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Applied Surface Science (v.256, #13)

Publisher Note (pp. 4053-4053).

Gap states at organic–metal interfaces: A combined spectroscopic and theoretical study by Shigeru Masuda (pp. 4054-4064).

A systematic understanding and controlling of gap states formed at the organic–metal interfaces is a key factor for fabricating functional organic–metal systems, as in case of heterojunctions in semiconductor devices. We report here the characterization of gap states near the Fermi level of metal substrate by metastable atom electron spectroscopy and first-principles density functional calculations. The gap states in organic–metal systems are classified into two types, i. e., chemisorption-induced gap states (CIGSs) and complex-based gap states (CBGSs). CIGSs can be further classified whether the metal wave function tails a short distance into the chemisorbed species with the exponential decay (damping type) or is exposed sufficiently to the chemisorbed species by mixing with the organic orbitals (propagating type). CIGSs observed in alkanethiolate and C₆₀ on Pt(111) are their typical examples, respectively. As a consequence, alkanethiolate serves as a poor mediator of metal wave function, whereas C₆₀ acts as a good mediator, which is responsible for tunneling mechanism and eventually electric conductivity in the relevant metal–organic–metal junctions. CBGSs are identified in bathocuproine films deposited on K-covered Au, where the K atoms migrate into the film to form an organic–metal complex. The CBGSs are distributed over the multilayer film, in contrast to the case of CIGS. With increasing film thickness, the CBGSs exhibit incommensurate energy shifts with the valence band top of the film, indicating that the Schottky-Mott model breaks down as evaluating charge transport in organic–metal systems.

Keywords: Organic–metal interface; Gap state; Metastable atom electron spectroscopy; Ultraviolet photoemission spectroscopy; First principles calculation; Alkanethiol; Benzenethiol; C; ₆₀; Bathocuproine

Structural, optical and electrochemical properties of TiO₂ thin films grown by APCVD method by C. Quiñonez; W. Vallejo; G. Gordillo (pp. 4065-4071).

Atmospheric pressure chemical vapor deposition (APCVD) of TiO₂ thin films has been achieved onto glass and onto ITO-coated glass substrates, from the reaction of TiCl₄ with ethyl acetate (EtOAc). The effect of the synthesis temperature on the optical, structural and electrochemical properties was studied through spectral transmittance, X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) measurements. It was established that the TiO₂ films deposited onto glass substrate, at temperatures greater than 400°C grown with rutile type tetragonal structure, whereas the TiO₂ films deposited onto ITO-coated glass substrate grown with anatase type structure. EIS was applied as suitable method to determine the charge transfer resistance in the electrolyte/TiO₂ interface, typically found in dye-sensitized solar cells.

Keywords: TiO; ₂; APCVD; Electrochemical properties; Optical properties; Structural properties; DSSC

Grease-lubricated tribological behaviour of nitrided layer on 2Cr13 steel in vacuum by Jianqun Yang; Yong Liu; Zhuyu Ye; Dezhuang Yang; Shiyu He; Xinlei Li (pp. 4072-4080).

Tribological behaviour of the nitrided layer sliding against self-mating under dry sliding and grease-lubricated conditions in vacuum was investigated on a pin-on-disk type tribometer, with the interaction among the nitrided layer and grease being focused on. The morphologies of the worn surfaces were observed by scanning electron microscopy (SEM). The chemical states of typical elements on the worn surfaces of the nitrided disks and pins were examined by means of X-ray photoelectron spectroscopy (XPS). The chemical compositions of grease samples taken from worn surfaces on the nitrided disks were analysed by Fourier transform infrared spectroscopy (FTIR). Experimental results show that under grease-lubricated conditions, the nitrided layer exhibits lower average friction coefficient and higher wear resistance than those for the dry sliding. In the former case, the wear of nitrided layer shows a transition from the mild adhesive to the severe adhesive wear and even to the delamination wear, with increasing normal load from 10 to 90N. In the latter case, a transition takes place from the mild abrasive wear to the micro-fatigue type one with increasing the normal load. Tribochemical reactions occur between the nitrided layer and perfluoropolyalkyl ether (PFPE) grease during the lubricated sliding of the nitrided disks against self-mating in vacuum.

Keywords: Nitrided layer; PFPE grease; Vacuum; Wear mechanism; Tribochemical reactions

Theoretical calculation of the temperature coefficient of surface excess entropy of pure liquid metals by Ahmed H. Ayyad (pp. 4081-4083).

The temperature coefficient of surface excess entropy d S_s/d T of pure liquid metals (Al, Ga and Bi) has been calculated in the framework of Skapski's nearest-neighbor interaction-broken-bond model. It is found that this coefficient varies by 47.2%, 69% and 85% for pure liquids Al, Bi and Ga, respectively, in the temperature range between the melting temperature T_m and T_m+400K. The value of the coefficient for pure liquid Ga is an order of magnitude larger than that of Al and Bi. The largest increase in d S_S/d T with temperature occurs in the first 100K away from T_m, being the largest for liquid Ga which is about 43%. This variation is experimentally inaccessible and therefore lacking in the literature and has never been reported.

Keywords: Liquid metals; Surface excess entropy; Temperature coefficient

Lateral manipulation of small clusters on the Cu and Ag(111) surfaces with the single-atom and trimer-apex tips: Reliability study by Yi-Qun Xie; Fen Liu; Lei Huang (pp. 4084-4088).

We study the reliability of the lateral manipulation of small Cu clusters (dimer and trimer) on the flat Cu(111) surface with both the single-atom and trimer-apex tips and that for the Ag/Ag(111) system, and compare the results between the two systems as well as with the single-atom manipulation on these surfaces. Manipulations are simulated using molecular statics method with semi-empirical potentials. The dependence of the manipulation reliability on the tip height and tip orientation are investigated. Overall, the manipulation reliability increases with decreasing tip height although it depends obviously on the tip orientation. For the Cu/Cu(111) system, the manipulation of the dimmer and trimer can be successful with both tips. The manipulation reliability can be improved by the trimer-apex tip, and the tip-height range for the successful manipulation is also broader, as compared to the single-atom apex tip. Differently from the single-atom manipulation, the tip orientation has a noticeable influence on the manipulation reliability even for the single-atom tip due to the stronger tip–cluster and surface–adatom interactions in cluster manipulation. For the Ag/Ag(111) system, successful manipulations only be achieved with the trimer-apex tip, and the manipulation reliability is worse than that of the Cu/Cu(111) system, indicating the difference in mechanic properties between the two surfaces at the atomic level.

Keywords: Lateral atom manipulation; Single crystal surface; Adatom; Silver; Copper; Computing simulations

Corrosion behavior and composition analysis of chromate passive film on electroless Ni-P coating by Songlin Mu; Ning Li; Deyu Li; Liying Xu (pp. 4089-4094).

A passive film was formed on electroless Ni-P coating (ENPC) in a bath of K₂Cr₂O₇ 30g/l. XPS and electrochemical methods were employed to analyze its chemical compositions and corrosion behaviors. The potentiodynamic polarization tests indicated the corrosion current of the passivated sample was 1/30 that of as-plated ENPC. The XPS analysis illustrated the film comprised Cr, Ni and O. The film thickness was evaluated to be a few nanometers according to the sputtering rate of Ar⁺ ion. High-resolution XPS spectra suggested that the detected Cr in film was in the form of trivalent compounds, Cr₂O₃ and Cr(OH)₃.

Keywords: Passive film; Electroless Ni-P coating; Corrosion behaviors; XPS analysis

Facile preparation of super-hydrophobic and super-oleophilic silica film on stainless steel mesh via sol–gel process by Hao Yang; Pihui Pi; Zhi-Qi Cai; Xiufang Wen; Xibo Wang; Jiang Cheng; Zhuo-ru Yang (pp. 4095-4102).

A super-hydrophobic and super-oleophilic silica film on stainless steel mesh was obtained by simple sol–gel method using tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) as precursors. The super-hydrophobic and super-oleophilic properties were achieved owing to the hierarchical structure of the silica film with methyl groups terminated domains constructed on the mesh. The effects of the particle size, molar ration of MTES/TEOS, molar concentration of TEOS and aging of the silica sol on the hydrophobicity of the silica film were discussed. With increasing the dimensional size of silica particle, molar ration of MTES/TEOS, molar concentration of TEOS and aging period, the hydrophobicity of the silica film can be enhanced due to the increase of the surface roughness or coverage of the methyl groups. Besides, diiodomethane droplet can spread out on the silica film within 6.71s for the capillary force and intrinsic oleophilicity of the methyl groups.

Keywords: Super-hydrophobic; Super-oleophilic; Silica film; Sol–gel process; Sol stability

Influence of absorbed moisture on desizing of poly(vinyl alcohol) on cotton fabrics during atmospheric pressure plasma jet treatment by Shujing Peng; Xiulan Liu; Jie Sun; Zhiqiang Gao; Lan Yao; Yiping Qiu (pp. 4103-4108).

