Laser ablation technique

Further modification of the above nanostructures is useful for obtaining new functional materials. Thirdly, we apply the dopant-induced laser ablation technique to site-selectively doped thin diblock copolymer films with spheres (sea-island), cylinders (hole-network), and wormlike structures on the nanoscale [19, 20]. When the dye-doped component parts are ablated away by laser light, the films are modified selectively. Concerning the laser ablation of diblock copolymer films, Lengl et al. carried out the excimer laser ablation of diblock copolymer monolayer films, forming spherical micelles loaded with an Au salt to obtain metallic Au nanodots [21]. They used the laser ablation to remove the polymer matrix. In our experiment, however, the laser ablation is used to remove one component of block copolymers. Thereby, we can expect to obtain new functional materials with novel nanostmctures. 

Tables 8.57 and 8.61 compare the performance of GD-MS to other inorganic mass-spectrometry techniques, including LA-ICP-MS which acts as a strong competitor. GD and laser ablation techniques offer the possibility to obtain information about the distribution of analyte within the sample, but on quite a different scale. Pulsed GD requires ToF-MS [374].

Despite the frequent use of arc-discharge and laser ablation techniques, both of these two methods suffer from some drawbacks. The first is that both methods involve evaporating the carbon source, which makes it difficult to scale up production to the industrial level using these approaches. Second, vaporization methods grow CNTs in highly tangled forms, mixed with unwanted forms of carbon and/or metal species. The CNTs thus produced are difficult to purify, manipulate, and assemble for building nanotube-device architectures in practical applications. 

The titanosilicate version of UTD-1 has been shown to be an effective catalyst for the oxidation of alkanes, alkenes, and alcohols (77-79) by using peroxides as the oxidant. The large pores of Ti-UTD-1 readily accommodate large molecules such as 2,6-di-ferf-butylphenol (2,6-DTBP). The bulky 2,6-DTBP substrate can be converted to the corresponding quinone with activity and selectivity comparable to the mesoporous catalysts Ti-MCM-41 and Ti-HMS (80), where HMS = hexagonal mesoporous silica. Both Ti-UTD-1 and UTD-1 have also been prepared as oriented thin films via a laser ablation technique (81-85). Continuous UTD-1 membranes with the channels oriented normal to the substrate surface have been employed in a catalytic oxidation-separation process (82). At room temperature, a cyclohexene-ferf-butylhydroperoxide was passed through the membrane and epoxidation products were trapped on the down stream side. The UTD-1 membranes supported on metal frits have also been evaluated for the separation of linear paraffins and aromatics (83). In a model separation of n-hexane and toluene, enhanced permeation of the linear alkane was observed. Oriented UTD-1 films have also been evenly coated on small 3D objects such as glass and metal beads (84, 85). 

Figure 6.17. Scheme, according to Roman etal. (1997), of the deposition of nano-laminate coatings via the pulsed laser ablation technique. 1 Vacuum, chamber, 2 Ti-6A1-4V substrate holder and heater, 3 deposit (nanometer range), 4 laser-induced plasma, 5 target (TiB2/TiN),... 

The double-spike technique of Rosman (1972) has been revived by Tanimizu et al. (2002), who used a Zn- Zn spike and obtained precisions in the range of a fraction of a per mil. Jackson and Gunther (2003) describe a laser-ablation technique of isotopic measurement, which provides a precision comparable to the standard solution nebulization methods. 

Kneipp et al. [34] showed that enhancement is independent of cluster sizes ranging from 100 nm to 20 pm. The data and the electron microscope images of the SERS particles are depicted in Figure 10.8 together with the nonresonance SERS spectrum of 10 6 M crystal violet. SERS enhancement is estimated to be on the order of 106 for the spatially isolated cluster and up to 108 for the colloidal clusters. The isolated silver clusters were made by the laser ablation technique mentioned earlier. 

The laser ablation technique was first used to synthesize C-Ns by Niu et al. [12] wherein high-energy fragments react with nitrogen atoms generated independently by an RF-plasma discharge. This technique attained a... 

Although the laser ablation technique is powerful, the extent of the contributions that these methods will make will depend on the degree of success achieved with improvements in transmission and sensitivity. The sensitivity of the P54 for Pb in solution mode is about 0.2%. The best sensitivity achieved with the UV laser at U-M is about 0.1%. However, the sensitivity for Pb in solution and laser ablation mode using some of the more recent instruments is already reported to be 1 %. 

Economically feasible large-scale production and purification techniques must still be developed. In arc discharge, a vapour is created between two carbon electrodes with or without catalyst. In the laser ablation technique, a high-powered laser beam impinges on a volume of carbon-containing feedstock gas. Flame synthesis is used in a controlled flame environment.8... 

Several factors affect the growth of SWNTs in the laser-ablation technique. Extensive studies on the development of the laser-vaporization technique have optimized the process conditions such as laser parameters, composition of graphite and metal, carrier gas, pressure, and temperature. Through these studies, a sigiuficant understanding of the SWNT s growth and propagation under laser-vaporization condition is achieved. ... 

Figure 24 High-resolutionX-ray diffraction of (A) MWNTs. (Ref 153. Reproduced by permission of Wiley-VCH) and (B) SWNTs produced by (a) arc-discharge and (b) laser-ablation techniques. Asterisk marks are graphite peaks and removed for clarity. (Reprinted with permission from Ref. 20. 1997 Macmillan Magazines Ltd)...

Liquid samples are typically analyzed, gaseous phase from hydride generation is easily accepted, and solids can be introduced as slurries or after appropriate pretreatment procedme aimed at solubilization and/or preconcentration of the analytes. However, laser ablation techniques continue to increase in popularity. 

Laser Ablation [7]. The modern method for quantitative solid analyses is carried out using a laser ablation technique (Figure 2.16). The laser, usually in the form of Nd YAG (Neodymium - Doped Yttrium Aluminium Garnet), is focused on to the surface of a sample which, by continuous pulsing, leads to vaporisation at that point and the vapour is transported directly to the plasma with argon for detection and quantification. Detection limits are... 

Figure 7.21 Depth profiling of samples obtained using the laser ablation technique. (Reproduced by kind permission of Cetac Technologies Ltd)...

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