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Driven by an ever-increasing demand for nanomaterials with specific functionalities, physical synthesis techniques such as Laser Ablation Synthesis in Solution (LASiS) have gained significant interest over in recent years. Commercial wet chemical synthesis methods, while having significantly higher nanomaterial yields than LASiS, typically have considerable negative environmental impact through the use of harmful reagents and solvents. LASiS therefore represents a route towards the sustainable “green” production of nanomaterials however the significant challenge to its commercialization is that of comparably low nanomaterial yields. Significant effort has been made towards increasing the production rates of LASiS, however many of the reported advances have relied on the use of high power (>20 W) or short pulse (

This paper presents the effect of laser ablation parameters on optical limiting properties of silver nanoparticles. The current applications of lasers such as range finding, guidance, detection, illumination and designation have increased the potential of damaging optical imaging systems or eyes temporary or permanently. The applications of lasers introduce risks for sensors or eyes, when laser power is higher than damage threshold of the detection system. There are some ways to protect these systems such as neutral density (nd) filters, shutters, etc. However, these limiters reduce the total amount of light that gets into the system. Also, response time of these limiters may not be fast enough to prevent damage and cause precipitation in performance due to deprivation of transmission or contrast. Therefore, optical limiting filters are needed that is transparent for low laser intensities and limit or block the high laser intensities. Metal nanoparticles are good candidates for such optical limiting filters for ns pulsed lasers or CW lasers due to their high damage thresholds. In this study we investigated the optical limiting performances of silver nanoparticles produced by laser ablation technique. A high purity silver target immersed in pure water was ablated with a Nd:YAG nanosecond laser at 532 nm. The effect of altering laser power and ablation time on laser ablation efficiency of nanoparticles was investigated experimentally and optimum values were specified. Open aperture Zscan experiment was used to investigate the effect of laser ablation parameters on the optical limiting performances of silver nanoparticles in pure water. It was found that longer ablation time decreases the optical limiting threshold. These results are useful for silver nanoparticles solutions to obtain high performance optical limiters.

Functionalized nanoparticles are important analytical tool for biomedical applications. Pulsed laser ablation of bulk targets in an aqueous media is the one-step method for the fabrication, size manipulation and biofunctionalization of nanoparticles. We performed kHz laser ablation of a silver target by nanosecond pulses in tetramethylammonium hydroxide (TMAH) and sodium dodecyl sulfate (SDS) aqueous solutions to prepare silver nanoparticles. It was shown that the formation efficiency was increased by addition of TMAH and SDS as well as the stability of nanoparticles. The size decrease of the nanoparticles by addition of SDS was more remarkable than in the laser ablation in TMAH aqueous solutions. Emitted nanoparticles interact with TMAH and SDS in the secondary laser irradiation process leads to the nanoparticles stabilization in aqueous solutions.

Ultrashort pulse laser ablation has become an important tool for material processing. Adding liquids to the process can be beneficial for a reduced debris and heat affected zone width. Another application is the production of ligand-free nanoparticles. By measuring the ablation rate of iron for femtosecond pulsed laser ablation in different solvents and solvent-mixtures, the influence of the solvent properties on the ablation process is studied. The ablation efficiency is quantified by measuring the ablation rate in dependency of the fluence from 0.05 J/cm2 up to 5 J/cm2 in water-ethanol and water-acetone mixtures which are varied in 25 % steps. The ablation rate is significantly influenced by the solvent-mixtures.

In this paper we study the photoluminescence properties of colloidal silicon nanoparticles (Si NPs) in distilled water, with the aim of clarifying the role of surface characteristics on the emission properties. We will show that double-pulse ns laser ablation (DPLA) of a silicon target in water with different inter-pulse delay times of i.e. 5 and 10 ns can result in production of colloidal Si NPs with different PL emission intensities at the visible spectral range of 550-650 nm. The results reveal that DPLA process at the different delay times can induce different oxide related surface characteristics on the Si NPs through the direct surface engineering of the nanoparticles. A detailed analysis of the PL emissions using the stochastic quantum confinement model explained that the different emission behaviors of the colloids are associated with the oxide-related surface states which are contributed as radiative centers in the PL process.