This paper studies the influence of moisture absorption of cotton fabrics on the effectiveness of atmospheric pressure plasma jet (APPJ) on desizing of polyvinyl alcohol (PVA). Cotton fabrics with three different moisture regains (MR), namely 1.8%, 7.3%, and 28.4% corresponding to 10%, 65%, and 98% of relative humidity respectively, are treated for 16s, 32s, 48s, and 64s. X-ray photoelectron spectroscopy analysis indicates that the plasma treated PVA has higher oxygen concentration than the control. Mass loss results show that the fabric with the highest MR has the largest mass loss after 64s plasma exposure. Solubility measurement reveals that the sample with the lowest MR has the highest desizing efficacy and the percent desizing ratio reaches 96% after 64s exposure plus a 20min hot wash, which is shown as clean as the unsized sample through scanning electron microscopy analysis. The yarn tensile strength test results show that APPJ has no negative effect on fabric tensile strength.

Keywords: Atmospheric pressure plasma jet; Polyvinyl alcohol; Desizing; Moisture; SEM; XPS

Synthesis and magnetic properties of Cu-coated Fe composite nanoparticles by Xia Zhang; Baosheng Wang; Xinxin Xu (pp. 4109-4113).

The Fe/Cu nanocomposites with iron as core and copper as shell have been successfully synthesized by a two-step reduction method. A spherical nanoparticle of γ-Fe was first fabricated by the reduction of ferrous chloride, and then the Fe particle was coated by nanocrystalline Cu through the reduction of copper sulfate. The thickness of copper shell has been tuned by varying the initial concentration of copper sulfate. The morphology, crystalline structure, chemical composition and magnetic properties of the products were investigated by using transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). It was found that the saturation magnetization ( M_s) values of the Fe/Cu core–shell particles are varied owing to the different thickness of copper layer. Though the M_s value of the Fe/Cu nanocomposite is lower than that of pure iron nanoparticles, the higher M_s value (22.411emu/g) of the Fe/Cu composites is also investigated. The result of the thermogravimetric analysis (TGA) showed the enhanced antioxidation capacity of the Fe/Cu nanocomposites. This kind of nanocomposites combined the excellent magnetism of iron and the electronic, thermal conductivity of copper, suggesting potential application as a novel electromagnetic material.

Keywords: Iron; Copper; Core–shell structure; Magnetic material; Thermal stability

Growth and characterization of thin ZnO films deposited on glass substrates by electrodeposition technique by T. Mouet; T. Devers; A. Telia; Z. Messai; V. Harel; K. Konstantinov; I. Kante; M.T. Ta (pp. 4114-4120).

Electrodeposition technique was used in order to produce nanometric zinc oxide films on glass insulating substrates. The effect of electrolyte concentration and applied current density on the formation and growth of electrodeposited Zn thin films in aqueous solutions of ZnSO₄ were studied. After a thermal oxidation, a characterization of the structural morphology of the films deposited was carried out by optical microscopy (OM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and by grazing incidence X-rays diffraction (GIXD). These characterization techniques show that the grains size of the films after oxidation at temperature 450°C is between 5 and 15nm, as well as the structure is polycrystalline nature with several orientations. UV/vis spectrophotometry confirms that it is possible to obtain transparent good ZnO films with an average transmittance of approximately 80% within the visible wavelength region, as well as the optical gap of obtained ZnO films is 3.17eV.

Keywords: Electrodeposition; ZnO; Dendritic deposits; Thin film; Nanostructure

Improving the electrical conductivity of CuCrO₂ thin film by N doping by Guobo Dong; Ming Zhang; Xueping Zhao; Hui Yan; Chunyu Tian; Yonggang Ren (pp. 4121-4124).

N-doped CuCrO₂ thin films were prepared by using radio frequency magnetron sputtering technique. The XRD and XPS measurements were used to confirm the existence of the N acceptors in CuCrO₂ thin films. Hall measurements show the p-type conduction for all films. The electrical conductivity increases rapidly with the increase in N doping concentration, and the maximum of the electrical conductivity of 17Scm⁻¹ is achieved for the film deposited with 30vol.% N₂O, which is about three orders of magnitude higher than that of the undoped CuCrO₂ thin film. Upon increasing the doping concentrations the band gaps of N-doped CuCrO₂ thin films increase due to the Burstein–Moss shift.

Keywords: CuCrO; ₂; film; Electronic properties; Optical properties

A simple method for large-scale preparation of ZnS nanoribbon film and its photocatalytic activity for dye degradation by Chao Wang; Yanhui Ao; Peifang Wang; Songhe Zhang; Jin Qian; Jun Hou (pp. 4125-4128).

ZnS nanoribbon film has been successfully prepared by solvothermal treating of Zn foil and S powder in hydrazine hydrate without any surfactant and post-high temperature treatment. The prepared samples were characterized by XRD, SEM and PL. Results show that the obtained films were with high crystallinity and uniformity. The obtained samples were used as a photocatalyst for degradation of dye X-3B, and results show that the dye can be photocatalytically degraded with high rate by as-prepared ZnS nanoribbon film under UV light irradiation.

Keywords: Photocatalysis; ZnS; Nanoribbon; X-3B

Effect of ambient gas on structural and optical properties of titanium oxynitride films by Sushant K. Rawal; Amit Kumar Chawla; Vipin Chawla; R. Jayaganthan; Ramesh Chandra (pp. 4129-4135).

Titanium oxynitride films have been deposited on glass substrates by reactive RF magnetron sputtering of titanium target. The influence of oxygen partial pressure in N₂+Ar and N₂+He mixtures was examined on structural and optical properties of titanium oxynitride films. The prepared samples were characterized by X-ray diffraction, EDS, surface profilometer, AFM and contact angle measurement system. With increase in oxygen partial pressure, the grain size decreases from ∼70nm to ∼50nm in N₂+Ar mixture, while from ∼60nm to ∼37nm in N₂+He mixture. The thickness calculated from optical transmission data and surface profilometer is in good agreement with each other. The deposited samples are hydrophobic by nature and the contact angle was found to decrease with increase in oxygen partial pressure. Samples prepared in oxygen partial pressure ≥5.5% show transmittance of about 97% in the visible region of the spectrum in both N₂+Ar and N₂+He mixtures. The atomic mass of the sputtering gas (Ar and He) significantly affects the primary crystallite size, orientation as well as band gap. We were able to relate the better crystallisation of titanium atoms with low partial pressure of oxygen when films are deposited in helium instead of argon due to Penning ionization.

Keywords: Titanium oxynitride; RF sputtering; Hydrophobic; Band gap; Penning ionization

Study of ammonia molecule adsorbing on diamond (100) surface by Yandong Ma; Hao Jin; Ying Dai; Baibiao Huang (pp. 4136-4141).

The diamond (100) surface with amino terminations is investigated based on density function theory within the generalized gradient approximation. Our calculated negative electron affinity of diamond (100) surface with hydrogen termination provides a necessary condition for initiating radical reaction. The results display that the ammonia molecule can form stable C–N covalent bonds on the diamond surface. In addition, due to the lower adsorption energy of one amino group binding on diamond surface, single amino group (SAG) model is easy to be realized in experiment with the comparison of double amino group (DAG) model. The adsorbed ammonia molecule will induce acceptor-like gap states with little change of the valence and conduction band of diamond in SAG model. The adsorption mechanism in the formation of ammonia monolayer on H-terminated diamond (100) surface, and two possible adsorption structures (SAG and DAG) were especially studied.

Keywords: Diamond (1; 0; 0) surface; Ammonia molecule; Density function theory

Drilling enhancement by nanosecond–nanosecond collinear dual-pulse laser ablation of titanium in vacuum by Nikša Krstulović; Slobodan Milošević (pp. 4142-4148).

Laser ablation of titanium in vacuum was performed using single- and dual-pulse regime in order to study crater formation. Crater profiles were analyzed by optical microscopy. It was found that the repetition-rate plays an important role in a process of laser ablation. The drilling is most effective for the highest repetition-rate. For the same total number of laser pulses clear drilling enhancement was achieved by dual-pulse regime of ablation in comparison to single-pulse regime. The strongest ablation rate in dual-pulse regime was achieved for the delay time between the pulses τ=370ns. Results are discussed in terms of decreased ablation threshold due to continuous heating of the target during the experiment.

Keywords: PACS; 52.38.Mf; 52.50.Jm; 42.62.CfLaser drilling; Laser ablation; Dual-pulse laser ablation; Double-pulse laser ablation; Laser-induced plasma; LIBS; Material removal; Titanium

Improvement of corrosion resistance of nitrided low alloy steel by plasma post-oxidation by Yang Li; Liang Wang; Dandan Zhang; Lie Shen (pp. 4149-4152).

