Ultra high-yield synthesis of self-assembled, conductive, and superhydrophobic three-dimensional mats of carbon nanofibers via full catalysis of unconstrained thin film

Efrat Shawat Avraham, Chemistry, Bar-Ilan university, Ramat-Gan, Israel

Carbon nanofibers (CNFs) are ideal candidates for a range of important applications; However, to realize industrial application of these materials, processes must be developed to produce CNfs with desired structural characteristics, and with high yields.

Using a specific weak adhesion layer between the CNf catalyst and the substrate, we produced a catalytic thin film that delaminates inside our chemical vapor deposition (CVD) reactor during synthesis.  Following delamination, removal of the mechanical constraint of the catalyst layer to the substrate led to mats of carbon nanofibers that were 3X to 5X larger than the substrate they originated from. The mass of these three-dimensional (3-D) CNF mats made of cm-long (fibers was over an order of magnitude that of the micron-tall entangled CNFs we obtained using the same process on samples with stronger adhesion layers).  Following an extensive characterization of the morphology and structure of the CNF mats in concert with a parametric study of the effect of temperature, pre-anneal conditions, growth duration, and substrate materials, we found evidence of a correlation between growth conditions and the 3-D mat morphological properties.  This work gives insight into a new growth process whereby high yields of 3-D carbon nanostructures can be directly obtained with from an unconstrained catalytic thin film, utilizing a rational choice of catalyst/underlayer combinations and growth conditions. This yield is over an order of magnitude higher compared to the “standard” substrate-constrained catalytic growth. Based on the extensive characterizations done to date, we can explain specific aspects of the new growth mechanisms based on thin film evolution, simultaneous delamination, and carbon nucleation of the catalytic thin film. Such materials have significant promise as conductive material scaffolds for a wide-range of next-generation materials that can take advantage of the high surface area and good mechanical robustness of such CNF structures. 

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