Nanosecond pulsed laser ablation of a Ag target in water was applied to prepare noble metal nanoparticles. The fundamental (λ = 1064 nm) wavelength and the second harmonic (λSHG = 532 nm) of a Nd-YAG laser system were used for the fabrication procedure. The effect of the liquid level over the target surface on the characteristics of the nanoparticles was investigated using four different values (5, 8, 16, 29 mm). The liquid volume was constant and the duration of the ablation process was 5 min. A second set of experiments were aimed at clarifying the influence of the duration of ablation. The process was interrupted after 5, 10, 15, 20, 25 min and the mass concentration of Ag in the colloid was measured. This enabled us to establish the dependence of the mass concentration of the Ag on the duration of ablation. The profile of the optical extinction spectra of the colloids was helpful in assessing the state of the solid phase and the morphology of the material. Images obtained by transmission electron microscopy were used to visualize the morphology of the nanostructures produced.

Fabrication of silver nanoparticle colloids using nanosecond pulsed laser ablation in liquid is studied. Laser ablations of silver target in chloroform, toluene and ethanol were performed to prepare different nanosize metal colloids. Both fundamental wavelength (1064 nm) and second harmonic (532 nm) of Nd: YAG laser system were used. The influence of the laser wavelength on the morphology, size distribution, shape and optical properties of the produced nanoparticles was studied by transmission electron microscopy (TEM) and UV-Visible absorption measurements. The selected area electron diffraction (SAED) was employed to identify the phase composition of the formed nanostructures. Nanoparticles in chloroform show a large difference in the mean size at both laser wavelengths used — 3,2 nm at 1064 nm and 43 nm at 532 nm. The laser ablation in toluene at both laser wavelength used results in formation of nanoparticles with relatively small mean size (up to 5 nm). Silver nanoparticles in ethanol produced by 1064 nm show mean size of 20 nm while those prepared by second harmonic — 45 nm. The nanoparticles produced by ablation in chloroform and toluene do not show surface plasmon resonance (SPR) absorption in their optical absorption spectra. In contrast the colloidal nanoparticles produced by laser ablation in ethanol exhibit plasmon behavior. The presented method is an alternative to the widely used chemical methods for the preparation of colloidal solutions with certain characteristics enabling their application in the printed electronics to obtain the conductive tracks, and also for the preparation of nanostructured surfaces for surface-enhanced Raman spectroscopy (SERS).

In this work, various types of pure nanoparticles are synthesized by pulsed laser ablation. A novel method using laser ablation is presented to synthesize and separate different sizes of nanoparticles. Laser ablation is applied as a physical and environmental friendly method to generate a variety of nanoparticles in air-based environments. By tuning laser beam horizontal and placing target materials vertically to the substrate, nanoparticles can be generated and separated automatically depending on their sizes. The size distribution is evaluated by optical microscope and nanoparticles are counted according to their diameters. The diameter of the particles ranges from 30nm to 5000nm. This work provides a versatile means to collect many types of uniform functional nanoparticles for a wide range of applications.

The laser ablation method was implemented for synthesis of ruby nanoparticles. Nanoparticles were obtained by nanosecond ablation of bulk ruby crystal in 10% ethanol water solution. The nanoparticles enable water colloid stability and exhibit narrow photoluminescent line at 694 nm when pumped at blue-green spectral range. The ruby nanoparticles were characterized by SEM and Z-sizer.