Post-oxidizing treatments can be performed to improve the corrosion resistance of nitrided steel samples. In this paper, plasma nitriding treatments were performed at 540°C for 4h using ammonia as the working gas, and plasma post-oxidizing treatments were carried out at temperatures ranging from 350°C to 500°C for 2h in oxygen gas. The treated samples were characterized by using optical microscopy, SEM, XRD, and electrochemical polarization. The X-ray analysis revealed the formation of iron-nitride phases of ɛ-Fe_2–3N and γ′-Fe₄N during plasma nitriding and iron oxide phases of hematite (Fe₂O₃) and magnetite (Fe₃O₄) through the post-oxidizing treatment. In particular, it was found that the very thin magnetite layer 0.8–1.5μm in thickness on top of the compound layer was obtained by plasma post-oxidized at 400°C and 450°C. It was also demonstrated that the corrosion characteristics of the nitrided compound layer were further improved by post-oxidation treatment.

Keywords: Plasma nitriding; Oxidation; Corrosion resistance; AISI 4140 steel

Nitrogen-doped ZnO prepared by capillaritron reactive ion beam sputtering deposition by Liang-Chiun Chao; Yu-Ren Shih; Yao-Kai Li; Jun-Wei Chen; Jiun-De Wu; Ching-Hwa Ho (pp. 4153-4156).

Nitrogen-doped ZnO thin films have been prepared by reactive ion beam sputtering deposition utilizing a capillaritron ion source. X-ray diffraction (XRD) analysis of the as-deposited film exhibits a single strong ZnO (002) diffraction peak centred at 34.40°. Post-growth annealing causes increase of grain size and decrease of c-axis lattice constant. Micro-Raman spectroscopy analysis of the as-deposited film shows strong nitrogen-related local vibration mode at 275, 582, 640 and 720cm⁻¹, whereas the E₂ mode of ZnO at 436cm⁻¹ can barely be identified. Annealing at 500–800°C causes decrease of 275, 582, 640 and 720cm⁻¹ and increase of 436cm⁻¹ intensity, indicating out-diffusion of nitrogen and improvement of ZnO crystalline quality. Unlike un-doped ZnO, the surface roughness of nitrogen-doped ZnO deteriorates after annealing, which is also attributed to the out-diffusion of nitrogen. A nitrogen concentration of ∼10²¹/cm³ was observed while type conversion from n-type to p-type was not achieved, which is likely due to the formation of Zn_I–N_O or (N₂)_O that act as donor/double donors.

Keywords: ZnO; Nitrogen; Raman scattering

Improvement of interfacial adhesion in vertical GaN-based LEDs by introducing O₂ plasma cleaning and intermediate layers by Sunjung Kim (pp. 4157-4161).

Interfacial adhesion between an indium tin oxide (ITO)/Ni/Ag/Ni/Au p-electrode, and Au and Ni/Au seeds in vertical GaN-based light emitting diodes (LEDs) was enhanced by O₂ plasma cleaning treatment of the Au surface in the p-electrode. However, AES and REELS analyses of the Au surface in the p-electrode detected surface damage to the p-electrode and photoresist (PR) passivation structure from O₂ plasma cleaning. W/Ni and Al/Ni adhesion layers were introduced in the Au seed to increase interfacial adhesion between Au seed and untreated PR passivation. Forward leakage current as low as 0.91nA at 2V was observed for the vertical LED with the Al/Ni/Au seed, for which adhesion strength to O₂ plasma-cleaned Au and untreated PR was 141.2MPa and 62.8MPa, respectively.

Keywords: Interfacial adhesion; Plasma cleaning; Adhesion layer; Light emitting diode (LED); Leakage current characteristics

The structure and magnetic properties of Cu-doped ZnO prepared by sol–gel method by Huilian Liu; Jinghai Yang; Zhong Hua; Yongjun Zhang; Lili Yang; Li Xiao; Zhi Xie (pp. 4162-4165).

The Cu-doped ZnO and pure ZnO powders were synthesized by sol–gel method. The structural properties of the samples were investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. All the results confirmed that copper ions were well incorporated into the ZnO lattices by substituting Zn sites without changing the wurtzite structure and no secondary phase existed in Cu-doped ZnO nanoparticles. The Zn_0.97Cu_0.03O nanoparticles exhibited ferromagnetism at room temperature, as established by the vibrating sample magnetometer analysis.

Keywords: Diluted magnetic semiconductor; Cu-doped ZnO; Sol–gel method; Ferromagnetism

Process and performance of hot dip zinc coatings containing ZnO and Ni–P under layers as barrier protection by Z. Abdel Hamid; A. Abdel Aal; H.B. Hassan; A. Shaaban (pp. 4166-4170).

A new coating system of under layer for hot dip zinc coating was explored as an effective coating for steel especially for application in relatively high aggressive environments. The influence of different barrier layers formed prior to hot dip galvanization was investigated to optimize high performance protective galvanic coatings. The deposition of ZnO and Ni–P inner layers and characteristics of hotdip zinc coatings were explored in this study. The coating morphology was characterized by scanning electron microscope (SEM) analysis. The hot dip zinc coatings containing under layer showed substantial improvement in their properties such as good adhesion, and high hardness. In addition, a decrease in the thickness of the coating layer and an enhancement of the corrosion resistance were found. Open circuit potential (OCP) of different galvanized layers in different corrosive media viz. 5% NaCl and 0.5M H₂SO₄ solutions at 25±1°C was measured as a function of time. A nobler OCP was exhibited for samples treated with ZnO and Ni than sample of pure Zn; this indicates a dissolution process followed by passivation due to the surface oxide formation. The high negative OCP can be attributed to the better alloying reaction between Zn and Fe and to the sacrificial nature of the top pure zinc layer.

Keywords: Hot dip zinc; Galvanized steel; Under layer; ZnO-rich barrier; Electroless Ni–P; Corrosion

Formation of amine groups on the surface of GaN: A method for direct biofunctionalization by R. Stine; B.S. Simpkins; S.P. Mulvaney; L.J. Whitman; C.R. Tamanaha (pp. 4171-4175).

Gallium nitride has attracted significant interest as a material for biosensors; however, techniques for biofunctionalizing GaN surfaces have received limited attention. Here, we present a method for producing amine groups directly on GaN surfaces through exposure to a glow discharge plasma fed with humidified air, thereby eliminating the need for complex organic functionalization chemistry. Amine formation is tracked via X-ray photoelectron spectroscopy (XPS) by labeling the plasma-formed surface groups with a fluorinated probe that binds specifically to primary amines. These amine groups can subsequently couple covalently to a wide range of biomolecules. The covalent immobilization of a NeutrAvidin layer is demonstrated using Fourier transform infrared spectroscopy (FT-IR) and fluorescent biotin-binding assays. Finally, we show that plasma exposure times sufficient for the formation of amine groups do not significantly alter the conductivity of the GaN substrate.

Keywords: Gallium nitride; Biofunctionalization; Surface modification; Plasma; Amine; Biosensor

Microstructures and properties of plasma sprayed FeAl/CeO₂/ZrO₂ nano-composite coating by Bin Yin; Guang Liu; Huidi Zhou; Jianmin Chen; Fengyuan Yan (pp. 4176-4184).

Commercial FeAl powders and ZrO₂ nano-particles as well as CeO₂ additive were reconstituted into a novel multi-compositional feedstock powders via spray drying. The resulting feedstock powders were used to deposit FeAl/CeO₂/ZrO₂ nano-composite coating by plasma spraying on 1Cr18Ni9Ti stainless steel. An X-ray diffractometer (XRD), a scanning electron microscope equipped with an energy dispersive spectrometer (SEM/EDS), and a field emission scanning electron microscope equipped with an energy dispersive spectrometer (FESEM/EDS) were employed to characterize the microstructure of the as-prepared feedstock powders and nano-composite coating. At the same time, the mechanical properties and friction and wear behavior of the nano-composite coating and pure FeAl coating were comparatively evaluated by using a Vickers microindentation tester and ball-on-disk sliding wear tribotester, respectively. And the wear mechanisms for the two types of coatings are discussed in terms of their microstructure and mechanical properties. Results indicate that the nano-composite coating has a much higher hardness and fracture toughness as well as drastically increased wear resistance than pure FeAl coating, which could be mainly attributed to the reinforcing effect of ZrO₂ nano-particles and partially attributed to the refining effect of CeO₂ in the nano-composite coating.

Keywords: Plasma spraying; Intermetallic compound; Nano-composite coating; Mechanical property; Friction and wear

Silicon MIS diodes with Cr₂O₃ nanofilm: Optical, morphological/structural and electronic transport properties by İbrahim Y. Erdoğan; Ö. Güllü (pp. 4185-4191).

