Laser-induced forward transfer technique for maskless patterning of amorphous V2O5 thin film

A laser-induced forward transfer technique has been applied for the maskless patterning of amorphous V₂O₅ thin films. A sheet beam of a frequency doubled (SHG) Q-switched Nd:YAG laser was irradiated on a transparent glass substrate (donor), the rear surface of which was pre-coated with a vacuum-deposited V₂O₅ 180 nm thick film was either in direct contact with a second glass substrate (receiver) or a 0.14 mm air-gap was maintained between the donor film and the receiving substrate. Clear, regular stripe pattern of the laser-induced transferred film was obtained on the receiver. The pattern was characterized using X-ray diffraction (XRD), optical absorption spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), atomic force microscopy (AFM), etc.     

Electroless plating of copper on polyimide films modified by surface-initiated atom-transfer radical polymerization of 4-vinylpyridine

Surface modification of polyimide (PI) films were first carried out by chloromethylation under mild conditions, followed by surface-initiated atom-transfer radical polymerization (ATRP) of 4-vinylpyridine (4VP) from the chloromethylated PI surfaces. The composition and topography of the PI surfaces modified by poly(4-vinylpyridine) (P4VP) were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The P4VP brushes with well-preserved pyridine groups on the PI surface was used not only as the chemisorption sites for the palladium complexes without prior sensitization by SnCl₂ solution during the electroless plating of copper, but also as an adhesion promotion layer to enhance the adhesion of the electrolessly deposited copper to the PI surfaces. The T-peel adhesion strength of the electrolessly deposited copper on the modified PI surface could reach about 6.6 N/cm. Effects of the polymerization time and the activation time in the PdCl₂ solution on the T-peel adhesion strength of the electrolessly deposited copper in the Sn-free process to the modified PI surface were also studied.     

Electroless plating of silver on cenosphere particles and the investigation of its corrosion behavior in composite silicon rubber

In this paper, silver coating on the surface of cenosphere particles was prepared by electroless plating method. The adhesion, oxidation resistance and corrosion resistance properties of silver coating mixed in silicone rubber were investigated. The corrosion characteristic of silver coating was evaluated by anodic polarization curves of the silicone rubber composite in sulfuric acid solution. The results showed that the silver coating on the surface of cenosphere particles was smooth and uniform. The silver film was not oxidized and peeling off during preparation of composite silicone rubber. The adhesion between the cenosphere particle and silver film was good enough. The anodic polarization curves of the silicone rubber composite showed typical activation and passivation transformation. The values of corrosion potential, the initiating passive potential and maintaining passivity potential of composites filled with different contents of Ag-coated cenosphere particles were the same and related to the nature of silver coating. The passive current density of composite increased with increase of the amount of Ag-coated cenosphere particles and was inversely proportional to the resistance of silicone rubber composite. The better the conductivity of silicone rubber composite is, the higher corrosion rate will be.     

Effect of fluence on the discoloration of marble cleaned with UV lasers

The effect of fluence level on the discoloration of marble surfaces after the removal of the encrustation by 355 nm laser pulses is comparatively studied. Considering the thermochemical reaction possibly occurring in the encrustation during laser irradiation, the mechanism responsible for the discoloration of the cleaned marble surface is analyzed. The reduction of iron oxides by graphite plays a key role in determining the final color of the cleaned marble surface. A two-dimensional laser ablative cleaning model including the reaction heat is applied to calculate the temperature distribution during laser heating. The kinetics of the thermochemical reaction is estimated based on the simulated temperature field. The occurrence of the thermochemical reaction is also verified indirectly with experiments. The marble surfaces before and after laser irradiation are characterized in terms of the chemical components through surface enhanced Raman spectroscopy. The surface color is measured with a chromameter using a 1976 CIE L^*a^*b^* color system. The proposed mechanism is also applied to numerically analyze the severe discoloration of marble cleaned with laser pulses at 1064 nm.     

Cleaning with water decomposed products obtained by laser irradiation

ArF excimer laser irradiation can decompose water, and decomposed products contain highly reactive substrates, such as radicals. We propose cleaning using pure water with the aid of water decomposed products obtained by ArF excimer laser irradiation. In this study, the oxidation potential of decomposed products was estimated in metal etching. Then, cleaning of cutting oil was examined. The focal point of the lens used was set at the water surface. Specimens were aligned parallel to the laser beam, so that only decomposed products affected contaminants. As a result, decomposed products could not etch nickel and copper plates, but only zinc plates. Cutting oil was cleaned after 18 000 irradiation pulses. The range of the region cleaned was 5 mm around the focal point.     

