Check out our New Publishers' Select for Free Articles

Applied Surface Science (v.252, #15)

Preface by Ulf O. Karlsson; Roger Wäppling (pp. 5243-5243).

Charge transfer in the atomic structure of Ge (105) by Y. Fujikawa; T. Sakurai; M.G. Lagally (pp. 5244-5248).

The atomic structure and charge transfer on the Ge (105) surface formed on Si substrates are studied using scanning tunneling microscopy and spectroscopy (STM and STS). The bias-dependent STM images of the whole Ge (105) facets formed on a Ge “hut�? structure on Si (001) are observed, which are well explained by the recently confirmed structure model. The local surface density of states on the Ge (105) surface is measured by STS. The localization of the electronic states expected from charge transfer mechanism is observed in the d I/d V spectra. The surface band gap is estimated as 0.8–0.9eV, which is even wider than the bulk bandgap of Ge, indicating the strong charge transfer effect to make the dangling bonds stable. The shape of normalized tunnel conductance agrees with the theoretical band structure published recently by Hashimoto et al.

Keywords: PACS; 68.35.Bs; 73.20.At; 68.37.Ef; 68.47.FgScanning tunneling microscopy and spectroscopy; High-index surface; Silicon; Germanium

Light emission from silicon nanocrystals: Probing a single quantum dot by I. Sychugov; R. Juhasz; J. Valenta; M. Zhang; P. Pirouz; J. Linnros (pp. 5249-5253).

Analysis of low-temperature photoluminescence measurements performed on single silicon nanocrystals is presented. The luminescence emission linewidth of Si nanocrystals is found to be less than thermal broadening at low temperature, confirming the atomic-like nature of their energetic states. Beside the main peak the low-temperature spectra reveal a ∼6meV replica, the origin of which is discussed. For some of the investigated dots, we also observe a ∼60meV transverse optical (TO) phonon replica. The regular arrangement of individual nanocrystals used in this work enables combined high-resolution transmission electron microscopy (TEM) and low-temperature photoluminescence characterization of the same single quantum dot.

Keywords: PACS; 78.67.Hc; 78.55.ApSilicon nanocrystal; Luminescence

Structure and thermal properties of supported catalyst clusters for single-walled carbon nanotube growth by Feng Ding; Kim Bolton; Arne Rosén (pp. 5254-5258).

Structure and thermal properties of supported iron clusters were studied using molecular dynamics simulations. When supported clusters are in the liquid state, their surfaces have spherical curvature, whereas solid clusters form a layered crystalline structure. The cluster freezing (melting) point increases dramatically with increasing cluster–substrate interaction strength, and rapid diffusion of cluster surface atoms is observed below the freezing point.

Keywords: PACS; 61.48.+c; 61.46.+w; 81.10.AjSupported cluster; MD simulation; Surface diffusion

Structure of the SiC (0001) 3×3 reconstruction studied by surface X-ray diffraction by W. Voegeli; K. Akimoto; T. Aoyama; K. Sumitani; S. Nakatani; H. Tajiri; T. Takahashi; Y. Hisada; S. Mukainakano; X. Zhang; H. Sugiyama; H. Kawata (pp. 5259-5262).

The surface structure of the 3×3 reconstruction of the 4H-SiC (0001) surface was investigated with surface X-ray diffraction (SXRD).Of the studied models, the twist model proposed by Starke et al. [U. Starke, J. Schardt, J. Bernhardt, M. Franke, K. Reuter, H. Wedler, K. Heinz, J. Furthmuller, P. Kackell, F. Bechstedt, Phys. Rev. Lett. 80 (1998) 758] gave the best fit to the experimental data. The structural parameters were determined accurately.

Keywords: PACS; 68.35.Bs; 68.47.FgSilicon carbide; SiC; Surface structure; Reconstruction; X-ray diffraction

Stable reconstruction and adsorbates of InAs(111)A surface by A. Taguchi; K. Kanisawa (pp. 5263-5266).

We investigated the surface properties of InAs(111)A by low-temperature scanning tunneling microscopy (LT-STM) with atomic resolution and first-principles calculation. Very clear atom image was observed, showing that the surface reconstruction is an In-vacancy structure. We also observed two kinds of adsorbates on the surface. The first-principles calculations indicate that the In-vacancy structure is the most stable surface reconstruction under any experimental conditions, which is consistent with the LT-STM observation. Investigations of adsorption properties of an In atom, an As atom, and an As₂ molecule by the first-principles calculations imply that the observed adsorbates are an In atom and an As₂ molecule.

Keywords: PACS; 68.37.Ef; 68.35.Bs; 68.43.BcInAs(1; 1; 1)A surface; STM; Adsorbate; First-principles calculations

Adsorption of Cs on InAs(111) surfaces by K. Szamota-Leandersson; M. Göthelid; M. Leandersson; U.O. Karlsson (pp. 5267-5270).

Caesiated InAs(111)B (1×1) and InAs(111)A (2×2) surfaces have been studied by photoelectron spectroscopy. On the InAs(111)B a new (√3×√3)R30° reconstruction was observed. During Cs evaporation remarkably small changes are observed in the lone pair states, and no sign of an accumulation layer at the surface can be observed. Instead, the additional charge provided by Cs is rapidly transported towards the bulk. On the InAs(111)A cesium behaves as a typical electropositive alkali metal donator that enhances the already existing accumulation layer.

Keywords: PACS; 79.60−i; 73.21−b; 68.43−hAdatoms; Indium arsenide; Cs; Photoemission; 2DEG

Study of arsenic for antimony exchange at the Sb-stabilized GaSb(001) surface by M.C. Righi; Rita Magri; C.M. Bertoni (pp. 5271-5274).

In this paper we present a first-principle study on the energetics of a single As₂ molecule on GaSb(001) reconstructed surface. In order to shed light into the mechanisms of anion exchange at the Sb-rich GaSb(001) surface, we studied firstly As₂ adsorption and then As for Sb exchange. We identify a surface region where both the processes are energetically favored. The results of this twofold analysis can be combined to derive possible reaction paths for the anion exchange process.

Keywords: PACS; 68.43.Bc; 71.15.MbAdsorption; Exchange reaction at surface; Density functional theory; III–V Compounds

Observation of Si(100) surfaces annealed in hydrogen gas ambient by scanning tunneling microscopy by Hitoshi Kuribayashi; Masahide Gotoh; Reiko Hiruta; Ryosuke Shimizu; Koichi Sudoh; Hiroshi Iwasaki (pp. 5275-5278).

We investigated the cleaning process of Si(100) surfaces by annealing in H₂ gas ambient following chemical treatments by scanning tunneling microscopy. We observed the monohydride Si structure: Si(100):2×1-H on the surfaces annealed at 1000°C in 2.5×10⁴Pa H₂ gas ambient without conspicuous contaminants. On the sample annealed for 10min or longer times, well-defined Si(100) structures with alternating S_A and S_B steps were observed, whereas the initial roughness still remained on the surfaces annealed for only 5min.

Keywords: PACS; 68.37.EfH; ₂; gas; STM; Si; H; ₂; anneal

Flattening of micro-structured Si surfaces by hydrogen annealing by Reiko Hiruta; Hitoshi Kuribayashi; Ryosuke Shimizu; Koichi Sudoh; Hiroshi Iwasaki (pp. 5279-5283).

We report atomic scale flattening of surfaces of microstructures formed on Si wafers by furnace annealing. To avoid thermal deformation of the fabricated structures, advantage was taken of hydrogen annealing, which enables us to decrease the relaxation rate of Si surfaces due to surface hydrogenation. We examined cross-sectional shape and sidewall morphology of 3μm deep trenches on Si(001) substrates after annealing at 1000°C under various H₂ pressures of 40–760Torr. We successfully formed Si trenches with flat surfaces composed of terraces and steps while preserving the designed trench profile by increasing H₂ pressure to 760Torr.

Keywords: PACS; 68.35.Bs; 68.37.PsSilicon; Microstructure; Flattening; Hydrogen annealing

Atomic structure of the carbon induced Si(001)– c(4×4) surface by Jiangping He; G.V. Hansson; R.I.G. Uhrberg (pp. 5284-5287).

The atomic and electronic structures of the Si(001)– c(4×4) surface have been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). To explain the experimental bias dependent STM observations, a modified mixed ad-dimer reconstruction model is introduced. The model involves three tilted Si dimers and a carbon atom incorporated into the third subsurface layer per c(4×4) unit cell. The calculated STM images show a close resemblance to the experimental ones.

Keywords: PACS; 68.35.Bs; 68.37.Ef; 73.20.AtAtomic structure; Electronic structure; Si(0; 0; 1); Scanning tunneling microscopy; Density functional theory

Study of the surface structure of Si(111)-6×1(3×1)-Ag using X-ray crystal truncation rod scattering by Kazushi Sumitani; Kosuke Masuzawa; Takashi Hoshino; Sinichiro Nakatani; Toshio Takahashi; Hiroo Tajiri; Koichi Akimoto; Hiroshi Sugiyama; Xiao-Wei Zhang; Hiroshi Kawata (pp. 5288-5291).

The structure of the Si(111)-6×1-Ag surface is investigated using crystal truncation rod (CTR) scattering along 00 rod. For the measurement, we developed a manipulator suitable for observing CTR scattering at large momentum transfer perpendicular to the surface. The heights of the silver and reconstructed silicon atoms from the substrate were determined. We also compared the obtained positions with those of the Si(111)-√3×√3-Ag surface and found that the heights of those reconstructed atoms are almost the same.

Keywords: PACS; 61.10.Nz; 68.43.FgSi(1; 1; 1)-6; ×; 1-Ag; Structure analysis; Surface X-ray diffraction; Crystal truncation rod

Surface electronic structure of the (3×2) reconstruction induced by Yb on a Si(111) surface by Shinya Takada; Kazuyuki Sakamoto; Keisuke Kobayashi; Toshihiro Suzuki; Ayumi Harasawa; Taichi Okuda; Toyohiko Kinoshita (pp. 5292-5295).

We have investigated the electronic structure of the Yb/Si(111)-(3×2) surface using angle-resolved photoelectron spectroscopy. Five surface states have been identified in the gap of the bulk band projection. Among these five surface state, the dispersions of three of them agree well with those of the surface states of monovalent atom adsorbed Si(111)-(3×1) surfaces. The dispersions of the two other surface states agree well with those observed on the Ca/Si(111)-(3×2) surface, whose basic structure is the same as that of monovalent atom adsorbed Si(111)-(3×1) surfaces. Taking these results into account, we conclude that the five surface states observed in the band gap originate from the orbitals of Si atoms that form a honeycomb-chain-channel structure.

Keywords: PACS; 73.20.At; 79.60.−i; 61.14.Hg; 68.35.−pPhotoelectron spectroscopy; Surface electronic structure; Silicon; Rare-earth metal; One-dimensional chain

K-induced surface structural change of Si(111)-7×7 probed by second-harmonic generation by Takanori Suzuki; Youichi Karaki; Dongmei Deng; Masatoshi Tanaka (pp. 5296-5299).

The growth of thin K films on Si(111)-7×7 has been investigated by selecting the input and output polarizations of second-harmonic generation (SHG) at room temperature (RT) and at an elevated temperature of 350°C. The SH intensity at 350°C showed a monotonic increase with K coverages up to a saturated level, where low energy electron diffraction (LEED) showed a 3×1 reconstructed structure. The additional deposition onto the K-saturated surface at 350°C showed only a marginal change in the SH intensity. These variations are different from the multi-component variations up to 1ML and orders of magnitude increase due to excitation of plasmons in the multilayers at RT. The variations of SHG during desorption of K at 350°C showed a two-step decay with a marked shoulder which most likely corresponds to the saturation K coverage of the Si(111)-3×1-K surface. The dominant tensor elements contributing to SHG are also identified for each surface.

Keywords: PACS; 68.35.Rh; 68.43.−h; 73.20.Mf; 78.66.D6Second-harmonic generation; SHG; Potassium; K; Si(1; 1; 1)-7; ×; 7; Si(1; 1; 1)-3; ×; 1; Plasmon

Hydrogen-induced metallization on Ge(111) c(2×8) by I.C. Razado; H.M. Zhang; G.V. Hansson; R.I.G. Uhrberg (pp. 5300-5303).

We have studied hydrogen adsorption on the Ge(111) c(2×8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom states to the adatom states. The surface states near the Fermi-level have been followed by ARPES as function of H exposure. Initially, there is strong emission from the rest atom states but no emission at the Fermi-level which confirms the semiconducting character of the c(2×8) surface. With increasing H exposure a structure develops in the close vicinity of the Fermi-level. The energy position clearly indicates a metallic character of the H-adsorbed surface. Since the only change in the STM images is the increased brightness of the adatoms neighbouring a H-terminated rest atom, we identify the emission at the Fermi-level with these adatom states.

