Silicon nanoparticles generated by femtosecond laser ablation in a liquid environment

Silicon nanoparticles were generated by femtosecond laser [387 nm, 180 fs, 1 kHz, pulse energy = 3.5 μJ (fluence = 0.8 J/cm²)] ablation of silicon in deionized water. Nanoparticles with diameters from ~5 up to ~200 nm were observed to be formed in the colloidal solution. Their size distribution follows log-normal function with statistical median diameter of ≈20 nm. Longer ablation time leads to a narrowing of the nanoparticle size distribution due to the interaction of the ablating laser beam with the produced nanoparticles. Raman spectroscopy measurements confirm that the nanoparticles exhibit phonon quantum confinement effects and indicate that under the present conditions of ablation they are partially amorphous.     

Fabrication of ZnO nanoparticles by laser ablation of sintered ZnO in aqueous solution

Fabrication of ZnO nanoparticles by laser ablation in liquid medium is reported. The possibility of using a sintered ZnO target for the ablation as well as a Zn plate is demonstrated. The appropriate aqueous solution of sodium dodecyl sulfate is found to be 1 mM for ZnO growing. The shape of ZnO nanoparticles is sphere and its diameter is 30∼60 nm. Fourier transform infrared spectra, Raman scattering spectra, and photoluminescence spectra reveal the optical properties of ZnO nanoparticles. Nanoparticles obtained by using ZnO targets show a smaller defect density compared with those by using Zn targets.     

Formation of silicon nanoparticles and web-like aggregates by femtosecond laser ablation in a background gas

We show that the mechanism of nanoparticle formation during femtosecond laser ablation of silicon is affected by the presence of a background gas. Femtosecond laser ablation of silicon in a H₂ or H₂S background gas yields a mixture of crystalline and amorphous nanoparticles. The crystalline nanoparticles form via a thermal mechanism of nucleation and growth. The amorphous material has smaller features and forms at a higher cooling rate than the crystalline nanoparticles. The background gas also results in the suspension of plume material in the gas for extended periods, resulting in the formation (on a thin film carbon substrate) of unusual aggregated structures including nanoscale webs that span tears in the film. The presence of a background gas provides additional control of the structure and composition of the nanoparticles during short pulse laser ablation. PACS 81.16.-c     

Red luminescence of Eu3+ doped ZnO nanoparticles fabricated by laser ablation in aqueous solution

Fabrication of Eu³⁺-doped ZnO nanoparticles by laser ablation in liquid medium is reported. Sintered disks made of mixed powders of ZnO and Eu₂O₃ are used for targets, and surfactant of sodium dodecyl sulfate or LiOH is included in solution. Round-shaped nanoparticles with the diameter of 5??30?nm are synthesized. When the ZnO host is photoexcited, broad green photoluminescence (PL) of oxygen vacancies in the ZnO host as well as red PL of Eu³⁺ is observed at room temperature. The red PL peak of Eu³⁺ included in the ZnO host lattice is different from that of the source material of Eu₂O₃. Energy transfer from the ZnO host to Eu³⁺ is demonstrated in site-selectively excited PL spectra and its excitation spectra. This result shows that the liquid-phase laser ablation is useful for doping active centers into nanoparticles.     

Ni nanoparticles fabricated by laser ablation in water

Nickel nanoparticles were fabricated by ablating a bulk Ni target with pulsed 337-nm laser radiation in distilled water. Transmission electron microscope images of the removed material show spherical particles with two size scales: tens of nm and hundreds of nm. Phase explosion and Rayleigh–Plateau hydrodynamic instability are suggested as being responsible for this distribution. An X-ray diffraction pattern of the ablated material demonstrates the presence of both nickel and nickel oxide.     

ZnO nanoparticles produced by reactive laser ablation

The paper presents the results of theoretical and experimental researches of the analysis of nanopowder ZnO and ZnO-based structures formation mechanisms by means of pulse laser reactive technology (λ = 1.06 μm, τ = 10⁻⁷ to 10⁻⁵ s). The developed 2D model combines non-stationary heat transfer and fluid motion along with the calculated profile of surface deformation. The characteristics of the dispersive and chemical compositions and structural parameters of the synthesized nanopowder together with the influence of the energy of laser impulse evaporation, its duration and gas pressure in the reaction chamber have been studied using X-ray diffractrometry (XRD), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM). Particle size distribution analysis of ZnO has shown that the majority of them range from 5 to 60 nm in size. The photoluminescence emission spectra of the initial ZnO nanopowder at room temperature have been identified.     

