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XPS (3d) and Auger spectra (MNN) of deposited Ag n -clusters on a non-sputtered HOPG surface have been measured. Most of the XPS and Auger spectra appear very similar to the corresponding bulk spectrum, caused by a high mobility and agglomeration of the clusters on the inert carbon surface, independent of the initial cluster size. The metallic fingerprint of the cluster-agglomerated islands is sustained under UHV conditions for several days. Oxidised Ag-islands reveal a positive binding energy shift in distinct contrast to the negative XPS shift usually observed for silver oxide bulk compounds. The XPS binding energy shift has been used for estimation of the diameter of the cluster-assembled nanoislands (6–9 nm) using an electrostatic model. [ABSTRACT FROM AUTHOR]

The shape and intensity of measured Auger peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and to intrinsic excitations induced by the sudden creation of the two static core holes. Following a method developed for XPS in a previous work [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17], we have calculated the effective energy-differential inelastic electron scattering cross-sections, including the effects of the surface and of the two core holes, within the dielectric response theory by means of the QUEELS-XPS software (QUantitative analysis of Electron Energy Losses at Surfaces for XPS). The Auger spectra are then modeled by convoluting this energy loss cross section with the primary excitation spectrum that accounts for all effects which are part of the initial Auger process, i.e. L–S coupling and vacancy satellite effects. The shape of this primary excitation spectrum is fitted to get close agreement between the theoretical and the experimental spectra obtained from X-ray excited Auger electron spectroscopy (XAES). We have performed these calculations of XAES spectra for various LMM Auger transitions of pure Cu ( L 3 M 45 M 45 , L 3 M 23 M 45 , L 3 M 23 M 23 and L 2 M 45 M 45 transitions). We compare the resulting primary excitation spectra with theoretical results published in the literature and obtain reasonable quantitative agreement. In particular, we extract from experimental spectra quantitative intensities due to Coster–Kronig, shake-off and shake-up processes relative to the intensity from the “normal” Auger process. [ABSTRACT FROM AUTHOR]

Abstract: The application of the Wagner plot and Auger parameter concepts as tools for the identification of chemical states of atoms in molecules or solids is growing steadily in the surface science literature. In several publications, however, the chemical and physical insights provided by such conceptual tools are not fully investigated. In this contribution it is shown how easy is to use the Wagner plot to get information on the local valence charge and Madelung (molecular) potential (initial-state effects) and on the extra-atomic relaxation energy gained from the environment (final-state effects) for a core-ionized atom. To cover the gap with previous reviews on the applications of the Wagner plot and the Auger parameter concepts, a brief overview of the contributions which appeared in the literature in the last 15years is presented. [Copyright &y& Elsevier]

Abstract: The quantum mechanical Bloch-wave method combined with the reciprocity principle has been used to describe electron transport in crystalline solids for determining the emission depth distribution function (EMDDF) of signal electrons in surface electron spectroscopy. The crystal structure and electron coherent scattering are explicitly taken into account; these are neglected in classical Monte Carlo methods. While electron inelastic scattering is treated with an optical potential, the EMDDF for Auger-electron emission from an Au (001) surface is calculated by the quantum method. The dependence of the EMDDF on emission angle and crystal structure has indicated that this quantum EMDDF strongly depends on the emission direction of Auger electrons and is sensitive to crystal structure. Comparisons made between the present results and classical Monte Carlo simulation results show pronounced differences due to electron-diffraction effects. The mean escape depth (MED) which describes the surface sensitivity of Auger electron spectroscopy, is also evaluated; the present calculation shows that the MED for a crystalline solid is about half that for an amorphous solid from a Monte Carlo calculation. [Copyright &y& Elsevier]

Abstract: Measurements of electron emission spectra from surfaces of aluminum fluoride impacted by keV noble gas ions show a high-energy structure, peaking around 7eV that increases in intensity with ion energy. The shape of this structure, identified by Factor Analysis, is independent of the nature and the energy of the impinging ions. We discuss one electron, two electron and plasmon excitation mechanisms and conclude that the high-energy structure results from the autoionization of F− 2p 4 nl n′l′ excited by electron promotion in close atomic collisions. [Copyright &y& Elsevier]

