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Physical and chemical phenomena reflected in electron spectra excited by photons from solids take place on very wide scales of space, time, and excitation energy, covering sometimes differences of many orders of magnitude. Therefore, the use of multiscale approaches seems to be promising when extracting information on electronic structure or chemical composition from such electron spectra. Following a summary of phenomena reflected in electron spectra induced from solids by photons and different type of models available for their interpretation, the challenges of characterization of advanced materials and the need for multiscale materials analysis and modeling will be discussed. Copyright © 2015 John Wiley & Sons, Ltd.

One of the main problems of palladium based catalysts for a direct formic acid fuel cell (DFAFC) is their low stability during a long-term operation. In these studies, the Pd-ZrO2 catalyst supported on the multiwall carbon nanotubes (MWCNTs) was prepared and thermo-chemically treated. These catalysts were tested in a fuel cell for formic acid electrooxidation, and their chemical composition and structure were characterised by the XPS, STEM, HR-TEM and XRD techniques. It was found that the Pd-ZrO2/MWCNTs catalyst after synthesis causes oscillations of the cell voltage during operation resulting in significantly higher deactivation resistance than that of Pd/MWCNTs. This may be attributed to the "self-cleaning" mechanism of poisoned Pd catalyst by carbon monoxide through the electrochemical oxidation of COads (adsorbed) to CO2 (gas).

Graphene oxide was prepared from commercial graphene powder (G) platelets of 8 nm thickness by oxidation in ozone (G-O3) and low-energy (cold) glow air plasma in a pink region (G-PP). X-ray photoelectron spectroscopy (XPS) was applied for chemical characterisation of the atomic content and for obtaining quantitative information on C hybridisation. Reflection electron energy loss spectroscopy (REELS) was used for characterising the surface structure including the content of surface and bulk carbon atoms of sp 2 and sp 3 hybridisation. The G-O3 and G-PP graphene oxide samples contain a low amount of C sp 3 bonds and carbon–oxygen groups in comparison to graphene oxide prepared by the “wet” chemical methods. Oxidation of commercial graphene platelets powder, especially in air plasma, leads to increasing surface C sp 3 and significantly bulk C sp 3 contributions, indicating intercalation by oxygen groups. The intensity ratio of the REELS π + σ C sp 2 bulk to the C sp 2 surface energy loss peaks, decreasing in the order G>G-O3>G-PP, indicates exfoliation of layers in G-O3 and G-PP by oxygen functional groups and water with decreasing average number of layers in graphene oxide nanostructures due to oxidation. Although, the “wet” chemical methods are more effective for oxidation leading to a larger amount of C sp 3 and oxygen groups, the proposed methods of oxidation by ozonation and in air plasma are inexpensive, safe, effective, environmentally friendly and do not result in toxic chemical waste products.

Energy loss processes of high energy electrons induced by hard X-rays are significantly influencing the shape of the measured electron spectra, therefore the consideration and deeper understanding of these processes is important for extracting information on electronic structure or chemical composition of bulk or near surface region of solids using Hard X-ray Photoelectron Spectroscopy (HAXPES). Beginning with fundamental concepts and definitions, through discussion of models describing energy loss processes of energetic electrons in the near surface regions of solids and finally discussing methods of corrections for these processes turned to be useful when evaluating hard X-ray induced electron spectra, this review intends to provide a brief summary on this field for users of the HAXPES method.

The X-ray PhotoElectron Energy Loss Spectroscopy (XP-EELS) and Reflection Electron Energy Loss Spectroscopy (REELS) were used for analysing surface layers of “as-received” and functionalised multiwall carbon nanotubes (MWCNT), and MWCNT decorated with Pd and Pd–Au particles after calcination/reduction. The decorated MWCNT were previously applied as catalysts in a reaction of formic acid electrooxidation. These spectroscopies, used as complementary methods of structural surface analysis, provide information on the energy position, intensity and full width at half maximum of the quasi-elastic peak and inelastic π and π + σ energy loss peaks. Analysing the π + σ energy loss peak, the bulk and surface C sp 2 /sp 3 components can be separated. Functionalisation of MWCNT, catalyst reduction and Ar + ion sputtering increase the C sp 3 content in comparison to the “as-received” MWCNT and calcined catalysts. The intensity ratios of surface and bulk C sp 3 and sp 2 components evaluated from the REELS π + σ energy loss peak indicate: (i) functionalisation leads to attachment of functional groups to the MWCNT surface, (ii) calcined catalysts show an amorphous carbon overlayer at the surface and (iii) reduction of calcined catalysts leads to increasing C sp 3 hybridisations.

