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The Fano resonance photoemission study of the Pb0.97Ge0.03Te crystal doped by sequential deposition of Sm atoms on the clean [111] surface was performed to determine the contribution of the Sm4f electrons to the valence band of the Pb0.97Ge0.03Te/Sm crystal and to monitor the process of introduction of Sm into the substrate crystal host lattice. After each deposition step and after subsequent thermal treatment the contribution of both Sm2+ and Sm3+ ions were assessed. The analysis of the acquired data and a comparison with the results of similar studies of Sm doped CdTe, ZnO and GaN show that the thermal treatment at 250 °C of the Sm/Pb0.97Ge0.03Te system leads to conversion of Sm2+ to Sm3+ and probably to Sm4+ which corresponds to the valence of the cations in the substrate crystal host lattice.

The paper presents photoemission study of core level binding energy shifts caused by local crystalline structure collapse in cubic Pb1−xCdxTe crystal. Photoemission spectra of two kinds of semiconductor samples are compared. The first one is ternary crystal of Pb0.94Cd0.06Te with the frozen rock salt structure where the crystalline local structure collapse is expected due to the difference of ion radii of Cd and Pb cations. The second sample was the CdTe(22 nm)/PbTe(6 nm)/CdTe(4 μm)/GaAs(1 1 1)B nanostructure grown by molecular beam epitaxy (MBE) method, where crystalline local structure is not expected to be created. The photoemission spectra show that for the crystal with local structure the electron binding energies of cations are higher (e.g. +0.2 eV) whereas for anions they are lower (e.g. −0.08 eV) than in the multilayer structure. A model is proposed to explain obtained results by the local crystalline structure collapse in Pb0.94Cd0.06Te crystal.

Resonant photoemission spectroscopy was applied to compare the valence band structure of Ge 0.9 Mn 0.1 Te and GeTe semiconductor layers deposited on BaF 2 substrate in monocrystalline and amorphous forms. In (Ge,Mn)Te the contribution of Mn 3 d 5 electronic orbitals to density of states was found in three binding energy regions: below the top of the valence band ( E b p – d hybridization effects, important for magnetic and optical properties of (Ge,Mn)Te, are stronger in monocrystalline than in amorphous (Ge,Mn)Te layers.

The paper presents photoemission studies of wide band gap semiconductors surfaces doped with gadolinium and samarium. The contribution of the Gd4f and Sm4f electrons to the electronic structure of the doped semiconductor systems (CdTe, GaN and ZnO) was evaluated based on the Fano resonance measured across the RE4d → RE4f intra-ion photoionization threshold. It was found that the RE valence and position of the RE4f shell varies significantly between the investigated semiconductor systems and depends not only on the used semiconductor matrix but also on the Fermi level position.

The resonant photoemission spectroscopy was used to study the surface electronic structure under La 4d→4f and Ni 3p→3d photo-excitation of thin LaNiO 3− δ films after annealing in ultrahigh vacuum above dehydration temperature. The giant resonance in La 5p and La 5s peaks intensity observed at excitation energy corresponding to a La 4d→4f threshold is accompanied by resonance of the N 4,5 O 2,3 O 2,3 and N 4,5 O 2,3 V Auger peaks. The enhancement in the intensity of valence band maxima (at about 6 eV) may be explained by the small mixing of the La 5d ionic character to the O 2p valence band. The week resonant features observed in the valence band spectra under Ni 3p→3d threshold indicate the loss of nickel species at the LaNiO 3− δ film surface after heat treatment.

Changes of the valence band electronic structure of 6H polytype SiC crystal were studied. The changes were caused by deposition of Mn atoms on SiC(0 0 0 1) surface cleaned by annealing at 773 K in ultra high vacuum (UHV) conditions. The Mn atoms were deposited in situ sequentially 1 and 2 ML, and the sample was annealed at 773 K. Synchrotron radiation in the energy range from 47 to 51 eV was applied to study photoemission spectra of the valence band. The photoemission spectra corresponding to the Fano resonance for Mn 3p–3d transition were measured and the contributions of Mn3d electrons to the valence band were determined. The results showed appearance of the contribution of Mn3d band corresponding to Mn islands on the SiC. The annealing of the sample leads to the Mn atoms diffusion into the crystal and appearance of the new structure.