Effect of a small increase in the Ni content on the properties of a laser surface clad Fe-based alloy

Two Fe-based alloys with a small variation in the Ni content, Fe-15.2Cr-5.1Ni and Fe-15.7Cr-7.1Ni (wt.%), were fabricated on a martensitic stainless steel 1Cr13 substrate by laser surface cladding (LSC) using a CO₂ laser and Ar shielding gas that was blown into a molten pool. Both LSC alloys exhibited typical rapid directional solidification structures. However, 2 wt.% Ni increase led to ∼9% increase in the weight fraction of austenite, and ∼5% increase in the area proportion of interdendritic regions, which contained the higher Cr contents. These microstructural changes caused a great reduction in the microhardness and great improvements in the resistance to electrochemical corrosion in 0.5 M H₂SO₄ solution and high temperature oxidation in air at 900 °C. The reasons for these differences are discussed in detail.     

Laser-assisted decontamination—A wavelength dependent study

We present here the experimental results on cleaning of radioactive dielectric particulates, loosely deposited on stainless steel, by coherent light of 1064 nm wavelength and its three harmonics occurring at 532 nm, 355 nm and 266 nm, derived from an Nd-YAG laser. For the initial few exposures, the decontamination factor has been found to be highest when exposed to 1064 nm radiation. With increasing number of exposures, however, the radiation with reducing wavelength assumes a more important role as a cleaning agent. The observation of almost no cleaning with 1064 nm and much reduced cleaning with its harmonics when the contamination is deposited on a transparent substrate confirms the dominant role played by metal substrate towards expelling the loose particulates from its surface.     

Doppler characterization of laser inter-satellite links for optical LEO satellite constellations

Because of ensuring very low propagation delay between satellites, and providing global space-based broadband network services, low earth orbit (LEO) satellite constellations with laser inter-satellite links (ISLs) are considered to be the enabling technology to satisfy the increasing data traffic demand. However, significant Doppler can be observed by the onboard terminals on the ISLs, due to the high relative speed of the two communicating LEO satellites. This paper describes an analytic derivation of the Doppler wavelength shift measured by the terminal onboard a satellite on the signal transmitted through the ISLs. The Point-Ahead Mechanism of the optical ISLs is considered in the analytical expression of the Doppler wavelength shift. Then, in terms of the ISLs characteristics of the satellite constellations, the expression of Doppler wavelength shift is deduced into two aspects. First, for the full time accessing ISLs, it evolves as a function of the constellation parameters. Thus, the Doppler characterization for two kinds of interorbit full time accessing ISLs of LEO satellite constellations is analyzed. Second, for the intermittent accessing ISLs, the expression of Doppler wavelength shift is given as a function of the minimum ISL distance between two communicating satellites. And the visibility duration of the destination satellite at the source satellite is estimated for the intermittent ISLs. This work is helpful to evaluate the design of constellation networking.     

Laser induced copper electroless plating on polyimide with Q-switch Nd:YAG laser

The results of laser induced deposition of copper on polyimide substrate from copper electrolyte solution are reported. Unlike most work reported in the literatures where CW Ar⁺ lasers were used, a second harmonic (532 nm wavelength) Q-switch Nd:YAG laser was used for our experiments. The deposition process was conducted by laser-catalyzing of the polyimide surface and subsequent photothermal-accelerated reduction of copper-complex ions in an alkaline reducing environment. The characteristics of the deposited copper line were investigated in terms of laser beam scanning speed, and the number of scans. The surface morphology and chemical composition of the deposited copper were analyzed using field emission scanning electron microscope (FESEM) and energy dispersive spectrometer (EDX). The optimum processing conditions have been identified. The copper deposit was found to adhere well to the substrate.     

Pulsed laser induced synthesis of scheelite-type colloidal nanoparticles in liquid and the size distribution by nanoparticle tracking analysis

Pulsed laser ablation (PLA) of ceramic target in liquid phase was successfully employed to prepare calcium tungstate (CaWO₄) and calcium molybdate (CaMoO₄) colloidal nanoparticles. The crystalline phase, particle morphology and optical property of the colloidal nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The produced stable colloidal suspensions consisted of the well-dispersed nanoparticles showing a spherical shape. The mechanism for the laser ablation and nanoparticle forming was discussed under consideration of photo-ablation process. Nanoparticle tracking analysis using optical microscope combined with image analysis was proposed to determine the size distribution function of the prepared colloidal nanoparticles. The mean size of the CaWO₄ and CaMoO₄ colloidal nanoparticles were 16 and 29 nm, with a standard deviations of 2.1 and 5.2 nm, respectively.     

