Angle Resolved UPS

UPS and XPS (Ultraviolet and X-Ray Photoemission Spectroscopy) and ARUPS (Angle-Resolved UPS)... 

Angle-resolved UPS studies of polymers and interfaces Although few polymer systems exist in the form of single crystals, it can be expected that in the future, polymer systems will be prepared which are more ordered. The studies reviewed here are prototypical of what can be done on ordered polymer systems, and lay the basis for future work on ordered systems using photoelectron spectroscopies. 

The measurements were carried out using polarized-light from synchrotron radiation. The angle-resolved UPS spectra were recorded for specific directions of photon incidence, photon polarization, and electron exit, chosen in order to resolve the momentum dependence of the 7t-electron energy bands which could be observed in this experiment. Details are available elsewhere63. The UPS results are analysed not only with the help of the valence effective Hamiltonian (VEH) method, but also with the help of new quantum-chemical calculations based upon the excitation model method64. The full VEH band structure is shown in Fig. 7.32. 

Angle-resolved UPS, LEED 50a Heating or exposure to H2S of a c(2 x 2) structure introduces a new binding state in the subsurface... 

Angle-resolved UPS 50b Study of the detailed electronic structure of c(2 x 2) and p 2 x 2) overlayers shows important differences in the S 3p levels. Sulfur adsorption causes changes in the Ni 3d bond... 

Ultra-violet photoemission spectroscopy (UPS) probes the density of states, and ion neutralization spectroscopy (INS) and surface Penning ionization (SPI) provide similar information with probes of ions and metastable atoms, respectively. Angle-resolved UPS can determine the valence band structure. X-ray Photoelectron Spectroscopy (XPS) provides information on chemical shifts of the atomic core levels, and this can also help in understanding chemical bonding at the surface. 

Identification of Bonding Effects and Adsorption Geometries - Angle-resolved UPS.—... 

X-ray (XPS) [58-61] and ultraviolet photoelectron spectroscopy (UPS) [62-65] provide rich information about the valence bands of extended systems. The further development of angle-resolved UPS (ARUPS) can even be used to directly observe the band structures. Then they can provide a tool to directly check theory. 

This was expertly demonstrated by Angle Resolved UPS (ARUPS) experiments [39] at the beginning of the 1990s, as illustrated in Fig. 36.6. A natural continuation of this work was to study the effects of structural perturbations such as conformational changes on the valence bands of stereoisomers. To illustrate this approach, a computer experiment has been conducted in the case of polyethylene [40]. A vibrational analysis [41] of crystalline samples suggests the possibility of four conformations of polyethylene trans (T), gauche... 

If the intermolecular band dispersion (E = EbI )) is measured with angle-resolved UPS, the effective mass of hole (wj ) is obtained experimentally as [20]... 

In addition to the energy, symmetry and momentum, the spin orientation of the initial states from which the electrons are excited can also be measured in a photoemission experiment (Siegmann 1975, Celotta et al. 1979, Kisker et al. 1980). Spin-polarized angle resolved UPS spectra allow one to determine the spin-dependent energy dispersion relations which are the most detailed information about the electronic states that one can hope to obtain by this technique. 

---