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Publikācija: Colossal Laser Ablation Threshold of Ge Crystal due to Formation of Geo2 Nanolayer: “Lid Effect” - Subsurface Boiling Mechanism

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Nosaukums oriģinālvalodā Colossal Laser Ablation Threshold of Ge Crystal due to Formation of Geo2 Nanolayer: “Lid Effect” - Subsurface Boiling Mechanism
Pētniecības nozare 2. Inženierzinātnes un tehnoloģijas
Pētniecības apakšnozare 2.5. Materiālzinātne
Pētniecības platforma Materiāli, procesi un tehnoloģijas
Autori Artūrs Medvids
Jevgenijs Kaupužs
Pāvels Onufrijevs
Līga Grase
Anzelms Zukuls
Atslēgas vārdi Boiling, Bubbles, GeO2 nanolayer, Laser ablation
Anotācija Colossally increased laser ablation threshold intensity Ith = 637.0 MW/cm2 of mechanically polished Ge crystal was found. It exceeds by factor of 100 that of chemically etched Ge single crystal (1 0 0), which is about 6.0 MW/cm2. This phenomenon is related to the formation of thin GeO2 layer during the action of laser pulse (wavelength λ = 1064 nm, pulse duration 6 ns, energy in a pulse W = 0.12 J, repetition rate of 10 Hz and beam diameter 2 mm) on the mechanically polished amorphous α-Ge. The increased threshold intensity is explained by the “lid effect”- a non-monotonous temperature distribution with maximum in the bulk of the crystal, where melting and even boiling of material takes place under a solid GeO2 nanolayer, preventing the ablation at a much lower intensity. Applying SEM and optical microscope methods, appearance of bubbles at the irradiated surface was observed. In experiments, the fundamental frequency of pulsed Nd:YAG laser in the regime of multi-pulse irradiation of the same surface spot was used. The thickness of GeO2 layer, estimated from SEM images and by the use of Casino simulation software, is up to 50 nm. According to our calculations of temperature field in GeO2/Ge structure, the maximum of temperature is located near the interface and Ge boiling temperature is reached under solid GeO2 layer at a sub-threshold laser intensity. The theoretical and experimental results are thus explained by the subsurface boiling mechanism of laser ablation in GeO2/Ge structure in the presence of solid GeO2 layer, acting as a “lid”. The possible applications of the investigation results are proposed.
DOI: 10.1016/j.optlastec.2019.105630
Hipersaite: https://www.sciencedirect.com/science/article/pii/S0030399218320073?via%3Dihub 
Atsauce Medvids, A., Kaupužs, J., Onufrijevs, P., Grase, L., Zukuls, A. Colossal Laser Ablation Threshold of Ge Crystal due to Formation of Geo2 Nanolayer: “Lid Effect” - Subsurface Boiling Mechanism. Optics and Laser Technology, 2019, Vol. 119, 1.-8.lpp. ISSN 0030-3992. Pieejams: doi:10.1016/j.optlastec.2019.105630
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ID 29783