Keywords: PACS; 68.37.Ef; 79.60.Dp; 68.35.Bs; 68.43.FgScanning tunneling microscopy; Angle-resolved photoelectron spectroscopy; Hydrogen adsorption; Ge(1; 1; 1); c; (2; ×; 8)

Ultrathin Fe films on single crystal and virtual Ge(001) substrates: Towards the control of magnetic properties by M. Cantoni; M. Riva; G. Isella; R. Bertacco; F. Ciccacci (pp. 5304-5307).

Ultrathin Fe films have been epitaxially grown at room temperature on standard single crystal Ge(001) substrates and virtual Ge/Si(001) substrates. Their magnetic and electronic properties have been investigated in situ by spin polarized inverse photoemission and magneto-optical Kerr effect. In both cases, the onset of ferromagnetism appears definitively at 3ML, and the overall behavior is very similar in the case of standard and virtual substrates, so that the latter can be employed for growing high quality Fe/Ge/Si interfaces. All the films investigated display uniaxial anisotropy, which is explained in terms of the surface morphology induced by the preparation conditions.

Keywords: PACS; 75.70.Cn; 85.75.-dSpintronics; Virtual substrate; Spin polarized inverse photoemission; Magnetic anisotropy; Nanostructures

Electronic structure and electron dynamics at the GaSb(001) surface studied by femtosecond pump-and-probe pulsed laser photoemission spectroscopy by Martin Månsson; Michael A. Grishin; Oscar Tjernberg; Tomas Claesson; Henrik S. Karlsson; Ulf O. Karlsson (pp. 5308-5311).

Transiently excited electron states at the GaSb(001) surface have been studied by means of time- and angle-resolved photoemission spectroscopy based on a femtosecond laser system. A normally unpopulated surface electron state has been found at ∼250meV above the valence band maximum with a strong confinement at the center of the surface Brillouin zone. The lifetime of transiently excited carriers at the intergap surface states has been found to be ∼11ps, associated with rapid carrier diffusion.

Keywords: PACS; 33.60.Cv; 71.20.Nr; 73.20.At; 73.25.+i; 79.60.−iLaser methods; Angle-resolved photoemission; Surface states; Gallium antimonide; Photoelectron emission

Study of the early stages of Cr/6H-SiC(0001) interface formation by I. Dontas; S. Karakalos; S. Ladas; S. Kennou (pp. 5312-5315).

The early stages of the Cr/6H-SiC(0001) interface formation at room temperature were investigated using XPS, LEED and work function (WF) measurements. Upon stepwise Cr evaporation in UHV up to a thickness of 5–10 monolayers (ML) at RT, the binding energy of the XPS Cr 2p_3/2 core level peak shifted from 576.1eV, at submonolayer coverage, to 574.7eV (corresponding to metallic Cr) for the final Cr deposit, while the binding energies of the substrate XPS core level peaks remained stable. The WF exhibited a steep decrease of about 0.5eV from the initial SiC substrate value, upon submonolayer coverage, but then increased gradually to saturation at a value of about 4.8eV (polycrystalline Cr film with some chemisorbed oxygen). The growth of the ultrathin film was via 3D-cluster formation. The height of the Schottky barrier for the Cr/6H-SiC(0001) contact was found by XPS to be 0.5±0.1eV. The results, generally, indicate the absence of any extended interfacial silicide-like interaction at RT.

Keywords: PACS; 73.30.+y; 79.60.Dp; 82.80.PvSilicon carbide; Chromium; Ohmic metal contacts

Formation of precipitates in heavily boron doped 4H-SiC by M.K. Linnarsson; M.S. Janson; N. Nordell; J. Wong-Leung; A. Schöner (pp. 5316-5320).

Secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) are utilized to study precipitation and the solubility of B in 4H-SiC epitaxial layers super saturated with B. Heat treatments are performed in Ar atmosphere in an rf-heated furnace at temperatures between 1700 and 2000°C. SIMS ion images, and TEM micrographs reveal the formation of two types of precipitates where the larger, more thermally stable one is suggested to be B₄C. The boron solubility is determined from SIMS depth profiles and is shown to follow the Arrhenius expression: 7.1×10²²exp(−1.4eV/ k_B T)cm⁻³ over the studied temperature range.

Keywords: PACS; 61.82.Fk; 66.16.Yc; 61.16.Bg; 64.75.+gSIMS; TEM; SiC; B; Solubility limit; Precipitates

Temperature dependent low energy electron microscopy study of Ge growth on Si(113) by T. Clausen; Th. Schmidt; J.I. Flege; A. Locatelli; T.O. Mentes; S. Heun; F.Z. Guo; J. Falta (pp. 5321-5325).

We investigated the initial Ge nucleation and Ge island growth on a Si(113) surface using low energy electron microscopy and low energy electron diffraction. The sample temperature was varied systematically between 380°C and 590°C. In this range, a strong temperature dependence of the island shape is observed. With increasing temperature the Ge islands are elongated in the[332¯] direction. Simultaneously, the average island size increases while their density decreases. From the Arrhenius-like behaviour of the island density, a Ge adatom diffusion barrier height of about 0.53eV is deduced.

Keywords: PACS; 68.37.−d; 68.65.−kGe; Si(1; 1; 3); Epitaxial growth; LEEM; LEED

Strain relaxation of epitaxial SiGe layer and Ge diffusion during Ni silicidation on cap-Si/SiGe/Si(001) by C.H. Jang; M.R. Sardela Jr.; S.-H. Kim; Y.-J. Song; N.-E. Lee (pp. 5326-5330).

Strain relaxation of the epitaxial SiGe layer and Ge diffusion during nickel silicidation by rapid thermal annealing the structure of Ni(≅14nm)/cap-Si(≅26nm)/Si_0.83Ge_0.17/Si(001) at the elevated annealing temperatures, T_A, were investigated by X-ray diffraction analyses of high-resolution ω–2 θ scan and reciprocal space mapping. The analyses showed a much larger strain relaxation at a lower T_A and a reduction in Ge content in the SiGe layer of Ni/SiGe/Si(001) after thermal annealing compared to the case of cap-Si/SiGe/Si(001). The results indicate that the strain relaxation of the SiGe layers in NiSi/SiGe/Si(001) is related to the phenomena of NiSi agglomeration and penetration into the SiGe layer during silicidation at elevated anneal temperatures ≥750°C. At elevated T_A≥750°C, Ge diffused into the intact cap-Si area during silicidation.

Keywords: PACS; 61.10.Nz; 68.55.JkNickel silicide; Silicon–germanium; Silicidation; Strain relaxation

Surface phase diagram and temperature induced phase transitions of Sn/Cu(100) by J. Martínez-Blanco; V. Joco; P. Segovia; T. Balasubramanian; E.G. Michel (pp. 5331-5334).

Room temperature deposition of Sn on Cu(100) gives rise to a rich variety of surface reconstructions in the submonolayer coverage range. In this work, we report a detailed investigation on the phases appearing and their temperature stability range by using low-energy electron diffraction and surface X-ray diffraction. Previously reported reconstructions in the submonolayer range are p(2×2) (for 0.2ML), p(2×6) (for 0.33ML), (32×2)R45° (for 0.5ML), and c(4×4) (for 0.65ML). We find a new phase with a−4204 structure for a coverage of 0.45ML. Furthermore, we analyze the temperature stability of all phases. We find that two phases exhibit a temperature induced reversible phase transition: the (32×2)R45° phase becomes (2×2)R45° phase above 360K, and the new−4204 phase becomes p(2×2) also above 360K. The origin of these two-phase transitions is discussed.

Keywords: PACS; 61.14Hg, 68.35.RhLow energy electron diffraction (LEED); Surface X-ray diffraction (SXRD); Surface reconstruction; Phase transitions; Copper; Tin

Thermal stability of nanoscale silver metallization in Ag/W/Co/Si(100) multilayer by O. Akhavan; A. Azarm; A.Z. Moshfegh; M.A. Bahrevar (pp. 5335-5338).

In this work, we have studied thermal stability of nanoscale Ag metallization and its contact with CoSi₂ in heat-treated Ag(50nm)/W(10nm)/Co(10nm)/Si(100) multilayer fabricated by sputtering method. To evaluate thermal stability of the systems, heat-treatment was performed from 300 to 900°C in an N₂ ambient for 30min. All the samples were analyzed by four-point-probe sheet resistance measurement ( R_s), Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and atomic force microscopy (AFM). Based on our data analysis, no interdiffiusion, phase formation, and R_s variation was observed up to 500°C in which the Ag layer showed a (111) preferred crystallographic orientation with a smooth surface and R_s of about 1Ω/□. At 600°C, a sharp increase of R_s value was occurred due to initiation of surface agglomeration, WSi₂ formation, and interdiffusion between the layers. Using XRD spectra, CoSi₂ formed at the Co/Si interface preventing W silicide formation at 750 and 800°C. Meantime, RBS analysis showed that in this temperature range, the W acts as a cap layer, so that we have obtained a W encapsulated Ag/CoSi₂ contact with a smooth surface. At 900°C, the CoSi₂ layer decomposed and the layers totally mixed. Therefore, we have shown that in Ag/W/Co/Si(100) multilayer, the Ag nano-layer is thermally stable up to 500°C, and formation of W-capped Ag/CoSi₂ contact with R_s of 2Ω/□ has been occurred at 750–800°C.

Keywords: PACS; 68.60.Dv; 68.37.Ps; 68.55.JkSilver; Nano-metallization; Co silicide; W interlayer

Swift ion irradiations of^natFe/⁵⁷Fe/Si trilayers by V. Milinovic; K.P. Lieb; P.K. Sahoo; P. Schaaf; K. Zhang; S. Klaumünzer; M. Weisheit (pp. 5339-5342).

We report here on changes in magnetism and microstructure when implanting, at 92 or 300K, up to 5×10¹⁵ Au²⁶⁺-ionscm⁻² of 350MeV into^natFe(45nm)/⁵⁷Fe(20nm)/Si trilayers. This choice of ions and energy allowed to test the irradiation effects in the regime of pure electronic stopping. The samples were analysed before and after irradiation by Rutherford back-scattering spectroscopy, X-ray diffraction, conversion electron Mössbauer spectroscopy, and magneto-optical Kerr effect. Up to 1×10¹⁵ionscm⁻², there was interface broadening at a mixing rate of Δ σ²/ Φ=55(5)nm⁴, followed by full Fe–Si inter-diffusion. The Mössbauer spectra revealed fractions of α-Fe and amorphous ferromagnetic and paramagnetic iron silicides, but no crystalline Fe–Si phase. The magnetic remanence in the as-deposited Fe-layer showed small components of uniaxial and four-fold magnetization. For increasing ion fluence, the component with four-fold symmetry grew at the expense of the uniaxial component. For the highest fluences, an isotropic magnetization was found.

Keywords: PACS; 61.80.Jh; 68.35.Ct; 75.70.Cn; 76.80.+ySwift heavy-ion irradiation; Ion beam mixing; Iron silicides; Magneto-optical Kerr effect; Mössbauer effect

Modification of wetting of copper (Cu) on carbon (C) by plasma treatment and molybdenum (Mo) interlayers by C. Eisenmenger-Sittner; C. Schrank; E. Neubauer; E. Eiper; J. Keckes (pp. 5343-5346).

Manipulating wetting and adhesion between the chemically immiscible elements Cu and C is of high interest for the production of C-fiber reinforced Cu–C metal matrix composites (MMC's) which are potential materials for high performance heat sinks.This work presents two approaches to adhesion manipulation: (i) the activation of the C-surface by a treatment in nitrogen (N₂) radio frequency (RF) plasma and (ii) the deposition of a Mo-interlayer on the C-surface.Both approaches yield a significant increase in adhesion for Cu-coatings deposited immediately after pre treatment. Heat treatment (30min, 800°C, high vacuum furnace) leads to a drastic loss in adhesion for the plasma treated samples while the samples containing the Mo-interlayer retain excellent adhesion values.Results of thermal cycling experiments (RT—500°C) combined with in situ X-ray diffraction (XRD) measurements show a similar picture. The Cu-coating on the plasma treated sample delaminates after one cycle. The sample with the Mo-interlayer can go through several cycles and is able to sustain thermally induced stresses.The difference in the response of the two sample types to post deposition thermal treatment can be tracked back to the de-wetting behavior of Cu on the different substrates. Void formation is observed at the Cu–C interface in the case of plasma treatment but not for samples with a Mo-interlayer.

Keywords: PACS; 68.08.Bc; 68.35.Np; 68.55.−a; 81.15.Cd; 81.20.Ev; 07.10.Lw; 61.10.NzCarbon; Copper; Metal matrix composite; Plasma treatment; Molybdenum interlayer; De-wetting

Equilibrium and kinetic surface segregation in binary alloy thin films by J.Y. Wang (pp. 5347-5350).

