Synthesis of Magnetite Particles by Pulsed Alexandrite Laser Processing of Metallic Glass Precursors

1995 ◽  
Vol 397 ◽  
Author(s):  
Monica Sorescu ◽  
S.A. Schafer ◽  
E.T. Knobbe
Keyword(s):  
Laser Processing ◽  
Alloy System ◽  
Alexandrite Laser ◽  
Magnetic Texture ◽  
Laser Fluences ◽  
High Laser ◽  
Oxide Phases ◽  
High Laser Fluences ◽  
Magnetite Particles ◽  
Kinetics Of

ABSTRACTSamples of Fe78B13Si9 and Fe81B13.5Si3.5C2 metallic glasses were irradiated with a pulsed alexandrite laser (λ=750 nm, τ=60 μs) using different laser fluences. Kinetics of laser-induced phase transformations and fluence dependence of magnetic properties were studied by scanning electron microscopy (SEM) and Mössbauer spectroscopy. Low laser fluences were found to induce changes in magnetic texture and onset of crystallization. High laser fluences, however, correlated with additional oxidation effects and the formation of stoichiometric Fe3O4 particles in the irradiated alloy system. An activation energy of 11.9 eV was estimated for the laser-driven synthesis of magnetite nanoparticles. Pulsed alexandrite laser processing is an intriguing alternative technique for the controlled synthesis of iron oxide phases from ferromagnetic glass precursors.

Observations on the Growth of YBa2Cu3O7 Thin Films at Very High Laser Fluences

1995 ◽  
Vol 388 ◽  
Author(s):  
Rand R. Biggers. ◽  
M. Grant Norton ◽  
I. Maartense ◽  
T.L. Peterson ◽  
E. K. Moser ◽  
...  
Keyword(s):  
Thin Films ◽  
Substrate Surface ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Organic Chemical ◽  
High Fluences ◽  
Laser Fluences ◽  
High Laser ◽  
High Laser Fluences ◽  
Very High

AbstractThe pulsed-laser deposition (PLD) technique utilizes one of the most energetic beams available to form thin films of the superconducting oxide YBa2Cu3O7 (YBCO). IN this study we examine the growth of YBCO at very high laser fluences (25 to 40 J/cm2); a more typical fluence for PLD would be nearer to 3 J/cm2. the use of high fluences leads to unique film microstructures which, in some cases, appear to be related to the correspondingly higher moveabilities of the adatoms. Films grown on vicinal substrates, using high laser fluences, exhibited well-defined elongated granular morphologies (with excellent transition temperature, Tc, and critical current density, Jc). Films grown on vicinal substrates using off-axis magnetron sputtering, plasma-enhanced metal organic chemical vapor deposition (PE-MOCVD), or PLD at more typical laser fluences showed some similar morphologies, but less well-defined. Under certain growth conditions, using high laser fluences with (001) oriented substrates, the YBCO films can exhibit a mixture of a- and c-axis growth where both crystallographic orientations nucleate on the substrate surface at the same time, and grow in concert. the ratio of a-axis oriented to c-axis oriented grains is strongly affected by the pulse repetition rate of the laser.

Photoresponse of high Tc superconductor thin films

1992 ◽  
Vol 70 (10-11) ◽  
pp. 1133-1137 ◽  
Author(s):  
F. A. Hegmann ◽  
J. S. Preston
Keyword(s):  
Magnetic Field ◽  
Pulse Width ◽  
Slow Component ◽  
Laser Pulses ◽  
Fast Component ◽  
High Tc ◽  
Small Magnetic Field ◽  
Laser Fluences ◽  
High Laser ◽  
High Laser Fluences

A fast photoresponse is observed in a current-biased epitaxial YBa2Cu3O7 thin-film bridge structure exposed to 100 ps laser pulses. A bolometric response, with a pulse width of the order of 10 ns, dominates at temperatures close to Tc and at high laser fluences. At lower temperatures and fluences, the observed transient response contains distinct fast and slow components. Preliminary results indicate a pulse width for the fast component less than 500 ps. Application of a small magnetic field perpendicular to the sample increases the amplitude of the slow component while leaving the fast component relatively unaffected. Comparison of these results with resistance versus temperature measurements in the same magnetic field suggests that the fast component is nonthermal in origin.

scholarly journals Analysis of Direct Optical Ablation and Sequent Thermal Ablation for the Ultrashort Pulsed Laser Photo-Thermal Micromachining

Coatings ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1151
Author(s):  
Chang-Wei Xiong ◽  
Ching-Yen Ho ◽  
Dong-Kai Qiao
Keyword(s):  
Laser Fluence ◽  
Thermal Effects ◽  
Thermal Ablation ◽  
Pulsed Laser ◽  
Processing Quality ◽  
Laser Fluences ◽  
High Laser ◽  
High Laser Fluences ◽  
Ultrashort Pulsed Laser ◽  
Residual Heat

