Applied Surface Science (v.238, #1-4)
Author Index (I-VII).
Subject Index (VIII-XVI).
Preface by A. Méndez-Vilas; M.L. González-Martı́n (1-2).
Scanning probe microscopy experiments in microgravity by Tanja Drobek; Michael Reiter; Wolfgang M. Heckl (3-8).
The scanning probe microscopy setups are small, lightweight and do not require vacuum or high voltage supply. In addition, samples can be investigated directly without further preparation. Therefore, these techniques are well-suited for applications in space, in particular, for operation on the International Space Station (ISS) or for high resolution microscopy on planetary missions. A feasibility study for a scanning tunneling microscopy setup was carried out on a parabolic flight campaign in November 2001 in order to test the technical setup for microgravity applications. With a pocket-size design microscope, a graphite surface was imaged under ambient conditions. Atomic resolution was achieved although the quality of the images was inferior in comparison to laboratory conditions. Improvements for future scanning probe microscopy experiments in microgravity are suggested.
Keywords: Microgravity; Microscopy; Scanning tunneling microscopy;
Some geometrical considerations about the influence of topography on the adhesion force as measured by AFM on curved surfaces by A. Méndez-Vilas; M.L. González-Martı́n; M.J. Nuevo (9-13).
A simple theoretical model, which assumes a perfect pyramidal tip, has been used in order to compute the dependence of the contact area on the slope of the imaged sample. The resulting expression has been computed for an azimuthal angle of 0° (null slope) and for 45°. The theoretical decrease ratio depends on the sidewall angle of the tip, which is about 10° in our case (Ultralevers, ThermoMicroscopes). For this tip geometry, the ratio between adhesion force for 0 and 45° is about 1.6. A very similar value of the decrease ratio of adhesion force has been obtained experimentally, by collecting force curves on mircrospheres of three different materials, which seems to confirm the geometrical nature of this observed dependence of the adhesion force with the surface topography.
Keywords: Atomic force microscope; Adhesion force; Topography;
Determination of uptake rate of sensitive diffusion sampler for formaldehyde in air by Yoshika Sekine; Daisuke Oikawa; Michio Butsugan (14-17).
Formaldehyde (HCHO) is a major indoor air pollutant. Authors have developed a sensitive diffusion sampler of gaseous HCHO in air at ppb level for 30 min exposure. An uptake rate of the sampler was determined by a small chamber experiment and theoretically evaluated by a dynamic sorption model based on Langmuir theory. Field tests proved successful use of the sampler in living environment.
Keywords: Diffusion sampler; Formaldehyde; Uptake rate; Dynamic sorption model;
Surface characterisation of two strains of Staphylococcus epidermidis with different slime-production by AFM by A. Méndez-Vilas; A.M. Gallardo-Moreno; M.L. González-Martı́n; R. Calzado-Montero; M.J. Nuevo; J.M. Bruque; C. Pérez-Giraldo (18-23).
Slime-producer Staphylococcus epidermidis is one opportunistic bacteria directly related to biomaterial infections inside the human body. The characterisation of the bacterial surface is crucial when trying to control its adhesion process and prevent the biofilm formation. This work aims to analyse the microscopic and submicroscopic surface structure of two strains of S. epidermidis with different slime production, as well as mapping the surface interaction forces. Atomic force microscopy (AFM) shows that S. epidermidis ATCC35984 is covered by a granular-like film, highly compacted with the presence of repeated “holes”. However, S. epidermidis ATCC35983 only shows a partial coverage by a less compacted granular-like film, mainly located in the inter-cellular zones. Both films are related to the slime of the two strains studied. As regards to the adhesion forces, results show a greater adhesion of the tip to the slime covering S. epidermidis ATCC35984, than that covering the surface of S. epidermidis ATCC35983. In addition, the adhesion to the free-slime zones of the last strain was higher than to the slime-covered parts.
Keywords: Staphylococcus epidermidis; Slime production; Biofilm; AFM;
Topography induced by sputtering in a magnetic sector instrument: an AFM and SEM study by E. Iacob; M. Bersani; A. Lui; D. Giubertoni; M. Barozzi; M. Anderle (24-28).
Due to the sensitivity, the good depth resolution and the great interest in ultra shallow profile, secondary ion mass spectrometry (SIMS) is one of the prime techniques used in the semiconductor industry. Low impact energy beams are required to profile shallow distributions. Since Cs+ beam sputtering can cause morphological artifacts as well as O2 + beam does, a detailed study is required to understand development and limiting analytical conditions. In this work we analyzed the effect of low energy Cs+ primary beam incident at 68° and 78° on different silicon samples. By using atomic force microscopy (AFM) and scanning electron microscopy (SEM) we underline their reliability and correlate the morphological effects to the SIMS analytical parameters and samples characteristics.
Keywords: AFM; Ripples; Sputtering; Morphological characterization; SIMS;
Scanning tunneling microscopy of titanium silicide nanoislands by I. Goldfarb; S. Grossman; G. Cohen-Taguri; M. Levinshtein (29-35).
In this work, ultrathin titanium silicide layers were grown on Si(1 1 1) substrates, with the aim to stimulate spontaneous growth of nanostructures by self-assembly. Scanning tunneling microscopy was used as a primary tool for a close, in situ monitoring of the related surface processes. This method enabled a detailed observation of the formation and subsequent evolution of the silicide nanoislands as a function of deposition parameters and annealing treatments. Nanoisland shape and, possibly, phase transformations were analyzed in real time and space with atomic, or near atomic resolution. The results of these measurements are discussed, and plausible explanations offered.
Keywords: Vapor-phase epitaxy; Self-assembled nanostructures; Silicides; Scanning tunneling microscopy;
Missing dimer defect on β-SiC(0 0 1)-c(2 × 2) surface—numerical analysis of the structure and STM profiles by Barbara Stankiewicz; Wojciech Kamiński; Leszek Jurczyszyn (36-41).
The carbon-terminated β-SiC(0 0 1) surface is known to be reconstructed with carbon triple-bond dimers at silicon bridge sites. STM investigations of this surface suggest asymmetric dimers tilted in the same direction and defects in form of missing dimer bordered on strongly tilted dimers and dimer rows. In order to verify this interpretation of experimental results we have performed LDA-MD calculations of the geometry and electronic structure of ideal and defected SiC(0 0 1)-c(2 × 2) surface, followed by a theoretical analysis of the formation of STM images for this system. Our results indicate existence of a structure of tilted dimers surrounding missing dimer defect in contrast to flat bridging dimers at undefected surface.
Keywords: Silicon carbide; Surface defects; Density functional calculations; Green’s function methods; Surface relaxation and reconstruction; Scanning tunneling microscopy; Scanning tunneling spectroscopies;
Artifacts in AFM images revealed using friction maps by A. Méndez-Vilas; M.L. González-Martı́n; L. Labajos-Broncano; M.J. Nuevo (42-46).
We have retrieved a clear wavy pattern form and AFM image taken in the friction mode, over a highly polished stainless steel surface, which is usually assumed to be due to an optical interference phenomenon. A clear spatial correlation has been found between the best resolved parts of the pattern observed, and the smoothest part of the original topographical image, which clearly support the idea that the observed effect (not appeared in the topographical image), is effectively due to an optical interference phenomenon.
Keywords: AFM image; Friction maps; Nanoscale;
Force spectroscopy of covalent bond rupture versus protein extraction by Rehana Afrin; Susumu Okazaki; Atsushi Ikai (47-50).
Development of protein extraction and identification methods from a live cell surface using minimally invasive technology has an important implication as a possible tool to study time-dependent changes of the distribution of intrinsic membrane proteins in specific locals on the cell membrane. We have approached to this problem using an atomic force microscope mounted with a chemically modified probe with amino reactive covalent crosslinkers against amino groups on the membrane proteins. We discuss the probability of protein extraction versus covalent bond rupture in the experimentally observed rupture force in protein extraction. Possibility of protein unfolding by mechanical stretching during extraction from the cell surface is discussed.
Keywords: Membrane protein; Atomic force microscope; Nano-mechanics; Protein stretching; Covalent bond;
Direct surface probing of cell wall-defective mutants of Saccharomyces cerevisiae by atomic force microscopy by A. Méndez-Vilas; I. Corbacho; M.L. González-Martı́n; M.J. Nuevo (51-63).
Contact and non-contact atomic force microscopy (AFM) has been used for analyzing the influence of the defects in N-glycosidic process in mnn9 mutants of S. cerevisiae in the cell wall physical properties. High-resolution non-contact AFM image have shown the mutant cell surface to present large highly rough areas (compared with wild type ones) and also some irregular but compact structures usually associated to the former areas. Since no crater-like rings (scars) were observed on the surface of mutant cells (unlike high-resolution imaging of these surface features in wild type cells), these structures are suggested to be deformed scars. These results would also confirm a critical influence of mannoproteins in the zone of the septum, which was already suggested in previous works. Force curves obtained on the irregular and rough areas have shown them to be physically softer than other parts of the cell surface and than wild type cells, and were easily deformed by the AFM tip while scanning in the contact mode. These results could be taken as a direct verification of the known highly osmotic fragility of these mutants. This is at our knowledge the first time defects on cell wall on mnn9 mutants have been directly probed and observed at nanometer scale.
Keywords: Surface probing; AFM; Mutants;
Domain size effects on the thermal properties of PS/PMMA blends by Glaura Goulart Silva; Patrı́cia Mara de Freitas Rocha; Patrı́cia Santiago de Oliveira; Bernardo Ruegger Almeida Neves (64-72).
Polystyrene/poly(methylmethacrylate) blends (PS/PMMA) are phase-separated materials and remain so even at elevated temperatures. Blends of PS/PMMA with 40:60, 50:50 and 60:40 wt.% ratio were prepared with PS showing glass transition (T g) at 64 °C and PMMA at T g = 119 °C. The constituents were mixed using three different methods: melt-mixing, casting from solution and spin-casting. The thermal properties of the blends were studied using thermogravimetry (TG) and temperature modulated differential scanning calorimetry (TMDSC). Insights into the morphology of phases were obtained by atomic force microscopy (AFM) using intermittent contact mode. The melt-mixing blends have domain sizes larger than a micron and the casting and spin-casting materials are submicron phase-separated. AFM indicated the co-continuous phase arrangement of spin-casting samples at 140 °C. TMDSC showed an increase of interfacial content along with a decrease in the difference between the glass transitions of the phase-separated materials when the preparation varies from melt-mixed to casting.
Keywords: Immiscible polymer blend; Thermal properties; Spin-casting deposition; Demixing; AFM;
The dynamics of H2 and N2 sorption in carbon nanotubes by Zs. Ötvös; Gy. Onyestyák; J. Valyon; I. Kiricsi; Z. Kónya; L.V.C. Rees (73-76).
Single-walled and multi-walled carbon nanotubes (SWNT and MWNT) were prepared by catalytic decomposition of methane and acetylene, respectively. The resulting catalyst/carbon composites were subjected to chemical treatments to obtain samples which were enriched in nanotubes. Isotherms and frequency response (FR) spectra of N2 and H2 were recorded at 195 and 77 K, respectively, in the 1–800 Pa pressure range. The adsorption isotherms for N2 were found to obey Henry’s law, while the isotherms of H2 adsorption indicated some energetic heterogeneity of the sorption sites. Stronger adatom–substrate interaction was detected for those samples which had been subjected to oxidative treatment. The FR measurements showed that treatment of MWNT in KMnO4 solution changed the rate-controlling mechanism of mass transport from one of sorption to one of diffusion. Results substantiated that the surface functional groups, generated by the oxidative treatment, have significant influence on both the equilibrium and the dynamic N2 and H2 sorption properties of the carbon nanotubes.
Keywords: Carbon nanotubes; Rate spectroscopy; Adsorption; Diffusion;
The effect of promoters on the electronic structure of ruthenium catalysts supported on carbon by Monica Guraya; Susanne Sprenger; Wioletta Rarog-Pilecka; Dariusz Szmigiel; Zbigniew Kowalczyk; Martin Muhler (77-81).
Alkali- and earth-alkali-promoted ruthenium catalysts supported on graphitized carbon were investigated by means of X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) in order to study the effect of promoters on the electronic structure of this metal–support system. Samples were measured as prepared and after thorough reduction in hydrogen. The C 1s spectra of reduced alkali-promoted catalysts showed a shift towards higher binding energies and an asymmetric broadening. Neither non-promoted nor Ba-promoted Ru/C samples exhibited such a behaviour after similar treatments. The most important feature in the UP spectra of the reduced alkali-promoted catalysts was the appearance of a well defined Fermi edge absent in the semimetal-like electronic structure of graphite. No significant effects appeared in the case of non-promoted or Ba-promoted catalysts. The increase in the density of occupied states at the Fermi energy indicates a shift of this level into the conduction band, due to a charge transfer from the promoter to the support. This interpretation also provides an explanation for the observed higher C 1s binding energy and asymmetric broadening, due to the off-set introduced in the binding energy scale and the increasing probability of inelastic excitations near the Fermi level. In addition to photoelectron spectroscopy, low energy ion scattering (ISS) was used to obtain information about the localisation of the promoters. Based on the mild sputtering effect during prolonged series of spectra, it was possible to conclude that potassium covers both the carbon support and the Ru metal particles.
