Applied Surface Science (v.255, #19)

Morphology and characterization of ITO–Ag–ITO films on fibers by layer-by-layer method by L.L. Yang; Dengteng Ge; Hua Wei; Fei He; X.D. He (8197-8201).
Indium tin oxide embedded with silver particles (ITO–Ag–ITO) multilayer films are deposited on the surface of fibers as reflective coatings through layer-by-layer method. Surface of fibers was modified by sodium dodecylbenzene sulfonate which is used as an excellent surfactant to increase the charge negativity of fibers. Silver layer was in situ obtained due to the reduction of SnCl2. Based on the electrostatic adsorption mechanism, scanning electron microscope (SEM) and electron dispersive spectroscopy (EDS) results show that multilayer films are well deposited onto fibers smoothly and densely. Transmission tests show that multilayer coated fibers have better near infrared (NIR) and Fourier transform infrared (FT-IR) reflectivity due to the embedded silver layer and the reflectivity is increased during high-temperature densification process.
Keywords: Reflective coating; Layer-by-layer adsorption; Surfactant; NIR reflectivity;

Effect of magnesium addition on the wetting of alumina by aluminium by Ali Sangghaleh; Mohammad Halali (8202-8206).
In this report the wetting behaviour between polycrystalline alumina substrates and molten aluminium doped with magnesium as a wetting agent has been studied using the sessile drop technique. The time required for equilibrium attainment is investigated. To explore the formation of possible phases at the interface, electron microscopic studies along with EDX analysis have been employed. It is found that magnesium reduces the time and temperature required for equilibrium in the Al/Al2O3 system. The Al–7 wt% Mg and Al–10 wt% Mg alloys can wet alumina at temperatures as low as 900 °C. It is also found that molten aluminium doped with magnesium can wet polycrystalline alumina at temperatures below 1000 °C. A thin reaction layer was observed at the Al–Mg/Al2O3 interface in the present study.
Keywords: Wetting; Alumina substrate; Contact angle; Sessile drop; Aluminium–magnesium alloy;

A facile method for preparing highly conductive and reflective surface-silvered polyimide films by Yuan Liao; Bing Cao; Wen-Cai Wang; Liqun Zhang; Dezhen Wu; Riguang Jin (8207-8212).
A novel method was developed for the preparation of reflective and electrically conductive surface-silvered polyimide (PI) films. The polyimide films were functionalized with poly(dopamine), simply by dipping the PI films into aqueous dopamine solution and mildly stirring at room temperature. Electroless plating of silver was readily carried out on the poly(dopamine) deposited PI (PI-DOPA) surface. The surface compositions of the modified PI films were studied by X-ray photoelectron spectroscopy (XPS). XPS results show that the PI-DOPA surfaces were successfully deposited with ploy(dopamine) and were ready for electroless deposition of silver. The poly(dopamine) layer was used not only as the chemi-sorption sites for silver particles during the electroless plating of silver, but also as an adhesion promotion layer for the electrolessly deposited silver. The as-prepared silvered PI films show high conductivity and reflectivity, with a surface resistance of 1.5 Ω and a reflectivity of 95%, respectively.
Keywords: Polyimide; Dopamine; Silver; Reflectivity; Conductivity;

An approach towards the growth of polyaniline nanograins by electrochemical route by D.S. Dhawale; R.R. Salunkhe; V.S. Jamadade; T.P. Gujar; C.D. Lokhande (8213-8216).
The growth of electropolymerized polyaniline nanograins has been carried out from aqueous solution of 0.45 M aniline (C6H5NH2) + 0.5 M H2SO4. These polyaniline nanograins were characterized using Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), contact angle measurement and optical studies. The presence of characteristic bonds of polyaniline was observed from Raman shift experiment. Based on field emission scanning electron microscopy and transmission electron microscopy analysis, the formation of the polyaniline nanograins with average diameter of about 50 nm was inferred. Surface of the polyaniline film was hydrophilic with contact angle 17 ± 1°. A blue shift of 0.30 eV with characteristic absorption peak at 427 nm has been attributed due to quantized size of polyaniline nanograins.
Keywords: Polyaniline; Nanograins; Thin films; Electrodeposition;

