Clusters boron nitride

The result of intensity alternation for the boron nitride cluster ions is in accordance with the generation of high cluster ion beams MnXn, for several systems (e.g. NaCl, CuBr or Csl26 49) by other methods of cluster formation such as by quenching condensation in a cold rare gas or by ion bombardment of hahdes. 

Before that time, experimental evidence for the existence of heterofullerenes was very rare. In 1991 Smalley and co-workers [4,5] reported on the mass spectrometric detection of borafullerenes C5q B (n = 1-6) generated by laser vaporization of graphite-boron nitride composites. Later, in the same year, the preparation of several clusters was reported [6-8]. However, none of these species has been isolated or structurally characterized. In 1994 Clemmer et al. presented evidence for heterofullerenes containing a metal as part of the framework [9]. Muhr etal. reported on the preparation of monoborafullerenes however, presumably due to the instability of these systems, no pure material could be isolated and completely characterized [10]. Real preparative heterofullerene chemistry began in 1995. The... 

So far, all efforts to generate, isolate and characterize heterofuUerenes via Kratsch-mer-Huffman vaporization of graphite in the presence of hetero-element-containing compounds such as boron nitride (BN) or cyanogen (CN)2 have failed. An alternative route for the direct formation of heterofuUerenes is cluster rearrangement within exohedral fullerene derivatives such as iminofullerenes and azafuUeroids. The first hints of success by this approach were obtained from mass spectrometry investigations of the cis-l-diazabishomo[60]fullerene 3 [12], the n-butylamine adduct 4 [12] the 1,2-epiminofullerene 5 [11] and the cluster opened ketolactam 6 [2]. 

The determination of trace impurities in boron nitride of the highest purity for the production of GaAs single crystals is hampered by the formation of disturbing polyatomic and cluster ions. 

Part of a mass spectrum for the determination of Fe and Cr contamination in boron nitride contaminated with carbon measured by LIMS is shown in Figure 6.9. The analyte ions 53Cr+ and 54Fe+ due to different masses of isobaric atomic and cluster ions are clearly separated from boron and boron carbide cluster ions as demonstrated in Figure 6.9. Cluster ion formation has been studied by laser ionization mass spectrometry (LIMS) on a boron nitride target.10... 

Figure 9.58 Cluster ion distribution (BnNn + and BnNn ) for boron nitride in a laser plasma.

New types of cluster ions have been formed by laser plasmachemical reactions in a graphite and boron nitride mixture (1 1) cluster ions which alternate with CB Nn 2+ ionic... 

Figure 9.59 Cluster ion formation of a boron nitride/graphite mixture in a laser plasma. (J. S. Becker and ff. J. Dietze, Fresenius ). Anal. Chem., 359, 338(1997). Reproduced by permission of Springer Science and Business Media.)...

A complex nanostructured catalyst for ammonia synthesis consists of ruthenium nanoclusters dispersed on a boron nitride support (Ru/BN) with barium added as a promoter (33). It was observed that the introduction of barium promoters results in an increase of the catalytic activity by 2—3 orders of magnitude. The multi-phase catalyst was first investigated by means of conventional HRTEM, but this technique did not succeed in identifying a barium-rich phase (34). It was even difficult to determine how the catalyst could be active, because the ruthenium clusters were encapsulated by layers of the boron nitride support. By HRTEM imaging of the catalyst during exposure to ammonia synthesis conditions, it was found that the... 

There is mass spectroscopic evidence for clusters C59B, C68B2,. ..C54 B6 in the products of laser ablation of boron nitride/graphite composites (Guo et al. 1991). It is proposed that these may be versions of the fullerene cage in which heteroatoms have occupied carbon sites with little disturbance of the framework. This is a plausible hypothesis for low doping ratios, in view of the ability of carbon to substitute for boron in carboranes. Bond-energy considerations suggest that... 

The influence of the laser and plasma parameters (such as wavelength, laser power density, pulse length, plasma temperature, electron and ion density and others) on the physical and chemical processes in a laser induced plasma with respect to the formation of polyatomic and cluster ions has been investigated for different materials (e.g. graphite, boron nitride, boron nitride/graphite mixture, boron carbide, tungsten oxide/graphite mixture and superconductors ). 

---