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Applied Surface Science (v.256, #12)

Effects of closed immersion filtered water flow velocity on the ablation threshold of bisphenol A polycarbonate during excimer laser machining by Colin Dowding; Jonathan Lawrence (pp. 3705-3713).

A closed flowing thick film filtered water immersion technique ensures a controlled geometry for both the optical interfaces of the flowing liquid film and allows repeatable control of flow-rate during machining. This has the action of preventing splashing, ensures repeatable machining conditions and allows control of liquid flow velocity. To investigate the impact of this technique on ablation threshold, bisphenol A polycarbonate samples have been machined using KrF excimer laser radiation passing through a medium of filtered water flowing at a number of flow velocities, that are controllable by modifying the liquid flow-rates. An average decrease in ablation threshold of 7.5% when using turbulent flow velocity regime closed thick film filtered water immersed ablation, compared to ablation using a similar beam in ambient air; however, the use of laminar flow velocities resulted in negligible differences between closed flowing thick film filtered water immersion and ambient air. Plotting the recorded threshold fluence achieved with varying flow velocity showed that an optimum flow velocity of 3.00m/s existed which yielded a minimum ablation threshold of 112mJ/cm². This is attributed to the distortion of the ablation plume effected by the flowing immersion fluid changing the ablation mechanism: at laminar flow velocities Bremsstrahlung attenuation decreases etch rate, at excessive flow velocities the plume is completely destroyed, removing the effect of plume etching. Laminar flow velocity regime ablation is limited by slow removal of debris causing a non-linear etch rate over ‘ n’ pulses which is a result of debris produced by one pulse remaining suspended over the feature for the next pulse. The impact of closed thick film filtered water immersed ablation is dependant upon beam fluence: high fluence beams achieved greater etch efficiency at high flow velocities as the effect of Bremsstrahlung attenuation is removed by the action of the fluid on the plume; low fluences loose efficiency as the beam makes proportionally large fluence losses at it passes through the chamber window and immersion medium.

Keywords: Ablation; Threshold; Polycarbonate; Liquid; Immersion

Micro-thermal analysis of polyester coatings by Hartmut R. Fischer (pp. 3714-3717).

The application and suitability of micro-thermal analysis to detect changes in the chemical and physical properties of coating due to ageing and especially photo-degradation is demonstrated using a model polyester coating based on neopentyl glycol isophthalic acid. The changes in chemical structure like chain scission and cross-linking are manifested by a shift of the LTA detectable T_g and by a change of the slope of the part of the LTA graph responsible for the penetration of the hot sensor into the material after passing the glass transition temperature. As such LTA is a valuable tool to have a quick look into coating surfaces and especially their ageing. The photo-degradation of polyester in air leads to the formation of a cross-linked network at a surface layer of about 3–4μm coupled with an increase in hardness and of the glass transition temperature by ∼90K, the effect is less drastic for a photo-degradation in a nitrogen environment. Moreover, the presence of a non-equilibrium dense surface layer with a higher T_g formed during the drying of the coating formulation and the film solidification can be shown.

Keywords: Coatings; Surface analysis; Photo-degradation

Cobalt–nickel mixed oxide surface: A promising adsorbent for the removal of PR dye from water by Al-Nakib Chowdhury; Abdur Rahim; Yusuf Jamal Ferdosi; Md. Shafiul Azam; M. Mufazzal Hossain (pp. 3718-3724).

A mixed oxide of cobalt (Co) and nickel (Ni) with an approximate composition of Co_0.4Ni_0.4O_0.2 was prepared chemically by precipitating from the corresponding metal carbonates and heating the mixture of carbonates at 650°C under ambient atmosphere. The mixed (Co–Ni) oxide thus prepared was characterized by IR, SEM and XRD methods. The composition of the mixed metal oxide was obtained by EDX analysis. The surface behavior of the Co–Ni mixed oxide matrix was tested by adsorption studies and pH_pzc measurement. The Co–Ni mixed oxide matrix behaves as a charged adsorbent at the pH media higher and lower than its pH_pzc value (9.50) and thus found to be capable of anchoring the oppositely charged species onto its surface. Removal of cationic and anionic dyestuffs, viz., methylene blue (MB) and procion red (PR), respectively, was attempted using the mixed oxide surface as adsorbent. Although both the dyes can be removed by the mixed oxide, the extent of PR removal (∼70%) seems to be much higher than that of MB (∼20%) demonstrating the superior performance of the Co–Ni mixed oxide for its use as adsorbent in removing the anionic PR dyestuff from water.

Keywords: Dye removal; Surface; Adsorption; Co–Ni mixed oxide; Procion red; Methylene blue

Numerical investigations of the effect of oblique impact on particle deformation in cold spraying by the SPH method by Wen-Ya Li; Shuo Yin; Xiao-Fang Wang (pp. 3725-3734).

In this study, a systematic examination of the oblique impacting of copper particles in cold spraying was conducted by using the smoothed particle hydrodynamics (SPH) method compared to the Lagrangian method. 3D models were employed owing to the asymmetric characteristic of the oblique impacting. It is found that in the oblique impact, the additional tangential component of particle velocity along the substrate surface could create a tensile force and decrease the total contact area and bonding strength between the particle and the substrate. The simulation results compare fairly well to the experiment results. Meanwhile, the asymmetric deformation can result in the focus of the shear friction on a small contact zone at one side, which may rise the interfacial temperature and thus facilitate the occurrence of the possible shear instability. Therefore, there probably exists an angle range, where the deposition efficiency may be promoted rather than the normal angle. Moreover, the particle deformation behavior simulated by the SPH method is well comparable to that simulated by the Lagrangian method and the experimental results, which indicates the applicability of the SPH method for simulating the impact process in cold spraying besides the previously used Arbitrary Lagrangian Eulerian (ALE) method.

Keywords: Cold spraying; Smoothed particle hydrodynamics (SPH) method; Oblique impact; Copper particle

The role of W doping in response of hydrogen sensors based on MAO titania films by Fujian Ren; Yunhan Ling; Jiayou Feng (pp. 3735-3739).

Anatase TiO₂ and W doped TiO₂ films were fabricated by micro-arc oxidation (MAO) on titanium substrates and their hydrogen sensing properties were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the oxide films and electrochemical impedance spectroscopy (EIS) was applied to investigate the gas sensing mechanism. It is found that the conductivity of TiO₂ films varies with the introduction of W dopant. EIS analysis reveals that the grains and especially the grain boundaries are mainly contributed to the hydrogen response and their equivalent circuits could be represented electrochemically by parallel resistor and constant phase element (CPE). The enhanced sensor signal at higher measuring temperature (300°C) is observed with an optimal doping concentration of W ions (1.81at.%).

Keywords: TiO; ₂; films; W doping; Micro-arc-oxidation; Hydrogen sensors

Efficient visible light-induced degradation of phenol on N-doped anatase TiO₂ with large surface area and high crystallinity by Guohui Tian; Yajie Chen; Kai Pan; Dejun Wang; Wei Zhou; Zhiyu Ren; Honggang Fu (pp. 3740-3745).

The N-doped anatase TiO₂ photocatalysts were prepared via solvothermal and ethylenediamine reflux treatment, followed by the sequential calcination in air and NH₃/N₂ atmosphere. The resulting photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and UV–vis diffuse reflectance spectra. The results revealed that the prepared N-doped anatase TiO₂ had characteristics of small crystallite size, large surface area, high crystallinity and visible light response. The prepared N-doped anatase TiO₂ photocatalysts showed much higher photocatalytic activity than N-doped Degussa P25 for the degradation of phenol under both ultraviolet and visible light irradiation, owing to more highly oxidizing hydroxyl radical which was the main oxidative species responsible for the degradation of phenol.

Keywords: Photocatalyst; Visible light; Thermal stability; Hydroxyl radical

KBr superstructure templates self-assembled on reconstructed A_IIIB_V semiconductor surfaces by Szymon Godlewski; Grzegorz Goryl; Jacek J. Kolodziej; Marek Szymonski (pp. 3746-3752).

In this report we present results of combined high resolution LT-STM and LEED studies of ultrathin epitaxial KBr films grown on an InSb(001) c(8×2) substrate. Based on atomically resolved STM maps and LEED diffractograms the film structure as well as superimposed electronic effects are explained. The origin of additional 4×4 superstructure observed on ultrathin films is discussed. Possible application of the KBr/InSb system as a template for growing organic molecule structures is suggested.