In this work we report the optical, morphological and structural characterization and diode application of Cr₂O₃ nanofilms grown on p-Si substrates by spin coating and annealing process. X-ray diffraction (XRD), non-contact mode atomic force microscopy (NC-AFM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) spectroscopy were used for characterization of nanofilms. For Cr₂O₃ nanofilms, the average particle size determined from XRD and NC-AFM measurements was approximately 70nm. Structure analyses of nanofilms demonstrate that the single phase Cr₂O₃ on silicon substrate is of high a crystalline structure with a dominant in hexagonal (110) orientation. The morphologic analysis of the films indicates that the films formed from hexagonal nanoparticles are with low roughness and uniform. UV–vis absorption measurements indicate that the band gap of the Cr₂O₃ film is 3.08eV. The PL measurement shows that the Cr₂O₃ nanofilm has a strong and narrow ultraviolet emission, which facilitates potential applications in future photoelectric nanodevices. Au/Cr₂O₃/p-Si metal/interlayer/semiconductor (MIS) diodes were fabricated for investigation of the electronic properties such as current–voltage and capacitance–voltage. Ideality factor and barrier height for Au//Cr₂O₃/p-Si diode were calculated as 2.15eV and 0.74eV, respectively. Also, interfacial state properties of the MIS diode were determined. The interface-state density of the MIS diode was found to vary from 2.90×10¹³eV⁻¹cm⁻² to 8.45×10¹²eV⁻¹cm⁻².

Keywords: MIS diode; Nanofilms; Cr; ₂; O; ₃; Metal oxides; Schottky barrier; Band gap

Switching of hydrophilic to ultra hydrophilic properties of flower-like gold nanostructures by Vinayak A. Dhumale; Preeti V. Shah; I.S. Mulla; R.B. Sharma (pp. 4192-4195).

Flower-like morphologies of gold nanostructures were obtained via chemical method by controlling molar concentration ratio of reducing agent and precursor. Chloroauric acid was used as a metal precursor while tri-sodium citrate as the reducing agent. These flower-like structures were characterized by UV–vis spectroscopy, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques. The basic crystallite size calculated via XRD measurement was found to be ∼10nm and remain unaffected by the different concentration ratios. The coating of these structures was made over clean glass substrate and analyzed for wettability by measuring their water contact angles. Our analysis indicates that the coatings of hierarchical flower-like structures of gold are able to provide ultra hydrophilic properties to glass substrate.

Keywords: Gold flower-like nanostructures; Wettability; Ultra hydrophilic

Effect of Fe state on electrocatalytic activity of Pd–Fe/C catalyst for oxygen reduction by Yawen Tang; Shuang Cao; Yu Chen; Tianhong Lu; Yiming Zhou; Lude Lu; Jianchun Bao (pp. 4196-4200).

The carbon-supported Pd–Fe catalyst (Pd–Fe/C) is prepared in the H₂O/tetrahydrofuran (THF) mixture solvent under the low temperature. The homemade Pd–Fe/C catalyst contains two forms of iron species, alloying and non-alloying Fe. The alloying Fe species is hardly dissolved in 0.5M H₂SO₄ solution, while the non-alloying Fe species is easily dissolved in 0.5M H₂SO₄ solution. The electrochemical measurements show the electrocatalytic activity of the Pd–Fe/C catalyst with the acid treatment for the oxygen reduction is higher than that of the Pd–Fe/C catalyst without the acid treatment, illustrating that the non-alloying Fe species suppresses the electrocatalytic activity of the Pd–Fe/C catalyst. In contrast, the alloying Fe species promotes the electrocatalytic activity of the Pd–Fe/C catalyst for the oxygen reduction, which is likely attributed to the change of the electron structure of Pd atom and/or bond length of Pd–Pd in the Pd–Fe/C catalyst.

Keywords: Pd–Fe nanoparticle; Catalyst; Alloy; Electrocatalytic activity; Oxygen reduction

Synthesis and characterization of Mn-doped ZnO column arrays by Mei Yang; Zhixing Guo; Kehui Qiu; Jianping Long; Guangfu Yin; Denggao Guan; Sutian Liu; Shijie Zhou (pp. 4201-4205).

Mn-doped ZnO column arrays were successfully synthesized by conventional sol–gel process. Effect of Mn/Zn atomic ratio and reaction time were investigated, and the morphology, tropism and optical properties of Mn-doped ZnO column arrays were characterized by SEM, XRD and photoluminescence (PL) spectroscopy. The result shows that a Mn/Zn atomic ratio of 0.1 and growth time of 12h are the optimal condition for the preparation of densely distributed ZnO column arrays. XRD analysis shows that Mn-doped ZnO column arrays are highly c-axis oriented. As for Mn-doped ZnO column arrays, obvious increase of photoluminescence intensity is observed at the wavelength of ∼395nm and ∼413nm, compared to pure ZnO column arrays.

Keywords: Mn-doped; ZnO column arrays; Photoluminescence

Calculation of temperature fields with a film-substrate interfacial layer model to discuss the layer-pair number effects on the damage thresholds of LaF₃/MgF₂ high reflectors at 355nm by Guanghui Liu; Ming Zhou; Guohang Hu; Xiaofeng Liu; Yunxia Jin; Hongbo He; Zhengxiu Fan (pp. 4206-4210).

Laser induced damage thresholds (LIDT) of LaF₃/MgF₂ high reflectors at 355nm were measured and investigated as a function of layer-pair number. Generally, LaF₃/MgF₂ coatings with more layer pairs possessed higher LIDT, but coatings with too high layer-pair number crazed because of high tensile stress, so the LIDT of them decreased badly. The temperature rise in the coatings was calculated based on a film-substrate interfacial absorption model, and the depth of the damage in the coatings were measured by a Veeco optical profilograph. The two characterization methods together were used to interpret the effects of layer-pair number on LIDT, and the damage mechanism of coatings at laser wavelength of 355nm was also discussed.

Keywords: LaF; ₃; /MgF; ₂; high reflectors; Temperature fields; Film-substrate interface; LIDT; Layer-pair number; Damage depth; Damage mechanism

Nitrogen bonding in aluminum oxynitride films by Paul W. Wang; Jin-Cherng Hsu; Yung-Hsin Lin; Huang-Lu Chen (pp. 4211-4214).

Assignment of oxidation states of N_1s in XPS spectra of aluminum oxynitride by curve fitting is difficult. The XPS curve fitting was previously discussed in the paper published in J. Non-Cryst. Solids, 224 (1998) 31, in which O_1s photoelectrons from GeO₂ glass were used to illustrate how to fit the XPS spectra. Three different ways were pointed out to eliminate the ambiguity caused by curve fitting such as comparing the data to data from standard samples, investigating the continuous surface modifications caused by slowly sputtering the surface, and monitoring the continuous surface modifications due to gradual increases in surface species under heating, cooling, or irradiation. Our recent work in aluminum oxynitride films provides another example of how to fit the XPS spectra of N_1s by three different oxidation states of N⁺, N²⁺, and N³⁺, by comparison of the measured data to data from previously published results, and by the gradual changes of spectra as functions of the oxygen contents in the films. Three oxidation states in different nitrogen bonding in the aluminum oxynitride, AlO₂N, Al₂O₅N₂, and AlO₃N, were clearly deduced.

Keywords: XPS data fitting; Aluminum oxynitride; Oxidation states; N; _1s; photoelectrons

STM/STS characterization of platinum silicide nanostructures grown on a Pt(111) surface by W. Koczorowski; M. Bazarnik; M. Cegiel; A. Petroutchik; A. Wawro; R. Czajka (pp. 4215-4219).

Formation of the platinum silicides nanostructures and their electronic properties have been studied using scanning tunneling microscopy and scanning tunneling spectroscopy. The investigated structures have been grown by solid state epitaxy upon deposition of the Si atoms (coverage about 0.2ML) and sequential annealing at temperature range 600–1170K. The formation of the Pt₂Si and PtSi islands was investigated until the Si atoms embedded into the Pt substrate at the 1170K. The images of the silicides structures and Pt substrates with atomic resolution have been recorded. The evolution of the spectroscopic curves both for substrates and nanostructures, corresponding to the structural and sizes changes, have been shown.

Keywords: Platinum silicides; Scanning tunneling microscopy; Scanning tunneling spectroscopy; Nanostructures

The friction property of super-hydrophobic cotton textiles by Changhong Su; Jun Li (pp. 4220-4225).

Two kinds of super-hydrophobic cotton textiles were prepared via dip-coating cotton textiles with nano-silica suspensions, and the cotton textiles exhibits high contact angle more than 160° and low sliding angle lower than 4°. A friction method was used to evaluate the durability of the as-prepared super-hydrophobic cotton textiles, the results shows that one of the as-prepared super-hydrophobic cottons exhibits better stability property against friction, and its contact angle remained higher than 150° and sliding angle remained lower than 15° after 1000 times friction. SEM analysis shows the reduction of hydrophobic property was resulted from the damage of surface structure during friction cycle.

