Angle-resolved photoelectron

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. 

Figure 4 Angle-resolved photoelectron spectra for Ni 100] ( 2x/2)R45°-CO. hv = 32 eV (a) angle of incidence, o = 60°, polar angle of emission, 0 = 0°. (b) a = 0 , 0 = 50°, Elk). Inset Gas phase photoelectron spectrum of CO at the same photon energy. After [10] and [11].

Figure 10 Angle-resolved photoelectron spectra from the system Cu 11D -HC00 for three different emission angles, hv = 25°, E j <110>. After [251.

All XPS or ESCA measurements were performed using a Perkin Elmer 5300 ESCA spectrometer equipped with a dual anode (Mg, Al) X-ray source, differentially pumped Ar+ sputter gun, and the variable angle measurement set-up for angle-resolved photoelectron spectroscopic measurements. The data collection and treatment, e.g. smoothing, curve-fitting, intensity measurements, were accomplished by a Perkin Elmer 7500 dedicated computer system using PHI software package. 

N. Choi, T. Jiang, T. Morishita, M.-H. Lee, C.D. Lin, Theory of probing attosecond electron wave packets via two-path interference of angle-resolved photoelectrons, Phys. Rev. A 82 (2010) 013409. 

Fleischauer, P.D. and Tolentino, L.U., Structural Studies of Sputtered MoSj Films by Angle-Resolved Photoelectron Spectroscopy, Proc, 3rd Inti. Conf. on Solid Lubrication, Denver, Colorado, (7-10 Aug. 1984), ASLE SP-14, p. 223. 

Bligaard T, Nprskov JK (2008) Heterogeneous Catalysis, In Nilsson A, Pettersson LGM, Nprskov JK (eds) Chemical bonding at surfaces and interfaces. Elsevier 255-322 AUyn CL, Gustafsson T, Plummer EW (1977) The chemisorption of CO on Cu(lOO) studied with angle resolved photoelectron spectroscopy. Sohd State Commun 24 531... 

Molecular alignment (see Section 8.11.2) can be probed by measurement of the circular dichroism in the photoelectron angular distribution (CDAD). CDAD spectra are obtained by taking the difference between angle-resolved photoelectron spectra for left and right circularly polarized light (Dubs, et al., 1986). 

Given adequately prepared surfaces, angle-resolved photoemission and the various yield spectroscopies have been used to investigate filled and empty surface states, respectively. Results of angle-resolved photoemission measurements have been published by Knapp and Lapeyre [181], Williams et al. [182], Knapp et al. [183] and Huijser et al. [184], A typical set of angle-resolved photoelectron energy distributions (AREDCs) due to Huijser et al. [184] is shown in Fig. 16, in which four structures labelled B , SM S2 and B2 are observed. They are ascribed to emission from filled intrinsic states since they disappear on exposure to 10s L of H2. As we shall see below, B , S and S2 are primarily As-derived, while B2 is mainly a Gas-like state bonded to Asp-states. 

A particularly useful variety of UPS is angle-resolved photoelectron spectroscopy (ARPES), also called angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) [, 62]. In this technique, measurements are made of the valence band photoelectrons emitted into a small angle as the electron emission angle or photon energy is varied. This allows for the simultaneous determination of the kinetic energy and momentum of the photoelectrons with respect to the two-dimensional surface Brillouin zone. From this information, the electronic band structure of a single-crystal material can be experimentally determined. 

Electron spectroscopy is a very powerful and well established tool to investigate the electronic structure of solids [1]. Angle resolving photoelectron spectroscopy directly enables to yield results on the electronic band structure. The use of tunable photon energies allows a band mapping across the Brillouin zone. 

Acronyms ARUPS (angle resolved ultraviolet photoemission spectroscopy) ARPES (angle resolved photoelectron spectroscopy)... 

The interface chemistry of thin films can also be studied by using angle resolved photoelectron spectroscopy (5). As the angle between the sample normal and the entrance slit of the analyzer (9) is increased, the sampled depth is decreased by the cos 0. At grazing electron take-off... 

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