共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Kumar 《Applied Physics A: Materials Science & Processing》2010,99(1):245-250
Controlled single step fabrication of silicon conical surface modulations on [311] silicon surface is reported utilizing KrF excimer laser [λ=248 nm] at laser fluence below ablation threshold laser fluence. When laser fluence was increased gradually from 0 to 0.2 J/cm2 for fixed 200 numbers of shots; first nanopores are observed to form at 0.1 J/cm2, then very shallow nanocones evolve as a function of laser fluence. At 0.2 J/cm2, nanoparticles are observed to form. Up to 0.15 J/cm2 the very shallow nanocone volume is smaller but increases at a fast rate with laser fluence thereafter. It is observed that the net material volume before and after the laser irradiation remains the same, a sign of the melting and resolidification without any ablation. 相似文献
2.
Falk Haehnel Rene Bertram Guenter Reisse Rene Boettcher Steffen Weissmantel 《Applied Physics A: Materials Science & Processing》2010,101(3):491-495
New results on three-dimensional microstructuring of fused silica, sapphire, calcium fluoride, magnesium fluoride, and PTFE
using pulsed laser ablation at 157 nm wavelength are presented. A largely automated high-precision fluorine laser micromachining
station was used for the investigations. 相似文献
3.
Jesús Alvarez Marien Lopez-Arias Rebeca de Nalda Margarita Martín 《Applied Physics A: Materials Science & Processing》2008,92(4):831-836
The neutral species present in CdS ablation plumes upon nanosecond 532 nm laser irradiation at a moderate fluence of 0.5–0.75 J cm−2 have been studied. Neutral Cd
n
S
m
clusters have been identified, some as large as (CdS)33−34 (1–2 nm in diameter). The analysis of the dynamics of neutral species shows an expansion with two components that differ
both in composition and dynamics. A fast, high kinetic energy component, dominated by S2 which acquires free-flow conditions at short distances from the target, is followed by a slower component characterized by
similar speeds for all species. This slower component shows dynamic features that are expected to favor aggregation processes
leading to effective cluster formation. 相似文献
4.
E. Cappelli C. Scilletta G. Mattei V. Valentini S. Orlando M. Servidori 《Applied Physics A: Materials Science & Processing》2008,93(3):751-758
The structure of thin films deposited by pulsed laser ablation (PLD) is strongly dependent on experimental conditions, like
laser wavelength and fluence, substrate temperature and pressure. Depending on these parameters we obtained various kinds
of carbon materials varying from dense, mainly tetrahedral amorphous carbon (ta-C), to less compact vertically oriented graphene
nano-particles.
Thin carbon films were grown by PLD on n-Si 〈100〉 substrates, at temperatures ranging from RT to 800°C, from a rotating graphite target operating in vacuum. The laser ablation of the graphite target was performed by a UV pulsed ArF excimer laser (λ=193 nm) and a pulsed Nd:YAG laser, operating in the near IR (λ=1064 nm).
The film structure and texturing, characterised by X-ray diffraction analysis, performed at grazing incidence (GI-XRD), and
the film density, evaluated by X-ray reflectivity measurements, are strongly affected both by laser wavelength and fluence
and by substrate temperature.
Micro-Raman and GI-XRD analysis established the progressive formation of aromatic clusters and cluster condensation into vertically
oriented nano-sized graphene structures as a direct function of increasing laser wavelength and deposition temperature. The
film density, negatively affected by substrate temperature and laser wavelength and fluence, in turn, results in a porous
bulk configuration and a high macroscopic surface roughness as shown by SEM characterisation. These structural property modifications
induce a relevant variation also on the emission properties of carbon nano-structures, as evidenced by field emission measurements.
This work is dedicated to our friend Giorgio who passed away 20th August. 相似文献
5.
T. Kobayashi T. Kato Y. Matsuo M. Kurata-Nishimura Y. Hayashizaki J. Kawai 《Applied Physics A: Materials Science & Processing》2008,92(4):777-780
By ablating solid C60 with a laser pulse, we observe various processes such as the prompt- and the delayed-ionization of C60, the fragmentation into molecular ions and the formation of cluster ions. We found these processes show distinct dependences
on the temporal pulse width, the power and the wavelength of the ablation laser. From the observations, we could confirm efficient
coupling of laser energy to C60 through the molecular absorption even with a laser pulse width less than the electron-phonon coupling time of the C60 molecule. 相似文献
6.
