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A joint experimental and theoretical investigation of epitaxial MnO films on Ag(001) also including the reference systems Ag(001) and MnO(001) is presented using photoelectron diffraction (XPD) supported by photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). MnO films have been grown with thicknesses 1 to 5 nm. The conditions of film growth (temperature and time) have been chosen to obtain information on the development of film structure with thickness and to permit comparison regarding film absorption and diffraction studies. Experimental angular distribution patterns (ADP) and angular distribution curves (ADC) have been recorded and analyzed by comparing the results to multiple scattering cluster calculations. Excellent agreement was obtained for the description of the ADCs of Ag(001) and MnO(001) surfaces, and fine structures due to multiple scattering effects have been clearly identified. The multiple scattering analysis has been found to be indispensable in particular for a structural analysis of the oxide material. ADPs of MnO films grown on Ag(001) have supported the epitaxial growth of the films from the beginning. The analysis of the ADCs in dependence on growing MnO film thickness has provided clear evidence for strained, tetragonally distorted MnO films for the first few nm, while the thicker films of about 5 nm have evidently adopted bulk structure and bulk lattice constants. These results are discussed in comparison to recent structural studies of MnO on non-lattice matched metal substrates resulting in a rather similar plot for the oxide growth.

The surface termination of oxide surfaces is of crucial importance for the growth of a second material like metals or other oxides. In this study we have investigated the surface of a BaTiO 3 (001) single crystal during sample preparation by various electron spectroscopic methods. It is shown by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and metastable induced electron spectroscopy (MIES) that during sputtering a Ba rich overlayer is formed, in which the Ba 2+ ions are under coordinated. Below this layer, an oxygen deficient BaTiO 3 layer is found. During annealing, we observe the reformation of the crystalline structure. UP and MIE spectra provide clear evidence of a BaO terminated surface. X-ray photoelectron diffraction studies support this result, comparing recorded polar angle scans with calculated intensity modulations using multiple scattering cluster models.

The atomic structure of a four layer thick film of CoO on a Ag(0 0 1) substrate has been determined by comparing experimental low-energy electron diffraction (LEED) I(V) curves with multiple scattering calculations. The CoO film has been prepared using reactive evaporation of Co in an oxygen atmosphere leading to almost layer-by-layer growth. Contrary to the surface of CoO crystals an outward relaxation of the two outermost CoO layers as well as rumpling in the top layer has been found. The supposed driving force of this relaxation is the in-plane compressive stress, which results from the pseudomorphic growth of the CoO film on the Ag(0 0 1) substrate and the lattice mismatch of the two materials.

We have investigated the structure of thin MnO films grown on a single-crystal Ag(0 0 1) surface in dependence on layer thickness by combination of low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) methods. The analysis of LEED profiles shows that the in-plane lattice constant of the epitaxial grown MnO film on Ag(0 0 1) depends strongly on the thickness of the film. The analysis of LEED data leads to the assumption that the lattice mismatch between MnO and Ag may be released by a tetragonal distortion of the film in comparison to bulk-MnO. In addition, XPD measurements in forward-scattering conditions are considered. Polar-angle scans have been recorded and analysed for Mn2p and O1s photoelectrons excited by Al Kα radiation to get detailed structural parameters. It is shown that, in contrast to thin films of simple metals, the forward-scattering model should be applied very carefully in the interpretation of XPD data.

The local structure of thin CoO films grown on a single crystal Au(1 1 1) surface has been studied by Auger electron diffraction (AED). Therefore, the angular dependence of the Auger electron intensity of Co-LMM and O-KLL Auger electrons was recorded in the total half-space above the film. Such 2π-scans immediately reflect the symmetry of the surface and the local structure of the film. The experimental data are compared to multiple-scattering cluster calculations, where both the influence of multiple-scattering effects and effects of Auger transition matrix elements have been investigated. We have found that the AED patterns of a CoO film in forward-scattering conditions do not always provide straightforward information on the local structure of the film, whereas the multiple-scattering approximation applied gives very good agreement between experimental and theoretical results.

