Engineering ultrasensitive probes of nanoscale physical and chemical processes
Sometimes, it seems as if molecules struggle to communicate with scientists. When it comes to junction plasmons, essentially light waves trapped at tiny gaps between noble metals, what the molecules have to say could radically change the design of detectors used for science and security. Single molecule detection sensitivity is feasible through Raman scattering from molecules coaxed into plasmonic junctions. Scientists at Pacific Northwest National Laboratory (PNNL) found that sequences of Raman spectra recorded at a plasmonic junction, formed by a gold tip and a silver surface, exhibit dramatic intensity fluctuations, accompanied by switching from familiar vibrational line spectra of a molecule to broad band spectra of the same origin. The fluctuations confirm the team's earlier model that assigns enhanced band spectra in Raman scattering from plasmonic nanojunctions to shorting of the junction plasmon through intervening molecular bridges.