Applied Surface Science (v.185, #3-4)

CONTENTS (v-vi).

Cupronickel alloys are known for their excellent corrosion resistance, especially in marine atmosphere. The development of an appropriate electroless bath involves the use of a reducing agent, complexing and stabilizing compounds and metallic salts. In this work, autocatalytic deposition of Ni–Cu–P alloys (28–95 wt.% Ni, 66–0 wt.% Cu, 7.5–3 wt.% P) has been carried out on 302 b steel sheets from bath containing: NiCl2·6H2O, CuCl2·2H2O, NaH2PO2, Na citrate, sulphosalicilic acid and triethanolamine. The effects of pH, temperature, and bath composition on the hardness and the composition of deposits have been studied. In addition, the deposition rates of alloy, nickel, copper and phosphorus were investigated and optimum conditions were obtained. The average rate of alloy deposition was 9 mg cm−2  h−1 and the optimum pH and temperature were 8.5 and 80 °C, respectively. The chemical stability of bath was desirable, and no spontaneous decomposition occurred. The changes in the structure of deposit by heat treatment were studied by the X-ray diffraction (XRD) method. The XRD patterns indicate that the copper content affects the structure changes. With increasing copper content, the phosphorus content decreased and the crystallinity of the deposits grew. After heat treatment of alloys with lower copper content at 400 °C for 1 h, the crystallization to Ni3P was observed.
Keywords: Electroless deposition; Copper–nickel–phosphorous alloy; X-ray diffraction patterns;

The origin of haze was investigated in antimony-doped tin oxide thin films, and in double-stack thin films of fluorine-doped tin oxide/antimony-doped tin oxide, both deposited by chemical vapor deposition onto soda-lime–silica float glass substrates. These transparent conductive oxide thin films are of great importance in the production of solar control architectural glazing units. Therefore, understanding the origins of haze is necessary to the development of coated, IR-reflecting glass windows with low overall haze levels. Haze measurements of as-prepared and polished samples were correlated with surface roughness and concentration of internal hole defects. Surface roughnesses were evaluated by atomic force microscopy, and characterized by estimated RMS values. In thin tin oxide films (<2000 Å) internal hole defects caused haze, while in thick tin oxide films (>4000 Å) surface roughness was the primary source of haze.
Keywords: Tin oxide thin films; Haze; Internal defects; Rugosity; Polishing; AFM;

Characteristics of thin films of hexagonal boron nitride mixed with copper controlled by a magnetron co-sputtering deposition technique by Masahiro Goto; Akira Kasahara; Masahiro Tosa; Takashi Kimura; Kazuhiro Yoshihara (172-176).
Thin film properties, such as surface morphology, internal stress and surface energy, of hexagonal boron nitride/copper mixtures, produced by a magnetron co-sputtering deposition technique, were investigated. Techniques included scanning electron microscopy, film deflection and contact angle measurements. It was possible to fabricate nano-scale islands on the surface of the film and to control the size of the islands by adjusting the sputter discharge conditions. The internal stress and surface energy can be significantly modified depending on these conditions indicating that they are dependent variables. This technique of co-sputtering deposition is a promising candidate for the control of nano-structures on a surface and for controlling internal stress and surface energy.
Keywords: Surface energy; Internal stress; Surface morphology; Thin film; Hexagonal boron nitride;

A thin polycrystalline film attached to a bulk substrate of different thermal expansion coefficient will experience a thermal strain when the temperature is changed. Calculations of the strain energies for various grain orientations relative to the film surface were made for an FCC polycrystalline film on a substrate. Results show that prior to yielding, the four lowest strain energy densities correspond to grains with (1 0 0), (5 1 1), (3 1 0) and (3 1 1) planes oriented parallel to the plane of the film. In a yielded film, the four lowest strain energy densities correspond to the grains with (1 1 0), (1 0 0), (5 1 1) and (2 1 1) planes oriented parallel to the plane of the film. From strain energy minimization, grains with (1 0 0), (5 1 1), (3 1 0) and (3 1 1) or (1 1 0), (1 0 0), (5 1 1) and (2 1 1) planes oriented parallel to the plane of the film should be favorable in an attached FCC-polycrystalline film after annealing, depending on the degree of deformation of the film.
Keywords: Strain energy; Rigid substrate; FCC-polycrystalline film;