Temperature-dependent photoluminescence spectra of Er–Tm-codoped Al2O3 thin film by Haonan Lou; Xiao Wang; Zhensheng Tao; Fang Lu; Zuimin Jiang; Lili Mai; Fei Xu (8217-8220).
Er–Tm-codoped Al2O3 thin films with different Tm to Er concentration ratios were synthesized by cosputtering from separated Er, Tm, Si, and Al2O3 targets. The temperature dependence of photoluminescence (PL) spectra was studied. A flat and broad emission band was achieved in the 1.4–1.7 μm and the observed 1470, 1533 and 1800 nm emission bands were attributed to the transitions of Tm3+: 3H4  →  3F4, Er3+: 4I13/2  →  4I15/2 and Tm3+: 3F4  →  3H6, respectively. The temperature dependence is rather complicated. With increasing measuring temperature, the peak intensity related to Er3+ ions increases by a factor of five, while the Tm3+ PL intensity at 1800 nm decreases by one order of magnitude. This phenomenon is attributed to a complicated energy transfer (ET) processes involving both Er3+ and Tm3+ and increase of phonon-assisted ET rate with temperature as well. It should be helpful to fully understand ET processes between Er and Tm and achieve flat and broad emission band at different operating temperatures.
Keywords: Rare earth doping; Al2O3 thin film; Photoluminescence; Energy transfer;

Modifications of AISI 1045 steel by picosecond Nd:YAG laser at 266 nm; comparison with 532 and 1064 nm pulses by J. Stasic; M. Trtica; B. Gakovic; D. Batani; T. Desai; G. Brankovic (8221-8225).
Interaction of Nd:YAG laser, operating at 266 nm wavelength and a pulse duration of 40 ps, with AISI 1045 steel was studied. Surface damage threshold was estimated to be 0.14 J/cm2. The steel surface modification was studied at the laser fluence of ∼1.0 J/cm2. The energy absorbed from Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following AISI 1045 steel surface morphological changes and processes were observed: (i) intensive damage of the target in the central zone of irradiated area; (ii) appearance of periodic surface structures at nano-level, with periodicity in agreement with the used wavelength; (iii) reduction of oxygen concentration in irradiated area; and (iv) development of plasma in front of the target. Generally, interaction of laser beam with AISI 1045 steel (at 266 nm) results in a near-instantaneous creation of damage, meaning that large steel surfaces can be modified in short times.
Keywords: AISI 1045 steel; Laser–matter interaction; Picosecond Nd:YAG laser; 266 nm wavelength;

Description of surface roughness of sol–gel films/coatings by X-ray reflectivity technique by Lili Yang; Dengteng Ge; Hua Wei; Huijie Zhao; Fei He; Xiaodong He (8226-8229).
As an excellent optical or photoelectric material, indium tin oxide (ITO) film was prepared by sol–gel dip-coating and subsequent annealing process. X-ray reflectivity measurement based on the first Born approximation theory was performed for the characterization of surface roughness of ITO film. It is found that the roughness can be described as self-affined over finite length scales and the surface roughness increases with the annealing temperature or holding time. The results were compared with complementary data obtained by atomic force microscope tests and it is found that they match very well. The first Born approximation theory provides a valuable tool for the rough surface characterization of sol–gel films/coating through X-ray reflectivity technique.
Keywords: Sol–gel film; Surface roughness; X-ray reflectivity; First Born approximation;

Planarization machining of sapphire wafers with boron carbide and colloidal silica as abrasives by XiaoKai Hu; Zhitang Song; Zhongcai Pan; Weili Liu; LiangCai Wu (8230-8234).
The as-cutted sapphire wafers are planarized by the grinding and polishing two-step machining processes with micrometer B4C and nanometer silica as abrasives, respectively. The material removal rates (MRRs) of two processes are measured. During the polishing process, the MRR increases with the down-pressure increased, whereas the rotational speeds have less effect on the MRR. The alkaline colloidal silica is more favorable than the acidic to polish sapphire wafer. The ground and polished surfaces of the substrate are compared by scanning electron microscopy, atomic force microscopy, and X-ray rocking curves. Our results show that B4C abrasives are effective in elimination of the ununiformity in thickness within a wafer. The colloidal silica can achieve a nanoscale flatness of wafer, but the lasting polishing time seems unfavorable. The polishing process is also analyzed in terms of chemical mechanical polishing mechanism.
Keywords: Sapphire; Abrasives; Grinding; Polishing; Planarization; Silica;

