Valerii V. Voronov

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).

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.

Growth and spectroscopic studies of NaLa(MoO4)2:Tm3+ crystals: A new promising laser material

Single crystals of scheelite-like disordered double molybdate NaLa(MoO4)2 doped with thulium ions with dopant concentrations of 3.0 × 1019 and 1.2 × 1020 cm−3 are grown by the Czochralski method. Spectral and luminescent studies of crystals grown are performed in wavelength ranges of 800 nm (the transitions 3H6↔3H4) and 2 μm (the transitions 3H6↔3F4), including the measurements of the polarized absorption and luminescence spectra of these crystals and the decay kinetics of their excited states. A model that satisfactorily describes the decay kinetics of the luminescence from the 3H4 level taking into account cross-relaxation interactions is proposed. The prospects for the use of these crystals as active media in two-micrometer solid-state lasers are discussed.

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.

A comparative study of partial reduction of ceria via laser ablation in air and soft chemical route

Abstract Experimental results are presented on the reduction of CeO2 (bandgap of 3.1 eV) either via irradiation in air with UV excimer lasers (KrF, XeCl) or via treatment with hydrazine at 100°C. Both kinds of treatment result in similar modifications of the diffuse reflectance spectra (DRS) of samples: the appearance of an absorption band in the visible which is assigned to oxygen vacancies and to charge transfer transitions between Ce3+ and Ce4+ ions. The influence of laser fluence on the DRS of ceria has been studied below and above the ablation threshold of ∼1 J/cm2. Electron spin resonance (ESR) spectra of ceria samples obtained from both kinds of treatment confirm the presence of paramagnetic species. The reduced ceria promotes the electroless deposition of Pd from a plating solution containing hydrazine. This finding has been applied to the selective metallization of composite oxides, that is to the selective deposition of Pd on ceria particle size of 2–8 nm supported on insulating carriers, such as alumina or silica.

Aggregate state of tin nanoparticles at room temperature

The aggregate state of tin nanoparticles produced by laser ablation of a solid target in liquid was studied. The study was performed using optical spectroscopy, electron and atomic-force microscopy, and photon correlation spectroscopy. Based on the experimental data obtained, it was shown that tin nanoparticles smaller than 50 nm are liquid under normal conditions. It is in agreement with presented theoretical estimates.

Second Harmonic Generation in Thin Zinc Sulfide Films

Optical second harmonic generation, mechanical stresses, and structure are investigated in thin polycrystalline zinc sulfide films. The resulting data indicate that there is no correlation between the mechanical stresses and the quadratic optical nonlinearity. In view of the X-ray diffraction results, the nature of the nonlinearity is explained using the model of a nanotextured film consisting of crystallites with the sphalerite or wurtzite structure. It is shown that this model allows satisfactory agreement between calculations and experiment.

Hydrogen generation by laser irradiation of colloids of iron and beryllium in water

The hydrogen generation under irradiation of aqueous colloids of iron and beryllium nanoparticles by 10-ns pulses of the first harmonic of a Nd : YAG laser with an energy density of about 80 J cm−2 in the solution is experimentally investigated. The partial hydrogen content in the atmosphere above the colloidal solutions of nanoparticles first increases with increasing irradiation time and then reaches a stationary level (400 − 500 Torr). The hydrogen generation rate, being nonzero in the case of irradiation of pure water, passes through a maximum with an increase in the nanoparticle concentration. The results obtained are discussed in terms of the dissociation of water molecules under a direct electron impact from the optical breakdown plasma formed in the liquid.