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Applied Surface Science (v.252, #22)

The barrier height inhomogeneity in Al/p-Si Schottky barrier diodes with native insulator layer by İlbilge Dökme; Şemsettin Altindal; M. Mahir Bülbül (pp. 7749-7754).

The current–voltage ( I– V) characteristics of Al/p-Si Schottky barrier diodes (SBDs) with native insulator layer were measured in the temperature range of 150–375K. The estimated zero-bias barrier height Φ_B0 and the ideality factor n assuming thermionic emission (TE) theory show strong temperature dependence. Evaluation of the forward I– V data reveals an increase of zero-bias barrier height Φ_B0 but decrease of ideality factor n with increase in temperature. The conventional Richardson plot exhibits non-linearity below 250K with the linear portion corresponding to activation energy of 0.41eV and Richardson constant ( A^*) value of 1.3×10⁻⁴Acm⁻²K⁻² is determined from intercept at the ordinate of this experimental plot, which is much lower than the known value of 32Acm²K² for holes in p-type Si. Such behavior is attributed to Schottky barrier inhomogene ties by assuming a Gaussian distribution of barrier heights (BHs) due to barrier height inhomogeneities that prevail at interface. Also, Φ_B0 versus q/2 kT plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values of Φ_B0=1.055eV and σ₀=0.13V for the mean BH and zero-bias standard deviation have been obtained from this plot, respectively. Thus, the modifiedln(I0/T2)−q2σo2/2k2T2 versus q/ kT plot gives Φ_B0 and A^* as 1.050eV and 40.08Acm⁻²K⁻², respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 40.03Acm⁻²K⁻² is very close to the theoretical value of 32AK⁻²cm⁻² for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I– V characteristics of the Al/p-Si Schottky barrier diodes with native insulator layer can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights.

Keywords: PACS; 73.30.+y; 73.40.Qv; 73.40.NsSchottky diodes; Temperature dependence; Gaussian distribution; Barrier height; Inhomogeneity; Native insulator layer

Performance enhancement of a heterojunction bipolar transistor (HBT) by two-step passivation by Ssu-I. Fu; Po-Hsien Lai; Yan-Ying Tsai; Ching-Wen Hung; Chih-Hung Yen; Shiou-Ying Cheng; Wen-Chau Liu (pp. 7755-7759).

An interesting two-step passivation (with ledge structure and sulphide based chemical treatment) on base surface, for the first time, is demonstrated to study the temperature-dependent DC characteristics and noise performance of an InGaP/GaAs heterojunction bipolar transistor (HBT). Improved transistor behaviors on maximum current gain β_max, offset voltage Δ V_CE, and emitter size effect are obtained by using the two-step passivation. Moreover, the device with the two-step passivation exhibits relatively temperature-independent and improved thermal stable performances as the temperature is increased. Therefore, the two-step passivationed device can be used for high-temperature and low-power electronics applications.

Keywords: Sulphide based chemical treatment; Ledge passivation; Temperature-dependent characteristics

Characterization of post-copper CMP surfaces with scanning probe microscopy by A. Dominget; J. Farkas; S. Szunerits (pp. 7760-7765).

We demonstrate in this paper for the first time the use of conductive atomic force microscopy (AFM) to measure surface leakage between copper structures with varying line width and spacing in the micro and sub micrometer ranges. Conducting atomic force microscopy allows subsequent measurement of the topography as well as the electrical properties of surfaces. The feasibility and interest of these measurements will be shown by studying the impact of chemical mechanical polishing (CMP) of an electrical interface bearing different micrometric copper structures. As expected the polishing time has a crucial impact on the current determined between closely spaced copper structures. This paper will also deal with issues observed during the measurement.

Keywords: Atomic force microscopy (AFM); Surface leakage; Chemical mechanical polishing (CMP); Copper interconnects

Surface properties of cubic boron nitride thin films by Jinxiang Deng; Guanghua Chen (pp. 7766-7770).

Studying the surface properties of cubic boron nitride (c-BN) thin films is very important to making it clear that its formation mechanism and application. In this paper, c-BN thin films were deposited on Si substrates by radio frequency sputter. The influence of working gas pressure on the formation of cBN thin film was studied. The surface of c-BN films was analyzed by X-ray photoelectron spectroscopy (XPS), and the results showed that the surface of c-BN thin films contained C and O elements besides B and N. Value of N/B of c-BN thin films that contained cubic phase of boron nitride was very close to 1. The calculation based on XPS showed that the thickness of hexagonal boron nitride (h-BN) on the surface of c-BN films is approximately 0.8nm.

Keywords: Cubic boron nitride; Surface; XPS

Influence of chemical composition of filler's surface on the burning of foam plastics by S.A. Trifonov; A.A. Malygin; Chul Tae Lee (pp. 7771-7773).

The influence of additives such as TiO₂, Al₂O₃ and their mechanical mixture as well as aluminium oxide, the surface of which contains phosphorous and titanium-oxide nanostructures, on the combustibility of foam plast (trade mark PEN-I), produced on the basis of epoxide novolak block-copolymers, was studied. It was stated that the incorporation both phosphorous-containing and titanium-containing oxides in the composition results in significant (in two to five times) decreasing of the samples’ combustibility. The probable mechanism of inhibition of burning process for those combustion retarders was discussed.

Keywords: PACS; 81.65.− b; 83.80.UvFillers; Surface; Molecular layering; Nanostructures; Aluminium oxide; Foam plast; Combustibility

Preparation of fluorocarbon thin film deposited by soft X-ray ablation and its electrical characteristics and thermal stability by Takeshi Kanashima; Osamu Maida; Norihiro Kohma; Masaki Okumoto; Masato Ueno; Satoshi Kitai; Masanori Okuyama; Haruhiko Ohashi; Yusuke Tamenori (pp. 7774-7780).

Fluorocarbon films were deposited by soft X-ray ablation of polytetrafluoroethylene (PTFE) and characterized as low-dielectric-constant interlayer dielectrics. Very rapid deposition of such films at approximately 1500 nm/min could be achieved at room temperature. Fourier-transform infrared spectroscopy (FT-IR) measurement results suggest that the films deposited are primarily formed as one-dimensional chains of (–CF₂–)_n which are partially cross-linked. The cross-link density increases with increasing deposition temperature, which improves the thermal stability. However, the dielectric constant of the films increased abruptly above 300°C. The dielectric constant and leakage current at 1.0 MV/cm of the film deposited at room temperature were approximately 2.1 and2.0×10−9 A/cm², respectively.

Keywords: PACS; 77.55.+f; 79.20.La; 73.40.QvFluorocarbon film; Polytetrafluoroethylene; Soft X-ray ablation; Low dielectric constant; Current–voltage characteristics; Thermal stability

Thermal expansion coefficient of alumina films developed by oxidation of a FeCrAl alloy determined by a deflection technique by A.M. Huntz; L. Maréchal; B. Lesage; R. Molins (pp. 7781-7787).

Thermal expansion coefficients of α alumina films formed by oxidation of an oxide dispersion strengthened (ODS) FeCrAl alloy have been determined between 20 and 900°C using an original deflection test. This technique is based on the curvature of a dissymmetrical sample consisting of a thin and elongated metallic substrate covered on one of its large sides by an oxide film. The average value of the expansion coefficient of the compact columnar α alumina film is found to equal 10.3×10⁻⁶K⁻¹ which is higher than most values given in the literature.