The Pd–Au multiwall carbon nanotubes (MWCNTs) supported catalyst prepared by polyol method was found to be catalytically active material in direct formic acid fuel cell electrooxidation reaction and during cyclic voltammetry (CV) measurements. The surface of the catalyst after calcination and reduction treatments was investigated previously. The effect of Ar ion bombardment modification on the calcinated catalyst was studied by electron spectroscopy. The chemical and structural changes were deduced from the X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) spectra. The XPS quantitative and qualitative analysis of different chemical forms of atoms indicated that the sputtering causes an increase of Pd surface content, accompanied by decreasing content of N, O, C sp2, and Au (due to preferential sputtering of Au) and significant increase of C sp3 amount. A decrease was also observed in the surface content of (i) carboxyl groups, (ii) water, and (iii) Pd oxide (mainly less stable PdO2). Analysis of XPS inelastic background shape by QUASES indicates that Pd crystallites phase is covered by PdOx + Camorphous overlayer of decreasing thickness after sputtering. Namely, thickness of PdOx overlayer decreased from 8.2 to 3.5 nm and the thickness of amorphous carbon overlayer located on the top increased from 2.3 to 3.5 nm. Significant increase of C sp3 content results from carbon nanotube (CNT) π bonds damaging, whereas decrease of PdO2 content from lower stability of PdO2. Larger thickness of Camorphous overlayer, in contrary to PdOx, may result from higher preferential sputtering of oxygen than carbon atoms and cracking of the MWCNTs structure by Ar+ ions.

Typical core-level X-ray photoemission spectra have plasmon loss bands in addition to a main sharp band. The loss of energy from the photoelectron may simultaneously occur in the excitation process (intrinsic loss) or when the photoelectron travels in the solid on its way out through the surface (extrinsic loss). They can interfere each other so these two loss mechanisms are not possible to separate. The quantum Landau formula which originally derived by Hedin et al., can explain overall plasmon loss features accompanied by core level photoemission where elastic scattering before and after the losses are completely neglected. We calculate plasmon loss features associated with Li 1s photoemission using the quantum Landau formula that includes elastic scattering before and after the losses. Li is light and a weak scatter, however we observe a prominent effect due to elastic scatterings from surrounding atoms. We also have found that the elastic scatterings can considerably change the relative intensities of bulk and surface plasmon peaks.

The Pd–Au multiwall carbon nanotubes (MWCNTs) supported catalyst exhibits higher power density in direct formic acid fuel cell (DFAFC) than similar Pd/MWCNTs catalyst. The Pd–Au/MWCNTs catalyst also exhibits higher activity and is more stable in electrooxidation reaction of formic acid during cyclic voltammetry (CV) measurements. After preparation by polyol method, the catalyst was subjected to two type of treatments: (I) annealing at 250 °C in 100% of Ar, (II) reducing in 5% of H2 in Ar atmosphere at 200 °C. It was observed that the catalyst after treatment I was completely inactive, whereas after treatment II exhibited high activity. In order to explain this effect the catalysts were characterized by electron spectroscopy methods. The higher initial catalytic activity of Pd–Au/MWCNTs catalyst than Pd/MWCNTs catalyst in reaction of formic acid electrooxidation was attributed to electronic effect of gold in Pd–Au solution, and larger content of small Au nanoparticles of 1 nm size. The catalytic inactivity of Pd–Au/MWCNTs catalysts annealed in argon is attributed to carbon amorphous overlayer covering of Pd oxide shell on the metallic nanoparticles.

The multiwall carbon nanotubes (MWCNTs) supported Pd catalyst, prepared by the polyol method and reduced in 5% of H2 in Ar atmosphere at temperature of 200 °C, exhibits high activity in electrooxidation of formic acid, whereas, the same catalyst calcinated at temperature of 250 °C in 100% of Ar is inactive. The structural and chemical properties of the catalyst surfaces after reducing and calcination treatments were investigated using electron spectroscopy. The catalytically active sample indicated smaller O content, with the same content of Pd and C at the surface. Simultaneously, the content of carbon–oxygen–hydrogen groups, i.e., carboxyl, carbonyl, ester, ether, and acid anhydride, was lower. In the surface layer of both catalysts, three chemical Pd forms were observed: Pd metallic crystallites, PdO and Pd in organic matrix. In active catalyst, similar content of Pd crystallites and smaller content of PdO were observed. The differences in activity of the investigated Pd/MWCNTs catalysts after reduction and calcination result from the amorphous carbon covering the PdO/Pd nanoparticles, where the PdO layer is of larger thickness for inactive catalyst. This overlayer is removed after reduction in 5% of H2 in Ar atmosphere at temperature of 200 °C.

Hard X-ray photoelectron spectroscopy (HAXPES or HXPS), using hard (2–15 keV) X-rays for excitation and high energy resolution, has shown a spectacular development recently, due to its capability for providing an insight into the bulk electronic structure of solids and the chemical composition of buried layers and interfaces lying at depths of several tens of nm. Following a summary of fundamentals concerning photoionization phenomena and transport processes of photoelectrons induced by hard X-rays from solids, examples of core level and valence band HAXPES spectra are presented to illustrate different physical effects. Examples are given of applications of HAXPES in determining electronic structure properties and in surface/interface chemical analysis of material systems of high practical interest. Finally, some perspectives for further developments are outlined.

This paper provides an updated overview, intended to be of practical value to analysts, of methods that can be applied to minimize or control the build-up of near-surface electrical charge during electron-induced Auger electron spectroscopy (AES). Although well-developed methods can be highly effective, dealing with insulating or ungrounded samples for which high spatial resolution is needed remains a challenge. Examples of the application of methods involving low-energy ion sources and sample thinning using a focused ion beam that can allow high-resolution measurements on a variety of samples are highlighted. The physical bases of newer and traditional methods are simply described along with strengths and limitations of the methods. Summary tables indicate methods that can be applied to most AES spectrometers, methods that require special instrumental capabilities and methods that require special sample preparation or mounting.