Thin LaNiO 3− δ films with pseudocubic (1 0 0) preferred orientation were prepared by reactive DC magnetron sputtering and in situ annealed in O 2 and vacuum. X-ray photoelectron spectroscopy (XPS) was used to determine the variation in composition of the films under high-temperature annealing. The experimental O 1s spectrum of LaNiO 3− δ films was analyzed in terms of “O 2− ”, “O − ”/“(OH) − ”, and weakly adsorbed oxygen species. It was shown that the change in the type of conductivity from the metallic to the semiconducting one is accompanied by a marked increase in the intensity of the lateral (∼531 eV) peak of oxygen. These variations in conductivity and surface composition were attributed to the loss of lattice oxygen with subsequent adsorption from ambient air “O − ” and “(OH) − ” anions and weakly adsorbed oxygen species.

The electronic structure of polycrystalline Ge 0.86 Mn 0.14 Te—ferromagnetic semiconductor with T C =110 K, has been studied by means of resonant photoemission spectroscopy for photon energies close to the Mn 3p→3d excitation. The contribution of Mn 3d states to the electronic structure of the system was revealed and position of the Mn ions in the crystal, characteristic of GeTe-based diluted magnetic semiconductors was proved.

The Fano resonance photoemission studies of Gd/(Pb,Gd)Te layers using synchrotron radiation were carried out and the electronic structure parameters like binding energies of Gd 4f and 5p shells, resonance and antiresonance energies for Gd were determined. The presence of Eu ions was observed in the (Pb,Eu)Te and (Eu,Gd)Te layers grown by MBE technique. The comparison of data for (Pb,Gd)Te compound with corresponding data for (Eu,Gd)Te and (Pb,Eu)Te layers indicates that we are not able to distinct the Eu4f and Gd4f electrons contribution to the valence band photoemission spectra because of small content od Gd and similar binding energy values. The key parameters allowing to prove exactly the presence of either Eu or Gd are the resonance and antiresonance energies which are significantly different for these ions and equal to 143 eV/137 eV and 150 eV/142 eV, respectively.

We present the results of the electronic band structure study of the Ge0.9Mn0.1Te epilayers, clean and modified in situ by deposition of manganese atoms under ultra high vacuum conditions. Ge1-xMnxTe is a ferromagnet with a relatively high Curie temperature (up to 140 K) strongly depending on Mn concentration [1]. Thus, investigation of its properties, including the band structure, attracts considerable interest, in view of possible applications of IV-VI-based systems in fabrication of spintronic devices. The Ge0.9Mn0.1Te layers were grown on BaF2 (111) substrates by an MBE method with use of effusion cells as GeTe, Te2 and Mn solid sources. The substrate temperature was 400-450 o C. The content of Mn in Ge0.9Mn0.1Te was checked by energy dispersive X-ray fluorescence analysis. The sample surface was protected by a layer of amorphous tellurium. Prior the photoemission experiments, the tellurium layer was removed by annealing. The Mn overlayers were deposited in situ at room temperature. The valence band and shallow core levels of Ge0.9Mn0.1Te and ultrathin Mn overlayers have been investigated by means of resonant photoemission spectroscopy (RPES). In this technique the radiation energy is tuned to the intra ion transition (like Mn 3p-3d) in order to enhance emission from partly occupied shells of transition metal atoms. Sets of resonant photoemission spectra were measured for the photon energy range covering the energy of the Mn 3p→3d transition (40

Epitaxial thin films of LaNiO3−x were deposited by using a reactive d.c. magnetron sputtering technique. High-energy X-ray photoelectron spectroscopy was used to analyze the composition and valence states of La and Ni in the films after long time aging in atmosphere. The obtained results show the existence lanthanum and nickel in oxide and hydroxide chemical states. The oxygen exists in four chemical states: lattice oxides, hydroxyl groups and in adsorbed water. Comparison of the spectra recorded at normal emission and grazing emission angle revealed that the hydroxyl group's concentration is mostly present at the surface of the film.

Ti/GaN interface formation on GaN(0 0 0 1 )-(1 × 1) surface has been investigated by means of resonant photoelectron spectroscopy (for photon energies near to Ti 3p → 3d excitation). The sets of photoelectron energy distribution curves were recorded for in situ prepared clean GaN surface and as a function of Ti coverage followed by post-deposition annealing. Manifestations of chemical reactions at the Ti/GaN interface were revealed in the valence band spectra as well as in the Ga 3d core level peak—the discerned contribution of Ti 3d states to the valence band turned out to be similar to that reported in the literature for titanium nitride. The interaction between Ti and N was further enhanced by post-deposition annealing. The study was complemented with SIMS and AFM measurements.

