Applied Surface Science (v.153, #2-3)

Laser surface engineered TiC coating on 6061 Al alloy: microstructure and wear by Lalitha R. Katipelli; Arvind Agarwal; Narendra B. Dahotre (65-78).
Hard and refractory TiC has been deposited on 6061 Al alloy by Laser Surface Engineering (LSE). A “composite” coating is obtained with TiC particles of various shapes and sizes embedded in Al alloy–Ti matrix. The coating is uniform, continuous and free of cracks. The various reactions occurring during laser processing were thermodynamically analyzed and related to the experimental observations. Microhardness measurements suggested high hardness values in the coating region and a strong bonding at the coating/substrate interface. Dry sliding wear tests were performed to measure the wear resistance and the coefficient of friction of the coating. Wear resistance of the coated surface was found to be high when compared to the substrate side. The coefficient of friction was found to be 0.64.
Keywords: Laser surface engineering; TiC particles; Wear; Coating; Bonding; Interface;

Behaviour of copper atoms in annealed Cu/SiO x /Si systems by N Benouattas; A Mosser; D Raiser; J Faerber; A Bouabellou (79-84).
Copper thin films of thickness 1000 Å are evaporated on (100) and (111) single crystal Si wafers in the presence of interfacial native silicon oxide (SiO x ). The behavior of copper and the mechanism of compound formation at the Cu/Si interface are studied at different temperatures using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Rutherford backscattering (RBS). Annealing in the 600–750°C temperature range leads to the formation of islands of two copper-rich silicides Cu3Si and Cu4Si. On the Si(100), after annealing at 750°C, we observe epitaxially grown Cu3Si crystallites with square and rectangular shapes. However, on Si(111) annealing at the same temperature yields Cu3Si and Cu4Si crystallites with droplet-like shapes and no sign of epitaxy. The presence of oxygen, after heat treatment under vacuum, is closely related to the formation of copper silicide crystallites.
Keywords: Copper; Silicon oxide; Annealing; Silicides; Epitaxy;

Study of late argon–nitrogen post-discharge interactions with oxidized iron surfaces by L Lefèvre; T Belmonte; T Czerwiec; A Ricard; H Michel (85-95).
Nitrogen-containing post-discharges are widely used for enhancement of polymer printability and adhesion and wettability properties. It has also applications in the field of remote plasma enhanced chemical vapour deposition of thin nitride films or nitriding. Interactions occurring between an argon–N2 post-discharge and oxidized iron surfaces are studied. Measurements are based on optical emission spectroscopy measurements. Two regimes are considered. First, the analysis of transient effects sheds light on the cleaning effects which modify permanently the topmost surface of oxidized iron substrates. They are evidenced by XPS measurements. Two steps occur. During the first one, a reaction between nitrogen atoms and carbon of ketones or carbonyl-like groups probably due to acetone residue, identified by XPS analyses, gives CN radicals. The CN(B2Σ,v)→CN(X2Σ,v′) transition is identified by optical emission spectroscopy. This emission vanishes progressively as carbon is consumed and the second step starts at the end of the violet emission where the loss probability γ N of nitrogen atoms increases. The increase of the recombination rate is attributed to abstraction reactions of adsorbed elements by nitrogen atoms to form nonemissive species. For example, hydroxide groups are removed by the post-discharge. The surface modifications induced by this treatment are reproducible. This was verified by comparison between the behaviours of the native oxide and a 0.5-μm-thick layer grown by controlled post-discharge oxidation. When the steady-state regime is reached, the loss probability γ N on the treated surfaces is determined in a range of temperatures (i.e., 300–473 K) where the nitrogen bulk-diffusion is assumed to be negligible. Nitrogen atoms recombine according to an Eley–Rideal mechanism and γ N=(8.2±0.5)×10−2 exp(−11400±500/RT).
Keywords: Loss probability; Nitrogen atom; Oxidized iron; Cleaning; Post-discharge;

