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Spherical Particle Formation Mechanism in Pulsed Laser Melting in Liquid under Controlled-Pulse-Number Irradiation Using a Slit Nozzle Flow System
摘要： A detailed mechanism of pulsed laser melting in liquid (PLML) has remained in a controversial issue because of the difficulty associated with tracking and observing particles irradiated with a specific number of pulses in conventional batch-style irradiation. In a previous study, we developed a flow irradiation technique with a new slit nozzle for PLML mass-production. The slit nozzle can precisely control pulse numbers irradiated onto particles flowing through the slit nozzle. In the present study, this unique feature of the slit nozzle was used to clarify the PLML mechanism by a specific pulse number irradiation. According to a numerical analysis of the flow with the slit nozzle, 79% of the particles flowing through the slit nozzle were irradiated with two or three pulses and other particles that were irradiated with three or more pulses upon one passage through the slit nozzle at a 1.1 mL s?1 volume flow rate for a particle suspension in 60 wt% glycerol aqueous solution. Submicrometer-sized hollow spherical particles were formed via few-pulse irradiation of aggregates. After hollow particles were formed, the void in the hollow particles disappeared with increasing laser pulse number. Thus, an initial process of spherical particle formation and morphological transition of the particles with a specific irradiated pulse number were observed for the first time using the slit nozzle. The reduction of Fe3O4 particles via laser pulse irradiation was also tracked as a function of flow passage.
关键词： spherical particle formation,PLML,Fe3O4 reduction,pulsed laser melting in liquid,slit nozzle,hollow spherical particles
更新于2025-09-12 10:27:22
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Synthesis of heavy fermion CeCoIn5 thin film via pulsed laser deposition
摘要： CeCoIn5 (Co115) thin films have been grown on Al2O3 (000l) substrates through the pulsed laser deposition (PLD). The films are grown mainly along the c-axis, with CeIn3 and In-related alloys. The rock-salt type grains are nucleated, where Co115 grains mixed with excess indium are evenly distributed over the substrate. The electrical resistivity of the films shows a Kondo coherence peak near 47 K and the zero-resistance superconducting state at 1.8 K, which is the first observation in the PLD grown thin films of Co115. The Rietveld refinement of the thin films shows that the c/a ratio (tetragonality) is suppressed to 1.6312 from 1.6374 of single crystals, which is consistent with the linear relationship between the superconducting transition temperature and tetragonality. The good agreement indicates that the PLD could provide an alternative route to tune the 2D character of the critical spin fluctuations to understand the superconducting pairing mechanism of Co115.
关键词： Metal thin film,CeCoIn5 thin film,Heavy fermions,Superconductivity,Pulsed laser deposition
更新于2025-09-12 10:27:22
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High transmittance Er-doped ZnO thin films as electrodes for organic light-emitting diodes
摘要： Rare earth element-Erbium (Er) doped ZnO (ErZO) thin films were deposited on glass substrates by pulsed laser deposition (PLD). The effect of the Er doping concentration on photoelectric properties of ErZO thin films was investigated in the range of 0–2.0 wt. %. The Er doping resulted in the improvement of n-type conductivity as compared with intrinsic ZnO thin films. The optimized ErZO thin films present the low resistivity of 3.4 (cid:2) 10(cid:3)4 X/cm, high carrier concentration of 5.9 (cid:2) 1020/cm3, and high visible optical transmittance ((cid:4)93%) when the Er content is 1.0 wt. %. The ErZO thin films were used as transparent anodes to fabricate organic light-emitting diodes (OLEDs). Impressively, with ErZO as the anode, the current efficiency of the OLED device can reach as high as 86.5 cd/A, which was increased by 14% when compared with the reference OLED device (76.0 cd/A) using indium tin oxide as the anode.
