Abstract:Nanostructured regular patterns on silicon surface are made by using femtosecond laser irradiations. This is a novel method that can modify the surface morphology of any large material in an easy, fast, and low-cost way. We irradiate a solid surface with a 400-nm double frequency beam from an 800-nm femtosecond laser, while the solid surface is submerged in a liquid or exposed in air. From the study of multiple-pulses and single-pulse irradiations on silicon, we find the morphologies of nanospikes and capillar… Show more
“…The spot size of the laser just before the light entering the solution is estimated to be about 50 μm (which is also the size of the cross-section of the following filament in the solution) for calculating the maximum fluence. The minimum spot size of laser damage on a silicon surface in water is measured to be about 50 μm, which agrees with the estimation 37 – 39 . Figure 1 An illustration of the experimental setup for the femtosecond laser irradiation, where the laser is focused vertically as shown in orange.…”
Section: Methodssupporting
confidence: 87%
“… cannot explain the change of since this only relates to the shape and size of the nanorods. cannot explain the increase, since observed is less than 100 femtosecond, which is shorter than the time it takes for absorbed energy to be transferred to the phonons from hot electrons 37 . For , the electron–electron scattering rate was studied as early as in 1958, by Gurzhi 51 , and it was calculated in detail later in 1973 by Lawrence 52 .…”
Intense femtosecond laser irradiation reshapes gold nanorods, resulting in a persistent hole in the optical absorption spectrum of the nanorods at the wavelength of the laser. Single-pulse hole-burning experiments were performed in a mixture of nanorods with a broad absorption around 800 nm with a 35-fs laser with 800 nm wavelength and 6 mJ/pulse. A significant increase in hole burning width at an average fluence of 106 J/m2 has been found, suggesting a tripled damping coefficient of plasmon. This shows that the surface plasmonic effect still occurs at extremely high femtosecond laser fluences just before the nanorods are damaged and the remaining 10% plasmonic enhancement of light is at the fluence of 106 J/m2, which is several orders of magnitude higher than the damage threshold of the gold nanorods. Plasmon–photon interactions may also cause an increase in the damping coefficient.
“…The spot size of the laser just before the light entering the solution is estimated to be about 50 μm (which is also the size of the cross-section of the following filament in the solution) for calculating the maximum fluence. The minimum spot size of laser damage on a silicon surface in water is measured to be about 50 μm, which agrees with the estimation 37 – 39 . Figure 1 An illustration of the experimental setup for the femtosecond laser irradiation, where the laser is focused vertically as shown in orange.…”
Section: Methodssupporting
confidence: 87%
“… cannot explain the change of since this only relates to the shape and size of the nanorods. cannot explain the increase, since observed is less than 100 femtosecond, which is shorter than the time it takes for absorbed energy to be transferred to the phonons from hot electrons 37 . For , the electron–electron scattering rate was studied as early as in 1958, by Gurzhi 51 , and it was calculated in detail later in 1973 by Lawrence 52 .…”
Intense femtosecond laser irradiation reshapes gold nanorods, resulting in a persistent hole in the optical absorption spectrum of the nanorods at the wavelength of the laser. Single-pulse hole-burning experiments were performed in a mixture of nanorods with a broad absorption around 800 nm with a 35-fs laser with 800 nm wavelength and 6 mJ/pulse. A significant increase in hole burning width at an average fluence of 106 J/m2 has been found, suggesting a tripled damping coefficient of plasmon. This shows that the surface plasmonic effect still occurs at extremely high femtosecond laser fluences just before the nanorods are damaged and the remaining 10% plasmonic enhancement of light is at the fluence of 106 J/m2, which is several orders of magnitude higher than the damage threshold of the gold nanorods. Plasmon–photon interactions may also cause an increase in the damping coefficient.
“…The catalyst was then degassed in vacuum for approximately 1 h to remove the carbon dioxide adsorbed on the surfaces. Nanoflakes were then formed on the particle surfaces after placing the Co powder in air at room temperature for 2 h. This method was reported in previous articles. − This sample preparation is cost effective, comparing the method with a femtosecond laser irradiation in water. ,,− Two grams of catalyst was loaded in a glass reactor (20 mL), and 350 mg of distilled water was added into the reactor to cover the catalyst. Afterward, the reactor was evacuated to about 1 × 10 –3 atm and then filled with CO 2 to an absolute pressure of 2 atm at a room temperature of about 20 °C.…”
Carbon dioxide (CO 2 ) and water (H 2 O) have been converted into hydrocarbons at temperature ranging from 58 to 242 °C through an artificial photosynthesis reaction catalyzed by nanostructured Co/CoO. The experimental results show that chain hydrocarbons (alkane hydrocarbons) (C n H 2n+2 , where 3 ≤ n ≤ 16) mainly form at a temperature higher than about 60 °C, the production rate reaches a maximum at 130 °C, and abruptly decreases above 130 °C, and then gradually increases until 220 °C. While the temperature is higher than 220 °C, benzene (C 6 H 6 ) and its derivatives such as toluene (C 7 H 8 ), p-xylene (C 8 H 10 ), and C 9 H 12 form. The modeling of temperature dependence of the reaction rate reveals that the vaporization of the adsorbed water contributes to the sharp peak; the activation energy is estimated as about 1 eV, which is in agreement with the reaction of CO and H 2 to synthesize chain hydrocarbons. The experimental results support the mechanism that the chemisorbed CO 2 and physisorbed H 2 O on the CoO surface are disassociated or excited with light, and the disassociated or excited molecules then synthesize hydrocarbons. When most of the water molecules leave from the CoO at temperature higher than 220 °C, the hydrogen source is of very low concentration while the carbon source remain the same because of the chemisorption, and thus benzene and its derivatives with low hydrogen atom number form.
“…Hence, they suggested that the water had a cooling effect that is more important than the heat flow in the substrate. The cooling effect of the surrounding water was recently modeled for femtosecond laser irradiation of silicon, indicating a large amount of heat removal caused by the water's latent heat of vaporization [48]. Indeed, bubbles nucleate in the water layer upon irradiation, removing heat and scattering and diffracting the laser light [44,49].…”
Ultrafast laser texturing allows the generation of micro- and nanostructures on steel substrates. Laser-ablated textures show a wide range of structure geometries, from the micro to the nanoscale, which can enable plastic product functionalization. Polymer processing technologies are used to replicate mold textures on a large manufacturing scale. To enable new product functionalities, developing novel texture geometries is critical. The laser-ablated texture dimensions are primarily linked to the laser light properties, such as the laser wavelength, thus limiting the achievable structure shapes. This work uses ultrafast laser to manufacture textures in air and water environments. The effect of the different mediums on structures formation is characterized. The irradiation is performed over a wide range of fluence values. The texture geometry and characteristics are evaluated by scanning electron microscopy. For decreasing fluence values, the structures transitioned from micro bumps, to LIPSS, to nanostructures, regardless of the irradiation environment. Conversely, structure morphology is affected by the irradiation environment. The LIPSS pitch is lower for the underwater environment due to the change in the laser angle of incidence, which changes with the refraction index ratio of the air and water. A novel nano-lamellae texture was generated when irradiating the steel surface underwater at relatively low fluence. The dynamics of different LIPSS generations are discussed, considering the irradiation medium’s optical, thermal, and physical properties.
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