We present X-ray Photoemission (XPS) and low energy electron diffraction (LEED) investigations of initial stages of GaN film growth on sapphire(0 0 0 1) and SiC(0 0 0 1)-√3 × √3:Ga. The growth of ultrathin films is performed by successive metal deposition and ion beam induced nitridation. Epitaxial GaN films have been obtained on both substrates, but in case of sapphire, additional domains rotated by 20° have been observed. The experimental data demonstrate that the growth on sapphire proceeds via a reactive spreading mechanism including a metallic wetting layer on the growing GaN fed by outdiffusion of the Ga metal from 3D droplets. In case of SiC(0 0 0 1) we provide evidence for a 2 ML thick Ga wetting layer on the reconstructed substrate, which forms after metal deposition. But further nitride growth also involves a Ga wetting layer on GaN.

Ultrathin manganese monoxide films on silver single crystal substrates are studied as a function of the thickness using X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). It was found that electronic and geometric properties in ultrathin films differ from the bulk. A tetragonal distortion of the oxide films is revealed by polarisation-dependent X-ray absorption measurements: the extent decreases with increasing film thickness. A structural relaxation of epitaxial oxide layers induced by heating also leads to a decrease of the tetragonal interface strain. The electronic structure of ultrathin manganese oxide films in the valence band region is very similar to that in the bulk oxide.

The molecular ordering and orientation of zinc phthalocyanine (ZnPc) on a ZnS film as well as the chemical properties of the interface were investigated by X-ray photoelectron and absorption spectroscopy with synchrotron radiation excitation. Core level photoelectron spectra of the substrate and the ZnPc film indicate a weak interaction at the interface. We observe a high molecular ordering, which is enhanced with increasing film thickness. A standing (or highly-tilted) molecular orientation in about 8 nm-thick ZnPc films is deduced from the polarization dependence of the N K X-ray absorption spectra. The same result was obtained from excitation energy dependence of the intensity ratio of the two carbon species in C 1s core level spectra. The annealing of the sample up to about 400 °C causes a desorption of ZnPc and a stronger interaction between remaining molecules and ZnS.

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.

We have performed quantum chemical calculations based on density functional theory on different surface structures modeling the sulfur treated InP(0 0 1) surface. The models were selected to explain new experimental results from electron diffraction and photoelectron emission, where a phase transition from a low temperature sulfur-rich InP(0 0 1):S (2×1)A-phase to a high temperature sulfur-poor InP(0 0 1):S (2×1)B-phase was observed. The energetic stability of models with different stoichiometry is compared by calculation of thermodynamic phase diagrams.The most probable candidate for the low temperature sulfur-rich structure seems to be a model which involves 0.5 monolayer (ML) sulfur in a PS-mixed-dimer on the surface, 1 ML sulfur inserted on phosphorus sites in the second layer and 0.5 ML sulfur inserted on phosphorus sites in the fourth layer. Additionally, one In-vacancy per (2×1) unit cell in the third layer has to be created to fulfil the electron counting rule. The sulfur-poor surface structure has only one sulfur component (0.5 ML). From the energetic point of view a model with InS-mixed-dimers on the surface is slightly favored in comparison with a model, where the surface sulfur in the InS-dimer is exchanged with phosphorus in the second layer.

Angle-resolved photoemission and low-energy electron diffraction (LEED) were used to study thin films of DyNi(0 0 1) grown in situ under ultra-high vacuum conditions by codeposition of Dy and Ni onto a W(1 1 0) substrate and subsequent annealing. Guided by the results of electronic structure calculations an observed (3×1) overstructure of the LEED pattern and the appearance of a Dy 5d-derived surface state at the Fermi energy are explained by a reconstruction of the (0 0 1) surface resulting from missing Ni rows in the topmost atomic layer. Similar to metallic Gd(0 0 0 1) the d-like behavior of the obtained surface state may influence surface magnetic properties of thin films of DyNi.