Synthesis of nanotructured metal-carbon materials by laser irradiation is an actual branch of laser physics and nanotechnology. Laser sources with different pulse duration allow changing the heating rate with realization of different transition scenarios and synthesis materials with various physical properties. We study the process of the formation of nanostructured metal-clusters and complexes using laser irradiation of colloidal systems which were consisted of carbon micro- nanoparticles and nanoparticles of noble metals. For carbon nanoparticles synthesis we use the method of laser ablation in liquid. For the realization of different regimes of laser surface modification of the target (glassycarbon and shungite) and the formation of micro- nanoparticles in a liquid the YAG:Nd laser with a pulse duration from 0.5 ms up to 20 ms (pulse energy up to 50J) was applied. We have used the CW-laser with moderate intensity in liquid (water or ethanol) for nanoparticle of noble metals synthesis. Thus, colloidal systems were obtained by using CW-laser with λ = 1.06 μm, I ~ 10 5-6 W/cm 2 , and t = 10 min. The average size of resulting particles was approximately about 10 to 100 nm. The nanoparticle obtaining was provided in the colloidal solution with different laser parameters. In this work we have investigated the mechanism of the metal-carbon cluster formation during the process of irradiation of colloidal system which were consisted of separate carbon, silver and gold nanoparticles. This system was irradiated by nanosecond laser (100 ns) with average power up to 50W.

Laser ablation of bulk targets in a fluid — a promising new method for the synthesis of "pure" nanocolloids. Nanocrystalline materials produced by laser ablation are widely used in biology, medicine, and catalysis. High local temperature during ablation and large surface area of the particles promote chemical reactions and the formation of a complex composition of nanoparticles. In this paper the characteristics of the process of ablation and the obtaining of nanoparticles in a liquid by laser ablation of active materials (Zn, Ce, Ti, Si) were studied. Ways of increasing the productivity of laser ablation were discussed. Characterization of nanocolloids and nanocrystalline powders were performed. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

An optical method to obtain a colloidal solution starting from a mixture of silver nanopowder and ethanol is presented. The particles of the silver nanopowder do not exhibit a specific shape, however in the colloidal solution are spherical. This method is carry out when the mixture is irradiated with a pulsed laser at 532 nm via optical fiber. Due to a stronger absorption of the laser light by silver nanoparticles arise both photofragmentation and photomelting processes. The photomelting process starts when the laser energy is 5 mJ/cm 2 , inducing an enlargement of nanoparticles whereas the photofragmentation occurs when the laser energy is 25 mJ/cm 2 causing a reduction on their sizes (the higher energy is, the smaller nanoparticles are). Results show that it is possible to obtain a colloidal silver solution and to control the particle size by adjusting the laser energy. Experiments were performed at 5 and 25 mJ/cm 2 , and the results are presented.

Approximately spherical nanoparticles of the II–VI semiconductor materials Cd 1-x Zn x S have been produced successfully by laser ablation of the bulk material in several liquids. The non-stabilized suspensions of particles are characterized by absorption spectroscopy and transmission electron microscopy (TEM). The procedure is not strongly size-selective, radii of 7±3 nm were found for Cd 1-x Zn x S by transmission electron microscopy. Acetonitrile stabilizes the particles for several days up to weeks. Prolonged irradiation leads effectively to a reduction in particles size, in which particle agglomeration may play an important role. Ablation in degassed liquids does not have a significant effect on the absorption of the suspended particles.

The synthesis of metal nanoparticles by femtosecond laser vaporization of nm-thickness metal films is explored with the goal of comparing the salient features of femtosecond-based through thin film laser ablation (TTFA) to that of ns TTFA, and testing the feasibility of direct synthesis of clean nanoparticle alloys to explore the synthesis of carbon nanotubes by chemical vapor deposition. It is demonstrated that evaporated metal films are cleanly removed from quartz substrates using the technique, producing a highly forward-directed plume of nanoparticles (angle of divergence of ~2.5°) which were cleanly deposited onto different supports for analysis. TEM showed the nanoparticles were spherical with diameters that ranged from a few nm to hundreds of nm in a bimodal fashion. Unlike ns-TTFA, it was found that raising the pressure had no effect on the intensity of the smaller mode within the distribution, suggesting that nanoparticle formation by gas phase condensation was not at play under the present conditions. Close examination of size distributions from a 20 and 10nm Pt film revealed an 80nm downshift in the position of the large mode within the distribution, suggesting film thickness may provide a route to controlling the modal distribution of nanoparticles produced by this method. Lastly, particles sourced by a Fe/Mo bilayer film were found to be effective in growing single wall carbon nanotubes by atmospheric chemical vapor deposition, indicating sufficiently small and catalytically active particles were produced.

