Molecular spectroscopy of dye aggregates by scanning-tunneling-microscope-induced light emission

Abstract

A bromide-modified silver (111) surface, covered by Jelly-type aggregates of a cyanine dye, is investigated by scanning tunneling microscopy (STM) in air. We show that, under appropriate conditions, light is emitted out of the junction by inelastic electron tunneling. Study of the relation between the light intensity and the tunnel bias clearly reveals a molecular influence on the light emission. Furthermore, through a spectral analysis, we show that sharp resonances appear for dye-covered surfaces by coupling of tip-induced plasmons with molecular excitations. This demonstrates that through STM-induced luminescence local spectroscopic information can be obtained on molecules.

Characterization of light emission from subphthalocyanine monolayers using scanning tunneling microscopy

“…The adsorption of molecules on metal surface is known to modify the plasmon-mediated emission spectra as the molecule acts as a spacer to change the dielectric property and junction geometry between the tip and surface [16 -18]. On the other hand, other reports suggest the contribution of molecular fluorescence to the STM-LE spectrum [14,15].…”

Modulation of local plasmon mediated emission through molecular manipulation

“…Extensive research of STM-induced luminescence has been reported on metal surfaces, 2,3 semiconductors, 4,5 and molecules. [6][7][8] Early studies of STM-induced luminescence from C 60 molecules adsorbed on Au͑111͒ suggested that photon emission was from molecules. 6 Only until 2002, Hoffmann et al 9 demonstrated that the adsorbed molecules in the first monolayer ͑ML͒ act merely as spacers to modify plasmon mediated emission from the metal surface.…”

Spectroscopic study of J aggregates of amphiphilic merocyanine dyes formed in their pure Langmuir films

“…[2][3][4][5][6] They exhibit a narrow and red-shifted electronic absorption band ͑J band͒ and strong fluorescence with a small Stokes shift. These characteristic optical properties, which are the origins of their expected functions, are nicely explained by the interaction between the transition dipole moments ( tr 's͒ of the dyes arranged in the so-called ''head-to-tail'' manner.…”