A general theoretical analysis of the effect of film thickness on equilibrium and kinetic surface segregation in binary alloy thin films is presented. In this analysis, a constrained condition that represents the finite size of thin film system has been introduced to the modified Darken model, which has been used to describe both equilibrium and kinetic surface segregation in bulk materials. Simulation of surface segregation for alloy thin films can be carried out for all composition ranges and all film thicknesses if only knowing the surface segregation parameters for bulk materials. Simulations of equilibrium and kinetic surface segregation in Cu(111)Ag binary alloy thin film are presented.

Keywords: PACS; 68.35.Dv; 68.55.−a; 61.43. DqEquilibrium; Kinetic; Surface segregation; Cu(Ag) alloy thin film

Thickness influence on surface morphology and ozone sensing properties of nanostructured ZnO transparent thin films grown by PLD by S. Christoulakis; M. Suchea; E. Koudoumas; M. Katharakis; N. Katsarakis; G. Kiriakidis (pp. 5351-5354).

Transparent zinc oxide (ZnO) thin films with a thickness from 10 to 200nm were prepared by the PLD technique onto silicon and Corning glass substrates at 350°C, using an Excimer Laser XeCl (308nm). Surface investigations carried out by atomic force microscopy (AFM) and X-ray diffraction (XRD) revealed a strong influence of thickness on film surface topography. Film roughness (RMS), grain shape and dimensions correlate with film thickness. For the 200nm thick film, the RMS shows a maximum (13.9nm) due to the presence of hexagonal shaped nanorods on the surface. XRD measurements proved that the films grown by PLD are c-axis textured. It was demonstrated that the gas sensing characteristics of ZnO films are strongly influenced and may be enhanced significantly by the control of film deposition parameters and surface characteristics, i.e. thickness and RMS, grain shape and dimension.

Keywords: PACS; 68.55.Jk; 68.37.Ps; 81.15.FgZinc oxide; PLD; AFM; Ozone

Evolution of epitaxial titanium silicide nanocrystals as a function of growth method and annealing treatments by I. Goldfarb; S. Grossman; G. Cohen-Taguri (pp. 5355-5360).

Titanium silicide grows on silicon in a form of discontinuous layers, which is the most serious obstacle to the formation of high-quality epilayers for VLSI applications. At the same time, nanometric dimensions of the epitaxial silicide islands attract interest as quantum nanostructures. However, for this purpose, nanocrystals in a self-assembled array have to be defect-free, and exhibit high shape and size uniformity. In this work titanium silicide was grown on Si(111) substrates by reactive deposition epitaxy and by solid-phase epitaxy. Since the reaction and phase-formation kinetics depend on the growth method, accordingly different lattice matching and facet energies may result in different morphological shapes of the nanocrystals. Nanocrystals from reaction in a solid-state could be characterized as highly non-uniform in both shape and size, and their evolution due to post-deposition anneals increased that non-uniformity even further. Relaxation of epitaxial mismatch strain by misfit dislocations could be inferred from a gradual reduction of the nanocrystal vertical aspect ratio and development of flat top facets out of the initially sharp conical crests, in accord with generalized Wulf–Kaishew theorem. On the other hand, the silicide nanocrystals formed by reactive deposition exhibited high uniformity and thermal stability. Significant strain relaxation, as could be judged by the nanocrystal flattening, took place only at temperatures in excess of 650°C, followed by progressive nanocrystal coalescence. It thus could be inferred, that better titanium silicide nanocrystal arrays (in the sense of uniformity and stability) are more easily obtained by reactive deposition epitaxy than by solid-phase epitaxy. While terminal, stable C54-TiSi₂ phase, did eventually form in the epilayers in both methods, different evolution pathways were manifested by different respective morphologies and orientations even in this final state.

Keywords: PACS; 81.15.Kk; 68.35.Bs; 61.16.Ch; 64.70.KbVapor-phase epitaxy; Self-assembled nanostructures; Silicides; Scanning tunneling microscopy

Optical band-edge absorption of oxide compound SnO₂ by L.S. Roman; R. Valaski; C.D. Canestraro; E.C.S. Magalhães; C. Persson; R. Ahuja; E.F. da Silva Jr.; I. Pepe; A. Ferreira da Silva (pp. 5361-5364).

Tin oxide (SnO₂) is an important oxide for efficient dielectrics, catalysis, sensor devices, electrodes and transparent conducting coating oxide technologies. SnO₂ thin film is widely used in glass applications due to its low infra-red heat emissivity. In this work, the SnO₂ electronic band-edge structure and optical properties are studied employing a first-principle and fully relativistic full-potential linearized augmented plane wave (FPLAPW) method within the local density approximation (LDA). The optical band-edge absorption α( ω) of intrinsic SnO₂ is investigated experimentally by transmission spectroscopy measurements and their roughness in the light of the atomic force microscopy (AFM) measurements. The sample films were prepared by spray pyrolysis deposition method onto glass substrate considering different thickness layers. We found for SnO₂ qualitatively good agreement of the calculated optical band-gap energy as well as the optical absorption with the experimental results.

Keywords: PACS; 71.15m; 72.80Jc; 73.61Le; 78.40Fy; 7866LiTin oxide; Transparent conducting thin film; SnO; ₂; Transparent electrodes

Optical properties of in situ doped and undoped titania nanocatalysts and doped titania sol–gel nanofilms by A. Ferreira da Silva; I. Pepe; James L. Gole; S.A. Tomás; R. Palomino; W.M. de Azevedo; E.F. da Silva Jr.; R. Ahuja; C. Persson (pp. 5365-5367).

In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO₂) as nanofilms prepared by the sol–gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO₂ thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0eV attributed to TiO₂ absorption, which subsequently yields a strong emission band at 600nm. The electronic band structure and optical properties of the rutile phase of TiO₂ are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO₂ films prepared for undoped sol–gels and by sputtering is performed.

Keywords: PACS; 71.15.Mb; 71.20.Nr; 78.20.ci; 81.40.TvPolymer; TiO; ₂; nanofilms; Electronic band structure; Rhodamine 6G doping

Synthesis and characterization of hydrophobic silica nanocomposites by Walid A. Daoud; John H. Xin; Xiaoming Tao (pp. 5368-5371).

Hydrophobically modified silica nanocomposites have been prepared using a low temperature sol–gel process. In this study, an alkyltriethoxysilane derivative, hexdecyltrimethoxysilane (HDTMS), was co-condensed with tetraethoxyorthosilicate (TEOS) with and without a cross-linking agent, 3-glycidoxypropyltrimethoxysilane (GPTMS), to produce the modified composites. The hydrophobic properties were determined using contact angle measurement. FESEM observations revealed a semispherical nanostructure of the composites with grain size of about 50–75nm in diameter. The chemical modification was studied by FTIR and EDX, whereas the physicothermal properties were analyzed by DSC and TGA. These long-chain alkyl modified silica nanocomposites are promising materials for use in hydrophobic and water-resistant applications.

Keywords: PACS; 81.20.F; 81.05.Y; 81.15; 81.20Sol–gel processing; Nanophase-materials; Coatings; Nanocomposites; Hydrophobicity

Electronic structure of CeAl₂ thin films studied by X-ray absorption spectroscopy by C.L. Dong; C.L. Chen; Y.Y. Chen; K. Asokan; J.F. Lee; J.-H. Guo; C.L. Chang (pp. 5372-5375).

We report X-ray absorption near edge structures (XANES) study of CeAl₂ thin films of various thicknesses, 40–120nm, at Al K- and Ce L₃-edges. The threshold of the absorption features at the Al K-edge shifts to the higher photon energy side as film thickness decreases, implying a decreased in Al p-orbital charges. On the other hand, from Ce L₃-edge spectra, we observed a decrease in the 5d4f occupancy as the surface-to-bulk ratio increases. The valence of Ce in these thin films, as revealed by the Ce L₃-edge spectral results, is mainly trivalent. From a more detailed analysis we found a small amount of Ce⁴⁺ contribution, which increases with decreasing film thickness. Our results indicate that the surface-to-bulk ratio is the key factor which affects the electronic structure of CeAl₂ thin films. The above observations also suggest that charge transfer from Al to Ce is associated with the decrease of the film thickness.

Keywords: PACS; 61.10.Ht; 71.24.+q; 75.20.HrXANES; Mixed valence; Surface; Thin film

Theoretical study of Ti and Fe surface alloys on Al(001) substrate by D. Spišák; J. Hafner (pp. 5376-5378).

Accurate density-functional calculations are performed to investigate the formation of Ti and Fe ultrathin alloys on Al(001) surface. It is demonstrated that a deposition of Ti monolayer on Al(001) substrate leads to the formation of Al₃Ti surface alloy with Ti atoms arranged according to the L1₂ stacking, distinct from the D0₂₂ structure characteristic of a bulk Al₃Ti compound. A quest for the reason of this distinct atomic arrangement led us to the study of the surface structure of Al₃Ti(001) compound. It is concluded that even the Al₃Ti(001) surface is terminated with three layers assuming a L1₂ stacking and hence this stacking fault can be classified as a surface-induced stacking fault. Several possibilities of Fe atoms distributed in the surface region of Al(001) have been examined. The most stable configuration is the one with the compact Fe monolayer on Al(001) and covered by one Al monolayer. Lastly, our calculations show that there is no barrier for the penetration of Fe adatoms below the Al(001) surface; however, such a barrier is present for a Ti-alloyed Al(001) surface.

Keywords: PACS; 68.35.-p; 68.55.Ac; 68.35.FxAluminum; Density-functional calculations; Iron; Metal–metal interfaces; Titanium

Resonant photoemission study of Eu1−_xGd_xTe layers by B.A. Orlowski; P. Dziawa; B. Kowalski; I. Kowalik; M. Pietrzyk; V. Osinniy; T. Story; S. Mickievicius; R. Jonhson (pp. 5379-5383).

Resonant photoemission study of electronic structure of molecular beam epitaxy grown Eu1−_xGd_xTe layers without and with cover protected layer of Te were performed using synchrotron radiation. The analysis of the valence band and shallow core levels spectra of the clean surface of Eu1−_xGd_xTe obtained in situ under UHV conditions showed the existence of Eu²⁺ and Eu³⁺ ions in the layers. The trivalent europium ions mostly are located at the surface and its amount strongly depends on sample surface preparation conditions. The prolonged annealing of Eu1−_xGd_xTe layers covered with protected layer of Te leads to formation of clean surface of the sample not changing the stoichiometry of it and without the accumulation of Eu³⁺ ions at the surface region.

Keywords: PACS; 73.20.AtMagnetic semiconductors; Synchrotron radiation; Photoemission spectroscopy; Europium chalcogenides; Gadolinium

An empirical model for free surface energy of strained solids at different temperature regimes by S. Garruchet; O. Politano; J.M. Salazar; A. Hasnaoui; T. Montesin (pp. 5384-5386).

We have developed an empirical formulation, based on the elastic theory, to calculate the variation of the surface free energy when a crystal is strained in the elastic regime. The model permits to obtain the variation of the surface energy at different strains and temperatures when are known the thermal dependence on the bulk and surface elastic constants. Molecular dynamics (MD) simulations were performed using the three low index surfaces of Al, to validate the accuracy of the model. The comparison between the empirical model and the MD simulations shows a good agreement for temperatures ranging between 0 and 900K, and for deformation between −2% and 2%.

Keywords: PACS; 68.35.Md; 31.15.QgMolecular dynamic; Modeling; Surface energy

Transport and optical properties of amorphous carbon and hydrogenated amorphous carbon films by A. Tibrewala; E. Peiner; R. Bandorf; S. Biehl; H. Lüthje (pp. 5387-5390).

In this paper we report on the electrical and optical properties of amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) films. Resistivity of both types of films decreases with increase in temperature. At lower temperatures (60–250K) the electron transport is due to variable range hopping for the a-C films. At higher temperatures (300–430K) it is thermally activated for both types of films. Analysis of the heterojunction between diamond-like carbon (DLC) and bulk silicon (Si) leads to the conclusion that our a-C films are of n-type and our a-C:H films are of p-type. The optical measurements with DLC revealed a Tauc bandgap of 0.6eV for the a-C films and 1–1.2eV for the a-C:H films. An Urbach energy around 170meV could be determined for the a-C:H films. Strain versus resistance plots were measured resulting in piezoresistive gauge factors around 50 for the a-C films and in between 100 and 1200 for the a-C:H films.

Keywords: PACS; 72.20; 73.40; 42.25.BAmorphous carbon films; Electrical conductivity; Optical absorption; Piezoresistive gauge factor

Optical properties of Fe-doped silica films on Si by G.J. Babonas; A. Reza; I. Simkiene; J. Sabataityte; M. Baran; R. Szymczak; U.O. Karlsson; A. Suchodolskis (pp. 5391-5394).

