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Applied Surface Science (v.267, #)

Editorial Board (pp. ii).

Electronic structure of SnSb₂Te₄ and PbSb₂Te₄ topological insulators by T.V. Menshchikova; S.V. Eremeev; E.V. Chulkov (pp. 1-3).

► It was shown that PbSb₂Te₄ and SnSb₂Te₄ are three-dimensional topological insulators. ► In MSb₂Te₄ (M=Pb, Sn) the Dirac point is located at the centre of the energy gap, i.e. is well separated from bulk states. ► There is no intraband scattering because of ideal shape of the Dirac cone in both PbSb₂Te₄ and SnSb₂Te₄. ► These compounds are well promising for practical applications.The bulk and surface electronic structure of SnSb₂Te₄ and PbSb₂Te₄ ternary compounds consisting of three septuple layer blocks separated by van der Waals gaps has been theoretically studied. It has been shown these systems are three dimensional topological insulators. The calculations of the MSb₂Te₄ (M=Pb, Sn) surface electronic structure show that these compound are well promising for practical application compared to parent Sb₂Te₃ compound.

Keywords: Topological insulators; Electronic structure; Surface states

CO adsorption on the Ni₂Pb/Ni(111) surface alloy: A DFT study by K. Kośmider; R. Kucharczyk; L. Jurczyszyn (pp. 4-7).

► The effect of Pb adsorption and alloying on the reactivity of Ni(111) surface towards CO adsorption is explored by DFT simulations. ► Very high activation barrier of about 2eV due to Pb adatoms makes CO chemisorption unfeasible for the Pb/Ni(111) overlayer. ► CO can adsorb on Ni₂Pb/Ni(111) surface alloy in on-top position with adsorption energy of 0.35eV, but causes substantial substrate reconstruction. ► Taking into account the substrate deformation energy leads to the same Ni-CO binding energy for pure Ni(111) and alloyed Ni₂Pb/Ni(111) surface. ► Considerably higher activation barrier as compared to pure Ni(111) explains suppression of CO chemisorption upon Ni₂Pb alloy formation.Structural and electronic properties of the Pb/Ni(111) overlayer and the Ni₂Pb/Ni(111) surface alloy have been investigated within a DFT-PBE approach in order to determine its reactivity towards adsorption of CO molecules. This work has been motivated by a photoemission study of CO adsorption on Pb/Ni(111) surface phases [V. Matolín et al., Phys. Rev. B 74 (2006) 075416] indicating that Pb adatoms inhibit CO adsorption in a purely geometrical way by site blocking at Ni(111), whereas surface alloying has a poisoning effect of the Ni–CO bond weakening. In general, our DFT computations confirm experimental findings for the Pb/Ni(111) overlayer, as the very high activation barrier of about 2eV due to the presence of Pb adatoms makes the CO chemisorption virtually impossible. For the Ni₂Pb/Ni(111) surface alloy, we show that CO can bind to Ni atoms in the on-top position, and this process occurs to be exothermic with the energy gain of 0.35 eV per CO molecule. Dramatic reduction of the computed adsorption energy with respect to the pure Ni(111) substrate is in apparent agreement with experiment. However, it follows from our simulations that the CO adsorption process is accompanied by a substantial rearrangement of Ni atoms within the Ni₂Pb surface alloy layer. Taking into account the associated deformation energy in the overall energetic balance yields nearly the same interaction energy between the CO molecules and the Ni atoms for the alloyed and the pure Ni(111) substrate, so the Ni–CO bond appears not to be weakened. The experimentally observed suppression of CO adsorption upon the alloy formation can be explained by a notable increase of the activation barrier for CO chemisorption from about 0.1 eV for the pure Ni(111) to roughly 0.5 eV for the Ni₂Pb/Ni(111) surface alloy, affecting the corresponding reaction rate.

Keywords: PACS; 68.35.–p; 68.43.FgNickel; Carbon monoxide; Adsorption; Density functional calculations

Structural and electronic properties of graphene-based junctions for spin-filtering: The graphene/Al/Ni(111) intercalation-like system by A.V. Generalov; E.N. Voloshina; Yu.S. Dedkov (pp. 8-11).

► We successfully prepare and study the graphene/Al/Ni(111) intercalation-like system. ► The properties of a free-standing-like graphene layer are restored. ► Graphene is slightly n-doped in this system.The atomic and electronic structure of the graphene/Al/Ni(111) system is studied via combination of LEED and spectroscopic methods (X-ray absorption, core-level and valence-band photoelectron spectroscopy), respectively. These data demonstrating the (2×2) overstructure and the decoupling of the graphene layer from the substrate (with respect to graphene/Ni(111)) are in very good agreement with DFT calculations supporting nearly free-standing state of graphene in this system (with small n-doping). The perspectives of application of Al-based intercalation-like systems are discussed.

Keywords: LEED; XPS; ARPES; NEXAFS; Graphene; Ni(1; 1; 1); Intercalation

Copper-ceria interaction: A combined photoemission and DFT study by Lucie Szabová; Tomáš Skála; Iva Matolínová; Stefano Fabris; Matteo Farnesi Camellone; Vladimír Matolín (pp. 12-16).

► Copper-ceria system as model catalyst. ► Cu was deposited on stoichiometric and partially reduced ceria surfaces on Ru(0001). ► Reduction of stoichiometric ceria was observed upon copper deposition. ► Copper reoxidates partially reduced ceria surface. ► Described copper-ceria interaction predicted by DFT+U calculations.Stoichiometric and partially reduced ceria films were deposited on preoxidized Ru(0001) crystal by Ce evaporation in oxygen atmosphere of different pressures at 700 K. Copper-ceria interaction was investigated by deposition of metalic copper on both types of substrate. The samples were characterized by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) of core states and resonant photoelectron spectroscopy (RPES) of the valence bands. Copper adsorption on stoichiometric ceria caused reduction of CeO₂, while on the oxygen-defficient ceria it partially reoxidized the substrate. This is in agreement with DFT+U calculations of copper adsorption on stoichiometric and defective ceria surfaces.

Keywords: Copper; Ceria; Photoemission; DFT+U

Si(111) surface functionalized with H-bonded SAM: A theoretical study by Francesca Risplendi; Giancarlo Cicero (pp. 17-20).

► The Si(111) surface fuctionalized with a H-bond SAM based on propyl-urea molecules is investigated. ► Optimal coverage corresponds to 1/2 ML for maximizing H-bond formation. ► The monomer gives raise to a different surface periodicity. ► Occurrence of the most stable structure is experimentally revealed by a decrease of the Si(111) ionization potential and the change in periodicity from the STM surface image.In this work we present a theoretical investigation of hydrogenated Si(111) surface functionalization by means of propyl-urea molecules. The molecules are found to attach at the silicon surface following an exothermic reaction when the coverage is half of a monolayer. Among the possible SAM configuration, we have found that the most favorable is the one maximizing H-bond interaction between the organic monomers.

Keywords: Functionalization; Si(1; 1; 1); Self Assembled Monolayer (SAM); Propyl-urea molecule; Hydrogen bond

New insight into the structure of saturated chlorine layer on Ag(111): LT-STM and DFT study by B.V. Andryushechkin; V.V. Cherkez; E.V. Gladchenko; G.M. Zhidomirov; B. Kierren; Y. Fagot-Revurat; D. Malterre; K.N. Eltsov (pp. 21-25).

► Saturated chlorine coverage on Ag(111) is a two-component system. ► Clusters Ag₃Cl₇ are formed on the boundaries between three antiphase (3×3) domains. ► Incomplete clusters Ag_xCl₆ can play a role of active centers for oxygen adsorption in the reaction of ethylene epoxidation.Atomic structures formed on the Ag(111) surface as a result of molecular chlorine adsorption have been studied with a low-temperature scanning tunneling microscopy (LT-STM) in a combination with DFT calculations. We have found that saturated chlorine coverage on Ag(111) is a complex system consisting of two different structural phases: small anti-phase domains of a (3×3) reconstruction and nanoclusters Ag₃Cl₇.

Keywords: Chlorine; Silver; Ethylene epoxidation; Scanning tunneling microscopy; Density functional theory

Probing organic nanostructures by photoelectron-emission microscopy by Thorsten Wagner; Daniel Roman Fritz; Peter Zeppenfeld / (pp. 26-29).

HighlightsDisplay Omitted► High energy photons needed to excite photoelectrons from the organic nanostructures. ► Organo–metallic interface shows increased photoemission intensity. ► The photoemission strongly depends on the polarization of the incident light. ► Polarized light used with PEEM to probe the optical anisotropy of the organic layer. ► Thin films of alpha-sexithiophene exhibit properties of a dichroic filter.Photoelectron-emission microscopy (PEEM) is a very versatile tool for studying dynamic processes like growth and phase transitions on surfaces. Here we have applied PEEM to the growth of α-sexithiophene ( α-6T) on Ag(110) surfaces to study the formation of the wetting layer and the initial stage of 3D growth. In this paper we want to point out how different light sources available in the lab can be used to obtain complementary information. We will also discuss the use of linear polarized light (Hg lamp) in this context.

Keywords: Photoelectron-emission microscopy (PEEM); Nanocrystallites; α; -sexithiophene; Ag(1; 1; 0); Surface anisotropy

Hydrogen behaviour in amorphous Si/Ge nano-structures after annealing by C. Frigeri; M. Serényi; N.Q. Khánh; A. Csik; L. Nasi; Z. Erdélyi; D.L. Beke; H.-G. Boyen (pp. 30-34).