Oxide-based ceramic matrix composites (CMCs) are prime candidates for high temperature turbine applications. Increasing demand of CMCs necessitates the development of quality monitoring procedures. Sol–gel derived Nextel-720 fiber/alumina matrix CMC is one of the potential candidate material for land-based gas turbine applications. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were utilized to investigate any surface/interface chemical alteration of the Nextel-720 fiber reinforcement and the alumina matrix during fabrication. The calculated XPS spectra of the composite were obtained by simply adding the spectra of the as-received Nextel-720 fiber and the alumina matrix. The calculated XPS spectra and the acquired XPS Al(2p), Si(2p3), and O(1s) spectra from the as-received materials were compared using a superimposition method to investigate any chemical alteration during composite fabrication for quality control measures. This paper is aimed to serve as a reference for future XPS studies of CMCs exposed to aggressive turbine environments.
Keywords: Ceramic matrix composites; Nextel-720 fiber; XPS or ESCA; TEM; Aluminosilicate; Gas turbines;

Electrochemical and XPS studies of 2,5-bis(n-pyridyl)-1,3,4-thiadiazoles adsorption on mild steel in perchloric acid solution by M El Azhar; M Traisnel; B Mernari; L Gengembre; F Bentiss; M Lagrenée (197-205).
The effect of isomers of 2,5-bis(n-pyridyl)-1,3,4-thiadiazole (n-PTH) on the corrosion of mild steel in perchloric acid solution (1 M HClO4) has been investigated using weight loss, electrochemical impedance spectroscopy and potentiodynamic polarisation. Inhibition efficiency is dependent upon the thiadiazole structure, with 3-PTH serving as a better inhibitor than 2-PTH. 2-PTH stimulates corrosion at low concentrations. Polarisation curves indicate that 3-PTH acts as an anodic-type inhibitor whereas 2-PTH is of the cathodic-type. X-ray photoelectron spectroscopy were also carried out to establish the mechanism of corrosion inhibition of 3-PTH and stimulation corrosion of 2-PTH of mild steel in acid solution. Adsorption of 3-PTH on the mild steel surface in 1 M HClO4 follows the Langmuir adsorption isotherm model.
Keywords: Thiadiazole; Corrosion; Stimulation; Mild steel; Perchloric acid; X-ray photoelectron spectroscopy;

Heterogeneous distribution of metal nanocrystals in glazes of historical pottery by I Borgia; B Brunetti; I Mariani; A Sgamellotti; F Cariati; P Fermo; M Mellini; C Viti; G Padeletti (206-216).
It has been recently shown that lustre decoration of medieval and renaissance pottery consists of silver and copper nanocrystals, dispersed within the glassy matrix of the ceramic glaze. Lustre surfaces show peculiar optical effects such as metallic reflection and iridescence. In many cases, lustre appears overlapped to colored drawings. Here we report the findings of a study on glazes, pigments and lustre of several shards belonging to Deruta and Gubbio pottery of XVI century. The components of glazes and pigments have been identified. Lustre is confirmed to be characterised by silver and copper metal nanocrystals inhomogeneously dispersed in the glassy matrix of the glaze. In the case of lustre overlapped to colored decorations, we found two contradictory cases. The first consists of a lustre surface successfully applied over a blue smalt geometrical drawing. The second consists of a lustre surface, unsuccessfully applied over a yellow lead-antimonate pigment. The yellow pigment hinders the formation of lustre and removes crystals of tin dioxide, normally present in the glaze as opacifier.
Keywords: Nanoparticles; Glass–metal composites; Historical pottery; Lustre;

Electron-induced surface chemistry on TiN in ultrahigh vacuum by Qing Ma; Dean R. Walters; Richard A. Rosenberg (217-225).
The property of a TiN/vacuum interface in ultrahigh vacuum (<3×10−9   Torr ) and under electron beam irradiation was studied using Auger electron spectroscopy. Electron-beam energies ranged from 1 to 9 keV. Without electron irradiation, about 1 monolayer (ML) of oxygen adsorbs on the TiN surface and metal oxidation occurs. The characteristic of oxygen adsorption is discussed in terms of the relationship of gas-sticking probability with coverage within the first ML regime. Under electron irradiation, carbon accumulates on the surface, in addition to oxygen adsorption, which modifies the surface chemistry to an extent that depends on the vacuum conditions, electron current density, and electron beam energy. For high-energy electron beams, electron bombardment induces TiC formation.
Keywords: Electron-induced surface chemistry; Auger; Ultrahigh vacuum; Carbon deposition; Carbide formation; Secondary electron yield;

