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Applied Surface Science (v.254, #1)

Preface (pp. 1-3).

Atomically precise self-assembly of one-dimensional structures on silicon by I. Barke; T.K. Rügheimer; Fan Zheng; F.J. Himpsel (pp. 4-11).

This work has three main themes: (1) fabricate atomically precise nanostructures at surfaces, particularly nanowires consisting of atom chains; (2) explore the behavior of one-dimensional electrons in atomic chains; (3) find the fundamental limits of data storage using an atomic scale memory. Semiconductor surfaces lend themselves towards self-assembly, because the broken covalent bonds create elaborate reconstruction patterns to minimize the surface energy. An example is the large 7×7 unit cell on Si(111), which can be used as building block. On semiconductors, the surface electrons completely de-couple from the substrate, as long as their energy lies in the band gap. Angle-resolved photoemission reveals surprising features, such as a fractional band filling and a spin-splitting at a non-magnetic surface. An interesting by-product is a memory structure with self-assembled tracks that are five atom rows wide and store a bit by the presence or absence of a single silicon atom. This toy memory is used to test the fundamental limits of data storage and to see how storage on silicon compares to storage in DNA.

Keywords: PACS; 68.65.La; 73.21.Hb; 73.20.At; 79.60.−iLow-dimensional structures; Atomic wires; Silicon surfaces; One-dimensional physics; Scanning tunneling microscopy; Scanning tunneling spectroscopy; Photoelectron spectroscopy

Thermal stability of atomically flat metal nanofilms on metallic substrates by F. Calleja; J.J. Hinarejos; M.C.G. Passeggi Jr.; A.L. Vázquez de Parga; R. Miranda (pp. 12-15).

By means of variable temperature scanning tunneling microscope we studied the morphology and electronic structure of Pb films grown on Cu(111). Due to the spatial confinement of electrons, the islands display quantized energy levels. At 300K, Pb forms 3D nanostructures with magic heights, that correspond to islands having a quantum well state (QWS) far from the Fermi energy. Below 100K Pb grows in a quasi-layer-by-layer fashion. The QWS that develop in the films determine their total energy and, accordingly, their thermal stability. Films of particularly magic thickness are stable upon heating to 300K.

Keywords: PACS; 68.35.; −; a; 68.60.Dv; 68.47.De; 68.37.EfQuantum size effects; Metallic films; Scanning tunneling microscopy; Scanning tunneling spectroscopy

Electron-stimulated desorption of lithium ions from lithium halide thin films by Leszek Markowski (pp. 16-19).

Electron-stimulated desorption of positive lithium ions from thin layers of lithium halides deposited onto Si(111) are investigated by the time-of-flight technique. The determined values of isotope effect of the lithium (⁶Li⁺/⁷Li⁺) are 1.60±0.04, 1.466±0.007, 1.282±0.004, 1.36±0.01 and 1.33±0.01 for LiH, LiF, LiCl, LiBr and LiI, respectively. The observed most probable kinetic energies of⁷Li⁺ are 1.0, 1.9, 1.1, 0.9 and 0.9eV for LiH, LiF, LiCl, LiBr and LiI, respectively, and seem to be independent of the halide component mass. The values of lithium ion emission yield, lithium kinetic energy and lithium isotope effect suggest that the lattice relaxation is only important in the lithium ion desorption process from the LiH system. In view of possible mechanisms and processes involved into lithium ion desorption the obtained results indicate that for LiH, LiCl, LiBr and LiI the ions desorb in a rather classical way. However, for LiF, ion desorption has a more quantum character and the modified wave packet squeezing model has to be taken into account.

Keywords: PACS; 68.43.Rs; 79.20.LaDesorption induced by electronic transitions; Ion emission; Alkali halides

Electronic structure of pristine CuPc: Experiment and calculations by V.Yu. Aristov; O.V. Molodtsova; V. Maslyuk; D.V. Vyalikh; V.M. Zhilin; Yu.A. Ossipyan; T. Bredow; I. Mertig; M. Knupfer (pp. 20-25).

The filled and unoccupied electronic states of the organic semiconductor copper-phthalocyanine (CuPc) have been determined by a combination of direct and resonant photoemission, near-edge X-ray absorption and first principles calculations. The experimentally obtained electronic states of CuPc are in very good agreement with results of ab initio density of states, allowing to derive detailed site specific information.

Keywords: PACS; 73.20.−r; 73.30.+y; 78.66.Qn; 71.20−bPES; NEXAFS; DFT; CuPc; Electronic structure

Study of electronic structures for Fe thin films deposited on Si- and C-faces of 4H–SiC substrates by soft X-ray emission spectroscopy by M. Hirai; T. Wakita; H. Okazaki; D. Koishihara; Y. Muraoka; T. Yokoya (pp. 26-28).

Silicon carbide (SiC) is a candidate material for electronic devices to operate upon crucial environment. Electronic states of silicides and/or carbide/graphite formed in metal/SiC contact system are fundamentally important from the viewpoint of device performance.We study interface electronic structure of iron thin film deposited on silicon (Si)- and carbon (C)-face of 4H–SiC(0001) by using a soft X-ray emission spectroscopy (SXES). For specimens of Fe (50nm)/4H–SiC (substrate) contact systems annealed at 700 and 900°C, the Si L_2,3 emission spectra indicate different shapes and peak energies from the substrate depending on thermal-treated temperature. The product of materials such as silicides is suggested. Further, from comparison of Si L_2,3 emission spectra between Si- and C-face for the same annealing temperature at 700°C, it is concluded that the similar silicides and/or ternary materials are formed on the two surfaces. However for those of 900°C, the film on substrate is composed of the different silicide and/or ternary materials.

Keywords: PACS; 68.35.−p; 73.20.−rSXES; 4H–SiC; Silicide; Si-face; C-face; Fe

Quantum size effects of Pb overlayers at high coverages by A. Ayuela; E. Ogando; N Zabala (pp. 29-31).

We have studied Pb thin films as a function of the thickness up to 60 monolayers (MLs) using ab initio first principles and model calculations. Magic heights corresponding to a modulated oscillatory pattern of the energy of Pb(1 1 1) films have been measured up to about 30 MLs. We demonstrate that this behaviour continues even for higher thickness due to an extra second modulation pattern in the energetics of the metal film as a function of the number of atomic layers. The origin of this second modulation is the nesting of two close values of the Fermi wavelength in the (1 1 1) direction.

Keywords: PACS; 73.21.Fg; 71.15.Mb; 68.35.; −; p Ab initio; calculations; Quantum wells; Thin films; Quantum size effects

Theoretical modeling of photocatalytic active species on illuminated TiO₂ by Patricia G. Belelli; Ricardo M. Ferullo; María M. Branda; Norberto J. Castellani (pp. 32-35).

A theoretical study of the H₂O and O₂ adsorption on an illuminated TiO₂ anatase surface is presented. The electronic structure and the spin distribution were examined by employing the DFT formalism and the BHandHLYP functional. The adsorbates geometries were fully optimized, including the cluster relaxation. Our results show the dissociative adsorption of the H₂O molecule on the photoactivated TiO₂ (001) surface. This reaction produces one hydroxyl group with radical character (OH) and an unpaired electron localized in the 5c-Ti atom. In case of the O₂ molecule, the non-dissociative chemisorption was obtained. This molecule shows one unpaired electron and a negative charge. In these sense, the adsorbed O₂ acts as a superoxide species (O₂⁻).

Keywords: TiO; ₂; photocatalyst; Anatase structure; Reactive species; Theoretical approach; DFT

The surface of TiO₂ gate of 2DEG-FET in contact with electrolytes for bio sensing use by Kazunari Ozasa; Shigeyuki Nemoto; Yuanzhi Lee; Katsumi Mochitate; Masahiko Hara; Mizuo Maeda (pp. 36-39).

In order to apply two-dimensional electron-gas-field-effect-transistors (2DEG-FETs) for cell-viability sensors, we investigated the chemical/electrical properties of TiO₂ thin films (13–17nm) prepared with the sol–gel technique on the gate surface of AlGaAs/GaAs 2DEG-FETs. Photochemical/electrochemical reactions on GaAs surface in electrolytes, which induce the degradation of 2DEG-FET performance, are effectively suppressed by introducing a TiO₂ thin film on the gate area of 2DEG-FETs. Compared to conventional ion-selective FETs (ISFETs), the TiO₂/2DEG-FETs in this study exhibit a high sensitivity (410mV/mM) for H₂O₂ detection. TiO₂ surfaces show better biocompatibility than GaAs surfaces as demonstrated by direct cell culture on these surfaces.

Keywords: PACS; 73.40.Qv; 73.90.+f; 73.61.Ng; 73.20.−rTiO; ₂; Sol–gel technique; GaAs; 2DEG-FETs; Bio-sensors; Cell culture

Electronic structure and anomalous photoemission line-shape of quasi-2D oxide η-Mo₄O₁₁ by M.A. Valbuena; J. Avila; S. Drouard; H. Guyot; M.C. Asensio (pp. 40-44).

The η-Mo₄O₁₁ compound is a layered two-dimensional (2D) metallic system whose reduced dimensionality originates non-linear properties as charge density wave (CDW) instabilities. We report on synchrotron radiation angle resolved photoemission spectroscopy (ARPES) measurements in order to obtain a detailed picture of the electronic structure of this material. The symmetry of the states near the Fermi level ( E_F) has been discussed in relation to the photoemission symmetry selections rules. Our results are in excellent agreement with previous tight-binding calculations and support the hidden nesting concept proposed to explain the CDW instabilities exhibited by this family of compounds. In addition, a very peculiar photoemission line-shape has been found with the presence of localized non-dispersive states. Some possible explanations are discussed.

Keywords: PACS; 71.45.Lr; 79.60.−I; 71.20.−b; 71.18.+yPhotoelectron spectroscopies; Charge density waves; Electronic structure; Low-dimensional solids

Electronic properties of (Co, Ag) self-organized nano dots on Au(1 1 1) vicinal surfaces by C. Didiot; Y. Fagot-Revurat; S. Pons; B. Kierren; D. Malterre; A. Tejeda; S. Rousset (pp. 45-49).

Electronic properties of (Ag, Co) nanostructures grown on Au(1 1 1) vicinal surfaces have been studied by angle resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy and spectroscopy (STM/STS). The growth and self-assembling of Co and Ag nano dots on Au(7 8 8) surface are described. Co island growth leads to the formation of repulsive energy barriers for the surface state, and subsequently to the appearance of confined states in between each group of four Co dots. On the contrary, when Ag nano dots are grown, the potential barrier for the surface electrons is not enough to suppress their dispersive behavior. Nevertheless, inside Ag islands appear new quantized states whose energies can be tailored by varying the deposition rate of the adsorbate and/or the Miller index of the vicinal surfaces. In both systems, high homogeneity of the electronic properties is achieved over a macroscopic scale.

Keywords: PACS; 73.20.At; 79.60.-i; 68.37.Ef; 73.22.-fEpitaxial growth of nanostructures; Self-organization; Photoemission and scanning tunneling spectroscopies

Silicon quantum wires on Ag(110): Fermi surface and quantum well states by M.A. Valbuena; J. Avila; M.E. Dávila; C. Leandri; B. Aufray; G. Le Lay; M.C. Asensio (pp. 50-54).

One-dimensional Si quantum wires have been grown on silver single crystals upon deposition of ∼0.25 monolayer of Si on Ag(110) surfaces. Scanning tunneling microscopy (STM) clearly shows parallel 1D Si chains along the [−110] Ag crystallographic direction. Low Energy Electron Diffraction (LEED) confirms the massively parallel assembly of these selforganized Nanowires (NWs). We have characterized these nano-objects by measuring the dispersion of the NWs valence band at room temperature using Angle-Resolved PhotoEmission Spectroscopy (ARPES). Also, the Fermi Surface (FS) of the Ag(110) substrate has been mapped before and after the silicon deposition, trying to put in evidence the metallic or semiconductor character of the NWs silicon's states close to the Fermi level. Our results show the existence of well-defined quantum states associated to the silicon super-structure. Both LEED and ARUPS results confirm that the NWs have typical 1D features, however their metallic or semiconductor character could not be confirmed.

Keywords: PACS; 73.; 73.21.Hb; 68.37.Uv; 79.60.−iSilver; Silicon; Self-assembly; Nanowires; Photoelectron spectroscopy; Scanning tunneling microscopy

Origin of localized states in graphite: Indirect photoemission processes or impurities? by M.E. Dávila; M.A. Valbuena; V. Pantín; J. Avila; P. Esquinazi; M.C. Asensio (pp. 55-61).

The electronic band structure of different types of graphite samples have been investigated in order to identify the origin of non-dispersive density of states recently reported in the literature. A systematic series of synchrotron radiation angle resolved photoemission spectroscopy (ARPES) measurements on graphite single crystal, highly oriented graphite (HOPG) and epitaxial grown graphite single crystal on 6H–SiC(0001) samples, have been carried out as well as compared with theoretical tight binding calculations. Our results indicate that these localized states are present in all the graphite-investigated samples showing the same non-dispersive character and at the same binding energies. The photoemission data taken at several photon energies demonstrate that these states are not surface states nor due to indirect photoemission processes. It seems that they are closely related to the level of impurities present in the studied samples.