Keywords: PACS; 65.70.+y; 68.55.−a; 68.60.Dv; 68.60.−pThermal expansion coefficient; Alumina films; Deflection tests; FeCrAl

Supercritical angle fluorescence biosensor for the detection of molecular interactions on cellulose-modified glass surfaces by Stephan Laib; Alexander Krieg; Michael Rankl; Stefan Seeger (pp. 7788-7793).

Cellulose films have been proposed as a convenient substrate for producing flat and homogeneous surface coatings. Additionally, amino-labelled cellulose species, like aminopropyltrimethylsilylethercellulose (ATMSC), are excellent support matrices for covalent binding of biomolecules, with low probe density and prevention of non-specific adsorption of unbound analyte molecules. Due to ATMSC films fulfil important requirements as substrate for analyse techniques of surface-tethered proteins and nucleic acids, we consequently report a new preparation for DNA-functionalised surfaces. Single-stranded DNA molecules are covalently coupled to cellulose-coated glass cover slips to interact with complementary free Cy5-labelled oligonucleotides in solution. Hybridisation efficiencies at the new substrate and at standard surface coatings are determined by detection of the surface-generated fluorescence. In order to discriminate against the fluorescence from unbound oligonucleotides the detection volume was restricted to the surface by collecting supercritical angle fluorescence (SAF). Thus, it is demonstrated that cellulose films are utilised to investigate DNA-hybridisation reactions highly sensitive.

Keywords: DNA-hybridisation; Cellulose; ATMSC; SAF-biosensor

Synergetic effect between ion energy and sample temperature in the formation of distinct dot pattern on Si(110) by ion-sputter erosion by Wei-Qing Li; Le-Jun Qi; Xinju Yang; Li Ling; Wen-Bin Fan; You-Yuan Zhao; Ming Lu (pp. 7794-7800).

We observed a synergetic effect between ion energy and sample temperature in the formation of distinct dot pattern on Si(110) by Ar⁺ ion sputtering. The ion flux was 20μA/cm², a value smaller than those used in preceding reports by one or two orders of magnitude. In experiments, the ion energy was from 1 to 5keV, and the temperature from room temperature to 800°C. A phase diagram indicating the ranges of ion energy and temperature within which distinct dot patterns can be achieved has been obtained. Data analyses and simulation results reveal that the synergetic effect is consistent with the effect of the Ehrlich–Schwoebel step-edge barrier, rather than the Bradley–Harper model.

Keywords: PACS; 68.35.Bs; 68.37.Ps; 68.49.SfSilicon; Surface structure, morphology, roughening and topography; Ion bombardment; Atomic force microscopy

Influence of silver on the anodic corrosion and gas evolution of Pb–Sb–As–Se alloys as positive grids in lead acid batteries by A. Tizpar; Z. Ghasemi (pp. 7801-7808).

The influence of silver addition in the range 0.01–0.09wt.% on the anodic corrosion and gas evolution of Pb–Sb–As–Se alloy in 1.28sp.gr. H₂SO₄ solution at 25°C was studied using linear sweep voltammetry, cyclic voltammetry, weight loss measurements and scanning electron microscopy. The results drawn from different techniques are comparable. The effect of different concentration of silver on the corrosion behavior of Pb–Sb–As–Se was investigated. The experimental results show that the silver added to Pb–Sb–As–Se alloy inhibits the growth of anodic corrosion layer. A decrease in the oxygen evolution overpotential and an increase in the hydrogen evolution overpotential with the addition of Ag were also observed during the experiments. Cyclic voltammetric measurements provided information on the effect of Ag on the oxidation of PbSO₄ to PbO₂.

Keywords: Corrosion; Lead alloy; Silver; Lead acid battery

The bond strength of Al–Si coating on mild steel by kinetic spraying deposition by Jingwei Wu; Jianguo Yang; Hongyuan Fang; Sanghoon Yoon; Changhee Lee (pp. 7809-7814).

Kinetic spraying (or cold gas dynamic spraying) works by accelerating small solid particles to supersonic velocities, and then impacting them onto a substrate. These high impact velocities, and low particle temperatures are the principal attributes of kinetic spraying technology. However, only recently has this technology's interfacial behavior, due to particle/substrate impaction, become well understood. In order to investigate the particle/substrate bond behavior, Al–Si feedstock was deposited onto mild steel, over a range of particle velocities; next, their respective coating bond strengths were measured by the stud pull coating adherence test. The effects of the particle velocity and the substrate surface roughness on the coating bond strength were presented, and a model of the particle/substrate bond generation was discussed in an effort to estimate the bond strength.

Keywords: Kinetic spraying; Cold gas dynamic spraying; Bond strength; High velocity impact

Polar oscillation and dispersion properties of quasi-confined optical phonon modes in a wurtzite GaN/Al_xGa1−_xN nanowire by Li Zhang; Jun-Jie Shi (pp. 7815-7822).

Under the dielectric continuum model and Loudon’s uniaxial crystal model, the properties of the quasi-confined (QC) optical phonon dispersions and the electron–QC phonons coupling functions in a cylindrical wurtzite nanowire are deduced via the method of electrostatic potential expanding. Numerical computations on a GaN/Al_0.15Ga_0.85N wurtzite nanowire are performed. Results reveal that, for a definite axial wave numberkz and a certain azimuthal quantum number m, there are infinite branches of QC modes. The frequencies of these QC modes fall into two regions, i.e. a high frequency region and a low frequency region. The dispersion of the QC modes are quite apparant only whenkz and m are small. The lower-order QC modes in the higher frequency region play more important role in the electron–QC phonon interactions. Moreover, for the higher-order QC modes in the high frequency region, the electrostatic potentials “escaping�? out of the well-layer material nearly could be ignored.

Keywords: PACS; 81.05.Ea; 78.67.Lt; 74.25.Kc; 63.20.KrQuasi-confined optical phonon; Wurtzite nanowires; Nitride semiconductor

High power single-shot laser ablation of silicon with nanosecond 355nm by D.M. Karnakis (pp. 7823-7825).

We report on high intensity single-shot laser ablation of monocrystalline silicon with a nanosecond Nd:YAG at 355nm. It is shown that for incident laser intensities exceeding ∼11.5GW/cm² on the silicon surface, unusually high etch depths can be achieved reaching values up to 60μm. The results support previous observations of dramatic increase in etch rates in single-shot laser ablation at 266nm. A laser-induced explosive boiling mechanism together with secondary plasma heating is believed to be associated with this effect.

Keywords: PACS; 42.62Cf; 42.55.XiDPSS lasers; Silicon; Single-shot laser ablation; Explosive boiling

ZnS thin film prepared through a self-assembled thin film precursor route by Jin Mu; Yunyan Zhang (pp. 7826-7829).

Poly(zinc 1,6-hexanedithiolate) thin film, a precursor to prepare ZnS thin film, was self-assembled on a quartz substrate. The UV–vis spectra monitored the annealing process of the poly(zinc 1,6-hexanedithiolate) film, which revealed that the ZnS thin film began to form at approximately 515K. The result of XRD confirmed the crystallinity of ZnS. With increase of annealing temperature, a red shift of the emission spectra was observed.

