N. V. Minaev

Laser fabrication of periodic microstructures from silver nanoparticles in polymer films

The fabrication of photoand thermostable periodic structures from silver nanoparticles in polymer plates (cross-linked oligourethanemethacrylate impregnated with silver precursors Ag(hfac) and Ag(fod) dissolved in the supercritical carbon dioxide) is studied. The process is based on the local (depending on the irradiated spot size) photochemical decomposition of the silver precursors in the polymer matrix that initiates the atomic aggregation and creation of silver nanoparticles with the plasmon resonance in absorption in the spectral range 420–430 nm. The third-harmonic radiation of a Nd:YAG laser (355 nm) and the Kr+-laser (521 nm) radiation are employed for the recording of periodic structures with submillimeter and micron resolutions. The photosensitivity of the polymer matrices impregnated with the silver precursors to the UV and visible radiation is discussed.

Compatibility of cells of the nervous system with structured biodegradable chitosan-based hydrogel matrices

Hydrogel matrices for cell cultivation have been generated by two-photon laser polymerization of unsaturated chitosan derivatives and methacrylated hyaluronic acid. The adhesive and toxic properties of the matrices have been assessed, and the matrices have been shown to have a good compatibility with primary hippocampal cell cultures. The formation of morphologically normal neural networks by cells of the nervous system cultured on the surface of hydrogel matrices has been observed. The metabolic status of dissociated hippocampal cells cultured on the matrices was similar to that of the control cultures, as shown by the results of MTT reductase activity assay. Thus, matrices based on unsaturated polysaccharide derivatives crosslinked by laser irradiation showed good compatibility with differentiated cells of the nervous system and considerable potential for use in neurotransplantation.

Structure and properties of ultra-high-molecular-weight polyethylene (UHMWPE) containing silver nanoparticles

Ultra-high molecular weight polyethylene (UHMWPE) containing silver particles was obtained by impregnation with a silver-containing precursor in supercritical carbon dioxide and its microstructure and mechanical properties were studied. The Ag-containing UHMWPE samples showed a 40–50% increase (on the average) in the elasticity modulus according to a study by the nanoindentation method. The hardness of the material did not change during modification. The friction coefficients of the starting and modified samples were comparable over the whole range of loads from 50 to 400 N under study.

Dynamics of a photothermal self-assembly of plasmon structures in polymer films containing gold and silver precursors

This work is devoted to considering mechanisms that form silver and gold nanoparticles (NPs) in thin (200 μm) cross-linked oligourethane methacrylate (OUM) polymer films impregnated with different precursors of these metals. The investigations are connected with recording the kinetics of variation in the transmission of films under the action of continuous laser radiation with wavelengths of 405 and 532 nm, resulting in the photolysis of precursor molecules. Precursor molecules were introduced into the matrix by the diffusion saturation of films in an ethanol medium or in supercritical carbon dioxide. It was established that the time dependences are determined by the metal type, wavelength, and laser radiation power, as well as by way of precursor impregnation. Two effects connected with laser action on such films were found. One of them corresponds to a jumplike change in transmission of samples with the gold precursor; the second is caused by the formation of dense NP structures in the form of films on the sample surface.

Synthesis and characterization of silver nanoparticles in a nanoporous glass

We obtained a metal-dielectric composite by thermal restoration of silver atoms from an alcohol solution of a precursor in nanoporous glass with pores with a radius of 2 nm. The concentration, size, and asphericity degree of metal nanoparticles formed in the pores are characterized according to the measured extinction spectra of the material.

Laser-induced effects in raman spectra of nanocrystalline silicon

Investigations into the action of continuous laser radiation with a wavelength of 532 nm on particles of nanocrystalline silicon (nc-Si) obtained by the method of laser pyrolysis of monosilane have been carried out for the first time using Raman (combination scattering (RS)) spectroscopy. It is established that the action of rather powerful radiation (105–106 W/cm2) causes substantial changes in the state of nc-Si which are associated with the development of thermooxidative processes in air, leading to a complex character of the change in the RS band belonging to nc-Si. The process of the matrix introduction of nc-Si particles into microparticles of low-density polyethylene is achieved with the use of SCF impregnation into a SC-CO2 medium. It is established that the action of laser radiation on nc-Si particles in a polymer matrix starts manifesting as a change in the RS band at power densities much greater than those in the case of a pure nc-Si powder.