Abstract: The desorption kinetics of hydrogen from polished 6H–SiC(0001) surfaces exposed to various sources of hydrogen have been determined using temperature programmed desorption (TPD). For (3×3) 6H–SiC(0001) surfaces prepared via annealing and cooling in SiH4, desorption of 0.2±0.05 monolayer of molecular hydrogen was observed to occur at ≈590°C. This β1 H2 desorption peak exhibited second order kinetics with an activation energy of 2.4±0.2eV. For (3×3) 6H–SiC surfaces exposed to atomic hydrogen generated via either a hot rhenium filament or remote hydrogen plasma, low energy electron diffraction patterns showed an eventual conversion back to (1×1) symmetry. Spectra acquired using Auger electron and X-ray photoelectron spectroscopies revealed that the atomic hydrogen exposure removed the excess Si. Photoelectron spectroscopy results also showed a 0.5eV increase in binding energy for the Si2p and C1s core levels after removal of the Si–Si bilayer that is indicative of a decrease in band bending at the SiC surface. TPD from the (3×3) 6H–SiC(0001) surfaces exposed to atomic hydrogen showed substantially more molecular hydrogen desorption (1–2ML) through the appearance of a new desorption peak (β2,3) that started at ≈200°C. The β2,3 peak exhibited second order desorption kinetics and a much lower activation energy of 0.6±0.2eV. A third smaller hydrogen desorption state was also detected in the 650–850°C range. This last feature could be resolved into two separate desorption peaks (α1 and α2) both of which exhibited second order kinetics with activation energies of 4.15±0.15 and 4.3±0.15eV, respectively. Based on comparisons to hydrogen desorption from Si and diamond surfaces, the β and α desorption peaks were assigned to hydrogen desorption from Si and C sites, respectively. [Copyright &y& Elsevier]

Abstract: The interaction of oxygen with the 10-fold-symmetry surface of the decagonal quasicrystal at high temperatures was investigated by low-energy-electron diffraction and Auger electron spectroscopy. The results are consistent with a well-ordered aluminum-oxide layer possessing a hexagonal antiphase domain structure with a limited lateral size of about 35Å. We claim that the separation distances of the domain boundaries, separating domains of equal orientation, are primarily a consequence of the preferential cluster nucleation on decagonal Al–Co–Ni. The domains are azimuthally oriented along one direction of the two sets of five twofold-symmetry axes lying on the decagonal surface in accordance with the local symmetry of the quasicrystal surface, while the size of the domains can be explained in terms of self-size-selecting arguments. [Copyright &y& Elsevier]

Abstract: Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) were applied to investigate the segregation of aluminum atoms on a Cu-9at.% Al(111) surface. We observed that the Al concentration in the top layer ranged between about 9 and 36at.% after the sample we used was annealed at different temperatures. The phenomenon of Al atoms segregating on the surfaces was explained well by considering the diffusion length of Al atoms in bulk Cu. LEED measurements showed that R30° structures grew as the concentration of Al atoms increased. The segregation phenomena on surfaces resulted in a stable two-dimensional Cu67Al33 alloy phase in the top layer. [Copyright &y& Elsevier]

Abstract: The formation of doubly excited states of He atoms during collisions of He2+ ions with energies between 60eV and 1keV with a Ni(110) surface is studied via Auger electron spectroscopy. We observe that the electron spectra from autoionization of doubly excited states of 2s 2, 2s2p, 2p 2 configurations show a pronounced dependence on the coverage of the target surface with oxygen. For a controlled O2 adsorption on the Ni(110) surface we can explain the resulting changes in the electron spectra by the modification of the work function of the target surface. Thermal desorption and dissolution into the bulk of surface contaminations at elevated temperatures provides an alternative interpretation of recent work where the local electron spin polarization of a Ni(110) surface was deduced from changes in the electron spectra as function of target temperature. [Copyright &y& Elsevier]

