Applied Surface Science (v.252, #18)
Effect of primary oxygen ion implantation on SIMS depth profiling in glasses by Marek Tuleta (6107-6110).
The influence of the primary oxygen ion implantation on SIMS in-depth profiles in halide and chalcogenide glasses was examined. Various behaviours of particular profiles were generally explained in terms of the chemical affinity of analysed reactants and modifications of the glass structure induced by primary ions.
Keywords: Ion implantation; SIMS depth profiles; Matrix effect;
Spatially defined silver mirror reaction on a micropatterned aldehyde-terminated self-assembled monolayer by Atsushi Hozumi; Masahiko Inagaki; Naoto Shirahata (6111-6114).
A simple microfabrication technique for silver (Ag) based on spatially defined silver mirror reaction using a photolithographically micropatterned aldehyde (CHO)-terminated self-assembled monolayer (SAM) is proposed. First, both a Si substrate covered with native oxide and a quartz glass plate were exposed to a vapor of triethoxysilylundecanal (TESUD) diluted with absolute toluene for 3 h at 403 K. This vapor phase treatment produced a 1.2-nm-thick TESUD-SAM with a flat, homogeneous surface. Several samples were then photolithographically micropatterned using an excimer lamp radiating 172 nm vacuum ultraviolet light, and subsequently employed as templates for area-selective electroless Ag plating. Optical microscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) confirmed that Ag metal was preferentially deposited on the CHO-terminated regions, resulting in the formation of well-ordered Ag microstructures composed of rectangular 5 μm × 25 μm features. The CHO terminal groups of the TESUD-SAM were found to be effective in reducing Ag ionic species at the solid/liquid interface.
Keywords: Self-assembled monolayer; Vacuum UV lithography; Aldehyde group; Silver mirror reaction; Silver microstructures;
Influence of temperature–pressure treatment on heavily hydrogenated silicon surface by J. Ciosek; J. Ratajczak (6115-6118).
Microstructure and related properties of hydrogenated silicon samples, Si:H, treated at high-temperature (HT) up to 1270 K under hydrostatic argon pressure (HP) up to 1.1 GPa are investigated. To prepare Si:H, Czochralski grown 0 0 1 oriented single crystalline Si wafer with 50 nm thick surface SiO2 layer was heavily implanted with hydrogen using the immersion plasma source of hydrogen ions with energy 24 keV.The surface of HT–HP treated Si:H was characterised by scanning electron microscopy. Reflectivity pattern measurements in the wavelength range of 350–2000 nm have been performed to analyse their surface and bulk properties. The volume averaging method for a model of layer-like structure has been used to simulate the HT–HP treated Si:H. The analysis of Si:H samples suggests the multi-layer structure composed of Si, Si:H, SiO, SiO2, and of porous Si layers in the sub-surface region. The porous Si:H samples model is in good consistency with experimental data from reflectance measurements.
Keywords: Hydrostatic pressure; Annealing; Hydrogen-implanted silicon; Pore; Buried layer; Surface;
Physical foundations of the oxide cathodes by Stanislaw Halas; Tomasz Durakiewicz (6119-6121).
A novel explanation of the low values of work function in case of activated (partly deoxidized) polycrystalline oxides of alkali and alkaline earth metals is offered. Use of the metallic plasma model to the conducting oxides leads to the following values (in eV): 1.00, 1.67, 1.50, 1.44, 1.46 and 1.59 for activated Cs2O, CaO, SrO, BaO, Y2O3 and La2O3, respectively. The main reason of low work function of the oxide cathodes is very low density of free electrons in the emitting surface layer.
Keywords: Work function; Metal oxides; Oxide cathodes; Cs2O; CaO; SrO; BaO; Y2O3; La2O3; LaB6; Thermionic emission;
Increasing surface hydrophilicity of titania thin films by doping by D. Luca; D. Mardare; F. Iacomi; C.M. Teodorescu (6122-6126).
The hydrophilicity of RF sputtered thin films of: (a) pure TiO2 and (b) TiO2 doped with 0.3% Ce, 0.4% Nb, and 0.4% N (atomic percents) was investigated macroscopically by measurements of the contact angle between water and film surface. The results are discussed in terms of the connection of the hydrophilic and photocatalytic properties of the materials with their structure, morphology and optical characteristics. The 280 nm thick films were deposited on optical glass substrates at 250 °C. Film structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy. The surface roughness was derived from atomic force microscopy and ellipsometric data. The contact angle of de-ionized water with film surface was monitored during photo-activation and after irradiating with near-UV light. The surface super-hidrophilicity of all the investigated samples decays, when samples are kept in darkness for 48 h after irradiation. The hydrophilic behavior of the doped TiO2 thin films is discussed in terms of the effects of surface roughness, phase transformations enhanced by doping and charge carrier recombination.
Keywords: Thin films; Doped titanium dioxide; Contact angle; Hydrophilicity; Sessile drop;
Metallicity of atomic wires by I.N. Yakovkin (6127-6134).
The variety of atomic “dimensional” wires can now be synthesized on furrowed and stepped surfaces. These adlayers provide a variety of opportunities for systematically tailoring the surface properties. One of key issue is the metallicity of an atomic wire (even a “supported” atomic wire). Monte-Carlo simulations provide insight into the parameters of indirect interaction that are the basis for the formation of the atomic wires and their stability. In some cases, these results can be directly compared with density functional theory (DFT) calculations of energies of the lateral interactions between adsorbed atoms—one of the most transparent example of Sr/Mo(1 1 2) is presented here as well. It is the surface band structure calculations that provide insights on how metallicity in such surface structures might be altered.Surprisingly, like most of “metallic” wires on semiconductor surfaces, linear chains of alkaline earth on the furrowed transition metal surfaces, such as the Mo(1 1 2) surface, also do not exhibit strong metallic character but, rather, may be considered dielectric atomic chains. The adsorption bonds result in a loss in electron itinerancy, leading to greater valence electron localization in the adlayer in some cases. The localized character of the bands near the Fermi level, associated with the adlayer, is replaced by a metallic band structure when the lattice period of the adsorbed layer becomes incommensurate with the substrate periodicity along the furrows with increasing coverage of the adlayer. With changes in adlayer coverage, both theory and experiment indicate that the adsorbed layers can undergo a Wilson type nonmetal-to-metal transition.
