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It is generally accepted that inducing molecular alignment in a polymer precursor via mechanical stresses influences its graphitization during pyrolysis. However, our understanding of how variations of the imposed mechanics can influence pyrolytic carbon microstructure and functionality is inadequate. Developing such insight is consequential for different aspects of carbon MEMS manufacturing and applicability, as pyrolytic carbons are the main building blocks of MEMS devices. Herein, we study the outcomes of contrasting routes of stress-induced graphitization by providing a comparative analysis of the effects of compressive stress versus standard tensile treatment of PAN-based carbon precursors. The results of different materials characterizations (including scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, as well as high-resolution transmission electron microscopy) reveal that while subjecting precursor molecules to both types of mechanical stresses will induce graphitization in the resulting pyrolytic carbon, this effect is more pronounced in the case of compressive stress. We also evaluated the mechanical behavior of three carbon types, namely compression-induced (CIPC), tension-induced (TIPC), and untreated pyrolytic carbon (PC) by Dynamic Mechanical Analysis (DMA) of carbon samples in their as-synthesized mat format. Using DMA, the elastic modulus, ultimate tensile strength, and ductility of CIPC and TIPC films are determined and compared with untreated pyrolytic carbon. Both stress-induced carbons exhibit enhanced stiffness and strength properties over untreated carbons. The compression-induced films reveal remarkably larger mechanical enhancement with the elastic modulus 26 times higher and tensile strength 2.85 times higher for CIPC compared to untreated pyrolytic carbon. However, these improvements come at the expense of lowered ductility for compression-treated carbon, while tension-treated carbon does not show any loss of ductility. The results provided by this report point to the ways that the carbon MEMS industry can improve and revise the current standard strategies for manufacturing and implementing carbon-based micro-devices.

Abstract Carbon's electrochemistry depends on its type and microstructure, and how these affect the electrode's electronic density of states. We demonstrate how pyrolysis of electro-mechanically stressed Polyacrylonitrile (PAN) nanofibers, infused with carbon nanotubes, will result in a unique graphitic electrode, which possesses enhanced and multifaceted electrochemical behavior. As corroborated by materials characterization, the microstructure of the stress-activated pyrolytic carbon (SAPC) characteristically contains a high proportion of disorders in the forms of edge planes and embedded heterogeneous nitrogen atoms. These disorders introduce a range of energy states near the Fermi level, yielding enhanced kinetics in the as-synthesized SAPC electrodes. A comprehensive electrochemical study of the SAPC electrode in surface sensitive ([Fe(CN) 6 ]3-/4-), surface insensitive ([IrCl 6 ]2-/3-), and adsorption sensitive (dopamine) redox probes demonstrates 5–14-fold increases in its heterogeneous electron transfer rate compared to regular PAN-based carbon electrodes. The fast kinetics of SAPC electrodes in adsorption sensitive analytes translates into its capability for simultaneous detection of dopamine, uric acid, and ascorbic acid. The results point to a new class of pyrolytic carbon electrodes with an attractive electrocatalytic capacity, geared toward electrochemical sensing platforms. Highlights • Pyrolysis of stress-treated polymer nanofibers results in graphitized carbon. • Microstructure of pyrolyzed carbon is rich in edge planes and nitrogen heteroatoms. • Disorder-induced electroactive sites enhance carbon probes electrochemical kinetics. • Stress-activated carbon can simultaneously detect dopamine, uric and ascorbic acids. • Electrocatalytic activity of stress-activated carbon holds promise for sensing. [ABSTRACT FROM AUTHOR]

Catalytic substrate, which is devoid of expensive noble metals and enzymes for hydrogen peroxide (H2O2), reduction reactions can be obtained via nitrogen doping of graphite. Here, we report a facile fabrication method for obtaining such nitrogen doped graphitized carbon using polyacrylonitrile (PAN) mats and its use in H2O2 sensing. A high degree of graphitization was obtained with a mechanical treatment of the PAN fibers embedded with carbon nanotubes (CNT) prior to the pyrolysis step. The electrochemical testing showed a limit of detection (LOD) 0.609 μM and sensitivity of 2.54 μA cm-2 mM-1. The promising sensing performance of the developed carbon electrodes can be attributed to the presence of high content of pyridinic and graphitic nitrogens in the pyrolytic carbons, as confirmed by X-ray photoelectron spectroscopy. The reported results suggest that, despite their simple fabrication, the hydrogen peroxide sensors developed from pyrolytic carbon nanofibers are comparable with their sophisticated nitrogen-doped graphene counterparts. [ABSTRACT FROM AUTHOR]

We report on the successful synthesis of a graphene–carbon nanotube (CNT) hybrid architecture by a parallel chemical vapor deposition (CVD) of the two carbon allotropes. The carbon hybrid is a three-dimensional (3D) nanostructure with tuneable architecture comprising vertically grown CNTs as pillars and a large-area graphene plane as the floor. The formation of CNTs and graphene occurs simultaneously in a single CVD growth that we describe as a synchronous synthesis method. Unique nature of the fabrication approach contributes significantly to the quality and composure of final nanohybrid. Detailed characterization elucidates the cohesive structure and robust contact between the graphene floor and the CNTs in the hybrid structure. The functionality of the synthesized graphene hybrid structure has been demonstrated by its incorporation into a supercapacitor cell. Our fabrication approach provides an attractive pathway for the fabrication of novel 3D hybrid nanostructures and efficient device integration. [ABSTRACT FROM AUTHOR]