Abstract: We describe a universal Monte Carlo algorithm that can be used for the efficient calculation of backscattering factors (BFs) for quantitative Auger-electron spectroscopy (AES). This algorithm makes use of the continuous slowing-down approximation and the electron stopping power instead of simulation of individual inelastic-scattering events. This approach is attractive because it can be applied to any material with an empirical formula for the stopping power, available data for differential elastic-scattering cross sections, and an empirical formula for inner-shell ionization cross sections. We report BFs for the Si KL23L23, Cu L3M45M45, Ag M5N45N45, and Au M5N67N67 Auger transitions in the corresponding elemental solids. These BFs were calculated for normal incidence of the primary beam, primary energies from near threshold for ionization of the relevant core levels to 20keV, and Auger-electron emission angles of 10°, 60°, and 80°. We found satisfactory agreement between these BFs and values obtained from a more accurate algorithm in which individual inelastic-scattering events were simulated. Percentage deviations between BFs from the two algorithms were <2% for Au, <5% for Ag, <7% for Cu, and <10% for Si for primary energies likely to be used in practical AES. These deviations arise mainly from our use of stopping powers from the empirical formula rather than more reliable values calculated from experimental optical data. [Copyright &y& Elsevier]

Acetonitrile (CH3CN) adsorbs on Si(001)-2×1 at room temperature under two forms, a cycloaddition-like adduct (Si–C＝N–Si) and a pendent cyano (Si–CH2–C≡N) resulting from the decomposition of the molecule. Resonant Auger spectroscopy has been used to study the excited-state-dependent electron transfer from the N 1s core-excited molecular adsorbate to the silicon substrate, using the core-hole lifetime (∼6fs) as an internal clock. It is shown that the πC＝N∗ NEXAFS state lies within the silicon bandgap because of a core-excitonic effect. Therefore no charge transfer of the excited electron to the substrate is observed. On the other hand the πC＝N∗ NEXAFS state is placed within the silicon conduction band. Excitation to this orbital leads to valence/Auger spectra in which both resonant and normal Auger contributions are observed. Therefore there is evidence for a charge transfer from the pendent C≡N to the silicon surface, on a timescale estimated to tens of femtoseconds. [Copyright &y& Elsevier]

Abstract: The interplay between swelling and milling phenomena in determining the morphology of Focused Ion Beam (FIB) -processed MgO(001) was investigated by atomic force microscopy. At the early stages of ion irradiation, before milling erosion is observed, MgO shows a relevant swelling behaviour with protrusion of the bombarded areas up to 6nm for a dose of 5×1016 ionscm−2. The effect is mainly ascribed to subsurface defect accumulation, while the low Ga ions concentration, as measured by in-depth Auger analysis, seems to exclude a contribution from ion implantation. In order to explain and control the morphology of Fe/NiO FIB patterned sub-micron structures on MgO substrates, we have also investigated FIB effects on Fe(001) and NiO(001) single crystals. Absent or negligible swelling has been observed on these materials. [Copyright &y& Elsevier]

Abstract: Recent joint theoretical and experimental investigations of Auger core–core–valence spectra of alkali adatoms on simple metals have revealed that such technique is capable to ascertain contributions from different adsorption environments in the signal [M.I. Trioni, S. Caravati, G.P. Brivio, L. Floreano, F. Bruno, A. Morgante, Phys. Rev. Lett. 93 (2004) 206802]. Consequently, to verify if such an effect is present also for other chemical species, we study theoretically the KLV transition of oxygen either as a bulk impurity or as an adsorbate in/on Al and Ag (jellium-like). We make use of the Fermi golden rule in which the matrix elements of the interaction are calculated within DFT. We verify that the relevant physical quantity of this phenomenon is the excited local density of states (LDOS), calculated within a region centered on the core ionized atom. The Auger rate for oxygen in Ag bulk displays a single asymmetric peak, while for adsorbed oxygen a second smaller feature at lower energies, and very close to the first one, appears. This unexpected result follows from the removal of the degeneracy of the m quantum number of the 2p states of oxygen at the surface. It is only displayed on the electronically less dense metal (Ag), but not on Al. [Copyright &y& Elsevier]