Report on the 47th IUVSTA Workshop ‘Angle-Resolved XPS: the current status and future prospects for angle-resolved XPS of nano and subnano films’ A. Herrera-Gomez,a,b∗ J. T. Grant,c P. J. Cumpson,d† M. Jenko,e F. S. Aguirre-Tostado,b C. R. Brundle,f T. Conard,g G. Conti,h C. S. Fadley,i J. Fulghum,j K. Kobayashi,k L. Kover,l H. Nohira,m R. L. Opila,n S. Oswald,o R. W. Paynter,p R. M. Wallace,b W. S. M. Wernerq and J. Wolstenholmer

The excitation of bulk and surface plasmons in the presence of a solid surface during the emission of electrons in X-ray photoemission spectroscopy (XPS) and in Auger electron spectroscopy (AES) is investigated. The modifications in the energy loss spectra as well as in the plasmon excitations due to the sudden creation of electron–hole pairs, electron transport phenomena and the presence of residual holes and furthermore the proximity of the surface are analysed. The results illustrate that, from a theoretical point of view, separation of extrinsic and intrinsic contributions could be ambiguous (in terms of independent processes) due to interference effects between the photoelectron and photohole present in both processes. A comparison of the results of our model with experimental spectra showed a good agreement.

A method is presented for analysing the energy loss part (dominated by contributions from extrinsic, intrinsic and surface plasmon excitations) of electron spectra excited from free-electron-like solids by X-rays. It is an improved version of the model originally proposed by Steiner, Hochst and Hufner and it accounts for contributions of electrons suffering multiple energy losses of different origin. Applied for analysing a Ge 2s photoelectron spectrum excited from a thin Ge layer, the applicability of the method to separate contributions to the inelastic background of the spectra due to intrinsic, extrinsic and surface plasmons is demonstrated. The aim of this work to give a detailed description of the simple statistical model applied in ref. [M. Novak, S. Egri, L. Kover, I. Cserny, W. Drube, W.S.M. Werner, Surf. Sci. 601 (2007) 2344] for practical analysis of photoelectron spectra. The effects of the application of energy loss distributions (for single bulk and single surface excitations) derived by using different methods are also investigated.

Recoil effects of photoelectrons excited by high-energy X-rays are studied beyond the simplest approximation where elastic scatterings of photoelectrons are completely neglected (single-site approximation). At first we have shown that the simple free atom energy shift is accurately obtained within the harmonic and the single-site approximations. Beyond the single-site approximation, this simple formula does not work, but still simple classically acceptable formula can be used to explain the recoil energy shift. Illustrative numerical calculations show that the energy shifts caused by the photoelectron diffraction amounts to 5–8 meV for graphite-like carbon and about 100 meV for LiI6 cluster at ek = 5–7 keV, and show oscillations as functions of the photoelectron energy. Furthermore we discuss the recoil effects in photoemission from extended levels by use of the tight-binding approach. Our approach naturally provides not only Debye–Waller factors but also the recoil factors. In addition to the phonon excitation, we also study the recoil effects associated with plasmon losses where intrinsic and extrinsic processes can interfere each other. Only the latter can contribute to the recoil energy shift. © 2008 Elsevier B.V. All rights reserved.

We investigate the energy loss process leading to the excitation of bulk and surface plasmons during the emission of electrons in X-ray photoemission spectroscopy (XPS) and in Auger electron spectroscopy (AES), in the presence of a solid surface. We take into account the effects due to the sudden creation of the electron–hole pair, to the electron transport and to the residual hole, as well as the proximity of the surface. We use the dielectric response theory for describing the material, and the specular reflection model for describing the process. The results illustrate that, from the theoretical point of view, to separate extrinsic and intrinsic contributions could be ambiguous (in terms of independent processes) due to interference effects between the photoelectron and the photohole present in both processes. These effects are intrinsic to the process and cannot be avoided. Besides, we have taken into account the distance from the surface in which the process develops. The proximity of the surface adds more interference to those processes.

In elastic peak electron spectroscopy (EPES), the nearest vicinity of elastic peak in the low kinetic energy region reflects electron inelastic and quasielastic processes. Incident electrons produce surface excitations, inducing surface plasmons, with the corresponding loss peaks separated by 1–20 eV energy from the elastic peak. In this work, X-ray photoelectron spectroscopy (XPS) and helium pycnometry are applied for determining surface atomic composition and bulk density, whereas atomic force microscopy (AFM) is applied for determining surface morphology and roughness. The component due to electron recoil on hydrogen atoms can be observed in EPES spectra for selected primary electron energies. Simulations of EPES predict a larger contribution of the hydrogen component than observed experimentally, where hydrogen deficiency is observed. Elastic peak intensity is influenced more strongly by surface morphology (roughness and porosity) than by surface excitations and quasielastic scattering of electrons by hydrogen atoms. Copyright © 2007 John Wiley & Sons, Ltd.