The electronic band structure of Mn/ZnTe(110) (1×1) has been studied by angle-resolved photoelectron spectroscopy. The sets of spectra were acquired for the clean surface and after in situ deposition of 0.4 ML of Mn, in order to compare the band structures and to reveal changes brought about by the presence of Mn. The experimental band structure diagram of Mn/ZnTe along the Γ−K direction in the Brillouin zone has been derived from the experimental data. Indications of interaction between the Mn 3d states and sp bands of the semiconductor are discussed.

Photoelectron spectroscopy has been used to study the Gd/EuTe multilayers structure covered with a thin (100 A) Al film. The study of the main core level and valence band photoemission spectra has shown no interaction between Gd and EuTe layers. Gadolinium was in pure metallic state and the ions of Eu were found divalent in the Gd/EuTe multilayers structure. The europium ions spectra analysis indicates that Ar+ ion sputtering of the sample surface leads to a deviation from stoichiometry in the near surface region of the EuTe layers and to the appearance of Eu3+ species in uppermost layers of the Gd/EuTe multilayers structure. The long-time exposure to the XPS ambient gases has been characterized from the analysis of europium 3d core level spectra.

The substitution of Gd 3+ for Eu 2+ ions introduces conducting electrons and qualitatively changes the model of description of magnetic properties of these semiconductor alloys: antiferromagnetic order observed in insulating layers of EuTe is replaced by ferromagnetic (RKKY interaction driven) state in metallic n-type (Eu, Gd)Te. The high-energy photoemission spectroscopy ( hν = 3000 eV) was used to study the electronic structure and valence of magnetic ions in about one micron thick monocrystalline, ferromagnetic n-type (Eu, Gd)Te layers grown by molecular beam epitaxy on BaF 2 (1 1 1) substrate with EuTe buffer layer. The photoemission spectra of Eu (3d, 4d, 4f), Gd (3d, 4d, 4f), Te (3d, 4d) electrons as well as valence band electrons were measured after sequential Ar ion etching. For surface of the sample exposed to the air the oxidation of surface takes place and measured spectra showed the dominant Eu 3+ contribution in comparison to Eu 2+ . The chemical shift of Te 3d and Te 4d peaks was observed for Te atoms oxidized on the surface. Surface sputtering by Ar ions removes the top layer with oxygen adsorbed at the surface and oxygen diffused in the surface region and clean (Eu, Gd)Te surface of the layer was measured. For clean surface the Eu 2+ dominate in the spectra and the peaks of oxidized Te atoms disappear. The contribution of Eu 2+ 4f electrons to the electronic structure of the (Eu, Gd)Te was found at the top of the valence band.

The surface and electronic structure of Ga0.92In0.08N layers grown by metal organic chemical vapor deposition (MOCVD) have been investigated by means of photoemission. Stability of chemical composition of the surface subjected to Ar+ ion sputtering was proven by means of X-ray photoemission spectroscopy. The analysis of the relative intensities of In 3d, Ga 3p, and N 1s peaks showed that argon ion bombardment does not change significantly the relative contents of the layer constituents. Simultaneous efficient removal of the main contaminants (O and C) was observed during the sputtering procedure, proving that argon sputtering can be used as a method for preparation of clean Ga1−xInxN surfaces. For a clean (0001)–(1×1) surface prepared by repeated cycles of Ar+ ion sputtering and annealing, electronic structure was investigated. The band structure was explored along the Γ–A direction of the Brillouin zone, measuring angle-resolved photoemission spectra along the surface normal. A similar set of data was also acquired for the same surface of GaN layer. Comparison of the collected data revealed an additional feature at the valence band edge, which can be ascribed to the presence of In in the layer.

The electronic structure of monocrystalline ZnTe was investigated for a clean, relaxed ( 110)-(1 x 1) surface and for the same surface after sequential deposition of Mn atoms. The resonant (Fano-type) photoemission technique was applied. The spectra were measured as energy distribution curves and in the constant initial state mode, for the valence band and Zn 3d core level. At very low Mn coverage (θ < 0.15 nm), manganese interaction with the crystal surface results in creation of ternary alloy Zn 1-x Mn x Te(110) surface. Further increasing of Mn deposition leads to formation of metallic manganese islands on the surface. The successive annealing leads to Mn atoms diffusion and to formation of Zn 1-x Mn x Te at the surface region.