关键词： Er-doped ZnO,transparent conducting oxides,pulsed laser deposition,thin films,organic light-emitting diodes
更新于2025-09-12 10:27:22
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Control of short-pulsed laser induced periodic surface structures with machining -picosecond laser nanotexturing with magnetic abrasive finishing-
摘要： An active area of research is the altering of surface functions (e.g., wettability and cell adhesion) by controlling fine surface structures such as laser-induced periodic surface structures (LIPSS). It has been found that micrometer-scale grooving (produced, for example, using ultraprecision cutting) followed by short-pulsed laser irradiation can result in efficient LIPSS coverage of a large area. However, micrometer-scale grooves can remain on the surface after short-pulsed laser irradiation. In this paper, to clarify the phenomenon and processing principle of groove-assisted short-pulsed laser irradiation, a finite-difference time-domain simulation is developed and experiments are conducted using 304 stainless steel and nickel-phosphorus (Ni–P) plating layer substrates. The use of magnetic abrasive finishing (MAF) is proposed for fabricating sub-micrometer-deep straight grooves with various peak-to-peak distances (pitch length) prior to the short-pulsed-laser irradiation. The subsequent short-pulsed-laser irradiation produces sub-micrometer-deep straight structures superimposed on the MAF-produced surface. While the pattern and depth of LIPSS are influenced by the groove depth made by MAF prior to the short-pulsed laser irradiation, the pitch length of LIPSS is dependent on the laser wavelength. This demonstrates the ability of MAF to produce grooves that guide the LIPSS and the efficacy of the developed method for fabricating fine LIPSS. The geometry of the sub-micrometer deep grooves—made prior to the short-pulsed laser irradiation—is the dominant factor in determining the pattern and geometry of the LIPSS.
关键词： Straight sub-micrometer groove,Surface roughness,Magnetic abrasive finishing,Short-pulsed laser
更新于2025-09-12 10:27:22
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Numerical simulation of the weld pool dynamics during pulsed laser welding using adapted heat source models
摘要： A transient simulation including the impact of the laser energy, the melting of the metal and the development of the weld pool was conducted to observe the evolution of the vapor capillary and the solidification of the melt in pulsed laser beam welding of AISI 304 steel. The phase field method was implemented to investigate the evolution and behavior of the liquid-gas interface during welding and to describe the condensed and vapor phases. The effects of phase transition, recoil pressure, thermo-capillary and natural convection, vaporization and temperature dependent material properties were taken into account. A Gaussian-like heat source under consideration of the Fresnel absorption model was used to model the energy input of the laser beam. The heat source model was extended by a newly developed empirical approach of describing multiple beam reflections in the keyhole. To validate this new model, the numerical results were compared to experimental data and good agreement regarding the size and shape of the weld pool was observed.
关键词： weld pool dynamics,multiple reflections,pulsed laser beam welding,vaporization
更新于2025-09-12 10:27:22
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Parabolic two-step model and accurate numerical scheme for nanoscale heat conduction induced by ultrashort-pulsed laser heating
摘要： Simulation of nanoscale heat transfer phenomena has attracted great attention, particularly the nano-scale heat conduction induced by ultrashort-pulsed laser heating. In this article, we propose a nanoscale parabolic two-step model and an accurate numerical scheme for thermal analysis of the nanoscale heat conduction induced by ultrashort-pulsed laser heating. To this end, we first introduce the Knudsen number (Kn) into the original parabolic two-step heat conduction equations and couple them with the Kn-dependent and temperature-jump boundary condition. We then develop a fourth-order accurate compact finite difference method for solving the nanoscale model. Stability and convergence of the obtained numerical scheme are analyzed theoretically. We finally test the accuracy and applicability of the nanoscale model and the obtained numerical scheme in three examples. By choosing various values of the Kn and the parameter α in the boundary condition, the simulation could be a tool for analyzing the nanoscale heat conduction induced by ultrashort-pulsed laser heating.
关键词： Nanoscale heat conduction,Convergence,Compact finite difference scheme,Stability,Ultrashort-pulsed laser heating
更新于2025-09-12 10:27:22
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Optical characterization of low temperature amorphous MoOX, WOX, and VOX prepared by pulsed laser deposition
摘要： Transition metal oxides are materials combining properties of electrical conductivity, optical transparency, and catalytical function. They are widely used in applications including solar cells, flat panel displays, and detectors. In particular, high work function oxides such as MoO3, WO3, and V2O5 have become popular. In many applications, low deposition temperatures are required, leading to amorphous structure. In this study, thin films of amorphous MoOX, WOX, and VOX were prepared by pulsed laser deposition, and their optical properties and work function were determined. Samples of polycrystalline ZnO were also prepared for comparison. Substrate temperature was varied in the range of 25 °C – 100 °C and oxygen pressure was varied in the range of 10 – 20 Pa during the process and also during the following sample cool-down and chamber venting. Optical characterization was based on photothermal deflection spectroscopy, which is a non-contact and non-destructive method for measuring directly absorptance spectra with sensitivity down to 10–4. Absorptance in the band gap serves as an indication of the presence of defects such as oxygen vacancies or metallic phases. Our optimized films achieved a sub-bandgap absorption coefficient as low as 103 cm-1 for MoOX, VOX, and 102 cm-1 in the case of the WOX. From the gradient of the absorption edge, Urbach energy was obtained, evaluating disorder in the semiconductor material. The work function of each material was obtained by Kelvin probe, and a slight correlation with Urbach energy was found. X-ray photoelectron spectroscopy indicated successful stochiometric transfer mainly for the lowest pressure and highest temperature samples.