Angular distribution of emitted photoelectrons is theoretically studied for high-energy X-rays where electric quadrupole and magnetic dipole transitions play some important roles in addition to the electric dipole transitions. We apply irreducible tensor expansion of photon field to discuss the high-energy photoelectron angular distribution instead of the usual power series expansion. The present numerical calculations show that the conventional power series expansion works so well up to quite high energy ( ≈ 10 keV) for core excitation. Photoelectron diffraction effects make the nondipole contribution sensitive to the geometrical setup of surrounding scattering atoms because of the strong focusing effect in the high-energy region. Total high-energy photoemission intensities from extended levels are well described by use of the Gelius formula because the interference terms are effectively smeared out by Debye–Waller factors.

Ge KL 23 L 23 Auger spectra photoexcited (using bremsstrahlung radiation) from thin Ge films were measured with high energy resolution. The measured spectra were corrected for effects of inelastic electron scattering within the films, using two different models for estimating inelastic backgrounds. From the corrected Auger spectra the relative transition energies, the relative intensities and the energy widths of the KL 23 L 23 Auger lines were evaluated and compared to earlier results obtained from X-ray induced Auger spectra, from Auger spectra emitted from radioactive isotopes and from Auger spectra induced by high energy electrons transmitted through ultrathin Ge layers.

High energy resolution KL 23 L 23 Auger spectra of polycrystalline Cu and Ni were measured using photon energies up to about 50 eV above the K-absorption edge and down to 5 eV (Cu KLL) and 4 eV (Ni KLL) below threshold. The spectra show strong satellite structures varying considerably as a function of the photon energy. In the sub-threshold region the linear dispersion of the diagram line energy positions and a distortion of the line shape as a function of photon energy, attributable to the Auger resonant Raman process, is clearly observed, indicating the one-step nature of the Auger emission. These changes in the resonant spectra are interpreted using a simple model based on resonant scattering theory in combination with partial density of states obtained from cluster molecular orbital (DV- X α) calculations.

Quasi-elastic scatterings of high-energy electrons are studied with quantum scattering theory including recoil effects by use of correlation functions. Two different types of recoil processes are investigated; one is free atom recoil and the other is phonon excited recoil processes within harmonic vibration approximation where Mermin’s theorem works. The recoil effects of photoelectrons excited by high-energy X-rays are also studied, where the atomic displacement after the core-hole production also plays some important roles. For practical calculations the Debye approximation is used for phonon spectra, which gives rise to the simple free atom recoil energy shift. The broadenings of the spectra depend on the temperature in contrast to the energy shift, and is quite different from the free atom approximation in particular at low temperature. Numerical calculations are carried out for Be, C (graphite), Si and Ge powders. The energy shifts for solids composed of light elements are comparable with typical chemical shifts.

The energy distribution of electrons backscattered elastically from polyethylene is studied. The separation between the carbon and hydrogen peak in the energy distribution is shown. Furthermore, the effect of the multiple scattering on the energy shifts and Doppler broadenings is determined using Monte Carlo (MC) simulations. Our MC simulations are in good agreement with our experimental observations.

Reflection electron energy loss spectra (REELS) are presented for medium energy (200 eV to 5 keV) electrons backscattered from Si, Ni, Ge and Ag surfaces. Multiple bulk inelastic scattering is eliminated from the experimental spectra and the differential surface excitation probability is retrieved from the resulting spectra. The differential as well as the integral surface excitation probabilities are compared with available theoretical results and experimental data published earlier. A material parameter is derived from the measurements that describes the dependence of the average number of surface excitations experienced in a single surface crossing on the electron energy and direction of surface crossing. While the shape of the distribution of energy losses in a single surface excitation is in reasonable agreement with theory, the integral surface excitation probability, i.e. the number of surface excitations experienced by the probing electron during a single surface crossing, exhibits a significant scatter when comparing results from different sources.

Elastic-peak electron spectra were recorded in the range of 2–10 keV primary electron energy in order to determine the inelastic mean free path (IMFP) of electrons in polycrystalline Ge samples using Ag as a reference material. The IMFPs of the studied material were calculated as functions of the reference IMFPs to examine the effects of different sources of errors on the accuracy of the resulting data. This representation gives the opportunity to easily re-determine IMFPs for any Ag reference data as well.

A first-principles, fully relativistic, many electron method was applied to the calculation of the multiplet energies in the KLL Auger transition of 3d transition metals from chromium to copper ( Z =24–29). The method is a configuration interaction (CI) method, combined with a fully relativistic molecular orbital (MO) theory using four-component MOs. Coulomb and spin–orbit interactions are fully considered in the active CI space with no adjustable parameters. All integrals in matrix elements are numerically calculated. The models of a free atom and a metal cluster having 13–19 atoms were used. The calculated multiplet splittings showed a systematic increase as the atomic number increased over the range from the KL 23 L 23 , KL 1 L 23 , to the KL 1 L 1 configurations. The trend originated from the increase in orbital contraction. The results obtained using metal clusters had smaller multiplet splittings between the 3 P 2 (KL 3 L 3 ) and 1 S 0 (KL 2 L 2 ) terms than in the case of free-atom models by about 0.2 eV. Two final-state configurations were compared to see the effect of CI in the KL 23 L 23 multiplets. The calculated energies were well comparable to the experimentally obtained peak positions. The 1 S 0 terms largely shifted by the inclusion of the CI with the KL 1 L 1 configuration.