Keywords: Super-hydrophobic; Cotton textiles; Nano-silica; Friction test

Formation and bioactivity of porous titania containing nanostructured Ag by Ming Wen; Limin Zhou; Weiming Guan; Yanqiong Li; Junmin Zhang (pp. 4226-4230).

In this work, porous titania were prepared on bulk Ti via chemical oxidation, and then nanostructured Ag was deposited on the surface of titania by ion beam sputtering. After annealing treatment, the nanostructured Ag titania were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The influence of nanostructured Ag on the morphology, grain growth, phase transformation, and bioactivity of titania was investigated.

Keywords: PACS; 61.46Df; 68.47 Jn; 81.07BcPorous titania; Nanostructured Ag; Phase transformation; Bioactivity

Surface treatment of nanoporous silicon with noble metal ions and characterizations by J. Kanungo; S. Maji; A.K. Mandal; S. Sen; E. Bontempi; A.K. Balamurugan; A.K. Tyagi; K. Uvdal; S. Sinha; H. Saha; S. Basu (pp. 4231-4240).

A very large surface to volume ratio of nanoporous silicon (PS) produces a high density of surface states, which are responsible for uncontrolled oxidation of the PS surface. Hence it disturbs the stability of the material and also creates difficulties in the formation of a reliable electrical contact. To passivate the surface states of the nanoporous silicon, noble metals (Pd, Ru, and Pt) were dispersed on the PS surface by an electroless chemical method. GIXRD (glancing incidence X-ray diffraction) proved the crystallinity of PS and the presence of noble metals on its surface. While FESEM (field emission scanning electron microscopy) showed the morphology, the EDX (energy dispersive X-ray) line scans and digital X-ray image mapping indicated the formation of the noble metal islands on the PS surface. Dynamic SIMS (secondary ion mass spectroscopy) further confirmed the presence of noble metals and other impurities near the surface of the modified PS. The variation of the surface roughness after the noble metal modification was exhibited by AFM (atomic force microscopy). The formation of a thin oxide layer on the modified PS surface was verified by XPS (X-ray photoelectron spectroscopy).

Keywords: Porous silicon; Surface treatment; Noble metals; Morphology; Surface oxide

Characterization of ZnO thin films grown on various substrates by RF magnetron sputtering by Kyu-Hang Lee; Nam-In Cho; Eui-Jung Yun; H.G. Nam (pp. 4241-4245).

In this study we investigated properties of ZnO thin films deposited on both oxygen-containing substrates and a substrate without oxygen content at various O₂/Ar reactant gas ratios. Deposition of ZnO on indium–tin oxide (ITO) resulted in the best crystallinity, whereas the least degree of crystallization was observed from ZnO deposited on glass. All the films were found to have compressive stress, which was relieved by annealing in O₂ environment. ZnO films deposited on glass revealed p-type conductivity when prepared at O₂/Ar ratio of 0.25 whereas those on SiN_x yielded p-type conductivity when prepared at O₂/Ar ratio of 4. In addition, shallower oxygen interstitial seemed to be found from films with better crystallinity. The largest shift in binding energy of Zn_2p3/2 was observed from ZnO prepared on glass at O₂/Ar ratio of 0.25, whereas that of O_1s was obtained from ZnO deposited on SiN_x at O₂/Ar ratio of 4. A model was proposed in terms of O₂ diffusion and hydrogen desorption in order to account for the observed property variations depending on substrates and O₂/Ar ratios.

Keywords: ZnO; Conductivity; RF magnetron sputtering; O; ₂; diffusion; Hydrogen desorption

A comparison study of scratch and wear properties using atomic force microscopy by Ampere A. Tseng (pp. 4246-4252).

The patterning technique that uses an AFM (atomic force microscopy) tip as a scratch tool, also known as AFM scratching, has been a vital technique for nanofabrication because of its low cost and potential to reach a resolution into the sub-nanometer domain. The AFM scratching technique was first used to study the scratch characteristics of silicon, with an emphasis on establishing its scratchability or the nanoscale machinability. The effects of the scratch parameters, including the applied tip force and number of scratches, on the size of the scratched geometry were specifically evaluated. The primary property that measures the scratchability was identified and assessed. To illustrate its suitability and reliability, the value of the scratchability, based on the present Si scratching experiments, was compared with the values based on the data available in the literatures for different scratching conditions or for materials other than Si. Since AFM scratching is in some aspects similar to the nanoscale wear test, the scratchability property identified is also compared with two major wear resistance indicators, wear coefficient and hardness. All comparison results indicate that the scratchability property identified, the scratch ratio, is an appropriate manufacturability indicator for measuring the degree of the ease or difficulty of a material scratched by an AFM tip and more suitable than the wear coefficient and hardness to gauge the nanoscale AFM scratchability.

Keywords: PACS; A6116P; A6825; A6860; A8140PAtomic force microscopy; Machinability; Scratch; Scratchability; Silicon; Wear coefficient

How photocatalytic activity of the MAO-grown TiO₂ nano/micro-porous films is influenced by growth parameters? by M.R. Bayati; F. Golestani-Fard; A.Z. Moshfegh (pp. 4253-4259).

Pure titania porous layers consisted of anatase and rutile phases, chemically and structurally suitable for catalytic applications, were grown via micro-arc oxidation (MAO). The effect of applied voltage, process time, and electrolyte concentration on surface structure, chemical composition, and especially photocatalytic activity of the layers was investigated. SEM and AFM studies revealed that pore size and surface roughness of the layers increased with the applied voltage, and the electrolyte concentration. Moreover, the photocatalytic performance of the layers synthesized at medium applied voltages was significantly higher than that of the layers produced at other voltages. About 90% of methylene blue solution was decomposed after 180min UV-irradiation on the layers produced in an electrolyte with a concentration of 10gl⁻¹ at the applied voltage of 450V.

Keywords: Oxide materials; Titanium dioxide; Photocatalysis; Micro-arc oxidation

Properties of carbon and iron modified TiO₂ photocatalyst synthesized at low temperature and photodegradation of acid orange 7 under visible light by Yongmei Wu; Jinlong Zhang; Ling Xiao; Feng Chen (pp. 4260-4268).

The nanoparticles of TiO₂ modified with carbon and iron were synthesized by sol–gel followed solvothermal method at low temperature. Its chemical composition and optical absorption were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence emission spectroscopy (PL), UV–vis absorption spectroscopy, and electron paramagnetic resonance (EPR). It was found that carbon and iron modification causes the absorption edge of TiO₂ to shift the visible light region. Fe(III) cation could be doped into the matrix of TiO₂, by which could hinder the recombination rate of excited electrons/holes. Superior photocatalytic activity of TiO₂ modified with carbon and iron was observed for the decomposition of acid orange 7 (AO7) under visible light irradiation. The synergistic effects of carbon and iron in modified TiO₂ nanoparticles were responsible for improving visible light photocatalytic activity.

Keywords: TiO; ₂; Modification; Visible light; Photocatalyst; Acid orange 7

GaAs(001) planarization after conventional oxide removal utilising self-governed InAs QD site selection by F. Bastiman; A.G. Cullis (pp. 4269-4271).

Native oxide removal on GaAs(001) wafers under conventional thermal desorption causes severe surface degradation in the form of pitting. Typical surface regeneration requires several hundred nanometres of buffer layer growth. This level of planarization is necessary to fill in the deep pits since Ehrlich–Schwoebel diffusion barriers cause a retardation of layer growth at multiple monolayer step edges. Pits are, however, attractive nucleation sites for quantum dots (QDs), and hence QDs fill the pits via a self-governing phenomenon. In this paper, we show how 1.7ML of InAs growth on GaAs(001) immediately after thermal oxide removal aids the healing of the surface and reduces the necessity for thick buffer layer growth.

Keywords: Scanning tunnelling microscopy; Molecular beam epitaxy; Quantum dots; InAs; GaAs

Tribological properties of the Ti–Al–N thin films with different components fabricated by double-targeted co-sputtering by Xuechao Li; Changsheng Li; Ye Zhang; Hua Tang; Guowei Li; Chaochao Mo (pp. 4272-4279).

Ti–Al–N films with different chemical compositions were deposited on stainless steel by changing the relative substrate position to targets using double-targeted reactive magnetron sputtering technique in the same process. The tribological behavior of the Ti–Al–N films was investigated in the temperature ranging from room temperature to elevated temperature in air without any lubricant on UMT-3 multifunctional friction and wear tribometer. The structure of the as-deposited films and the worn surface after tribometer testing were identified using XRD, EDS and SEM. It was found that the chemical composition of the as-deposited films altered with substrate position from Ti_0.82Al_0.18N to Ti_0.12Al_0.88N. XRD results revealed that the sputtered films before heat treatment were amorphous, but different phases such as TiN, AlN and TiAlN were formed after heat treatment of 700°C×1h. Friction and wear tests indicated the films with x=0.57, 0.65 exhibited the best tribological performance during the Ti1−_xAl_xN films system because of its hard phase and the formation of transfer films.