Optical properties of Fe-doped silica films on Si were investigated by ellipsometric technique in the region 1–5eV. Samples were produced by sol–gel method. Precursors were prepared by mixing tetraethoxysilane (TEOS) solution in ethanol and water with aqueous solution of Fe-chloride or Fe-acetate. The coating solution was deposited on Si substrates by spin on technique. The size of Fe-containing nanometric-sized particles depended on technology and varied from 20 to 100nm. Optical response of complex hybrid samples SiO₂:Fe/Si was interpreted in a multi-layer model. In the inverse problem, the Maxwell equations were solved by transfer matrix technique. Dielectric function of Fe-doped silica layers was calculated in the model of effective media. Analysis of optical data has shown that various Fe-oxides formed. Experimental data for films obtained from precursors with Fe-acetate and annealed in hydrogen were well described by the model calculations taking into account a small contribution 1–5% of metal Fe imbedded in silica. The Fe/Fe–O contribution to optical response increased for samples grown from FeCl₃-precursor. Ellipsometric data for Fe-doped silica films on Si were interpreted taking into account the structural AFM studies as well as the results of magnetic measurements.

Keywords: PACS; 76.66.Sq; 61.46.+n; 68.37.PsOptical properties of composite materials; Structure of nanoscale materials; AFM of surfaces

Modelling of phase transitions and reaction at CO adsorption on oxygen precovered Pd(111) by G. Zvejnieks; V.N. Kuzovkov; V. Petrauskas; E.E. Tornau (pp. 5395-5398).

Using the interaction parameters up to the third neighbors and activated form of O and CO diffusion and their reaction, the model has been proposed for Monte-Carlo simulations describing the catalytic O+CO→CO₂ reaction and occurring phase transitions on Pd(111) surface. Upon adsorption of CO the pre-adsorbed oxygen transforms from p(2×2)_O phase into3×3R30O° and3×3R30O°→p(2×1)O phases in the limit of room and moderate temperatures, respectively. We demonstrate that the kinetic effects determine both the occurrence of the p(2×1)_O and disappearance of the3×3R30O° phases at moderate and low temperatures, respectively. Using reaction rate as a fit parameter, we show that at room temperature the start of the reaction can be synchronized with the occurrence of3×3R30O° phase.

Keywords: PACS; 68.43.Fg; 68.43.Hn; 68.43Mn; 64.60.CnCatalytic reaction; Oxidation of CO; Pd(1; 1; 1) surface; Kinetic Monte-Carlo method; Phase transitions

Dynamics of molybdenum nano structure formation on the TiO₂(110) surface: A kinetic Monte Carlo approach by G. Le Saux; P. Krüger; B. Domenichini; L. Imhoff; S. Bourgeois (pp. 5399-5402).

The rutile TiO₂(110) surface is a highly anisotropic surface exhibiting “channels�? delimited by oxygen rows. In previous experimental and theoretical DFT works we could identify the molybdenum adsorption sites. They are located inside the channels. Moreover, experimental studies have shown that during subsequent annealing after deposition, special molybdenum nano structures can be formed, especially two monolayer high pyramidal chains of atoms.In order to better understand the dynamics of nano structure formation, we present a kinetic Monte Carlo study on diffusion and adsorption of molybdenum atoms on a TiO₂(110) surface. A quasi one-dimensional lattice gas model has been used which describes the possible adsorption sites of a Mo atom in a single channel of the surface. The atomic positions of a 1.5 monolayer thick Mo film formed of pyramidal chains define the lattice sites of the model. Thereby the formation of three-dimensional clusters could be studied. Here we have studied the cluster formation as a function of parameters that can be controlled in a growth experiment by physical vapor deposition: deposition and annealing temperature, flux and total amount of deposited Mo. Good qualitative agreement with recent experiments is obtained.

Keywords: PACS; 68.47.Jn; 68.43.JkOxide surface; Metal film; Diffusion kinetics; Monte Carlo simulation

Electrodeposition of well adherent metallic clusters on carbon substrates by M.F. De Riccardis; D. Carbone (pp. 5403-5407).

The good adhesion of electrodeposited Ni clusters on carbon supports was demonstrated; the metallic clusters were deposited on recompressed graphite (Papyex) and PAN-based fibres (Toray T300) by electrodeposition technique. For both substrates, the process parameters were optimized in order to obtain a uniform and dense spatial distribution of the Ni clusters with narrow size distribution peaked around 50nm. The morphology of the Ni clusters was characterized by SEM and AFM.The cluster adhesion to the substrates was tested with several experiments: Ni coated carbon substrates were dipped into different liquids, processed with a variety of treatments (immersion, magnetic stirring, centrifugation and ultrasonic bath) and then observed with SEM. Moreover, nano-scratch tests were performed on Ni coated supports by means of an AFM equipped with a diamond tip.

Keywords: PACS; 81.15PqElectrodeposition; Ni clusters; Carbon fibres; Papyex; Adhesion; Nanoscratch

Fabrication of Al nanoparticles and their electrical properties studied by capacitance–voltage measurements by T. Noda; T. Mano; N. Koguchi (pp. 5408-5410).

Nanometer-scale Al particles are fabricated and are embedded in a GaAs matrix using molecular beam epitaxial technique. The Al particle is self-assembled on GaAs by supplying an Al molecular beam. The average particle size is found to be 25nm. The density is 7×10¹⁰cm⁻² when Al of 6.2×10¹⁵atoms/cm² is supplied on (100)GaAs at a substrate temperature of 300°C. Clear hysteresis and plateaus in capacitance–voltage ( C– V) curves are found in an Al-embedded sample, whereas monotonic increase of capacitance is obtained in a reference sample having an AlAs layer instead of Al. This difference results from trapping of electrons by the Al particles, suggesting that the particles have metallic character.

Keywords: PACS; 73.22.-f; 73.63.-bNanoparticle; Capacitance; Molecular beam epitaxy

Mg 2p shallow core-level and local atomic structure of i-ZnMgRE quasicrystals by V. Karpus; A. Suchodolskis; U.O. Karlsson; G. Le Lay; L. Giovanelli; W. Assmus; S. Brühne; E. Uhrig (pp. 5411-5414).

We present a detailed analysis of the Mg 2p shallow core-levels measured on icosahedral single-grain ZnMgY, ZnMgHo, and ZnMgEr quasicrystals during a photoelectron microscopy study. The synchrotron radiation photoemission measurements were performed on in situ cleaved samples at a pressure of 10⁻¹⁰mbar and at low temperature, typically 90–150K. The Mg 2p photoemission lines are essentially broadened as compared to those of the Mg 2p spin–orbit doublet recorded on the Zn₂Mg crystalline Laves phase. The broadening is associated to the coordination shifts of the Mg 2p level due to the inequivalent magnesium sites in the quasicrystalline lattice. The coordination shifts are calculated on the basis of i-ZnMg(Ho, Y) atomic structure data, recently determined from the pair distribution function analysis. The coordination shifts obtained are up to 0.2eV. The Mg 2p experimental spectral intensity is nicely reproduced by a superposition of coordination-shifted Mg 2p spin–orbit doublets.

Keywords: PACS; 71.23.FQuasicrystals; Photoemission spectroscopy; Coordination shift

Charge-density-wave partial gap opening in quasi-2D KMo₆O₁₇ purple bronze studied by angle resolved photoemission spectroscopy by M.A. Valbuena; J. Avila; V. Pantin; S. Drouard; H. Guyot; M.C. Asensio (pp. 5415-5418).

Low dimensional (LD) metallic oxides have been a subject of continuous interest in the last two decades, mainly due to the electronic instabilities that they present at low temperatures. In particular, charge density waves (CDW) instabilities associated with a strong electron–phonon interaction have been found in Molybdenum metallic oxides such as KMo₆O₁₇ purple bronze. We report an angle resolved photoemission (ARPES) study from room temperature (RT) to T ∼40K well below the Peierls transition temperature for this material, with CDW transition temperature T_CDW ∼120K. We have focused on photoemission spectra along ΓM high symmetry direction as well as photoemission measurements were taken as a function of temperature at one representative k_F point in the Brillouin zone in order to look for the characteristic gap opening after the phase transition. We found out a pseudogap opening and a decrease in the density of states near the Fermi energy, E_F, consistent with the partial removal of the nested portions of the Fermi surface (FS) at temperature below the CDW transition. In order to elucidate possible Fermi liquid (FL) or non-Fermi liquid (NFL) behaviour we have compared the ARPES data with that one reported on quasi-1D K_0.3MoO₃ blue bronze.

Keywords: PACS; 71.45.Lr; 79.60.−I; 71.20.−b; 71.18.+yPhotoelectron spectroscopies; Charge density waves; Electronic structure; Fermi surface

Characteristics of surface nano-structural modifications in nitrogen ion implanted W as a function of temperature by H. Savaloni; F. Modiri; H. Hajihosseini; A. Shokouhy (pp. 5419-5423).

The surface modifications of tungsten massive samples (0.5mm foils) made by nitrogen ion (30keV; 1×10¹⁸ N⁺cm⁻²) implantation are studied by XRD, AFM, and SIMS. XRD patterns clearly showed WN₂ (018) (rhombohedral) very close to W (200) line. Crystallite sizes obtained from WN₂ (018) line, showed an increase with substrate temperature. AFM images showed the formation of grains on W samples, which grew in size with temperature. These morphological changes are similar to those observed for thin films by increasing substrate temperature (i.e. structure zone model (SZM)). Surface roughness variation with temperature, showed a decrease with increasing temperature. The density of implanted nitrogen ions, and the depth of nitrogen ion implantation in W are studied by SIMS. The results show a minimum for N⁺ density at a certain temperature consistent with XRD results (i.e. IW(20₀₎/ IW(21₁₎). This minimum in XRD results is again similar to that obtained for different thin films by Savaloni et al. [Physica B, 349 (2004) 44; Vacuum, 77 (2005) 245] and Shi and Player [Vacuum, 49 (1998) 257].

Keywords: PACS; 68.55.Ln; 68.49.Sf; 82.80.Ms; 68.37.PsSEM; AFM; XRD; SIMS; Ion implantation; Depth profile

Oxidation of a cesium-covered Ni (110) surface studied by metastable-induced electron spectroscopy by T. Ikari; S. Arikado; K. Kameishi; H. Kawahara; K. Yamada; A. Watanabe; M. Naitoh; S. Nishigaki (pp. 5424-5427).

An initial stage of oxidation of a cesium-covered Ni (110) surface has been studied by metastable-induced electron spectroscopy (MIES) and low-energy electron diffraction (LEED). The MIES brought spectra with Cs 6s induced peak (P_6s), Cs 5p (P_5p), O 2p induced peak (P_ox) and a structure related to the substrate Ni 3d states (P_3d). The work function change Δ φ showed an oscillatory behavior in the progress of surface oxidation. The process is divided into three stages: (i) at low O₂ exposures, Δ φ>0 with unchanging P_5p and P_6s; (ii) at moderate exposures, Δ φ<0 with a drastic decrease in the P_6s intensity; (iii) at higher exposures, Δ φ>0 with shifts of peaks P_5p and P_ox to higher energies, together with an appearance of peak P_3d. A three-step model of initial oxidation of alkali-covered Ni (110) surfaces is presented.

Keywords: PACS; 79.20.Rf; 73.20.−r; 81.65.Mq; 71.20.Dg; 79.60.DpMetastable-induced electron spectroscopy; Auger ejection; Oxidation; Alkali metals; Nickel

Structure and electronic properties of gold adsorbed on Ti(0001) by N. Tsud; F. Šutara; I. Matolínová; K. Veltruská; V. Dudr; V. Cháb; K.C. Prince; V. Matolín (pp. 5428-5431).

The Au/Ti(0001) adsorption system was studied by low energy electron diffraction (LEED) and photoemission spectroscopy with synchrotron radiation after step-wise Au evaporation onto the Ti(0001) surface. For adsorption of Au at 300K, no additional superstructures were observed and the (1×1) pattern of the clean surface simply became diffuse. Annealing of gold layers more than 1ML thick resulted in the formation of an ordered Au–Ti surface alloy. Depending on the temperature and annealing time, three surface reconstructions were observed by LEED: (√3×√3) R30°, (2×2) and a one-dimensional incommensurate (√3×√3) rectangular pattern. The Au 4f core level and valence band photoemission spectra provided evidence of a strong chemical interaction between gold and titanium. The data indicated formation of an intermetallic interface and associated valence orbital hybridization, together with diffusion of gold into the bulk. Au core-level shifts were found to be dependent on the surface alloy stoichiometry.

Keywords: PACS; 73.61.At; 68.35.Bs; 61.14.Hg; 79.60.DpGold; Titanium; Metal–metal interfaces; Low energy electron diffraction; Photoelectron spectroscopy; Synchrotron radiation

Loss of adhesion strength of PVD Cu films on carbon substrates after heat treatment and correlated effects on the thermal interface properties by Erich Neubauer; S. Chotikaprakhan; D. Dietzel; B.K. Bein; J. Pelzl; C. Eisenmenger-Sittner; C. Schrank; G. Korb (pp. 5432-5436).

