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Applied Surface Science (v.254, #11)

Two-dimensional magnetic cluster growth with a power–law interaction by Xiaojun Xu; Yiqi Wu; Gaoxiang Ye (pp. 3249-3254).

A two-dimensional cluster model in which the morphology of clusters depends on power–law magnetic interactions that decay with distance r as a r−^α law is introduced. The growth algorithm is a generalization of diffusion-limited aggregation (DLA) model. The particles with spin degree diffuse on a square lattice and each spin is allowed to flip under a Monte Carlo probability. The simulation shows that, for the antiferromagnetic coupling, the spins of the particles in clusters tend to be oriented alternately. For the ferromagnetic coupling, however, the spin distribution depends on the exponent α: for large value of α, domains with different sizes are observed in the clusters; while for small α, during the earlier stage of the growth process, the clusters exhibit approximately antiferromagnetic structure, then, in subsequent growth of the outer part of the clusters, the spin states of all particles are similar. The magnetization and system energy of the clusters as well as their evolutions with the growth parameters are also studied in detail.

Keywords: PACS; 61.43.Hv; 05.50.+q; 64.60.Ak; 82.20.wtDiffusion-limited aggregation; Power–law interactions; Spin distribution; Magnetization; Energy

Interactions at tetraphenyl-porphyrin/InP interfaces observed by surface photovoltage spectroscopy by Y. Zidon; Yoram Shapira; H. Shaim; Th. Dittrich (pp. 3255-3261).

Illumination induced charge separation processes at tetraphenyl-porphyrin (H₂TPP)/InP interfaces are characterized. The results indicate that upon illumination an electronic transition takes place between the organic highest occupied molecular orbital (HOMO) and the InP conduction band. A 70meV blue shift in the characteristic modulated surface photovoltage spectrum of a 50nm H₂TPP film was observed when n-InP substrate was used. Such blue shift was not observed when Au, SnO₂:F or p-InP substrates were used. The shift may suggest a presence of an ordered interfacial sub-layer in an almost lying orientation, due to chemical or physical interactions at the interface. The results indicate that the Fermi level is unpinned at the interface. An exciton diffusion barrier in close proximity to the H₂TPP/n-InP interface has been demonstrated.

Keywords: PACS; 73.20.−r; 73.50.Pz; 73.40.−c; 73.61.PSurface photovoltage; Interfaces; Tetraphenyl-porphyrin; InP; Charge separation

Low temperature ITO thin film deposition on PES substrate using pulse magnetron sputtering by Y.C. Lin; J.Y. Li; W.T. Yen (pp. 3262-3268).

Experiments were conducted using pulse magnetron sputtering (PMS) to deposit transparent conducting indium tin oxide (ITO) thin film onto flexible polyethersulfone (PES) plastic substrates. The thin film microstructure, optoelectronic and residual stress were analyzed using the modulating PMS power, work pressure, pulse frequency, duty cycle and cycle time process parameters. The residual stress of the thin film was determined by scanning electron microscopy (SEM) combined with the Sony equation. The experimental results show that PMS has a lower process temperature, higher deposition rate and lower resistivity compared with the radio frequency process at the same output power. The duty cycle increase produces the optimum optoelectronic characteristics. When the pressure, power, duty cycle and sputter time are increased, the thin film stress will also increase, causing flexural distortion in the PES plastic substrate. When the deposition thickness reaches 1.5μm, ITO thin film will appear with a distinct split. Under 5mtorr work pressure, 60W power, 33μs duty time and 2μs pulse reverse time at duty cycle 95%, thin film with an optimized electrical 3.0×10⁻⁴Ω-cm, RMS surface roughness of 0.85nm and visible region optical transmittance will be achieved with acquisition of over 85%.

Keywords: Pulse magnetron sputter; ITO; PES plastic substrate; Duty cycle

Room temperature synthesis and characterization of CdO nanowires by chemical bath deposition (CBD) method by D.S. Dhawale; A.M. More; S.S. Latthe; K.Y. Rajpure; C.D. Lokhande (pp. 3269-3273).

A chemical synthesis process for the fabrication of CdO nanowires is described. In the present work, transparent and conductive CdO films were synthesized on the glass substrate using chemical bath deposition (CBD) at room temperature. These films were annealed in air at 623K and characterized for the structural, morphological, optical and electrical properties were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), optical and electrical resistivity. The XRD analysis showed that the as-deposited amorphous can be converted in to polycrystalline after annealing. Annealed CdO nanowires are 60–65nm in diameter and length ranges typically from 2.5 to 3μm. The optical properties revealed the presence of direct and indirect band gaps with energies 2.42 and 2.04eV, respectively. Electrical resistivity measurement showed semiconducting behavior and thermoemf measurement showed n-type electrical conductivity.

Keywords: Chemical bath deposition; Cadmium oxide; Nanowires; Structural; Optical and electrical studies

Noise in boron doped amorphous/microcrystallization silicon films by Shibin Li; Zhiming Wu; Yadong Jiang; Wei Li; Naiman Liao; Junsheng Yu (pp. 3274-3276).

Hydrogenated silicon (Si:H) film was grown by radio frequency plasma enhanced chemical vapor deposition (PECVD) method. The transition between hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) was characterized by X-ray diffraction analysis. A semiconductor system was used to measure low frequency noise (1/ f noise) and random telegraph switching noise of Si:H films. The results show that the 1/ f noise of μc-Si:H is 4 orders of magnitude lower than that of a-Si:H and no RTS noise was found in both films. It also shows that using μc-Si:H instead of a-Si:H film as a sensing layer will enable the development of high performance uncooled microbolometer.

Keywords: PACS; 52.77.−j; 61.72.Tt; 68.55.−a; 71.23.Cq; 85.60.GzHydrogenated silicon; Microcrystallization; 1/; f; noise; RTS noise; Bolometer

Inhomogeneities in 130MeV Au¹²⁺ ion irradiated Au/n-Si (100) Schottky structure by Sandeep Kumar; Y.S. Katharria; V. Baranwal; Y. Batra; D. Kanjilal (pp. 3277-3281).

The electrical characteristics of Au/n-Si (100) Schottky rectifier have been studied in a wide irradiation fluence range using conventional current–voltage ( I– V) and capacitance–voltage ( C– V) measurements. The I– V characteristics showed an abnormal increase in forward current at low voltage. The device shows a bend in forward I– V and reverses bias C– V characteristics due to extra current, suggesting that there are two independent contributions to thermionic current, corresponding to two levels of the Schottky barrier. It is shown that the excess current at low voltage can be explained by taking into account the role of heavy ion irradiation induced defects at the metal semiconductor interface.

Keywords: PACS; 61.80.Jh; 73.30.+y; 73.40.−c; 73.40.QVIon irradiation; Schottky barrier; I; –; V; characteristics

Electroless deposition of copper and fabrication of copper micropatterns on CVD diamond film surfaces by Jianwen Zhao; Ruhai Tian; Jinfang Zhi (pp. 3282-3287).

Electroless deposition of copper on as-grown and amino-modification diamond substrates was investigated. The compact and uniform copper films were successfully electrolessly deposited on as-grown and amino-modification diamond substrates after activation by Pd/Sn colloid nanoparticles. The adhesion interaction between copper films and diamond substrates was roughly estimated by the ultrasonic treatment. The results showed the higher adhesion interaction between copper films and amino-modification diamond substrates than that between the copper films and as-grown diamond substrates due to the greater attractive force between the Pd/Sn colloid nanoparticles and amino-modified diamond surface. The favorable copper micropatterns were successfully constructed on diamond film surfaces by means of the catalyst lift-off method and the copper lift-off method. Furthermore, the electrochemical behavior of copper-modified boron-doped diamond (BDD) was studied for glucose oxidation in 0.2M sodium hydroxide solution by using cyclic voltammetry, and the result indicated that copper-modified BDD exhibited high catalytic activity to electrochemical oxidation of glucose in alkaline media.