Keywords: Ruthenium; Carbon; Supported catalyst; Ammonia synthesis; Alkali promoter; XPS; UPS; ISS;
Adsorption of Pd atoms on γ-Al2O3: a density functional study of metal–support interactions by Antonio M. Márquez; Javier Fernández Sanz (82-85).
The Pd/γ-Al2O3 interface at low coverage has been theoretically studied by means of periodic-supercell density functional calculations. The most stable (1 1 0) γ-Al2O3 clean surface plane has been modelled by using a six layers slab stoichiometric model of 40 atoms. A single Pd atom has been deposited on top of the surface in different positions, first freezing the surface structure and later allowing the surface to relax. The results indicate that the metal–support interaction is dominated by the strong Lewis acid properties of the tetrahedral cationic sites. It is also shown that in the octahedral cationic sites, adsorption of single Pd atoms induces a significant relaxation of the substrate. While the interaction energy with the preferred site is strong (∼3.8 eV), small differences are found for nearby sites, indicating a high mobility of Pd atoms on the surface, at least on the channels.
Keywords: Aluminum oxide; Palladium; Density functional calculations; Periodic calculations;
Ethanol pretreatment effect and particle diameter issues on the adsorption of Candida rugosa lipase onto polypropylene powder by M.Laura Foresti; M.Luján Ferreira (86-90).
Lipase from Candida rugosa (CR) was adsorbed onto low-molecular-weight polypropylene powder (PP). Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) techniques, and conversion yield of CR/PP-mediated-ethyl oleate synthesis in solvent-free media, demonstrated lipase adsorption onto PP and its affinity towards biggest polypropylene particles (590–1180 μm). An ethanol pretreatment was assayed in order to decrease the hydrophobic nature of PP. Long periods of ethanol pretreatment led to immobilised particles with different average size and associated activity. Molecular mechanics software packages were used to study the interaction between polypropylene and CR’s lid.
Keywords: Ethanol pretreatment; Adsorption; Particle size; Interaction;
An intermittent temperature-programmed desorption method for studying kinetics of desorption from heterogeneous surfaces by F. Gaillard; M. Abdat; J.P. Joly; A. Perrard (91-96).
Reported results show the interest of an intermittent temperature-programmed desorption (ITPD) technique for gaining information on thermodynamics and desorption kinetics of small molecules from the surface of dispersed solids. This technique is a differential form of TPD where a saw-tooth heating program is used to generate a sequence of interrupted desorptions. Two examples are described and discussed in terms of heat of desorption, activation energy of desorption and frequency factors. We first considered ammonia desorption from two different zeolites, that is H-ZSM5 and H-Ω, in order to get information on their surface acidity. Secondly, oxygen desorption from SnO2 was investigated in order to get quantitative data on O2/SnO2 interaction, this oxide being used in sensors of reducing gases in the atmosphere.
Keywords: Ammonia; Zeolites; Oxygen; SnO2; Temperature-Programmed Desorption; ITPD;
The effect of ultrasound on the catalytic activity of alkaline carbons: preparation of N-alkyl imidazoles by C.J. Durán-Valle; S. Ferrera-Escudero; V. Calvino-Casilda; J. Dı́az-Terán; R.M. Martı́n-Aranda (97-100).
N-Alkyl imidazoles have been prepared by sonochemical irradiation of imidazole and 1-bromobutane using alkaline promoted carbons. Under the experimental conditions, N-alkyl imidazoles can be prepared with a high activity and selectivity. It is observed that imidazole conversion increases in parallel with increasing basicity of the catalyst. For comparison, the alkylation of imidazole has also been performed in a batch reactor system under thermal activation.
Keywords: Sonocatalysis; Basicity; Activated carbons; Imidazole; Alkylation;
Adsorbtion of polyelectrolyte multilayers on plasma-modified porous polyethylene by George Greene; Rina Tannenbaum (101-107).
Hydrophilic and chemically reactive porous media was prepared by adsorbing functional polymers at the surface of sintered polyethylene membranes. Modification of the membrane was accomplished by first exposing the membrane to an oxygen glow discharge gas plasma to render electrostatic charge at the membrane surfaces. A cationic polyelectrolyte was adsorbed from solution to the anionically charged surface to form an adsorbed monolayer. The adsorption of a second anionic polyelectrolyte allowed further modification of the membrane surface with a polyelectrolyte bilayer complex. In this paper we probe the effect of polymer structure on the conformation and stability of the adsorbed polyelectrolyte monolayers and bilayers on the modified polyethylene surface. Using the wicking rate of deionized, distilled water through the porous membrane to gauge the interfacial energy of the modified surface, we show that the wicking rate of the multilayer membrane can be controlled by varying the chemistry of the adsorbing polyelectrolytes and their molecular weights.
Keywords: Polyelectrolyte; Polyethylene; Molecular weight;
Analyses of thin films and surfaces by cold neutron depth profiling by G.P. Lamaze; H.H. Chen-Mayer; K.K. Soni (108-112).
Neutron depth profiling (NDP) has been employed to examine manufacturing processes and starting materials for several high-technology applications. NDP combines nuclear and atomic physics processes to determine the concentration profile of several light elements in the near surface region (∼1–8 μm) of smooth surfaces. The method is both quantitative and non-destructive. Analyses are performed at the Center for Neutron Research at NIST on samples prepared at Corning Incorporated. Two types of samples have been analyzed: (1) Boron profiles are measured in glasses to determine B loss due to its volatilization during manufacturing. Surface depletion of B is a key characteristic of borosilicate materials for both chemical vapor deposition and conventional melting processes. (2) For lithium niobate, a quantitative measure of Li concentration can differentiate congruent and stoichiometric compositions and any surface depletion in commercial wafers.
Keywords: Neutrons; Depth profiling; Lithium niobate; Boron; Borosilicate glass;
Ion beam processing of magnesium oxide thin films for PDP application by Hiroshi Nomura; Shigeto Murakami; Ari Ide-Ektessabi; Yoshikazu Tanaka; Yuji Tsukuda (113-116).
In plasma display panels (PDPs), MgO (magnesium oxide) thin film is used as a protective layer that is placed between the electrodes on the front glass panel on one side of the discharge cells. The aim of this study is to improve the secondary electron emission coefficient of the protective layer. This improvement leads to reduction in consumption of energy. In this study, MgO thin films were prepared using electron beam evaporation method. The ion beam-assisted deposition (IBAD) technique is used to control the crystal orientation, surface nano-morphology, density, and composition. Oxygen ion beam was utilized to irradiate the growing films. In order to control the film properties, the acceleration energy and current density of ion beam and the deposition rate were taken as the variables. The crystallinity, density, composition of the films were analyzed by X-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS). The secondary electron emission coefficients were measured by an apparatus developed in this study. The experimental results show that the irradiation of ion beam during deposition changes the crystal structure of the films and it influences their secondary electron emission coefficient.
Keywords: Plasma display panel; MgO thin film; Secondary electron emission; Ion beam-assisted deposition;
Erbium-doped thin amorphous carbon films prepared by mixed CVD sputtering by G. Speranza; L. Calliari; M. Ferrari; A. Chiasera; K. Tran Ngoc; A.M. Baranov; V.V. Sleptsov; A.A. Nefedov; A.E. Varfolomeev; S.S. Fanchenko (117-120).
Carbon possesses the unique property to get hybridized in two different forms: the sp2 and the sp3. Moreover, carbon easily bonds with hydrogen and other chemical elements to form carbon-based materials with different properties. Here, Er3+-doped amorphous hydrogenated carbon (a-C:H) films deposited via a mixed CVD magnetron sputtering process are studied. The deposition parameters are related to the physical and optical properties of the Er-doped carbon films.
Keywords: Carbon films; Luminescence; XPS; CVD; Magnetron sputtering;
Dry laser cleaning of mechanically thin films by F. Bloisi; A.C. Barone; L. Vicari (121-124).
Laser-assisted particle removal has acquired a growing importance in last few years, finding applications in several fields ranging from microelectronics to conservation and restoration of materials having cultural or historical interest. Recently new ‘indirect’ laser cleaning techniques such as ‘shock’ and ‘verso’ laser cleaning have been developed. Here we present a simple laser cleaning mechanical model in order to associate cleaning efficiency to surface deformation characteristics during cleaning pulse and apply it to examine the behaviour of ‘verso’ laser cleaning which has experimentally shown promising results on cellulosic (paper and cotton) materials.
Keywords: Applied optics; Laser applications; Dry laser cleaning; Indirect laser cleaning; Verso laser cleaning;
Microstructure and bactericidal ability of photocatalytic TiO2 thin films prepared by rf helicon magnetron sputtering by Lei Miao; Sakae Tanemura; Yoichi Kondo; Misao Iwata; Shoichi Toh; Kenji Kaneko (125-131).
The present study investigates the microstructure and bactericidal ability of polycrystalline and epitaxial TiO2 thin films with anatase and rutile structure. Phase formation and the distortion of the lattice of the film compared with bulk are proved by TEM observation. HRTEM images assure the good crystal quality and compact structure of the films prepared by rf helicon magnetron sputtering. This obtained larger band gap due to the lattice deformation could contribute to the better photocatalytic effect of the anatase film.Bactericidal abilities evaluated by the photokilling E. Coli using film stick method under UV irradiation show the following result: Both single and polycrystal anatase films exhibit obvious bactericidal abilities while no distinguishing difference for them. On the other hand, no bactericidal ability is observed for rutile films in this work. The band gap value of rutile film is lower than the energy potential required to O2/O2 − reductions according to the principle proposed by Fujishima et al. This resulted in the observed poor photocatalyst effect of rutile film.
Keywords: TiO2 thin film; Bactericidal abilities; TEM analysis; Helicon sputtering; Optical band gap;
Silver nanoparticle formation in thin oxide layer on silicon by silver-negative-ion implantation for Coulomb blockade at room temperature by Hiroshi Tsuji; Nobutoshi Arai; Takuya Matsumoto; Kazuya Ueno; Yasuhito Gotoh; Kouichiro Adachi; Hiroshi Kotaki; Junzo Ishikawa (132-137).
Formation of silver nanoparticles formed by silver negative-ion implantation in a thin SiO2 layer and its I–V characteristics were investigated for development single electron devices. In order to obtain effective Coulomb blockade phenomenon at room temperature, the isolated metal nanoparticles should be in very small size and be formed in a thin insulator layer such as gate oxide on the silicon substrate. Therefore, conditions of a fine particles size, high particle density and narrow distribution should be controlled at their formation without any electrical breakdown of the thin insulator layer. We have used a negative-ion implantation technique with an advantage of “charge-up free” for insulators, with which no breakdown of thin oxide layer on Si was obtained. In the I–V characteristics with Au electrode, the current steps were observed with a voltage interval of about 0.12 V. From the step voltage the corresponded capacitance was calculated to be 0.7 aF. In one nanoparticle system, this value of capacitance could be given by a nanoparticle of about 3 nm in diameter. This consideration is consistent to the measured particle size in the cross-sectional TEM observation. Therefore, the observed I–V characteristics with steps are considered to be Coulomb staircase by the Ag nanoparticles.
Keywords: Nanoparticle; Negative ion implantation; Coulomb blockade;
Spectromicroscopy of ultrathin Pd films on W(1 1 0): by L. Aballe; A. Barinov; A. Locatelli; S. Heun; S. Cherifi; M. Kiskinova (138-142).
We have studied the growth of Pd thin films on W(1 1 0), by means of low-energy electron microscopy (LEEM), X-ray photoelectron microscopy (XPEEM), and microspot low-energy electron diffraction (μLEED). Real-time LEEM measurements of the evolution of the film morphology as a function of deposition time showed substantial differences in the growth mechanism at 380 and 1000 K. Imaging the valence band structure with spatial resolution of 60 nm revealed clear differences for the interfacial monolayer film and the 3D islands growing on top at 1000 K. The observed spatial variations in the electronic structure are attributed to bonding, structural and electron confinement effects.
Keywords: Ultrathin Pd films; Morphology; XPEEM; LEEM; Electronic structure;
Equilibrium and non-equilibrium 1/f noise in AlGaN/GaN TLM structures by S.A. Vitusevich; S.V. Danylyuk; M.V. Petrychuk; O.A. Antoniuk; N. Klein; A.E. Belyaev (143-146).
