المؤلفون: DOMKE, Matthias, FELSL, Dominik, RAPP, Stephan, SOTROP, Jürgen, HUBER, Heinz P., SCHMIDT, Michael

المصدر: Journal of Laser Micro / Nanoengineering; 2015, Vol. 10 Issue 2, p119-123, 5p

مصطلحات موضوعية: MOLYBDENUM compounds, P-waves (Seismology), LASER ablation, METALLIC thin films, METAL formability, THERMAL expansion

مستخلص: The selective laser structuring of thin molybdenum films from the glass substrate side using ultra-short laser pulses displays a by up to a factor of 10 higher ablation efficiency compared to the direct laser ablation from the film side. Moreover, holes can be created without burrs, melt formations or micro cracks. A recent simulation of the glass side ablation process, also known as confined laser ablation, suggests that the laser-matter interaction in the molybdenum leads to a confined ultrafast thermal expansion during heating and melting, which generates a pressure wave that causes the metal film to bulge. However, this model disagrees with the general understanding that the confinement of an expanding gas is the driving ablation mechanism. In order to verify this new model, a pump-probe microscopy setup is utilized to investigate the propagation of a pressure wave in the glass substrate. The results show that pressure waves can be detected already at fluences that are not sufficient for evaporation and that they are generated during heating and melting. These observations support the model of ultrafast thermal expansion during heating and melting generating a pressure wave that causes the metal film to bulge. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Laser Micro / Nanoengineering is the property of Japan Laser Processing Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Sotrop, Jürgen, Kersch, Alfred, Domke, Matthias, Heise, Gerhard, Huber, Heinz

المصدر: Applied Physics A: Materials Science & Processing; Nov2013, Vol. 113 Issue 2, p397-411, 15p

مصطلحات موضوعية: LASER ablation, ULTRASHORT laser pulses, COMPUTER simulation, MOLYBDENUM, METALLIC thin films, FINITE element method

مستخلص: Recently, a so-called 'directly induced' laser ablation effect has been reported, where an ultra-short laser pulse (660 fs and 1053 nm) irradiates a thin Mo film through a glass substrate, resulting in a 'lift-off' of the irradiated layer in form of a thin, solid, cylindrical fragment. This effect provides a new and very energy-efficient selective structuring process for the Mo back electrode in thin-film solar cell production. To understand the underlying physical mechanisms, a 3D axisymmetric finite element model was created and numerically solved. The model is verified by a direct comparison of experimental and numerical results. It includes volume absorption of the laser pulse, heat diffusion in the electron gas and the lattice, thermal expansion of the solid phase and further volume expansion from phase transition to fluid and gas, and finally the mechanical motion of the layer caused by the resulting stress wave and the interaction with the substrate. The simulation revealed that irradiation of the molybdenum layer with an ultra-short pulse causes a rapid acceleration in the direction of the surface normal within a time frame of a hundred picoseconds to a peak velocity of about 100 m/s. The molybdenum layer continues to move as an oscillating membrane, and finally forms a dome after about 100 ns. The calculated strain at the edges of the dome exceeds the tensile stress limit at fluences that initiate the 'lift-off' in experimental investigations. In addition, the simulation reveals that the driving mechanism of the 'lift-off' is the ultrafast expansion of the interface layer and not the generated gas pressure. [ABSTRACT FROM AUTHOR]

: Copyright of Applied Physics A: Materials Science & Processing is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Heise, Gerhard¹ gerhard.heise@hm.edu, Domke, Matthias¹, Konrad, Jan¹, Sarrach, Sebastian¹, Sotrop, Jürgen¹, Huber, Heinz P.¹

المصدر: Journal of Physics D: Applied Physics. 8/8/2012, Vol. 45 Issue 31, p1-1. 1p.

مصطلحات موضوعية: *MOLYBDENUM, *SOLAR cells, *ULTRASHORT laser pulses, *METALLIC thin films, *LASER ablation

مستخلص: Molybdenum thin films on glass substrates play an important role as contact layer for thin film solar cells. They can be ablated by picosecond laser pulses irradiated from the substrate side at low laser fluences of less than 1 J cm−2, while structured trenches remain free from thermal damage and residues. The fluence for that so-called direct induced ablation from the substrate side is in contrast to metal side ablation reduced by approximately one order of magnitude and is far below the thermodynamic limit for heating, melting and evaporating the complete layer. For an extended investigation of the direct induced laser ablation and the underlying mechanism, further thin film materials, chromium, titanium and platinum, with thicknesses between 200 nm and 1 µm were examined. Finally, a simple thermo-dynamical model is able to connect the observed ablation energetics with the mechanical ductility and stress limit of the metal thin films. [ABSTRACT FROM AUTHOR]