Keywords: Insulating thin film; Semiconductor surface; STM; Epitaxial growth; Template

Preparation and magnetic properties of nano-Ni coated cenosphere composites by Xian-feng Meng; Dong-hong Li; Xiang-qian Shen; Wei Liu (pp. 3753-3756).

Ni coated cenosphere composites are successfully fabricated by heterogeneous precipitation method using metal salts, ammonium hydro-carbonate and cenospheres as the raw materials. The cenosphere particles are characterized by scanning electron microscope (SEM)/energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) during and after the coating process. All results show that relatively uniform, smooth and compact Ni layer has been successfully coated onto cenospheres under the given conditions, furthermore, the nanometer Ni crystallite has a face-centered cubic structure. Magnetic property of Ni coated cenosphere composites can be adjusted by controlling the synthesis conditions and content of magnetic metal. The low density Ni coated cenosphere composites may be utilized for electromagnetic wave shielding and microwave absorbing materials.

Keywords: Heterogeneous precipitation; Nano-Ni; Fly-ash cenosphere; Magnetic property

Growth of SiO₂ on InP substrate by liquid phase deposition by Po Hsun Lei; Chyi Da Yang (pp. 3757-3760).

We have grown silicon dioxide (SiO₂) on indium phosphorous (InP) substrate by liquid phase deposition (LPD) method. With inserting InP wafer in the treatment solution composed of SiO₂ saturated hydrofluorosilicic acid (H₂SiF₆), 0.1M boric acid (H₃BO₃) and 1.74M diluted hydrochloric acid (HCl), the maximum deposition rate and refractive index for the as-grown LPD-SiO₂ film were about 187.5Å/h and 1.495 under the constant growth temperature of 40°C. The secondary ion mass spectroscope (SIMS) and energy dispersive X-ray (EDX) confirmed that the elements of silicon, oxygen, and chloride were found in the as-grown LPD-SiO₂ film. On the other hand, the effects of treatment solution incorporated with the hydrogen peroxide (H₂O₂) that can regulate the concentration of OH⁻ ion were also shown in this article. The experimental results represented that the deposition rate decreases with increasing the concentration of hydrogen peroxide due to the reduced concentration of SiO₂ saturated H₂SiF₆ in treatment solution.

Keywords: Liquid phase deposition (LPD); Indium phosphorous (InP); Hydrochloric acid (HCl); Silicon dioxide (SiO; ₂; )

Direct patterning of microelectrode arrays using femtosecond laser micromachining by C.J. Hayden; C. Dalton (pp. 3761-3766).

Micron-resolution microelectrodes and microelectrode arrays are commonly used in Lab-on-a-chip applications, typically for particle and fluidic sensing or pumping applications. The common method of fabricating such structures is to use conventional photolithography, which involves several steps, any of which can affect the quality and dimension of the final structure. Here we present an alternative method of creating microelectrodes using direct laser patterning. This is a significantly simpler and faster fabrication route requiring a single patterning step, and which also allows design changes to be implemented quickly, without having to re-manufacture a photolithographic mask. To confirm the suitability of this approach to fabricating microelectrodes, a complex multielectrode array design for neuron stimulation was directly laser-patterned.

Keywords: Lab-on-a-chip; Microelectrode; Femtosecond; Laser micromachining

Fabrication and evolution of Cu nanoparticles in Al₂O₃ crystal by ion implantation and annealing at different atmospheres by Yanyan Shen; Lili Zhang; Zhaodong Li; Xiaodong Zhang; Dacheng Zhang; Xu Li; Zhuo Wang; Bing Yuan; Mengkai Li; Changlong Liu (pp. 3767-3771).

Single crystal Al₂O₃ samples were implanted with 45keV Cu ion implantation at a dose of 1×10¹⁷ions/cm², and then subjected to furnace annealing in vacuum or with a flow of oxygen gas. Various techniques, such as ultraviolet–visible spectroscopy, X-ray diffraction spectroscopy and atomic force microscopy, have been used to investigate formation of Cu NPs and their evolution. Our results clearly show that the evolution of Cu NPs depends strongly on annealing atmosphere in the temperature range up to 600°C. Annealing in vacuum only gives rise to a slight change in the size of Cu NPs. No evidence for oxidization of Cu NPs has been revealed. Remarkable modifications in Cu NPs, including the size increase and the effective transformation into CuO NPs, have been observed for the samples annealed at oxygen atmosphere. The results have been tentatively discussed in combination with the role of oxygen from atmosphere in diffusion of Cu atoms towards the surface and its interactions with Cu NPs during annealing.

Keywords: Single crystal Al; ₂; O; ₃; Cu ion implantation; Nanoparticles; Annealing atmosphere

Low-temperature and ambient-pressure synthesis and shape evolution of nanocrystalline pure, La-doped and Gd-doped CeO₂ by Joysurya Basu; R. Divakar; Jonathan P. Winterstein; C. Barry Carter (pp. 3772-3777).

Nanocrystalline cuboidal ceria has been synthesized by low-temperature hydrothermal reaction of cerium nitrate hexahydrate with hexamethylene tetramine. The particles have been doped with La and Gd by adding aqueous solution of the nitrate salts of the metals to the reaction mixture. The pure and doped particles are cubic in crystal structure and 10–25nm in size. The pure and La-doped ceria are cuboidal in morphology, whereas the Gd-doped particles are irregular in shape. High-resolution TEM imaging and image simulation indicates that atomic level steps are present on the particle surfaces. The particles are faceted parallel to the {111} and {100} crystallographic planes and a continuous switching takes place between the two possible surface facets. It appears that the surface energies of the {111} and {100} facets are quite similar in magnitude and the interplay of surface energy determines the particle shape. Chemically sensitive imaging and spectroscopy shows that the dopants are homogeneously distributed within the particles and that the oxidation state of Ce is a mixture of +3 and +4. No preferential segregation either of the dopant or the oxidation state was observed. However, since the facet switching does depend on the chemistry of the dopant, there must be an affect on the atomic scale.

Keywords: Ceria; Hydrothermal; Doping; Faceting; HRTEM

Temperature dependence of the sticking coefficient in atomic layer deposition by M. Rose; J.W. Bartha; I. Endler (pp. 3778-3782).

The temperature dependence of the sticking coefficient (SC) of precursor molecules used in atomic layer deposition (ALD) was investigated. Tetrakis(ethylmethylamino)hafnium (TEMAHf) and Pentamethylcyclopentadienyltitan-trimethoxid (Cp*Ti(OMe)₃) were used in combination with ozone to deposit hafnium dioxide and titanium dioxide films at different substrate temperatures. The SC of TEMAHf was determined at 180, 230, and 270°C. The SC of TEMAHf depends exponentially on the substrate temperature. The activation energy and the pre-exponential factor were obtained for this ALD process. The SC of Cp*Ti(OMe)₃ was determined at 270°C. A possible explanation for the small SC of Cp*Ti(OMe)₃ could be the reduced symmetry of the precursor molecule. Therefore, symmetric precursor molecules and high process temperatures appear beneficial for efficient ALD processes.

Keywords: Atomic layer deposition; Sticking coefficient; Temperature dependence; Deep trench; Simulation; TEMAHf

Characteristics of nodular defect in HfO₂/SiO₂ multilayer optical coatings by Xiaofeng Liu; Dawei Li; Yuan’an Zhao; Xiao Li; Jianda Shao (pp. 3783-3788).

Laser-induced damage is associated with nodular defects in HfO₂/SiO₂ multilayer films. In order to investigate the damage characteristics of HfO₂/SiO₂ multilayer mirrors and find the information of improving laser-induced damage threshold, nodular defects are characterized by multiple analytical techniques; the damage morphologies induced by nodular-ejections are presented; the depths of nodular-ejection pits are investigated; the laser-induced damage threshold of zero probability and the stabilities of nodular-ejection pits exposed to repetitive illuminations are studied. Results show that domes in the film surface are nodular defects. Reliable depth information of nodular-ejection pits is obtained by counting layers from the damage edge. The depth statistical result implies nodular defects in these samples are usually originated from deep seeds. Some process optimizations suggestions are given based on the depth information. A simple tractable method is proposed to determine the functional damage threshold of these HfO₂/SiO₂ multilayer films basing on the damage experiments.