The low frequency noise of AlGaN/GaN transmission line model (TLM) structures has been investigated in a wide temperature range. Deviation of low frequency noise from 1/f dependence has been observed. The results indicate that the structure become more non-linear upon increasing of power. The observed features have been explained as a result of non-equilibrium condition in TLM structures, equilibrium and non-equilibrium noise cases have been studied. The non-equilibrium fluctuations in gateless TLM structures were analysed taking into account the influence of the positive surface charge, formed by polarization effects on dynamics of non-uniform potential redistribution along the channel.
Keywords: 1/f noise; Surface states; Semiconductor heterojunction; Two-dimensional electron gas; Wide band gap semiconductors;
Study of GaN x As1−x semiconducting films grown by laser pulsed deposition on crystalline and amorphous substrates by Jairo A. Cardona-Bedoya; Alfredo Cruz-Orea; Julio G. Mendoza-Alvarez; M.Lucero Gomez-Herrera; Mario H. Farias; Jesus A. Diaz (147-150).
The search for semiconductors with band gap energies in the green–blue region of the visible spectra has stimulated the development of new ternaries in the II–VI and III-nitrides systems. In the GaN-side of the GaNAs ternary compound it is expected that the band gap energy could be adjusted for all the visible spectra by changing the N concentration in the compound. We report on the growth of the ternary compound semiconductor GaN x As1−x thin films by using the laser ablation deposition technique in a reactive nitrogen gas atmosphere, on crystalline GaAs(1 0 0) and Si(0 0 1) substrates and also on Corning glass substrates. We have studied the optical properties of these GaN x As1−x films by means of the photoacoustic (PA) and the low temperature photoluminescence (PL) spectroscopies. PL spectra for GaNAs samples showed a broad emission band peaked at around 2.50 eV, a weak broad emission band at about 3.05 eV, and a double-peaked structure located at energies corresponding to violet luminescence band; besides, a very weak emission could be measured at energies of about 1.65–1.68 eV. We interpret these results in terms of the presence of the ternary GaNAs phase and cubic and hexagonal GaN phases.
Keywords: GaN-based alloys; Laser pulsed deposition; Photoluminescence of nitride semiconductors; Photoacoustic in III-V semiconductors;
Electron inelastic mean free paths and surface excitation parameters for GaAs by C.M. Kwei; Y.C. Li (151-154).
Surface excitation parameters and inelastic mean free paths of electrons are of importance in the analyses of surface sensitive electron spectroscopies. When probe electrons are near the surface of a solid or the interface of an overlayer system, electron inelastic mean free paths become depth-dependent. These mean free paths and surface excitation parameters were calculated for electrons crossing the surface of GaAs. Calculations were performed for both incident and outgoing electrons by the use of a dielectric response theory. Applications were made to estimate the elastic backscattering intensity of electrons at different emission angles using the Monte Carlo simulations. Good agreement was found between calculated results and experimental data on the ratio of the elastic reflection coefficient for a GaAs sample relative to a Ni reference. Such a ratio was used to determine the effective electron inelastic mean free paths in GaAs by employing the surface excitation parameter obtained from Monte Carlo simulations.
Keywords: Surface excitation parameter; Inelastic mean free path; Monte Carlo simulation;
Ni–Mn–Ga films on Si, GaAs and Ni–Mn–Ga single crystals by pulsed laser deposition by A. Hakola; O. Heczko; A. Jaakkola; T. Kajava; K. Ullakko (155-158).
We report the deposition of thin films of the magnetic shape-memory (MSM) alloy Ni–Mn–Ga on different substrates by pulsed laser deposition (PLD). Both standard semiconductors – Si and GaAs – and Ni–Mn–Ga single crystals were used. The films on silicon had a relatively smooth surface and showed large saturation magnetizations, up to 60% of the bulk value, when deposited at substrate temperatures between 500 and 600 °C. The films on GaAs, on the contrary, were non-ferromagnetic with a granular surface. In addition, preliminary results of films deposited on Ni–Mn–Ga single crystals indicate that the Ni–Mn–Ga film exhibits the same 6% strain in the magnetic field as the bulk.
Keywords: Magnetic shape-memory effect; MSM; Ferromagnetic shape memory; FSMA; Ni–Mn–Ga; Pulsed laser deposition; Thin film;
Ion beam synthesis of 3C-SiC layers in Si and its application in buffer layer for GaN epitaxial growth by Y. Ito; T. Yamauchi; A. Yamamoto; M. Sasase; S. Nishio; K. Yasuda; Y. Ishigami (159-164).
A 180 keV carbon implantation with an ion dose of 8.0 ± 1.0 × 1017 C+/cm2 into Si(1 1 1) wafer has been investigated in order to examine the synthesis of 3C-SiC at the substrate temperature T s = RT to 800 °C and in the subsequent annealing treatment at the temperature T a = 1000–1250 °C/2 h. The combination at T s ≈ 500 °C and at T a > 1200 °C is the most suitable for the synthesis of crystalline 3C-SiC with the same orientation of the Si(1 1 1) substrate.The crystalline 3C-SiC layer was used as a buffer layer for the formation of GaN/SiC/Si structure using MOVPE for the GaN growth. After removal of upper layers on the 3C-SiC by chemical etching, a crack-free epitaxial GaN layer of 3 μm thickness has been successfully synthesized.
Keywords: High-dose carbon implantation; Substrate temperature; Annealing; Crystalline 3C-SiC; MOVPE growth GaN; GaN/SiC/Si structure;
Crystallization kinetics of hydrogenated amorphous silicon thick films grown by plasma-enhanced chemical vapour deposition by J. Farjas; Chandana Rath; P. Roura; P. Roca i Cabarrocas (165-168).
The crystallization kinetics of hydrogenated amorphous silicon thick films grown by plasma-enhanced chemical vapour deposition is studied by differential scanning and isothermal calorimetry in a wide temperature range varying from 600 to 720 °C. The reported kinetics is found to correspond to three-dimensional growth. The kinetic parameters obtained are in good agreement with those already published on thin films.
Keywords: Crystallization kinetics; Amorphous silicon; DSC;
SEM and HRTEM study of porous silicon—relationship between fabrication, morphology and optical properties by J. Dian; A. Macek; D. Nižňanský; I. Němec; V. Vrkoslav; T. Chvojka; I. Jelı́nek (169-174).
We studied the dependence of porous silicon (PS) morphology on fabrication conditions and the link between morphology, porosity and optical properties. P-type (1 0 0) silicon wafers with resistivity of 10 Ω cm were electrochemically etched in a HF:ethanol:water mixture at various HF concentrations and current densities. Porosity and thickness of the samples were determined gravimetrically. Detailed information about evolution of porous silicon layer morphology with variation of preparation conditions was obtained by scanning electron microscope (SEM), the presence of silicon nanoparticles was confirmed by high resolution transmission electron microscopy. Decrease of the mean size of silicon nanoparticles with increasing porous silicon porosity was revealed in a monotonous blue shift of photoluminescence (PL) maximum in room temperature photoluminescence spectra of studied samples. This blue shift is consistent with quantum confinement model of photoluminescence mechanism. We observed that total porosity of porous films cannot fully explain observed photoluminescence behavior and correct interpretation of the blue shift of photoluminescence spectra requires detailed knowledge of porous silicon morphology.
Keywords: Porous silicon; Photoluminescence; Quantum confinement; Scanning electron microscopy; High resolution transmission electron microscopy;
Heating-sol–gel template process for the growth of TiO2 nanorods with rutile and anatase structure by Lei Miao; Sakae Tanemura; Shoichi Toh; Kenji Kaneko; Masaki Tanemura (175-179).
Densely assembled nanorods consist of the nanoparticles of rutile and those of anatase have been fabricated successfully by a heating-sol–gel template process, respectively. The size of nanorods varies as a diameter of 100–300 nm and a length of several micrometers, which are controllable by the pore size of the template. The similarities and/or differences of the fabricated process and microstructure for rutile and anatase nanorods were discussed. TEM image revealed that anatase nanorods are the aggregates of many indistinct polygonal nanoparticles up to ∼10 nm in diameter, while rutile nanorods are the aggregates of irregular octagon and/or hexagon nanoparticles in 10–30 nm diameter. XRD, ED and HRTEM lattice image confirmed the nanorods fabricated by the heating-sol–gel process are well assembled by many individual nanoparticles. The nanoparticles in rutile nanorods were larger than those in anatase nanorods possibly due to the different heat-treatment procedure.
Keywords: Heating-sol–gel template process; Nanorods synthesis; Titanium dioxide; TEM analysis; Chemical composition;
Structural and morphological properties of Cu(In, Ga)Se2 thin films on Mo substrate by R. Caballero; C. Guillén (180-183).
The objective of this work was to study the structural and morphological properties of Mo/Cu(In, Ga)Se2 thin films deposited onto glass substrate by different techniques and thermal treatment in different atmospheres. Electron beam evaporated Mo thin film was better back contact than the sputtered Mo film due to the structural improvements of CIGS film deposited on it. It was also observed that an increase of the grain size and a better morphology for Ar selenized CIGS films than for the vacuum ones. These results could lead to a decrease of the number of defects for Ar selenized CIGS films on evaporated Mo, which could imply an enhancement of the solar cell efficiency.
Keywords: Cu(In, Ga)Se2; Mo; Selenization; Structural properties; Morphological properties;
Characterization of copper selenide thin films deposited by chemical bath deposition technique by Al-Mamun; A.B.M.O. Islam (184-188).
A low-cost chemical bath deposition (CBD) technique has been used for the preparation of Cu2−x Se thin films onto glass substrates and deposited films were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV–vis spectrophotometry. Good quality thin films of smooth surface of copper selenide thin films were deposited using sodium selenosulfate as a source of selenide ions. The structural and optical behaviour of the films are discussed in the light of the observed data.
Keywords: AFM; CBD; Copper selenide; XPS; XRD;
Homo-epitaxial growth of rutile TiO2 film on step and terrace structured substrate by Y. Yamamoto; Y. Matsumoto; H. Koinuma (189-192).
The atomically finished rutile TiO2 (1 0 1) substrate was obtained by an appropriate surface cleaning and subsequent annealing of commercially available single crystals. The morphology, composition and crystallinity of the ultrasmooth surface were confirmed by an atomic force microscope (AFM), an X-ray photoelectron spectroscopy (XPS) and a reflection-high-energy-electron diffraction (RHEED), respectively. The optimum process for obtaining the ultrasmooth surface was found to be the annealing at the temperature of 700 °C for 1 h in air after the ultrasonic cleaning immersing in organic solvents and subsequent 20% HF water solution. Furthermore, the homo-epitaxial growth on the ultrasmooth substrate was performed and compared with the hetero-epitaxial growth of TiO2 film on a stepped α-Al2O3 (1 0 1 ̄ 2) substrate.
Keywords: Rutile; TiO2 (1 0 1); Step and terrace; Ultrasmooth surface; Homo-epitaxial growth; Hetero-epitaxial growth; α-Al2O3 (1 0 1 ̄ 2);
Effect of UV irradiations on the structural and optical features of porous silicon: application in silicon solar cells by S. Aouida; M. Saadoun; M.F. Boujmil; M. Ben Rabha; B. Bessaı̈s (193-198).
The aim of this paper is to investigate the structural and optical stability of porous silicon layers (PSLs) planned to be used in silicon solar cells technology. The PSLs were prepared by a HNO3/HF vapor etching (VE) based method. Fourier transform infrared (FT-IR) spectroscopy shows that fresh VE-based PSLs contain NH and SiF bonds related to a ammonium hexafluorosilicate (NH4)2SiF6 minor phase, and conventional SiH x and SiO x bonds. Free air exposures of PSLs without and with UV irradiation lead to oxidation or photo-oxidation of the porous layer, respectively. FT-IR characterisation of the PSLs shows that UV irradiations modify the transformation kinetics replacing instable SiH x by SiO x or SiOH bonds. When fresh PSLs undergo free air oxidation within 7 days, the surface reflectivity decreases from 10 to about 8%, while it drops to about 4% when a 10 min free air UV irradiation is applied. Long periods of free air oxidation do not ensure the reflectivity to be stable, whereas it becomes stable after only 10 min of UV irradiation. This behaviour was explained taking into account the kinetic differences between oxidation with and without UV irradiation. Fresh VE-based PSLs were found to improve efficiently the photovoltaic (PV) characteristics of crystalline silicon solar cells. The passivating action of VE-based PSLs was discussed. An improvement of the PV performances was observed solely for stable oxidized porous silicon (PS) structures obtained from UV irradiations.
Keywords: Porous silicon; Infrared spectra; Reflectivity; Silicon solar cells;
Silicon dissolution regimes from chemical vapour etching: from porous structures to silicon grooving by A.Ben Jaballah; M. Saadoun; M. Hajji; H. Ezzaouia; B. Bessaı̈s (199-203).
