Monitoring Conductivity of Flexible Stretchable Conductive Films Using Terahertz Time-Domain Spectroscopy and Imaging

Thin, flexible, conductive materials that can be deposited on a variety of substrates are required for applications as varied as wearable electronic devices or coatings for shielding electronic devices from electromagnetic interference. Examples of such materials include flexible polymers loaded with carbon nanomaterials or 2D MXenes, or liquid metals based on gallium^1-3. Their requisite property is the ability to maintain high conductivity during deformation. Here, we demonstrate that terahertz time-domain spectroscopy (THz TDS) and imaging provide a way for in-situ non-contact monitoring of conductivity under strain and deformation⁴. Broadband THz pulses with 0.2 – 3 THz bandwidth are strongly absorbed by the free charge carriers, while the flexible polymers typically used as substrates for flexible electronic devices are, for the most part, transparent in the THz range. Thus, measuring absorption and reflection of THz pulses with ~ 1 mm spatial resolution allows monitoring conductivity as well as electromagnetic interference shielding efficiency in the THz range. Relating the changes in transmission and reflection to the applied strain also allows determination of the failure threshold of the flexible conductive materials.<br/><br/>MZ acknowledges support from NASA Rhode Island Space Grant Undergraduate Fellowship, and LLF acknowledges support from the Clare Boothe Luce Graduate Fellowship.<br/><br/>1. Park, S.; Vosguerichian, M.; Bao, Z. A review of fabrication and applications of carbon nanotube film-based flexible electronics. Nanoscale 2013, 5 (5), 1727-1752, 10.1039/C3NR33560G. DOI: 10.1039/C3NR33560G.<br/>2. Li, L.; Fu, X.; Chen, S.; Uzun, S.; Levitt, A. S.; Shuck, C. E.; Han, W.; Gogotsi, Y. Hydrophobic and Stable MXene–Polymer Pressure Sensors for Wearable Electronics. ACS Applied Materials & Interfaces 2020, 12 (13), 15362-15369. DOI: 10.1021/acsami.0c00255.<br/>3. Chen, S.; Cui, Z.; Wang, H.; Wang, X.; Liu, J. Liquid metal flexible electronics: Past, present, and future. Applied Physics Reviews 2023, 10 (2). DOI: 10.1063/5.0140629.<br/>4. Jepsen, P. U.; Cooke, D. G.; Koch, M. Terahertz Spectroscopy and Imaging–Modern Techniques and Applications. Laser & Photonics Reviews 2011, 5 (1), 124-166.