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Applied Surface Science (v.253, #18)

The structure and tribological behaviors of CrN and Cr–Ti–N coatings by G.A. Zhang; P.X. Yan; P. Wang; Y.M. Chen; J.Y. Zhang (pp. 7353-7359).

The Cr–Ti–N coatings with different composition were deposited in a medium frequency magnetron sputtering system on Si (111) substrates. The structures, surface morphology and wear properties were measured. The binary CrN coatings, formed a single-phase fcc structure with nearly random (111), (200) and (220) orientation, while for the Ti was introduced, coatings show a preferred orientation of (200). Cr–Ti–N coating shows a much smoother surface than CrN coating. Cr–Ti–N coating with 31.75% Ti content shows the best wear behavior. The excellent tribological properties of this composition coating are corresponding to the solid solution nitride structures.

Keywords: Magnetron sputtering; Cr–Ti–N coatings; Structure; Tribological properties

Fabrication of waveguides in Yb:YCOB crystal by MeV oxygen ion implantation by Yang Jiao; Feng Chen; Xue-Lin Wang; Ke-Ming Wang; Lei Wang; Liang-Ling Wang; Huai-Jin Zhang; Qing-Ming Lu; Hong-Ji Ma; Rui Nie (pp. 7360-7364).

Oxygen ions with energies of 6.0 or 3.0MeV were implanted into y-cut Yb:YCOB crystals at fluences ranging from 5.0×10¹³ to 2.0×10¹⁵ions/cm² at room temperature, forming optical planar waveguide structures. Dark-mode line spectroscopy was applied at two wavelengths, 633 and 1539nm, in various excitation configurations, showing strong enhancement of one of the indices ( n_x) in the implanted near surface. The n_x refractive index profile is reconstructed by a reflectivity calculation method and compared to the ion energy losses profiles deduced from SRIM-code simulation. Moreover, the near-field patterns were imaged by an end-fire coupling arrangement.

Keywords: PACS; 61.72.Ww; 42.65.WiIon implantation; Optical waveguide; Yb:YCOB crystal

Preparation of well-aligned carbon nanotubes by pyrolysis of phenolic resin in anodic alumina pores by Ke-Zhi Li; Jian Wei; He-Jun Li; Yu-Lei Zhang; Chuang Wang; Dang-She Hou (pp. 7365-7368).

Well-aligned carbon nanotubes (CNTs) of high quality were synthesized by pyrolysis of phenolic resin at 800°C in anodic alumina oxide (AAO) pores under argon protection. The innocuous source materials and safe operational conditions permit this method to synthesize well-aligned CNTs in large-scale and low cost. The formation mechanism of the synthesized CNTs is also proposed in this work by a series of visual sketches and is proved with obvious evidence. Firstly, phenolic resin nanotubes form in the template pores through the evaporation of solvent. Heat treatment then transfers these tubes into CNTs.

Keywords: Carbon nanotubes; Resins; Pyrolysis; Electron microscopy

Dependence of critical pitting temperature on the concentration of sulphate ion in chloride-containing solutions by Bo Deng; Yiming Jiang; Jiaxing Liao; Yunwei Hao; Cheng Zhong; Jin Li (pp. 7369-7375).

Effects of varying concentration of sulphate (SO₄²⁻) ion on the pitting behavior of 316SS have been investigated using potentiostatic critical pitting temperature (CPT) measurements, potentiostatic current transient technique and scanning electron microscopy in NaCl solution containing 0.5% Cl⁻ ions. The results demonstrated that when the concentration of SO₄²⁻ ion is less than 0.42%, the CPT is surprisingly lower than that without SO₄²⁻ ion, showing an accelerating effect of the SO₄²⁻ ion on pit initiation, which is different from the traditional concept. As the concentration of SO₄²⁻ ion increases beyond 0.42%, the CPT is higher than that without SO₄²⁻ ion, displaying an inhibiting effect of the SO₄²⁻ ion on pit initiation. Based on the above results, a qualitative model is proposed to explain the inhibiting and accelerating effect of SO₄²⁻ ion on the pit initiation using the mechanism of ions-competitive adsorption between SO₄²⁻ and Cl⁻ ions. The electric charges calculated in the process of pitting corrosion indicated that the pit morphology and its dimension are dependent on the content of SO₄²⁻ ion in chloride-containing solutions. The higher the concentration of SO₄²⁻ ion, the larger the dimension of the pit, reflecting an accelerating effect on pit growth.

Keywords: PACS; 47.55.drStainless steel; Critical pitting temperature (CPT); Sulphate and chloride

Modification of the electronic properties of the TiO₂ (110) surface upon deposition of the ultrathin conjugated organic layers by A.S. Komolov; P.J. Møller; J. Mortensen; S.A. Komolov; E.F. Lazneva (pp. 7376-7380).

A few nm thick 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) and Cu-phthalocyanine (CuPc) overlayers were thermally deposited in situ in UHV onto TiO₂ (110) surface. Atomic composition of the surfaces under study was monitored using Auger electron spectroscopy (AES). The formation of the interfacial potential barrier and the structure of the unoccupied electronic states located 5–25eV above the Fermi level ( E_F) was monitored using a probing beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. The work function values upon the overlayer deposition changed from 4.6 to 4.9eV at the PTCDA/TiO₂ (110) interface and from 4.6 to 4.3eV at the CuPc/TiO₂ (110) interface. Band bending in the TiO₂ substrate, molecular polarization in the organic film and changes in the work function due to the change in the surface composition were found to contribute to the formation of the interfacial potential barriers. Oxygen admixture related peaks were observed in the AES and in the TCS spectra of the CuPc overlayers. A mechanism of the transformations in the PTCDA and CuPc overlayers on the TiO₂ (110) upon elevating temperature from 25 to 400°C was suggested.

Keywords: PACS; Condensed matter; Electronic propertiesSurface electronic phenomena; Metal oxide surfaces; Conjugated organic molecules; Titanium dioxide

Electron field emission from boron doped microcrystalline diamond by M. Roos; V. Baranauskas; M. Fontana; H.J. Ceragioli; A.C. Peterlevitz; K. Mallik; F.T. Degasperi (pp. 7381-7386).

Field emission properties of hot filament chemical vapor deposited boron doped polycrystalline diamond have been studied. Doping level ( N_B) of different samples has been varied by the B/C concentration in the gas feed during the growth process and doping saturation has been observed for high B/C ratios. Threshold field ( E_th) for electron emission as function of B/C concentration has been measured, and the influences of grain boundaries, doping level and surface morphology on field emission properties have been investigated. Carrier transport through conductive grains and local emission properties of surface sites have been figured out to be two independent limiting effects in respect of field emission. Emitter current densities of 500nAcm⁻² were obtained using electric fields less than 8V/μm.

Keywords: Boron doped diamond surface; Electron field emission; Chemical vapor deposited diamond; Threshold field for electron emission; Emission properties of surface sites

The changes in morphology of Si(100) surface upon dipping in ultrapure water by Yuichi Sano; W.B. Ying; Kazuhisa Nakatsuka; Yuki Morikage; Yoshitomo Kamiura; Yusuke Mizokawa (pp. 7387-7392).

