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Applied Surface Science (v.253, #9)

Atomic layer deposition of iridium(III) acetylacetonate on alumina, silica–alumina, and silica supports by R.J. Silvennoinen; O.J.T. Jylhä; M. Lindblad; J.P. Sainio; R.L. Puurunen; A.O.I. Krause (pp. 4103-4111).

The deposition of noble metal particles and films by atomic layer deposition (ALD) has recently gained interest in the fields of catalysis and microelectronics. However, there is little information on the mechanisms governing the reactions of noble metals with high surface area supports. In this work, iridium(III) acetylacetonate was deposited from gas phase onto alumina, silica–alumina, and silica supports to gain insight into the reaction mechanisms. According to elemental analysis and infrared spectroscopy, ligand exchange reaction between iridium acetylacetonate and surface OH groups took place on all substrate surfaces, but the iridium deposition on alumina and silica–alumina appeared to be hindered by sterical effects of the acetylacetonate ligands. Part of the iridium on silica was in metallic form. To reduce the content of iridium, reactive sites of the support surfaces were blocked with H-acetylacetonate (2,4-pentanedione). The blocking reduced the iridium content by more than 90% on alumina but by only 30–50% on silica–alumina. The attempted blocking had almost no effect on silica as expected. According to the results of this work, ALD can provide a feasible method for preparing iridium catalyst with reasonable iridium loadings.

Keywords: PACS; 81.15.GhAtomic layer deposition (ALD); Iridium; Alumina; Silica; Silica–alumina

Quantitative analysis of surface amine groups on plasma-polymerized ethylenediamine films using UV–visible spectroscopy compared to chemical derivatization with FT-IR spectroscopy, XPS and TOF-SIMS by Jinmo Kim; Donggeun Jung; Yongsup Park; Yongki Kim; Dae Won Moon; Tae Geol Lee (pp. 4112-4118).

A quantitative analysis of the surface density of amine groups on a plasma-polymerized ethylenediamine thin film deposited on a platinum surface using inductively coupled plasma chemical vapor deposition method is described. UV–visible spectroscopy together with a chemical derivatization technique using Fourier transform infrared (FT-IR) spectroscopy was used to obtain the quantitative information. Chemical tags of pentafluorobenzaldehyde were hybridized with the surface amine groups and were easily detected due to the characteristic absorption bands of C–F stretching, aromatic ring and CN stretching vibrations in the reflection–absorption FT-IR spectra. The surface amine density was reproducibly controlled as a function of deposition plasma power and quantified using UV–visible spectroscopy. A good linear correlation was observed between the FT-IR intensities of the characteristic absorption bands and the surface amine densities, suggesting the possibility of using this chemical derivatization technique to quantify the surface densities of specific functional groups on an organic surface. Chemical derivatization was also used with X-ray photoelectron spectroscopy on the same samples, and the results were compared with those obtained from FT-IR and time-of-flight secondary ion mass spectrometry. Although each analysis technique has different probing depths from the surface, the three different data sets obtained from the chemical tags correlated well with each other since each analysis technique measured the chemical tags on the sample surface.

Keywords: PACS; 68.47.Mn; 81.15.Gh; 87.64.JePlasma polymerization; Ethylenediamine; Inductively coupled plasma chemical vapor deposition (ICP-CVD); Fourier transform infrared (FT-IR) spectroscopy; X-ray photoemission spectroscopy (XPS); Time-of-flight secondary ion mass spectrum (TOF-SIMS); Quantitative analysis

Preparation and microwave absorption properties of electroless Co–Ni–P coated strontium ferrite powder by Xifeng Pan; Guohong Mu; Haigen Shen; Mingyuan Gu (pp. 4119-4122).

A new type of Co–Ni–P coated strontium ferrite nanocomposite was prepared with electroless plating enhanced by ultrasonic wave at room temperature. The plating process was studied carefully. The morphology, crystal structure and microwave absorption properties of the Co–Ni–P coated powder were studied with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDX) and vector network analyzer. The results show that the strontium ferrite powder was successfully coated with Co–Ni–P alloy and possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder reaches −44.12dB. The bandwidth with the loss above −10dB exceeds 13.8GHz.

Keywords: Electroless plating; Strontium ferrite; Alloy coating; Microwave absorption; Powder

Molecular engineered silica surfaces with an assembled anthracene monolayer as a fluorescent sensor for organic copper(II) salts by Fengting Lü; Lining Gao; Huihui Li; Liping Ding; Yu Fang (pp. 4123-4131).

A novel fluorescence film has been fabricated by covalently coupling anthracene on a glass plate surface via a long flexible “Y” type spacer. Fluorescence measurement demonstrated that the emission of the film is dominated by anthracene monomer emission, and the emission can be selectively quenched by organic copper(II) salts including copper acetate, copper citrate, copper tartrate, etc. Addition of inorganic copper(II) salts like Cu(NO₃)₂, CuSO₄, CuCl₂, etc., however, has little effect upon the emission of the film. This observation was explained by considering the screening effect of the spacer layer, or spacer clusters, or even spacers adopting compact coiled conformation. Different from the reported fluorescence films with similar structures, immobilization of anthracene via a “Y” type spacer on a glass plate surface makes the fluorophore moieties exist in two different states, that is some of them were embedded within the spacer structures, and some of them might stay out of the structures. This hypothesis has been confirmed by model system, solvent effect and quenching mechanism studies. The emission of the film is sensitive to the presence of organic copper(II) salts like copper acetate. The response of the film to copper acetate is fully reversible. Presence of other inorganic salts, including Pb(Ac)₂, Cd(Ac)₂, Zn(Ac)₂, and inorganic copper(II) salts has little effect upon the sensing performance of the film to copper acetate.

Keywords: PACS; 87.64.N; 07.07.DAnthracene; Fluorescence; Sensing; Organic copper(II) salts

Auger electron spectroscopy depth profiling of Fe-oxide layers on electromagnetic sheets prepared by low temperature oxidation by J. Kovač; M. Bizjak; B. Praček; A. Zalar (pp. 4132-4136).

Auger electron spectroscopy depth profiling was applied to characterize the Fe-oxide layers prepared by low temperature oxidation of Fe electromagnetic sheets produced on an industrial line for applications in the field of electrical motors. In addition the surface morphology, layer composition and layer structure were analysed by electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. We found that the oxide layers on Fe-sheets with good adhesion between the oxide layer and Fe-substrate, consist mainly of magnetite and to a smaller extent of haematite; the layers are typically thinner than 1μm and the interface between the oxide layer and the Fe-substrate is relatively broad, i.e. up to 0.3μm. On the contrary, a decrease of adhesion between the oxide layer and the Fe-substrate was found when the layer is thicker than 1μm and the layer/substrate interface is narrow and contaminated by foreign elements.

Keywords: PACS; 68.55.NqAES depth profiling; Oxide layers; Oxidation; Electromagnetic sheets; Adhesion

Imperviousness of the hydrophobic silica aerogels against various solvents and acids by A. Venkateswara Rao; Nagaraja D. Hegde; Poonam M. Shewale (pp. 4137-4141).

The experimental results on the imperviousness of the silica aerogels against various organic solvents and acids, are reported. Various types of hydrophobic silica aerogels were prepared using methyltrimethoxysilane (MTMS); tetraethoxysilane (TEOS) with ethyltriethoxysilane (ETES) and phenyltriethoxysilane (PTES) as co-precursors. The organic solvents used were: methanol, ethanol and acetone, and the acids used were: hydrochloric acid (HCl), nitric acid (HNO₃) and sulphuric acid (H₂SO₄). The imperviousness of the aerogels against these solvents and acids were tested with the variation of the percentage of organic solvents and acids in water from 10 to 100% and was characterized by the contact angle measurements. It was observed that in all the cases, the contact angle decreased with an increase in the percentage of solvent in water. While there was no absorption of the solvent up to 20% in water by the ETES and PTES modified aerogels, the MTMS-based aerogels showed the imperviousness up to 60% of the solvent in water. The MTMS aerogels were also impervious against all the three acids up to 100%, while the ETES and PTES modified aerogels could withstand only up to 80% of acids in water.