Keywords: Ti–Al–N films; Tribological performance; Double-targeted reactive magnetron sputtering technique; Heat treatment

AFM, XPS and RBS studies of the growth process of CdS thin films on ITO/glass substrates deposited using an ammonia-free chemical process by D.A. Mazón-Montijo; M. Sotelo-Lerma; L. Rodríguez-Fernández; L. Huerta (pp. 4280-4287).

This paper deals with a detailed study of the growth stages of CdS thin films on ITO/glass substrates by chemical bath deposition (CBD). The chemical and morphological characterization was done through X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), and atomic force microscopy (AFM) techniques. On the other hand, optical transmission and X-ray diffraction (XRD) measurements were performed in order to study the optical and structural properties of the films. The time, the chemistry, and morphology of the different stages that form the growth process by CBD were identified through these results. Furthermore, clear evidence was obtained of the formation of Cd(OH)₂ as the first chemical species adhered to the substrate surface which forms the first nucleation centers for a good CdS formation and growth. On the other hand, the ITO coating caused growth stages to occur earlier than in just glass substrates, with which we can obtain a determined thickness in a shorter deposition time. We were able to prove that CBD is a good technique for the manufacture of thin films of semiconductor materials, since the CdS film does not have any impurities. Completely formed films were transparent, uniform, with good adherence to the substrate, of a polycrystalline nature with a hexagonal structure. These results indicate that films obtained by CBD are good candidates to be applied in different optoelectronic devices.

Keywords: Chemical bath deposition; Ammonia-free; Cadmium sulphide; Cadmium hydroxide; X-ray photoelectron spectroscopy; Semiconductor thin films

A simple way to prepare monolayer films of the magnetite nanocrystal by the Langmuir–Blodgett-like technique by Degang Li; Xianjin Yu; Yunhui Dong; Lipeng Zhang; Zhongfang Li; Zengdian Zhao (pp. 4288-4291).

A simple preparation of water-soluble magnetite nanoparticles protected by sodium oleate has been demonstrated. The magnetite particles are nanocrystal, which are confirmed with XRD. This kind of magnetite nanocrystal can be changed into amphiphilic particles and steadily exist at the interface of water/toluene. The amphiphilic nanocrystal can form monolayer film on hydrophilic substrate by the Langmuir–Blodgett-like technique. The results of SEM indicate that the magnetite nanocrystal film is a uniform compact monolayer film that is composed of nanosized magnetite particles. We also proposed a possible mechanism for the formation of the nanocrystal monolayer film.

Keywords: Magnetite nanocrystal; Amphiphilic; Monolayer nanoparticles film; Langmuir–Blodgett-like technique

Facile controlled synthesis of micro/nanostructure MCrO₄ (M=Ba, Pb) by using Gemini surfactant C₁₂-PEG-C₁₂ as a soft template by Wengui Chang; Yuhua Shen; Anjian Xie; Xue Liu (pp. 4292-4298).

Gemini surfactants, double sodium α-sulfonic polyethylene glycol laurate (abbreviated C₁₂-PEG-C₁₂), were prepared and applied as soft templates in the controlled synthesis of BaCrO₄ and PbCrO₄ micro/nanocrystals. The template effects were investigated by adjusting the length of the spacer, using PEG400 and PEG4000, of the Gemini surfactant. The results indicated that the size and morphology of BaCrO₄ and PbCrO₄ micro/nanocrystals varied with the change in spacer length of C₁₂-PEG-C₁₂, suggesting that the different lengths of the polyethylene glycol group spacers in the Gemini surfactants played a key role in determining the size and shape of the MCrO₄ micro/nanoparticles. The dynamic process of the formation of the novel morphology BaCrO₄ crystals showed that the morphology grew from a round-bar polyhedron, to regular polyhedron, to approximate octahedron to a uniform pistachio nut shape. The growth mechanism of the BaCrO₄ micro/nanocrystals was explained that C₁₂-PEG-C₁₂ had a greater interfacial adsorption and would effectively control the shape evolution during the crystal growth, while PbCrO₄ could be explained that the Gemini surfactants can undergo liquid-crystalline phase transitions with long channels providing a soft template effect and derived the nanorods formation. Room temperature fluorescence spectra were studied and these showed that the pistachio-shaped BaCrO₄ microcrystals and PbCrO₄ nanorods possess photoactive luminescence properties with emission peaks at 470 and 549nm, respectively.

Keywords: Barium chromate; Lead chromate; Gemini surfactant; Micro/nanostructures; Luminescence

Optical characterization and determination of carrier density of ultrasonically sprayed CdS:Cu films by S. Kose; F. Atay; V. Bilgin; I. Akyuz; E. Ketenci (pp. 4299-4303).

In this work, CdS and Cu doped CdS films (at the Cu percentages of 1, 3 and 5) have been deposited onto glass substrates at 350±5°C by ultrasonic spray pyrolysis technique and their application potential for photovoltaic solar cells have been investigated. Optical properties and thicknesses of the films have been investigated by spectroscopic ellipsometry (SE). Ellipsometric angle ψ was used as the source point for optical characterizations. The optical constants ( n and k) and the thicknesses of the films have been fitted according to Cauchy model. Also, optical properties of the produced films have been analyzed by transmittance and reflectance spectra. Refractive index ( n), extinction coefficient ( k) and reflectance ( R) spectra have been taken by spectroscopic ellipsometer, while transmittance spectra have been taken by UV/vis spectrophotometer. The optical method has been used to determine the band gap type and value of the films. Mott-Schottky (M-S) measurements have been made to determine the conductivity type and carrier concentration of the films. Samples showed n-type conductivity and carrier concentration of undoped CdS sample was found to be 1.19×10¹⁹cm⁻³. Also, it was concluded that Cu doping has an acceptor effect in CdS samples. From the results of these investigations, the application potential of CdS:Cu films for photovoltaic solar cells as window layer was searched.

Keywords: Ultrasonic spray pyrolysis; CdS:Cu films; Spectroscopic ellipsometry; Optical characterization; Mott-Schottky measurements

The Al-doping and post-annealing treatment effects on the structural and optical properties of ZnO:Al thin films deposited on Si substrate by J.J. Ding; H.X. Chen; S.Y. Ma (pp. 4304-4309).

Al-doped ZnO (ZnO:Al) thin films with different Al contents were deposited on Si substrates using the radio frequency reactive magnetron sputtering technique. X-ray diffraction (XRD) measurements showed that the crystallinity of the films was promoted by appropriate Al content (0.75wt.%). Then the ZnO:Al film with Al content of 0.75wt.% was annealed in vacuum at different temperatures. XRD patterns revealed that the residual compressive stress decreased at higher annealing temperatures. While the surface roughness of the ZnO:Al film annealed at 300°C became smoother, those of the ZnO:Al films annealed at 600 and 750°C became rougher. The photoluminescence (PL) measurements at room temperature revealed a violet, two blue and a green emission. The origin of these emissions was discussed and the mechanism of violet and blue emission of ZnO:Al thin films were suggested. We concluded that the defect centers are mainly ascribed to antisite oxygen and interstitial Zn in annealed (in vacuum) ZnO:Al films.

Keywords: PACS; 78.20.−e; 78.55.Et; 78.66.Hf; 68.55.JkZnO thin films; RF magnetron sputtering; X-ray diffraction; Optical properties

The comparison of photocatalytic activity of synthesized TiO₂ and ZrO₂ nanosize onto wool fibers by Hadi Fallah Moafi; Abdollah Fallah Shojaie; Mohammad Ali Zanjanchi (pp. 4310-4316).

TiO₂ and ZrO₂ nanocrystals were successfully synthesized and deposited onto wool fibers using the sol–gel technique at low temperature. The photocatalytic activities of TiO₂-coated and ZrO₂-coated wool fibers were measured by studying photodegradation of methylene blue and eosin yellowish dyes. The initial and the treated samples were characterized by several techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and X-ray diffraction. The TEM study shows dispersed particles with 10–30nm in size for TiO₂-coated and 20–40nm in size for ZrO₂-coated samples on the fiber surface. Comparison of the photocatalytic activity of the coated samples reveals superiority of TiO₂ modified sample with respect to that of ZrO₂ for degradation of both dyes. Our observations indicate that by applying this technique to the fabrics, self-cleaning materials could be designed for practical application.

Keywords: Titania; Zirconia; Sol–gel; Photocatalysis; Self-cleaning; Wool

Evolution of MoTeO_x/SiO₂ and MoBiTeO_x/SiO₂ catalysts in the partial oxidation of propane to acrolein by Yiming He; Ying Wu (pp. 4317-4321).