Keywords: PACS; 81.05.Uw; 81.15.−z; 81.65.Cf; 82.45.Fk; 95.75.DeElectroless deposition; Diamond; Copper micropattern; Electrochemical; Glucose

X-ray photoelectron spectroscopic studies on initial oxidation of iron and manganese mono-silicides by Naofumi Ohtsu; Masaoki Oku; Akiko Nomura; Takamasa Sugawara; Toetsu Shishido; Kazuaki Wagatsuma (pp. 3288-3294).

Initial oxidation of iron and manganese mono-silicides (FeSi and MnSi) surfaces was studied by X-ray photoelectron spectroscopy (XPS). Clean surfaces of these silicides were prepared by fracturing in an ultra high vacuum, and then the fractured surfaces were oxidized by exposing to high-purity oxygen at pressures up to 1.3Pa. For the clean FeSi surface, positive chemical shifts of the Fe 2p_3/2 and Si 2p peaks from elemental Fe and Si were 0.5eV and 0.1eV, respectively. For the clean MnSi surface, a negative chemical shift of the Si 2p peak from elemental Si was 0.1eV. Iron on the FeSi surface was oxidized at an oxygen pressure of 1.3Pa, whereas the silicon was oxidized under the pressure of 1.3×10⁻⁶Pa, indicating that oxidation of silicon occurred prior to that of iron. Manganese and silicon on the MnSi were simultaneously oxidized in the range from 1.3×10⁻⁶Pa to 1.3×10⁻³Pa; however, over the pressure of 1.3Pa, the oxidation of manganese occurs prior to that of silicon. These oxidation behaviors at low oxygen pressures were similar to those of the FeSi and MnSi fractured in air.

Keywords: X-ray photoelectron spectroscopy; Iron silicide; Manganese silicide; Initial oxidation; Fracturing

Influence of absorption mechanisms on laser-induced plasma plume by Robert Rozman; Igor Grabec; Edvard Govekar (pp. 3295-3305).

In modelling laser-induced plasma plume formation, the proper description of laser absorption in the plasma plays an important role. In the present model, absorption is described by means of three different mechanisms: inverse bremsstrahlung (IB), photoionization (PI) and absorption by small condensed clusters. Numerical solutions of the model are given for KrF laser beam irradiation (wavelengthλ=248nm) impinging on a nickel target at various fluences. The influence of particular absorption mechanisms on the absorbed laser beam energy in the plasma plume during the pulse is shown for different fluences. Using all three absorption mechanisms, the calculated plasma properties show good agreement with the experimental results of other authors.

Keywords: PACS; 52.38.Dx; 52.38.MfLaser–matter interaction; Absorption in plasma; Modelling

Structural investigation of n-hexadecanoic acid multilayers on mica surface: Atomic force microscopy study by Yonghai Song; Yong Yao; Chuangye Chen; Kang Cui; Li Wang (pp. 3306-3312).

The structure of n-hexadecanoic acid (HA) multilayers formed by spreading an ethanol solution containing this molecule onto a freshly cleaved mica surface has been studied by atomic force microscopy (AFM). AFM images of multilayers obtained with different coating time showed that HA molecules first formed some sporadic domains on mica surface. With the proceeding of the coating process, these domains gradually enlarged and coalesced, until formed a continuous film finally. It was observed that HA molecules were always adsorbed on mica surface with tilted even-numbered layers structure. The height of the repeated tilted bilayer film was measured to be approximately 3.8±0.2nm, which implied a ∼60° tilt molecular conformation of the HA bilayers on mica surface. Phase image confirmed that the HA multilayers terminated with the hydrophilic carboxylic acid groups. The formation mechanism of the HA multilayers was discussed in detail. Thus, resulted hydrophilic surfaces are of special interest for further study in biological or man-made member systems.The tilted even-numbered layers structure of n-hexadecanoic acid formed by spreading ethanol solution containing this molecule onto mica surface with different coating time was studied by atomic force microscopy. ▪

Keywords: PACS; 33.80.−b; 68.43.−h; 68.37.Ps; 81.16.Dn; 68.65.Ac n; -Hexadecanoic acid (HA); Multilayers; Atomic force microscopy (AFM); Self-assembled monolayers (SAMs)

Characterization and field emission characteristics of carbon nanotubes modified by titanium carbide by Yuxiang Qin; Ming Hu (pp. 3313-3317).

Carbon nanotubes (CNTs) were modified by depositing a thin layer of titanium film on the surface using magnetron sputtering method, followed by vacuum annealing at 900°C for 2h. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed that the as-deposited thin titanium film reacted with carbon atoms to form titanium carbide after annealing. The experiment results show that the thickness of sputter-deposited titanium film has significant effect on the field emission J– E characteristic of modified CNTs film. The titanium carbide-modified CNTs film obtained by controlling the titanium sputtering time to 2min showed an improved field emission characteristics with a significant reduction in the turn-on electric field and an obvious increase in the emission current density as well as an improvement in emission stability. The improvement of field emission characteristics achieved is attributed to the low work function and good resistance to ion bombardment of titanium carbide.

Keywords: PACS; 79.70.+q; 61.46.+w; 82.45.−hCarbon nanotubes; Titanium carbide; Electrophoretic deposition; Field emission

Electrochemical elaboration of adherent poly(3,4-ethylene-dioxythiophene) films and hybride nanowires on nickel by F. Lallemand; F. Plumier; J. Delhalle; Z. Mekhalif (pp. 3318-3323).

In the line of elaboration of conducting polymer on oxidizable metal, electropolymerization of 3,4-ethylene-dioxythiophene (PEDOT) was performed in ammonium oxalate aqueous solution on nickel. The advantageous effect of the oxalate ions on the electropolymerization process as well as on the physical characteristics of the resulting polymer film has been evidenced. Among these properties, adhesion has been drastically improved. Hybride nanowires nickel/PEDOT have been elaborated to highlight the nickel–PEDOT adhesion. The protective effect of the PEDOT film against corrosion in NaCl is nevertheless very slight.

Keywords: Electropolymerization; PEDOT; Oxidizable metal; Nickel; Adhesion; Nanowires

The influence of Fermi energy on structural and electrical properties of laser crystallized P-doped amorphous silicon by Rosari Saleh; Norbert H. Nickel (pp. 3324-3330).

A series of phosphorous-doped hydrogenated amorphous silicon films (a-Si:H) were crystallized using step-by-step laser crystallization process. The structural changes during the sequential crystallization process were detected by Raman measurements. The dehydrogenation was monitored by measuring the Si–H local vibrational modes using Raman spectroscopy and hydrogen effusion measurements. Interestingly, hydrogen bonding is affected by doping of the amorphous material. The influence of doping concentrations, thus the Fermi energy on electronic properties has been investigated employing secondary ion mass spectroscopy (SIMS), dark-conductivity- and Hall-effect measurements. The results from hydrogen effusion are consistent with the results obtained from Raman spectroscopy, Hall-effect- and dark-conductivity measurements.

Keywords: P-doped polycrystalline silicon; Laser crystallization; Structural and transport properties; H bonding

S180 cell growth on low ion energy plasma treated TiO₂ thin films by Marshal Dhayal; Su-In Cho; Jun Young Moon; Su-Jin Cho; Anna Zykova (pp. 3331-3338).

