Angle-resolved photoemission spectra

The lower panel of Fig. 4 reproduces angle-resolved photoemission spectra [43] showing the dispersion of the state, i.e. how its BE changes with the angle of emission with respect to the normal. The dotted line in Fig. 3 shows schematically the E(k ) upwards parabolic dispersion of the surface state. The Binding Energy (BE) of the Cu(lll) surface state at the center of the 2D Brillouin Zone (BZ) is —400 meV relative to the Fermi energy. The effective mass for the electrons in this state is obtained from the curvature... 

Fig. 12a, b. Angle resolved photoemission spectra of CO adsorbed on Ni(100) at a photon energy of 28 eV. (a) Nearly p-polarized light (b) s-polarized light [76Smi]. 

The above discussion also holds for valence band emission, with the exception of the line positions. In angle-resolved photoemission spectra, the peak positions move on the energy scale when the emission direction relative to the crystal axes is varied. From this peak dispersion, the energy versus momentum relation e k) of the solid bulk or surface can be deduced by simple kinematical arguments (Section 3.2.2.4.2). 

Figure 3.2.2.24 Angle-resolved photoemission data from the Shockley surface state on the clean Cu(lll) surface. In (a), spectra near the Fermi energy and near normal emission are displayed for equidistant polar angles between —8° (top spectrum) and -F8° (bottom spectrum). Note that the selected energy scale renders binding energies as negative numbers, (b) A corresponding data...

In the investigations of molecular adsorption reported here our philosophy has been to first determine the orientation of the adsorbed molecule or molecular fragment using NEXAFS and/or photoelectron diffraction. Using photoemission selection rules we then assign the observed spectral features in the photoelectron spectrum. On the basis of Koopmans theorem a comparison with a quantum chemical cluster calculation is then possible, should this be available. All three types of measurement can be performed with the same angle-resolving photoelectron spectrometer, but on different monochromators. In the next Section we briefly discuss the techniques. The third Section is devoted to three examples of the combined application of NEXAFS and photoemission, whereby the first - C0/Ni(100) - is chosen mainly for didactic reasons. The results for the systems CN/Pd(111) and HCOO/Cu(110) show, however, the power of this approach in situations where no a priori predictions of structure are possible. 

Fig. 3. Angle resolved He ll ultraviolet photoemission spectrum of a V205(010) surface sample taken at normal incidence from Refs. [93,94].

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