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

Publication Type Scientific article indexed in SCOPUS or WOS database
Funding for basic activity Other research projects
Defending: ,
Publication language English (en)
Title in original language Colossal Laser Ablation Threshold of Ge Crystal due to Formation of Geo2 Nanolayer: “Lid Effect” - Subsurface Boiling Mechanism
Field of research 2. Engineering and technology
Sub-field of research 2.5 Materials engineering
Research platform Materials, Processes, and Technologies
Authors Artūrs Medvids
Jevgenijs Kaupužs
Pāvels Onufrijevs
Līga Grase
Anzelms Zukuls
Keywords Boiling, Bubbles, GeO2 nanolayer, Laser ablation
Abstract 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
Hyperlink: https://www.sciencedirect.com/science/article/pii/S0030399218320073?via%3Dihub 
Reference 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, Article number 105630. ISSN 0030-3992. Available from: doi:10.1016/j.optlastec.2019.105630
Additional information Citation count:
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ID 29783