A novel method of surface sulfurization based on in situ PbS deposition at elevated substrate temperatures followed by successive annealing has been used for investigation of sulfur-induced surface reconstructions on InP(0 0 1)-(2×4). Two different (2×1) reconstructions have been observed by low-energy electron diffraction at 200–410°C and 420–445°C, respectively, separated from each other by a (1×1) pattern in the range of 410–420°C. A consistent examination of the results provided by electron diffraction and photoemission techniques has allowed us to propose models of atomic arrangement for both observed (2×1) structures.

We have prepared ordered thin films of CoO by evaporating cobalt in an O2 atmosphere on to a heated (500 K) Ag(100) substrate. The geometric and electronic structure of the films was characterized by means of Auger electron diffraction (AED) and angle-resolved photoemission spectroscopy (ARUPS), respectively. The experimental AED results were compared with simulated data, which showed that the film grows in (100) orientation on the Ag(100) substrate. Synchrotron-radiation-induced photoemission investigations were performed in the photon energy range from 25 eV to 67 eV. The dispersion of the transitions was found to be similar to that of previous results on a single-crystal CoO(100) surface. The resonance behaviour of the photoemission lines in the valence-band region was investigated by constant-initial-state (CIS) spectroscopy. The implications of this behaviour for assignment of the photoemission lines to specific electronic transitions is discussed and compared with published theoretical models of the electronic structure.

A circular dichroism in the angular distribution of photoelectrons (CDAD) can be observed as the so-called ‘peak rotation’. The symmetry of this CDAD is broken by magnetic scattering. It is shown that this symmetry-breaking can be related directly to the relative difference between the scattering cross-sections σ tot for spin-up and spin-down electrons. For the system Fe/W(110) with one monolayer of iron, the expressions are evaluated for the W 4f 7/2 core-level photoelectrons.

When Ag is deposited onto InP(001), interfacial reactions lead to an ill-defined interface between metal and semiconductor. In this paper we have investigated the influence of a H2S surface pre-treatment of InP(001) on the reactivity at the interface. In high-resolution synchrotron radiation photoemission (SXPS) experiments we find that H2S treatment slightly suppresses the reaction between Ag adatoms and the InP substrate. Also, the sulfurization results in a suppression of the onset of three-dimensional clustering of Ag at InP(001) and inhibits segregation of the released In atoms to the surface. Monitoring the movement of the Fermi level in the band gap at the surface during overlayer growth, we observe a significantly higher position by 350 meV of the Fermi level for the sulfurized samples compared to that on the untreated InP(001) surface, indicating an interface donor effect following H2S treatment.

NiO(100) films have been prepared by deposition of Ni onto Ag(100) in an O2 atmosphere. As deduced from low-energy electron diffraction and photoelectron spectroscopy the films are ordered and grow in a layer-by-layer mode. Auger electron diffraction of such films has been measured for the O (512 eV) and Ni (848 eV) Auger transitions in the entire halfspace above the sample surface by using a toroidal electrostatic energy analyzer. The results are compared with computations which have been obtained by multiple scattering cluster calculations including spherical wave corrections. The agreement between experimental and theoretical data is promising for the O transitions. For the Ni transitions we have found an unexpected intensity behavior which is tentatively ascribed to dominant contributions of inelastically scattered electrons.

Spin and angular resolved photoelectron spectra for magnetite at room temperature are calculated, first neglecting, then including the magnetisation. Using the occurring symmetry breaking, the effect of the magnetisation can be clearly separated from the spectra. Second, the surface relaxation is shown to be subject to an investigation by means of PED and SPED.

The effect of an intermediate arsenic monolayer on the evolution of an Ag InP (110) interface has been studied using high resolution photoemission. The interface reaction is suppressed by the intermediate layer very effectively. Part of the As layer segregates on top of the growing Ag film and acts as a surfactant during the initial stages of the growth. The growth mode during the initial stages of the silver film formation is changed from island to Stranski—Krastanov-like growth. There is an increase of the Schottky barrier by 0.1 eV due to the As interlayer. Experimental results of Schottky barrier heights are discussed in terms of both reaction-induced defect formation and theoretical predictions regarding dangling bond saturation.