Keywords: PACS; 82.33.Ln; 61.43.Gt; 82.70.Uv; 06.30.BpAerogels; Porous materials; Hydrophobic interactions; Contact angle

Laser-induced desorption of overlayer films off a heated metal substrate by Xiang Gu; Herbert M. Urbassek / (pp. 4142-4149).

The temperature-induced desorption of adsorbed overlayer films with thicknesses between 4 and 200 ML off a suddenly heated metal substrate is studied using molecular-dynamics simulation. We observe that the rapid heating vaporizes the surface-near part of the overlayer film. The initial heating-induced thermoelastic pressure and the vapor pressure in the vapor film drive the remaining film as a large relatively cold cluster away from the surface. In our simulations, the material present in the developing vapor film amounts to roughly 2 ML and is quite independent of the overlayer film thickness. For cluster thicknesses beyond 40 ML, the desorption time increases only little with film thickness, while the resulting cluster velocity decreases only slightly.

Keywords: PACS; 68.10.Jy; 64.70.Fx; 79.20.DsDesorption; Laser ablation; Molecular dynamics

Surface chemical functionalized single-walled carbon nanotube with anchored phenol structures: Physical and chemical characterization by Jong Hyun Bae; A.M. Shanmugharaj; Woo Hyun Noh; Won Seok Choi; Sung Hun Ryu (pp. 4150-4155).

Surface functionalization of single-walled carbon nanotube was carried out by introducing ylides groups containing anchored phenol structures. The functionalized nanotube is characterized using elemental analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and zeta potential measurements. Elemental and FT-IR analysis reveal the successful functionalization of azomethine ylides. Raman spectroscopic studies corroborates that the surface functionalization does not affect the basic crystal domain size of the nanotubes. Functionalized carbon nanotubes exhibit higher zeta potential values showing its higher dispersant ability in water and acetone solvent in comparison to pure carbon nanotube.

Keywords: PACS; 81.07.De; 87.64.Je; 87.64.Hd; 87.64.Ee; 81.65.−bNanotube; Raman spectroscopy; Ylides groups

Oxidizing agent concentration effect on metal-assisted electroless etching mechanism in HF-oxidizing agent-H₂O solutions by Toufik Hadjersi (pp. 4156-4160).

The mechanism of metal-assisted electroless etching of silicon in HF-oxidizing agent-H₂O etching system as a function of oxidizing agent concentration was studied. Three types of oxidizing agent were experimented namely Na₂S₂O₈, K₂Cr₂O₇ and KMnO₄. Their concentrations were varied from 0.05M to 0.3M. The layers formed on silicon were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX). It is shown that an insoluble solid-phase film (K₂SiF₆) form on silicon surface when concentration of K₂Cr₂O₇ or KMnO₄ increases in chemical solutions. On other hand, when Na₂S₂O₈ concentration increases, the surface roughness decreases without any chemical complex formation.

Keywords: PACS; 81.65.cf; 81.05.Rm; 82.45.jnInsoluble solid phase K; ₂; SiF; ₆; Dissolution; Silver; Electroless etching

Synthesis and properties of aligned ZnO microtube arrays by Meng-Ke Li; De-Zhen Wang; Sheng Ding; Yong-Wen Ding; Jun Liu; Zhao-Bin Liu (pp. 4161-4165).

Two kinds of different aligned zinc oxide (ZnO) crystal microtube arrays were prepared on silicon (100) substrates by using of a simple thermal chemical reaction vapor transport deposition method. The synthesizing processes were done by using of heating the mixture of zinc oxide and graphite powders at 1150°C in a quartz tube with one side opened to the air. The O₂ gas (99.9%) and air had been introduced as the assistant gases, respectively. Both the flow rates were 100ml/min. And the temperature of the Si (100) substrate region was about 400°C. There is no other metal catalyst on the Si wafers in the process. After growing for 30min, one kind of synthesized sample is trumpet-shaped hexagonal microtube arrays assisted with O₂ gas and another produced sample is the uniform hexagonal microtubes only assisted with air. As the increasing of preparing time, their maximal lengths can range from several 10μm to mm scale. The microstructure, room temperature photoluminescence properties and growth mechanism of both aligned microtube arrays were investigated and discussed.

Keywords: ZnO; Microtube arrays; Growth mechanism

Understanding deviations in lithographic patterns near interfaces: Characterization of bottom anti-reflective coatings (BARC) and the BARC–resist interface by Joseph L. Lenhart; Daniel Fischer; Sharadha Sambasivan; Eric K. Lin; Wen-Li Wu; Douglas J. Guerrero; Yubao Wang; Rama Puligadda (pp. 4166-4175).

Interactions between a bottom anti-reflective coating (BARC) and a photoresist can critically impact lithographic patterns. For example, a lithographic pattern can shrink or spread near a BARC interface, a process called undercutting or footing respectively, due to incompatibility between the two materials. Experiments were conducted on two industrial BARC coatings in an effort to determine the impact of BARC surface chemistry on the footing and undercutting phenomena. The BARC coatings were characterized by near edge X-ray absorption fine structure (NEXAFS), contact angle measurements, and neutron and X-ray reflectivity. Contact angle measurement using a variety of fluids showed that the fluid contact angles were independent of the type of BARC coating or the BARC processing temperature. NEXAFS measurements showed that the surface chemistry of each BARC was also independent of the processing temperature. These results suggest that acid–base interactions at the BARC–resist interface are not the cause of the footing–undercutting phenomena encountered in lithographic patterns.

Keywords: Anti-reflective coating; Photolithography; Footing; Undercutting; BARC; Photoresist; Lithography; Interface

Molecular recognition of chromophore molecules to amine terminated surfaces by Rosangelly Flores-Perez; Albena Ivanisevic (pp. 4176-4181).

We report the design and characterization of quartz surfaces that can bind to three retinal based chromophores. The amine terminated surfaces were engineered in order to mimic the environment of the opsin protein that accommodates binding of chromophore molecules in the human eye. Each surface coupling step was characterized by water contact angle measurements, ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, and transmission infrared spectroscopy. The spectroscopic techniques confirmed that the three chromophore molecules can bind to the surface using a Schiff base mode. Our data suggests that the availability of the amine groups on the surface is critical in the accommodation of the binding of different chromophores.

Keywords: Ellipsometry; Atomic force microscopy; X-ray photoelectron spectroscopy; Infrared spectroscopy; Biomimetic surfaces

The different self-assembled way of n- and t-dodecyl mercaptan on the surface of copper by Degang Li; Xianjin Yu; Yunhui Dong (pp. 4182-4187).

The self-assembled monolayers (SAMs) of n- and t-dodecyl mercaptan on the surface of copper have been obtained. As evidenced by electrochemical impedance spectroscopy (EIS), two kinds of the alkanethiols can self-assemble on the copper surface. But the results of the quartz crystal microbalance (QCM) show that the self-assembled way of the two alkanethiols are different. The SAMs of n-dodecyl mercaptan can increase the weight of the QCM electrode and the SAMs of t-dodecyl mercaptan, on the contrary, make the weight of the QCM electrode decrease. Inspected with the SEM, it is found that a lot of pits spread all over the copper surface after having been modified with t-dodecyl mercaptan. All the results suggest that the self-assemble of t-dodecyl mercaptan on the copper surface can erode and dissolve copper surface sharply.

Keywords: SAMs; n; - and; t; -dodecyl mercaptan; EIS; QCM; SEM

Structural changes of diamond-like carbon films due to atomic hydrogen exposure during annealing by H. Nakazawa; T. Kawabata; M. Kudo; M. Mashita (pp. 4188-4196).

We have deposited diamond-like carbon (DLC) films by radio-frequency magnetron sputtering, and have annealed the films under various conditions to investigate the effects of annealing on the structural properties by visible Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. The structural ordering of hydrogenated DLC films occurs during annealing below 400°C in a vacuum and a hydrogen gas atmosphere, while unhydrogenated DLC films are not ordered during annealing even at 700°C. On the other hand, the ordering and the decrease of the sp³ content are observed for both the films after annealing under an atomic hydrogen exposure. The ordering progresses as the annealing temperature and time are increased. The reduction of the film thickness after annealing is suppressed with increasing annealing temperature. The results suggest that both the preferential etching by atomic hydrogen and the hydrogen evolution encourage the structural changes under an atomic hydrogen exposure.