X-ray photoelectron spectroscopy (XPS) was used to characterise the effects of low energy (<2eV) argon ion plasma surface modification of TiO₂ thin films deposited by radio frequency (RF) magnetron sputter system. The low energy argon ion plasma surface modification of TiO₂ in a two-stage hybrid system had increased the proportion of surface states of TiO₂ as Ti³⁺. The proportion of carbon atoms as alcohol/ether (COX) was decreased with increase the RF power and carbon atoms as carbonyl (CO) functionality had increased for low RF power treatment. The proportion of C(O)OX functionality at the surface was decreased at low power and further increase in power has showed an increase in its relive proportion at the surface. The growth of S180 cells was observed and it seems that cells are uniformly spreads on tissue culture polystyrene surface and untreated TiO₂ surfaces whereas small-localised cell free area can be seen on plasma treated TiO₂ surfaces which may be due to decrease in C(O)OX, increase in CO and active sites at the surface. A relatively large variation in the surface functionalities with no change in the surface roughness was achieved by different RF plasma treatments of TiO₂ surface whereas no significant change in S180 cell growth with different plasma treatments. This may be because cell growth on TiO₂ was mainly influenced by nano-surface characteristics of oxide films rather than surface chemistry.

Keywords: TiO; ₂; thin film; Functionalisation; Surface treatment; XPS; Surface state

Large-quantity synthesis of ZnO hollow objects by thermal evaporation: Growth mechanism, structural and optical properties by Ahmad Umar; Yoon-Bong Hahn (pp. 3339-3346).

Synthesis of large-quantity uniformly distributed ZnO hollow objects, i.e. cages and spheres have been performed on Si(100) and steel alloy substrates by the direct heating of metallic zinc powder in the presence of oxygen. Extensive structural observations revealed that the formed products are crystalline ZnO with the wurtzite hexagonal phases. The Raman-active optical phonon E₂ modes, attributed to wurtzite hexagonal phase of ZnO, were observed at 437cm⁻¹ for the products grown on both the substrates. The room-temperature photoluminescence spectra showed a broad band in the visible region with a suppressed UV emission, indicating the presence of oxygen vacancies and structural defects in the as-grown structures. Additionally, post growth annealing was also carried out to further investigate the photoluminescence properties of the as-grown products. It was observed that the formation of hollow objects consists of several stages which include the formation of Zn clusters, oxidation on the sheath and sublimation/evaporation of the Zn from the interiors, resulted in the formation of hollow objects.

Keywords: PACS; 81.10.Bk; 81.05.Dz; 78.66.HfZnO; II–VI Semiconductors; Optical characterization; Photoluminescence

Characterization of ion beam sputter deposited W and Si films and W/Si interfaces by grazing incidence X-ray reflectivity, atomic force microscopy and spectroscopic ellipsometry by A. Biswas; A.K. Poswal; R.B. Tokas; D. Bhattacharyya (pp. 3347-3356).

An ion beam sputtering system, which uses a commercial ECR microwave based plasma ion source, has been designed and fabricated in-house for deposition of soft X-ray multilayer mirrors. To begin with, in the ion beam sputtering system W, Si thin films, W/Si bi-layer and W/Si/W tri-layer samples have been deposited on c-Si substrates as precursors to W/Si multilayer stack. The samples have been characterized by grazing incidence X-ray reflectivity (GIXR), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE) techniques. By analyzing the results, density, thickness, surface roughness of the single layer samples and interface width of the bi-layer and tri-layer samples have been estimated.

Keywords: IBS; GIXR; SE

Electrochromic properties of nano-composite nickel oxide film by Sheng-Hui Lin; Fu-Rong Chen; Ji-Jung Kai (pp. 3357-3363).

In this study, we develop a nano-composite nickel oxide (NNO) film on the indium tin oxide (ITO)-coated glass substrate for electrochromic applications. The NNO film is composed of the core–shell structure of NiO/conducting ITO nano-particles. High porosity in the NNO film offers large active surface area for redox reaction. Electrochromic electrodes fabricated with the NNO films produce high transmittance variation (66.2% at a wavelength of 550nm), fast switching speed (coloring: 3.5s; bleaching: 4s) and good durability, which are much better than those of ones made with the traditional nickel oxide films. The structure, morphology, and electrochromic properties are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and UV–vis spectroscopy.

Keywords: PACS; 61.46.Df; 78.40.HaElectrochromic; Nano-composite; Nickel oxide; Electro-deposition

A comparative study of gadolinium gallium garnet growth by femtosecond and nanosecond pulsed laser deposition by M.S.B. Darby; T.C. May-Smith; R.W. Eason; T. Donnelly; J.G. Lunney; K.D. Rogers (pp. 3364-3369).

The growth of epitaxial Nd:Gd₃Ga₅O₁₂ (GGG) on Y₃Al₅O₁₂ (YAG) by femtosecond pulsed laser deposition is reported. We have used a Ti:sapphire laser at a wavelength of 800nm and pulse length of 130fs, operating at a repetition rate of 1kHz. The film properties have been studied systematically as a function of the deposition parameters of laser fluence, spot-size, oxygen pressure, target-substrate distance and temperature. Scanning electron microscopy, atomic force microscopy and X-ray diffractometry were used to characterise the surface structure and crystallinity of the films. X-ray diffraction analysis shows that epitaxial growth has occurred. A comparison between the ion velocities produced by nanosecond and femtosecond laser ablation of the GGG target material has been investigated by the Langmuir probe technique. The results indicate a large difference in the plasma characteristics between femtosecond and nanosecond ablation, with ion velocities up to eight times faster observed in the femtosecond case.

Keywords: PACS; 68.55.jk; 81.15.-z; 77.55.+f; 52.27.CmPulsed laser deposition; Plasmas; Femotsecond; Langmuir probe; Thin films; Garnet crystal; Epitaxy

In situ observation of photo-bleaching in human single living cell excited by a NIR femtosecond laser by Sung-Hak Cho; Won-Seok Chang; Jae-Goo Kim; Kyoung-Hyun Whang; Kyeong-Sook Choi; Seong-Hyang Sohn (pp. 3370-3375).

The photo-bleaching of single living cells excited by femtosecond laser irradiation was observed in situ to study the nonlinear interaction between ultrafast laser pulses and living human breast MDA-MB-231 cells. We conducted a systematic study of the energy dependence of plasma-mediated photo-disruption of fluorescently labeled subcellular structures in the nucleus of living cells using near-infrared (NIR) femtosecond laser pulses through a numerical aperture objective lens (0.75 NA). The behavior of photo-bleached living cells with fluorescently labeled nuclei was observed for 18h after femtosecond laser irradiation under a fluorescence microscope. The photo-bleaching of single living cells without cell disruption occurred at between 470 and 630nJ. To study the photo-disruption of subcellular organelles in single living cells using the nonlinear absorption excited by a NIR femtosecond laser pulse, the process of photo-bleaching without photo-disruption provides key information for clarifying the nonlinear interaction between NIR ultrashort, high-intensity laser light and transparent fluorescently labeled living cells.

Keywords: PACS; 87.17.−d; 52.38.Mf; 42.62.BeFemtosecond laser; Photo-bleaching; Laser internal processing; Living cell; Nucleus; Fluorescence; Photo-disruption

Enhanced infrared response of Si base p–n diode with self-assembled Ge quantum dots by thermal annealing by Qijia Cai; Hao Zhou; Fang Lu (pp. 3376-3379).

The effects of thermal annealing in Si base p–n diode with self-assembled Ge dots stacked in eight layers structure are investigated. The effects of annealing are discussed based on the photovoltage spectra, the PL spectra and the Raman spectra. Three main effects occur after thermal annealing: the reduction of point defects, the intermixing of Si–Ge and the strain relaxation. The experimental result shows that 800°C might be a suitable annealing temperature for photovoltaic applications.

Keywords: PACS; 78.67.Hc; 81.40.Ef; 81.40.JjQuantum dots; Thermal annealing; Raman spectra; PL spectra

Influence of nano-SiO₂ on dilational viscoelasticity of liquid/air interface of cetyltrimethyl ammonium bromide by Huanrong Wang; Yong Gong; Weichang Lu; Banglin Chen (pp. 3380-3384).

