Laser vaporization/ablation plumes

Significant progress in defining the general nature of laser vaporization /ablation plumes, used for thin film deposition, has been made in recent years [1,2]. Our current understanding... 

Laser radiation can be used to vaporize the surface of a material. Laser vaporization (laser ablation) creates a large number of ions in the vapor plume and these can be accelerated to the substrate surface. This technique has been used to deposit hydrogen-free DLC hlms. Laser vaporization with concurrent ion bombardment has been used to deposit high quality, high temperature superconductor hlms at relahvely low substrate temperatures.t" ... 

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. 

Solid samples can be introduced into plasmas by vaporizing them with an electrical spark or with a laser beam. Laser volatilization, often called laser ablation, has become a popular method to introduce samples into inductively coupled plasmas. Here a high-powered laser beam, usually a Nd YAG or excimer laser, is directed onto a portion of the solid sample. The sample is then vaporized by radiative heating. The plume of vapor produced is swept into the plasma by means of a carrier gas. 

For the case of both electrically conducting and electrically non-conducting samples, laser ablation combined with AAS may be useful. In this case AAS measurements can be performed directly at the laser plume. Measurement of the non-element specific absorption will be very important, because of the presence of particles, molecules and radicals as well as due to the emission of continuum radiation. In addition, the absorption measurements should be made in the apprppriate zones. When applying laser ablation for direct solids sampling, the atomic vapor produced can also be led into a flame for AAS work, as has previously been described by Kantor et al. [299] in their early work. 

In laser ablation, a solid sample is irradiated with a laser pulse that ablates the point of laser-solid contact to produce a plume of ions and neutrals in the vapor space just above the point of laser-solid contact with the sample surface. If this plume is swept into an ionization source or if reactant ions are electrically focused into the ablated sample plume, product ions are formed. These ions can be electrically focused into an IMS for ion mobility analysis. Direct laser ablation followed by ionization from... 

Laser ablation has been broadly applied and developed for the synthesis of diverse nanomaterials [21,22], In this approach, an incident laser pulse penetrates into the surface of the material within a certain penetration depth. Electrons are removed from the bulk and the irradiated surface is then heated up and vaporized. At a high enough laser flux, the material is converted to plasma. Consequently, the large pressure difference between the laser produced initial seed plasma and ambient atmosphere causes a rapid expansion of the plasma plume and then it cools down. The plasma species will nucleate and grow into desirable nanostructures, either on a substrate or in a cool Hquid medium [21]. 

The ablation devices for solids described in Section 8C-2 are also available from several makers of ICP instruments. With these types of sample-introduction systems, the plume of vapor and particulate matter produced by interaction of the sample with an electric arc or spark or with a laser beam are transported by a flow of argon into the torch where further atomization and excitation trccur. 

There has been renewed interest in the method, mainly due to the availability of improved Nd YAG laser systems. In addition, different types of detectors, such as microchannel plates coupled to photodiodes and CCDs, in combination with multi-channel analyzers make it possible for an analytical line and an internal standard line to be recorded simultaneously, by which the analytical precision can be considerably improved. By optimizing the ablation conditions and the spectral observation, detection limits obtained using the laser plume as a source for atomic emission spectrometry are in the 50-100 pg/g range and RSDs are in the region of 1% as shown by the determination of Si and Mg in low-alloyed steels [255, 259]. This necessitates the use of slightly reduced pressure, so that the atom vapor cloud is no longer optically very dense and the background emission intensities become lower. In the case of laser ablation of brass samples at normal pressure and direct... 

In laser diagnostic methods developed to study the vaporization behavior of ZrC (7), a vapor phase was produced by laser ablation of a ZrC target. The temperatures of the plasmas are estimated to be between 9000 and 12,000 K. Thermodynamic calculations for 9000 K predict that C3 has the highest partial pressure, followed by C2 and C5. Zirconium has the lowest calculated partial pressure. The dominant neutral gas species of an expanding plasma plume are predicted to be Zr and C followed by, in decreasing order of importance, C2, C3, C4, and Cs. The optical emission spectra of the ablated ZrC from 200 to 500 nm at delay times from 10 p.s to 1 ms (Fig. 5) contain lines only for excited Zr. Emission peaks from C, C2, and C3 were absent from the spectra, apparently because of the inherently low emission intensities of these species compared with that of Zr, which has a very strong spectrum in the ultraviolet frequency range. 

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