Balsam M. Mirdan Luca Antonelli Dimitri Batani Rashida Jafer Katarzyna Jakubowska Saad al Tarazi 《辐射效应与固体损伤》2013,168(7):610-619
The interaction of 40 ps pulse duration laser emitting at 532 nm wavelength with human dental tissue (enamel, dentin, and dentin–enamel junction) has been investigated. The crater profile and the surface morphology have been studied by using a confocal auto-fluorescence microscope (working in reflection mode) and a scanning electron microscope. Crater profile and crater morphology were studied after applying consecutive laser pulses and it was found that the ablation depth increases with the number of consecutive pulses, leaving the crater diameter unchanged. We found that the thermal damage is reduced by using short duration laser pulses, which implies an increased retention of restorative material. We observe carbonization of the irradiated samples, which does not imply changes in the chemical composition. Finally, the use of 40 ps pulse duration laser may become a state of art in conservative dentistry. 相似文献
7.
Aaron Sellinger Elodie Leveugle James M. Fitz-Gerald Leonid V. Zhigilei 《Applied Physics A: Materials Science & Processing》2008,92(4):821-829
Coarse-grained molecular dynamics simulations are applied to investigate the origins of the surface features observed in films
deposited by the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The formation of transient balloon-like structures
with a polymer-rich surface layer enclosing matrix vapor, observed in earlier simulations of slow heating of polymer-matrix
droplets, has been explored in this work at higher rates of thermal energy deposition. Tensile stresses generated in the regime
of partial stress confinement are found to induce an internal boiling in the overheated droplets and associated generation
of “molecular balloons” at thermal energy densities at which no homogeneous boiling takes place without the assistance of
tensile stresses. Simulations of the dynamic processes occurring upon the collision of a polymer-matrix droplet with a substrate
provide the molecular-level pictures of the droplet impact phenomenon and reveal the connections between the droplet landing
velocity and the shapes of the polymer features observed in scanning electron microscopy images of films deposited in MAPLE
experiments. The distinct types of surface features observed in MAPLE experiments, namely, wrinkled “deflated balloons,” localized
arrangements of interconnected polymer filaments, and elongated “nanofibers,” are shown to emerge from different scenarios
of droplet landing and/or disintegration observed in the simulations. 相似文献
8.
We analyze the morphology of ablated nanoparticles after their laser-induced deposition on various substrates. We show that, at moderate laser intensity of the 210 ps pulses on the surface of nanoparticle-containing materials (<5×109 W?cm?2), the deposited material remains approximately the same as the initial nanoparticles. We compare these deposited nanoparticles with the debris obtained by the laser ablation of bulk material of the same origin as nanoparticles at different intensities of laser radiation. The presence of nanoparticles in laser plumes allowed for analyzing high-order nonlinear optical properties of nanoparticles. The efficient high-order harmonic generation was achieved during propagation of femtosecond pulses through such plasmas. 相似文献
9.
S. Cockcroft C. D. Walton R. Zakaria 《Applied Physics A: Materials Science & Processing》2010,100(2):379-383
We report on the laser ablation of composite prismatic structures using a vacuum ultraviolet (VUV) 157 nm F2 laser. Polycarbonate and CR-39 substrates have been intentionally seeded with silver wires and silicon carbide whiskers respectively.
The seed particles remain attached to the underlying substrate after laser ablation, forming composite silver-polycarbonate
and silicon carbide-CR-39 interfaces. Strong optical absorption at 157 nm in the polymeric substrates allows precise control
over the depth between the base of the substrate and composite interface. The surface roughness of the as-received seed particles
has a significant effect on the final surface quality of the ablated structures. The textured surface on the silicon carbide
whiskers is resolved on the walls of the ablated structures. This is in contrast to the composite structures formed using
silver wires, which have a comparatively smoother surface. 相似文献
10.
