Search Results
Data on single pulse fs laser induced submicron bubbles in the subsurface region of soda-lime glass
Submicron bubble formation in the subsurface range of soda-lime glass is investigated. The bubbles are induced by single femtosecond laser pulse irradiation with the wavelength of λ = 775 nm, the pulse duration of tp = 150 fs and the laser beam diameter of ∼12 μm. The data shows the changes of the morphologies of the soda-lime glass after laser irradiation with different pulse energy. Moreover, the data shows the detail of the cross-section view of the bubble during the Focused ion beam (FIB) cutting. It is found that the bubbles can be formed in a rather narrow pulse energy range with the bubbles in the size of 300 nm ∼3 μm which is much smaller than the laser beam diameter. Data presented in this article are related to the research article “Submicron bubbles/voids formation in the subsurface region of soda-lime glass by single pulse fs laser-induced spallation” [1]. © 2020
Nanostructuring of Fused Silica Assisted by Laser-shaped Metal Triangles Using a Nanosecond Laser
Self-organized processes are of special interest for the laser-induced nanostructuring of surfaces. In this study we combined two self-organized processes: the microsphere lithography and the molten phase transformation for the nanostructuring of dielectrics. A fused silica substrate was covered with periodically ordered polystyrene (PS) spheres and the system was subsequently covered with 30 nm chromium. Afterwards the PS spheres were removed and the bare and resultant periodic Cr triangles were irradiated in two steps using a KrF excimer laser. First step: A low laser fluence treatment results in a melting and shape transformation of the triangles. Second step: A high laser fluence treatment of the pre-treated surface results in a nanostructuring of the dielectric surface (and removal of the metal). The surface topography was studied by scanning electron microscopy. Furthermore, the different steps were simulated and compared with the experimental results.
Laser-induced reactive microplasma for etching of fused silica
The ultra-precise machining (UPM) of surfaces with contact-free, beam-based technologies enables the development of flexible and reliable fabrication methods by non-vacuum processes for future application in advanced industrial fields. Laser machining by laser ablation features limitations for ultra-precise machining due to the depth precision, the surface morphology, and laser-induced defect formation. Contrary to physically-based etching, chemical-based dry and wet processing offer high quality, low damage material removal. In order to take advantage of both principles, a combined laser-plasma process is introduced. Ultra-short laser pulses are used to induce a free-standing microplasma in a CF4 gas atmosphere due to an optical breakdown. CF4 gas, with a pressure of 800–900 mbar, is ionized only near the focal point and reactive species are generated therein. Reactive species of the laser-induced microplasma can interact with the surface atoms of the target material forming volatile products. The release of these products is enhanced by the pulsed, laser-induced plasma resulting in material etching. In the present study, SiO2 surfaces were etched with reactive species of CF4 microplasma generated by their laser-induced break down with 775 nm pulses of an fs-laser (150 fs) at a repetition rate of 1 kHz. The dependency of the depth, the width, and the morphology of the etching pits were analysed systematically against the process parameters used. In particular, a linear increase of the etching depth up to 10 µm was achieved. The etched surface appears smooth without visible cracks, defects, or LIPSS (Laser-induced periodic surface structures). © 2020, The Author(s).
Self-cleaning stainless steel surfaces induced by laser processing and chemical engineering
Nanostructured surfaces show a variety of beneficial macroscopic effects. The combination of hierarchic nanostructures with a suitable chemical surface composition allows for the fabrication of surfaces with interesting fluidic properties beyond such effects. This approach enables the specification of nano/microstructure and chemical composition independent of each other. Various hierarchical micro- and nanostructures can be realized by laser texturing of stainless steel surfaces with infrared picosecond laser. Simultaneously, the surface is activated for chemical processing. The surface can now be tuned by bonding of a self-assembled monolayer on the laser-treated surface by chemical treatment. This two-step functionalization process allows the for separated adjusting of the surface topography and chemical composition and thus for the well-defined setting of the surface properties. The fabrication of superhydrophobic surfaces with self-cleaning properties are performed that can be functionalized further by subsequent laser-irradiation. Furthermore, the long-time stability of the surface functionalization in relation to the impact chemicals or radiation was investigated.
Residual Layer Removal of Technical Glass Resulting from Reactive Atmospheric Plasma Jet Etching by Pulsed Laser Irradiation
Ultrahigh-precision machining of glass is indispensable for optical component fabrication and therefore for applications. In this regard, plasma jet assisted chemical etching technologies enable new fabrication processes for enhanced optical functionalities due to their deterministic localized machining capabilities. This technique has been successfully applied to fused silica and silicon. However, applications require specific glass properties are related to complex material compositions of the glass. Hence, reactive plasma etching of these optical glasses is a challenging task. For instance, etching of metal oxide containing glass like N-BK7 by a fluorine-based reactive atmospheric plasma jet (RAPJ) exhibits currently limitations due to the formation of non-volatile reaction products that remain on the glass surface as a layer. Therefore, a procedure consisting of RAPJ etching and laser ablation is proposed for the machining of N-BK7. The capability of laser-based removal of residual layers is compared to water-based solving of the residual layer. After RAPJ etching of N-BK7 using a CF4–O2 gas mixture with an average microwave power of 16 W, the samples are cleaned either by a water-based solvent or by the ablation with a nanosecond-pulsed ultraviolet laser. The laser irradiation with fluences of 2.8 J/cm2 results in a localized removal of the residual layer. It is demonstrated that the roughness of the laser-cleaned N-BK7 surface is similarly low as solvent-based cleaned samples but the pulsed laser enhanced cleaning allows a dry processing at atmospheric pressure as well as a localized processing with a high lateral resolution.
