Laser vaporization method

In the absence of an electric field, the dome-closed conformation must be the most stable tip structure, even when spot-welds are considered, since only the perfectly dome-closed tip has no dangling bonds (i.e., it is a true hemifullerene). At the 3000°C temperature of the arc, the rate of tip annealing should be so fast that it is sure to find its most stable structure (i.e., to close as a dome). Clear evidence of this facile closure is the fact that virtually all nanotubes found in the arc deposit are dome-closed. (Even stronger evidence is the observation of only dome-closed nanotubes made at 1200°C by the oven laser vaporization method.) Such considerations constituted the original motivation for the electric field hypothesis. 

The first ever reported molecule to undergo encapsulation was fullerene, which spontaneously and accidentally ended up in the tubes during post-processing of raw tubes prepared via the pulsed laser vaporization method. This could be considered a milestone in the self-assembling of a new class of nanomaterials [78]. 

Metal catalysts are necessary to synthesize SWNTs of carbon for both the arc discharge (8— 10) and laser vaporization methods (41). Typical catalysts for synthesizing SWNTs are listed in Table 10.2.1. The yield of SWNTs strongly depends not only... 

The quantities produced with the laser vaporization method were however not even sufficient for doing experiments to verify the proposed structure. This was solved by Kratschmer, Huffman and their students who had as early as in 1982, [144-146] i.e. three years before the discovery of Ceo in 1985, produced Ceo without knowing it. They used an electric arc in a helium atmosphere of 150 torr and produced a special kind of soot with a unique type of optical absorption known as the camel hump smoke in the UV region. Their recorded spectrum fitted however very nicely to some predictions of the present author [147]. After a number of trials, they found in 1990 [148] that the special carbon soot could be dissolved in benzene, which provided the possibility to separate Ceo from the carbon particles [149], record a UV visible spectrum and even fabricate crystals of Ceo and C70 and determine the crystal structure. Suddenly a new kind of carbon material had been found in addition to the commonly known diamond and graphite. 

Since the discovery by Kratschmer and Huffman last year of a simple method for producing macroscopic quantities of Cjo, C70, and some of the higher empty fullerenes, we have searched for a means of extending this technique to fill the void and make macroscopic quantities of internally substituted fullerenes— endohedral fullerene complexes. We report below our first success in this search. It involves a simple revision to the laser-vaporization method originally used in 1985 just do it in an oven at 1200 C. 

At the same time cis Smalley and students at Rice University, Houston Texas, developed the laser vaporization method for production of clusters [84], a similar set-up was built at Exxon s Research Laboratory, New Jersey, USA, by the group of Kaldor and Cox [102,103]. They studied in particular transition metal clusters but also produced clusters of carbon containing up to more than hundreds of atoms as shown in the mass spectrum in Fig. 12. 

A pulsed Nd YAG laser beam has been used at 532 and 1064 nm to irradiate graphite-metal composites in many studies.High efficiency laser-vaporization methods such as ultrafast pulses from a free electron laser and... 

Figure 3 (upper trace) displays the X-ray diffraction pattern of the ZnO nanoparticles synthesized by the laser vaporization method. For comparison we also include the pattern of the particles prepared in methanol (lower trace) according to the method of Henglein and coworkers (55). In both cases, the hexagonal Wurtzite structure is evident thus demonstrating that the bulk crystal structure is kept when the size of the semiconductor crystals falls into the nanometer scale. The results are consistent with the work of Spanhel and Anderson (36). The particle s size can be... 

Mixed Oxides. One of the significant advantages of the laser vaporization method is the ability to synthesize mixtures of nanoparticles of controlled composition or particles of mixed metals or metal oxides. This can be achieved by sequential or... 

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