An ultra-fast pulsed laser for materials processing can obtain submicrometer- to nanometer-sized parts or patterns (precision or accuracy) because the heat cannot diffuse in time for an ultra-fast pulsed duration, and this causes a threshold of ablation in multi-photoabsorption. The optical and thermal effects significantly affect the processing quality of an ultrashort pulsed laser for materials. This study utilizes a Laplace transform method to display the optical and thermal effects on the temperature field and the ablated depth of an ultrashort pulsed laser processing of materials. The results reveal that If an ultrafast pulsed laser-induced heat can keep the irradiated region above the evaporated temperature until the thermal diffusion occurs in the lattice of materials, thermal ablation occurs. The optical ablation can get a better processing quality due to less thermal diffusion. This study theoretically elucidates that the depth of optical ablation approximates the product of an optical absorption length and the logarithm of the ratio of laser fluence to laser fluence threshold. It has also been shown that the optical and thermal ablation, respectively, occur in low and high laser fluence because the optical ablation depends directly on the main source of the incident ultrashort pulsed laser. However, the thermal ablation is determined by the residual heat directly from the incident ultrashort pulsed laser after the optical ablation. The increase rate of the ablated depth per pulse with laser fluence is actually lower at high laser fluences than that at low laser fluences because the thermal ablation using the residual heat directly from the incident ultrashort pulsed laser is governed at high laser fluences. This study will provide the closed-form of a solution that elucidate the direct optical ablation and sequent thermal ablation for the ultra-fast pulsed laser photo-thermal processing.

scholarly journals The nature of the ultrafast magnetic phase transition in nickel revealed by correlating EUV-MOKE and ARPES spectroscopies

2019 ◽  
Vol 205 ◽  
pp. 04002
Author(s):  
Zhensheng Tao ◽  
Wenjing You ◽  
Phoebe Tengdin ◽  
Cong Chen ◽  
Xun Shi ◽  
...  
Keyword(s):  
Phase Transition ◽  
Magnetic Phase Transition ◽  
Extreme Ultraviolet ◽  
Magnetic Phase ◽  
Recovery Process ◽  
Time Resolved ◽  
Laser Fluences ◽  
High Laser ◽  
Show Evidence ◽  
High Laser Fluences

By correlating time- and angle-resolved photoemission (Tr-ARPES) and time-resolved transverse- magneto-optical Kerr effect (Tr-TMOKE) measurements, both at extreme ultraviolet (EUV) wavelengths, we uncover the nature of the ultrafast photoinduced magnetic phase transition in Ni. This allows us to explain the ultrafast magnetic response of Ni at all laser fluences - from a small reduction of the magnetization at low laser fluences, to complete quenching at high laser fluences. We provide an alternative explanation to the fluence-dependent recovery timescales commonly observed in ultrafast magneto-optical spectroscopies on ferromagnets: it is due to the bulk-averaging effect and different depths of sample exhibit distinct dynamics, depending on whether a magnetic phase transition is induced. We also show evidence of two competing channels with two distinct timescales in the recovery process, that suggest the presence of coexisting phases in the material.

Pulsed Laser Crystallization of Amorphous Silicon Films: Effects of Substrate Temperature and Laser Shot Density

1992 ◽  
Vol 258 ◽  
Author(s):  
R. I. Johnson ◽  
G. B. Anderson ◽  
S. E. Ready ◽  
D. K. Fork ◽  
J. B. Boyce
Keyword(s):  
Grain Size ◽  
Pulsed Laser ◽  
Laser Shot ◽  
Substrate Bias ◽  
Laser Crystallization ◽  
Film Properties ◽  
X Ray ◽  
Laser Fluences ◽  
High Laser ◽  
Current Report

ABSTRACTA recent report on pulsed laser crystallization of a-Si thin films concluded that substrate bias temperatures up to 400°C in combination with laser fluences below 500 mJ/cm2 had little effect on grain size and transport properties. The current report describes the effects of substrate bias temperature up to 500°C and laser fluence up to 540 mJ/cm2 on grain size, mobility and Si (111) x-ray peak intensities. Results indicate that substrate bias temperatures above 400°C, in combination with high laser shot densities and large laser beam spot energies (> 500 mJ/cm2), are a factor in Improving these film properties.

Mössbauer Spectroscopy Evidence for Phase Selectivity in Excimer Laser Induced Amorphization of Thermally Annealed FeCoBSi Metallic Glass

1996 ◽  
Vol 51 (5-6) ◽  
pp. 389-395
Author(s):  
M. Sorescu ◽  
E.T. Knobbe
Keyword(s):  
Metallic Glass ◽  
Excimer Laser ◽  
Surface Oxidation ◽  
Alloy System ◽  
Laser Pulses ◽  
Magnetic Texture ◽  
Induced Magnetic Anisotropy ◽  
Bulk Data ◽  
Phase Selectivity ◽  
Excimer Laser Irradiation

