Characterization of light emission from subphthalocyanine monolayers using scanning tunneling microscopy

Monolayers of subphthalocyanine were prepared by molecular beam epitaxy and self-assembled depositions on the Au (111) surface. Light emission from the monolayers was measured by photoexcitation as well as tunneling current excitation using scanning tunneling microscopy under ultrahigh vacuum. The photoexcited spectra of the monolayers deposited by both methods exhibited the fluorescence bands of π-electronic transition of the subphthalocyanine macrocycle although their lifetime was very shortened due to quenching by the Au surface. The tunneling induced emission was taken from the self-assembled monolayers in which the subphthalocyanine molecules were chemically bound onto the surface by alkylthio substituents. The observed spectra were ascribed to the radiative decay of tip-induced surface plasmon of Au. The molecules in the self-assembled monolayers shifted the emission peak due to modification of the dielectric property and distance between the tip and surface.