Laser surface melting (LSM) is known to enhance the wear and corrosion resistance of Mg alloys, but its effect on microstructural evolution of Mg alloys is not well understood. An effort has been made to study the effect of rapid solidification following LSM on the microstructural evolution of AZ91D Mg alloy. The results of X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy indicated that the solidification microstructure in the laser-melted zone was mainly cellular/dendrite structure of primarily α-Mg phase and continuous network of β-Mg17Al12 phase. Numerical prediction of the laser-melted zone suggested that cooling rates increased strongly from the bottom to the top surface in the irradiated regions. An attempt has been made to correlate dendrite cell sizes of the solidification microstructure with the cooling rates in the laser-treated AZ91D Mg alloy.
Keywords: Magnesium alloy; Laser surface melting; Rapid solidification; Microstructure;

In this study, a reinforced silver-embedded silica matrix was designed by utilizing the interaction between the [AlO4] tetrahedral and the Ag+ in sol–gel process using sodium silicate as a silica precursor. The Ag+ mole ratio in each sample was significantly varied to examine the influence of silver concentration on the properties of the final product. Aluminium ions were added to reinforce and improve the chemical durability of silver-embedded silica. A templated sample at Al/Ag = 1 atomic ratio was also synthesized to attempt a possibility of controlling porosity of the final product. Also, a sample neither embedded with silver nor templated was synthesized and characterized to serve as reference. The material at Al/Ag = 1 was found to have a desirable properties, compared to its counterparts, before and even after calcination up to 1000 °C. The results demonstrate that materials with desirable properties can be obtained by this unprecedented method while utilizing sodium silicate, which is relatively cheap, as a silica precursor. This may significantly boost the industrial production of the silver-embedded silicas for various applications.
Keywords: Silver-embedded; Silica matrix; Sodium silicate; Aluminium; Sol–gel method; BET;

Hydrogenated diamond-like carbon film deposited on UHMWPE by RF-PECVD by Xingling Shi; Qingliang Wang; Lingli Xu; Shirong Ge; Chao Wang (8246-8251).
In this work, investigations were conducted to analyze the properties of diamond-like carbon (DLC) film deposited on ultra-high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) at a low temperature of 50 °C. Composition and structure of the films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Hardness and wettability of the film were tested. Tribological characterizations were carried out on a universal micro-tribometer, and reciprocating friction against ZrO2 ball was adopted with 25% bovine serum as lubrication. Results show that DLC film was successfully deposited on UHMWPE surface by RF-PECVD and the sp3 content was about 20% in the film. The film increased the macrohardness of the substrate by about 42% and the wettability was improved too. Tribology test showed a higher friction coefficient but a much smaller wear volume after the deposition due to the surface roughening and strengthening.
Keywords: UHMWPE; Diamond-like carbon film; RF-PECVD; Tribology;

Raman scattering analysis is used to study the residual stress in metal-induced crystallized amorphous silicon thin film. The influence of the crystallization parameters on thin film properties is investigated as a function of annealing temperature, annealing time, and nickel top-seed-layer thickness. Thin films produced under optimal annealing conditions are measured to have crystallization efficiency of about 98%, which is full crystallization. Residual stress analysis reveals clear stress reduction with prolonged annealing time and Ni capping layer thickness. A very low tensile stress of about 87 MPa is achieved. The relationships between optimal crystallization temperature, crystallization time, and Ni-layer thickness are described.
Keywords: Metal-induced crystallization (MIC); Nickel; Raman spectrum; Amorphous silicon; Polycrystalline; Residual stress;

Study of defects in proton irradiated GaAs/AlGaAs solar cells by Fenfen Zhan; Jianmin Hu; Yifan Zhang; Fang Lu (8257-8262).
The properties of GaAs/AlGaAs solar cells irradiated with 40, 70, 100 and 170 keV protons have been studied. Current–voltage (IV) measurement showed that the worst degradation was found in the cells irradiated by 100 keV protons. The degradation was found defect dependent. Defect profile was obtained by the stopping and range of ions in matter (SRIM) simulation and deep-level transient spectroscopy (DLTS) measurement. In order to obtain the deep-level defect profile in depletion layer by DLTS measurement, the traditional calculation formula of defect concentration has been modified. DLTS measurement showed good agreement with that of the SRIM simulation.
Keywords: Solar cells; Proton irradiation; Defect profile; IV; DLTS;

