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1.
In the present paper, polyimide surfaces were processed with pulsed KrF laser radiation at fluences near the ablation threshold.
The morphology of the processed surfaces was studied by scanning electron microscopy and chemical analyses performed by electron
dispersive spectroscopy. The formation of conical structures was observed for radiation fluences lower than 0.5 J/cm2. The areal density of cones increases with the number of pulses and decreases with the radiation fluence. At low fluences
(<150 J/cm2), cones are formed due to shadowing by calcium phosphate impurities while for higher fluences the main mechanism of cones
formation is believed to be radiation hardening. 相似文献
2.
A phenomenological mixed-propagation model that describes the expansion of an ablation plume through a buffer gas is introduced.
Selected experiments including LaMnO3 and tin ablation in oxygen, as well as tungsten ablation in argon, are analysed. For given ablation conditions the expansion
parameters required to model the growth of clusters in the expanding plasma plume are deduced and the average asymptotic size
of the clusters is calculated and compared (for tungsten) with the size of clusters measured by transmission electron microscopy. 相似文献
3.
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
4.
R. Hannachi S. Boussaïdi P. Teulet G. Taieb Y. Cressault A. Gleizes Zohra Ben Lakhdar 《Applied Physics A: Materials Science & Processing》2008,92(4):933-937
A spectroscopic study of the plasma plume created by a laser beam on the surface of NaCl aqueous solution is presented. Optical
emission spectra are recorded and temporally analyzed; electron number density is determined from the Stark broadening of
the NI nitrogen line, and temperature is obtained from relative intensity of OI oxygen lines. The intensity of an atomic line
from sodium was used to quantitate its molar percentage in the Oceanic and Mediterranean sea, and calibration curves have
been constructed for concentrations ranging up to 1.5%. 相似文献
5.
S. R. John S. C. Langford J. T. Dickinson 《Applied Physics A: Materials Science & Processing》2008,92(4):981-985
We report time- and mass-resolved measurements on neutral particles emitted from polytetrafluoroethylene (PTFE) during exposure
to 157-nm laser radiation at fluences where etching is observed. By comparing the time-of-flight signals over a range of masses,
we conclude that (CF2)
N
fragments for N=1–6 are emitted directly from the surface in substantial quantities. In contrast, the monomer (N=2) is the principal product during irradiation at 248 nm, where thermal decomposition is important. The time-of-flight signals
of all the (CF2)
N
fragments show fast components with kinetic energies on the order of an electron volt. These high kinetic energies are consistent
with photochemical scission of the polymer backbone, where a fraction of the excitation energy is delivered to the fragment
as kinetic energy. Although clean etching is observed under these conditions, the great majority of the mass removed from
the target appears as much larger fragments that do not reach our detector. The nature of this material and its affect on
the velocity distribution of the observed (CF2)
N
fragments is discussed. 相似文献
6.
K. Sekimoto M. Takayama 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(3):297-305
The dependence of negative ion formation on the inhomogeneous electric field
strength in atmospheric pressure negative corona discharge with
point-to-plane electrodes has been described. The distribution of negative
ions HO-, NOx
- and COx
- and their abundances on the
plane electrode was obtained with a mass spectrometer. The ion distribution
on the plane was divided into two regions, the center region on the needle
axis and peripheral region occurring the dominant NOx
- and
COx
- ions and HO- ion, respectively. The calculated electric
field strength in inhomogeneous electric field established on the needle tip
surface suggested that the abundant formation of NOx
- and
COx
- ions and HO- ion is attributed to the high field
strength at the tip apex region over 108 Vm-1 and the low field
strength at the tip peripheral region of the order of 107 Vm-1,
respectively. The formation of HO-, NOx
- and COx
-
has been discussed from the standpoint of negative ion evolution based on
the thermochemical reaction and the kinetic energy of electron emitted from
the needle tip. 相似文献
7.
