Defining the surface binding energy in dynamic Monte Carlo simulation for reactive sputtering of compounds

In Monte Carlo simulations of reactive sputtering, it is commonly assumed that the surface binding energy (SBE) for the different phases in the target exhibits a linear behaviour in the transition between the metal mode and the compound mode. In this work we study how the transition between the two modes takes place, and more specifically attempt to experimentally identify how the SBE for the different phases behaves in the transition between the two modes. In essence, this is done by comparing XPS measurements of the aluminium 2p binding energy on samples comprising pure aluminium, stoichiometric aluminium nitride and aluminium oxide with the corresponding measurements on understoichiometric aluminium nitride samples. In this work, it is assumed that the binding energy of the core level is directly correlated to the SBE of the phase in question. That is to say, if the aluminium 2p binding energy in aluminium nitride exhibits a constant and discrete value independent of the nitrogen concentration, the SBE for the compound exhibits a constant and discrete value independent of the surface concentration of nitrogen. It was found by the XPS measurement that the aluminium 2p binding energy in aluminium nitride exhibits a constant and discrete value independent of the nitrogen concentration in the samples and it was, therefore, concluded that the SBE for the different phases exhibits constant and discrete values independent of the surface concentration of nitrogen. The discrete behaviour of the SBE was implemented in the TRIDYN program and the results from these simulations were compared with simulations in which it is assumed that the SBE of the different phases exhibits a linear behaviour in the transition between the metal mode and the compound mode.