ZrN x films were sputtered in an Ar + N2 atmosphere, with different substrate biases (0 to −200 V) at various nitrogen flow ratios (%N2  = 0.5–24%). The surface morphology, resistivity, crystllinity, and bonding configuration of ZrN x films, before and after vacuum annealing, were investigated. As compared with ZrN x films grown without substrate bias, before and after annealing, the resistivity of 1% and 2% N2 films decreases with increasing substrate biases. Simultaneously, if the applied bias is too high, the crystallinity of ZrN x film will decrease. The surfaces of 1% and 2% N2 flow films deposited without bias have small nodules, whereas the surface morphology of films deposited at −100 V of substrate bias exhibits large nodules and rugged surface. Once a −200 V of substrate bias is applied to the substrate, the surface morphology of ZrN x films, grown at 1% and 2% nitrogen flow ratios, is smooth. Furthermore, there are two deconvoluted peaks in XPS spectra (i.e., Zr–O and Zr–N) of ZrN x films deposited at −200 V of substrate bias before and after annealing. On the other hand, the surface morphology changes dramatically from rugged surfaces for film deposited at lower nitrogen flow ratio (%N2  < 1%) to smoother and denser surfaces for film grown at higher nitrogen flow ratio (%N2  ≥ 1%). The Zr–N bonding in 2% N2 films still exist after annealing at 700 °C, while the Zr–N bonding in 0.5% and 16% N2 flow film vanish at the same temperature. The connection between the resistivity, crystallinity, surface morphology, and bonding configuration of ZrN x films and how they are influenced by the substrate bias and nitrogen flow ratio are discussed in this paper.
Keywords: Nitrogen flow ratio; Zirconium nitride; Surface morphology; Substrate bias;

Carbon nanotube (CNT)/europium hydroxide core–shell nanowires were prepared easily on a large scale under the boiling reflux of water assisted by the surfactant, sodium polystyrenesulfonate (SPS). The core–shell nanowires are characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectrum. A possible formation mechanism has been suggested as follows: The phenyl rings of SPS can react with the carbon ring of CNTs to form the π–π noncovalent bond, which makes the SPS cover the surface of CNTs entirely, and thus the surface of modified CNTs is negatively charged, which repel with each other resulting in the good dispersion. In addition, the negatively charged surface of CNTs adsorbs europium ions (positive). The adsorbed europium ions in situ react with OH ions to create europium hydroxide nanoparticles, and subsequently, the nanoparticles fuse together to form a dense coating layer on CNTs.
Keywords: Carbon nanotube; Europium hydroxide; Composite; Coating; Nanowire;

Large-area fibrous network of polyaniline formed on the surface of diatomite by Xingwei Li; Xiaohan Li; Na Dai; Gengchao Wang (8276-8280).
Large-area fibrous network of polyaniline is obtained on the surface of diatomite by in situ polymerization of aniline without stirring. And it is characterized via Fourier-transform infrared spectroscopy, Raman spectroscopy, thermal analysis technology, four-probe technique and cyclic voltammetry, as well as specific surface, total pore volume, average pore size and pore size distribution. This composite contains 85% polyaniline, which conductivity is 5.08 S cm−1 at 25 °C. It is more significant that its film electrode not only possesses good redox reversibility in the aqueous media ranging from pH 1.0 to 7.0, but also shows good electrochemical cycling stability in the aqueous media of pH 4.0. It will be a promising material for several applications due to increasing the operating pH window in the aqueous media and good conductivity.
Keywords: Polyaniline; Diatomite; Fibrous network;

Properties of electropolymerised polypyrrole thin film on silver by Shivaji A. Jamadade; Vijaya Puri (8281-8285).
This paper reports the properties of electropolymerised polypyrrole thin film on silver. The transmission, reflection, conductivity and dielectric behavior of polypyrrole coated silver has been studied in the 8–12 GHz frequency range of the electromagnetic spectrum. The polypyrrole thin film makes silver a better conductor for microwaves. The microwave conductivity is larger than the DC conductivity by many orders of magnitude. The real and imaginary part of dielectric constant increases in magnitude with increasing doping level and also it decreases in magnitude with increasing frequency.
Keywords: Polypyrrole thin film; Transmission; Reflection; Microwave conductivity; Permittivity;