A new method of silicon grooving is developed based on chemical vapour etching (CVE) of silicon substrates. The CVE consists of exposing silicon wafers to acid vapours issued from a mixture of HF and HNO3. It was found that CVE of silicon results in the formation of Porous Silicon (PS). However, we noticed that, depending on the volume ratio of HF/HNO3, PS may transform in a white powder essentially composed of (NH4)2SiF6. It was shown that PS is a major phase above a volume ratio of 9:1, while the (NH4)2SiF6 phase becomes major at HF/HNO3 ranging between 2:1 and 4:1. The structural differences between PS and the (NH4)2SiF6 white powder was investigated by Fourier transformation infrared (FTIR) spectroscopy. The formation kinetics of the (NH4)2SiF6 white powder was found to depend on both acid mixture and silicon substrate temperatures. The high solubility of the (NH4)2SiF6 white powder enables us to groove silicon at different depth, with an accuracy of 0.2 μm. This grooving technique could be introduced in microelectronic engineering as well as for buried metal contact in solar cells processing.
Keywords: Porous silicon; Etching; Grooving;
Quantum Hall effect devices based on AlGaAs/GaAs structures studied by photoreflectance spectroscopy by L. Zamora-Peredo; M. López-López; Z. Rivera; A. Guillén; A.G. Rodrı́guez-Vázquez; G. Ramı́rez-Flores; A. Lastras-Martı́nez; V.H. Méndez-Garcı́a (204-208).
The optical properties of MBE-grown quantum Hall effect devices have been studied by photoreflectance spectroscopy (PR) at different temperatures. The room temperature PR spectra show two typical signals around 1.42 and 1.85 eV attributed to the energy band edges of GaAs and AlGaAs, respectively. Between the former band edge transitions broad oscillations (BO) are observed. 15 K PR spectra from samples and photoluminescence spectroscopy reveal that a component of the BO is originated from the surface quantum well (SQW) created by the AlGaAs–GaAs–vacuum discontinuity. This signal experience a blue shift when the GaAs is gradually etched-off in good agreement with the PR spectra behavior from SQWs previously reported. Besides, PR measurements were performed at low temperatures. In this process, the near-surface band bending of the structures is virtually flattened during the cooling procedure. We observed a signal whose intensity decreased as the temperature is lowered. Therefore, the former results suggest that BO consist in two superimposed signals coming from the SQW and the electric field cap region.
Keywords: Photoreflectance; Optical properties; Surface quantum wells; Quantum Hall effect; High electron mobility transistor;
Energy transfer in PbS quantum dots assemblies measured by means of spatially resolved photoluminescence by N.O. Dantas; A.F.G. Monte; Fanyao Qu; R.S. Silva; P.C. Morais (209-212).
PbS nanocrystals embedded in glasses have been considered as inexpensive and robust materials for optical communication and photonics applications. PbS quantum dots (QDs) embedded in S-doped oxide glass matrix were synthesized by means of fusion method using three different annealing times (3, 5, and 12 h). Measurements of photoluminescence (PL) and micro-PL have been carried out as a function of the sample temperature. A large redshift in the PL emission is found by increasing the annealing time, which indicates an increase of QD size. To evaluate the coupling-strength between PbS quantum dots, spatially resolved PL has been performed. The energy-dependent transfer rate of excitons from smaller to larger dots via electronic coupling is observed. Based on these findings, we anticipate that further improvements in size selectivity, luminescence quantum yield, and controlled growth will permit highly efficient energy flows in nanocrystals.
Keywords: Nanocrystals; Quantum dots; Energy transfer;
Polaronic states in II–VI quantum dot by M. Triki; S. Jaziri (213-217).
In self-assembled quantum dots, the strong electron–phonon interaction should lead to some polaron effects in optical spectra (absorption and Raman scattering). We study the influence of the longitudinal optical phonons on polaron formation in CdS/ZnS self-assembled quantum dots.
Keywords: Polaronic states; Self-assembled quantum dots; Electron–phonon interaction;
Deposition of phospholipid layers on SiO2 surface modified by alkyl-SAM islands by R. Tero; M. Takizawa; Y.J. Li; M. Yamazaki; T. Urisu (218-222).
Formation of the supported planar bilayer of dipalmitoylphosphatidylcholine (DPPC) on SiO2 surfaces modified with the self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) has been investigated by atomic force microscopy (AFM). DPPC was deposited by the fusion of vesicles on SiO2 surfaces with OTS-SAM islands of different sizes and densities. The DPPC bilayer membrane formed self-organizingly on the SiO2 surface with small and sparse OTS islands, while did not when the OTS islands were larger and denser. The relative size between the vesicles and the SiO2 regions is the critical factor for the formation of the DPPC bilayer membrane.
Keywords: Self-assembly; Bilayer; Phospholipid; Fusion; Atomic force microscopy; Silicon oxides;
Molecular dynamics simulation of Cu cluster deposition on Au(0 0 1) surfaces by J.C. Jiménez-Sáez; A.M.C. Pérez-Martı́n; J.J. Jiménez-Rodrı́guez (223-227).
The deposition of Cu clusters (a few monolayers) on an Au(0 0 1) surface has been simulated by molecular dynamics. The bombardment energies were 0.25, 0.5 and 1 eV/atom. The growth effects for different cluster structures have been investigated. Cu and Au crystals have been chosen since they show a great misfit in their lattice parameters (12.8%). The behaviour of the atomic distances at the interface has been analysed and mean changes in the lattice parameters have been quantified. Pseudomorphic growth (gradual adaptation of the in-plane atomic distances) took place only in the bombardments with higher energy. The cluster lateral size has also influence for intermediate energies. A study of induced defects and atomic mixing at the interface has been also accomplished.
Keywords: Molecular dynamics; Cluster deposition; Metallic Cu/Au interfaces;
First principles simulations of Cu and Au deposition on α-Al2O3 (0 0 0 1) surface by Norge Cruz Hernández; Javier Fdez. Sanz (228-232).
A theoretical study of the interaction between single gold atoms and the regular Al-terminated α-Al2O3 (0 0 0 1) surface is reported. The surface is simulated by means of periodic slabs and the calculations have been undertaken within the density functional theory using a generalized gradient approach (GGA). For the metal adsorption five different sites have been considered, two on top of Al and O atoms, and three on hollow positions in which the transition metal binds three surface O atoms. Adsorption energy is found to be in the range between 0.39 and 0.81 eV, the preferred site being on top of surface oxygen atoms in contrast with the results obtained for Cu adsorption, where the preferred site was a hollow position with an Al atom underlying in the subsurface plane. Although for both Cu and Au a noticeable contribution to the adsorption energy from the surface relaxation is observed, the analysis of density of states plots and electron density differences suggest a change in the metal-surface bonding mechanism.
Keywords: Gold; Adsorption kinetics; Aluminium oxide; Density functional calculations;
In situ GISAXS study of the growth of Pd on MgO(0 0 1) by F. Leroy; C. Revenant; G. Renaud; R. Lazzari (233-237).
The morphology of growing Pd nano-particles on MgO(0 0 1) surfaces have been investigated in situ, during growth, by grazing incidence small angle X-ray scattering, for different substrate temperatures. The 2D patterns obtained are quantitatively analyzed, and the average morphological parameters (shape, size) deduced. Above 650 K, the aggregates adopt their equilibrium shape of truncated octahedron, and the interfacial energy is deduced.
Keywords: Morphology; Pd nano-particles; GISAXS; Growth; Pd/MgO(0 0 1) interface;
Deposition of 10-undecenoic acid self-assembled layers on H–Si(1 1 1) surfaces studied with AFM and FT-IR by Y.J. Li; R. Tero; T. Nagasawa; T. Nagata; T. Urisu (238-241).
Self-assembling layers of 10-undecenoic acid (UA) were deposited on H-terminated Si(1 1 1) surfaces and characterized with atomic force microscopy (AFM) and Fourier-transform infrared (FT-IR) spectroscopy measurements for the first time. The unique island structures are deposited by layer-by-layer growth mechanism. The IR spectra suggest that the multilayers grown over the first monolayer are deposited by weak intermolecular interactions such as Van der Waals force and hydrogen bonding.
Keywords: 10-Undecenoic acid; Self-assembled layers; AFM; FT-IR; Si(1 1 1);
Numerical simulation of surface deformation and residual stresses fields in laser shock processing experiments by J.L. Ocaña; M. Morales; C. Molpeceres; J. Torres (242-248).
Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical surface treatments for improving fatigue, corrosion and wear resistance of metals, and has recently been developed as a practical process amenable to production engineering.Although valuable experimental work has been performed exploring the capability of the technique to provide enhanced mechanical properties, an important lack of work exists on the theoretical predictive assessment of the required process parameters.In this paper, a model is presented able to provide a predictive estimation of the residual stresses and surface deformation induced by laser action relevant for the analysis the influence of the different parameter in the process. Special emphasis will be posed on the part of the model devoted to the analysis of the solid material mechanical behaviour under the surface pressure pulse exerted by the expansion of the laser generated plasma.With the aid of the model, the influence of pulse duration, pulse pressure peak, spot radius, number of shots, overlapped shots and material properties have been analyzed. The great influence of 3D deformation effects in the process is clearly shown as one of the most important limiting factors of the process traditionally neglected in previous literature.
Keywords: Laser shock processing; Surface treatment; Shock waves; Residual stress; Numerical modeling;
Deformation behaviour induced by point defects near a Cu(0 0 1) surface by M. Said-Ettaoussi; J.C. Jimenez-Saez; A.M.C. Perez-Martin; J.J. Jimenez-Rodriguez (249-253).
In order to attain a satisfactory understanding of many of the properties of metallic surfaces, it is necessary to take into account the distorting effect of self-interstitials and vacancies. The present work is focused on the study of the behaviour of neighbouring atoms around point defects. The conjugate gradient method with an empiric many-body potential has been used to study the point defect–surface interaction. Point defects have been generated at several depths under a Cu(0 0 1) surface and then the whole system driven to the minimum energy state. The displacement field has been obtained in the vicinity to the defect. An energetic analysis is also carried out calculating formation and migration energies.
Keywords: Displacement field; Formation and migration energies; Point defects in Cu(0 0 1);
Study of interfacial properties and its effect on magnetization behaviour of Fe/Ni multilayer structure by Rachana Gupta; Ajay Gupta; S.M. Chaudhari; Mukul Gupta; P. Allenspach (254-261).
This paper deals with the investigation of interfacial properties and their influence on magnetization behaviour of Fe/Ni multilayer (ML) structures. Two types of multilayer structures with nominal composition of [Fe(29 Å)/Ni(86 Å)]10 and [Fe(50 Å)/Ni(50 Å)]10 were prepared with e-beam evaporation technique under ultra high vacuum (UHV) conditions. Grazing incidence X-ray reflectivity (GIXRR) and X-ray diffraction (GIXRD) techniques have been employed to determine the micro-structural parameters and indicates formation of FeNi3 alloy phase at the interface. GIXRD measurements on as-deposited Fe50/Ni50 ML samples show highly textured growth and its structure remains the same upto annealing temperature of 350 °C. The magnetization behavior of the MLs has been obtained using extraction dc magnetometry. The M–H loops corresponding to the Fe50/Ni50 ML structure of as-deposited sample show gradual changes with applied field whereas the as-deposited Fe29/Ni86 ML shows a perfectly square loop. Upon annealing of the Fe29/Ni86 MLs upto 300 °C show change in the loop shape from square to the smoother one. This is mainly attributed to release of stress in deposited layer and the change in magnetostriction. However, square loops observed in this case at higher annealing temperature of 300 and 400 °C is result of magnetically soft FeNi3 phase formation at interface. On the other hand, Fe50/Ni50 ML samples annealed upto 400 °C show no change in the shape even though there is variation in HC values. The observed changes in the HC values are mainly attributed in this case to the different magnetostriction effects involved due to the increase in grain size with temperature.
Keywords: e-beam evaporation; Fe/Ni ML structure; Thermal study; Magnetization study co-relation with structure parameters;
Structure and interface properties of Mo/B4C/Si multilayers deposited by rf-magnetron sputtering by A. Patelli; J. Ravagnan; V. Rigato; G. Salmaso; D. Silvestrini; E. Bontempi; L.E. Depero (262-268).