► We study hydrogenated amorphous Si/Ge superlattices annealed to form SiGe alloy. ► Annealing causes extensive blistering in hydrogenated samples. ► Blisters due to accumulation into bubbles of hydrogen released upon annealing. ► Hydrogen released more easily from Ge layers than from the Si ones. ► The amount of hydrogen in the bubbles is calculated.The relationship between blistering, H content and de-passivation of the dangling bonds has been studied in annealed hydrogenated a-Si/a-Ge superlattice (SL) nanostructures grown by RF sputtering. Measurements have been carried out by ERDA, IR absorbance and AFM. By comparison with parallel investigations on a-Si and a-Ge single layers it has been established that the bubbles causing blistering in the annealed SLs very likely start to grow in the Ge layers of the SL because H is released from Ge much earlier than from Si. It is shown that the H forming the bubbles is only a fraction of the H liberated during the annealing.

Keywords: Amorphous Si/Ge superlattice; Hydrogen; Annealing; Nanostructure; Blistering

The23×23R30 surface reconstruction of alkali/Si(111):B semiconducting surfaces by C. Tournier-Colletta; L. Chaput; A. Tejeda; L.A. Cardenas; B. Kierren; D. Malterre; Y. Fagot-Revurat; P. Le Fèvre; F. Bertran; A. Taleb-Ibrahimi (pp. 35-39).

► We solve the23×23R30 surface reconstruction of Alkali–Metal/Si(111):B interfaces. ► The23×23R30 surface structure is common to K, Rb, Cs and K–Rb alloys. ► HR-XPS and STM measurements agree with an inhomogeneous doping of Si-B sites. ► DFT calculations explain the surface reconstruction and its insulating character.The surface structure of alkali doped Si(111):B ultra-thin films has been studied by low-energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). A comparative study of K/Si(111)-3×1 and K/Si(111):B-23×23R30 interfaces allowed us to determine the saturation coverage to be 0.5 monolayer in the later case. The23-surface reconstruction is shown to be a common property of pure K, Rb, Cs materials and K_0.4Rb_0.6 alloys but progressively disappears if Rb is replaced by Ca. Taking into account the existence of two distinct boron sites in the ratio 1/3 as seen from B-1s core levels spectra, LAPW-DFT calculations have been carried out in order to optimize the atomic structure. As a result, alkali adatoms are shown to form trimers leading to a large modulation of the SiB bonds accompanied by an inhomogeneous doping of the dangling bonds in agreement with voltage dependent STM images.

Keywords: 3; -reconstructed semiconducting surfaces; Alkalioverlayers; LEED; XPS; STM; LAPW-DFT calculations

Surface morphology of Si layers grown on SiO₂ by A.A. Shklyaev; A.S. Kozhukhov; V.A. Armbrister; D.V. Gulyaev (pp. 40-44).

► Si crystals appear to be larger and uniform when Si is grown on SiO₂ covered with an array of Ge islands. ► Si crystals grown on SiO₂ have a rounded shape at the surface, indicating the presence of high concentration of threading dislocations. ► Si crystals grown on SiO₂ at temperatures in the 430–550°C range produce photoluminescence in the 1.5μm region.Layers of Si crystals grown on SiO₂ surfaces are investigated by scanning tunneling and atomic force microscopy. The deposition of an array of Ge islands on SiO₂ surfaces prior to Si growth is found to significantly decrease the concentration of Si crystals and make them more uniform in size. The Si crystals grown at temperatures from 430 to 550°C have a rounded shape of the growing surface. This indicates the presence of a high concentration of threading dislocations and that is confirmed by the observation of dislocation-related photoluminescence in the 1.5μm region. Layers of Si crystals grown on SiO₂ are of interest for the fabrication of optical resonant structures for the near-infrared region.

Keywords: Surface morphology; Silicon growth; Dislocations; Photoluminescence in the 1.5-μm region; Scanning tunneling microscopy; Atomic force microscopy

Spectral studies on sulfur poisoning of Pd/Mg₆Ni by NEXAFS and XPS by S. Yagi; M. Nambu; C. Tsukada; S. Ogawa; G. Kutluk; H. Namatame; M. Taniguchi (pp. 45-47).

Display Omitted► We have studied on Sulfur Poisoning for the hydrogen storage materials based on Mg-Ni alloy by means of XPS and Sulfur K-edge NEXAFS measurements. ► Those materials have been fabricated the sample constructed with the Pd thin layer (TL) on Mg6Ni alloy substrate by magnetron sputtering method. ► Most of the adsorbed molecules desorb from the Pd TL surface during exposure to the atmosphere. ► Therefore the Pd TL might be able to decrease the degree of the sulfur poisoning caused by the adsorption of the sulfur-containing molecule.We have studied on the hydrogen storage materials based on Mg–Ni alloy and fabricated the sample constructed with the Pd thin layer (TL) on Mg₆Ni alloy substrate. The adsorption behavior of the dimethyl disulfide (DMS) molecules on the sample has been measured to reveal the sulfur poisoning of the Pd TL/Mg₆Ni by means of XPS and Sulfur K-edge NEXAFS techniques. The chemisorbed DMS, methanethiolate (MT) and atomic S have been observed on the surface. Especially, it is clear that some atomic S has been oxidized by air and detected the adsorbate of the SO₃²⁻ and SO₄²⁻ species. During exposure to the atmosphere, most of the adsorbed DMS and MT adsorbates desorb from the Pd TL surface. We thus conclude the Pd TL might be able to prevent the hydrogen storage materials from the sulfur poisoning.

Keywords: Sulfur poisoning; Pd/Mg; ₆; Ni; He-path; NEXAFS; XPS

Morphological and spectroscopic studies on enlargement of Pd nanoparticle inl-cysteine aqueous solution by AFM and XPS by C. Tsukada; S. Ogawa; H. Niwa; T. Nomoto; G. Kutluk; H. Namatame; M. Taniguchi; S. Yagi (pp. 48-52).

Display Omitted► We have studied the enlargement mechanism of Pd nanoparticles (NPs) on SiO₂/Si, when thel-cysteine adsorbs on the Pd NPs under water environment. ► The Pd NPs possess an interaction with the SiO₂/Si surface. ► However, the interaction becomes small and the Pd NPs can be more easily migrated on the SiO₂/Si surface due to the contributions of the H₂O and/or thel-cysteine adsorbates. ► Because the Pd NPs aggregate each other, the enlargement of the Pd NPs occurs.We have revealed the enlargement mechanism of Pd nanoparticles (NPs) on SiO₂/Si by the AFM observation and the XPS measurement, when the Pd NPs react with thel-cysteine under water environment. Furthermore, the adsorbates on the Pd NPs/SiO₂/Si have been confirmed by the XPS measurement. The Pd NPs with clean surface are fabricated and deposited on the SiO₂/Si substrate by the gas evaporation method. In that aspect, the Pd NPs possess an interaction with the SiO₂/Si surface. When the Pd NPs/SiO₂/Si is reacted into thel-cysteine aqueous solution, the adsorbates originated from thel-cysteine exist on the Pd NPs surface. On the contrary, thel-cysteine hardly adsorb on the SiO₂/Si. The enlargement of the Pd NPs is stimulated by the contributions of the H₂O and/or thel-cysteine molecules because the Pd NPs can be more easily migrated on the SiO₂/Si surface due to those contributions.

Keywords: Pd nanoparticle; SiO; ₂; /Si; l; -Cysteine; Enlargement; Migration; XPS

Formation mechanism of peculiar structures on vicinal Si(110) surfaces by M. Yamashita; Y. Nakamura; R. Sugimoto; J. Kikkawa; K. Izunome; A. Sakai (pp. 53-57).

► We formed peculiar structures to Si(110) vicinal surfaces under various conditions. ► The peculiar structure size strongly depended on annealing ambient and temperature. ► We proposed the plausible formation mechanism of the peculiar structures.We investigated the formation mechanism of peculiar structures on vicinal Si(110) surfaces caused by annealing. The shapes of the peculiar structures strongly depended on the tilt angle of the vicinal surface from the exact Si(110) surface. The size of these structures varied with temperature and pressure during annealing. The dependence of the peculiar structure size on the annealing conditions can be explained by considering nucleation of the peculiar structures that is strongly related to Si surface diffusion during the annealing.

Keywords: Si(1; 1; 0); Vicinal surface; Surface structure; Formation mechanism; Surface diffusion; Atomic force microscopy

SHG enhancement by roughness-induced surface plasmon excitation in alkali-metal overlayers grown on Si(111)-7×7 by Takanori Suzuki; Kenichi Fujiwara; Akifumi Kokabu; Tatsuya Momose; Haruki Okamoto; Masatoshi Tanaka (pp. 58-61).

► K, Rb and Cs adsorbed on Si(111)-7×7 show a large SHG in the coverages above the saturation monolayer. ► SHG spectroscopy shows resonance energies exactly coinciding with the surface plasmon excitation. ► The observed resonance is related to the roughness-coupled excitation of a surface plasmon. ► Custers of identical size observed by STM at RT are discussed to be responsible for the resonance.Thin Alkali metal (AM) films of K, Rb, and Cs were grown on Si(111)-7×7, and second-harmonic generation (SHG) was observed at several wavelengths in the near-IR region at room temperature (RT) in an ultra-high vacuum (UHV) chamber. A large SHG signal was obtained for films deposited at low temperatures. This observation qualitatively agrees with the fact that films deposited at low temperatures are rough. For coverages above the saturation monolayer, resonance enhancement was identified centered at 2.5, 2.4 and <2.2eV for K, Rb and Cs adsorption, respectively; these observations are in rough agreement with the reported resonance energies of surface plasmons.