Oscillation of surface in-plane lattice spacing during epitaxial growth of BaTiO3 and SrTiO3 on SrTiO3(1 0 0) by T. Koida; M. Lippmaa; D. Komiyama; M. Kawasaki; H. Koinuma (226-230).
In-plane lattice spacing oscillation was observed as functions of surface coverage and growing film thickness by reflection high-energy electron diffraction during the growth of strained BaTiO3 and unstrained SrTiO3 epitaxial layers on SrTiO3(1 0 0). For BaTiO3/SrTiO3, the oscillation continued until the critical thickness is reached, whereas for SrTiO3/SrTiO3, oscillation was observed only at the initial few monolayer growth. The origin of oscillations is discussed in relation to the non-tetragonal elastic distortion occurring at the free edges of 2D single monolayer islands. The amplitude of the oscillation strongly depended on the island size and density.
Keywords: BaTiO3 growth; In-plane lattice spacing oscillation; Lattice relaxation process; Reflection high-energy electron diffraction (RHEED); Surface morphology;

Surface investigation of adhesive formulation consisting of UV sensitive triblock poly(styrene–b-butadiene–b-styrene) copolymer by Maud Staeger; Eric Finot; Claire-Hélène Brachais; Stéphane Auguste; Hervé Durand (231-242).
Atomic force microscopy (AFM) analysis in conjunction with macroscopic studies such as peel testing and contact angle measurement have been undertaken to explain the nanomechanical properties of adhesive formulation consisting of triblock poly(styrene–b-butadiene–b-styrene) (SBS) copolymers. The cross-linking of this photosensitive copolymer was investigated by analyzing the mechanical and morphological changes of each phase induced by the UV exposure. Main result is that the adhesive properties are strongly influenced by the cross-linking of the polybutadiene (PB) phase leading to an increase in the surface stiffness without affecting the surface energy. AFM analysis shows that the adhesion force is mostly governed by the contact area between the adhesive and the probe. The surface mobility may explain the increase in adhesion for this pressure sensitive copolymer.
Keywords: Surface treatment; Triblock copolymer; Adhesion force; Atomic force microscopy; Contact angle; Peel testing;

Field electron emission from amorphous carbon films grown in pure methane plasma by Yang-Gyu Baek; Takashi Ikuno; Jeong-Tak Ryu; Shin-ichi Honda; Mitsuhiro Katayama; Kenjiro Oura; Takashi Hirao (243-247).
By using RF plasma-enhanced chemical vapor deposition, amorphous carbon films were grown in pure methane plasma. Field emission of the films were examined as a function of substrate temperature. It was found that the emission current from the samples prepared at substrate temperatures higher than 600 °C were considerably improved. According to the results by Raman spectroscopy, growth of graphite crystallites were promoted with high substrate temperatures. Moreover, the surface morphology was abruptly changed at high substrate temperatures over 600 °C. We discuss the field emission characteristics of the amorphous carbon films with regard to the structural features and the surface morphology.
Keywords: Amorphous carbon films; Field electron emission; Methane plasma; Graphite crystallite growth; Surface morphology;

Thin films of Y2O3 were deposited on the surface of a zinalco alloy (Zn–22Al–2Cu) in order to modify the surface and increase the corrosion resistance. By means of ion sputtering and surface analysis using Auger electron spectroscopy, in-depth relative elemental intensity profiles were obtained. The growth mechanism of the surface oxides layer is modified by the deposited yttrium oxide film. On samples without film, corrosion progresses mainly at the surface as indicated by the zinc excess, while on samples with film, the growth of the oxides layer occurs at inner points of the film where migrating anions and cations are allowed to find each other. The growth of the corrosion products layer is about nine times smaller in samples with a film of 1600 Å of Y2O3 with respect to samples without a film. Migration of aluminum particles is higher than that of zinc particles, producing a surface highly enriched in aluminum.
Keywords: Zn–Al–Cu; Alloys; Reactive element effect; Y2O3; AES; Corrosion;