The changes in morphology and chemical states of Si(100) surface upon dipping in ultrapure water were investigated by using atomic force microscope and X-ray photoelectron spectroscopy. The oxidation and the etching competitively progressed at the HF-treated Si(100) surface in ultrapure water, which made the smooth surface rough. However, the surface covered with a thick native oxide film was not etched at all. During the repetition of the oxidation and the etching, the SiO₂-nuclei was, by chance, able to grow up to some size of islands and worked as the protective barrier against the water etching. Thus, the SiO₂-islands would remain without being etched off, whereas rest parts of the surface could be etched off. This selective etching leads the surface morphology to become rough. Both the oxidation and the etching progressed violently as the water temperature and the dipping time increased.

Keywords: XPS; AFM; Roughness; Ultrapure water treatment; Etching; Oxidation

Surface treatment of magnesium hydroxide to improve its dispersion in organic phase by the ultrasonic technique by Fangzhi Zhang; Hong Zhang; Zhixing Su (pp. 7393-7397).

Micron magnesium hydroxide [Mg(OH)₂] was modified by means of ultrasonic method with stearic acid (SA) as modifier in water. The Fourier transform infrared spectroscopy (FT-IR) and element analysis showed all SA was bonded upon the surface of the Mg(OH)₂ forming a coating layer and no free SA was detected after the modifying process. The thickness of coating SA on the Mg(OH)₂ was determined by X-ray photoelectron spectroscopy (XPS). Compared with the unmodified Mg(OH)₂, the modified Mg(OH)₂ had better dispersion property in xylene, slower sedimentation velocity of dilute suspension in xylene and lower viscosity of suspension in paraffin liquid. The results showed that the modified Mg(OH)₂ could be dispersed much better than the unmodified Mg(OH)₂ in organic phase.

Keywords: Magnesium hydroxide; Stearic acid; Surface treatment

Transparent and conducting Zn-Sn-O thin films prepared by combinatorial approach by J.H. Ko; I.H. Kim; D. Kim; K.S. Lee; T.S. Lee; B. Cheong; W.M. Kim (pp. 7398-7403).

Zn-Sn-O (ZTO) films with continuous compositional gradient of Sn 16–89at.% were prepared by co-sputtering of two targets of ZnO and SnO₂ in a combinatorial method. The resistivities of the ZTO films were severely dependent on oxygen content in sputtering gas and Zn/Sn ratio. Except for the films with Sn 16at.%, all the as-prepared films were amorphous and maintaining the stable amorphous states up to the annealing temperature of 450°C. Annealing at 650°C resulted in crystallization for all the composition, in which ZnO, Zn₂SnO₄, ZnSnO₃, and SnO₂ peaks were appeared successively with increasing Sn content. Above Sn 54at.%, the ZTO films were deduced to have a local structure mixed with ZnSnO₃ and SnO₂ phases which were more conductive and stable in thermal oxidation than ZnO and Zn₂SnO₄ phases. The lowest resistivity of 1.9×10⁻³Ωcm was obtained for the films with Sn 89at.% when annealed at 450°C in a vacuum. The carrier concentrations of the amorphous ZTO films that contained Sn contents higher than 36at.% and annealed at 450°C in a vacuum were proportional to the Sn contents, while the Hall mobilities were insensitive to Sn contents and leveling in the range of 23–26cm²/Vs.

Keywords: PACS; 73.61.−r: 78.20−eZinc tin oxide; Amorphous; Transparent conducting oxide; Thin film

Silicon carbonitride by remote microwave plasma CVD from organosilicon precursor: Physical and mechanical properties of deposited Si:C:N films by I. Blaszczyk-Lezak; A.M. Wrobel (pp. 7404-7411).

Silicon carbonitride (Si:C:N) films produced by the remote microwave hydrogen plasma chemical vapor deposition (RP-CVD) using bis(dimethylamino)methylsilane as single-source precursor and hydrogen as an upstream gas for plasma generation, were examined in terms of their physical (density) and mechanical (hardness, elastic modulus, friction coefficient, and “plasticity index”) properties. The effect of substrate temperature (varied in the range of 30–400°C) on the properties of Si:C:N films is presented. A reasonable compositional and structural dependencies of film properties were determined using, respectively, the XPS atomic concentration ratios N/Si and C/Si, as well as the relative integrated intensities of the IR absorption bands from the SiN and SiC bonds (controlled by deposition temperature), evaluated in the first part of this work. In view of their good mechanical properties, Si:C:N films seem to be useful coatings for improving surface mechanics of engineering materials.

Keywords: Slicon carbonitride film; Density; Hardness; Elastic modulus; Friction coefficient; Plasticity index

The influence of exciton behavior on luminescent characteristics of organic light-emitting diodes by D.W. Zhao; F.J. Zhang; S.F. Song; C. Xu; Z. Xu (pp. 7412-7415).

We used N, N′-bis-(1-naphthyl)- N, N′-1-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), 4,4′- N, N′-dicarbazole-biphenyl (CBP) and tris(8-hydroxyquinoline) aluminum (Alq₃) to fabricate tri-layer electroluminescent (EL) device (device structure: ITO/NPB/CBP/Alq₃/Al). In photoluminescence (PL) spectra of this device, the emission from NPB shifted to shorter wavelength accompanying with the decrease of its emission intensity and moreover the emission intensity of Alq₃ increased relatively with the increase of reverse bias voltage. The blue-shifted emission and the decrease in emission intensity of NPB were attributed to the polarization and dissociation of NPB excitons under reverse bias voltage. The increase of emission intensity of Alq₃ benefited from the recombination of electrons (produced by the dissociation of NPB exciton) and holes (injected from the Al cathode).

Keywords: Photoluminescence (PL); Electroluminescence (EL); Polarization; Dissociation; Exciton

Inhibition performance of 2-mercaptobenzothiazole derivatives in CO₂ saturated solution and its adsorption behavior at Fe surface by Junping Zhang; Qiuyu Zhang; Hua Ren; Wen Zhao; Hepeng Zhang (pp. 7416-7422).

Two 2-mercaptobenzothiazole derivatives, N, N′-bis-(2-thionobenzothiazolin-3-yl-methyl)- n-dodecylamine (BTBMDA) and N, N′-bis-(2-thionobenzothiazolin-3-yl-methyl)- n-octadecylamine (BTBMOA), were synthesized under microwave irradiation. Their inhibition performance for N80 steel in CO₂ saturated solution at 90°C were tested by weight loss method and the surface analysis was performed by SEM. The adsorption behavior of two inhibitors at the Fe surface was studied by the molecular dynamics simulation method and the quantum chemistry calculations. Results showed that the two inhibitors could inhibit the corrosion of N80 steel in simulated solution significantly. There were two types of end configurations for two inhibitors at the Fe surface in the molecular dynamics simulation, and the two inhibitors adsorbed at the surface mainly through one of the two types.

Keywords: 2-Mercaptobenzothiazole; Inhibitor; Molecular dynamics simulation; Quantum chemistry

Characterization of free-standing GaN substrate grown through hydride vapor phase epitaxy with a TiN interlayer by T.B. Wei; R.F. Duan; J.X. Wang; J.M. Li; Z.Q. Huo; P. Ma; Zh. Liu; Y.P. Zeng (pp. 7423-7428).