Keywords: HfO; ₂; /SiO; ₂; multilayer films; Nodular defects; Nodular-ejection pits; Depth information; Process optimizations; Functional damage threshold

Nanoscratch behavior of Zn1−_xCd_xSe heteroepitaxial layers by Chien-Huang Tsai (pp. 3789-3794).

This paper describes the nanoscratch behavior of Zn1−_xCd_xSe epilayers grown using molecular beam epitaxy (MBE). Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Hysitron Triboscope nanoindenter techniques were employed to determine the microstructures, morphologies, friction coefficients ( μ), and hardnesses ( H) of these materials, and thereby propose an explanation for their properties in terms of nanotribological behavior. Nanoscratch analysis revealed that the coefficient of friction of the Zn1−_xCd_xSe epilayer system decreased from 0.172 to 0.139 upon increasing the Cd content ( x) from 0.07 to 0.34. Furthermore, studies of the scratch wear depth under a ramping load indicated that a higher Cd content provided the Zn1−_xCd_xSe epilayers with a higher shear resistance, which enhanced the strength of the CdSe bonds. These findings suggest that the greater stiffness of the CdSe bond, relative to that of the ZnSe bond, enhances the hardness of the epilayers. Indeed, the effect of the Cd content on the growth of the Zn1−_xCd_xSe epilayers is manifested in the resulting nanotribological behavior.

Keywords: Molecular beam epitaxy; Scanning electron microscopy; Transmission electron microscopy

Theoretical study of CO adsorption on the illuminated TiO₂ (001) surface by E. Bostandoust Nik; R. Sadighi-Bonabi (pp. 3795-3798).

A quantum modeling of the CO adsorption on illuminated anatase TiO₂ (001) is presented. The calculated adsorption energy and geometries of illuminated case are compared with the ground state case. The calculations were achieved by using DFT formalism and the BH and HLYP. Upon photoexcitation, an electron–hole pair is generated. Comparing of natural population in the ground state and the exited state, shows that an electron is trapped in a Ti⁴⁺ ion and a hole is localized in an oxygen ion. The photoelectron helps generation of a CO₂ molecule on the TiO₂ surface. As shown by optimization of these systems, the CO molecule adsorbed vertically on the TiO₂ (001) surface in the ground state case while the CO molecule made an angle of 134.3° to this surface at the excited state case. Based on the here used model the obtained adsorption energy was 0.36eV which is in excellent agreement with the reported experimental value. In the present work the C–O stretch IR frequencies are calculated which are 1366.53 and 1423.16cm⁻¹. These results are in good agreement with the earlier reported works for the surface carbonaceous compounds, and oxygenated carbon species.

Keywords: CO; TiO; ₂; DFT; Adsorption; Anatase

Study of multilayer packaging delamination mechanisms using different surface analysis techniques by Álvaro Garrido-López; María Teresa Tena (pp. 3799-3805).

Multilayer packaging, consisting of different layers joined by using an adhesive or an extrusion process, is widely used to promote different products, such as food, cosmetics, etc. The main disadvantage in using this form of packaging is the delamination process. In this work, different surface techniques (X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy) are used to analyse the delaminated surfaces in order to study the mechanisms that cause delamination of multilayer packaging. According to our results, the reaction of migrated molecules with adhesive-aluminium bonds is the main cause of the chemical delamination process. In contrast, the delamination of extruded materials would seem to be caused by the breaking of Van der Waals bonds.

Keywords: Delamination; Multilayer packaging; Surface analysis

MAO-synthesized Al₂O₃-supported V₂O₅ nano-porous catalysts: Growth, characterization, and photoactivity by M.R. Bayati; H.R. Zargar; R. Molaei; F. Golestani-Fard; N. Zanganeh; A. Kajbafvala (pp. 3806-3811).

V₂O₅-loaded Al₂O₃ layers were successfully grown via micro-arc oxidation (MAO) process for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). It was found that the composite layers had a porous structure with a rough surface which is suitable for catalytic applications. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS) techniques were also employed to study phase structure and chemical composition of the composite layers. The layers consisted of γ-alumina, α-alumina, and vanadium pentoxide phases in which their relative contents varied with the applied voltage. Meanwhile, optical properties of the composite layers were investigated using UV–vis spectrophotometry technique, and the band gap energy was calculated as 3.15eV. Furthermore, photocatalytic performance of the synthesized composite layers was determined by measuring the decomposition rate of methylene blue solution, as a model compound, on the surface of the layers under ultra violet photo-irradiation. It was found that more than 91% of the methylene blue was degraded after 120min with a rate constant of k=0.0192min⁻¹.

Keywords: Alumina; Vanadia; Micro-arc oxidation; Catalyst; Porous; Composite

Synthesis of PMA stabilized silver nanoparticles by chemical reduction process under a two-step UV irradiation by D. Spadaro; E. Barletta; F. Barreca; G. Currò; F. Neri (pp. 3812-3816).

Poly(methacrylic acid) (PMA) stabilized silver nanoparticles (Ag NPs), also used in the surface modification of clothing fibers, were fabricated via chemical reduction processes under UV irradiation. To obtain an uniform size distribution it has been designed a new “two-step” process which employs two different UV radiation densities in order to control the kinetics of NPs nucleation. The as produced nanoparticles were characterized by UV–vis absorption spectroscopy and TEM microscopy. The results show the reduction of the Ag ions and the nanoparticles nucleation in the first step. In the second step, the final Ag NPs size distribution is controlled through a quick cross-linking of the PMA that freezes out any further modification. A narrow size distribution with more than 80% NPs smaller than 10nm and none larger than 25nm was obtained and the long-term stability (one month) of the colloidal solution was verified.

Keywords: Silver nanoparticles; Polymethacrylic acid; Chemical reduction; UV irradiation; Bio-packaging

Synthesis of nanocrystalline titania in pure water by pulsed Nd:YAG Laser by P. Jafarkhani; S. Dadras; M.J. Torkamany; J. Sabbaghzadeh (pp. 3817-3821).

Synthesis of titania (TiO₂) nanoparticles (NPs) has been performed with pulsed laser ablation (PLA) approach by irradiating a 1064nm Nd:YAG laser pulses on the titanium target immersed in pure water. A systematic characterization on the products, synthesized in different laser pulse energies, illustrated the conspicuous dependence of crystalline phase and size distribution of the NPs on this parameter. Emission spectroscopy of the induced plasma was exploited to justify the formation of titania NPs through the synthesis process, as well as the emergence of rutile phase beside the anatase by increasing the laser pulse energies. In addition, UV–vis optical absorption and Raman spectroscopy, associated with X-ray diffraction (XRD) were employed to quantitatively determine the crystalline phases of the products. Morphological observations by means of transmission electron microscopy (TEM), demonstrating the spherical shape of the synthesized NPs, was utilized to investigate the variation of particle size distribution with the laser pulse energy.

Keywords: Nanocrystalline titania; Pulsed laser ablation; Anatase; Rutile

Amorphous Ni–Al underlayer-accelerated L1₀ ordering transition of FePt thin films by Xiaohong Li; Fengqing Wang; Zhe Guo; Hang Li; Defeng Guo; Baoting Liu; Xiangyi Zhang (pp. 3822-3825).

In the present study, we succeeded in accelerating the L1₀ ordering transition of FePt thin films by employing amorphous Ni–Al as underlayers. The coercivity H_c=5kOe and ordering parameter S=0.67 of FePt thin films deposited on a Ni–Al underlayer with a thickness of ∼5nm after 380°C annealing for 30min are significantly higher than those H_c=0.4kOe and S=0.35 of the films without the Ni–Al underlayer. The L1₀ ordering process of and the coercivity of FePt thin films can be significantly tuned by varying the thickness of the Ni–Al underlayer.

Keywords: FePt thin film; Ordering; Underlayer; Coercivity

Nanopore formation on low-doped p-type silicon under illumination by N. Chiboub; N. Gabouze; J.-N. Chazalviel; F. Ozanam; S. Moulay; A. Manseri (pp. 3826-3831).