The stable colloid with silver nanoparticles has been produced by irradiation of metal target in deionized water by pulse 1064 nm laser. The dependences of the nanoparticle size and colloid stability on fluence, ablation time, surface conditions of the target, and thickness of the water layer have been studied. The sizes and shape of nanoparticles have been measured by dynamic light scattering and by scanning electron microscopy. It has been shown that decrease of the water layer thickness above the target surface leads to increase of the colloid stability. The proper number of treatment cycles allowed to prepare the target surface for production of the nanoparticles with average size about 34 nm obtained by statistical analysis of the scanning electron microscope images. Several methods have been used to increase the colloid stability: (1) increase of the laser fluence, (2) decrease of the water layer thickness above the target surface, (3) the treatment of the target surface by laser beam scanning. The subsequent increase of the colloid concentration by partial drying slightly enhanced the nanoparticle size. The optimized synthesis conditions and drying parameters allowed to produce the pure colloid with concentration about 0.5 g/l and stability over a month of almost spherical silver nanoparticles with typical size 45±5 nm.

We present laser trapping behaviors of 200 nm-polystyrene particles in D2O solution and at its surface using a focused continuous-wave laser beam of 1064 nm. Upon focusing the laser beam into the solution surface, the particles are gathered at the focal spot, and their assembly is expanded to the outside and becomes much larger than the focal volume. The resultant assembly is observed colored under halogen lamp illumination, which is due to a periodic structure like a colloidal crystal. This trapping behavior is much different compared to the laser irradiation into the inside of the solution where a particle-like assembly with a size similar to that of the focal volume is prepared. These findings provide us new insights to consider how radiation pressure of a focused laser beam acts on nanoparticles at a solution surface.

A method of non-vacuum synthesis of CuInSe 2 (CIS) thin films is presented. The method is based on electrophoretic deposition (EPD) of Cu-In composite nanoparticles in liquid solvents. Colloidal suspensions of Cu-In composite nanoparticles are prepared with pulsed laser ablation without additional stabilizing agents. The charge acquisition of the nanoparticles in solvents, deposition of particles on electrode surfaces will be explained. After selenization in selenium vapor in atmospheric pressure, polycrystalline CIS films and solar cell devices are produced. We will demonstrate EPD as a new choice of low-cost synthesis of thin film solar absorbers.

Laser induced breakdown at copper-water interface was used to synthesize Copper@CopperOxide nanocomposites in the colloidal form. The antibacterial activities of these nanoparticles were studied using UV-Vis and Raman spectroscopy.

We have prepared nanoparticles of five organic dye molecules by laser ablation of their microcrystals in poor solvents using the third harmonics of nanosecond Nd3+:YAG laser as an excitation light source. Their colloidal solutions were stable for longer than 1 week without any surfactants. The mean size was almost common to all the dyes (about 50 nm) and its distribution was narrow, which was confirmed by SEM observation. By applying electrophoretic deposition, the homogeneous thin film of quinacridone nanoparticles was fabricated on an indium-tin-oxide electrode. It was demonstrated that the films with different grain size and crystalline phase can be fabricated arbitrarily by using different nanoparticles. Laser ablation is also useful for crystallization of organic molecules, which was demonstrated for a representative organic nonlinear optical material.

Zinc oxide nanoparticles were synthesized by pulsed laser ablation technique in water with further deposition on the single-crystalline silicon substrate. The composition, morphology, absorbance and luminescent properties of the formed structures were studied. The study revealed that films of high structural and optical quality can be prepared by the developed method.

