Synchrotron radiation photoelectron

Accurate investigation of the valence ionization spectra is important subject to elucidate the electronic structure of molecules. Ionization spectra of five-membered aromatic compounds have also been intensively studied. The high-resolution synchrotron radiation photoelectron spectra (SRPES) of furan and thiophene were measured and analyzed with asymmetry parameter up to about 40 eV [63,64]. The electron momentum spectroscopy (EMS) was also applied to furan up to 30-40 eV [65]. The ionization spectra of these molecules were also studied by several theoretical methods. However, there were some controversial assignments even for the outer-valence region, in particular for the peak position of Ibi(TTi) state and the inner-valence spectra have not been theoretically reproduced. 

Among the related methods, specific experimental designs for applications are emphasized. As in-system synchrotron radiation photoelectron spectroscopy (SRPES) will be applied below for chemical analysis of electrochemically conditioned surfaces, this method will be presented first, followed by high-resolution electron energy loss spectroscopy (HREELS), photoelectron emission microscopy (PEEM), and X-ray emission spectroscopy (XES). The latter three methods are rather briefly presented due to the more singular results, discussed in Sections 2.4-2.6, that have been obtained with them. Although ultraviolet photoelectron spectroscopy (UPS) is an important method to determine band bendings and surface dipoles of semiconductors, the reader is referred to a rather recent article where all basic features of the method have been elaborated for the analysis of semiconductors [150]. 

SRPES synchrotron radiation photoelectron spectroscopy. For photon energies less than 300 eV also SXPS soft X-ray photoelectron spectroscopy. 

SRPS Synchrotron radiation photoelectron spectroscopy PSD Photon-stimulated desorption... 

Keywords Conjugated molecules. Semi-empirical models and model calculations. Synchrotron radiation photoelectron spectroscopy. Near edge X-ray absorption fine structure... 

Powis I, Rennie EE, Hergenhahn U, Kugeler O, Bussy-Socrate R (2003) Investigation of the gas-phase amino acid alanine by synchrotron radiation photoelectron spectroscopy. J Phys Chem A 107 25... 

Ultraviolet photoelectron spectroscopy (UPS) is a variety of photoelectron spectroscopy that is aimed at measuring the valence band, as described in sectionBl.25.2.3. Valence band spectroscopy is best perfonned with photon energies in the range of 20-50 eV. A He discharge lamp, which can produce 21.2 or 40.8 eV photons, is commonly used as the excitation source m the laboratory, or UPS can be perfonned with synchrotron radiation. Note that UPS is sometimes just referred to as photoelectron spectroscopy (PES), or simply valence band photoemission. 

Smith N V and Himpsel F J 1983 Photoelectron spectroscopy Handbook on Synchrotron Radiation ed E E Koch (Amsterdam North-Holland)... 

Eland, J. H. D. (1983) Photoelectron Spectroscopy. 2nd edn, Butterworth-Heinemann, London. Huffier, S. (2001) Photoelectron Spectroscopy Principles and Applications. 3rd edn. Springer, Berlin. Prince, K. C. (1995) Photoelectron Spectroscopy of Solids and Suifaces Synchrotron Radiation Techniques and Applications, World Scientific Publishing, Singapore. 

Figure 2 Molybdenum K-edge X-ray absorption spectrum, ln(i /i ) versus X-ray energy (eV), for molybdenum metal foil (25- jjn thick), obtained by transmission at 77 K with synchrotron radiation. The energy-dependent constructive and destructive interference of outgoing and backscattered photoelectrons at molybdenum produces the EXAFS peaks and valleys, respectively. The preedge and edge structures marked here are known together as X-ray absorption near edge structure, XANES and EXAFS are provided in a new compilation of literature entitled X-rsy Absorption Fine Structure (S.S. Hasain, ed.) Ellis Norwood, New York, 1991.

Extensive discussion on the ionization potentials of 1,2,5-thiadiazole and its derivatives can be found in CHEC(1984) and CHEC-II(1996) <1984CHEC(6)513, 1996CHEC-II(4)355>. Hel photoelectron spectroscopy, inner-shell electron energy loss spectroscopy involving the S2p, S2s, Cls and Nls edges, and Sis synchrotron radiation photoabsorption spectroscopy were used to probe the occupied and unoccupied valence levels of benzothiadiazole 2 <1991MI165>. 

An ozone treatment (10 minutes at room temperature) of the HF-etched SiC surface before the metallization step was introduced as a very convenient processing step to produce Schottky diode gas sensors with an increased stability and reproducibility. The use of spectroscopic ellipsometry analysis and also photoelectron spectroscopy using synchrotron radiation showed that an oxide, 1-nm in thickness, was formed by the ozone exposure [74, 75]. The oxide was also found to be close to stochiometric SiO in composition. This thin oxide increased the stability of the SiC Schottky diodes considerably, without the need for any further interfacial layer such as Ta or TaSi which have been frequently used. Schottky diodes employing a porous Pt gate electrode and the ozone-produced interfacial layer have been successfully operated in both diesel exhausts and flue gases [76, 77]. 

As we have seen, the most advanced photoelectron techniques, especially those which necessitate the use of synchrotron radiation sources, have been applied until now only to U and Th systems. Application on Pu and Am systems as well as to heavier actinides is to be expected in the future. The same development is likely to occur as for neutron experiments, where more and more these hazardous actinides are investigated at high levels of instrumental sophistication. Difficulties arising from handling and protection problems are, of course, much greater for photoelectron spectroscopy. 

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