Photo–induced processes in Ag and Eu β-diketonates incorporated into aerogel matrix of silicon dioxide by supercritical fluid impregnation

Samples of silicon dioxide aerogel with embedded Ag and Eu β-diketonate molecules are obtained by impregnation in supercritical carbon dioxide (SC-CO2). The sample impregnated by Eu(tta)3 molecules possesses photoluminescence properties. Moreover, adsorption of Eu(tta)3 on the walls of the pores results in a strong broadening of the Stark components of its photoluminescence spectra. It is found that aerogel impregnation by AgFOD molecules followed by laser irradiation causes the formation of Ag nanoparticles in the sample volume as a result of AgFOD photolysis and subsequent diffusion self-assembly. The Ag nanoparticles assemble into filament structures due to self-organization as they focus laser radiation.

Formation of filament structures of noble-metal nanoparticles in transparent dielectrics under the action of continuous laser radiation

The formation of filamentary structures (up to 5 mm in length and 5–90 mm thick) of gold and silver nanoparticles (NPs) was studied in porous Vycor glass and polymer material (crosslinked oligouretanmetakrilate) doped with appropriate organic and inorganic precursors of these metals (H[AuCl4] · 4H2O, AgNO3, Ag(hfac)COD) under the action of continuous laser radiation in the visible wavelength range of 5–100 mW power. The formation of such structures along the direction of a laser beam was observed both in the course of laser exposure and after it ended. The mechanism of self-assembling of filaments from metal NPs is rationalized by the photolysis of precursor molecules in the zone of irradiation, the release of metal atoms, and their assembly into NPs. The very process of particle assembly in the filaments are ordered by the effects of self-focusing of laser radiation on a micro lens arising in the matter and channeling it into a medium with a varying refractive index. The features of formation of filamentary structures in the matrices under laser irradiation with different wavelengths are discussed.

Improving the efficiency of laser-induced backside wet etching of optically transparent materials as a result of generation of carbon and silver nanoparticles

The processes of laser-induced backside wet etching (LIBWE) and microstructuring of silicate glass by laser impulses with a wavelength of 527 nm and a duration of about 5 ns have been studied in different aqueous solutions that provide different etching modes, namely, volume (in a solution of dye), volume + surface (in a solution of dye and polyethylene glycol (PEG)), and surface modes (in an aqueous solution of AgNO3). It is shown that the etching rate and the quality of the obtained structures depend on two different processes: the chemical etching of the material surface by water in the supercritical state (fluid produced at fast laser heating) and the shockwave or cavitational destruction of a material. The LIBWE rate and the quality of the formed microstructures are determined by a dominating mechanism of the process. In the case of an aqueous dye solution, the shockwave and cavitational destruction dominates, which makes it impossible to create well-replicated craters and tracks with smooth walls. Upon the addition of PEG to a solution of dye and, especially, upon using an aqueous solution of the silver precursor (AgNO3), the laser-induced processing of carbon or silver nanoparticles gives rise to a strong absorption on the surface of the formed structure, the undesirable cavitational destruction of a material is suppressed, and the process of etching of the glass surface by supercritical water becomes a dominating mechanism of LIBWE. As a result, it is possible to create highly effective and well-reproducible LIBWE technology for the fabrication of precision optical microstructures on the surface of advanced optical materials on the basis of high-performance and reliable lasers with a wavelength of 527 nm.

Fabrication of microstructured materials based on chitosan and D,L-lactide copolymers using laser-induced microstereolithography

The graft copolymers of chitosan and oligo(D,L-lactide) obtained by solid-phase synthesis have been used as the basis of photosensitive compositions for the fabrication of three-dimensional microstructures by laser-induced stereolithography. The electronic absorption spectra of the copolymers are close to the sum of the spectra of native chitosan and polylactide, which has been chosen as a model of grafted oligolactide chains. The fundamental absorption bands of the copolymers lie in a range to 500 nm, and their contribution to the absorption intensity of a photosensitive composition based on the copolymers at second harmonic laser frequency is insignificant. Depending on the macromolecular characteristics of the copolymers, the three-dimensional crosslinking of photosensitive compositions on their basis in the course of microstructuring occurs with different efficiency.