Abstract: The growth and chemical composition of Co on Cu(100) has been studied by He ion scattering and Auger electron spectroscopy (AES) at different temperatures (T=130K, T=300K and T=410K). Based on different information depths for electron-induced Cu-MNN and Cu-LMM Auger signals and inner shell production by grazingly scattered protons restricted to the topmost layer, we have modeled the Auger data in order to obtain quantitative information on the chemical composition of ultrathin intermixed Co–Cu films. We find that intermixing and Cu diffusion is not only important for film growth at elevated temperatures, but also for heterogeneous Co/Cu epitaxy at room temperature. [Copyright &y& Elsevier]

Abstract: The spreading of Pb and Bi adsorbed layers from pure bulk sources, and their intermixing, on a Cu substrate, has been studied by scanning Auger microscopy at 473K. The pure Pb layer spreads faster than the Bi layer. When the pure layers meet, two phenomena are observed. The junction line of the two adsorbed layers drifts due to a replacement of adsorbed Pb by Bi. Superimposed on this drift, the Pb and Bi layers undergo interdiffusion. The interdiffusion coefficient has been analyzed by the Boltzmann–Matano method. [Copyright &y& Elsevier]

The adsorption of O2, CO and H2O on a hydrogen precovered beryllium surface was studied using direct recoils spectrometry and Auger electron spectroscopy. It was found that preadsorbed hydrogen, in addition to adsorption site blocking, changes the Be electronic structure in a way that hinders the adsorption of O2 and CO on the surface. Apparently, repulsion between the preadsorbed hydrogen and adsorbed oxygen or CO creates depletion zones between them. For oxygen it also promotes agglomeration and penetration into the subsurface and leads to oxide nucleation at lower oxygen overages. For H2O, only a minor delay of adsorption and hydrogen replacement was observed. [Copyright &y& Elsevier]

Dissociative chemisorption of O2 on Cu(1 0 0), S/Cu(1 0 0) and Ag/Cu(1 0 0) surface alloy has been investigated by Auger electron spectroscopy (AES). A strong reduction in the initial O2 chemisorption probability (S0) from 0.05 to 7.4 × 10−3 is observed already at an Ag coverage of 0.02 ML. Further Ag deposition results only in a moderate decrease in S0. Similar inhibition of O2 dissociation is observed on S/Cu(1 0 0). It is concluded that at very low Ag coverages, the reduced reactivity of Ag/Cu(1 0 0) towards O2 dissociation is primarily due to the steric blocking of the surface defects and that any electronic effects are only secondary and present only at higher Ag coverages. [Copyright &y& Elsevier]

Carbon adsorbate-induced (√3×√3)R30° reconstruction has been observed on the Ge(1 1 1) surface by reflection high-energy electron diffraction and Auger spectroscopy. The superlattice evolves in a continuous fashion to a (1 × 1) structure in a phase transition with a critical temperature Tc∼1040 K; a temperature very close to the well-known high-temperature phase transition on clean Ge(1 1 1). The temperature dependence of the superlattice diffraction intensity near Tc is investigated. [Copyright &y& Elsevier]

Desorption of Sb from Si1−xGex layers (x=0, 0.05, 0.1, 0.2, 1) grown by molecular beam epitaxy (MBE) on Si(1 0 0) substrates is investigated using Auger electron spectroscopy thermodesorption (TD-AES). Sb desorption process on Si1−xGex is well described by a first-order reaction. No extra TD-AES peaks are observed on Si1−xGex compared to Si. For 1 ML of Sb coverage the TD-AES peak shifts to lower temperature when Ge bulk concentration increases. The Sb monolayer desorbs at 801, 752, 740, 715, and 706 °C for x=0, 0.05, 0.1, 0.2 and 1, respectively. We explain the non-linear decrease of the Sb desorption energy when x increases by the strong Ge surface segregation during the MBE growth of Si1−xGex layers, resulting in an almost pure Ge surface even for low x. [Copyright &y& Elsevier]

