Modification of the Cu(110) Shockley surface state by an adsorbed pentacene monolayer

The modification of the Cu(110) Shockley-type surface state by an adsorbed pentacene layer was determined using high-resolution angle-resolved photoelectron spectroscopy. It was found that the surface state is shifted by 80–120 meV to higher binding energies, depending on the pentacene coverage. In addition, an increase in the surface-state population is measured for the sample adsorbed with one monolayer of pentacene. The modification of the surface state by the adsorption of pentacene is put into relation to a complex interplay of different phenomena such as the hybridization and mixing of electronic states, the polarization of the adsorbate in the surface dipole, and the Pauli repulsion. Thus, this observation of a molecular adlayer shifting a surface state away from the Fermi energy sheds more light on the adsorbate-adsorbent interactions.

Figure 1

(Color online) Observed adlayer structures for submonolayer and monolayer coverages of pentacene on Cu(110): (a) 0.8 ML; (b) 1.0 ML. Top: STM images $30\times 40{\text{nm}}^2$. Insets: corresponding LEED patterns taken at (a) 53.5 and (b) 63.0 eV. Bottom: structural models with unit cells marked in pale gray (yellow).

Figure 2

(Color online) Dispersion of the $\overline{Y}$ surface state of the clean Cu(110) surface. (a) Dispersion along $\overline{Y}\text{−}\overline{S}$. (b) Cut through the $\overline{Y}$ surface state at the Fermi energy. Inset: sketch of the upper-right quadrant of the surface Brillouin zone with the Fermi line of the surface state marked in gray (red). (c) Dispersion along $\overline{\Gamma }\text{−}\overline{Y}$. The grayscale plots represent the photoelectron intensity after normalization by a Fermi step function and conversion to $k$-vector scale (dark corresponds to high intensity). The pale gray (yellow) lines mark the fit of a paraboloid to the experimental data.

Figure 3

(Color online) Dispersion of the $\overline{Y}$ surface state of a Cu(110) surface, covered with (a)–(c) 0.8 ML pentacene and (d)–(f) 1.0 ML pentacene. The straight lines marked in pale gray (yellow) mark the fit of a paraboloid to the experimental data. The dotted lines marked in gray (red) correspond to the paraboloid fitted to the experimental data of the clean Cu(110) surface from Fig. 2.