Photoelectron diffraction pattern from Ga 3d core level photoemission have been recorded for various III–V (110) semiconductor surfaces (GaP, GaAs, GaSb) at low photon energies (40–90 eV) for the first time. The resolved bulk and surface contributions exhibit strong dependence on photon energy and emission direction reflecting the different atomic environment associated with surface and bulk emitters. The observed anisotropies are quite distinct for each compound. They are more pronounced for compounds with constituents of different scattering properties like GaSb and less for those with similar ones like GaAs. The experimental results are compared to calculations within a multiple-scattering cluster model including spherical-wave corrections in order to study the surface relaxation.

Surface chemistry of n- and p-doped InP(001) after treatment with sulfur from different sources has been investigated by XPS/XAES measurements. Core level lines, valence band spectra and Auger transitions were related to changes in surface chemistry and band bending. Both high resolution chemical shifts and the Auger parameter concept were used for the identification of chemical species. Sulfurization was performed by dipping the chemically cleaned sample into a (NH 4 ) 2 S solution or by exposing it to S 2 or H 2 S molecules in UHV. Depending on the source and on the annealing temperature several sulfur compounds were observed on the surface and identified as sulfides with sulfur substituting phosphorus or with sulfur as surface atom, and as polysulfide probably with one sulfur atom in a terminal position. Changes of surface Fermi energy position and thus band bending were investigated.

A method is considered to calculate core photoelectron spectra including multiple scattering contributions and all curved wave corrections. Furthermore this method allows to calculate the spectra in dependence on the polarization (linearly or circularly) of the X-ray beam and on the spin-polarization of the photoelectrons. The results show that the spin-polarized spectra give more detailed information on the structure of the surface layer. Results are shown for the Sb 4 d 3 2 and 4 d 5 2 spectra of the Sb InP (110) surface where we found a strong circular dichroism of the spin-polarization. Furthermore the system Cr Ag (100) is investigated where experimental spectra are available for the Cr 2 p 1 2 level. In this case it is shown to what extent the spectra depend on the orientation of the magnetization of the Cr layers besides the dichroism. The results should encourage experimentalists to do spin-polarized measurements with circularly polarized light.

A theoretical photoelectron diffraction (PD) study was performed on the (110) surface of III–V semiconductors like InSb, GaSb, InP, GaP, InAs and GaAs at low photon energies (40–90 eV) in order to probe the influence of the scattering properties of the different atoms in these semiconductors as well as that of the geometric structure. The atoms at the surface are chemically different from their bulk counterparts and by achieving the photoelectron diffraction intensities from each one, it is possible to probe independently the structural environment around each atomic species. In a photoemission experiment as a consequence of high surface sensitivity and overall experimental resolution the core-level peaks can be decomposed into bulk and surface components. As an example experimental and theoretical photoelectron diffraction data for InP(110) are compared to find out the sensitivity of the PD pattern to the structural parameters.

The adsorption of Sb on InAs(110) was studied for room temperature (RT) deposition and subsequent annealing using high-resolution soft X-ray photoemission (SXPS). A line shape analysis of the Sb 4d core level emission reveals that the Sb deposition at RT does not lead to perfectly ordered growth of the first monolayer. Subsequent annealing, however, results in a highly ordered first monolayer which is stable up to 620 K. This was confirmed by the Sb 4d core level emission line shape consisting of two well resolved chemically shifted components, which can be assigned to two different adsorption sites in the epitaxial Sb monolayer. The changes of surface band bending were determined as a function of Sb coverage and annealing temperature revealing that an accumulation layer was formed. The geometrical structure of the epitaxial Sb monolayers was investigated using low-energy photoelectron diffraction, i.e. the intensity of the Sb 4d core level emission was monitored as a function of polar angles and photon energy. The resulting patterns which show strong variations for both components are compared to calculations using a multiple scattering cluster model for different adsorption models of the Sb monolayer.