Large-scale GaN free-standing substrate was obtained by hydride vapor phase epitaxy directly on sapphire with porous network interlayer. The bottom surface N-face and top surface Ga-face showed great difference in anti-etching and optical properties. The variation of optical and structure characteristics were also microscopically identified using spatially resolved cathodoluminescence and micro-Raman spectroscopy in cross-section of the GaN substrate. Three different regions were separated according to luminescent intensity along the film growth orientation. Some tapered inversion domains with high free carrier concentration of 5×10¹⁹cm⁻³ protruded up to the surface forming the hexagonal pits. The dark region of upper layer showed good crystalline quality with narrow donor bound exciton peak and low free carrier concentration. Unlike the exponential dependence of the strain distribution, the free-standing GaN substrate revealed a gradual increase of the strain mainly within the near N-polar side region with a thickness of about 50μm, then almost kept constant to the top surface.

Keywords: PACS; 68.55.−a; 73.61.Ey; 81.15.Kk; 78.60.HkGaN; HVPE; Cathodoluminescence; Micro-Raman scattering

Investigation of structural and optical properties of nanoporous GaN film by F.K. Yam; Z. Hassan; L.S. Chuah; Y.P. Ali (pp. 7429-7434).

The structural and optical characteristics of porous GaN prepared by Pt-assisted electroless etching under different etching durations are reported. The porous GaN samples were investigated by scanning electron microscopy (SEM), high-resolution X-ray diffraction (HR-XRD), photoluminescence (PL) and Raman scattering. SEM images indicated that the density of the pores increased with the etching duration; however, the etching duration has no significant effect on the size and shape of the pores. XRD measurements showed that the (0002) diffraction plane peak width of porous samples was slightly broader than the as-grown sample, and it increased with the etching duration. PL measurements revealed that the near band edge peak of all the porous samples were red-shifted; however, the porosity-induced PL intensity enhancement was only observed in the porous samples; apart from that, two additional strain-induced structural defect-related PL peaks observed in as-grown sample were absent in porous samples. Raman spectra showed that the shift of E₂ (high) to lower frequency was only found in samples with high density of pores. On the contrary, the absence of two forbidden TO modes in the as-grown sample was observed in some of porous samples.

Keywords: PACS; 61.43.Gt; 73.61.Ey; 78.55Mb; 81.05.RMPorous GaN; Electroless etching; Characterizations

Radical functionalization of single-walled carbon nanotubes with azo(bisisobutyronitrile) by Xianbao Wang; Shaoqing Li; Yang Xu; Li Wan; Haijun You; Qin Li; Shimin Wang (pp. 7435-7437).

The isobutyronitryl groups from thermal decomposition of azobisisobutyronitrile in a 1,2-dichlorobenzene solution were successfully attached to the sidewalls of single-walled carbon nanotubes; thermogravimetic analysis shows a weight loss of 20% (compared to raw SWNTs), which was calculated to be ca. 1 isobutyronitryl group in 23 carbon atoms.

Keywords: Radical functionalization; Single-walled carbon nanotubes; Fourier transform infrared spectroscopy

rf reactive co-sputtered Au–Ag alloy nanoparticles in SiO₂ thin films by P. Sangpour; O. Akhavan; A.Z. Moshfegh (pp. 7438-7442).

We have studied formation of Au–Ag alloy nanoparticles in sputtered SiO₂ thin films. Silica thin films containing Au–Ag nanoparticles were deposited on quartz substrates using rf reactive magnetron co-sputtering technique. The films heat-treated in reducing Ar+H₂ atmosphere at different temperatures. They were analyzed by using UV–vis spectrophotometry, atomic force microscopy and X-ray photoelectron spectroscopy (XPS) methods for their optical, surface morphological as well as structural and chemical properties. The optical absorption of the Au–Ag alloy nanoparticles illustrated one plasmon resonance absorption peak located at 450nm between the absorption bands of pure Au and Ag nanoparticles at 400 and 520nm, respectively, for the thin films annealed at 800°C. XPS results showed that the alloys were in metallic state, and they had a greater tendency to lose electrons as compared to their corresponding monometallic state. Using lateral force microscopy analysis, we have found that the alloy particles were uniformly distributed on the surface with grain size of about 20nm.

Keywords: Au–Ag alloy nanoparticles; Reactive co-sputtering; Silica thin films; Optical property

A study of nano-sized surface coating on LiMn₂O₄ materials by Fei-Yi Hung; Truan-Sheng Lui; Hung-Chi Liao (pp. 7443-7448).

The present study used the Pechini process with a heat treatment to synthesize LiMn₂O₄ powder (LMO). After surface coating, a nano-sized oxidative film of Li–Ni–Mn formed on the surface of the LMO–Ni powders. The concentration of Mn³⁺ for the LMO–Ni powder was lower and the average electrovalence of Mn exceeded the theoretical value, resulting in the initial capacity of the LMO–Ni powder being lower than the LMO powder. However, the LMO–Ni powder with the Li/Ni film not only restrained Mn ions from dissolving into the electrolyte, but also improved the charge–discharge cycling capacity.

Keywords: LiMn; ₂; O; ₄; Charge–discharge capacity; Surface coating

The effects of powder properties on in-flight particle velocity and deposition process during low pressure cold spray process by Xian-Jin Ning; Jae-Hoon Jang; Hyung-Jun Kim (pp. 7449-7455).

In cold spray process, impacting velocity and critical velocity of particles dominate the deposition process and coating properties for given materials. The impacting velocity and critical velocity of particles depend on the powder properties and cold spray conditions. In the present study, the in-flight particle velocity of copper powder in low pressure cold spraying was measured using an imaging technique. The effects of particle size and particle morphology on in-flight particle velocity and deposition efficiency were investigated. The critical velocity of copper powder was estimated by combining the in-flight particle velocity and deposition efficiency. The effect of annealing of feedstock powder on deposition and critical velocity was also investigated. The results showed that the irregular shape particle presents higher in-flight velocity than the spherical shape particle under the same condition. For irregular shape particles, the in-flight velocity decreased from 390 to 282m/s as the particle size increases from 20 to 60μm. Critical velocities of about 425m/s and more than 550m/s were estimated for the feedstock copper powder with spherical and irregular shape morphology, respectively. For the irregular shape particles, the critical velocity decreased from more than 550 to 460m/s after preheating at 390°C for 1h. It was also found that the larger size powder presents a lower critical velocity in this study.

Keywords: Cold gas dynamic spray; In-flight particle velocity; Critical velocity; Powder property; Low pressure cold spray

Effects of substrate temperature and oxygen pressure on the magnetic properties and structures of CoFe₂O₄ thin films prepared by pulsed-laser deposition by Jian-ping Zhou; Hong-cai He; Ce-Wen Nan (pp. 7456-7460).

CoFe₂O₄ thin films were grown on silicon substrates by pulsed-laser deposition techniques at various temperatures from 350°C to 700°C and different pressures from 0.1Pa to 10Pa. The CoFe₂O₄ films with highly (111)-preferred orientation and smooth surfaces were obtained. The high coercivities of the films were attributed to the residual stress in the films, and the saturation magnetizations were mainly dependent on the oxygen pressure. Higher oxygen pressure could decrease the oxygen deficiencies in the films. Sufficient oxygen ions in the films enhanced the exchange interactions between the magnetic ions, as a result, increasing the saturation magnetization.

Keywords: Cobalt ferrite; Crystal structures; Magnetism; Pulsed-laser deposition

Effect of organic additives on characterization of electrodeposited Co-W thin films by Guoying Wei; Hongliang Ge; Xiao Zhu; Qiong Wu; Junying Yu; Baoyan Wang (pp. 7461-7466).