Keywords: Nonmetal-to-metal transitions; Surface electronic structure; Metallicity of adsorbed layers; Low-dimensional systems; Band structure;
Growth instability and surface phase transition of Ti thin film on Si(1 1 1): An atomic force microscopy study by Deeder Aurongzeb (6135-6140).
Evolution of surface structure during the annealing of e-beam evaporated Ti films is studied by means of atomic force microscopy (AFM). Image variography and power spectral density analysis are used to study scaling properties of the films, ranging from 50 nm to 20 μm length scale. No particular grain size is observed up to 473 K. At 673 K, grain size of ∼250 nm are formed and coalesced to form bigger grain size upon further annealing. At 473 K, RMS roughness dropped at all length scale and became rougher at 673 K with an increasing trend up to 873 K. Clustering at 673 K indicates Kosterlitz–Thaouless [J.M. Kosterlitz, D.J. Thaouless, J. Phys. Chem. 6 (1973) 1181] type phase transition at the surface. The observed transition is also consistent with existing scaling laws.
Keywords: Annealing; Scaling properties; Atomic force microscopy;
Microstructure, mechanical properties, and oxidation resistance of nanocomposite Ti–Si–N coatings by C.H. Zhang; X.C. Lu; H. Wang; J.B. Luo; Y.G. Shen; K.Y. Li (6141-6153).
Ti–Si–N coatings with different silicon contents (0–12 at.%) were deposited onto Si(1 0 0) wafer, AISI M42 high speed steel, and stainless steel plate, respectively. These coatings were characterized and analyzed by using a variety of analytical techniques, such as XRD, AES, SEM, XPS, nanoindentation measurements, Rockwell C-type indentation tester, and scratch tester. The results revealed that the hardness was strongly correlated to the amount of silicon addition into a growing TiN film. The maximum hardness of 47.1 GPa was achieved as the Si content was 8.6 at.%. In the mechanical and oxidation resistance measurements, the Ti–Si–N coatings showed three distinct behaviors. (i) The coatings with Si contents of no more than 8.6 at.% performed good adhesion strength quality onto the HSS substrates. (ii) The fracture toughness of the coatings decreased with the increase in Si content. (iii) The Ti–Si–N coating with 8.6 at.% Si showed the excellent oxidation resistance behavior. The cutting performance under using coolant conditions was also evaluated by a conventional drilling machine. The drills with Ti–Si–N coatings performed much better than the drills with TiN coating and the uncoated drills.
Keywords: Ti–Si–N coating; Mechanical properties; Oxidation resistance; Cutting performance;
Theoretical and experimental investigations on the structures of purified clay and acid-activated clay by Tao Yang; Xiao-Dong Wen; Junfen Li; Liming Yang (6154-6161).
The purified and acidified montmorillonite clay were characterized by XRD, BET and TPD. These results show that acidified clay is provided with more surface area and acid sites. For NH3-TPD, molecular NH3 desorption on purified clay and acidified clay occurs at temperatures with 873 and 1000 K, respectively. It is shown for the existence for strong acid sites. By two reactions of the tetrahydropyranylation of n-propanol and the esterification of cyclo-2-pentene with acetic acid, it is shown that the acidified clay displays better catalytic activity for above two organic reactions. By density-functional theory (DFT) method, we have analyzed the structures of different substituted montmorillonite and the effect sorption behavior of Na+ in different montmorillonite models. The result shows that the process of substitution will occur apart from octahedral aluminums. The adsorption of NH3 on clay surfaces have been investigated using TPD and DFT. This is shown that acid sites locate at round the octahedral aluminums, and substitution of Al3+ for tetrahedral Si will be favorable to NH3 adsorption.
Piperidin-1-yl-phosphonic acid and (4-phosphono-piperazin-1-yl) phosphonic acid: A new class of iron corrosion inhibitors in sodium chloride 3% media by H. Amar; J. Benzakour; A. Derja; D. Villemin; B. Moreau; T. Braisaz (6162-6172).
The inhibiting effect of the piperidin-1-yl-phosphonic acid (PPA) and (4-phosphono-piperazin-1-yl) phosphonic acid (PPPA) on the behavior of iron in 3% NaCl media has been examined by electrochemical and gravimetric measurements. Potentiodynamic polarization studies clearly reveal the fact that the addition of increasing concentrations of phosphonic acids moves the corrosion potential towards negative values and reduces the corrosion rate. In uninhibited and inhibited solutions, the increasing of temperature reduces the inhibition efficiency. Changes in impedance parameters (R t and C dl) are indicative of adsorption of PPA and PPPA on the metal surface leading to the formation of protective films. Gravimetric measurements reveal that the presence of PPA and PPPA increases the inhibition efficiency by decreasing the corrosion rate. The results obtained by corrosion weight loss tests reveal that adsorption of compounds tested on the ARMCO iron surface obeys to Langmuir adsorption isotherm.
Keywords: Inhibitor; Phosphonic acids; Polarization curves; EIS; Gravimetric;
Research of rapid and direct thick coatings deposition by hybrid plasma-laser by Ying-ping Qian; Hai-ou Zhang; Gui-lan Wang (6173-6178).
In this paper, a new technology of direct and rapid thick coatings fabrication with hybrid plasma-laser deposition manufacturing (PLDM) technology is advanced which is also suitable for functional prototyping and tooling applications. It emphasizes on the influence of laser to the microstructure of coatings and physical properties of surface layers. Unlike the direct rapid plasma deposition manufacturing (PDM), in hybrid plasma-laser deposition manufacturing, the laser beam enters into plasma arc beam and focuses on the molten pool as assisting heat energy. A 280 W pulsed Nd:YAG (yttrium–aluminum garnet) laser machine is used to inspect the effect. The experimental results show that the laser beam could improve the surface state; the elements distribution of coatings deposited by PLDM was even; the physical properties of surface coatings fabricated with PLDM were better than that deposited by PDM.