S. Gaspard M. Oujja R. de Nalda M. Castillejo L. Bañares S. Lazare R. Bonneau 《Applied Physics A: Materials Science & Processing》2008,93(1):209-213
We have recently shown that irradiation of self-standing films of the biopolymers collagen and gelatine with single femtosecond
laser pulses produces a nanofoaming layer with regular bubble size which can be controlled by wavelength selection. Following
these initial studies, here we report on the temporal evolution of the foaming effect by measurements in situ and in real
time of the change in the transmittance of a cw probe HeNe laser through the irradiated films. Self standing films of the
biopolymers were irradiated with 90 fs laser pulses at 800, 400, and 266 nm. For fluences below and above the modification
threshold a permanent attenuation of the transmission occurs (increasing with fluence). The initial decay of the transmission
is fast (around few tens of ns), and is followed by dynamics in the longer timescale (micro and milliseconds). The temporal
evolution of the transmission measured upon fs laser irradiation is similar with that determined in the irradiation of the
biopolymer films at 248 nm with 25 ns laser pulses. The method allows separating in time the different processes occurring
after irradiation that lead to a permanent nanofoaming structure, while the results allow us to understand the mechanisms
of femtosecond laser processing of the biopolymers and their interest in biomedical applications. 相似文献
8.
R. Riahi P. Teulet Y. Cressault A. Gleizes Z. Ben Lakhdar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(2):185-192
A method is presented to calculate the radiative transition probabilities and the radiative recombination rate coefficients
between electronic molecular states. Total transition probabilities are determined from vibrational transition probabilities
without considering the detailed rotational structure of the molecular electronic states. Radiative recombination rate coefficients
are obtained from the computation of vibrational photo-ionisation cross sections. Concerning spontaneous emission, Lyman (B
→ X) and Werner (C → X) band systems of H2 and Meinel (A → X), (B → A) and (B → X) band systems of OH are investigated. For radiative recombination, transitions between
H2+ (X) and H2(X), and between OH+(X, a, A, b, and c) and OH(X) are considered. Transition probabilities and recombination rate coefficients are calculated
as a function of temperature in the range 1500–15 000 K. 相似文献
9.
V. Antoni M. Bagatin A. Buffa G. Della Mea F. Freyre Jr. P. Mazzoldi F. Romanato 《Il Nuovo Cimento D》1991,13(4):435-453
To investigate the ion flux escaping from the plasma and the impurity flux released by the wall, collector probes made of
graphite, silicon and titanium have been exposed to the deuterium plasma confined in the toroidal device ETA BETA II. The
damages on the collector surfaces have been surveyed by a scanning electron microscopy (SEM) apparatus. The deuterium and
impurity retention have been measured by elastic recoil detection (ERD) and Rutherford backscattering spectroscopy (RBS) techniques
respectively. The implantation build-up has been investigated as a function of the exposure time. The deuterium dose in graphite
saturates after a few discharges, whereas the metal impurities exhibit a linear increase in time. The deuterium flux and its
radial dependence, inferred from the implanted concentrations, have been compared with those measured by Langmuir probes.
Metal impurities have been identified and their relative abundances have been compared with the material wall composition.
The impurity flux is found consistent with the global content in the plasma derived by spectroscopic measurements. The deuterium
dose measured in different samples has been related to the backscattering coefficient of the materials. Finally, to investigate
the damage on sample probes facing the plasma particle flow, erosion probes made of vitreous graphite with silver implanted
at a fixed depth have been exposed to the plasma and the thickness change after exposure recovered. 相似文献
10.
Junjie Zhang Tao Sun Yongda Yan Yingchun Liang Shen Dong 《Applied Physics A: Materials Science & Processing》2009,94(3):593-600
Three-dimensional molecular dynamics simulation of groove fabrication using atomic force microscopy (AFM)-based nanometric
cutting technique is set up, fabrication processes of grooves with two types (line, and folder line) and five folder angles
(0°, 30°, 45°, 60°, 90°) are simulated to investigate the effect of groove geometry on the fabrication process. The results
show that the Normal force, Lateral force, and Resultant forces are almost symmetric with respect to the critical folder angle
of 45°. The best surface quality of fabricated groove can be obtained at the folder angle of 45°. It reveals that the groove
geometry has a significant effect on the groove fabrication process due to the material anisotropy on the atomic scale. 相似文献
11.