The study of coating–substrate systems consisting of a thin copper film on a flat carbon substrate is of great interest in order to get information on the interfacial behaviour of such systems. This work is focused on the mechanical adhesion strength and the correlated interfacial thermal contact resistance which are influenced by heat treatment. Using plasma-assisted pre-treatment of the carbon substrate prior to the deposition of copper coatings via physical vapor deposition (PVD), the adhesion strength between copper coatings and substrate has increased significantly, while the thermal contact resistance decreased in the as deposited state. After heat treatment at 800°C for 1h, considerably decreased adhesion strengths have been observed, accompanied by increased values of the thermal contact resistance.

Keywords: PACS; 68.35.−p; 68.35.Ct; 68.37.−dInterface; Adhesion; PVD coating; AFM; Surface topography; Thermal transport properties; Photothermal measurements

Study of Be δ-doped GaAs/AlAs multiple quantum wells by the surface photovoltage spectroscopy by B. Čechavi�?ius; J. Kavaliauskas; G. Krivaitė; V. Karpus; D. Seliuta; G. Valušis; M.P. Halsall; M.J. Steer; P. Harrison (pp. 5437-5440).

We report a surface photovoltage and differential surface photovoltage (DSPV) study of Be δ-doped GaAs/AlAs multiple quantum wells (QWs) with widths ranging from 3 to 20nm and sheet doping densities from 2×10¹⁰ to 2.5×10¹²cm⁻² per well aiming to characterize their electronic properties and structural quality. From a line shape analysis of room temperature DSPV spectra the interband excitonic transition energies and broadening parameters for a large number of QW-related subbands have been established. A study of well-width and quantum number dependencies of the excitonic linewidths allowed us to evaluate the various broadening contributions to the spectral line shapes in QWs of different design. It was found that an average half monolayer well-width fluctuations are the dominant broadening mechanism of the excitonic line for QWs thinner than 10nm. In QWs thicker than 10nm, the spectral line broadening originates mainly from thermal broadening as well as Stark broadening due to random electric fields of ionized impurities and exciton scattering by free holes.

Keywords: PACS; 78.67.De; 73.21.FgPhotovoltage spectroscopy; Modulation spectroscopy; Quantum wells

Temperature dependencies of frequency characteristics of HTSC RLC curcuit by Vahe V. Buniatyan; V.M. Aroutiounian; G.Sh. Shmavonyan; Vaz. V. Buniatyan (pp. 5441-5444).

Analytical expressions of temperature dependencies of magnitude–frequency and phase–frequency characteristics of a HTSC RLC parallel circuit are obtained, where the resistance and inductance are non-linearly depended on the optical signal modulated by the intensity. It is shown that the magnitude–frequency and phase–frequency characteristics of circuits can be controlled by choosing the parameters of the HTSC thin film and optical “pump�?.

Keywords: PACS; 74.25Gz; 74.25 NfSuperconductivity; Microwave impedance; Magnitude–frequency

A new model of noise characteristics of SiC Schottky barrier MESFET with deep impurity levels and traps by V.M. Aroutiounian; G.A. Avetisyan; V.V. Buniatyan; P.G. Soukiassian; Vaz.V. Buniatyan (pp. 5445-5448).

Noise characteristics of silicon carbide Schottky barrier field effect transistors (MESFET) are examined for the case of the operation in small-signal regime and the presence of deep impurity levels and electron traps in the band gap of the channel. A new model of calculations of noise is suggested. It is shown that the noise measure of the short channel MESFET can be decreased within certain high frequency range.

Keywords: PACS; 85. 30.Tv; 73. 50.TdField effect transistor; Deep levels; Traps; Noise characteristic; Schottky barrier

Growth of copper phthalocyanine on hydrogen passivated vicinal silicon(111) surfaces by Yu Suzuki; Michael Hietschold; Dietrich R.T. Zahn (pp. 5449-5452).

Using ultra-high vacuum scanning tunneling microscopy (UHV-STM), we show that copper-phthalocyanine (CuPc) grows in a well ordered manner on hydrogen passivated vicinal silicon surfaces. CuPc grows one-dimensionally parallel to the monatomic steps on the vicinal silicon surface. Surprisingly, elongated clusters of the CuPc parallel to the step directions are formed even on the middle of the terraces well away from the step edges. The one-dimensional growth mode continues even after the full monolayer coverage on the substrate which results in strongly oriented growth mode of a thin film of CuPc on the vicinal silicon surfaces.

Keywords: PACS; 68.43.HnVicinal surface; Low dimensional structure; Organic molecular engineering

Charge-transfer at silver/phthalocyanines interfaces by Mihaela Gorgoi; Dietrich R.T. Zahn (pp. 5453-5456).

Valence band photoemission spectroscopy (VB-PES) and inverse photoemission spectroscopy (IPES) were employed to determine the occupied and unoccupied density of states upon silver deposition onto layers of two phthalocyanines (H₂Pc and CuPc). The two different Pc molecules give rise to very distinct behaviour already during the initial stage of silver deposition. While in the CuPc case no shift occurs in the energy levels, the H₂Pc highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are shifting simultaneously by 0.3eV, i.e., the HOMO shifts away from the Fermi level while LUMO shifts towards the Fermi level. As the silver quantity increases the HOMO levels of both Pcs are shifting towards the Fermi level. When the Fermi level is resolved in the VB spectra, the characteristic features of H₂Pc and CuPc are smeared out to some extent. Shifts in HOMO and LUMO energy positions as well as changes in line shapes are discussed in terms of charge-transfer and chemical reactions at the interfaces.

Keywords: PACS; 79.20.Kz; 71.20.RvMetal free phthalocyanine; Copper phthalocyanine; Valence band photoemission; Inverse photoemission; Charge-transfer

Self-assembled formation of uniform InP nanopore arrays by electrochemical anodization in HCl based electrolyte by Taketomo Sato; Toshiyuki Fujino; Hideki Hasegawa (pp. 5457-5461).

Attempts were made to optimize the electrochemical anodization process for the formation of high-density, regular and straight nanopore arrays on InP. The structure, shape and size of the pores were very sensitive to substrate orientations, electrolyte concentrations and anodization voltages. Among (111)A, (111)B and (001) substrate orientations, the most uniform and most straight nanopore arrays were obtained on (001) substrates at anodization voltages of 5–7V by using 1.0–1.5M HCl electrolyte containing HNO₃. The pore depth could be controlled up to 80μm by the anodization time.

Keywords: PACS; 81.05.Ea; 81.05.Rm; 81.65.CfElectrochemical anodization; Porous structure; InP; (0; 0; 1); (1; 1; 1)A; (1; 1; 1)B

Monitoring the ordering in biomolecular films on vicinal silicon surfaces by reflectance difference/anisotropy spectroscopy by Simona D. Silaghi; Dietrich R.T. Zahn (pp. 5462-5465).

DNA base molecules, adenine, thymine, guanine, and cytosine may be employed as charge transport molecules in biomolecular electronic devices. Their electronic properties are comparable with those of inorganic wide bandgap materials, e.g. GaN with the absorption onset in the near ultra-violet (UV) range. A recent field effect transistor study based on a modified DNA base revealed that the prototype bio-transistor gives rise to a better voltage gain compared to one based on carbon nanotubes (CNTs) [G. Mauricio, P. Visconti, V. Arima, S. D’Amico, A. Biasco, E. D’Amone, R. Cingolani, R. Rinaldi, Nanoletters 3 (2003) 479]. Here, in situ reflectance difference/anisotropy spectroscopy (RDS/RAS) is employed under ultra-high vacuum (UHV) conditions for monitoring the growth of DNA base molecules on vicinal hydrogen passivated Si(111) surfaces. Such vicinal substrates consisting of steps and terraces may serves as suitable templates for molecular ordering. Indeed, RDS/RAS measurements reveal information about molecular ordering of DNA bases induced by the density of steps on silicon surfaces. All four molecules, however, behave differently on the vicinal substrates. The first transition dipole moments corresponding to adenine and thymine molecules align mainly perpendicular to the step edge direction while for guanine and cytosine they align parallel to this direction, however, only in very thin layers. The RDS/RAS signal of the guanine and cytosine layers with thicknesses above 20nm saturates due to a loss of ordering at higher coverages. Additionally, time-resolved RDS/RAS measurements at the silicon E₂ (4.25eV) critical point (CP) demonstrate the sensitivity to the biomolecular/inorganic interface formation.

Keywords: PACS; 33.20.Kf; 68.47.Pe; 78.40.-qDNA bases; Vicinal Si(1; 1; 1); Reflectance difference/anisotropy spectroscopy

Experimental studies of solid state surface wetting of tin (Sn) on aluminium (Al) by C. Eisenmenger-Sittner; B. Schwarz; C. Tomastik; P.B. Barna; A. Kovacs (pp. 5466-5469).

Under ultra high vacuum (UHV) conditions tin (Sn) forms a monoatomic wetting layer on aluminium (Al) surfaces if Sn-islands formed by a preceding deposition process are present. Previous experimental observations and Kinetic Monte Carlo (KMC) simulations suggest that wetting layer formation is governed by thermally activated surface diffusion and adsorption processes.This paper presents a systematic study of the wetting of the inner and outer interfaces of Al by Sn in sandwich systems consisting of a 400nm Al-base layer, a 10nm Sn interlayer and a 400nm thick Al capping layer. The morphology and chemical composition of the sandwich systems is investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wetting process is studied by scanning auger electron spectroscopy (AES) under UHV conditions. Depositing the Al-capping layer at different deposition rates allows for the assessment of the influence of the grain boundary density on the velocity of Sn-transport through the Al-capping layer. Studying the permeation speed of Sn through the capping layer at different temperatures shows that Sn penetrates the capping layer much more rapidly at elevated temperatures thus corroborating the involvement of thermally activated mechanisms in the transport process.

Keywords: PACS; 81.15.–z; 68.55.–a; 73.50.–h; 68.35.Fx; 68.43.–h; 61.72.MmVapor deposition; Wetting; Spreading; Surface diffusion; Activation

Origins of interdiffusion, crystallization and layer exchange in crystalline Al/amorphous Si layer systems by D. He; J.Y. Wang; E.J. Mittemeijer (pp. 5470-5473).

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/a-Si and a-Si/Al bilayers was studied upon annealing at low temperatures between 165 and 250°C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer exchange in both types of bilayers. The change in bulk energy of the Al phase (release of macrostress and microstrain, increase of grain size) promotes the occurrence of layer exchange, whereas changes in surface and interface energies counteract the layer exchange.

Keywords: PACS; 05.70.Np; 68.35.Rh; 61.72.Cc; 61.10.Nz; 81.70.Jb; 82.80.PvAluminium-induced; Crystallization; Layer exchange; Thermodynamic analysis

High-resolution scanning tunneling microscopy and d I/d V map studies of peptidenucleic acid and fluorescein isothiocyanate by Hiroyuki Tanaka; Tomoji Kawai (pp. 5474-5476).

We used scanning tunneling microscopy (STM) to spatially map the local density of states of individual PNA molecules labeled with fluorescein isothiocyanate (FITC) on a Cu(111) surface. From the observed bias voltage dependences of the topographic height and the d I/d V map of FITC and individual PNA molecules, we confirmed that FITC and PNA have different electrical properties. We clearly differentiated the FITC and PNA molecules by mapping the density of states feature. This study shows that STM with the d I/d V map method is useful in FITC mapping.

Keywords: PACS; 87.64.D; 85.65; 73.20STM; d; I; /d; V; map; PNA; DNA; FITC; Fluorescence

EFM phase investigation of the metal–organic film interface by A. Das; C.H. Lei; H.E. Thomas; M. Elliott; J.E. Macdonald; P. Glarvey; M.L. Turner (pp. 5477-5480).

Phase sensitive electrostatic force microscopy (EFM phase) investigations of semiconducting polymers, poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene) (F8), are described, aimed at understanding the metal/polymer interfaces. The electrostatic behaviour and potential distributions of the Au/polymer/Au structure under various biases with emphasis on top and bottom Au contacts are presented. We observe, by analysing EFM phase data, that the top and bottom contacts of Au can have drastic effects on the device performance. Moreover, differences in conductivity of conjugated polymers (P3HT>F8) are also reflected in EFM phase measurements, which correlate well with I– V measurements. Detailed analysis indicates that the influence of metal/film interfaces depends strongly on both the ability of charge transport properties of the organic films and the type of surface modification.

Keywords: PACS; 36.20.−r; 73.40.Cg; 73.40.SxConjugated polymers; P3HT; F8; Electrostatic force microscopy; Metal contacts

A modular scanning tunneling microscope with an interchangeable elastic closed cell and external actuators by Elias H. Bjarnason; Unnar B. Arnalds; Sveinn Olafsson (pp. 5481-5484).

