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Applied Surface Science (v.253, #22)

Electrocatalytic oxidation of formaldehyde on platinum well-dispersed into single-wall carbon nanotube/polyaniline composite film by Zhe Wang; Zan-Zan Zhu; Jin Shi; Hu-Lin Li (pp. 8811-8817).

Single-walled carbon nanotubes (SWNTs)/polyaniline (PANI) composite films with good uniformity and dispersion were prepared by electrochemical polymerization of aniline containing well-dissolved SWNTs. The composite films were dispersed Pt by electrodeposition technique. The presence of SWNTs and platinum in the composite film was confirmed by XRD analysis and scanning electron microscopy (SEM). Four-point probe investigation and electrochemical impedance spectroscopy (EIS) revealed that the well arrangement of PANI coated SWNTs in these films enhanced electric conductivity and facilitated the charge-transfer of the composite films. Cyclic voltammogram (CV) and chronoamperogram showed that Pt-modified SWNT/PANI composite film performs higher electrocatalytic activity and better long-term stability than Pt-modified pure PANI film toward formaldehyde oxidation. The results imply that the SWNT/PANI composite film as a promising support material improves the electrocatalytic activity for formaldehyde oxidation greatly.

Keywords: PACS; 81.07.De; 82.35.Cd; 82.45.YzSingle-walled carbon nanotubes; Polyaniline; Composite film; Formaldehyde electrooxidation; Electrocatalytic activity

Fabrication and anti-frosting performance of super hydrophobic coating based on modified nano-sized calcium carbonate and ordinary polyacrylate by Hao Wang; Liming Tang; Xiaomin Wu; Wantian Dai; Yipeng Qiu (pp. 8818-8824).

Nano-sized calcium carbonate (CaCO₃) particles were modified by heptadecafluorodecyl trimethoxysilane under acidic water condition. An ordinary polyacrylate prepared via radical copolymerization of methyl methacrylate, butyl acrylate, acrylic acid and β-hydroxyethyl methacrylate was used as the binder to form hydrophobic coatings with the modified CaCO₃. Super hydrophobic coating with water contact angle of 155° was obtained from modified CaCO₃ and the polyacrylate at their weight ratio of 8/2 by a simple procedure. Based on surface analysis by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), the super hydrophobicity can be attributed to both the surface microstructure and surface enrichment of fluoroalkyl chains. Due to a low water sliding angle, carbon black powder on super hydrophobic surface was easily removed by rolling water droplet. Furthermore, the anti-frosting performance of different surfaces was investigated, which indicated that the frost formed on superhydrophobic surface was greatly retarded compared with that on bare copper surface. The surface kept super hydrophobicity even after freezing–thawing treatment for 10 times.

Keywords: Super hydrophobic coating; Nano-calcium carbonate; Polyacrylate; Anti-frosting performance

Atomistic simulation of Pt trimer on Pt(1 1 1) surface by Jianyu Yang; Wangyu Hu; Guojun Yi; Jianfeng Tang (pp. 8825-8829).

The diffusion of Platinum trimer on Pt(1 1 1) is studied at different temperatures by molecular dynamics (MD) simulation. The structure stability is studied by cluster binding energy. The interaction between adatoms and surface atoms is discussed based on the calculated phonon density of state of Pt trimer. The diffusion coefficients of Pt trimer are derived from mean square displacement of cluster’s mass-center, which is obtained by long simulation times (≃0.2μs) and tracing of interstitial atoms on surface. Then the diffusion prefactor and migration energy are deduced from Arrhenius relation. The calculated results are in reasonable agreement with experiment. In addition, using the diffusion prefactor and migration energy, the efficiency of Pt trimer as a critical nucleus for three-dimensional growth of thin films is discussed.

Keywords: PACS; 68.35.Fx; 31.15.Qg; 68.47.De; 63.20.DjPt trimer; Molecular dynamics; Surface diffusion; Arrhenius plot; Phonon density of state

Controlling the micro/nanostructure of self-cleaning polymer coating by Xu Kang; Wei-Wei Zi; Zhu-Guo Xu; Hao-Li Zhang (pp. 8830-8834).

Polypropylene bio-mimic self-cleaning surfaces with porous micro-nano-binary morphology structures were prepared by a simple casting method. The influence of the cooling process and solvent composition on water contact angle, sliding angles and self-cleaning properties has been investigated. Detailed SEM morphology studies revealed that the polymer used in this work is commercial-grade granular low-density polyethylene (LDPE) forms petal-like crystalline, which are of micrometer scale in length and nanometer scale in thickness. The nano-crystallines on the surface represent a porous three-dimensional micro-nano-binary structure. It was found that a compromise to the film porosity and crystal nano structure is essential for achieving a satisfied self-cleaning surface. Under optimum condition, a water contact angle of 152.2°, and a sliding angle of 1.7° can be obtained using this simple method.

Keywords: PACS; 81.07.-b; 82.35.Np; 68.08.Bc; 68.47.Mn; 81.65.C; 81.05.RmCrystallization; Superhydrophobic; Polyethylene; Self-cleaning

Structure evolution and mechanical properties enhancement of Al/AlN multilayer by G.A. Zhang; Z.G. Wu; M.X. Wang; X.Y. Fan; J. Wang; P.X. Yan (pp. 8835-8840).