Keywords: PLDM (hybrid plasma-laser deposition manufacturing); Direct and rapid thick coatings deposition; Physical properties;
Effects of Cl−, NO3 − and SO4 2− anions on the anodic behavior of carbon steel in deaerated 0.50 M NaHCO3 solutions by M.M. El-Naggar (6179-6194).
The effects of Cl−, NO3 − and SO4 2− aggressive anions on the corrosion and passivation behavior of carbon steel electrode in deaerated 0.50 M NaHCO3 solutions were studied using potentiodynamic anodic polarization and SEM techniques. It was found that the presence of Cl−, NO3 − and SO4 2− anions stimulates the anodic dissolution rate in both the active and the pre-passive potential regions. Moreover, significantly great effects were observed in both the passive and the trans-passive potential regions. Pitting corrosion was observed only in the presence of Cl− anions, while the presence of NO3 − and SO4 2− anions facilitate only passivation by oxygen of water without themselves participating in the cathodic process. Also, it was observed that the effect of NO3 − anion, which is a strong oxidizing agent acting “primarily” as stimulator of the cathodic process and then its reaction product acts “indirectly” retarding the anodic process. On the other hand, the effect of SO4 2− anion, which is a non-oxidizing agent, exerts an “indirect” effect on the cathodic reaction increasing its rate and then “directly” influence on the anodic reaction, retarding it.
Keywords: Anodic polarization; Aggressive anions; Pitting corrosion; Passivation;
Features of film growth during plasma anodizing of Al 2024/SiC metal matrix composite by Wenbin Xue (6195-6200).
Plasma anodizing is a novel promising process to fabricate corrosion-resistant protective films on metal matrix composites. The corrosion-resistant films were prepared by plasma anodizing on SiC reinforced aluminum matrix composite. The morphology and microstructure of films were analyzed by scanning electron microscopy. Specifically, the morphology of residual SiC reinforcement particles in the film was observed. It is found that the most SiC reinforcement particles have been molten to become silicon oxide, but a few tiny SiC particles still remain in the film close to the composite/film interface. This interface is irregular due to the hindering effect of SiC particles on the film growth. Morphology and distribution of residual SiC particles in film provide direct evidence to identify the local melt occurs in the interior of plasma anodizing film even near the composite/film interface. A model of film growth by plasma anodizing on metal matrix composites was proposed.
Keywords: Plasma anodizing; Aluminum matrix composites; Ceramic films;
Effect of an absorbent overlay on the residual stress field induced by laser shock processing on aluminum samples by C. Rubio-González; G. Gomez-Rosas; J.L. Ocaña; C. Molpeceres; A. Banderas; J. Porro; M. Morales (6201-6205).
Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field, which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 2.5 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto aluminum samples. Density of 2500 pulses/cm2 with infrared (1064 nm) radiation was used. The effect of an absorbent overlay on the residual stress field using this LSP setup and this energy level is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the overlay makes the compressive residual stress profile move to the surface. This effect is explained on the basis of the vaporization of the coat layer suppressing thermal effects on the metallic substrate. The effect of coating the specimen surface before LSP treatment may have advantages on improving wear and contact fatigue properties of this aluminum alloy.
Keywords: Laser shock processing; Residual stress;
Microstructure and interfacial properties of HfO2–Al2O3 nanolaminate films by M. Liu; G. He; L.Q. Zhu; Q. Fang; G.H. Li; L.D. Zhang (6206-6211).
High-k HfO2–Al2O3 composite gate dielectric thin films on Si(1 0 0) have been deposited by means of magnetron sputtering. The microstructure and interfacial characteristics of the HfO2–Al2O3 films have been investigated by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and spectroscopic ellipsometry (SE). Analysis by XRD has confirmed that an amorphous structure of the HfO2–Al2O3 composite films is maintained up to an annealing temperature of 800 °C, which is much higher than that of pure HfO2 thin films. FTIR characterization indicates that the growth of the interfacial SiO2 layer is effectively suppressed when the annealing temperature is as low as 800 °C, which is also confirmed by spectroscopy ellipsometry measurement. These results clearly show that the crystallization temperature of the nanolaminate HfO2–Al2O3 composite films has been increased compared to pure HfO2 films. Al2O3 as a passivation barrier for HfO2 high-k dielectrics prevents oxygen diffusion and the interfacial layer growth effectively.
Keywords: Interface; Magnetron sputtering; Crystallization;
Inhibition of steel corrosion in 2 M H3PO4 by artemisia oil by M. Benabdellah; M. Benkaddour; B. Hammouti; M. Bendahhou; A. Aouniti (6212-6217).
Artemisia oil (Ar) is extracted from artemisia herba alba collected in Ain es-sefra-Algeria, and tested as corrosion inhibitor of steel in 2 M H3PO4 using weight loss measurements, electrochemical polarisation and EIS methods. The naturally oil reduces the corrosion rate. The inhibition efficiency was found to increase with oil content to attain 79% at 6 g/l. Ar acts as a cathodic inhibitor. The effect of temperature on the corrosion behaviour of steel indicates that inhibition efficiency of the natural substance decreases with the rise of temperature. The adsorption isotherm of natural product on the steel has been determined.
Keywords: Corrosion; Inhibition; Steel; Artemisia; Adsorption;
Structural and electrical characterization of S x Se100−x thin films by M.M. El-Nahass; M.A.M. Seyam; H.E.A. El-Sayed; A.M. Abd El-Barry (6218-6227).
