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Microhole Formation Behavior of Polypropylene Film Using CO<sub>2 </sub>Laser Irradiation
摘要： Biaxially oriented polypropylene films produced by simultaneous equi-biaxial stretching to the draw ratio of 4 (cid:186) 4 were perforated by the carbon dioxide laser under various laser fluences up to 426.3 J/cm2. After applying various laser fluences, the irradiated area was observed using a laser scanning confocal microscope. With the increase of fluence, the surface deformation with the formation of a crater surrounded by a doughnut-like rim was firstly observed at the laser fluence of 49.7 J/cm2, followed by the starting of the formation of a microhole surrounded by the rim at 113.7 J/cm2. The diameter of the microhole and the size of the rim increased rapidly with the increase of laser fluence. Mechanisms for the formation of a crater, the opening of a microhole, and the formation of surrounding rim were considered to be related to the surface tension and the shrinkage caused by molecular orientation relaxation. On the other hand, volume loss from the laser irradiated area was negligibly small at the moment of microhole opening, and started to increase rapidly when the fluence reached around 150 J/cm2. The microhole formation behavior was also observed by a high-speed camera. The velocity of microhole opening increased rapidly at first, presumably during the laser irradiation, and then slowed down after the cessation of laser irradiation. Theoretically estimated temperature distribution along the film thickness was compared with the laser perforation behavior. Starting of the deformation of film matched well with the starting of melting of the film surface. Film temperature was lower than the thermal decomposition temperature at the moment of the opening of a microhole, whereas at the moment of the starting of volume loss, film temperature was lower than the decomposition temperature estimated based on the heating rate of laser irradiated area, indicating that the decomposition and vaporization continues for a while after the cessation of laser irradiation.
关键词： microhole formation,molecular orientation relaxation,Polypropylene,laser fluence,CO2 laser,surface tension
更新于2025-09-19 17:13:59
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Improved growth conditions of pulsed laser-deposited PbI2 nanostructure film: towards high- photosensitivity PbI2/CNTs/Si photodetectors
摘要： Nanostructured PbI2 films were grown by laser deposition technique at a substrate temperature of 45?°C was demonstrated. Herein, we attempted to improve and control the crystal growth of PbI2 film and p-PbI2/MWCNTs/p-Si photodetector by finding the optimum laser fluence. X-ray diffraction XRD results illustrate that the grown PbI2 films are polycrystalline with hexagonal structure along (001) and the film crystallinity degraded with increasing the laser fluence. Scanning electron microscope SEM revealed that the particle size decreases as laser fluence increase and film deposited at 3.9?J/cm2 was dense and the grains distributed uniformly over the surface of the film. Energy dispersive X-ray EDX data confirms that the film stoichiometry depends on laser fluence and the film deposited at 3.9?J/cm2 was stoichiometric PbI2. The Photosensitivity investigations reveal that responsivity as high as 0.4 A/W at 610?nm was obtained for the p-PbI2/MWCNTs/p-Si photodetector prepared at 3.9?J/cm2 without post-deposition annealing.
关键词： photodetector,nanostructure film,PbI2,pulsed laser deposition,laser fluence
更新于2025-09-12 10:27:22
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Laser—synthesised Ag <sub/>2</sub> S nanoparticles in liquid: effect of laser fluence on structural and optical properties
摘要： In this study, we report for the first time the preparation and characterization of silver sulfide nanoparticles (NPs) by one-step laser ablation of the silver target in thiourea aqueous solution without using a catalyst. The effect of laser fluence on the crystal structure, morphology, size and elemental composition of Ag2S NPs was investigated. X-ray diffraction (XRD) results show Ag2S NPs are polycrystalline with monoclinic phase and the variation in laser fluence affects the crystallinity of the synthesized NPs. The optical energy gap decreases from 2.2eV to 1.6eV as the laser fluence increases from 2.38 Jcm-2 to 6.77Jcm-2. Transmission electron microscope (TEM) investigation confirms the formation of spherical Ag2S NPs and nanosheets morphologies and the particle size is found increases from 30nm to 65nm when the laser fluence increases from 2.38 Jcm-2 to 6.77Jcm-2. The Raman spectra of Ag2S NPs show the presence of six active Raman peaks and their intensity increased with laser fluence.
关键词： Silver sulfide,Laser ablation,Nanoparticles,Laser fluence
更新于2025-09-12 10:27:22
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Effects of Laser Fluence and Pulse Overlap on Machining of Microchannels in Alumina Ceramics Using an Nd:YAG Laser
摘要： The quality of micro-features in various technologies is mostly affected by the choice of the micro-fabrication technique, which in turn results in several limitations with regard to materials, productivity, and cost. Laser beam micro-machining has a distinct edge over other non-traditional methods in terms of material choices, precision, shape complexity, and surface integrity. This study investigates the effect of laser fluence and pulse overlap while developing microchannels in alumina ceramic using an neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Microchannels 200 μm wide with different depths were machined using different laser peak fluence and pulse overlap (percentage of overlap between successive laser pulses) values. It was found that high pulse overlaps and fluences should be avoided as they give rise to V-shaped microchannels i.e., 100% bottom width errors. The optimal peak fluence range was found to be around 125–130 J/cm2 corresponding to 3–5 μm depth per scan. In addition, channels fabricated with moderate pulse overlap were found to be of good quality compared to low pulse overlaps.
关键词： microchannels,laser,fluence,alumina,micromachining
更新于2025-09-11 14:15:04