An investigation was reported on the interfacial rheology of nano-SiO₂ dispersions in the presence of cetyltrimethyl ammonium bromide (CTAB). The interfacial dilational viscoelasticity had been measured as a function of the nano-particle concentration. The properties of the interface were affected by different processes such as the surfactants adsorption at the liquid or at the particle interfaces. It was found that the influence of nano-SiO₂ particles on the interfacial properties was evident and complex. The property of SiO₂ particles would change from hydrophilic to hydrophobic when CTAB molecules absorbed at their surface. The reorganization of surfactants and the participation of hydrophobic SiO₂ at the surface were offered to explain the process. In particular, the interaction between surfactants and particles, and the transfer of particles from bulk to the surface played an important role in changing the properties of the interface.The adsorption of SiO₂ at the surface and the reorganization change the rheology of the interface film. At the appropriate concentration, the participation of SiO₂ endows the interface film with more elasticity. ▪

Keywords: PACS; 47.55.drNano-SiO; ₂; Cetyltrimethyl ammonium bromide (CTAB); Liquid/air interface; Dilational viscoelasticity; Relaxation process

Optical probe of InAs/GaAs self-assembled quantum dots grown using low growth rate and growth interruptions by M. Lachab; H. Sakaki (pp. 3385-3390).

We have investigated the optical properties of InAs/GaAs self-assembled quantum dots (QDs), grown at 500°C using a low growth rate (0.014ML/s), growth interruptions and a two-stage capping process. The samples exhibited large-size dots with densities in the range (3–4.5)×10⁹cm⁻². Macro-photoluminescence (macro-PL) measurements revealed the presence of five electronic sub-bands in the dots, with the ground state (GS) emission exhibiting a linewidth of ∼70meV. Because of the dots large size and composition dispersions, associated with the growth method, it was possible to resolve single dots emissions using micro-PL (μ-PL) excitation in the barrier layers of the as-grown samples. The sharp PL lines were detected 60–140meV above the GS peak energy. High-resolution resonant optical excitation of the dots PL evidenced that these fine lines originate from exciton complexes confined to the GS of individual dots. Non-resonant power dependence μ-PL spectroscopy results further confirmed the occurrence of both single exciton (X) and biexciton (XX) radiative recombinations. Finally, with increasing lattice temperature up to 95K, PL emissions from most of these nanostructures suffered the usual thermal quenching, with activation energies ( E_a) ranging between 12 and 41meV. The relatively small values of E_a suggest that the growth technique implemented here favors the formation of defects centers in the vicinity of the QDs.

Keywords: InAs; Quantum dots; Macro- and micro-photoluminescence

Titania surface modification and photovoltaic characteristics with tungsten oxide by Ping Cheng; ChangSheng Deng; DaNian Liu; XiaMing Dai (pp. 3391-3396).

WO₃-coated TiO₂ film was prepared by depositing TiO₂ suspension containing small amounts of ammonium tungstate solution. The morphology and structure of the samples were characterized with high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL) emission spectrum. The results showed that WO₃ formed a coating layer on surface of TiO₂ and significantly reduced the surface traps of TiO₂ nanoparticles. Transient photovoltage and electrochemical impedance measurements (EIS) were employed to study the charge separation/recombination process. The results revealed that the charge recombination was greatly retarded and the electron lifetime was increased due to the coating layer of WO₃. These observations showed good correlation with current–voltage analyses of dye-sensitized solar cell fabricated from these films, with WO₃ overlayer resulting in an increase in open-circuit voltage of up to 37mV and 11% improvement in overall device efficiency.

Keywords: Titania photoelectrode; Surface modification; Morphology; Dye-sensitized solar cell

Tribochemical investigation of DLC coating in water using stable isotopic tracers by X. Wu; T. Ohana; A. Tanaka; T. Kubo; H. Nanao; I. Minami; S. Mori (pp. 3397-3402).

Tribochemical reaction of DLC coating in water was investigated by using a stable isotopic tracer,¹⁸O labeled water (H₂¹⁸O), to carry out the friction test of DLC coating and 440C ball pair, and using ToF-SIMS to analyze the worn surfaces. The result showed that DLC coating tribochemically reacted with water to form hydrophilic hydroxyl and carboxyl groups on surface, and suggested that the formed hydroxyl mainly combined with the secondary or tertiary carbons on the surface. The surface layer on the counter ball mainly consisted of C from the coating, Cr, Fe from the ball and¹⁸O from water, and was rich in¹⁸OH. It is thought that the hydrophilic groups formed at the interfaces play an important role in low friction and wear behaviors of DLC coating and the counter part in a water environment. Comparing with that obtained from the test in D₂O, the result also suggests that hydrogen/deuterium exchange is easy to occur between the products containing OD on the mated ball and some adsorbates in an ambient air environment.

Keywords: Tribochemistry; Diamond-like carbon; Isotopic tracer; ToF-SIMS

Study on successively preparation of nano-TiO₂ ethanol colloids by pulsed laser ablation and fluorescence property by Xiu-xiu Huang; Wen-gong Zhang (pp. 3403-3407).

Nano-TiO₂ colloids have been successively prepared by focused, pulsed laser ablation (PLA) at the interface of solid titanium dioxide and flowing liquid. Three factors influenced the luminescence of the nano-TiO₂ colloids. The first factor was the flowing rates of the flowing liquid. The second factor was the pulsed laser output power. The third factor was the age of the colloids. The nano-TiO₂ colloids products were characterized by transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–vis) and fluorescence spectroscopy. The results revealed that anhydrous ethanol was the best flowing liquid, and cyclohexane or water was found to be not suitable for this system; under the conditions of the lowest flowing rates of the flowing liquids in the range of 0.017–0.15mL/s, the highest pulsed laser output power in the range of 100–250mJ/pulse and with the proper aging time of the colloids, nano-TiO₂ ethanol colloids with strong fluorescence emission intensity at about 414nm can be obtained.

Keywords: Nano-TiO; ₂; Ethanol colloids; Pulsed laser ablation; Flowing liquid; Decoration in situ; Fluorescence

Variable morphology of PTFE-like polymer nanocrystals fabricated by oriented plasma polymerization at atmospheric pressure by Ying Guo; Jing Zhang; Jinzhou Xu; Jianyong Yu (pp. 3408-3411).

Rapid formation of PTFE-like polymer nanocrystals was achieved by a novel synthesis method—oriented plasma polymerization (OPP) at atmospheric pressure. The entire process was completed within a short period of time ranging between a few seconds to several minutes through dielectric barrier discharge (DBD) at atmospheric pressure. The surface morphology of the coated organic crystal film was observed through scanning electronic microscope (SEM) and different morphology nanocrystals were found such as nanorods and nanotubes. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the single-crystalline phase of these nanocrystals. The sizes of the nanosingle crystals were from 10nm to 1μm. The effects of discharge conditions such as discharge time, ratio of the monomer to carrier gas and power on the nanocrystalline morphology and crystallinity were investigated. As a result, the physical morphology and structures could be controlled through the conditions of the oriented plasma polymerization to some extent. This novel polymerization method opened a new way to nanofabricate polymeric crystallines fast and effectively.

Keywords: Plasma polymerization; Dielectric barrier discharge (DBD); Organic crystals; Fluorocarbon; Microcrystals

Milling and dispersion of multi-walled carbon nanotubes in texanol by Nono Darsono; Dang-Hyok Yoon; Jaemyung Kim (pp. 3412-3419).

Rheological results were used to determine the optimum type of dispersant and its concentration for six commercial dispersants for the dispersion of multi-walled carbon nanotube (MWCNT) agglomerates in texanol. An unsaturated polycarboxylic acid copolymer (BYK P-104) exhibited the optimum performance with the lowest MWCNT slurry viscosity in texanol. The cutting and dispersion efficiencies of MWCNTs with 20wt.% of BYK P-104 dispersant were compared using conventional ball milling and high energy milling, whereby the latter was found to be more effective. High energy milling for 2h produced a large portion of MWCNT agglomerates smaller than 150nm, showing a drastic increase in slurry viscosity due to the dispersion into individual CNTs. On the other hand, 120h ball milling was required to achieve the agglomerate size of 300nm with less viscosity increase upon milling. Decrease in the degree of MWCNT crystallinity was observed by both milling, even though 2h high energy milling showed slightly less damage than 120h ball milling based on XRD and Raman spectroscopy results.