Thin films of samples of the glassy S x Se100−x system with 0 ≤ x ≤ 7.28 have been prepared by thermal evaporation technique at room temperature (300 K). X-ray investigations show that the structure of pure selenium (Se) does change seriously by the addition of small amount of sulphur S ≤7.28%. The lattice parameters were determined as a function of sulphur content. Results of differential thermal analysis (DTA) of the glassy compositions of the system S x Se100−x were discussed. The characteristic temperatures (T g, T c and T m) were evaluated. Dark electrical resistivities, ρ, of S x Se100−x thin films with different thicknesses from 100 to 500 nm, were measured in the temperature range from 300 to 423 K. Two distinct linear parts with different activation energies were observed. The variation of electrical resistivity of examined compositions has been discussed as a function of the film thickness, temperature and the sulphur content. The application of Mott model for the phonon assisted hopping of small polarons gave the same two activation energies obtained from the resistivity temperature calculations.
Keywords: S x Se100−x ; Chalcogenide; Thin films; Semiconductors; Structural and electrical properties;
Desorption and photopolymerization behavior of mixed and multilayered styrene–pyrrole nanofilms by Seth Washburn; Ethan Townsend; Jochen Lauterbach; Christopher M. Snively (6228-6235).
The molecular arrangement and polymerization of adsorbed styrene–pyrrole films were explored using two different dosing schemes: simultaneous dosing to form an intimately mixed film of the two monomers and sequential dosing to form films with distinct layers of styrene and pyrrole. It was found that the desorption of pyrrole was delayed until 175 K when either simultaneously dosed with styrene or in the presence of an overlying styrene layer, whereas it normally desorbs at 165 K when dosed alone. No such effects were observed with styrene in any dosing configuration. The polymerization rate of pyrrole was unaffected in the films when present as the top layer and was observed to decrease by 50% when beneath a styrene layer. Moreover, the rate of polymerization increased by two orders of magnitude in the case of the intimately mixed film. The rate of styrene polymerization was not found to change in any of the explored geometries. These effects are explained by considering the proximity of the components and the potential for screening UV radiation based on their molecular structure.
Keywords: Vacuum deposition; Conjugated polymers; Polypyrroles; Polystyrene; Photo induced polymerization; Thin-films;
Synergistic effect of iodide ions on the corrosion inhibition of steel in 0.5 M H2SO4 by new chalcone derivatives by M. Bouklah; B. Hammouti; A. Aouniti; M. Benkaddour; A. Bouyanzer (6236-6242).
The effect of addition of 4′,4-dihydroxychalcone (P1), 4-aminochalcone (P2) and 4-bromo, 4′-methoxychalcone (P3) on the corrosion of steel in 0.5 M sulphuric acid has been studied by weight loss measurements, potentiodynamic and EIS measurements. We investigate the synergistic effect of iodide ions on the corrosion inhibition of steel in the presence of chalcone derivatives. The corrosion rates of the steel decrease with the increase of the chalcones concentration, while the inhibition efficiencies increase. The addition of iodide ions enhances the inhibition efficiency considerably. The presence of iodide ions increases the degree of surface coverage. The synergism parameters S Θ and S I, calculated from surface coverage and the values of inhibition efficiency, in the case of chalcone derivatives are found to be larger than unity. The enhanced inhibition efficiency in the presence of iodide ions is only due to synergism and there is a definite contribution from the inhibitors molecules. E (%) obtained from the various methods is in good agreement. Polarisation measurements show also that the compounds act as cathodic inhibitors.
Keywords: Steel; Chalcone; Inhibition; Corrosion; Sulphuric acid; Synergistic effect;
Nanomechanical characterization of amorphous hydrogenated carbon thin films by Te-Hua Fang; Win-Jin Chang (6243-6248).
Amorphous hydrogenated carbon (a-C:H) thin films deposited on a silicon substrate under various mixtures of methane–hydrogen gas by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD) was investigated. Microstructure, surface morphology and mechanical characterizations of the a-C:H films were analyzed using Raman spectroscopy, atomic force microscopy (AFM) and nanoindentation technique, respectively. The results indicated there was an increase of the hydrogen content, the ratio of the D-peak to the G-peak (I D/I G) increased but the surface roughness of the films was reduced. Both hardness and Young's modulus increased as the hydrogen content was increased. In addition, the contact stress–strain analysis is reported. The results confirmed that the mechanical properties of the amorphous hydrogenated carbon thin films improved using a higher H2 content in the source gas.
Keywords: Nanoindentation; Amorphous hydrogenated carbon films; ECR-MPCVD; Raman spectra; AFM;
Closed-form solutions for the frequency shift of V-shaped probes scanning an inclined surface by Shueei-Muh Lin; Sen-Yung Lee; Bin-Shin Chen (6249-6259).
The analytical method to determine the frequency shift of an AFM V-shaped probe scanning the relative inclined surface in non-contact mode is proposed. If the tip is not perpendicular to the surface plane, the lateral force to the tip will occurs. Consequently, there exists a moment to the end of probe. The closed-form solution of the partial differential equation with a nonlinear boundary condition is derived. The error of transforming the distributed-masses system into lumped-masses one in the force gradient method or the perturbation method is eliminated. The dimensionless parameters are introduced for reducing the numerical transaction error. The limiting case such as a uniform or tapered beam can be obtained easily from the general system. The assessments of the force gradient method, the perturbation method and the propose method determining the frequency shift of a V-shaped probe are made. It is discovered that increasing the absolute inclined angle θ decreases the frequency shift especially for a small tip–surface distance.
Keywords: Closed-form solution; Frequency shift; V-shaped probe; AFM;
Synthesis and characterization of molybdenum incorporated mesoporous aluminophosphate by Li-Ngee Ho; Tasuku Ikegawa; Hiroyasu Nishiguchi; Katsutoshi Nagaoka; Yusaku Takita (6260-6268).
A synthesis of molybdenum incorporated mesoporous aluminophosphate with long-chain n-alkylamine as template material had been prepared under non-aqueous condition. These materials were extensively characterized by using X-ray diffraction (XRD), nitrogen sorption isotherms, nuclear magnetic resonance of 27Al and 31P (NMR), inductive coupled plasma (ICP), electron spin resonance (ESR), Fourier transform infrared (FTIR) and thermogravimetric–differential thermal analysis (TG–DTA). Morphology of the materials had been observed by using transmission electron microscope (TEM) that revealed the mesoporous materials possessed wormhole-like structures. Alkaline solvent extraction using n-butylamine/ethanol had been efficiently removed the n-alkylamine from the mesoporous samples which yielded BET surface areas around 550–730 m2/g. BJH analysis showed a narrow pore size distribution which increased with increasing of the carbon chain length of alkylamine (template). Valence state and coordination of the molybdenum in the obtained samples were investigated by using ESR and FTIR where it was found that Mo4+ and Mo6+ molybdenum species existed in the molybdenum incorporated mesoporous aluminophosphate in tetrahedral coordination.