We introduce a novel modular cell based scanning tunneling microscope with external piezoelectric actuators. A tip and a sample are contained in a closed interchangeable cell, consisting of a stiff top plate and a bottom part, fastened together by an elastic material. The bottom part, containing a scanning tip, is fastened to a base unit while the top plate, containing a sample, is capable of scanning motion by external piezoelectric actuators mounted in the same base unit. The actuators are pre-loaded by the deformation of the elastic material of the cell, giving an increased stability. This design is expected to simplify the scanning tunneling microscope (STM) operation in difficult environments greatly by enclosing only the tip and sample in a small cell-module, which is pluggable to a scanning mechanism and other supportive functionalities. A frequency characterization and an image scan showing atomic resolution of highly oriented graphite in air, at room temperature, is presented.

Keywords: PACS; 07.79.Cz.Scanning tunneling microscope; STM design; STM construction; Nanotechnology

An externally cooled beetle type scanning tunneling microscope for imaging in cryogenic liquids by Unnar B. Arnalds; Elias H. Bjarnason; Kristjan Jonsson; Sveinn Olafsson (pp. 5485-5488).

We describe a variable temperature cryogenic scanning tunneling microscope designed for imaging and research in cryogenic liquids. It has an external Dewar type large scale cooling system with a temperature control range of roughly 85–110 K using pressure controlled liquid nitrogen cooling. The liquid nitrogen is kept in a closed chamber surrounding the STM and maintained at a pressure to suit the chosen temperature. Several gases have triple points in this temperature range and can therefore be liquified, such as argon, methane, silane and germane. The STM is based on a beetle type design built into a small cube vacuum chamber to fit into the cooling dewar. The system has been used for atomic resolution of highly oriented graphite submerged in a methane liquid at a temperature of 100 K.

Keywords: PACS; 07.79.Cz; 07.20.MCSTM construction; Cryogenic cooling

Study on orientation mechanisms of poly(vinylidenefluoride-trifluoroethylene) molecules aligned by atomic force microscopy by Kuniko Kimura; Kei Kobayashi; Hirofumi Yamada; Toshihisa Horiuchi; Kenji Ishida; Kazumi Matsushige (pp. 5489-5494).

We have developed a molecular orientation control technique for polymers utilizing contact-mode atomic force microscopy (AFM). In this paper, we studied the molecular alignment mechanism of this technique by applying it to poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)). The resultant alignment and formed crystal size were strongly dependent on the temperature during the modification. They also depended on the scan line spacing of the modification. These results made the alignment mechanism clear. The obtained molecular alignment was stable against the heat treatment even at the temperatures just below T_m.

Keywords: PACS; 82.37GK; STM and AFM manipulation of single molecules 61.41+e; Polymers elastomers and plasticsMolecular manipulation; Atomic force microscopy; Ferroelectric polymer; P(VDF-TrFE); Orientation control

Tunneling spectra for single molecules of HEX-fluorescent dye attached to DNA adsorbed on Cu(111) surfaces by Toshio Kawahara; Takuya Takahashi; Hiroyuki Tanaka; Tomoji Kawai (pp. 5495-5498).

We used the scanning tunneling microscope (STM) to examine single-stranded deoxyribonucleic acid (DNA) oligomers deposited on a metal surface. Because STM can be used to study the electrical properties of materials via the tunneling spectra, we used it to visualize DNA oligomers at the single molecule resolution. The 5′-hexachloro-fluorescein phosphoramidite (HEX)-labeled oligomers (sequence, AGCTTC) were observed on an atomically flat Cu(111) surface. At large tip–sample distances at large set-point biases, the lowest unoccupied molecular orbit (LUMO) peak of the empty state can be observed for the dye molecules on the tunneling spectra. When this distance becomes small, similar spectra as for the Cu substrate were observed for the dye molecule on the LUMO-related peak. Cu gave peaks at small bias voltages in the filled state. From comparison of these peaks on each subunit of the molecules, the measured values of d I/d V on HEX were smaller to those on Cu because of the large size of the HEX molecule, but the normalized values of d I/d V/( I/ V) were apparently equal. We believe that the tunneling current is able to pass through the HEX molecules to the Cu substrate, thus reflecting the density of the Cu(111) surface. Molecular size therefore affects the intensity of d I/d V. LUMO-related peaks sometimes cannot be observed for HEX because of conformational differences, but Cu peaks can almost always be observed for HEX molecules. These peaks for the counter ions are almost the same as those for the Cu substrate. Thus, tunneling spectra can assist in the molecular mapping of DNA.

Keywords: PACS; 68.37.Ef; 87.15.−v; 73.20.AtScanning tunneling microscope, STM; DNA oligomers; Hexachloro-fluorescein phosphoramidite, HEX

Probing of local dissolution of Al-alloys in chloride solutions by AFM and SECM by A. Davoodi; J. Pan; C. Leygraf; S. Norgren (pp. 5499-5503).

Local dissolution of Al alloys was probed in situ in chloride solutions by using atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM). Preferential dissolution in the boundary region between some intermetallic particles (IMPs) and alloy matrix, and trench formation around large IMPs during free immersion and under electrochemical anodic polarization were observed, which indicate different dissolution behavior associated to different types of IMPs. Moreover, by using an integrated AFM/SECM system with a dual mode cantilever/microelectrode probe, simultaneous probing of electrochemical active sites and topographic changes over the same area was performed with sub-micron resolution. This allowed the ongoing localized corrosion processes related to the IMP to be revealed.

Keywords: PACS; 82.45.BbLocalized corrosion; Al alloys; Intermetallic particles; EC-AFM and SECM

Physical properties of epitaxial La₂NiO4+_δ thin films by V. Faucheux; M. Audier; S. Pignard (pp. 5504-5507).

Epitaxial thin films of layered nickelates La₂NiO4+_δ were grown on single crystal substrates by metalorganic chemical vapour deposition with the (110) plane of the nickelate parallel to the surface of substrate. High resolution transmission electron microscopy (HRTEM) confirms the epitaxial relationship between film and substrate and reveals planar structural faults.Magnetization and resistivity of the films have been measured as a function of temperature. A surprising ferromagnetic behaviour is observed until 400K which is the highest temperature to be reached; this ferromagnetic component does not come from the nickelate film but most probably from an iron oxide impurity which has been evidenced by X-ray energy dispersive spectroscopy. The temperature dependence of the resistivity, measured from room temperature down to 30K, corresponds to a semiconductor. In order to examine the electrical conduction mechanism, data have been analysed according to different conduction models; the best description is obtained in the case of a variable range hopping mechanism; this form of conductivity is discussed in relation with the disorder of the structure observed by HRTEM.

Keywords: PACS; 73.50.-h Electronic transport phenomena in thin films; 75.70.Ak Magnetic properties of monolayers and thin films; 68.37.Lp Transmission electron microscopy; 81.15.Gh Chemical vapour depositionLa; ₂; NiO; ₄; layered perovskite; Transport properties and conduction models; Magnetic measurements; Epitaxy

Van der Pauw resistivity measurements on evaporated thin films of cadmium arsenide, Cd₃As₂ by M. Din; R.D. Gould (pp. 5508-5511).

Cadmium arsenide is a II–V semiconductor, exhibiting n-type intrinsic conductivity with high mobility and narrow bandgap. It is deposited by thermal evaporation, and has shown the Schottky and Poole-Frenkel effects at high electric fields, but requires further electrical characterisation. This has now been extended to low-field van der Pauw lateral resistivity measurements on films of thickness up to 1.5μm. Resistivity was observed to decrease with increasing film thickness up to 0.5μm from about 3×10⁻³Ωm to 10⁻⁵Ωm, where the crystalline granular size increases with film thickness. This decrease in resistivity was attributed to a decrease in grain boundary scattering and increased mobility. Substrate temperature during deposition also influenced the resistivity, which decreased from around 10⁻⁴Ωm to (10⁻⁵ to 10⁻⁶)Ωm for an increase in substrate deposition temperature from 300K to 423K. This behaviour appears to result from varying grain sizes and ratios of crystalline to amorphous material. Resistivity decreased with deposition rate, reaching a minimum value at about 1.5nms⁻¹, before slowly increasing again at higher rates. It was concluded that this resulted from a dependence of the film stoichiometry on deposition rate. The dependence of resistivity on temperature indicates that intercrystalline barriers dominate the conductivity at higher temperatures, with a hopping conduction process at low temperatures.

Keywords: PACS; 72.20.Fr; 72.80.Ey; 81.15.EfCadmium arsenide; Resistivity; Deposition conditions

Light-induced ultrafast phase transitions in VO₂ thin film by S. Lysenko; A.J. Rua; V. Vikhnin; J. Jimenez; F. Fernandez; H. Liu (pp. 5512-5515).

Vanadium dioxide shows a passive and reversible change from a monoclinic insulator phase to a metallic tetragonal rutile structure when the sample temperature is close to and over 68°C. As a kind of functional material, VO₂ thin films deposited on fused quartz substrates were successfully prepared by the pulsed laser deposition (PLD) technique. With laser illumination at 400nm on the obtained films, the phase transition (PT) occurred. The observed light-induced PT was as fast as the laser pulse duration of 100fs. Using a femtosecond laser system, the relaxation processes in VO₂ were studied by optical pump–probe spectroscopy. Upon a laser excitation an instantaneous response in the transient reflectivity and transmission was observed followed by a relatively longer relaxation process. The alteration is dependent on pump power. The change in reflectance reached a maximum value at a pump pulse energy between 7 and 14mJ/cm². The observed PT is associated with the optical interband transition in VO₂ thin film. It suggests that with a pump laser illuminating on the film, excitation from the d θ,_ɛ – state of valence band to the unoccupied excited mixed d θ,_ɛ– π* – state of the conduction band in the insulator phase occurs, followed by a resonant transition to an unoccupied excited mixed d θ,_ɛ– π* – state of the metallic phase band.

Keywords: PACS; 42.65.Re; 71.35.−y; 78.66.−w; 42.62.Fi; 71.30.+h; 78.20.−eVO; ₂; Exciton; Ultrafast; Laser excitation; Phase transition; Thin film

Correlation between morphology and transport properties of composite films: Charge transport in composites by Rudolf Hrach; Stanislav Novák; Martin Švec (pp. 5516-5520).

Metal/dielectric composite films consisting of metal objects located in dielectric matrix are investigated by computer simulation. The complete computer experiment is devoted to the study of correlation between structural properties and electrical characteristics of composite films. In the present analysis transport properties of films are calculated near the metal–dielectric transition when the basic mechanism of charge transport is the tunnel effect. The conductivity of composite film is disseminated into individual percolation paths influenced by object arrangements in the composite film.

Keywords: PACS; 68.55.Jk; 73.40.Gk; 73.50.YgComposite films; Discontinuous metal films; Metal–dielectric transition; Morphology; Charge transport; Tunnelling; Infinite cluster

Impact of electric currents on the insulator–metal phase transition in epitaxial thin films of La1−_xA_xMnO₃ (A=Sr, Ca, and Ba) by J. Gao; F.X. Hu; H. Yao (pp. 5521-5524).

The influence of dc currents with a high current density on the transport properties of epitaxial La1−_xA_xMnO₃ (A=Sr, Ca, and Ba) thin films were studied. An application of a large current could lead to a remarkable reduction in the insulator–metal phase transition peak, demonstrating a significant electroresistance effect. After removing such currents the samples could completely return to its pristine state. Our experiments reveal that such an electroresistance should be a common feature for the perovskite manganites, rather than the results caused by the self-heating or self magnetic field. It may be ascribed to the two aspects: one is the strong interaction between carrier spins and localized spins in Mn ions, the other is the percolative mechanism of phase separation.

Keywords: PACS; 73.50.−h; 75.47.Gk; 75.70.−iEpitaxial thin films; Perovskite manganites; Electroresistance

Optimising uniformity of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy by Linda Höglund; E. Petrini; C. Asplund; H. Malm; J.Y. Andersson; P.O. Holtz (pp. 5525-5529).

A route towards optimisation of uniformity and density of InAs/(InGaAs)/GaAs quantum dots grown by metal organic vapor phase epitaxy (MOVPE) through successive variations of the growth parameters is reported. It is demonstrated that a key parameter in obtaining a high density of quantum dots is the V/III ratio, a fact which was shown to be valid when either AsH₃ (arsine) or tertiary-butyl-arsine (TBA) were used as group V precursors. Once the optimum V/III ratio was found, the size distribution was further improved by adjusting the nominal thickness of deposited InAs material, resulting in an optimum thickness of 1.8 monolayers of InAs in our case. The number of coalesced dots was minimised by adjusting the growth interruption time to approximately 30s. Further, the uniformity was improved by increasing the growth temperature from 485°C to 520°C. By combining these optimised parameters, i.e. a growth temperature of 520°C, 1.8 monolayers InAs thickness, 30s growth stop time and TBA as group V precursor, a full-width-half-maximum (FWHM) of the low temperature luminescence band of 40meV was achieved, indicating a narrow dot size distribution.