Keywords: PACS; 61.43.−j ;68.55.−a ;68.60.DvDiamond-like carbon; Sputtering; Raman spectroscopy; X-ray photoelectron spectroscopy; Atomic force microscopy; Hydrogen; Structural properties

Characterization of AZ91 magnesium alloy and organosilane adsorption on its surface by J. Kim; K.C. Wong; P.C. Wong; S.A. Kulinich; J.B. Metson; K.A.R. Mitchell (pp. 4197-4207).

Oxide formation on a clean AZ91-Mg alloy surface has been characterized by X-ray photoelectron spectroscopy (XPS), while the chemical composition of a mirror-polished sample was assessed by scanning Auger microscopy (SAM) and scanning electron microscopy (SEM) at different microstructural regions, referred to as the grain boundary, matrix and particle regions. XPS and SAM confirmed that Mg and Al are always present in the surface regions probed, whereas bulk characterization with energy dispersive X-ray (EDX) analysis was necessary to detect the additional alloying elements, Mn and Zn. Coating by 1% solutions of BTSE, γ-GPS and γ-APS at their natural pH values gave etching of the surface Mg oxide. Adsorption occurs on the different regions, but the attachment is weak, especially because of the fragile nature of the underlying substrate. However, increasing the concentration of BTSE to 4% formed a thicker and denser coating with better prospects for substrate protection.

Keywords: PACS; 81.65.Kn; 81.05.Bx; 68.37.XyMagnesium alloy; Silane coating; Surface microstructure; Auger electron spectroscopy

Surface morphology of cellulose films prepared by spin coating on silicon oxide substrates pretreated with cationic polyelectrolyte by Shingo Yokota; Takuya Kitaoka; Hiroyuki Wariishi (pp. 4208-4214).

Flat cellulose films were prepared and morphologically modified by spin coating a cellulose/ N-methylmorpholine- N-oxide/H₂O solution onto silicon oxide substrates pre-coated with a cationic polyelectrolyte. Spin-coated cellulose films were allowed to stably form on the silicon oxide substrates by pretreatment with either polydiallyldimethylammonium chloride (PDADMAC) or polyvinylamine (PVAm). The film surfaces obtained were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). AFM topographical images of the cellulose film surfaces showed a different morphology depending on the underlying polymer, where PVAm pretreatment brought about an anisotropic surface topology. These results suggest that the specific attraction acting at the cellulose/polymer interface influences both the film formation and surface morphology of the cellulose layer. Differences in the solvent used to precipitate cellulose caused variations in the surface roughness by affecting the cellulose separation behavior. The morphological features of spin-coated cellulose film surfaces could be altered to some extent by these film preparation techniques.

Keywords: PACS; 68. 47. Mn; 68. 55. −a; 82. 35. PqCellulose film; Spin coating; Surface morphology; Polydiallyldimethylammonium chloride; Polyvinylamine; Deposition solvents

Ordered nano-scale domains in lithium niobate single crystals via phase-mask assisted all-optical poling by I.T. Wellington; C.E. Valdivia; T.J. Sono; C.L. Sones; S. Mailis; R.W. Eason (pp. 4215-4219).

We report the formation of directionally ordered nano-scale surface domains on the +z face of undoped congruent lithium niobate single crystals by using UV illumination through a phase mask of sub-micron periodicity with an energy fluence between ∼90mJ/cm² and 150mJ/cm² at λ=266nm. We clearly show here that the UV-induced surface ferroelectric domains only nucleate at and propagate along maxima of laser intensity. Although the domain line separation varies and is greater than 2μm for this set of experimental conditions, this enables a degree of control over the all-optical poling process.

Keywords: PACS; 77.84.Dy; 81.65.CfLithium niobate; Ferroelectric domain inversion; Chemical etching

Mechanics of plasma exposed spin-on-glass (SOG) and polydimethyl siloxane (PDMS) surfaces and their impact on bond strength by Shantanu Bhattacharya; Yuanfang Gao; Venumadhav Korampally; M.T. Othman; Sheila A. Grant; Keshab Gangopadhyay; Shubhra Gangopadhyay (pp. 4220-4225).

Silicone polymer (PDMS), widely used for micro-fluidic and biosensor applications, possesses an extremely dynamic surface after it is subjected to an oxygen plasma treatment process. The surface becomes extremely hydrophilic immediately after oxygen plasma exposure by developing silanol bond (SiOH), which promotes its adhesion to some other surfaces like, silicon, silicon dioxide, glass, etc. Such a surface, if left in ambient dry air, shows a gradual recovery of hydrophobicity. We have found an identical behavior to occur to surfaces coated with a thin continuous film of SOG (methyl silsesquioxane). The chemistry induced by oxygen plasma treatment of a spin-on-glass (SOG) coated surface provides a much higher density of surface silanol groups in comparison to precleaned glass, silicon or silicon dioxide substrates thus providing a higher bond strength with polydimethyl siloxane (PDMS). The bonding protocol developed by using the spin coated and cured SOG intermediate layer provides an universal regime of multi level wafer bonding of PDMS to a variety of substrates. The paper describes a contact angle based estimation of bond strength for SOG and PDMS surfaces exposed to various combinations of plasma parameters. We have found that the highest bond strength condition is achieved if the contact angle on the SOG surface is less than 10°.

Keywords: PACS; 47.54.Jk; 47.55.D−; 47.55.dr; 47.57.NgPDMS; SOG; Plasma; ATR-FTIR; Contact angle; Bond strength

Investigation of a biofunctional polymeric coating deposited onto silicon microcantilevers by P. Bergese; E. Bontempi; M. Chiari; P. Colombi; F. Damin; L.E. Depero; G. Oliviero; G. Pirri; M. Zucca (pp. 4226-4231).

The paper deals with an appealing route to activate silicon microcantilevers (90, 110 and 130μm long, 35μm wide and 2μm thick) for specific binding of biochemical species. The method consists in coating the underivatized microcantilevers with a biofunctional copolymer (based on N, N-dimethylacrylamide bearing silanating moieties) that was developed for low-density microarray assays on microscope glass slides. Coating deposition was obtained by dip-coating and its microstructure investigated by analyzing the resonance frequency values of bare and coated microcantilevers, by SEM and SFM imaging, SFM tip-scratch tests and XRR experiments. Results indicate that the coating is 2.5nm thick and has a density of 1.22g/cm³. The coating surface is nanostructured, displaying nanoblobs, which are from few up to 20nm wide and, on average, 1.6nm high. The diameter of the biggest nanoblobs is of the same order of magnitude of the gyration radius of the copolymer chains, suggesting that nanoblobs may identify individual macromolecules.

Keywords: PACS; 68.37.-d; 87.80.-yCoating; Polymers; Microcantilevers; Biofunctionalization

Experimental constants, characterizing the process of a plasma polymer modification by D.M. Svirachev; N.A. Tabaliov (pp. 4232-4241).

In the following paper, empirical constants are determined by a plasma-chemical model and experimental data of the wetting contact angle. The constants characterize the alteration of the contact angle as a function of the time of the polymer treatment and the kind of the plasma-creating gas. The presented equations of the model connect the contact angle with the empirical constants for arbitrary time intervals of treatment and arbitrary percentage content of the researched gas mixtures and gasses. The chemical rate constants, which describe the process of the plasma modification of the polymer material, are determined.

Keywords: Plasma modification; Surface treatment; Experimental constants; Contact angle; PET; Kinetic model

Plasma–chemical model, describing the surface treatment of polymers in RF-discharge by N.A. Tabaliov; D.M. Svirachev (pp. 4242-4248).