Strategy of manufacturing components with designed internal structure by selective laser melting of metallic powder

Application of selective laser melting for manufacturing three-dimensional objects represents one of the promising directions to solve challenging industrial problems. This approach permits to extend dramatically the freedom of design and manufacture by allowing, for example, to create an object with desired shape and internal structure in a single fabrication step. The design of the part can be tailored to meet specific functions and properties (e.g. physical, mechanical, chemical, biological, etc.) using different materials. Metallic objects were manufactured by Phenix PM 100 machine from Inconel 625 powder. The objective was to analyze the influence of the manufacturing strategy on the internal structure and mechanical properties of the components manufactured by selective laser melting technology. Anisotropy of the internal structure and mechanical properties of the fabricated objects were studied.     

Surface morphology of laser tracks used for forming the non-smooth biomimetic unit of 3Cr2W8V steel under different processing parameters

Aiming to form the high quality of non-smooth biomimetic unit, the influence of laser processing parameters (pulse energy, pulse duration, frequency and scanning speed in the present work) on the surface morphology of scanned tracks was studied based on the 3Cr2W8V die steel. The evolution of the surface morphology was explained according to the degree of melting and vaporization of surface material, and the trend of mean surface roughness and maximum peak-to-valley height. Cross-section morphology revealed the significant microstructural characteristic of the laser-treated zone used for forming the functional zone on the biomimetic surface. Results showed that the combination of pulse energy and pulse duration plays a major role in determining the local height difference on the irradiated surface and the occurrence of melting or vaporization. While frequency and scanning speed have a minor effect on the change of the surface morphology, acting mainly by the different overlapping amount and overlapping mode. The mechanisms behind these influences were discussed, and schematic drawings were introduced to describe the mechanisms.     

Laser induced synthesis of nanoparticles in liquids

The review of results on nanoparticles formation is presented under laser ablation of Ag, Au, and Cu-containing solid targets in liquid environments (H₂O, C₂H₅OH, C₂H₄Cl₂, etc.). X-ray diffractometry (XRD), UV-vis optical transmission spectrometry, and high resolution transmission electron microscopy (HRTEM) characterize the nanoparticles. The morphology of nanoparticles is studied as the function of both laser fluence and nature of the liquid. The possibility to control the shape of nanoparticles by ablation of an Au target by an interference pattern of two laser beams is demonstrated. Formation of alloyed Au-Ag and Ag-Cu nanoparticles is reported under laser exposure of a mixture of individual nanoparticles. The effect of internal segregation of brass nanoparticles is discussed due to their small lateral dimensions. The factors are discussed that determine the distribution function of particles size under laser ablation. The influence of laser parameters as well as the nature on the liquid on the properties of nanoparticles is elucidated.     

Influence of transparent coating thickness on thermoelastic force source and laser-generated ultrasound waves

A numerical model is established to investigate the influence of transparent coating thickness on the laser-generated thermoelastic force source and ultrasound waves in the coating-substrate system by using the finite element method (FEM). Taking into account the effects of thermal diffusion, the finite width and duration of the laser source, as well as the temperature dependence of material properties, the transient temperature distributions are obtained firstly. Applying this temperature field to structure analyses as thermal loading, the thermoelastic stress field and laser-generated ultrasound wave in the specimen are obtained. The generation and propagation of the laser thermoelastically induced stress field and ultrasonic waves in coating-substrate system are presented in detail. The influence of transparent coating thickness on the transient temperature distribution, thermoelastic force source and the laser-generated ultrasound waveforms is investigated. The numerical results indicate that the thermoelastic force source and laser-generated ultrasound waveform are strongly affected by the coating thickness due to the constraint of coating. This method can provide insight into the generation and propagation of the laser-generated stress field in coating-substrate system consisting of a transparent coating and an opaque metallic substrate. It provides theoretical basics to optimize ultrasonic signal generation in particular applications and invert the physical and geometrical parameter of the coating-substrate system more accurately in the experiment.     

Laser surface alloying of Ni-plated steel with CO2 laser

Laser surface alloying of low carbon steel electroplated with thin (10 μm) Ni using an 850 W CW CO₂ laser is reported for the first time. Fe-Ni binary alloys of different concentrations are formed by varying laser traverse speed from 0.5 to 5 m/min. The phase transformation from α to α + γ is discussed as a function of Ni contents. Development of microstructure in the modified zone is analysed in terms of solidification rate and Ni concentration. A three-fold increase in the microhardness of the binary alloy is observed. Formation of homogenous, adherent and crack free surface alloys is reported.     