The interaction of submonolayer lead deposits with oxygen pre-exposed Ni(1 0 0) has been investigated by Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). By comparison with the Auger line shapes of metallic lead and orthorhombic lead oxide, chemical effects have been evidenced in the Pb Auger spectrum, for submonolayer lead deposits performed on the NiO phase (hydroxylated or not). Inversely, it has been shown that no chemical effect occurred for lead deposits performed on an O-adsorbed phase. This difference of chemical state has been used to investigate the growth mode of NiO on Ni(1 0 0). The nucleation and growth of NiO islands among an O-adsorbed phase have been proved through this lead deposit approach, which appeared distinctly more sensitive than LEED to evidence the beginning and the end of the “biphased” domain. Under annealing to T&ges;500 K, the decomposition of a full oxide thin film, into a mixture of oxide islands and O-adsorbed phase, has also been evidenced through this lead deposit method. [Copyright &y& Elsevier]

We studied the adsorption of CO on ultrathin Cr layers on Ru(0 0 0 1) as a function of Cr coverage and deposition temperature. The preparation of the Cr layers was characterized by Auger electron spectroscopy, low energy electron diffraction, and the subsequent CO adsorption itself. At 90 K Cr grows statistically on Ru(0 0 0 1). For Cr deposition at 700 K, a pseudomorphic monolayer is formed; thereafter Cr grows in three dimensional islands and the formation of a highly ordered bcc(1 1 0) Cr phase is observed. For Cr deposition at 1000 K we propose the formation of a stable surface alloy. Temperature programmed desorption of CO after dosing onto the Cr layers prepared at 700 and 1000 K indicates an enhanced reactivity of the layers towards CO dissociation upon heating as compared to Ru(0 0 0 1). In both cases a high temperature CO desorption state (above 700 K) is observed that is attributed to recombinative desorption of CO; its intensity increases up to a nominal Cr coverage of 1 ML. For the Cr layers prepared at 700 K, this state is observed already at the lowest Cr coverage studied (0.12 ML); for 1 ML Cr, 47% of the saturated CO layer decompose upon heating. For the Cr layers prepared at 1000 K (surface alloy) significant decomposition is observed only for Cr coverages larger than 0.5 ML; a maximum fraction of 18% of the saturated CO layer decomposes upon heating. Thus, the Cr layer prepared at 700 K is more reactive towards CO dissociation than the one prepared at 1000 K. [Copyright &y& Elsevier]

We have measured the initial (zero coverage) photon (1.5) and electron emission from the reaction of a Cl2 molecular beam with a potassium surface for a range of molecular velocities (460 m/s). Three distinct features are observed: (1) A majority of the photons are emitted with hν>eΦ, where eΦ is the work function of K (=2.25 eV), i.e. energies where electrons can also be emitted. (2) The photon spectrum is shifted towards shorter wavelengths at higher Cl2 velocities. (3) The photon yield varies only weakly with increasing Cl2 velocities. The photon and exoelectron emission observations are generally consistent with the basic picture that both electrons and photons are created by energetic (non-adiabatic) transitions from valence band states of potassium to a Cl 3p5 hole state, shifted up to ∼4 eV below the Fermi energy. The third point above, the weak variation of the photon emission yield with vCl2 is in stark contrast to the exoelectron results, where a strong yield increase with the molecular velocity is observed. Details of the velocity dependence of photon and electron emission are still not fully understood, and require advanced calculations. [Copyright &y& Elsevier]

The graphite core–valence–valence (CVV) Auger spectrum is analysed, within a one-particle approximation, by comparison to the X-ray excited valence band (VB) photoemission spectrum, whose structure is well understood in terms of the graphite density of states (DOS). The aim is to identify the electron states originating the components into which the CVV spectrum is resolved by double differentiation. Contributions assigned to self-folds of VB photoemission features and hence due to transitions coupling electrons from the same DOS feature, dominate the spectrum away from the middle region, while folds between different features are important in the middle region. A single particle approximation proves to be adequate to account for the low binding energy, mostly p-like, part of the spectrum. It brakes down however in the high binding energy, mainly s-like, region where spectral distortion is ascribed to a nonnegligible (&ap;2 eV) Coulomb repulsion between final state holes of s-symmetry. [Copyright &y& Elsevier]

