We report the functionalization of Si/SiO2 Quantum Dots (QDs) synthesised by laser ablation. Our interest has been to
increase the affinity of the QDs surface for organic substances, in order to obtain QD-immunoglobulin conjugates,
particularly for biolabeling. We have studied the UV-induced graft polymerization of the freestanding nanoparticles.
High resolution transmission electron microscopy and laser granulometry, were used to obtain information on particle
and cluster size distribution, degree of agglomeration, etc. The polymer-dot complexes appeared as relatively well-defined
clusters, QDs being surrounded by a polymer layer with thickness 3-10 nm. The size of the primary clusters was
in the range 60-500 nm. The polymerization and filtration process (0.1 μm pores) involved a diminution of the clusters
size in the range of 18-65 nm, and moreover, by a subsequent dialyses process the cluster size decreased to 5-15 nm.
A quantum dot - immunoglobulin conjugate specific for pig IgG, was obtained by carbodiimide chemistry. We used a
Western blot technique for detecting specific antibodies against Actinobacillus pleuropneumoniae (A. pp), which cause
porcine pleuropneumonia. The antigen used in this technique was Apx haemolysin which is an important virulence factor of
A. pp and it induces protective immunity in vaccined pigs. The detection on Western blot membrane was possible at 1/50
dilution of quantum dot conjugate at a dilution of pig serum till 1/6400. The results for pig serum demonstrated a higher
sensitivity of QD-based Western blot technique for the presence of antibodies specific for Apx haemolysin in comparison
with similar classical techniques (with coloured substrate for enzyme present in secondary antibody conjugate).
Despite of the fact that in the last years a significant effort have been devoted to pulsed laser ablation (PLA), the problem of micro and nanoparticles have not been unambiguous presented (to our knowledge). In this work, we studied the size, size distribution and structure of the particles produced by laser ablation and luminescence as well. Scanning and transmission electron microscopy, X-ray diffraction and optical spectroscopy have been used. The investigations were made on Si/SiO2 nanopowders as produced, without any post-treatment (chemical, thermal, etc.). The experimental parameters were: silicon target, laser wavelength 355/532 nm, pulse duration 5 ns, repetition rate 10 Hz, fluence 4-8 J/cm2, argon/helium, 250-550 mbar, flow rate 1 l/min. Our investigations have shown that the particles are distributed in two main classes: one, with the size 0.1-1 μm, and the other with the diameter less than 14 nm. Our evaluation for optimal experimental conditions shown that around 78% (vol.) of particles are < 10 nm and almost 50% have diameters in the range 2-5 nm. The photo and cathodoluminescence were in the range 400-1000 nm, with main peak at 690-725 nm.
Between other sensing and identification technologies that of Surface Acoustic Waves, (SAW), is a unique sensing
system. The principal advantage to most SAW systems is that they can use two or three SAW sensors and compare the
measurements between them, providing a good accuracy. We have carried out the design of both piezoelectric substrate
and interdigital transducers, (IDTs), and has tested them in a delay line mode operation. The measurement of changes in
the surface waves characteristics were materialized by applying of a radio frequency electric field to the piezoelectric
crystal by means of IDTs. The finger width of the IDTs was measured by high accuracy optical coherent method. The
results are presented in the work. The potential development of microsensors as an array of four or five miniature
sensors, sensitive to Werent chemicals may be used as mobile chemical detecting units carried by remote control
vehicles to the site chemical contamination.
KEYWORDS: Particles, Plasma, Monte Carlo methods, 3D modeling, Reflectors, Systems modeling, Pulsed laser deposition, Reflection, Thin film deposition, Optical simulations
A novel three-dimensional model has been proposed for simulating plume behavior and 'micron-sized particles'
movement and interaction. It describes particles expansion in vacuum or into an environmental gas and particles
interaction with various obstacles. The model simulates 'standard' Pulsed Laser Deposition (PLD) system behavior, but
also some droplet reduction techniques used in PLD (e.g. shadow mask technique) having good results in plasma
expansion for the first several centimeters from target. The carried out simulations have shown that in the PLD with
plasma reflection (PLDPR) the influence of mass and particle's surface area on the droplets trajectory is significant. By
increasing of the particle mass or by decreasing particle's surface, the probability of the particle to be driven into the
deposition area by plume fine particles is considerably decreasing.