Tomas Kocourek Miroslav Jelinek Vladimír Vorlíček Josef Zemek Tomáš Janča Věra Žížková Jiří Podlaha Cyril Popov 《Applied Physics A: Materials Science & Processing》2008,93(3):627-632
Textile blood vessels with a length of 30 cm were coated with amorphous diamond-like carbon (DLC) layers with thicknesses
up to 200 nm. The layers were created by pulsed laser deposition in vacuum or argon ambient. The percentage of sp3 carbon was evaluated using X-ray photoelectron spectroscopy, X-ray excited Auger electron spectroscopy and Raman spectroscopy.
Depending on the deposition conditions the sp3 content varied from ∼40% to 60%. The adhesion of the DLC layers to the textile vessels was checked. The preliminary biocompatibility
results from in vivo tests with sheep are also given. 相似文献
12.
H. Nowakowska M. Jasiński J. Mizeraczyk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):511-518
We present results from simulations of 2D distributions of the electromagnetic field inside a waveguide-based axial-type microwave
plasma source (MPS) used for hydrogen production via methane reforming. The studies are aimed at optimization of discharge
processes and hydrogen production. We derive equations for determining electromagnetic field distributions and next determine
the electromagnetic field distributions for two cases – without and with plasma inside the MPS. For the first case, we examine
the influence of the length of the inner conductor of the coaxial line on electromagnetic field distributions. We have obtained
standing wave patterns along the coaxial line and found resonances for certain positions of the coaxial line inner conductor.
For the case with plasma inside the MPS, we perform calculations assuming that distributions of plasma parameters are known.
Simulations are done for several values of maximum electron density. We have found that for values of electron density greater
than strong skin effect in the plasma is observed. Consequently, plasma may be treated as an extension of the inner conductor
of the coaxial line. We have used FlexPDE software for the calculations. 相似文献
13.
Spectrally selective splitters with metal-dielectric-metal (MDM) subwavelength waveguides are proposed in this paper. The
method is based on the Bragg grating structure with periodically modulated MDM waveguide width, which delivers a stop band
effect for the surface plasmon propagating in the waveguide. By adding appropriate Bragg grating structure in one or more
arms of the waveguide splitters, light in a certain frequency range can be readily guided into the desired directions, as
demonstrated numerically by the finite-difference time-domain method. Dependence and optimization of the geometrical parameters
are also considered in this paper. 相似文献
14.
Spatially resolved measurements of vibrational and rotational temperature determined from the N2(C) nitrogen bands intensities have been performed by means of optical scanner of original construction. It has been found
that radial variations of studied bands are independent of pressure and discharge current under our experimental conditions,
i.e. in the pressure range (100–300) Pa and for discharge current up to 40 mA. Moreover, it has been found that vibrational
as well as rotational temperatures stay almost constant in the radial direction. No radial changes of both temperatures can
be explained by good thermal conductivity of the positive column of DC glow discharge.
This research was supported by grants: Charles University No. GAUK 194/01, Ministry of Education of Czech Republic MSM 11320002,
and Grant Agency of Czech Republic GAČR 202/03/0827. The theme of presented article was included in the EU project No. G1RT-CT-2002-05083
“Plasmatech”. 相似文献
15.
C. Hecht H. Kronemayer T. Dreier H. Wiggers C. Schulz 《Applied physics. B, Lasers and optics》2009,96(1):119-125
The iron-atom concentration distribution as well as the gas-phase temperature was measured via laser-induced fluorescence
(LIF) during iron-oxide nanoparticle synthesis in a low-pressure hydrogen/oxygen/argon flame reactor using ironpentacarbonyl
(Fe(CO)5) as precursor. Temperature measurements based on multi-line NO-LIF imaging are used to correct for temperature-dependent
ground-state populations. The concentration measurement is calibrated based on line-of-sight absorption measurements. The
influence of the precursor on the flame is observed at precursor concentrations larger than 70 ppm as the flame front moves
closer to the burner surface with increasing Fe(CO)5 concentration. 相似文献
16.