Keywords: Mesoporous; Aluminophosphate; Molybdenum; Alkylamine; Solvent extraction;
Current–voltage analysis of a-Si:H Schottky diodes by Mehmet Şahin; Haziret Durmuş; Ruhi Kaplan (6269-6274).
Direct current (dc)–voltage (I–V) characteristics of the hydrogenated amorphous silicon (a-Si:H) Schottky diode have been measured at different temperatures under dark and light. From the fourth quadrant of illuminated characteristics, fill factor (FF) values were obtained for each temperature measured (173–297 K). We have found that FF increases very little as the temperature is decreased. The measured data from I–V characteristics has been analyzed in detail. In particular, from dark I–V characteristics obtained, the density of state (DOS) near the Fermi level was determined using a simple model based on the space-charge limited current (SCLC). On the other hand, from the illuminated I–V characteristics, the density of carriers was calculated for each temperature using the analysis of diode equation as known. A comparison of the carrier density and the measured photocurrent as a function of the reverse temperature was also made and a good correspondence was obtained.
Keywords: A-Si:H Schottky diode; Fill factor; Space-charge limited current; DOS; Carrier density;
Injection of holes at indium tin oxide/dendrimer interface: An explanation with new theory of thermionic emission at metal/organic interfaces by Ying-Quan Peng; Fei-Ping Lu (6275-6279).
The traditional theory of thermionic emission at metal/inorganic crystalline semiconductor interfaces is no longer applicable for the interface between a metal and an organic semiconductor. Under the assumption of thermalization of hot carriers in the organic semiconductor near the interface, a theory for thermionic emission of charge carriers at metal/organic semiconductor interfaces is developed. This theory is used to explain the experimental result from Samuel group [J.P.J. Markham, D.W. Samuel, S.-C. Lo, P.L. Burn, M. Weiter, H. Baessler, J. Appl. Phys. 95 (2004) 438] for the injection of holes from indium tin oxide into the dendrimer based on fac-tris(2-phenylpyridyl) iridium(III).
Keywords: Thermionic emission; Injection; Densdrimer; Interface;
Surface characterisation of ethylene–propylene–diene rubber upon exposure to aqueous acidic solution by Susanta Mitra; Afshin Ghanbari-Siahkali; Peter Kingshott; Søren Hvilsted; Kristoffer Almdal (6280-6288).
Two types of pure ethylene propylene diene rubbers were exposed to two different acids for varying period of time. Surface characterisation was carried out using X-ray photoelectron spectroscopy (XPS). Two EPDM rubbers selected for this study were comparable in co-monomer compositions but significantly different with respect to molar mass and the presence of long chain branching. Both rubbers contained 5-ethylidene-2-norbornene (ENB) as diene. Solution cast films of pure EPDM samples were exposed in two different acidic solutions, viz. chromosulphuric (Cr (VI)/H2SO4) and sulphuric acid (H2SO4) (20%, v/v) at ambient temperature from 1 to 12 weeks. XPS analysis indicated that several oxygenated species were formed on the surface of both rubbers after exposure. It was postulated from the XPS analyses that both aqueous acidic solutions attacked the olefinic double bonds (C＝C) of ENB. Furthermore, 20% Cr (VI)/H2SO4 also attacked the allylic carbon–hydrogen (C―H) bonds of ENB resulting in more oxygenated species on the surface compared to 20% H2SO4 under identical conditions. Cr (VI) in the 20% Cr (VI)/H2SO4 was found to play an important role in alteration of surface chemistry. Studies using a model system consisting of EPDM mixed with Cr (VI) and Cr (III) salts revealed that the change of oxidation state from Cr (VI) to Cr (III) as a consequence of direct involvement of Cr (VI) in the chemical alteration of EPDM surfaces. Interestingly, the presence of long chain branching and molar mass did not significantly influence the chemical processes owing to the acid treatment.
Keywords: X-ray photoelectron spectroscopy (XPS); Surface characterisation; Elastomer; EPDM;
MFM and Raman studies in PEMBE-grown (Ga,Mn)N thin films showing room-temperature ferromagnetism by Moon-Ho Ham; Sukho Yoon; Yongjo Park; Jae-Min Myoung (6289-6293).
We present the room-temperature ferromagnetism in the (Ga,Mn)N films grown on n-type GaN templates by plasma-enhanced molecular beam epitaxy for semiconductor spintronic device applications. Despite of the possible interface effects between the (Ga,Mn)N layers and n-type GaN templates, the (Ga,Mn)N films were found to exhibit the ferromagnetic ordering above room temperature. The magnetic force microscopy identified the magnetic domains with the different magnetic orientations at room temperature, indicating the existence of the ferromagnetic long-range ordering. In Raman spectra, an additional peak at 578 cm−1 was observed, which is attributed to the local vibration of substitutional Mn in the (Ga,Mn)N lattice. Therefore, it is believed that the ferromagnetic ordering in (Ga,Mn)N is due to the carrier-mediated Ruderman–Kittle–Kasuya–Yosida interaction.
Keywords: (Ga,Mn)N; PEMBE; Room-temperature ferromagnetism; MFM; Raman scattering;
Formation processes of CuCl and regenerated Cu crystals on bronze surfaces in neutral and acidic media by Julin Wang; Chunchun Xu; Guocheng Lv (6294-6303).
