Laser-based Techniques and Applications - LATA
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1. Pulsed Laser Deposition (PLD)

The PLD technique is today a widely used and versatile method for the growth of almost any kind of thin films. This is due mainly to its simplicity: the basic components needed are : (1) a powerful pulsed (usually a few nsec) laser and (2) a vacuum chamber where the film growth takes place. Mostly, an excimer laser or a Nd:YaG laser and its harmonics are used. The laser beam is focused on the target inside the vacuum chamber. The targets are either metallic foils or ceramic compounds that are sintered and pressed to a pill and are mounted on a rotating holder to avoid being drilled. The film is deposited on the substrate, usually silicon, microscope glass or quartz and can be heated up to several hundreds degrees. It turned that the substrate temperature is a very important parameter that affects significantly the film properties.

Another important PLD parameter is the kind and pressure of the gas inside the deposition chamber during film growth. For the deposition of oxides, oxygen with pressures of a few tens of Pa is used. In certain cases, oxygen pressure may be even less. Nitrogen may be used for the deposition of nitrides and CH4 for the deposition of carbides. In a different approach, the latter two may be grown directly from nitride or carbide targets under vacuum.

The above short description of the PLD principles fully justifies the versatility of the technique. But PLD has further advantages: (1) it is considered as a low-temperature deposition technique because the ablated material (target) is in room temperature, (2) the high kinetic energies (several tens of eV) of the ablated particles results to a good film adhesion on the substrate, (3) epitaxial growth and good crystallinity is achieved on heated substrates. The PLD technique may therefore compete with the MBE (Molecular Beam Epitaxy) one.

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2. Laser-Induced Plasma Spectroscopy

The LIPS technique (Laser Induced Plasma Spectroscopy, LIPS or Laser Induced Breakdown Spectroscopy, LIBS) has received increased attention in the last 15 years as a laser-based analytical technique for rapid, multi-elemental determination, both for the laboratory as well as for in-situ applications and remote analysis in hostile environments.

This is due to both its broad field of applications as well as to its simplicity: The technique can be applied on solid (metals, ceramics, polymers, drugs, wood, paper), liquid (water, colloids, industrial and biological liquids) and gaseous (industrial exhaust gases, air particulates) samples, where the samples require minimal or no preparation at all. The technique can therefore be considered as (almost) a non destructive one. On the other side, the principle of the technique is rather simple: when a powerful pulsed laser is focused on a surface, a tiny amount of the material is vaporized, and through further photon absorption, it is heated up until it ionizes. This laser-induced plasma is a microsource of light that is analyzed by a spectrometer. The obtained spectra consist of the emission lines corresponding to the elements evaporated from the sample surface.

Although there have been a lot of papers published over the last years dealing with the LIBS technique and its applications as an analytical method, considerable research is still continuing in the Laboratory, in order to further develop the method: one aspect of the development effort aims to further optimize various experimental parameters to improve the capabilities of the technique in each particular case (e.g. in view of reducing the lowest amount detectable, LOD—lowest order of detection); a second aspect is to extend the analytical applicability of LIBS to elements that for various reasons could not be determined efficiently thus far, by incorporating  new and improved instrumentation.


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