Near infrared ultrafast pulsed laser is used to ablate pure metal and metal alloy targets in a vacuum chamber. We find that by optimizing the ablation conditions, as a direct result of ultrafast laser ablation, crystalline nanoparticles can be abundantly produced without intermediate nucleation and growth processes. Combining with different background gases, versatile structural forms can also be obtained for the nanocrystals. Using metal nickel as a sample material, we have produced Ni/NiO core/shell nanospheres and NiO nanocubes. We also study the production of alloy nanoparticles, which has been challenging in fabrication. We demonstrate production of nanoparticles containing up to three metal elements using ultrafast laser ablation. The laser ablation process is investigated using an ion probe in real-time. Nanoparticle samples are examined using atomic force microscopy and high resolution transmission electron microscopy for morphological, structural, and chemical analysis. This study provides a simple physical method for generating nanoparticles with a narrow particle size distribution, a high particle yield, versatile chemical compositions and structural forms.

We report the successful fabrication of layers of functionalized nanoparticles using a novel infrared, laser-based deposition technique. A frozen suspension of nanoparticles was ablated with a laser tuned to a vibrational mode of the solvent, resulting in the disruption of the matrix and ejection of the nanoparticles. The solvent was pumped away and the nanoparticles collected by a receiving substrate in a conformal process. Photoluminescence measurements of nanoparticles containing two common dyes showed no significant change to the emission properties of either dye, suggesting that no damage occurred during the laser ablation process. The process is generally applicable to particles of various sizes, shapes, and chemistries provided that an appropriate solvent is chosen. Deposition through shadow masks turned out to be straightforward using this technique, suggesting its potential utility in preparing designer sensor structures using functionalized nanoparticles.

In the present work, we report the synthesis of ZnO nanoparticles by adopting femtosecond laser ablation of ZnO targets in pure ethanol, and in a solution of Tetramethylrhodamine B isothiocyante. An ultrafast intensified CCD device was used to study the plasma formation in the liquid environment. Dye molecules were grafted onto the ZnO nanoparticles by adding the dye solution to the ablated ZnO-ethanol solution. From the optical studies of the ZnO nanoparticles by photoluminescence spectroscopy, we observed energy transfer from the ZnO to the attached dye molecules. Strongly facetted nanohybrid particles were observed with an average size of 15 nm, by HRTEM measurements. Finally, we show that the in situ ablation in the dye solution allows to increase the efficiency of the energy transfer from the ZnO nanoparticle to the grafted dye molecules.

We have formed nanoparticles of Si, C, Ti, and Fe by pulsed laser ablation and have explored the feasibility of passivating these particles during the synthesis process in order to minimize particle coarsening. Passivation was done by forming the nanoparticles in an Ar/N 2 background, which allowed the formation of a thin nitride layer on the nanoparticle surface. In this paper we describe the synthesis procedure for synthesizing and passivating the nanoparticles. The characterization results indicate the nanoparticle synthesis in N 2 does not significantly affect agglomeration.

The review of results on nanoparticles formation is presented under laser ablation of Ag, Au, and Cu-containing solid targets in liquid environments (H2O, C2H5OH, C2H4Cl2, etc.). X-ray diffractometry (XRD), UV-Vis optical transmission spectrometry, and High Resolution Transmission Electron Microscopy (HRTEM) characterize the nanoparticles. The morphology of nanoparticles is studied as the function of both laser fluence and nature of the liquid. The possibility to control the shape of nanoparticles by ablation of an Au target by an interference pattern of two laser beams is demonstrated. Formation of alloyed Au-Ag and Ag-Cu nanoparticles is reported under laser exposure of a mixture of individual nanoparticles. Self-influence of the beam of a femtosecond laser is discussed under ablation of the Ag target in liquids under Ti:sapphire laser. The factors are discussed that determine the distribution function of particles size under laser ablation. The influence of laser parameters as well as the nature on the liquid on the properties of nanoparticles is elucidated.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report the synthesis of silver nanoparticles by laser ablation of the bulk material in water and five other organic solvents employing a frequency doubled Nd:YAG laser at 532 nm. The colloidal suspensions were characterized by means of UV/VIS absorption spectroscopy and transmission electron microscopy. The reproducibility of the particles' size distribution and yield, which strongly depends on the solvent and the ablation condition, is critically reviewed. The agglomeration behaviour of silver particles was investigated as a function of temperature. The unusual role of water in the ablation process and upon agglomeration will be discussed.