Keywords: Alkali metals; Second-harmonic generation; Silicon; Surface plasmon; Adsorption

The complex nature of phthalocyanine/gold interfaces by Susi Lindner; Uwe Treske; Martin Knupfer (pp. 62-65).

► CoPc/Au: 2 types of charge transfer (CT). ► CT: opposite direction, independent. ► First type: formation of interfacial dipole. ► Second type: local CT to Co.We compare the electronic properties of the interface between Au(100) and cobalt phthalocyanine (CoPc), fluorinated F₁₆CoPc as well as CuPc using X-ray photoemission spectroscopy and valence band ultra-violet photoemission spectroscopy. Our results show that in addition to the formation of an interface dipole at the interfaces of CoPc and F₁₆CoPc to gold, there is a local charge transfer to the central Co ion, which as a result is reduced to Co(I).

Keywords: Organic semiconductor; Phthalocyanine; Interface state; PES

Electronic structures in unoccupied states of Bi thin film studied with two-photon photoemission spectroscopy by Masaki Imamura; Shuji Fujimasa; Kazutoshi Takahashi; Isamu Yamamoto; Junpei Azuma; Masao Kamada (pp. 66-69).

► In this study, we performed the angle-resolved two-photon photoemission of Bi(111) thin film with the thickness of 12 bilayers grown on Si (111) – 7×7. ► The electronic structures and energy dispersion in the unoccupied region above the Fermi-energy were determined. ► These observed unoccupied electronic states were attributed to the quantum-well states derived from the quantization of the 6p-derived bulk bands.We have performed synchrotron-radiation angle-resolved photoemission and angle-resolved two-photon photoemission (2PPE) study of Bi(111) films with the thickness of 12 bilayers grown on Si(111) – 7×7. From the detailed analysis of the excitation energy dependence of angle-resolved 2PPE spectra, we have determined the electronic structures in the occupied and unoccupied regions. The observed electronic structures in the unoccupied states above the Fermi-energy were attributed to the quantum-well states originate from the quantization of the 6p-derived bulk bands.

Keywords: Bismuth; Two-photon photoemission spectroscopy; Quantum well states; Electronic structure

First-principles study of chlorine atom diffusion on Si(111)–5×5 reconstructed surfaces by Yusuke Asari; Jun Nara; Takahisa Ohno (pp. 70-73).

► Cl diffusion on Si(111) surface is investigated by first-principles calculations. ► Cl atom diffuses on the surface in a SiCl complex form. ► The activation energy and the diffusion path are very similar to the F case. ► The complex diffusion corresponds to the Si diffusion with carrying a halogen atom.Diffusion mechanisms of Cl atom adsorbed on Si(111)–(5×5) reconstructed surfaces are investigated by means of the first-principles density functional calculations. We compare two diffusion models for Cl diffusion; one is simple atom hopping model and the other is SiCl complex diffusion one, which is originally proposed to explain the diffusion process for another halogen, F. The energy barrier for the former model is calculated to be 1.73eV, while that of the latter is 1.34eV. This means that the complex diffusion model is preferred for Cl diffusion, similarly to the F case. It is expected that the enhancement of the diffusion frequency by the additional deposition of Si atoms found for F diffusion would be found even for Cl diffusion.

Keywords: Chlorine diffusion; Si(1; 1; 1) surface; Density functional theory

Bandgap formation in graphene on Ir(111) through oxidation by K. Schulte; N.A. Vinogradov; M.L. Ng; N. Mårtensson; A.B. Preobrajenski (pp. 74-76).

► Graphene on Ir(111) has been studied using angle-resolved photoemission spectroscopy (ARPES). ► Upon exposure to atomic oxygen, the pi-band broadens and shifts away from the Fermi level. ► The opening of a gap of at least 0.35eV in the occupied density of states was observed. ► The process is to a high degree reversible.A graphene monolayer on single crystal Ir(111) has been studied using angle-resolved photoemission spectroscopy (ARPES) before and after exposure to atomic oxygen. With increasing oxygen coverage the Dirac cone, centered on the K-point of the Brillouin zone, broadens and finally transforms to a parabolic rather than linear feature, introducing a pronounced energy bandgap at the Fermi level. The opening of a bandgap of at least 0.35eV was observed at the oxygen exposure close to the saturation coverage.

Keywords: PACS; 73.22.Pr; 79.60.Dp; 68.55.LnGraphene; Oxidation; Electronic structure: photoelectron spectroscopy; Adsorbates: binding site geometry; Electronic structure

TEM-study of free-standing self-assembled InSb quantum dots grown on InAs surface by N.A. Bert; V.N. Nevedomsky; P.A. Dement’ev; K.D. Moiseev (pp. 77-80).

► We studied the morphology of self-assembled InSb QDs free-standing on InAs surface. ► Characterization by TEM of the single InSb QD was performed for the first time. ► We can evaluate the size of the InSb QD using moire pattern in plan-view image.We have investigated the morphology of free-standing self-assembled InSb quantum dots (QDs) grown by liquid-phase epitaxy (LPE) under conventional growth conditions on InAs(001) substrate. Two growth modes, Volmer–Weber for low-density (5×10⁸cm⁻²) large QDs with 10–12nm in a height and Stranski–Krastanow for high-density (1×10¹⁰cm⁻²) small QDs with a height of 3–4nm, were identified in dependence on a critical growth temperature of InSb QDs formation. Characterization of the sample surface was performed using transmission electron microscopy (TEM) that allowed us to observe some features of the InSb QD shape which transforms from a full dome to truncated one with increasing QD lateral size from 15 to 40nm, respectively. Using pseudo-moiré pattern appearing in plan-view diffraction TEM image the critical size of the InSb QD for plastic deformation was evaluated.

Keywords: PACS; 68.37.Lp; 81.07.Ta; 81.15.Lm; 81.15.Gh; 81.16.DnLow dimensional structures; Transmission electron microscopy; Liquid phase epitaxy; Antimonides; InAs

Mapping of X-ray induced luminescence using a SNOM probe by F. Jandard; C. Fauquet; M. Dehlinger; A. Ranguis; A. Bjeoumikhov; S. Ferrero; D. Pailharey; B. Dahmani; D. Tonneau (pp. 81-85).

► A new apparatus for simultaneous topography and luminescence mapping is developed. ► Luminescence is induced by X-ray illumination of the samples. ► Topography is acquired by a Shear Force Microscope using a sharp optical fibre. ► Highly fluorescent materials are used for equipment test.In this work we show the feasibility of simultaneous topographic and luminescence mapping with an home-built Shear-Force Microscope under X-ray irradiation with a tabletop microfocused X-ray source (maximum electric power of 30W). A commercial fluorescent screen, containing europium uranyl compounds, is used as test sample. Simultaneous topography and luminescence maps on the fluorescent screen are first obtained with the apparatus. The two images totally overlap, however the luminescence is not homogeneous on the whole scanned area. Moreover, a photoluminescence spectrum is presented with a good signal-to-noise ratio under X-ray irradiation on a grain of the fluorescent screen and shows peaks in agreement with Europium uranyl compounds.A ZnO/ZnS powder mixture embedded in PMMA is then studied with the same equipment. A 20μm-wide grain is clearly visible on the topographic image. With the instrument, the grain could be unambiguously identified as containing mainly ZnO.

Keywords: Scanning probe microscopy; Photoluminescence; X-ray spectroscopy

Structural characterization of GaAs self-assembled quantum dots grown by Droplet Epitaxy on Ge virtual substrates on Si by C. Frigeri; S. Bietti; G. Isella; S. Sanguinetti (pp. 86-89).

► We investigate self-assembled AlGaAs/GaAs quantum dots grown by Droplet Epitaxy. ► We use thin Ge virtual substrates on Si. ► Depletion of Ga at the top of the quantum dots is found by TEM. ► The GaAs quantum dots contain defects identified as hexagonal As precipitates. ► The As precipitates nucleate in a metastabile pseudocubic phase.The structure of self-assembled quantum dots (QDs) grown by Droplet Epitaxy on Ge virtual substrates has been investigated by TEM. The QDs have a pyramidal shape with base and height of 50nm. By (002) dark field TEM it was seen that the pyramid top is Ga poor and Al rich most likely because of the higher mobility of Ga along the pyramid sides down to the base. The investigated QDs contain defects identified as As precipitates by Moirè fringes. The smallest ones (3–5nm) are coherent with the GaAs lattice suggesting that they could be a cubic phase of As precipitation. It seems to be a metastable phase since the hexagonal phase is recovered as the precipitate size increases above ∼5nm.

Keywords: Self-assembled quantum dot; AlGaAs/GaAs; Droplet Epitaxy; Virtual substrate; TEM

Preparation of clean and well-ordered hydrogen-terminated Si(110)-(1×1) surfaces and the measurements of vibrational modes by S. Suto; K. Matsui; S.Y. Matsushita; H. Kato; H. Nakaya; T. Taoka; A. Kasuya; T. Yamada (pp. 90-92).

