K.H. Nam, M. Abdulhafez, G.N. Tomaraei, M. Bedewy
University of Pittsburgh,
Keywords: graphene, direct-write, heteroatoms, microelectrodes, laser processing
Summary:Laser-induced graphene (LIG) has been shown to form directly on flexible substrates, owing to the rapid absorption of infrared radiation, which locally graphitizes aromatic polyimides (PIs). This elegant process enables the scalable manufacturing of functional microelectrodes with hierarchical three-dimensional graphene structures in a direct-write fashion. Nevertheless, the atomic structure of the produced graphene, as well as the presence of any chemical dopants, has been largely limited hitherto by the chemical formulation of commercial polyimides. In this work, we present a facile approach for patterning heteroatom-doped, hierarchically porous graphene from PI films using a continuous-wave 10.6 μm CO2 laser in ambient air. First, we utilize conventional two-step polymerization to synthesize molecularly controlled PIs from 4,4'-oxydianiline and three different commercially available tetracarboxylic dianhydrides with different internal linkages such as phenylene, trifluoromethyl or sulfone groups. We show that controlling both the chemical structure of PIs and the laser fluence uniquely enables tuning the physicochemical transformation to heteroatom self-doped graphene with N-doping, F-doping, and S-doping. Accordingly, we demonstrate the ability to tailor the electrical and electrochemical properties of doped LIG. Importantly, our F-doped LIG exhibits electrical resistivity lower than ~13 Ω sq–1. Also, we demonstrate the use of both the F-doped and S-doped LIG electrodes for electrochemical sensing of neurotransmitters. Moreover, we leverage this technique to create superhydrophobic and parahydrophobic surfaces with anisotropic wetting and switchable adhesion. Hence, our one-step direct-write fabrication process paves the way for a number of technological innovations requiring spatial control of doped graphene patterns on flexible substrates.