Papers by Keyword: Laser Ablation

Abstract: The mechanism of destruction of a material by high-speed impact is known to be complex, and it is hard to analyze the inner state of the material during the destruction process. In particular, it is difficult to measure the temperature changes within a material during a high-speed impact. In this study, we propose a new method for estimating this temperature change by measuring the plasma produced at the impact point using a triple probe. A plasma produced by laser ablation was measured to ascertain that the triple probe actually worked. Further, some of the parameters related to the triple probe were varied, and the obtained results were compared, in order to determine the optimal parameters for measuring plasmas. A pulsed Nd-YAG laser with a fundamental wavelength of 1064 nm was employed to produce laser ablation. The laser was irradiated on a thin A2024 plate coated with a black paint. The expanding plasma plume was recorded with a high-speed camera, and the signal from the plasma was measured with the triple probe.

Abstract: The field of application of electrochemical analysis has been significantly widened after modified electrodes appeared. Metallic nanoparticles are ones of the most common used modifiers of the electrode surface to increase the sensitivity and selectivity of the analysis. Increasing of selectivity is extremely important in cases when two or more analyts have electro-chemical signals at nearly the same values of electrode potential. Dopamine and ascorbic acid are an example of such case. In present work Au, Pt, Pd, and Ni “pure” nanoparticles obtained by laser ablation without stabilizing agents were used to modify the surface of a glassy carbon electrode. Modified electrodes were tested in solutions of ascorbic acid and dopamine at their simultaneous electro-oxidation. It was shown that Au, Pt, and Ni nanoparticles on the electrode surface increase the selectivity of analysis giving two separate peaks of analyts.

Abstract: Dispersions of cerium oxide nanoparticles in water, ethanol, and water-ethanol solution were synthesized for the first time using laser ablation of metallic target. The fundamental harmonic of nanosecond Nd:YAG laser was used. Nanocrystalline powders of cerium oxide were obtained from the dispersions. The average size of the crystallites was 17-19 nm. Phase composition of nanoparticles was confirmed by X-ray diffraction and Raman spectroscopy. It was found that carbon present on the surface of CeO₂ particles. The materials obtained may be used as catalyst carriers for CO oxidation, and as active components of sunscreen cosmetic products.

Abstract: Gold (Au) nanoparticles (NPs) were prepared by pulsed laser (Nd:YAG, 1064 nm) ablation of an individual target in deionized water (DIW), pure ethanol, and mixture of DIW and ethanol with different concentrations of ethanol. The effects of ambient liquid environment on ablation efficiency, stability, and size of Au NPs were experimentally investigated. The optical spectral characterization and morphological observations were determined by UV-Vis spectrophotometer and transmission electron microscopy, respectively. Particles are nearly spherical in shape in all liquid environments. The ablation experiment was initially performed by using DIW as the reference sample. The obtained Au NPs have an average particle size of about 18.71±7.50 nm. The comparison of the experimental results with the reference sample after a storage time of 48 h revealed that Au NPs in pure ethanol medium were not stable and exhibited much lower ablation efficiency and broader size distribution with an average particle size of 23.83±11.65 nm. Addition of ethanol with different volumes to the DIW significantly improved Au NPs properties in the mixture. The optimum ethanol concentration in the mixture was determined to be 70 vol%, which yielded the maximum ablation efficiency, rather narrow size distribution, and controllable size (12.43±8.10 nm) of Au NPs. A simple method for controlling the properties of Au NPs produced in the binary mixture of DIW-ethanol by laser ablation technique is presented.

Abstract: The conditions of formation of the ZrO₂ and HfO₂ high-temperature (tetragonal and cubic) phases in the ablated nanoparticles were investigated. X-ray diffraction and transmission electron microscopy data demonstrate that laser intensities above 10⁹ W/m² ensure the formation of the ZrO₂ high-temperature phases, while intensities above 5·10⁹ W/m² do the formation of the HfO₂ high-temperature phases. Quantitative content of the high-temperature phases in layers of the ablated nanoparticles increases with raising the intensity. The obtained nanoparticles exhibit good thermal stability.