Surface modification of polytetrafluoroethylene by nitrogen ion implantation by Jizhong Zhang; Xiaojun Yu; Hengde Li; Xianghuai Liu (255-261).
Polytetrafluoroethylene (PTFE) was implanted in vacuum by N ions. The influence of experimental parameters was studied by varying ion energy from 2 to 20 keV with the same fluence of 1.4×1017   ions/cm 2 . The ion energy strongly affected the surface composition, microstructure, and wettability of PTFE. Five chemical bonds, CF3, CF2, CF, C–O, and elemental carbon bonds, were observed on the surface of all the as-implanted samples. The content of the various chemical bonds changed with increasing ion energy. The content of elemental carbon bond reached a maximum value of 45.81% on the surface of the sample implanted with ion energy of 5 keV. Displacement of the binding energies of the C 1s peak components was observed on the surfaces of samples implanted with ion energies equal to or greater than 5 keV. Numerous microfibers drawn up in the same orientation were observed on the ion-irradiated surfaces. The droplet contact angle of the as-implanted samples increased gradually with increasing ion energy, and reached a maximum value of 117.4° on the surface of the sample implanted with ion energy of 20 keV.
Keywords: PTFE; Nitrogen ion; Implantation; Wettability;

SiCN thin film prepared at room temperature by r.f. reactive sputtering by X.C Wu; R.Q Cai; P.X Yan; W.M Liu; J Tian (262-266).
Silicon–carbon nitride (SiCN) thin films were deposited on Si substrate at room temperature by r.f. reactive sputtering. Fourier transform infrared spectroscopy (FTIR), optical absorption spectra (α(λ)) and electrical conductivity (σ) were studied for the thin films. The effect of the annealing on IR and σ was investigated at different temperatures. IR analysis indicates that Si–H, C–N, Si–C, Si–N, C–N and CN bonds are present in a-SiCN:H films. A shift of the stretching mode for Si–H bond to the high-wavenumber side is observed with increasing the nitrogen flow ratio γ N2 (=N2/(Ar+H2+N2+CH4)). The shift is from 2000 to 2190 cm−1 when γ N2 =13.7%. The study shows that the film structure and optical and electrical properties are obviously modified readily by controlling the process parameters of deposition. The improvement in the film properties, e.g., good thermal stability, is explained mainly in terms of the cross-linked structure between the Si, C and N atoms.
Keywords: SiCN thin film; Room temperature; r.f. reactive sputtering;

Electroless polymerization of aniline on platinum and palladium surfaces by Yongjun Chen; E.T Kang; K.G Neoh (267-276).
Aniline was found to polymerize slowly and spontaneously on the platinum and palladium metal surfaces in an aqueous acid solution of the monomer. The phenomenon was thus equivalent to an “electroless polymerization” process. The polyaniline (PANI) so-deposited were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The chemical state of the electroless deposited PANI film was near to that of the 75% intrinsically oxidized nigraniline (NA) state of PANI. The electrolessly deposited PANI films exhibited similar protonation–deprotonation behavior as that of the aniline homopolymer. The amount of the PANI deposited on the metal surface was affected by the monomer concentration, the nature of the acid medium, and the oxygen content in the reaction medium.
Keywords: Platinum; Palladium; Polyaniline; Polymerization; XPS; FTIR; AFM;

Optoacoustic analysis of the laser-cleaning process by V.B Bregar; J Možina (277-288).
Laser cleaning is an optodynamic process in which the optically induced removal of a liquid or a solid contaminant from a substrate is accompanied by a optoacoustic wave in the surrounding air. In our experiments we used both dry and steam laser-cleaning techniques for various samples. Optoacoustic wave, produced by the abrupt heating and detachment of the contaminants, was observed with a probe-beam deflection technique. We determined two characteristic parameters of the optoacoustic wave: the amplitude and the time-of-flight of the acoustic signal. With an analysis of these waves we also determined possible generating mechanisms. The decrease of the amplitude and the velocity of propagation, which approaches sonic speed, of the consecutive waves indicate that the dynamics during the laser-cleaning process is progressively weakened. The cleaning process is over when both the parameters reach a constant value, so with measuring optoacoustic waves the progress of the cleaning process could be observed on-line.
Keywords: Optoacoustic wave; Laser cleaning; Monitoring; Laser-beam probe;

A low cost, selective electroless metallisation of integrated circuit (IC) copper bond pads with nickel and gold is demonstrated. This metallurgy can function as a barrier layer/bondable material when deposited as a thin layer or as the chip bump for flip chip applications when deposited to greater heights. Four alternative activation steps for selective electroless nickel deposition on bond pad copper are demonstrated. Selective low cost deposition has been achieved with a proprietary electroless plating bath developed at NMRC and three commercial baths on both sputtered copper substrates and electrolessly deposited copper on titanium nitride barrier layer material.
Keywords: Electroless deposition; Copper bond pads; Barrier layer; Flip chip;