Co-W thin films were electrodeposited from aqueous bath with different organic additives. Electrochemical analysis showed that the transient state was limited and polarization behaviors were more evident during Co-W electrodeposition in the presence of organic additives. SEM measurement indicated that the surface morphology was affected by the nature of the organic additives to a large extent. Homogeneous Co-W thin films were obtained from the solutions containing ethyl methacrylate. Moreover, it was obvious that the presence of organic additives, in the electroplating bath, modified the structure and magnetic properties of the Co-W thin films according to the XRD and VSM measurements.

Keywords: PACS; 81.15. Pq; 82.45. Mp; 75.70Electrodeposition; Co-W thin films; Organic additives

Prediction of lateral barrier height in identically prepared Ni/ n-type GaAs Schottky barrier diodes by H. Doğan; H. Korkut; N. Yıldırım; A. Turut (pp. 7467-7470).

We have identically prepared Ni/ n-GaAs/In Schottky barrier diodes (SBDs) with doping density of 7.3×10¹⁵cm⁻³. The barrier height for the Ni/ n-GaAs/In SBDs from the current–voltage characteristics have varied from 0.835 to 0.856eV, and ideality factor n from 1.02 to 1.08. We have determined a lateral homogeneous barrier height value of 0.862eV for the Ni/ n-GaAs/In SBD from the experimental linear relationship between barrier heights and ideality factors.

Keywords: Schottky barrier diodes; Metal-semiconductor contacts; Barrier inhomogeneities; GaAs

Molecular dynamics simulation about porous thin-film growth in secondary deposition by Huawei Chen; A. Kiet Tieu; Qiang Liu; Ichiro Hagiwara; Cheng Lu (pp. 7471-7477).

The thin film growth has been confirmed to be assembled by an enormous number of clusters in experiments of CVD. Sequence of clusters’ depositions proceeds to form the thin film at short time as gas fluids through surface of substrate. In order to grow condensed thin film using series of cluster deposition, the effect of initial velocity, substrate temperature and density of clusters on property of deposited thin film, especially appearance of nanoscale pores inside thin film must be investigated. In this simulation, three different cluster sizes of 203, 653, 1563 atoms with different velocities (0, 10, 100, 1000 and 3000m/s) were deposited on a Cu(001) substrate whose temperatures were set between 300 and 1000K. Four clusters and one cluster were used in primary deposition and secondary deposition, respectively. We have clarified that adhesion between clusters and substrate is greatly influenced by initial velocity. As a result, the exfoliation pattern of deposited thin film is dependent on initial velocity and different between them. One borderline dividing whole region into porous region and nonporous region are obtained to show the effect of growth conditions on appearance of nanoscale pores inside thin film. Moreover, we have also shown that the likelihood of porous thin film is dependent on the point of impact of a cluster relative to previously deposited clusters.

Keywords: PACS; 61.46. +w; 82.20. WtComputer simulation; Chemical vapor deposition processes; Molecular dynamics; Growth models; Epitaxial growth; Thin film; Secondary deposition

Analysis of the Ge1−_xC_x films deposited by MFMST by C.Y. Zhan; L.W. Wang; N.K. Huang (pp. 7478-7482).

Ge1−_xC_x films deposited by using a medium frequency magnetron sputtering technique (MFMST) were analyzed with X-ray photoelectron and Raman spectroscopy. The deposited Ge1−_xC_x films consist of C, Ge, GeC and GeO_y. The GeC content in the Ge1−_xC_x films linearly decreases, and the C content linearly increases with increasing deposition temperature from 150 to 350°C. The GeC content decreases from 11.6% at a substrate bias of 250V to a lowest value of 9.6% at 350V, then increases again to 10.4% at 450V. While the C content increases from 49.0% at the bias of 250V to a largest value of 58.0% at 350V and then maintains this level at 450V. It is found that selecting a bias parameter seems more effective than deposition temperature if we want to obtain a higher content of GeC in the deposited films. In addition, a new method is presented in this paper to estimate the changes of GeC content in the Ge1−_xC_x films by observing the shifts of Ge–Ge LO phonon peak in Raman spectra for the Ge1−_xC_x films. The related mechanism is also discussed in this paper.

Keywords: PACS; 68.55.Nq; 61.43.DqGe; 1−; _x; C; _x; films; XPS; Raman spectra; m.f. Magnetron sputtering deposition

Electrostatic spray deposited zinc oxide films for gas sensor applications by Camelia Matei Ghimbeu; Joop Schoonman; Martine Lumbreras; Maryam Siadat (pp. 7483-7489).

In this work, thin films of zinc oxide (ZnO) for gas-sensor applications were deposited on platinum coated alumina substrate, using electrostatic spray deposition (ESD) technique. As precursor solution zinc acetate in ethanol was used. Scanning electron microscopy (SEM) evaluation showed a porous and homogeneous film morphology and the energy dispersive X-ray analysis (EDX) confirmed the composition of the films with no presence of other impurities. The microstructure studied with X-ray diffraction (XRD) and Raman spectroscopy indicated that the ZnO oxide films are crystallized in a hexagonal wurtzite phase. The films showed good sensitivity to 1ppm nitrogen dioxide (NO₂) at 300°C while a much lower sensitivity to 12ppm hydrogen sulphide (H₂S).

Keywords: PACS; 68.37.Yz; 68.47.Gh; 68.55.Jk; 78.30−jZinc oxide; Electrostatic spray deposition; Gas sensors; NO; ₂

Electrical behaviour of catalytic nanostructured CeO₂/CuO_x composites under air–methane gas impulses by Sébastien Saitzek; Sylvie Villain; Gilles Nolibé; Jean Raymond Gavarri (pp. 7490-7496).

Nanostructured composites based on copper oxide and cerium dioxide phases [CuO–CeO₂] were elaborated from sol–gel route, with weight fractions of CuO phase ranging between 0 and 0.4. They are interesting potential catalysts allowing conversion of CH₄ and CO into CO₂ and H₂O and might be used in miniaturized gas sensors. An electrical study of this nanostructured system was carried out to determine catalytic behaviours under air–methane impulses at 350°C. The electrical analysis was based on a specific homemade electronic device. Time dependent interactions between gas pulses and solid catalyst (CuO/CeO₂) were analyzed from a frequency modification of the electronic device. Kinetic parameters were determined from a model describing adsorption and desorption of gases adapted to short interaction time between gas and solid. These time dependent electrical behaviours were then correlated with infrared spectroscopy analyses allowing time dependent analysis of methane conversion into CO₂ gas, for long interaction time between gas and solid.

Keywords: PACS; 61.46.+w,72.80.Tm; 73.63.Bd; 82.65.+rNanocomposite; Ceria; Copper oxide; Electric measurements; Catalytic sensor

Raman study of phase transformation of TiO₂ rutile single crystal irradiated by infrared femtosecond laser by H.L. Ma; J.Y. Yang; Y. Dai; Y.B. Zhang; B. Lu; G.H. Ma (pp. 7497-7500).

Titanium dioxide (TiO₂) rutile single crystal was irradiated by infrared femtosecond (fs) laser pulses with repetition rate of 250kHz and phase transformation of rutile TiO₂ was observed. Micro-Raman spectra show that the intensity of E_g Raman vibrating mode of rutile phase increases and that of A_1g Raman vibrating mode decreases apparently within the ablation crater after fs laser irradiation. With increasing of irradiation time, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO₂ single crystal is partly transformed into anatase phase. The anatase phase content transformed from rutile phase increased to a constant with increasing of fs pulse laser irradiation time. The study indicates the more stable rutile phase is transformed into anatase phase by the high pressure produced by fs pulse laser irradiation.

