In recent years, nickel nanoparticles (NPs) have increased scientific interest because of their extensive prospects in catalysts, information storage, large-scale batteries and biomedicine. Several works on Ni NPs generation by laser ablation have appeared in the literature in the last years, using different pulsed laser regimes and different media have been published recently. In this work we analyze the characteristics of species, structure (bare core or core-shell), configuration and size distribution of NPs generated by fs pulse laser ablation over a Ni solid target in n-heptane and water. We explore the presence of NiO-Ni core-shell and hollow Ni (or air-Ni) NPs in the colloids obtained. These were experimentally characterized using AFM and TEM microscopy, as well as Optical Extinction Spectroscopy (OES). Extinction spectra were modeled using Mie theory through an appropriate modification of the complex experimental dielectric function, taking into account a size-dependent corrective term for each free and bound electron contribution. Experimental UVvisible- NIR spectra were reproduced considering a size distribution of bare core, hollow and core-shell structures NPs. In both media, Ni NPs shape and size distribution agrees with that derived from TEM and AFM analysis.
The synthesis and study of optical properties of copper nanoparticles are of great interest since they are
applicable to different areas such as catalysis, lubrication, conductive thin films and nanofluids. Their optical properties
are governed by the characteristics of the dielectric function of the metal, its size and environment.
The study of the dielectric function with radius is carried out through the contribution of free and bound
electrons. The first one is corrected for size using the modification of the damping constant. The second one takes into
consideration the contribution of the interband transitions from the d-band to the conduction band, considering the larger spacing between electronic energy levels as the particle decreases in size below 2 nm.
Taking into account these specific modifications, it was possible to fit the bulk complex dielectric function, and
consequently, determine optical parameters and band energy values such as the coefficient for bound electron
contribution Qbulk = 2 x 1024, gap energy Eg = 1.95 eV, Fermi energy EF = 2.15 eV and damping constant for bound electrons γb = 1.15 x 1014 Hz.
The fit of the experimental extinction spectra of the colloidal suspensions obtained by 500 μJ ultrashort pulse
laser ablation of solid target in water and acetone, reveals that the nanometric and subnanometric particles have a Cu-
Cu2O structure due to an oxidation reaction during the fabrication. The results were compared with those obtained by AFM, observing a very good agreement between the two techniques, showing that Optical Extinction Spectroscopy (OES) is a good complementary technique to standard electron microscopy.
In this work we have studied the fragmentation of gold nanoparticles (NPs) after generation by femtosecond laser
ablation of a solid target in deionized water. The fragmentation process was carried out using two different types of
radiation: direct ultra-fast pulses and super-continuum radiation focused in the colloidal solution. In the former case, IR
pulses were applied both in low and high fluences regime, while in the latter, super-continuum was generated by an
external sapphire crystal. In this last case, to assess the effects of the different spectral bands present in the super-continuum
for fragmentation, we have determined different efficiency regions. From the analysis of optical extinction
spectra and Transmission Electron Microscopy (TEM) histograms we can conclude that the main mechanism is linear
absorption in the visible region. Likewise, the super-continuum generated in water during fragmentation resulted more
efficient than that obtained externally by the sapphire crystal. This fact can be attributed to the broadening of the water
continuum band originated due to large intensity used for generation. TEM and Small Angle X-ray Scattering (SAXS)
measurements support the results found from optical extinction spectroscopy.
Optical single backscattering spectroscopy can be used for sizing particles suspended in aqueous solution. In this work, we present results of backscattering spectroscopy applied to the determination of radii of calibrated spherical latex microparticles when a beam of white light is incident on the sample. From Mie calculations and Fourier analysis, we can determine the radius of particles covering the range between 0.5 and 12 µm for monomodal samples, with a mean error of 0.7 µm. To improve the accuracy, a correlation algorithm is applied that reduces the uncertainty in more than an order of magnitude and compares to the traceable error given by the manufacturer. The method can be also applied to bimodal and trimodal samples, allowing the separation of different size components.
