Applied Surface Science (v.158, #3-4)

Ferroelectric Pb0.95La0.05Zr0.53Ti0.47O3 (PLZT) thin films were prepared on quartz substrates by pulsed laser deposition (PLD) technique at a deposition temperature of 750°C. The crystalline structure of the film was evaluated by X-ray diffraction. The dispersion of refractive indices and optical nonlinearities of the PLZT thin films were investigated by optical transmittance and Z-scan techniques, respectively. The film exhibited strong third-order nonlinear optical effect. A nonlinear refractive index as high as 1.3×10−6 esu was displayed in the PLZT thin film. These results show that PLZT ferroelectric thin films have potential applications in nonlinear optics.
Keywords: Ferroelectric thin film; PLZT; Pulsed laser deposition; Optical transmittance; Optical nonlinearity;

Inhibition of chloride localized corrosion of mild steel by PO4 3−, CrO4 2−, MoO4 2−, and NO2 anions by S.A.M Refaey; S.S Abd El-Rehim; F Taha; M.B Saleh; R.A Ahmed (190-196).
The effect of phosphate (PO4 3−), chromate (CrO4 2−), molybedate (MoO4 2−) and nitrite (NO2 ) ions on the pitting corrosion of steel in 0.1 M NaCl solution has been studied using potentiodynamic polarization and SEM techniques. The addition of increasing concentrations of PO4 3−, CrO4 2−, MoO4 2− and NO2 anions causes a shift of the pitting potential (E pit) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. The adsorption characteristics of these anions on the steel surface play a significant role in the inhibition processes. The PO4 3−anion has a strong inhibitive effect of chloride pitting corrosion. The effect of different inorganic anions on the pitting corrosion of steel samples I and II (with different composition) was also studied in 0.1 M NaCl solution.
Keywords: Mild steel; Localized corrosion; Potentiodynamic; Inorganic anions; Inhibition;

Profiling of patterned metal layers by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) by Melody Bi; Antonio M Ruiz; Igor Gornushkin; Ben W Smith; James D Winefordner (197-204).
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used for profiling patterned thin metal layers on a polymer/silicon substrate. The parameters of the laser and ICP-MS operating conditions have been studied and optimized for this purpose. A new laser ablation chamber was designed and built to achieve the best spatial resolution. The results of the profiling by LA-ICP-MS were compared to those obtained from a laser ablation optical emission spectrometry (LA-OES) instrument, which measured the emission of the plasma at the sample surface, and thus, eliminated the time delay caused by the sample transport into the ICP-MS system. Emission spectra gave better spatial resolution than mass spectra. However, LA-ICP-MS provided much better sensitivity and was able to profile thin metal layers (on the order of a few nanometers) on the silicon surface. A lateral spatial resolution of 45 μm was achieved.
Keywords: Laser ablation inductively coupled plasma spectroscopy; Surface profiling;

Density variations in scanned probe oxidation by K Morimoto; Francesc Pérez-Murano; J.A Dagata (205-216).
Total oxide thickness and molar volume ratio for scanned probe microscopy (SPM) oxide nanostructures are obtained for a wide range of silicon substrates and exposure conditions by high-resolution cross-sectional transmission electron microscopy (HR XTEM) and atomic force microscopy (AFM). Oxide density is shown to be a function of substrate doping and voltage pulse parameters. Dislocations produced by the SPM voltage pulse within the silicon substrate are reported from direct XTEM observation for the first time. These dislocations are completely annealed out at 600°C. The dimensional response of SPM oxides to annealing and/or mechanical stress imposed by metal deposition are found to be negligible for n-type substrates, but SPM oxide films on p-type substrates are strongly compressed or expanded. This behavior is attributed to the formation of positively charged defects and ionic/electronic recombination near the growing Si/SiO x interface. Implications of these results for use of SPM oxide in silicon nanodevice processing are discussed.
Keywords: Silicon nanofabrication; Field-enhanced oxidation; Scanned probe microscopy; Transmission electron microscopy;