Keywords: PACS; 79.20.Ds; 64.60.−iFemtosecond laser; Titanium dioxide crystal; Raman spectroscopy

A density functional theory study on the adsorption and dissociation of N₂O on Cu₂O(111) surface by Bao-Zhen Sun; Wen-Kai Chen; Xia Wang; Chun-Hai Lu (pp. 7501-7505).

Density functional theory has been employed to investigate the adsorption and the dissociation of an N₂O at different sites on perfect and defective Cu₂O(111) surfaces. The calculations are performed on periodic systems using slab model. The Lewis acid site, Cu_CUS, and Lewis base site, O_SUF are considered for adsorption. Adsorption energies and the energies of the dissociation reaction N₂O→N₂+O(s) at different sites are calculated. The calculations show that adsorption of N₂O is more favorable on Cu_CUS adsorption site energetically. Cu_CUS site exhibits a very high activity. The Cu_CUS–N₂O reaction is exothermic with a reaction energy of 77.45kJmol⁻¹ and an activation energy of 88.82kJmol⁻¹, whereas the O_SUF–N₂O reaction is endothermic with a reaction energy of 205.21kJmol⁻¹ and an activation energy of 256.19kJmol⁻¹. The calculations for defective surface indicate that O vacancy cannot obviously improve the catalytic activity of Cu₂O.

Keywords: Density functional theory; Adsorption; Dissociation; N; ₂; O; Cu; ₂; O(1; 1; 1)

Fabrication of ZnO and its enhancement of charge injection and transport in hybrid organic/inorganic light emitting devices by J.P. Liu; S.C. Qu; X.B. Zeng; Y. Xu; X.F. Gou; Z.J. Wang; H.Y. Zhou; Z.G. Wang (pp. 7506-7509).

ZnO nanocrystals were synthesized by hydrolysis in methanol. X-ray diffraction and photoluminescence spectra confirm that good crystallized ZnO nanoparticles were formed. Utilizing those ZnO nanoparticles and poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV), light emitting devices with indium tin oxide (ITO)/poly(3,4-oxyethyleneoxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS)/ZnO:MDMO-PPV/Al and ITO/PEDOT:PSS/MDMO-PPV/Al structures were fabricated. Electroluminescence (EL) spectra reveal that EL yield of hybrid MDMO-PPV and ZnO nanocrystals devices increased greatly as compared with pristine MDMO-PPV devices. The current–voltage characteristics indicate that addition of ZnO nanocrystals can facilitate electrical injection and charge transport. The decreased energy barrier to electron injection is responsible for the increased efficiency of electron injection.

Keywords: ZnO; Conjugated polymer; Electron injection; Bulk heterojunction; Light emitting devices

Electrochemical impedance spectroscopic analysis of activation of Al–Zn alloy sacrificial anode by RuO₂ catalytic coating by S.M.A. Shibli; Sony George (pp. 7510-7515).

The uniform surface activation characteristics of RuO₂-coated Al–Zn alloy sacrificial anodes were studied in the present work. Electrochemical impedance spectroscopic and SEM/EDAX analyses were carried out to evaluate the galvanic dissolution characteristics of the anodes. The conventional electrochemical methods were also followed. Persistence and retention of catalytic RuO₂ on the anode surface even after a large extent of galvanic dissolution of the anode surface was confirmed based on the EDAX spectroscopy. The anodes showed the same polarization performances even after the anodes were disintegrated to one-third of its original size, revealing the sustained catalytic activity of RuO₂.

Keywords: PACS; 82.45.BbCorrosion; Ruthenium oxide; Electrochemical impedance spectroscopy; Aluminium; Sacrificial anodes; Pitting

The study on magnetite particles coated with bilayer surfactants by Xuman Wang; Caining Zhang; Xiaoliang Wang; Hongchen Gu (pp. 7516-7521).

Magnetite particles were prepared by co-precipitation, then sodium oleic (SO) and sodium dodecyl benzene sulfonate (SDBS) were applied as inner and outer surfactants, respectively. IR and TG were used to study the surface adsorption of SO and SDBS on magnetite particles. The experimental results demonstrated that SO molecules were linked to the magnetite particles through chemical bond and SDBS coated on the surface of magnetite particles covered with SO by means of Van der Waals attraction. Furthermore, based on the adsorption isotherms of surfactants on the magnetite particles and the dependence of Zeta potential of particles on the surfactants concentrations, the adsorption mechanisms of these two surfactants on the magnetite particles were studied. The isotherm adsorption model for SO on magnetite particles showed excellent correlation to Langmuir type and the adsorption equation wasΓ=0.162c1+0.303c (25°C), while that for SDBS on magnetite particles coated with SO showed excellent consistence with Freundlich type and the adsorption equation was Γ=0.32 c^0.475 (25°C). In addition, the results demonstrated that both SO and SDBS formed monolayer adsorption on the surface of magnetite particles.

Keywords: PACS; 68.43.−hMagnetite; Surfactant; Adsorption; Nanoparticles

Influence of the current applied to the silver target on the structure and the properties of Ag–Cu–O films deposited by reactive cosputtering by J.F. Pierson; D. Horwat (pp. 7522-7526).

Ag–Cu–O films were deposited on glass substrates by reactive magnetron cosputtering of silver and copper targets. In this manuscript, the current applied to the copper target and the oxygen flow rate introduced into the deposition chamber were kept constant, whereas the current applied to the silver target ( I_Ag) was varied. Films deposited without silver crystallised into the paramelaconite structure (Cu₄O₃). At low silver target current, incorporation of Ag into Cu₄O₃-based did not modify the film structure. Silver atoms substituted some Cu(+I) atoms leading to the formula: Ag2−_xCu2+_xO₃. On the other hand, when I_Ag exceeded a critical value, X-ray diffraction analyses revealed a biphased structure: Ag2−_xCu2+_xO₃ and Ag. Contrary to the diffraction peak intensity of the Ag2−_xCu2+_xO₃ phase, that of silver was increased with I_Ag. For the highest value of I_Ag, no silver–copper oxide was detected and the mean crystal size of silver grains was close to 2nm. Due to the occurrence of the nanocrystallised silver phase, the film electrical resistivity strongly decreased. Optical reflectance measurements confirmed the structural changes versus the silver target current.

Keywords: Silver–copper oxides; Reactive sputtering; Nanocrystallised silver; Structure; Electrical and optical properties

Characteristics, apatite-forming ability and corrosion resistance of NiTi surface modified by AC anodization by M.H. Wong; F.T. Cheng; H.C. Man (pp. 7527-7534).