Keywords: PACS; 81.05.Uw; 61.46.Fg; 81.20.YmCarbon nanotubes; High energy milling; Dispersion; Raman spectra

Electrical resistivity due to electron scattering with magnetic domain walls and magnetic properties of Ni–Fe alloy thin films by Y.C. Yeh; C.W. Huang; J.T. Lue (pp. 3420-3424).

The physical properties of magnetic domain walls and electrical conductivity of permalloy thin films under external magnetic fields were studied. Using a magnetic force microscope (MFM), we observed the variation of domain configurations with the change of applied magnetic field for different film thicknesses of 245, 320, and 415nm. A superconducting quantum interference device (SQUID) was exploited to measure the magnetization loop for the applied magnetic field either parallel or perpendicular to the normal direction of the surface. We also found that the resistivity increases significantly as the electrical current conduction changed from parallel to perpendicular to the domain walls.

Keywords: Magnetization loop; CPW and CIW resistivities; Direct current and magnetic force microscopy

Influence of complexing agent on the electrodeposited Co–Pt–W magnetic thin films by Guoying Wei; Hongliang Ge; Lihong Huang; Qiong Wu; Xinqing Wang; Liming Huang (pp. 3425-3430).

Complexing agents are often used to improve the quality of electrodeposited alloys. Influence of different complexing agents with hydroxycarboxylic acid group on the electrodeposited Co–Pt–W thin films has been investigated. Cathodic polarization curves show that the polarization behaviors of electroplating bath with different complexing agents are very different. Surface morphology, phase composition and magnetic properties are observed by means of FESEM, XRD and vibrating sample magnetometer (VSM), respectively. It has been found out that, if citrate was used as complexing agent, the Co–Pt–W thin films were homogeneous and the granular crystals with the average grain size of 2μm have been observed. Co–Pt–W thin films exhibited hexagonal close packed (hcp) lattice and strong perpendicular anisotropic magnetic behavior ( H_c⊥=215.5kA/m; H_c∥=55.4kA/m). In the presence of gluconate, needle-like deposits were obtained and a strong face centered cubic (fcc(111)) texture was measured. The Co–Pt–W thin films showed isotropic magnetic behavior. In the case of tartate and malate, the coexistence of needle-like deposits and cellular deposits appeared. The XRD patterns showed that the mixed fcc and hcp phase formed. Perpendicular anisotropic magnetic behaviors of thin films, from malate or tartate baths, were not obvious.

Keywords: PACS; 81.15.Pq; 82.45.Mp; 75.70.AkComplexing agents; Electrodeposition; Co–Pt–W thin films

Synthesis and characterization of Gd_0.1Ce_0.9O_1.95 thin films by spray pyrolysis technique by M.G. Chourashiya; S.H. Pawar; L.D. Jadhav (pp. 3431-3435).

The Gd doped ceria (CGO) in thin layers is of great interest for low temperature operation. In the present investigation, we report on the use of spray pyrolysis technique for the synthesis of CGO thin films. The process parameters were optimized for synthesizing Gd_0.1Ce_0.9O_1.95 films. Films were characterized by XRD, EDS, SEM, and AFM and are observed to be phase pure and dense with surface roughness of the order of ∼5nm. The d.c. conductivity was also measured and is observed to be ∼0.5S/cm at 623K.

Keywords: PACS; 73.50.−h; 52.77.Fv; 81.15.Rs; 82.47.Ed; 68.37.−dCGO; Electrical conductivity of thin films; Spray coating techniques; SOFC; Surface microscopy

Molecular dynamics and experimental studies on deposition mechanisms of ion beam sputtering by Te-Hua Fang; Win-Jin Chang; Chao-Ming Lin; Wen-Chieh Lien (pp. 3436-3441).

Molecular dynamics (MD) simulation and experimental methods are used to study the deposition mechanism of ionic beam sputtering (IBS), including the effects of incident energy, incident angle and deposition temperature on the growth process of nickel nanofilms. According to the simulation, the results showed that increasing the temperature of substrate decreases the surface roughness, average grain size and density. Increasing the incident angle increases the surface roughness and the average grain size of thin film, while decreasing its density. In addition, increasing the incident energy decreases the surface roughness and the average grain size of thin film, while increasing its density. For the cases of simulation, with the substrate temperature of 500K, normal incident angle and 14.6×10⁻¹⁷J are appropriate, in order to obtain a smoother surface, a small grain size and a higher density of thin film. From the experimental results, the surface roughness of thin film deposited on the substrates of Si(100) and indium tin oxide (ITO) decreases with the increasing sputtering power, while the thickness of thin film shows an approximately linear increase with the increase of sputtering power.

Keywords: Molecular dynamics; Thin film deposition; Ionic beam sputtering

Microstructure evolution on the surface of stainless steel by Nd:YAG pulsed laser irradiation by Chengyun Cui; Jiandong Hu; Yuhua Liu; Zuoxing Guo (pp. 3442-3448).

New structure phenomena with the grain sizes of 60nm to 1μm would be expected on the stainless steel surface by Nd:YAG pulsed laser irradiation. Nano-structures with various shapes and sizes were formed mainly during the solidification and most shapes of particles were diversiform according to different distances from the center of the spot. The morphologies were of equiaxed nano-particles and faceted hexagons. The surface re-solidification velocities have been estimated according to the numeral simulation of the thermal conditions. It was proved by the XRD that they were mainly consisted of γ-Fe and manganese oxides. The XPS results confirmed the EDS results that on the surface the alloy elemental composition in the outermost layer were rich in Mn and poor in Fe and in reverse in the center of the laser spot. Through observation of morphologies grown on the laser irradiated surfaces, direct evidence of growth mode transition from a continuous form to a lateral form was provided in one laser spot.

Keywords: Pulsed laser; Stainless steel; Numerical simulation; Nano-structure; Hexagon

Comparison of fractal and profilometric methods for surface topography characterization by S. Mahovic Poljacek; D. Risovic; K. Furic; M. Gojo (pp. 3449-3458).

In this study microstructural and roughness characterization of surface of aluminium foils used in lithographic printing process was performed by contact and non-contact profilometric methods and fractal analysis. Significant differences in roughness parameters values inferred from stylus method in respect to those inferred from the non-contact measurements were observed. The investigation of correlation between various fractal dimensions obtained from gray-scale SEM micrographs and binary images resulting from median filtering of the original SEM micrographs as well as selected relevant roughness parameters shows that there is a strong correlation between certain roughness parameters and particular fractal dimensions. This correlations permit better physical understanding of fractal characteristics and interpretation of the dynamics of surface roughness change through processing. Generally these correlations are more suitable for parameters obtained by stylus method than those inferred from the laser-based measurements.

Keywords: PACS; 05.45.Df; 61.43.Bn; 68.35.Ct; 81.05.Bx; 81.05.Rm; 81.70.Bt; 82.45.CcAluminium oxide film; Microporous surfaces; Profilometry; Fractal analysis

Understanding barium sulfate precipitation onto stainless steel by Franca Jones; Phillip Jones; Roland De Marco; Bobby Pejcic; Andrew L. Rohl (pp. 3459-3468).

This paper investigates the influence of barium sulfate scaling and scaling inhibitors on the electrochemical behaviour of stainless steel. The results of a synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) and electrochemical impedance spectroscopy (EIS) study on stainless steel shows that different scaling inhibitors interact uniquely with the substrate when barium sulfate is precipitated on the electrode surface. The main effect of the substrate in the presence of inhibitor is a tendency to form smaller barium sulfate particles. The SR-GIXRD patterns obtained in the presence of the two inhibitors were different to each other and to the control, with the carboxylate showing greater amounts of barite solids precipitated together with iron(III) and (II) sulfate, while the phosphonate showed low amounts of barite solid were precipitated. The presence of iron sulfates on the electrode surface as detected by SR-GIXRD, in the case of NTA, suggests that scaling inhibitors are not always benign, and can promote the dissolution of iron species from the substrate.

