Vanadium oxidation as a result of cw CO2 laser irradiation in atmospheric air

Laser Thermochemical High-Contrast Recording on Thin Metal Films

Laser-induced thermochemical recording of nano- and microsized structures on thin films has attracted intense interest over the last few decades due to essential applications in the photonics industry. Nevertheless, the relationship between the laser parameters and the properties of the formed oxide structures, both geometrical and optical, is still implicit. In this work, direct laser interference patterning of the titanium (Ti) film in the oxidative regime was applied to form submicron periodical structures. Depending on the number of laser pulses, the regime of high contrast structures recording was observed with the maximum achievable thickness of the oxide layer. The investigation revealed high transmittance of the formed oxide layers, i.e., the contrast of recorded structures reached up to 90% in the visible range. To analyze the experimental results obtained, a theoretical model was developed based on calculations of the oxide formation dynamics. The model operates on Wagner oxidation law and the corresponding optical properties of the oxide–metal–glass substrate system changing nonlinearly after each pulse. A good agreement of the experimental results with the modeling estimations allowed us to extend the model application to other metals, specifically to those with optically transparent oxides, such as zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), and tantalum (Ta). The performed analysis highlighted the importance of choosing the correct laser parameters due to the complexity and nonlinearity of optical, thermal, and chemical processes in the metal film during its laser-induced oxidation in the air. The developed model allowed selecting the suitable temporal–energetic regimes and predicting the optical characteristics of the structures formed with an accuracy of 10%. The results are promising in terms of their implementation in the photonics industry for the production of optical converters.

Nanostructured carbon generated by chemical vapor deposition from acetylene on surfaces pretreated by a combination of physical and chemical methods

Chemical vapor deposition of carbon nanotubes by catalytic decomposition of acetylene on V2O5microtube crystals is presented. The catalyst was prepared by laser irradiation of vanadium sheets and treated with cobalt acetate solution. The carbon deposits generated on this novel type of catalyst were characterized by transmission electron microscopy measurements. Both carbon nanofibers and carbon nanotubes were found to be formed. This catalyst system, generated by the combined laser irradiation and chemical impregnation methods, is a new and promising way to study the differences in the mechanism of the generation of nanostructures.