Keywords: PACS; 68.65.Hb; 81.07.Ta; 81.16.DnQuantum dot; Epitaxy; MOVPE; InAs/GaAs; TBA; Growth

Structure and homoepitaxial growth of GaAs(631) by V.H. Méndez-García; F.J. Ramirez-Arenas; A. Lastras-Martínez; E. Cruz-Hernandez; A. Pulzara-Mora; J.S. Rojas-Ramirez; M. Lopez-Lopez (pp. 5530-5533).

We have studied the surface atomic structure of GaAs(631), and the GaAs growth by molecular beam epitaxy (MBE) on this plane. After the oxide desorption process at 585°C reflection high-energy electron diffraction (RHEED) showed along the [−120] direction a 2× surface reconstruction for GaAs(631)A, and a 1× pattern was observed for GaAs(631)B. By annealing the substrates for 60min, we observed that on the A surface appeared small hilly-like features, while on GaAs(631)B surface pits were formed. For GaAs(631)A, 500nm-thick GaAs layers were grown at 585°C. The atomic force microscopy (AFM) images at the end of growth showed the self-formation of nanoscale structures with a pyramidal shape enlarged along the [5−9−3] direction. Transversal views of the bulk-truncated GaAs(631) surface model showed arrays of atomic grooves along this direction, which could influence the formation of the pyramidal structures.

Keywords: PACS; 81.16.Dn; 81.15.Hi; 61.46.tw; 68.37.PsAtomic force microscopy; Nanostructures; Molecular beam epitaxy; Semiconducting III–V materials

STM study of the initial stages of C₆₀ adsorption on the Pt(110)-(1×2) surface by T. Orzali; M. Petukhov; M. Sambi; E. Tondello (pp. 5534-5537).

We have studied the initial stages of adsorption of C₆₀ on the Pt (110)-(1×2) surface by means of STM. At room temperature, fullerene molecules adsorb in the troughs between two adjacent Pt rows of the missing row reconstruction. Mobility over the terraces is negligible, denoting strong bonding with the surface, also testified by a well-defined orientation of fullerene monomers with respect to the substrate. Upon annealing at 750K, molecular migration towards kinks and step edges occurs, where small islands nucleation begins. A commensurate registry with the substrate is maintained by small (5–10 molecules) C₆₀ aggregates, leading to expanded nearest-neighbour distances with respect to those found in hexagonal close packed fullerene ad-islands grown on other metallic substrates.

Keywords: PACS; 61.48.+c; 68.37.EfFullerene; Platinum; Scanning tunnelling microscopy

Study of DNA coated nanoparticles as possible programmable self-assembly building blocks by Björn Högberg; Jing Helmersson; Svante Holm; Håkan Olin (pp. 5538-5541).

Nanoparticles coated with single stranded DNA have been shown to efficiently hybridize to targets of complementary DNA. This property might be used to implement programmable (or algorithmic) self-assembly to build nanoparticle structures. However, we argue that a DNA coated nanoparticle by itself cannot be used as a programmable self-assembly building block since it does not have directed bonds. A general scheme for assembling and purifying nanoparticle eight-mers with eight geometrically well-directed bonds is presented together with some preliminary experimental work.

Keywords: PACS; 81.07.−b; 81.16.DnNanoparticles; Nanostructure; DNA coated nanoparticles; Programmable self-assembly; Gold particles

Photoluminescence scanning on InAs/InGaAs quantum dot structures by M. Dybiec; L. Borkovska; S. Ostapenko; T.V. Torchynska; J.L. Casas Espinola; A. Stintz; K.J. Malloy (pp. 5542-5545).

The photoluminescence spectra of InAs quantum dots (QDs) embedded into four types of In_xGa1−_xAs/GaAs ( x=0.10, 0.15, 0.20 and 0.25) multi quantum well MBE structures have been investigated at 300K in dependence on the QD position on the wafer. PL mapping was performed with 325nm HeCd laser (35mW) focused down to 200μm (110W/cm²) as the excitation source. The structures with x=0.15In/Ga composition in the In_xGa1−_xAs capping layer exhibited the maximum photoluminescence intensity. Strong inhomogeneity of the PL intensity is observed by mapping samples with the In/Ga composition of x≥0.20–0.25. The reduction of the PL intensity is accompanied by a gradual “blue�? shift of the luminescence maximum at 300K as follows from the quantum dot PL mapping. The mechanism of this effect has been analyzed. PL peak shifts versus capping layer composition are discussed as well.

Keywords: PACS; 78.67.−n; 78.30.−j; 78.55.−mInAs quantum dots; PL scanning spectroscopy

Self-organized arrays of submicrometer particle of organic dye and its near-field optical study by Akihiro Tomioka; Sinji Kinosita; Yasuyuki Ido; Yasuaki Itakura; Tooru Motokubota (pp. 5546-5551).

Organic dye particles of micrometer and submicrometer diameters were prepared by a wetting/dewetting procedure on a hydrophilic glass surface and a self-organized one- or two-dimensional registration was observed. To analyze the molecular assembly in these particles the near-field-excited near-field fluorescence from single particles were detected, while the majority of particles with diameters around 2μm or less did not show fluorescence. Far-field fluorescence, in contrast, was observed for every particle, and the intensity depended on the excitation polarization when a polarized evanescent field was used for excitation, indicating that the molecules’ transition moment within dye particles orient parallel to the substrate surface. These two observations suggest that the near-field at the tip of the probe was polarized parallel to the probe axis. Another observation, that neighboring particles show similar molecular orientations, suggests that the dewetting process contributed to the alignment of the molecular directions in adjacent particles, which further proves that the dye particles were formed by a self-organizing mechanism.

Keywords: PACS; 78.67.Bf; 78.55.Kz; 33.50.Dq; 33.70.Jg; 33.90.+h; 36.40.VzSelf-assembled; Organic dye; Near-field

Micro-ring cavity mode of dye-doped thin film: Dependence on the excitation energy by Yasuaki Itakura; Akihiro Tomioka; Sinji Kinosita; Tooru Motokubota (pp. 5552-5554).

We have prepared π-conjugated organic dye specimens embedded in a transparent polymer film and observed a characteristic photoluminescence peak, having very narrow peak width as compared with the fluorescence in solution, when we prepared the film around the perimeter of a multimode silica fiber. The peak position showed no dependence on the excitation wavelength, indicating that it could not be explained by a whispering gallery mode. The peaks can be explained by amplified spontaneous emissions (ASE) because the intensity depended linearly on the excitation intensity with some threshold. When the excitation laser was directly coupled to the fiber core, we observed ASE peaks of the optical fiber itself. These fiber ASE peaks shifted to longer wavelength when we varied the excitation to shorter wavelength, which clearly ruled out the possibility of silicate Raman scattering as the origin.

Keywords: PACS; 78.55.Kz; 33.50.Dq; 33.70.Jg; 33.90.+h; 36.20.Kd; 36.90.+fMicro-ring Cavity; Dye-doped; Polymer film; Photoluminescence

Self-organized formation of shell-like InAs/GaAs quantum dot ensembles by U.W. Pohl; K. Pötschke; M.B. Lifshits; V.A. Shchukin; D.E. Jesson; D. Bimberg (pp. 5555-5558).

Formation of a multimodal quantum dot (QD) ensemble by strained layer epitaxy of InAs on GaAs near the critical value for the onset of the 2D–3D transition is studied. Reflection anisotropy spectroscopy is employed to confirm that a smooth surface is maintained during strained layer growth prior to QD formation. Instantaneous capping after deposition leads to InAs quantum wells with some thickness flucuations. Multimodal QD InAs ensembles form after an at least short growth interruption prior to cap layer deposition. The QDs consist of pure InAs with heights varying in steps of complete InAs monolayers. Related exciton energies indicate a simultaneous increase of both height and lateral extension, i.e. a shell-like increase of sizes. The formation of the multimodal QD ensemble is described by a kinetic approach. A growth scenario is presented where QDs having initially shorter base length stop vertical growth at a smaller height, accounting for the experimentally observed shell-like sub-ensemble structure.

Keywords: PACS; 81.07.Ta; 81.16.Dn; 81.05.Ea; 81.15.Gh; 78.66.FdQuantum dot formation; Multimodal distribution

Effect of magnetic field on self-assembling of colloidal Co magnetic nanoparticles by L. Chitu; Y. Chushkin; S. Luby; E. Majkova; G. Leo; A. Satka; M. Giersig; M. Hilgendorff (pp. 5559-5562).

In this paper the formation of 3-D structures composed of Co nanoparticles (NPs) is reported. Structures were obtained by drying a droplet of a colloidal solution of NPs in a magnetic field perpendicular to the substrate. The Co nanoparticles were prepared by thermolysis of Co₂(CO)₈. The 3-D NP structures were characterized by scanning electron microscopy (SEM) and atomic and magnetic force microscopy (AFM/MFM). It has been found that at the border of the droplet, NPs assemble into hexagonally ordered 3-D columns or they form a labyrinthine structure. The formation of the 3-D structures can be explained by the outflow of NPs to the border of the droplet during the drying process. Within this model the pattern formation is dependent on the concentration of the NPs and the degree of alignment of the magnetic moments of NPs in the 3-D columns.

Keywords: PACS; 61.46.+w; 81.16 DnCobalt nanoparticles; 3-D structures; Columns; Labyrinthine configurations

Growth of nanorods and mesoscale stars prior to an orientation transition in thin Bi films on graphite by S.A. Scott; M.V. Kral; S.A. Brown (pp. 5563-5567).

We report on the growth of unusual star shaped Bi islands and ordered arrays of nanorods on highly ordered pyrolitic graphite (HOPG) substrates. The rods and stars grow with {012}_Bi||{001}_HOPG and are preferentially aligned with the high symmetry directions of the substrate. As more Bi is deposited, the film undergoes a transition to the {001} orientation. These features are a result of a complex interplay between kinetics, thermodynamics, and the crystallography of the substrate and island material.

Keywords: PACS; 81.16Rf; 81.05.Bx; 64.70.Nd; 68.43.JkBismuth; Graphite; Morphology; Self-assembly

Morphology of pentacene films deposited on Cu(119) vicinal surface by Mattia Fanetti; Luca Gavioli; Massimo Sancrotti; Maria Grazia Betti (pp. 5568-5571).

We investigate the morphology of a pentacene (C₂₂H₁₄) film adsorbed on the Cu(119) vicinal surface by scanning tunnelling microscopy (STM). Thermal treatment of a thick film of molecules generates a long-range ordered structure. Series of molecular rows are alternated with areas where the molecules assume two equivalent orientations. STM data analysis suggests that the ordered structure can be described by a rippled morphology. The behaviour of the film at different annealing temperatures suggests a possible explanation of the film structure as due to an adsorbate-induced modification of the substrate.

Keywords: PACS; 68.37.Ef; 68.55.-aScanning tunnelling microscopy; Pentacene; Organic layers; Long-range order

Nanowire growth on Si wafers by oxygen implantation and annealing by Elder A. de Vasconcelos; Fábio R.P. dos Santos; Eronides F. da Silva Jr.; Henri Boudinov (pp. 5572-5574).

We report on nanowire formation on oxygen implanted Si wafers. In this method, a Si wafer is first oxygen-implanted and then annealed at high temperatures in Ar ambient to promote growth of nanowires with high aspect ratio. Their lengths range from several micrometers to thousands of micrometers and their diameters range from tens of nanometers to a few microns.

Keywords: PACS; 61.46.−w; 73.21.HbSilicon nanowires; Ion implantation; Stress

Carbon nanotubes based nanocomposites for photocurrent improvement by Carla D. Canestraro; Mariane C. Schnitzler; Aldo J.G. Zarbin; M.G.E. da Luz; Lucimara S. Roman (pp. 5575-5578).

We measure the optical and electrical properties of nanocomposites thin films made of poly-3-hexilthiophene and multi-walled carbon nanotubes (MWNT) filled with iron/iron-oxide, as well as the performance of photovoltaic devices built with such films. We find that the devices efficiency has a maximum for a certain MWNT concentration and that the electrical behavior is mainly dependent on the charge transport properties of the MWNT. To improve some engineering aspects, a bilayer geometry is proposed, allowing rectifying J× V characteristics curves.

Keywords: PACS; 73.50.Pz; 73.61.Ph; 73.61.Wp; 73.63.Fg; 81.07.DeCarbon nanotubes; Semiconducting polymers; Photodetectors; Nanocomposites

Electrical transport characteristic of carbon nanotube after mass-separated ultra-low-energy oxygen ion beams irradiation by Kazuhiro Yamamoto; Takafumi Kamimura; Kazuhiko Matsumoto (pp. 5579-5582).