Electrical resistivity of vacuum-arc-deposited platinum thin films by M Avrekh; O.R Monteiro; I.G Brown (217-222).
We report on our investigations of the electrical resistivity of very thin platinum films, with thickness in the range from 2.6 to 19 nm, formed using a filtered vacuum arc plasma deposition method. We find that the resistivity of these films can be well described by a grain-boundary scattering model, especially for thickness less than ∼5 nm. We also find that the grain size, and consequently the resistivity of the deposited film, is a function of the ion deposition energy, with measured grain size varying from ∼8 nm for ion deposition energy of 100 eV up to ∼11 nm at 2.2 keV.
Keywords: Resistivity; Vacuum arc deposition; Platinum;

Effects of Si doping on ordering and domain structures in GaInP by Sang-Moon Lee; Tae-Yeon Seong; R-T Lee; G.B. Stringfellow (223-228).
The effects of Si doping on ordering and domain structures in GaInP grown by organometallic vapour phase epitaxy on (001) GaAs singular and vicinal substrates at 620°C have been investigated by transmission electron microscopy (TEM) and transmission electron diffraction (TED). TEM results show that the behaviour of antiphase boundaries (APBs) in the singular samples differs from that of the vicinal samples. As the carrier concentration increases, the density of APBs in the vicinal samples increases slightly, whilst that of the singular samples varies insignificantly. APBs are inclined some degrees from the [001] growth surface. TEM results show that for the highly doped samples, the ordered domains contain dark mottled contrast corresponding to either much less ordered regions or disordered regions. TED results show that the ordering is present in layers exceeding a concentration of ∼2.0×1018 cm−3.
Keywords: Ordering; Organometallic vapour phase epitaxy (OMVPE); GaInP; Transmission electron microscopy (TEM); Si doping;

Triboelectromagnetic phenomena of an emission of negatively and positively charged particles were measured during sliding of a diamond on a carbon film with various hydrogen contents under perfluoropolyether (PFPE) fluid lubrication. This tribosystem simulates the material combination of a head slider coated with a diamond-like carbon film and the magnetic recording disk coated with hydrogenated carbon films under PFPE lubrication. The emission intensities were low on the carbon film with low hydrogen content. There was a transition from low to high emission intensity with increasing hydrogen content. The minimum friction coefficient occurred in the regime in which triboemission was high. Tribocharging increased with the increase of the hydrogen content.
Keywords: Magnetic recording media; Triboelectromagnetic phenomena; Hydrogenated carbon film; PFPE; Triboemission; Tribocharging;

Interface analysis of CVD diamond on TiN surfaces by O. Contreras; G.A. Hirata; M. Avalos-Borja (236-245).
We prepared polycrystalline diamond thin films on smooth silicon substrates with the help of a titanium nitride (TiN) buffer layer. TiN layers of different thickness were deposited first on crystalline silicon substrates with mirror finish. The TiN layers were placed by physical vapor deposition (PVD) assisted by direct current reactive magnetron sputtering. Later, diamond thin films were grown by hot filament chemical vapor deposition (HF-CVD). Scanning electron microscopy observations show a notable increase in the size of diamond particles on the substrates with the TiN buffer layer, as opposed to the plain, only scratched substrates. The diamond films were characterized by high-resolution transmission electron microscopy (HRTEM), electron energy loss (EELS) and energy dispersive spectroscopies (EDS). A buffer layer ∼0.8 nm thick is observed between the diamond particles and the TiN layer. EDS experiments reveal a carbon nitride compound at the interphase. There is no evidence of degradation (cracking, delamination, etc.) of the TiN layers for thickness below 0.5 μm.
Keywords: Diamond; TiN; Interface; TEM; EDS;

