, low-resistance electrical contact with the substrate. Fulfilling those requirements is often challenging, particularly when copper is used as the substrate material. Herein, we report production of tall (270 μm maximum height) CNT forests on copper foils, by chemical vapor deposition by combining a supported catalyst structure with gaseous carbon preconditioning of the catalyst prior to film dewetting and annealing. Incorporation of tungsten in the catalyst support prevents diffusion of the iron catalyst into the underlying copper and promotes the formation of a high density population of catalyst particles. We find that the electrical resistance of the CNT forest scales with height, and correlated with X-ray scattering measurements of CNT density.