Mn/GaN interface formation on a GaN(0 0 0 1)-(1 × 1) surface has been investigated by means of resonant photoelectron spectroscopy, as a function of Mn coverage. A contribution of Mn 3d states to the emission from the valence band of the system was discerned in photoemission spectra taken for photon energies near to Mn 3p → 3d excitation. Interaction between Mn and GaN was also monitored by spectroscopy of the Ga 3d core level. It was shown that Mn on GaN formed a reactive interface with contribution of a compound containing Mn and Ga. Annealing of Mn/GaN at 400 °C changed the surroundings of large part of Mn ions. The Mn 3d related emission spectrum was found to be similar to that characteristic of Mn built into tetrahedrally coordinated semimagnetic semiconductors.

High-energy photoemission spectroscopy (hν=3510 eV) was used to study the electronic structure of EuS buried layers deposited on a thick PbS layer and covered by about 30 A of PbS layer. The study of Eu 3d, 4d and valence band photoemission spectra showed the existence of only Eu2+ ions in the as-grown buried EuS layer. The angular behavior of the Eu 3d spectra revealed that Ar ion bombardment of the sample surface, i.e. initially the PbS cap layer, leads to a change of stoichiometry in the near surface region of the EuS layer leading to depletion of S and concomittant accumulation of Eu3+ at the surface. In addition, prolonged X-ray exposure is found to gradually increase the Eu3+ concentration in the surface region. The contribution of Eu2+ 4f electrons to the electronic structure of the PbS/EuS/PbS multilayer is found at the top of the valence band.

We report on a comprehensive study of the Sm/GaN(0 0 0 1 ) interface using synchrotron radiation photoemission. Spectra were taken after stepwise Sm deposition onto a clean GaN(0 0 0 1 ) surface at room temperature and after annealing. Based on the analysis of resonant photoemission spectra taken for hν=136 eV (divalent samarium resonance) and hν=141 eV (trivalent samarium resonance) we find that both divalent and trivalent samarium states are present in the GaN–Sm interface layer after each step of deposition. The average valence of the system increases from 2.57 for a coverage of 0.6 A to 2.73 for 3.2 A. Above this coverage the average valence drops and reaches a final value of 2.63 for a coverage of 10 A. The Ga3d core level evolution confirms that two valence Sm states are present in the interface region. A large chemical shift of the Ga3d core level after samarium deposition and a moderate decrease in the Ga3d attenuation curve indicate that a reactive interface is created when Sm atoms are deposited on the GaN(0 0 0 1 ) surface. Annealing of the Sm/GaN system to 500 °C induces a valence change from Sm2+ to Sm3+ and promotes diffusion of Sm from the interface into the bulk.

The Fe/Si multilayers structure was grown by direct current magnetron sputtering technique and was studied by means of X-ray photoelectron spectroscopy. The iron silicide formation at the oxidized Fe/Si interface is inhibited at room and elevated temperatures and it occurs at T ≥500 °C. The prolonged annealing of the Fe/Si interface to 500 °C leads to the steady growth of the Si 3+ and Si 4+ oxygen-related components in the sample.

The ultraviolet photoemission and resonant photoemission spectroscopy were used to study the electronic structure of EuS/PbS multilayers with the contribution of europium’s 4f orbitals to the density of states of the valence band. The valence band photoemission spectra of galena and europium monosulfide layers show good agreement with theoretical density of state computations. The relative ratio of Eu 3+ and Eu 2+ ions located at the surface of EuS layer strongly depends on conditions of preparation procedures of the sample surface. For the buried EuS layer only Eu 2+ ions were observed.

Resonant photoemission spectroscopy, with application of synchrotron radiation, was used to study of the valence band electronic structure of clean surface of the Si crystal doped with Gd and of these surface after deposition of 1 2 ML of Gd atoms. Fano-type resonant photoemission spectra corresponding to the Gd 4d–4f transition were measured to determine the contribution of Gd 4f electrons to the valence band of Gd/Si crystal surface. The resonant and antiresonant photon energies of Gd atoms deposited on Si surface were found as equal 151.8 and 146.8 eV, respectively. Position of Gd 4f electrons contribution was found at 9.8 eV below the valence band edge of Gd/Si valence band.

