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1.
We show that nanosecond pulsed laser interference can be used to structure surfaces on a nanoscale. With this method, we are able to create hollow structures on various thin films like Ta, Ni, Au, Cu, Co, and NiTi. We find that the structuring mechanism is related to the mechanical effect of thermal expansion upon melting. To corroborate this model, we study materials with an abnormal behavior at the melting point like Si, Ge, or Bi, as they contract upon melting.  相似文献   

2.
Micromachining of CuInSe2 (CIS)-based photovoltaic devices with short and ultrashort laser pulses has been investigated. Therefore, ablation thresholds and ablation rates of ZnO, Mo and CuInSe2 thin films have been measured for irradiation with nanosecond laser pulses of ultraviolet and visible light and subpicosecond laser pulses of a Ti:sapphire laser. The experimental results were compared to the theoretical evaluation of the samples heat regime. In addition, the cells photo-electrical properties were measured before and after laser machining. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses were employed to characterise the laser-induced ablation channels. Using nanosecond laser pulses, two phenomena were found to limit the laser-machining process. Residues of Mo that were projected onto the walls of the ablation channel and the metallization of the CuInSe2 semiconductor close to the channel lead to a shunt. The latter causes the decrease of the photovoltaic efficiency. As a consequence of these limiting effects, only subpicosecond laser pulses allowed the selective or complete ablation of the thin layers without a relevant change of the photo-electrical properties.  相似文献   

3.
Nanostructuring of an extended surface area is performed by ultra-short-pulse laser ablation in the low-fluence regime. A layer of micrometer-sized quartz spheres is used as a lens array in direct contact with the sample. The thickness of a transparent spacer layer under the spheres is adjusted so that the sample is struck by an array of well-focused spots. The threshold character of the ablation process allows the formation of sub-diffraction-limited structures, down to 500-nm holes with 800-nm light. The deposition of the lens array directly on the surface makes the technique broadly applicable, also to samples that show great variations in height. PACS 61.80.Ba; 78.47.+p; 81.16.Rf; 81.65.Cf  相似文献   

4.
5.
Pulsed ultraviolet laser ablation of two polyurethane films has been studied in terms of ablation rate behaviour and time-of-flight mass spectroscopy of the positively charged photofragments. Three excimer laser wavelengths (193, 248 and 308 nm; 17–30 ns pulse duration) and short-pulse laser system (pulse duration 500 fs or 5 ps, at 248 nm) were employed. The results of the influence of energy fluence on the ablation rate are tested against other photoablation models and a table of fitted physical constants is presented. The upper limit of the mean activation energy for desorption is found to be considerably lower than the energy required to break single covalent bonds. The mass analysis of the positively charged species produced during the photoablation process provides valuable insight into the photofragmentation mechanism.  相似文献   

6.
Novel experimental data on microstructuring of thin (60 nm) gold films by femtosecond laser pulses are presented and discussed. Material modifications are induced by different laser field distributions on the sample surface. Images of specially fabricated masks are transferred onto the gold surface with a 50× and 100× demagnifications. It is shown that, in the irradiated region of the gold film, the heated material tends to concentrate in the center. For example, a square-like field distribution on the target surface produces a cross with a jet in the middle. It is shown that this technique allows producing of a variety of microstructures with controllable nanorelief. Possible mechanisms leading to the observed material modifications as well as the resolution limits of this technique are discussed.  相似文献   

7.
Nanostructuring with spatially localized femtosecond laser pulses   总被引:6,自引:0,他引:6  
Spatially localized femtosecond pulses have been produced by a combination of scanning near-field optical microscopy with ultrashort pulse lasers. With these pulses direct ablative writing on metal surfaces is demonstrated. Possible applications of this technique for nanostructuring, repair, and production of lithographic masks are discussed.  相似文献   

8.
Modifications in thin metal films under intensive laser irradiation were studied. Gold, silver, copper, chromium and aluminum films with the thickness of 100 nm were deposited on the glass substrate. Back-side irradiation through the substrate with a burst of nanosecond pulses tightly focused to a line was applied. The film removal threshold with a single pulse Fth was estimated for every material and laser fluence was kept above it in the range of 1.5-3 Fth during experiments. Diverse behavior of the films depending on the metal, the shift between pulses and laser fluence was observed. In chromium, the regular structures were developed in a quite wide range of processing parameters. In gold, three kinds of ripples were observed: transverse (similar to ripples in chromium), longitudinal and a structure of ripples oriented at 60° to each other. The combination of physical properties facilitated the regular assembly of the molten metal in chromium and to some extent in gold.  相似文献   