Mo/Si multilayer mirrors with reflectance higher than 70% at 13 nm have been developed in last years by the introduction of diffusion barriers, but many physical aspects concerning their growth and interface formation need to be investigated. As a matter of fact knowing the growth kinetic, a tight control of the process can lead to a multilayer structure with sharp and smooth interfaces. The aim of the present work is to investigate the effects of the ion energy and flux on the growing surfaces during sputtering deposition of Mo/B4C/Si multilayers.The multilayers presented in this paper have been produced by static deposition in a UHV chamber equipped with three magnetron sputtering sources driven by rf power supplies. Ion energy has been varied by dc biasing the sample holder. Plasma diagnostic has been performed by Langmuir probe measurements in order to determine the Ar ion flux and energy impinging the growing film. The ion energy and flux effects on crystal structure have been investigated by XRD and μ-XRD. The effects on roughness and interfaces have been observed by XRR measurements. Clear dependence of Mo nano-crystal size, texture and interface smoothness on the deposition parameters is pointed out. XRD analyses have been used for a Mo nano-crystal nucleation study in presence of the carbide buffer layer. Interface composition and structure is characterised by Rutherford backscattering (RBS) and nuclear reaction analysis (NRA).
Keywords: Mo/Si multilayers; X-ray mirrors; Diffusion barrier; Ion-assisted deposition; rf magnetron sputtering;
Membrane surface modification and characterization by X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements by M. Khayet (269-272).
Surface modifying macromolecules (SMMs) were used to modify the top surface of polymeric membranes. SMMs are oligomeric fluoropolymers synthesized by polyurethane chemistry and tailored with fluorinated end groups. In this study, the surface of polyetherimide (PEI) flat-sheet membranes prepared by the phase inversion method was modified using 2 wt.% of SMM and 15 wt.% PEI concentration in the polymer casting solution. The effect of solvent evaporation time on membrane surface modification was investigated. X-ray photoelectron spectroscopy analysis shows enrichment of fluorine on the modified PEI membrane surfaces and their contact angles were higher than those of the unmodified PEI membrane. Both the surface fluorine content and contact angles of the SMM/PEI blended membrane increased when the solvent evaporation time was increased up to 5 min. The SMM modified and unmodified PEI membranes were characterized by means of tapping mode atomic force microscopy (TM-AFM). The mean pore size, nodule size, pore density, surface porosity and mean roughness of the modified membranes were determined and compared with those of the unmodified membrane.
Keywords: Membrane surface modification; Surface properties; XPS; AFM; Contact angles;
Variability between chitosan membrane surface characteristics as function of its composition and environmental conditions by A. Larena; D.A. Cáceres (273-277).
The object of the present work is investigate the morphological modifications of several composition chitosan films, due to components concentration changes, under temperature and relative humidity controlled conditions. For the surface analysis study results obtained by conventional optical and polarization microscopies so as UV–vis spectroscopy are used. Different capacity adsorption of different chitosan membranes introduce changes in thermo-mechanical properties.
Keywords: Surface analysis; Microscopy; Chitosan membranes;
Advanced generation of green conversion coatings for aluminium alloys by M. Bethencourt; F.J. Botana; M.J. Cano; M. Marcos (278-281).
Anticorrosive cerium based treatments have been proved as efficient green alternatives to those based on environmentally undesirable Cr(VI) compounds. Thus, full immersion in cerium salt solutions allows reaching similar protection level against aluminium alloys corrosion that chromates treatments. However, treatment time is too high for being considered in industrial applications.In this work, accelerated methods for obtaining cerium-rich conversion coatings on aluminium–magnesium alloys are proposed. The films developed have been characterised by SEM and EDS. These studies have revealed that the coatings have a mixed or heterogeneous nature, being composed of a layer of alumina covering the matrix, together with islands of cerium formed over the cathodic intermetallics that are present on the surface of the alloy. Furthermore, studies conducted employing electrochemical techniques indicate that the degree of protection provided by these coatings is several orders of magnitude superior to that achieved with other treatments.
Keywords: Corrosion; Aluminium alloys; Conversion coatings; Cerium; Green treatments;
Organization of copper-phthalocyanine molecules on mono-molecular organic buffer layers by Daisuke Takajo; Takashi Nemoto; Hiroyuki Ozaki; Yasuhiro Mazaki; Seiji Isoda (282-287).
After 17,19-dotetracontadiyne (DTDY) mono-molecular layer was formed onto highly ordered pyrolytic graphite by vacuum deposition, copper-phthalocyanine (CuPc) was successively deposited on the DTDY layer. Depending on the coverage of CuPc molecules on the DTDY layer, the CuPc changed in their aggregation states. When a small amount of CuPc molecule was deposited, one-dimensional alignment of CuPc molecules was formed along a line of the DTDY columnar axis. With increasing the amount of deposited CuPc, two-dimensional domains were formed and exhibit the point-on-line coincidence with respect to the underlying DTDY layer. The one-dimensional alignment of CuPc was observed also along a column axis of the n-tetratriacontane mono-molecular layer prepared in the same way.
Keywords: One-dimensional array; Organic buffer layer; Point-on-line; Molecular organization;
Microstructure and mechanical properties of ceramic coatings on Ti and Ti-based alloy by B. Surowska; J. Bieniaś; M. Walczak; K. Sangwal; A. Stoch (288-294).
Results of a study of silica and silica–titania sol–gel coatings for the creation of intermediate interfaces between commercially pure Ti or titanium alloy Ti6Al4VELI and dental porcelain are presented. Coatings of SiO2 on Ti6Al4V alloy and SiO2–TiO2 on Ti were deposited using sol–gel method. Surface microstructures and wear behaviour of the coatings were studied by using scanning electron microscopy with electron diffraction spectroscopy and pin-on-disc method. It is found that (1) Ti6Al4V/SiO2 and Ti/SiO2–TiO2 coatings obtained by the sol–gel method are compact, chemically homogeneous and relatively rough, and (2) the smaller wear of SiO2 coatings than that of SiO2–TiO2 coatings is associated with differences in their microstructure and roughness.
Keywords: Titanium; Ceramic coatings; Sol–gel process; Pin-on-disc; Surface morphology;
Molecular-scale structure fabrication at liquid/solid interfaces by Daisuke Takajo; Takashi Nemoto; Hiroki Kurata; Seiji Isoda (295-298).
Nano-fabrication of organic molecules at liquid/solid interfaces is a promising method to form nano-structures of thermally unstable molecules on surfaces. Perylene-3,4,9,10-tetracarboxylic-dianhydride mono-molecular layer was formed on HOPG (0001) surface by vacuum-deposition as a canvas layer for nano-fabrication. After a droplet of 1-octylbenzene solution of 3-imino-4,5,6,7-tetrachloroisoindolin-1-one (ITCII) was placed on the surface, an STM tip was inserted into the droplet and a part of the canvas layer was scratched by the STM tip by increasing tunneling current. The scratched area was found to be immediately covered by ITCII molecules. In such way, ITCII mono-molecular layer with a designed shape could be fabricated. Structures of the formed layer are discussed in comparison to that of freely adsorbed layer.
Keywords: Nano-fabrication; Liquid/solid interface; Surface; Organic molecules; STM;
Spontaneous aggregation of lipids in supported membranes with geometrical barriers by Tae-Young Yoon; Cherlhyun Jeong; Joon Heon Kim; Myung Chul Choi; Mahn Won Kim; Sin-Doo Lee (299-303).
We report on a spontaneous aggregation of specific lipids in a supported membrane with geometrical barriers. When two types of lipids with different effective molecular shapes, correspondingly different spontaneous curvatures, are mixed in a supported membrane, the lipids with a nonzero spontaneous curvature spontaneously aggregate at the geometrical barriers so as to relax the free energy increase resulting from elastic distortions. Further we have found that this spontaneous aggregation is attained without disturbing the physical properties of the supported membrane such as the lateral fluidity. The results show that the geometrical barriers introduced of the solid support provide a viable patterning technique in a supported membrane depending on the particular molecular shapes.
Keywords: Lipid bilayer; Supported membrane; Surface patterning; Biosensors;
High value carbon materials from PET recycling by J.B. Parra; C.O. Ania; A. Arenillas; F. Rubiera; J.J. Pis (304-308).
Poly(ethylene) terephthalate (PET), has become one of the major post-consumer plastic waste. In this work special attention was paid to minimising PET residues and to obtain a high value carbon material. Pyrolysis and subsequent activation of PET from post-consumer soft-drink bottles was performed. Activation was carried out at 925 °C under CO2 atmosphere to different burn-off degrees. Textural characterisation of the samples was carried out by performing N2 adsorption isotherms at −196 °C. The obtained carbons materials were mainly microporous, presenting low meso and macroporosity, and apparent BET surface areas of upto 2500 m2 g−1. The capacity of these materials for phenol adsorption and PAHs removal from aqueous solutions was measured and compared with that attained with commercial active carbons. Preliminary tests also showed high hydrogen uptake values, as good as the results obtained with high-tech carbon materials.
Keywords: Carbon materials; Plastic waste; Adsorption; H2 storage;
Porous texture of activated carbons prepared by phosphoric acid activation of woods by M.A. Dı́az-Dı́ez; V. Gómez-Serrano; C. Fernández González; E.M. Cuerda-Correa; A. Macı́as-Garcı́a (309-313).
Activated carbons (ACs) have been prepared using chestnut, cedar and walnut wood shavings from furniture industries located in the Comunidad Autónoma de Extremadura (SW Spain). Phosphoric acid (H3PO4) at different concentrations (i.e. 36 and 85 wt.%) has been used as activating agent. ACs have been characterized from the results obtained by N2 adsorption at 77 K. Moreover, the fractal dimension (D) has been calculated in order to determine the AC surface roughness degree. Optimal textural properties of ACs have been obtained by chemical activation with H3PO4 36 wt.%. This is corroborated by the slightly lower values of D for samples treated with H3PO4 85 wt.%.
Keywords: Porous texture; Chemical activation; Fractal dimension;
Synthesis and application of hydroxyapatite/polylactide composite biomaterial by Nenad Ignjatovic; Dragan Uskokovic (314-319).
Hydroxyapatite/bioresorbable-polymer composite biomaterials can be used for the bone tissue reconstruction. There are different methods to obtain hydroxyapatite/poly-l-lactide (HAp/PLLA) composite biomaterial, but up to now only hot pressing and forging have been successfully used to produce blocks with mechanical properties similar to the natural bone tissue. By dissolving PLLA polymer mixed with HAp, highly porous HAp/PLLA composite biomaterial was obtained. A wide spectrum of blocks with different properties was produced by hot pressing, varying the pressing parameters. HAp/PLLA blocks were implanted into mice (intraperitoneally) and after implantation, the phenomenon was studied histopathologically and by FT-IR spectroscopy. The obtained composite biomaterial blocks have a compressive strength of up to 140 MPa and elasticity module of up to 10 GPa. After implantation, good adhesion of the surrounding tissue on the surface of the implant as well as its integration indicate high degree of its biocompatibility.
Keywords: Hydroxyapatite/poly-l-lactide; Structure designing; Hot pressing; Mechanical properties; In vitro and in vivo research;
Synthesis and characterization of lanthanum incorporated mesoporous molecular sieves by C. Pesquera; F. González; C. Blanco; L. Sanchez (320-323).
A series of mesoporous materials under reflux conditions have been synthesized with two silicon sources (fumed silica and sodium silicate) and lanthanum added. The following Si/La molar ratio was used in the samples: 100; 75; 50 and 25. The calcined products were characterized by means of X-ray diffraction, nitrogen adsorption isotherms and energy dispersive X-ray spectrometry (EDS). The BET surface area gradually decreases with an increase in the lanthanum content of the LaxMCM-41 samples. Moreover, the average pore size tends to decrease along with the increase in the La content in the samples.
Keywords: Mesoporous sieves; Lanthanum incorporation MCM-41; Adsorption properties;
3D imprint technology using substrate voltage change by Jun Taniguchi; Masamichi Iida; Takayuki Miyazawa; Iwao Miyamoto; Kiyoshi Shinoda (324-330).
Spin-on-glass (SOG) is used as an electron beam (EB) resist whose depth is controlled by changing the EB acceleration voltage. Exposed SOG area and depth were developed with only 1 EB exposure using buffered hydrofluoric acid (BHF), yielding a three-dimensional (3D) SOG mold. Two acceleration voltage changes were used, i.e., changing the EB gun bias and changing the substrate voltage. When the EB gun bias was changed, patterned depth increased linearly by increasing with acceleration voltages and depth deviations of each acceleration voltages were within ±3%. The width resolution was 125 nm on SOG using a 100 nm EB diameter and the depth resolution was 10 nm per 100 V of acceleration voltage change. When the substrate voltage was changed, the relationship between the apparent acceleration voltage and pattern depth almost coincided with the change in EB gun bias, and the deviation in acceleration voltage was within ±4.4%. The depth gradation resolution limit was less than 10 nm changing the substrate voltage. Imprinted patterns were transferred by pressing the fabricated 3D SOG mold onto photocurable resin at 0.5 MPa and curing with a 1 J/cm2 ultraviolet dose. Transferred patterns of photocurable resin were faithful and multigradational, corresponding to the mold pattern and attaining both 10 nm mold depth resolution and 10 nm transfer resolution.