The photoelectron diffraction technique has been applied to investigate the geometrical structure of an epitaxial Sb monolayer (ML) on GaAs(110) using low photon energies. Ultra-high surface sensitivity is combined with high experimental resolution (⩽ 200 meV) providing additional information about chemically shifted components. The ordered Sb monolayer was prepared by depositing 3–4 ML onto a UHV-cleaved GaAs(110) surface and subsequent annealing up to 620 K. Photoelectron spectra of the Sb 4d and Ga 3d core level emission lines were recorded as a function of polar angles. The Sb 4d core level emission line clearly exhibits two chemically shifted components which are due to the distinct bonding sites of the Sb atoms. The two corresponding diffraction patterns with marked modulations are compared with calculated ones using a multiple scattering cluster model for various adsorption geometries of Sb. These results are in good agreement to previous LEED and total-energy-minimization studies and demonstrate the potential of this technique. In addition, a clear assignment of the two chemically shifted components of the Sb 4d core level to the two distinct adsorption sites is achieved.

A photoemission study was performed in order to investigate the interaction of arsenic with InP(110) at room temperature. Formation of a saturated layer of As has been observed, which consists of two different species of As. The adsorbed layer is stable during annealing to temperatures up to 250°C. Annealing to higher temperatures is accompanied by both a significant loss of arsenic from the surface due to desorption and partial incorporation into surface sites of the substrate. The electronic structure of the annealed surface is hardly affected, although As has been incorporated into the semiconductor. The results are discussed in comparison with recent experimental and theoretical investigations.

Core photoelectron diffraction is considered to investigate the geometrical structure of surface layers. Due to the chemical shift of the core level the spectrum can be split off into a bulk and a surface contribution. Besides this chemical shift there is an additional shift due to the influence of the core hole potential and of the core hole spin. This shift includes an exchange splitting and a configuration interaction which changes the angular momentum character of the final state. The influence of this configuration interaction on the shape of the angular resolved photoelectron spectrum is calculated for the 3s spectrum of Fe. It is shown that the difference is more pronounced in the circular dichroism of the spectrum than in the total spectrum. The dichroism of the spin-up and spin-down spectrum, respectively, is a measure for the strength of the configuration interaction. Thus, it allows to make a distinction between the chemical shift at the surface and the influence of the core hole charge.

The molecular beam deposition of selenium onto ultra-high-vacuum cleaved (110) surfaces of GaAs and InP and subsequent annealing leads to the formation of a thin, stable, Se rich reacted layer with distinct structural and electronic properties. The Se treated surfaces were investigated using both angle resolved core level and valence band soft X-ray photoemission spectroscopies at the TGM2 beamline of the BESSY storage ring in order to determine the Se induced surface band structure and the geometric arrangement within the Se modified layer. The surface bands were determined along the Γ - X and the Γ - X ′ directions of the substrate. The comparison between clean cleaved and Se treated surfaces reveals strong modifications due to the Se incorporation. An ordered arrangement of the Se atoms gives rise to diffraction effects in the photoemission signals. The diffraction patterns were calculated for different Se adsorption models using the multiple scattering cluster approximation with spherical wave corrections (MSCA-SWC).

The formation of the Cs⧸GaP(110) interface at low temperature has been studied using core and valence level photoemission. It is found that a nonmetallic first adsorption layer is followed by a transition to a metallic film. Valence level spectra show that Cs induces a new peak above the valence band maximum, which from the appearance of the core level spectra is assigned to adsorbate-substrate charge transfer. At higher coverages an intermediate species is identified on the basis of Cs 5p core level spectra. The metallic layer of Cs is characterised by metallic surface and bulk core level emission, the occurrence of plasmon satellites, and the emergence of a metallic Fermi edge. The relative separation of the different Cs core level line contributions are analysed through a Born-Haber cycle and qualitative arguments based on final state screening.