9.
10.
We investigate the effects of carbon (C) on hydrogen (H) solubility in copper (Cu) using a first-principles method. We show C can increase the solution energy of H in the bulk Cu originated from the charge density redistribution, which leads to a weak repulsion between H and C in Cu. On the contrary, we demonstrate the C-vacancy (C-V) complex can serve as a trapping centre of H, and one C-V complex can hold up to six H atoms. Moreover, it is found that C can effectively decrease the solution energy of a single H in the vacancy, 0.68 eV lower than that of H in the C-free vacancy, changing the solution process of H in the vacancy from endothermic to exothermic. This can be attributed to the strong bonding interaction between H and C in the vacancy. Based on analyzing the role of C in different metals, we propose that the effects of C on the H solubility in the vacancy mainly depend on the difference between the H-C interaction and the C-metal atom interaction. These indicate that C plays a key role in H trapping behavior in Cu.  相似文献   

11.
Nanostructures formed by Au nanoparticles on ZnO thin film surface are of interest for applications which include medical implants, gas-sensors, and catalytic systems. A frequency tripled Nd:YAG laser (λ = 355 nm, τFWHM ∼ 10 ns) was used for the successive irradiation of the Zn and Au targets. The ZnO films were synthesized in 20 Pa oxygen pressure while the subsequent Au coverage was grown in vacuum. The obtained structures surface morphology, crystalline quality, and chemical composition depth profile were investigated by acoustic (dynamic) mode atomic force microscopy, X-ray diffraction, and wavelength dispersive X-ray spectroscopy. The surface is characterized by a granular morphology, with average grain diameters of a few tens of nanometers. The surface roughness decreases with the increase of the number of laser pulses applied for the irradiation of the Au target. The Au coverage reveals a predominant (1 1 1) texture, whereas the underlying ZnO films are c-axis oriented. A linear dependence was established between the thickness of the Au coverage and the number of laser pulses applied for the irradiation of the Au target.  相似文献   

12.
Manfredi G  Hervieux PA 《Optics letters》2005,30(22):3090-3092
Self-consistent simulations of the ultrafast electron dynamics in thin metal films were performed. A regime of nonlinear oscillations was observed that corresponds to ballistic electrons bouncing back and forth against the films' surfaces. When an oscillatory laser field is applied to the film, the field energy is partially absorbed by the electron gas. Maximum absorption occurs when the period of the external field matches the period of the nonlinear oscillations, which, for sodium films, lies in the infrared range. Possible experimental implementations are discussed.  相似文献   

13.
Ultrashort laser pulses are used to ablate a thin molybdenum layer from glass by irradiating the metal film through the transparent substrate. The trajectories of ablated molybdenum fragments are recorded using a shadowgraphic setup with a time resolution in the nanosecond range. In addition, the shape of collected molybdenum fragments is examined as a function of applied fluence. It is confirmed that in a fluence regime close to the ablation threshold one single disc is ablated as a whole and its velocity is determined in the order of 50 ms?1. In a second fluence regime, partial melting at the center of the disc is found and small melt droplets are recorded on their flight. Mo fragments ablated in this regime feature a ring-like structure with a brittle fracture at the outer and a molten appearance at the inner edge.  相似文献   

14.
The synthesis by pulsed laser deposition of ZnO thin films with a Nd:YAG laser system delivering pulses of 40 ps @ 532 nm is reported. The laser beam irradiated the target placed inside a vacuum chamber evacuated down to 1.33×10−1 Pa. The incident laser fluence was of 28 J/cm2 in a spot of 0.1 mm2. The ablated material was collected onto double face polished (111) Si or quartz wafers placed parallel at a separation distance of 7 mm. The AFM, SEM, UV-Vis, FT-IR and absorption ellipsometry results indicated that we obtained pure ZnO films with a rather uniform surface, having an average roughness of 37 nm. We observed by SEM that particulates are present on ZnO film surface or embedded into bulk. Their density and dimension were intermediary between particulates observed on similar structures deposited with fs or ns laser pulses. We noticed that the density of the particulates is increasing while their average size is decreasing when passing from ns to ps and fs laser pulses. The average transmission in the UV-Vis spectral region was found to be higher than 85%.  相似文献   