Transient effects in pulsed laser irradiation

Theoretical analysis of the influence of the temporal profile (rectangular, triangular, Gaussian) of the laser pulse on heating/cooling and phase transition velocities and quantity of ablated material was performed on the basis of a multifront Stephan problem. Modeling showed that material removal under stationary conditions (that correspond to long pulses) is entirely controlled by specific heat and material density, while in the case of transient regimes (short pulses) thermal conductivity and heat capacity play a predominant role. Interaction of the melting and evaporation fronts characterized by an evaporation front velocity far exceeding the melting front one is one of the examples of the transient nature of the phenomena influenced by the laser pulse parameters.     

Alumina-zirconium ceramics synthesis by selective laser sintering/melting

In the present paper, porous refractory ceramics synthesized by selective laser sintering/melting from a mixture of zirconium dioxide, aluminum and/or alumina powders are subjected to optical metallography and X-ray analysis to study their microstructure and phase composition depending on the laser processing parameters. It is shown that high-speed laser sintering in air yields ceramics with dense structure and a uniform distribution of the stabilizing phases. The obtained ceramic-matrix composites may be used as thermal and electrical insulators and wear resistant coating in solid oxide fuel cells, crucibles, heating elements, medical tools. The possibility to reinforce refractory ceramics by laser synthesis is shown on the example of tetragonal dioxide of zirconium with hardened micro-inclusion of Al₂O₃. By applying finely dispersed Y₂O₃ powder inclusions, the type of the ceramic structure is significantly changed.     

Magnetic properties of core-shell catalyst nanoparticles for carbon nanotube growth

Two types of core-shell nanoparticles have been prepared by laser pyrolysis using Fe(CO)₅ and C₂H₂ or [(CH₃)₃Si]₂O as precursors and C₂H₄ as sensitizer. The first type (about 4 nm diameter) - produced by the decomposition of Fe(CO)₅ in the presence of C₂H₄ and C₂H₂ - consists of Fe cores protected by graphenic layers. The second type (mean particle size of about 14 nm) consists also of Fe cores, yet covered by few nm thick γ-Fe₂O₃/porous polycarbosiloxane shells resulted from the [(CH₃)₃Si]₂O decomposition and superficial oxidation after air exposure. The hysteresis loops suggest a room temperature superparamagnetic behavior of the Fe-C nanopowder and a weak ferromagnetic one for larger particles in the Fe-Fe₂O₃-polymer sample. Both types of nanoparticles were finally used as a catalyst for the carbon nanotube growth by seeding Si(100) substrates via drop-casting method. CNTs were grown by Hot-Filament Direct.Current PE CVD technique from C₂H₂ and H₂ at 980 K. It is suggested that the increased density and orientation degree observed for the multiwall nanotubes grown from Fe-Fe₂O₃-polymer nanoparticles could be due to their magnetic behavior and surface composition.     

Experimental generation of high-contrast Talbot images with an ultrashort laser pulse

A femtosecond Ti:sapphire laser oscillator emitting pulses with 800 nm central wavelength, 10.9 fs pulse width, and 75 MHz repetition rate, combined with a dispersion-compensated diffractive system, was used to implement a large-area, high-contrast, broadband optical interference technique based on the Talbot effect. Chromatic artifacts associated with the huge spectrum of the optical source (approximately 150 nm) are compensated for with an air-separated hybrid diffractive-refractive lens doublet. The spatial resolution of the chromatically compensated Talbot images under femtosecond illumination is nearly identical to that achieved under continuous wave monochromatic illumination. Furthermore, the temporal width of the signal at the Talbot planes is limited by the group-delay-dispersion coefficient which is shown to be small. High-contrast one-dimensional periodic structures of 96.1 μm spacing generated by Talbot diffractometry are experimentally demonstrated.     

空腔铜靶的化学镀制研究

介绍了在预处理芯轴(聚甲基丙烯酸甲酯)表面采用化学镀的方法制备铜空腔的技术,研究了镀液中硫酸铜含量、甲醛含量,镀液pH值、温度等对化学镀铜沉积速率和溶液稳定性的影响。根据实验确定了适宜的化学镀铜工艺规范：硫酸铜质量浓度10~20 g/L,TART·K·Na质量浓度10~30 g/L,EDTA·2Na质量浓度10~28 g/L,甲醛体积浓度10~25 mL/L,添加剂质量浓度10 mg/L,pH值12~13,温度35~65 ℃。通过该工艺制备出的镀层厚度达到10～25 μm,均匀性达到95%,表面无砂眼、裂纹等缺陷,刻蚀芯轴后空腔能自持。该方法为ICF研究制备金属或合金材料靶提供了新的途径。