Mass-separated ultra-low-energy oxygen ion beams were irradiated to the single-walled carbon nanotubes (SWCNTs) under an ultra-high-vacuum pressure of 10⁻⁷Pa for the purpose of achieving n-type conduction of nanotubes. The ion beam energy was 25eV, which was close to the displacement energy of graphite. The incident angle of the ion beam was normal to the target nanotube. The ion dose ranged from 3.3×10¹¹ to 3.8×10¹²ions/cm². The structure of SWCNTs after the ion irradiation was investigated. The CNTs still have a clear single-walled structure after the ion irradiation. The graphite structure is distorted and some defects are induced in the nanotube by the oxygen irradiation. The oxygen ions with the ion energy of 25eV are irradiated to the field effect transistor (FET) device with the nanotube channel. The n-type characteristic appears upon the oxygen ion irradiation, and the device exhibits ambipolar behavior. The defects induced by the ion irradiation may act as the n-type dopants.

Keywords: PACS; 73.63.Fg; 61.46.+wCarbon nanotube; SWCNT; Doping; Low-energy ion beam; Ion implantation; CNT-FET

PMMA nanofibers production by electrospinning by S. Piperno; L. Lozzi; R. Rastelli; M. Passacantando; S. Santucci (pp. 5583-5586).

Electrospinning is a process by which polymer nanofibers (with submicron scale diameters) can be formed when a droplet of viscoelastic polymer solution is subjected to high voltage electrostatic field. As this droplet travels in air, the solvent evaporates leaving behind a charge fiber that can be electrically deflected on a substrate. A series of nanofibers with various wt.% of PMMA (poly-methyl-methacrylate) to acetone were produced and characterized regarding their morphology and chemical composition. The nanofibers were characterized by Secondary Electron Microscopy, Atomic force microscopy and X-ray photoelectron spectroscopy.

Keywords: PACS; 61.18.−j; 1.41.+e; 61.46.+w; 68; 68.37.−d; 68.49.−hElectrospinning; Polymer nanofibers; Semiconductors oxide; Gas sensing

Growth of boron nano-junctions by S.H. Yun; A. Dibos; H.S. Lee; J.Z. Wu; U.O. Karlsson (pp. 5587-5589).

In this work, we demonstrate the synthesis of various types of boron nanowire junctions in a self-assembled manner by simple closed-tube thermal vapor transfer method. The Y-type boron nano-junctions and lateral boron–silicon alloy nano-junctions were grown on Si substrates, based on the oxide assisted VLS growth mode at a relatively low processing temperature regime and the VLS growth mode at the high processing temperature regime, respectively.

Keywords: PACS; 81.05.Cy; 81.16.−C; 81.16.BeNano-junction; Alloy; Thermal vapor deposition; Semiconductor

Application of optical and luminescent techniques to the characterization of oxide thin films by J.H. Hao; J. Gao (pp. 5590-5593).

The interaction between light and electrons in oxide compounds forms the basis for many interesting and practical effects, which are related to microstructure, energy band, traps, carrier transport and others. Thin films of oxides like WO₃, Ga₂O₃, Y₂O₃ and SrTiO₃ were investigated using various improved optical and luminescent techniques. The home-made systems for optical and luminescent measurements were described in detail. The facilities of photo-Hall and photoconductivity transients have been proven to be powerful tools in the studies, which allow us to perform photoinduced process and relaxation measurements over a wide time range from 10⁻⁸ to 10⁴s. Furthermore, we extended the measurement capabilities of the commercial luminoscope by using an interferometer system with optical fiber and illuminance meter instead of an optical microscope. The cathodoluminescent measurements can be performed at a relative high pressure (20–60mTorr) compared to ultra-high-vacuum condition of most commercial products. Luminescent characterization was employed as a probe to study doping ions, oxygen vacancies, trap and/or exciton levels in oxide thin films. Our results suggest that various traps and/or excitons in thin films of WO₃, Ga₂O₃ and SrTiO₃ involve in the process of photoconductivity relaxation and emission.

Keywords: PACS; 78.60.HK; 78.66.-W; 07.60.-jCharacterization; Photoconductivity; Luminescence; Oxide thin films; Trap

Influence of annealing temperature on the properties of ZnO thin films deposited by thermal evaporation by N. Bouhssira; S. Abed; E. Tomasella; J. Cellier; A. Mosbah; M.S. Aida; M. Jacquet (pp. 5594-5597).

ZnO thin films were deposited by thermal evaporation of a ZnO powder. The as-deposited films are dark brown, rich zinc and present a low transmittance. Then, these films were annealed in air atmosphere at different temperatures between 100 and 400°C. Their microstructure and composition were studied using XRD and RBS measurements respectively. By increasing the temperature, it was found that film oxidation starts at 250°C. XRD peaks related to ZnO appear and peaks related to Zn decrease. At 300°C, zinc was totally oxidised and the films became totally transparent. The electrical conductivity measurement that were carried out in function of the annealing temperature showed the transition from highly conductive Zn thin film to a lower conductive ZnO thin film. The optical gap ( E_g) was deduced from the UV–vis transmittance, and its variation was linked to the formation of ZnO.

Keywords: PACS; 61.10.Nz; 73.61.−rZnO thin films; Thermal evaporation; Structure; Electrical properties

The nano-structural properties of hydrogenated a-Si and Si–C thin films alloys by GISAXS and vibrational spectroscopy by D. Gracin; K. Juraic; P. Dubcek; A. Gajovic; S. Bernstorff (pp. 5598-5601).

Amorphous hydrogenated silicon (a-Si:H) with high hydrogen content (10–40at.%), and non-stehiometric silicon–carbon (Si1−_xC_x) thin films with a variation of the carbon to silicon ratio up to 0.3, were deposited by using a magnetron sputtering source. The Si1−_xC_x thin films were partially crystallised after deposition by thermal annealing up to 1050°C.The GISAXS (Grazing Incidence Small Angle X-ray Scattering) spectra of all of the prepared specimens indicate the presence of “particles�? in the “bulk�? of the films. For the a-Si:H samples, “particles�? are most probably voids agglomerates with a variation in size between 3 and 6nm. The mean value of the size distribution of the “particles�? increases while its width slightly decreases with the hydrogen content in the film. This indicates a better structural ordering which is consistent with the results of Raman spectroscopy that show a decrease of the ratio between intensities of transversal acoustic (TA) and transversal optic (TO) phonon peaks, I_TA/ I_TO, and a narrowing of the TO peak with increasing hydrogen content. These results are discussed as a consequence of the beneficial influence of hydrogen bombardment during the film growth.For Si1−_xC_x thin films, the “particles�? are assumed to be SiC nano-crystals with a size between 2 and 14nm and they are larger in films with a higher carbon concentration. Inside each of the films, the crystals are larger closer to surface and they grow faster in the direction parallel to the surface than in that which is perpendicular to it.

Keywords: PACS; 61.43.Dq; 68.55.-a; 61.10.Eq; 61.72.HhAmorphous silicon carbide; Nano-structure; GISAXS; FTIR; Raman

High resolution hard X-ray photoemission using synchrotron radiation as an essential tool for characterization of thin solid films by J.J. Kim; E. Ikenaga; M. Kobata; A. Takeuchi; M. Awaji; H. Makino; P.P. Chen; A. Yamamoto; T. Matsuoka; D. Miwa; Y. Nishino; T. Yamamoto; T. Yao; K. Kobayashi (pp. 5602-5606).

Recently, we have shown that hard X-ray photoemission spectroscopy using undulator X-rays at SPring-8 is quite feasible with both high resolution and high throughput. Here we report an application of hard X-ray photoemission spectroscopy to the characterization of electronic and chemical states of thin solid films, for which conventional PES is not applicable. As a typical example, we focus on the problem of the scatter in the reported band-gap values for InN. We show that oxygen incorporation into the InN film strongly modifies the valence and plays a crucial role in the band gap problem. The present results demonstrate the powerful applicability of high resolution photoemission spectroscopy with hard X-rays from a synchrotron source.

Keywords: PACS; 79.60.Bm; 71.55.EqHigh resolution hard X-ray photoemission spectroscopy; InN; Oxygen incorporation

Electrical behaviour of SiO_xN_y thin films and correlation with structural defects by F. Rebib; E. Tomasella; S. Aida; M. Dubois; J. Cellier; M. Jacquet (pp. 5607-5610).

Silicon oxynitride thin films were deposited by reactive r.f. sputtering from a silicon target. Different Ar:O₂:N₂ gas atmospheres were used at fixed power density (3.18Wcm⁻²) and pressure (0.4Pa) to obtain various film composition. Pt–SiO_xN_y–Pt sandwich type structure was realised for electrical property investigations. The C– V measurements showed the absence of a Schottky barrier and thus confirmed that Pt electrode provides an ohmic contact. The evolution of the current density showed a decrease of the film conductivity when the oxygen concentration in the films increases. The various layer composition leads to two different conduction mechanisms which were identified as space charge limited current (SCLC) and Poole–Frenkel effect. Finally, the structural defects of the films were studied by EPR analysis and the spin densities were correlated to both the composition and the electrical behaviour of the films.

Keywords: PACS; 52.80.Pi; 73.61.−rSilicon oxynitride; Sputtering; Electrical properties; Structural defects

Optical emission spectroscopy investigation of sputtering discharge used for SiO_xN_y thin films deposition and correlation with the film composition by F. Rebib; E. Tomasella; L. Thomas; J. Cellier; T. Sauvage; M. Jacquet (pp. 5611-5614).

The r.f. discharge of sputtering silicon target using argon–oxygen–nitrogen plasma was investigated by optical emission spectroscopy. Electronic temperature ( T_e) and emission line intensity were measured for different plasma parameters: pressure (from 0.3 to 0.7Pa), power density (0.6–5.7Wcm⁻²) and gas composition. At high oxygen concentration in the plasma, both T_e and the target self-bias voltage ( V_b) steeply decrease. Such behaviour traduces the target poisoning phenomenon. In order to control the deposition process, emission line intensity of different species present in the plasma were compared to the ArI ( λ=696.54nm) line intensity and then correlated to the film composition analysed by Rutherford Backscattering Spectroscopy.

Keywords: PACS; 52.80.Pi; 52.70.GwSilicon oxynitride; Reactive sputtering; Optical emission spectroscopy

Uranium oxides investigated by X-ray absorption and emission spectroscopies by M. Magnuson; S.M. Butorin; L. Werme; J. Nordgren; K.E. Ivanov; J.-H. Guo; D.K. Shuh (pp. 5615-5618).

X-ray absorption and resonant X-ray emission measurements at the O 1s edge of the uranium oxides UO₂, U₃O₈ and UO₃ are presented. The spectral shapes of the O Kα X-ray emission spectra of UO₃ exhibit significant excitation energy dependence, from an asymmetric to a symmetric form, which differs from those of UO₂ and U₃O₈. This energy dependence is attributed to a significant difference in the oxygen–uranium hybridization between two different sites in the crystal structure of UO₃. The spectral shapes of UO₂ and U₃O₈ are also found to be different but without significant energy dependence. The experimental spectra of the valence and conduction bands of the uranium oxides are compared to the results of electronic structure calculations available in the literature.

Keywords: Actinides; X-ray emission; X-ray absorption

Theoretical analysis of the spectra of X-ray resonant magnetic reflectivity by M.A. Andreeva; A.G. Smekhova (pp. 5619-5621).

We have developed the general computer code for the calculations of reflectivity with polarization analysis from an arbitrary anisotropic multilayer, which allows us to test different approaches for the Bragg reflectivity spectrum treatment. We have proved the validity of the usage of the Bragg peak position for the determination of the energy dependence of the diagonal component of resonant susceptibility tensor, but revealed the essential discrepancy of this procedure for the off-diagonal term determination. The explanation lies in the polarization mixture by multiple reflections at large glancing angles. By the model calculations we have shown that in L-MOKE geometry the observed difference of the integrated Bragg peak reflectivity for the (+) and (−) field direction is predominantly caused by the magnetization of the central part of resonant layer at the first-order Bragg peak, but it is very sensitive to the interface magnetization at the second-order Bragg peak.

Keywords: PACS; 75.70.Cn; 78.70.Ck; 68.35.CtMagnetic circular reflectivity; Fe/Co superlattice; Magnetic moment; Interface roughness

Electrospray deposition in vacuum by Janine C. Swarbrick; J. Ben Taylor; James N. O'Shea (pp. 5622-5626).

We have used the established technique of electrospray in developing a portable vacuum electrospray system which can deposit, in vacuo, dissolved molecules onto a sample which may then be analysed by UHV techniques. As an initial test of the system we have analysed silicon samples with an electrosprayed layer of poly(ethylene) oxide (PEO) using atomic force microscopy (AFM). The polymer forms different structures depending on the voltage applied to the emitter, and solution composition. The system is part of our ongoing effort to deposit other materials such as nanoparticles, and large dye molecules for developing molecular dye sensitised solar cells.

Keywords: PACS; 07.30.−t; 39.10.+j; 68.37.Ps; 81.15.RsElectrospray; Electrospray deposition; Vacuum deposition; PEO; Polymer morphology

Sections

Personal tools

Applied Surface Science (v.252, #15)

Sections

Personal tools

Local resources

Applied Surface Science (v.252, #15)