Lasers metal vapors

Deposition of Thin Films. Laser photochemical deposition has been extensively studied, especially with respect to fabrication of microelectronic stmctures (see Integrated circuits). This procedure could be used in integrated circuit fabrication for the direct generation of patterns. Laser-aided chemical vapor deposition, which can be used to deposit layers of semiconductors, metals, and insulators, could define the circuit features. The deposits can have dimensions in the micrometer regime and they can be produced in specific patterns. Laser chemical vapor deposition can use either of two approaches. 

Isotope photoseparation techniques for actinides probably will include only gaseous systems, hexafluorides and metal vapors. Hence, aqueous actinide photochemistry is not likely to influence isotope separations. However, the intense interest in laser separation techniques for the gaseous systems promotes interest in the aqueous systems. 

Since the demonstration by Schumacher et al ) of the use of alkali metal vapor inclusion into a supersonic beam to produce clusters, there have been a number of attempts to generalize the approach. It has recently been recognized that instead of high temperature ovens, with their concommitant set of complex experimental problems, an intense pulsed laser beam focused on a target could be effectively used to produce metal atoms in the throat of a supersonic expansion valve. ) If these atoms are injected into a high pressure inert gas, such as helium, nucleation to produce clusters occurs. This development has as its most important result that clusters of virtually any material now can be produced and studied with relative ease. 

Figure 1. Schematic illustration of the laser-vaporization supersonic cluster source. Just before the peak of an intense He pulse from the nozzle (at left), a weakly focused laser pulse strikes from the rotating metal rod. The hot metal vapor sputtered from the surface is swept down the condensation channel in dense He, where cluster formation occurs through nucleation. The gas pulse expands into vacuum, with a skinned portion to serve as a collimated cluster bean. The deflection magnet is used to measure magnetic properties, while the final chaiber at right is for measurement of the cluster distribution by laser photoionization time-of-flight mass spectroscopy.

Another thin film technology based nanoparticle preparation route is gas condensation, in which metal vapor is cooled to high levels of supersaturation in an inert gas ambient [126-128]. In these experiments particles necessarily nucleate in the gas phase. In a promising extension of this technique a pulsed laser beam replaces the conventionally used thermal metal vapor source [120,121,129-134]. 

Metal-vapor discharge tubes, 17 371-372 Metal-vapor lasers, 14 667 Metal working... 

A further improvement and more freedom in the choice of laser wavelengths can be expected with the use of dye vapors. In liquids, the phase-matching concentration is set by the requirement that the anomalous dispersion of the dye compensates for the normal dispersion of the solvent. The latter is a new parameter that can be varied at will in the gas phase by changing the nature and partial pressure of the buffer gas. The broader resonances of dyes as opposed to metal vapors, which are sometimes used for this purpose, is an advantage for tunable frequency tripling of dye lasers. Another advantage results from the possibility of working at much lower temperatures than with metal vapors. 

Fig. I. Methods for forming metal vapors, (a) Evaporation from a resistance-heated, alumina-coated Mo or W spiral. This is a method suitable for Cr, Mn, Fe, Co, Ni, Cu, Pd, Ag, Au and other metals that do not attack alumina, (b) Evaporation from a resistance-heated Ta or W boat. This method is useful for V, Cr, and some lanthanides, (c) Sublimation from a resistance-heated free-hanging loop of wire, e.g., Ti, Mo, or W. (d) Evaporation from a cooled hearth using laser or electron bombardment heating. This method may be used with all metals.

CL Cocondensation of the vapor of a compound and a metal vapor formed by laser beam evaporation of the metal... 

Lanthanide triflates, for allylic tin reactions, 9, 354 Laser beam heating, in metal vapor synthesis, 1, 224 Laser methods, in mechanistic studies, 1, 248 Laser photochemical vapor deposition, with organometallic complexes, 1, 259... 

Ablation is a powerful technique that uses high-energy lasers to vaporize or ablate materials from the surface. The wavelength of the laser is tuned for the specific material to achieve maximum absorption of the energy, most often ultraviolet. The target is vaporized, creating a plume of neutral metal atoms. The plume is then cooled with a carrier gas to form clusters. It is possible to couple laser evaporation with laser pyrolysis to form alloys. 

This characteristic results from reabsorption of some of the emitted light by the colored part of the matrix. The Intensity of the features in the RR spectra obtained from the white part of the sample quickly and steadily decreased as the laser was moved away from the color boundary. Parts of the sample with widely varying metal concentrations could therefore be studied in the same experiment. Mixed Fe/Ni deposits were generated by stringing two filaments, one of each metal, side by side across the water-cooled electrodes of the metal vapor furnace. An Fe/Ni sample had the same color as a sample with Fe alone. 

Several attempts have been made during the last few years to study the formation of alkali hydrides in the vapor phase when a mixture of alkali metal vapor and hydrogen is exposed to laser irradiation which photoexcites the alkali atom. The present work is devoted to the following overall reactions ... 

Lasers of virtually any visible wavelength incident on alkali metal vapors will produce light at a variety of wavelengths as well as some ionization (e.g. lasers at resonant and quasireso-nant wavelengths)... 

Plasma Formation in Alkali Metal Vapors by Quasi-Resonant Laser Excitation... 

Regarding future laser developments which make use of alkali metal vapors, several interesting possibilities exist, which all allow for tunable lasers. 

Laser-assisted chemical vapor deposition a CVD in which the excitation is delivered from photons delivered from a laser Metal-organic chemical vapor deposition (MOCVD) the same as CVD, except that the precursor is a volatile organometallic or coordination compound with carbon-containing ligands... 

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