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G. A. Shafeev

Publications and source records attributed to G. A. Shafeev.

At least 19 recordsLinked to original sources
arXiv2022

Laser synthesis of ruby for photo-conversion of solar spectrum

Ruby grains are synthesized by laser heating of the dry mixture of Al$_2$O$_3$ and Cr$_2$O$_3$. Quasi-continuous radiation of a Nd:YAG laser was used for this purpose with average power of 15 W. Synthesized ruby grains demonstrate strong photo-luminescence in the vicinity of 700 nm. Synthesized ruby grains were integrated into a matrix made of flouro-polymer. Luminescene map acquired with the help of a photo-fluorimeter confirms efficient photo-conversion of green-blue radiation of the synthesize ruby into red region. Ruby grans can further be fragmented to smaller particles using the technique of laser fragmentation in liquids.

physics.gen-ph↗
arXiv2022

Laser ablation and fragmentation of Boron in liquids

Nanoparticles of elemental Boron are generated for the first time by laser ablation of a sintered Boron target in liquid isopropanol and subsequent laser fragmentation of the suspension. For this purpose an ytterbium doped fiber laser was used at wavelength of 1060-1070 nm, pulse repetition rate of 20 kHz, and pulse duration of 200 ns. The size of Boron nanoparticles after ablation and fragmentation of the suspension is around 30 nm. Nanoparticles are made mostly of Boron and carbon, some particles have carbon shell. Allotropic composition of nanoparticles differs from that of the initial Boron target. Possible applications are discussed.

physics.gen-ph↗
arXiv2019

Generation of nanoparticles of phtalocyanines by laser fragmentation and their interaction with gold nanoparticles

Optical properties and morphology of laser generated Aluminum and Copper phthalocyanine nanoparticles (nAlPc and nCuPc) in water are experimentally studied. Near infrared laser source of nanosecond pulse duration was used for fragmentation of Pc micro-powder suspended in H2O. Extinction spectra in the visible and near IR range of NPs colloidal solutions in MQ water were acquired by means of optical spectroscopy. The optical density of both nCuPc and nAlPc increases with laser fragmentation time. Transmission electron microscopy was used for characterization of nanoparticle morphology and size analysis. It is found that nCuPc are made of short (100 nm) rectangular bars interconnected at various angles with other bars. Similar experiments were carried out for a colloidal solution, which is a mixture of Au and AlPc nanoparticles. It turned out that Au NPs in presence of nAlPc form large agglomerates of Au.

physics.gen-ph↗
arXiv2018

Laser-assisted generation of elongated Au nanoparticles and subsequent dynamics of their morphology under pulsed irradiation in water and calcium chloride solutions

One-step laser generation of Au elongated nanoparticles (NPs) and their successive fragmentation and agglomeration are experimentally studied for the first time. In the present work, laser-assisted formation of Au elongated nanoparticles by ablation of a solid Au (99.99%) target in water was done using a ytterbium-doped fiber laser sources with pulse duration of 200 ns and pulse energy of 1mJ. Extinction spectrum correlating with TEM shows the appearance of absorption signal in red region and near IR-spectrum that corresponds to longitudinal plasmon resonance of electrons in elongated Au NPs. In addition, generated elongated Au nanoparticles were exposed to pulsed laser beam with various pulse energy and laser exposure time. It was found that at early stages of irradiation NPs agglomerate as the NPs chains with size of order of 1 micrometer long. Further laser exposure results in fragmentation of these chains. Possible processes of laser-assisted formation of elongated Au NPs in aqueous solutions of calcium chloride and their subsequent interaction with pulsed laser irradiation are discussed.

physics.gen-ph↗
arXiv2017

Stable products of laser-induced breakdown of aqueous colloidal solutions of nanoparticles