Antimony is known to form well ordered epitaxial monolayers on clean cleaved (110) surfaces of III–V semiconductors like InP, GaP, and GaAs. These monolayers provide ideal candidates for photoelectron diffraction (PED) studies. At low photon energies (40–90 eV) the Sb 4d core level emission can be resolved into two chemically shifted spin-orbit split doublets indicative of the two distinct adsorption sites on the surface. The intensity of these two doublets together with that of the In 4d or Ga 3d subtrate emission was monitored as a function of polar angles and photon energy utilizing an ADES 400 photoelectron spectrometer at the BESSY TGM2 beamline. Strong variation of the intensity ratio of the doublets clearly demonstrates the usefulness of resolving chemical shifts. The experimental results are compared to theoretical calculations using the multiple-scattering cluster model including spherical-wave corrections for different adsorption models of the Sb monolayer.

Platinum overlayers on InP(110) and GaP(110) have been studied by photoelectron spectroscopy and measurement of current-voltage ( I – V ) and capacitance-voltage ( C – V ) characteristics. The reaction processes at these interfaces were monitored in parallel with the Fermi level movement in the gap up to the formation of the interfacial potential barrier, φ b . Synchrotron radiation photoemission studies reveal the reaction between Pt and phosphorus, and also the alloying of indium and gallium with the Pt layer. For both surfaces, the band bending measurement is affected by a surface photovoltage caused by the photoemission light source. I – V (and C – V ) measurements were carried out in situ, at different substrate temperatures in order to evaluate the bulk barrier height, and to obtain an experimental value for the Richardson constant. The values of φ b (0.84 V for p-GaP(110) and 0.53 V for n-InP(110)) are in agreement with the values deduced from the photoemission measurements. These results are compared with data for other metals and are discussed in the context of current theories of barrier formation.

A strong debate exists in the literature concerning the adsorption sites of K atoms on the Si(001)2 × 1 surface at different K coverages. X-ray photoelectron diffraction (XPD) is a powerful tool for the study of local surface structures. Azimuthal K2p XPD simulations discussed for several positions and coverages of K on the Si(001)2 × 1 surface. Whereas in the standard calculation of XPD data the small scattering centre approximation is used, a curved wave theory is applied to the final state of photoelectrons in this paper. The study on a single-domain K/Si(001)2 × 1 surface should improve the knowledge on this surface essentially.

The Pt p-WSe 2 interface has been studied by synchrotron induced core-level and He I excited valence band photoelectron spectroscopy. Platinum forms a continuous metallic overlayer. The deposition of platinum creates selenium defects at the surface leading to an initial band bending of 540 meV which is reduced by subsequent deposition of platinum. The origin of the reactivity is attributed to the high condensation energy of the deposited metal rather than to a possible metal exchange reaction.

The Pt/GaP(110) interface has been studied by core and valence level photoemission using synchrotron radiation. The results are characteristic of a reactive interface, where the GaP substrate is disrupted by the deposited platinum layer resulting in an increasing reacted Ga emission and a strong attenuation of the substrate Ga emission. The detailed analysis of band bending shows that Pt, being a high work-function material, nevertheless has a final pinning position which is close to that of other materials. The value for the Schottky barrier inferred from the photoemission data, Φ b n is 1.56 eV. We observe a distortion of the equilibrium band arrangement by the incident photons, giving rise to a surface photovoltage even at room temperature. This effect can strongly influence the determination of surface band bending.

Results of multiple-scattering cluster calculations are presented for angle-resolved M 2,3 VV Auger electron intensities from a clean Ni(110) surface, which are obtained using the reduced angular momentum expansion (RAME). This method goes beyond the popular plane-wave approximation and takes into account both the spherical character and the anisotropy of the electron waves. The positions of the maxima and minima in the calculated polar intensity profiles agree well with the experimentally determined structures.