Keywords: PACS; 71.20.b; 71.23.kPhotoelectron spectroscopies; Electronic structure; Low-dimensional solids; Graphite

Experimental and theoretical study of charge transfer in hydrogen ion scattering from a graphite surface by F. Bonetto; E.A. García; R. Vidal; J. Ferrón; E.C. Goldberg (pp. 62-64).

Ion scattering spectrometry (ISS) with time of flight (TOF) analysis is employed to measure the ion fraction of positively charged hydrogen (H⁺) projectiles scattered from a well characterized highly oriented pyrolitc graphite (HOPG) surface at a 45° scattering angle, various ingoing/outgoing angles and two different incoming energies (4 and 5keV). In the theoretical approach, the negative ionization probability is calculated by employing a Green's function formalism to solve the dynamic collisional process. Both theoretical and experimental results are analyzed and contrasted. The theoretical negative ion fraction evolution during the collisional process is described in detail.

Keywords: PACS; 68.49.−h; 34.70.+e; 81.05.UwCharge transfer; Graphite surface; Hydrogen scattering

Influence of the charge concentration on the density of states in a two-dimensional superconducting system by S. Orozco; M.A. Ortiz; R.M. Méndez-Moreno; M. Moreno (pp. 65-68).

The gap and the density of states of high-Tc superconductors have been a subject of paramount interest. In order to explain the observed experimental behavior several pairing mechanisms in high-temperature superconductivity have been considered, by theoretical calculations. In this work, within the BCS scheme, a two-band model with energy band overlapping is introduced. The gap parameter and the density of states in a two-dimensional superconducting system are studied as functions of the charge concentration. This model is applied to Bi2212 in order to obtain numerical results.

Keywords: PACS; 74.20.Fg; 74.72; −; h; 74.25.KcHigh-; T; c; Cuprate superconductor; Doping; Energy bands; Charge carrier

Anisotropic ac dissipation at the surface of mesoscopic superconductors by Alexander D. Hernández; Arturo López; Daniel Domínguez (pp. 69-71).

In this work we study the ac dissipation of mesoscopic superconductors at microwave frequencies using the time dependent Ginzburg–Landau equations. Our numerical simulations show that the ac dissipation is strongly dependent on the orientation of the ac magnetic field (hac) relative to the dc magnetic field (Hdc). Whenhac is parallel toHdc we observe that each vortex penetration event produces a significant suppression of the ac losses because the imaginary part of the ac susceptibility as a function ofHdc increases before the penetration of vortices, and then it decreases abruptly after vortices have entered into the sample. In the second case, whenhac is perpendicular toHdc, we observe that the jumps in dissipation occur at the same values ofHdc but are much smaller than in the parallel configuration. The behavior of the dissipation in the perpendicular configuration is similar to previous results obtained in recent microwave experiments using mesoscopic lithographed squares of Pb [A.D. Hernández, O. Arés, C. Hart, D. Domínguez, H. Pastoriza, A. Butera, J. Low Temp. Phys. 135 (2004) 119].

Keywords: PACS; 74.78.Na; 74.20.DeMesoscopic superconductors; ac dissipation

Surface phase transformation induced by the dezincification of a beta Cu–Zn alloy on highly deformed systems by A. Baruj; P. Arneodo Larochette; S. Sommadossi; H.E. Troiani (pp. 72-75).

When Cu–Zn alloys are annealed under dynamical vacuum the Zn component evaporates. The process is called dezincification. This paper presents the results of the dezincification of highly mechanically deformed surfaces of samples initially in the beta (bcc) phase by a combination of in situ optical microscopy observations together with TEM measurements. It is shown that grinding lines remaining from the sample preparation process act as nucleation centers for the alpha (fcc) phase. Under this surface preparation conditions the new fcc phase nucleates with a different geometry than the one reported in previous papers in which surfaces were finished by electropolishing. In the present case, we observe individual fcc precipitates with a well defined geometry. The typical size of precipitates is in the micron range, and depends on the dezincification parameters: final temperature, dezincification time and prior surface preparation. TEM observations show that the fcc precipitates contain a large density of defects, mainly dislocations and twin boundaries.

Keywords: PACS; 68.43.MN; 68.18.Jk; 65.55.AcBrass; Zinc loss; TEM; Corrosion; Material properties; Surface transformation

The role of reconstruction in self-assembly of alkylthiolate monolayers on coinage metal surfaces by D.P. Woodruff (pp. 76-81).

Through a combination of standard laboratory-based surface science methods, together with synchrotron radiation-based normal incidence X-ray standing wave (NIXSW) experiments, the interface structure of simple alkylthiolate ‘self-assembled monolayers’ on Cu(111), Ag(111) and Au(111) has been investigated over the last ∼15 years. A key conclusion is that in all cases the adsorbate produces a substantial, density-lowering, reconstruction of the outermost metal layer, although the nature of these reconstructions is quite different on the three metals. The main results of these investigations are briefly reviewed and contrasted.

Keywords: alkylthiolate; self-assembly; surface structure; copper; Silver; Gold

Comparative study of H₂ adsorption on W(100)-c(2×2)Cu and W(100): Surface alloying effects by A.E. Martínez; W. Dong; H.F. Busnengo (pp. 82-86).

The interactions of H and H₂ with W(100)-c(2×2)Cu and W(100) have been investigated through density functional theory (DFT) calculations to elucidate the effect of Cu atoms on the reactivity of the alloy. Cu atoms do not alter the attraction towards top-W sites felt by H₂ molecules approaching the W(100) surface but make dissociation more difficult due to the rise of late activation barriers. This is mainly due to the strong decrease in the stability of the atomic adsorbed state on bridge sites, the most favourable ones for H adsorption on W(100). Still, our results show unambiguously that H₂ dissociative adsorption on perfect terraces of the W(100)-c(2×2)Cu surface is a non-activated process which is consistent with the high sticking probability found in molecular beam experiments at low energies.

Keywords: PACS; 68.43.BcAdsorption; Hydrogen; Surface alloys

Monolayer adsorption of water on NaCl(100) by Pepa Cabrera-Sanfelix; Stephen Holloway; George R. Darling (pp. 87-91).

Density functional theory calculations have been applied to investigate the adsorption geometry of water overlayers on the NaCl(100) surface in the monolayer regime. Competition between H–H intermolecular repulsion and the attraction of the polar molecules to the surface ions results in the most stable structure having a 2×1 adsorption symmetry with an adsorption energy of 415meV. Overlayers of 1×1 symmetry, as observed in experiment, have slightly lower adsorption energies. The layers are also unstable with respect to rotation of individual molecules. Multiple hydrogens/oxygens interacting with a single substrate ion can pull that ion out of the surface, although the examples considered are energetically very unfavourable. Overlayers of 1×1 symmetry with a coverage of one water molecule per NaCl do not have a high enough adsorption energy to wet the surface.

Keywords: PACS; 68.43.Bc,Fg; 68.43.−h; 68.55.JkH; ₂; O; Salt; Wetting; DFT

Atomistic simulation of Fe deposition and alloy formation on Pt substrates by Cary Pint; Guillermo Bozzolo; Jorge E. Garcés (pp. 92-95).

Fe–Pt alloys are of significant importance toward future applications of high-density magnetic recording media. In this work, we apply the BFS method for alloys to study the energetic pathway for subsurface Fe–Pt alloy formation upon deposition of Fe atoms on Pt(100), Pt(111), and vicinal Pt(997) substrates. The simulation results indicate preference for Fe atoms to occupy sites in the Pt subsurface layers and form an ordered alloy phase upon deposition on a low-index Pt surface. This behavior results in Pt surface segregation leading to nucleation of 3D Pt islands. However, the energetics behind deposition of Fe on Pt(997) indicate that Fe atoms prefer decoration of Pt step edges prior to formation of the ordered Fe–Pt surface alloy, where the ordered alloy is observed to form at the edges of the monoatomic surface steps. In each case presented here, the results are in agreement with experiment, and the formation of a Fe–Pt subsurface alloy is explained by a simple analysis emerging from the competition between BFS strain and chemical energy contributions.

Keywords: Surface segregation; Semi-empirical methods; Computer simulations

A theoretical study of Fe adsorption along Bi-nanolines on the H/Si(001) surface by R.H. Miwa; W. Orellana; G.P. Srivastava (pp. 96-98).

We have investigated the energetic stability and equilibrium geometry of the adsorption of transition metal Fe atoms near the self-organized Bi lines on hydrogen passivated Si(001) surface. Our total energy results show that there is an attractive interaction between Fe adatoms along the Bi-nanolines. For the energetically most stable configuration, the Fe adatoms are seven-fold coordinated, occupying the subsurface interstitial sites aside the Bi-nanolines. With increased coverage, Fe atoms are predicted to form two parallel lines, symmetrically on both sides of the Bi line. Within our local spin-density functional calculations, we find that for the most stable geometries the Fe adatoms exhibit an antiferromagnetic coupling.

Keywords: PACS; 71.15.Mb; 71.15.Nc; 71.20.BeSi(0; 0; 1) surface; Bi-nanolines; Fe adsorption; Density functional theory

Silver on copper phthalocyanine: Abrupt and inert interfaces by O.V. Molodtsova; V.Yu. Aristov; V.M. Zhilin; Yu.A. Ossipyan; D.V. Vyalikh; B.P. Doyle; S. Nannarone; M. Knupfer (pp. 99-102).

The chemistry and electronic structure evolution were studied upon the formation of the interfaces between copper phthalocyanine and Ag and Sn deposited on it in ultra high vacuum conditions. The measurements were performed by means of high-resolution photoemission spectroscopy of core-levels and the valence band, and using synchrotron-radiation facilities. The investigations demonstrate the formation of chemically inert and abrupt interfaces.

Keywords: PACS; 61.10.Ht; 68.35.−pPES; CuPc; In and Sn; Interface formation

Growth of pentacene on Ag(111) surface: A NEXAFS study by M. Pedio; B. Doyle; N. Mahne; A. Giglia; F. Borgatti; S. Nannarone; S.K.M. Henze; R. Temirov; F.S. Tautz; L. Casalis; R. Hudej; M.F. Danisman; B. Nickel (pp. 103-107).

Thin films of pentacene (C₂₂H₁₄) have become widely used in the field of organic electronics. Here films of C₂₂H₁₄ of thickness ranging from submonolayer to multilayer were thermally deposited on Ag(111) surface. The determination of molecular geometry in pentacene films on Ag(111) studied by X-ray absorption at different stages of growth up to one monolayer is presented.XAS spectra at the C K-edge were collected as a function of the direction of the electric field at the surface. The different features of the spectra were assigned to resonances related to the various molecular unoccupied states by the comparison with the absorption coefficient of the pentacene gas phase. The transitions involving antibonding π states show a pronounced angular dependence for all the measured coverages, from submonolayer to multilayer. The spectra analysis indicates a nearly planar chemisorption of the first pentacene layer with a tilt angle of 10°.

Keywords: PACS; 71.20.Rv; 73.20.−r; 61.10.Ht; 68.55.−aPentacene; Ag(1; 1; 1); Polymers and organic compounds; Electron states at surfaces and interfaces; X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.; Thin film structure and morphology

Electronic and geometric structure of methyl oxirane adsorbed on Si(100)2×1 by M.N. Piancastelli; Z. Bao; F. Hennies; O. Travnikova; D. Céolin; T. Kampen; K. Horn (pp. 108-112).

Electronic and geometric properties of the adsorbate–substrate complex formed upon adsorption of methyl oxirane on Si(100)2×1 at room temperature is reported, obtained with synchrotron radiation-induced valence and core-level photoemission. A ring-opening reaction is demonstrated to occur, followed by a five-membered ring formation involving two of the Si surface atoms bound to a surface dimer. Core-level photoemission spectra support the ring-opening reaction and the SiO and SiC bond formation, while from the valence spectra a more extended molecular fragmentation can be ruled out. We discuss the most likely geometry of the five-membered ring.

Keywords: PACS; 79.60.−i; 79.60.Dp; 78.70.DmAdsorption; Electronic structure; Geometrical structure; Semiconductors

Effects of hyperthermal proton bombardment on alkanethiol self-assembled monolayer on Au(1 1 1) by Luan Xi; Zhi Zheng; Ngai-Sze Lam; Oscar Grizzi; Woon-Ming Lau (pp. 113-115).

The effects of hyperthermal proton bombardment on alkanethiol self-assembled monolayer (SAM) on Au(1 1 1) are studied with scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS). The STM and XPS results show that proton bombardment with proton energy as low as 2 eV can induce cross-linking of the adsorbed alkanethiols and transform the original ordered SAM lattice to an array of nanoclusters of the cross-linked alkanethiols. For a bombardment at 3 eV with a fluence of3×1015 cm⁻², the typical cluster size is about 5 nm. In addition, the cluster size distribution is narrow, with no cluster larger than 8 nm. The cluster growth can be promoted by increasing the fluence at a fixed bombardment energy or increasing the energy at a fixed fluence. This indicates that surface diffusion of alkanethiols and cluster growth can be harnessed by the control of the bombardment energy and fluence.

