Hydrogenation of fragment cations produced by femtosecond laser ablation of boron nitride

摘要

Cations (positive ions) produced by laser ablation of boron nitride (BN) have been mass analyzed and the size-dependent hydrogenation reactivity is revealed for the first time. The main product cations determined by femtosecond laser ablation (fsLA) were a series of B(BN)_n~+, with much lesser production of B_2(BN)_k~+ and N(BN) _mO~+ series cations. Least-squares fitting of the relative yields of hydrogenated cations indicates that the yield of B(BN) _nH~+ almost diminishes for n ≥ 5 and that of B(BN) _nH_2~+ increases as n increases. Based on the different n-dependence and electronic structures of B(BN)_n and B(BN)_n~+, B(BN)_n is likely to be the precursor of B(BN)_nH~+, and B(BN)_n~+ that of B(BN)_nH2~+. In contrast to fsLA, the production of H~+ by nanosecond laser ablation is not observed and the production of various cationic species makes it difficult to identify either the fragment species or their hydrogenated products. This observation highlights the significant efficiency of fsLA in producing H~+ (and presumably H) from the surface adsorbates.