M. Fukuda T. Mishima N. Nakayama T. Masuda 《Applied physics. B, Lasers and optics》2010,100(2):377-382
The factors determining temperature and current coefficients of lasing wavelength are investigated and discussed under monitoring
CO2-gas absorption spectra. The diffusion rate of Joule heating at the active layer to the surrounding region is observed by
monitoring the change in the junction voltage, which is a function of temperature and the wavelength (frequency) deviation
under sinusoidal current modulation. Based on the experimental results, the time interval of monitoring the wavelength after
changing the ambient temperature or injected current (scanning rate) has to be constant at least to eliminate the monitoring
error induced by the deviation of lasing wavelength, though the temperature and current coefficients of lasing wavelength
differ with the rate. 相似文献
11.
Yudi Rosandi Herbert M. Urbassek 《Applied Physics A: Materials Science & Processing》2010,101(3):509-515
The optical properties of blue-violet InGaN light-emitting diodes under normal and reversed polarizations are numerically
studied. The best light-emitting performance under normal and reversed polarization is obtained in a single quantum-well structure
and double quantum-well structure, respectively. The key factors responsible for these phenomena are presumably the carrier
concentration distribution and the amount of carriers in quantum wells. The turn-on voltage of light-emitting diodes under
reversed polarization is lower than that of light-emitting diodes under normal polarization, due mainly to lower potential
heights for electrons and holes in the active region. 相似文献
12.
K. Yuyama T. Sugiyama T. Asahi S. Ryo I. Oh H. Masuhara 《Applied Physics A: Materials Science & Processing》2010,101(4):591-596
Quinacridone nanoparticles with a mean size of about 200 nm are successfully prepared using nanosecond near-infrared (NIR)
laser ablation of its microcrystalline powders in heavy water. The absorption spectra of the formed colloidal solutions depend
on the excitation wavelengths, which is eventually ascribed to number and energy of absorbed photons. β-carotene has low photostability and is easily decomposed upon UV/VIS laser ablation of its solid, while its nanoparticles
are prepared utilizing this NIR laser ablation technique. The advantage of nanoparticle preparation by NIR laser ablation
is discussed. 相似文献
13.
14.
Esther Rebollar Giannis Bounos Alexandros Selimis Marta Castillejo Savas Georgiou 《Applied Physics A: Materials Science & Processing》2008,92(4):1043-1046
Following previous studies on the influence of the polymer molecular weight (MW) on the ablation of poly(methyl methacrylate) (PMMA) at 248 nm, this work extends the examination to the ablation of polystyrene
(PS) at 248 nm. The ablation threshold and the etching rates are found to be nearly independent of MW. Optical microscopy demonstrates an excellent crater morphology, few small bubbles are formed on the surface of the low MW. Examination of the formation kinetics of products in the irradiation of samples doped with the photoreactive iodophenanthrene
demonstrates that high temperatures develop upon irradiation, suggesting that thermal mechanism dominates in the ablation
of PS at 248 nm. In similarity to the etching rates, the attained temperatures are largely independent of the PS MW. The factors for the weak dependence of the process on PS MW are discussed. 相似文献
15.
Irina N. Zavestovskaya Peter G. Eliseev Oleg N. Krokhin Natalia A. Men’kova 《Applied Physics A: Materials Science & Processing》2008,92(4):903-906
The mechanisms of nonlinear absorption in transparent materials under irradiation with ultrashort laser pulses are considered
theoretically. Nitride semiconductor, sapphire and others transparent dielectrics were investigated. The ablation threshold
for these materials is within multi-TW/cm2 range. The model was used based on the tunneling absorption under the irradiation by high-intensity ultrashort pulses in
terms of the theory of ionization of solid in a field of strong electromagnetic wave. The effect of the energy gap of material
on the threshold of laser ablation was adequately explained. 相似文献
16.
The generation and measurement of complex ultraviolet laser pulse shapes is demonstrated in the SG-III laser facility. Relatively high contrast ratio of 300∶1 required by the physics experiment is achieved and successfully measured. Two continuous main shots validate the reproduction and the stability of the pulse shape, which provide solid foundation for precise physics experiment and laser power balance. 相似文献
17.