Abstract: We report a hybrid hetero p-n junction between Zinc Oxide (ZnO) microspheres and p-GaN thin film or poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS). ZnO microspheres, which have high crystalline quality, were synthesized by ablating a ZnO sintered target with focused pulsed laser at high fluence. Recent investigation has demonstrated that ZnO microspheres had high optical property and laser actions in the WGM (whispering gallery mode) from the microshperes under pulsed laser irradiation. In this study, we fabricated a hybrid hetero p-n junction between ZnO microspheres and p-GaN or PEDOT:PSS, and both p-n junctions with p-GaN or PEDOT:PSS had a good rectifying characteristic. In the case of p-GaN, electroluminescence was observed under forward bias.

Abstract: We study laser ablation of nanoparticles (NPs). The interaction of a high-intensity laser pulse with NPs brings the NP into a highly non-equilibrium state. Depending on the energy input from the laser, it will melt and may fragment and evaporate off atoms and clusters. We employ molecular dynamics simulation to study this interaction since thermodynamic properties can be extracted from output data of this simulation. The interatomic interaction is modeled by a Lennard-Jones (LJ) potential. The intensity of the laser is above the ablation threshold. The NP has been chosen to have a spherical shape with diameter 50 s in LJ units. The laser energy is given to the NP instantaneously at the beginning of the simulation and homogenously to all atoms; it corresponds to an energy input of 5.4 e per atom. The simulation is continued up to a time 200 t in LJ units. Temperature-density phase-space trajectories show that the nanoparticle density and temperature strongly decrease after the irradiation. The pressure in the sphere becomes strongly tensile after irradiation. The ablation proceeds by spallation of the irradiated cluster. We provide an analysis of the fragments produced by the ablation of the spherical NP. Our results are contrasted to the case of laser ablation of a thin-film target.

Abstract: Mechanical blade dicing is a state-of-the-art technique for the chip separation of SiC devices. Due to the hardness of SiC this technique suffers from low feed rate and high wear of the diamond coated dicing blade, resulting in the risk of uncontrolled tool breakage during the dicing process. With the upcoming transition to 150 mm diameter of SiC wafers this technique will most probably reach its limit. For dicing SiC wafers of those diameters on a productive scale three alternative dicing technologies are considered in this paper: ablation laser dicing, Stealth Dicing and Thermal Laser Separation. All these methods are based on laser processing. The benefits of these technologies are discussed in detail and compared to the classical mechanical diamond blade dicing, including a brief summary of first experimental results on each of the three laser dicing technologies.

Abstract: The special features of nanoparticles formation by laser ablation of volume metallic zinc targets in various solvents using sulfur precursors are studied. Semiconductor cadmium sulphide nanoparticles with average sizes 10–15 nm are synthesized by zinc ablation in the presence of hydrogen sulfide and thioacetamide, and their composition, structure, and optical properties are investigated. It is established that with the use of H₂S, only CdS particles are formed in the medium.

Abstract: The transparent conductive film (TCF) is the conductive material with higher light transmittance and good conductivity in the visible light range. Up to now, it is popular to print transparent conductive film with metal grid. From the perspective of making transparent conductive film by gravure printing, the printing effect of the fine lines on the TCF is analyzed by diverse gravure plate-making method. According to the requirements of the fine lines and conductivity for TCF, the two kinds of plate are made respectively by laser ablation method and laser engraving method, and applied respectively in proofing. The advantages and disadvantages of the two plate-making methods are evaluated, according to the analysis on the line width, conductivity and light transmittance of the TCF. The research results show that the laser ablation method can obtain the good electric conductivity and light transmittance of the TCF, but a relatively larger printing line width, the laser engraving method can get better relatively small line width, but the poor conductivity and light transmittance. So, the plate-making process needs to be improved.