Keywords: Nanoimprint lithography; Electron beam lithography; Spin-on-glass; Three-dimensional surface fabrication; Acceleration voltage;
Polycrystalline SiC growth and characterization by C. Ricciardi; E. Aimo Boot; F. Giorgis; P. Mandracci; U.M. Meotto; G. Barucca (331-335).
Growth of 3C–SiC on (1 0 0) Si wafers has been carried out by low pressure chemical vapor deposition (LPCVD), using a H2 + SiH4 + C3H8 gas mixture at about 1000 °C. No carbonization layer was performed. Micro-Raman measurements yield the presence of microcrystalline SiC matrix, while neither carbon nor silicon clusterization in amorphous phase was detected with optimized deposition conditions. Transmission electron microscopy has been used to analyze the orientation of the films and the surface growth: the presence of voids and edge dislocations at the interface was revealed.
Keywords: SiC; Raman spectroscopy; TEM; MEMS;
Plasma-assisted SiC oxidation for power device fabrication by P. Mandracci; S. Ferrero; S. Porro; C. Ricciardi; G. Richieri; L. Scaltrito (336-340).
In this work we show a plasma-assisted process for the deposition of good quality a-SiO2 layers on 4H–SiC as a possible alternative to thermal oxidation. We used the plasma enhanced chemical vapor deposition (PECVD) technique for the growth of a-SiO2 layers on 4H–SiC using SiH4 and CO2 as precursor gases in H2 dilution. We showed that good quality oxide layers could be obtained by this method, with a growth rate varying from 1.3 to 2.1 Å/s, depending on the RF power. An estimation of the interface charge was obtained by high frequency capacitance voltage (HFCV) characteristic, obtaining values comparable to the ones typical of thermally grown oxides. This process was used for the growth of a-SiO2 insulating and protecting layers in the fabrication of Schottky diodes based on 4H–SiC, obtaining a breakdown voltage higher than 600 V.
Keywords: Silicon oxide; Silicon carbide; PECVD;
Evaluation and quantification of reprocessing modification in single-use devices in interventional cardiology by Francesco Tessarolo; Paolo Ferrari; Bortoluzzi Silvia; Antonella Motta; Claudio Migliaresi; Lucio Zennaro; Adelio Rigo; Giovanni Maria Guarrera; Giandomenico Nollo (341-346).
The increasing demand in interventional cardiology urges for reprocessing of single-use-labelled medical devices. To fulfil this aim, accurate and validated regeneration protocols are mandatory to guarantee sterility, functionality and safeness. The reprocessing protocol was realized by decontamination with chloro-donors, cleaning with enzymatic solutions and hydrogen peroxide gas plasma sterilization. Reprocessing effects on ablation and electrophysiology catheters were evaluated by assessing physical–chemical changes on surfaces and bulks, as a function of the reprocessing cycles number. Conventional optical microscopy and environmental scanning electron microscopy (ESEM) underlined the presence of micro-scratches on the polyurethane shaft surface. A clear correlation was found between surface damages and number of reprocessing cycles. Atomic force microscopy (AFM) confirmed the occurrence of physical–chemical etching of the polyurethane shaft caused by the hydrogen peroxide plasma sterilization, with increasing of nano-roughness at increasing number of the reprocessing cycles. UV–Vis spectra performed on the incubation solution of polymeric shaft sample, showed an absorbance increase at about 208 nm. This fact could be attributed to the water elution from the polymer of low molecular weight oligomers. The presence of hydrolysis products of the polymeric shaft after incubation demands both the characterization of the products released in the solution and the chemical characterization of the water exposed surface.
Keywords: Reprocessing; Disposable device; Plasma sterilization;
Preparation of activated carbons from bituminous coal pitches by J. Gañan; C.M. González-Garcı́a; J.F. González; E. Sabio; A. Macı́as-Garcı́a; M.A. Dı́az-Dı́ez (347-354).
High-porosity carbons were prepared from bituminous coal pitches by combining chemical and physical activation. The chemical activation process consisted of potassium hydroxide impregnation followed by carbonization in nitrogen atmosphere. The effect of the KOH impregnation ratio on the surface area and pore volumes evolution of the carbons derived from mesophase pitch was studied. The optimum KOH:pitch ratio was fixed to realize a physical activation process in order to increase the textural parameters of the KOH-activated carbons. Physical activation was performed by carbonizing the KOH-activated carbons followed by gasifying with air. The influence of the carbonization temperature and the residence time of the gasification with air were explored to optimize those preparation parameters.
Keywords: Pitch; Anisotropic phase; Chemical activation; Physical activation; Activated carbons;
Well-aligned Co-filled carbon nanotubes: preparation and magnetic properties by Radinka Kozhuharova; Manfred Ritschel; Dieter Elefant; Andreas Graff; Albrecht Leonhardt; Ingolf Mönch; Thomas Mühl; Stefka Groudeva-Zotova; Claus M. Schneider (355-359).
Carpet-like flakes (area ≤ 9 mm2; thickness < 50 μm) of well-aligned Co-filled multi-walled carbon nanotubes were grown by decomposition of cobaltocene. The nanotubes have outer diameters of 50–90 nm and a metal core of 15–30 nm diameter. They are discontinuously filled with f.c.c.-Co nanowires of up to a few micrometers in length. Magnetometry studies show a weak uniaxial magnetic anisotropy with the easy axis along the nanowires and a high coercivity of about 59 mT. Electron holography provides information about the magnetic characteristics of individual nanowires.
Keywords: Carbon nanotubes; Co nanowires; Magnetism;
Optical properties of metal and semiconductor SmS thin films fabricated by rf/dc dual magnetron sputtering by S. Tanemura; L. Miao; S. Koide; Y. Mori; P. Jin; A. Terai; N. Nabatova-Gabain (360-366).
Optical properties of both metal and semiconductor phases of SmS thin films on Si substrate grown at a room temperature by dual targets (dc for metal Sm and rf for pressed powdered chalcogenide Sm2S3) magnetron sputtering system with the concurrent adjustment of the applied power to respective target, were evaluated by SE at the photon energy range between 0.75 to 5.0 eV. This is the first work performed on the intrinsically prepared metallic sample while the former works done for the sample transformed from semiconductor to metal phase by hard polishing.The followings are concluded: (1) in the metallic film, the refractive indices n have maximum value of 2.20 at 4.10 eV, while extinction coefficient k decreases monotonically and reaches 0.03 at 5.0 eV. The absorption coefficient derived from the obtained k and the complex dielectric constant from n and k agree satisfactorily with those cited in the preceding literatures for the bulk samples; (2) in the case of semiconductor, the refractive indices n have the maximum 3.66 at 3.93 eV, while extinction coefficient k increase monotonically from 0 at 2.31 eV to 1.633 at 5.0 eV. The optical transition mode from valence to conduction band is difficult to determine as either indirect allowed or direct forbidden mode because of the insignificant difference between the linear behavior of the curves α 1/2 and that of α 2/3 (α: absorption coefficient) as a function of photon energy beyond 3.5 eV. Hence the optical band gap E g followed by indirect allowed mode and direct forbidden mode is given as 2.67 and 2.78 eV, respectively. The agreement between the derived dielectric constant and those in the preceding literatures for bulk semiconductors is not satisfactory.
Keywords: SmS thin films; Metallic phase; Semiconductor phase; Spectroscopic ellipsometry; Complex refractive indices;
Optical and structural properties of amorphous silicon–carbon films for optoelectronic applications by T. Stapinski; B. Swatowska; S. Kluska; E. Walasek (367-374).
The authors developed the RF plasma enhanced chemical vapour deposition method for preparation of a-Si:C:H films of potential optoelectronic properties. The films were obtained on glass and (0 0 1) Si in optimised technological parameters such as content of gaseous mixture of SiH4, and CH4, gas pressure, temperature and RF power density. The surface morphology, chemical composition, optical properties, chemical bonding structure, were investigated. The film structure and composition depended on process parameters and configuration. The results of optical investigations show that these materials are characterised by variable optical gap dependent on carbon content. In chosen conditions it is possible to produce material of optimal optical properties for solar application as antireflective and protective coatings for solar cells.
Keywords: Thin films; Amorphous silicon–carbon; Optical properties; CVD;
Comparison between optical techniques and confocal microscopy for defect detection on thin wires by Philip Siegmann; Luis Miguel Sanchez-Brea; Juan Carlos Martinez-Anton; Eusebio Bernabeu (375-379).
Conventional microscopy techniques, such as atomic force microscopy (AFM), scanning electron microscopy (SEM), and confocal microscopy (CM) are not suitable for on-line surface inspection of fine metallic wires. In the recent years, some optical techniques have been developed to be used for those tasks. However, they need a rigorous validation. In this work, we have used confocal microscopy to obtain the topography z(x,y) of wires with longitudinal defects, such as dielines. The topography has been used to predict the light scattered by the wire. These simulations have been compared with experimental results, showing a good agreement.
Keywords: Wires; Surface structures; Surface defects; Metallic surfaces;
Optical characterization of surfaces by robust reflectance determination based on air-gap interference by J.C. Martinez-Antón; J.A. Quiroga; R. González-Moreno; E. Bernabeu (380-384).
In this work we present an optical tool for characterizing the reflectance and polarimetric properties of surfaces. It uses only the image of the interference fringe pattern produced in a thin air-gap between the surface of interest and a glass surface acting as a reference. From only the contrast of the fringe pattern captured with a CCD we may obtain the reflectance of the surface, no need of measuring a reference beam. By taking two images with polarized light, we may get then the polarized reflectance R p and R s, but also the ellipsometric magnitude Δ, simply as a phase shift between fringes in p and s polarization. A sample of silicon with a thin layer of thermally grown silica is used to test the method.
Keywords: Photo-interferometric envelope analysis; Newton rings; Optical characterization; Spectrophotometry;
Determination of surface anchoring energies of liquid crystals by optical diffraction by Chang-Jae Yu; Jae-Hong Park; Sin-Doo Lee (385-389).
We propose a simple method of determining the surface anchoring energies of liquid crystals (LCs) in a binary grating structure. In the configuration of an alternating hybrid and homeotropic geometry, the director of the LC molecules is linearly deformed near domain boundaries according to the continuum theory. From the far-field optical diffraction formula for the phase profile in a form of a trapezoid, the extrapolation lengths, corresponding to the distorted lengths at a domain boundary, were obtained. The surface anchoring energies of the LCs are directly determined from the measured extrapolation lengths.
Keywords: Liquid crystal devices; Anchoring energy; Diffraction grating; Continuum theory;
Isomeric states of polar molecules on ionic surfaces: electrostatic model and FTIR studies by P.Yu. Storozhev; V.S. Yanko; A.A. Tsyganenko; G. Turnes Palomino; M. Rodrı́guez Delgado; C. Otero Areán (390-394).
Interaction of diatomic (polar) molecules with the surface of ionic solids is analysed by means of an electrostatic model which takes into account ion–dipole and ion–quadrupole interactions. This model was found to be capable of predicting the geometry of the adsorption complex, formation of isomeric states and relevant features of characteristic vibrational spectra. The theoretical model is demonstrated by considering the case of CO adsorbed on cation-exchanged zeolites for which a wealth of experimental data is available from both, vibrational spectroscopy and adsorption calorimetry. However, extension to other systems should be fairly straightforward.
Keywords: Electrostatic interactions; Isomeric states; Localized adsorption; Surface complexes; Vibrational spectroscopy;
Infrared characterization of strontium titanate thin films by B.G. Almeida; A. Pietka; J.A. Mendes (395-399).
Strontium titanate thin films have been prepared at different oxygen pressures with various post-deposition annealing treatments. The films were deposited by pulsed laser ablation at room temperature on Si(0 0 1) substrates with a silica buffer layer. Infrared reflectance measurements were performed in order to determine relevant film parameters such as layer thicknesses and chemical composition. The infrared reflectance spectra were fitted by using adequate dielectric function forms for each layer. The fitting procedure provided the extraction of the dielectric functions of the strontium titanate film, the silica layer and the substrate. The as-deposited films are found to be amorphous, and their infrared spectra present peaks corresponding to modes with high damping constants. As the annealing time and temperature increases the strontium titanate layer becomes more ordered so that it can be described by its SrTiO3 bulk mode parameters. Also, the silica layer grows along with the ordering of the strontium titanate film, due to oxidation during annealing.
Keywords: Strontium titanate; Infrared spectroscopy; Modeling;
Photoluminescence studies in highly Te-doped Ga1−x In x As y Sb1−y epitaxial layers grown on GaSb by liquid phase epitaxy by J. Diaz-Reyes; J.L. Herrera-Perez; M.L. Gomez-Herrera; J.A. Cardona-Bedoya; J.G. Mendoza-Alvarez (400-404).
