Core level spectroscopies

Flimpsel F J, McFeely F R, Morar J F, Taleb-lbrahimi A and Yarmoff J A 1990 Core level spectroscopy at silicon surfaces and interfaces Proc. Enrico Fermi School on Photoemission and Adsorption Spectroscopy and Interfaces with Synchrotron Radiation vo course CVIII, eds M Campagna and R Rose (Amsterdam Elsevier) p 203... 

Core level spectroscopy (XPS) provides information about the energetic position of localized core states. Core level energies are characteristic of the element (atom)... 

Since the pirn and mpim molecules are quite large, any ab initio calculation including a cluster of metal atoms will necessarily be very tedious. Therefore, it is desirable to model the ligands by a subsystem which includes only the part that is primarily involved in the interaction with the copper surface. As mentioned in the introduction, data from XPS core level spectroscopy show that the nitrogen atom is the primary reaction site in the interaction between pirn and a copper surface, and that the effect of this interaction does not extend significantly into the benzene moiety of the pirn molecule. Therefore, we chose as a model system for pirn the molecule NH(CHO)2 (di-formimide, see Figure 1). As will be shown in the next section, the electronic structure of this model molecule has an electronic structure which very much resembles that of the imide part... 

One particular example of the application of these ideas would be the analysis of CeO which from both band structure calculations (Koelling, Boring Wood (1983) (16)) and core level spectroscopy, has about nf = 0.5, the f electron is, however, bonded to the oxygen p-electrons. The real space analysis for these bonding, delocalized character, f-orbitals show that - 0.4 n 0.2, a value... 

G.A. Sawatzky, in J. Kanamori and A. Kotani (Eds ), Core Level Spectroscopy in Condensed Systems, Springer Verlag Series in Solid State Sciences, Vol. 81, Springer-Verlag, Berlin, 1988. 

Senanayake SD, Idriss H (2006) Photo-catalysis and the origin of fife. The synthesis of nucleotides from formamide on HO fOOl) single crystal surfaces. Proc Natl Acad Sci USA 103 1194 Ariga H, Taniike T, Morikawa H, Tero R, Kondoh H, Iwasawa Y (2008) Lattice-work structure of a 1102(001) surface studied by STM, core level spectroscopy and DFT calculations. Chem Phys Lett 454 350... 

Nilsson A (2002) Application of core level spectroscopy to adsorbates. J El Spec Rel Phenom 126 3... 

R. de Groot, A. Kotani, Core Level Spectroscopy of Solids (CRC Press, Boca Raton, 2008) chap 4... 

The scheme is recommended for atomic volumes in which better precision is needed in the core region e.g. for total energy, hyperfine interactions, and core-level spectroscopy. 

De Groot F, Kotani A (2008) Core level spectroscopy of solids. CRC Press, Taylor Francis Group, 6000 Broken Sound Parkway NW... 

Instabilities of valence (viz. atoms flipping from one state of valence to another as a function of changes in the environment) and mixed valence (an atom exhibits simultaneously two valences, or two valence states coexist on the same site) are both related to intermediate valence (the atom in the condensed phase exhibits some mean, nonintegral valence). The effects are usually encountered when dealing with 4/ and 5/ electrons, and it is therefore very relevant to determine the / count, or effective number of / electrons on a given site. Various core-level spectroscopies have been used to probe / electron occupancies, and there is a vast literature on this field (see the review by Fuggle [615]). 

R.L. Park. Core-Level Spectroscopies. In R.L. Park and M.G. Lagally, editors. Solid State Physics Surfaces, Methods of Experimental Physics, Volume 22. Academic Press, New York, 1985. 

Experimentaly, the Si 2p core-level spectroscopies have been interpreted within the buckling model, the presence of two different charges on the two silicon atoms of the dimer leading to two core levels [21-24]. However, other explanations have been proposed within symmetric models. Artacho [9] and Redondo [12] have found an excellent agreement with experiment when the spin-orbit coupling is introduced. 

Core excitation of clusters is reviewed as a unique approach to probe element- and site-speciflcally size-dependent properties of free clusters in the gas phase. The fundamental characteristics of core level spectroscopies that rely on resonant excitation are briefly reviewed. Specifically, this includes primary photoabsorption as well as subsequent processes, such as photoionization, electronic relaxation, radiative relaxation, and finally fragmentation of the singly or multiply charged clusters. Elxper-imental techniques as well as selected results on simple model systems, such as variable size rare gas clusters, are presented. 

These unique properties of core level excitation spectroscopies are briefly reviewed. The fundamentals of core level spectroscopies, such as X-ray absorption, X-ray absorption fine structure, inner-shell photoionization, electronic and radiative relaxation, and fragmentation in the regime of core level excitation, are outlined along with their characteristics to size effects... 

In most studies of mctal/polymer interfaces involving XPS, this technique is used as a core level spectroscopy to detect changes in the surface chemical... 

Core-level spectroscopies are the appropriate tools to study the electronic distribution around free atoms and the changes induced in this distribution on condensation or on the formation of compounds involving other elements. These spectroscopies are also very useful to track the formation of clusters which finally coalesce to form well-defined solid phases. For the R, X-ray absorption spectroscopy is very useful because of the simplicity of the final multiplet structure, as the transitions obey dipole selection rules. Generally, two types of transitions are observed one in which the 4f electron participates in the transition and another in which it remains as a spectator. In the former case, a transition of a d electron to the empty f shell is involved. This leads to the formation of the nd 4f - d 4f + ( = 3,4) multiplets which are in fact finger prints of the R atom configurations. In the same way, the transitions from p levels scan the empty sd states of the conduction band. 

Natural line widths are of fundamental importance in studies of fluorescence yield and lineshapes by various core-level spectroscopies. In the context of the 3d corelevel lifetimes in R, Crecelius et al. (1978) determined the 3d level widths fi om the X-ray photoelectron spectra (XPS) of La-Pr metals and compared them with the theoretical lifetime widths obtained by McGuire (1972). In the case of La, the appreciable... 

Puglia C, Nilsson A, Hemnas B, Karis O, Bennich P, Martensson N (1995) Physisorbed, chemisorbed and dissociated O2 on Pt(lll) studied by different core level spectroscopy methods. Surf Sci 342(1-3) 119-133... 

Experimental observation of the Eu Mossbauer spectra in EuFe4Alg and the unit cell size indicate that the Eu ion is in the mixed-valence (MV) state. However, at low temperature it behaves like an Eu " ion due to the hypeifine field of the Fe sublattice acting below ordering temperature (Felner and Nowik 1978). Also, XPS-3d core level spectroscopy (Malik et al. 1981) and X-ray absorption near edge structure (XANES) results (Darshan and Padalia 1984) showed the Eu ion to be in the MV state with V=2.80 at 300 K. In turn, both unit cell size volume (Felner and Nowik 1978) and X-ray spectroscopy show that the Ce ion is in the MV state as well, and the valence v amounts to 3.28 (Shcherba et al. 1992). 

As the most important result, APS has proven to be an appropriate technique for the investigation of the electronic structure of lanthanide compounds in a way similar to other core-level spectroscopies such as XPS, XAS and CEELS, with the advantage of a rather simple experimental setup. Furthermore, when applied to 4f systems, APS offers the potential of studying correlation effects directly because of the allowed addition of two electrons to the partially occupied 4f level. 

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