Highly Stable, Protected Plasmonic Nanostructures for Tip Enhanced Raman Spectroscopy

An ultrathin aluminum oxide (Al2O3) coating improves significantly the stability of plasmonic structures used in tip enhanced Raman spectroscopy (TERS). The coating does not alter the favorable optical properties of metallic structures yet improves wear resistance and inhibits degradation, so that signal enhancement remains constant over 40 days for structures with a 3 nm thick protective coating. Most unprotected structures show substantial losses in enhancement over periods as short as 10 days when stored and used in ambient conditions.