Earlier studies on Ge KLL Auger spectra photoexcited from thin films or emitted from thin layer radioactive sources showed a strong satellite of the main 1 D 2 peak. This was interpreted as a consequence of inelastic scattering of electrons in these systems. Similar intense satellites were observed in Ge 1s photoelectron spectra. To clarify the origin of these satellites, Ge KL 23 L 23 spectra were induced from polycrystalline Ge films of 100 nm thickness, using bremsstrahlung radiation. The KLL Auger spectra were measured with high energy resolution by a high energy electron spectrometer based on a hemispherical analyzer. Correction of the experimental spectra for inelastic background was performed using experimental cross-sections for inelastic scattering of electrons, obtained from our high energy resolution REELS measurements applying Tougaard’s method. The measured and background corrected spectra are compared to model spectra calculated within the frame of a theory developed by Yubero and Tougaard to describe both extrinsic and intrinsic losses in XPS experiments. On the basis of the comparison between our experimental and model spectra, the strong satellite is attributed to plasmon losses. Our analysis of the experimental spectra indicates a significant (∼30%) contribution of intrinsic plasmon losses, in reasonable agreement with the prediction of the theory.

Correction of photoelectron and Auger spectra excited from solids for the effect of electron scattering is a key problem in quantitative surface analytical applications of XPS and AES. Based on analysis of the spectral shape of the background caused by scattering of the signal electrons, powerful methods have been developed recently and applied successfully for obtaining the 'source functions' (i.e. the background-corrected spectra) as well as the in-depth concentration profile from the measured spectra. The QUASES analysis has been proposed as a general tool for quantification in XPS, probing depths up to ∼10 inelastic electron mean free paths (λ) using Tougaard's 'universal' cross-section for inelastic scattering and the λ(E) values recommended by Powell and Jablonski. Effects of elastic scattering and surface excitations are neglected with this approach and intrinsic excitations are considered a part of the source function. In the partial intensity approach, the observed spectrum can be decomposed into its constituent parts, i.e. the source function as well as contributions due to intrinsic bulk losses and surface extrinsic losses. This is achieved for an arbitrary emission mechanism. In particular, elastic scattering and different scattering mechanisms at different depths can be accounted for simply and consistently. Both methods have been applied for background correction of KLL Auger spectra of the 3d transition metals Cu and Ni excited by photons from metallic thin films vacuum-evaporated onto Si substrates. The respective source functions obtained are very similar, especially in the case of thinner films, indicating that elastic scattering and surface effects play only a minor role in influencing the spectral shape at these high energies. A detailed analysis of the differences is given, focusing on the contributions from intrinsic excitations.

In the elastic peak electron spectroscopy (EPES) method, an electron with a given kinetic energy backscattered from a surface probes the surface region which is smaller than the layer analysed by X-ray photoelectron spectroscopy and Auger electron spectroscopy. Additionally, the depth analysed by the EPES method can be varied by changing the electron energies. This work presents a possibility of estimating the surface composition using the EPES approach on the example of AuPd alloys. The method involves measurements of intensity ratios of electrons backscattered elastically from alloy surface and a standard material, and then comparison to the intensity ratios resulting from the Monte Carlo simulation. The proposed method is tested by the Monte Carlo simulations of the elastic backscattering probabilities. It has been shown that the proposed method can be applied for fast estimation of the first monolayer composition in selected uniform binary alloy systems.

A detailed study of the line shape of high energy Cu X-rays excited Auger- and photoelectron spectra of layered samples is presented. The samples consisted of polycrystalline Cu and Ni overlayers of various thicknesses deposited on a Si substrate. The raw data show that the contribution caused by bulk inelastic scattering in the spectra increases significantly with overlayer thickness. Employing a general deconvolution procedure, the contribution of bulk inelastic scattering was consistently eliminated. The resulting spectra are in excellent agreement. The contribution caused by surface excitations has a very moderate effect at these high energies, while intrinsic losses were estimated to make up ∼30–50% of the total intensity. The true energy distribution at the source as seen by the spectrometer was established by elimination of the features due to surface excitations and the contribution from intrinsic excitations of the delocalized electronic states was determined.

The inelastic mean free paths (IMFPs) of three AuPd alloys were determined by means of elastic peak electron spectroscopy (EPES) in a round-robin study in four laboratories using different types of electron spectrometers in the energy range 0.5–2 keV. The scatter of the IMFP values was in the range of 25%. Within this accuracy the inverse IMFP of these alloys can be calculated by the weighted sum of the inverse IMFPs of the alloying elements. Reflected electron energy loss spectra also were measured and the Kl curves, calculated by the method of Tougaard, were used for estimating the inelastic processes in the alloys. The source of the scatter in the IMFPs obtained in the present work is discussed. Copyright  2002 John Wiley & Sons, Ltd.

