Researchers in the Duke Physics and ECE departments have demonstrated that nanometer-sized antennas can greatly enhance local electromagnetic fields in the ultraviolet. The field of plasmonics explores how to engineer metallic structures to control and concentrate electromagnetic fields, especially in dimensions very small compared to the wavelength of the radiation. It has been known for some time that gold and silver nanostructures act as antennas for infrared and visible wavelength radiation, and the local field concentrations produced by these nanostructures can easily enhance the strength of spectra from nearby analytes by factors of greater than one million. However, gold and silver do not work in the ultraviolet where even greater opportunities for field enhancement lie, so a search for new plasmonic metals with ultraviolet responses was needed.
Profs. Henry Everitt (Physics) and April Brown (ECE) had been studying the growth and optical properties of metallic films of gallium deposited by molecular beam epitaxy. Gallium naturally forms arrays of nanometer-scale hemispheroidal droplets after an initial wetting layer covers the substrate surface. Graduate student Yang Yang and research scientist Tong-Ho Kim made several such arrays of gallium nanoparticles, and with research engineer John Callahan, they observed the spectra of the dye crystal violet to be locally enhanced by as much as ten million. This groundbreaking work in ultraviolet nanoplasmonics was published in May, 2013 in the journal "NanoLetters" which can be read here.