The chemical compositions of physical vapor-deposited (PVD) and chemical vapor-deposited (CVD) titanium nitride (TiN) thin films were investigated by X-ray photoelectron spectroscopy (XPS). The effect of a H2/N2 plasma treatment on the chemical composition of CVD TiN thin film was also evaluated. The wafers were air-exposed before the XPS analysis. XPS depth profiles show that the PVD TiN has a N/Ti ratio of 1:1 with a small amount of oxygen in the film (less than 5 at.%). Significant amounts (∼20 at.%, respectively) of carbon and oxygen were observed in the air-exposed CVD TiN thin film, which has a N/Ti ratio of 0.5:1. The H2/N2 plasma treatment greatly reduced the carbon content in the CVD TiN thin film (less than 10 at.%) and a N/Ti ratio of 1:1 was achieved. High resolution XPS spectra indicate that the oxygen in all three TiN thin films analyzed was chemically bonded to Ti. The C1s peak of the as-deposited CVD TiN thin film was resolved into two peaks with binding energies of 282.2 and 284.7 eV, corresponding to the chemical states of carbide and organic carbon. After the H2/N2 plasma treatment, most of the organic carbon was removed with the remaining carbon present mainly as carbide in the CVD TiN thin film.
Keywords: Titanium nitride; Chemical vapor deposition; Physical vapor deposition; Plasma; X-ray photoelectron spectroscopy; Chemical composition;

XPS surface study of nanocrystalline Ti–Ru–Fe materials by J.J. Suñol; M.E. Bonneau; L. Roué; D. Guay; R. Schulz (252-262).
The surface properties of Ti:Ru:Fe (2−x:1+x/2:1+x/2) (with x=0, 0.25, 0.5, 0.75, and 1) and Ti:Ru:Fe:O (2:1:1:w) (with w=0.0, 0.5, 1.0, 1.5, and 2.0) have been determined by X-ray photoelectron spectroscopy (XPS) in both their as-milled state and after being in contact with a chlorate oxidizing solution. The O surface concentrations of both sets of samples are almost identical, indicating that the O-free samples readily react with air. All samples in their as-milled state have an elemental Ti, Ru and Fe surface contents that closely follow that expected from their bulk composition, indicating that there is no surface enrichment in any of the elements. In the as-milled state, more than 90% of Ti and Fe atoms are in the highest possible oxidation state, while Ru is in the metallic state. Following immersion of the samples in an oxidizing chlorate electrolyte, the Ru surface concentration decreases by a factor of two. This is also accompanied by an increase in the oxidation state of the Ru atoms left at the surface from 0 to +4. From a comparison between the Ru 3d 5/2,3/2 core level spectra of the electrodes with those of crystalline and hydrated RuO2, it is postulated that dissolution and re-deposition of Ru in the form of hydrated RuO2 occurs at open circuit potential in the chlorate electrolyte. The consequences of these findings for the electrocatalytic activity of the electrodes in chlorate electrolyte are finally discussed.
Keywords: XPS; Nanocrystalline; Ti–Ru–Fe; Ball milling;

Recombination of neutral oxygen atoms on stainless steel surface by Miran Mozeti c ̌ ; Anton Zalar (263-267).
The recombination coefficient of neutral oxygen atoms on polycrystalline AISI 304 stainless steel surface was determined experimentally. The source of neutral oxygen atoms was an inductively coupled RF oxygen plasma. The density of oxygen atoms was determined with a nickel catalytic probe and was between 3×1019 and 2×1021 m−3. A virgin stainless steel disc was activated by exposure to atomic oxygen at the density of 1.5×1021 m−3 for 120 s. During the activation, a layer of oxide with the thickness of about 10 nm was formed on the surface. After successful activation, the temperature of the stainless steel disc during exposures to atomic oxygen was measured at different O density and different pressure in the system. It was found that the recombination coefficient was a constant at the value of 0.070±0.009.
Keywords: Plasma processing; Oxygen; Stainless steel; Adatoms;

The photovoltage spectra of the porous silicon/silicon (PS/Si) formed on the p-type silicon substrates of 〈111〉 and 〈100〉 orientation by different electrochemical anode etching conditions are measured. The photovoltage expressions with relation to the characteristic parameters are derived. The characteristic parameters: the bandgap, the carrier lifetime, and the intrinsic carrier concentration of the porous silicon layer, and the heterojunction barrier width of the PS/Si, are calculated from the measured photovoltage by using the theoretical expressions. Some calculated results are compared with the experiments. It is shown that the results are basically reasonable.
Keywords: Porous silicon/silicon; Photovoltage spectra; p-Type silicon;