In the present work our experimental results on the energy shifts and energy widths (full width of half-maximum) of the quasi-elastic peaks (1-5 keV) obtained using a high-energy-resolution electron spectrometer and different (C, Si, Ni and Au) surfaces are compared with those calculated by assuming single elastic scattering on free atoms having a Maxwell-Boltzmann thermal velocity distribution. There is a good agreement in the case of the energy shifts as well as for the energy broadenings obtained using higher atomic number polycrystalline samples (Ni, Au). In the case of Si, however, the measured energy broadening is systematically larger by 15-20% than the calculated broadening for the whole primary beam energy range. Compared with the calculated values, considerably larger broadenings (by 30-60%, depending on the primary beam energy) were observed for carbonic samples. The contribution of the multiple elastic scattering to the yield of the electrons backscattered elastically, and the effect of the multiple scattering on the energy shifts and Doppler broadenings, have been determined using Monte Carlo simulations. Our results show that multiple scattering causes only small changes in energy shifts and energy broadenings of elastic peaks in the case of the samples and primary electron energy region studied.

Considerable chemical effects have been found on the satellite structures of F KLL Auger spectra in fluorides recently, which could be important for surface chemical identification and could provide information on the origin and the atomic or molecular character of particular Auger satellite lines. In the case of alkali fluorides unassigned satellites were found and interpreted on the basis of a new concept, resonant orbital rearrangement. In the present work we study the structure of the Auger satellites induced from rutile-type fluorides. F KLL Auger spectra were excited by Al Kα and Cu Lα x-rays from polycrystalline powder samples of MgF2, ZnF2, NiF2, and CoF2 and measured by a high luminosity electron spectrometer. Excitation by Cu Lα increased the peak to background ratio in the spectra significantly. Similar to the alkali fluorides, a satellite has been found in the high kinetic energy part of the measured F KLL spectra. From the satellite intensities the fluorescence yield for the doubly ionized states in MgF2 has been determined. An inverse proportionality has been found between the satellite/diagram x ray and the corresponding Auger intensity ratios, while the latter ratios have been found to be proportional to the linewidth of the new Auger satellites. These observations indicate the resonant nature of the Auger transition identified. For determining the energy difference between the molecular orbitals in resonance, discrete variational Xα cluster molecular orbital calculations have been performed and the experimental results have been interpreted on the basis of the resonant orbital rearrangement model. Multiplet structure calculations for K6F clusters indicate that multiplet splitting cannot explain the origin of the above satellite peak in the F KLL spectrum of solid KF.

The inelastic mean free path (IMFP) is an important parameter for quantitative surface characterisation by Auger electron spectroscopy, X-ray photoelectron spectroscopy or electron energy loss spectroscopy. An extensive database of the IMFPs for selected elements, inorganic and organic compounds has been recently published by Powell and Jablonski. As it follows from this compilation, the published material on IMFPs for conductive polymers is very limited. Selected polymers, such as polyacetylenes and polyanilines, have been investigated only recently. The present study is a continuation of the research on IMFPs determination in conductive polymers using the elastic peak electron spectroscopy (EPES) method. In the present study three polythiophene samples have been studied using high energy resolution spectrometer and two standards: Ni and Ag. The resulting experimental IMFPs are compared to the respective IMFP values determined using the predictive formulae proposed by Tanuma and Powell (TPP-2M) and by Gries (G1), showing a good agreement. The scatter between the experimental and predicted IMFPs in polythiophenes is evaluated. The statistical and systematic errors, their sources and the possible contributions to the systematic error due to influence of the accuracy of the input parameters, such as the surface composition and density, on the IMFPs derived from the experiments and Monte Carlo calculations, are extensively discussed.

Quantitative characterization of overlayer nanostructures is important for many practical applications and has become a feasible task for electron spectroscopy. The QUASES (Quantitative Analysis of Surfaces by Electron Spectroscopy) software package, developed recently, provides a general tool for quantification in XPS by analysing the spectral shape of the background caused by inelastic scattering of the signal electrons and has been applied successfully for determining the thickness of surface films in the nanometre range. In this work the application of such analysis is extended to metallic films having several tens of nanometre thickness and the accuracy of the results is tested by using independent methods. Both Ni and Cu KLL Auger spectra were photoexcited from Ni and Cu overlayers (deposited onto Si substrates) of different thicknesses in the 10-60 nm range, and were measured with high energy resolution. The film thickness values from the QUASES spectral shape analysis are compared with the data obtained by using a quartz crystal microbalance, cross-sectional transmission electron microscopy and scanning probe microscopy (SPM). Good consistency has been found for the thickness values obtained from the spectral shape analysis and from microscopy, especially for Ni films. Assuming nominal film thickness, the values of the inelastic mean free path of 6-7 keV energy electrons in Ni and Cu were also determined, showing good (Ni) or reasonable (Cu) agreement with those proposed by Powell and Jablonski. The effect of island formation was shown by the QUASES spectral shape analysis and confirmed by SPM.

The radiative Auger (RA) KLL spectra of silicon, phosphorus and sulphur (as silica, phosphate and sulphate) have been measured and compared with the corresponding ‘real’ Auger spectra. The extra features in the RA spectra, over and above those that can be directly correlated with peaks in the Auger spectra, are shown to correspond to the structure that can be observed in K edge absorption spectra, save only for one peak that is due to a transition to the KL 2,3 L 2,3 3 P.