Keywords: PACS; 71.55.Gs; 68.55.−aZnS thin film; Self-assembled thin film precursor; Thermolysis

Adsorption behavior of protein onto siloxane microspheres by Bailing Liu; Shunsheng Cao; Xiaobo Deng; Songjun Li; Rong Luo (pp. 7830-7836).

The siloxane microspheres with core-shell structure (PMMA/PMPS) (MMA, methyl methacrylate; MPS, 3-methacryloxypropyl-trimethoxysilane) have been prepared by dispersion polymerization as described in our previous work. In this paper, the developed poly(MMA-MPS) microspheres, as a carrier, are used to investigate the adsorption behavior of bovine serum albumin (BSA) on them. The Langmuir and Freundlich models have been applied to describe the adsorption behavior. The experimental results indicated that the presence of PMPS evidently increases the adsorption rate and the amount of protein, and it also influences the interaction of BSA molecules. The adsorption of BSA on the poly(MMA-MPS) microspheres seems to be sensitive to pH and ionic strength. The fittings curves from Langmuir and Freundlich models showed that the adsorption was actually more complicated than ideal situation because one or more interactions were involved in the process. For understanding the electronic contribution, the Zeta potential was used to measure the reactive system before and after protein adsorption.

Keywords: Siloxane microspheres; Bovine serum albumin (BSA); Protein adsorption

Adsorption model determination of N₂O/Ag(110) by theoretical studies of near-edge X-ray absorption fine structure by Tai-Quan Wu; Jing-Chang Tang; Hai-Yang Li (pp. 7837-7843).

The nitrogen 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of the N₂O adsorbed on Ag(110) have been studied by the multiple-scattering cluster (MSC) and self-consistent field (SCF) DV-Xα methods. Two adsorption models, in which the N₂O molecule attached to the Ag substrate through the central nitrogen (N_C) atom and the terminal nitrogen (N_T) atom, respectively, have been checked up thoroughly. The MSC calculation and the R-factor analysis show that the N₂O molecule is attached to the Ag substrate through the terminal nitrogen atom with the adsorption height h=3.4±0.1Å. In the overlayer the N₂O molecules arrange themselves into a tilted chain due to the interaction between the cations and the anions in the molecules. The physical cause of the resonances in the NEXAFS spectra mentioned above has been discussed by the DV-Xα method, which confirms the MSC calculations.

Keywords: PACS; 61.10.HtN; ₂; O/Ag(1; 1; 0); Near-edge X-ray absorption fine structure; Multiple-scattering cluster method; Reliability factor; DV-Xα method

Physical properties of ZnO thin films deposited by spray pyrolysis technique by A. Ashour; M.A. Kaid; N.Z. El-Sayed; A.A. Ibrahim (pp. 7844-7848).

Thin films of ZnO have been prepared on glass substrates at different thicknesses by spray pyrolysis technique using 0.2M aqueous solution of zinc acetate. X-ray diffraction reveals that the films are polycrystalline in nature having hexagonal wurtzite type crystal structure. The resistivity at room temperature is of the order 10⁻²Ωcm and decreased as the temperature increased. Films are highly transparent in the visible region. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for a sprayed film is also reported. Optical bandgap, E_g, has been reported for the films. A shift from E_g=3.21eV to 3.31eV has been observed for deposited films.

Keywords: ZnO thin films; Spray pyrolysis; Structural; Electrical resistivity; Optical properties

The nature of antimony-enriched surface layer of Fe–Sb mixed oxides by Yan Huang; Patricio Ruiz (pp. 7849-7855).

Antimony segregation is a common feature in Fe–Sb mixed oxides, which have been widely applied as catalysts in selective oxidation and ammoxidation reactions. This paper attempts to shed a light on the cause of such a common feature and on the nature of the antimony-enriched surface layer over FeSbO₄ by means of XPS surface analysis. Single-phase FeSbO₄ samples prepared by different methods were studied, and the antimony in their surface layer is a mixture of both Sb⁵⁺ and Sb³⁺ rather than single Sb⁵⁺. Their surface composition is close to FeSb₂O₆, which could be described as (FeSbO₄)(Sb₂O₄)_δ, δ=0.5, and it is not “Fe(II)Sb(V)₂O₆�? as suggested in literature. Fe–Sb mixed oxides with Sb/Fe>1 (mol/mol) are mixtures of FeSbO₄ and Sb₂O₄, and the surface of FeSbO₄ grains would be a layer of (FeSbO₄)(Sb₂O₄)_δ, δ≥0.5. Fe–Sb mixed oxides with Sb/Fe<1 are mixtures of FeSbO₄ and Fe₂O₃, and the surface of FeSbO₄ grains would be a layer of (FeSbO₄)(Sb₂O₄)_δ, δ≤0.5, but the remaining Fe₂O₃ would be encapsulated by a layer of FeSbO₄.

Keywords: Surface segregation; X-ray photoelectron spectroscopy; FeSbO; ₄; FeSb; ₂; O; ₆; Sb; ₂; O; ₄; Fe; ₂; O; ₃

Surface-modification in situ of nano-SiO₂ and its structure and tribological properties by Xiaohong Li; Zhi Cao; Zhijun Zhang; Hongxin Dang (pp. 7856-7861).

The preparation of a series of dispersible nano-SiO₂ by surface-modification in situ was described in this paper. It is found that some silane coupling agents can be combined with nano-SiO₂ by covalent bonds, which change the nanoparticle's surface properties and make nano-SiO₂ disperse well and steadily in many organic mediums. The structure of nanoparticles was characterized by transmission electron microscopy (TEM), infrared spectrum (IR), X-ray photoelectron spectra (XPS) and thermogravimetric analysis (TG). The dispersivity of these nanoparticles in organic solvents was measured by light transmittance. Considering such superior dispersion in oily solvents and very small size, we primarily investigated their tribological behaviors as additive in lubricant on wear testers. The results show that they can evidently increase anti-wear ability and reduce the friction coefficient of lubricant.

Keywords: Nanosilica; Surface-modification; Dispersion; Tribology

Electron microscopy and EXAFS studies on oxide-supported gold–silver nanoparticles prepared by flame spray pyrolysis by Stefan Hannemann; Jan-Dierk Grunwaldt; Frank Krumeich; Peter Kappen; Alfons Baiker (pp. 7862-7873).

Gold and gold–silver nanoparticles prepared by flame spray pyrolysis (FSP) were characterized by electron microscopy, in situ X-ray absorption spectroscopy (XANES and EXAFS), X-ray diffraction (XRD) and their catalytic activity in CO oxidation. Within this one-step flame-synthesis procedure, precursor solutions of dimethyl gold(III) acetylacetonate and silver(I) benzoate together with the corresponding precursor of the silica, iron oxide or titania support, were sprayed and combusted. In order to prepare small metal particles, a low noble metal loading was required. A loading of 0.1–1wt.% of Au and Ag resulted in 1–6nm particles. The size of the noble metal particles increased with higher loadings of gold and particularly silver. Both scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDXS) and X-ray absorption spectroscopy (XAS) studies proved the formation of mixed Au–Ag particles. In case of 1% Au–1% Ag/SiO₂, TEM combined with electron spectroscopic imaging (ESI) using an imaging filter could be used in addition to prove the presence of silver and gold in the same noble metal particle. CO oxidation in the presence of hydrogen was chosen as a test reaction sensitive to small gold particles. Both the influence of the particle size and the alloying of gold and silver were reflected in the CO oxidation activity.