Keywords: PACS; 81.10.Dn; 82.45.Bb; 84.37.+q; 82.80.Fk; 61.72.Ss; 68.55.Jk; 68.37.−d; 68.08.−p; 61.10.NzBarium sulfate; Precipitation; Scale; Electrochemical impedance spectroscopy; Inhibitors; Morphology; Interfaces; X-ray diffraction

Origin of grey spots on the surface of metallic glasses under Ar⁺ ion irradiation: The surface and volume properties by V.D. Okunev; Z.A. Samoilenko; T.A. D’yachenko; E.I. Pushenko; M. Baran; R. Szymczak; H. Szymczak; P. Gierłowski; V.S. Khmelevskaya; I.A. Antoshina (pp. 3469-3478).

The nature of grey spots on the surface of amorphous Fe₆₇Cr₁₈B₁₅ metglass ribbons irradiated by 30keV Ar⁺ ions is investigated. Changes in the surface and volume properties of samples are analyzed bearing in mind the presence of competitive processes of ordering and disordering in the structure under irradiation at initial stage of crystallization ( T=500°C). Changes in the volume properties of the samples become apparent in their structure, electrical and magnetic properties and are caused by radiation-enhanced diffusion at high gradients in the concentration of defects generated by Ar⁺ irradiation. It is established that grey spots are shown by decrease in the reflection coefficient in a visible range. They emerge as a result of reorganization in the electronic structure of irradiated ribbons due to damage in the short-range order and formation of non-uniformly scaled atomic structure during transition from the medium-range to the long-range atomic order. Experimental data are in accord with the calculations in the framework of the free electrons model.

Keywords: PACS; 61.10. Nz; 71.23Cq; 73.22. −f; 75.50. KjMetglass; Ion irradiation; Surface grey spot; Atomic disorder

Hydrostatic pressure effects on impurity states in InAs/GaAs quantum dot by Congxin Xia; Yaming Liu; Shuyi Wei (pp. 3479-3483).

Within the framework of effective-mass approximation, the hydrostatic pressure effects on the donor binding energy of a hydrogenic impurity in InAs/GaAs self-assembled quantum dot(QD) are investigated by means of a variational method. Numerical results show that the donor binding energy increases when the hydrostatic pressure increases for any impurity position and QD size. Moreover, the hydrostatic pressure has a remarkable influence on the donor binding energy for small QD. Realistic cases, including the impurity in the QD and the surrounding barrier, are considered.

Keywords: PACS; 73.21.La; 71.55.-i; 78.66.FdQuantum dot; Hydrogenic impurity; Hydrostatic pressure

Optical characterization of PLD grown nitrogen-doped TiO₂ thin films by B. Farkas; J. Budai; I. Kabalci; P. Heszler; Zs. Geretovszky (pp. 3484-3488).

Nitrogen-doped TiO₂ thin films were prepared by pulsed laser deposition (PLD) by ablating metallic Ti target with pulses of 248nm wavelength in reactive atmospheres of O₂/N₂ gas mixtures. The layers were characterized by UV–VIS spectrophotometry and variable angle spectroscopic ellipsometry with complementary profilometry for measuring the thickness of the films. Band gap and extinction coefficient values are presented for films deposited at different substrate temperatures and for varied N₂ content of the gas mixture. The shown tendencies are correlated to nitrogen incorporation into the TiO2–_xN_x layers. It is shown that layers of significantly increased visible extinction coefficient with band gap energy as low as 2.89eV can be obtained. A method is also presented how the spectroscopic ellipsometric data should be evaluated in order to result reliable band gap values.

Keywords: PACS; 78.66.−w; 81.15.Fg; 68.55.LnPulsed laser deposition; Titanium-dioxide; Substitutional doping; Visible light; Photocatalytic material

Nucleation and growth mechanisms during electropolymerization of substituted 3-alkylthiophenes by J.P. Soto; F.R. Díaz; M.A. del Valle; J.H. Vélez; G.A. East (pp. 3489-3496).

In the present work the electrochemical study of compounds based on 3-((ω-bromoalkyloxy) methyl) thiophene, varying the length of the alkyl chain between 6 and 12 carbon atoms, is reported. Electropolymerization of the monomers was achieved by potentiodynamic (cyclic voltammetry, CV) and potentiostatic (constant potential) techniques. Voltammograms obtained by CV show that all monomers can be electrochemically oxidized at potentials about 1800mV to synthesize the respective polymer. Besides, the potential shifts to more anodic potentials on successive scans, increasing thus the resistivity of the material. Nucleation and growth mechanism (NGM) of electropolymerization was investigated by a potentiostatic technique ( j– t). Deconvolution of the current–time transient data fitted with a theoretical model suggests that at short times the instantaneous nucleation with two-dimensional growth (IN2D) contribution prevails, followed by an instantaneous nucleation with three-dimensional growth controlled by the charge transfer (IN3Dct) contribution and, finally at longer times, the instantaneous nucleation with three-dimensional growth controlled by diffusion (IN3Ddif) contribution becomes important. The predominance of each contribution to the NGM depends on the monomer being electropolymerized, and the electrolysis time. The morphology predicted from these NGMs fully correlates with that determined by SEM.

Keywords: Poly 3-alkylthiophenes; Electropolymerization; Nucleation and growth mechanisms of electropolymerization; Conducting polymer; Thiophene

Adsorption of aromatic compounds from the biodegradation of azo dyes on activated carbon by P.C.C. Faria; J.J.M. Órfão; J.L. Figueiredo; M.F.R. Pereira (pp. 3497-3503).

The adsorption of three selected aromatic compounds (aniline, sulfanilic acid and benzenesulfonic acid) on activated carbons with different surface chemical properties was investigated at different solution pH. A fairly basic commercial activated carbon was modified by means of chemical treatment with HNO₃, yielding an acid activated carbon. The textural properties of this sample were not significantly changed after the oxidation treatment. Equilibrium isotherms of the selected compounds on the mentioned samples were obtained and the results were discussed in relation to their surface chemistry. The influence of electrostatic and dispersive interactions involved in the uptake of the compounds studied was evaluated. The Freundlich model was used to fit the experimental data. Higher uptakes are attained when the compounds are present in their molecular form. In general, adsorption was disfavoured by the introduction of oxygen-containing groups on the surface of the activated carbon.

Keywords: Activated carbon; Adsorption; Surface chemistry; Aromatic compounds

Thickness dependence of structural, electrical and optical properties of indium tin oxide (ITO) films deposited on PET substrates by Lei Hao; Xungang Diao; Huaizhe Xu; Baoxia Gu; Tianmin Wang (pp. 3504-3508).

Without intentionally heating the substrates, indium tin oxide (ITO) thin films of thicknesses from 72nm to 447nm were prepared on polyethylene terephthalate (PET) substrates by DC reactively magnetron sputtering with pre-deposition substrate surfaces plasma cleaning. The dependence of structural, electrical, and optical properties on the films thickness were systematically investigated. It was found that the crystal grain size increases, while the transmittance, the resistivity, and the sheet resistance decreases as the film thickness was increasing. The thickest film (∼447nm) was found of the lowest sheet resistance 12.6Ω/square, and its average optical transmittance (400–800nm) and the 550nm transmittance was 85.2% and 90.4%, respectively. The results indicate clearly that dependence of the structural, electrical, and optical properties of the films on the film thickness reflected the improvement of the film crystallinity with the film thickness.

Keywords: PACS; 42.70.−a; 68.55.Jk; 78.66.−w; 78.67.−n; 78.40.−q; 81.40−zMulti-arc ion plating; DC magnetron sputtering; Indium tin oxide (ITO); PET substrates; Sheet resistance; Optical transmittance

Gas barrier properties of titanium oxynitride films deposited on polyethylene terephthalate substrates by reactive magnetron sputtering by M.-C. Lin; L.-S. Chang; H.C. Lin (pp. 3509-3516).