A set of Al/AlN multilayers with various modulation periods were prepared using DC magnetron sputtering method. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the films was investigated with grazing angle X-ray diffraction (GAXRD). LAXRD results indicate that well-defined multilayer modulation structures are formed for the relatively larger modulation periods. However, the loss of mutilayered structure is detected in the multilayer with low modulation period. A very wide amorphous peak is observed in multilayer with modulation period of 4nm. The multilayers show obvious crystallization at larger modulation periods, however, the diffraction peaks are much wider than the Al single layer because of the interruption of the continuous columnar grain growth by alternating deposition processes. Nanoindentation experiments were performed to study the mechanical properties as a function of multilayer modulation period. It is found that the hardness of the multilayers is greater than the hardness calculated from rule of mixtures. With the modulation periods adjusted, the multilayers are even harder than its hard component (AlN). A maximum hardness of 24.9GPa, about 1.9 times larger than its hard component (AlN) and 3.7 times larger than the hardness calculated from the rule of mixtures, is found at the multilayer with modulation period of 16nm. The wear test results show that the multilayers possess lower and stable friction coefficient, and superior wear properties.

Keywords: Magnetron sputtering; Al/AlN multilayer; Structure; Hardness; Wear properties

Superhydrophobicity of polytetrafluoroethylene thin film fabricated by pulsed laser deposition by H.Y. Kwong; M.H. Wong; Y.W. Wong; K.H. Wong (pp. 8841-8845).

Superhydrophobic polytetrafluoroethylene (PTFE) thin films were obtained by pulsed laser deposition (PLD) technique carried out with KrF excimer laser ( λ=248nm) of about 1J/cm² at a pressure of 1.33Pa. The samples exhibit high water contact angle of about 170° and the sliding angle smaller than 2°. From studying the surface morphology of the prepared films, it is believed that the nano-scale surface roughness has enhanced the hydrophobic property of the PTFE. The increase of trapping air and reducing liquid–solid contact area due to the rough surface, as suggested by the Cassie-Baxter's model, should be responsible for superhydrophobicity of the PLD prepared films. This study thus provides a convenient one-step method without using wet-process to produce a superhydrophobic surface with good self-cleaning properties.

Keywords: Superhydrophobic; PLD; PTFE

Surface analysis monitoring of polyelectrolyte deposition on Ba_0.5Sr_0.5TiO₃ thin films by Angel L. Morales-Cruz; Estevão R. Fachini; Félix A. Miranda; Carlos R. Cabrera (pp. 8846-8857).

Thin films are currently gaining interest in many areas such as integrated optics, sensors, friction, reducing coatings, surface orientation layers, and general industrial applications. Recently, molecular self-assembling techniques have been applied for thin film deposition of electrically conducting polymers, conjugated polymers for light-emitting devices, nanoparticles, and noncentrosymmetric-ordered second order nonlinear optical (NOL) devices. Polyelectrolytes self-assemblies have been used to prepare thin films. The alternate immersion of a charged surface in polyannion and a polycation solution leads usually to the formation of films known as polyelectrolyte multilayers. These polyanion and polycation structures are not neutral. However, charge compensation appears on the surface. This constitutes the building driving force of the polyelectrolyte multilayer films.The present approach consists of two parts: (a) the chemisorption of 11-mercaptoundecylamine (MUA) to construct a self-assembled monolayer with the consequent protonation of the amine, and (b) the deposition of opposite charged polyelectrolytes in a sandwich fashion. The approach has the advantage that ionic attraction between opposite charges is the driving force for the multilayer buildup. For our purposes, the multilayer of polyelectrolytes depends on the quality of the surface needed for the application. In many cases, this approach will be used in a way that the roughness factor defects will be diminished. The polyelectrolytes selected for the study were: polystyrene sulfonate sodium salt (PSS), poly vinylsulfate potassium salt (PVS), and polyallylamine hydrochloride (PAH), as shown in . The deposition of polyelectrolytes was carried out by a dipping procedure with the corresponding polyelectrolyte. Monitoring of the alternate deposition of polyelectrolyte bilayers was done by surface analysis techniques such as X-ray photoelectron spectroscopy (XPS), specular reflectance infrared (IR), and atomic force microscopy (AFM). The surface analysis results are presented through the adsorption steps of the polyelectrolytes layer by layer.

Keywords: BSTO; Polyelectrolytes; Self-assemblies; XPS; Polystyrene sulfonate sodium; Polyvinylsulfate potassium; Polyallylamine hydrochloride

Effect of substrate bias voltages on the diffusion barrier properties of Zr–N films in Cu metallization by Ying Wang; Chunhui Zhao; Zhongxiao Song; Fei Cao; Dawei Yang (pp. 8858-8862).

Zr–N diffusion barriers were deposited on the Si substrates by rf reactive magnetron sputtering under various substrate bias voltages. Cu films were subsequently sputtered onto the Zr–N films by dc pulse magnetron sputtering without breaking vacuum. The Cu/Zr–N/Si specimens were then annealed up to 650°C in N₂ ambient for an hour. The effects of deposition bias on growth rate, film resistivity, microstructure, and diffusion barrier properties of Zr–N films were investigated. An increase in negative substrate bias resulted in a decrease in deposition rate together with a decrease in resistivity. It was found that the sheet resistances of Cu/Zr–N(−200V)/Si contact system were lower than those of Cu/Zr–N(−50V)/Si specimens after annealing at 650°C. Cu/Zr–N(−200V)/Si contact systems showed better thermal stability so that the Cu₃Si phase could not be detected.

Keywords: PACS; 81.07.−bDiffusion barrier; Cu metallization; Zr–N; Semiconductor

Benzotriazole as an inhibitor of brass corrosion in chloride solution by Tadeja Kosec; Ingrid Milošev; Boris Pihlar (pp. 8863-8873).