Keywords: Gold–silver alloys; Nanoparticles; EXAFS; TEM/STEM; Flame spray pyrolysis

Surface functionalisation of polymer nanofibres by sputter coating of titanium dioxide by Q.F. Wei; F.L. Huang; D.Y. Hou; Y.Y. Wang (pp. 7874-7877).

The surface properties of nanofibres are of importance in various applications. In this work, electrospun polyamide nanofibres were used as substrates for creating functional nanostructures on the nanofibre surfaces. A RF magnetron sputter coating was used to deposit the functional layer of titanium dioxide (TiO₂) onto the nanofibres. Atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and environmental scanning electron microscopy (ESEM) were employed to study the topography, grain structure and wetting of the nanofibre surfaces, respectively. The AFM results indicated a significant difference in the morphology of the nanofibres before and after the TiO₂ sputter coating. The XRD analysis showed the amorphous structures of the TiO₂ deposition layer. XPS spectra reflected the chemical features of the deposited nanostructures. The ESEM observation revealed that the surface wettability of TiO₂ sputter coated nanofibres was significantly improved after UV irradiation.

Keywords: PACS; 52.77.Bn; 81.65.Cf; 87.64.EeNanofibres; TiO; ₂; Sputtering; AFM; XRD; XPS; ESEM

Effect of process parameters on surface morphology and characterization of PE-ALD SnO₂ thin films for gas sensing by Gwangpyo Choi; L. Satyanarayana; Jinseong Park (pp. 7878-7883).

Tin dioxide (SnO₂) thin films were deposited by plasma enhanced-atomic layer deposition (PE-ALD) on Si(100) substrate using dibutyl tin diacetate (DBTA) ((CH₃CO₂)₂Sn[(CH₂)₃-CH₃]₂) as precursor. The process parameters were optimized as a function of substrate temperature, source temperature and purging time. It is observed that the surface phenomenon of the thin films was changed with film thickness. Atomic force microscopy (AFM) images and X-ray diffraction (XRD) pattern were used to observe the texture and crystallanity of the films. The films deposited for 100, 200 and 400 cycles were characterized by XPS to determine the chemical bonding properties. XPS results reveal that the surface dominant oxygen species for 100, 200 and 400 cycles deposited films are O₂⁻, O⁻ and O²⁻, respectively. The 200 cycles film has exhibited highest concentration of oxygen (O⁻) species before and after annealing. Conductivity studies revel that this film has best adsorption strength to the oxygen ions forming on the surface. The sensor with 200 cycles SnO₂ thin film has shown highest sensitivity to CO gas than other films. A correlation between the characteristics of Sn3d_5/2 and O1s XPS spectra before and after annealing and the electrical behavior of the SnO₂ thin films is established.

Keywords: PACS; 81.15.Gh; 68.55.Jk; 07.07.DfThin film; Tin oxide; PE-ALD; Gas sensing

Effects of O₂ and H₂O plasma immersion ion implantation on surface chemical composition and surface energy of poly vinyl chloride by Wei Zhang; Paul K. Chu; Junhui Ji; Yihe Zhang; Zhimin Jiang (pp. 7884-7889).

Oxygen and water plasma immersion ion implantation (PIII) was used to modify poly vinyl chloride (PVC) to enhance oxygen-containing surface functional groups for more effective grafting. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and contact angle measurements. Our experimental results show that both oxygen and water PIII can greatly improve the O to C ratios on the surface. The optimal plasma processing conditions differ for the two treatments. The hydrophilicity and surface energy of the plasma-implanted PVC are also improved significantly. Our results indicate that O₂ and H₂O PIII increase both the polar and dispersion interactions and consequently the surface energy. It can be explained by the large amount of oxygen introduced to the surface and that many CC bonds are transformed into more polar oxygen containing functional groups.

Keywords: PACS; 52.77.Dq; 82.35.Gh; 81.15.JjPlasma immersion ion implantation (PIII); Poly vinyl chloride (PVC); Surface energy; Hydrophilicity

XPS, electric and photoluminescence-based analysis of the GaAs (100) nitridation by Z. Benamara; N. Mecirdi; B. Bachir Bouiadjra; L. Bideux; B. Gruzza; C. Robert; M. Miczek; B. Adamowicz (pp. 7890-7894).

In this paper, nitridation process of GaAs (100) substrates was studied in-situ using X-ray photoelectron spectroscopy (XPS) and ex-situ by means of electrical method I– V and photoluminescence surface state spectroscopy (PLS³) in order to determine chemical, electrical and electronic properties of the elaborated GaN/GaAs interfaces.The elaborated structures were characterised by I– V analysis. The saturation current I_S, the ideality factor n, the barrier height Φ_Bn and the serial resistance R_S are determined.The elaborated GaN/GaAs structures are also exhibited a high PL intensity at room temperature. From the computer-aided analysis of the power-dependent PL efficiency measurements (PLS³ technique), the value of the interface state density N_SS( E) close to the mid-gap was estimated to be in the range of 2–4×10¹¹eV⁻¹cm⁻², indicating a good electronic quality of the obtained interfaces.Correlation among chemical, electronic and electrical properties of the GaN/GaAs interface was discussed.

Keywords: Nitridation; XPS; Electrical measurements; Photoluminescence

Electron energy loss spectra from polycrystalline Cr and Cr₂O₃ before and after surface reduction by Ar⁺ bombardment by Jason F. Weaver; Helena A.E. Hagelin-Weaver; Gar B. Hoflund; Ghaleb N. Salaita (pp. 7895-7903).

Electron energy loss spectra (ELS) have been obtained from polycrystalline Cr and Cr₂O₃ before and after surface reduction by 2keV Ar⁺ bombardment. The primary electron energy used in the ELS measurements was systematically varied from 100 to 1150eV in order to distinguish surface versus bulk loss processes. Two predominant loss features in the ELS spectra obtained from Cr metal at 9.0 and 23.0eV are assigned to the surface and bulk plasmon excitations, respectively, and a number of other features arising from single electron transitions from both the bulk and surface Cr 3d bands to higher-lying states in the conduction band are also present. The ELS spectra obtained from Cr₂O₃ exhibit features that originate from both interband transitions and charge-transfer transitions between the Cr and O ions as well as the bulk plasmon at 24.4eV. The ELS feature at 4.0eV arises from a charge-transfer transition between the oxygen and chromium ions in the two surface layers beneath the chemisorbed oxygen layer, and the ELS feature at 9.8eV arises from a similar transition involving the chemisorbed oxygen atoms. The intensity of the ELS peak at 9.8eV decreases after Ar⁺ sputtering due to the removal of chemisorbed oxygen atoms. Sputtering also increases the number of Cr²⁺ states on the surface, which in turn increases the intensity of the 4.0eV feature. Furthermore, the ELS spectra obtained from the sputtered Cr₂O₃ surface exhibit features characteristic of both Cr⁰ and Cr₂O₃, indicating that Ar⁺ sputtering reduces Cr₂O₃. The fact that neither the surface- nor the bulk-plasmon features of Cr⁰ can be observed in the ELS spectra obtained from sputtered Cr₂O₃ while the loss features due to Cr⁰ interband transitions are clearly present indicates that Cr⁰ atoms form small clusters lacking a bulk metallic nature during Ar⁺ bombardment of Cr₂O₃.