Porous silicon layers were elaborated by anodization of highly resistive p-type silicon in HF/ethylene glycol solution under front side illumination, as a function of etching time, HF concentration and illumination intensity. The porous layer morphology was investigated by scanning electron microscopy (SEM). The illumination during anodization was provided by a tungsten lamp or lasers of different wavelengths. Under anodization, a microporous layer is formed up to a critical thickness above which macropores appear. Under illumination, the instability limiting the growth of the microporous layer occurs at a critical thickness much larger than in the dark. This critical thickness depends on HF concentration, illumination wavelength and intensity. These non-trivial dependencies are rationalized in a model in which photochemical etching in the electrochemically formed porous layer plays the central role.

Keywords: Porous silicon; Photoelectrochemical; SEM; Resisitive silicon; Illumination

The multilayered spherical quantum dot under a magnetic field by F.K. Boz; S. Aktas; A. Bilekkaya; S.E. Okan (pp. 3832-3836).

The binding energy of an impurity located at the center of multilayered spherical quantum dot (MSQD) is reported as a function of the dot and barrier thickness for different alloy compositions under the influence of a magnetic field. Within the effective mass approximation, the binding energy has been calculated using the fourth order Runge–Kutta method without magnetic field. A variational approach has been employed if a magnetic field is present. The binding energy in MSQD with equal dot and barrier thickness is calculated. It is shown that the binding energy in MSQD differs from that of a single quantum dot. Also, the geometry is dominant on the binding energy for thin MSQDs, but the magnetic field becomes more effective for thick MSQDs.

Keywords: PACS; 73.21.La ;71.15.Nc; 71.55.EqQuantum dot; Binding energy; Magnetic field

Super-hydrophobic surface on pure magnesium substrate by wet chemical method by Yanhua Wang; Wei Wang; Lian Zhong; Jia Wang; Quanliang Jiang; Xiangyang Guo (pp. 3837-3840).

A layer of flower-like super-hydrophobic film was fabricated on pure Mg surface by chemical etching in H₂SO₄, H₂O₂ and subsequent immersion in stearic acid (CH₃(CH₂)₁₆COOH) ethanol solution. The super-hydrophobic surface showed a static water contact angle of 154° with the sliding angle of about 3°. With scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Fourier-transform infrared (FT-IR) spectrometer, the microstructure and composition of the sample were analyzed. Results showed that the flower-like structure and the bonding of the CH₃(CH₂)₁₆COO⁻ on Mg surface can be responsible for the superior water-repellent property. Electrochemical impedance spectroscopy revealed that the transfer resistance of super-hydrophobic surface was increased about four times than bare Mg after one-hour immersion in 0.1mol/L NaCl solution.

Keywords: Magnesium; Super-hydrophobic; Wet chemical method; Stearic acid

Synthesis and surface characterization of alumina–silica–zirconia nanocomposite ceramic fibres on aluminium at room temperature by M. Mubarak Ali; V. Raj (pp. 3841-3855).

Alumina–silica–zirconia nanocomposite (ASZNC) ceramic fibres were synthesized by conventional anodization route. Scanning Electron Microscopy (SEM), Atomic Force microscopy (AFM), X-Ray Diffraction (XRD) and Energy Dispersive X-Ray spectroscopy (EDAX) were used to characterize the morphology and crystalloid structure of ASZNC fibres. Current density (DC) is one of the important parameters to get the alumina–silica–zirconia nanocomposite (ASZNC) ceramic fibres by this route. Annealing of the films exhibited a drastic change in the properties due to improved crystallinity. The root mean square roughness of the sample observed from atomic force microscopic analysis is about 71.5nm which is comparable to the average grain size of the coatings which is about 72nm obtained from X-Ray diffraction. The results indicate that, the ASZNC fibres are arranged well in the nanostructure. The thickness of the coating increased with the anodizing time, but the coatings turned rougher and more porous. At the initial stage the growth of ceramic coating increases inwards to the metal substrate and outwards to the coating surface simultaneously. Subsequently, it mainly grows towards the metal substrate and the density of the ceramic coating increases gradually, which results in the decrease of the total thickness as anodizing time increases. This new approach of preparing ASZNC ceramic fibres may be important in applications ranging from gas sensors to various engineering materials.

Keywords: Ceramics; Composite materials; Anodization; X-Ray diffraction; AFM; SEM

Surface modification of ceria nanoparticles and their chemical mechanical polishing behavior on glass substrate by Zefang Zhang; Lei Yu; Weili Liu; Zhitang Song (pp. 3856-3861).

To improve their chemical mechanical polishing (CMP) performance, ceria nanoparticles were surface modified with γ-aminopropyltriethoxysilane (APS) through silanization reaction with their surface hydroxyl group. The compositions, structures and dispersibility of the modified ceria particles were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), laser particle size analyzer, zeta potential measurement and stability test, respectively. The results indicated that APS had been successfully grafted onto the surface of ceria nanoparticles, which led to the modified ceria nanoparticles with better dispersibility and stability than unmodified ceria particles in aqueous fluids. Then, CMP performance of the modified ceria nanoparticles on glass substrate was investigated. Experimental results showed that the modified ceria particles exhibited lower material removal rate (MRR) but much better surface quality than unmodified ceria particles, which may be explained by the hardness reduction of ceria particles, the enhancement of lubrication of the particles and substrate surfaces, and the elimination of the agglomeration among the ceria particles.

Keywords: Surface modification; Ceria; γ-Aminopropyltriethoxysilane; Chemical mechanical polishing

Influence of annealing temperature on the photoluminescence properties of ZnO quantum dots by Xiangqiang Zhang; Shili Hou; Huibing Mao; Jiqing Wang; Ziqiang Zhu (pp. 3862-3865).

The properties of ZnO quantum dots (QDs) synthesized by the sol–gel process are reported. The primary focus is on investigating the origin of the visible emission from ZnO QDs by the annealing process. The X-ray diffraction results show that ZnO QDs have hexagonal wurtzite structure and the QD diameter estimated from Debye–Scherrer formula is 8.9nm, which has a good agreement with the results from transmission electron microscopy images and the theoretical calculation based on the Potential Morphing Method. The room-temperature photoluminescence spectra reveal that the ultraviolet excitation band has a red shift. Meanwhile, the main band of the visible emission shifts to the green luminescence band from the yellow luminescence one with the increase of the annealing temperature. A lot of oxygen atoms enter into Zn vacancies and form oxygen antisites with increasing temperature. That is probably the reason for the change of the visible emission band.

Keywords: PACS; 73.21.La; 78.55.Et; 78.67.HcQuantum dots; Annealing; Point defects; Photoluminescence

Biocompatibility of pure titanium modified by human endothelial cell-derived extracellular matrix by Xiaoqing Xue; Jin Wang; Ying Zhu; Qiufen Tu; Nan Huang (pp. 3866-3873).

Extracellular matrix (ECM) used to modify biomaterial surface is a promising method for improving cardiovascular material hemocompatibility. In the present work, human umbilical vein endothelial cells (HUVECs) are cultured and native ECM is obtained on pure titanium surface. Fourier infrared spectrum (FTIR) test proves the existence of amide I and amide II band on the modified titanium surface. X-ray photoelectron spectroscopy (XPS) further confirms the chemical composition and binding types of the ECM proteins on the titanium substrate. The results of light microscopy and atomic force microscopy (AFM) exhibit the morphology of HUVEC derived ECM. There are higher water contact angles on the ECM modified samples. Furthermore, some ECM components, including fibronectin (FN), laminin (LN) and type IV collagen (IV-COL) are presented on ECM-covered titanium surface by immunofluorescence staining. The biological behavior of cultured HUVECs and adherent platelets on different samples are investigated by in vitro HUVECs culture and platelet adhesion. Cells exhibit better morphology and their proliferation ability greatly improve on the ECM-covered titanium. At the same time, the platelet adhesion and spreading are inhibited on ECM-covered titanium surface. These investigations demonstrate that ECM produced by HUVECs cannot only improve adhesion and proliferation ability of endothelial cell but also inhibit adhesion and activation of platelets. Thus, the approach described here may provide a basis for preparation of modified surface in cardiovascular implants application.

