共查询到20条相似文献,搜索用时 93 毫秒
1.
S.-S. Wellershoff J. Hohlfeld J. Güdde E. Matthias 《Applied Physics A: Materials Science & Processing》1999,69(7):S99-S107
Femtosecond laser pulses were applied to study the energy deposition depth and transfer to the lattice for Au, Ni, and Mo films of varying thickness. The onset of melting, defined here as damage threshold, was detected by measuring changes in the scattering, reflection and transmission of the incident light. Experiments were done in multi-shot mode and single-shot threshold fluences were extracted by taking incubation into account. Since melting requires a well-defined energy density, we found the threshold depends on the film thickness whenever this is smaller than the range of electronic energy transport. The dependence of the threshold fluence on the pulse length and film thickness can be well described by the two-temperature model, proving that laser damage in metals is a purely thermal process even for femtosecond pulses. The importance of electron-phonon coupling is reflected by the great difference in electron diffusion depths of noble and transition metals. 相似文献
2.
J. Hohlfeld J.G. Müller S.-S. Wellershoff E. Matthias 《Applied physics. B, Lasers and optics》1997,64(3):387-390
\valunit{10}{nm} to have been measured by femtosecond time-resolved pump-probe experiments. A conspicuous change of the relaxation behavior was
found around for pump pulse fluences of . Thicker films show a nearly exponential decay of the transient linear reflectivity, which turns into a linear decay during
the first for films with thicknesses of or less. This observation is evidence of a mean free path of about for hot electrons with temperatures around .
Received: 17 December 1996 相似文献
3.
E. Matthias M. Reichling J. Siegel O. W. Käding S. Petzoldt H. Skurk P. Bizenberger E. Neske 《Applied Physics A: Materials Science & Processing》1994,58(2):129-136
Single-shot ablation thresholds of nickel and gold films in the thickness range from 50 nm to 7 m have been measured for 14 ns laser pulses at 248 nm, using photoacoustic shock wave detection in air. The metal films were deposited on fused silica substrates. The ablation threshold was found to increase linearly with film thickness up to the thermal diffusion length of the film. Beyond this point it remains independent of film thickness. The proportionality between threshold fluence and thickness allows the prediction of ablation thresholds of metal films from the knowledge of their optical properties, evaporation enthalpies and thermal diffusivities. Physically it proves that ablation is driven by the energy density determined by the thermal diffusion length. A simple thermodynamic model describes the data well. Thermal diffusivities, an essential input for this model, were measured using the technique of transient thermal gratings. In addition, the substrate dependence of the ablation threshold was investigated for 150 nm Ni films. 相似文献
4.
5.
D. Kim M. Ye C.P. Grigoropoulos 《Applied Physics A: Materials Science & Processing》1998,67(2):169-181
2 CrO4 are irradiated by a KrF excimer laser (λ=248 nm, FWHM=24 ns) with moderate energy density (up to 100 MW/cm2) below the plasma-formation threshold. The ablation process, including the vapor-cavity formation and the acoustic-wave propagation
is visualized by laser-flash photography. The ablation thresholds are determined by measuring the generated pressure transients
and vapor-phase kinetics using a broadband piezoelectric pressure transducer and a simultaneous optical-transmission probe,
respectively. The mechanisms of liquid ablation and acoustic-pulse generation are investigated based on the thermoelastic
behavior of the liquid medium and the evaporation dynamics. A numerical model is proposed to describe the explosive-vaporization
process at high laser fluences. The computation results are compared with the experiment.
In short-pulse heating, ablation can be initiated at low laser fluences by the tensile component of the thermoelastic stress
without a significant increase in the liquid temperature. On the other hand, if the heating rate is rapid enough to achieve
a high degree of superheating of the liquid, the abrupt increase of the homogeneous-bubble-nucleation rate leads to explosive
vaporization, which then plays the major role in the ablation dynamics. The pressure transient in the liquid is generated
thermoelastically at low laser fluences, but the contribution of the vapor-phase expansion and/or the recoil momentum exerted
by the ablation plume becomes significant at high laser fluences. Shock waves are formed in the ambient air in the case of
explosive vaporization. The propagation of these wave fronts is in good agreement with the numerical-computation results.