GaSb-based semiconductors are being developed because of the possibility to grow materials with band-gap energies covering a substantial range of the medium infrared spectrum. In particular, GaInAsSb alloys can be grown epitaxially on GaSb and InAs substrates, resulting in semiconductor layers with band-gap energies in the range 0.8–4.3 μm. In this work we present results on the study of the influence of tellurium doping on the optical properties of Ga1−x In x As y Sb1−y epitaxial layers through the low temperature photoluminescence (PL) spectroscopy. These quaternary layers were grown by liquid phase epitaxy on high resistivity (1 0 0) GaSb substrates under lattice-matching conditions. PL measurements were carried out by exciting the sample with the 488 nm line of an Ar-ion laser and varying the exciting power in the range between 40 and 200 mW. All PL measurements were done at 15 K. Sample radiative emission was analyzed through an Acton monochromator and detected with an InSb infrared detector. The PL spectrum for the low-doped sample showed two emission bands corresponding to different bounded excitons and free-to-bound transitions; the assignation of each transition is accomplished by studying the behavior of the PL spectra with the excitation power. The increase in Te doping above the degeneracy limit results in the substantial broadening of the low temperature PL spectra. The individual lines due to the band-to-band transitions and band-to-acceptor transitions (A) completely overlap each other for those samples with the higher Te concentrations. Additionally, at very high Te concentrations, the luminescence band becomes highly asymmetric and shifts to higher energies, which is interpreted as due to a band-filling effect. We discuss these effects and their correlation to the free carrier density due to Te-doping.
Keywords: Semiconductor; Photoluminescence spectroscopy; Acton monochromator;
Physical characteristics and photoluminescence properties of phosphorous-implanted ZnO thin films by Chin-Ching Lin; San-Yuan Chen; Syh-Yuh Cheng (405-409).
ZnO films were implanted with phosphorus in the range from 5×1012 to 5×1015 cm−2. Effect of phosphorus concentration on structural characteristics and photoelectric behavior of phosphorus-implanted ZnO films under different atmosphere and annealing treatment was investigated. It has been demonstrated that below solubility (1.5×1018 ions/cm3), the defect formation will be dominated by annealing atmosphere and more defects can be formed in oxygen ambient than in nitrogen atmosphere as revealed from PL spectra. However, excess phosphorus doping, above solubility (1.5×1018 ions/cm3), will induce the formation of the phosphide compounds in ZnO films and seriously deteriorate the crystallinity and optical property of the films. However, a high-resistive but not p-type ZnO film is obtained by phosphorus doping.
Keywords: ZnO; Phosphorus implantation; Photoluminescence; Defect chemistry;
Mesoscopic modelling of the interaction of infrared lasers with composite materials: an application to human dental enamel by A. Vila Verde; Marta M.D. Ramos; Marshall Stoneham; R. Mendes Ribeiro (410-414).
The mesostructure and composition of composite materials determine their mechanical, optical and thermal properties and, consequently, their response to incident radiation. We have developed general finite element models of porous composite materials under infrared radiation to examine the influence of pore size on one of the determining parameters of the stress distribution in the material: the temperature distribution. We apply them to the specific case of human dental enamel, a material which has nanometer scale pores containing water/organic, and predict the maximum temperature reached after a single 0.35 μs laser pulse of sub-ablative fluence by two lasers: Er:YAG (2.9 μm) and CO2 (10.6 μm). For the Er:YAG laser, the results imply a strong dependence of the maximum temperature reached at the pore on the area-to-volume ratio of the pore, whereas there is little such dependence for CO2 lasers. Thus, CO2 lasers may produce more reproducible results than Er:YAG lasers when it comes to enamel ablation, which may be of significant interest during clinical practice.More generally, when ablating composite materials by infrared lasers researchers should account for the material’s microstructure and composition when designing experiments or interpreting results, since a more simplistic continuum approach may not be sufficient to explain differences observed during ablation of materials with similar optical properties or of the same material but using different wavelengths.
Keywords: Dental enamel; Laser ablation; Finite element modelling; Mesoscopic modelling; Er:YAG laser; CO2 laser;
Effect of radiation and thermal treatment on structural and transport parameters for cellulose regenerated membranes by M.I. Váquez; P. Galán; J. Casado; M.J. Ariza; J. Benavente (415-422).
Modifications caused by different types of ionizing radiation and thermal treatment on transport, chemical and structural parameters of polymeric (regenerated cellulose) membranes have been studied. Particularly, the effect of different types of radiation (ultraviolet light (UV) and ionising radiation (Ir) with different doses) and heating at 60 °C on transport and electrical parameters for a cellophane membrane has been considered by determining salt permeability and electrical resistance for the different samples. These parameters were obtained from salt diffusion and impedance spectroscopy (IS) measurements with the membranes in contact with NaCl solutions at different concentrations. Chemical surface and structural modifications of the polymer matrix due to the treatments have also been determined by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (ATR mode).Results obtained from infrared spectroscopy seem to indicate that ionising radiation modifies the proportion of OH links, which is related to the dose of irradiation. XPS analysis only shows small differences in the atomic concentration and shape of the C 1s spectra. On the other hand, an increase of salt permeability for heated and UV-treated membranes was obtained, while this parameter decreases in the case of irradiated membranes. This result could be related to a change in the packing of the polymer chains, which results in an increase of the fractional void volume in the case of heat- and UV-treated membranes and the opposite effect for the irradiated ones; for these latter, a correlation between the irradiation dose and the decrease in permeability values was also obtained. IS results show a decrease in the electrical resistance of all treated samples. This fact can be due to the most open structure of heated and UV-treated samples, previously indicated; however, due to the closer structure assumed for the irradiated sample, this point might be related to the presence of free radicals in agreement with ATR results.
Keywords: Membrane modification; ATR infrared spectra; XPS characterization; Salt diffusion; Electrical resistance;
Registration of heavy metal ions and pesticides with ATR planar waveguide enzyme sensors by Alexei Nabok; Saharudin Haron; Asim Ray (423-428).
The proposed novel type of enzyme optical sensors is based on a combination of SiO2/Si3N4/SiO2 planar waveguide ATR (attenuated total reflection) transducer, fabricated by standard silicon planar technology, with the composite polyelectrolyte self-assembled coating containing both organic chromophores and enzyme molecules. Such devices were deployed to monitor typical industrial and agricultural water pollutants, such as heavy metal ions and pesticides, acting as inhibitors of enzyme reactions. The sensitivity of registration of these pollutants in the range of 1 ppb was achieved. The use of different enzymes in the sensitive membrane provides a background for pattern recognition of the above pollutants.
Keywords: Attenuated total reflection; Planar waveguide; Enzyme reactions; Inhibition of enzyme activity; Heavy metal ions; Pesticides;
Interfacial microstructure and electrical properties of PT/Al2O3/Si annealed at high temperatures by San-Yuan Chen; Chi-Sheng Hsiao; Jung-Jui Hsu (429-432).
Pb1+x TiO3 (PT) thin films were deposited on Al2O3(10 nm)/Si using lead acetate trihydrate and titanium isopropoxide with the addition of glycerol (GL) chelating agent as precursors. It was found that perovskite PT phase can be well crystallized at a lower temperature of 600 °C and excellent memory properties are obtained. However, with increasing annealing temperature above 700 °C, charge-injection mode instead of ferroelectric behavior was detected. Cross-sectional TEM results illustrate that with an increase of annealing temperature and Pb content in the PT films, diffusion envelops and even composition separations were detected in the interface of PT/Al2O3/Si. It was believed that the degradation in the ferroelectric memory properties is strongly related to the change of microstructure and composition in the interface of PT/Al2O3/Si.
Keywords: PbTiO3/Al2O3/Si; Ferroelectric; Interfacial microstructure; Memory properties;
Characterization of pulsed plasma-ion streams emitted from RPI-type devices applied for material engineering by M.J. Sadowski; J. Baranowski; E. Skladnik-Sadowska; V.N. Borisko; O.V. Byrka; V.I. Tereshin; A.V. Tsarenko (433-437).
The paper reports on studies of pulsed plasma-ion streams generated by rod plasma injectors (RPI), and particularly by the IBIS device used for modifications of different materials. Measurements showed that the energy flux density can be from 5 to 25 J/cm2, and the corresponding pressure—from 0.5 to 2.5 bars. Spectroscopic measurements showed that the electron concentration (N e) amounts to (1.5–3.5)×1016 cm−3; and the electron temperature (T e)—to 1.5–6 eV. A study of the interaction of pulsed plasma streams with reversible getters (made of Zr50V50 alloys) showed that a shielding layer has an average density >1017 cm−3 and it reduces the transmitted energy flux considerably (to 30–60%), what makes possible the shielding of material surfaces.
Keywords: Plasma stream; RPI device; IONOTRON; Shielding layer; Reversible getter;
Effect of molecular properties on the performance of polymer light-emitting diodes by Marta M.D. Ramos; A.M. Almeida; Helena M.G. Correia; R.Mendes Ribeiro; A.M. Stoneham (438-443).
The performance of a single layer polymer light-emitting diode depends on several interdependent factors, although recombination between electrons and holes within the polymer layer is believed to play an important role. Our aim is to carry out computer experiments in which bipolar charge carriers are injected in polymer networks made of poly(p-phenylene vinylene) chains randomly oriented. In these simulations, we follow the charge evolution in time from some initial state to the steady state. The intra-molecular properties of the polymer molecules obtained from self-consistent quantum molecular dynamics calculations are used in the mesoscopic model. The purpose of the present work is to clarify the effects of intra-molecular charge mobility and energy disorder on recombination efficiency. In particular, we find that charge mobility along the polymer chains has a serious influence on recombination within the polymer layer. Our results also show that energy disorder due to differences in ionization potential and electron affinity of neighbouring molecules affects mainly recombinations that occur near the electrodes at polymer chains parallel to them.
Keywords: Modelling; Charge mobility; Recombination efficiency; Conducting polymer;
Morphological change of polycrystalline copper after ion irradiation followed by annealing by T. Hino; T. Taguchi; Y. Yamauchi; Y. Hirohata; M. Nishikawa (444-448).
For etchings of LSI and MEMS, a dry etching makes the process simple. In the present study, helium ion etching for polycrystalline copper was conducted, and after that the surface uniformity was examined. The irradiated surface showed unevenness with a roughness of sub-micron size, caused by growth of blisters. When the ion was injected obliquely to the surface, the roughness was reduced owing to the selective etching for the protuberance parts. However, the blisters still existed and the roughness was not significantly reduced. For the irradiated surface, annealing with temperature of 1000 K was conducted for the blisters to be ruptured. After the annealing, the blisters disappeared and the surface significantly became smooth. Thus, the ion irradiation followed by annealing can be recognized as a useful etching method.
Keywords: Ion etching; Copper; Surface roughness; Blister; Annealing;
Singular points of electrochemical impedance function by J.J. Garcı́a-Jareño; D. Giménez-Romero; F. Vicente (449-456).
A model of EIS response for a system with two consecutive monoelectron transfers is developed in this work. Relevant information on the mechanism of these electrochemical systems is provided by the parametrical identification of the theoretical faradaic impedance function. The kinetic parameters of this model are easily calculated through the calculus of the characteristic points of this function. This calculus allows to interpret the metals anodic dissolution according to the reaction mechanism and, therefore, allows us to establish easily the kinetic and thermodynamic behaviour of these systems with respect to any experimental parameter.
Keywords: EIS simulation; EIS fitting; Characteristics points and zinc anodic dissolution;
Ab initio calculations of the LaMnO3 surface properties by R.A. Evarestov; E.A. Kotomin; D. Fuks; J. Felsteiner; J. Maier (457-463).
We present the results of ab initio Hartree–Fock calculations of the LaMnO3 (0 0 1) and (1 1 0) polar surfaces. Using 7- and 8-plane slabs periodic in 2D along the x, y-axes, we compare the properties of a stoichiometric slabs with structural oxygen vacancies, and non-stoichiometric, defect-free slabs, analyze the dispersion of the effective charges near the surface, and calculate the surface energy, for both ferromagnetic and antiferromagnetic spin orderings in a slab.
Keywords: Surfaces and interfaces; Electronic band structure; Ab initio calculations; LaMnO3;
Surface segregation phenomena of solute elements in Al–Pb and Al–Fe dilute binary alloys by H. Tsubakino; A. Nogami; Y. Yamamoto; A. Yamamoto; M. Terasawa; T. Mitamura; A. Kinomura; Y. Horino (464-468).