Angle-resolved photoemission measurements on gallium nitride single crystals and epitaxial thin films with wurtzite structure were performed using synchrotron radiation. Calculated theoretical final state bands were used to determine the corresponding k vectors in reciprocal space using the direct transition model. We were able to identify several previously unobserved features including several surface states and transitions to non-free-electron final states. Significant differences in the surface electronic band structure between thin film and single crystal samples were observed. 2002 Elsevier Science B.V. All rights reserved.

X-ray photoelectron and ultraviolet resonant photoemission spectroscopy was used to study the Sn0:96Mn0:04Te MBE layers. The surface chemical composition of the samples after different treatment conditions was studied by means of XPS. Resonant photoemission spectroscopy with application of the synchrotron radiation was applied to investigate the electronic structure and the contribution of Mn 3d electrons to the valence band of Sn0:96Mn0:04Te layers. The contribution of the Mn 3d electrons to the valence band electronic structure appears at the valence band with the maximum located at 4.0 eV below the valence band edge. 2002 Published by Elsevier Science B.V.

Experimental photoemission results on GaN (0 0 0 1 ) and CdTe(1 0 0) surfaces on a function of samarium adsorbate coverage are presented. Energy distribution curves were recorded at photon energies around the Sm 4 d →4 f threshold (135–136 eV) to reveal the Sm contribution to the electronic structure and enhance the sensitivity. The evolution of core-level Ga 3d and Cd 4d spectra was also studied. The interaction of Sm with both GaN and CdTe leads to reactive interface formation. In the case of CdTe, it results in creation of an interfacial Sm–CdTe compound, which inhibits further diffusion of Sm into the bulk. The interaction of Sm with GaN leads to the release of Ga atoms on the surface and segregation of Ga clusters.

Photoemission spectroscopy was applied to determine the valence band density-of-states in zinc blende MnTe grown by MBE on a CdTe(100) substrate. The Mn 3d derived contribution to the electronic structure was revealed by resonant photoemission experiments. Our experimental results are compared to the available configuration-interaction cluster models. An important role of the core hole screening (through charge transfer from ligand orbitals) on the whole Mn 3d derived photoemission spectrum (including the satellite structure observed below the valence band) was clearly confirmed.

A lamellar semimagnetic semiconductor, Sn 1− x Mn x Se 2 , has been investigated by photoemission, both in the UV and X-ray photoenergy ranges. The partial Mn 3d DOS has been determined from resonant photoemission spectra; the valence of the several constituting atomic species was ascertained from XPS results.

The contributions of Mn3d, Fe3d and Co3d electrons to the valence band electronic structure of Hg1−xTMxSe (TM=Mn, Fe, Co) crystals were investigated by means of resonant photoemission. The comparison of photoemission spectra with the results of theoretical calculations made by the CPA (coherent potential approximation) method shows that the valence band of Hg1−xTMxSe diluted magnetic semiconductors is strongly influenced by TM3d electrons. We find out that for all TM incorporated in the HgSe matrix, 3d electrons with t2g symmetry hybridize strongly with the valence band of the crystal, whereas 3d electrons with e2g symmetry are not hybridized with the valence band. The contribution of 3dt2g electrons is spread over the valence band with the maximum at 3.4–3.8 eV below the Fermi level. The contributions of 3de2g electrons were found in the middle part of the valence band and, in the Fe and Co case, also at the edge of the valence band.

The paper presents the experimental results of the electronic band structure study of the semiconductor crystal clean surface and this surface doped by transition metal or rare earth metal atoms. For clean surfaces of the CdTe crystal the two-dimensional electronic band structure E( k ) dependence was determined for surface states located in the valence band energy region. The doping of the clean surface of CdTe was performed by the controlled, sequential deposition of metal atoms (Fe, Gd or Yb) on the surface. After each deposition the synchrotron radiation was used to measure the resonant photoemission spectra (energy distribution curve – EDC, constant initial states – CIS and constant finale states – CFS). The results of the study showed that in the first stages of the metal atoms' deposition in the range of thickness equal to about 0.5 ML the effect of the crystal clean surface doping occurs. For bigger metal layer deposition the metallic islands electronic structure gave the contribution to the measured spectra. Heating of the sample surface covered by metal atoms leads to the diffusion of the atoms into the sample and results in an increase of the crystal doping and decrease of the metallic islands contribution to the measured spectra.