Effect of an electric field on the electronic subbands in strained In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells has been investigated theoretically with the goal of producing the large Stark shifts and of their application possibilities to a tunable photodetector. The energy states, the corresponding energy wavefunctions, the absorption peaks, and the Stark shifts in strained In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells under applied electric fields are calculated by the transfer matrix method taking into account strain effects. The operation of this device is based on the infrared absorption by the electrons in the ground state transited from the ground state subband to the excited state subbands of the coupled double quantum wells. When an electric field is applied to a coupled double quantum well, the shifts of the intersubband energy transitions and the absorption peaks in the coupled double quantum well are shifted much larger than those in the single quantum well. The excited energy states with and without applied electric fields in the In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells are strongly dependent on the In0.65Ga0.35As well width in comparison with their ground states. The coupling of the electronic subband energies in the two In0.65Ga0.35As/In0.52Al0.48As quantum wells leads to an enhancement of the quantum-confined Stark effect. These results indicate that strained In0.65Ga0.35As/In0.52Al0.48As coupled double quantum wells hold promise for potential applications to new kinds of optical modulation devices and tunable photodetectors.
Keywords: In0.65Ga0.35As/In0.52Al0.48As; Stark effect; Absorption peak;

Lattice mismatch and atomic structure studies of In x Ga1−x As/In y Al1−y As coupled double-step quantum wells have been performed by transmission electron microscopy (TEM) and electron-diffraction pattern measurements. The high-resolution TEM image of the In x Ga1−x As/In y Al1−y As coupled double-step quantum well showed that two sets of a 60-Å In0.65Ga0.35As deep quantum well and a 60-Å In0.53Ga0.47As shallow step quantum wells bounded by two thick In0.52Al0.48As barriers are separated by a 38-Å In0.52Al0.48As embedded potential barrier. The selective-area electron-diffraction pattern obtained from TEM measurements on the In x Ga1−x As/In y Al1−y As double-step quantum well showed that In x Ga1−x As active layers were grown pseudomorphologically on the InP buffer layer. The value of the lattice mismatch between the In0.53Ga0.47As and the In0.65Ga0.35As layers obtained from the high-resolution TEM measurements is 1.6%. A possible crystal structure for the In x Ga1−x As/In y Al1−y As coupled double-step quantum well is presented based on the TEM results. These results can help improve understanding of the structural properties for the applications of strained In x Ga1−x As/In y Al1−y As coupled double-step quantum wells in new kind of the optoelectronic devices.
Keywords: In x Ga1−x As/In y Al1−y As; Atomic structure; Strain effects;

We investigate the formation of silicide layers in (111) Si wafers with a high-current implanter. Cr ions form a disilicide layer of low sheet resistance. If the sample is also implanted with Ni, the total number of Cr atoms is reduced by sputtering, and the previously prepared CrSi2 layer is disordered. However, a stable textured Cr1−x Ni x Si2 phase can be prepared by proper annealing. Above 1150°C the ternary phase segregates into CrSi2 and NiSi2. Thus the introduction of Ni can result in well-defined and stable Cr1−x Ni x Si2 alloys.
Keywords: Ion beam synthesis; Secondary implantation; Alloy–silicide;

Auger and X-ray photoelectron spectroscopies have been used to study the surface composition of Mn x Co1−x O (0≤x≤1) solid solutions. The polycrystalline materials, which are bulk homogeneous, present clear signs of deviation in surface composition at x bulk≈0.2–0.4 to become surface-enriched in manganese at the expense of the cobalt. Whether on stoichiometric or cobalt-depleted surfaces, cobalt retains the characteristic XPS 2p satellite structure and binding energies of the rock salt monoxide (CoO or Mn x Co1−x O) environment. Manganese 2p XP spectra are appropriately monoxide-like for the stoichiometric surfaces but broaden and give evidence for a second manganese species with Mn4+ character for the bulk-enriched samples. Oxygen O 1s spectra also show two different surface species, one the characteristic rock salt lattice oxide at 529.4 eV and a second at 531.3 eV. However, the two peaks are observed for all samples, regardless of whether the surface and bulk compositions were found to differ. The second O 1s peak cannot be unequivocally identified, but is most likely defect-oxide or hydroxyl-like in origin. The 531.3-eV O 1s species forms at the expense of the lattice oxide, and the net oxide-surface concentration is approximately that of the stoichiometric surface.
Keywords: Oxides; Solid solutions; Cobalt oxide; Manganese oxide; Defects;