The formation of stable products of water decomposition under laser exposure of aqueous colloidal solutions of nanoparticles is experimentally studied. Laser exposure of colloidal solutions leads to formation of H2, O2, and H2O2. The dependence of the yield of these products depends on the energy density of laser radiation inside the liquid and concentration of nanoparticles. The ratio H2/O2 depends on laser fluence and is shifted towards H2. There are at least to sources of H2O2, namely, laser-induced breakdown plasma and ultrasound induced by laser pulses in the liquid. The formation of both H2 and O2 is tentatively assigned to direct dissociation of H2O molecules by electron impact from laser-induced plasma.

physics.chem-ph↗
arXiv2017

Balance of O2 and H2 content under laser-induced breakdown of aqueous colloidal solutions

Formation of molecular H2 and O2 is experimentally studied under laser exposure of water colloidal solution to radiation of a Nd:YAG laser at pulse duration of 10 ns and laser fluence in the liquid of order of 100 J/cm2. It is found the partial pressure of both H2 and O2 first increases with laser exposure time and saturates at exposures of order of 1 hour. The balance between O2 and H2 content depends on the laser energy fluence in the solution and is shifted towards H2 at high fluences. Possible mechanisms of formation of the dissociation products are discussed, from direct dissociation of H2O molecules by electrons of plasma breakdown to emission of laser-induced plasma in liquid.

physics.gen-ph↗
arXiv2016

Influence of external magnetic field on laser breakdown plasma in aqueous Au nanoparticles colloidal solutions

Influence of permanent magnetic field up to 7.5 T on plasma emission and laser-assisted Au nanoparticles fragmentation in water is experimentally studied. It is found that presence of magnetic field causes the breakdown plasma emission to start earlier regarding to laser pulse. Field presence also accelerates the fragmentation of nanoparticles down to a few nanometers. Dependence of Au NPs fragmentation rate in water on magnetic field intensity is investigated. The results are discussed on the basis of laser-induced plasma interaction with magnetic field.

physics.gen-ph↗
arXiv2016

Hydrogen emission under laser exposure of colloidal solutions of nanoparticles

We report the generation of molecular hydrogen from water by laser irradiation, without any electrodes and photocatalysts. A near infrared pulsed nanosecond laser is used for exposure of colloidal solution of Au nanoparticles suspended in water. Laser exposure of the colloidal solution results in formation of plasma of laser breakdown of liquid and emission of H2. The rate of H2 emission depends critically on the energy of laser pulses. There is a certain threshold in laser fluence in liquid (around 50 J/cm2) below which plasma disappears and H2 emission stops. H2 emission from colloidal solution of Au nanoparticles in ethanol is higher than that from similar water colloid. It is found that formation of plasma and emission of H2 or D2 can be induced by laser exposure of pure liquids, either H2O or D2O, respectively. The results are interpreted as water molecules splitting by direct electron impact from breakdown plasma.

physics.gen-ph↗
arXiv2014

Contactless transfer of angular momentum by rotating laser beam

Contactless transfer of angular momentum from rotating laser beam to a solid target is experimentally demonstrated. The effect is observed under irradiation of a glassy carbon target immersed in water by a pulsed laser beam that is scanned across the target surface along circular trajectory. The direction of target rotation coincides with that of the laser beam at small thickness of the liquid layer above the target while is opposite in case of higher thickness of the layer. The effect is interpreted as the interplay between thermocapillary and convective flows induced in the liquid by laser heating.

physics.gen-ph↗
arXiv2013

Laser-induced synthesis and decay of Tritium under exposure of solid targets in heavy water

The processes of laser-assisted synthesis of Tritium nuclei and their laser-induced decay in cold plasma in the vicinity of solid targets (Au, Ti, Se, etc.) immersed into heavy water are experimentally realized at peak laser intensity of 10E10-10E13 Watts per square centimeter. Initial stages of Tritium synthesis and their laser-induced beta-decay are interpreted on the basis of non-elastic interaction of plasma electrons having kinetic energy of 5-10 eV with nuclei of Deuterium and Tritium, respectively.