Keywords: ELS; XPS; Cr metal; Cr; ₂; O; ₃

Pulsed laser ablation of borax target in vacuum and hydrogen DC glow discharges by A.N. Kale; A. Miotello; P. Mosaner (pp. 7904-7910).

The aim of our experiment was to produce a material with BH bonds for applications in hydrogen storage and generation. By using KrF excimer laser ( λ=248nm) ablation of borax (Na₂B₄O₇) target, thin films were deposited on KBr and silicon substrates. Ablation was performed both in vacuum and in hydrogen atmosphere. DC glow discharge technique was utilized to enhance hydrogen gas ionization. Experiments were performed using laser fluence from 5 to 20J/cm². Films were deposited under gas pressure of 1×10⁻⁵ to 5×10⁻²mbar and substrate temperatures of 130–450°C. Scanning electron microscopy analysis of films showed presence of circular particulates. Film thickness, roughness and particulates number increased with increase in laser fluence. Energy dispersive X-ray spectroscopy analysis shows that sodium content in the particulates is higher than in the target. This effect is discussed in terms of atomic arrangements (both at surface and bulk) in systems where ionic and covalent bonds are present and by looking at the increased surface/bulk ratio of the particulates with respect to the deposited films. The Fourier transform infrared spectroscopy measurements showed presence of BO stretching and BOB bending bonds. Possible reasons for absence of BH bonds are attributed to binding enthalpy of the competing molecules.

Keywords: PACS; 52.38.Mf 68.37.HkPulsed laser deposition; Thin films; DC glow discharge

Microstructure characteristic of ceramic coatings fabricated on magnesium alloys by micro-arc oxidation in alkaline silicate solutions by H.F. Guo; M.Z. An; H.B. Huo; S. Xu; L.J. Wu (pp. 7911-7916).

Micro-arc oxidation (MAO) of AZ31B magnesium alloys was studied in alkaline silicate solutions at constant applied current densities. The microstructure, phase composition and elemental distribution of ceramic coatings were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDX). There are two inflections in the voltage–time response, three regions were identifiable and each of the regions was almost linear. The pores with different shapes distributed all over the coating surface, the number of the pores was decreasing, while the diameter was apparently increasing with prolonged MAO treatment time. There were also cracks on the coating surface, resulting from the rapid solidification of the molten oxide. The ceramic coating was comprised of two layers, an outer loose layer and an inner dense layer. The ceramic coating was mainly composed of forsterite phase Mg₂SiO₄ and MgO; the formation of MgO was similar to conversional anodizing technology, while formation of Mg₂SiO₄ was attributed to a high temperature phase transformation reaction. Presence of Si and O indicated that the electrolyte components had intensively incorporated into coatings.

Keywords: Magnesium alloy; Micro-arc oxidation; Ceramic coating; Microstructure

The morphologies of fractured surfaces and fracture toughness in some As–Se–Sb–S–I glasses by S.R. Lukić; D.M. Petrović; F. Skuban; L. Šiđanin; I.O. Gúth (pp. 7917-7920).

As part of a general physical characterization of amorphous materials in the pseudobinary system (As₂Se₃)100−_x(SbSI)_x type, their indentation fracture toughness was determined. It is a system with the variable ratio of classical amorphous compound As₂Se₃ and the molecule of antimony sulfoiodide, SbSI, which in the monocrystal form is characterized as ferroelectrics. Because of chalcogenides are generally very brittle and under load they crack very easily, these glasses have been studied with the aim of examining the possibility of obtaining some new structures on the basis of the materials with amorphous internal network, the structures that will have a higher quality in respect of mechanical properties. The morphologies of fractured surfaces were investigated by scanning electron microscope.

Keywords: PACS; 61.43.Fs; 81.05.Kf; 62.20.Mk; 68.35.Gy; 68.37.HkChalcogenides; Fracture toughness; Fractured surfaces; Amorphous structure

Effect of the heat treatment on the corrosion behaviour of amorphous Fe–Cr–P–C–Si alloy in 0.5M H₂SO₄ by M. Belkhaouda; L. Bazzi; A. Benlhachemi; R. Salghi; B. Hammouti; S. Kertit (pp. 7921-7925).

The effect of the heat treatment on the corrosion behaviour of amorphous Fe₈₅Cr₅P₆C₃Si alloy in 0.5M H₂SO₄ has been investigated using electrochemical techniques. Heat treatment was carried out at temperatures varying between 250 and 650°C at different times 30, 60, 120 and 240min. The evolution of crystallization processes after annealing was identified by differential thermal analysis (DTA) and by X-ray diffraction (XRD). The diagrams obtained by DTA show that the structure of samples treated at high temperature changes towards a crystalline state. This crystallization phenomenon is confirmed by the analysis with the XRD. The results obtained from the polarization curves reveal that for all the studied temperatures of annealing, Fe–Cr–P–C–Si exhibits a phenomenon of passivation without breakdown of passivity. The best corrosion resistance is obtained at the temperature of annealing 350°C. For an annealing at higher temperatures, Fe₈₅Cr₅P₆C₃Si becomes less corrosion resistant than same amorphous alloy treated with temperatures lower than 350°C.

Keywords: Amorphous; Corrosion; Heat treatment; Polarization; X-ray diffraction

The effects of chain number and state of lipid derivatives of nucleosides on hydrogen bonding and self-assembly through the investigation of Langmuir–Blodgett films by Yiguang Jin; Yingxin Qiao; Xinpu Hou (pp. 7926-7929).

The long-chain lipid derivatives of acyclovir—a nucleoside analogue were used to prepare Langmuir–Blodgett (LB) films, including the single-chained derivative (SGSA) and the double-chained derivative (DASA). The bilayer LB film of DASA or the SGSA/cholesterol (SGSA/Chol) mixture (1:1, mol/mol) on quartz plates was investigated with ultraviolet absorption spectroscopy, and the blue-shifted absorption with 4nm (DASA) or 18nm (SGSA/Chol) wavelength changes was observed in comparison with their solutions in chloroform. The rigid double chains of DASA prevented adjacent molecules from approach, while the flexible single chains of SGSA did not. Then the strength of intermolecular hydrogen bonding between the nucleoside moieties of DASA was much more weaker than one of SGSA, and their blue-shifted wavelength in LB films was different. DASA and SGSA/Chol also showed the different bilayer LB films on mica according to the atomic force microscopic observation. The former was prone to tilting on solid supports while the latter would like to stand vertically with the help of cholesterol that could insert into the flexible single chains of SGSA. The chain number (one or two) and state (flexible or rigid) of lipid derivatives of nucleosides strongly impact intermolecular hydrogen bonding and self-assembly behavior.