15.
Experimental results related to the influence of time delayed pulses for ablation efficiency with short multi pulses (pulse duration of 5 ps) are reported. A significant improvement of the micro structuring quality at relatively high fluence regime in metals is obtained. Less removed or recast matter is observed and the processed surface appears to be smoother with better roughness. Ablation depths and burr heights are compared for single pulses and double pulses in steel, Al and Cu as a function of scans number. Best results are obtained for weak time delays, typically less than 1 ps. PACS 79.20.Ds; 42.62.Cf; 81.65.Cf  相似文献   

16.
Time-resolved luminescence experiments have been set up in order to study the interaction of 193-nm laser radiation with dielectric thin films. At room temperature, Al2O3 coatings show photoluminescence upon ArF excimer laser irradiation, with significant intensity contributions besides the known substrate emission. Time- and energy-resolved measurements indicate the presence of oxygen-defect centers in Al2O3 coatings, which suggests a strong single-photon interaction at 193 nm by F+ and F center absorption. Measurements on highly reflective thin-film stacks, consisting of quarter-wave Al2O3 and SiO2 layers, indicate similar UV excitations, mainly from color centers of Al2O3. Received: 20 February 2002 / Accepted: 11 April 2002 / Published online: 5 July 2002  相似文献   

17.
Fluorescence experiments have been performed to study the interaction of 193-nm laser radiation with dielectric thin films of LaF3, AlF3, and MgF2. Spectral- and time-resolved measurements reveal the presence of cerium in LaF3 and the influence of hydrocarbons in MgF2 and LaF3. Virtually no fluorescence response is observable in the case of AlF3. Supplementary measurements on multilayer stacks confirm the contribution of hydrocarbon and cerium emission in high-reflective UV mirrors upon ArF excimer laser irradiation. Energy density dependent measurements indicate a linear absorption process as the origin of UV laser induced fluorescence in LaF3. Luminescence calculations are applied as a helpful tool in order to account for interference effects that are inherently to be found in the multilayer emission spectra. Received: 21 May 2002 / Accepted: 23 May 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +49-3641/807-601, E-mail: heber@iof.fraunhofer.de  相似文献   

18.
The thin-film solar cell technologies based on complex quaternary chalcopyrite and kesterite materials are becoming more attractive due to their potential for low production costs and optimal spectral performance. As in all thin-film technologies, high efficiency of small cells might be maintained with the transition to larger areas when small segments are interconnected in series to reduce photocurrent and related ohmic losses in thin films. Interconnect formation is based on the three scribing steps, and the use of a laser is here crucial for performance of the device. We present our simulation and experimental results on the ablation process investigations in complex CuIn1?x Ga x Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSe) cell’s films using ultra-short pulsed infrared (~1 μm) lasers which can be applied to the damage-free front-side scribing processes. Two types of processes were investigated—direct laser ablation of ZnO:Al/CIGS films with a variable pulse duration of a femtosecond laser and the laser-induced material removal with a picosecond laser in the ZnO:Al/CZTSe structure. It has been found that the pulse energy and the number of laser pulses have a significantly stronger effect on the ablation quality in ZnO:Al/CIGS thin films rather than the laser pulse duration. For the thin-film scribing applications, it is very important to carefully select the processing parameters and use of ultra-short femtosecond pulses does not have a significant advantage compared to picosecond laser pulses. Investigations with the ZnO:Al/CZTSe thin films showed that process of the absorber layer removal was triggered by a micro-explosive effect induced by high pressure of sublimated material due to a rapid temperature increase at the molybdenum-CZTSe interface.  相似文献   

19.
We show that a dramatic field-free molecular alignment can be achieved after exciting molecules with proper trains of strong ultrashort laser pulses. Optimal two- and three-pulse excitation schemes are defined, providing an efficient and robust molecular alignment. This opens new prospects for various applications requiring macroscopic ensembles of highly aligned molecules.  相似文献   

20.
A measurement of the decay in time of nuclei excited by an intense short laser pulse of energy E0E0 yields the Fourier transform of the autocorrelation function of the associated scattering matrix. We determine the optimal length (in time) of the pulse and evaluate the time-decay function using random-matrix theory. That function is shown to contain information not otherwise available. We approximate that function in a manner that is useful for the analysis of data. For E0E0 below the threshold energy EnEn of the first neutron channel, the time-decay function is exponential in time t while it is the product of an exponential and a power in t   for E0>EnE0>En. The comparison of the measured decay functions in both energy domains yields an unambiguous and novel test of random-matrix theory in nuclei.  相似文献   

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