The current research explores the formation of protective layers on copper, zinc and copper–zinc (Cu–10Zn and Cu–40Zn) alloys in chloride solution containing benzotriazole (BTAH), by use of electrochemical techniques, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Electrochemical reactions and surface products formed at the open circuit potential and as a function of the potential range are discussed. The addition of benzotriazole to aerated, near neutral 0.5M NaCl solution affects the dissolution of copper, zinc, Cu–10Zn and Cu–40Zn alloys. The research also compares the inhibition efficiency and Gibbs adsorption energies of the investigated process. Benzotriazole, generally known as an inhibitor of copper corrosion is also shown to be an efficient inhibitor for copper–zinc alloys and zinc metal. The surface layer formed on alloys in BTAH-inhibited solution comprised both oxide and polymer components, namely Cu₂O and ZnO oxides, and Cu(I)-BTA and Zn(II)-BTA polymers. The formation of this mixed copper–zinc oxide polymer surface film provides an effective barrier against corrosion of both metal components in chloride solution.

Keywords: Copper; Brass; Benzotriazole; Inhibition

Surface ablation of lithium tantalate by femtosecond laser by Yishuai Zhang; Xianfeng Chen; Hongyun Chen; Yuxing Xia (pp. 8874-8878).

We report measurements of the laser induced breakdown threshold in lithium tantalate with different number of pulses delivered from a chirped pulse amplification Ti: sapphire system. The threshold fluences were determined from the relation between the diameter D² of the ablated area and the laser fluence F₀. The threshold of lithium tantalite under single-shot is found to be 1.84J/cm², and the avalanche rate was determined to be 1.01cm²/J by calculation. We found that avalanche dominates the ablation process, while photoionization serves as a free electron provider.

Keywords: Laser ablation; Femtosecond laser; Lithium tantalate

Corrosion resistance of cerium-based conversion coatings on alumina borate whisker reinforced AA6061 composite by J. Hu; X.H. Zhao; S.W. Tang; W.C. Ren; Z.Y. Zhang (pp. 8879-8884).

Cerium-based conversion coatings on Al₁₈B₄O₃₃w/6061Al composite surface were obtained by immersing the composite into a solution containing various concentrations of CeCl₃. Results indicate that the susceptibility to pitting for the conversion-coated composites was much lower than that of the untreated composite, and the corrosion resistance of the coated composites was improved markedly; moreover, the concentration of CeCl₃ in the cerium solution affects significantly the corrosion behaviors of the coated composites. The coating obtained from a solution containing 7.5g CeCl₃ into 1000ml produced better corrosion resistance on the composite due to the surface being almost covered by conversion coating. EDX and XPS experimental results indicated that the coatings were made up of oxygen, cerium, and aluminum.

Keywords: Cerium; Conversion coating; Aluminum matrix composite; Corrosion

Optical activation of patterned Si nanowires grown from sol–gel prepared gold/Er-doped aluminous film by Lingling Ren; Won young Jeung; Heon-Jin Choi (pp. 8885-8888).

Optical activation of patterned Si nanowires grown from sol–gel prepared gold/Er-doped aluminous film is investigated. The growth of patterned Si nanowires (SiNWs), the doping of Er ions and the sintered process are completed by one step. Si nanowires were grown from a sol–gel solution containing both Au catalysts and Er ions by the vapor–liquid–solid method. Such Er-activated Si nanowires achieve both high carrier-mediated excitation efficiency and high Er luminescence efficiency while at the same time providing high areal density of Er and easy current injection, indicating the possibility of activated patterned Si nanowires grown from sol–gel film as a material platform for Si-based photonics.

Keywords: Si; Nanowires; Erbium; Photoluminescence; Patterned; Vapor–liquid–solid

Synthesis and characterization of zinc oxide nanoparticles by laser ablation of zinc in liquid by R.K. Thareja; Shobha Shukla (pp. 8889-8895).

We report formation of colloidal suspension of zinc oxide nanoparticles by pulsed laser ablation of a zinc metal target at room temperature in different liquid environment. We have used photoluminescence, atomic force microscopy and X-ray diffraction to characterize the nanoparticles. The sample ablated in deionized water showed the photoluminescence peak at 384nm (3.23eV), whereas peaks at 370nm (3.35eV) were observed for sample prepared in isopropanol. The use of water and isopropanol as a solvent yielded spherical nanoparticles of 14–20nm while in acetone we found two types of particles, one spherical nanoparticles with sizes around 100nm and another platelet-like structure of 1μm in diameter and 40nm in width. The absorption peak of samples prepared in deionized water and isopropanol are seen to be substantially blue shifted relative to that of the bulk zinc oxide due to the strong confinement effect. The technique offers an alternative for preparing the nanoparticles of active metal.

Keywords: PACS; 52.38.Ph; 61.46.Df; 78.67.BfAblation; Photoluminscence; Zinc oxide; Ftir

Atomic-level investigation of Al and Ni thin film growth on Ni(111) surface: Molecular dynamics simulation by Soon-Gun Lee; Yong-Chae Chung (pp. 8896-8900).

Using molecular dynamics (MD) simulation, the structural characteristics of Al and Ni thin film growth on Ni(111) substrate according to the incident energy of adatoms were investigated. In case of Al on Ni(111), Al adatoms were grown basically through the layer-by-layer growth mode. On the other hand, Ni thin films on Ni(111) surface at low incident energy were shown to favor island growth. The steering effect due to atomic attraction, which results in rougher surface, was significantly observed at low incident energy. The growth mode of Ni film was, however, changed to follow layer-by-layer growth mode for the incident energy of 6eV. The different aspects of surface morphology between Al and Ni deposition on Ni(111) surface could be successfully explained by the surface diffusion and impact cascade diffusion.