Keywords: PACS; 82.30.Rs; 81.16.DnHydrogen bonding; Self-assembly; Nucleosides; Langmuir–Blodgett films; Ultraviolet absorption spectroscopy; Atomic force microscope

Synthesis of β-Ga₂O₃ nanowires through microwave plasma chemical vapor deposition by Feng Zhu; Zhongxue Yang; Weimin Zhou; Yafei Zhang (pp. 7930-7933).

In this study, we demonstrate the large-scale synthesis of beta gallium oxide (β-Ga₂O₃) nanowires through microwave plasma chemical vapor deposition (MPCVD) of a Ga droplet in the H₂O and Ar atmosphere at 600W. Unlike the commonly used MPCVD method, the H₂O, not mixture of gas, was employed to synthesize the nanowires. The ultra-long β-Ga₂O₃ nanowires with diameters of about 20–30nm were several tens of micrometers long. The morphology and structure of products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM). The growth of β-Ga₂O₃ nanowires was controlled by vapor–solid (VS) crystal growth mechanism.

Keywords: PACS; 52.50.Sw; 81.05.Hd; 81.07.Bc; 81.10.BkNanowires; Semiconductor β-Ga; ₂; O; ₃; Microwave plasma

Rebuilding of metal components with laser cladding forming by Jianli Song; Qilin Deng; Changyuan Chen; Dejin Hu; Yongtang Li (pp. 7934-7940).

Laser cladding forming (LCF) is a novel powerful tool for the repairing of metal components. Rebuilding of V-grooves on medium carbon steel substrates has been carried out with laser cladding forming technique using stainless steel powder as the cladding material. Microstructure of the deposited layers has been characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDAX), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Mechanical properties of the rebuilt V-groove samples have been evaluated by tensile and impacting tests and microhardness measurement. Experimental results show that good fusion bonding between the rebuilt layers and the substrate has been formed, and the microstructure of the cladding layers is mainly composed of fine, dense and defect-free epitaxial columnar dendrites. Due to the effect of grain size refinement, the tensile strength, impacting toughness, elongation and microhardness of the rebuilt samples have been greatly enhanced compared to those of the substrate. Microhardness is also very uniform throughout the rebuilt regions. With the growth of the deposited layers, the microhardness increases gradually. The good ductility of the deposited regions is verified by the SEM fracture analysis.

Keywords: Laser cladding forming (LCF); Rebuilding; V-groove; Stainless steel powder

Pressure induced anisotropy of electrical conductivity in polycrystalline molybdenum disulfide by V. Sánchez; E. Benavente; V. Lavayen; C. O’Dwyer; C.M. Sotomayor Torres; G. González; M.A. Santa Ana (pp. 7941-7947).

Anisotropic specimens of MoS₂ are obtained by pressing the microcrystalline powder into special die. This inelastic compression results in a rearrangement of the disulfide micro platelets observed by atomic force microscopy and reflected in the macroscopic anisotropy in electrical conductivity in these samples. The conductivity measured parallel and perpendicular to the direction of applied pressure exhibits an anisotropy factor of∼10 at 1 GPa. This behaviour of the conductivity as a function of applied pressure is explained as the result of the simultaneous influence of a rearrangement of the micro platelets in the solid and the change of the inter-grain distances.

Keywords: PACS; 61.66.; −; f; 68.35.; −; p; 68.37.; −; d; 72.80.; −; r; 73.25.+iAnisotropy; Conductivity; Molybdenum; Surface pressure

The application of Raman and anti-stokes Raman spectroscopy for in situ monitoring of structural changes in laser irradiated titanium dioxide materials by Stephanie J. Rigby; Ala H.R. Al-Obaidi; Soo-Keun Lee; Daniel McStay; Peter K.J. Robertson (pp. 7948-7952).

The use of Raman and anti-stokes Raman spectroscopy to investigate the effect of exposure to high power laser radiation on the crystalline phases of TiO₂ has been investigated. Measurement of the changes, over several time integrals, in the Raman and anti-stokes Raman of TiO₂ spectra with exposure to laser radiation is reported. Raman and anti-stokes Raman provide detail on both the structure and the kinetic process of changes in crystalline phases in the titania material. The effect of laser exposure resulted in the generation of increasing amounts of the rutile crystalline phase from the anatase crystalline phase during exposure. The Raman spectra displayed bands at 144cm⁻¹ (A1g), 197cm⁻¹ (Eg), 398cm⁻¹ (B1g), 515cm⁻¹ (A1g), and 640cm⁻¹ (Eg) assigned to anatase which were replaced by bands at 143cm⁻¹ (B1g), 235cm⁻¹ (2 phonon process), 448cm⁻¹ (Eg) and 612cm⁻¹ (A1g) which were assigned to rutile. This indicated that laser irradiation of TiO₂ changes the crystalline phase from anatase to rutile. Raman and anti-stokes Raman are highly sensitive to the crystalline forms of TiO₂ and allow characterisation of the effect of laser irradiation upon TiO₂. This technique would also be applicable as an in situ method for monitoring changes during the laser irradiation process.

Keywords: TiO; ₂; Photocatalyst; Raman spectroscopy; Laser irradiation

p-Type conduction in phosphorus-doped ZnO thin films by MOCVD and thermal activation of the dopant by Yan Miao; Zhizhen Ye; Weizhong Xu; Fugang Chen; Xincui Zhou; Binghui Zhao; Liping Zhu; Jianguo Lu (pp. 7953-7956).

Phosphorus-doped p-type ZnO thin films have been realized by metalorganic chemical vapor deposition (MOCVD). The conduction type of ZnO films is greatly dependent on the growth temperature. ZnO films have the lowest resistivity of 11.3Ωcm and the highest hole concentration of 8.84×10¹⁸cm⁻³ at 420°C. When the growth temperature is higher than 440°C, p-type ZnO films cannot be achieved. All the films exhibited p-type conduction after annealing, and the electrical properties were improved comparing with the as-grown samples. Secondary ion mass spectroscopy (SIMS) test proved that phosphorus (P) has been incorporated into ZnO.

Keywords: PACS; 61.72.V; 72.80.E; 73.61.G; 78.66.Hp-Type conduction; Doping; Metalorganic chemical vapor deposition; Zinc compounds; Semiconducting II–VI materials

The surface chemistry resulting from low-pressure plasma treatment of polystyrene: The effect of residual vessel bound oxygen by Marshal Dhayal; Morgan R. Alexander; James W. Bradley (pp. 7957-7963).

The surface chemistry of plasma treated polystyrene samples has been studied in a specially designed low-pressure argon discharge system incorporating in situ XPS analysis. By using an electrostatic grid biasing technique, the plasma source can also be used in a mode preventing ion interactions with the sample.The system, which utilizes a vacuum transfer chamber between plasma and XPS analysis has allowed us to differentiate between the level of oxygen incorporated at the polystyrene surface from residual gas during treatment and that from the exposure of the treated sample to the laboratory atmosphere. Using typical base pressures of about 5×10⁻³Pa (4×10⁻⁵Torr) the XPS results show that significant oxygen surface incorporation resulted from oxygen containing species in the plasma itself (i.e. water vapour with 2×10⁻³Pa partial pressure). The surface concentration of O was measured at 7.6at.%. Subsequent atmospheric exposure of the treated samples resulted in only a small increase (of 0.6at.%) in oxygen incorporation in the form of acid anhydride functionalities.XPS measurements of PS samples exposed to plasmas with no ion-surface component (i.e. exposure from VUV, UV and excited neutral species only) showed no appreciable change in oxygen incorporation compared to those with low-energy ion bombardment from the plasma (<20eV). Given the energetics of the remaining bombarding species, it indicates that VUV radiation may be chiefly responsible for the production of free radical sites in this discharge regime.