A novel oxidation process for silicon nitride films of various compositions have been undertaken utilizing nitrous oxide (N2O) plasma. Careful studies using elastic backscattering (EBS) technique to determine the composition and capacitance–voltage (CV) measurements to determine the insulator charge density (Q o) and the interface state density (D it) have been made on the films before and after N2O plasma oxidation. The incorporation of oxygen into the silicon nitride films of various compositions due to the N2O plasma treatment is confirmed. The insulator charge density (Q o) as well as the minimum interface state density (D it)min are observed to be more for the N2O oxidized samples compared with the corresponding virgin samples.
Keywords: Plasma oxidation; Elastic backscattering; C–V measurement; Insulator charge density; Interface state density; PECVD;

Nanocrystalline Ga0.62In0.38Sb particles embedded in SiO2 matrix were grown by radio frequency (RF) magnetron co-sputtering. X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) strongly support the existence of separated nanocrystalline Ga0.62In0.38Sb material in a SiO2 matrix. XPS core level data also reveal that there exists a SiO2 layer with a 1.1 eV chemical shift compared to that of pure SiO2, indicating that the SiO2 chemically adheres to the Ga0.62In0.38Sb. Room temperature Raman spectrum shows that the Raman peaks of Ga0.62In0.38Sb–SiO2 composite film have a larger red shift of 95.3 cm−1 (LO) and 120.1 cm−1 (TO) than those of bulk GaSb, suggesting the existence of phonon confinement and tensile stress effects.
Keywords: Nanocrystalline Ga0.62In0.38Sb; Ga0.62In0.38Sb–SiO2 composite film; XRD and XPS; Optical properties;

Investigation of oxygen adsorption on Pd (100) with defects by Weixin Huang; Runsheng Zhai; Xinhe Bao (287-291).
Pd (100) with mesoscopic defects was prepared, and oxygen adsorption on this surface was studied by photoemission electron microscopy (PEEM). The defect surfaces behaved differently towards oxygen adsorption from the Pd (100) surface. Besides the oxygen species adsorbed on the surface, the formation of surface oxide and subsurface oxygen on different facets, as well as surface restructure, was observed by PEEM during oxygen adsorption.
Keywords: Electron emission methods; Adsorption; Oxygen; Palladium; Surface defects;

Core-level photoemission study of the BiGaAs(111)A interface by C. McGinley; A.A. Cafolla; E. McLoughlin; B. Murphy; D. Teehan; P. Moriarty; D.A. Woolf (292-300).
Core-level photoemission spectra of the As 3d, Ga 3d and Bi 5d core levels were recorded for the BiGaAs (111)A-(2×2) surface. From the early stages of Bi growth, there are two distinct chemical environments for Bi. Surface Bi is bonded to both As and Ga atoms. The deposition of approximately 1 ML of Bi removes the dangling bonds from the surface As and Ga atoms, which are associated with the (2×2) vacancy-buckling structure. Annealing to 350°C reverses this process and surface dangling bonds for Ga reappear. When the Bi had fully desorbed at 425°C, photoemission and LEED results showed that the surface recovers the (2×2) vacancy structure but with a larger degree of surface disorder than that found before the deposition of Bi.
Keywords: Low-energy electron diffraction; Synchrotron radiation photoelectron spectroscopy; Surface relaxation and reconstruction; Gallium arsenide (111)A; Bismuth; Metal–semiconductor interfaces;

We investigated the effect of the surface condition on luminescence processes in a surface layer of single CaF2 crystals under the excitation by vacuum-ultraviolet (VUV) light (≤13.5 eV). It has been shown that the intensity of the excitonic emission at 4.4 eV in polished crystals essentially decreases with respect to that in freshly cleaved crystals. The decrease at the interband excitation is larger than that at the direct optical creation of excitons. A new luminescence band peaking at 2.55 eV has been discovered and ascribed to the oxygen-related centres situated in a surface layer of CaF2. The main excitation band of this band is in strict correlation with the excitonic absorption band at 11.2 eV. It is almost absent in polished crystals. The ageing of the cleaved surface of CaF2 crystals causes decrease in the intensities of the 4.4 and 2.55 eV emissions with different rates. The etching of a polished surface restores both emission bands. The correlation has been established between the evolution of these luminescence phenomena and the changes in VUV transmission spectra at 7.5–10.2 eV near the fundamental absorption edge of CaF2, induced by the cleavage, polishing or etching of the sample.
Keywords: CaF2; Fluoride; Surface; Luminescence; Exciton; VUV radiation;