A. Krupa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):265-270
The paper presents investigations of back discharge occurring in air and flue gases produced by the process of burning of
liquefied petroleum gas or charcoal. The discharge was generated between a multineedle electrode and plate covered with fly
ash layer. The aim of this work was to determine the effects of back discharge in multineedle-to-plate electrode configuration
on the fly ash layer covering the plate electrode. Level of NOx and CO emission was also measured. It was found that the chemical composition of flue gas can be changed in the domains where
the back discharge occurs, for example, additional amounts of nitrogen oxides (NO and NO2) are produced and also carbon oxide (CO) was produced at higher discharge current. 相似文献
17.
T. Yatsui K. Hirata W. Nomura Y. Tabata M. Ohtsu 《Applied physics. B, Lasers and optics》2008,93(1):55-57
We propose a new method of optical near-field etching where a nonadiabatic process is applied to a synthetic silica substrate using a continuum wave laser (λ=532 nm) with a Cl2 gas source. Because the absorption band edge energy of Cl2 is higher than the photon energy of the light source, we preclude the conventional adiabatic photochemical reaction. An optical near field, generated on the nanometrically rough substrate, induces the nonadiabatic chemical reaction to the Cl2 molecules and thereby selectively etches away the roughness, leaving an ultra-flat synthetic silica surface with a minimum average surface roughness R a of 1.37 Å. 相似文献
18.
Microdischarges in ceramic foams and honeycombs 总被引:1,自引:0,他引:1
K. Hensel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):141-148
Microdischarges in spatially confined geometries, such as microcavities and micropores of various materials, present a promising
method for the generation and maintenance of stable discharges at atmospheric pressure. They have been successfully used in
many biomedical, environmental and industrial applications. The paper presents two relatively new types of discharges in confined
volumes – a capillary microdischarge in ceramic foams and a sliding discharge inside the capillaries of ceramic honeycombs
– and describes their basic physical properties and mechanisms. Microdischarges inside the microporous ceramic foams develop
from the surface barrier discharge if the amplitude of the applied voltage reaches given threshold, but only for a specific
pore size. Sliding discharge inside the honeycomb capillaries is produced by a combination of AC barrier discharge inside
catalytic pellet bed coupled in series with DC powered honeycomb monolith. Both discharges produce relatively cold microplasmas
with high level of non-equilibrium. The basic characteristics of the microdischarges, addressing the effects of the applied
voltage, discharge power, pore size, length and diameter of the capillaries are discussed. 相似文献
19.
E.?Havlí?ková O.?Mar?álek R.?Hrach 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):313-318
In the presented contribution two groups of techniques of computational physics were used for the study of sheath structure
in the DC glow discharge in argon plasma – the fluid modelling describing macroscopic plasma phenomena and the particle modelling
providing more detailed insight into the plasma processes. A comparison of different computational methods is given with attention
to the efficiency of computer codes in two dimensions. Another point of interest is the inclusion of external magnetic field
into the models and its effect on the sheath structure. 相似文献
20.
J. T. Dickinson 《Applied Physics A: Materials Science & Processing》2008,92(4):1025-1030
Below laser fluences where a plasma is formed (the so-called plasma or plume formation threshold) a number of fundamental
phenomena can occur where particles such as atomic and molecular ions, atoms and molecular neutrals, and electrons can be
emitted. An understanding of such processes is necessary to develop predictive models for material removal from laser irradiated
surfaces—at the foundation of laser etching, machining, and pulsed laser deposition. We have reported on a number of the mechanisms
for such emission processes. Here, due to space limitations, we present a summary of our studies on the formation of negative
alkali ions from single crystal KCl during exposure to pulsed 248-nm radiation at fluences well below the threshold for plasma
formation. Despite the high electron affinities of the corresponding halogen atoms, negative halogen ions were not detected.
Significantly, the positive and negative alkali ion distributions overlap strongly in time and space, consistent with K formation
by the sequential attachment of two electrons to K+. Negative alkali ions are also observed under comparable conditions from LiF, NaCl, and KBr. In each material, the strong
overlap between the positive and negative alkali ion distributions, and the lack of detected negative halogen ions, suggest
that negative ion formation involves a similar mechanism. 相似文献