G.A. Shafeev

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).

Laser-induced forward transfer of ultra-fine diamond particles for selective deposition of diamond films

Abstract A laser-induced forward transfer (LIFT) technique is used for area-selective prenucleation of Si substrates with ultra-fine diamond powder for subsequent diamond film deposition via a conventional CVD process. The influence of the laser parameters (wavelength, energy density, etc.) on the features of the ablation-deposition process is experimentally studied with the aim of improving the spatial selectivity of diamond patterning.

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.

Fast etching and metallization of SiC ceramics with copper-vapor-laser radiation

The etching of polycrystalline SiC is studied with the help of radiation of a copper-vapor laser either in air or under the layer of a liquid (H2O, DMSO). The etching rate in air is as high as 0.24 μm/pulse, in DMSO 0.07 gm/pulse at an energy density of 16 J/cm2. The etched surface is characterized with Scanning Electron Microscopy (SEM) and X-ray diffractometry. Etching of SiC ceramics in air revealed the partial amorphization of SiC and the formation of microcrystals of elementary Si with an average size of 300 Å. The etched surface of SiC ceramics takes on the ability to reduce Cu from a corresponding electroless plating solution. The adherence of the deposit is as high as 30 N/mm2 and is a function of the scanning velocity of the laser beam.

Laser induced surface modifications on ZrO2 ceramics

Zirconia is widely used as a solid electrolyte due to its high ionic conductivity and as a biocompatible material, and tailoring its properties is of great importance. In the present paper, experimental results are presented on modifications of surface properties of ZrO2 ceramics doped with 3% of Y2O3 exposed to radiation of either an excimer KrF (λ=248 nm) or ArF laser (λ=248 nm), pulse duration of 15–20 ns in air. The modification of porosity of irradiated areas and its diffuse reflectance spectra (DRS) are studied as a function of laser beam parameters. The morphology of laser treated zirconia ceramics along with its microhardness and roughness are shown to depend significantly on the laser fluence. The catalytic activity of laser treated zirconia ceramics towards the electroless deposition of Cu and Ni is analyzed with respect to DRS modifications.

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.

Light-enhanced electroless Cu deposition on laser-treated polyimide surface

Abstract Laser ablation of polyimide (PI) surface results in the formation of a glassy carbon layer on its surface, especially at near-threshold fluence. Glassy carbon can mediate the electroless metal deposition resulting thus in a local metallization of the surface, as it has been shown recently for the ablated surfaces of PI (cw argon ion laser) and diamond. In the present work, this carbon layer is produced by irradiation of PI in air by a cw Ar+ ion laser (wavelength of 514 nm). The ability of this layer to promote the electroless Cu deposition from the corresponding plating solution is studied as the function of laser processing parameters and conditions of deposition. The effect of exposure of the glassy carbon layer to visible radiation on the rate of deposition is studied. The possible mechanisms of the electroless deposition on the glassy carbon are discussed.