Terahertz spectroscopy reaches single molecules

Abstract

Terahertz spectroscopy has become a useful tool for studying materials because the energy and timescale of terahertz radiation match those of electron transitions, molecular vibrations, and other molecular excitations. But the radiation’s long wavelengths have prevented researchers from using the technique to study single molecules. One team of researchers now reports they’ve used an antenna to observe vibrations in a single 60-carbon buckyball (Nat. Photonics 2018, DOI: 10.1038/s41566-018-0241-1). Terahertz wavelengths are about 100 µm, 100,000 to 1 million times as large as a typical molecule, even a large one like a buckyball, which is about 1 nm across. To overcome that size discrepancy, Kazuhiko Hirakawa and postdoctoral researcher Shaoqing Du of the University of Tokyo and colleagues trapped a buckyball at the tips of two triangular gold electrodes, which acted as an antenna to focus the radiation. The researchers applied a voltage across the electrodes, allowing them to measure changes