Formation, structure and nonlinear optical properties of carbon nanoparticles synthesized by pulsed laser ablation

Carbon nanoparticles were prepared by pulsed laser ablation in argon gas for studying their formation, properties and applications. The nanoparticles were produced at different background pressures and different substrate temperatures, respectively. Micro-Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the samples. Nonlinear optical limiting properties of the carbon nanoparticles were characterized using nanosecond laser pulses. Uniform carbon nanoparticles can be synthesized in a background gas for nonlinear optical applications. PACS 61.46.+w; 81.07.-b; 78.20.-e     

Noble metal nanoparticles produced by nanosecond laser ablation

Silver and gold thin films were deposited by pulsed laser ablation in a controlled Ar atmosphere at pressures between 10 and 100 Pa. Different morphologies, ranging from isolated nanoparticle arrays up to nanostructured thin films were observed. Fast imaging of the plasma allowed deducing the expansion dynamics of the ablated plume. Plasma velocity and volume were used together with the measured average ablated mass per pulse as input parameters in a model to estimate the average size of nanoparticles grown in the plume. The nanoparticle size is expected to decrease from 4 nm down to 1 nm with decreasing Ar pressure between 100 and 10 Pa: this was confirmed by transmission electron micrographs which indicate a reduced dispersion of particle size over narrow size ranges. The production of substrates for surface enhanced Raman scattering whose performances critically depend on nanoparticle size, shape, and structure is discussed.     

Size-selected copper oxide nanoparticles synthesized by laser ablation

Size-tuned copper oxide nanoparticles with sizes of 9, 12, and 15 nm were fabricated by laser ablation and on-line size selection using a differential mobility analyzer at a gas pressure of 666 Pa. The dependence of the particle properties on the in situ annealing temperatures and selection sizes was investigated. The crystalline phases of the nanoparticles fabricated at temperatures below 973 K were assigned to monoclinic cupric oxide (CuO) which converted into cubic cuprous oxide (Cu₂O) when the annealing temperature was above 1,173 K. This indicates that the crystalline phases can be easily controlled by changing the annealing temperature. TEM images confirmed that well-crystallized and well-dispersed CuO and Cu₂O nanoparticles with narrow size distributions were obtained using this method. This fabrication process is useful and promising for the future investigation of the intrinsic size-dependent properties of CuO and Cu₂O.     

Formation of microvias in epoxy-glass composites by laser ablation

Single CO₂ laser pulses, of 10.6μm wavelength, are used to form blind microvias (holes in electronic boards for through-plating conducting paths) in copper-clad epoxy-glass laminates. The microvia dimensions depend on pulse energy and duration, the thicknesses of the epoxy-glass laminate and copper cladding, and the distribution of glass within the epoxy-glass laminate. The useful range of laser parameters, especially pulse energy, is primarily determined by the ability to metallize subsequently the blind microvias. Several conclusions can be drawn from the data. The pulse enegy should be within ±20% of the optimum value in order to form vias with a cylindrical geometry. For 300 μm thick laminates, the thickness of the copper on the bottom should be 18 μm or more. A larger range of pulse energies could be used if the glass fibre density was more uniform and if subsequent copper metallization of the blind vias could be improved.     

Preparation of silver nanoparticles by laser ablation in polyvinylpyrrolidone solutions

We performed laser ablation of a silver plate in polyvinylpyrrolidone (PVP) aqueous solutions to prepare silver nanoparticles. Secondary laser irradiation onto the prepared colloidal solutions was also carried out. It was revealed that the formation efficiency was increased by addition of PVP as well as the stability of nanoparticles. The result of shadowgraph measurements suggested that the increased ablation efficiency by PVP is attributable to increased secondary etching efficiency by the solvent-confined plasma toward the silver plate. On the other hand, the size decrease of the nanoparticles by addition of PVP was more remarkable during the secondary irradiation process than in the laser ablation (nanoparticle preparation) process. This result indicates that emitted materials interact less sufficiently with PVP molecules in the laser ablation process than in the secondary laser irradiation process.     

