Particle bombardment cluster formation

There are several methods in use for producing these clusters. Particle bombardment or laser vaporization of a graphite surface leads to direct formation of ions that can be detected by mass spectrometry. These are normally of relatively small size (n<30). By laser vaporization of graphite into a molecular beam neutral... 

Film morphology can also be modified because fast particle bombardment can damage the substrate surface and create local sites with more dangling bonds. These are relatively reactive with adatoms, having extra bonds available, and can serve as preferential nucleation sites. At the same time, disruption of clusters increases the critical nucleus size making nucleation more difficult. These two effects do not cancel each other out because early and late nucleation are subject to different constraints. The first nuclei to form do so in the absence of sinks for adatoms. Therefore the adatom density can increase until the adatom supersaturation favors nucleation enough to counteract the disruption of clusters by fast particles. At the same time, the creation of favored nucleation sites also contributes to favoring nucleation. On balance, fast particle bombardment may accelerate the formation of the early nuclei. 

Once nucleation has occurred sinks for adatoms are available. Thus disruption of later nuclei allows the associated adatoms to escape to previously formed nuclei rather than allowing secondary nucleation to occur. This is equivalent to increasing the capture radius of a nucleus (see Section 10.6). At the same time the effective increase in critical nucleus size due to disruption of small clusters also works against cluster formation. In the presence of existing stable nuclei the formation of preferential nucleation sites is important because not enough adatoms are present to allow nucleation under conditions of fast particle bombardment. 

Little is known so far about the chemical properties, yet first results suggest a reactivity similar to that of multiwalled carbon nanotubes. Furthermore, a transformation of nano-onions into other forms of carbon can be achieved by heating (equihbration as faceted nanoparticles) or electron bombardment. In large carbon onions, a formation of small diamond clusters due to internal self-compression has been observed. These grow up to be nanoscale diamond particles under complete consumption of the onion structure. 

Static Secondary Ion Mass Spectrometry (S-SIMS) is a more sensitive (sensitivity of 10 atoms/cm ) surface analysis technique than X ray Photoelectron Spectroscopy (10 atoms/cm ) [6,18]. Under primary bombardment with a focused ion beam the solid surface emits secondary particles. As illustrated in Fig. 5, the bom bardment with primary ions such as Ga, Ar, or other molecular ion sources like SF5 [19-21] or C0O [22], which should enhance molecular ion formation at high masses vs fragmentation, provokes the emission of neutral, positively, or negatively charged fragments and clusters. 

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