Keywords: PACS; 31.15.Q; 68.66; 81.15.AGrowth morphology; Molecular dynamics simulation; Ni/Ni(1; 1; 1); Al/Ni(1; 1; 1)

Controlled growth and field emission properties of zinc oxide nanopyramid arrays by Hongsheng Chen; Junjie Qi; Yue Zhang; Xiaomei Zhang; Qingliang Liao; Yunhua Huang (pp. 8901-8904).

Single-crystalline, pyramidal zinc oxide nanorods have been synthesized in a large quantity on p-Si substrate via catalyst-free thermal chemical vapor deposition at low temperature. SEM investigations showed that the nanorods were vertically aligned on the substrate, with diameters ranging from 60 to 80nm and lengths about 1.5μm. A self-catalysis VLS growth mechanism was proposed for the formation of the ZnO nanorods. The field emission properties of the ZnO nanopyramid arrays were investigated. A turn-on field about 3.8V/μm was obtained at a current density of 10μA/cm², and the field emission data was analyzed by applying the Fowler–Nordheim theory. The stability of emission current density under a high voltage was also tested, indicating that the ZnO nanostructures are promising for an application such as field emission sources.

Keywords: PACS; 79.70.+q; 81.05.Dz; 81.07.Bc; 81.15.Gh; 85.45.DbField emission; Zinc oxide; Nanostructures; Chemical vapor deposition

Angular distributions of atoms sputtered from NiAl{110} and Ni{100} by Ming Tan (pp. 8905-8910).

Using the laser post-ionization surface analysis technique, I have for the first time studied angular distributions of Ni and Al atoms sputtered from NiAl{110}. Emission angular distributions from Ni{100} have also been measured. I have observed preferential emissions of Ni and Al atoms along 〈111〉 and 〈100〉crystallographic directions for NiAl{110} and of Ni atoms along 〈110〉 and 〈100〉 directions for Ni{100}. The observed preferential ejections can be explained in terms of the theory of focusing-collision sequences. Because of the difference in surface binding energy between Al and Ni atoms, preferential ejection angles of Ni atoms are slightly different from those of Al atoms along the 〈111〉 ejections. For NiAl, the 〈111〉 preferential ejections were less prominent than the 〈100〉 preferential ejections and this can be related to the low efficiency of momentum transfer in Ni–Al collision sequences along 〈111〉 lattice directions. The low efficiency of momentum transfer due to the mass mismatch can also be responsible for the experimental observation that the preferential ejections in the alloy were less prominent than those in the Ni metal.

Keywords: PACS; 79.20.Rf; 68.47.De; 32.80.FbAngular distribution; Sputtered atoms; Alloy; single crystal

Effects of annealing on laser-induced damage threshold of TiO₂/SiO₂ high reflectors by Jianke Yao; Jianda Shao; Hongbo He; Zhengxiu Fan (pp. 8911-8914).

The mechanism of improving 1064nm, 12ns laser-induced damage threshold (LIDT) of TiO₂/SiO₂ high reflectors (HR) prepared by electronic beam evaporation from 5.1 to 13.1J/cm² by thermal annealing is discussed. Through optical properties, structure and chemical composition analysis, it is found that the reduced atomic non-stoichiometric defects are the main reason of absorption decrease and LIDT rise after annealing. A remarkable increase of LIDT is found at 300°C annealing. The refractive index and film inhomogeneity rise, physical thickness decrease, and film stress changes from compress stress to tensile stress due to the structure change during annealing.

Keywords: PACS; 42.79.Wc; 68.37.Yz; 68.55.Nq; 68.60.WmAnnealing; TiO; ₂; /SiO; ₂; High reflectors; Absorption; Laser damage; X-ray photoelectron spectroscopy

Immobilization/hybridization of amino-modified DNA on plasma-polymerized allyl chloride by Zhi Hong Zhang; Chuan Liang Feng (pp. 8915-8922).

The present work describes the fabrication and characterization of chloride-derivatized polymer coatings prepared by continuous wave (cw) plasma polymerization as adhesion layers in DNA immobilization/hybridization. The stability of plasma-polymerized allyl chloride (ppAC) in H₂O was characterized by variation of the thickness of polymer films and its wettability was examined by water contact angle technique. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to study polymer matrix properties and oligonucleotide/DNA binding interaction. With the same carrier gas rate and process pressure, plasma polymers deposited at different input powers show various comparable immobilization properties; nevertheless, low input power plasma-polymerized films gives a lower sensitivity toward DNA binding than that from high input power plasma-deposited films. The following DNA immobilization on chloride-functionalized surfaces was found dependence on the macromolecular architecture of the plasma films. The hybridization between probe DNA and total mismatch target DNA shows no non-specific adsorption between target and ppAC.

Keywords: Plasma polymerization; Allyl chloride; DNA immobilization/hybridization; XPS

Growth and field emission of tungsten oxide nanotip arrays on ITO glass substrate by Kai Huang; Qingtao Pan; Feng Yang; Shibi Ni; Deyan He (pp. 8923-8927).

High-density and uniformly aligned tungsten oxide nanotip arrays have been deposited by a conventional thermal evaporation on ITO glass substrates without any catalysts or additives. The temperature of substrate was 450–500°C. It was shown that the tungsten oxide nanotips are single-crystal grown along [010] direction. For commercial applications, field emission of the tungsten oxide nanotip arrays was characterized in a poor vacuum at room temperature. The field emission behaviors are in agreement with Fowler–Nordheim theory. The turn-on field is 2.8Vμm⁻¹ as d is 0.3mm. The excellent field emission performances indicated that the tungsten oxide nanotip arrays grown by the present approach are a good candidate for application in vacuum microelectronic devices.