► We propose electrochemical and wet chemical processes for H-terminated Si(110)-(1×1). ► Clear (1×1) LEED patterns indicated the two-dimensional space group of p2mg. ► The intrinsic SiH bending and stretching modes were observed by HREELS. ► The electrochemical etching in a NH₄F solution yielded the best ordered surface. ► The wet chemical etching produced the samples suitable for HREELS measurements.We propose electrochemical and wet chemical processes to prepare the clean and well-ordered hydrogen-terminated Si(110)-(1×1) surfaces, with our evaluation by low-energy electron-diffraction (LEED), high-resolution electron-energy-loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). Clear (1×1) LEED patterns indicated the two-dimensional space group of p2mg. The intrinsic SiH bending and stretching modes and surface phonon modes, as well as hydrocarbon impurities were observed by HREELS. Among the procedures tested, the electrochemical etching in a NH₄F solution yielded the best ordered surface. The wet chemical etching produced the clean samples suitable for HREELS measurements.

Keywords: Si(1; 1; 0); Etching; LEED; HREELS; p2mg

Substrate surface polariton splitting due to thin zinc oxide and aluminum nitride films presence by N.N. Novikova; V.A. Yakovlev; E.A. Vinogradov; S.S. Ng; Z. Hassan; H. Abu Hassan (pp. 93-96).

► Surface polariton splitting in thin ZnO films on LiF and CaF₂ substrates. ► Surface polariton splitting in thin AlN films on sapphire substrate. ► Splitting is proportional to the square root of the film thickness. ► For ZnO films on CaF₂ “long range” surface polaritons were observed. ► Film thickness and Lorentz oscillator parameters for ZnO films were obtained.Surface polariton (SP) is the non-radiative interface electromagnetic mode, propagating along the interface between two media, if one of them is absorbing (metal, semiconductor or dielectric with the strong absorption bands) and exponentially decaying out of the interface. The introduction of a transition layer at this interface results in the shift and broadening of SP. This effect can be used to obtain film parameters (thickness and optical constants) in the region of SP existence. Zinc oxide (ZnO) films (100–300nm thick) have been prepared on the LiF and CaF₂ substrates and aluminum nitride films (40 and 400nm thick) have been prepared on sapphire substrates. The SP spectra have been measured by attenuated total reflection (ATR) technique. IFS66v (BRUKER) infrared Fourier-transform spectrometer was used for ATR and near normal incidence external reflection spectral measurements. Angular dependencies of the absorption bands positions in the ATR spectra give the dispersion of SP. The measured SP dispersion is compared with one calculated using the film parameters obtained by dispersion analysis of the external reflectivity spectra. The splitting of the dispersion curves of substrate SP was found. It is due to the resonance interaction of substrate SP with the film optical phonons. This splitting is proportional to the square root of the film thickness. For ZnO films on CaF₂ “long range” SPs were observed. These effects allow estimate film complex dielectric function in the region under consideration.

Keywords: Surface polariton; Attenuated total reflection spectra; Thin film; Zinc oxide; Aluminum nitride; Optical phonon

Near surface layer evolution in Zn⁺ ions implanted Si upon annealing treatments by V.V. Saraykin; K.D. Shcherbachev; D.V. Petrov; V.V. Privezentsev (pp. 97-100).

► SIMS revealed a significant redistribution of Zn atoms after annealing. ► After thermal annealing at 800°C nanoparticles on the sample surface were revealed. ► After 1000°C annealing Zn atoms are revealed in the near-surface layer only. ► XRD confirms a presence of Zn containing phases after 700–900°C annealing.The damaged layer in Zn implanted n-type CZ-Si(100) substrates was investigated by a secondary ion mass-spectrometry (SIMS), an X-ray diffraction (XRD) and an atomic force microscopy (AFM). The substrates were implanted with⁶⁴Zn⁺ ions at an energy of 100keV and an ion dose of 2×10¹⁶cm⁻² with subsequent annealing at 400, 600, 700, 800, 900 and 1000°C for 60min in neutral/inert and oxygen atmosphere. A significant redistribution of Zn atoms in the damaged layer caused by the thermal annealing was found by SIMS. Zn concentration maximum exceeds a Zn solubility limit in Si; therefore, a decomposition of Zn solid solution in Si resulting in formation of zinc-containing phases in the surface layer should be expected. In an as-implanted state, the amorphous layer with thickness about 100nm, which located inside of a substrate on the depth more than value Rp, is formed. After thermal annealing at 800°C nanoparticles on the sample surface were revealed. After 1000°C annealing the radiation-induced defects completely disappeared, and Zn implanted atoms are revealed in the near surface layer.

Keywords: Ion implantation; Silicon; ZnO; Nanoparticle

Diameter dependence of 1/ f noise in carbon nanotube field effect transistors using noise spectroscopy by Toshio Kawahara; Satarou Yamaguchi; Yasuhide Ohno; Kenzo Maehashi; Kazuhiko Matsumoto; Shin Mizutani; Kenji Itaka (pp. 101-105).

► We used a noise spectroscopy for noise in CNT-FETs to split their origins. ► We observed the crossover of noise properties in CNTs related to the transition between different origins depending on their diameter. ► We observed the crossover of noise properties in CNTs in the noise spectroscopy between in air and vacuum environments. ► Environmental and diameter controls of noise are useful for the stochastic operation of CNT-FETs.Carbon nanotubes (CNTs) have many interesting properties for nano devices such as high sensitive sensors or noise enhanced nonlinear devices. A field effect transistor (FET) structure is one of the key features for these applications, and the control of noise in FETs is important for the actual operation of the application. Several origins of noise have been proposed, and defects and/or surface adsorption of molecules seem to be dominant for the 1/ f type noise in CNTs. To study the origins of noise, the diameter dependence of noise properties was studied. We analyzed the noise properties in CNTs using noise spectroscopy with different fabrication parameters or ambient environments. We observed the crossover of noise properties in CNTs, which involved transition between different origins of noise depending on their diameter. Additionally, noise spectroscopy was used to observe such crossover between air and vacuum environments. We can control noise intensity using the gate voltage, and noise properties can be controlled by the fabrication parameters. These phenomena are useful for the stochastic operation of CNT-FETs.

Keywords: Carbon nano tube; Field effect transistors; 1/; f; noise

Structure, reactivity, electronic configuration and magnetism of samarium atomic layers deposited on Si(001) by molecular beam epitaxy by Nicoleta G. Gheorghe; George A. Lungu; Marius A. Husanu; Ruxandra M. Costescu; Dan Macovei; Cristian M. Teodorescu (pp. 106-111).

► Sm deposited on Si(001) at temperatures below 400°C is ferromagnetic. ► Sm/Si(001) forms a mixture of Sm metal, Sm₄Si₃ and SmSi₂. The first two phases are ferromagnetic. ► The Sm magnetic moment in the ferromagnetic phases (about 2.3Bohr magnetons) exceeds its value for bulk Sm (1.7Bohr magnetons).The surface structure, interface reactivity, electron configuration and magnetic properties of Sm layers deposited on Si(001) at various temperatures are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and magneto-optical Kerr effect (MOKE). It is found that metal Sm is present on samples prepared at low temperature, with an interface layer containing SmSi₂ and Sm₄Si₃. When samples are prepared at high temperature, much less metal Sm is found, with an increasing amount of SmSi₂. Room temperature ferromagnetism is observed for all prepared layers, with a decrease of the saturation magnetization when samples are prepared at high temperature. It is found that ferromagnetism implies mostly a compound with approximate stoichiometry Sm₄Si₃. Also, the decrease in the intensity of the XAS 2p_3/2→3d white lines with the corresponding increasing amount of SmSi₂ may be explained by assuming a higher occupancy of Sm 5d orbitals (5d² configuration), most probably due to hybridation effects.

Keywords: Samarium; Samarium silicide; Si(0; 0; 1); MBE; LEED; XPS; X-ray absorption; MOKE

Two-dimensional metal nano-particles and layers in dielectric calcium fluoride crystals by A.E. Angervaks; A.S. Shcheulin; A.I. Ryskin; P.P. Fedorov; R.V. Gainutdinov (pp. 112-114).

► Metal inclusions form at concentration of color centers ∼10¹⁷cm⁻³ in CaF₂. ► These nano-sized inclusions are two-dimensional. ► Their thickness is 1.3–1.4nm at lateral size of 30–300nm. ► At concentration of ∼10¹⁸cm⁻³ they coalesce into metal film fragments.Highly aggregated color centers in wide-band-gap dielectric calcium fluoride crystal, heated in a reduction atmosphere of Ca vapors (an “additive coloration” of the crystal), have been studied using spectroscopic and atomic-force microscopic techniques. These centers are large aggregates of anion vacancies and electrons that transform into metal structures. Evolution of these structures with increasing the number of such components has been traced from individual two-dimensional particles to large metal film fragments.

Keywords: Calcium fluoride; Additive coloration; Color center; Colloidal particles; Metal layer; AFM

Theoretical study of the influence of vacancies in the magnetic stability of V-, Cr-, and Mn-doped SnO₂ by Pablo D. Borges; Luisa M.R. Scolfaro; Horácio W. Leite Alves; Eronides F. da Silva Jr.; Lucy V.C. Assali (pp. 115-118).