Keywords: Endothelial cell-derived extracellular matrix; Biocompatibility; Endothelial cell; Platelet adhesion; Titanium

Microstructure and high-temperature corrosion behaviors of aluminide coatings by low-temperature pack aluminizing process by Zhaolin Zhan; Zhong Liu; Jianxiong Liu; Li Li; Zeng Li; Pibo Liao (pp. 3874-3879).

Aluminide coatings were produced on carbon steel and Fe–5Cr–Mo alloy at a relatively lower temperature below 600°C in shorter treatment time by a combination of surface refinement process and pack aluminizing process. Repetitive ball impact, generated by mechanical vibration, caused the top-layer refinement of substrates in a conventional pack aluminizing process. The effects of temperature and treatment time on the formation of aluminide coatings were analyzed. The microstructure of the coatings was investigated by SEM, AFM and XRD. The aluminide coatings were one-layer, compacted structure with ultrafine grains and uniform elemental distribution. High-temperature oxidation and sulphidation tests were carried out at 600°C in air for 200h and 10% SO₂+Ar gas mixture atmosphere for 50h, respectively. The mass gains and spallation indicated that the aluminide coatings significantly improved the high-temperature oxidation and sulphidation resistance.

Keywords: Low-temperature pack aluminizing; Surface refinement; Ultrafine coatings; Oxidation; Sulphidation

A comparative study of fibre-textured and epitaxial Nb-doped Pb(Zr_0.53Ti_0.47)O₃ thin films on different substrates by Zhi-Xiang Zhu; Jing-Feng Li (pp. 3880-3887).

Fibre-textured and epitaxial Nb-doped Pb(Zr_0.53Ti_0.47)O₃ (PNZT) thin films were grown on the different substrates by a sol–gel process. The [100]- and [111]-fibre-textured polycrystalline PNZT films were obtained on platinized silicon substrates by introducing PbO and TiO₂ seeding layers, while the [001]- and [111]-oriented epitaxial PNZT films were formed directly on Nb-doped SrTiO₃ (Nb:STO) single-crystal substrates with (100) and (111) surfaces, respectively. The preferential orientation and phase structure of the fibre-textured and epitaxial PNZT films, as well as their influences on the electrical properties were investigated. Higher remnant polarization ( P_r) and piezoelectric coefficient ( d₃₃) were obtained for the epitaxial PNZT films on Nb:STO substrates than that for the fibre-textured ones on platinized silicon substrates. For both fibre-textured and epitaxial cases, the PNZT films with [100]/[001] orientations show higher piezoelectric responses than [111]-oriented ones, whereas better ferroelectric properties can be obtained in the latter. The intrinsic and extrinsic contributions were discussed to explain the difference in electrical properties for differently oriented fibre-textured and epitaxial PNZT films on different substrates.

Keywords: PZT films; Ferroelectricity; Texture; Epitaxial growth; Crystallographic orientation

Surface modification of polyimide films using unipolar nanosecond-pulse DBD in atmospheric air by Tao Shao; Cheng Zhang; Kaihua Long; Dongdong Zhang; Jue Wang; Ping Yan; Yuanxiang Zhou (pp. 3888-3894).

DBD-induced surface modification is very versatile to increase the adhesion or hydrophilicity of polymer films. In this paper, the DBD is produced by repetitive unipolar nanosecond pulses with a rise time of 15ns and a full width at half maximum of about 30ns. The power densities of the homogeneous and filamentary DBDs during plasma treatment are 158 and 192mW/m², respectively, which are significantly less than that using ac DBD processing, and the corresponding plasma dose is also mild compared to AC DBD treatment. Surface treatment of polyimide films using the homogeneous and filamentary DBDs is studied and compared. The change of chemical and physical modification of the surface before and after plasma processing has been evaluated. It can be found that both surface morphology and chemical composition are modified, and the modification includes the rise of hydrophilicity, surface oxidation and the enhancement of surface roughness. Furthermore, the homogeneous DBD is more effective for surface processing than the filamentary DBD, which can be attributed to the fact that the homogeneous DBD can modify the surface more uniformly and introduce more polar functional groups.

Keywords: Dielectric barrier discharge (DBD); Polyimide; Surface modification; Nanosecond pulse; Homogeneous DBD; Filamentary DBD

Chemical surface composition of the polyethylene implanted by Ag⁺ ions studied by phase imaging atomic force microscopy by S. Strbac; M. Nenadovic; Lj. Rajakovic; Z. Rakocevic (pp. 3895-3899).

High density polyethylene (HDPE) has been modified by Ag⁺ ion implantation with the energy of 60keV. The total amount of implanted silver ions was 1, 5 and 12×10¹⁵ ions/cm². The surface topography was observed by atomic force microscopy (AFM), while the surface composition changes were detected using phase imaging AFM. Surface topography changes were studied in detail using 3D surface parameters analyses. The average roughness decreased for the implanted HDPE indicating the flattening of the surface. Phase AFM images indicated the homogenization of the polyethylene during ion implantation, while histogram analyses confirmed the change in surface composition.

Keywords: Polyethylene; Silver; Ion implantation; Surface composition; AFM

Photoconductivity of thin organic films by Nikolai V. Tkachenko; Vladimir Chukharev; Petra Kaplas; Antti Tolkki; Alexander Efimov; Kimmo Haring; Jukka Viheriälä; Tapio Niemi; Helge Lemmetyinen (pp. 3900-3905).

Thin organic films were deposited on silicon oxide surfaces with golden interdigitated electrodes (interelectrode gap was 2μm), and the film resistivities were measured in dark and under white light illumination. The compounds selected for the measurements include molecules widely used in solar cell applications, such as polythiophene (PHT), fullerene (C₆₀), pyrelene tetracarboxylic diimide (PTCDI) and copper phthalocyanine (CuPc), as well as molecules potentially interesting for photovoltaic applications, e.g. porphyrin–fullerene dyads. The films were deposited using thermal evaporation (e.g. forC₆₀ andCuPc films), spin coating forPHT, and Langmuir–Schaeffer for the layer-by-layer deposition of porphyrin–fullerene dyads. The most conducting materials in the series are films ofPHT andCuPc with resistivities 1.2×10³Ωm and 3×10⁴Ωm, respectively. Under light illumination resistivity of all films decreases, with the strongest light effect observed forPTCDI, for which resistivity decreases by 100 times, from 3.2×10⁸Ωm in dark to 3.1×10⁶Ωm under the light.

Keywords: Thin organic film conductivity; Light conductivity

Low-temperature deposition of α-Al₂O₃ films by laser chemical vapor deposition using a diode laser by Yu You; Akihiko Ito; Rong Tu; Takashi Goto (pp. 3906-3911).

We prepared Al₂O₃ films by laser chemical vapor deposition (LCVD) using a diode laser and aluminum acetylacetonate (Al(acac)₃) precursors and investigated the effects of laser power ( P_L), deposition temperature ( T_dep), and total pressure ( P_tot) in a reaction chamber on the crystal phase, microstructure, and deposition rate ( R_dep). An amorphous phase was obtained at P_L=50W, whereas an α-phase was obtained at P_L>100W. At P_L=150 and 200W (104)- and (012)-oriented α-Al₂O₃ films were obtained, respectively. The R_dep of α-Al₂O₃ films increases with decreasing P_L and P_tot. Single-phase α-Al₂O₃ film was obtained at T_dep=928K, which is about 350K lower than that obtained by conventional thermal CVD using Al(acac)₃ precursor.

Keywords: Laser CVD; α-Al; ₂; O; ₃; Low-temperature deposition

Influence of field evaporation treatment on the field emission properties of carbon nanotubes array by Xin Bai; Wen-Jing Zhang; Gengmin Zhang (pp. 3912-3916).

Field evaporation was used in the post-fabrication treatment of a carbon nanotubes (CNTs) array and effectively modified the CNTs morphology in favor of the field emission under a moderate field. After the field evaporation treatment, the uniformity of the emission site distribution improved but the onset voltage rose. Using the Fowler–Nordheim theory, the actual onset field and the evaporation field around the CNT were calculated to be −4.6–5 and 9–12V/nm, respectively. These values are close to those obtained from the individual CNT samples. The above results have provided an alternative to modify the configuration of an array sample and demonstrated the feasibility of tackling the problem of the disparity in the field emission capability of different CNTs in an array.