Synthesis of silver nanoparticles by laser ablation in pure water

We have successfully produced silver nanoparticles by irradiating an Ag target with a 532-nm laser beam in pure water. By working with high laser power and small spot sizes, we were able to synthesize very small spherical particles with a typical size of 2–5 nm. The influence of the beam spot size, the laser power, and the ablation time were studied, and the possible mechanisms of particle formation are discussed. PACS 79.20.Ds; 81.07.-b     

Characterization of Copper nanoparticles obtained by laser ablation in liquids

We prepared copper nanoparticles by ns laser ablation in pure water and in aqueous solutions of 1,10-phenanthroline at 1064 nm and 532 nm wavelengths. Although not fully impairing progressive oxidation, ligand molecules prevent the colloids to collapse. UV–vis absorption spectroscopy showed that particle production is more efficient at 1064 nm, while transmission electron microscopy gave evidence that 532-nm pulses cause photofragmentation of the structures, resulting in reduced particle size. Furthermore, from Raman and fluorescence tests we found that colloids obtained at 1064 nm show better Surface Enhanced Raman activity, while colloids obtained at 532 nm exhibit a more intense fluorescence emission.     

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. PACS 42.62.-b; 61.46.+w; 78.66.-w     

Iron carbide nanoparticles produced by laser ablation in organic solvent

Laser ablation of iron in an organic solvent (pentane, hexane, or decane) was performed using an air-tight cell to produce iron carbide nanoparticles. M?ssbauer spectra of the nanoparticles were obtained at room temperature. They revealed that the nanoparticles consisted of two paramagnetic components and magnetic components. The two paramagnetic components were a high-spin Fe(II) species and an amorphous iron carbide containing a large amount of carbon. Whereas the magnetic components measured at room temperature exhibited superparamagnetism, those measured at low temperature were fitted by a combination of four sextets, which were assigned to Fe₇ C ₃. The Fe₇ C ₃ yield was higher in higher molecular weight solvents. Transmission electron microscopy (TEM) images of the samples showed that the nanoparticles were spherical with diameters in the range 10–100?nm.     

The effect of liquid environment on size and aggregation of gold nanoparticles prepared by pulsed laser ablation

The effects of liquid environment on nucleation, growth and aggregation of gold nanoparticles were studied. Gold nanoparticles were prepared by pulsed laser ablation in deionised water with various concentrations of ethanol and also in pure ethanol. UV/visible extinction and TEM observations were employed for characterization of optical properties and particle sizes respectively. Preparation in water results in smaller size, shorter wavelength of maximum extinction and stable solution with an average size of 6 nm. Nanoparticles in solution with low concentration ethanol up to 20 vol% are very similar to those prepared in water. In the mixture of deionised water and 40 up to 80 vol% ethanol, wavelength of maximum extinction shows a red shift and mean size of nanoparticles was increased to 8.2 nm. Meanwhile, in this case, nanoparticles cross-linked each other and formed string type structures. In ethanol, TEM experiments show a mean size of 18 nm and strong aggregation of nanoparticles. The data were discussed qualitatively by considering effects of polarity of surrounding molecules on growth mechanism and aggregation. This study provided a technique to control size, cross-linking and aggregation of gold nanoparticles via changing the nature of liquid carrier medium.     

Preparation of polyynes by laser ablation of graphite in aqueous media

Polyynes were prepared by liquid-phase laser ablation of a graphite target at 1064 nm and identified by analyzing UV absorption spectra in deionized water and various aqueous solutions. We observed that major UV absorption peaks coincide with the electronic transitions corresponding to linear hydrogen-capped polyynes (C_nH₂: n = 6, 8, 10). The peak intensities increased when polyynes were produced by irradiating the target immersed in acidic media, while those were relatively weak in basic media. This leads us to conclude that OH⁻ or H⁺ ions play a certain role in the formation of polyynes.     

Silicon nanoparticles formation by means of laser ablation in liquid media

The possibility to produce silicon nanoparticles by the method of the pulse laser ablation of monocrystaline silicon targets in the water, glycerol and liquid nitrogen have been shown. Studies by the atomic-force microscopy and Raman scattering methods revealed the nanoparticles have a crystalline structure and their mean size depends on the buffer liquid composition.     

Photoluminescence of ZnO nanoparticles generated by laser ablation in deionized water

Zinc oxide (ZnO) nanoparticles were synthesized using pulsed laser ablation of a Zn metal plate in deionized water without using surfactant. The beam of a Q-switched Nd:YAG laser of 1064-nm and 532-nm wavelengths at 6-ns pulse width and different fluences is employed to irradiate the solid target in water. Transmission electron microscopy images revealed that the size of the ZnO nanoparticles formed by the 532-nm wavelength laser beam is smaller than that of the nanoparticles generated by the 1064-nm wavelength laser beam. The room-temperature photoluminescence spectra of the ZnO nanoparticles show intense violet emission along with emission in blue and green bands. The excellent ultraviolet emission indicates that the ZnO nanostructures have a low defect concentration.