The surface modification of the polymers has been studied in RF-discharge. A plasma–chemical model is presented, describing the alteration of the adhesion work and the wetting contact angle of the treated materials. It is presumed that the adhesion work can be expressed by its volume and surface components. In the first approximation, only the surface adhesion work is changed in the course of the plasma treatment and it is due to creating of two common functional groups. We suggest a basic system of kinetic equations for quantitatively determining these groups. The system is solved analytically. This gives possibilities to obtain the analytical solutions of the adhesion work and the contact angle as a function of the time of treatment.

Keywords: Plasma modification; Polymer; PET; Kinetic model; Contact angle

Ca/Ag bilayer cathode for transparent white organic light-emitting devices by C.J. Lee; R.B. Pode; J.I. Han; D.G. Moon (pp. 4249-4253).

We have demonstrated that the compositional modification of the Ca/Ag films is principally responsible for a high transmittance (over 70% in the visible range) and low sheet resistance (10–12Ω/sq). X-ray photoelectron spectroscopy (XPS) sputter depth profiling of Ca/Ag structure reveals the presence of Ca(OH)₂ and Ca metal. A chemical model of the Ca/Ag cathode is proposed. Using transparent ITO anode and Ca (10nm)/Ag (10nm) cathode, efficient white organic light-emitting devices (WOLEDs) emitting from both sides have been fabricated. Brightness of 3813cd/m² and Commission Internationale de l’Eclairage (CIE) coordinates (0.36, 0.34) at 10V through ITO anode and values of 1216cd/m² and (0.33, 0.30) through Ca/Ag cathode are reported. A low turn-on voltage of 5.5V is measured.

Keywords: PACS; 85.60JbCa/Ag semitransparent cathode; Transmittance; XPS; Transparent WOLEDs

Conformal coverage for two-dimensional arrays of microcavites with quasi-three dimensional confinement by distributed Bragg reflectors by San Chen; Bo Qian; Kunji Chen; Wei Li; Peigao Han; Jun Xu; Zhongyuan Ma; Wei Li; Xinfan Huang (pp. 4254-4259).

Different from conventional three-dimensional confined microcavity fabrication method in which micropillar microcavities were obtained through the etching of planar semicoductor microcavities, we adopted the conformal coverage to fabricate two-dimensional arrays of quasi three-dimensional confined optical microcavities providing both vertical and lateral optical confinement by the distributed Bragg reflectors (DBRs). Our microcavity samples were directly deposited on the patterned substrates with two-dimensional arrays of air holes. The SEM and cross-section TEM images show that the periodicity of the patterned substrate was still kept after deposition while the growth of DBRs along the sidewalls occurred simultaneously, which provided the transverse optical confinement. In order to probe the optical modes of this kind of microcavities, room temperature photoluminescence signals from prepared microcavities were detected. Three resonant modes were presented and exhibited obvious angular dependence. We attributed these phenomena to quantization of the in-plane wave vector components confined by lateral DBRs.

Keywords: Microcavity; Conformal coverage; Photoluminescence

First-principles study of oxygenated diamond (001) surfaces with and without hydrogen by Hongxin Yang; Lifang Xu; Changzhi Gu; S.B. Zhang (pp. 4260-4266).

The structural characterization of oxygenated diamond (001) surface with and without H-presence has been investigated by the density-functional theory within the generalized gradient approximation and the plane-wave pseudopotential method. It is shown that, without the H, the O-bridge site has lower energy than the O-on-top site for both half and fully monolayer (ML) oxygen coverage. For hydrogenated diamond (001) surfaces, we found for half ML O coverage, a more stable (2×2):0.5H&0.5(OH) phase than the previously reported (2×1):0.5H&0.5(OH) phase [H. Tamura, H. Zhou, K. Sugisako, Y. Yokoi, S. Takami, M. Kubo, K. Teraishi, A. Miyamoto, A. Imamura, M.N. Gamo, T. Ando, Phys. Rev. B 61 (2000) 11025]. Furthermore, at one ML O coverage, a (2×2):(OH) phase is the most stable structure than the previously reported (2×1):(OH) phase. With the increase of the (OH) coverage, the importance of the hydrogen bonds increases in terms of stabilizing these structures.

Keywords: Diamond surface; Oxygenated; Hydroxylated; Stability; First principles

Growth characteristics of micro-plasma oxidation ceramic coatings on Ti alloy by inductively coupled plasma-atomic emission spectrometer technique by Zhongping Yao; Zhaohua Jiang; Fuping Wang; Wei Xue (pp. 4267-4272).

The aim of this work was to study the growth characteristics of micro-plasma oxidation ceramic coatings on Ti–6Al–4V alloy. Compound ceramic coatings were prepared on Ti–6Al–4V alloy by pulsed micro-plasma oxidation (MPO) in NaAlO₂ solution. The phase composition and surface morphology of the coating were investigated by X-ray diffractometry and scanning electron microscopy. The solution of Ti from the substrate and the content of Al in the electrolyte were studied by inductively coupled plasma-atomic emission spectrometer (ICP-AES) technique. Ti from the substrate dissolved and came into the coating and the electrolyte during MPO process. The content of Ti in the electrolyte under the pulsed bi-polar mode was more than that of the pulsed single-polar mode. The phase composition and structure of the coating was attributable to the space steric hindrance of Al congregated on the electrode surface due to the effect of the electric field and the electrolyte characters. For the pulsed single-polar mode, the coating was mainly composed of a large amount of α-Al₂O₃ and a small amount of γ-Al₂O₃. And the coating was mainly structured by Al from the electrolyte. However, the coating was composed of a large amount of Al₂TiO₅ and a little α-Al₂O₃ and rutile TiO₂ for the pulsed bi-polar mode. And the coating was structured both by Ti from the substrate and Al from the electrolyte.

Keywords: Micro-plasma oxidation; Ti alloy; Ceramic coatings; ICP-AES

Electrodeposited metals at conducting polymer electrodes by Nada F. Atta; A. Galal; F. Khalifa (pp. 4273-4282).

Conducting polymers are electrochemically polymerized at platinum electrode substrates. The thickness, porosity and surface morphology of the resulting films are controlled by the charge passing during electropolymerization step and the synthesis conditions. The polymer films are modified by electrochemically depositing platinum particles. The technique of deposition depends on applying a programmed potential pulse at the polymer film from a solution containing platinum complex that resulted in the formation of platinum particles of controlled size and distribution. The effect of changing the size of platinum particles and polymer film thickness on the voltammetric behavior of the resulting hybrid material showed noticeable changes in the electro-catalytic current in acid medium. On the other hand, the electrochemical impedance spectroscopy experiments showed that diffusion and charge-transfer rate increased in the order: unmodified polymer films, thin polymer films containing small size/amount of platinum particles and relatively thick polymer films containing larger size/amount of platinum particles. The morphology of polymer films, size and distribution of platinum particles in the film were studied by scanning electron microscopy. The presence of platinum and its distribution over the film surface was confirmed from the X-ray dispersive analysis and surface mapping. The hybrid materials are good candidates for the application in devices for exchange of hydrogen ions.

Keywords: Conducting polymers; Nano-particles in polymers; Electrochemistry; Electrocatalytic activity; EIS; SEM

Formation of the Si/Ti interface by C. Palacio; A. Arranz (pp. 4283-4288).

The formation of the Si/Ti interface during the deposition of silicon on titanium polycrystalline substrates has been studied at room temperature (RT) using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS (ARXPS), ultraviolet photoelectron spectroscopy (UPS) and ion scattering spectroscopy (ISS). The experimental results are consistent with a two-stage mechanism for Si growth: a first stage characterized by the simultaneous formation of a uniform titanium silicide layer, that reaches a limiting thickness of ∼3 monolayer (ML), and pure silicon islands 1ML thick that grow on top of this layer up to coalescence, followed by a second stage in which pure silicon islands, with an average thickness of 9ML, grow on top of the uniform titanium silicide layer+pure silicon ML structure formed during the first stage. As a whole, pure silicon species grows according to a Stranski–Krastanov mechanism, where the first ML is formed during the first stage and the islands during the second stage. The comparison of Ti/Si and Si/Ti interfaces shows that the structure and composition of the interface do not depend substantially on the deposition sequence, suggesting that the bulk chemistry of the compound formed at the interface dominates over the surface kinetics and the bulk substrate chemistry in determining the composition and structure of the interface.

