Photoemission spectroscopy structure

All analytical methods that use some part of the electromagnetic spectrum have evolved into many highly specialized ways of extracting information. The interaction of X-rays with matter represents an excellent example of this diversity. In addition to straightforward X-ray absorption, diffraction, and fluorescence, there is a whole host of other techniques that are either directly X-ray-related or come about as a secondary result of X-ray interaction with matter, such as X-ray photoemission spectroscopy (XPS), surface-extended X-ray absorption fine structure (SEXAFS) spectroscopy, Auger electron spectroscopy (AES), and time-resolved X-ray diffraction techniques, to name only a few [1,2]. 

Suitable characterization techniques for surface functional groups are temperature-programmed desorption (TPD), acid/base titration [29], infrared spectroscopy, or X-ray photoemission spectroscopy, whereas structural properties are typically monitored by nitrogen physisorption, electron microscopy, or Raman spectroscopy. The application of these methods in the field of nanocarbon research is reviewed elsewhere [5,32]. 

We next discuss x-ray absorption studies. To put matters in context, it is useful to understand that conventional studies using Auger electron spectroscopy (AES) and x-ray photoemission spectroscopy (XPS) can be carried out only ex situ in high vacuum after electrochemical treatment since the techniques involve electron detection. X-ray absorption spectroscopy can, in contrast, be used for valence and structural environment studies. As x-rays only are involved, they can be carried out in situ in an electrochemical or similar cell. 

One way of experimentally exploring the electronic structure of solids is by means of photoemission spectroscopies such as UPS and X-ray photoelectron spectroscopy (XPS), where photoexcited electrons are analyzed dispersively as a function of their kinetic energy. The electronic structure of the reference material TTF-TCNQ will be extensively discussed in Section 6.1. Figure 1.31 shows the XPS spectra of the S2p core line for (TMTTF)2PF6 (black dots) and BEDT-TTF (grey dots). 

Thanks to the extensive literature on Aujj and the related smaller gold cluster compounds, plus some new results and reanalysis of older results to be presented here, it is now possible to paint a fairly consistent physical picture of the AU55 cluster system. To this end, the results of several microscopic techniques, such as Extended X-ray Absorption Fine Structure (EXAFS) [39,40,41], Mossbauer Effect Spectroscopy (MES) [24, 25, 42,43,44,45,46], Secondary Ion Mass Spectrometry (SIMS) [35, 36], Photoemission Spectroscopy (XPS and UPS) [47,48,49], nuclear magnetic resonance (NMR) [29, 50, 51], and electron spin resonance (ESR) [17, 52, 53, 54] will be combined with the results of several macroscopic techniques, such as Specific Heat (Cv) [25, 54, 55, 56,49], Differential Scanning Calorimetry (DSC) [57], Thermo-gravimetric Analysis (TGA) [58], UV-visible absorption spectroscopy [40, 57,17, 59, 60], AC and DC Electrical Conductivity [29,61,62, 63,30] and Magnetic Susceptibility [64, 53]. This is the first metal cluster system that has been subjected to such a comprehensive examination. 

Tanaka S, Kanai K, Kawahe E, Iwahashi T, Nishi T, Ouchi Y, Seki K (2005) Doping effect of tetrathianaphthacene molecule in organic semiconductors on their interfacial electronic structures studied by UV photoemission spectroscopy. Jpn J Appl Phys 44 3760... 

The crucial experiment to identify whether this satellite structure is due to a localized 5 f hole, is claimed to be photoemission spectroscopy, in which the excitation (provided by synchrotron radiation) is tuned through the 5d-5f threshold energy . At the threshold energy an empty 5 f state just beyond Ep becomes occupied... 

From the perspective of this symposium, analysis of the atomic dynamics and electronic structure of surfaces constitutes an even more exotic topic than surface atomic geometry. In both cases attention has been focused on a small number of model systems, e.g., single crystal transition metal and semiconductor surfaces, using rather specialized experimental facilities. General reviews have appeared for both atomic surface dynamics (21) and spectroscopic measurements of the electronic structure of single-crystal surfaces (, 22). An important emerging trend in the latter area is the use of synchrotron radiation for studying surface electronic structure via photoemission spectroscopy ( 23) Moreover, the use of the very intense synchrotron radiation sources also will enable major improvements in the application of core-level photoemission for surface chemical analysis (13). 

Due to its close relation with the electronic structure of the compounds, photoemission spectroscopy (PES) has been applied in some cases of interest and combined with theoretical investigations. This accounts for 1,2-dihydro-lA3,2A3-diphosphetes 1 <19970M4551> and Mb-clusters 29a and 29b <2003OM2897>, for example. 

The chemisorption bond between CO or NO and Pt is mainly attributed to the interaction of a electron of the adsorbate with the d hole of Pt, whereas the site selection of the adsorbate is assisted by the interaction between the adsorbate 2tt and the Pt 5d orbital. The shape of the d orbital is important for this site selection. The five d orbitals in the Oh space group are generally classified into eg (dx2 y2 and d3,2 r2) and r2g (dxy, dyz, and dM) orbitals with respect to the cubic coordinate. Of the two states of Pt, t2g has more d hole character [90], and furthermore, only the f2g state is upward-shifted and the eg is preferentially filled as a result of s-d hybridization [89]. The d band filling in the eg state due to the s-d hybridization for the alloy is supported by the band structure of this alloy in the Y-L direction observed by angle-resolved photoemission spectroscopy using synchrotron radiation [88]. 

Ultraviolet photoemission spectroscopy( UPS) measurements of a Pd/ SiCVa-Si H structure indicate (Fortunato et al., 1984) that the mechanism responsible for the transport property variations is a change in the contact potential. In these experiments a few angstroms of a-Si have been deposited by an in situ evaporation onto a Pd/SiO substrate. Figure 5 shows the photoemission spectra obtained by synchrotron radiation at a photon energy of 30 eV and for three different conditions (1) after the a-Si deposition, (2) after the H2 exposure at 10-2 Torr for 2 min, and (3) after 02 exposure at 5 X 10-5 Torr and 110°C for 7 min. 

Angle-Resolved Photoemission. The best experimental technique to resolve the electronic structure of crystals in the momentum-energy space, and, consequently, the Fermi surface, is angle resolved photoemission spectroscopy (ARPES). 

Comparison between the core-level X-ray absorption spectroscopy (XAS), emission (XES), and X-ray photoemission spectroscopies (XPS) usually shows that the spectral edges rarely coincide with each other and with the Fermi level. It is common practice, however, to place F at the emission threshold which corresponds to a fully relaxed ion core (16). For defining the structure of the edge, an energy resolution of at least 1-2 eV is required in the range of 5-20-keV X-ray photons. This can be achieved with Bonse-Hart channel-cut silicon monochromator crystals. 

ARUPS Angle-Resolved Ultras violet Photoemission Spectroscopy Electrons photoemitted from the valence and conduction bands of a surface are detected as a function of angle. This gives information on the dispersion of these bands (which is related to surface structure), and also structural information from the diffraction of the emitted electrons. 

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