► Oxygen vacancies play an important change in magnetic stability of V-, Cr-, and Mn-doped SnO₂. ► High spin (HS) ground state and low spin (LS) were observed for these systems. ► The spin crossover energies from the LS to the HS where calculated. ► Our findings suggest that these materials may be used in applications that require different magnetization states.In this work we study, theoretically, the magnetic properties of transition metals (TMs)-doped SnO₂ (with TM=V, Cr, and Mn) in a diluted magnetic oxide configuration, focusing in particular in the role played by the presence of O vacancies, V_O, nearby the TM. We present the results of first-principles electronic structure calculations of Sn_0.96TM_0.04O₂ and Sn_0.96TM_0.04O_1.98( V_O)_0.02 alloys. The calculated total energy as a function of the total magnetic moment per cell shows a magnetic metastability, corresponding to a high-spin (HS) ground state, respectively, with 2 and 3μ_B/cell, for Cr and Mn, and a metastable low-spin (LS) state, with 0 (Cr) and 1 (Mn)μ_B/cell. For vanadium, only a state with 1μ_B/cell was found. The spin-crossover energy ( E_SCO) from the LS to the HS is 114meV for Cr and 42meV for Mn. By creating O vacancies close to the TM site, we show that the metastability and E_SCO change. For chromium, a new HS state appears (4μ_B/cell), with an energy barrier of 32meV relative to the 2μ_B/cell state. For manganese, the metastable LS state of 1μ_B/cell disappears, while for vanadium the HS state of 1μ_B/cell remains. In all cases, the ground state corresponds to the expected HS. These findings suggest that these materials may be used in applications that require different magnetization states.

Keywords: Dilute magnetic semiconductor; Magnetic metastability; Spintronics; Tin dioxide; Spin-crossover

Nanostructured Pt–CeO₂ thin film catalyst grown on graphite foil by magnetron sputtering by Mykhailo Vorokhta; Ivan Khalakhan; Iwa Matolínová; Masaaki Kobata; Hideki Yoshikawa; Keisuke Kobayashi; Vladimir Matolín (pp. 119-123).

► The Pt–CeO₂ catalyst sputtered on graphite shows highly porous surface morphology. ► The Ce³⁺/Ce⁴⁺ and Pt²⁺/Pt⁴⁺ ratios are affected by plasma–substrate interaction. ► Oxygen–carbon interaction is responsible for Pt–CeO₂ reduction at the interface. ► The oxygen atoms interact with the carbon surface forming CO and CO₂ molecules.Layers of different thickness of CeO₂ doped by Pt were prepared by magnetron sputtering on different substrates: Si (100) and a graphite foil. The structure and chemical composition of the Pt–CeO₂ catalysts have been investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and hard X-ray photoelectron spectroscopy (HAXPES). SEM showed that the layers prepared on different substrates had very different morphology. XPS and HAXPES studies demonstrated that Pt was dispersed only in Pt²⁺ and Pt⁴⁺ oxidation states in CeO₂. Intensity of Pt²⁺- and Pt⁴⁺-peaks was affected by the plasma substrate interaction effects showing that carbon substrate played an active role by determining the film structure. The Pt²⁺/Pt⁴⁺ and Ce³⁺/Ce⁴⁺ ratios depend on the layer thickness and increases in the case of the graphite substrate. The reduced character of porous layer was explained by a general effect of formation of defects and oxygen vacancies at oxide edges and steps, and oxygen reaction with carbon which is responsible of formation of oxygen deficient cerium oxide at the interface.

Keywords: Cerium oxide; Graphite foil; Magnetron sputtering; Nanoporous; Photoelectron spectroscopy; HAXPES

Study of solid/liquid and solid/gas interfaces in Cu–isoleucine complex by surface X-ray diffraction by Pilar Ferrer; Juan Rubio-Zuazo; German R. Castro (pp. 124-127).

► Surface atomic structure of Cu(Ile)₂ complex with N₂ gas and a supersaturated Cu(Ile)₂ solution. ► Intensity variation along CTRs shows modifications at the atomic surface structure. ► Surface signal are compared with the ideal bulk and with the relaxed structure. ► The packing conditions influence the atomic structure.The enzymes could be understood like structures formed by amino acids bonded with metals, which act as active sites. The research on the coordination of metal–amino acid complexes will bring light on the behavior of metal enzymes, due to the close relation existing between the atomic structure and the functionality. The Cu–isoleucine bond is considered as a good model system to attain a better insight into the characteristics of naturally occurring copper metalloproteins. The surface structure of metal–amino acid complex could be considered as a more realistic model for real systems under biologic working conditions, since the molecular packing is decreased. In the surface, the structural constrains are reduced, keeping the structural capability of surface complex to change as a function of the surrounding environment.In this work, we present a surface X-ray diffraction study on Cu–isoleucine complex under different ambient conditions. Cu(Ile)₂ crystals of about 5mm×5mm×1mm have been growth, by seeding method in a supersaturated solution, presenting a surface of high quality. The sample for the surface diffraction study was mounted on a cell specially designed for solid/liquid or solid/gas interface analysis. The Cu–isoleucine crystal was measured under a protective dry N₂ gas flow and in contact with a saturated metal amino acid solution. The bulk and the surface signals were compared, showing different atomic structures. In both cases, from surface diffraction data, it is observed that the atomic structure of the top layer undergoes a clear structural deformation. A non-uniform surface relaxation is observed producing an inhomogeneous displacement of the surface atoms towards the surface normal.

Keywords: Atomic surface structure; Surface diffraction; Cu–amino acid complex; Solid/liquid and solid/gas interfaces

Evolution of subsurface nanocavities in copper under argon bombardment and annealing by D.V. Kulikov; O. Kurnosikov; V.S. Kharlamov; Yu.V. Trushin (pp. 128-131).

► Vacancy–argon complexes are formed in copper under Ar irradiation at room temperature. ► Nanocavities appears due to diffusion of vacancy–argon complexes at high temperatures. ► Long high temperature annealing leads to decomposition of nanocavities and Ar losses.The experimental and theoretical studies of evolution of nanocavities in argon-irradiated copper under annealing are presented. The subsurface argon-filled nanocavities are formed during a short annealing at a temperature around 1000K by migration and interaction of complexes of the simplest defects created by argon irradiation at room temperature. A long-time annealing at a temperature above 1075K leads to decomposition of nanocavities and desorption of argon from the sample. Using the X-ray photoelectron spectroscopy and scanning tunneling microscopy and spectroscopy, valuable data sets including the density of nanocavities and their size and depth distribution are obtained. A theoretical model describing the nucleation and evolution of nanocavities is developed. Computer simulations based on this model show that the nanocavities grow at elevated temperatures by absorption of argon–vacancy complexes formed during the ion irradiation. By comparison the calculations with experimental results, the migration energy of these complexes is estimated to be around 2.5–2.75eV. Also, the value of dissociation energy of a complex, consisting of two vacancies and two argon atoms, is found to be equal to approximately 1.10–1.18eV. The calculation of concentration of nanocavities at different annealing conditions reveals a satisfactory agreement with the experimental observations.

Keywords: Nanocavity; Scanning tunneling microscopy; Computer simulation; Cobalt; Copper

Features of metal atom 2p excitations and electronic structure of 3d-metal phthalocyanines studied by X-ray absorption and resonant photoemission by K.A. Simonov; A.S. Vinogradov; M.M. Brzhezinskaya; A.B. Preobrajenski; A.V. Generalov; A.Yu. Klyushin (pp. 132-135).

► A strong influence of the 3d-shell occupancy and 3d–3d exchange interaction on the formation and decay of 2p core excitations in MPc's. ► The high-lying occupied as well as the low-lying unoccupied electronic states in NiPc, CoPc and FePc are mainly 3d derived states. ► Low-lying unoccupied electronic states of MPc's are strongly localized within the MN₄ quasi-molecule.The metal atom 2p core excitations in 3d-metal phthalocyanines (MPc's, M=Ni, Co, Fe) have been studied via a combination of near edge X-ray absorption fine structure (NEXAFS) and resonant photoemission (ResPE) spectroscopy. On the basis of comparison of the corresponding spectra of NiPc, CoPc and FePc it has been shown that the presence of a partly filled molecular orbital (MO) dramatically affects the formation and decay processes of the M 2p core excitation in CoPc and, to a greater extend, in FePc due to the significant 3d–3d exchange interaction. It has been found that the low-lying unoccupied electronic states of NiPc, CoPc and FePc are strongly localized within the MN₄ quasi-molecule and have nearly pure 3d character. Moreover, mainly 3d metallic character of the high-lying occupied MOs of NiPc, CoPc and FePc has been proved.

Keywords: Phthalocyanine; NEXAFS; Resonant photoemission; Exchange interaction

Structural analysis of vicinal Si(110) surfaces with various off-angles by M. Yamashita; Y. Nakamura; A. Yamamoto; J. Kikkawa; K. Izunome; A. Sakai (pp. 136-140).

► The founding is appearance of peculiar structures to Si(110) vicinal surface. ► Peculiar structures strongly influenced the use of Si(110) surface in MOS-FET. ► We proposed the plausible models of the peculiar structures.We have investigated vicinal Si(110) surfaces with various off-angles using atomic force microscopy and transmission electron microscopy. The vicinal surfaces were tilted from the exact Si(110) surfaces by 2–8° toward the[11¯0] direction. Peculiar surface structures were observed with a strong dependence on the off-angles, including triangular pyramid-like structures on 2° off surfaces, line structures on 4° and 8° off surfaces and nanometer-height mountain structures on 6° off surfaces. The structures on 2° and 4° off surfaces were based on the stair-like structure composed of Si(110) terraces and monolayer steps. On the other hand, 6° and 8° off surfaces could be understood in terms of Si(110) terraces and bunched steps.