A thorough investigation of the catalysts Mo₁Te₁O_x/SiO₂ and Mo₁Bi_0.05Te₁O_x/SiO₂ in the partial oxidation of propane is presented in this paper, in order to elucidate the nature and behavior of the active surface. The catalysts’ structures and redox properties were investigated by means of X-ray powder diffraction, Raman spectroscopy, in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and H₂-TPR techniques. The results indicate that Te-polymolybdate is the main active phase on fresh catalysts. During reaction, the catalysts underwent a progressive reduction, resulting in the reconstruction of the active surface and the formation of a MoO₃ phase. The synergistic effect between Te-polymolybdate and MoO₃ was assumed to promote catalytic performance. The different stabilities of Mo₁Te₁O_x/SiO₂ and Mo₁Bi_0.05Te₁O_x/SiO₂ catalysts are also discussed.

Keywords: Propane; Te-polymolybdate; Volatilization; Reconstruction

Corrosion and oxidation properties of NiCr coatings sprayed in presence of gas shroud system by M.F. Morks; C.C. Berndt (pp. 4322-4327).

The oxidation of a NiCr bond coat during air plasma spraying was controlled by designing a gas shroud system attached to the plasma torch nozzle. Two nozzles, termed as “normal” and “high-speed” nozzles examined the effect of nozzle internal design on the microstructure and phase structure of coatings. X-ray diffraction and SEM morphologies showed that the shroud system reduced the oxidation of NiCr particles during the spray process. Compared with conventional air plasma spraying, the argon gas shroud reduced the coating hardness because the volume fraction of partially melted particles increased. The high-speed nozzle reduced the oxidation and hardness of NiCr coatings due to the increase of partially melted particles in the coatings.

Keywords: Plasma spraying; NiCr coatings; Gas shroud; Oxidation; Microstructure; Hardness; Corrosion

Synthesis of SnS thin films via galvanostatic electrodeposition and fabrication of CdS/SnS heterostructure for photovoltaic applications by Biswajit Ghosh; Rajarshi Roy; Sumit Chowdhury; Pushan Banerjee; Subrata Das (pp. 4328-4333).

In this work SnS thin films were electrochemically deposited on ITO coated glass substrate by galvanostatic electrodeposition at different pH of the plating bath. The working electrode used in these studies was low cost high purity graphite rod. The as-deposited films were found to be smooth, pinhole free and well adherent to the substrate with no powdery deposition. EDX measurements revealed that all the SnS films were non-stoichiometric in nature with variation from Sn-excess to S-excess compositions. XRD pattern showed that all the SnS thin films had orthorhombic polycrystalline structure. The direct bandgaps of all the films were found to be in the range 1.54–1.58eV. ITO/SnS/In structure exhibited linear current–voltage characteristics, establishing the ohmic nature of both ITO/SnS and SnS/In junctions. Furthermore, SnS layer was grown on CdS film using electrodeposition technique. The heterostructure ITO/CdS/SnS/In was characterized under dark and illuminated conditions. From forward biased I– V characteristics several junction parameters like barrier height, diode ideality factor and series resistance of the heterostructure were extracted using Cheung model.

Keywords: SnS; Electrochemical deposition; pH; Characterization; Heterostructure

Deposition of thick and adherent Teflon-like coating on industrial scale stainless steel shell using pulsed dc and RF PECVD by A. Satyaprasad; S.K. Nema; N.K. Sinha; Baldev Raj (pp. 4334-4338).

A unique combination of pulsed dc and radio frequency (RF) discharge deposition was used to deposit thick (∼5μm) and adherent (2–4MPa) Teflon-like coatings on a stainless steel (SS) shell of 2m diameter size, through plasma enhanced chemical vapor deposition (PECVD). The details of deposition on such a big industrial scale component are reported for the first time. In this method, highly adherent thin interface layers were grown on SS shell that was electrically grounded, using pulsed dc discharge, followed by RF discharge deposition to build up the required coating thickness. The fluorocarbon precursor molecules, required for the deposition of Teflon-like coating, are generated indigenously by pyrolyzing the Teflon powder. The deposited coating was studied for its chemical bond state, surface roughness (Ra), morphology, thickness, and adhesive strength. These studies were carried out by using XPS, AFM, SEM, etc. The adhesive strength of the coating was measured by pin-pull test as per ASTM D4541 standard test. The coatings deposited with pulsed dc discharge were observed to have higher adhesive strength when compared with those deposited with RF discharge.

Keywords: Teflon-like coating; Plasma; PECVD; Pulsed dc; RF; Box coater

Preparation and electrochemistry of one-dimensional nanostructured MnO₂/PPy composite for electrochemical capacitor by Juan Li; Li Cui; Xiaogang Zhang (pp. 4339-4343).

One-dimensional nanostructured manganese dioxide/polypyrrole (MnO₂/PPy) composite was prepared by in situ chemical oxidation polymerization of pyrrole in the host of inorganic matrix of MnO₂, using complex of methyl orange (MO)/FeCl₃ as a reactive self-degraded soft-template. The morphology and structure of the composite were characterized by infrared spectroscopy (IR) X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the MnO₂/PPy composite consists of α-MnO₂ and PPy with nanotube-like structure. Electrochemical properties of the composite demonstrated the material showed good electrochemical reversibility after 500 charge–discharge cycles in the potential range of −0.4 to 0.6V, the tube-like nanocomposite has the potential application in electrochemical capacitor.

Keywords: Soft-template; One-dimensional nanostructure; Manganese dioxide; Polypyrrole; Electrochemical capacitor

Morphology and composition on Al surface irradiated by femtosecond laser pulses by Xiaohong Li; Chunhua Yuan; Hongdao Yang; Jiawen Li; Wenhao Huang; Duochang Tang; Qin Xu (pp. 4344-4349).

We study the surface chemicals and structures of aluminum plates irradiated by scanning femtosecond laser pulses in air for a wide range of laser fluence from 0.38 to 33.6J/cm². X-ray photoelectron spectroscopy and X-ray diffraction analyses indicate clearly that crystalline anorthic Al(OH)₃ is formed under femtosecond laser pulse irradiation. Besides aluminum hydroxide, crystallineαAl₂O₃ is also found in the samples irradiated at high laser fluence. Field emission scanning electron microscopy demonstrates that the surfaces of the samples irradiated with low laser fluence are colloidal-like and that nanoparticles with a few nanometers in size are embedded in glue-like substances. For high laser fluence irradiated samples, the surfaces are highly porous and covered by nanoparticles with uniform size of less than 20nm.

Keywords: PACS; 61.80.Ba; 79.20.Ds; 68.35.bd; 81.65.MqAluminum; Femtosecond pulsed laser; Oxidation

Densification behavior of gas and water atomized 316L stainless steel powder during selective laser melting by Ruidi Li; Yusheng Shi; Zhigang Wang; Li Wang; Jinhui Liu; Wei Jiang (pp. 4350-4356).

The densification during selective laser melting (SLM) process is an important factor determining the final application of SLM-part. In the present work, the densifications under different processing conditions were investigated and the densification mechanisms were elucidated. It was found that the higher laser power, lower scan speed, narrower hatch spacing and thinner layer thickness could enable a much smoother melting surface and consequently a higher densification.The gas atomized powder possessed better densification than water atomized powder, due to the lower oxygen content and higher packing density of gas atomized powder. A large number of regular-shaped pores can be generated at a wider hatch spacing, even if the scanning track is continuous and wetted very well. The densification mechanisms were addressed and the methods for building dense metal parts were also proposed as follows: inhibiting the balling phenomenon, increasing the overlap ratio of scanning tracks and reducing the micro-cracks.

Keywords: Selective laser melting; Densification; Stainless steel powder

Synthesis of micro- or nano-crystalline diamond films on WC-Co substrates with various pretreatments by hot filament chemical vapor deposition by Qiu-ping Wei; Z.M. Yu; Michael N.R. Ashfold; J. Ye; L. Ma (pp. 4357-4364).

Diamond films deposited on tungsten carbide can lead to major improvements in the life and performance of cutting tools. However, deposition of diamond onto cemented tungsten carbide (WC-Co) is problematic due to the cobalt binder in the WC. This binder provides additional toughness to the tool but results in poor adhesion and low nucleation density of any diamond film. A two-step chemical etching pretreatment (Murakami reagent and Caro acid, (MC)-pretreatment) and a boronization pretreatment have both been used extensively to improve adhesion of CVD diamond film on WC-Co substrates. Here we discuss the applicability of MC-pretreatment for a range of Co-containing WC-Co substrates, and demonstrate a controlled synthesis process based on liquid boronizing pretreatment for obtaining smooth and dense micro- or nano-crystalline diamond films on high Co-containing WC-Co substrates. Substrate treatments and deposition parameters were found to have major influences on the smoothness, structure and quality of the diamond films. The best quality diamond films were achieved under conditions of relatively high substrate temperature ( T_s) and the best adhesion was achieved at T_s=800°C.