Synchrotron radiation photoemission has been used to study the formation of Sm overlayer on the surface of CdTe(1 0 0) crystal. The data were recorded at room temperature for Sm coverage ranging from 0 to 9 ML. The analysis of constant initial state spectra and energy distribution curves taken in the valence band region showed that at very low Sm coverage (0.1 and 0.2 ML) the trivalent Sm state dominates. For higher coverages the average valence of the system drops down from the value of 2.7 to 2.2 for 1.8 ML. The analyses of Sm4f multiplet peaks binding energy lead to the conclusion that the average valence of Sm in the Sm/CdTe(1 0 0) system is heterogeneous (the valence has site-dependent but integer value). The photoemission results indicate strong Sm–CdTe interaction and confirm the assumption about the creation of a surface compound with spinel CdSm 2 Te 4 structure.

We present the results of photoemission studies on (0 0 0 1 ) (N-polar) surfaces of bulk gallium nitride crystals. The procedures that yield clean and well-ordered (0 0 0 1 ) (1×1) surfaces were developed and tested. The surface crystallinity was assessed by low-energy electron diffraction. Angle-resolved photoemission spectroscopy with synchrotron radiation was used to determine the valence-band electronic structure of GaN along the Γ – Δ – A direction of the Brillouin zone. The band structure derived from our experimental data is compared with the results of recent band structure calculations.

A few monolayers of Gd atoms were evaporated on a clean CdTe(p)(100) (bulk crystal) and CdTe(n)(100) (epitaxial layer) surface. Constant initial state (CIS) spectra were measured at the Gd4d → Gd4f Fano resonance (in the photon energy range of 140–160 eV) both after evaporation and heating processes. The binding energy of the Gd4f state was determined after Gd evaporation (9.43 and 9.50 eV for p- and n-type crystals, respectively) and after heating (9.00 and 9.80 eV). Energy distribution curves (EDCs) measured in the photon energy range (50–100 eV) show additional density of states at the valence band edge only for CdTe(n)/Gd crystal.

A CdTe(1 11)A (I X 1) surface, prepared in situ by argon ion bombardment and annealing (at 250°C), was oxidized at the pressure of 1 X 10 -5 -5 X 10 -5 Torr of molecular oxygen excited by the hot filament of the ion gauge. The surface atomic structure was studied by low-energy electron diffraction (LEED). The surface chemical composition and the oxidation process were monitored by recording the energy position and shape of Te 3d, Cd 3d, O 1 s and C Is core level peaks by X-ray photoemission spectroscopy. The excess of Te on the clean CdTe(111)A (1 × 1) surface was detected. Then, the increase of oxygen bound on the surface was observed as a function of the gas exposure. Symptoms of selective oxidation of Te atoms on the surface and in subsurface region were revealed.

The aim of the work is to present the XPS and UPS studies of a new kind of material MBE grown -CdYbTe thin layers. The analysis of the valence band electron states was performed for three samples (with different Yb contents and different crystallographic quality) by means of resonant photoemission based on the electronic transition between Yb 4d–4f shells. Analysis of Cd 3d, Te 3d and Yb 4d core levels made by XPS gave the qualitative information about the samples before and after Argon ion sputtering. The photoemission spectra for the CdYbTe sample containing 5% Yb, which corresponds to the limit of Yb solubility, were compared with the spectra of the CdYbTe sample with 1% Yb. By means of resonant photoemission Ytterbium was found in two charge states Yb(+2) and Yb(+3).

Atomic force microscopy (AFM) and Fano-type resonant photoemission spectroscopy (RPS) of Gd atoms deposited on Si(1 1 1) surface are presented. Layers of thicknesses 0.2, 2 and 15 nm were deposited under UHV conditions. Anomalously deep craters were observed on the Si(1 1 1) surface side of the interface below the Gd layer. We expect that anomalously high chemical activity of Gd and a dominating diffusion of Si atoms are responsible for the effect. Application of synchrotron radiation in the energy region hν corresponding to the Gd 4d–4f transition (140–170 eV) enabled Fano-type resonant photoemission spectra. Si(1 1 1) surface valence band spectra with contributions from Gd 4f electrons were detected for a 0.2-nm-thick Gd layer deposited onto a clean Si(1 1 1) surface. The photoemission study revealed a Fano resonance shape of the curve with resonance and antiresonance energies hv =151.8 and 146.8 eV, respectively. The Gd 4f localized electrons contribute to the valence band density of states located at 9.8 eV below the valence band edge.