Keywords: PACS; 01.30.Cc; 68.49.; −; h; 68.37.EfSTM; Low energy ion beam; Proton; XPS; SAM

Optical properties of thiol terminated biphenyloxazole ordered monolayers on gold surface by A.V. Kukhta; I.N. Kukhta; E.E. Kolesnik; A.P. Lugovskii; O.L. Neyra; E. Meza (pp. 116-119).

New thiol terminated biphenyloxazole molecules are synthesized. A self assembled monolayer has been prepared on gold surface and spectral and luminescent properties of free molecules and ordered films have been studied experimentally and theoretically (DFT). The luminescence polarization degree is about 40%. New absorption and luminescence bands have been found experimentally and confirmed theoretically. The highest occupied and the lowest unoccupied molecular orbitals of adsorbed molecules strongly differ from not adsorbed thiol molecules.

Keywords: PACS; 81.07.Nb; 71.15.Mb; 71.20.Rv; 78.40.Me; 78.55.KzBiphenyloxazole; Thiol; SAM; Polarization; Absorption and luminescence spectrum; DFT calculation

Methanol decomposition on the β-Ga₂O₃ (100) surface: A DFT approach by María M. Branda; Graciela R. Garda; Horacio A. Rodriguez; Norberto J. Castellani (pp. 120-124).

Density functional theory (DFT) cluster model calculations on methanol reactions on the β-Ga₂O₃ (100) surface have been realized. β-Ga₂O₃ structure has tetrahedral and octahedral ions and the results of gallia–methanol interaction are different depending on the local surface chemical composition. The surface without oxygen vacancies is very reactive and produces the methanol molecule decomposition. The unsaturated surface oxygen atoms strongly oxidize the methanol molecule. CO₂ and H₂O molecules are produced when methanol reacts with a free oxygen vacancy surface on octahedral gallium sites. On the other hand, H₂CO is found after the reaction of this molecule with a free O vacancy surface on tetrahedral gallium sites. A weak interaction between the remaining CO₂ molecule and the oxide surface was found, being this molecule easy to desorb. Otherwise, H₂CO has a stronger surface bond and it could suffer a later oxidation.

Keywords: PACS; 73.20.HbDFT; Gallia surface; Methanol decomposition; Catalysis

Footprint organization of chiral molecules on metallic surfaces by R.O. Uñac; A.V. Gil Rabaza; A.M. Vidales; G. Zgrablich (pp. 125-130).

We study the behavior of chiral molecules adsorbed on clean metallic surfaces using a lattice-gas model and Monte Carlo simulation. The aim is to model and simulate the structure (footprints and organization) formed by molecules on the surface as they adsorb. The model, which is applicable to chiral species like S- and R-alanine, or similar, discloses the conditions to generate different ordered phases that have been observed in experiments by other authors.In our model, each enantiomer may adsorb in two different configurations (species) and several effects are taken into account: inhibition, blockage of neighboring adsorptive sites (steric effects) and promotion of sites representing, in some sense, modifications in the surface properties due to molecule-surface interactions. These adsorption rules are inspired by the enantiomeric character of adsorbed species. We perform a systematic study of the different phases formed in order to qualitatively understand the mechanism for the formation of adsorbate structures experimentally found by other authors.

Keywords: PACS; 68.35.Md; 68.43.Fg; 68.43.Hn; 68.43.−hAdsorption; Chiral molecules; Extended chiral phases

Study of the influence of the acrylic acid plasma parameters on silicon and polyurethane substrates using XPS and AFM by C. Vilani; D.E. Weibel; R.R.M. Zamora; A.C. Habert; C.A. Achete (pp. 131-134).

XPS and AFM have been used to investigate surface modifications produced by acrylic acid (AA) vapor plasma treatment of silicon (Si)(100) substrates and polyurethanes (PUs) membranes. XPS analyses of Si and PUs treated substrates at low plasma power (5–20W) revealed the formation of a thin film on the surfaces, which chemically resembles the poly(acrylic acid) film conventionally synthesised. No signal of the Si substrate could be seen under these low plasma power applications on silicon. However, when the plasma power is higher than 30W one can clearly see XPS silicon signatures. AFM measurements of silicon substrates treated with AA plasma at low power (5–20W) showed the formation of a thin polymer film of about 220–55nm thickness. Further, applications of high plasma power (30–100W) displayed a marked difference from low plasma modifications and it was found sputtering of the silicon substrate. Pervaporation results of AA plasma treated PUs membranes revealed that the selectivity for the separation of methanol from methyl- t-butyl ether is higher at 100W and 1min treatment time, than the other conditions studied. This last finding is discussed concerning the surface modifications produced on plasma treated silicon substrates and PU membranes.

Keywords: PACS; 47.54.Jk (materials science applications); 47.57.Ng (polymers and polymer solutions); 96.15.Lb (surfaces)Polyurethane; Plasma polymerization; XPS; AFM; Acrylic acid; Pervaporation

Tailoring of nickel silicide contacts on silicon carbide by S.A. Pérez-García; L. Nyborg (pp. 135-138).

Co-deposition technique by means of simultaneous ion beam sputtering of nickel and silicon onto SiC was performed for tailoring of Ni-silicide/SiC contacts. The prepared samples were analysed by means of XRD and XPS in order to obtain information about the surface and interface chemistry. Depth profiling was used in order to analyse in-depth information and chemical distribution of the specimens. XRD results showed that the main phase formed is Ni₂Si. The XPS analysis confirmed the formation of the silicide on the surface and showed details about the chemical composition of the layer and layer/substrate interface. Moreover, the XPS depth profiles with detailed analysis of XPS peaks suggested that tailoring of C distribution could be monitored by the co-deposition technique employed.

Keywords: PACS; 81.05.Hd; 82.80.Pv; 68.35.Fx; 81.70.JbSilicon carbide; Co-deposition; Interfacial reactions; XPS; Depth profiles

Investigation of Ni/Ta contacts on 4H silicon carbide upon thermal annealing by Y. Cao; S.A. Pérez-García; L. Nyborg (pp. 139-142).

Nickel and Tantalum thin films with 3:5 thickness ratios were deposited in succession onto 4H–SiC substrate at room temperature. The samples were then heated in situ in vacuum at 650, 800 or 950°C for 30min. Glancing angle X-ray diffraction (XRD), Auger electron spectroscopy (AES) and current–voltage ( I– V) technique were used for characterising the interfacial reactions and electrical properties. Amorphous Ni–Ta can be formed by solid-state reaction at 650°C. The minor dissolved Ni in the Ta metal promotes the reaction between Ta and SiC. With increasing annealing temperature up to 950°C, the dominant carbide changes from Ta₂C to TaC and a layer structure is developed. Electrical measurements show that ohmic contact is formed after annealing at or above 800°C.

Keywords: PACS; 81.05.Hd; 81.15.cd; 81.70.Jb; 82.80 PvSilicon carbide; Metal contact; Interfacial reactions; Nickel; Tantalum; Thin films

Solid phase epitaxy of Ge films on CaF₂/Si(111) by E.P. Rugeramigabo; C. Deiter; J. Wollschläger (pp. 143-147).

At room temperature deposited Ge films (thickness<3nm) homogeneously wet CaF₂/Si(111). The films are crystalline but exhibit granular structure. The grain size decreases with increasing film thickness. The quality of the homogeneous films is improved by annealing up to 200°C. Ge films break up into islands if higher annealing temperatures are used as demonstrated combining spot profile analysis low energy electron diffraction (SPA-LEED) with auger electron spectroscopy (AES). Annealing up to 600°C reduces the lateral size of the Ge islands while the surface fraction covered by Ge islands is constant. The CaF₂ film is decomposed if higher annealing temperatures are used. This effect is probably due to the formation of GeF_x complexes which desorb at these temperatures.

Keywords: PACS; 61.14.Hg; 68.55.−a; 68.69.Dv; 81.15.Np; 82.20.PvSpot profile analysis of low energy electron diffraction; Semiconductor–insulator multilayers; Molecular beam epitaxy; Solid phase epitaxy; CaF; ₂; Silicon; Germanium

Photocatalytic activity of dc magnetron sputter deposited amorphous TiO₂ thin films by K. Eufinger; D. Poelman; H. Poelman; R. De Gryse; G.B. Marin (pp. 148-152).

For photocatalytic thin film applications TiO₂ is one of the most important materials. The most studied TiO₂ crystal phase is anatase, though also rutile and brookite show good photoactivity. Usually anatase or a mixture of rutile and anatase is applied for powder or thin film catalysts. It has been claimed that amorphous films do not exhibit any or only a very low photocatalytic activity.We have deposited amorphous thin films by dc magnetron sputtering from sub-stoichiometric TiO2−_x targets. The coatings are transparent and show a photocatalytic activity half of that of a thin layer of spin-coated reference photocatalyst powder. Annealing the thin films to yield anatase crystallization more than doubles their photocatalytic activity. At the same film thickness these thin films show the same activity as a commercially available photocatalytic coating.The dependence of the photocatalytic activity on deposition parameters like gas pressure and sputter power is discussed. A decrease in film density, as deduced from the refractive index and the microstructure, resulted in an increase in photocatalytic activity. Film thickness has a marked influence on the photocatalytic activity, showing a strong increase up to 300–400nm, followed by a much shallower slope.

Keywords: PACS; 81.15.Cd; 81.40.Ef; 82.65.+rPhotocatalysis; dc magnetron sputtering; XRD amorphous TiO; ₂; Thin films

Growth of ultra-thin cerium oxide layers on Cu(111) by V. Matolín; J. Libra; I. Matolínová; V. Nehasil; L. Sedláček; F. Šutara (pp. 153-155).

The reactive vacuum deposition of CeO₂ on Cu(111) surface in oxygen atmosphere provides high quality epitaxial ceria overlayers. We report the growth characteristics of Ce oxide, the structures, and the temperature stability of the oxide phases as investigated by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy. We find that Ce oxide on the Cu(111) grows initially in the form of islands giving sharp hexagonal LEED pattern of the CeO₂(111) structure corresponding to the (1.5×1.5) structure. The CeO₂–Cu(111) films exhibited mixed valence states and temperature dependent CeO₂–Ce₂O₃ transition above 900K due to the vacuum annealing. The transition progressed more rapidly at the surface, probably by formation of oxygen vacancies.

Keywords: PACS; 71.20.Eh; 79.60.−iPhotoelectron spectroscopy; LEED; Copper; Cerium oxide; Epitaxy; Thin film

Two-step nitridation of photocatalytic TiO₂ films by low energy ion irradiation by Masahisa Okada; Yasusei Yamada; Pin Jin; Masato Tazawa; Kazuki Yoshimura (pp. 156-159).

Nitridation of TiO₂ films is performed by the simultaneous irradiation of low-energy N₂⁺ and H₂⁺ ions under substrate-heating condition. Spectroscopic observations of the resultant films clarify the formation of nitrogen-substituted TiO₂ (TiO2−_xN_x) with large N fractions and the agglomeration of undesirable oxynitride species attributed to the deep states in the band gap. We find that the addition of a thin TiO₂ cap layer on the ion-irradiated films improves the nitrogen bonding structure and distribution near the surfaces, leading to a good photocatalytic performance even in the visible region.

Keywords: PACS; 79.60.−i; 81.15.Cd; 81.65.Lp; 82.65.+rNitridation; TiO; ₂; Photocatalyst; Sputtering; Ion-irradiation; XPS

Crystalline orientation of BiMnO₃ thin films grown by rf-sputtering by E.E. Kaul; N. Haberkorn; J. Guimpel (pp. 160-163).

BiMnO₃ thin films were deposited by means of rf-sputtering onto [1 0 0] oriented SrTiO₃ substrates. X-ray diffraction measurements revealed epitaxial growth with [0 0 l]_m orientation in the monoclinic structure representation, equivalent to the[111]pc direction of the pseudocubic cationic lattice. This [0 0 l]_m orientation was obtained in a wide deposition parameters range. Preliminary magnetization measurements suggest that these films do not present ferromagnetism below the bulk Curie temperature,TC=105 K.

Keywords: Multiferroic materials; BiMnO; ₃; Multiferroism; Thin films; Magnetoelectric; rf-sputtering

Photoluminescence properties of nitrogen-doped ZnO films deposited on ZnO single crystal substrates by the plasma-assisted reactive evaporation method by A. Nakagawa; F. Masuoka; S. Chiba; H. Endo; K. Megro; Y. Kashiwaba; T. Ojima; K. Aota; I. Niikura; Y. Kashiwaba (pp. 164-166).