Silver nanoparticles have been fabricated by laser ablation of a silver metal foil in solution. The presence of sodiumbis(2-ethylhexyl) sulfosuccinate increases the yield of the nanoparticles and enhances their stability. The optical limitingperformance of the silver nanoparticles embedded in a PMMA film is compared to that in an aqueous solution.Keywords: laser ablation, nanoparticles, optical limiting 1. INTRODUCTION Nanoparticles exhibiting unique optical properties continue to generate a lot of interest because of their potential application in the areas of optical limiting [1-3], fast optical switching [4] and data storage [5J. Silver nanoparticles havebeen reported to offer excellent optical limiting properties [6], allowing high transmission oflaser at low input power butlow transmission at high input power. These optical limiters can be used to protect sensitive detectors and the human eye.Various methods have been used to fabricate silver nanoparticles such as rapid expansion of a supercritical fluid solution,chemical [7] and laser induced [8, 9] reduction of silver salts, and laser ablation ofmetallic silver [10-13]. Laser ablationis a simple and convenient method to fabricate metallic nanoparticles free of residual chemical reagents with good size

This paper describes a new growth method of ZnO nano-rods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nano-structured-ZnO thin films. Under an optimized deposition conditions, ZnO nano-rods with a diameter of about 300 nm and 6 μm in length have been synthesized without any catalyst by nanoparticle assisted laser ablation deposition. The laser action was observed in the nano-rods under an optical excitation at 355 nm, indicating a high quality of the crystal.

This paper describes a new growth method of ZnO nano-rods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nano-structured-ZnO thin films. Under an optimized deposition conditions, ZnO nano-roods with a diameter of about 300 nm and 6 μm in length have been synthesized without any catalyst by nanoparticle assisted laser ablation deposition. The laser action was observed in the nano-rods under an optical excitation at 355 nm, indicating a high quality of the crystal.

This paper describes a new growth method of ZnO nano-rods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nano-structured-ZnO thin films. Under an optimized deposition conditions, ZnO nano-rods with a diameter of about 300 nm and 6 μm in length have been synthesized without any catalyst by nanoparticle assisted laser ablation deposition. The laser action was observed in the nano-rods under an optical excitation at 355 nm, indicating a high quality of the crystal.

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.

The work is focused on the refinement of the laser ablation method for a nanosized silver colloid preparation with regards to the nanoparticle size distribution, as well as to the reproducibility and stability of the ablated hydrosol. In the adopted procedure, additionally to the variation of the laser pulse energy, beam focusation and duration of laser ablation, we developed a technique based on further fragmentation of the ablated colloid solution by subsequent treatment with the 1064 and 532 nm nanosecond laser pulses. The method yields redistribution of nanoparticle diameters to a smaller mean size, as it was observed by transmission electron microscopy, quasielastic light scattering studies and surface plasmon (SP) optical extinction. It was shown that a similar fragmentation procedure is also effective in reduction of nanoparticle size and polydispersity of silver hydrosol prepared by routine chemical procedures and leads to a narrower SP extinction profile.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Possibilities of the control of the size and size distribution of the colloidal gold particles produced by the 110-fs laser ablation from a gold plate in aqueous environment are studied. Compared to pure deionized water, significant reduction of the mean size and size dispersion of the produced particles was observed when the ablation was performed in aqueous solutions of cyclodextrins (CDs), while the efficiency of the size reduction depended on the concentration and type of the CD (α-CD, β-CD or γ-CD). In particular, ablation at 10 mM of β-CD led to a production of 2-2.4 nm particles with narrow size distribution of less than 1-1.5 FWHM, which were very stable under aerobic conditions without any protective agent present. In the UV-vis spectrum, the gold nanoparticles exhibited an absorption band at 520 nm due to the generation of plasmon resonances. The fabricated particles are of importance for biosensing applications.

