Domain Sensitive Contrast in Photoelectron Emission Microscopy

We have investigated the adsorption of cesium on the Si(100) surface with photoelectron emission microscopy using linearly polarized green laser light. We observe a polarization dependent contrast between the ($2\times 1$) or ($1\times 2$) reconstructed terraces. Density-functional calculations reveal the geometric and electronic structure of the $\mathrm{Cs}/\mathrm{Si}(100)$ surface. The contrast between the ($2\times 1$) or ($1\times 2$) reconstructed domains is explained on the basis of dipole selection rules for the photoemission matrix elements.

Figure 1

PEEM image of the cesiated Si(100) surface at room temperature using linearly polarized green laser light. The two different types of terraces (A and B) show different photoemission yield depending on the polarization of the incident light. The shown figure is an asymmetry image between a micrograph taken with $p$-polarized light and one taken with $s$-polarized light to enhance the contrast.

Figure 2

Polarization dependence of domain contrast between areas A and B from Fig. 1. The solid line is a fit to the data according to Eq. (3) together with an additional exponential decay due to the slight desorption of Cs during the experiment.

Figure 3

Kohn-Sham band-structure of the $\mathrm{Cs}/\mathrm{Si}(001)$ surface at 0.5 ML coverage in valley-bridge adsorption geometry. Brown marked surface bands are characterized by Cs states, the yellow marked band is derived from the empty $p$-like state at the lower Si atom of the buckled dimer. The blue surface bands are derived from the filled states at the upper Si-dimer atom and the $\pi$ bonding state at the symmetric dimer. The red marked surface band is characterized by a ${\pi }^{*}$-antibonding state at the symmetric dimer. The green hatched area denotes that part of the band-structure from which electrons excited with a 2.33 eV photon can be emitted into the vacuum.

Figure 4

Definition of the angle of polarization $\phi$ and angle of incidence of the light $\theta$.