Received: 8 February 1998/Accepted: 10 February 1998 相似文献
6.
Chengbin Li Donghai Feng Tianqing Jia Haiyi Sun Xiaoxi Li Shizhen Xu Xiaofeng Wang Zhizhan Xu 《Solid State Communications》2005,136(7):389-394
The damage morphologies, threshold fluences in ZnO films were studied with femtosecond laser pulses. Time-resolved reflectivity and transmissivity have been measured by the pump-probe technique at different pump fluences and wavelengths. The results indicate that two-phase transition is the dominant damage mechanism, which is similar to that in narrow band gap semiconductors. The estimated energy loss rate of conduction electrons is 1.5 eV/ps. 相似文献
7.
Laser ablation of thin Ni films on fused silica by 0.5 ps KrF-excimer-laser pulses at 248 nm is reported. The onset of material removal from different film thicknesses (0.1, 0.3, 0.6 and 1.0 m) was measured in a laser ionization time-of-flight mass spectrometer by the amount of Ni atoms vs laser fluence. Significant amounts of metal atoms are already evaporated at laser fluences around 20 mJ/cm2, a threshold up to 100 times smaller compared to the one for 14 ns pulses. In contrast to ns laser pulses, the ablation threshold for 0.5 ps pulses is independent of the film thickness. These results reflect the importance of thermal diffusion in laser ablation of strongly absorbing and thermally good conducting materials and prove that for ablation with short pulses, energy loss to the bulk is minimized. 相似文献
8.
9.
测量了LN晶体的表面和体损伤阈值,以及重复频率脉冲的积累效应,研究了晶体中的非线性吸收过程。分析了损伤机理,发现在表面和体内都会发生多光子吸收,并且是引起晶体破坏的根源,造成宏观破坏的原因在体内是应力炸裂,在表面是热烧熔化和等离子体抛射。 相似文献
10.
Production and characterization of Nd,Cr:GSGG thin films on Si(001) grown by pulsed laser ablation 总被引:2,自引:0,他引:2
P.R. Willmott P. Manoravi K. Holliday 《Applied Physics A: Materials Science & Processing》2000,70(4):425-429
Nd,Cr:Gd3Sc2Ga3O12 (GSGG) thin films have been produced for the first time. They were grown on Si(001) substrates at 650 °C by pulsed laser
ablation at 248 nm of a crystalline Nd,Cr:GSGG target rod. The laser plume was analyzed using time-of-flight quadrupole mass
spectroscopy, and consisted of elemental and metal oxide fragments with kinetic energies typically in the range 10 to 40 eV,
though extending up to 100 eV. Although films deposited in vacuum using laser fluences of 0.8±0.1 J cm−2 reproduced the Nd,Cr:GSGG bulk stoichiometry, those deposited using fluences above ≈3 J cm−2 resulted in noncongruent material transfer and were deficient in Ga and Cr. Attempts to grow films using synchronized oxygen
or oxygen/argon pulses yielded mixed oxide phases. Under optimal growth conditions, the films were heteroepitaxial, with GSGG(001)[100]∥Si(001)[100],
and exhibited Volmer–Weber-type growth. Room-temperature emission spectra of the films suggest efficient non-radiative energy
transfer between Cr3+ and Nd3+ ions, similar to that of the bulk crystal.
Received: 1 October 1999 / Accepted: 15 October 1999 / Published online: 23 February 2000 相似文献
11.
2 at 1064 nm, vaporization/fragmentation of soot primary particles and aggregates occurs. Optical measurements are performed
using a second laser pulse to probe the effects of these changes upon the LII signal. With the exception of very low fluences,
the structural changes induced in the soot lead to a decreased LII intensity produced by the second laser pulse. These two-pulse
experiments also show that these changes do not alter the LII signal on timescales less than 1 μs for fluences below the vaporization
threshold.