Keywords: Carbon nanotubes; Field evaporation; Field emission

Synthesis of camptothecin-loaded gold nanomaterials by Zhimin Xing; Zhiguo Liu; Yuangang Zu; Yujie Fu; Chunjian Zhao; Xiuhua Zhao; Ronghua Meng; Shengnan Tan (pp. 3917-3920).

Camptothecin-loaded gold nanomaterials have been synthesized by the sodium borohydride reduction method under a strong basic condition. The obtained gold nanomaterials have been characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV–vis absorption spectroscopy. The camptothecin-loaded gold colloidal solution was very stable and can be stored for more than two months at room temperature without obvious changes. The color of the colloidal solution can change from wine red to purple and blue during the acidifying process. It was revealed that the release of camptothecin and the aggregation of gold nanoparticles can be controlled by tuning the solution pH. The present study implied that the gold nanomaterials can be used as the potential carrier for CPT delivery.

Keywords: Gold nanoparticles; Gold nanochains; Camptothecin; CPT; TEM; AFM

Zwitterionic monomer graft copolymerization onto polyurethane surface through a PEG spacer by Jingjing Huang; Weilin Xu (pp. 3921-3927).

A new zwitterionic surface was obtained by a novel three-step grafting procedure. The zwitterionic monomer was introduced by cerium-induced graft copolymerization in the presence of N,N′-methylene bisacrylamide (MBAA) as cross-linking agent. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the MBAA could stimulate zwitterionic monomer grafting onto the membrane surface. Surface properties were also determined by atomic force microscope (AFM) and water contact angle. The hemocompatibility of the modified PU membranes was evaluated by the activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT). The TT and APTT of PU were significantly prolonged by the zwitterion of sulfobetaine monomer grafting copolymerization. The new polyurethane membrane could have a great potential in biomedical applications.

Keywords: Graft copolymerization; Polyurethane; Surface modification; Zwitterions; Hemocompatibility

Effect of pulse frequency on the microstructure, phase composition and corrosion performance of a phosphate-based plasma electrolytic oxidation coated AM50 magnesium alloy by P. Bala Srinivasan; J. Liang; R.G. Balajeee; C. Blawert; M. Störmer; W. Dietzel (pp. 3928-3935).

An AM50 magnesium alloy was plasma electrolytic oxidation treated using a pulsed DC power supply at three different pulse frequencies viz., 10Hz, 100Hz and 1000Hz with a constant pulse ratio for 15min in an alkaline phosphate electrolyte. The resultant coatings were characterized by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy for their phase composition and microstructural features. The 10Hz condition yielded relatively thick and rough coatings, which was attributed to the higher energy input per individual pulse during the PEO processing. The phase composition was also found to be influenced by the processing frequency. Electrochemical impedance spectroscopy studies performed in 0.1M NaCl solutions revealed that the coatings produced at 10Hz condition had a better corrosion resistance, which was attributed to the higher thickness, more compact microstructural features and a relatively stable phase composition.

Keywords: Magnesium alloy; Plasma electrolytic oxidation; Pulse frequency; Microstructure; Phase composition; Corrosion behaviour

Ultrasonic flexural vibration assisted chemical mechanical polishing for sapphire substrate by Wenhu Xu; Xinchun Lu; Guoshun Pan; Yuanzhong Lei; Jianbin Luo (pp. 3936-3940).

The sapphire substrates are polished by traditional chemical mechanical polishing (CMP) and ultrasonic flexural vibration (UFV) assisted CMP (UFV–CMP) respectively with different pressures. UFV–CMP combines the functions of traditional CMP and ultrasonic machining (USM) and has special characteristics, which is that ultrasonic vibrations of the rotating polishing head are in both horizontal and vertical directions. The material removal rates (MRRs) and the polished surface morphology of CMP and UFV–CMP are compared. The MRR of UFV–CMP is two times larger than that of traditional CMP. The surface roughness (root mean square, RMS) of the polished sapphire substrate of UFV–CMP is 0.83Å measured by the atomic force microscopy (AFM), which is much better than 2.12Å obtained using the traditional CMP. And the surface flatness of UFV–CMP is 0.12μm, which is also better than 0.23μm of the traditional CMP. The results show that UFV–CMP is able to improve the MRR and finished surface quality of the sapphire substrates greatly. The material removal and surface polishing mechanisms of sapphire in UFV–CMP are discussed too.

Keywords: Ultrasonic flexural vibration (UFV); Chemical mechanical polishing (CMP); Sapphire substrate; Material removal rate (MRR); Surface roughness

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) by argon plasma by Hengjun Liu; Yanan Pei; Dong Xie; Xingrui Deng; Y.X. Leng; Yong Jin; Nan Huang (pp. 3941-3945).

In this work, argon (Ar) plasma generated by microwave electron cyclotron resonance (MWECR) has been used to modify the UHMWPE in order to increase the wear resistance. The results showed that the wettability, anti-scratch and wear resistance of UHMWPE treated by the Ar plasma had been improved, comparing with native UHMWPE. The FTIR and XPS spectra indicated the improvement of wettability should come from the oxygen based functional groups generated on the surface of UHMWPE. The improvement of anti-scratch and wear resistance may come from the enhancement of crosslinking of UHMWPE by Ar plasma treatment.

Keywords: UHMWPE; Argon plasma; Surface modification; Wear resistance

Surface composition of the steel powders pre-alloyed with manganese by E. Hryha; C. Gierl; L. Nyborg; H. Danninger; E. Dudrova (pp. 3946-3961).

The determination of the surface oxide layer composition is vital to facilitate the adjustment of the sintering conditions for sufficient removal of the surface oxides for providing strong metal bonding between the metal particles during sintering. To systematically investigate the composition, morphology and thickness of the surface oxide the influence of manganese content from 0.3 to 1.8wt.% on the surface products composition in the case of water atomized steel powder was evaluated. Analysis of the powder surfaces by X-ray photoelectron spectroscopy and high-resolution scanning electron microscopy in combination with X-ray microanalysis showed that powder particles in all cases are covered by heterogeneous oxide layer, composed of particulate features of thermodynamically stable oxides (Cr–Mn–Si) and homogeneous iron surface oxide layer in between. For increasing alloying content the fraction of stable oxide cations in the surface layer increases linearly, whereas the thickness of the iron oxide layer decreases. Moreover, from the investigation of the sintering and degassing behavior by thermal analysis coupled with mass-spectrometry (TG/DTA+MS), three different stages of carbothermal reduction process were observed and their correlation with surface oxides composition was established during sintering in argon.

Keywords: PM steels; Surface oxides; XPS analysis; Thermal analysis; Mass-spectroscopy; Carbothermal reduction

Diamond deposition on siliconized stainless steel by F. Álvarez; M. Reinoso; H. Huck; M. Rosenbusch (pp. 3962-3966).

Silicon diffusion layers in AISI 304 and AISI 316 type stainless steels were investigated as an alternative to surface barrier coatings for diamond film growth. Uniform 2μm thick silicon rich interlayers were obtained by coating the surface of the steels with silicon and performing diffusion treatments at 800°C. Adherent diamond films with low sp² carbon content were deposited on the diffused silicon layers by a modified hot filament assisted chemical vapor deposition (HFCVD) method. Characterization of as-siliconized layers and diamond coatings was performed by energy dispersive X-ray analysis, scanning electron microscopy, X-ray diffraction and Raman spectroscopy.

Keywords: Diamond; HFCVD; Siliconization; Stainless steel

Comparative studies on p-type CuI grown on glass and copper substrate by SILAR method by Sunetra L. Dhere; Sanjay S. Latthe; Charles Kappenstein; S.K. Mukherjee; A. Venkateswara Rao (pp. 3967-3971).

Depending upon the method of synthesis and the nature of substrate surface, there is variation in the physico-chemical properties of the material. Cuprous iodide films are deposited at room temperature on the glass and copper substrates by a simple SILAR method and the obtained results are compared. The p-type material with optical band gap 2.88eV is found to be possessing face-centered cubic crystal structure with lattice parameter 6.134Å. We observed irregular particles for the CuI film on the glass substrate while patterned arrays of micro-rods with cabbage like tips on copper substrate, for the same preparative conditions. Also, the material deposited on copper is showing superhydrophobic nature (contact angle ∼156°) while that on glass it is hydrophilic (contact angle ∼88°). We have characterized the thin films by X-ray diffraction, scanning electron microscopy, surface roughness and contact angle measurement, thermoelectric power measurement and optical studies. This hydrophobic, p-type material with wide band gap will be helpful in the development of optoelectronic devices.