Photoluminescence (PL) spectra of nitrogen-doped ZnO films (ZnO:N films) grown epitaxially on n-type ZnO single crystal substrates by using the plasma-assisted reactive evaporation method were measured at 5K. In PL spectra, free exciton emission at about 3.375eV was very strong and emissions at 3.334 and 3.31eV were observed. These two emissions are discussed in this paper. The nitrogen concentration in ZnO:N films measured by secondary ion mass spectroscopy was 10^19–20cm⁻³. Current–voltage characteristics of the junction consisting of an n-type ZnO single crystal substrate and ZnO:N film showed good rectification. Also, ultraviolet radiation and visible light were emitted from this junction under a forward bias at room temperature. It is therefore thought that ZnO:N films have good crystallinity and that doped nitrogen atoms play a role as acceptors in ZnO:N films to form a good pn junction. From these phenomena and the excitation intensity dependency of PL spectra, emissions at 3.334 and 3.31eV were assigned to neutral acceptor-bound exciton (A⁰X) emission and a donor–acceptor pair (DAP) emission due to doped nitrogen, respectively.

Keywords: PACS; 78.55.Et; 78.55.−m; 81.05.Dz; 81.15−zZnO; Plasma-assisted reactive evaporation; Homoepitaxial growth; Nitrogen doping; Photoluminescence

Epitaxial growth of Ba₈Ga₁₆Ge₃₀ clathrate film on Si substrate by RF helicon magnetron sputtering with evaluation on thermoelectric properties by L. Miao; S. Tanemura; T. Watanabe; M. Tanemura; S. Toh; K. Kaneko; Y. Sugahara; T. Hirayama (pp. 167-172).

Epitaxial Ba₈Ga₁₆Ge₃₀ clathrate thin films were successfully grown on Si substrate by using helicon magnetron sputtering. The (100) lattice of Ba₈Ga₁₆Ge₃₀ was identified grown on four Si(200) lattices in small mismatch (0.1%). Both the color of samples and XRD results suggest 600°C is the optimal substrate temperature for the growth of high quality Ba–Ga–Ge clathrate film on Si substrates. High Seebeck coefficients and electrical resistivities for the deposited clathrate thin films in comparison with those of bulk are obtained. The high crystal quality and thermionic effects in heterostructures may contribute to the larger Seebeck coefficients, while the increasing of interface scattering for electrons probably is the reason for large electrical resistivities. Although the thermoelectric (TE) results are not ideal as designed, our results are significant due to the first successful work on epitaxial growth of Ba₈Ga₁₆Ge₃₀ clathrate thin films on Si substrate with large Seebeck coefficient.

Keywords: PACS; 68.55; 81.15; 81.15.C; 73.50.LEpitaxial growth; Clathrate; Thin film; Sputtering; Thermoelectric properties

Deposition of polymeric perfluored thin films in proton ionic membranes by plasma processes by Peter Lubomir Polak; Ana Paula Mousinho; Nelson Ordonez; Luis da Silva Zambom; Ronaldo Domingues Mansano (pp. 173-176).

In this work the surfaces of polymeric membranes based on Nafion (proton conducting material), used in proton exchange membranes fuel cells (PEMFC) had been modified by plasma deposition of perfluored polymers, in order to improve its functioning in systems of energy generation (fuel cells). The deposition increases the chemical resistance of the proton ionic polymers without losing the electrical properties. The processing of the membranes also reduces the permeability of the membranes to the alcohols (methanol and ethanol), thus preventing poisoning of the fuel cell. The processing of the membranes of Nafion was carried through in a system of plasma deposition using a mixture of CF₄ and H₂ gases. The plasma processing was made mainly to increase the chemical resistance and result in hydrophobic surfaces. The Fourier transformed infrared (FTIR) technique supplies a spectrum with information about the CF_n bond formation. Through the Rutherford back scattering (RBS) technique it was possible to verify the deposition rate of the polymeric layer. The plasma process with composition of 60% of CF₄ and 40% of H₂ presented the best deposition rate. By the spectrum analysis for the optimized configuration, it was possible to verify that the film deposition occurred with a thickness of 90nm, and fluorine concentration was nearly 30%. Voltammetry made possible to verify that the fluorination increases the membranes chemical resistance, improving the stability of Nafion, becoming an attractive process for construction of fuel cells.

Keywords: PACS; 52.77.Dq; 81.05.Lg; 81.65.−bSurface treatments; Plasma deposition; Proton ionic membranes

The approach to diamond growth on levitating seed particles by Satoshi Shimizu; Tetsuji Shimizu; Beatrice M. Annaratone; Wolfgang Jacob; Christian Linsmeier; Stefan Lindig; Robert W. Stark; Ferdinand Jamitzky; Hubertus Thomas; Noriyoshi Sato; Gregor E. Morfill (pp. 177-180).

We demonstrate the approach of diamond growth on levitating seed particles in a rf plasma. We introduce a hot filament chemical vapor deposition (CVD) technique into the rf plasma chamber in order to obtain improved crystal growth. Firstly, we confirmed diamond nucleation on seed particles placed on a Si substrate using the hot filament CVD. The deposition conditions, namely the total pressure and the rf power, were chosen so that they correspond to particles levitation conditions. We observe that a hydrogen pre-treatment on the seed particles improves the nucleation. Secondly, we confirm the levitation of particles at high temperatures. Fine particles levitated in a plasma are particularly sensitive to thermophoretic effects due to inhomogeneities in the gas heating. Therefore, proper heating procedures are required for successful particles levitation.

Keywords: PACS; 52.27.Lw; 81.05.Uw; 81.15.GhDiamond; CVD; Hot filament; Particle; Levitation

Hard carbon coatings deposited on steel by M. Reinoso; F. Álvarez; H. Huck (pp. 181-184).

We report results of steel substrates coated with hard amorphous carbon and with diamond films. In order to enhance the adherence to the substrate, steel substrates were pretreated by means of a silicon ion beam. Raman spectroscopy was used to analyze the structure of silicon interface while the elastic recoil detection analysis method was applied to determine their composition and thickness. The a-C adherence to the substrate and hardness were also tested. The diamond films were observed by SEM.

Keywords: PACS; 81.05.Uw; 81.15.Jj; 81.15.−z; 83.60.−aDiamond-like carbon; Steel; Adherence; Silicon

Characterization of the laser ablation plasma used for the deposition of amorphous carbon by Enrique Camps; L. Escobar-Alarcón; V.H. Castrejón-Sánchez; M.A. Camacho-López; Stephen Muhl (pp. 185-188).

The plasma produced by laser ablation of a graphite target was studied by means of optical emission spectroscopy and a Langmuir planar probe. Laser ablation was performed using a Nd:YAG laser with emission at the fundamental line with pulse length of 28ns. In this work, we report the behavior of the mean kinetic energy of plasma ions and the plasma density, as a function of the laser fluence (J/cm²), and the target to probe (substrate) distance. The characterized regimes were employed to deposit amorphous carbon at different values of kinetic energy of the ions and plasma density. The mean kinetic energy of the ions could be changed from 40 to 300eV, and the plasma density could be varied from 1×10¹² to 7×10¹³cm⁻³. The main emitting species were C⁺ (283.66, 290.6, 299.2 and 426.65nm) and C⁺⁺ (406.89 and 418.66nm) with the C⁺ (426.65nm) being the most intense and that which persisted for the longest times. Different combinations of the plasma parameters yield amorphous carbon with different structures. Low levels (about 40eV) of ion energy produce graphitic materials, while medium levels (about 200eV) required the highest plasma densities in order to increase the CC sp³ bonding content and therefore the hardness of the films. The structure of the material was studied by means of Raman spectroscopy, and the hardness and elastic modulus by depth sensitive nanoindentation.

Keywords: PACS; 78.40.Fy, 81.05.Hd, 81.15.FgAmorphous carbon; Laser ablation

Influence of the plasma parameters and nitrogen addition on the electrical characteristics of DLC films deposited by inductively coupled plasma deposition by Ana Paula Mousinho; Ronaldo Domingues Mansano (pp. 189-192).

This work has been based on studies of the plasma parameters influence and nitrogen addition over on the electrical characteristics of diamond-like carbon (DLC) films deposited by inductively coupled plasma deposition (ICP) system. For these studies, it was used a mixture of methane with different flows of nitrogen, two different pressure processes and three different coil powers. The nitrogenated DLC films, had presented a great variation in their electric and structural properties with the nitrogen variation in the plasma. With the nitrogen addition, an increase in its dielectric constant of 1.7–7.4 to concentration of the 40% of the nitrogen has occurred. For high nitrogen concentrations (80% of nitrogen), the dielectric constant decreases (of 7.4 for 5.0). The resistivity of the films decreases with the nitrogen concentration increase (1.2×10⁹Ωcm). Attributing semiconductors characteristics to DLC films. With the increase of nitrogen concentration, the sp³ hybridization increases, too. These characteristics were excellent for innumerable applications in electronic devices.

Keywords: PACS; 71.23.Cq; 77.55.+f; 78.30.HvCVD process; Diamond-like carbon; Thin films; Electrical characteristics

Crystallization of amorphous zirconium thin film using ion implantation by a plasma focus of 1kJ by L. Rico; B.J. Gómez; J. Feugeas; O. de Sanctis (pp. 193-196).

In this work preliminary results of amorphous zirconium crystallization using ion beam pulses are presented. Energetic argon- and oxygen-ion beams generated by a plasma focus device were used to promote crystallization on amorphous ZrO₂–2.5mol% Y₂O₃ film deposited by chemical solution deposition onto silica glass substrate. The films were burnt at 370°C for 1h in normal atmosphere previous to plasma irradiation. The irradiation was performed by means of successive pulses of ion beams. The evolution of the surface morphology and crystallization was followed by AFM and X-rays diffraction in a grazing incidence asymmetric Bragg geometry (GIAB), respectively. Argon-irradiated films showed highly nucleated cubic zirconia after 10 pulses. On the other hand, oxygen-irradiated films showed a delayed and less extensive cubic nucleation, but a more ordered structure and well-defined grains.

Keywords: PACS; 61.80.Jh; 52.58.Lq; 52.40.Hf; 68.55.JkIon implantation; Zirconia; Crystallization; Plasma focus

Effect of high energy ion irradiation on silicon substrate in a pulsed plasma device by H. Bhuyan; M. Favre; E. Valderrama; G. Avaria; F. Guzman; H. Chuaqui; I. Mitchell; E. Wyndham; R. Saavedra; M. Paulraj (pp. 197-200).

We have performed an experimental analysis on the investigation of high energy ion beam irradiation on Si(100) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beams are characterized using standard surface science diagnostic tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive X-ray (EDX) analysis and atomic force microscope (AFM) and the results are reported. In particular, it has been found that with silicon targets, the application of PF carbon ion beams results in the formation of a surface layer of hexagonal (6H) silicon carbide, with embedded self-organized step/terrace structures.

Keywords: PACS; 52.58.Lq; 52.77.Dq; 61.72.TtIon beam irradiation; Silicon carbide; Plasma focus

Damage zone produced by the bombardment of stainless steel using Ti nitride PVD coatings by H.A. Colorado; A.A. Ghilarducci; H.R. Salva; S. Suárez (pp. 201-206).

This paper presents the damage zone and defects produced by TiN thin film deposition on stainless steel using DC magnetron sputtering to produce collisions between the TiN ions and the substrate. The PVD process used a low operative pressure, reducing the bombardment damage on the substrate, in comparison with other methods.Internal friction (IF) and elastic modulus measurements were carried out in TiN-PVD coated AISI 304 stainless steel, using a sub-resonant torsion pendulum ( f≅1Hz) and a vibrant-reed instrument ( f≅10³Hz). Some experiments showed several internal friction peaks, which are attributed to dislocation relaxation and to martensitic transformation from γ to α′. The characterization was carried out with X-ray, AFM and SEM. Analysis of X-ray peaks indicates a residual deformation in the order of 0.0005–0.0009 for γ-phase and 0.0006–0.00204 for α′-phase. Two methods are presented to determine the adhesion energy by IF in coated materials: for the first the enthalpy is determined by means of isochronal IF measurements, while for the second it is determined using isothermal measurements. These produce an image of damage caused by the bombardment on the substrate, especially of the residual defects.

Keywords: PACS; 68.35.Np; 62.40.+I; 81.15.−zThin solid films; Damage zone; Internal friction; Adhesion

Structural and surface properties of Si1−_xGe_x thin films obtained by reduced pressure CVD by R.C. Teixeira; I. Doi; J.A. Diniz; J.W. Swart; M.B.P. Zakia (pp. 207-212).

This paper investigates the structure and surface characteristics, and electrical properties of the polycrystalline silicon-germanium (poly-Si1−_xGe_x) alloy thin films, deposited by vertical reduced pressure CVD (RPCVD) in the temperature range between 500 and 750°C and a total pressure of 5 or 10Torr. The samples exhibited a very uniform good quality films formation, with smooth surface with rms roughness as low as 7nm for all temperature range, Ge mole fraction up to 32% (at 600°C), textures of 〈220〉 preferred orientation at lower temperatures and strong 〈111〉 at 750°C, for both 5 and 10Torr deposition pressures. The³¹P⁺ and¹¹B⁺ doped poly-Si1−_xGe_x films exhibited always lower electrical resistivity values in comparison to similar poly-Si films, regardless of the employed anneal temperature or implantat dose. The results indicated also that poly-Si1−_xGe_x films require much lower temperature and ion implant dose than poly-Si to achieve the same film resistivity. These characteristics indicate a high quality of obtained poly-Si1−_xGe_x films, suitable as a gate electrode material for submicron CMOS devices.