Received: 20 October 1997/Revised version: 16 February 1998 相似文献
12.
J. M. Liu L. A. Lompre H. Kurz N. Bloembergen 《Applied Physics A: Materials Science & Processing》1984,34(1):25-29
Picosecond time-resolved reflectivity measurements on bare silicon surfaces and silicon surfaces with oxide layers reveal very fast heat diffusion and material evaporation on subnanosecond time scales. With a thick oxide layer resolidification of a molten silicon surface can take place in a few hundred picoseconds. At high laser fluences, vaporization processes take only a couple of 100 ps. 相似文献
13.
Quantitative roughness and microstructural analysis of as-deposited and swift heavy ion (SHI) (107 MeV Ag and 58 MeV Ni) irradiated 10 and 20 nm thick Au films were performed by atomic force microscopy (AFM). Power spectral density (PSD) analysis was done from the AFM images. The energies chosen for the two different ions eliminated the velocity effect of SHI in materials modification. The rms roughness estimated from the AFM data did not show either monotonic increase or decrease with ion fluences. Instead, it increased at low fluences and decreased at high fluences for 20 nm thick film. In 10 nm film, the roughness first increased with ion fluence, then decreased and again increased at higher fluences. Though the 10 and 20 nm films exhibited very different patterns of rms roughness variation with ion fluence, the pattern of variation in both cases was identical for Ni and Ag beams. The PSD analysis for both 10 and 20 nm films (pristine and irradiated) showed similar variation of low frequency roughness with ion fluence as that of the rms roughness. In the high frequency regime, PSD analysis suggests that surface morphology of the irradiated samples is governed by the combined effect of evaporation-recondensation and diffusion dominated processes. 相似文献
14.
M. Geoghegan F. Boué G. Bacri A. Menelle D.G. Bucknall 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):83-96
We have used neutron reflectometry to measure interfacial widths between two polystyrene films, where either one or both films
are crosslinked. The observed interfacial width between two networks is larger than the size expected for “dangling ends”,
which suggests motion of heterogeneous regions of the networks. In the case when one of the networks is replaced by a linear
polymer, the interfacial profile can be asymmetric with a diffusion “front” of linear polymer penetrating the network to a
length scale of up to 200 ?. In the case of a more densely crosslinked network and a high molecular weight linear polymer
the interface is symmetric implying negligible penetration.
Received: 4 December 1996 / Revised: 13 October 1997 / Accepted: 23 December 1997 相似文献
15.
StudyonLaserConditioningofOpticalCoatings¥ZHAOQiang;FANZhengxiu;WANGZhijiang(ShanghaiInstituteofOpticsandFineMechanics,Chines... 相似文献
16.
N. Layadi P. Roca i Cabarrocas M. Gerri W. Marine J. Spousta 《Applied Physics A: Materials Science & Processing》1994,58(5):507-512
We combine the deposition of Hydrogenated amorphous Silicon (a-Si:H) by rf glow discharge with XeCl-excimer laser irradiation of the growing surface in order to obtain different kinds of silicon films in the same deposition system. In-situ UV-visible ellipsometry allows us to measure the optical properties of the films as the laser fluence is increased from 0 up to 180 mJ/cm2 in separate depositions. For fixed glow-discharge conditions and a substrate temperature of 250° C we observe dramatic changes in the film structure as the laser fluence is increased. With respect to a reference a-Si:H film (no laser irradiation) we observe at low laser fluences (15–60 mJ/cm2) that the film remains amorphous but demonstrates enchanced surface roughness and bulk porosity. At intermediate fluences (80–165 m/Jcm2), we obtain an amorphous film with an enhanced density with respect to the reference film. Finally, at high fluences (165–180 mJ/cm2), we obtain microcrystalline films. The in-situ ellipsometry measurements are complemented by ex-situ measurements of the dark conductivity, X-ray diffraction, and Elastic Recoil Detection Analysis (ERDA). Simulation of the temperature profiles for different film thicknesses and for three laser fluences indicates that crystallization occurs if the surface temperature reaches the melting point of a-Si:H ( 1420 K). The effects of laser treatment on the film properties are discussed by taking into account the photonic and thermal effects of laser irradiation.Presented at LASERION 93, Munich, June 21–23, 1993 相似文献
17.