The paper is devoted to investigating the formation of CuCl and regenerated Cu crystals on bronze. Electrochemical behaviour of bronze in simulated anoxic edaphic media and occluded cell (O.C.) solutions was studied with cycle voltammetry (CV) and X-ray diffraction (XRD). Within potential range of −800 to +800 mV, oxidation occurred was largely a process in which Cu is oxidized to CuCl and the reduction process was a reverse of it. An atomic force microscopy (AFM) was used to observe the morphology of CuCl crystals, regenerated Cu crystals and corrosion interface at nm level. The deposition of regenerated Cu on simulated archaeological bronzes was simulated under experimental conditions for the first time. CuCl could be thoroughly reduced to pure Cu if reduction time interval were sufficiently prolonged. This provided a theoretical and experimental basis for getting rid of harmful CuCl patina from archaeological bronzes with electrochemical means.
Keywords: Bronze; Harmful patina; Regenerated Cu; Powdery patina; AFM; Localized corrosion;
Influence of initial oxygen on the formation of thiol layers by T. Laiho; J.A. Leiro (6304-6312).
In this study, X-ray photoelectron spectroscopy (XPS) has been used to study thin organic films. For comparison, monolayers were formed on clean and air-exposed metal substrates. Obtained results show that thiols remove contamination oxygen from gold, silver, platinum and copper surfaces. The tightly packed thiolate layers can be formed. In addition, oxygen does not take part in the final bonding of molecules to the surfaces.
Keywords: Self-assembled monolayers (SAMs); X-ray photoelectron spectroscopy (XPS); n-Dodecanethiol; Adsorption; Surfaces;
Etching of mercuric iodide in cation iodide solutions by J.P. Ponpon; M. Amann (6313-6322).
The surface properties of mercuric iodide after etching in various cation iodide solutions have been investigated in terms of dissolution rate, morphology, electrical properties and reaction with water vapour. No significant differences have been observed in the etching rates. However, dissolution of HgI2 in NH4I, NaI, KI or RbI leaves the surface more or less covered with a residual iodo mercurate compound whose electrical properties and stability with regard to humidity may noticeably influence the behaviour of mercuric iodide devices. The smallest effect has been observed for etching in NaI.
Keywords: Mercuric iodide; Etching; Surface properties; Iodo mercurates;
Investigation on hexamethyldisilazane vapor treatment of plasma-damaged nanoporous organosilicate films by T. Rajagopalan; B. Lahlouh; J.A. Lubguban; N. Biswas; S. Gangopadhyay; J. Sun; D.H. Huang; S.L. Simon; D. Toma; R. Butler (6323-6331).
Hexamethyldisilazane (HMDS) vapor treatment of plasma-damaged nanoporous organosilicate thin films has been studied as a function of treatment temperature in this work. Although, the HMDS vapor treatment facilitated incorporation of methyl (CH3) groups subsequent to the removal of free hydroxyl (OH) groups in the damaged films at treatment temperature as low as 55 °C, the bonded OH groups were not removed. More significantly, detailed analysis of the results reveals that HMDS vapor modified only the surface of the plasma-damaged samples and not the entire film as expected. This is attributed to the formation of a thin solid layer on the surface, which effectively prevents penetration of HMDS vapors into the bulk. The Fourier transform-infrared (FT-IR) absorption and dielectric constant measurements confirm that the vapor treatment assists only partial curing of the plasma-damaged films. Alternative processes of curing the films with HMDS dissolved in supercritical carbon dioxide (SCCO2) as a medium of reaction in static and pulsed modes were also attempted and the results are presented in this paper.
Keywords: Plasma-damage; Porous films; Low-k; Supercritical CO2;
Accelerated life ac conductivity measurements of CRT oxide cathodes by A.A. Hashim; D.S. Barratt; A.K. Hassan; A. Nabok (6332-6336).
The ac conductivity measurements have been carried out for the activated Ba/SrO cathode with additional 5% Ni powder for every 100 h acceleration life time at the temperature around 1125 K. The ac conductivity was studied as a function of temperature in the range 300–1200 K after conversion and activation of the cathode at 1200 K for 1 h in two cathodes face to face closed configuration. The experimental results prove that the hopping conductivity dominate in the temperature range 625–770 K through the traps of the WO3 associate with activation energy E a = 0.87 eV, whereas from 500–625 K it is most likely to be through the traps of the Al2O3 with activation energy of E a = 1.05 eV. The hopping conductivity at the low temperature range 300–500 K is based on Ni powder link with some Ba contaminants in the oxide layer stricture which indicates very low activation energy E a = 0.06 eV.
Keywords: Oxide cathode; Ba and Sr oxides; Electron emission; Electrical conductivity; CRT;
NaCl/Ca/Al as an efficient cathode in organic light-emitting devices by Shengwei Shi; Dongge Ma (6337-6341).
An efficient cathode NaCl/Ca/Al used to improve the performance of organic light-emitting devices (OLEDs) was reported. Standard N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′ biphenyl 4,4′-dimaine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3) devices with NaCl/Ca/Al cathode showed dramatically enhanced electroluminescent (EL) efficiency. A power efficiency of 4.6 lm/W was obtained for OLEDs with 2 nm of NaCl and 10 nm of Ca, which is much higher than 2.0 lm/W, 3.1 lm/W, 2.1 lm/W and 3.6 lm/W in devices using, respectively, the LiF (1 nm)/Al, LiF (1 nm)/Ca (10 nm)/Al, Ca (10 nm)/Al and NaCl (2 nm)/Al cathodes. The investigation of the electron injection in electron-only devices indicates that the utilization of the NaCl/Ca/Al cathode substantially enhances the electron injection current, which in case of OLEDs leads to the improvement of the brightness and efficiency.
Keywords: Organic semiconductors; Optoelectronic devices; Electrical properties and measurements; Alkali metals;
Addition of carbon to anatase TiO2 by n-hexane treatment—surface or bulk doping? by Cristina S. Enache; Joop Schoonman; Roel van de Krol (6342-6347).
