International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The theory of laser-induced oxidation of metals, namely Ti, was developed. The theory accounts for the action of the strong temperature gradient due to laser irradiation as well as the oxygen concentration gradient. This theory is based on the Wagner differential oxidation equation and determines the oxide film thickness depending on the number of laser pulses. Theoretical calculations were confirmed experimentally using a YAG:Nd laser beam at 1.06 μm, a pulse duration of 15 nm and an intensity of 2 MW/cm², which is 10% less than the ablation threshold. Raman and SEM studies show the formation of a TiO2 film of mixing structural phase (anatase and rutile). It was found that the volume fraction of these phases depends on the intensity of the laser irradiation.

A quantum cone is a structure consisting of a large number of quantum dots with a gradually decreasing diameter from the base to the top of the cone. This distribution of quantum dots leads to a dispersive radiated spectrum. The red edge of the spectrum is determined by the band gap of the bulk semiconductor, and the blue edge by the quantum confinement of excitons on top of the cones. We observe the kinetics of photoluminescence, obeying the stretched exponential law, from quantum cones formed on the surface of DLC. They are explained by an increase in the lifetime of excitons along the height of the cone from the top to the base of the cone and an increasing concentration of excitons at the base due to their drift in the quasi-built-in electric field of the quantum cone. Such time dependence of the photoluminescence spectrum gives the possibility of its discrimination spectrum on time. The possible visualization of the quantum cones of DLC using irradiation by a UV light source is shown. A quantum cone is a new type of nano light source, as it replaces two elements in a conventional spectrometer – a light source and a dispersive element: an ultra-fast monochromator. These features will make it possible to build a spectrometer to measure the absorption spectrum of individual nanoparticles or viruses.

A laser-induced oxidation method for the formation of a TiO2 layer on a Ti substrate was used. The TiO2 phase can be controlled by an Nd:YAG laser with fundamental frequency at an intensity I = 52.8 MW/cm2 and three different doses. Dose D1 = 3.1×1020 phot/cm2 forms a TiO2 layer in the anatase phase, which possesses the highest photocatalytic, antibacterial and adhesion properties. As the laser dose increases, the TiO2 layer thickness increases from 40 nm to 100 nm, but the photocatalytic decomposition reaction constant decreases. The observed super-linear increase of the TiO2 layer thickness with the laser dose is explained by the presence of positive feedback during the irradiation process. The temperature rises with increasing of the thickness due to the interference-caused decrease of the reflection coefficient. As the thickness increases, TiO2 on Ti structure adhesion decreases from 800 mN to 400 mN due to the formation of a layer with a mixture of phases.