We investigate the synergistic effect of iodide ions on the corrosion inhibition of manganese-14 steel in 0.5 M H2SO4 in the presence of cyclohexylamine using potentiodynamic polarization and linear polarization techniques. In 0.5 M H2SO4, the corrosion rates of the steel decrease when amine the concentration decreases, while the inhibition efficiencies increase. The addition of iodide ions enhances the inhibition efficiency considerably. The presence of iodide ions increases the degree of surface coverage, while at low concentrations cyclohexylamine forms an insoluble complex by undergoing adsorption. The synergism parameters (Sθ ) calculated from surface coverage in the case of cyclohexylamine are found to be larger than unity. In addition, the adsorption of this amine on manganese-14 steel is found to follow a Langmuir isotherm. Thus inhibition occurs by adsorption.
Keywords: Corrosion; Inhibition; Synergistic effect; Cyclohexylamine;

Hydrogen plasma irradiation and postannealing effects on crystalline quality at vicinal Si (100) surface by Koyu Asai; Kyoichi Komachi; Kazuhito Kamei; Hisashi Katahama (134-142).
Relationships between density of total incident hydrogen ions and full peak width at half maximum (FWHM) at (400) diffraction spot in reflection high-energy electron diffraction (RHEED) from vicinal Si (100) surface during plasma irradiation and postannealing are first reported. At the density of total incident hydrogen ions of 6.0×1014 ions/cm2, the FWHM, which is normalized by that before plasma irradiation, is almost saturated at 1.8. No damaged layer and no defect are observed in cross-sectional transmission electron microscopic (XTEM) images. On the other hand, at the density of 3.6×1015 ions/cm2, the normalized FWHM is slightly increased to 1.9. However, the drastic degradation of surface crystalline quality, a uniform 50-nm thick damaged layer and a lot of extended planar defects, is observed in XTEM images. During postannealing of Si wafer irradiated at the density of 6.0×1014 ions/cm2, the FWHM drastically decreases between 700°C and 800°C. Considering the causes of FWHM broadening and thermal stabilities of defects and disordered lattice, it is considered that this drastic improvement of FWHM is caused by annihilation of Si point defects and rearrangement of disordered lattice at Si surface.
Keywords: Semiconductors; Ion radiation effects; Reflection high-energy electron diffraction; Kinetics of defect formation and annealing; Surface crystalline quality; Electron cyclotron resonance plasma;

Surface morphology of cubic and wurtzite GaN films by E.M Goldys; M Godlewski; R Langer; A Barski (143-149).
We describe a comparative study of surfaces of gallium nitride films grown by a variety of techniques at low growth temperatures (molecular beam epitaxy and laser-assisted chemical vapour deposition) as well as by metalorganic chemical vapour deposition. The cubic, wurtzite and mixed phase cubic–wurtzite films were grown on buffers, these included ultrathin (4 nm) SiC as well as more commonly used AlN. We find that the surface morphology of GaN films grown by MBE shows micrometer-scale structures which reflect the symmetry of the film. Surface topography may thus be used as an identification measure of film symmetry. Monochromatic cathodoluminescence images taken at the maximum of the band edge emission show granular structures reflecting surface morphologies, whereas similar structures are only very weakly visible in the red/yellow band.
Keywords: Gallium nitride; Surface morphology; Cubic phase; Wurtzite phase low temperature growth;