NiTi samples were anodized in the non-sparking regime using AC voltage in a solution containing calcium and phosphate ions (solution Ca-P). The as-anodized samples were subsequently treated hydrothermally in water (sample A-W-NiTi) or in solution Ca-P (sample A-CaP-NiTi). Thin-film X-ray diffractometry (TF-XRD) analysis confirmed the existence of anatase in the hydrothermally treated samples, but not in the as-anodized sample, while hydroxyapatite (HA) was detected only in sample A-CaP-NiTi. Cross-sectional micrograph by scanning-electron microscopy (SEM) revealed that the thickness of the modified surface layer formed on sample A-CaP-NiTi was ∼200nm. X-ray photoelectron spectroscopy (XPS) analysis showed that the Ni concentrations at the surface of sample A-W-NiTi and sample A-CaP-NiTi were in the order of 0.4 and 0.3at.%, respectively, which were about an order of magnitude lower than that for bare NiTi. Both Ca and P were present in the surface layer on as-anodized NiTi and sample A-CaP-NiTi, but negligible on sample A-W-NiTi, as determined from XPS composition depth profiling. Immersion tests in a conventional simulated body fluid (SBF) of the Kokubo type to study apatite-forming ability showed that growth of apatite was induced on A-W-NiTi and much more abundantly on A-CaP-NiTi, but not on bare NiTi and as-anodized NiTi, suggesting that the presence of anatase and HA is favorable for apatite growth. The apatite-forming ability of the samples in the present study may be ranked in ascending order as: bare NiTi

Keywords: NiTi; Apatite; Titanium oxide; Corrosion; Anodization; Hydrothermal treatment

Nanostructured TiN coating prepared by reactive plasma spraying in atmosphere by Lisong Xiao; Dianran Yan; Jining He; Lin Zhu; Yanchun Dong; Jianxin Zhang; Xiangzhi Li (pp. 7535-7539).

In the present study, the nanostructured TiN coatings are obtained by means of reactive plasma spraying in the air. The XRD analysis shows the coating was mainly composed of TiN (max. 86.3%) and a small quantity of Ti₃O. Their microstructures were observed by SEM and TEM. The TEM pictures show the TiN coatings were composed of the nanoscaled grains (range from 70 to 90nm), and the Scherrer equation analysis on the average grain size corresponded with that result. The effects on the average grain size also were studied by changing the spraying power and the spraying distance.

Keywords: TiN; Coating; Reactive plasma spraying; Nanostructure

Electronic and structural studies of immobilized thiol-derivatized cobalt porphyrins on gold surfaces by Simon Berner; Hans Lidbaum; Greger Ledung; John Åhlund; Katharina Nilson; Joachim Schiessling; Ulrik Gelius; Jan-E. Bäckvall; Carla Puglia; Sven Oscarsson (pp. 7540-7548).

The immobilisation of thiol-derivatized cobalt porphyrins on gold surfaces has been studied in detail by means of combined scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). S-thioacetyl has been used as a protective group for the thiol. Different routes for deprotection of the acetyl groups were performed in acidic and in basic conditions. The results show the formation of monolayer films for the different preparation schemes. The immobilisation of the molecules on the gold surface takes place through the thiol-linkers by the formation of multiple thiolate bonds. In the case of layers formed with protected porphyrins approximately 60% of the linkers are bonded to the gold surface whereas for deprotected layers the amount of bonded linkers is increased up to about 80%. STM measurements revealed that the molecules arrange in a disordered overlayer and do not exhibit mobility on the gold surface. Annealing experiments have been performed in order to test the stability of the porphyrin layers. Disordered patterns have been observed in the STM images after annealing at T=400°C. XPS revealed that the sulphur content disappeared completely after annealing at T=180°C and that the molecules did undergo significant modifications.

Keywords: PACS; 68.37.Ef; 68.43.Hn; 79.60.Dp; 81.16.DnPorphyrin; Thiol-functionalized; Immobilization; Scanning tunnelling microscopy; X-ray photoelectron spectroscopy

Surface restoration induced by lubricant additive of natural minerals by Yang Yu; Jialin Gu; Feiyu Kang; Xianqing Kong; Wei Mo (pp. 7549-7553).

The effect of a new-fashioned lubricant additive is studied. The additive is prepared out of natural minerals containing flaky silicate, schungite and some other catalyzers. Applications of the additive obviously improve the surface mechanics properties of steel–steel friction pairs, and the nanohardness and the modulus of the friction surface are increased by 67 and 90%, respectively. The friction surface is especially examined with the high resolution transmission electron microscope (HRTEM), and an amorphous restoration film mostly made up of C with some Si or Si–O amorphous structure doped was found. Considering all research results about the restoration film, this study suggests the film is a sort of diamond-like carbon film (DLC film).

Keywords: PACS; 81.40.Pq; 82.45.JnFriction; Lubricant additive; Schungite; Silicate; Restoration; DLC film

Interfacial kinetic enhancement of metal ion adsorption on binary mixed self-assembled monolayers by Jungwoo Moon; Taewook Kang; Seogil Oh; Inhee Choi; Surin Hong; Jongheop Yi (pp. 7554-7558).

The adsorption of metal ions, a type of surface reaction on binary mixed self-assembled monolayers (SAMs) on a gold surface composed of 1,6-hexanedithiol (HDT) with 11-mercaptoundecanoic acid (MUA), was monitored by in situ surface plasmon resonance (SPR) measurements. The differential SPR reflectance (Δ R) enables the kinetics of adsorption of Pt²⁺ on the mixed SAMs to be investigated. Unlike single HDT SAM, kinetic analyses of the mixed SAMs showed that the rate of adsorption of Pt²⁺ was enhanced and that it was highly dependent on the fraction of MUA present. These SPR measurements suggest that the adsorption rate of metal ions can be readily manipulated simply by using mixed SAMs.

Keywords: Self-assembled monolayers; Mixed SAM; Surface plasmon resonance; Kinetics; Adsorption

Micro-gated-field emission arrays with single carbon nanotubes grown on Mo tips by Wensheng shao; Ming Q. Ding; Changqing Chen; Xinghui Li; Guodong Bai; Jin Jun Feng (pp. 7559-7562).

Using our approach previously reported, we have fabricated relatively large area micro-gated-field emission arrays with carbon nanotube (CNT) grown on Mo tips. By redesigning the device and fabrication processes, the percentage of single CNTs increased to about 50–70% with a substantial improvement in leakage current between gate and cathode and gate interceptive current. The I– V measurement of a 11000 cell array at a gate to cathode voltage of 92V showed an anode current of 1.2mA, corresponding to a current density of 0.57A/cm², with a gate current only 3.3% of the anode current.

Keywords: Conventional lithography; Micro-gated-field emission arrays; Single carbon nanotube emitters

Surface anisotropy of Cr_xN1−_x films prepared on an inner wall by magnetic sputtering by F. Zeng; R. Liang; X.W. Li; S.P. Wen; Y. Gao; Y.L. Gu; F. Pan (pp. 7563-7568).

The Cr_xN1−_x films were prepared by magnetic sputtering on an inner wall of a column. Their surface morphologies were studied by atomic force microscopy (AFM) and found to be anisotropic. The 3-D AFM images indicate the grains grow upward along the rotational axis of the system. The AFM top views show a mosaic-like pattern for all samples. Analysis of the height–height correlation function demonstrates that correlation length along the rotational axis of the system is longer than that vertical to the axis. The correlation length and RMS roughness increase with the flow rate of N₂. A deposition model proposed that the shadowing effect of the reactive gas N₂ is the dominant factor for surface anisotropy. The bias added on the substrate is regarded to modulate the grain direction to the rotation axis and enhance roughness and defects.

Keywords: PACS; 68.55-a, 81.15.Cd, 82.37.GkAtomic force microscopy; Growth; Surface roughening; Nitrides

Imaging of wood tissue by ToF-SIMS: Critical evaluation and development of sample preparation techniques by E.N. Tokareva; P. Fardim; A.V. Pranovich; H.-P. Fagerholm; G. Daniel; B. Holmbom (pp. 7569-7577).