Keywords: SILAR; Band gap; Thin film; Hydrophobic

Preparation of lotus-like superhydrophobic fluoropolymer films by Z.J. Wei; W.L. Liu; D. Tian; C.L. Xiao; X.Q. Wang (pp. 3972-3976).

Styrene and 2,2,3,4,4,4-hexafluorobutyl methacrylate copolymers were synthesized by bulk polymerization, and the superhydrophobic copolymer films were prepared subsequently using phase separation technique. The copolymer was dissolved in tetrahydrofuran, and then added ethanol into the solution thereafter, to induce phase separation. The microstructures of the polymer films were controlled by the degree of phase separation, which was enhanced properly by the concentration of ethanol. The surface morphology of the films, observed by environmental scanning electron microscope, is similar to that of the lotus leaf. The contact angle and sliding angle were measured as 154.3° and 5.8°, respectively. The excellent superhydrophobic property demonstrated that the phase separation technique is useful for preparing lotus-like fluoropolymer films.

Keywords: Bulk polymerization; Phase separation; Superhydrophobic; Lotus-like; Fluoropolymer film

Effects ofl-arginine immobilization on the anticoagulant activity and hemolytic property of polyethylene terephthalate films by Yun Liu; Yun Yang; Feng Wu (pp. 3977-3981).

Surface modification of polyethylene terephthalate (PET) films was performed withl-arginine (l-Arg) to gain an improved anticoagulant surface. The surface chemistry changes of modified films were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The in vitro anticoagulant activities of the surface-modified PET films were evaluated by blood clotting test, hemolytic test, and the measurement of clotting time including plasma recalcification time (PRT), activated partial thromboplastin time (APTT), and prothrombin time (PT). The data of blood coagulation index (BCI) forl-arginine modified PET films (PET-Arg) was larger than that for PET at the same blood-sample contact time. The hemolysis ratio for PET-Arg was less than that for PET and within the accepted standard for biomaterials. The PRT and APTT for PET-Arg were significantly prolonged by 189s and 25s, respectively, compared to those for the unmodified PET. All results suggested that the currently described modification method could be a possible candidate to create antithrombogenic PET surfaces which would be useful for further medical applications.

Keywords: PACS; 87.85.jjSurface modification; Polyethylene terephthalate; l; -arginine; Anti-coagulant activity; Hemolysis

Surface self-organization: From wear to self-healing in biological and technical surfaces by Michael Nosonovsky; Bharat Bhushan (pp. 3982-3987).

Wear occurs at most solid surfaces that come in contact with other solid surfaces. While biological surfaces and tissues usually have the ability for self-healing, engineered self-healing materials only started to emerge recently. These materials are currently created using the trial-and-error approach and phenomenological models, so there is a need of a general first-principles theory of self-healing. We discuss the conditions under which the self-healing occurs and provide a general theoretical framework and criteria for self-healing using the concept of multiscale organization of entropy and non-equilibrium thermodynamics. The example of epicuticular wax regeneration of plant leaves is discussed as a case study.

Keywords: Self-healing materials; Wear; Biomimetics

Self filling of Ni nanoparticles in amorphous AlN nanotubes and its field emission property by R. Thapa; B. Saha; N.S. Das; U.N. Maiti; K.K. Chattopadhyay (pp. 3988-3992).

Unique aluminum nitride amorphous nanotubes filled with Ni nanoparticles have been successfully synthesized through the reaction of NH₃ over Ni–Al thin film at 1000°C, which is similar to the extended vapor–liquid–solid technique. The X-ray diffraction and high-resolution transmission electron microscopic results are in good agreement with the amorphous nature of AlN nanotubes and crystallinity of Ni nanoparticles. The AlN nanotubes were having average diameter 35nm and length ∼4μm, whereas the Ni nanoparticles were having 5nm in diameter. The unique structure showed excellent field emission property and high electrical conductivity ∼0.43kmho/m at room temperature. The mechanism of good field emission property has been explained in detail.

Keywords: Aluminum nitride; Nanotube; Nanoparticle; Field emission; VLS technique

Electrochemical fabrication and characterization of lepidocrocite (γ-FeOOH) nanowire arrays by A. Jagminas; K. Mažeika; E. Juška; J. Reklaitis; D. Baltrūnas (pp. 3993-3996).

We report on the fabrication of γ-phase iron oxyhydroxide (γ-FeOOH, lepidocrocite) nanowire ( nw) arrays within the alumina pores by electrodeposition. An aqueous solution, friendly to alumina matrix, was generated and applied in this study for uniform deposition of γ-FeOOH nw arrays directly through the alumina barrier layer using an alternating current ( ac) mode. As-deposited nanowired products were characterized using⁵⁷Fe Mössbauer spectroscopy (MS), atomic absorption spectrophotometry analysis, field-emission scanning electron microscopy, UV–vis transmission spectroscopy, transmission electron microscopy and X-ray diffraction. The formation of pure lepidocrocite nw arrays in the alumina pores with the average Ø_pore of 45 and 150nm was verified by transmission MS at cryogenic temperatures.

Keywords: Nanomaterials; Template synthesis; Lepidocrocite; Mössbauer spectroscopy

Study of ethylene adsorption on zeolite NaY modified with group I metal ions by Niramai Sue-aok; Tipaporn Srithanratana; Kunwadee Rangsriwatananon; Sunantha Hengrasmee (pp. 3997-4002).

The adsorption of ethylene by zeolite NaY and zeolite NaY modified by cation exchange with potassium, rubidium, and cesium ions was studied. Cation exchanges were carried out using KNO₃, RbNO₃, and CsNO₃ in the concentration ranges of 0.2–10mM. XRD patterns and specific surface areas illustrated that modification of NaY zeolite by very dilute solutions containing K⁺, Rb⁺ and Cs⁺ did not lead to significant changes in the crystallinity. Analysis of metals content (ICP-OES) showed that Cs⁺ can replace Na⁺ better than Rb⁺ and K⁺. Particle analysis indicated slight decreases in surface area but pore volumes and pore diameters remained unchanged. Ethylene adsorption isotherms indicated that Na-Y zeolite which was modified by 5.0mM KNO₃, 0.5mM RbNO₃ and 1.0mM CsNO₃ could adsorb ethylene better than zeolite Na-Y. K-NaY zeolite adsorbed up to 102.45cm³/g ethylene, while Rb-NaY and Cs-NaY zeolites adsorbed up to 98.50cm³/g and 90.15cm³/g ethylene, respectively. Ethylene adsorption capacities depended on number of adsorption sites and surface interactions.

Keywords: Zeolite Na-Y; Cation exchange; Ethylene adsorption

A novel precursor for synthesis of metallic copper nanocrystals by thermal decomposition approach by Masoud Salavati-Niasari; Noshin Mir; Fatemeh Davar (pp. 4003-4008).

[Bis(2-hydroxy-1-naphthaldehydato)copper(II)] complex, as a novel precursor, was employed in thermal decomposition process to synthesize metallic copper nanoparticles using oleylamine (C₁₈H₃₇N) as capping agent. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–vis) spectroscopy. The synthesized copper nanoparticles have a fcc structure with average size 20–35nm.

Keywords: Metallic nanoparticles; Copper; Capping agent; Inorganic precursors

Formation of nanostructured weldments in the Al–Si system using electrospark welding by J. Milligan; D.W. Heard; M. Brochu (pp. 4009-4016).

Electrospark welding (ESW) electrodes were manufactured from three binary aluminum–silicon alloys consisting of 12 and 17wt% silicon, produced using chill and sand casting. The electrodes were used to assess the feasibility of producing aluminum–silicon weldments consisting of nano-sized silicon particles embedded in nanostructured aluminum matrix, using the ESW process. Line tests were performed to determine the optimal processing parameters resulting in a high quality deposit. X-ray diffraction (XRD) as well as optical and field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) was performed to determine the composition and microstructure of the depositions. It was determined that a capacitance of 110μF and a voltage of 100V resulted in the highest quality deposition. Furthermore it was determined that the ESW process was capable of producing a microstructure consisting of an extremely fine-grained silicon phase ranging from ∼6 to 50nm for the eutectic composition, and 10–200nm for the hypereutectic compositions. Finally it was determined that the functional thickness limit of the aluminum–silicon deposit produced under these process parameters was 120μm.