physics.gen-ph↗
arXiv2012

Self-organization of ascending bubbles ensemble

Self-organization of hydrogen bubbles generated by laser-treated areas of an aluminum plate etched in a basic aqueous solution of ammonia is studied experimentally and theoretically. A dynamics of establishment of stationary pattern of gas bubbles is experimentally is shown. In the theoretical model the velocity field of liquid flows around an ensemble of several bubbles is obtained. Modeling of the process of self-organization of gas bubbles is performed on the basis of continuum model of bubbles jet. Under certain assumptions, the pressure of diluted gas bubbles is described by equation similar to that for non-ideal gas that follows the van der Waals equation of state. The model predicts an alignment of gas bubbles along bisectors of the laser-treated area limited by a square, which is in good agreement with experimental observations. Further development of the model leads to the equation with negative diffusion coefficient that may be responsible for symmetry breakdown and pattern formation.

physics.flu-dyn↗
arXiv2011

Accelerated alpha-decay of 232U isotope achieved by exposure of its aqueous solution with gold nanoparticles to laser radiation

Experimental results are presented on laser-induced accelerated alpha-decay of Uranium-232 nuclei under laser exposure of Au nanoparticles in aqueous solutions of its salt. It is demonstrated that the decrease of alpha-activity strongly depends on the peak intensity of the laser radiation in the liquid and is highest at several terawatt per square centimeter. The decrease of alpha-activity of the exposed solutions is accompanied by the deviation of gamma-activities of daughter nuclides of Uranium-232 from their equilibrium values. Possible mechanisms of the laser influence on the alpha-activity are discussed on the basis of the amplification of the electric field of laser wave on metallic nanoparticles.

physics.gen-ph↗
arXiv2011

Self_organization of gas bubbles

Self_organization of hydrogen bubbles is reported under etching of metallic Aluminum in a weakly basic solution. The ascending gas bubbles drift to the areas with higher density of bubbles due to pressure difference. As a result, ascending bubbles form various stationary structures whose symmetry is determined by the symmetry of the etched area. The process is modeled on the basis of numerical solution of Bernoulli equation.

cond-mat.other↗
arXiv2010

Size distribution of Au NPs generated by laser ablation of a gold target in liquid with time-delayed femtosecond pulses

The influence of delay-time between two sequential femtosecond pulses on the properties of nanoparticles obtained via laser ablation of gold in ethanol has been studied. The morphological and optical properties of the nanoparticles attained were characterized using high resolution transmission electron microscopy and UV_Vis absorption spectroscopy, respectively. Furthermore, the size distribution of nanoparticles was determined by means of a centrifugal sedimentation particle size analyzer. It is found that the time delay variations lead to corresponding changes in size distribution, plasmon resonance position as well as the rate of nanoparticles generation.

cond-mat.mes-hall↗
arXiv2010

Internal structure of nanoparticles of Al generated by laser ablation in liquid ethanol

Al NPs are synthesized by laser ablation of a bulk Al target immersed into liquid ethanol saturated with hydrogen at atmospheric pressure. The nanoparticles possess a well-distinguished core-shell structure. High Resolution Transmission Electron Microscopy shows several layers inside the Al nanoparticle: oxide layer, amorphous Al, single crystal Al, and a cavity in the center. Formation of the cavity is attributed to the sharp increase of hydrogen dissolution in Al upon its melting and its eventual release after the solidification.

cond-mat.mes-hall↗
arXiv2010

Laser-assisted coloration of Ti: oxides or nanostructures?

Coloration of a Ti target under its ablation with picosecond laser pulses in liquids is ascribed to the formation of self-organized nanostructures. The density of nanostructures increases in an avalanche-like way with the number of laser pulses. The Raman peaks observed in the laser-exposed areas may be due to the auto-SERS effect.

cond-mat.mes-hall↗
arXiv2010

Deviation from secular equilibrium

Laser exposure of gold nanoparticles in aqueous solutions of Uranium salt leads to accelerated decay of U238 nuclei and significant deviation from secular equilibrium. The samples demonstrate the enhanced gamma emission in the range of 54 keV during laser exposure.

physics.gen-ph↗