The X-ray excited KLL Auger spectra of polycrystalline Cu and Ni films, measured with high energy resolution and presented here, show intensive satellite structures of intrinsic origin. A good agreement is between the determined relative KL 23 L 23 energies or KL 3 L 3 relative intensities and their experimental (Cu) and theoretical (free atoms) values obtained earlier. However, the deviation is significant for the absolute Auger transition energies and very large for the relative intensity of the Ni KL 2 L 2 ( 1 S 0 ) line or of the initial state shakeup satellites.

Application of x-ray photoelectron spectroscopy, Auger electron spectroscopy and electron energy loss spectroscopy for quantitative characterisation of surfaces requires knowledge of the electron inelastic mean free path and its energy dependence. Inelastic mean free path values have been determined for a wide variety of solids using theoretical and experimental methods. However, the number of published inelastic mean free path values for polymers is limited. In principle, these values for polymers can be estimated using predictive formulae such as TPP-2M and the G1 formula of Gries. An alternative method for inelastic mean free path determination in polymers is elastic peak electron spectroscopy. In the present work, the surface chemical composition of polyaniline samples (undoped and doped with palladium) was analysed quantitatively using x-ray photoelectron spectroscopy. The inelastic mean free path values were determined by elastic peak electron spectroscopy using a high-energy-resolution hemispherical analyser in the energy range 500– 5000 eV. The resulting inelastic mean free path values evaluated using Ni and Ag standards are smaller than the values resulting from the G1 predictive formula of Gries and the TPP-2M predictive formula of Tanuma et al. The discrepancies in the inelastic mean free path values are discussed extensively. Copyright © 2000 John Wiley & Sons, Ltd.

Intensity ratios of electrons backscattered elastically from thick, amorphous Si, polycrystalline Ag and Au, as well as various (vacuum evaporated, electrodeposited layers and metallic sheets) polycrystalline Ni samples, were measured using high energy resolution and two different experimental geometries (0° and 50° primary and 50° and 0° scattered beam angles relative to the surface normal, respectively) in the range of 1-5 keV primary electron beam energy. The elastic yield ratios obtained experimentally are compared to the results computed by Monte Carlo simulations using different algorithms and different sets of parameters. In the case of measured elastic yield ratios Si/Ni, Ag/Ni and Au/Ni, systematic differences were observed between the respective values obtained for two experimental geometries, whereas each Monte Carlo calculation predicted similar ratios for the different geometries. For the Si/Ag, Si/Au and Ag/Au elastic yield ratios, however, good agreement is observed between experiment and calculation, resulting in similar ratios for each geometry. As a conclusion to our study, we suggest that when using a polycrystalline Ni standard reference sample for measuring elastic yield ratios the homogeneity of the sample should be ensured. Our results confirm the applicability of elastic peak electron spectroscopy in the case of these solids for deriving IMFP values, i.e. no significant role of surface effects on the elastic yield ratios can be identified in the primary beam energy range studied.

The understanding of the structure of high energy Auger spectra in metals and alloys of practical interest is relevant for studying solid state effects on core potentials, charge transfer and localization in these systems. In previous work evidence was found for the presence of intrinsic satellites in the LMM Auger spectra of 4d metals. Here we report the results of a study of the satellite structure identified in the high resolution KLL spectra of 3d metals Cu, Ni and some of their alloys. KLL spectra excited by Cu X-rays from polycrystalline Cu, Cu-noble metal and Ni-Fe alloy samples, were measured by a high luminosity hemispherical electron spectrometer. The satellite structures revealed in the spectra are compared to the structures obtainable on the basis of the spectator vacancy model. For the case of these metals and alloys, our results show that the KLL satellites can be attributed to intra-atomic 3d shake-up processes.

The inelastic mean free path (IMFP) values for organic materials are very limited. Numerous data have been published mainly for elemental solids, binary alloys and semiconductors. Generally, the IMFP values for different energies can be determined from the theoretical models involving the optical data, from predictive formulas, and from the experimental method called the elastic peak electron spectroscopy (EPES). In the present work the IMFPs in N–(CH)x polyacetylene (unstretched), synthesised according to Naarmann and Theophilou, and this polyacetylene doped with Pd were determined. The IMFPs energy dependence for the above samples has been obtained from the EPES in the primary electron energy range of 200–5000 eV. The experimental data have been recorded using three different spectrometers and compared with the theoretical data available.

ISO/TR 18394 provides guidance for the identification of chemical effects on x-ray or electron-excited Auger electron spectra as well as for applications of these effects in chemical characterization of surface/interface layers of solids. In addition to elemental composition, information can be obtained on the chemical state and the surrounding local electronic structure of the atom with the initial core hole from the changes of Auger electron spectra upon the alteration of its local environment. The methods of identification and use of chemical effects on Auger electron spectra, as described in this Technical Report, are very important for accurate quantitative applications of Auger electron spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.

ISO Technical Report 18392 provides the guidance for determining backgrounds in X-ray photoelectron spectra. The methods of background determination described in this report are applicable for the quantitative evaluation of the spectra of photoelectrons and Auger electrons excited by X-rays from solid surfaces and surface nanostructures. Copyright © 2006 John Wiley & Sons, Ltd.

