Laser-induced reactions

Conventional routes to ceramics involve precipitation from solution, drying, size reduction by milling, and fusion. The availability of well-defined mono-dispersed particles in desired sizes is an essential requirement for the formation of advanced ceramics. The relationship between the density of ceramic materials and the sizes and packing of their parent particles has been examined theoretically and modeled experimentally [810]. Colloid and surface chemical methodologies have been developed for the reproducible formation of ceramic particles [809-812]. These methodologies have included (i) controlled precipitation from homogeneous solutions (ii) phase transformation (iii) evaporative deposition and decomposition and (iv) plasma- and laser-induced reactions. 

Laser-induced reactions involving small organosilicon... 

Plasma chemical synthesis Laser induced reaction... 

Interpretation. The data for hydrogen rich flames is most satisfactorily explained by invoking laser induced reactions between the excited states of the alkali metal and H2O and H2 which constitute the major flame species. 

Muller, C. K. Schofield, K. Steinberg, M. "Laser Induced Reactions of Lithium in Flames", 1978, Proceedings of the NBS 10th Materials Research Symposium, Gaithersburg, Md. 

KrF excimer laser-induced reactions in the mixture of hydrocarbon/02/C02 under sub- and super-critical conditions were investigated. In the ethylene mixtures, the main products were ethylene oxide and acetaldehyde. The total quantum yield decreased with the increase of mixture density, but the branching ratio between the two products were almost independent on the density. The branching ratio was found to be what is expected if the reactive species is 0(3P). The reaction for other hydrocarbons including ethane and cyclohexane is also discussed. 

The local resolution of laser-induced reactions depends on primary effects, i.e., the laser light, and secondary effects induced by the system. Laser-induced metal nucleation and crystal growth and the relevant mechanisms depend mainly on the electronic properties of the substrate, but also on interfacial and electrolyte properties. Depending on the system parameters, focused laser light can influence overvoltage-dependent terms particularly by local heat formation or by local activation of the solid state/electrolyte interface. As the electric properties of the substrate material is of strong influence, the effects will briefly be discussed for metal, semiconductor and polymer substrates. 

Quantitative fluorination of CO, to COF, has been achieved by the laser-induced reaction between SFg and CO, [1305,1640] ... 

Arnolds, H. (2004) Femtosecond laser-induced reactions with 0-2 on... 

Laser-induced reaction has been widely used to stimulate gas-surface interaction. Lasers are also used to probe molecular dynamics in heterogeneous systems as well. In the applied area, the laser photochemical techniques are successfully applied to produce well defined microstructures and new materials for microelectronic devices (1). Enhanced adsorption and chemical reaction on surfaces can be achieved by a photoexcitation of gaseous molecules, adsorbed species as well as solid substrates. The modes of the excitation include vibrational and electronic states of the gaseous species and of the adsorbates surface complexes. Both a single and a multiple photon absorption may be involved in the excitation process. 

Apart from desorption, surface reaction with adsorbate can be stimulated by the laser irradiation. In this chapter we will demonstrate the formation of new surface species by the CO2 laser induced reaction of CDF3 with the surface of SIO2 (17,18). In order to elucidate the mechanism of the reaction especially to determine the surface species, ir spectroscopy was used. A systematic investigation was performed Including the determination of reaction yields as a function of the laser frequency, the laser intensity and the gas pressure as well as the reaction products, and the determination of the correlation between the excited species and the reaction path. 

Finally in this Section on infrared photochemistry, the i.r. laser-induced reaction of SF with a Si surface has been described. Pulsed COj laser radiation in the absence of SF causes momentary heating of a Si target, but no Si removal in the presence of a few Torr of SF, etching of the Si is observed. The mechanism for the process is yet to be established, but it appears that both the reactions of excited species produced by the laser, and the effect of the laser radiation at the gas-surface interface are of importance. ... 

Table II lists a number of the high-pressure laser-induced reactions that have been studied. (References 29 to 30 contain more extensive tables of similar reactions not included here.) These reactions are carried out either directly or with a second component added as a sensitizer. Reaction (21) proceeds only in the presence of a sensitizer such as SiF4, since...

The reactions listed in Table II illustrate the utility that this technique may have in conventional pyrolysis reactions. The homogeneous nature of the laser-induced reaction minimizes undesirable secondary products and results in cleaner processes with higher yields. Laser-induced pyrolysis may prove to be a useful synthetic technique. 

Infrared laser-induced reactions with difluorovinylidene (26)... 

As mentioned in Section 9.2, there is an important distinction between action spectroscopies based on the absorption of multiple photons, as is possible with FEL excitation, and those based on single photon absorption, such as messenger spectroscopy [26,27], laser-induced reaction spectroscopy [73] or indeed direct absorption experiments. When the signal (in this case, the depletion of the parent ion and creation of product ious) depends on the absorption of multiple photons, the signal intensity may not be compared directly to computed linear (single-photon) absorption spectra, as is the normal fashion. There are several reasons why intensities may differ. Thus, baudpositiou (frequency) is considered usually to be more reliable than band intensity when comparing computed and experimentally-measured spectra. 

Carbothermal nitridation of silica, including rice huUs Diimide synthesis Vapor-phase synthesis Plasmachemical synthesis Laser-induced reactions Pyrolysis of organosilicon compounds... 

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