Yu. K. Verevkin

Bactericidal activity of titanium dioxide ultraviolet-induced films

TiO2 films are used as a self-sterilization surface due to their property to form reactive oxygen species (ROS) when irradiated with ultraviolet light. These ROS attack bacteria and kill them. We present a new way to enhance the bactericidal activity of TiO2-films: formation of nanopores on the surface by four-beam high-power laser irradiation. Such surfaces have significantly higher antibacterial activity as compared to conventional TiO2 surfaces after 15 and 60min of UV irradiation. Study of the bacterial cell morphology by atomic force microscopy after 60min irradiation showed that Staphylococcus aureus 956 and Escherichia coli 321-5 undergo significant morphological changes. S. aureus assume atypical elongated shapes after UV treatment alone and swollen forms with protrusions after UV treatment on TiO2 surface. E. coli exhibit oval or round forms after UV treatment alone, and round forms with small protrusions, and destroyed cells after incubation under UV on the TiO2 film.

Arrays of magnetic wires created in phase-separating Fe-containing alloys by interference laser irradiation

Using the interference of laser beams, we have fabricated the periodic arrays of submicron wires in Fe/C and Fe/Cr thin-film alloys. The array formation is found to arise from iron agglomeration in interference maxima. The dramatic decay of the in-plane magnetic anisotropy was observed in the fabricated arrays with decrease in the interference periodicity down to 170 nm. This decay can rather be explained by transforming the wires into separate granules than a smallness of the temperature modulation at small periodicities. Such an explanation is supported by the electronmicroscopic and ferromagnetic resonance data.

Observation of Laser-Induced Local Modification of Magnetic Order in Transition Metal Layers

Laser-induced local modifications of magnetic order in thin Fe-Cr layers were investigated. Local modification in the layers were induced by interfering laser beams. The results of the study give evidence for the formation of submicron-sized anisotropically shaped ferromagnetic regions with a well-defined direction of the easy magnetic axis in the interference maxima at the modification threshold. It was also found that the magnetic anisotropy of a medium is drastically reduced with changing the shapes of these local regions and distances between them. This may be due to the strengthening of the interaction between the regions through the paramagnetic matrix.

Formation of two-dimensional periodic nanostructures on fused quartz, polyimide, and polycrystalline diamond by pulsed four-wave interference laser modification

Atomic force microscopy is used to examine the topography of submicron periodic structures formed on the surfaces of synthetic polycrystalline diamond and polyimide films. The films are deposited on fused quartz substrates by four-wave interference modification using a pulsed 308-nm UV XeCl excimer laser. It is demonstrated that a two-dimensional periodic relief with a submicron period can be formed on the diamond surface directly by laser evaporation in the absence of a photoresist. Depending on the exposure, two mechanisms of polyimide film modification are observed. At exposures less than 100 mJ/cm2, the relief is formed due to swelling at the positions of interference maxima. At exposures greater than 100 mJ/cm2, holes are formed in the films. A periodic relief on the fused quartz surface is formed by using a UV photoresist exposed to pulsed interference laser radiation and subsequent Ar ion etching.

Photoinduced bactericidal activity of TiO2 films

A decrease in CFU of gram-positive and gram-negative bacteria on the surface of UV illuminated TiO2 films (wavelength of 380 nm) is shown. A 29, 45, and 47% decrease in bacterial viability of Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli, respectively, was seen after 12-min exposition. It was first discovered that the reuse of TiO2 films to test a bacterial suspension for viability removes UV-induced bactericidal activity. However, annealing of TiO2 at a temperature above 400°C restores the photoinduced bactericidal activity to its initial state.

Formation of magnetic nanosize gratings in the illumination of thin-film Fe-Cr mixtures by interfering laser beams

The conditions for formation of nanosize gratings (∼100 nm) of ferromagnetic stripes in the illumination of thin-film (10–15 nm) paramagnetic Fe-Cr mixtures by interfering beams from an excimer laser are investigated. The ferromagnetic ordering arises as a result of the thermally stimulated clustering of Fe atoms. The gratings are formed in a certain energy interval of the laser radiation. The width of this interval depends substantially on both the interference period and the illumination time τi. For τi=10 ns there exists an energy interval in which gratings with periods as small as 300 nm are formed.

Interference nanolithography with a UV laser

The sensitivity and resolution of a photoresist composed of a two-layer (polymer-metallic indium) film are measured. 2D masks used to create nanodimensional metallic and insulating islands on a silicon substrate are prepared by direct laser action. Conditions are found for preparing submicron periodic structures on TiO2 films that are applied on a glass substrate by the sol-gel technology. Optical properties of these arrays are measured, and it is shown that they can be used for exciting plane electromagnetic waves.

Analysis and creation of chirped gratings with interference of two laser beams

We created structures with spatially variable period (chirped gratings) on fused quartz and TiO2 films. Expressions for the interference pattern of two coherent-radiation beams with quadratic and plane phase fronts are obtained. Results of the analysis are used for calculation and diagnostics of the created structures.

Self-organization of nanoislands on the surface of silicon and gallium arsenide single crystals stimulated by spatially periodic laser radiation fields

Four interfering laser beams acting upon the surface of silicon and gallium arsenide single crystals stimulate the self-organization of nanoislands, which is manifested by the development of processes controlling the size of islands in a two-dimensional periodic structure formed on the sample surface. The influence of the polarization of interfering beams on the character of this self-organization has been studied. Islands with lateral dimensions from 60 to 100 nm and a height of 6–12 nm have been obtained. The lateral dimensions of nanoislands are 5–10 times smaller than the period of a standing wave of the laser radiation field, which is explained by the influence of elastic stresses developed at the crystal surface.

Addition of frequencies of two complex-conjugate optical fields

Studies were made of the characteristic features of parametric mixing of complex-conjugate optical fields. It was shown that compensation of phase inhomogeneities of the initial fields in the sum-frequency field occurred in the relevant planes within the limits of the phase-matching angles. A study was also made of the distortions of the wavefront of the sum-frequency field due to the anisotropy of a nonlinear crystal.