Surface segregation in high-purity Al–100 ppm Pb foil annealed for 4 h at 540 °C was studied mainly by transmission electron microscopy (TEM) observations. TEM–EDX demonstrated that almost of the lead element segregated not to aluminum surface but predominantly to the oxide amorphous film formed just above aluminum surface. The enrichment of lead in the oxide film was about 30 000 fold.
Keywords: Al–Pb; Segregation; Oxide film; TEM; EDX;

Preparation of diamond films by hot filament chemical vapor deposition and nucleation by carbon nanotubes by Ya-Qi Hou; Da-Ming Zhuang; Gong Zhang; Min-Sheng Wu; Jia-Jun Liu (303-308).
Preparation of diamond films by hot filament chemical vapor deposition (HF-CVD) and nucleation of carbon nanotubes on diamond films were investigated. The optimum parameters for preparing diamond film were explored. Diamond films of high quality were deposited on silicon substrates seeded with carbon nanotubes as nucleation precursors. Diamond grains grew essentially perfectly with no congregation occurring during long depositions. The effect of the quality of the carbon nanotubes on the character of the deposited diamond are discussed.
Keywords: Diamond film; HF-CVD; Carbon nanotube; Nucleation precursor;

The use of small angle X-ray scattering (SAXS) for the characterisation of lustre surfaces in Renaissance majolica by P Fermo; F Cariati; C Cipriani; M Canetti; G Padeletti; B Brunetti; A Sgamellotti (309-316).
In this work some Renaissance lustre decorated ceramics have been examined. Our attention was directed to lustre which is a thin decorative metallic film applied on the surfaces of previously glazed ancient pottery.Some 16th century lustre ceramics shards from Deruta, Umbria (Italy) have been analysed by small angle X-ray scattering (SAXS) in order to characterise the dimension of the metal nanocrystals forming the thin lustre layer. This technique appeared to be a powerful tool to characterise lustre films nanostructure and may be successfully used for this purpose together with transmission electron microscopy (TEM). Furthermore, SAXS measurements are extremely suitable for the determination of polydispersity and average interparticle distance.The lustre surfaces have been also analysed by scanning electron microscopy plus X-ray energy dispersive spectrometry (SEM–EDX) in order to identify the metals present (silver, copper or both of them) and to establish copper/silver ratios. From the comparison between SAXS results and compositional data, it was possible to conclude that copper particles are smaller than the silver ones. We have evidenced how the microtexture as well as the chemical composition of the lustre layers are responsible for the gold or red colour typical of the lustre films.
Keywords: SAXS; Ancient ceramic; Lustre decorated majolica; Metallic colloids; Nanoparticles;

Laser annealing of SiO x thin films by B Gallas; C.-C Kao; S Fisson; G Vuye; J Rivory; Y Bernard; C Belouet (317-320).
SiO x remains the main starting material for obtaining nanocrystalline Si embedded in a SiO2 matrix. A SiO x layer grown by co-evaporating Si and SiO2 has been successfully annealed using a KrF pulsed excimer laser operating at 248 nm. Abrasion of the film surface was observed above 85 mJ/cm2 and phase separation between Si-rich and SiO2-rich phases was initiated above this fluence as observed by XPS.
Keywords: Laser annealing; Nanocrystalline Si; Silica matrix;

Nanocrystalline diamond thin films deposited by 35 kHz Ar-rich plasmas by J.M López; F.J Gordillo-Vázquez; J.M Albella (321-325).
We give evidence of nanometric size (5–15 nm) crystalline diamonds in carbon thin films obtained at low substrate temperature (15 °C) under the action of low pressure (0.1–0.3 Torr) 35 kHz excited CH4/Ar (80–95%) plasmas. The decrease in Ar concentration was found to lead to higher film hardness while crystalline nanodiamonds are observed in a wide interval (1–3.5 h) of deposition times but only for very high Ar concentration (95%). The polycrystalline nanodiamond grains are found over 10–20% within an amorphous carbon matrix. It is suggested that the distribution of nanodiamond grains might be connected to the nonuniform ion energy distribution in the Ar-rich plasma generated at 35 kHz. Morphological and structural features of the deposited films were also investigated.
Keywords: CVD; Plasma; Diamond films;

AUTHOR INDEX (326-327).

SUBJECT INDEX (328-332).