T. Kobayashi T. Kato Y. Matsuo M. Kurata-Nishimura Y. Hayashizaki J. Kawai 《Applied Physics A: Materials Science & Processing》2008,92(4):817-819
We investigate the so-called “matrix effect” on the relative intensities of ions in mixed solutions of alkali salts by using
femtosecond laser ablation time-of-flight mass spectrometry (fsLA-TOFMS). For the 1:1 mixed solution of sodium and potassium
salts, the intensity ratio of cations (Na+/K+) decreases as the total concentration increases. From the measurement for the mixed solution of lithium, sodium, potassium,
rubidium, and cesium solutions, we find out significant dependence of each ion intensity on the total concentration. The results
suggest that the electron transfer from neutral atoms to cations coexistent in the ablation plasma affects the relative ion
intensities observed with TOFMS when the total ion concentration is high. 相似文献
18.
In this paper, a thin film polarizer at the wavelength of 1540 nm in infrared region was designed and optimized using differential evolution method. It is shown how the algorithm’s parameters can change the output result to obtain the best consequence of optimization. This polarizer consists of a few pairs of high and low refractive index dielectric materials, titanium dioxide and silicon dioxide, respectively, with \(BK_{7}\) glass substrate and the angle of incident light was supposed 56° that is the Brewster angle for \(BK_{7}\) glass. Our final optimized polarizer has 91.20 and 0.336% transmittance for P and S polarization, respectively, and a 271 ratio of \(\frac{{T_{P} }}{{T_{S} }}\) which has high significance for this polarizer. It consists of eight pairs of layers with low and high refractive index materials and 3369.1 nm physical thickness which is used to separate S and P polarized light for Q-switching process. 相似文献
19.
Comparison of plume expansion in femtosecond laser ablation on oxidized and non-oxidized Sm surfaces
M. Kurata-Nishimura Y. Matsuo T. Kobayashi T. Kato Y. Hayashizaki J. Kawai 《Applied Physics A: Materials Science & Processing》2008,92(4):1047-1050
Time development of Sm+ and Sm ablation plume produced by the femtosecond laser irradiation has been investigated. The two-dimensional spatial profiles
of Sm and Sm+ emitted from oxidized and non-oxidized Sm surface were visualized using a planar laser-induced fluorescence method. It was
observed that the flow velocity of Sm+ is much faster than that of Sm plume in both surfaces. The plumes from the oxidized Sm surface show higher velocity than
that from non-oxidized surface, which is originated by the small electric conductivity at the surface. Expansion property
observed for Sm+ and Sm plume in the oxidized Sm surface ablation implies the formation of the Knundsen layer nearby the surface. Meanwhile,
continuous emission of Sm indicates the large contribution of heating effect to emission process at the non-oxidized surface.
We conclude that the fsLA process strongly depends on the electric property of the ablated surface and the heating effect
contributes to the particle emission process on the conductive material surface. 相似文献
20.
Seisuke Nakashima Koji Sugioka Katsumi Midorikawa 《Applied Physics A: Materials Science & Processing》2010,101(3):475-481
By using a second harmonic of near infrared femtosecond (fs) laser (λ=387 nm, 150 fs) with high NA objective lens, fabrication resolution has been greatly improved in nano-fabrication of wide
band-gap semiconductor gallium nitride (GaN). We have carried out a wet-chemical-assisted fs laser ablation method, in which
the laser beam is focused onto a single-crystal GaN substrate immersed in a concentrated hydrochloric (HCl) acid solution.
A two-step processing involving irradiation with a fs laser beam in air followed by wet chemical treatment is also performed
for comparison. In the wet-chemical-assisted ablation, theoretical diameters of ablation craters are calculated as a function
of pulse energy by assuming that the reaction is based on two-photon absorption. In lower energy, the calculated curve is
close to the experimental value, while the actual measured diameters in the region of higher energy are larger than calculated
values. In the condition of the highest fabrication resolution, we obtained ablation craters smaller than 200 nm at full width
at half maximum. We have also demonstrated the fabrication of two-dimensional (2D) periodic nanostructures on surface of a
GaN substrate using the second harmonic single fs-laser pulse. Uniform ablation craters with the size as small as 410 nm in
diameter are arranged with a periodicity of 1 μm. Such structures are applicable to 2D photonic crystals which improve the
light extraction efficiency for blue LEDs in the near future. 相似文献