Keywords: Si(1; 1; 0); Vicninal surfaces; Surface structures; Atomic force microscopy; Transmission electron microscopy

X-ray photoemission spectroscopy investigation of the early stages of the oxygen aided Cr growth on Fe(001) by A. Brambilla; A. Calloni; A. Picone; M. Finazzi; L. Duò; F. Ciccacci (pp. 141-145).

► Oxygen aided growth of ultra-thin chromium films on Fe(001). ► Growth of the Cr films at different temperatures, namely 380K and 570K. ► Oxygen always segregates to the surface. ► Cr/Fe interfacial mixing is observed since the early stages of growth.We report on an X-ray photoemission spectroscopy investigation of the early stages of growth of ultra-thin Cr films on the oxygen-passivated Fe(001)– p(1×1)O surface. The Cr coverages ranged from sub-monolayer up to a few atomic layers. Cr has been grown either at 380K or at 570K. Our investigation reveals that during the Cr film growth oxygen floats toward the free surface. The presence of a metallic Cr signal from the very beginning of film growth is discussed in relation to Cr–Fe intermixing and alloy formation at the interface. Our findings are independent from the growth temperature, indicating that it has a very little influence on the chemical interactions at the interface, at variance with the oxygen-free Cr/Fe interface.

Keywords: Chromium; Iron; Surfactant effect; X-ray photoemission spectroscopy

Bulk and surface electronic structure of SnBi₄Te₇ topological insulator by M.G. Vergniory; T.V. Menshchikova; S.V. Eremeev; E.V. Chulkov (pp. 146-149).

► Study of the bulk and surface electronic structure of SnBi₄Te₇. ► By means of DFT and introducing the spin–orbit interaction we find the inverted bands at the bulk Γ point. ► We study the surface of this compound with 2 different terminations. ► We find a robust topological surface state in both cases but with different localization.Using density functional theory with the spin–orbit coupling included we analyze the bulk and surface electronic structure of SnBi₄Te₇ ternary compound. It was revealed that this material is a strong topological insulator with a bulk band gap of about 100meV and a robust surface state around theΓ¯ point. We find that the topological nature of the surface state remains robust with different terminations of the surface.

Keywords: Topological insulators; Electronic structure; Surface states

Au-CeO₂ nanoporous films/carbon nanotubes composites prepared by magnetron sputtering by Ivan Khalakhan; Mykhailo Vorokhta; Mykhailo Chundak; Vladimír Matolín (pp. 150-153).

► Carbon exhibits a significant influence on morphology and stoichiometry of the sputtered CeO₂ thin films. ► Au-CeO₂ catalyst films prepared by simultaneous magnetron sputtering exhibit high concentration of Au⁺ and Au³⁺ ions. ► Distribution of gold oxidation states on the surface of the catalyst as well as surface roughness were found to be depending on the film thickness.CeO₂ and Au-CeO₂ thin films with different thickness were deposited on the carbon nanotubes by using magnetron sputtering of cerium dioxide and gold. The catalyst films were tested using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). XPS showed that thickness has significant influence on CeO₂ films stoichiometry and in turn ceria stoichiometry influences gold oxidation states in Au doped CeO₂ catalyst.

Keywords: SEM; XPS; Carbon nanotubes; Cerium oxide; Gold; Magnetron sputtering

Time-resolved two-photon photoemission study of silicon surface at initial stage of oxidation by Kazutoshi Takahashi; Kazunori Ishibashi; Yusuke Kurahashi; Masaki Imamura; Junpei Azuma; Masao Kamada (pp. 154-158).

► A TR-2PPE study for silicon surface at the initial oxidation stage. ► Transient 2PPE intensity from CBM and surface state depend on the amount of oxygen dosage. ► The prolonged lifetime of 2PPE intensity from CBM after a large amount of O₂ dosage is caused by the disappearance of metallic surface state.Time-resolved two-photon photoemission study has been performed on Si(111) surface at initial oxidation stage that is characterized by synchrotron-radiation photoemission spectroscopy. Transient 2PPE intensity from the conduction band minimum (CBM) shows a maximum at the delay time between 0.5 and 2ps depending on the oxygen dosage. The temporal profile of 2PPE intensity from surface state within the bulk band-gap shows a more rapid decrease than that on Si(001) surface, indicating that the metallic surface state on Si(111) surface causes the shorter lifetime of unoccupied surface state. The prolonged lifetime of 2PPE intensity from CBM after a large amount of O₂ exposure is caused by the disappearance of metallic surface state.

Keywords: Electron dynamics; Synchrotron radiation photoemission; Silicon oxide; Two-photon photoemission

Impact of Ir gate interfacial oxide layers on performance of AlGaN/GaN HEMT by Martin Vallo; Tibor Lalinský; Edmund Dobročka; Gabriel Vanko; Andrej Vincze; Ivan Rýger (pp. 159-163).

► The impact of 15nm Schottky gate contact layer based on conductive Ir oxides grown by RTA in O₂ ambient at 500°C for 1 and 10min. ► X-ray diffraction and depth profiles of SIMS revealed the mixture of Ir and Ir oxides (IrO, IrO₂) that have not been formed in the whole gate contact layer thickness. ► Ir oxides based gate contact layers for design of thermally stable HEMT devices with an enhancement mode of operation could be available.The impact of 15nm thick Schottky gate contact layer based on conductive Ir oxides grown by thermal oxidation in O₂ ambient at 500°C for 1 and 10min, respectively, on performance of circular high electron mobility transistor (C-HEMT) has been investigated. Besides the effects of the gate barrier height increase (∼0.32eV) and gate leakage current decrease (2–4 orders) with the time of oxidation, the shift of both threshold voltage (∼1V) and peak of transconductance (∼2V) of the C-HEMT device towards the zero gate voltage has been introduced. X-ray diffraction and depth profiles of secondary ion mass spectroscopy are employed to analyze the microstructure and composition of the gate contacts. They revealed the mixture of Ir and Ir oxides (IrO, IrO₂) that have not been formed in the whole gate contact layer thickness. All results confirmed the oxidation proceeding from the top of the Ir gate contact layer up to the interface. A promise of Ir oxides based gate contact layers for design of thermally stable HEMT devices with an enhancement mode of operation could be available.

Keywords: Iridium; AlGaN/GaN HEMT; Thermal stability; Iridium oxides; Schottky gate contact

Decay of photo-induced conductivity in Sb-doped SnO₂ thin films, using monochromatic light of about bandgap energy by E.A. Floriano; L.V.A. Scalvi; J.R. Sambrano; A. de Andrade (pp. 164-168).

► Decay of photo-induced conductivity in Sb-doped SnO₂, with different light sources, above and below the matrix bandgap. ► Modeling of the decay and evaluation of the capture energy. ► Electronic structure evaluation according to Density Functional Theory. ► Evaluation of competing mechanisms: trapping by thermally activated defects and time–temperature dependent mobility.Doping tin dioxide (SnO₂) with pentavalent Sb⁵⁺ ions leads to an enhancement in the electrical conductivity of this material, because Sb⁵⁺ substitutes Sn⁴⁺ in the matrix, promoting an electronic density increase in the conduction band, due to the donor-like nature of the doping atom. Results of computational simulation, based on the Density Functional Theory (DFT), of SnO₂:4%Sb and SnO₂:8%Sb show that the bandgap magnitude is strongly affected by the doping concentration, because the energy value found for 4at%Sb and 8at%Sb was 3.27eV and 3.13eV, respectively, whereas the well known value for undoped SnO₂ is about 3.6eV. Sb-doped SnO₂ thin films were obtained by the sol–gel-dip-coating technique. The samples were submitted to excitation with below theoretical bandgap light (450nm), as well as above bandgap light (266nm) at low temperature, and a temperature-dependent increase in the conductivity is observed. Besides, an unusual temperature and time dependent decay when the illumination is removed is also observed, where the decay time is slower for higher temperatures. This decay is modeled by considering thermally activated cross section of trapping centers, and the hypothesis of grain boundary scattering as the dominant mechanism for electronic mobility.

Keywords: Tin dioxide; Electronic structure; Electrical conductivity; Sol–gel; Thin films

Influence of the Ge–Sb sublattice atomic composition on the topological electronic properties of Ge₂Sb₂Te₅ by I.V. Silkin; Yu.M. Koroteev; G. Bihlmayer; E.V. Chulkov (pp. 169-172).

► Bulk electronic structure of the ordered compound Ge₂Sb₂Te₅ by full-potential linearized augmented plane wave method. ► Ge₂Sb₂Te₅ compound turns into a topological insulator when the layers of mixed composition have equal number of Ge and Sb atoms. ►ℤ2 topological invariant does not depend on a specific location of the Ge and Sb atoms in the mixed layer. ► Theℤ2 topological invariant depends only on the concentration of the components in the Ge/Sb mixed layers. ► In a realistic Ge₂Sb₂Te₅ crystal the disorder is not expected to affect the existence of the topological state.We present ab initio calculations of an electronic structure and a topological invariant ν₀ of the Ge₂Sb₂Te₅ compound. We have found that in the case of equiatomic composition of Ge/Sb layers the Ge₂Sb₂Te₅ compound is the topological insulator. The ν₀ invariant does not depend on a specific location of Ge and Sb atoms in the mixed layers, and depends only on their concentration. The variation of the concentration in the Ge/Sb layers leads to a change of the topological invariant of the compound.

