Studies of low energy ion bombardment of cubic boron nitride (111) surfaces by reflection electron energy loss spectroscopy

Cubic boron nitride (c-BN) films promise many potential applications, because of their outstanding mechanical, electrical, and optical properties. Most of the deposition methods for c-BN films involve the bombardment of the substrate by energetic atoms or ions, which is also known to produce non-cubic phases, such as hexagonal (h-BN) and amorphous boron nitride (a-BN). Therefore, it is important to understand the phase transformation induced by the incident ions onto the c-BN surface. In this work, we studied the phase transformation of c-BN (111) surface induced by argon ion bombardment. Reflection electron energy-loss spectroscopy (REELS) was developed as a quantitative method for measuring phase composition in the near-surface region of BN (111) surface. It was found that the c-BN phase was transformed into h-BN and a-BN after argon ion bombardment. Also, the effective transformation of c-BN to h-BN and a-BN strongly depended on ion energy. A near-complete transformation was observed when the ion energy approached 500 eV. Our work gives a quantitative explanation of the difficulty in growing pure c-BN films with ion-assisted deposition, and the presence of an upper-bound in ion energy above which the formation of phases other than the cubic phase dominate.