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[en] A combined experimental and computational study is performed to investigate the origin and characteristics of the surface features observed in SEM images of thin polymer films deposited in matrix-assisted pulsed laser evaporation (MAPLE). Analysis of high-resolution SEM images of surface morphologies of the films deposited at different fluences reveals that the mass distributions of the surface features can be well described by a power-law, Y(N) ∝ N -t, with exponent -t ∼ -1.6. Molecular dynamic simulations of the MAPLE process predict a similar size distribution for large clusters observed in the ablation plume. A weak dependence of the cluster size distributions on fluence and target composition suggests that the power-law cluster size distribution may be a general characteristic of the ablation plume generated as a result of an explosive decomposition of a target region overheated above the limit of its thermodynamic stability. Based on the simulation results, we suggest that the ejection of large matrix-polymer clusters, followed by evaporation of the volatile matrix, is responsible for the formation of the surface features observed in the polymer films deposited in MAPLE experiments
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[en] Lanthanum-based thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated glass substrate by a self-assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The tribological properties of the films sliding against GCr15 steel ball were evaluated on a UMT-2MT reciprocating friction and wear tester. As the results, the target film was obtained and reaction may have taken place between the film and the glass substrate. The tribological results show that lanthanum-based thin films are superior in reducing friction and resisting wear compared with APTES-SAM and phosphorylated APTES-SAM. SEM observation of the morphologies of worn surfaces indicates that the wear of APTES-SAM and the phosphorylated APTES-SAM is characteristic of brittle fracture and severe abrasion. Differently, slight abrasion and micro-crack dominate the wear of lanthanum-based thin films. The superior friction reduction and wear resistance of lanthanum-based thin films are attributed to the enhanced load-carrying capacity of the inorganic lanthanum particles in the lanthanum-based thin films as well as good adhesion of the films to the substrate
Journal
[en] Dielectric barrier discharge (DBD) of Helium and Helium + air modify the surface of Angora rabbit fibers. DBD treatment carried out at different power densities, changes the morphology and chemical composition of the surface of Angora fiber. Scanning electron microscopy (SEM) results reveal that the DBD treatment eliminates fibrosity from the fiber surface. X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer (FTIR) spectrum confirm the increase in oxygen bonding at the surface. These changes reduce shedding of the fibers and improve dye-uptake property. However, even after 10 min of plasma exposure the thermal insulation (heat keeping ratio) of Angora fibers nearly remain unchanged. It has been noticed that DBD treatment (10 min) reduces whiteness of the fiber
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[en] Pt/N-codoped TiO2 nanotubes were prepared and characterized by various analytical methods, such as transmission electron microscope (TEM), diffuse reflection spectra (DRS), X-ray powder diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS) and fluorescence spectra (FL). The photocatalytic efficiency was evaluated by the photodegradation of Rhodamine B (RB) in an aqueous solution under visible light irradiation. It has been confirmed that Pt/N-codoped TiO2 nanotubes could be excited by visible light and the recombination rate of electron-hole pairs declined significantly. The higher visible light activity is due to the codoping of nitrogen and platinum
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[en] The corrosion products of a TM 23 bronze-leaded alloy (Cu 72%, Pb 15%, Zn 8% and Sn 5%) were obtained in a salt spray cabinet after exposition during 120 h and 1000 h. The products obtained were studied using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The major products of bronze-leaded corrosion were oxides and basic salts of Cu, CuCl2.3Cu(OH)2, and Pb, Pb(OH)Cl. The results can be attributed to a kinetic control of the corrosion reactions
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[en] Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of γ-FeCr0.29Ni0.16C0.06 austenite solid solution dendrites as the dominant and very small amount of super-fine dispersed Ni3Al γ' phase and Laves particles as well as MC needle-like carbides distributed in the interdendritic regions. Although the microhardness of the laser-welded seam was lower than that of the base metal, the strength of the joint was equal to that of the base metal and the fracture mechanism showed fine ductility
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[en] The CdSe and Fe doped CdSe (Fe:CdSe) thin films have been electrodeposited potentiostatically onto the stainless steel and fluorine doped tin oxide (FTO) glass substrates, from ethylene glycol bath containing (CH3COO)2.Cd.2H2O, SeO2, and FeCl3 at room temperature. The doping concentration of Fe is optimized by using (photo) electrochemical (PEC) characterization technique. The deposition mechanism and Fe incorporation are studied by cyclic voltammetry. The structural, surface morphological and optical properties of the deposited CdSe and Fe:CdSe thin films have been studied by X-ray diffraction, scanning electron microscopy (SEM) and optical absorption techniques respectively. The PEC study shows that Fe:CdSe thin films are more photosensitive than that of undoped CdSe thin films. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure. SEM studies reveal that the films with uniformly distributed grains over the entire surface of the substrate. The complete surface morphology has been changed after doping. Optical absorption study shows the presence of direct transition and a considerable decrease in bandgap, E g from 1.95 to 1.65 eV
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[en] Silicon carbonitride (Si:C:N) films produced by the remote microwave hydrogen plasma chemical vapor deposition (RP-CVD) using bis(dimethylamino)methylsilane as single-source precursor and hydrogen as an upstream gas for plasma generation, were examined in terms of their physical (density) and mechanical (hardness, elastic modulus, friction coefficient, and 'plasticity index') properties. The effect of substrate temperature (varied in the range of 30-400 oC) on the properties of Si:C:N films is presented. A reasonable compositional and structural dependencies of film properties were determined using, respectively, the XPS atomic concentration ratios N/Si and C/Si, as well as the relative integrated intensities of the IR absorption bands from the Si-N and Si-C bonds (controlled by deposition temperature), evaluated in the first part of this work. In view of their good mechanical properties, Si:C:N films seem to be useful coatings for improving surface mechanics of engineering materials
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[en] Previous work by the authors on micromachining of Al2O3-TiC ceramics using excimer laser radiation revealed that a columnar surface topography forms under certain experimental conditions. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations show that the columns develop from small globules of TiC, which appear at the surface of the material during the first laser pulses. To understand the mechanism of formation of these globules, a 2D finite element ablation model was developed and used to simulate the time evolution of the temperature field and of the surface topography when a sample of Al2O3-TiC composite is treated with KrF laser radiation. Application of the model showed that the surface temperature of TiC rises much faster than that of Al2O3, but since TiC has a very high boiling temperature, its vaporization is significant only for a short time. By contrast, the surface temperature of Al2O3 rises above its boiling temperature for a much longer period, leading to a greater ablation depth than TiC. As a result, a small TiC globule stands above the Al2O3 surface. The results of the model are compared with experimental measurements performed by AFM. After three pulses, the height of the globules predicted by the model is about 340 nm, in good agreement with the height measured experimentally, about 400 nm
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