Keywords: HFCVD; Nano-crystalline diamond film; Cemented carbide; Substrate pretreatment

Ternary semiconductor compounds CuInS₂ (CIS) thin films synthesized by electrochemical atomic layer deposition (EC-ALD) by Shaoxiong Lin; Xuezhao Shi; Xin Zhang; Huanhuan Kou; Chunming Wang (pp. 4365-4369).

In this paper the formation and characterization of the I-III-VI₂ semiconductor compound CuInS₂ (CIS) on gold substrate at room temperature by electrochemical atomic layer deposition (EC-ALD) method are reported. Optimum deposition potentials for each element are determined using cyclic voltammetry (CV) technique and Amperometric I– t method is used to prepare the semiconductor compound. These thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FT-IR). XRD results indicate that the CIS thin films have a (112) preferred orientation. The XPS analyses of the films reveal that Cu, In and S are present in an atomic ratio of approximately 1:1:2. And their semiconductor band gaps are found to be 1.50eV by FT-IR.

Keywords: CuInS; ₂; Gold substrate; Electrochemical atomic layer deposition; Underpotential deposition

Removal of tarnishing and roughness of copper surface by electropolishing treatment by A.M. Awad; N.A. Abdel Ghany; T.M. Dahy (pp. 4370-4375).

Tarnishing and roughness of copper surface can be removed by electropolishing treatment (EP) imparting a bright and smooth surface at suitable conditions, e.g. current density, time, temperature, and viscosity. It was carried out by using an electrolytic cell containing phosphoric acid 55% as the electrolytic solution. Both copper working electrode and lead counter electrode, and reference electrode (SCE) were connected to a Potentiostat/Galvanostat to allow an electric current to pass through the solution. Some additives such as soluble starch, ethylene glycol, and methanol were added to reduce defects formed on the copper surface during EP process. The results showed that the highest gloss value was obtained by applying electric potential 1.5V at the passive region of polarization curve. The surface was investigated after EP treatment, where SEM and EDX showed lower roughness in case of addition of both soluble starch and ethylene glycol more than methanol. Moreover, AFM analysis showed the lowest roughness in case of soluble starch more than other additives.

Keywords: Electropolishing; Anodic oxidation; Tarnishing; Brightness; Roughness; Leveling

Numerical modeling of laser shock peening with femtosecond laser pulses and comparisons to experiments by Benxin Wu; Sha Tao; Shuting Lei (pp. 4376-4382).

A physics-based model has been developed for laser shock peening (LSP) with femtosecond (fs) laser pulses (fs-LSP), which has never been reported in literature to the authors’ best knowledge. The model is tested by comparing simulations with measured plume/shock wave front transient propagations and the LSP-induced hardness enhancement layer thickness. Reasonably good agreements have been obtained. The model shows that fs-LSP can produce much higher pressure than LSP with nanosecond (ns) laser pulses (ns-LSP), and it can also generate very large compressive residual stress in the workpiece near-surface layer with a thickness up to ∼100μm. The developed model provides a powerful guiding tool for the fundamental study and the practical applications of fs-LSP. This study, together with the recently reported work by Nakano et al. [Journal of Laser Micro/Nanoengineering 4(1) (2009) 35–38], has confirmed the feasibility of fs-LSP on both theoretical and experimental sides.

Keywords: Keyword; Laser shock peening

Properties of boron and phosphorous incorporated tetrahedral amorphous carbon films grown using filtered cathodic vacuum arc process by O.S. Panwar; Mohd Alim Khan; B.S. Satyanarayana; Sushil Kumar; Ishpal (pp. 4383-4390).

This paper reports the electrical, mechanical, structural and field emission properties of as grown and also boron and phosphorous incorporated tetrahedral amorphous carbon (ta-C) films, deposited using a filtered cathodic vacuum arc process. The effect of varying boron and phosphorous content (up to 2.0at.% in to ta-C) on the conductivity ( σ_D), activation energy (Δ E₁), hardness, microstructure, emission threshold ( E_turn-ON) and emission current density ( J) at 12.5V/μm of ta-C: B and ta-C: P films deposited at a high negative substrate bias of −300V are reported. It is observed that both boron and phosphorous incorporation leads to a nearly an order increase in σ_D and corresponding decrease in Δ E₁ and a slight increase in hardness as compared to as grown ta-C films. In the case of field assisted electron emission, it is observed that E_turn-ON increases and J decreases. The changes are attributed to the changes in the sp³/sp² ratio of the films due to boron and phosphorous incorporation. The effect of boron on ta-C is to give a p-type effect whereas the effect of phosphorous gives n-type doping effect.

Keywords: Conductivity; Activation energy; Field emission; ta-C: B; ta-C: P; FCVA

Simulation of polyurethane/activated carbon surface interactions by Tamara Travinskaya; Andrey Perekhrest; Yuri Savelyev; Nick Kanellopoulos; Kyriakos Papadopoulos; Kali Agiamarnioti (pp. 4391-4396).

The influence of interfacial structure on interfacial properties between activated carbon filler and surrounding organic matrix of composites has been studied by infrared and NMR spectroscopy. Urea, semicarbazide and ethylurethane, component parts of polyurethane, have been used as organic model compounds in order to predict the interactions between the activated carbon surface and polar groups of real polyurethane molecule. It was shown that organic matrix/activated carbon interphase presented a region where the filler and matrix phases were chemically and/or physically combined. The spectra of the organic matrix undergo significant changes with increase of carbon content. Due to the surface reactive functionalities the activated carbon is considered not only as filler, influenced on the sorption properties of the composition, but also as a physicochemical modifier of the polyurethane matrix.

Keywords: Urea; Semicarbazide; Ethylurethane; Polyurethane; Activated carbon; Surface

Photoelectrochemical property and photocatalytic activity of N-doped TiO₂ nanotube arrays by Jingjing Xu; Yanhui Ao; Mindong Chen; Degang Fu (pp. 4397-4401).

N-doped TiO₂ nanotube arrays (NTN) were prepared by anodization and dip-calcination method. Hydrazine hydrate was used as nitrogen source. The surface morphology of samples was characterized by SEM. It showed that the mean size of inner diameter was 65nm and wall thickness was 15nm for NTN. The ordered TiO₂ nanotube arrays on Ti substrate can sustain the impact of doping process and post-heat treatment. The atomic ratio of N/Ti was 8/25, which was calculated by EDX. Photoelectrochemical property of NTN was examined by anodic photocurrent response. Results indicated the photocurrent of NTN was nearly twice as that of non-doped TiO₂ nanotube arrays (TN). Photocatalytic activity of NTN was investigated by degrading dye X-3B under visible light. As a result, 99% of X-3B was decomposed by NTN in 105min, while that of TN was 59%.

Keywords: Photoelectrochemical; N-doped; TiO; ₂; nanotube arrays; Visible light; Photocatalysis

Atomistic modeling of β-Sn surface energies and adatom diffusivity by Michael S. Sellers; Andrew J. Schultz; Cemal Basaran; David A. Kofke (pp. 4402-4407).

Energies for low number Miller index surfaces of β-Sn (b.c.t. structure) were computed and the (100) plane was found to have the lowest un-relaxed energy of 0.0497eV/Å². We then used the Dimer method to find mechanisms and corresponding activation energies, E_A, for a Sn adatom moving on a β-Sn (100) surface. After extensive dimer searches and comparison to long molecular dynamics simulations, we conclude that two simple hopping mechanisms dominate transitions on this surface. For each, we determined hopping rates of the adatom using transition state theory and computed its tracer diffusivity. A hop of the adatom in the lattice c-direction gives D300_K=1.893×10⁻⁰⁶cm²/s ( E_A=0.1493eV), while in the lattice a-direction D300_K=3.994×10⁻⁰⁶cm²/s ( E_A=0.1138eV). When compared to studies on the existence of low energy multi-atom adatom diffusion on Cu and Al (100), we assert that β-Sn's successive (200) plane layering in the [100] direction provides for significantly lower activation energies and may contribute to the inability to locate any concerted atomic motion mechanisms.

Keywords: Tin surface diffusion; Tin surface energy; Electromigration

Stoney equation limits for samples deformed as a cylindrical surface by J.M. Pureza; F. Neri; M.M. Lacerda (pp. 4408-4410).

This paper proposes a three-dimensional system for modelling stress in thin films deposited on thick substrates deformed as a small cylindrical surface by means of the minimization of the deformation energy. The results show the validity limits of the well-established Stoney equation and indicate the necessity of a correction term for substrates with Poisson ratio ( ν_s) in the range of 0.25< ν_s≤0.4.

Keywords: PACS; 62.20.Dc, 81.40.Jj, 68.60.BsStress; Strain; Stoney equation; Deformation energy

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Applied Surface Science (v.256, #13)