Yttrium implanted and unimplanted low manganese and low manganese–carbon steel samples were analyzed at T=700°C and under an oxygen partial pressure PO2 =0.04 Pa for 24 h to show the yttrium implantation effect on sample high temperature oxidation resistances. Sample oxidation weight gains were studied by thermogravimetry and structural analyses were performed by in-situ high temperature X-ray diffraction (XRD) with the same experimental conditions. The aim of this paper is to show the initial nucleation stage of the main compounds induced by oxidation at high temperature according to the initial sample treatment (yttrium implanted or unimplanted). The results obtained by in-situ high temperature XRD will be compared to those by thermogravimetry to a better understanding of the weight gain curves observed during the oxidation test at 700°C and P O2 =0.04 Pa. This study allows us to show the improved corrosion resistance of yttrium implanted low manganese and low manganese–carbon steel at high temperature.
Keywords: Steel; Yttrium; Ion implantation; Oxidation; X-ray diffraction;

Luminescence properties of anodically etched porous Zn by Sung-Sik Chang; Sang Ok Yoon; Hye Jeong Park; Akira Sakai (330-334).
Anodization of Zn in HF/ethanol and NaOH solution yields porous structure, which luminesces in the visible region. It is observed that the luminescence properties of these samples have been found quite different. The p-Zn prepared in NaOH displays two luminescence peaks near 420 and 520 nm. On the contrary, the p-Zn prepared in HF displays luminescence peak centered at 410 nm. These samples are further studied by annealing in O2 and N2 ambience. Further, temperature dependence photoluminescence (PL) spectra, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) have been performed on these samples, and the possible mechanisms causing the observed PL properties from p-Zn are discussed.
Keywords: Anodization; Semiconductor; Photoluminescence; XPS; Porous Zn;

XPS and AES investigation of two electroless composite coatings by Xianghua Yu; Hongyan Wang; Zhenrong Yang; Ping Yin; Xinquan Xin (335-339).
The morphology and composition of the Ni–P–SiO2 and Ni–P–CeO2 electroless composite coatings were investigated by SEM, XPS, and AES. The surfaces of the coatings are homogeneous, polished, and with strong corrosion resistance. For the Ni–P–SiO2 coating, the atomic percentages are Ni: 74.6%, P: 12.4%, Si: 2.77%, Fe: 2.32%, and O: 6.65%, and the compositions are Ni–P: 93.5%, SiO2: 3.27%, FeO: 1.56%, and Fe: 1.33%.
Keywords: XPS; AES; SiO2/CeO2; Electroless composite coating;

Variation of bonding structure near the surface of carbon nitride films by Liudi Jiang; A.G Fitzgerald; M.J Rose (340-344).
Amorphous carbon nitride (a-C:N) films were deposited by reactive direct current magnetron sputtering of graphite using a gaseous mixture of Ar and N2. X-ray photo electron spectroscopy analysis (XPS) showed that there is an optimum volume ratio of nitrogen:argon in the sputter gas that results in a maximum content of incorporated nitrogen in the films. By using different take-off angles in XPS experiments, the variation gradient of bonding structure near the surface of a-C:N films has also been studied. In the surface layer of the a-C:N films, it was found that some of the initially formed β-C3N4-like phase transforms to a graphite-like carbon–nitrogen phase. This structural change is driven by the nitrogen in the sputter gas during deposition.
Keywords: Carbon nitride; XPS; Take-off angle;