Surface characterization of collagen/elastin based biomaterials for tissue regeneration by J. Skopinska-Wisniewska; A. Sionkowska; A. Kaminska; A. Kaznica; R. Jachimiak; T. Drewa (8286-8292).
Collagen and elastin are the main proteins of extracellular matrix. Collagen plays a crucial role in tensile strength of tissues, whereas elastin provides resilience to many organs. Both biopolymers are readily available and biocompatible. These properties point out that collagen and elastin are good components of materials for many potential medical applications. The surface properties of biomaterials play an important role in biomedicine as the majority of biological reactions occur on the surface of implanted materials. One of the methods of surface modification is UV-irradiation. The exposition of the biomaterial on ultraviolet light can alterate surface properties of the materials, their chemical stability, swelling properties and mechanical properties as well.The aim of our work was to study the surface properties and biocompatibility of new collagen/elastin based biomaterials and consideration of the influence of ultraviolet light on these properties.The surface properties of collagen/elastin based biomaterials modified by UV-irradiation were studied using the technique of atomic force microscopy (AFM) and contact angle measurements. On the basis of the results the surface free energy and its polar component was calculated using Owens–Wendt method. To assess the biological performance of films based on collagen, elastin and their blends, the response of 3T3 cell was investigated.It was found that the surface of collagen/elastin film is enriched in less polar component – collagen. Exposition on UV light increases polarity of collagen/elastin based films, due to photooxidation process. The AFM images have shown that topography and roughness of the materials had been also affected by UV-irradiation. The changes in surface properties influence on interaction between the material's surface and cells. The investigation of 3T3 cells grown on films based on collagen, elastin and their blends, leads to the conclusion that higher content of elastin in biomaterial promotes the cell adhesion and their viability on the surface. Also the suitable dose of UV light (1, 2 h) improves the biocompatibility of the materials.
Keywords: Collagen; Elastin; Surface modification; UV-irradiation;

Poly(ethylene terephthalate) (PET) film was modified by reaction with hydrazine (HD), ethylenediamine (EDA), 1,2-diaminopropane (1,2-DAP) and 1,3-diaminopropane (1,3-DAP). The maximal amount of amine functionalities introduced in the chosen conditions on the surface was found as 0.07, 3.35, 0.76 and 1.99 nmol cm−2 for HD, EDA, 1,2-DAP and 1,3-DAP respectively. During the modification process etching of the sample and an increase of stiffness takes place. FTIR-ATR spectra prove that the surface chemistry after modification in amine solution is very complex. The lack of clear correlation between the surface tension and surface concentration of amine functionalities seems to confirm that. For immobilization purpose invertase, laccase and tyrosinase were used. The amount of covalently attached proteins at first increases with the increase of surface concentration of amine groups but after reaching a certain level of amine groups, decrease of the immobilization level was observed. All enzymes tested showed highest activity for a moderate level of aminolysis and this activity had the highest values for EDA-modified PET.
Keywords: PET film; Aminolysis; Invertase; Tyrosinase; Laccase; Enzyme activity;

A method to prepare intermetallic composite coatings employing the cost-efficient electric arc spraying twin wires assistant with suitable heat treatment was developed. In this study, a Fe–Al composite coating was produced by spraying twin wires, i.e. a carbon steel wire as the anode and an aluminum wire as the cathode. The inter-deposited Fe–Al coating was transformed in-situ to Fe–Al intermetallic composite coating after a post annealing treatment. The effect of annealing treatment conditions on phase composition, microstructure and mechanical properties of the coating was investigated by using XRD, SEM, EDS and OM as well as microhardness tester. The results show that the desirable intermetallic phases such as Fe2Al5, FeAl and Fe3Al are obtained under the annealing condition. The main oxide in the coating is FeO which can partially transform to Fe3O4 up to the annealing condition.
Keywords: Twin-wire electric arc spraying; Heat treatment; Iron aluminide; Composite coating; Iron oxide;

The [(Pb0.90La0.10)Ti0.975O3/PbTiO3] n (PLT/PT) n (n  = 1–6) multilayer thin films were deposited on the PbO x (1 0 0)/Pt/Ti/SiO2/Si substrates by RF magnetron sputtering method. The layer thickness of PbTiO3 in one periodicity kept unchanged, and the layer thickness of (Pb0.90La0.10)Ti0.975O3 is varied. The electrical properties of the (PLT/PT) n multilayer thin films were investigated as a function of the periodicity (n) and the orientation. The studied results show that the PbO x buffer layer results in the (PLT/PT) n films’ (1 0 0) orientation, and the (1 0 0)-oriented (PLT/PT) n multilayer thin films with n  = 2 exhibit better pyroelectric properties and ferroelectric behavior than those of (PLT/PT) n films with other periodicities and orientations. The underlying physical mechanism for the enhanced electrical properties of (PLT/PT) n multilayer thin films was carefully discussed in terms of the periodicities and orientations.
Keywords: Multilayer structure; Ferroelectric thin films; Ferroelectric properties; Orientation dependence;