In the small gain approximation and the unsaturated regime in this paper we report some original results concerning the
evaluation of the Fano factor, statistical fluctuation and spontaneous emission factor which characterize the photon
statistics on the number of excited modes, dopant concentration and power pumping in the single and double pass Er3+ -
doped LiNbO, straight waveguide amplifiers pumped near 1484 nm using erfc, Gaussian and constant profile of the
Er3+ ions in LiNbO, crystal. We demonstrated that for 50 mW input pump power the Poisson photon statistics are
maintained in the above mentioned amplifiers for concentrations of the Er ions smaller than l026 m-3 and also high gains
and low noise figures are achievable. The obtained results can be used for the design of optoelectronic integrated
circuits.
KEYWORDS: Particles, 3D modeling, Monte Carlo methods, Plasma, Pulsed laser deposition, Protactinium, Picosecond phenomena, Laser ablation, Systems modeling, Reflection
A novel three-dimensional model has been proposed for simulating pulsed laser ablation plume behvior and 'micron-sized particles' movement. It describes the plume expansion in vacuum or into an environmental gas. The model combined the advantages of Monte-Carlo and Finite Element methods, being able to give a detailed image of particles behavior, both from microscopic and macroscopic points of view. The particle interaction with obstacles is aimed to provide us a more comprehensive understanding of Pulsed Laser Deposition (PLD) techniques, with the final objective of obtaining droplets-free surfaces.
The paper presents the experimental results on adsorption properties of carbon nanopowders which have been obtained by laser pyrolysis of hydrocarbon-based mixtures. We have investigated the adsorption of benzene, n-hexane and ciclohexane. The influence of the nanocarbon morphology (which depends on gaseous precursors and synthesis conditions) on adsorption characteristics is reported.
We have investigated thin films of Ni, Pt, Pd, Ni-Pt and Ni-Pd deposited by pulsed laser ablation. Our study was focused on the correlation of layer morphology and composition vs. synthesis parameters (material, laser fluence and wavelength). In order to obtain bimetallic films we alternatively irradiated two different metal targets. A Nd:YAG laser (λ = 355 and 532 nm, 5 ns pulse duration, fluence 15 - 30 J/cm2) was used. Film analysis was made by AFM and RBS. The synthesized layers had a roughness (Ra) between 15 and 40 nm for Pt and Pd and between 80 and 120 nm for Ni. The rate deposition was in the range of 0.04 - 0.8 Å. In the composite layers, in condition of equally radiated targets, the Ni/Pd at. concentration was 50/50%, while for the Ni/Pt layer was 30/70%.
Pulsed laser deposition (PLD) is widely used to prepare various kinds of thin films. From many experimental results the film surface has been found to be strongly affected by so-called droplets, which are relatively large target material particles in solid or liquid state carried with the plume. In order to satisfy both purposes of high deposition rate and good quality by the PLD, we have investigated the plume reflection process from the viewpoint to avoid the big particles deposited on the substrate. In the present paper we investigate the influences of the system parameters on surface thin film quality and the deposition rate. Some optimization proposals are also included for this deposition technique.
The biological effects of the laser radiation emitted by the Nd:YAG laser (second harmonic, wavelength 532 nm /fluence 32 mJ/cm2/pulse duration 6 ns) on the Mycoplasma agalactiae bacterium were studied. The radiation was found to intensify the multiplication of the bacteria irradiated in TRIS buffer (0.125 M), without however affecting the proteinic composition of the cell membrane. When the bacteria were irradiated in their growth medium (PPLO broth) being later cultivated on a solid medium (PPLO agar), the exclusive presence of the atypical colonies (granular and T-like ones) was noticed.
Plume reflection has been studied as a possibility for depositing on a direction perpendicular to target, convenient for manipulation of big size substrates and for avoiding the presence of droplets on film surface. Plume behaviour during reflection on a 45 degree(s) oriented plane surface has been monitored by a high- speed camera. Thin film, deposited by reflected plume, has been analysed by scanning electron microscopy (SEM) and atomic forces microscopy (AFM). Comparing with a standard deposition a 1-2 order of magnitude improvement for film roughness (RMS) has been noticed at the expense of one order of magnitude diminuation of deposition rate. The results have shown significant dependencies of film thickness and surface quality on plume reflection angle. Some aspects of big particles movement in deposition process are also presented.
In Pulsed Laser Deposition (PLD) surface roughness of a deposited film is an important parameter for many thin films applications. Plume free expansion and propagation in a plane shadow mask experimental setup have been investigated together with film roughness for several deposition parameters. In this paper we propose a simplified formula for a RMS variation. A comparison between theoretical and experimental results is presented. The model is considered to be useful for quick roughness (RMS) estimation in PLD deposition.
We have investigated the influence of the laser fluence, ambient nitrogen and target material on the synthesis of aluminum nitride nanosized powders by reactive laser ablation. Pure aluminum and aluminum nitride were used as targets. The study revealed that were pure nanosized AlN powders (3-25 nm in diameter) can be synthesized for laser fluences higher than 11 J/cm2(approximately 1.6 GW/cm2). AlN powders were obtained at any nitrogen pressure in case of AlN target, while aluminum target pressure >= 100 Torr was required.