The characterization of semiconductor heterostructures from their mobility spectra has originally been proposed, some 12 years ago, as an improvement of Hall effect measurements. However, the application is far from being trivial and often leads to the occurrence of extra peaks without any physical interpretation. They are generally referred to as “mirror peaks” and are interpreted in terms of computational artifacts.The present paper comments upon such peaks from a set of data concerning van der Pauw test structures. Our main conclusion is that from an experimental point of view, the transverse component (ρ xy ) of the resistivity tensor is more precisely determined than the longitudinal one (ρ xx ). Thus, we are left with the possibility of artifacts within the experimental procedure.Starting from an adjustment of all available information (ρ xx and ρ xy ), a preferential adjustment of ρ xy leads to the disappearance of “mirror peaks”. As a matter of example, we report the study of an InP-based bilayered structure and show how the mobility spectrum evidences the highly conducting channel of a HEMT device.
Keywords: Magnetoresistance; Hall effect; InGaAs/AlGaAs HEMT; “Mirror” peaks;

We followed the surface oxidation of a 7-nm Co layer epitaxied on sapphire as a function of the oxygen coverage. Ultra-violet photoemission spectroscopy, atomic force microscopy and scanning tunneling microscopy were used to determine the thickness, surface roughness and electronic gap of the Co oxide.
Keywords: Thin films growth; Surface oxidation; Photoemission spectroscopy; Scanning probe microscopy;

Polymethylphenylsilane (PMPS), prototype of polysilanes, is considered as photoaligning material for liquid crystals (LC). The LC photoalignment on PMPS is characterized by the singular low exposure energy (E≤50 mJ) necessary to produce LC alignment. Dependence of the azimuthal anchoring energy W a on the exposure time τ exp is non-monotonous; curve W(τ exp) sharply increases, goes through a maximum and decreases to the values close to zero. The easy axis of LC alignment is induced in the direction of light polarization. Possible microscopic mechanisms of LC photoalignment on PMPS layers are discussed.
Keywords: Liquid crystals; Polysilanes; Photoalignment;

Secondary ion yields Y(Xi q) increase considerably when changing from atomic to molecular primary ions, whereas the parallel increase in the corresponding damage cross sections σ(Xi q) is much smaller. This results in a net increase of ion formation efficiencies E(Xi q)=Y/σ. For a more detailed understanding of the complex sputtering and ion formation processes, in particular for molecular primary ion bombardment, the secondary ion emission of well-defined polymethacrylate LB mono- and multilayers on Ag was investigated. For characteristic secondary ions Xi q emitted from these overlayers Y(Xi q) and σ(Xi q) for 11 keV Ne+, Ar+, Xe+, O2 +, SF5 +, C7H7 +, C10H8 +, C6F6 + and C10F8 + bombardment were determined and compared. The influence of primary ion energy was investigated in the energy range between 0.5 and 10 keV for Xe+ and SF5 + bombardment.For multilayers we found yield increases up to nearly a factor of 1000, when changing from Ne+ to SF5 + bombardment. We found a more pronounced yield and efficiency enhancement for multi than for monolayer coverages, a saturation of Y, σ and E enhancement for primary ions made of more than 6 heavy constituents at constant primary ion energy, no chemical effect on the secondary ion yields under static SIMS conditions (SF5 + / C7H7 + e.g.), and a pronounced decrease in secondary ion yields and secondary ion formation efficiencies for SF5 + primary ions with impact energies below 2 keV.
Keywords: Secondary ion mass spectroscopy; Secondary ion emission; Polyatomic primary ions; Langmuir–Blodgett films;

Titanium nitride was grown epitaxially on MgO(001) by a pulsed laser deposition (PLD) method, and the oscillations of reflection high energy electron diffraction (RHEED) for this system were observed for the first time. The RHEED patterns and atomic force microscope (AFM) analysis revealed the two-dimensional growth of highly flat TiN films. The high-resolution reciprocal space mapping of X-ray diffraction of the TiN film showed that the lattice dimensions of the TiN shrunk along the plane parallel to the surface of the MgO(001) substrate by 0.6% with no structural relaxation and no mosaic disorder, demonstrating the deposition of the high-quality epitaxial film.
Keywords: Titanium nitride; Epitaxy; RHEED oscillation; Pulsed laser deposition;

Index (379-382).

Index (383-393).