Anatase TiO2 can be sensitized to visible light by adding carbon as a dopant. Towards this end, TiO2 photoelectrodes were subjected to a thermal treatment in a hexane-rich environment. By comparing the optical and photoelectrochemical characteristics of both thin film and nanocrystalline nanoporous photoelectrodes, carbon is found to be located mainly at the surface of the TiO2. The amount of carbon that diffuses into the bulk of the material is too small to significantly enhance the visible light response and only a small shift of the absorption edge towards higher wavelengths is observed. The presence of carbon in TiO2 shifts the anatase-to-rutile transformation temperature beyond 800 °C, and X-ray diffraction shows that spray deposition of TiO2 under a CO2 atmosphere results in a higher bulk carbon concentration than a post-deposition thermal treatment in a hexane-rich environment.
Keywords: Anatase; Titanium oxide; Photoelectrode; Thin films; Carbon dopant; Surface defects; Photoconductivity;
Surface treatment of cotton using β-cyclodextrins sol–gel method by C.X. Wang; Sh.L. Chen (6348-6352).
β-Cyclodextrin can be added into sol–gel solution which consists of 3-glycidyloxypropyl-trimethoxysilane (GPTMS), tetraethoxysilane (TEOS), catalyzer and solvent. This β-cyclodextrianto sol–gel solution is able to anchor β-cyclodextrin on cotton fabrics in gelation process in order to impart new surface property of cotton. The suitable technical conditions of forming stable β-cyclodextrin sol–gel solution were presented. β-Cyclodextrins are able to form inclusion complexes with other guest components. As a result of the inclusions, the treated fabrics achieved new functional properties by the selective inclusion of the guest substances into the fixed cavities on fabrics. A novel functional surface treatment of fabrics is presented by sol–gel methods. The new functionalities were verified simply by decreasing the rate of volatile fragrance substances.
Keywords: Surface treatment; β-Cyclodextrin; Sol–gel method; Cotton;
Study of nitrogen ion implantation and diffusion phenomena on thin chromium layers followed by the atomic force microscopy and secondary ion mass spectroscopy techniques characterization by M. Esmaeelpour; G. Kavei (6353-6359).
This research investigates the effect of ion implantation dosage level and further thermal treatment on the physical characteristics of chromium coatings on Si(1 1 1) substrates. Chromium films had been exposed to nitrogen ion fluencies of 1 × 1017, 3 × 1017, 6 × 1017 and 10 × 1017 N+ cm−2 with a 15 keV energy level. Obtained samples had been heat treated at 450 °C at a pressure of 2 × 10−2 Torr in an argon atmosphere for 30 h. Atomic force microscopy (AFM) images showed significant increase in surface roughness as a result of nitrogen ion fluence increase. Secondary ion mass spectroscopy (SIMS) studies revealed a clear increased accumulation of Cr2N phase near the surface as a result of higher N+ fluence. XRD patterns showed preferred growth of [0 0 2] and [1 1 1] planes of Cr2N phase as a result of higher ion implantation fluence. These results had been explained based on the nucleation-growth of Cr2N phase and nitrogen atoms diffusion history during the thermal treatment process.
Keywords: Atomic force microscopy; Secondary ion mass spectroscopy; X-ray diffraction; Scanning probe microscopy; Lateral force microscopy;
Surface modification of polyester to produce a bacterial cellulose-based vascular prosthetic device by Paul A. Charpentier; Anne Maguire; Wan-kei Wan (6360-6367).
The surface of medical grade polyesters was modified to impart hydrophilic character for attachment to bacterial synthesized cellulose to produce a vascular prosthetic device. The polyesters were treated with UV/ozone, air plasma, and nitrogen plasma for various lengths of time. The unmodified and modified surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and advancing contact angle measurements. The surfaces were then coated with bacterial produced cellulose to study adhesion properties through tensile testing (peel testing). UV/ozone and plasma treatment XPS results indicated an increase in the oxygen concentration in the form of C―O(H) on the treated polyester surfaces. The treatment time to reach steady state in the case of air and nitrogen plasmas took the order of seconds, while 7 min and longer were required for UV/ozone treatment. Peel strength tests to measure adhesion of modified polyester to cellulose reached their maximum values when the C―O(H) concentrations were at the highest level. It was also at this level that the contact angle measurements showed no further decrease.
Keywords: Bacterial cellulose; Polyester; Vascular graft; Surface modification; Plasma treatment; XPS analysis;
(2 × 1)-Na surface reconstruction induced by NaCl dissociation on Ag(1 1 0) during LEED analysis by K. Aït-Mansour; M. Bielmann; O. Gröning; P. Ruffieux; R. Fasel; P. Gröning (6368-6374).
This study first reports the initial growth stages of sodium chloride (NaCl) on Ag(1 1 0) at room temperature. NaCl grows in bi-layer mode along its [1 0 0] axis and gives rise to (4 × 1) and (1 × 2) reconstructed domains for coverages lower than two monolayers (ML), a minimal thickness inducing a bi-dimensional closed film. In addition, a 10 ML NaCl film has been examined by low energy electron diffraction (LEED). LEED analysis leads to the dissociation of the NaCl deposit in a few minutes. The NaCl dissociation implies Cl desorption from the surface and Na remaining on it. The residual Na is arranged in the form of a (2 × 1) surface reconstruction and is found to be strongly bounded to the Ag substrate. These findings have been established by using the X-ray photoelectron spectroscopy technique.
Keywords: Sodium chloride (NaCl); NaCl dissociation; Ag(1 1 0); Low energy electron diffraction and bombardment; X-ray photoelectron spectroscopy; Surface reconstructions;
Study of ion bombardment effect for Alq3 films by Yu-Hung Cheng; Kang-Yi Lin; Yang-Che Hung; Chien-Hong Cheng; Kao-Chih Syao; Ming-Chang Lee (6375-6378).
This paper investigated the blue shift of photoluminescence and the changes of surface morphology of Alq3 films by ionic argon plasma bombardment. Plasma with different conditions was applied to bombard thin Alq3 films, modifying both the physical and chemical properties of the films. After characterizing Alq3 films treated with different RF power by XPS, PL and AFM, we proposed the mechanisms to explain the absence of PL blue shift and chemical shift after the films were exposed in the air for more than 3 h. Experimental results showed that molecular structure damages would affect the bandgap of Alq3, leading to the blue shift effect. XPS results also showed that binding energy shifts are caused by enriched oxygen covalent bonds formed inside the films after plasma treatment. Also, surface roughness improves as RF power is increased.