Abstract Pulsed excimer laser irradiation effects (λ = 308 nm, τ = 10 ns, w = 3 J/cm2 , N = 2 laser pulses/spot, repetition rate 1 Hz) on the magnetic properties and phase composition of thermally annealed Fe66Co18B15Si1 metallic glass have been studied by transmission and conversion electron Möss-bauer spectroscopy (CEMS). Radiation-driven surface modifications were examined by scanning electron microscopy (SEM). Excimer laser induced amorphization was observed in partially crystallized Fe66Co18B15Si1 samples (T A = 648 K, t A = 1 hour) and was found to be accompanied by the development of laser-induced magnetic anisotropy. In totally crystallized Fe66Co18B15Si1 specimens (T A = 723 K, = 1 hour), the effect of excimer laser induced amorphization exhibited phase selectivity with respect to the crystalline components of the alloy system. When compared to bulk data, a different behavior of the surface magnetic texture and relative abundance of alloy phases was observed. The laser-induced phase transformation of thermally annealed Fe66Co18B15Si1 specimens was shown to consist of partial amorphization and surface oxidation of the irradiated material.

scholarly journals Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing

2011 ◽  
Vol 11 (3) ◽  
pp. 995-1007 ◽  
Author(s):  
Z. Shi ◽  
S. Bonneville ◽  
M. D. Krom ◽  
K. S. Carslaw ◽  
T. D. Jickells ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Climate Models ◽  
Dissolution Kinetics ◽  
Low Ph ◽  
Iron Dissolution ◽  
Fundamental Parameters ◽  
First Order Kinetics ◽  
Atmospheric Processing ◽  
Oxide Phases ◽  
Kinetics Of

Abstract. We investigated the iron (Fe) dissolution kinetics of African (Tibesti) and Asian (Beijing) dust samples at acidic pH with the aim of reproducing the low pH conditions in atmospheric aerosols. The Beijing dust and three size fractions of the Tibesti dust (<20 μm: PM20; <10 μm: PM10; and <2.5 μm: PM2.5) were dissolved at pH 1, 2 and/or 3 for up to 1000 h. In the first 10 min, all dust samples underwent an extremely fast Fe solubilisation. Subsequently, the Fe dissolution proceeded at a much slower rate before reaching a stable dissolution plateau. The time-dependant Fe dissolution datasets were best described by a model comprising three acid-extractable Fe pools each dissolving according to first-order kinetics. The dissolution rate constant k (h−1) of each pool was independent of the source (Saharan or Asian) and the size (PM20, PM10 or PM2.5) of the dust but highly dependent on pH. The "fast" Fe pool had a k (25 h−1 at pH = 1) of a similar magnitude to "dry" ferrihydrite nanoparticles and/or poorly crystalline Fe(III) oxyhydroxide, while the "intermediate" and "slow" Fe pools had k values respectively 50–60 times and 3000–4000 times smaller than the "fast" pool. The "slow" Fe pool was likely to consist of both crystalline Fe oxide phases (i.e., goethite and/or hematite) and Fe contained in the clay minerals. The initial mass of the "fast", "intermediate" and "slow" Fe pools represented respectively about 0.5–2%, 1–3% and 15–40% of the total Fe in the dust samples. Furthermore, we showed that in systems with low dust/liquid ratios, Fe can be dissolved from all three pools, whereas at high dust/liquid ratios (e.g., in aerosols), sufficient Fe may be solubilised from the "fast" phase to dominate the Fe dissolved and to suppress the dissolution of Fe from the other Fe pools. These data demonstrated that dust/liquid ratio and pH are fundamental parameters controlling Fe dissolution kinetics in the dust. In order to reduce errors in atmospheric and climate models, these fundamental controlling factors need to be included.

scholarly journals Enhanced Microsphere-Assisted Picosecond Laser Processing for Nanohole Fabrication on Silicon via Thin Gold Coating

Micromachines ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 611
Author(s):  
Qiuling Wen ◽  
Xinyu Wei ◽  
Pengcheng Zhang ◽  
Jing Lu ◽  
Feng Jiang ◽  
...  
Keyword(s):  
Silicon Substrate ◽  
Laser Processing ◽  
Picosecond Laser ◽  
Ablation Rate ◽  
Gold Coating ◽  
Cross Sectional ◽  
Simple Method ◽  
Ordered Arrays ◽  
Laser Fluences ◽  
Nanohole Arrays

The nanohole arrays on the silicon substrate can effectively enhance the light absorption in thin film silicon solar cells. In order to optimize the solar energy absorption, polystyrene microspheres with diameters of 1 μm are used to assist picosecond laser with a wavelength of 1064 nm to fabricate nanohole arrays on silicon substrate. The experimental results show that the morphology and size of the silicon nanoholes strongly depend on the laser fluence. At 1.19–1.59 J/cm2 laser fluences, well-ordered arrays of nanoholes were fabricated on silicon substrate, with diameters domain from 250 to 549 nm and depths ranging from 60 to 99 nm. However, large amounts of sputtered nanoparticles appeared around the silicon nanoholes. To improve the surface morphology of silicon nanoholes, a nanolayered gold coating is applied on silicon surface to assist laser processing. The results show that, for gold-coated silicon substrate, sputtered nanoparticles around the nanoholes are almost invisible and the cross-sectional profiles of the nanoholes are smoother. Moreover, the ablation rate of the nanoholes on the gold-coated silicon substrate have increased compared to that of the nanoholes on the uncoated one. This simple method allows fast fabrication of well-ordered nanoholes on silicon substrate without sputtered nanoparticles and with smooth inner surface.

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