关键词： work function,Urbach energy,optical spectroscopy,pulsed laser deposition,transparent metal oxide,photothermal deflection spectroscopy
更新于2025-09-12 10:27:22
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Evidence for vacancy trapping in Au-hyperdoped Si following pulsed laser melting
摘要： Nanosecond pulsed laser melting can be used to rapidly recrystallize ion-implanted Si through liquid phase epitaxy. The rapid resolidification that follows the melting results in a supersaturation of impurities and hyperdopes the Si, inducing novel optoelectronic properties with a wide range of applications. In this work, structural changes in the Si lattice in Au-hyperdoped Si are studied in detail. Specifically, we show that the local skewing of the lattice observed previously in regions of extremely high Au concentrations (>1.4 at. %) can be related to the displacement of Au from perfect lattice positions. Surprisingly, although the incorporation of the larger Au atoms into Si is expected to cause swelling of the lattice, reciprocal space mapping shows that a small amount (0.3 at. %) of lattice contraction (decrease in lattice parameter) is present in the hyperdoped layer. Furthermore, positron annihilation spectroscopy shows an elevated concentration of vacancies in the hyperdoped layer. Based on these observations and with the aid of density functional theory, we propose a phenomenological model in which vacancies are kinetically trapped into lattice sites around substitutional Au atoms during resolidification. This vacancy trapping process is hypothesized to occur as a means to minimize lattice strain and may be universal in pulsed laser melted Si systems.
关键词： vacancy trapping,lattice contraction,positron annihilation spectroscopy,density functional theory,pulsed laser melting,Au-hyperdoped Si
更新于2025-09-12 10:27:22
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Polarization Dependence of Pulsed Laser-Induced SEEs in SOI FinFETs
摘要： Pulsed current laser-induced measurements on SOI FinFETs at sub-bandgap wavelength (1260 nm) are affected by the polarization of the laser light used in the experimental testing setup. Such a polarization dependence is not observed during pulsed laser single event effects testing on large area silicon diodes, suggesting that the polarization dependence arises due to the presence of the nanoscale fin. Plasmonic enhancement is proposed as a likely mechanism for the polarization effects due to the metal/dielectric interfaces in the fin region. The observed polarization dependence has ramifications for collection and interpretation of data acquired by pulsed laser testing. Device orientation of FinFETs and other nanoscale devices during pulsed laser testing should be considered in order to ensure consistent testing conditions and reproducible measurement results across multiple measurement campaigns.
关键词： Pulsed laser,FinFET,single-event effects,single-event transients
更新于2025-09-12 10:27:22
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Morphological design of complex oxides during pulsed-laser deposition: The role of plasma-plume expansion
摘要： Complex oxides such as tin-doped indium oxide (ITO) are widely utilized as transparent conductors in a variety of functional devices. Typically, they are fabricated by sputtering, which often requires additional annealing to achieve high transparency and conductivity. Using pulsed laser deposition (PLD), both high transparency and high conductivity have been achieved without annealing, using instead selected gas species and pressures. However, the relative roles of Stranski-Krastanov-like and vapor-liquid-solid (VLS) growth modes during morphological transitions remain controversial. Here, we report on PLD of ITO in an inert-gas environment, identifying the role of plasma-plume expansion in the selection of VLS vs vapor-solid (VS) growth. For the lowest N2 pressure, indium-tin droplet formation, followed by self-catalyzed VLS growth, is observed. With increasing N2 pressure, a transition from VLS to VS growth is apparent. It is hypothesized that oxygen scattering at the lowest N2 pressure induces a metal-rich plume, which leads to metal droplet formation, followed by VLS growth. As the N2 pressure is increased, the plasma-plume and its metal-rich core are compressed, resulting in a transition to VS growth. This tunable compression of the plasma-plume o?ers a route to the morphological design of a wide range of functional complex oxide devices with tunable optical and electronic performance.
关键词： plasma-plume expansion,morphological design,VLS growth,pulsed laser deposition,complex oxides,VS growth
更新于2025-09-12 10:27:22