Keywords: PACS; 81.07.−b; 81.10.−h; 79.70.+qTungsten oxide; Nanotip arrays; Field emission

Effects of ion damage on the surface of ITO films during plasma treatment by Hyunjung Shin; Chanhyung Kim; Changdeuck Bae; Jang-Sik Lee; Jaegab Lee; Sunghan Kim (pp. 8928-8932).

During a surface treatment using CF₄/O₂ gas plasma, energetic ions affected the defect structures on the top surface of ITO thin films. C-AFM and local I– V measurements showed the formation of the depleted layer after a plasma treatment with a bias of 20W; XPS showed the creation of new defect structures. Donor concentration in the damaged top surface of the ITO films was found to be decreased. Sn-based neutral defect complexes and reduced oxygen, which could trap the electrons, have been proposed to be formed. This can also explain the increase of the work function of ITO.

Keywords: Ion damage; ITO; Conducting atomic force microscopy

Optical second harmonic generation from Pt nanowires by N. Hayashi; K. Aratake; R. Okushio; T. Iwai; A. Sugawara; H. Sano; G. Mizutani (pp. 8933-8938).

We have measured optical second harmonic intensity from arrays of Pt nanowires of 20nm and 9nm average widths, as a function of the incident and output light polarizations, the azimuthal angle, and the excitation photon energy. The nanowires were fabricated through shadow deposition on self-organized NaCl(110) faceted templates. The anisotropy of the SH intensity from the Pt nanowires was found to be stronger than that from the Au nanowires reported previously. The effective nonlinear susceptibility elementχ222(2), with the suffix 2 indicating the direction[11¯0], was observed for Pt nanowires, although it was not observed for Au nanowires. This difference is suggested to be due to the weaker suppression of the incident fundamental fields by the depolarization field in the Pt nanowires and the larger anisotropy in the nonlinearity of Pt nanowires due to the thinner widths.

Keywords: PACS; 78.66.Bz; 42.65.KyOptical second harmonic generation; Nanowire; Pt; NaCl

Tensile property of H13 die steel with convex-shaped biomimetic surface by Z.H. Zhang; H. Zhou; L.Q. Ren; X. Tong; H.Y. Shan; Y. Cao (pp. 8939-8944).

The H13 steel specimens with non-smooth surface were fabricated by biomimetic method and laser technique, and the effect of these biomimetic surfaces on the tensile properties was investigated. The results indicated that the biomimetic surface has an advantageous effect on improving the tensile properties of H13 steel. As the area ratio occupied by non-smooth units on the biomimetic surface grows to 26.7%, the ultimate tensile strength (UTS) and 0.2% yield strength (YS) of materials linearly increase by about 8.4% and 17.2%, respectively. The elongation to fracture of materials reaches to the peak value of about 41.3% at the point of 17.1% area ratio, and further heightening the area ratio can result in a reduced ductility relative to this peak value. This improvement of tensile properties can be attributed to the combined effects of the microstructure characteristics within the unit zone and the unit-distribution features on the surface. Meanwhile, the regressed relation equations of UTS, YS and elongation regarding the area ratio were obtained via statistical theory. The tests of regression significance showed that the confidence of these equations achieved 99% above.

Keywords: PACS; 81.05.−t; 81.40.Lm; 87.68.+zBiomimetic surface; Tensile property; H13 steel; Laser

Surface modification of multi-walled carbon nanotubes by O₂ plasma by Tao Xu; Jinghui Yang; Jiwei Liu; Qiang Fu (pp. 8945-8951).

The surface modification of multi-walled carbon nanotubes (MWCNTs) by O₂ plasma was carried out in this study. In order to achieve a relatively homogeneous treatment of MWCNTs powder, a rotating barrel fixed between the two discharge electrodes was used. The effect of plasma treatment parameters, such as power, time, and positions of samples (inside and outside the barrel), on the morphology and structure of MWCNTs surface was systematically analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that the direct discharge (outside the barrel) could result in not only a quick grafting of polar functional groups but also an easy damage of MWCNTs after longer time, particularly under intensive power. It was found that the surface of MWCNTs powder might be changed in three steps—expansion (loosed structure formed), peel off and oxidization with increasing of treatment time during the irradiation. In this way, a complete purification of MWCNTs powder could be finished within 30min via plasma treatment. Our work suggested that plasma treatment could be a simple and nonpolluting method for a large scale purification of MWCNTs.

Keywords: Multi-walled carbon nanotubes; Plasma; Purification

Spectroscopic studies of interfacial structures of CeO₂–TiO₂ mixed oxides by Jun Fang; Xinzhen Bi; Dejun Si; Zhiquan Jiang; Weixin Huang (pp. 8952-8961).