Surface segregation of Pb in Al-0.13–13 at.-ppm Pb foils and Fe in Al-6–140 at.-ppm Fe foils after heat treatment was studied by Rutherford back-scattering spectroscopy (RBS) and transmission electron microscopy (TEM). The degree of segregation (segregated composition/foil composition) was greater than 1500 in the Al–Pb system but is less than 160 in the Al–Fe system. The maximum segregation temperature was 923 K in the Al–Pb system, but was 723 K in the Al–Fe system. Lead segregated not to the aluminum surface but to the oxide film. Iron, however, segregated at the aluminum surface, i.e., at the interface of the oxide film/aluminum matrix.
Keywords: Electrolytic capacitor; Surface segregation; Lead; Iron; Aluminum; RBS; TEM;
Characterisation of YAG:Ce powders thermal treated at different temperatures by G. Del Rosario; S. Ohara; L. Mancic; O. Milosevic (469-474).
Submicronic, spherical, polycrystalline YAG:Ce powders with luminescence properties were synthesised through aerosol processing route from the corresponding nitrates solution. Additional heat treatment was performed in the temperature range from 1000 to 1200 °C in order to increase the crystallinity of the obtained cubic garnet phase. SEM examination and subsequent morphological analysis allowed studying the surface properties and particle size distributions. An Image Processor was used to measure particle surface roughness. Quantitative SEM/EDS analysis indicated the synthesised materials present high purity and compositional homogeneity. TEM and selected area electron diffraction (SAED) showed a high crystallinity of the samples. XRD patterns of the powders were recorded in the region of 2θ = 10°–80°. The evolution of crystallite size was performed measuring of the broadening of a particular peak using the Scherrer equation. It was found that the crystallite size and bulk particles size vary with the applied temperature. The observed changes in function of the different thermal treatments were correlated with the photoluminescence (PL) properties of these materials.
Keywords: Aerosol; SEM/EDS; TEM; XRD; SAED; Luminescence;
Physical and rheological properties of petroleum fluids under the radio-frequency electromagnetic field effect and perspectives of technological solutions by L.A. Kovalyova; A.M. Khaydar (475-479).
Keywords: Petroleum fluids; Radio-frequency; Electromagnetic field;
A new drop-shape methodology for surface tension measurement by M.G. Cabezas; A. Bateni; J.M. Montanero; A.W. Neumann (480-484).
Drop-shape techniques, such as axisymmetric drop-shape analysis (ADSA), have been widely used to measure surface tension. In the current schemes, theoretical curves are fitted to the experimental profiles by adjusting the value of surface tension. The best match between theoretical and experimental profiles identifies the surface tension of the drop. Extracting the experimental drop profile using edge detection, is an important part of the current drop-shape techniques. However, edge detections fail when acquisition of sharp images is not possible due to experimental or optical limitations. A new drop-shape approach is presented, which eliminates the need for the edge detection and provides a wider range of applicability. The new methodology, called theoretical image fitting analysis (TIFA), generates theoretical images of the drop and forms an error function that describes the pixel-by-pixel deviation of the theoretical image from the experimental one. Taking surface tension as an adjustable parameter, TIFA minimizes the error function, i.e. fits the theoretical image to the experimental one. The validity of the new methodology is examined by comparing the results with those of ADSA. Using the new methodology it is finally possible to enhance the study of the surface tension of lung surfactants at higher concentrations. Due to the opaqueness of the solution, such studies were limited to the low concentrations of surfactants heretofore.
Keywords: Surface tension; Drop-shape methodology; Axisymmetric drop-shape analysis;
Characterization of silicon–YBCO buffered multilayers grown by sputtering by A. Chiodoni; V. Ballarini; D. Botta; C. Camerlingo; F. Fabbri; S. Ferrari; R. Gerbaldo; G. Ghigo; L. Gozzelino; F. Laviano; B. Minetti; C.F. Pirri; G. Tallarida; E. Tresso; E. Mezzetti (485-489).
In recent years, the scientific community has considered with interest the possibility to integrate YBCO-based devices with silicon-based electronics. In fact, the proved YBCO radiation hardness makes this integration appealing from the point of view of space and telecommunication applications. In this paper we report on the influence of buffered substrate properties on the superconducting performances of YBCO films. In this framework we here consider the Si/CeO2/YBCO multilayer. The non-satisfying quality of the YBCO film in this multilayer is attributed to an unavoidable interlayer of SiO2 between Si and CeO2. On the other hand, we prove, by means of quantitative magneto-optical analysis, the excellent properties of the bi-layer CeO2/YBCO on YSZ substrate. Thus, these measurements indicate YSZ as the best candidate to be deposited between Si and CeO2 for optimal YBCO performances on silicon.
Keywords: YBCO film; CeO2 buffer layer; Silicon; Sputtering;
Manipulation and conductivity measurements of gold nanowires by M. Wilms; J. Conrad; K. Vasilev; M. Kreiter; G. Wegner (490-494).
A low drift nanomanipulation device operating in a scanning electron microscope was constructed. The device allowed to manipulate and to characterize the electrical properties of flexible and highly conductive gold nanowires with diameters down to 15 nm. Individual nanowires could be electrically contacted either to substrate electrodes or to movable tip electrodes of the nanomanipulation device. Measuring the total resistance of a single nanowire at different lengths gave the intrinsic conductivity (σ ≈ 2.6 × 107 S/m) close to that of the bulk material (σ = 4.3 × 107 S/m). At high current densities the phenomenon of electromigration could be observed. The problem of spontaneous deposition of insulating layers on the gold objects from contaminations in the SEM chamber is addressed.
Keywords: Gold nanowire; Nanomanipulation; Scanning electron microscopy; Electrical conductivity; Electromigration;
Characterization of a new sensing device based on hydrocarbon groups (CH x ) coated porous silicon by H. Cheraga; S. Belhousse; N. Gabouze (495-500).
A gas sensing device based on hydrocarbons (CH x )/porous silicon structure was fabricated. Porous silicon was prepared by electrochemical etching of p-type silicon in HF/ethanol (50/50) by volume. The porous samples were coated with hydrocarbons groups deposited by plasma of methane. Sensitivity of these devices, response time and capacitance response to different gas exposure (ethane, ethylene and propane) have been investigated. Current–voltage and capacitance–voltage characterizations show that heterojunction are modified by the gas reactivity on the PS/CH x surface. Based on these results and IR spectroscopy measurements, mechanism of electrical conduction was interpreted in term of charge carrier transport through shallow traps associated with the surface. Finally, it was noted that, after 6 months, our sensor preserves its features such as, short response time, stability and reproducibility.
Keywords: Porous silicon; Gas sensor; Thin films;
Experimental assessment of the influence of irradiation parameters on surface deformation and residual stresses in laser shock processed metallic alloys by J.L. Ocaña; C. Molpeceres; J.A. Porro; G. Gómez; M. Morales (501-505).
Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical surface treatments for improving fatigue, corrosion and wear resistance of metals, and has recently been developed as a practical process amenable to production engineering.In the present paper a summary is provided of different experimental results obtained from the most recent LSP experiments carried out by the authors along with some conclusions for the assessment of LSP technology as a profitable method for the extension of fatigue life in critical heavy duty components.In particular, a principle demonstration has been obtained on the capability of frequency doubled Nd:YAG lasers to induce compressive residual stresses in a highly deformable material as aluminium, although reasonable doubts arise on their capability to induce these tensions over extended depths (what is really an objective in comparison with other competitive technologies) or in less deformable materials (i.e. stainless steels).
Keywords: Laser shock processing; Surface treatment; Residual stresses; Optical instrumentation;
Metal–ceramic interfaces: joining silicon nitride–stainless steel by R. Polanco; A. De Pablos; P. Miranzo; M.I. Osendi (506-512).
Joining of hot pressed silicon nitride using three types of stainless steel (AISI 304, 316 and 321) as interlayer was done by diffusion bonding at 1100 °C for 120 min. An extensive reaction zone of about 7 μm was formed in the contact region, where Cr2N, Fe x Si y and α-Fe were observed, outside that region the austenitic phase with precipitates of chromium nitride was observed. In the Mo-containing stainless steel (AISI 316) formation of Mo3Si was also detected. Moderate strengths were measured by shear testing for these joints.
Keywords: Silicon nitride; Stainless steel; Interfaces; Strength;
Multifractal analysis of growing surfaces by Ajay Chaudhari; Ching-Cher Sanders Yan; Shyi-Long Lee (513-517).
Multifractal scaling analysis is applied to the growing surfaces of random deposition model. The effect of number of deposited particles and lattice size on multifractal spectra is studied. Three cases of the growing surfaces are considered: (1) Same total number of particles deposited on different square lattice so that the number of particles deposited per surface site is different. (2) Different total number of particles deposited on different square lattice so that the number of particles deposited per surface site is the same. (3) Different total number of particles deposited on same square lattice to study the effect of number of deposited particles on multifractal spectra. The multifractal spectra are related to the surface irregularity of the growing surfaces. It has been observed that the surface with more surface roughness gives greater non-linearity in q–τ(q) multifractal spectra results in wider range of α values in α–f(α) multifractal spectra.
Keywords: Growing surface; Multifractal analysis; Surface roughness;
Release of a chitosan–hydroxyapatite composite loaded with ibuprofen and acetyl-salicylic acid submitted to different sterilization treatments by A. Larena; D.A. Cáceres; C. Vicario; A. Fuentes (518-522).
It has been demonstrated that chitosan–hydroxyapatite composite induces osteoconductivity in osseous defects but also could act as drug vehicle. It is important be able to load these composites with short-time life and controlled action anti-inflammatories to reduce or eliminate undesirable inflammatory processes. The goal of the present study is to define the variation between surface properties that this composite experiments as consequence of several sterilization treatments, and application of several pharmaceutical products relating with physical properties. Morphological changes on surface, achieved by polarization and confocal microscopies, thermal and physical properties of chitosan composites and the NSAIDs release process kinetics so as the sterilization treatment effects observed by UV–vis spectroscopy were studied. In this article, it has been demonstrated that the kind of sterilization has no important influence in NSAIDs release in chitosan membranes or composites but differs a little with chitosan membranes no submitted to sterilization treatments.
Keywords: Surface analysis; Microscopy; Chitosan; Ibuprofen;
Interfacial interactions of structural adhesive components with cement pastes by Inês Baeta Neves; Maud Chabut; Christian Perruchot; Mohamed M. Chehimi; Karim Benzarti (523-529).
The surface energy of hardened cement pastes, before and after treatment by organic coating, and two individual cement paste components (CSH and ettringite) have been characterized by inverse gas chromatography (IGC) at 35 °C, using n-alkanes, 1-alkenes, benzene, chloroform and CCl4 molecular probes. The cement pastes were prepared by mixing an ordinary Portland cement (OPC) with water at a water/cement ratio (W/C) equal to 0.3 and 0.5. They were further coated with an epoxy resin (R) and triethylenetetramine hardener (H), separately, at a mass loading of 1 and 10 wt.%, respectively. Changes in the dispersive contribution to the surface energy (γ s d) and Lewis acid–base interaction energies were found to be significantly dependent on the W/C parameter on the one hand, and the adsorption of H and R, on the other hand.
Keywords: Cement paste; Resin; Hardener; Inverse gas chromatography; Surface energy; Dispersive interactions; Acid–base interactions;
Use of different surface analysis techniques for the study of the photo-degradation of a polymeric matrix composite by A. Larena; S.Jimenez de Ochoa (530-537).
Polypropylene matrix composites, with different reinforcement degrees of long glass fibres, are usually used in different fields of the industry, like aeronautics or automotive. Owed to their huge application field, and work under diverse and severe conditions, samples of the materials were exposed to artificial accelerated photo ageing in UV chamber (Heraeus Xenotest 15OS). Although the oxidative mechanism of the PP is known enough, the fact that the material presents a high content of glass fibre, cause a surface degradation higher than that the case of no reinforced materials, owed to the presence of the fibres near the surface. In order to study this topographic modifications, the optical confocal microscopy is used that allows us the analysis of the material surface with more accuracy than a surface profiler, and with nanometric precision. We also want a correlation between surface degradation studied by confocal microscopy and reflectometer measurements. By this way, we can know the surface state, and the degradation evolution, by means of a set of easy measurements, taken with a portable reflectometer, in samples at work, without preparation. Since these materials shall fulfil some aesthetic requirements, we study also, by means of UV–vis spectroscopy, Yellow Index and White Index variations, trying to explain the photochemical processes causing these modifications. Also, the fact that these materials are usually subjected to surface treatments like adhesion or painting makes necessary the study of surface energy. We study the variation of this factor with exposing time and percentage of fibre, by means of contact angle measurements, with different liquids of known surface tensions.
Keywords: Photo-oxidation; PP-GF composite; Surface roughness; Optical confocal microscopy; Industrial colorimetry; Contact properties;