The reaction of B 2O 3 with the β-rhombohedral boron (111) surface

Abstract

We have studied the reaction of isotopically pure 10B 2O 3 with the (111) surface of β-rhombohedral boron using temperature-programmed desorption. The 10B 2O 3 was directly deposited on the boron surface from a Knudsen cell operated at 1200 K. The boron crystal contained the natural abundance ratio of the 11B : 10B isotopes of 4:1. The thermal desorption results show a B 2O 3 peak near 1200 K consisting solely of the 10B 2O 3 isotope followed by B 2O 2 and B 2O 3 peaks in the range 1300–1350 K with a B 2O 2: B 2O 3 peak area ratio of about 2:1. The higher temperature B 2O 2 and B 2O 3 desorption peaks follow zero-order desorp kinetics with an activation energy of 554 ± 41 kJmol −1. The higher temperature peaks show substantial incorporation of the 11B isotope from the substrate. The results are consistent with a reaction mechanism in which boron from the substrate first dissolves in the molten B 2O 3 layer and then reacts to form a B 6O suboxide which then decomposes to yield B 2O 3 and B 2O 2. However, we have no direct evidence for the presence of the B 6O suboxide on the surface.