Keywords: Blue shift; Binding energy; Ion bombardment;
Improving surfactant grafting in magnetic colloids by Kezheng Chen; A.F. Bakuzis; Weili Luo (6379-6382).
The grafting number of surfactant coating on magnetite nanoparticles in a magnetic colloid (magnetic fluid), defined as the number of surfactant molecules adsorbed per surface area of nanoparticles, was successfully obtained from the atomic absorption spectroscopy and transmission electron microscopy. We found that the increases of grafting number with the molar concentration of surfactant and the adsorption temperature can be quantitatively measured, making it possible to produce well controlled, stable magnetic colloids that are precursors for many magnetic nanostructures.
Keywords: Magnetic colloids; Grafting number; Nanostructures;
Carbon-plasma produced in vacuum by 532 nm–3 ns laser pulses ablation by L. Torrisi; F. Caridi; D. Margarone; A. Picciotto; A. Mangione; J.J. Beltrano (6383-6389).
A study of VIS laser ablation of graphite, in vacuum, by using 3 ns Nd:YAG laser radiation is reported. Nanosecond pulsed ablation gives an emission mass spectrum attributable to C n neutral and charged particles. Mass quadrupole spectroscopy, associated to electrostatic ion deflection, allows estimation of the velocity distributions of several of these emitting species within the plume as a function of the incident laser fluence. Time gated plume imaging and microscopy measurements have been used to study the plasma composition and the deposition of thin carbon films. The multi-component structure of the plume emission is rationalized in terms of charge state, ions temperature and neutrals temperature. A special regard is given to the ion acceleration process occurring inside the plasma due to the high electrical field generated in the non-equilibrium plasma conditions. The use of nanosecond laser pulses, at fluences below 10 J/cm2, produces interesting C-atomic emission effects, as a high ablation yield, a high fractional ionization of the plasma and presence of nanostructures deposited on near substrates.
Keywords: Laser ablation; Carbon plasma; Plasma temperature;
Promotion of surface SO x on the selective catalytic reduction of NO by hydrocarbons over Ag/Al2O3 by Feng Ouyang; Rong-shu Zhu; Kazuhito Sato; Masaaki Haneda; Hideaki Hamada (6390-6393).
The promotion of sulfur oxides on the selective catalytic reduction (SCR) of NO by hydrocarbons in the presence of a low concentration of sulfur oxides over Ag/Al2O3 has been investigated by a flow reaction test and in situ infrared spectroscopy. When the C3H6 (or C10H22) + NO + O2 feed-flow reaction was tested, maximum NO reduction was below 30% over fresh Ag/Al2O3. After the addition of SO2 to the feed flow, conversion increased slightly. Conversion increased further after SO2 was cut-off from the feed flow. This demonstrated that the increase in NO reduction activity of the catalyst was related to SO x adsorbed on the catalyst. SO x adsorbed on the catalytic surface (1375 cm−1) was detected by IR spectroscopy and was stable within the temperature range. NCO species, as an intermediate in NO reduction, on SO x -adsorbed Ag/Al2O3 in a C3H6 + NO + O2 feed flow was observed in in situ IR spectra during the elevation of the reaction temperature from 473 to 673 K, while it was only observed at 673 K on fresh Ag/Al2O3 under the same experimental conditions. We suggest that SO x in low concentrations depressed the combustion of reductants by contaminating hydrocarbon combustion active sites on the catalyst, resulting in an increase in NO reduction efficiency of the reductants.
Keywords: NO x reduction; Hydrocarbon; Ag/Al2O3; Sulfate;
Synergistic effect between 4-(2-pyridylazo) resorcin and chloride ion on the corrosion of cold rolled steel in 0.5 M sulfuric acid by Libin Tang; Xueming Li; Guannan Mu; Lin Li; Guangheng Liu (6394-6401).
The corrosion inhibition of 1-(2-pyridylazo)-2-naphthol (PAR) on the corrosion of cold rolled steel in 0.5 M sulfuric acid (H2SO4) was studied using weight loss method and potentiodynamic polarization method. Results obtained revealed that together with chloride ion, PAR is an effective corrosion inhibitor for steel corrosion in sulfuric acid. It was found that for steel corrosion inhibition in the presence of single PAR in sulfuric acid the Temkin adsorption isotherm may be used to explain the adsorption phenomenon. For the mixture of PAR and NaCl used as corrosion inhibitor, however, the Langmuir adsorption isotherm can be used to satisfactorily elucidate the adsorption of mixture of PAR and NaCl. Potentiodynamic polarization studies showed that single PAR mainly acts as a cathodic inhibitor for the corrosion of steel in 0.5 M sulfuric acid. The mixture of PAR and chloride ion, however, acts as a mixed type inhibitor that mainly inhibits cathodic reaction of the steel corrosion in sulfuric acid. By means of electrochemical polarization tests, a desorption potential at ca. −370 mV was observed for the adsorption of mixture of PAR and chloride ion, when potential reaches this value, adsorbed inhibitor molecule heavily departs from the steel surface. For the mixture of PAR and chloride ion, thermodynamic parameters such as adsorption heat, adsorption entropy and adsorption free energy were obtained from experimental data of the temperature studies of the inhibition process at four temperatures ranging from 30 to 45 °C, the kinetic data such as apparent activation energies and pre-exponential factors at different concentrations of the inhibitor were calculated, and the effect of the apparent activation energies and pre-exponential factors on the corrosion rates of cold rolled steel was discussed. The most suitable range of inhibitor concentration was discussed. The inhibitive action was satisfactorily explained by using both thermodynamic and kinetic models. Synergism between chloride ion and PAR was proposed. The results obtained from weight loss and potentiodynamic polarization were in good agreement.
Keywords: PAR; Corrosion inhibition; Cold rolled steel; Sulfuric acid; Synergistic inhibition; Chloride ion;