Keywords: PACS; 52.50Dg; 79.60Fr; 52.77 BnPlasma; Low-pressure; Polymer; Surface treatment; Modification; XPS; Base-pressure; Residual water; Vacuum

Platinum particles dispersed poly(diphenylamine) modified electrode for methanol oxidation by P. Santhosh; A. Gopalan; T. Vasudevan; Kwang-Pill Lee (pp. 7964-7969).

A modified potentiostatic method, termed the ‘pulse pontentiostatic method’ (PPSM) was used to get nano fibrillar poly(diphenylamine) (PDPA) film on Indium tin oxide (ITO) coated glass electrode and also for making modified electrode with platinum particles dispersed in PDPA. Platinum clusters were electrodispersed under constant potential on PDPA films to obtain catalytic electrodes for methanol oxidation. Energy dispersive analysis of X-rays (EDAX) results showed that the Pt microparticles are deposited into PDPA film. Scanning electron micrograph, SEM images show that the deposition results spherical catalytic particles. X-ray photoelectron spectroscopy (XPS) results inform that the net electronic charge on carbon atom and also the imine/amine ratio was not affected by Pt loadings. The modification of electrode surface by nano fibular PDPA improves the electrocatalytic activity for methanol oxidation.

Keywords: Polydiphenylamine; Platinum; Modified electrode; Morphology; Methanol oxidation

A study of the optical properties of titanium oxide films prepared by dc reactive magnetron sputtering by Li-Jian Meng; V. Teixeira; H.N. Cui; Frank Placido; Z. Xu; M.P. dos Santos (pp. 7970-7974).

TiO₂ thin films were deposited on the glass substrates by dc reactive magnetron sputtering technique at different sputtering pressures (2×10⁻³ to 2×10⁻²mbar). The films prepared at low pressures have an anatase phase, and the films prepared at high pressures have an amorphous phase. The optical properties were studied by measuring the transmittance and the ellipsometric spectra. The optical constants of the films in the visible range were obtained by fitting the transmittance combined with the ellipsometry measurements using the classical model with one oscillator. The refractive index of the films decreases from 2.5 until 2.1 as the sputtering pressure increases from 2×10⁻³ to 2×10⁻²mbar. The films prepared at the pressure higher than 6×10⁻³mbar show a volume inhomogeneity. This volume inhomogeneity has been calculated by fitting the transmittance and the ellipsometric spectra. The volume inhomogeneity of the film prepared at the highest sputtering pressure is about 10%. Although the films prepared at high pressures show a large volume inhomogeneity, they have low extinction coefficients. It is suggested that the anatase phase results in more light scattering than amorphous phase does, and then a high extinction coefficient.

Keywords: Titanium oxide; Thin films; Ellipsometry; Optical properties; Sputtering

Atomic force microscopy study of thermal stability of silver selenide thin films grown on silicon by Bhaskar Chandra Mohanty; B.S. Murty; V. Vijayan; S. Kasiviswanathan (pp. 7975-7982).

Silver selenide thin films were grown on silicon substrates by the solid-state reaction of sequentially deposited Se and Ag films of suitable thickness. Transmission electron microscopy and particle-induced X-ray emission studies of the as-deposited films showed the formation of single phase polycrystalline silver selenide from the reaction of Ag and Se films. Atomic force microscopy images of the as-deposited and films annealed at different temperatures in argon showed the film morphology to evolve into an agglomerated state with annealing temperature. The results indicate that when annealed above 473K, silver selenide films on silicon become unstable and agglomerate through holes generated at grain boundaries.

Keywords: PACS; 68.55.−a; 68.37.Lp; 68.37.Ps; 68.35.DvAg; ₂; Se; AFM; Agglomeration

Optical band gap of zinc nitride films prepared on quartz substrates from a zinc nitride target by reactive rf magnetron sputtering by Fujian Zong; Honglei Ma; Wei Du; Jin Ma; Xijian Zhang; Hongdi Xiao; Feng Ji; Chengshan Xue (pp. 7983-7986).

Polycrystalline zinc nitride films have been synthesized onto quartz substrates from the zinc nitride target and the nitrogen working gas by reactive rf magnetron sputtering at room temperature. X-ray diffraction study indicates that polycrystalline zinc nitride films are of cubic structure with the lattice constant a=0.979(1)nm and have preferred orientations with (321) and (442). Its absorption coefficients as well as the film thickness are calculated from the transmission spectra, which are measured with a double beam spectrophotometer. The optical band gap has been determined from the photon energy dependence of absorption coefficient, an indirect transition optical band gap of 2.12(3)eV has been obtained.

Keywords: PACS; 78.20.-e; 78.40.-q; 61.10.Nz; 71.35.Cc; 81.15.CdOptical band gap; Zinc nitride films; Zinc nitride target; Reactive rf magnetron sputtering; Absorption coefficient

Effect of PVA functionalization on hydrophilicity of Y-junction single wall carbon nanotubes by Harindra Vedala; Jun Huang; Xiang Yang Zhou; Gene Kim; Somenath Roy; Won Bong Choi (pp. 7987-7992).

Hydrophilic surface of carbon nanotubes (CNTs) are of great interest for various applications including chemical and biological sensing. Surface functionalization of single wall carbon nanotubes (SWNTs) mats with a biocompatible polymer polyvinyl alcohol (PVA) was studied. PVA modification induced a drastic change in water wettability of the SWNT surface transforming it from hydrophobic to highly hydrophilic. These PVA modified SWNTs mats have also demonstrated increasing impedance variation in relative humidity compared to the pristine nanotubes. An appreciable change in conductivity of Y-junction SWNT mats as a function of relative humidity indicates its potential application as humidity sensor. This higher sensitivity for humidity variation shown in Y-junction SWNT mats could be attributed to the greater portion of semiconducting nanotubes in these mats revealed by Raman analysis. A possible conductance changing mechanism of surface modified SWNTs mats is discussed.

Keywords: Carbon nanotubes; Y-junction; Surface modification; PVA; Humidity sensor

Structural and optical properties of amorphous hydrogenated silicon carbonitride films produced by PECVD by E. Vassallo; A. Cremona; F. Ghezzi; F. Dellera; L. Laguardia; G. Ambrosone; U. Coscia (pp. 7993-8000).

