Charles Otieno Ogolla (Siegen / DE), Marco Hepp (Siegen / DE), Huize Wang (Potsdam / DE), Jim Ciston (Berkeley, CA / US), Colin Ophus (Berkeley, CA / US), Gyanendra Panchal (Berlin / DE), Simon Delacroix (Paris / FR), Daniel Cruz (Berlin / DE; Mülheim an der Ruhr / DE), Danny Kodja (Berlin / DE), Axel Knop-Gericke (Mülheim an der Ruhr / DE; Berlin / DE), Klaus Habicht (Potsdam / DE; Berlin / DE), Benjamin Butz (Siegen / DE), Volker Strauss (Potsdam / DE)
Abstract text (incl. figure legends and references)
Nitrogen-doped carbon materials (NCM) have emerged as cost-effective, environmentally friendly, and readily available starting materials for gas sensing device fabrication. They allow for the systematic tuning of properties for superior selectivity and sensitivity to specific analytes (volatile organic compounds and specific gases) by carefully choosing the precursor materials. CO2 sensing is one of the major applications where such materials have been implemented. So far, miniaturized CO2 sensors are based on sophisticated nanomaterials like selected, doped carbon nanotubes [1].
In this study, a one-step laser patterning procedure is applied to an optimized ink coating to directly generate complete and highly porous sensor architectures (~50 micrometer overall thickness) even on flexible PET substrates. The versatile ink is based on abundant organic precursors like adenine (nitrogen source for sensing functionality) and glucose as a pore-forming agent. Thermal laser treatment of the precursor material in an oxygen-containing environment allows us to fabricate complete sensor heterostructures with defined nitrogen and oxygen functionalities. The attenuation of the laser irradiation is depth dependent and results in the formation of a defined graphitic surface layer and a nitrogen-rich lower region (sensing layer) separated by a transition region.
To understand the structure formation by laser treatment as well as device functionality, a thorough scale-bridging investigation was conducted. Microtomic cross sectioning is employed to prepare high quality TEM cross-sections (0.25 - 0.5 t/λ) [2].
Elemental distribution maps from STEM-EELS data depicted a clear separation between the upper and lower layers. STEM-EELS chemical and bond analysis across the whole device allowed the clear differentiation between distinct amorphous and crystalline phases, and thus between different functional layers of the heterostructure. Therefore, principal component analyses were applied due to the complexity of the laser-generated material.
The distribution of the crystalline graphitic phase, the degree of ordering graphitization and the alignment of the basal planes were investigated in detail by 4D-STEM (see Fig 1.)as those parameters impact on the electrical conductivity of the sensor. In addition, the data analysis method employed, sparse correlation matching, as implemented in py4DSTEM [3] facilitates the detailed analysis of the structural peculiarities of the amorphous phases.
Keywords: laser-patterned CO2 sensor, graphitic, nitrogen-doped carbon
Acknowledgements: We acknowledge funding support from the Fonds der Chemischen Industrie and the Max Planck Society, use of the DFG-funded Micro-and Nanoanalytics Facility (MNaF) at the University of Siegen (INST 221/131-1) and the National Center for Electron Microscopy (NCEM) in the Molecular Foundry (MF) at the Lawrence Berkeley National Laboratory (LBNL) supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
[1] Inagaki, Michio, et al. Carbon 2018, 132, 104-140.
[2] Hepp, Marco, et al. npj Flexible Electronics 2022, 6.1, 1-9.
[3] Ophus, Colin, et al. Microscopy and Microanalysis 2022, 28.2, 390-403.