Shock-wave-induced Thin-film Delamination (SWIFD): A Non-thermal Structuring Method of Functional Layers
The laser structuring of thermally sensitive functional layers is a challenge for laser methods. However, already ultrashort laser pulses can induce thermal modifications. The spatial separation of the laser pulse absorption from the functional layer removal process allows a non-thermal structuring process. Therefore, the rear side of the substrate is irradiated and the following laser ablation process induces a transverse shock wave through the substrate. Finally, the interaction of the shock wave with the substrate/functional layer interface results in a delamination of the functional layer. This shock-wave-induced thin-film delamination (SWIFD) method was tested on a layer system (1.5 μm thick epoxy-based negative photoresist SU 8, 250 nm–1 μm chromium layer) on a 25 μm polyimide flexible substrate where the influence of the systematic variation of the thickness of the metallic intermediate layer on the delamination process was studied. The resultant surface morphology was analyzed by optical microscopy as well as by white light interferometry (WLI).
Dry etching of monocrystalline silicon using a laser-induced reactive micro plasma
Dry etching is a prevalent technique for pattern transfer and material removal in microelectronics, optics and photonics due to its high precision material removal with low surface and subsurface damage. These processes, including reactive ion etching (RIE) and plasma etching (PE), are performed at vacuum conditions and provide high selectivity and vertical side wall etched patterns but create high costs and efforts in maintenance due to the required machinery. In contrast to electrically generated plasmas, laser-induced micro plasmas are controllable sources of reactive species in gases at atmospheric pressure that can be used for dry etching of materials. In the present study, we have demonstrated the laser-induced plasma etching of monocrystalline silicon. A Ti:Sapphire laser has been used for igniting an optically pumped plasma in a CF4/O2 gas mixture near atmospheric pressure. The influence of process parameters, like substrate temperature, O2 concentration, plasma-surface distance, etching duration, pulse energy and crystal orientation on etching rate and surface morphology has been investigated. Typical etching rates of 2–12 µm x min−1 can be achieved by varying mentioned parameters with a decreasing etching rate during the process. Different morphologies can be observed due to the parameters set, smooth as well as rough surfaces or even inverted pyramids. The presented etching method provides an approach for precise machining of silicon surfaces with good surface qualities near atmospheric pressure and sufficiently high material removal rates for ultraprecise surface machining. © 2021 The Author(s)
Laser Patterning of CIGS thin Films with 1550 nm Nanosecond Laser Pulses
The results of laser scribing experiments of CIGS thin films deposited on Mo-coated stainless steel sheets, using laser pulses with a wavelength of 1550 nm and a pulse duration of 6 ns, are presented in this study. It is shown that a removal of the CIGS from the Mo film is possible without edge melting of the CIGS or damaging of the Mo. The critical parameter for inducing the delamination lift-off process of the CIGS from the Mo was identified to be the scribing speed of the laser. In dependence on the laser parameters two different material removal processes were found. For a low pulse overlap the laser pulse penetrates the CIGS film and is absorbed in the interface between the CIGS and the Mo causing a lift-off process of the CIGS from the Mo back contact. For a high pulse overlap an ablation process starting from the top side of the CIGS film was found. The composition and morphology of the sample material after the laser patterning were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and micro-Raman spectroscopy.
Influence of wavelength and accumulated fluence at picosecond laser-induced surface roughening of copper on secondary electron yield
Ultrashort-pulse laser processing of copper is performed in air to reduce the secondary electron yield (SEY). By UV (355 nm), green (532 nm), and IR (1064 nm) laser-light induced surface modification, this study investigates the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence) on the ablation depth, surface oxidation, topography, and ultimately on the SEY. Increasing the accumulated laser fluence results in a gradual change from a Cu 2 O to a CuO-dominated surface with deeper micrometer trenches, higher density of redeposited surface particles from the plasma phase, and a reduced SEY. While the surface modifications are less pronounced for IR radiation at low accumulated fluence (,1000 J/cm2 ), analogous results are obtained for all wavelengths when reaching the nonlinear absorption regime, for which the SEY maximum converges to 0.7. Furthermore, independent of the extent of the structural transformations, an electron-induced surface conditioning at 250 eV allows a reduction of the SEY maximum below unity at doses of 5×10 -4 C/mm2 . Consequently, optimization of processing parameters for application in particle accelerators can be obtained for a sufficiently low SEY at controlled ablation depth and surface particle density, which are factors that limit the surface impedance and the applicability of the material processing for ultrahigh vacuum systems. The relations between pro- cessing parameters and surface features will provide guidance in treating the surface of vacuum components, especially beam screens of selected magnets of the Large Hadron Collider or of future colliders.
Secondary electron yield engineering of copper surfaces by 532 nm ultrashort laser pulses
Nanostructured surfaces exhibit outstanding properties and enable manifold industrial applications. In this study the laser surface processing of polycrystalline, flat copper surfaces by 532 nm picosecond laser irradiation for secondary electron yield (SEY) reduction is reported. The laser beam was scanned in parallel lines across the sample surface in order to modify large surface areas. Morphology and SEY are characterized in dependence of the process parameters to derive correlations and mechanisms of the laser-based SEY engineering process. The nano- and microstructure morphology of the laser-modified surface was characterized by scanning electron microscopy and the secondary electron yield was measured. In general, an SEY reduction with increasing accumulated laser fluence was found. In particular, at low scanning speed (1 mm/s - 10 mm/s) and “high” laser power (~ 1 W) compact nanostructures with a very low SEY maximum of 0.7 are formed.