Keywords: Silicides; Metal–semiconductor interfaces; Surface chemical reaction; Photoelectron spectroscopy; Low energy ion scattering

Thin film stress measurement by instrumented optical fibre displacement sensor by S. Chowdhury; M.T. Laugier (pp. 4289-4294).

Residual stress can adversely affect the mechanical, electronic, optical and magnetic properties of thin films. This work describes a simple stress measurement instrument based on the bending beam method together with a sensitive non-contact fibre optical displacement sensor. The fibre optical displacement sensor is interfaced to a computer and a Labview programme enables film stress to be determined from changes in the radius of curvature of the film–substrate system. The stress measurement instrument was tested for two different kinds of thin film, hard amorphous carbon nitride (CN) and soft copper (Cu) films on silicon substrates deposited by RF magnetron sputtering. Residual stress developed in 500nm thick CN thin films deposited at substrate temperatures in the range 50–550°C was examined and it was found that stress in CN films decreased from 0.83 to 0.44GPa compressive with increase of substrate temperature. Residual stress was found to be tensile (121MPa) for Cu films of thickness 1500nm deposited at room temperature.

Keywords: Thin film; Stress measurement; Bending beam method; Carbon nitride; Copper

Laser induced modification of surface structures by L.L. Sartinska; S. Barchikovski; N. Wagenda; B.M. Rud’; I.I. Timofeeva (pp. 4295-4299).

The results on surface modification of materials of different structures; morphology, grain sizes, density and porosity by exposure to nanosecond laser light are given. Laser induced changes in their surface characteristics are presented. Surface layers of Si₃N₄, SiC dense ceramics and BN graphite and turbostratic pressed powders are studied by scanning electron microscopy to reveal the new nanostructures (nanowires or nanotubes) and new morphologies. A pronounced evolution in structure and grain size of BN graphite powders was demonstrated in laser processing layers.

Keywords: Surface; Laser modification; Ceramics; Nanostructures; Nanowires; Nanotubes

Nanoscale imaging of surface piezoresponse on GaN epitaxial layers by T. Stoica; R. Calarco; R. Meijers; H. Lüth (pp. 4300-4306).

Surfaces of GaN films were investigated by atomic force microscopy (AFM) with implemented piezoelectric force microscopy technique. A model of PFM based on the surface depletion region in GaN films is discussed. The local piezoelectric effect of the low frequency regime was found to be in phase with the applied voltage on large domains, corresponding to a Ga-face of the GaN layer. Low piezoresponse is obtained within the inter-domain regions. The use of frequencies near a resonance frequency enhances very much the resolution of piezo-imaging, but only for very low scanning speed the piezo-imaging can follow the local piezoelectric effect. An inversion of the PFM image contrast is obtained for frequencies higher than the resonance frequencies. The effect of a chemical surface treatment on the topography and the piezoresponse of the GaN films was also investigated. Textured surfaces with very small domains were observed after the chemical treatment. For this kind of surfaces, piezo-induced torsion rather than bending of the AFM cantilever dominates the contrast of the PFM images. A small memory effect was observed, and explained by surface charging and confinement of the piezoelectric effect within the carrier depletion region at the GaN surface.

Keywords: PACS; 77.84.Bw; 68.37.Ps; 68.47.Fg; 61.72.Qq; 81.05.EaGallium nitride; Molecular beam epitaxy; Scanning probe techniques; Piezoresponse

The periodicity in translation of Ag (001) and (110) twist grain boundary by Xiu-Mei Wei; Jian-Min Zhang; Ke-Wei Xu (pp. 4307-4310).

The energies of Ag (001) and (110) twist grain boundary (GB) in translation have been calculated with the modified analytical embedded atom method (MAEAM). The energy period corresponds exactly to the DSC lattice unit cell and the area of the energy period referred to the CSL unit cell is 1/ Σ². The ‘energy grooves’ are parallel to the sides of the CSL or DSC lattice unit cell. The most preferable sliding direction is parallel to identical sides of the square CSL unit cell for (001) boundaries and to the short side of the rectangular CSL unit cell for (110) boundaries. From energy minimization, the stable configuration appears when two adjacent grains are translated relatively to the corners, centre or sides’ midpoint of the DSC lattice unit cell.

Keywords: PACS; 61.43.Bn; 61.72.Mm; 98.38.BnGrain boundary; Translation; Periodicity; MAEAM

Electrostatic assembly of protein lysozyme on DNA visualized by atomic force microscopy by Tao Yang; Gang Wei; Zhuang Li (pp. 4311-4316).

In the present work, atomic force microscopy (AFM) has been used to study the assembly of protein lysozyme on DNA molecule. Based on the electrostatic interaction, the positively charged lysozyme can easily bind onto the negatively charged DNA molecule surface. The protein molecules appear as globular objects on the DNA scaffold, which are distinguishable in the AFM images. At the same time, lysozyme molecules can be assembled onto DNA as dense or sporadic pattern by varying the protein concentration. This work may provide fundamental aspects for building protein nanostructures and studying of DNA–protein interaction.

Keywords: PACS; 36.20; 41.20.C; 61.16.CProtein; Electrostatic; Atomic force microscopy

Implanted ZnO thin films: Microstructure, electrical and electronic properties by J. Lee; J. Metson; P.J. Evans; R. Kinsey; D. Bhattacharyya (pp. 4317-4321).

Magnetron sputtered polycrystalline ZnO thin films were implanted using Al, Ag, Sn, Sb and codoped with TiN in order to improve the conductivity and to attempt to achieve p-type behaviour. Structural and electrical properties of the implanted ZnO thin films were examined with X-ray diffractometry (XRD), scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM) and conductivity measurements. Depth profiles of the implanted elements varied with the implant species. Implantation causes a partial amorphisation of the crystalline structure and decreases the effective grain size of the films. One of the findings is the improvement, as a consequence of implantation, in the conductivity of initially poorly conductive samples. Heavy doping may help for the conversion of conduction type of ZnO thin films. Annealing in vacuum mitigated structural damage and stress caused by implantation, and improved the conductivity of the implanted ZnO thin films.

Keywords: PACS; 78.66.Hf; 61.72.Vv; 68.55ZnO; Ion implantation; Microstructure; Electrical and electronic properties

Characterization of the “native” surface thin film on pure polycrystalline iron: A high resolution XPS and TEM study by G. Bhargava; I. Gouzman; C.M. Chun; T.A. Ramanarayanan; S.L. Bernasek (pp. 4322-4329).

The characterization of the “native” surface thin film on pure polycrystalline iron has been studied by high resolution X-ray photoelectron (XP) spectroscopy of Fe 2p and O 1s regions. The film was allowed to form by exposing the sample to atmosphere at ambient conditions for a period of 1h. The systematic approach used here includes the determination of curve fitting parameters from external standards and their use in fitting the raw data for the surface thin film. The quantitative high resolution XPS analysis involved an angle resolved study of the surface to determine the chemical composition and thickness of this native film. The film was found to be a mixture of Fe₃O₄ and Fe(OH)₂ with a thickness of 1.2±0.3nm. This conclusion is consistent with thermodynamics as indicated by the Pourbaix diagram for the Fe–H₂O system and the phase diagram for the Fe–oxygen system. A detailed TEM study of the native surface film also supports this conclusion.

Keywords: Iron; Surface; Oxide; Hydroxide; XPS; TEM

Properties of NiO thin films deposited by intermittent spray pyrolysis process by B.A. Reguig; A. Khelil; L. Cattin; M. Morsli; J.C. Bernède (pp. 4330-4334).

