Field-ionization source induced phase transition from hBN to cBN during pulsed laser deposition

Abstract

Boron nitride (BN) thin films were deposited on Si(111) substrate using an ArF excimer laser for ablating the hexagonal boron nitride (hBN) target and a field-ionization source for activating N2. The phases present in the films were determined by Fourier transformation infrared spectroscopy (FTIR). The results show that BN thin films containing a large amount of cubic BN (cBN) phase on Si(111) substrate were successfully prepared by field-ionization source assisted pulsed laser deposition (PLD). It is clearly seen that activated N2 and ion bombardments seem necessary for the formation of cBN during the process of deposition using the field-ionization source assisted PLD method. Supplied as activated ions, nitrogen can easily form chemical bonds with boron atoms and can form nearly stoichiometric BN. The bombarding ions are supposed to have a strong influence on the formation of residual stress in BN films and this induces the formation of the cBN phase. The stoichiometric effect and largely the residual compressive stress in BN thin films seem the key factors determining the content of cBN phase.