Tissue of Norway spruce wood was investigated by time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and field-emission scanning electron microscopy (FE-SEM). Different sample preparation techniques (including sectioning and drying) traditionally used for SEM analysis were compared and critically evaluated. A high contamination of wood surfaces by polytetrafluoroethylene (PTFE) introduced onto the sample during sectioning was detected by ToF-SIMS. A new protocol was developed and images of wood sections dried in different ways were compared. Main location of Mg, Na, K and Ca, but no lignin in membranes of bordered pits in spruce section surfaces was detected by ToF-SIMS imaging if critical point drying (CPD) or acetone extraction followed by drying under nitrogen flow (AEND) was applied. No specific locations of wood components as well as low signals from metal ions (Mg and Na) were observed on the wood surfaces of freeze-dried (FD) or air-dried (AD) sections. It was found that extractive substances, presenting on surfaces of FD and AD wood section, were evenly distributed on the surfaces and interfered with ToF-SIMS analysis. Our results indicated that ToF-SIMS imaging was critically sensitive to the sample preparation technique and a strict protocol for characterization of metals, lignin and polysaccharides in wood was suggested.

Keywords: Wood sections; Sample preparation; ToF-SIMS; FE-SEM; Extractives; FD

Synthesis of nano and micro crystals of Cd(OH)₂ and CdO in the shape of hexagonal sheets and rods by Tandra Ghoshal; Soumitra Kar; Subhadra Chaudhuri (pp. 7578-7584).

Cd(OH)₂ and CdO nano/micro crystals were synthesized in ethanol–water medium using cadmium foil as a source under solvothermal condition. The experimental parameters such as ratio of ethanol to water, concentration of NaOH and synthesis temperature all play important role in determining the size, shape and crystalline phase of the products. The products were characterized by X-ray diffraction and scanning electron microscopy. Nano/micro crystals of CdO were also achieved by thermal treatment of Cd(OH)₂ crystals in air at different temperatures.

Keywords: PACS; 81.10.Dn; 68.37.Hk; 61.82.RxCrystal Structure; Hydrothermal crystal growth; Cadmium compounds

Simulation of KrF laser ablation of Al₂O₃–TiC by V. Oliveira; R. Colaço; R. Vilar (pp. 7585-7590).

Previous work by the authors on micromachining of Al₂O₃–TiC ceramics using excimer laser radiation revealed that a columnar surface topography forms under certain experimental conditions. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations show that the columns develop from small globules of TiC, which appear at the surface of the material during the first laser pulses. To understand the mechanism of formation of these globules, a 2D finite element ablation model was developed and used to simulate the time evolution of the temperature field and of the surface topography when a sample of Al₂O₃–TiC composite is treated with KrF laser radiation. Application of the model showed that the surface temperature of TiC rises much faster than that of Al₂O₃, but since TiC has a very high boiling temperature, its vaporization is significant only for a short time. By contrast, the surface temperature of Al₂O₃ rises above its boiling temperature for a much longer period, leading to a greater ablation depth than TiC. As a result, a small TiC globule stands above the Al₂O₃ surface. The results of the model are compared with experimental measurements performed by AFM. After three pulses, the height of the globules predicted by the model is about 340nm, in good agreement with the height measured experimentally, about 400nm.

Keywords: PACS; 61.80.Ba; 81.05.JeFinite element simulation; Al; ₂; O; ₃; –TiC; Laser ablation; AFM; SEM

Structure and properties of electrodeposited Fe–Ni–W alloys with different levels of tungsten content: A comparative study by Fengjiao He; Juan Yang; Tongxin Lei; Chunyan Gu (pp. 7591-7598).

Fe–Ni–W alloys with 18wt%, 35wt% and 55wt% tungsten have been obtained by electrodeposition from an ammoniacal citrate bath. The deposits are smooth, of nice appearance, and adhere well to iron and steel. The morphology and structure of Fe–Ni–W alloys were studied by SEM and XRD, respectively. The structure of the as-plated deposits changed from crystalline to amorphous with increasing tungsten content. The amorphous structure crystallized under heat treatment condition. The wear and corrosion resistance of the deposits were tested by MPX-2000 wear-tear equipment and neutral salt spray test (NSS), respectively. The alloys with 55wt% tungsten, after heat treatment at proper temperatures, appear to have good wear resistance and hardness. The alloys with 18wt% tungsten are very corrosion-resistant.

Keywords: PACS; 81.15.Pq; 81.05.Bx; 82.45.Jn; 82.45.Bb; 81.40.PqElectrodeposition; Fe–Ni–W alloys; Structure; Corrosion resistance; Wear resistance

Epitaxial LSMO films grown on MgO single crystalline substrates by M. Španková; Š. Chromik; I. Vávra; K. Sedláčková; P. Lobotka; S. Lucas; S. Stanček (pp. 7599-7603).

The manganite La_0.67Sr_0.33MnO₃ (LSMO) layers are deposited on single crystal MgO(001) substrates using a magnetron dc sputtering. The crystalline perfection of the layers, both the as-prepared and the annealed, are characterized by X-ray diffraction technique, rocking curve measurements, Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). TEM analyses give evidence of the epitaxial growth of the annealed LSMO with a nanocrystalline surface layer. The temperature dependence of resistance in the 77–340K range is measured by a standard four-probe technique. While the as-prepared film does not show any transition from paramagnetic to ferromagnetic state, the film annealed in oxygen shows steep R( T) dependence with a peak at 330K and maximal slope (d R/d T) at 290K where the maximal sensitivity is 3%K⁻¹.

Keywords: LSMO films; Magnetron sputtering; X-ray diffracion; Transmission electron microscopy; Rutherford backscattering; Electrical properties

Comparison of the Monte Carlo estimation of surface electrostatic potential at the hematite (0 0 0 1)/electrolyte interface with the experiment by Piotr Zarzycki (pp. 7604-7612).

The Monte Carlo simulations of the surface electrostatic potential are presented for the hematite (0 0 0 1) crystal plane. According to the ab initio calculations, the Fe-terminated (0 0 0 1) plane contains only one type of surface groups. The charge of this surface group is predicted using quantum population analyses, and the result is very close to this of the 1-pK model assumption. The surface topology and topography were constructed using the relaxed crystal plane structure. The Monte Carlo simulations for the reduced (including only hydrogen ions) and the extended (containing also electrolyte) models give the linear non-Nernstian pH-profile of surface potential. The simulation results are in agreement with the experimental measurements carried out by Kallay et al. [N. Kallay, Z. Dojnović, A. Cop, J. Colloid Interface Sci. 286 (2005) 610–614.] in the point of zero charge vicinity. This suggests that in this pH-region the surface properties are basically governed by the H⁺ ions uptake/release and the electrolyte ions complexations. The discrepancy for strongly acidic and basic regions suggests that some additional processes take place in the single-crystal electrode measurement, which results in the non-linearψ0=f(pH) profile.

Keywords: Surface electrostatic potential; Hematite monocrystal surface; Monte Carlo Simulation; Quantum population analysis

XPS investigations of ruthenium deposited onto representative inner surfaces of nuclear reactor containment buildings by C. Mun; J.J. Ehrhardt; J. Lambert; C. Madic (pp. 7613-7621).