Photoemission study of oxygen adsorption on Rb6C60 film surface by J.X Wu; X.M Liu; M.S Ma; M Bai; M.R Ji; J.S Zhu (150-155).
X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) have been used to investigate oxygen adsorption on the surface of Rb6C60 film at room temperature. The results show that the Rb6C60 surface is sensitive to oxygen adsorption. The absorbed oxygen changes the crystal structure of the film by pulling intercalated Rb atoms to the surface, forming Rb oxides. An initial rapid oxygen uptake is mainly related to the formation of rubidium peroxide (Rb2O2). There exists a strong reaction between C60 and Rb2O2, leading to the formation of rubidium carbonate (Rb2CO3). At high oxygen exposures, a slow further adsorption of oxygen is associated with the intensity increases of both Rb2CO3 and rubidium superoxide (RbO2) species.
Keywords: Photoelectron spectroscopy; Oxidation; Fullerenes; Alkali metals;

Surface-modification effects induced by yttrium implantation on pure iron and various steels by E Caudron; H Buscail; V.A.C Haanapel; Y.P Jacob; C Josse-Courty; M.F Stroosnijder (156-165).
Pure iron and various steel samples were yttrium implanted using the ion-implantation technique. Sample compositions and structures were investigated before and after yttrium implantation to determine the yttrium distributions and the main compounds formed after the ion implantation. Yttrium-implantation effects were characterized using analytical and structural techniques such as Rutherford backscattering spectrometry (RBS), reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD) and glancing angle X-ray diffraction (GAXRD). This paper shows that correlation between composition and structural analyses allows understanding and comparison of the surface-modification effects of implanting yttrium into pure iron and various steels before high-temperature oxidation study.
Keywords: Pure iron; Steel; Yttrium implantation; Rutherford backscattering spectrometry; X-ray diffraction;

Laser-induced radiative rising of defects on the surface and metal surface destruction by A.F. Banishev; V.Ya. Panchenko; A.V. Shishkov (166-171).
The paper presents the results of the study on nonthermal glow from the surface of metals, which is initiated by thermal deformations resulting from laser pulse action. The temporal dependences of the glow intensity have been investigated. Oscillations of glow intensity were revealed, which are interpreted by a certain order of dislocations rising on the surface.
Keywords: Mechanoluminescence; Laser action; Defects;

XPS characterisation of plasma-treated and alumina-coated PMMA by S Ben Amor; G Baud; M Jacquet; G Nansé; P Fioux; M Nardin (172-183).
The present study is entirely devoted to an XPS analysis of (i) the surface of as received and plasma (argon, CO2) treated poly(methyl–methacrylate) (PMMA) and (ii) the interface between PMMA and alumina thin films, deposited by r.f. magnetron sputtering respectively on untreated and CO2 plasma-treated polymer films. As expected, important chemical modifications of PMMA surface are observed when this polymer is plasma-treated. Such modifications increase the level of interactions between alumina and the substrate. However, if the formation of aluminium carboxylate is observed at the interface, no covalent bonds between the alumina film and the polymer are evidenced.
Keywords: Poly(methyl–methacrylate); Alumina film; Plasma treatment; XPS analysis;

Ionisation probabilities in gas field ion sources by Caio M.C. de Castilho (184-191).
Ionisation probabilities per unit of time, for a gas atom in the close vicinity of a supertip-gas field ion source, are analytically calculated and interpreted accordingly with the operational conditions of these devices. The results obtained for realistic values of the local electric field intensities are significantly smaller than the ones said to be expected and necessary for an “instantaneous” ionisation of a gas atom. Considerations about the effect of the local electric field and ionisation probabilities on the beam narrowness and intensity are also done when discussing their dependence on position and direction at the vicinity of the emitter.
Keywords: Field ionisation; Charged particles sources; Ion beams; Whiskers;