We study the angular and energy dependence of surface and bulk plasmon losses accompanying deep core excitations in simple metals. Here full multiple scatterings of photoelectrons are taken into account before and after the plasmon losses within the quantum Landau formula, which can describe overall features of the photoemission bands. For example, multiple plasmon loss features can be calculated by use of the formula. Two simple metals, Al and Na, are studied here. The depth profiles of the plasmon losses are strongly influenced by the elastic scatterings. The model assuming single elastic scatterings overestimates the losses from deep emitters due to the forward focusing effects, whereas the model accounting for full multiple scatterings gives a much rapidly decaying function of the depth due to the defocusing effects and rich structures due to the photoelectron diffraction. The single elastic scattering approximation gives a poor result both for the depth profiles and for the loss spectra. The present multiple scattering calculations successfully explain the azimuthal dependence of the loss spectra, which reflect the local geometry around the emitters.

The energy distribution of the electrons backscattered in the direction of the surface normal of polycrystalline silver samples was studied using reflected electron energy loss spectroscopy (REELS) at 200 eV and 2 keV primary beam energies. For modeling the electron scattering processes, the Monte Carlo simulation technique was used and the REELS spectra were calculated at various (25°, 50° and 75°, with respect to the surface normal) angles of primary beam incidence. The effects of the surface energy loss process in REELS are evaluated from the comparison of the experimental and simulated spectra.

High resolution (1.0–1.6 eV) X-ray excited KLL and KLM Auger spectra and the respective Auger parameters of V, Cr, Mn and Fe, obtained from thin metallic layers, are reported. The corresponding experimental (Auger) transition energies (the first high resolution experimental data except for Mn) and relative Auger intensities are compared with data obtained earlier following electron capture in the decay of radioactive isotopes, and also with available theoretical estimates. Differences in the surface chemical states of the samples and in the methods applied for evaluation of the spectra could explain the considerable deviations between the two sets of experimental results, rather than differences in the Auger process following photoionization and electron capture. The number of Auger transitions identified in the KLL spectra shows the applicability of the intermediate coupling model for these cases.

The electron energy distribution of the backscattered electrons from a polycrystalline silver sample was studied in the direction of the surface normal of the specimen, at the 200 eV and 2 keV energy of the primary beam. The angle of the incident electron beam was 50° with respect to the surface norm. For simulation of the backscattered electron energy distributions the Monte Carlo technique was used and the computed spectra were compared to the measured reflected electron spectra in the energy range of few times 10 eV from the elastic peak. The probable reasons of the observed discrepancies between the measured reflected electron energy loss spectra and the calculated spectra are discussed. In addition, the yield of the backscattered electrons as a function of the number of elastic and inelastic collisions is compared for different parts of the backscattered electron spectra.

High-resolution core and valence band photoemission as well as photoinduced Auger spectra of metallic Sn, polycrystalline SnO and SnO2 ((110) natural single-crystal cassiterite and polycrystalline) samples were measured in order to give information on local electronic and geometric structures around the core-ionized atoms and far providing data for facilitating quantitative analysis of systems containing these species, The SnO surfaces were obtained without the use of ion sputtering by using a special preparation procedure based on in vacuo surface scraping, The respective experimental valence land spectra could be utilized in quantitative analysis of layered tin oxide structures. Valence band spectral shapes are compared to spectra calculated by using a cluster-type (DV-X alpha) MO model. From the Sn Auger parameter measurements, using a simple electrostatic model, the similarity of the initial-state effects for the two oxides was deduced, while the oxygen Auger parameter values indicated large polarizability and the respective final-state hole-hole repulsion energies were determined.

The electronic structures of different phosphates were studied by using the DV-X alpha cluster molecular orbital method, Experimental data on crystal structures from x-ray diffraction measurements were used to set up realistic model clusters. Theoretical XPS valence band spectra obtained from the DV-X alpha calculations were compared to our high-resolution XPS measurements on polycrystalline powder Li3PO4, Na3PO4, Na4P2O7 and (NaPO3)(n) samples, These new measurements made possible a more rigorous test of the theoretical approach and more reliable shape analysis than the previous set of data obtained by non-monochromatized measurements combined with the resolution enhancement technique, Systematic study of different clusters showed that the cations around the PO4 cluster and the distortion of the PO4 tetrahedra due to the anisotropic crystal forces play only a minor role and their influence on the valence band spectra was found to be negligible, In the case of polyphosphates, considerable changes were found in the valence band spectra as a consequence of small changes in the bond angle of the P-O-P bridges, Our results, based on cluster parameters specific to the anhydrous crystals, are in good agreement with the experiments.

Core-valence (KLV, KVV, LVV) Auger and valence band XPS spectra of aluminium have been measured by high resolution and high sensitivity electron spectrometers and interpreted by different theoretical models. For core-core-valence transitions both the Green function formalism, applied to account for the distortion of the local density of states due to the presence of the final state core hole, and the cluster MO (DVXα) calculation, using a cluster potential with a core hole, describe well the shape of the measured spectra. In the case of the Al KVV spectrum, a spectral width (FWHM) of 14.5 e.V has been observed which is considerably smaller, than predicted by previous experiments. The shape of the core-valence-valence Auger spectra can be interpreted successfully using the ground state density of states obtained from the cluster MO model.