Amorphous hydrogenated silicon carbonitride thin films (a-Si:C:N:H), deposited by plasma enhanced chemical vapour deposition (PECVD) using hexamethyldisilazane (HMDSN) as monomer and Ar as feed gas, have been investigated for their structural and optical properties as a function of the deposition RF plasma power, in the range of 100–300W. The films have been analysed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV–vis–NIR spectrophotometry and atomic force microscopy (AFM). From the analysis of the FT-IR spectra it results that the films become more amorphous and inorganic as RF plasma power increases. The incorporation of oxygen in the deposited layers, mainly due to the atmospheric attack, has been evaluated by XPS and FT-IR spectroscopy. Reflectance/transmittance spectra, acquired in the range of 200–2500nm, allow to descrive the film absorption edge for interband transitions. A relationship between the optical energy band gap, deduced from the absorption coefficient curve, and the deposition RF plasma power has been investigated. The reduction of the optical energy gap from 3.85 to 3.69eV and the broadening of the optical absorption tail with RF plasma power increasing from 100 to 300W are ascribed to the growth of structural disorder, while the increase of the refractive index, evaluated at 630nm, is attributed to a slight densification of the film. The AFM analysis confirms the amorphous character of the films and shows how the deposited layers become rougher when RF plasma power increases. The wettability of the film has been studied and related to the chemical composition and to the morphology of the deposited layers.

Keywords: a-Si:C:N:H films; PECVD; HMDSN; Chemical composition; Optical properties; Morphology

Study of the structure and electrical properties of the copper nitride thin films deposited by pulsed laser deposition by C. Gallardo-Vega; W. de la Cruz (pp. 8001-8004).

Copper nitride thin films were prepared on glass and silicon substrates by ablating a copper target at different pressure of nitrogen. The films were characterized in situ by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and ex situ by X-ray diffraction (XRD). The nitrogen content in the samples, x=[N]/[Cu], changed between 0 and 0.33 for a corresponding variation in nitrogen pressure of 9×10⁻² to 1.3×10⁻¹Torr. Using this methodology, it is possible to achieve sub-, over- and stoichiometric films by controlling the nitrogen pressure. The XPS results show that is possible to obtain copper nitride with x=0.33 (Cu₃N) and x=0.25 (Cu₄N) when the nitrogen pressure is 1.3×10⁻¹ and 5×10⁻²Torr, respectively. The lattice constants obtained from XRD results for copper nitride with x=0.25 is of 3.850Å and with x=0.33 have values between 3.810 and 3.830Å. The electrical properties of the films were studied as a function of the lattice constant. These results show that the electrical resistivity increases when the lattice parameter is decreasing. The electrical resistivity of copper nitride with x=0.25 was smaller than samples with x=0.33.

Keywords: Copper nitride; Thin films; Characterization methods; Pulsed laser deposition

Nanoindentation on carbon thin films obtained from a C₆₀ ion beam by A.G. Dall’Asén; M. Verdier; H. Huck; E.B. Halac; M. Reinoso (pp. 8005-8009).

Raman spectra, atomic force microscope (AFM) images, hardness ( H) and Young's modulus ( E) measurements were carried out in order to characterize carbon thin films obtained from a C₆₀ ion beam on silicon substrates at different deposition energies (from 100 up to 500eV). The mechanical properties were studied via the nanoindentation technique. It has been observed by Raman spectroscopy and AFM that the microstructure presents significant changes for films deposited at energies close to 300eV. However, these remarkable changes have not been noticeable on the mechanical properties: apparently H and E increase with higher deposition energy up to ∼11 and ∼116GPa, respectively. These values are underestimated if the influence of the film roughness is not taken into account.

Keywords: PACS; 68.37.Ps; 68.55.Jk; 68.60.Bs; 78.30.Na; 81.05.Tp; 81.15.JjC; ₆₀; fullerene; Ion beam deposition; Thin films; Nanoindentation; Raman spectroscopy; AFM

Dry etching of MgCaO gate dielectric and passivation layers on GaN by M. Hlad; L. Voss; B.P. Gila; C.R. Abernathy; S.J. Pearton; F. Ren (pp. 8010-8014).

MgCaO films grown by rf plasma-assisted molecular beam epitaxy and capped with Sc₂O₃ are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs), respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively coupled plasmas of CH₄/H₂/Ar produced etch rates only in the range 20–70Å/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates (∼100Å/min) were obtained with Cl₂/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH₄/H₂/Ar plasma chemistry produced a selectivity of around 2 for etching the MgCaO with respect to GaN.

Keywords: GaN; Dielectrics; Dry etching

Energy level alignment between C₆₀ and Al using ultraviolet photoelectron spectroscopy by J.H. Seo; S.J. Kang; C.Y. Kim; S.W. Cho; K.-H. Yoo; C.N. Whang (pp. 8015-8017).

The energy level alignment between C₆₀ and Al has been investigated by using ultraviolet photoelectron spectroscopy. To obtain the interfacial electronic structure between C₆₀ and Al, C₆₀ was deposited on a clean Al substrate in a stepwise manner. The valence-band spectra were measured immediately after each step of C₆₀ deposition without breaking the vacuum. The measured onset of the highest occupied molecular orbital energy level was located at 1.59eV from the Fermi level of Al. The vacuum level was shifted 0.68eV toward lower binding energy with additional C₆₀ layers. The observed vacuum level shift means that the interface dipole exists at the interface between C₆₀ and Al. The barrier height of electron injection from Al to C₆₀ is 0.11eV, which is smaller value than that of hole injection.

Keywords: PACS; 72.80.Le; 73.20.−r; 73.20.At; 85.30.TvC; ₆₀; Al; Ultraviolet photoelectron spectroscopy; Electronic structure

Study of asymmetric charge writing on Pb(Zr,Ti)O₃ thin films by Kelvin probe force microscopy by Jian Shen; Huizhong Zeng; Zhihong Wang; Shengbo Lu; Huidong Huang; Jingsong Liu (pp. 8018-8021).

Polycrystalline Pb(Zr_0.55Ti_0.45)O₃ thin film was deposited on Pt/Ti/SiO₂/Si(1 0 0) by radio-frequency-magnetron sputtering method, and the writing of charge bits on the surface of PZT thin film was studied by Kelvin probe force microscopy. It is found that the surface potential of the negative charge bits are higher than those of the corresponding positive ones. When ferroelectric polarization switching occurs, the potential difference becomes even more remarkable. A qualitative model was proposed to explain the origin of the asymmetric charge writing. It is demonstrated that the internal field in the interface layer, which is near the ferroelectric/electrode interface in ferroelectric film, is likely to be the cause for the occurrence of this phenomenon.

Keywords: PACS; 73; 77; 77.80.FmKelvin probe force microscopy; Asymmetric charge writing; PZT thin film; Internal field

Structural investigation of thin tetracene films on flexible substrate by synchrotron X-ray diffraction by S. Milita; C. Santato; F. Cicoira (pp. 8022-8027).

Structural properties of tetracene thin films grown by vacuum sublimation on a flexible Mylar^© substrate have been investigated by means of synchrotron X-ray diffraction. The films are polycrystalline and are made up of crystalline domains oriented with the (00 l) planes almost parallel to the substrate and completely misoriented around the surface normal. Two crystallographic phases (α and β thin film phases) have been identified. They differ for the d h k_l interplanar spacing, both larger than that of the bulk. As a comparison, results from tetracene films grown on SiO₂ have been reported to investigate the different charge transport properties of films grown on Mylar and on SiO₂ substrates.

Keywords: Tetracene; Thin films; Synchrotron X-ray diffraction; Flexible substrate

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Applied Surface Science (v.252, #22)