Aleksandr V. Simakin

NANOPARTICLES PRODUCED BY LASER ABLATION OF SOLIDS IN LIQUID ENVIRONMENT

A review of results on nanoparticles formation is presented under laser ablation of Ag, Au, and Ti solids targets in liquid environments (H2O, C2H5OH, C2H4Cl2, etc.). X-ray diffractometry (XRD), UV-Vis optical transmission spectrometry, and high-resolution transmission electron microscopy (HRTEM) characterise the nanoparticles. The morphology of nanoparticles is studied as a function of both laser fluence and nature of the liquid. The evidence of an intermediate phase of Au-Ag alloy is presented under exposure of a mixture of individual nanoparticles to laser radiation. Self-influence of the beam of a femtosecond laser is discussed under the ablation of the Ag target in liquids under Ti:sapphire laser. The factors are discussed that determine the distribution function of particle size under laser ablation. The influence of laser parameters as well as the nature on the liquid on the properties of nanoparticles is elucidated.

Nanodisks of Au and Ag produced by laser ablation in liquid environment

Abstract Ablation of Au and Ag targets in water by a Cu vapor laser generates Au and Ag sols. The metal nanoparticles obtained after evaporation are disk-shaped (diameter in the 20–60 nm range, thickness of few nanometers). Their formation is observed at laser fluence between 10 and 20 J / cm 2 . Both aqueous sols are characterized by well-resolved plasmon bands around 400 nm (Ag) and 520 nm (Au).

Formation of ZnSe and CdS quantum dots via laser ablation in liquids

Abstract Formation of nanoparticles of both ZnSe and CdS under ablation of corresponding bulk semiconductors in liquid environment (diethyleneglycol, ethanol, etc.) using radiation of a Cu vapor laser is reported. X-ray diffraction (XRD), resonance Raman scattering (RRS), and transmission electron microscopy (TEM) confirm that the nanoparticles are crystalline and have average size of ca 10–20 nm. RRS of nanoparticles are characterized by several peaks multiple to frequency of corresponding phonon (LO replicas).

Fast etching of sapphire by a visible range quasi-cw laser radiation

Abstract Experimental results are presented on laser-assisted etching of sapphire by a copper vapour laser radiation (wavelength 510 nm, pulse duration 10 ns, repetition rate 8 kHz, energy density ∼ 10 J/cm2). The etching is carried out under the laser irradiation through the sapphire substrate of the interface sapphire/absorbing liquid. The self-modulation of the groove depth is observed in a certain range of scanning velocities of laser beam. A qualitative model of the etching process is proposed where the maximal etching depth per pulse is limited by the thermal diffusion length of sapphire during the laser pulse. The corresponding etching rate of 0.3 μm/pulse (∼ 2 mm/s) is observed experimentally. The etched areas of sapphire show the ability to reduce Cu from the electroless plating solution. Area-selective Cu metallization of the etched grooves, via- and blind holes is reported with adherence up to 18 N/mm2.

Nanoparticle formation during laser ablation of solids in liquids

The experimental data on the generation of metal and semiconductor nanoparticles during their laser ablation in liquids is reviewed. The dependence of the morphology of noble metal nanoparticles on the liquid type and laser parameters is discussed. The data on the kinetics of the formation of alloyed Au-Ag nanoparticles under laser irradiation of a mixture of colloid solutions of individual nanoparticles are presented. The effect of femtosecond laser beam self-action during metal ablation in liquids via the second harmonic generation at Ag nanoclusters is discussed. The data on the generation of core-shell nanoparticles during laser ablation of alloys and in the presence of the chemical interaction of formed nanoparticles with surrounding liquid are presented. It was shown that laser ablation of CdS and ZnSe crystals leads to the formation of quantum dots of these semiconductors in solution. The parameters controlling the properties of nanoparticles during ablation in liquids and possible applications of the method are discussed.

Initiation of nuclear reactions under laser irradiation of metal nanoparticles in the presence of thorium aqua ions

Laser irradiation of tungsten and gold nanoparticles in aqueous solutions of Th(NO3)4 was experimentally studied. Picosecond Nd:YAG lasers with a wavelength of 1.06 µm and a peak power from 1011 to 1013 W cm−2 were used. The composition of colloidal solutions before and after laser irradiation was analyzed using atomic absorption and gamma spectrometry. It was found that laser irradiation initiates nuclear reactions involving thorium nuclei, occurring via two different channels. Radioactive decay of thorium nuclei within its radioactive series is enhanced under laser irradiation in D2O; one of the fission fragments is 137Cs. Possible mechanisms of the process are discussed.

Laser-induced carbon deposition from supercritical benzene

Abstract A catalyst-free deposition of carbon onto a Si substrate immersed into benzene under supercritical pressure and temperature is induced by radiation of a Cu vapor laser. Raman analysis shows the signal typical of that for glassy carbon with a broadened D-peak. HRTEM indicates that the carbonaceous species have the shape of hollow rolls of 3–5 nm in diameter with multilayered walls with interlayer distance of 0.9 nm. The remaining liquid shows a strong luminescence in the visible, which is tentatively attributed to formation of polyaromatic compounds.

Internal segregation of nanoparticles irradiated by laser radiation

The effect of the removal of zinc from brass nanoparticles has been experimentally discovered upon irradiating their suspension in ethanol by laser radiation. The analysis of the absorption spectra of nanoparticles shows that brass nanoparticles are transformed to copper nanoparticles during irradiation. The results are interpreted in terms of the high-pressure-induced modification of the phase diagram of nanoparticles. This pressure is caused by, first, the small radius of nanoparticles and, second, the pressure of the surrounding-liquid vapors upon the laser heating of nanoparticles.

Laser-assisted etching-like damage of Si

Abstract Experimental results are presented on localized Si damage induced by high repetition rate copper-vapor laser pulses under a liquid layer. The damage is confined to the laser spot and is supposed to be due to accumulation of defects in the Si surface layer and material fatigue. These defects are dislocations with lateral dimensions close to that of the laser spot. The time of damage increases exponentially with the decrease of the energy density of the laser pulse and does not depend on the crystallographic orientation of the Si wafer. The rate of etching-like damage in electrolytes increases with external polarization of the Si wafer. The laser writing of porous Si is observed in a certain range of anodic polarization of a Si wafer at scanning velocities of the laser beam of 30–300 μm/s with a spatial resolution of ∼ 20 μm.

Biofunctional magnetic ‘core–shell’ nanoparticles generated by laser ablation of iron in liquid

Biofunctional ‘core–shell’ nanoparticles were generated via pulsed laser ablation of a bulk iron target in liquid containing a stabilizer agent. This novel technique for generation of magnetic nanoparticles is a prospect for potential applications in laser diagnostics and treatment of damaged cartilage. We studied the absorption spectra, magnetic properties of magnetite nanoparticles and their colloidal solutions to be used for impregnation into cartilage. Core–shell magnetite nanoparticles of 10–15 nm size have stable size distribution, low velocity of sedimentation and do not agglomerate during more than three months of storage time.