NiO thin films have been grown on glass substrates by intermittent spray pyrolysis deposition of NiCl₂·6H₂O diluted in distilled water, using a simple “perfume atomizer”. The effect of the solution molarity on their properties was studied and compared to those of NiO thin films deposited with a classical spray system. It is shown that NiO thin films crystallized in the NiO structure are achieved after deposition. Whatever the precursor molarity, the grain size is around 25–30nm. The crystallites are preferentially oriented along the (111) direction. All the films are p-type. However, the thickness and the conductivity of the NiO films depend on the precursor contraction. By comparison with the properties of films deposited by classical spray technique, it is shown that the critical precursor concentration, which induces strong thin films properties perturbations, is higher when a perfume atomizer is used. This broader stability domain can be attributed to better chlorides decomposition during the rest time used in the perfume atomizer technique.

Keywords: p-Type transparent semiconductor; NiO thin films; Spray pyrolysis

Preparation and characterization of ZnTe thin films by SILAR method by S.S. Kale; R.S. Mane; H.M. Pathan; A.V. Shaikh; Oh-Shim Joo; Sung-Hwan Han (pp. 4335-4337).

Nanocrystalline zinc telluride (ZnTe) thin films were prepared by using successive ionic layer adsorption and reaction (SILAR) method from aqueous solutions of zinc sulfate and sodium telluride. The films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and optical absorption measurement techniques. The synthesized ZnTe thin films were nanocrystalline with densely aggregated particles in nanometer scale and were free from the voids or cracks. The optical band gap energy of the film was found to be thickness dependent. The elemental chemical compositional stoichiometric analysis revealed good Zn:Te elemental ratio of 53:47.

Keywords: ZnTe; Thin films; Solution chemistry; XRD; SEM; Optical studies

Influence of coupling agent chain lengths on interfacial performances of polyarylacetylene resin and silica glass composites by Z.X. Jiang; L.H. Meng; Y.D. Huang; L. Liu; C. Lu (pp. 4338-4343).

The influence of chain lengths on interfacial performances of polyarylacetylene (PAA)/silica glass composites was studied. In order to obtain different chain lengths on substrates, methyltrimethoxysilane, propyltrimethoxysilane, octyltrimethoxysilane and dodecyltrimethoxysilane were grafted onto silica glass surface. Topographies of silica glass surface and the wetting ability of PAA resin on silica glass surface were characterized by atomic force microscopy (AFM) and surface free energy along with contact angles, respectively. At the same time, the interfacial adhesion was evaluated by shear strength testing. The failure mechanisms of composites were also analyzed by fracture morphologies. The results of the study indicate that with chain lengths of coupling agents on silica glass surface increasing, interfacial shear strengths of PAA/silica glass composites increase, while the wetting ability of PAA resin on silica glass surface decreases. The main mechanism for the improvement of the interfacial adhesion is physical entanglement interaction between the chain of coupling agent and the chain of PAA resin.

Keywords: PACS; 73.61.PhCoupling agent; Polyarylacetylene resin; Entanglement

Enhanced luminescence of GdTaO₄:Eu³⁺ thin-film phosphors by K doping by Xiaolin Liu; Xin Xu; Mu Gu; Lihong Xiao; Kun Han; Rui Zhang (pp. 4344-4347).

The effect of K⁺ ions on GdTaO₄:Eu³⁺ thin-film phosphors was investigated in order to improve their luminescent properties. The GdTaO₄:Eu_0.1, K_x thin films were synthesized by sol–gel process, and characterized through measuring their microstructure and luminescence. The results indicated that photoluminescence (PL) intensity of GdTaO₄:Eu³⁺ film was improved remarkably by K doping. There were two maxima in the curve of PL intensity against K⁺ dopant concentration, where one was improved up to 2.1 times at x=0.001 and the other was enhanced up to 2.7 times at x=0.05. The first maximum was regarded as the alteration of the local environment surrounding the Eu³⁺ activator by incorporation of K⁺ ions, and the second maximum was due to the flux effect. Additionally, the luminescence increased with the increase of firing temperature from 800°C to 1200°C.

Keywords: PACS; 77.84.Dy; 78.20.−e; 78.55.−m; 81.20.FwK doped GdTaO; ₄; :Eu; ³⁺; Thin films; Sol–gel process; Luminescence

Preparation and characterisation of electrodeposited amorphous Sn–Co–Fe ternary alloys by C. Chisholm; E. Kuzmann; M. El-Sharif; O. Doyle; S. Stichleutner; K. Solymos; Z. Homonnay; A. Vértes (pp. 4348-4355).

Electrochemical deposition was investigated as a process to obtain alloys of Sn–Co–Fe, which to date have not been reported in the literature. A constant current technique was used to electrochemically deposit tin–cobalt–iron alloys from a gluconate electrolyte. The gluconate system was chosen as an electrolyte, which could potentially provide an environmentally safe process. The effect of plating parameters such as current density, deposition time, temperature and pH are discussed. Results are reported for current density and plating time using an electrolyte temperature of 20–60°C and pH of 7.0 in relation to phase composition, crystal structure and magnetic anisotropy of the deposited alloys.Investigations were conducted using⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS),¹¹⁹Sn CEMS, transmission Mössbauer Spectroscopy and XRD. The⁵⁷Fe and¹¹⁹Sn CEMS spectra and XRD showed that the dominant phase in the deposits was amorphous Sn–Co–Fe. The relative area of the 2nd and 5th lines of the sextets representing the magnetic iron containing phases was found to decrease continuously with increasing current density while at the same time no significant changes in the magnetic anisotropy was found with plating time. Magnetically split¹¹⁹Sn spectra reflecting a transferred hyperfine field were also observed.A range of good quality amorphous Sn–Co–Fe ternary alloys was obtained over a range of operating conditions from an environmentally acceptable gluconate electrolyte.

Keywords: PACS; 81.15.Pq; 73.61.At; 61.10.Nz; 61.18.FsElectrodeposition; Sn–Co–Fe alloy; XRD; Mössbauer spectroscopy

Thermochemical process in preparation of ZnO film by TFA-MOD method by Youming Zou; Yuxia Wang; Hongjuan Zhang; Zheng Chen; Jianwen Wang; Yun Li (pp. 4356-4360).

The excess weight loss due to the evaporation of zinc compound is observed in the growth of ZnO film by trifluoroacetate metalorganic deposition (TFA-MOD) method. Higher temperature (>90°C) aging and/or addition of monoethanolamine (MEA) are effective to prevent the evaporation of zinc compound and increase the yield of ZnO. The mechanism of preventing evaporation is that zinc trifluoroacetate is hydrolyzed into Zn₄O(CF₃COO)₆. A three-dimensional structure of Zn₄O(CF₃COO)₆ is proposed. It is shown that higher temperature aging does harm to the surface morphology of ZnO films. The addition of MEA reduces the required aging temperature thus improves the surface morphology.

Keywords: PACS; 81.15−z; 81.70.PgZinc oxide; Films; Trifluoroacetate metalorganic deposition

Electron beam-physical vapor deposition of SiC/SiO₂ high emissivity thin film by Jian Yi; XiaoDong He; Yue Sun; Yao Li (pp. 4361-4366).

When heated by high-energy electron beam (EB), SiC can decompose into C and Si vapor. Subsequently, Si vapor reacts with metal oxide thin film on substrate surface and formats dense SiO₂ thin film at high substrate temperature. By means of the two reactions, SiC/SiO₂ composite thin film was prepared on the pre-oxidized 316 stainless steel (SS) substrate by electron beam-physical vapor deposition (EB-PVD) only using β-SiC target at 1000°C. The thin film was examined by energy dispersive spectroscopy (EDS), grazing incidence X-ray asymmetry diffraction (GIAXD), scanning electron microscopy (SEM), atomic force microscopy (AFM), backscattered electron image (BSE), electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS) and Fourier transformed infra-red (FT-IR) spectroscopy. The analysis results show that the thin film is mainly composed of imperfect nano-crystalline phases of 3C-SiC and SiO₂, especially, SiO₂ phase is nearly amorphous. Moreover, the smooth and dense thin film surface consists of nano-sized particles, and the interface between SiC/SiO₂ composite thin film and SS substrate is perfect. At last, the emissivity of SS substrate is improved by the SiC/SiO₂ composite thin film.

Keywords: EB-PVD; SiC; SiO; ₂; High emissivity; Thermal protection

RF-CF₄ plasma surface modification of paper: Chemical evaluation of two sidedness with XPS/ATR-FTIR by Halil Turgut Sahin (pp. 4367-4373).