Resonant photoemission spectroscopy has been applied to study the group of Pb 1− x RE x B VI (RE=Eu, Gd; B=Te, Se, S) diluted magnetic semiconductors. Energy distribution curves, as well as constant-initial-state or constant-final-state photoemission spectra have been taken for photon energies near to the intra-ion Eu 4d→4f or Gd 4d→4f transitions. The Eu 4f and Gd 4f contributions to the electronic structures of the crystals have been determined by comparison of photoemission spectra taken on and off resonance. The localized character of the Eu(Gd) 4f 7 shell has been confirmed by the analysis of the shape of the corresponding spectral feature. The influence of the host crystal ionicity on the position of the RE 4f shells with respect to the valence band is discussed.

The electronic structure of Cd 0.985 Fe 0.015 Te has been studied by resonant photoemission in the synchrotron radiation photon energy range from 48 to 67 eV. Photoemission spectra revealed that Fe contributions to the valence band density of states are situated at 1.2 eV, 4.1 eV and 5.9 eV below the valence band maximum. The contribution of Fe 3d states to the valence band electronic structure was also observed in situ during evaporation of Fe atoms on the clean CdTe(110) surface. Photoemission measurements show that after Fe evaporation and heating to 265°C the CdTe(110)/Fe crystal, a ternary compound Cd 1− x Fe x Te is created in the surface region. The results of photoemission experiments are consistent with the theoretical calculations made by the CPA (coherent potential approximation) method.

Surface differential reflectivity and surface sensitive electron spectroscopies have been applied to study the optical properties of CdTe(110) surface. The comparison of the results acquired for the surfaces prepared by two different methods (cleavage and Ar + ion sputtering) enabled us to propose a model explaining the experimental results in a coherent way.

Electronic states of 4f samarium ions were investigated by photoemission spectroscopy in samarium-rich CdSmTe sample obtained by MBE. The photon energy of synchrotron radiation allowed to investigate Fano-type resonance and antiresonance. The energy distribution curve spectra were attributed to the Sm 4d-4f transition. The shape of the constant initial states spectra was compared with this one obtained for atomic samarium. PACS numbers: 73.20.At, 79.60.-i, 79.60.Bm

A CdTe(110) surface, prepared in situ by argon ion bombardment and annealing, was oxidised at a pressure of 1×10 −5 –5×10 −5 Torr of molecular oxygen excited by the hot filament of the ion gauge. The adsorption on the surface was monitored by recording the energy position and shape of Te 3d, Cd 3d, O 1s and C 1s core level peaks by X-ray photoemission spectroscopy. The increase of oxygen and carbon bound on the surface was observed as a function of the gas exposure. Simultaneously, the development of additional features connected with the Te 3d peaks was revealed. The extremely slow formation of the oxide layer with strongly enhanced uptake of gaseous carbon compounds (probably CO) has been demonstrated.

Resonant photoemission spectroscopy was applied to the study contribution of Gd 4f states to the electronic structure ofSn 1− x Gd x Te. The energy distribution curves (EDC) were analyzed and the binding energy of Gd 4f shell was determined. The correspondence between the charge state of Gd ions and the binding energy of Gd 4f electrons was discussed.

Fe atoms were evaporated on a clean CdTe(111) crystal surface. Constant initial state spectra measured across the Fe 3p-3d threshold after evaporation and heating processes indicate the coexistence of two Fano-like resonances (at energies of 56.0 and 57.7 eV). Our results suggest that the resonance at 56.0 eV is derived from Fe evaporated on theCdTe(111)/Fe surface, while the resonance at energy 57.7 eV is derived from the iron incorporated in the parent CdTe crystal. This effect allows to separate two different Fe 3d contributions to the valence band density of states corresponding to two Fe states.

Synchrotron radiation tuned to the Fe 3p–3d transition (hv = 56eV) was used to study Fano type resonant photoemission spectra for a clean CdTe(110) surface sequentially covered in the monolayer (ML) range by Fe atoms and annealed. The results showed that, in the first stage of the deposition, the Fe atoms are mainly involved in the creation of a Cd1−xFexTe ternary crystal (0.2–0.6 ML). At higher coverages (1.2 ML), the contribution of Fe metallic islands becomes visible. CdTe dissociation in the surface region leads to the appearance of Cd Fe interaction at higher Fe deposition (3.6 ML). After deposition of 20 ML, sample annealing in the 300°C range leads to Fe diffusion into the crystal and the measured spectra correspond well to the Cd1−xFexTe calculated spectra.