Keywords: PACS; 68.55.-a; 68.55.Jk; 73.61.-r; 81.15.Gh; 84.37.+q; 85.40.SzPoly-Si; 1−; _x; Ge; _x; CVD; Thin films; Structural and surface properties; Resistivity

Microstructural characterization of La_0.4Sr_0.6Co_0.8Fe_0.2O3–_δ films deposited by dip coating by L. Baqué; A. Serquis (pp. 213-218).

The dip-coating method has been successfully used for depositing porous electrodes of La_0.4Sr_0.6Co_0.8Fe_0.2O3–_δ (LSCF) films. Perovskite oxide cobaltites powders have been prepared by an acetic acid-based gel route. Then, cathode films were deposited onto ceramic substrates of the usual electrolyte Cerium Gadolinium Oxide (CGO) by dip coating. The structure and morphology of the powders and films were characterized by X-ray, diffraction (XRD) and scanning electron microscopy (SEM) respectively, to study the correlation between microstructure and deposition parameters. Optimum parameters for obtaining continuous, homogeneous and crack free LSCF films were determined.

Keywords: PACS; 81.15.-zDip coating; Lanthanum cobaltite; SOFC cathode

Roughness in manganite-based superlattices by J.C. Rojas Sánchez; M. Granada; L.B. Steren; I. Mazzaro; D.H. Mosca (pp. 219-221).

In this work we present a structural analysis of La_0.75Sr_0.25MnO₃/LaNiO₃ (LSMO/LNO) superlattices, performed by X-ray diffraction spectroscopy and X-ray reflectivity. The samples were deposited by dc magnetron sputtering on single-crystalline (001) oriented SrTiO₃. The strain relaxation and the roughness at the interfaces were estimated from the analysis of the X-ray patterns. The thickness of LSMO reference layers has been measured by means of low-angle X-ray reflectivity, finding a very good agreement with the nominal values.

Keywords: PACS; 61.10.Kw; 61.10.Nz; 68.55.−a; 68.55Jk; 68.65Cd; 73.43QtPerovskite multilayers; Crystalline structure

Hall effect in a GdBa₂Cu₃O7−_δ/La_0.75Sr_0.25MnO₃ perovskite bilayer by N. Haberkorn; G. Bridoux; E. Osquiguil; G. Nieva; J. Guimpel (pp. 222-224).

We present results on the Hall coefficient R_H in the normal state for a GdBa₂Cu₃O7−_δ/La_0.75Sr_0.25MnO₃ bilayer and a La_0.75Sr_0.25MnO₃ film grown by dc magnetron sputtering on (100) SrTiO₃. We find that the electric transport on the bilayer can be qualitatively described using a simple parallel layers model. The GdBa₂Cu₃O7−_δ layer presents a carrier density approximately equal to that reported for 7− δ=6.85 oxygen doping. Also we observe an unexpected presence of two Hall resistivity regimes, effects that may be associated with the internal magnetic field induced on the superconducting layer by the ferromagnetic layer.

Keywords: PACS; 73.50.Jt; 73.61.Jc; 74.78.Bz; 75.47.LxHall effect; Perovskite Bilayer

Magnetic molecular nanostructures: Design of magnetic molecular materials as monolayers, multilayers and thin films by E. Coronado; C. Martí-Gastaldo; S. Tatay (pp. 225-235).

In this paper we summarize the importance and versatility of the molecular approach in the design and development of novel magnetic molecular materials. These materials processing, in order to obtain controlled molecular structures at the nanoscale, will also be remarked.

Keywords: PACS; 75.50.Xx; 75.75.+a; 81.07.−b; 81.07.Nb; 81.16.Nd; 81.16.DnMolecular magnetism; Coordination chemistry; SMMs; Multilayers

Advance in next Century nanoCMOSFET research by Huey-Liang Hwang; Yan-Kai Chiou; Che-Hao Chang; Chen-Chan Wang; Kun-Yu Lee; Tai-Bor Wu; Raynien Kwo; Minghwei Hong; Kuei-Shu Chang-Liao; Chun-Yuan Lu; Chun-Chang Lu; Fu-Chien Chiu; Chun-Heng Chen; Joseph Ya-Min Lee; Albert Chin (pp. 236-241).

It is well known that Taiwan's IC industry is in the very leading front of the world, and production of 65nm devices was launched in 2006. Within a few years, the need of high-k dielectrics and metal gates is eminent and truly indispensable. Professor H.L. Hwang (the author) organized 12 professors and 50 graduate students of National Tsing Hua University and Chiao Tung University, and executed this particular project, which is sponsored by the Ministry of Economic Affairs of Republic of China, and is aimed at treating efficiently this problem and transferred the critical technologies to industry in a time frame of 3 years.

Keywords: PACS; 73.40.Qv; 73.61.At; 73.61.Ng; 77.55.+fNano; MOSFET; High-k dielectric; Metal gate

Surface modification of silicon with single ion irradiation by Iwao Ohdomari; Takefumi Kamioka (pp. 242-246).

In order to solve the issues in Si nanoelectronics such as fluctuation in the device functions and poor reliability of devices due to relative increase in mass transport in nm size structures and to yield novel functions by rather taking advantage of the nm size, we need to understand the phenomena peculiar to nm size structures. Based on the fact that a practical method to fabricate nm structures in terms of throughput, process time, and cost is to combine modification of solid surfaces with energetic particles (especially with single ions) and subsequent chemical processing in solutions, we describe single ion irradiation effects as a tool to modify solid surfaces in nm scale, a method for nm scale in-situ observation of solid surfaces, and some examples of the acquired knowledge.

Keywords: PACS; 34.50.Dy; 85.40.Ry; 87.64.DzSi nanoelectronics; Single ion; Surface modification; nm size phenomena; In-situ observation

Surface characterization of oxygen-functionalized multi-walled carbon nanotubes by high-resolution X-ray photoelectron spectroscopy and temperature-programmed desorption by Wei Xia; Yuemin Wang; Ralf Bergsträßer; Shankhamala Kundu; Martin Muhler (pp. 247-250).

Multi-walled carbon nanotubes were exposed either to nitric acid or to an oxygen plasma to synthesize oxygen-containing functional groups which were characterized by high-resolution X-ray photoelectron spectroscopy (XPS). The C 1s spectra revealed that the treatment with nitric acid mainly resulted in the formation of carboxylic (COOR) and phenolic (COR) groups, whereas the plasma treatment led to a higher amount of carbonyl (CO) groups. Furthermore, the nitric acid treatment yielded a 60% higher surface oxygen concentration compared to the plasma treatment, and created a minor amount of nitrogen-containing functional groups. Thus, the nitric acid treatment was found to be more effective in creating acidic functional groups. The presence and the thermal stability of these groups was also investigated by temperature-programmed desorption (TPD). The release of carbon dioxide was detected at about 350 and 450°C, indicating the decomposition of COOR groups. The CO groups were more stable decomposing even above 600°C. In addition, ammonia was adsorbed as probe molecule followed by TPD to derive the amount and the acidity of the carboxylic and phenolic groups.

Keywords: PACS; 82.65.+rMulti-walled carbon nanotubes (MWCNT); Surface functionalization; X-ray photoelectron spectroscopy (XPS); Temperature-programmed desorption (TPD)

Synthesis of carbon nanotubes by CVD: Effect of acetylene pressure on nanotubes characteristics by Mariano Escobar; M. Sergio Moreno; Roberto J. Candal; M. Claudia Marchi; Alvaro Caso; Pablo I. Polosecki; Gerardo H. Rubiolo; Silvia Goyanes (pp. 251-256).

The effect of acetylene partial pressure on the structural and morphological properties of multi-walled carbon nanotubes (MWCNTs) synthesized by CVD on iron nanoparticles dispersed in a SiO₂ matrix as catalyst was investigated. The general growing conditions were: 110cm³/min flow rate, 690°C synthesis temperature, 180Torr over pressure and two gas compositions: 2.5% and 10% C₂H₂/N₂. The catalyst and nanotubes were characterized by HR-TEM, SEM and DRX. TGA and DTA were also carried out to study degradation stages of synthesized CNTs. MWCNTs synthesized with low acetylene concentration are more regular and with a lower amount of amorphous carbon than those synthesized with a high concentration. During the synthesis of CNTs, amorphous carbon nanoparticles nucleate on the external wall of the nanotubes. At high acetylene concentration carbon nanoparticles grow, covering all CNTs’ surface, forming a compact coating. The combination of CNTs with this coating of amorphous carbon nanoparticles lead to a material with high decomposition temperature.

Keywords: PACS; 81.07.−b; 81.15.GhCarbon nanotubes; Chemical vapor deposition; Acetylene decomposition; Iron catalysts; X-ray diffraction; Scanning and transmission electron microscopy; Thermal analysis

High-density and well-aligned carbon nanotubes formed by surface decomposition of SiC by M. Kusunoki; H. Kato (pp. 257-261).

The structure and diameter of the densely aligned carbon nanotubes (CNTs) by surface decomposition ofSiC(0001¯) C-face in vacuum were investigated by cross-sectional, plan-view transmission electron microscopy and electron diffraction methods. Zigzag-type CNTs were confirmed to be selectively formed and the formation mechanism was proposed from crystallographic analysis. Furthermore, the wall number of CNTs was found to be directly proportional to the diameter of CNTs. Comparing with the theoretical calculation, it was revealed that all of the carbon atoms remained on the surface after the selective evaporation of Si atoms by decomposition of each monolayer ofSiC(0001¯), and then constructed the CNT walls with the minimum diffusion distance at the interface.

Keywords: PACS; 81.07.−b; 81.07.De; 68.35.−p; 68.37.LpCarbon nanotube; SiC; Surface decomposition; TEM; Self-organization

Carbon nanotubes as reinforcement of styrene–butadiene rubber by Alejandro De Falco; Silvia Goyanes; Gerardo H. Rubiolo; Iñaki Mondragon; Angel Marzocca (pp. 262-265).

This study reports an easy technique to produce cured styrene–butadiene rubber (SBR)/multi-walled carbon nanotubes (MWCNT) composites with a sulphur/accelerator system at 150°C. Significant improvement in Young's modulus and tensile strength were achieved by incorporating 0.66wt% of filler without sacrificing SBR elastomer high elongation at break. A comparison with carbon black filled SBR was also made. Field emission scanning electron microscopy was used to investigate dispersion and fracture surfaces. Results indicated that the homogeneous dispersion of MWCNT throughout SBR matrix and strong interfacial adhesion between oxidized MWCNT and the matrix are responsible for the considerable enhancement of mechanical properties of the composite.

Keywords: PACS; 81.07.−b; 81.05.QkCarbon nanotubes; Styrene–butadiene rubber; Nanocomposite; Mechanical properties; Field emission scanning electron microscopy

Nanostructured cathode thin films with vertically-aligned nanopores for thin film SOFC and their characteristics by Jongsik Yoon; Roy Araujo; Nicolás Grunbaum; Laura Baqué; Adriana Serquis; Alberto Caneiro; Xinghang Zhang; Haiyan Wang (pp. 266-269).

Nanostructured cathode thin films with vertically-aligned nanopores (VANP) were processed using a pulsed laser deposition technique (PLD). These VANP structures enhance the oxygen-gas phase diffusivity, thus improve the overall thin film SOFC performance. La_0.5Sr_0.5CoO₃ (LSCO) and La_0.4Sr_0.6Co_0.8Fe_0.2O₃ (LSCFO) were deposited on various substrates (YSZ, Si and pressed Ce_0.9Gd_0.1O_1.95 disks). Microstructures and properties of the nanostructured cathodes were characterized by TEM, HRTEM, SEM and electrochemical measurements. Additionally these well-aligned VANP structures relieve or partially relieve the internal thermal stress and lattice strain caused by the differences of thermal expansion coefficients and lattice mismatch between the electrode and the electrolyte.

Keywords: Thin film cathode; Vertically-aligned nanopores; Electrochemical property

Growth, structure and electrical conduction of WO₃ nanorods by M. Gillet; R. Delamare; E. Gillet (pp. 270-273).

We present a very simple method to obtain tungsten trioxide nanorods. The nanorods are epitaxially grown on a mica substrate in low supersaturation conditions. Investigations of morphology, crystallographic structure and chemical composition of the nanorods allow us to propose a growth model in which the potassium ions of the substrate play a major role inducing the one-dimensional structure. The nanorod growth is initiated by the formation of a hexagonal tungsten bronze (HTB) epitaxially oriented on the mica. By using a conductive atomic force microscopy technique, we characterise the electrical conduction of WO₃ networks.

