Electrically Gated Organic-Based Metadevice for THz Amplitude Modulation

In the last years, the interest in THz technologies has increased rapidly due to their applicability across several application scenarios like telecommunication and sensing, with recent developments overarching the fields of optics and electronics [1]. Despite their scientific and technological appeal, THz waves have a major drawback coming from the absence of optoelectronic techniques and devices that can manipulate such light waves. To solve this issue, one of the most promising approaches relies on the use of metasurfaces [2], engineered composites whose optical properties can be specifically tailored to interact with THz waves. Therefore, research is now focused on trying to design reconfigurable metamaterials, also known as metadevices, able to modulate the amplitude, phase, and frequency of THz pulses, to achieve the highest modulation depth and switch speed possible [3]. Among the plethora of proposed modulation strategies based on optical, electro-mechanical, or thermal stimuli, electrically-tuned THz metadevices represent a flourishing approach that directly benefits from the development of novel and unconventional transistor configurations.<br/>In our work, we explore for the first time the functioning and the effectiveness of an organic semiconductor-driven metadevice based on a matrix of metal Split-Ring Resonators, which can modulate the amplitude of a THz pulse passing through them [4]. This approach has already been shown to work nicely in the microwave spectral region [5] but has not yet been applied in the THz range. The modulation capabilities come from the electrically driven change of charge carrier density in the organic semiconductor, which enables the metadevice to act as an optical transistor, varying THz transmission around a specific frequency (~0.7 THz) with modulation depths of approximately 65%. These performances, which are comparable with current state-of-the-art technologies but with a way lower driving voltage (&lt;1 V) result from the unique 3-dimensional charge modulation properties of a new class of organic mixed ion-electron conductors based on conjugated polymers with glycolated sidechains, such as the emerging p(g2T-TT) semiconductor.<br/>Also, another key aspect of our work is to show that it is then possible to shift towards mass-scalable and cost-effective manufacturing techniques exploiting high-throughput deposition methods for both the metamaterial matrix and the organic semiconductor, on either rigid or flexible plastic substrates, without losing modulation efficiency.<br/>In conclusion, we hope that this work will lead to the further development of metadevice technologies based on organic semiconductors, with the future aim of improving the effectiveness of this modulating technique in the THz spectral region, especially in terms of modulating speed. Moreover, this device development comes together with an ongoing study on the THz properties of this emerging class of organic semiconductors, leading to fundamental scientific insights that could also find application in other areas, such as electronics and bioelectronics.<br/>[1] Samizadeh Nikoo, M., & Matioli, E. (2011). <i>Nature</i> <b>614</b>, 451–455 (2023). https://doi.org/10.1038/s41586-022-05595-z<br/>[2] Degl’Innocenti, R., Lin, H. & Navarro-Cía, M. (2022). Nanophotonics, 11(8), 1485-1514. https://doi.org/10.1515/nanoph-2021-0803<br/>[3] Wang, L., Zhang, Y., Guo, X., Chen, T., Liang, H., Hao, X., Hou, X., Kou, W., Zhao, Y., Zhou, T., Liang, S., & Yang, Z. (2019). Nanomaterials, 9(7), 965. https://doi.org/10.3390/nano9070965<br/>[4] Chen, H., Padilla, W. J., Zide, J. M. O., Gossard, A. C., Taylor, A. J., & Averitt, R. D. (2006). Nature, 444(7119), 597–600. https://doi.org/10.1038/nature05343<br/>[5] Bonacchini, G. E., & Omenetto, F. G. (2021). Nature Electronics, 4(6), 424–428. https://doi.org/10.1038/s41928-021-00590-0