In the case of a hypothetical severe accident in a nuclear power plant, interactions of gaseous RuO₄ with reactor containment building surfaces (stainless steel and epoxy paint) could possibly lead to a black Ru-containing deposit on these surfaces. Some scenarios include the possibility of formation of highly radiotoxic RuO₄(g) by the interactions of these deposits with the oxidizing medium induced by air radiolysis, in the reactor containment building, and consequently dispersion of this species. Therefore, the accurate determination of the chemical nature of ruthenium in the deposits is of the high importance for safety studies. An experiment was designed to model the interactions of RuO₄(g) with samples of stainless steel and of steel covered with epoxy paint. Then, these deposits have been carefully characterised by scanning electron microscopy (SEM/EDS), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The analysis by XPS of Ru deposits formed by interaction of RuO₄(g), revealed that the ruthenium is likely to be in the IV oxidation state, as the shapes of the Ru 3d core levels are very similar with those observed on the RuO₂· xH₂O reference powder sample. The analysis of O 1s peaks indicates a large component attributed to the hydroxyl functional groups. From these results, it was concluded that Ru was present on the surface of the deposits as an oxyhydroxide of Ru(IV). It has also to be pointed out that the presence of “pure” RuO₂, or of a thin layer of RuO₃ or Ru₂O₅, coming from the decomposition of RuO₄ on the surface of samples of stainless steel and epoxy paint, could be ruled out. These findings will be used for further investigations of the possible revolatilisation phenomena induced by ozone.

Keywords: PACS; 28.41Te (safety (fission reactor)); 33.60Fy (X-ray photoelectron spectroscopy); 82.65+r (surface interface chemistry)Ruthenium oxides; Ruthenium deposit; XPS; Ruthenium oxyhydroxides

Room temperature synthesis of needle-shaped ZnO nanorods via sonochemical method by Rizwan Wahab; S.G. Ansari; Young-Soon Kim; Hyung-Kee Seo; Hyung-Shik Shin (pp. 7622-7626).

Single crystalline needle-shaped zinc oxide nanorods were synthesized via sonochemical methods using zinc acetate dihydrate and sodium hydroxide at room temperature. Morphological investigation revealed that the nanoneedles are of hexagonal surfaces along the length. The typical diameter and length vary from 120 to 160nm and 3 to 5μm, respectively. Sonication time appears to be a critical parameter for the shape determination. Detailed structural characterization confirmed that the nanorods are single crystalline with wurtzite hexagonal phase. A standard peak of zinc oxide was observed at 520cm⁻¹ from the Fourier transform infrared spectroscopy. The ultra-violet visible and room temperature photoluminescence (PL) spectroscopic results demonstrate that the synthesized material has good optical properties.

Keywords: ZnO; Needle-shaped nanorods; Sonochemical method

Spectroscopic investigations of Cr, CrN and TiCr anti-multipactor coatings grown by cathodic-arc reactive evaporation by G.G. Fuentes; R.J. Rodríguez; M. García; L. Galán; I. Montero; J.L. de Segovia (pp. 7627-7631).

Cr, CrN, TiCr coatings have been investigated as potential anti-multipactor coatings. The coatings were synthesized by cathodic-arc reactive evaporation in Ar–N₂ atmosphere where the ion energy is controlled by substrate biasing. Chemical state analysis and surface composition were studied by X-ray photoemission spectroscopy (XPS), whereas bulk composition and depth profile were studied by glow discharge optical emission spectroscopy (GDOES). The surface morphology was studied by optical profilometry (OP) and scanning electron microscopy (SEM). The compositions of the coatings were CrN and Ti₄₀Cr₆₀ and they were homogeneous in depth. Surface oxidation was higher in Ti₄₀Cr₆₀ than in CrN. Coatings deposited at high negative bias show lower deposition rate and had lower surface roughness than those obtained at low bias. Secondary electron emission yield (SEY) was higher for CrN than for Ti₄₀Cr₆₀, both before and after low-energy Ar⁺ ion bombardment. The SEY of Ti₄₀Cr₆₀ (1.17 maximum) was clearly smaller than the others. The maximum yield, σ_m, and the first crossover electron energy, E₁, are the most important parameters, and ( E₁/ σ_m)^1/2 is a good figure of merit. This quantity was approximately 3eV^1/2 for Cr and CrN and 4eV^1/2 for Ti₄₀Cr. After Ar⁺ ion bombardment, the average value improved significantly to 8.9eV^1/2 for Cr and CrN and 10.2eV^1/2 for Ti₄₀Cr₆₀. The radio-frequency multipactor performance of these materials was simulated using the experimentally determined SEY parameters.

Keywords: PACS; 79.20.Hx; 79.60.−I; 74.62.BfSecondary electron emission; Multipactor; TiCr; XPS

Difference between chemical structures of the interface at the Al-oxide tunneling barrier prepared by plasma or by radical oxidation by Jongill Hong; Donkoun Lee; Yoonsung Han; Kyenam Lee; Inwoo Jang; Youngjin Park; Min Kyu Lee; Ha Jin Song; Hyun-Joon Shin; Koji Tsunekawa; Naoki Watanabe (pp. 7632-7638).

We have studied chemical structures of the interface between the Al-oxide tunneling barrier and the underlying Co₉₀Fe₁₀ layer in magnetic tunnel junctions when a 1-nm thick metallic Al barrier was oxidized by two different methods: plasma oxidation and radical oxidation. Our chemical analyses confirmed that the underlying CoFe layer was unavoidably attacked by oxygen during the oxidation and that this left different oxide states at the AlO_x/CoFe interface, depending on the oxidation method. The radical oxidation required long oxidation time for optimizing tunneling performance and resulted in a large amount of oxygen at the interface, which, in turn, resulted in the formation of mostly α-Fe₂O₃ and Al₂O₃. Conversely, the plasma oxidation required a relatively short oxidation time for optimization and left FeO as a dominant phase at the interface. Our results also show that the thermal treatment helped AlO_x, an oxygen-deficient phase, to be re-oxidized and transformed into Al₂O₃, the thermodynamically stable stoichiometric phase. The oxygen that diffused from the reduced CoFe layer into the barrier is likely responsible for this oxygen enrichment. We show that such differences in the chemical structure of the interface are critical clues to understanding what causes the change in tunneling properties of magnetic tunnel junctions.

Keywords: PACS; 61.10.Ht; 68.55.−a; 75.70.CnX-ray absorption spectroscopy; Near-edge X-ray absorption fine structure; Metal–insulator interface; Iron oxide; Cobalt oxide; Radical oxidation; Plasma oxidation; Magnetic tunnel junction

Microstructural and compositional studies of liquid-phase deposition derived PbTiO₃ thin films on LaNiO₃ substrates by Ming-Chi Hsu; Yu-Ming Sun; Ing-Chi Leu; Min-Hsiung Hon (pp. 7639-7644).

PbTiO₃ thin films were successfully deposited on the LaNiO₃ (LNO) substrates by the liquid-phase deposition (LPD) method and post-annealing at various temperatures. The structure, morphology and composition of the films were investigated by some analytical techniques. The as-deposited films are amorphous and composed of densely packed spherical particles. The films with the grain size of 180nm start to decompose and crystallize into perovskite structure at 450°C and show a perovskite single phase with tetragonal structure after annealing at 650°C. X-ray photoelectron spectroscopy (XPS) analysis reveals that the as-deposited film contains fluorine and carbon as major impurities. Fluorine could be completely eliminated by annealing at 650°C in air.

Keywords: Perovskite; Liquid-phase deposition; Microstructure

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Applied Surface Science (v.253, #18)