Keywords: PACS; 81.07 Bc; 61.46HkTungsten oxide; Nanorods; Epitaxial growth; Conductive nanostructure network

Order–disorder transformation in FePt nanoparticles studied by ferromagnetic resonance by J.M. Vargas; R.D. Zysler; A. Butera (pp. 274-277).

We have investigated the ferromagnetic resonance (FMR) response of as-made and temperature annealed FePt magnetic nanoparticles. The as-made nanoparticles, which have been fabricated by a chemical route, crystallize in the low magnetic anisotropy fcc phase and have a diameter in the range of 2–4nm. The annealing of the particles at high temperatures (TA=550, 650 and750°C) in an inert Ar atmosphere produces a partial transformation to the high magnetocrystalline anisotropy L1₀ phase, with a significant increase in particle size and size distribution. FMR measurements at X-band (9.5GHz) and Q-band (34GHz) show a single relatively narrow line for the as-synthesized particles and a structure of two superimposed lines for the three annealed samples. The origin of this line shape has been attributed to the presence of the disordered fcc phase. Assuming that the system consists of a collection of identical particles with a random distribution of easy axes, we have been able to estimate a mean value for the magnetic anisotropy constant of the particles in the fcc phase,K∼2×106erg/cm³. The measured line shape in the annealed samples can be explained if we consider that the magnetic anisotropy of the particles has a gaussian distribution with a relatively broad width.

Keywords: PACS; 75.75.+a; 75.50.Tt; 75.50.Vv; 75.30.Gw; 75.50.Bb; 76.50.+gFePt nanoparticles; High anisotropy L1; ₀; phase; Ferromagnetic resonance

Core-level electronic properties of nanostructured NiO coatings by S. Palacín; A. Gutiérrez; I. Preda; M. Hernández-Vélez; R. Sanz; J.A. Jiménez; L. Soriano (pp. 278-280).

Nanostructured NiO films with different thicknesses were grown on nanoporous alumina membrane substrates by reactive evaporation of Ni in an oxygen atmosphere. The reactive deposition process was assisted by a low energy oxygen ion-beam in order to increase the NiO input into the pores. Surface morphology and structure of the films were analyzed by SEM and XPS. SEM observations reveal a well adhered film of NiO on the substrate. This film appears to be uniform and presents a rather irregular nanostructured morphology, built of NiO clusters with sizes ranging between 5 and 30nm. The core-level electronic properties of this nanostructured NiO film result to be similar to those of an ultrathin film about one monolayer thick. This behaviour can be explained by the large surface to volume ratio of both systems.

Keywords: Alumina membrane substrates; Core-level electronic properties; NiO films

Characterization and applications of Ag nanoparticles in waveguides by M.V. Roldán; A. Frattini; O. de Sanctis; H. Troiani; N. Pellegri (pp. 281-285).

This work reports the preparation, characterization and applications of silver nanoparticles synthesized through the chemical reduction of AgNO₃ and protected by surface modifier. In order to characterize the formation of nanoparticles and the role of synthesis parameters (time, temperature) several studies were made, such as UV–vis spectroscopy, TEM and AFM. We present the incorporation of Ag nanoparticles in sol–gel obtained matrix, because this technique allows the incorporation of larger concentrations of active optical agents and the obtainment of full-dense films at lower temperature than those possible by other methods. The final goal of this work is the preparation of 80SiO₂·20B₂O₃ films for active optical waveguides doped with Ag nanoparticles and Erbium. We are looking for the reinforcement of the fluorescence intensity due to the effect of the resonant coupling of both optical agents (Er and nanoparticles) to produce optical amplifiers.

Keywords: PACS; 61.46.−Df; 42.82.Et; 81.20.FwNanoparticles; Waveguides; Ag; Sol–gel; Films

Formation of gold nanoparticles in heat-treated reactive co-sputtered Au-SiO₂ thin films by P. Sangpour; O. Akhavan; A.Z. Moshfegh; M. Roozbehi (pp. 286-290).

In this work, formation of gold nanoparticles in radio frequency (RF) reactive magnetron co-sputtered Au-SiO₂ thin films post annealed at different temperatures in Ar+H₂ atmosphere has been investigated. Optical, surface topography, chemical state and crystalline properties of the prepared films were analyzed by using UV–visible spectrophotometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD) techniques, respectively. Optical absorption spectrum of the Au-SiO₂ thin films annealed at 800°C showed one surface plasmon resonance (SPR) absorption peak located at 520nm relating to gold nanoparticles. According to XPS analysis, it was found that the gold nanoparticles had a tendency to accumulate on surface of the heat-treated films in the metallic state. AFM images showed that the nanoparticles were uniformly distributed on the film surface with grain size of about 30nm. Using XRD analysis average crystalline size of the Au particles was estimated to about 20nm.

Keywords: PACS; 61.46.Df; 78.67.BfAu nanoparticles; Co-sputtering; SiO; ₂

Quantum confinement in layer-by-layer deposited colloidal HgTe nanocrystals determined by spectroscopic ellipsometry by Veronika Rinnerbauer; Kurt Hingerl; Maksym Kovalenko; Wolfgang Heiss (pp. 291-294).

We report spectroscopic ellipsometry studies in the energy range of 0.5–5eV on samples of 1–10 bilayers of polymer and HgTe nanocrystals, which exhibit strong transitions at higher critical points in the dispersion relation. We show that the dispersion relation for nanocrystals can be modelled with the same concepts for critical points as used in semiconductor bulk optics. We find an energy shift of up to 0.4eV of the critical points to higher energies compared to the HgTe bulk properties, caused by quantum confinement in the nanocrystals, which increases with decreasing nanocrystal size.

Keywords: PACS; 78.67.Bf; 78.20.Ci; 78.55.Et; 85.30.VwSemiconductor nanocrystals; Optical properties; Quantum confinement

Synthesis and characterization of organic/inorganic heterostructure films for hybrid light emitting diode by Toshihiko Toyama; Tokuyuki Ichihara; Daisuke Yamaguchi; Hiroaki Okamoto (pp. 295-298).

Thin-film light emitting devices based on organic materials have been gathering attentions for applying a flat-panel display and a solid-state lighting. Alternatively, inorganic technologies such as Si-based thin-film technology have been growing almost independently. It is then expected that combining the Si-based thin-film technology with the organic light emitting diode (OLED) technology will develop innovative devices. Here, we report syntheses of the hybrid light emitting diode (LED) with a heterostructure consisting of p-type SiC_x and tris-(8-hydroxyquinoline) aluminum films and characterization for the hybrid LEDs. We present the energy diagram of the heterostructure, and describe that the use of high dark conductivities of the p-type SiC_x as well as inserting wide-gap intrinsic a-SiC_x at the p-type SiC_x/Alq interface are effective for improving device performance.

Keywords: PACS; 78.60.Fi; 73.21.Ac; 73.40.Lq; 72.80.Le; 79.60.−I; 79.60.JvLight emitting diode; Thin film; Silicon carbide; Organic semiconductor; Electronic structure; Trapped-charge-limited current

Effects of ZnS:Mn/AlN multilayer structure on luminescent properties of nanostructured thin-film EL device by Daisuke Adachi; Kohei Takei; Toshihiko Toyama; Hiroaki Okamoto (pp. 299-302).

Effects of ZnS:Mn/AlN multilayer structure on luminescent properties of nanostructured (NS) thin-film electroluminescent (TFEL) device of which emission layer is a multilayer composed with ZnS:Mn layers and 0.7-nm-thick AlN interlayers were studied. The bandgap widening and the increased PL efficiency of Mn²⁺ 3d–3d transitions with a decrease in the ZnS:Mn single-layer thickness down to 5nm were observed, which is ascribed to quantum confinement effects. Meanwhile, the multilayer with 2-nm-thick ZnS:Mn single-layers shows a drop of PL efficiency, indicating the presence of defective region just on AlN. The tendency of the luminous efficiency of the NS-TFEL device against the ZnS:Mn single-layer thickness is similar to the tendency found in the PL efficiency, indicating the importance of the ZnS:Mn/AlN interface for the device performance.

Keywords: PACS; 78.60.Fi; 73.63.Bd; 85.60.Pg; 81.15.CdElectroluminescence; Nanocrystals; Sputtering; Thin-film; ZnS; AlN

Low-cost 3D nanocomposite solar cells obtained by electrodeposition of CuInSe₂ by M. Valdés; M.A. Frontini; M. Vázquez; A. Goossens (pp. 303-307).

Thin CuInSe₂ films have been prepared by electrodeposition from a single bath aqueous solution on both dense and nanoporous TiO₂. The films are deposited potentiostatically using a N₂-purged electrolyte at different potentials. Various deposition times and solution compositions have been employed. The effect of annealing in air and in argon at different temperatures and times is also investigated. Thin films and nanocomposites of TiO₂ and CuInSe₂ have been studied with electron microscopy, X-ray diffraction, Raman spectroscopy, and optical absorption spectroscopy. After a thermal anneal in argon at 350°C for 30min excellent CuInSe₂ is obtained. In particular the nominal crystal structure and the bandgap of 1.0eV are found. Although pinholes are present occasionally, good samples with diode curves showing a rectification ratio of 24 at ±1V are obtained. Upon irradiation with simulated solar light of 1000Wm⁻² a clear photoconductivity response is observed. Furthermore, also some photovoltaic energy conversion is found in TiO₂|CuInSe₂ nanocomposites.

Keywords: PACS; 73.40.Kp; 73.50.PzTiO; ₂; Nanoporous; CISe; Electrodeposition; Solar cells

Preparation of five-layered Si/Si_xGe1−_x nano-films by RF helicon magnetron sputtering by S. Tanemura; L. Miao; T. Watanabe; M. Imaoka; M. Tanemura; Y. Mori (pp. 308-311).

Five-layered Si/Si_xGe1−_x films on Si(100) substrate with single-layer thickness of 30nm, 10nm and 5nm, respectively were prepared by RF helicon magnetron sputtering with dual targets of Si and Ge to investigate the feasibility of an industrial fabrication method on multi-stacked superlattice structure for thin-film thermoelectric applications. The fine periodic structure is confirmed in the samples except for the case of 5nm in single-layer thickness. Fine crystalline Si_xGe1−_x layer is obtained from 700°C in substrate temperature, while higher than 700°C is required for Si good layer. The composition ratio ( x) in Si_xGe1−_x is varied depending on the applied power to Si and Ge targets. Typical power ratio to obtain x=0.83 was 7:3, Hall coefficient, p-type carrier concentration, sheet carrier concentration and mobility measured for the sample composed of five layers of Si (10nm)/Si_0.82Ge_0.18 (10nm) are 2.55×10⁶/°C, 2.56×10¹²cm⁻³, 1.28×10⁷cm⁻², and 15.8cm⁻²/(Vs), respectively.

Keywords: PACS; 73.50.L; 68.65; 81.15.c; 73.50.J; 68.60.DSputtering deposition; Five-layered Si/Si; _x; Ge; 1−; _x; film; Thermoelectric thin-film; Hall effect

Silicon-based thin films as bottom electrodes in chalcogenide nonvolatile memories by Seung-Yun Lee; Sung-Min Yoon; Kyu-Jeong Choi; Nam-Yeal Lee; Young-Sam Park; Sang-Ouk Ryu; Byoung-Gon Yu; Sang-Hoon Kim; Sang-Heung Lee (pp. 312-315).

The effect of the electrical resistivity of a silicon–germanium (SiGe) thin film on the phase transition in a GeSbTe (GST) chalcogenide alloy and the manufacturing aspect of the fabrication process of a chalcogenide memory device employing the SiGe film as bottom electrodes were investigated. While p-type SiGe bottom electrodes were formed using in situ doping techniques, n-type ones could be made in a different manner where phosphorus atoms diffused from highly doped silicon underlayers to undoped SiGe films. The p–n heterojunction did not form between the p-type GST and n-type SiGe layers, and the semiconduction type of the SiGe alloys did not influence the memory device switching. It was confirmed that an optimum resistivity value existed for memory operation in spite of proportionality of Joule heating to electrical resistivity. The very high resistivity of the SiGe film had no effect on the reduction of reset current, which might result from the resistance decrease of the SiGe alloy at high temperatures.

Keywords: PACS; 85.40.−e; 81.05.GcSilicon–germanium; Electrode; Chalcogenide; Memory; Resistivity; Joule heat

Nanoscale observations of the operational failure for phase-change-type nonvolatile memory devices using Ge₂Sb₂Te₅ chalcogenide thin films by Sung-Min Yoon; Kyu-Jeong Choi; Nam-Yeal Lee; Seung-Yun Lee; Young-Sam Park; Byoung-Gon Yu (pp. 316-320).

