Modification of Ag(111) surface electronic structure via weak molecular adsorption of adenine measured with low temperature scanning tunneling microscopy and spectroscopy.

Low temperature scanning tunneling microscopy and spectroscopy have been used to resolve modifications to the Ag(111) surface electronic structure due to the weak adsorption of the nucleobase adenine. Differential conductance spectroscopy recorded at 15 K reveals an upward energetic shift of the surface state native to Ag(111) from a band edge of -67 meV on the clean surface to +82.5 meV recorded over adenine islands. Differential conductance images show the impact of adenine domains on the density of available states as a function of energy relative to the uncovered Ag terraces as well as free-electron-like scattering in the adenine domains. Dispersion of the parallel wave vector of scattered electrons in the adenine domains is compared with the dispersion for electron scattering in bare silver and the ratio of effective masses for electrons in those bands is 1.1±0.2. It is hypothesized that this shift occurs due to a combination of effects brought on by the adsorption of adenine including dielectric screening of the first image potential. [ABSTRACT FROM AUTHOR]