This paper describes a new growth method of ZnO nanorods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nanostructured-ZnO thin films. Under an optimized deposition conditions, ZnO nanoroods with a diameter of about 300 nm and 6 μm in length have been synthesized without any catalyst by nanoparticle assisted laser ablation deposition. The laser action was observed in the nanorods under an optical excitation at 355 nm, indicating a high quality of the crystal.

Nanometer-sized particles of silicon and titanium dioxide were generated by Nd:YAG laser ablation of solid substrates in a low pressure atmosphere. A low-pressure differential mobility analyzer (LP-DMA) was used to control the size of generated particles. The LP-DMA and a transmission electron microscopy (TEM) were used to measure the change in size distribution and morphology of nanoparticles with laser power and pressure. Finally, we succeeded to synthesize the almost spherical nanoparticles of 2-50 nm in diameter.

We have utilized pulsed-laser ablation in ambient inert gas to synthesize silicon (Si) nanoparticles and to perform surface modification and impurity doping. The dynamical growing process of Si nanoparticles has been investigated by measuring time-resolved light emission induced by the second pulsed-laser irradiation with a delayed time. It was found from the time-resolved measurements that the onset of the formation of Si nanoparticles appears at around 1 ms, on inert gas pressure and laser fluence. We demonstrate that light emission can be controlled by adding hydrogen or oxygen gas to inert gas. It is also demonstrated that the thermal quenching which has been serious problem in Er-doped semiconductors can be removed in 1.54 micrometers photoluminescence of Er-doped Si nanocrystallites. These results suggest that laser ablation is useful not only for synthesis of nanostructured materials such as nanoparticles and nanowires/nanotubes, but for their surface modification and impurity doping that are important techniques for realizing functional nanostructures.

The recent rapid advances in the field of laser ablation have led to an important new tool for both material synthesis and material processing. Experiments in our laboratory have served as examples of both types of contributions from this new technique. The kinetic differences of growth between standard solid state synthesis and in situ growth by laser ablation have allowed the substitution of Ce, Tb and Th for Y in Y1Ba2Cu3O7 for the first time. The effects of substitution for Y on the material Tc is discussed within the framework of the existing models for the Pr system. We suggest that localization of the holes by trapping may provide a suitable mechanism to account for the observed properties of the Pr and Ce substituted compounds. As an example of new material processing, polytetrafluoroethylene (PTFE) films were deposited by the laser ablation of a bulk PTFE target using the 4th harmonic, at 266 nm, of a Nd-YAG laser. The films are found to be stoichiometric with bulk- like optical properties. We propose a model which suggests that UV absorption onsets the pyrolitic decomposition of PTFE leading to monomer as the main ablation product. The monomer, ejected from the target at high velocity, subsequently re-polymerizes on the substrate.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The dynamics of pulsed excimer laser ablation of thin films of organic material from a metal surface was investigated using optically excited surface plasmons. The metal substrate is formed by a 500 A thick silver film adjacent to the base of a glass prism, which serves for optical excitation and detection of the surface plasmons propagating at the silver-vacuum interface. The organic films were prepared by cooling the sample to 77 K and depositing the materials (isopropanol, tetrafluoromethane, acetone) from the vapor phase; ablation of the films was accomplished by KrF excimer laser ( = 248nm). Detection of the surface plasmon resonance allows to monitor the ablation process on a nanosecond time scale and with a resolution far better than a monolayer. At the same time, the surface plasmons provide an in- situ probe for time-resolved measurements of the substrate temperature. This allows to determinate the temperature at which the ablation sets in. For tetrafluoromethane, the ablation temperature was found to be independent of the laser fluence, suggesting a thermal desorption process. On the other hand, for isopropanol and acetone, a strong dependence of the ablation temperature on the fluence was observed. From the large delay between the leading edge of the laser pulse and the onset of ablation, we conclude that ablative photodecomposition is not present in our experiment. There is, however, evidence for laser- induced chemical transformations in the organic films. Solid films of transformed material, which were stable at room-temperature and under atmospheric conditions, were formed during the isopropanol experiments. We suggest these transformation process to be connected to the observed fluence dependence of the ablation temperature.