In this study, a phase-change memory device was fabricated and the origin of device failure mode was examined using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Ge₂Sb₂Te₅ (GST) was used as the active phase-change material in the memory device and the active pore size was designed to be 0.5μm. After the programming signals of more than2×106 cycles were repeatedly applied to the device, the high-resistance memory state ( reset) could not be rewritten and the cell resistance was fixed at the low-resistance state ( set). Based on TEM and EDS studies, Sb excess and Ge deficiency in the device operating region had a strong effect on device reliability, especially under endurance-demanding conditions. An abnormal segregation and oxidation of Ge also was observed in the region between the device operating and inactive peripheral regions. To guarantee an data endurability of more than1×1010 cycles of PRAM, it is very important to develop phase-change materials with more stable compositions and to reduce the current required for programming.

Keywords: PACS; 68.35.Rh; 72.15.; −; v; 68.55.Nq; 73.61.Jc; 85.30.; −; zNonvolatile memory; Ge; ₂; Sb; ₂; Te; ₅; (GST); TEM; Reliability; PRAM

Nanoscale intrinsic heterogeneities in Ag–Ge–Se glasses and their correlation with physical properties by B. Arcondo; M.A. Ureña; A. Piarristeguy; A. Pradel; M. Fontana (pp. 321-324).

Ag–Ge–Se glass forming system is dominated by liquid immiscibility. Glasses in the Se–GeSe₂–Ag₂Se triangle may have different morphologies according to their composition. In this work inhomogeneous morphology is observed in Ag_x(Ge_ySe1−_y)100−_x bulk glasses with y=0.20, 0.25at.% fraction. Electron microscopy reveals that the scale of heterogeneity strongly depends on the sample composition. The physical properties of these glasses are also dependent on their composition and can be easily correlated to their morphology. Accordingly, the electric conductivity evolves from semiconducting to ionic conductivity whereas a percolation transition occurs in a narrow Ag concentration range.Mössbauer spectrometry let us to analyse the local order of these intrinsically heterogeneous glasses employing⁵⁷Fe as a probe.

Keywords: Chalcogenide glasses; Fast ionic conductors; Percolation transition

Characterization of Pd–CeO_x interaction on α-Al₂O₃ support by C.E. Gigola; M.S. Moreno; I. Costilla; M.D. Sánchez (pp. 325-329).

The Pd–Ce interaction was studied over CeO₂ (0.3–2.5wt.%)–Pd (1wt.%)/α-Al₂O₃ catalysts used in the reforming reaction of CH₄ with CO₂. The samples were characterized by using high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The activity and selectivity behavior was in good agreement with that of other supported metal catalysts (Ni and Pd) modified with different promoters. The preliminary results of HRTEM would indicate that the CeO_x forms small crystallites around the Pd particle. The XPS analysis for the regions of Ce 3d and Pd 3d, gives an account of Ce being present mostly as Ce³⁺ and a high binding energy for Pd 3d_5/2 (335.3eV), an evidence of Pd–Ce chemical interaction. The Pd/Al XPS intensity ratios vs. the Pd average particle size, determined by TEM, show an excellent correlation for fresh and used catalyst. These results indicate that the diminution of the Pd/Al ratios was due to Pd sintering. Consequently, the small amounts of CeO_x species do not cover the Pd particle, in agreement with the HRTEM results. The overall results stand for the promoter action mechanism of the CeO_x for the reforming reaction with CO₂.

Keywords: PACS; 82.65.Jv; 82.80.−d; 82.80.PvCatalyst; Palladium; Cerium; Methane reforming whit carbon dioxide

Silicon nanowire and polyethylene superhydrophobic surfaces for discrete magnetic microfluidics by Ana Egatz-Gómez; John Schneider; P. Aella; Dongqing Yang; P. Domínguez-García; Solitaire Lindsay; S.T. Picraux; Miguel A. Rubio; Sonia Melle; Manuel Marquez; Antonio A. García (pp. 330-334).

A microfluidic method to manipulate small drops of water is studied on two different superhydrophobic surfaces. Using this digital magnetofluidic method, water drops containing paramagnetic carbonyl-iron microparticles were displaced on silicon nanowire (Si NW) and low-density polyethylene (LDPE) superhydrophobic surfaces using magnetic fields. Horizontal, vertical, or upside-down drop movement is made possible by the action of capillary forces induced by paramagnetic particles aligning and following a magnetic field, indicating that three-dimensional digital microfluidics is possible. Also, both Si NW and LDPE superhydrophobic surfaces combine surface chemistry with nano and microscale surface roughness to make drop movement possible. Si NW superhydrophobic surfaces were prepared using vapor–liquid–solid growth systems followed by coating with a perfluorinated hydrocarbon. LDPE superhydrophobic surfaces were prepared by growing polyethylene crystals on a polyethylene substrate through careful rate control.

Keywords: PACS; 47.55.D; 47.55.dr; 81.07.−b; 87.83.+aLDPE; Polyethylene; Silicon nanowire; Microfluidic; Magnetofluidic

Soft X-ray resonant magnetic scattering study of magnetization reversal in low dimensional magnetic heterostructures by Jorge Miguel; Julio Camarero; Jan Vogel; Joost F. Peters; Nick B. Brookes; Jeroen B. Goedkoop (pp. 335-338).

Soft X-ray resonant magnetic scattering (SXRMS) has been used to investigate the microscopic magnetization reversal behavior of complex magnetic systems. SXRMS is a unique technique, providing chemical, spatial and magnetic sensitivity, which is not affected by external magnetic fields. The study of two selected thin magnetic heterostructures is presented, amorphous rare-earth transition metal alloys and perpendicular exchange coupled antiferromagnetic/ferromagnetic films. In the first system, the internal structure of magnetic stripe domains on nanometer length scales is obtained by measuring bi-dimensional (2D) scattering images. In the second system, the element specificity is exploited to identify the role of the uncompensated spins in the antiferromagnetic layer on the exchange coupling phenomena. Future trends are also discussed.

Keywords: PACS; 75.70.Cn; 75.60.Jk; 75.30.Et; 75.50.Ee; 78.70.Dm; 07.85.QeMagnetic properties of interfaces, multilayers, superlattices, heterostructures; Exchange and superexchange interactions; Antiferromagnetics; Magnetization reversal mechanisms; X-ray absorption spectra; Synchrotron radiation instrumentation

Magnetization reversal in Gd_0.67Ca_0.33MnO₃: Comparison between epitaxial thin films and bulk by Octavio Peña; Yanwei Ma; Maryline Guilloux-Viry; Carlos Moure (pp. 339-342).

Rare-earth-based manganites ABO₃ may present interesting properties when the lanthanide (A-site) and/or the manganese (B-site) are partially substituted by divalent elements. Heavy lanthanides are particularly appealing because of the expected interplay between the intrinsic magnetic properties of the rare-earth element (Ln) and those of the ferromagnetic manganese sublattice. As such, a spin reorientation has been observed during magnetization- versus-temperature cycles due to a negative exchange interaction between Mn and Ln. We present herein high-quality epitaxial thin films (∼200nm thick) of Gd_0.67Ca_0.33MnO₃ deposited onto (100) SrTiO₃ substrates by pulsed-laser deposition. Enhanced properties were observed in comparison with bulk samples. The magnetic transition temperature T_c of the as-grown films is much higher than the corresponding bulk values. Most interesting, magnetization measurements performed under small applied fields, exhibit magnetization reversals below T_c, no matter whether the film is field-cooled (FC) or zero-field-cooled (ZFC). The reversal mechanism is discussed in terms of a negative exchange f– d interaction and magnetic anisotropy, this latter enhanced by strain effects induced by the lattice mismatch between the film and the substrate.

Keywords: PACS; 75.25.+z; 75.30.Et; 75.47.Lx; 75.70.AkThin films; Spin reversal; Magnetic oxides; Magnetic exchange

Large phase coherence effects in GaMnAs-based nanostructures: Towards a quantum spintronics by R. Giraud; L. Vila; A. Lemaître; G. Faini (pp. 343-346).

Quantum coherent transport of spin-polarized carriers is observed on a very unusual large scale within epitaxial nanowires of GaMnAs, a diluted ferromagnetic semiconductor. From the analysis of the amplitude of strong universal conductance fluctuations, an effective phase coherence length of about 100nm is inferred atT=100mK, which is one order of magnitude larger than in a granular 3d-metal ferromagnets. Together with the temperature and bias dependence of these reproducible fluctuations, their wire-length dependence is studied in single-domain sub-micron long nanowires with a perprendicular anisotropy. In particular, variations for two equivalent probe configurations are shown when the length becomes comparable to the actual phase coherence length. This result forecasts the possible observation of non-local voltage drops in GaMnAs nanostructures smaller than about 200nm. Generally speaking, this research contributes to pave the way towards the realization of quantum spintronics devices.

Keywords: Nanomagnetism; Mesoscopic transport; Quantum coherence; Diluted ferromagnetic semiconductors

Mössbauer spectroscopy and magnetic properties in thin films of Fe_xNi100−_x electroplated on silicon (100) by L.S. de Oliveira; J.B.M. da Cunha; E.R. Spada; B. Hallouche (pp. 347-350).

Fe_xNi100−_x thin films were produced by galvanostatic electrodeposition on Si (100), nominal thickness 2800nm, and x ranging 7–20. The crystalline structure of the sample was determined by X-ray diffraction (XRD). The magnetic properties were investigated by vibration sample magnetometry (VSM) and room temperature⁵⁷Fe Mössbauer spectroscopy. Conversion Electron Mössbauer spectroscopy (CEMS) in both film surfaces for the thick self-supported films showed that the magnetic moment direction is in the plane and conventional transmission (MS) that the directions are out of the plane films. The results were interpreted assuming a three-layer model where the external layer has in-plane magnetization and the internal one, out of plane magnetization.

Keywords: PACS; 75.20.En Metals and alloys; 75.30.Gw Magnetic anisotropy; 76.80+y Mössbauer effect; Other γ-ray spectroscopyMössbauer spectroscopy; thin films; electrodeposition; iron-nickel

Ferromagnetic resonance studies in Co/SiO₂ multilayers by M.J.M. Pires; J.C. Denardin; I. Dumitru; L. Spinu (pp. 351-354).

The uniaxial in-plane and out-of-plane anisotropies of [Co/SiO₂]×10 multilayers have been studied by ferromagnetic resonance, magnetometry and transmission electron microscopy. The surface and volume anisotropy constants are in the range of values typical for multilayers with Co and transition metals of the iron group. The influence of the intermixed Co–SiO₂ region is discussed.

Keywords: PACS; 52.77.Dq; 81.05.Lg; 81.65.−bMagnetic anisotropy; Magnetic nanostructures

Structural and magnetic properties of Ni/Pt multilayers by Matías A. Quiroga; Gabriela F. Cabeza; Norberto J. Castellani (pp. 355-359).

In this work, the variation of the magnetic moments of the Ni/Pt multilayers are studied using the linearized augmented plane waves (LAPW) method in the framework of the density functional theory (DFT) implemented in the version of WIEN2K program. The systems have been modeled by seven layers slab separated in z direction by a vacuum region of four substrate layers. We present the results of the dependence of the magnetic properties with respect to the thickness variation of the different multilayers. The modeling of these systems finds an important empirical support. Experiment and theory show the same trends for the magnetic moments: hybridization effects between Ni and Pt are mostly localized at the interface.

Keywords: PACS; 75.70.Ak; 71.00.00Multilayers; Ab initio; calculations; Ni/Pt

Influence of V and Mo overlayer on magneto-optical Kerr effect in ultrathin Co films by K. Postava; Z. Kurant; A. Maziewski; A. Stupakiewicz; L.T. Baczewski; A. Wawro; M. Aoyama; T. Yamaguchi (pp. 360-364).

A method for characterization of sub-nanometer thick Co/V and Co/Mo interfaces is proposed that uses magneto-optical ellipsometry. Both the polar Kerr rotation and ellipticity are fitted simultaneously to different models of interface layer. The magneto-optical data are measured for varying thicknesses of the cobalt layer and overlayer by scanning of a laser beam over the samples with two orthogonal wedges. Decrease of magneto-optical effect at both interfaces Co/V and Co/Mo were observed, which corresponds to interface layers of thicknesses ranging from one to two monoatomic layers. In the case of vanadium, the interface layer is sharper and can be explained either by reduced magnetic moment of cobalt, or by anti-parallel magnetic moment of vanadium near the Co/V interface.

Keywords: PACS; 78.20.Ls; 75.70.Ak; 75.70.Cn; 75.60.; −; dMagneto-optic Kerr effect; V/Co and Mo/Co interfaces; Ultrathin Co film

Magnetic and structural study of Cu-doped TiO₂ thin films by C.E. Rodríguez Torres; F. Golmar; A.F. Cabrera; L. Errico; A.M. Mudarra Navarro; M. Rentería; F.H. Sánchez; S. Duhalde (pp. 365-367).