Reactive pulsed laser ablation deposition of thin films is a technique which has already given good results for the formation of metal and semiconductor oxide and nitride films. To improve the quality of the deposited films it is important to understand the ablation process and the materials transport phenomena from the target to the collecting substrate. Optical emission spectroscopy of the plasma plume, formed by the interaction of the laser pulse with the target is generally used to try to understand the reaction mechanisms during the transport process. An eight speed camera was also used to determine plasma plume expansion velocity and the total duration of luminous emission of the plume. The effect of ambient pressure in the ablation chamber on the plasma composition was observed.
The laser ablation is one of the best ways to obtain smooth thin film deposited on various substrates. However, to obtain a 'droplets-free' surface some special experimental setups are necessary.ONe of them is the 'eclipse' method, using a plane shadow mask. Based on studies on the plume behavior in a 'standard' deposition and in a plane shadow mask eclipse deposition, we prose a new shadow mask having a an helicoidal shape, which permit to obtain a abetter film quality - maximum droplets size about 10 times smaller than for the plane shadow mask. The plume behavior and thin film quality are presented and discussed.
Fast-framing photography was used to study the effect of various parameters on the expansion of the visible plasma plume produced by KrF laser irradiation of a YBa2Cu3O7-x target. The ambient gas pressure has a considerable effect on the evolution and structure of the plasma. In vacuum, the visible emission is strongly forward-directed and has a relatively short duration. In the presence of an oxygen atmosphere, a long-lived, highly luminous front is formed, whose expansion may be well described by a drag model or a shock model (spherical or plane shock). Ahead of the luminous front there is weak emission, which for pressures over about 700 mTorr evolves into a highly emissive `tip'. The decrease of energy density on the target by increase of the laser spot (defocusing) leads to a more forward-directed motion of the visible species. Larger energy densities obtained by increasing the energy/pulse lead to a sharper, `V' shaped front. The effect of a biased ring electrode placed 0.5 cm to 2 cm in front of the target was also studied. The emission characteristics in the electrode's presence change greatly. The effect of ring-target distance, voltage magnitude and polarity, and pressure were observed.
Nanosize powders of AlN was successfully synthesized by pulsed laser ablation. The target can be either Al or AlN, with ambient gas nitrogen. With Al targets, typical powder diameters were in the range of 2.5 divided by 25 nm. In order to study the process of powder formation, we have used a high-speed camera and a time-resolved spectrum analyzing system to investigate the behavior of the ablation plasma and the ion species in the plasma. For the diagnostic experiments, the target was Al and the ambient gas was oxygen.
Ultrafine alumina powder was produced by aluminum target ablation with a Nd:YAG laser beam (1064 nm wavelength; 340 mJ/pulse energy; 7 ns pulse duration; 10 pps repetition rate), in a 120 Torr O2 atmosphere. A theoretical approach for the ablation process, based on laser energy absorption and energy balance in the target, is used for comparison with the experimental production rate. Three experimental irradiation conditions were chosen: (1) energy density of 5 J/cm2, considered reference (RDE), (2) lower energy density of 2.5 J/cm2 (LDE) and (3) RDE with auxiliary discharge between an auxiliary electrode and target, triggered by the ablation plume (RDA). Calculated and experimental data of target weight loss show good agreement (135 ng/pulse, calculated, and 100, 110, 120 ng/pulse, experimentally, for RDE, LDE, RDA conditions, respectively). The X-Ray Diffraction spectra of alumina show formation of (gamma) -alumina particles only, especially in LDE and RDA conditions. From Scanning Electron Microscopy size analysis, a decrease of particle size, in LDE and RDA irradiating conditions, is observed. The decrease of laser beam fluence or aiding of ablation using an auxiliary discharge is both favorable for the production of high quality powder, without diminishing the production rate. This can be a good basis for future improvement of the ultrafine powder production process.
Structured modifications are produced by interaction of solid state media with high intensity laser beams. The most useful beams for such purposes are generated by CO2-TE lasers in IR field, and excimer lasers in UV field. The paper describes laser pumping circuits for both lasers with significant temporal decays that occurs between trigger and laser pulses. Also, temporal behavior of above mentioned lasers: pulse duration, delays and jitters, in various operation conditions, i.e., gases mixture, pressure and pumping energy, is made by temporal determination of pulses and delays involved. Finally, synchronization methods, electrical or optical are recommended in relation with necessary conditions of synchronization between beams.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.