The microstructure and magnetic properties of FePt films grown on Cr and CrW underlayers were investigated. The FePt films that deposited on Cr underlayer show (2 0 0) orientation and low coercivity because of the diffusion between FePt and Cr underlayer. The misfit between FePt magnetic layer and underlayer increases by small addition of W element in Cr underlayer or using a thin Mo intermediate layer, which is favorable for the formation of (0 0 1) orientation and the transformation of FePt from fcc to fct phase. A good FePt (0 0 1) texture was obtained in the films with Cr85W15 underlayer with substrate temperature of 400 °C. The FePt films deposited on Mo/Cr underlayer exhibit larger coercivity than that of the films grown on Pt/Cr85W15 because 5 nm Mo intermediate layer depressed the diffusion of Cr into magnetic layer. 相似文献
18.
Junlin Yuan Weixiang Weng Zhilong Lin Tailiang Guo 《Journal of Physics and Chemistry of Solids》2009,70(12):1496-1500
Understanding the oxidation process of Cr/Cu/Cr laminated thin film electrode is important for developing new oxidation-resistant electrodes. By studying the evolution of crystal structure, morphology and electric resistivity of Cr/Cu/Cr thin films and electrodes that were post-annealed at different temperatures, the oxidation mechanism and process of Cr/Cu/Cr electrode were proposed. Copper is first oxidized into Cu2O at low temperatures (<310 °C), and converts to CuO phase at higher temperatures. Two pathways for oxygen diffusion were identified: diffusion from the protective Cr layer, and diffusion from the sidewall of electrode, of which the latter one leads to total oxidation of copper interlayer at high temperatures (>310 °C). As a result, the passivation of Cu metal at electrode sidewalls is crucial in reducing oxidation of Cr/Cu/Cr electrodes or designing new copper-containing oxidation-resistant electrodes. 相似文献
19.
The rapid melting and resolidification of gold films irradiated by laser pulses less than 100 fs are investigated using the dual-hyperbolic two-step model. The solid–liquid interfacial velocity in the ultrafast phase change process is obtained by coupling a hyperbolic interfacial energy balance equation and nucleation dynamics. The results are compared with the experimental data for the 28-fs laser. The effects of laser pulse widths and fluences on melting process are investigated. A phase chart of the variations of pulse widths and fluences is established. The relationship between the melting threshold and ablation threshold is also presented. 相似文献
20.
Bhupendra Singh Rathore 《辐射效应与固体损伤》2013,168(9):767-778
Polycarbonate/polystyrene bilayer films prepared by solvent-casting method were irradiated with 55 MeV carbon ion beam at different fluences ranging from 1×1011 to 1×1013 ions cm?2. The structural, optical, surface morphology and dielectric properties of these films were investigated by X-ray diffraction (XRD), UV–visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, optical microscopy and dielectric measurements. The XRD pattern shows that the percentage of crystallinity decreases while inter-chain separations increase with ion fluence. UV–visible spectroscopy shows that the energy band gap decreases and the number of carbon atoms in nanoclusters increase with the increase in ion fluences. The refractive index is also found to decrease with the increase in the ion fluence. Optical microscopy shows that after irradiation polymeric bilayer films color changes with ion fluences. The FTIR spectra evidenced a very small change in cross-linking and chain scissoring at high fluence. Dielectric constant decreases while dielectric loss and AC conductivity increase with ion fluences. 相似文献