Titanium oxynitride (TiN_xO_y) films were deposited on polyethylene terephthalate (PET) substrates by means of a reactive radio frequency (RF) magnetron sputtering system in which the power density and substrate bias were the varied parameters. Experimental results show that the deposited TiN_xO_y films exhibited an amorphous or a columnar structure with fine crystalline dependent on power density. The deposition rate increases significantly in conjunction as the power density increases from 2W/cm² to 7W/cm². The maximum deposition rate occurs, as the substrate bias is −40V at a certain power densities chosen in this study. The film's roughness slightly decreases with increasing substrate bias. The TiN_xO_y films deposited at power densities above 4W/cm² show a steady Ti:N:O ratio of about 1:1:0.8. The water vapor and oxygen transmission rates of the TiN_xO_y films reach values as low as 0.98g/m²-day-atm and 0.60cm³/m²-day-atm which are about 6 and 47 times lower than those of the uncoated PET substrate, respectively. These transmission rates are comparable to those of DLC, carbon-based and Al₂O₃ barrier films. Therefore, TiN_xO_y films are potential candidates to be used as a gas permeation barrier for PET substrate.

Keywords: Titanium oxynitride; Sputtering; Polyethylene terephthalate (PET); Gas permeation

Porous ZnO nanobelts evolved from layered basic zinc acetate nanobelts by Qingyue Cui; Ke Yu; Ning Zhang; Ziqiang Zhu (pp. 3517-3521).

Novel porous ZnO nanobelts were successfully synthesized by heating layered basic zinc acetate (LBZA) nanobelts in the air. The precursor of LBZA nanobelts consisted of a lamellar structure with two interlayer distances of 1.325 and 0.99nm were prepared using a low-temperature, solution-based method. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy are used to characterize the as-products. PL measurements show that the porous ZnO nanobelts have strong ultraviolet emission properties at 380nm, while no defect-related visible emission is detected. The good performance for photoluminescence emission makes the porous ZnO nanobelts promising candidates for photonic and electronic device applications.

Keywords: PACS; 81.05.Dz; 81.05.Rm; 78.55.EtZnO nanostructures; Porous morphology; PL spectra

Engineering and characterization of mesoporous silica-coated magnetic particles for mercury removal from industrial effluents by Jie Dong; Zhenghe Xu; Feng Wang (pp. 3522-3530).

Mesoporous silica coatings were synthesized on dense liquid silica-coated magnetite particles using cetyl-trimethyl-ammonium chloride (CTAC) as molecular templates, followed by sol–gel process. A specific surface area of the synthesized particles as high as 150m²/g was obtained. After functionalization with mercapto-propyl-trimethoxy-silane (MPTS) through silanation reaction, the particles exhibited high affinity of mercury in aqueous solutions. Atomic force microscopy (AFM), zeta potential measurement, thermal gravimetric analysis (TGA), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS) were used to characterize the synthesis processes, surface functionalization, and mercury adsorption on the synthesized magnetite particles. The loading capacity of the particles for mercury was determined to be as high as 14mg/g at pH 2. A unique feature of strong magnetism of the synthesized nanocomposite particles makes the subsequent separation of the magnetic sorbents from complex multiphase suspensions convenient and effective.

Keywords: Mesoporous silica; Magnetic particle; Molecular templating; Sol–gel reaction; Surface functionalization; Atomic force microscope; In situ imaging; Mercury removal

Finite element modeling of the mechanical effects of the UV laser ablation of polymer coatings by Ioannis N. Koukoulis; Christopher G. Provatidis; Savas Georgiou (pp. 3531-3539).

Laser ablation constitutes the basis of a number of techniques aiming at the processing and diagnosis of polymeric coatings on a variety of substrates. In all these applications, however, the issue is raised about the mechanical effects of the procedure on the substrate integrity. To this end, we employ finite element modeling for simulating the mechanical effects of UV laser ablation on a polymer specimen, with particular emphasis on the structural modifications that may be induced at areas away from the ablation spot. The cylindrical specimen consists of a poly(methylmethacrylate) (PMMA) film on a silica substrate. The analysis shows that stresses of high enough amplitude may propagate to distances far away from the irradiated spot and may induce deleterious mechanical deformations (e.g., cracks or delaminations). The dependence of the distribution of the tensile stresses on the thickness of the two components, as well as on size of the ablation spot area, is examined. Finally, the possibility of growth of pre-existing defects is shown. The results are overall in very good agreement with experimental observations.

Keywords: UV laser ablation; Finite element modeling

Synthesis of n-type boron phosphide films and formation of Schottky diode: Al/n-BP/Sb by S. Dalui; A.K. Pal (pp. 3540-3547).

Phosphorous rich BP in thin film form was deposited onto fused silica substrates by co-evaporating boron (99.99%) and phosphorous (99.995%) from a tantalum boat and indirectly heated alumina crucible, respectively. Schottky diode structures for n-type BP (Al/n-BP/Sb) were fabricated out of these films. Corresponding current–voltage and capacitance–voltage characteristics of the Schottky diodes were recorded and analyzed in the light of the existing theories.

Keywords: Boron phosphide; Thin films; III–V compounds; Schottky diode

Exciplex emission in the blend of two blue luminescent materials by Dewei Zhao; Fujun Zhang; Chao Xu; Jianyuan Sun; Shufang Song; Zheng Xu; Xiaowei Sun (pp. 3548-3552).

Organic light-emitting diodes (OLEDs) based on the blend of two blue luminescent materials N, N′-bis(1-naphthyl)- N, N′-diphenyl-1,1′-diphenyl-4,4′-diamine (NPB) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) were fabricated. The electroluminescence (EL) spectra of this device showed a new emission that is different from their intrinsic exciton emission. Compared with the photoluminescence (PL) spectra of single layer NPB and PBD, respectively, there was an apparent red shift in that of their blend. Thus the exciplex formation in the blend can be concluded due to the similar emission in both PL and EL spectra. The exciplex formation process and the effect of applied voltage were analyzed by Gaussian fitting.

Keywords: Exciplex emission; Red shift; Gaussian fitting

Growth of nanofilaments on carbon-based materials from microwave-assisted decomposition of CH₄ by B. Fidalgo; Y. Fernández; L. Zubizarreta; A. Arenillas; A. Domínguez; J.J. Pis; J.A. Menéndez (pp. 3553-3557).

The aim of this work was to study the growth of nanofilaments on two carbon-based materials (i.e. an activated carbon and carbon fibres) from microwave-assisted decomposition of CH₄. It was found that the nature of grown nanofilaments differed depending on the carbon support, probably due to the presence of diverse metals which catalyze the nanofilaments growth. Besides, it was also studied the influence of the composition of the in-flow gases on the growth of nanofilaments. Thus, tests with pure CH₄ and different CH₄/N₂ mixtures were carried out, the yield in nanofilaments being higher when mixtures were fed in. No nanofilaments were found after analogous tests carried out under conventional heating, therefore it can be stated that microwave heating is a promising technology for growing nanofilaments.

Keywords: PACS; 81.05.Uw; 81.07.−b; 84.90.a+Nanostructures; Carbon support; Nickel; Iron; Microwave

Determination of the laterally homogeneous barrier height of thermally annealed and unannealed Au/p-InP/Zn-Au Schottky barrier diodes by S. Asubay; Ö. Güllü; A. Türüt (pp. 3558-3561).