Keywords: Electronic structure; Density functional theory; Topological insulator; Topological invariant; Atomic composition

Contribution analysis of the van der Waals term on electronic structures of carbon related systems by Youky Ono; Takahisa Ohno (pp. 173-176).

► Contribution of van der Waals (vdW) interaction on polymer systems are analyzed. ► Two methods, GGA and vdW density functional (vdW-DF), are compared. ► vdW-DF is self-consistently implemented into ab initio program to analyze electronic structures. ► Contributions of vdW term qualitatively differ depending on the bonding structure.Contribution of the van der Waals term in the electron densities and the band structures of covalent bonding one-dimensional networks are studied. Calculations are performed with self-consistently implemented nonlocal van der Waals density functional (vdW-DF) into a first principle program. Results indicate that the contribution of the van der Waals term on band structures qualitatively depends on the bonding types, whether π orbitals are included or not in calculated systems.

Keywords: van der Waals interaction; Electronic structures; Carbon related systems; First principle calculations

Electronic properties of a single heterojunction in InSb/InAs quantum dot system by P.A. Dement’ev; K.D. Moiseev (pp. 177-180).

► We studied transport properties of a InSb QDs free-standing on the InAs surface. ► I– V characteristics of InSb/InAs QD system were for the first time obtained. ► Unique AFM method of local transport study without destruction of the sample surface.We report on electronic transport properties of a single InSb quantum dot free-standing on the surface of a binary InAs matrix. The samples under study were grown by liquid phase epitaxy method. Characterisation of the sample surface was performed using atomic force microscopy (AFM). Uniform high-density (1×10¹⁰cm⁻²) coherent InSb quantum dots with a height of 3–4nm and a diameter of 13–18nm were obtained at T=430°C. It was established that the sample surface has been covered by 3nm-thick oxide layer in ambient environment at room temperature. Unique method of measurement of local tunnel transport across a type II broken-gap InSb/InAs heterojunction was proposed and developed. Electrical characteristics were measured in a contact mode with average force F=75nN that is enough to get repeatable I– V characteristics through the InSb oxide layer and to avoid destruction of the heterostructure. I– V characteristics of the single uncapped InSb quantum dot were for the first time obtained.

Keywords: PACS; 68.37.Ps; 81.07.Ta; 81.15.Lm; 81.15.Gh; 81.16.DnLPE; Quantum dots; Heterostructures; III–V semiconductors; AFM; I; –; V; characteristics

Structural features and surface morphology of Al_xGa_yIn1− x−_yAs_zP1−_z/GaAs(100) heterostructures by P.V. Seredin; A.V. Glotov; E.P. Domashevskaya; I.N. Arsentyev; D.A. Vinokurov; I.S. Tarasov (pp. 181-184).

► Al_xGa_yIn1− x−_yAs_zP1−_z is good material for laser diodes excluding necessity of control of their working temperature. ► Along with the main phase Al_xGa_yIn1− x−_yAs_zP1−_z in the solid solution appears an additional phase. ► Surface of heterostructures with the new phase present nanoscale objects shaped nanoislands. ► Nanoscale heterogeneity on the surface of the epitaxial film is based on the phase of Al_xGa1−_xAs solid solution.Epitaxial metal–organic chemical vapor deposition (MOCVD) heterostructures on the basis of the five-component Al_xGa_yIn1− x−_yAs_zP1−_z alloys (solid solutions) were grown in the range of compositions isoperiodic to GaAs. Using X-ray diffraction technique and atomic force microscopy it was shown that on the surface of heterostructures nanosize objects were present with islets-like shape which can be aligned on the surface of solid solution in the linear direction. On the basis of calculations of the crystal lattice parameters taking into account internal stresses it is possible to assume that the new compound is a phase on the basis of Al_xGa_yIn1− x−_yAs_zP1−_z alloy.

Keywords: Al; _x; Ga; _y; In; 1−; x; −; _y; As; _z; P; 1−; _z; Heterostructure; Nanoscale heterogenety

Effect of surface treatment with different sulfide solutions on the ultrafast dynamics of photogenerated carriers in GaAs(100) by Mikhail V. Lebedev; Katsuyoshi Ikeda; Hidenori Noguchi; Yusuke Abe; Kohei Uosaki (pp. 185-188).

► Free carriers dynamics in GaAs treated with various sulfide solutions are studied. ► Treatment with sulfide solutions decreases surface recombination velocity in GaAs. ► Alcoholic solution reduces surface recombination in greater extent than aqueous one. ► Mechanism of interaction of HS⁻ ions with GaAs is different in different solvents.The ultrafast carrier dynamics of GaAs(100) surfaces passivated with different sulfide solutions is studied by time-resolved measurements of infrared absorption using the femtosecond visible-pump infrared-probe technique. After passivation of n-GaAs(100) surface with the solution of ammonium sulfide in 2-propanol the three-fold decrease of the surface recombination velocity is observed. The treatment of the n-GaAs(100) surface with the aqueous sulfide solution has a smaller impact on the surface recombination velocity. The different effect of aqueous and alcoholic sulfide solutions on the efficiency of surface passivation is caused by the different mechanisms of charge transfer at the semiconductor/solution interfaces.

Keywords: GaAs; Sulfur passivation; Surface recombination; Semiconductor/solution interface; Ammonium sulfide; Solvent effect

Electrons scattering and conductivity in monolayer graphene by Natalie E. Firsova; Sergey A. Ktitorov (pp. 189-191).

► In this study we consider electrons scattering in graphene. ► Short range potential asymmetric with respect to band indices is considered. ► Characteristic equations and scattering matrix are investigated.Resonance electronic states and scattering by point defects are studied for the monolayer graphene solving the 2+1-dimensional Dirac equation. Exact S- and T-matrices are calculated for the model potential. This effective potential takes into account possible band asymmetry of the point defect potential matrix elements. Regularization of the scattering problem for a singular potential has been carried out. Asymptotic analysis allowed us to obtain the conductivity dependence on the Fermi level position in the low-energy limit. Numerical calculations were carried out in the wide range of electronic energies. The transport relaxation time behaves as 1/E in the limit of E tending to zero and oscillates around a constant value due to the resonance scattering at higher energy magnitudes.

Keywords: Dirac equation; Graphene; Scattering matrix

Nanoscale Si template for the growth of self-organized one-dimensional nanostructures by Laurence Masson; Houda Sahaf; Patrick Amsalem; Florent Dettoni; Eric Moyen; Norbert Koch; Margrit Hanbücken (pp. 192-195).

► We have fabricated in a one-step process a highly perfect nanoscale Si template. ► The template consists of a self-assembled Si nanostripe array with a pitch of 2nm. ► The adsorption of Co and C₆₀ gives rise to the growth of well ordered nanolines.Through silicon deposition onto the silver (110) surface, we have fabricated in a one-step process a highly perfect nanoscale template consisting of a self-assembled Si nanostripe array with a pitch of 2nm, covering uniformly the entire surface. Scanning tunneling microscopy investigations show that this system can be used, in a very simple way, as a template for the growth of identical highly ordered one-dimensional nanostructures. The adsorption of Co at room temperature and C₆₀ at 190°C gives rise to the growth of self-organized one-dimensional nanostructures reproducing the one-dimensional pattern of the Si template.

Keywords: Nanopatterning; Self-assembly; Nanostructures; Silicon; Scanning tunneling microscopy

Magnetic anisotropy of cobalt nanoparticle 2D arrays grown on corrugated MnF₂(110) and CaF₂(110) surfaces by D.A. Baranov; B.B. Krichevtsov; S.V. Gastev; A.G. Banschikov; V.V. Fedorov; K.V. Koshmak; S.M. Suturin; N.S. Sokolov (pp. 196-199).

► Corrugated surface of substrate affect magnetic anisotropy of Co films. ► Cobalt nanoparticles forms linear chains. ► The anisotropy is measured by LMOKE. ► The anisotropy is due to magnetic dipole interaction between nanoparticles.Cobalt nanoparticle 2D arrays with different effective thicknesses of cobalt layer (2nm< d_eff<10nm) were grown by molecular beam epitaxy on CaF₂(110)/Si(001) and MnF₂(110)/CaF₂(110)/Si(001) substrates with corrugated morphology of the surface. Surface morphology analysis showed that for effective thickness of cobalt layer d_eff=5nm the lateral dimensions of cobalt islands are about 5–10nm and the distances between the islands differs in a half along and across the grooves. In both types of the heterostructures the shape of hysteresis loops measured by LMOKE depend on orientation of in-plane magnetic field relative to the direction of the grooves. The azimuthal dependence of coercive field H_c in Co/CaF₂(110)/Si(001) structures corresponds to Stoner–Wohlfarth model's predictions, which takes into account the anisotropy of individual particles. In contrast to that, in Co/MnF₂(110)/CaF₂(110)/Si(001) structures these dependences are analogous to those predicted by the model based on account of magnetic–dipole interaction between particles which are placed in chains (chain-of-spheres-model). Possible explanations of the difference in magnetic anisotropy are suggested.

Keywords: Magnetism; Nanoparticles; Anisotropy; Magnetic dipolar interaction

Interface formation of nanostructured heterojunction SnO₂:Eu/GaAs and electronic transport properties by Tatiane F. Pineiz; Evandro A. de Morais; Luis V.A. Scalvi; Cristina F. Bueno (pp. 200-205).

