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Colossal Absorption of Molecules Inside Single Terahertz Nanoantennas

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journal contribution
posted on 10.04.2013 by Hyeong-Ryeol Park, Kwang Jun Ahn, Sanghoon Han, Young-Mi Bahk, Namkyoo Park, Dai-Sik Kim
Molecules have extremely small absorption cross sections in the terahertz range even under resonant conditions, which severely limit their detectability, often requiring tens of milligrams. We demonstrate that nanoantennas tailored for the terahertz range resolves the small molecular cross section problem. The extremely asymmetric electromagnetic environment inside the slot antenna, which finds the electric field being enhanced by thousand times with the magnetic field changed little, forces the molecular cross section to be enhanced by >103 accompanied by a colossal absorption coefficient of ∼170 000 cm–1. Tens of nanograms of small molecules such as 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and lactose drop-cast over an area of 10 mm2, with only tens of femtograms of molecules inside the single nanoslot, can readily be detected. Our work enables terahertz sensing of chemical and biological molecules in ultrasmall quantities.