We have investigated the geometric and electronic structures of the cerium oxide (CeO₂)–titanium dioxide (TiO₂) mixed oxides with various Ce/TiO₂ weight ratios prepared by the sol–gel method in detail by means of X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (XPS), Raman spectroscopy excited by 325 and 514.5nm lasers, and scanning electron microscope (SEM). Existence of cerium effectively inhibits the phase transition of TiO₂ from the anatase phase to the rutile phase. XRD peaks of TiO₂ anatase attenuate continuously with the increasing amount of CeO₂ in the mixed oxide, but the XRD peaks of cubic CeO₂ appear only after the weight ratio of Ce/TiO₂ reaches 0.50. The average crystalline sizes of TiO₂ anatase and cubic CeO₂ in CeO₂–TiO₂ mixed oxides are smaller than those in the corresponding individual TiO₂ anatase and cubic CeO₂. Raman spectroscopy excited by the 514.5nm laser detects CeO₂ after the weight ratio of Ce/TiO₂ reaches 0.70 whereas Raman spectroscopy excited by the 325nm laser detects CeO₂ after the weight ratio of Ce/TiO₂ reaches 0.90. XPS results demonstrate that Ti exists in the form of Ti⁴⁺ in the CeO₂–TiO₂ mixed oxide. Ce is completely in the form of Ce³⁺ in the mixed oxides with a 0.05 weight ratio of Ce/TiO₂. With the increasing weight ratio of Ce/TiO₂, Ce⁴⁺ dominates. On basis of these results, we proposed that CeO₂ initially nucleates at the defects (oxygen vacancies) within TiO₂ anatase, forming an interface bridged with oxygen between CeO₂ and TiO₂ anatase. At the interface, Ce species cannot substitute Ti⁴⁺ in the lattice of TiO₂ anatase whereas Ti⁴⁺ can substitute Ce⁴⁺ in the lattice of cubic CeO₂. The decreasing concentration of oxygen vacancies, the Ti–O–Ce interface, and the decreasing average crystalline size of TiO₂ anatase act to inhibit the phase transformation of TiO₂ anatase. With the increasing amounts of CeO₂, the CeO₂ clusters continuously grow and form cubic CeO₂ nanocrystals. Spectroscopic results strongly demonstrate that the surface region of CeO₂–TiO₂ mixed oxide is enriched with TiO₂.

Keywords: CeO; ₂; –TiO; ₂; mixed oxides; Interfacial structure; Spectroscopic techniques

Selective electroplating of copper lines on pre-patterned tantalum oxide thin films by H. El-Sayed; M.T. Greiner; P. Kruse (pp. 8962-8968).

Direct selective metal deposition on semiconductors is of interest to electronic device technology, in particular for interconnects and Schottky devices. In this study, we investigate selective copper electrodeposition on patterned tantalum oxide thin films. Cyclic voltammetry studies show that thick tantalum oxide thin films have insulating properties while oxide films thinner than a critical value are semiconductors. Copper films electrodeposited on tantalum oxide thin films are known to form Schottky contacts. We demonstrate the formation of copper patterns on pre-patterned tantalum oxide films by a simple process: an insulating tantalum oxide film was grown electrochemically, the film was then mechanically scratched followed by mild oxidation to produce a thin tantalum oxide film inside the scratch. Based on the differential behavior of thin and thick tantalum oxide films, metal lines were electrodeposited selectively under formation of Schottky junctions. The process demonstrated in this paper is compatible to standard processes for semiconductor device fabrication while permitting flexible prototyping for research at small scales.

Keywords: PACS; 61.46.−w; 68.37.Hk; 68.47.Gh; 68.55.−a; 81.15.Pq; 81.16.Nd; 82.45.Cc; 82.80FkElectroplating; Lithography; Copper; Tantalum oxide

Surface chemistry and optimization of focused ion beam iodine-enhanced etching of indium phosphide by Victor Callegari; Philipp M. Nellen; Tianhe Yang; Roland Hauert; Ulrich Müller; Francisco Hernández-Ramírez; Urs Sennhauser (pp. 8969-8973).

Focused ion beam physical sputtering and iodine-enhanced etching of indium phosphide (InP) were performed. Up to 15× enhanced etching rates over sputtering were measured at room temperature, due to the addition of iodine to the sputter-process. Reaction mechanisms and products are discussed and characterized. The reaction is limited by the desorption of indium triiodide (InI₃) at room temperature. InI₃ has to be removed by sputtering, which simultaneously amorphizes the underlying substrate. Surface roughness and stoichiometry of InP are compared for sputtering and etching. Gallium-contamination and the damaged zone in InP are significantly reduced by iodine-enhanced etching. Based on the reaction mechanisms, an optimum beam scanning strategy is proposed which allows precise microfabrication in reduced time and minimizes damage to the substrate. The method is also applicable for other halide gas etching processes of III–V semiconductors.

Keywords: PACS; 79.20.Rf; 81.65.Cf; 82.40.−g; 82.65.+rFocused ion beam; Indium phosphide; Sputtering rate; Gas-enhanced etching; Beam scanning strategy

CO adsorption on MgO, CaO and SrO crystals periodic Hartree–Fock calculations by W.S. Abdel Halim (pp. 8974-8980).

The adsorption of carbon monoxide at the defect-free (100), (110) and (210) five-atomic layer slab of the three oxides: MgO, CaO, and SrO has been investigated using the periodic Hartree–Fock level of ab initio theory, together with the 1×1 supercell model. All the calculated CO/oxide interaction energies exhibit exothermic character. The HF interaction energies increase monotonically in the order MgO

Keywords: Ab initio; Alkaline-earth oxides; Adsorption; CO

Effects of NH₃, O₂, and N₂ co-implantation on Cu out-diffusion and antimicrobial properties of copper plasma-implanted polyethylene by Wei Zhang; Junhui Ji; Yihe Zhang; Qing Yan; E.Z. Kurmaev; A. Moewes; Jun Zhao; Paul K. Chu (pp. 8981-8985).

Metal antibacterial reagents are effective in the enhancement of the antimicrobial properties of medical polymers. However, incorporation of metal antibacterial reagents into polymers using conventional methods usually results in unstable antimicrobial effects. Our previous research demonstrates that plasma immersion ion implantation (PIII) can be used to effectively incorporate metal antibacterial reagents such as Cu into polyethylene (PE) in the near surface region up to several hundred nanometers without causing noticeable damage to the polymer matrix. In this work, various gases including NH₃, O₂, and N₂ were plasma-implanted in concert with Cu plasma immersion ion implantation to study the effects of these gas species on the release rate of Cu from the substrate. Our experimental results reveal that the copper depth profiles are not affected significantly by NH₃, O₂, or N₂ co-implantation and these gas elements have similar depth profiles as Cu. Chemical analyses demonstrate that polar functional CO, CO, CN, CN, and CN bonds formed in the substrate play an important role in regulating Cu out-diffusion. Among the three gas species, N₂ shows the best effects in regulating Cu out-diffusion and produces the best long term antibacterial properties. The Cu retention and out-diffusion mechanism in the ion-implanted polyethylene is described.