► Deposition of Eu-doped SnO₂ thin films by the sol–gel dip coating technique, topped by a GaAs layer grown by the resistive evaporation technique. ► Electrical conductivity of the heterojunction is higher than the conductivity of individual thin films. ► Morphology analysis shows good performance of interfaces. ► Raman spectra show incorporation of Eu³⁺ ions.Thin films of tin dioxide (SnO₂) are deposited by the sol–gel-dip-coating technique, along with GaAs layers, deposited by the resistive evaporation technique. The as-built heterojunction has potential application in optoelectronic devices, combining the emission from the rare-earth doped transparent oxide (Eu³⁺-doped SnO₂ presents very efficient red emission) with a high mobility semiconductor. The advantage of this structure is the possibility of separation of the rare-earth emission centers from the electron scattering, leading to a strongly indicated combination for electroluminescence. Electrical characterization of the heterojunction SnO₂:Eu/GaAs shows a significant conductivity increase when compared to the conductivity of the individual films, and the monochromatic light irradiation (266nm) at low temperature of the heterojunction GaAs/SnO₂:Eu leads to intense conductivity increase. Scanning electron microscopy (SEM) of the heterojunction cross section shows high adherence and good morphological quality of the interfaces substrate/SnO₂ and SnO₂/GaAs, even though the atomic force microscopy (AFM) image of the GaAs surface shows disordered particles, which increases with sample thickness. On the other hand, the good morphology of the SnO₂:Eu surface, shown by AFM, assures the good electrical performance of the heterojunction. The observed improvement on the electrical transport properties is probably related to the formation of short conduction channels at the semiconductors interface, which may exhibit two-dimensional electron gas (2DEG) behavior.

Keywords: Tin dioxide; Gallium arsenide; Heterojunction; Interface; Electrical conductivity

Very low drift and high sensitivity of nanocrystal-TiO₂ sensing membrane on pH-ISFET fabricated by CMOS compatible process by W. Bunjongpru; A. Sungthong; S. Porntheeraphat; Y. Rayanasukha; A. Pankiew; W. Jeamsaksiri; A. Srisuwan; W. Chaisriratanakul; E. Chaowicharat; N. Klunngien; C. Hruanun; A. Poyai; J. Nukeaw (pp. 206-211).

► We can fabricate sensing membrane layer from TiN with low drift rate. ► The EIS device incorporating TiN film annealed at 850°C exhibited a highest sensitivity. ► pH-sensing device fabrication process is fully compatible with CMOS technology.High sensitivity and very low drift rate pH sensors are successfully prepared by using nanocrystal-TiO₂ as sensing membrane of ion sensitive field effect transistor (ISFET) device fabricated via CMOS process. This paper describes the physical properties and sensing characteristics of the TiO₂ membrane prepared by annealing Ti and TiN thin films that deposited on SiO₂/p-Si substrates through reactive DC magnetron sputtering system. The X-ray diffraction, scanning electron microscopy and Auger electron spectroscopy were used to investigate the structural and morphological features of deposited films after they had been subjected to annealing at various temperatures. The experimental results are interpreted in terms of the effects of amorphous-to-crystalline phase transition and subsequent oxidation of the annealed films.The electrolyte–insulator–semiconductor (EIS) device incorporating TiON membrane that had been obtained by annealing of TiN thin film at 850°C exhibited a higher sensitivity (57mV/pH), a higher linearity (1), a lower hysteresis voltage (1mV in the pH cycle of 7→4→7→10→7), and a smaller drift rate (0.246mV/h) than did those devices prepared at the other annealing temperatures. Furthermore, this pH-sensing device fabrication process is fully compatible with CMOS fabrication process technology.

EXAFS analysis of LiFePO₄ and Li₄Ti₅O₁₂ samples produced via chemical technique by M.D. Sharkov; D.V. Agafonov; A.V. Bobyl; M.E. Boiko; E.M. Ershenko; S.G. Konnikov; K.Ju. Pogrebitsky; Y.V. Zubavichus (pp. 212-215).

► We made a method to treat EXAFS obtaining oscillations by the variation principle. ► The new EXAFS treatment method estimates both the Fourier window limits. ► Composition of two LiFePO₄ and one Li₄Ti₅O₁₂ samples is studied via EXAFS method. ► Both the LiFePO₄ samples may contain several percent of other substances. ► The Li₄Ti₅O₁₂ sample may contain about one half of anatase TiO₂.EXAFS (extended X-ray absorption fine structure) spectra of two triphylite (lithium iron phosphate) samples and a lithium titanate (lithium titanium oxide) sample have been measured and processed. A new method of EXAFS data analysis including a procedure to separate spectrum oscillations based on the variation principle and estimating Fourier window limits has been applied to all the spectra. The volume fractions of impurity phases in the samples are estimated. An assumption is made that the titanate sample contains about 40vol% titanium oxide in the anatase phase. It is shown that triphylite sample #1 may contain about 1% maghemite (magnetic phase of iron-III oxide) and triphylite sample #2 may include 5–10% iron-III phosphate.

Keywords: EXAFS spectroscopy; EXAFS treatment; Lithium iron phosphate; Lithium titanate

Microscopy of carbon steels: Combined AFM and EBSD study by P.G. Ulyanov; D.Yu. Usachov; A.V. Fedorov; A.S. Bondarenko; B.V. Senkovskiy; O.F. Vyvenko; S.V. Pushko; K.S. Balizh; A.A. Maltcev; K.I. Borygina; A.M. Dobrotvorskii; V.K. Adamchuk (pp. 216-218).

► The etching is anisotropic, while the etching rate is determined by the orientation of the grain. ► The (100) face is the most resistant to chemical etching, while the etching rate of the other faces, including the most close-packed (110), is much larger. ► The rate of etching of iron crystals decreases over time due to the formation of the oxide layer on the surface.Atomic force microscopy (AFM) and electron backscatter diffraction were used to study formation of the low-carbon steel surface relief upon chemical etching with nital. The combination of these techniques allowed quantitative characterization of the iron etch depth dependence on the crystallographic orientation of individual ferrite grains. The obtained results demonstrate high potential of AFM for quantitative metallography.

Keywords: AFM; EBSD; Steel; Grain; Ferrite; Metallography; Etching anisotropy

High resolution STM imaging with oriented single crystalline tips by A.N. Chaika; S.S. Nazin; V.N. Semenov; N.N. Orlova; S.I. Bozhko; O. Lübben; S.A. Krasnikov; K. Radican; I.V. Shvets (pp. 219-223).

Display Omitted► [001]-oriented single crystalline W tips have been applied for high resolution STM studies. ► Electron orbitals of the tungsten tip atom have been imaged with sub-Ångstrom lateral resolution using carbon atomic orbitals. ► The electron orbitals responsible for STM imaging can be selected by bias voltage and tip-sample distance.Precise knowledge of the atomic and electronic structure of scanning tunneling microscopy (STM) tips is crucial for a correct interpretation of atomically resolved STM data and an improvement of the spatial resolution. Here we demonstrate that tungsten probes with controllable electronic structure can be fabricated using oriented single crystalline tips. High quality of the [001]-oriented W tips sharpened in ultra high vacuum was proved by electron microscopy. Distance dependent STM studies carried out on a graphite (0001) surface demonstrate that application of crystallographically oriented single crystalline tips allows one to control the tip electron orbitals responsible for high resolution imaging under specific tunneling conditions.

Keywords: PACS; 68.37.Ef; 73.40.Gk; 73.20.AtSTM imaging; Electron orbital; Tungsten; Graphite

Charge-controlled fixation of DNA molecules on silicon surface and electro-physical properties of Au–DNA–Si interface by N.V. Bazlov; O.F. Vyvenko; P.A. Sokolov; N.A. Kas’yanenko; Yu V. Petrov (pp. 224-228).

► Conditions of DNA fixation on surface of n-type silicon crystal were investigated. ► In darkness immobilizing of molecules leads to form DNA ropes. ► Fixation under illumination results in forming of single DNA mesh. ► Different types of DNA conformations result in different types of interface states. ► Estimations of interface state densities are presented.Light-induced fixation of DNA molecules on silicon surface was done and electro-physical properties of Schottky diodes with DNA on interfaces were investigated. Thymus DNA molecules were deposited on silicon from a water solution. Fixed molecular structures were observed with helium ionic microscopy and atomic force microscopy and then they were covered with thermal sputtered gold film. Obtained structures Au–DNA–( n-Si) were examined with current–voltage and frequency dependent admittance measurements. In darkness immobilizing of molecules leaded to form DNA ropes with thickness up to 10nm and distances between them about 1mkm. Fixation under illumination resulted in forming of single DNA mesh with thickness about 1nm and cell size about 100nm. Presence of molecular mesh on interface leaded to increasing of charge density controlled by metal Fermi level and improved diode quality. Presence of molecular ropes resulted in increasing of charge density controlled by semiconductor. From the estimation of interface state density values the origin of the states at the interface between DNA and silicon substrate is suggested to be DNA phosphate groups contacting or being close to the substrate surface.

Keywords: DNA fixation; Silicon surface; Interface state; Schottky diode; Admittance

Retraction notice to “Chemical densification of plasma sprayed yttria stabilized zirconia (YSZ) coatings for high temperature wear and corrosion resistance” [Appl. Surf. Sci. 263 (2012) 827] by Yaping Ye; Karl Thomas Fehr; Martin Faulstich; Gerhard Wolf (pp. 229-229).

Publisher Note (pp. 230-230).

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Applied Surface Science (v.267, #)