Surface ablation with nanosecond laser pulses was applied to preservation, cleaning and compositional identification of objects of cultural value. On one hand, treatments of fabrics, coins, bones, and other archeological objects are shown, as well as applications to the preservation of covers, front of books and old manuscripts made in rag paper. Damage fluence thresholds for 17 different XIXth century types of papers, made by processing textiles, were determined. On the other hand, we use the spectroscopic analysis of the plasma generated as a result of laser ablation (LIBS- laser Induced Breakdown Spectroscopy-) for the determination of the elementary composition of unique pieces in anthropology and archaeology. In particular, we show applications to the identification of trace elements in Hominide teeth, of interest concerning the analysis of eating habits. We also apply LIBS to the determination of the composition of acheological objects belonging to different pre-Columbian cultures.
In an excavation performed in 1999 at the Campo del Pucara, Alamito site, which belongs to the Condorhuasi Culture (from 0 to 500 AD), and is placed near the frontier of Catamarca and Tucuman provinces in the Northwest of Argentina, Victor Nunez Regueiro and Marta Tartusi Paz found an intriguing archaeological artifact: Remains of a thin slab of schist covered by a mica sheet, dated from 360 and 480 AD. The mica was analyzed by photometric and interferometric procedures and experimental results suggest that it behaves as an interferential dielectric mirror.
A low cost portable spectroradiometer able to operate in the 4 bands of the satellite system Landsat MSS was developed. The radiometer was designed to measure the spectral reflectance of spatially extended targets. Spectral bands were selected with 10 nm bandwidth filters. Measurements were made during 2003, from seedtime to harvest, on an experimental plot of wheat. The culture was divided in parcels that received different treatments (seed variety, fertilizer, herbicide and fungicide). Weekly measurements with the detector at nadir and the sun near midday were made. As result of the spectral measurements of reflectance, the normalized difference vegetation index (NDVI) was calculated. As a comparison, LAI, chlorophyll concentration and diverse gravimetric determinations, were carried out. The results were analyzed by means of statistical techniques and showed a good correlation between the optical index and the culture variables. In the future the geometry of the measurement will be improved to reduce the effect of the canopy and other channel in the near infrared will be added to distinguish water and nitrogen stress.
Optical backscattering spectroscopy offers instrumental advantages over fixed wavelength multiangle scattering measurements. We present results of backscattering spectroscopy of calibrated spherical latex micro particles in aqueous solution when a beam of white light is incident on the sample. From Mie calculations and Fourier analysis, the radius of the particles can be retrieved, both in monomodal (single particle size present) and bimodal (two particle size present) samples.
This work continues with the development of a non-dispersive UV optical sensor for stack emissions for SO2 and NO2. These gases are among the most important ones in the emissions of the petrochemical industry. The NDUV consists of three optical channels sensing different spectral regions: 300 nm for SO2, 380 nm for NO2 and 320 nm used as a common reference. Each channel has an interference filter centered at each channel's wavelength, and a photodiode with control electronics. Calibration curves and the effect of cross interference on concentration measurements of these gases are shown.
12 Optical spectroscopy related to analytical techniques have attracted much interest in recent years and became a central part of versatile instruments used for trace gas monitoring. Optical methods are based on different interactions between radiation and matter (absorption, emission and scattering) and use different sources of radiation such as conventional lamps, lasers, the sun, etc. Differential Optical Absorption Spectroscopy is a good example of these kind of techniques where commercial instruments are available today. Typically, it consists of a collimated broadband radiation source that shines a beam of light through an open atmospheric path several hundred meters long; at the other end, a receiving telescope is located which focus the beam on a medium resolution spectrometer-photodetector system that analyzes the wavelength spectrum of the incoming light within a certain range. The absorption bands of a specific gas component failing in this range are thus detected. For multicomponent analysis, the spectrometer must be scanned across different wavelength ranges introducing potential error sources.
12 Non-dispersive analyzers have been used for measurement of gases for many years and were recently introduced as on-line meters for continuous stack emission measurements in industrial plants. SO2 and NO2 are among the most important gases in the emissions of the petrochemical industry. The development of a UV-visible meter for these gases is presented. It consists of three optical channels sensing different spectral regions: 300 nm for SO2, 380 nm for NO2 and 320 nm used as a common reference. Each channel has an interference filter of 10 nm bandwidth centered at each channel's wavelength. Each filter is followed by a photodiode and its electronics which are housed in a single compartment with no moving parts. An incandescent lamp with high output in the UV region was selected and mounted on the opposite side of the stack by appropriate flanges. The equipment was designed to measure in the range between 0 and 500 ppmv with a resolution of about 2 ppmv. Performance parameters like signal stability, dark current, detection limit and calibration curves are shown.
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