Keywords: PACS; 82.35.-x Polymers: properties; Reactions; polymerization; 52.25.-b Plasma properties; 87.15.-v Biomolecules: structure and physical propertiesAntimicrobial; Plasma immersion ion implantation; Copper; Polyethylene

Effect of sulfide pollution on the stability of the protective film of benzotriazole on copper by F.M. Al Kharafi; A.M. Abdullah; I.M. Ghayad; B.G. Ateya (pp. 8986-8991).

Benzotriazole (BTAH) is an excellent inhibitor for the corrosion of copper and many of its alloys in unpolluted media. Protection is attributed to the formation of a film of Cu(I)BTA. Injection of sulfide ions into a benzotriazole inhibited salt water damages the protective Cu(I)BTA film very rapidly, increases the corrosion rate and leads to the formation of copper sulfide. This effect is quite marked at a sulfide concentration as low as 10⁻⁵M (about 0.3ppm sulfur) in the presence of 10⁻²M BTAH, which is 1000-fold greater than that of the sulfide ion. The intensity of sulfide attack increases with its concentration.Prolonged pre-passivation of copper in the BTAH protected medium even at high concentration does not markedly improve the resistance of the protective film to sulfide attack. This finding is contrary to a well-documented phenomenon in unpolluted media where the inhibiting efficiency of BTAH increases with the time of immersion and the concentration of the inhibitor. X-ray photoelectron spectroscopy (XPS) reveals the presence of both sulfide and BTAH on the corroded surface indicating that sulfide attack is localized.

Keywords: PACS; 82.45.Bb; 81.65.KnCorrosion; Inhibitor; Copper; Benzotriazole; Sulfide

Effects of electron-beam irradiation on surface oxidation of polymer composites by Marian Żenkiewicz; Marta Rauchfleisz; Joanna Czupryńska; Julian Polański; Tomasz Karasiewicz; Włodzimierz Engelgard (pp. 8992-8999).

The aim of this article was to show the effects of an electron radiation dose and presence of a compatibilizer on the oxidation of composites made of blends of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET) as well as of blends of LDPE, HDPE, and PP. As the compatibilizers, the styrene-ethylene/butylene-styrene elastomer grafted with maleic anhydride (SEBS- g-MA) and trimethylol propane trimethylacrylate (TMPTA) were used; they were added in the amounts of 5, 10, and 15wt% and 1, 2, and 3wt%, respectively. The oxidation of the surface layer (SL) was investigated by the X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). It was found that the extent of the composite oxidation increased with the increasing dose of the electron radiation. The addition of the compatibilizers enhanced the oxidation of the SL but hindered the oxidation of the bulk of the material.

Keywords: PACS; 81.05.Lg; 81.40.Wx; 81.65.Mg; 82.35.GhPolymer composites; Electron-beam irradiation; XPS; FTIR; Recycling

Friction and wear of rare earths modified carbon fibers filled PTFE composite under dry sliding condition by Shangguan Qian-qian; Cheng Xian-hua (pp. 9000-9006).

Carbon fibers (CF) were surface treated with air-oxidation and rare earths (RE), respectively. The friction and wear properties of polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under dry sliding condition, were investigated on a block-on-ring M-2000 tribometer. Experimental results revealed that RE treatment largely reduced the friction and wear of CF reinforced PTFE (CF/PTFE) composites. The RE treated composite exhibited the lowest friction and wear under dry sliding. Scanning electron microscopy (SEM) investigation of worn surfaces and transfer films of CF/PTFE composites showed that RE treated CF/PTFE composites had the smoothest worn surface under given load and sliding speed, and a continuous and uniform transfer film formed on the counterface. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RE treatment, and more carboxyl groups were introduced onto CF surfaces after RE treatment. The increase in the amount of oxygen-containing groups increased the interfacial adhesion between CF and PTFE matrix, and accordingly increased the tribological properties of the composite.

Keywords: PTFE composite; Carbon fiber; Rare earths; Friction and wear; Surface treatment

Electrical discharge machining of titanium alloy (Ti–6Al–4V) by Ahmet Hasçalık; Ulaş Çaydaş (pp. 9007-9016).

In this study, the electrical discharge machining (EDM) of titanium alloy (Ti–6Al–4V) with different electrode materials namely, graphite, electrolytic copper and aluminium and process parameters such as, pulse current and pulse duration were performed to explore the influence of EDM parameters on various aspects of the surface integrity of Ti6Al4V. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and hardness analysis were performed. The experimental results reveal that the value of material removal rate, surface roughness, electrode wear and average white layer thickness are tendency of increase with increasing current density and pulse duration. However, extremely long-pulse durations such as 200μs led to decrease MRR and surface roughness. Furthermore, the surface hardness is increasing due to the Ti₂₄C₁₅ carbides formed on the surface and obvious cracks are always evident in re-solidified layer when machining copper electrode. The surface crack densities and critical crack lines were determined for the tested material. The graphite electrode is beneficial on material removal rate, electrode wear and surface crack density but relatively poorer surface finish.

Keywords: EDM; Ti alloy; Non-traditional machining; Surface quality; Electrode material

Surface oxidation behavior of MgNd alloys by X.M. Wang; X.Q. Zeng; G.S. Wu; S.S. Yao; L.B. Li (pp. 9017-9023).