Transparent pure and Cu-doped (2.5, 5 and 10at.%) anatase TiO₂ thin films were grown by pulsed laser deposition technique on LaAlO₃ substrates. The samples were structurally characterized by X-ray absorption spectroscopy and X-ray diffraction. The magnetic properties were measured using a SQUID. All films have a FM-like behaviour. In the case of the Cu-doped samples, the magnetic cycles are almost independent of the Cu concentration. Cu atoms are forming CuO and/or substituting Ti in TiO₂. The thermal treatment in air promotes the CuO segregation. Since CuO is antiferromagnetic, the magnetic signals present in the films could be assigned to Cu substitutionally replacing cations in TiO₂.

Keywords: PACS; 75.70.Ak; 75.60.Ej; 75.50.PpFerromagnetic; Semiconductors; Thin films

Magnetic interactions in ferromagnetic manganite nanotubes of different diameters by J. Curiale; R.D. Sánchez; H.E. Troiani; A.G. Leyva; P. Levy (pp. 368-370).

In this work we present a magnetic study of La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO) nanotubes with nominal external diameters ( ϕ) of 100, 200, 600 and 800nm. The 800nm diameter nanotubes have walls of around 50nm thickness in all the cases. The walls are constituted by an assembly of nanoparticles with a non-Gaussian size distribution presenting a maximum at 24±6nm (LSMO) and 25±8nm (LCMO). We carried out isothermal remanent magnetization (IRM) and dc demagnetization (DCD) experiments. We determined that the crystallites are single magnetic domains with a magnetic dead layer on the surface which avoids exchange interactions among grains. We conclude that the dominating interactions are of dipolar type of the same magnitude for all the samples.

Keywords: PACS; 75.75.+a; 75.47.Lx; 76.30.−v; 75.47.Lx; 75.50.Tt; 68.37.Lp; 68.37.HkManganite nanotubes; Magnetic interaction; Magnetization; Materials for spintronics

Magnetic characterization of vanadium oxide/polyaniline nanotubes by M.E. Saleta; J. Curiale; H.E. Troiani; S. Ribeiro Guevara; R.D. Sánchez; M. Malta; R.M. Torresi (pp. 371-374).

We present a magnetic study of vanadium oxide nanotubes (VO_x-NTs) with polyaniline (PAni). Transmission electron microscopy (TEM) shows the tubular shape and the multi-wall structure of the nanotubes. The static magnetic susceptibility measured at different magnetic fields shows a Curie behavior, while the magnetization versus magnetic field presents a non-linear dependence at low temperatures. Both experiments can be explained by the presence of paramagnetic ions with S=1/2. Using Electron Paramagnetic Resonance technique, we identified as V⁴⁺(3d¹) the paramagnetic ions present in the nanostructures. All the experimental results can be explained by a fraction between 14% and 18% of V⁴⁺ with respect to the total V atoms in the system.

Keywords: PACS; 75.75.+a; 68.37.Lp; 76.30.−v; 33.35.+rMagnetic properties of nanostructures; Vanadium oxide; EPR; TEM

Superconducting behaviour of Nb/Co superlattices by C. Monton; J. Guimpel; F. de la Cruz (pp. 375-377).

We study the superconducting and magnetic behaviour of Nb/Co superlattices, for superconducting Nb layer thickness of 44nm and Co layer thickness less than 1nm. In this limit no ferromagnetism is observed for Co. The superlattice behaves as independent superconducting Nb layers. We obtain the penetration depth and superconducting gap of the material, and analyze the results in terms of microscopic models and theories.

Keywords: Superlattice; Superconducting; Ferromagnetism

A unified model for metal/organic interfaces: IDIS, ‘pillow’ effect and molecular permanent dipoles by H. Vázquez; Y.J. Dappe; J. Ortega; F. Flores (pp. 378-382).

A unified model, embodying the induced density of interface states (IDIS) model, the reduction of the metal work function due to the adsorbed molecules (‘pillow’ effect) and molecular permanent dipoles, is presented for describing the barrier formation at metal/organic interfaces. While the IDIS model and ‘pillow’ effect have been described in previous approaches, in this paper we show how to introduce molecular permanent dipoles in the interface barrier formation. Examples for Au or Al/organic interfaces are discussed, which show the validity of our results and the generality of our formalism.

Keywords: PACS; 73.30.+y; 71.20.Rv; 73.61.PhMetal/organic interface; Change neutrality level; Energy level alignment; Fermi level pinning; Interface states

Dynamics of electrons and holes at surfaces by E.V. Chulkov; A. Leonardo; I.Yu. Sklyadneva; V.M. Silkin (pp. 383-386).

We present ab initio calculation results for electron–phonon (e–ph) contribution to hole lifetime broadening of theX¯ surface state on Al(001). We show that e–ph coupling in this state is significantly stronger than in bulk Al at the Fermi level. It makes the e–ph decay channel very important in the formation of the hole decay in the surface state atX¯. We also present the results for e–e lifetime broadening in a quantum-well state in 1ML K/Cu(111). We show that this contribution is not negligible and is much larger than that in a surface state on Ag(111).

Keywords: PACS; 73.20.; −; rMany-body theories; Single-particle excitations; Decay mechanisms; Metal surfaces; Surface states; Quantum-well states

Properties of the Ising magnet confined in a corner geometry by Ezequiel V. Albano; Andres de Virgiliis; Marcus Müller; Kurt Binder (pp. 387-391).

The properties of Ising square lattices with nearest neighbor ferromagnetic exchange confined in a corner geometry, are studied by means of Monte Carlo simulations. Free boundary conditions at which boundary magnetic fields±h are applied, i.e., at the two boundary rows ending at the lower left corner a field+h acts, while at the two boundary rows ending at the upper right corner a field−h acts. For temperatures T less than the critical temperatureTc of the bulk, this boundary condition leads to the formation of two domains with opposite orientation of the magnetization direction, separated by an interface which for T larger than the filling transition temperatureTf(h) runs from the upper left corner to the lower right corner, while forTz-direction normal to the interface simply is linear and the interfacial width scales asw∝L, while forT>Tf(h) it scales asw∝L. The distributionP(ℓ) of the interface positionℓ (measured along the z-direction from the corners) decays exponentially forTTf(h). Unlike the findings for critical wetting in the thin film geometry of the Ising model, the Monte Carlo results for corner wetting are in very good agreement with the theoretical predictions.

Keywords: PACS; 05.50.+q; 68.45.Gd; 75.70.; −; i; 05.10.LnConfined magnetic films; Interfaces; Monte Carlo simulations

Modeling of the deposition of Ni and Pd on Mo(110) by Adrian Canzian; Hugo Mosca; Guillermo Bozzolo (pp. 392-396).

Recent experimental work on the deposition of fcc metals on a bcc substrate motivates this atomistic modeling analysis of Ni and Pd deposition on Mo(110). A detailed atom-by-atom analysis of the early stages of growth, focusing on the formation of surface alloys and 3D islands is presented, identifying the interactions leading to each type of behavior. Further analysis describes the growth pattern as a function of coverage. Temperature effects are studied via Monte Carlo simulations using the Bozzolo–Ferrante–Smith (BFS) method for alloys for the energetics.

Keywords: Semi-empirical methods; Computer simulations; Nickel; Palladium; Molybdenum

Structural and electronic properties of PbTe (rocksalt)/CdTe (zinc-blende) interfaces by R. Leitsmann; F. Bechstedt; H. Groiss; F. Schäffler; W. Heiss; K. Koike; H. Harada; M. Yano (pp. 397-400).

We study interfaces between highly ionic crystals with different crystal structure by first-principles total-energy calculations in the repeated-slab approximation and compare the results with experimental data extracted from high-resolution transmission electron micrographs. The non-polar (110) interface between PbTe (rocksalt) and CdTe (zinc-blende) crystals gives rise to a lateral spatial offset between the two crystal halves. At the polar (100) interfaces a strong variation of the interface extent with respect to the cation or anion termination is observed. Furthermore, we calculate band offsets and projected interface band-structures for PbTe/CdTe interfaces. The results are discussed versus the interface orientation.

Keywords: PACS; 68.35.Ct; 68.37.Lp; 68.65.HbPbTe; CdTe; Interfaces; Band offset; Bandstructure; HRTEM

Neutralization mechanisms in He⁺–Al surface collisions by N. Bajales; J. Ferrón; E.C. Goldberg (pp. 401-404).

From a quantum mechanical calculation where the populations of He ground and first excited states are properly taken into account, we can identify for the first time the neutralization to the He first excited state as an operative mechanism in He⁺–Al surface collisions. This identification allows us to understand the presence of high energy electrons in the ion induced electron emission spectra, through the inclusion of Auger deexcitation as an electron emission source, as well as to suggest a possible cause for the disagreement still found between theory and experiments in low energy ion scattering (LEIS) for this system.

Keywords: PACS; 68.49.−h; 68.49.Sf; 73.23.HkIon scattering; Electron emission; Auger; Aluminum

Inexpensive two-tip nanomanipulator for a SEM by D. Nakabayashi; P.C. Silva; D. Ugarte (pp. 405-411).

One of the major obstacles for nanotechnology progress is the lack of effective tools and processes to build, characterize and manipulate nanosystems. Here, we present the development of a low-cost nanomanipulator with two probe tips that operates inside a scanning electron microscope. This manipulation system is based on parallel-guiding-plate-spring mechanism and inexpensive materials. The movements are divided on coarse and fine displacements, which are based on picomotors and piezoelectric elements, respectively. The nanomanipulator was applied to transport and manipulate nanotubes and semiconductor nanowires. The probe tips have independent electrical contacts, so that electrical two point measurements can be performed in situ. The system is expected to be a valuable tool for research laboratories working with nanostructures.

Keywords: PACS; 85.40.Ux; 06.60.Sx; 07.78.+s; 85.30.Vw; 81.05.YsNanomanipulator; Scanning electron microscope (SEM); Nanomanipulation; Nanowires

An alternative procedure for the determination of the optical band gap and thickness of amorphous carbon nitride thin films by L. Escobar-Alarcón; A. Arrieta; E. Camps; S. Muhl; S. Rodil; E. Vigueras-Santiago (pp. 412-415).

In this work, we propose an alternative procedure to obtain the optical band gap and the thickness of amorphous carbon nitride thin films that requires only the measurement of the absorbance spectrum of the samples. The method is based on an absorbance spectrum fitting (ASF) procedure using the Tauc model, which is widely applied to the study of amorphous semiconductors. With the aim of evaluating the proposed method two sets of carbon nitride samples deposited on glass substrates were analyzed; one prepared by pulsed laser ablation (PLA) and the second by magnetron sputtering. The obtained results using different conventional methods were compared with the results of the ASF method and a good agreement between the values and the tendencies with the experimental conditions used to prepare the films were observed.

Keywords: PACS; 78.40.Fy; 81.05.Hd; 81.15.FgOptical band gap; Carbon nitride; Laser ablation; DC sputtering

Optical measurements of silicon wafer temperature by K. Postava; M. Aoyama; J. Mistrik; T. Yamaguchi; K. Shio (pp. 416-419).

An optical technique for precise, non-contact, and real time measurement of silicon wafer temperature that uses the polarized reflectivity ratioRp/Rs is described. The proposed method is based on temperature dependence of the optical functions of silicon. Expected strong temperature sensitivity is obtained near band gap. Simultaneous monitoring of temperature and oxide layer thickness is discussed using measurements at four wavelength 365nm, 405nm, 546nm, and 820nm.

Keywords: PACS; 07.20.Dt; 78.20.Ci; 78.40.Fy; 07.60.FsNon-contact temperature measurement; Silicon wafer; Polarized reflectivity; Ellipsometry

A method for thin foil thickness determination by transmission electron microscopy by M.V. Castro Riglos; A. Tolley (pp. 420-424).

With the intention of determining the local thickness within a crystalline thin foil specimen, by means of transmission electron microscopy (TEM), a method previously proposed by Zuo and Shi [J.M. Zuo, Y.F. Shi, Microsc. Microanal. 7 (Suppl. 2) (2001) 224–225] was applied. Using the convergent beam technique, with the incident beam parallel to a zone axis with low indices, diffraction patterns were obtained for some aluminum alloys with low solute content. These patterns were contrasted with those obtained from simulations based on the dynamic theory with Bloch's waves formalism. The local thickness of the thin foil was then obtained by visually comparing the simulated patterns with the experimental one.Comparison of the proposed method with that based on the analysis of two-beam convergent beam patterns [P.M. Kelly, A. Jostsons, R.G. Blake, J.G. Napier, Phys. Stat. Solidi (a) 31 (1975) 771–780] and with that based on the ratio of intensity of the zero loss peak to the total intensity in an electron energy loss spectrum [R.F. Egerton, Electron Energy Loss Spectroscopy in the Electron Microscope, second ed., Plenum Press, New York, 1996] was carried out. A very good agreement between thicknesses determined using the different methods was found. The sensitivity of the method of Zuo et al. was found to be about 1 or 2nm. The advantages and limitations of the different methods are discussed. The method of Zuo et al. can provide fast and reliable results and can be applied in all modern instruments.

Keywords: PACS; 61.14.Lj; 68.37.−dFoil thickness determination; Thin foil characterization; Transmission electron microscopy; Convergent beam electron diffraction

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Applied Surface Science (v.254, #1)