The study was performed to examine the correlation between the initial roughness and surface fluorination of paper under RF-CF₄ plasma environment.Based on the experimental observations, a correlation was observed between surface fluorination and plasma parameters, e.g. RF-power, treatment time and gas pressure. The level of fluorination with RF-CF₄ plasma treatment was found to be extensive in both side of paper. Even very short treatment time, as low as 1min at 300W power, provides effective implantation of fluorine (38.7%) on surfaces. It was observed that, CF₄ plasma treatment had a significant effect on the molecular fragmentation on both side of paper. However, the felt side have a much stronger effect on plasma-induced dissociation and fluorination than in the wire side of paper.

Keywords: PACS; 81.15.Fg; 52.38.Ph; 52.77.Bn; 52.40 Hx; 82.33.XjPlasma; Film deposition; Etching; Plasma surface interaction; Paper; Two sidedness

A novel hole-blocking layer NaF between the α-naphthylphenyliphenyl diamine and ITO by Su Zhan; Xie Ying-Ge; Li Xia; Yu Tao (pp. 4374-4376).

Organic light-emitting devices (OLEDs) with the hole-blocking layer NaF between the α-naphthylphenyliphenyl diamine and ITO were fabricated using a vacuum evaporation method. Compared to the different thickness of the hole-blocking layer, the OLEDs with the 1.0nm thickness layer showed the maximum efficiency. The enhancements in efficiency were resulted from an improved balance of hole and electron injections. After comparing different hole-blocking layer density, NaF was a good candidate for the hole-blocking layer, and 1.0-nm thickness NaF layer showed better operational durability and life.

Keywords: Organic light-emitting devices; NaF; Indium tin oxide; Hole-blocking layer; Current efficiency

Tribological properties of rare earth oxide added Cr₃C₂–NiCr coatings by Zhenyu Zhang; Xinchun Lu; Jianbin Luo (pp. 4377-4385).

A novel supersonic plasma spraying was used to prepare rare earth oxide added Cr₃C₂–NiCr coatings. X-ray diffractometer, contact surface profiler, hardness tester, micro-friction and -wear tester, environmental scanning electron microscope equipped with energy dispersive spectroscopy were employed to investigate the phase structure, surface morphology, microhardness, and friction properties of deposited coatings, respectively. The results show that surface roughness, microhardness, brittle fracture, friction extent and wear resistance of rare earth oxide added Cr₃C₂–NiCr coatings are effectively improved compared with that of unadded one. The friction and friction mechanism are also discussed.

Keywords: Supersonic plasma spraying; Cr; ₃; C; ₂; –NiCr coating; Rare earth oxide; Tribological property

Fabrication of self-lubricating coating on aluminum and its frictional behaviour by Hui Wang; Haowei Wang (pp. 4386-4389).

A self-lubricating anodic film has been formed on aluminum by anodization in phosphoric acid–base electrolyte and a subsequent technique containing ultrasonic impregnation and heat treatment. The results show that the ultrasonic impregnation after anodization of aluminum in an electrolyte of phosphoric acid and some additives can fill some PTFE into the holes of alumina and the surface hardness decreases little within appropriate ultrasonic time. The final heat treatment technology can increase the coating hardness greatly, especially to the alumina acquired by general anodization. With this fabricating method, the properties of anti-attrition and abrasion resistance of self-lubricating coating improved greatly.

Keywords: Anodization; Self-lubricating; Ultrasonic impregnation; Heat treatment

Study on the mechanisms of photoinduced carriers separation and recombination for Fe³⁺–TiO₂ photocatalysts by Baifu Xin; Zhiyu Ren; Peng Wang; Jia Liu; Liqiang Jing; Honggang Fu (pp. 4390-4395).

The iron(III)-ion doped TiO₂ (Fe³⁺–TiO₂) with different doping Fe³⁺ content were prepared via a sol–gel method. The as-prepared Fe³⁺–TiO₂ nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and the photoelectrochemical properties of Fe³⁺–TiO₂ catalysts with different Fe³⁺ content are performed by electrical impedance spectroscopy (EIS) as well as photocatalytic degradation of RhB are studied under illuminating. Based on the experiment results, the mechanism of photoinduced carriers separation and recombination of Fe³⁺–TiO₂ was revealed: that is, the Fe³⁺ captures the photoinduced electrons, inhibiting the recombination of photoinduced electron–hole pairs, this favors to the photocatalytic reaction at low doping concentration (Fe/Ti≤0.03mol%); while Fe³⁺ dopant content exceeds 0.03mol%, Fe₂O₃ became the recombination centers of photoinduced electrons and holes because of that the interaction of Fe₂O₃ with TiO₂ leads to that the photoinduced electrons and holes of TiO₂ transfer to Fe₂O₃ and recombine quickly, which is unfavorable to the photocatalytic reaction.

Keywords: PACS; 73.50.Pz; 73.90.+f; 84.37.+qFe; ³⁺; doped TiO; ₂; Photocatalysis; Photoinduced carrier characteristics

Stress-induced leakage currents of the RF sputtered Ta₂O₅ on N-implanted silicon by N. Novkovski; E. Atanassova; A. Paskaleva (pp. 4396-4403).

The electrical ( C– V and I– V) and reliability (constant current stress technique) properties of RF sputtered 30nm thick Ta₂O₅ on N-implanted Si have been investigated. The dependence on the parameters of both Ta₂O₅ and the implanted interfacial layers on the stress time are discussed. The leakage current characteristics are analyzed by previously proposed comprehensive model. It is established that the reliability of the Ta₂O₅-based capacitors can be effectively improved if the Si substrate is a subject to preliminary N-implantation—markedly smaller stress induced leakage current as compared to the films on bare Si are detected. The stress mainly affects the properties of the interfacial layer and the generation of neutral traps is identified to be the primary cause for the stress-induced degradation. It is concluded that the implantation results in a strengthening of the interfacial layer against stress degradation.

Keywords: Constant current stress; Tantalum pentoxide; N-implantation; Silicon

Laser etching of Thoria pellets for microstructural investigations by Sucharita Sinha; E. Ramadasan; V.P. Jathar; K. Dasgupta; K.C. Sahoo; L.M. Gantayet (pp. 4404-4408).

Metallographic investigation of the microstructure of sintered Thoria pellets necessitates appropriate surface preparation of these pellets. Conventional etching methods involving either chemical or thermal etching techniques being unsuitable for surface etching of irradiated Thoria fuel, laser-based surface treatment was envisaged as a potential alternative technique. Thoria pellets were subjected to laser surface treatment using a pulsed Nd:YAG laser.Our preliminary studies have successfully demonstrated laser etching of sintered Thoria pellets with good reproducibility, clearly revealing grain structures and well-defined grain boundaries. Detailed parametric investigations determining optimum laser parameters for the process, are presented. Our results on ultra-short laser-based etching of sintered Thoria pellets are also discussed.

Keywords: Etching; Laser processing; Laser beams; Surface structure

Microstructure evolution of WC/steel composite by laser surface re-melting by You Xianqing; Zhang Chengjun; Song Xuefeng; Huang Manping; Ma Jianguo (pp. 4409-4414).

WC/steel composites fabricated by electro-slag melting and casting were re-melted by transverse flow CO₂ laser. Optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and transmission electron microscopy were used to analyze the microstructure evolution in laser melted layer. It was found that the laser-affected zone has three distinguished zones, the melted, transient and heat affected zone. The phases of the melted zone were composed of WC, Fe₃W₃C, (Cr,Fe)₇C₃, martensite and retained austenite. The microstructure evolution in the melted zone was represented by the transformation of three parts including the steel matrix, WC particles cluster and dispersed carbides. A significant reactant was herringbone eutectic carbide of Fe₃W₃C. The effect of laser scanning rate was mainly behaved in affecting the melt depth, microstructure of transient zone and dissolution of medium carbides. In comparison with the substrate, the melted zone has much higher microhardness.