The oxidation kinetics of MgNd alloys oxidized in pure O₂ at high temperatures has been investigated. The results revealed two stages of the reaction: A fast initial oxidation was followed by a slow oxide growth with a parabolic kinetics. For MgNd alloys (Nd=25wt.%), the oxidation rate increased with the enhancement of the oxidation temperature. A sudden ignition was found for this alloys oxidized at 873K up to about 80min. Moreover, the increase of the Nd content would harm the oxidation resistance of the MgNd alloys. By Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, it was found that a triplex structure of oxide film formed. The outer layer was composed of MgO, Nd₂O₃ and Nd(OH)₃, the middle layer mainly consisted of MgO and Nd₂O₃, and the inner layer was the transitional layer made of MgO, Nd₂O₃ and the content of the substrate. The protective oxidation was associated with the formation of the dense Nd₂O₃/MgO layer during isothermal oxidation process. The oxidation mechanisms for the formation of oxide film are discussed.

Keywords: MgNd alloys; Oxidation; Auger electron spectroscopy (AES); X-ray photoelectron spectroscopy (XPS)

Simultaneous determination of thermal conductivities of thin film and substrate by extending 3ω-method to wide-frequency range by Zhao Liang Wang; Da Wei Tang; Xing Hua Zheng (pp. 9024-9029).

A technique using 3ω-method with a wide-frequency range from 0.5Hz to 0.5MHz was developed to determine simultaneously the thermal conductivities of individual layers in a two-layered structure. The technique utilizes 3ω measurements in high and low frequency ranges separately. To evaluate the validity and accuracy of the technique, we performed measurements on a double-layered specimen consisting of a SiO₂-film on a Si-substrate, and found that the measured conductivities of both the film and substrate agree well with literature values. Uncertainty analysis was given finally. This new technique overcomes a critical shortcoming of conventional techniques, which cannot measure the thermal conductivity of both film and substrate simultaneously.

Keywords: PACS; 0720; 4450; 6500; 68603ω-Method; Thermal conductivity; Film/substrate structure; Critical frequency

Preparation, characterization, and property of polyaniline/Prussian blue micro-composites in a low-temperature hydrothermal process by Xiaoli Zhang; Chunhong Sui; Jian Gong; Rui Yang; Yunqing Luo; Lunyu Qu (pp. 9030-9034).

Polyaniline/Prussian blue micro-composites have been synthesized by a low-temperature hydrothermal process. Prussian blue is obtained using the single iron-source precursor K₃[Fe(CN)₆] in acidic aqueous solution. The composite was characterized by field-emission scanning electron microscopy (FE-SEM), Fourier transmission infrared spectroscopy (FT-IR), and X-ray diffractometer (XRD). The magnetic behavior of polyaniline/Prussian blue composites and the effect of the concentration of K₃[Fe(CN)₆] on the morphology of polyaniline/Prussian blue micro-composites have been investigated.

Keywords: Polyaniline; Prussian blue; Magnetic properties

Fabrication of large-scale periodic silicon nanopillar arrays for 2D nanomold using modified nanosphere lithography by Wei Li; Ling Xu; Wei-Ming Zhao; Ping Sun; Xin-Fan Huang; Kun-Ji Chen (pp. 9035-9038).

We present a fabrication procedure that can form large-scale periodic silicon nanopillar arrays for 2D nanomold which determines the feature size of nanoimprint lithography, using modified nanosphere lithography. The size of silicon nanopillars can be easily controlled by an etching and oxidation process. The period and density of nanopillar arrays are determined by the initial diameter of polystyrene (PS) spheres. In our experiment, the smallest nanopillar has a full width half maximum (FWHM) of approximately 50nm, and the density of silicon pillar is ∼10⁹/cm². Using this approach, it is possible to fabricate 2D nanoimprint lithography mask with 50nm resolution.

Keywords: Silicon nanopillar; Modifiled nanosphere lithography

Spin-deposited nanocrystalline lithium ferrite thin films: Fabrication and characterization by Nutan Gupta; Subhash C. Kashyap; D.C. Dube (pp. 9039-9045).

Thin films of lithium ferrite (with general composition Li_0.5Fe_2.5O₄) were fabricated at low temperatures (up to 650°C) by citrate-route using spin-deposition technique. Deposited films consisted of nanometer-sized grains as evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD patterns for annealed films showed broad peaks exhibiting a spinel phase. Size of nanocrystallites is estimated to be 3–7nm using Scherrer's equation. Average grain size ∼8.5nm is observed from TEM images of films annealed at 650°C. Scanning electron micrographs show the formation of spherical aggregates of around 130nm in diameter. The AFM analysis clearly evidenced the development of nanograins even at low (∼500°C) annealing temperatures. Significant decrease in complex dielectric permittivity ( ∈′−j ∈″) with frequency is observed in the low frequency (100Hz–1MHz) as well as in X-band microwave frequency (8–12GHz) region. ∈′ is found to be in the range of 15.7–33.9 in low frequency region, whereas in X-band microwave frequency region, it is found to lie between 3.9 and 4.9. Similarly, ∈″ is found to be 0.16–5.9 in the low frequency region, and 0.002–0.024 in the X-band microwave frequency region. Room temperature dc resistivity of these films is estimated to lie in the range of 10⁶–10⁸Ωcm. These results strongly suggest that citrate-route processed nanocrystalline lithium ferrite thin films are promising candidates for monolithic microwave integrated circuits (MMICs).

Keywords: PACS; 67.70.+n; 78.70.Gq; 81.15.−zLithium ferrite; Spin-deposition; Nanocrystalline; Thin films; AFM; Dielectric behavior; Microwave behavior

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Applied Surface Science (v.253, #22)

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Applied Surface Science (v.253, #22)