Keywords: Aluminum–silicon alloys; Electrospark welding; Nano-materials

Characterization of calcium containing plasma electrolytic oxidation coatings on AM50 magnesium alloy by P. Bala Srinivasan; J. Liang; C. Blawert; M. Störmer; W. Dietzel (pp. 4017-4022).

An attempt was made to produce calcium containing plasma electrolytic oxidation (PEO) coatings on AM50 magnesium alloy using an alkaline electrolyte. This study was performed in three alkaline electrolytes containing calcium hydroxide and sodium phosphate with three different mass ratios viz., 1:2.5, 1:5 and 1:7.5. All the three coatings produced were found to contain Ca and P in appreciable amounts. The concentration of P was found to be higher in the coatings obtained in the electrolytes with higher concentration of phosphate ions. Even though all the three coatings were found to be constituted with magnesium oxide and magnesium phosphate phases, X-ray diffraction analyses revealed that the phase composition was influenced by the phosphate ion concentration/conductivity of the electrolyte. Further, the PEO coating obtained in the 1:7.5 ratio electrolyte was found to contain di-calcium phosphate (monetite) and calcium peroxide phases, which were absent in the other two coatings. Potentiodynamic polarization studies performed in 0.1M NaCl solution showed that the coatings obtained from the 1:5 ratio electrolyte possessed a superior corrosion resistance, which is attributed to the combined effect of thickness, compactness and phase/chemical composition of this coating.

Keywords: Magnesium alloy; Plasma electrolytic oxidation; Microstructure; Corrosion behaviour

Thermodynamic analysis on the stability and evolution mechanism of self-assembled quantum dots by X.L. Li (pp. 4023-4026).

A quantitative thermodynamic model addressing the stability and evolution mechanism during growth process of quantum dots (QDs) in Stranski–Krastanow (SK) system is established by taking into account the thickness-dependent surface energy of wetting layer (WL). It is found that the thickness-dependent surface energy of WL prevents QDs from growing up without limit. The competition between relaxation energy of QDs and thickness-dependent surface energy of WL results in a puzzling phenomenon that WL not only can hardly capture atoms to grow, but also need release atoms into QDs during deposition process and annealing. Agreement between theoretical results and experiments implies that the established thermodynamic model could be expected to be a general approach to pursue the physical mechanisms of self-assembly of quantum dots.

Keywords: Quantum dots; Self-assembly; Thermodynamics; Stranski–Krastanow system

The effects of Dresselhaus and Rashba spin–orbit interactions on the electron tunneling in a non-magnetic heterostructure by Jian-Duo Lu; Jian-Wen Li (pp. 4027-4030).

We theoretically investigate the electron transport properties in a non-magnetic heterostructure with both Dresselhaus and Rashba spin–orbit interactions. The detailed-numerical results show that (1) the large spin polarization can be achieved due to Dresselhaus and Rashba spin–orbit couplings induced splitting of the resonant level, although the magnetic field is zero in such a structure, (2) the Rashba spin–orbit coupling plays a greater role on the spin polarization than the Dresselhaus spin–orbit interaction does, and (3) the transmission probability and the spin polarization both periodically change with the increase of the well width.

Keywords: PACS; 72.25.; −; b; 73.23.; −; b; 72.25.Dc; 73.40.GkNon-magnetic heterostructure; Spin–orbit coupling; Spin polarization

Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica by Nan Shen; Manyalibo J. Matthews; James E. Fair; Jerald A. Britten; Hoang T. Nguyen; Diane Cooke; Selim Elhadj; Steven T. Yang (pp. 4031-4037).

Nano- to micrometer-sized surface defects on UV-grade fused silica surfaces are known to be effectively smoothed through the use of high-temperature localized CO₂ laser heating, thereby enhancing optical properties. However, the details of the mass transport and the effect of hydroxyl content on the laser smoothing of defective silica at sub-micron length scales are still not completely understood. In this study, we examine the morphological evolution of sub-micron, dry-etched periodic surface structures on type II and type III SiO₂ substrates under 10.6μm CO₂ laser irradiation using atomic force microscopy (AFM). In situ thermal imaging was used to map the transient temperature field across the heated region, allowing assessment of the T-dependent mass transport mechanisms under different laser-heating conditions. Computational fluid dynamics simulations correlated well with experimental results, and showed that for large effective capillary numbers ( N_c>2), surface diffusion is negligible and smoothing is dictated by capillary action, despite the relatively small spatial scales studied here. Extracted viscosity values over 1700–2000K were higher than the predicted bulk values, but were consistent with the surface depletion of OH groups, which was confirmed using confocal Raman microscopy.

Keywords: Viscosity; Capillarity; Laser polishing; Damage mitigation; Fused silica; Hydroxyl group

Surface growth of single-walled carbon nanotubes from ruthenium nanoparticles by Yong Qian; Chunyan Wang; Guangyuan Ren; Bin Huang (pp. 4038-4041).

In this paper, we report that ruthenium is an active and efficient catalyst for growth of single-walled carbon nanotubes (SWNTs) by a chemical vapor deposition (CVD) process for the first time. High density random and horizontally superlong well-oriented SWNTs on substrate can be fabricated via CH₄ or EtOH as carbon source under suitable conditions. Scanning and transition electron microscopy investigations, Raman spectroscopy and atomic force microscopy measurements show the tubular structure, the high crystallinity, and the properties of the grown nanotubes. The results show that the SWNTs from ruthenium have better structural uniformity with less defects and provides an alternative catalyst for SWNTs growth. The successful growth of SWNTs by Ru catalyst provides new experimental information for understanding the growth mechanism of SWNTs, which may be helpful for their controllable synthesis.

Keywords: Ruthenium; Chemical vapor deposition; Single-walled carbon nanotube

Adsorption of NO and N₂O on Fe-BEA and H-BEA zeolites by Yuli Wang; Zhigang Lei; Biaohua Chen; Quanhui Guo; Ning Liu (pp. 4042-4047).

FT-IR (Fourier-transform infrared) spectroscopy and density function theory (DFT) methods have been applied to the investigation of the interaction of NO and N₂O with Fe³⁺ species in a beta zeolite (BEA). The geometries for H-BEA and Fe-BEA represented as 10T cluster, and NO and N₂O adsorption on them in η¹-O and η¹-N modes have been completely optimized. The results show that NOx could be adsorbed on Fe³⁺ species and Brønsted acid sites in two modes, but NOx is mainly bonded by N to H or Fe atom and the iron site is preferred. NOx adsorbed on Fe³⁺ species is more stable than on Brønsted acid sites. Adsorption energies for N₂O and NO follow the order of NO>N₂O, predicating that the affinity of NO molecule on BEA zeolite is much stronger than N₂O molecule on BEA zeolite.

Keywords: NOx adsorption; Fe-BEA; Density functional theory (DFT); FT-IR

Biological functionalization and patterning of porous silicon prepared by Pt-assisted chemical etching by Hong-Fang Li; Huan-Mei Han; Ya-Guang Wu; Shou-Jun Xiao (pp. 4048-4051).

Porous silicon fabricated via Pt-assisted chemical etching of p-type Si (100) in 1:1:1 EtOH/HF/H₂O₂ solution possesses a longer durability in air and in aqueous media than anodized one, which is advantageous for biomedical applications. Its surface SiH x ( x=1 and 2) species can react with 10-undecylenic acid completely under microwave irradiation, and subsequent derivatizations of the end carboxylic acid result in affinity capture of proteins. We applied two approaches to produce protein microarrays: photolithography and spotting. The former provides a homogeneous microarray with a very low fluorescence background, while the latter presents an inhomogeneous microarray with a high noise background.

Keywords: Porous silicon; Protein microarray; Surface chemistry; Metal-assisted chemical etching; NTA

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Applied Surface Science (v.256, #12)

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Applied Surface Science (v.256, #12)