The angular dependence of Auger electrons excited from single-crystal surfaces is treated theoretically within a multiple-scattering cluster model taking into account the full Auger transition matrix elements. In particular the model has been used to discuss the influence of multiple scattering and angular momentum of the Auger electron wave on Auger electron diffraction (AED) patterns in the region of low kinetic energies. Theoretical results of AED patterns are shown and discussed in detail for Cu(0 0 1) and Ni(0 0 1) surfaces, respectively. Even though Cu and Ni are very similar in their electronic and scattering properties recently strong differences have been found in AED patterns measured in the low-energy region. It is shown that the differences may be caused to superposition of different electron diffraction effects in an energy-integrated experiment. A good agreement between available experimental and theoretical results has been achieved. [Copyright &y& Elsevier]

Fe films 10 monolayers thick were prepared in ultrahigh vacuum by thermal deposition on in-air cleaved MgO(0 0 1) substrate held at room temperature and 500 °C. Auger electron spectroscopy, low energy electron diffraction, and scattering-interference of primary and backscattered electrons were used to investigate the growth mode and the structure of the film. The room temperature deposition results in a nearly continuous (90% fractional coverage) body-centred-tetragonal film with the Fe[0 0 1]&par;MgO[0 0 1] and Fe〈1 0 0〉&par;MgO〈1 1 0〉 orientation relationships. Film annealing at 300 °C increases the quality of the film. In-plane expansion of +2.4% and out-of-plane contraction of −3.2% of the Fe cubic cell has been determined. A complete removal of the tetragonal distortion and a strong islanding (35% fractional coverage) occur for annealing temperature of 500 °C. Film deposition at 500 °C substrate temperature leads to body centred Fe islands that cover about 55% of the substrate. [Copyright &y& Elsevier]

Abstract: Silicon (Si) nanocrystals (NCs) less than 5nm in diameter are grown on SiO2 surfaces using hot wire chemical vapor deposition in an ultrahigh vacuum chamber and the dangling bonds are passivated using atomic deuterium. The passivated NCs are subsequently exposed to BDx radicals formed by dissociating deuterated diborane (B2D6) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of additional D2 desorption peaks beyond those found for surfaces that have only been passivated by atomic deuterium. The additional peaks appear at lower temperatures and this can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination leading to photoluminescence quenching. [Copyright &y& Elsevier]

• Nanofocusing photoelectron spectroscopy using zone-plate X-ray optics. • Exploration of Ag-nanoparticles (2–20 nm) on free-standing graphene via X-ray photoelectron and Auger spectroscopy. • Formation of a thin passivating oxide layer upon oxidation of Ag-nanoparticles. • Size-dependent morphology change (3D→2D) of Ag-nanoparticles. • Final state Coulomb shift upon photoionization of oxidized Ag-nanoparticles. Silver nanoparticles with a mean diameter of 15 nm have been grown on free-standing graphene and explored by soft X-ray synchrotron radiation using the ESCAmicroscopy beamline at Elettra. In particular, the 3 d core orbitals and valence band (4 d /5 s) of pristine and plasma-oxidised Ag-nanoparticles have been investigated by X-ray photoelectron spectroscopy (XPS), X-ray induced valence band photoemission, and MNN Auger spectroscopy. The X-ray spectra of the pristine Ag-nanoparticles, i.e. XPS, Auger and UPS spectra, are very similar to these of the metallic Ag-bulk film while the spectra of the oxidised Ag-nanoparticles exhibit distinct differences with respect to the oxidised Ag-bulk film. This is inferred from a larger valence band width, an extended valence band photoemission intensity nearly up to the Fermi level of the bulk metal, a smaller two-hole Coulomb correlation energy and a rather bulk-like Auger spectrum. We interpret this as to result from a shell-like composition of the Ag-nanoparticles with a thin passivating oxide layer and an inner metallic core. Moreover, the 3 d photoemission peak of the oxidised nanoparticles is shifted to higher binding energy with respect to the bulk oxide peak. This is attributed not only to an XPS chemical shift but also to an additional final state Coulomb charging according to the electrostatic liquid drop model. Comparing the core binding energy shift of Ag-nanoparticles with the electrostatic potential of a spherical compact particle and a flat nanoislands a morphology transformation of the oxidised nanoparticles from 3D to 2D is obvious in the size range 5–15 nm. Image, graphical abstract [ABSTRACT FROM AUTHOR]