We have identically prepared Au/p-InP Schottky barrier diodes (SBDs). The diodes were annealed up to 400°C thermally. The barrier height (BH) for the as-deposited Au/p-InP/Zn-Au SBDs from the current–voltage characteristics have varied from 0.58 to 0.72eV, and ideality factor n from 1.14 to 1.47. The BH for the annealed SBDs from the current–voltage characteristics have varied from 0.76 to 0.82eV, and ideality factor n from 1.17 to 1.39. As a result of the thermal annealing, it has been seen that the BH values of the annealed SBDs are larger than those of the as-deposited SBDs. We have determined a lateral homogeneous BH value of 0.72eV for the as-deposited Au/p-InP SBD from the experimental linear relationship between barrier heights and ideality factors, and a value of 0.85eV for the annealed Au/p-InP SBD. The increase of 0.13eV in the BH value by means of 400°C annealing has been ascribed to the formation of the excess charges that electrically actives on the semiconductor surface.

Keywords: PACS; 73.30.+; y; 73.40.Ei; 73.40.Ns; 73.40.SxInP semiconductor; Schottky barrier height; Metal–semiconductor-metalcontacts; Barrier inhomogeneity

Non-chromate deoxidation of AA2024-T3: Sodium bromate–nitric acid (20–60°C) by T.G. Harvey; A.E. Hughes; S.G. Hardin; T. Nikpour; S.K. Toh; A. Boag; D. McCulloch; M. Horne (pp. 3562-3575).

The effect of a non-chromate deoxidiser (bromate–nitric acid) on AA2024-T3 has been examined by SEM, TEM/EELS and XPS. At low temperatures (20°C) the deoxidiser removed all intermetallics but had little effect on the surface oxide. At 40°C, attack on the intermetallics was again extensive but there was also evidence of attack on the surface oxide covering the matrix after 10min of immersion, leaving a roughened porous oxide. At 60°C, removal of intermetallics was complete and longer immersion times resulted in a characteristic scalloped structure across the surface which became more pronounced with increasing immersion time.

Keywords: Non-chromate; Chromate-free; Bromate; Deoxidation; Deoxidiser; Aluminium; Alloy; Nanostructure

Properties of deep etched trenches in silicon: Role of the angular dependence of the sputtering yield and the etched species redeposition by G. Marcos; A. Rhallabi; P. Ranson (pp. 3576-3584).

A Monte–Carlo etching simulation code modelling the temporal evolution of a silicon substrate submitted to a SF₆/O₂ plasma mixture was developed to complete and improve the experimental results found in an induced coupled plasma reactor (ICP). It reproduces the different plasma–surface interaction mechanisms occurring during this kind of process, predicts the trench profile evolution, calculates the etching rates and gives the chemical composition on the sidewalls. It is also a powerful tool for scientific investigation, with the possibility to add and test new surface processes, which cannot be directly controlled or measured by experiments. The object of this article is to investigate the role of two of them: the angular dependence of the sputtering yield and the redeposition of the sputter products. The study is focused on their topographic and kinetic consequences, and reveals that these mechanisms can explain some common defects appearing like microtrenching and faceting.

Keywords: Plasma; Etching; Silicon; ICP; Modelling; Simulation; SF; ₆; /O; ₂

Gold coatings on polyethyleneterephthalate nano-patterned by F₂ laser irradiation by P. Slepička; E. Rebollar; J. Heitz; V. Švorčík (pp. 3585-3590).

In this work we present periodic surface structures generated by linearly polarized F₂ laser light (157nm) on polyethyleneterephthalate (PET). Atomic force microscopy was used to study the topological changes induced by the laser irradiation. The laser irradiation induces the formation of periodic ripple structures with a width of ca 130nm and a height of about 15nm in the fluence range 3.80–4.70mJ/cm² and the roughness of the polymer surface increases due to the presence of these periodic structures. Subsequently, the laser modified PET foils were coated with a 50nm thick gold layer by sputtering. After Au deposition on the PET foils with ripple structure, the roughness of surface decreases in comparison to PET with ripples without Au coating. For 50nm thick Au layers, the ripple structure is not directly transferred to the gold coating, but it has an obvious effect on the grain size of the coating. With considerably thinner Au layers, the ripple structures are smoothened but preserved.

Keywords: Polyethyleneterephthalate; F; ₂; laser; Polymer modification; Surface topology; Periodic surface structure; Sputtering

Polymer adsorption on the surface of highly dispersed silica by Katarzyna Siwińska-Stefańska; Jędrzej Walkowiak; Andrzej Krysztafkiewicz; Teofil Jesionowski (pp. 3591-3600).

Attempts at modification of silica surface with a polymer (natural latex) directly in the course of the precipitation process have been made. The effects of temperature, non-ionic surfactants and silane coupling agent in preparation of poly[ cis-isoprene]-coated silica on the precipitation of polymer/silica composites initiated by ammonium salts (NH₄Cl, (NH₄)₂SO₄, NH₄HCO₃), have been studied. The influence of the process parameters on the quality of the silicas obtained and the character of the polymer adsorption on the silica surface has been determined along with the effect of the surface impregnation with natural latex on physicochemical parameters of the silicas (bulk density, capacities to absorb water, dibutyl phthalate and paraffin oil) and their surface structure.

Keywords: Impregnation of silica surface; Latex milk; Hydrophobisation and surface modification; Polymer adsorption

Enhanced field emission from LaB₆ thin films with nanoprotrusions grown by pulsed laser deposition on Zr foil by Dattatray J. Late; Kalyani S. Date; Mahendra A. More; Pankaj Misra; B.N. Singh; Lalit M. Kukreja; C.V. Dharmadhikari; Dilip S. Joag (pp. 3601-3605).

Lanthanum hexaboride (LaB₆) films have been deposited on a zirconium foil by pulsed laser deposition method. The field emission studies of the LaB₆ deposited film have been performed in the planar diode configuration under ultra high vacuum conditions. The Fowler–Nordheim plots were found to be linear in accordance with the quantum mechanical tunneling phenomenon. A typical field emission current of 7.02μA was drawn at an applied electric field of 2V/μm. The field enhancement factor is calculated to be 8913cm⁻¹, indicating that the field emission is from nanoscale protrusions present on the emitter surface. The atomic force microscope (AFM) investigation of the surface clearly shows the conical shaped nanoprotrusions of few hundred nanometers with asperities of 20–40nm on its top. The emission current–time plot recorded at the pre-set value of emission current of 5μA over a period of more than 3h exhibits an initial increase and subsequent stabilization of the current. The results reveal that the LaB₆/Zr field emitter obtained by the pulsed laser deposition (PLD) is a promising cathode material for practical applications in field emission-based devices.

Keywords: Field emission; Pulsed laser deposition; LaB; ₆; Current stability; Nanostructures

Investigation of the adsorption mechanism of water nanocluster on the substrate: The size and interaction strength effect by Shin-Pon Ju; Chun-Yi Chang; Wen-Jay Lee; Sheng-Hui Yang; Chien-Hsiang Chao; Jian-Yuan Huang; Hui-Lung Chen; Jee-Gong Chang; Kuan-Chuan Fnag (pp. 3606-3612).

Molecular dynamics simulation is utilized to investigate the effects of both the size of a water nanocluster and the interaction strength between the water nanocluster and a solid surface on the dynamic behavior of the water nanocluster when it is adsorbed on a solid surface. The simulation results demonstrate that both the size and the interaction strength influence the adsorption behavior of the water nanocluster on the substrate. When the interaction strength between water molecules and the substrate is strong, the morphology of the water nanocluster adsorbed on the substrate will tend to be flatter in shape. However, when the interaction strength is weak, the morphology of the water nanocluster is a semi-spherical shape. The size of the water nanocluster causes the water molecules in the first layer to lay flatter on the substrate at stronger interaction strengths. As the interaction strengths exceed 1.5kcalmol⁻¹, the value of orientation factor will reverse its trend for water nanoclusters with different sizes, with the smaller water nanocluster having the smallest orientation factor.

Keywords: Molecular dynamics; Water nanocluster; F3C water potential; Nosé-Hoover thermostat

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Applied Surface Science (v.254, #11)

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Applied Surface Science (v.254, #11)