Keywords: Electro-slag melting and casting; Laser surface melting; WC/steel composites; Microstructure

The effect of bias voltage and working pressure on S/Mo ratio at MoS₂–Ti composite films by F. Bülbül; İ. Efeoğlu; E. Arslan (pp. 4415-4419).

S/Mo ratio has a crucial effect on the tribological properties of MoS₂–Ti composite films. The deposition parameters as such bias voltage and working pressure play a dominant role on the change of this ratio value. To determine the effect of working pressure and bias voltage on S/Mo ratio, MoS₂–Ti composite films were deposited on glass wafers by pulsed-dc magnetron sputtering (PMS). The deposition process was performed for nine different test conditions at various levels of target current, working pressure, and substrate voltage using the Taguchi L₉(3⁴) experimental method. It was observed that the chemical composition of MoS₂–Ti composite films was significantly affected by sputtering parameters. It was also observed that S/Mo ratio decreased as the bias voltage increased at a constant working pressure and S/Mo ratio increased with increasing working pressure at a constant bias voltage.

Keywords: MoS; ₂; –Ti; Bias; Working pressure; Sputtering; S/Mo

Effect of a small increase in the Ni content on the properties of a laser surface clad Fe-based alloy by Xiu-Ying Yang; Xiao Peng; Jiang Chen; Fu-hui Wang (pp. 4420-4426).

Two Fe-based alloys with a small variation in the Ni content, Fe–15.2Cr–5.1Ni and Fe–15.7Cr–7.1Ni (wt.%), were fabricated on a martensitic stainless steel 1Cr13 substrate by laser surface cladding (LSC) using a CO₂ laser and Ar shielding gas that was blown into a molten pool. Both LSC alloys exhibited typical rapid directional solidification structures. However, 2wt.% Ni increase led to ∼9% increase in the weight fraction of austenite, and ∼5% increase in the area proportion of interdendritic regions, which contained the higher Cr contents. These microstructural changes caused a great reduction in the microhardness and great improvements in the resistance to electrochemical corrosion in 0.5M H₂SO₄ solution and high temperature oxidation in air at 900°C. The reasons for these differences are discussed in detail.

Keywords: PACS; 42.62.−b; 61.82.BgFe-based alloy; Laser surface cladding; Microhardness; Electrochemical corrosion; High temperature oxidation

Theoretical and experimental study of methane steam reforming reactions over nickel catalyst by C. Pistonesi; A. Juan; B. Irigoyen; N. Amadeo (pp. 4427-4437).

In this work we perform DFT theoretical calculations of methane and steam interactions on Ni(111) surface. The calculations allow us to improve our understanding of the competition between these reactants by catalytic sites in methane steam reforming (MSR) process. For this purpose we compare theoretical results with kinetic measurements of MSR on a Ni(II)–Al(III) catalyst prepared from lamellar double hydroxides as precursor. This comparison shows that, for low H₂O/CH₄ ratios methane and water intermediate species adsorb on different catalytic sites. While CHO species adsorbs on top of Ni atom, OH one occupies preferentially a tri-coordinate surface site. On the other hand, for high H₂O/CH₄ ratios a competency between these species by Ni sites would establish, diminishing methane conversion. In addition competition between methane and steam for Ni sites would lead to a decrease in CO production. Nevertheless, intermediate species adsorbed on different active sites would produce CO₂, whatever the steam/methane ratio. Thus, it would be optimum steam concentration in hydrocarbon feed and active sites distribution on catalyst surface, which could maximize H₂ production and minimize CO selectivity. The theoretical findings agree with kinetic measurements, which show that maximum methane conversion depends on steam partial pressure in the feed; whereas always, selectivity to CO₂ increases and to CO diminishes.

Keywords: Methane steam reforming process; DFT calculations; CO and CO; ₂; production; Ni/Al catalyst

Light induced adsorption of Si nano-composites in LiF crystals at 157nm by E. Sarantopoulou; Z. Kollia; A.C. Cefalas; S. Kobe (pp. 4438-4444).

Si nano-composites were precipitated on LiF crystals following ablation from Si targets with laser light at 157nm. The LiF/Si interface was analyzed with scanning electron microscopy, atomic force microscopy and energy dispersive X-ray microanalysis. It was found that Si composites were strongly attached to LiF ionic sites to form inhomogeneous structures consisted of small isotropic crystals 0.1–1μm long, rich in Si and fluorine, which eventually further agglomerate to form larger structures. The thickness of the LiF/Si interface was increased from 50nm to 2μm following laser irradiation at 157nm, due to accelerated adsorption of Si in the LiF interface by VUV light.

Keywords: PACS; 81.15Fg; 68.43.−h; 68.37.psSilicon contamination; Silicon adsorption in LiF; 157; nm laser; Vacuum ultraviolet light; Interfaces

Combined EELS, LEED and SR-XPS study of ultra-thin crystalline layers of indium nitride on InP(100)—Effect of annealing at 450°C by C. Robert-Goumet; M. Petit; L. Bideux; B. Gruzza; G. Monier; V. Matolín; T. Skála; N. Tsud; K.C. Prince (pp. 4445-4449).

In this study, InP(100) surfaces were bombarded by argon ions in ultra high vacuum. Indium metallic droplets were created in well controlled quantities and played the role of precursors for the nitridation process. A glow discharge cell was used to produce a continuous plasma with a majority of N atomic species. X-ray photoelectron spectroscopy (XPS) studies indicated that the nitrogen combined with indium surface atoms to create InN thin films (two monolayers) on an In rich-InP(100) surface. This process occurred at low temperature: 250°C. Synchrotron radiation photoemission (SR-XPS) studies of the valence band spectra, LEED and EELS measurements show an evolution of surface species and the effect of a 450°C annealing of the InN/InP structures. The results reveal that annealing allows the crystallization of the thin InN layers, while the LEED pattern shows a (4×1) reconstruction. As a consequence, InN related structures in EELS and valence bands spectra are different before and after the annealing. According to SR-XPS measurements, the Fermi level is found to be pinned at 1.6eV above the valence band maximum (VBM).

Keywords: PACS; 79.60.Dp; 81.65.Lp; 81.05.Ea; 79.20.Uv; 79.60.−I; 61.14.HgNitridation; III–V semiconductors; Thin films; EELS; Synchrotron radiation; SR-XPS; LEED

An investigation of the surface-enhanced Raman scattering (SERS) effect from laser irradiation of Ag nanoparticles prepared by trisodium citrate reduction method by Li-Ping Ding; Yan Fang (pp. 4450-4455).

By irradiating a Ag colloid solution, produced by trisodium citrate reduction method, employing the active Quanta Ray Nd:YAG laser system, λ=1064nm, we prepared relatively small, spherical Ag nanoparticles with a narrow size distribution. The irradiated particles not only improve the configuration, but also the spectroscopy properties to some extent. The influence of the laser fluence on the irradiated energy was studied, via transmission electron micrograph (TEM) images, surface plasmon absorption (SPA) spectra, and surface-enhanced Raman scattering (SERS) spectra. Those benefit to understanding the spectroscopy properties of irradiated particles to obtain precise understanding of the mechanism. And probably the reasonable explanations are given.

Keywords: SERS; Laser irradiated; Ag nanoparticles

Speciation of functional groups formed on the surface of ammoxidised carbonaceous materials by XPS method by Leszek Wachowski; Janusz W. Sobczak; Magdalena Hofman (pp. 4456-4461).

X-ray photoelectron spectroscopy (XPS) has been used to investigate the fate of nitrogen functional groups present in carbonaceous materials obtained from European plum ( Prunus domestica) stones and modified by ammonia–air mixture at 250 or 300°C. Peaks have been found in the XPS patterns, corresponding to different nitrogen functional forms i.e. pyrrolic, pyridinic, pyridone, amine and chemisorbed nitrogen oxides. It has been found that the distribution of nitrogen functional forms changes as a result of the modification processes.

Keywords: Waste plum stones; Organic material enriched in nitrogen; X-ray photoelectron microscopy; Nitrogen functionalities

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Applied Surface Science (v.253, #9)

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Applied Surface Science (v.253, #9)