Theoretical calculation of B-K ELNES (electron energy loss near edge structure) from 3d transition metal-boron systems

Electronic structures of 3d transition metal-boron systems are calculated u sing molecular orbital(MO) theory in order to interpret their B-K ELNES(ele ctron energy loss near edge structure). The ELNES is analyzed from two poin ts. One is the absolute transition energy and the other is the spectrum sha pe. The former is investigated using the simplest model, i.e. M6B (M = 3d t ransition elements) clusters. The energy shows systematic chemical shifts d epending on M elements. The origin of the chemical shift is found to be two -fold: 1) The strength of M-B anti-bonding interactions, and 2) the electro negativity of M. The spectrum shape is discussed for M2B (M = Ti, Fe, Co an d Ni) compounds, since their spectra are experimentally available. These sp ectra show four distinct peaks in common, except for the case of Ti2B. Amon g the four peaks, electronic origins of the three peaks can be understood b y the analogy of the results by the M6B clusters; they are determined by M- B interactions. The other remaining peak originats from B-B interactions. A lthough the B-B bond-lengths in the M2B compounds are approximately 20% lar ger than the bond-lengths in pure B, MB and MB2, the B-B interaction affect s the spectram shape. This fact can be explained by the spatial delocalizat ion of the wave functions in the unoccupied bands.