Plasma Creation

As most commonly used, the technique employs a pulsed laser and a focusing lens to generate a plasma that vaporizes a small amount of a sample. A portion of the plasma light is collected and directed to a spectrometer. The spectrometer disperses the light emitted by excited atoms, ions, and simple molecules in the plasma, a detector records the emission signals, and electronics take over to digitize and display the results. 

Double pulse approach became recently very popular. One of its advantages is that it may be easily introduced in industrial analyzers. The main difference from the single pulse approach can be summarized as follows (i) the first laser pulse creates a plasma and the second pulse propagates at high velocity in the rarified medium created by the first pulse, (ii) the plume size is wider in the double-pulse 

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Hot filament PECVD uses thermal energy for plasma creation and has been used successfully for carbon nanofiber production by Chen et al. [40,41]. Hot filament PECVD, as in the case of direct current PECVD... 

PVD methods differ in the means for producing the metal vapor and the details of plasma creation. The primary PVD methods are ion plating, ion implantation, sputtering, and laser surface allo5dng. 

A completely different emission process, which can in principle provide table-top ultrashort X-ray sources up to 100 keV has been recently discovered and studied, both from an experimental and a theoretical viewpoint [9]. It can be understood as one consider that the electrons, trapped and accelerated in a plasma wake as described earlier, can also experience, in some cases, a transverse force pulling them toward the beam axis. This force is basically due to the creation of a sort of plasma channel at low electron density, which is a consequence of the ponderomotive force that expels the electrons from the laser beam axis (the ions, due to their larger inertia, being fixed). The trapped electrons thus undergo a sort of wiggler motion, thus producing so-called betatron radiation. 

The plasma is maintained at a temperature of 10 000° C by an external radio frequency current, as described in Section 3.3. At this temperature, many molecular species are broken down, and approximately 50% of the atoms are ionized. So far this is identical to ICP-OES, but for ICP-MS we are not interested in the emission of electromagnetic radiation, but rather in the creation of positive ions. To transfer a representative sample of this plasma ion population to the mass spectrometer, there is a special interface between the plasma and the mass spectrometer. This consists of two sequential cones... 

As with pure SmS under pressure (37), the above metallized ICF conditions yield 9c) a free-carrier plasma edge which, though reaching well into the visible, is found to be restrained by 1/2 eV, compared with simple J metals like YS 9c) or LaS (or/" d GdS 12a) also). In line with this observation, and even more striking, is that the nett d.c. resistivity is actually increased upon going from B to M. Clearly, after the Sm/ d sites finally do become joined in d-band activities, the continual annihilation and creation of carriers at the Sm sites constitutes a strong scattering... 

Plasma CVD has been used since the middle of the 1970s. For the creation of the plasma, DC glow discharge [224], RF glow discharge [219, 225-227], microwave plasma [228, 229], or plasma jets [230] are used. 

Fig. 6.6. Schematic illustration of the electrode structure of the positron trap of Greaves, Tinkle and Surko (1994). The variation of the electrical potential along the trap, together with the gas pressure in the various regions, is also shown. The letters A, B and C indicate energy-loss collisions of the positrons with the N2 buffer gas. Reprinted from Phys. Plasmas 1, Greaves et at, Creation and uses of positron plasmas, 1439-1446, copyright 1994, by the American Institute of Physics.

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