Direct printing of graphene terahertz closed-ring resonator array from periodic single droplets via enhanced coffee-ring effect

Graphene terahertz (THz) devices have emerged as a pivotal player in the THz area, and drop-on-demand (DOD) printing technology enables cost-effective patterning of THz microstructures. However, fast printing of THz microstructures and devices suffers from low efficiency owing to the drop-by-drop overlapping process. Here, we have developed a facile direct printing method to fabricate graphene THz closed-ring resonator (CRR) arrays from periodic single droplets ascribing to the enhanced coffee-ring effect. The construction of a complete graphene micro-ring was achieved using small reduced graphene oxide sheets, enabling the strategy of a graphene CRR from one single droplet. We attributed the mechanism of strengthened coffee-ring effect to the swift pinning, gapless between the contact line and the solute line, and close packing. Finally, we prepared a graphene THz CRR array featuring fine rings with widths of ∼12.3 μm, a high THz extinction ratio of 66.9%, and the highest measurement λ (relative THz response) of 9.8 documented so far for graphene-based THz microstructures and devices. Such an array from the expeditious DOD printing process exhibits a pronounced THz response and possible fast switching speed, which suggests new possibilities in building graphene THz microstructures, benefiting the future development of graphene THz devices. [Display omitted] •Fabrication of graphene terahertz closed-ring resonator array by direct printing.•Single-droplet printing strategy with high-efficiency by enhanced coffee-ring effect.•Complete graphene micro-rings via small flakes due to fast pinning and close packing.•Array with fine rings of ∼12.3 μm in width and strong terahertz response was built.